Tag Archives: Materials Science

Absorption of Axion Dark Matter in a Magnetized Medium [CL]

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http://arxiv.org/abs/2305.05681


Detection of axion dark matter heavier than a meV is hindered by its small wavelength, which limits the useful volume of traditional experiments. This problem can be avoided by directly detecting in-medium excitations, whose $\sim \text{meV} – \text{eV}$ energies are decoupled from the detector size. We show that for any target inside a magnetic field, the absorption rate of electromagnetically-coupled axions into in-medium excitations is determined by the dielectric function. As a result, the plethora of candidate targets previously identified for sub-GeV dark matter searches can be repurposed as broadband axion detectors. We find that a $\text{kg} \cdot \text{yr}$ exposure with noise levels comparable to recent measurements is sufficient to probe parameter space currently unexplored by laboratory tests. Noise reduction by only a few orders of magnitude can enable sensitivity to the QCD axion in the $\sim 10 \ \text{meV} – 10 \ \text{eV}$ mass range.

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A. Berlin and T. Trickle
Thu, 11 May 23
47/55

Comments: 10 pages, 2 figures

Discovery of a new lunar mineral rich in water and ammonium in lunar soils returned by Chang'e-5 mission [EPA]

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http://arxiv.org/abs/2305.05263


The origin and distribution of lunar water are among the most important issues in understanding the earth-moon system. After more than half a century of laboratory research and remote detection, only hydroxyl contained minerals and lunar ice (H2O) are identified. Here we report the discovery of a hydrous mineral (NH4)MgCl3(H2O)6 in the lunar soil returned by Chang’e-5 mission, which contains 417,000 parts per million H2O. The determined structure and composition are similar to novograblenovite-a terrestrial fumarole mineral formed by reaction of hot basalt in water-rich volcanic gases, whereas the measured isotope composition delta37Cl reached 20.4 parts per thousand, a high value that only found in lunar minerals. We rule out the possibility that this hydrate originated from terrestrial contaminants or rocket exhaust through analysis of its chemical, isotopic compositions as well as the formation conditions. Our finding indicates that water can exist on some parts of the sunlit Moon in the form of hydrate compounds. Moreover, this hydrate is rich in ammonium, providing new information in understanding the origin of the Moon.

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S. Jin, M. Hao, Z. Guo, et. al.
Wed, 10 May 23
11/65

Comments: 17 pages, 4 figures

Applications of Gaussian Processes at Extreme Lengthscales: From Molecules to Black Holes [CL]

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http://arxiv.org/abs/2303.14291


In many areas of the observational and experimental sciences data is scarce. Data observation in high-energy astrophysics is disrupted by celestial occlusions and limited telescope time while data derived from laboratory experiments in synthetic chemistry and materials science is time and cost-intensive to collect. On the other hand, knowledge about the data-generation mechanism is often available in the sciences, such as the measurement error of a piece of laboratory apparatus. Both characteristics, small data and knowledge of the underlying physics, make Gaussian processes (GPs) ideal candidates for fitting such datasets. GPs can make predictions with consideration of uncertainty, for example in the virtual screening of molecules and materials, and can also make inferences about incomplete data such as the latent emission signature from a black hole accretion disc. Furthermore, GPs are currently the workhorse model for Bayesian optimisation, a methodology foreseen to be a guide for laboratory experiments in scientific discovery campaigns. The first contribution of this thesis is to use GP modelling to reason about the latent emission signature from the Seyfert galaxy Markarian 335, and by extension, to reason about the applicability of various theoretical models of black hole accretion discs. The second contribution is to extend the GP framework to molecular and chemical reaction representations and to provide an open-source software library to enable the framework to be used by scientists. The third contribution is to leverage GPs to discover novel and performant photoswitch molecules. The fourth contribution is to introduce a Bayesian optimisation scheme capable of modelling aleatoric uncertainty to facilitate the identification of material compositions that possess intrinsic robustness to large scale fabrication processes.

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R. Griffiths
Tue, 28 Mar 23
25/81

Comments: PhD Thesis submitted at the University of Cambridge, August 2022. The thesis is based on a number of previous works also available on arXiv (see Introduction)

Chiral phonons as dark matter detectors [CL]

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http://arxiv.org/abs/2301.07617


We propose a method for detecting light dark matter particles via their creation of chiral phonons in standard model matter. We suggest metal-organic frameworks (MOFs) as candidate materials for such detectors, as their structural flexibility yields low-energy chiral phonons with magnetic moments that are large enough to detect using sensitive magnetometers, and their anisotropy leads to directional sensitivity, which mitigates background contamination. To demonstrate our proposal, we calculate the phononic structure of the MOF InF$_3$($4,4’$-bipyridine), and show that it has highly chiral acoustic phonons. Detection of such chiral phonons via their magnetic moments would dramatically lower the excitation energy threshold to the energy of a single phonon. We show that single phonon detection in a MOF would extend detector reach ten or more orders of magnitude below current limits, enabling exploration of a multitude of as-yet-unprobed dark matter candidates.

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C. Romao, R. Catena, N. Spaldin, et. al.
Thu, 19 Jan 23
24/100

Comments: 11 pages, 4 figures

Glycine amino acid transformation under impacts by small solar system bodies, simulated via high-pressure torsion method [EPA]

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http://arxiv.org/abs/2301.06927


Impacts by small solar system bodies (meteoroids, asteroids, comets and transitional objects) are characterized by a combination of energy dynamics and chemical modification on both terrestrial and small solar system bodies. In this context, the discovery of glycine amino acid in meteorites and comets has led to a hypothesis that impacts by astronomical bodies could contribute to delivery and polymerization of amino acids in the early Earth to generate proteins as essential molecules for life. Besides the possibility of abiotic polymerization of glycine, its decomposition by impacts could generate reactive groups to form other essential organic biomolecules. In this study, the high-pressure torsion (HPT) method, as a new platform for simulation of impacts by small solar system bodies, was applied to glycine. In comparison with high-pressure shock experiments, the HPT method simultaneously introduces high pressure and deformation strain. It was found that glycine was not polymerized in the experimental condition assayed, but partially decomposed to ethanol under pressures of 1 and 6 GPa and shear strains of <120 m/m. The detection of ethanol implies the inherent availability of remaining nitrogen-containing groups, which can incorporate to the formation of other organic molecules at the impact site. In addition, this finding highlights a possibility of the origin of ethanol previously detected in comets.

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K. Edalati, I. Taniguchi, R. Floriano, et. al.
Wed, 18 Jan 23
58/133

Comments: N/A

EXCEED-DM: Extended Calculation of Electronic Excitations for Direct Detection of Dark Matter [CL]

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http://arxiv.org/abs/2210.14917


Direct detection experiments utilizing electronic excitations are spearheading the search for light, sub-GeV, dark matter (DM). It is thus crucial to have accurate predictions for any DM-electron interaction rate in this regime. EXCEED-DM (EXtended Calculation of Electronic Excitations for Direct detection of Dark Matter) computes DM-electron interaction rates with inputs from a variety of ab initio electronic structure calculations. The purpose of this manuscript is two-fold: to familiarize the user with the formalism and inputs of EXCEED-DM, and perform novel calculations to showcase what EXCEED-DM is capable of. We perform four calculations which extend previous results: the scattering rate in the dark photon model, screened with the numerically computed dielectric function, the scattering rate with an interaction potential dependent on the electron velocity, an extended absorption calculation for scalar, pseudoscalar, and vector DM, and the annual modulation of the scattering rate in the dark photon model.

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T. Trickle
Fri, 28 Oct 22
12/56

Comments: 48 pages, 7 figures

Optimal anti-ferromagnets for light dark matter detection [CL]

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http://arxiv.org/abs/2210.13516


We propose anti-ferromagnets as optimal targets to hunt for sub-MeV dark matter with spin-dependent interactions. These materials allow for multi-magnon emission even for very small momentum transfers, and are therefore sensitive to dark matter particles as light as the keV. We use an effective theory to compute the event rates in a simple way. Among the materials studied here, we identify nickel oxide (a well-assessed anti-ferromagnet) as an ideal candidate target. Indeed, the propagation speed of its gapless magnons is very close to the typical dark matter velocity, allowing the absorption of all its kinetic energy, even through the emission of just a single magnon.

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A. Esposito and S. Pavaskar
Wed, 26 Oct 22
12/73

Comments: N/A

Molecular Structure, Dynamics, and Vibrational Spectroscopy of the Acetylene:Ammonia (1:1) Plastic Co-Crystal at Titan Conditions [CL]

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http://arxiv.org/abs/2210.12188


The Saturnian moon Titan has a thick, organic-rich atmosphere, and condensed phases of small organic molecules are anticipated to be stable on its surface. Of particular importance are crystalline phases of organics, known as cryominerals, which can play important roles in surface chemistry and geological processes on Titan. Many of these cryominerals could exhibit rich phase behavior, especially multicomponent cryominerals whose component molecules have multiple solid phases. One such cryomineral is the acetylene:ammonia (1:1) co-crystal, and here we use density functional theory-based ab initio molecular dynamics simulations to quantify its structure and dynamics at Titan conditions. We show that the acetylene:ammonia (1:1) co-crystal is a plastic co-crystal (or rotator phase) at Titan conditions because the ammonia molecules are orientationally disordered. Moreover, the ammonia molecules within this co-crystal rotate on picosecond timescales, and this rotation is accompanied by the breakage and reformation of hydrogen bonds between the ammonia hydrogens and the {\pi}-system of acetylene. The robustness of our predictions is supported by comparing the predictions of two density functional approximations at different levels of theory, as well as through the prediction of infrared and Raman spectra that agree well with experimental measurements. We anticipate that these results will aid in understanding geochemistry on the surface of Titan.

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A. Thakur and R. Remsing
Tue, 25 Oct 22
80/111

Comments: 11 pages, 9 figures, 2 tables

Electrical and Thermal Conductivity of High-Pressure Solid Iron [CL]

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http://arxiv.org/abs/2210.10132


We study the electrical and thermal conductivity of iron at high pressures using time-dependent density functional theory. In doing so, we particularly consider the impact of a Hubbard correction (+\textit{U}) specifically for regions where strong electron correlations are present. Using the TDDFT+U methodology, we examine the anisotropy in the thermal conductivity of HCP iron, which may provide insights into the transport properties at conditions relevant to the core-mantle boundary and the interior of the Earth.

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K. Ramakrishna, M. Lokamani, A. Baczewski, et. al.
Thu, 20 Oct 22
41/74

Comments: N/A

Revisiting Thermal Charge Carrier Refractive Noise in Semiconductor Optics for Gravitational-Wave Interferometers [CL]

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http://arxiv.org/abs/2209.09994


The test masses in next-generation gravitational-wave interferometers may have a semiconductor substrate, most likely silicon. The stochastic motion of charge carriers within the semiconductor will cause random fluctuations in the material’s index of refraction, introducing a noise source called Thermal Charge Carrier Refractive (TCCR) noise. TCCR noise was previously studied in 2020 by Bruns et al., using a Langevin force approach. Here we compute the power spectral density of TCCR noise by both using the Fluctuation-Dissipation theorem (FDT) and accounting for previously neglected effects of the standing wave of laser light which is produced inside the input test mass by its high-reflecting coatings. We quantify our results with parameters from Einstein Telescope, and show that at temperatures of 10 K the amplitude of TCCR noise is up to a factor of $\sqrt{2}$ times greater than what was previously claimed, and from 77 K to 300 K the amplitude is around 5 to 7 orders of magnitude lower than previously claimed when we choose to neglect the standing wave, and is up to a factor of 6 times lower if the standing wave is included. Despite these differences, we still conclude like Bruns et al. that TCCR noise should not be a limiting noise source for next-generation gravitational-wave interferometers.

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H. Siegel and Y. Levin
Thu, 22 Sep 22
54/65

Comments: 7 pages, 1 figure

A Systematic Error in the Internal Friction Measurement of Coatings for Gravitational Waves Detectors [IMA]

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http://arxiv.org/abs/2209.06106


Low internal friction coatings are key components of advanced technologies such as optical atomic clocks and high-finesse optical cavity and often lie at the forefront of the most advanced experiments in Physics. Notably, increasing the sensitivity of gravitational-wave detectors depends in a very large part on developing new coatings, which entails developing more suitable methods and models to investigate their loss angle. In fact, the most sensitive region of the detection band in such detectors is limited by the coating thermal noise, which is related to the loss angle of the coating. Until now, models which describe only ideal physical properties have been adopted, wondering about the use of one or more loss angles to describe the mechanical properties of coatings. Here we show the presence of a systematic error ascribed to inhomogeneity of the sample at its edges in measuring the coating loss angle. We present a model for disk-shaped resonators, largely used in loss angle measurements, and we compare the theory with measurements showing how this systematic error impacts on the accuracy with which the loss model parameters are known.

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A. Amato, D. Lumaca, E. Cesarini, et. al.
Wed, 14 Sep 22
25/90

Comments: N/A

Swarm of lightsail nanosatellites for Solar System exploration [CL]

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http://arxiv.org/abs/2208.10980


This paper presents a study for the realization of a space mission which employs nanosatellites driven by an external laser source impinging on an optimized lightsail, as a valuable technology to launch swarms of spacecrafts into the Solar System. Nanosatellites propelled by laser can be useful for the heliosphere exploration and for planetary observation, if suitably equipped with sensors, or be adopted for the establishment of network systems when placed into specific orbits. By varying the area-to-mass ratio (i.e., the ratio between the sail area and the payload weight) and the laser power, it is possible to insert the spacecraft into different hyperbolic orbits with respect to Earth, thus reaching the target by means of controlled trajectories in a relatively short amount of time. A mission involving nanosatellites of the order of 1 kg of mass is envisioned, by describing all the on-board subsystems and satisfying all the requirements in term of power and mass budget. Particular attention is paid to the telecommunication subsystem, which must offer all the necessary functionalities. To fabricate the lightsail, the thin films technology has been considered, by verifying the sail thermal stability during the thrust phase. Moreover, the problem of mechanical stability of the lightsail has been tackled, showing that the distance between the ligthsail structure and the payload plays a pivotal role. Some potential applications of the proposed technology are discussed, such as the mapping of the heliospheric environment.

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G. Santi, A. Corso, D. Garoli, et. al.
Wed, 24 Aug 22
62/67

Comments: N/A

AtoMEC: an open-source average-atom Python code [CL]

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http://arxiv.org/abs/2206.01074


Average-atom models are an important tool in studying matter under extreme conditions, such as those conditions experienced in planetary cores, brown and white dwarfs, and during inertial confinement fusion. In the right context, average-atom models can yield results with similar accuracy to simulations which require orders of magnitude more computing time, and thus they can greatly reduce financial and environmental costs. Unfortunately, due to the wide range of possible models and approximations, and the lack of open-source codes, average-atom models can at times appear inaccessible. In this paper, we present our open-source average-atom code, atoMEC. We explain the aims and structure of atoMEC to illuminate the different stages and options in an average-atom calculation, and facilitate community contributions. We also discuss the use of various open-source Python packages in atoMEC, which have expedited its development.

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T. Callow, D. Kotik, E. Kraisler, et. al.
Fri, 3 Jun 22
6/57

Comments: 9 pages, 8 figures. Submitted to Proceedings of the 21st Python in Science Conference (SciPy 2022)

Nested sampling for physical scientists [CL]

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http://arxiv.org/abs/2205.15570


We review Skilling’s nested sampling (NS) algorithm for Bayesian inference and more broadly multi-dimensional integration. After recapitulating the principles of NS, we survey developments in implementing efficient NS algorithms in practice in high-dimensions, including methods for sampling from the so-called constrained prior. We outline the ways in which NS may be applied and describe the application of NS in three scientific fields in which the algorithm has proved to be useful: cosmology, gravitational-wave astronomy, and materials science. We close by making recommendations for best practice when using NS and by summarizing potential limitations and optimizations of NS.

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G. Ashton, N. Bernstein, J. Buchner, et. al.
Wed, 1 Jun 22
5/65

Comments: 20 pages + supplementary information, 5 figures. preprint version; published version at this https URL

The specific heat of astro-materials: Review of theoretical concepts, materials and techniques [EPA]

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http://arxiv.org/abs/2205.08212


We provide detailed background, theoretical and practical, on the specific heat cp of minerals and mixtures thereof, ‘astro-materials’, as well as background information on common minerals and other relevant solid substances found on the surfaces of solar system bodies. Furthermore, we demonstrate how to use specific heat and composition data for lunar samples and meteorites as well as a new database of endmember mineral heat capacities (the result of an extensive literature review) to construct reference models for the isobaric specific heat cP as a function of temperature for common solar system materials. Using a (generally linear) mixing model for the specific heat of minerals allows extrapolation of the available data to very low and very high temperatures, such that models cover the temperature range between 10 and 1000 K at least (and pressures from zero up to several kbars). We describe a procedure to estimate cp(T) for virtually any solid solar system material with a known mineral composition, e.g., model specific heat as a function of temperature for a number of typical meteorite classes with known mineralogical compositions. We present, as examples, the cp(T) curves of a number of well-described laboratory regolith analogues, as well as for planetary ices and ‘tholins’ in the outer solar system. Part II will review and present the heat capacity database for minerals and compounds and part III is going to cover applications, standard reference compositions, cp(T) curves and a comparison with new and literature experimental data.

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J. Biele, M. Grott, M. Zolensky, et. al.
Wed, 18 May 22
65/66

Comments: submitted to Special Issue for International Journal of Thermophysics ‘Thermophysics of Advanced Spacecraft Materials and Extraterrestrial Samples’ Part II to be submitted still in 2022

Strategies to reduce the thermoelastic loss of multimaterial coated finite substrates [CL]

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http://arxiv.org/abs/2204.09808


Thermoelastic loss is one of the main energy dissipation mechanisms in resonant systems. A careful analysis of the thermoelastic loss is critical to design low-noise resonators for high-precision applications, such as gravitational-wave detectors. This paper presents an analytical solution to the thermoelastic loss in multimaterial coated finite substrates with realistic assumptions on the model structure and the elastic fields. The mechanism responsible for thermoelastic loss is taken as a function of material properties, operating temperature and frequency, and other design parameters. We calculate the thermoelastic loss for specific applications over a wide range of frequencies (1 Hz to 10 GHz) and temperatures (1 K to 300 K), and for a variety of substrate and coating materials. The result is relevant for gravitational-wave detectors and for experiments sensitive to mechanical dissipation.

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R. Zhou, M. Molina-Ruiz and F. Hellman
Fri, 22 Apr 22
37/64

Comments: N/A

Electrical Conductivity of Iron in Earth's Core from Microscopic Ohm's Law [CL]

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http://arxiv.org/abs/2203.06025


Understanding the electronic transport properties of iron under high temperatures and pressures is essential for constraining geophysical processes. The difficulty of reliably measuring these properties under Earth-core conditions calls for sophisticated theoretical methods that can support diagnostics. We present results of the electrical conductivity within the pressure and temperature ranges found in Earth’s core from simulating microscopic Ohm’s law using time-dependent density functional theory. Our predictions provide a new perspective on resolving discrepancies in recent experiments.

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K. Ramakrishna, M. Lokamani, A. Baczewski, et. al.
Mon, 14 Mar 22
22/67

Comments: N/A

Ultrahigh-Pressure Magnesium Hydrosilicates as Reservoirs of Water in Early Earth [CL]

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http://arxiv.org/abs/2202.00752


The origin of water on the Earth is a long-standing mystery, requiring a comprehensive search for hydrous compounds, stable at conditions of the deep Earth and made of Earth-abundant elements. Previous studies usually focused on the current range of pressure-temperature conditions in the Earth’s mantle and ignored a possible difference in the past, such as the stage of the core-mantle separation. Here, using ab initio evolutionary structure prediction, we find that only two magnesium hydrosilicate phases are stable at megabar pressures, $\alpha$-Mg$_2$SiO$_5$H$_2$ and $\beta$-Mg$_2$SiO$_5$H$_2$, stable at 262-338 GPa and >338 GPa,respectively (all these pressures now lie within the Earth’s iron core). Both are superionic conductors with quasi-one-dimensional proton diffusion at relevant conditions. In the first 30 million years of Earth’s history, before the Earth’s core was formed, these must have existed in the Earth, hosting much of Earth’s water. As dense iron alloys segregated to form the Earth’s core, Mg$_2$SiO$_5$H$_2$ phases decomposed and released water. Thus, now-extinct Mg$_2$SiO$_5$H$_2$ phases have likely contributed in a major way to the evolution of our planet.

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H. Li, A. Oganov, H. Cui, et. al.
Thu, 3 Feb 22
28/56

Comments: N/A

Condensation of cometary silicate dust using an induction thermal plasma system I. Enstatite and CI chondritic composition [EPA]

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http://arxiv.org/abs/2111.10955


Glass with embedded metal and sulfides (GEMS) is a major component of chondritic porous interplanetary dust particles. Although GEMS is one of the most primitive components in the Solar System, its formation process and conditions have not been constrained. We performed condensation experiments of gases in the system of Mg-Si-O (MgSiO3 composition) and of the S-free CI chondritic composition (Si-Mg-Fe-Na-Al-Ca-Ni-O system) in induction thermal plasma equipment. Amorphous Mg-silicate particles condensed in the experiments of the Mg-Si-O system, and their grain size distribution depended on the experimental conditions (mainly partial pressure of SiO). In the CI chondritic composition experiments, irregularly shaped amorphous silicate particles of less than a few hundred nanometers embedded with multiple Fe-Ni nanoparticles of ~<20 nm were successfully synthesized. These characteristics are very similar to those of GEMS, except for the presence of FeSi instead of sulfide grains. We propose that the condensation of amorphous silicate grains smaller than a few tens of nanometers and with metallic cores, followed by coagulation, could be the precursor material that forms GEMS prior to sulfidation.

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T. Kim, A. Takigawa, A. Tsuchiyama, et. al.
Tue, 23 Nov 21
41/84

Comments: N/A

C60 Cation as the Carrier of the 9577 and 9632 Angstrom Diffuse Interstellar Bands: Further Support from the VLT/X-Shooter Spectra [GA]

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http://arxiv.org/abs/2111.05769


Ever since their first detection over 100 years ago, the mysterious diffuse interstellar bands (DIBs), a set of several hundred broad absorption features seen against distant stars in the optical and near infrared wavelength range, largely remain unidentified. The close match both in wavelengths and in relative strengths recently found between the experimental absorption spectra of gas-phase buckminsterfullerene ions (C60+) and four DIBs at 9632, 9577, 9428 and 9365 Angstrom (and, to a lesser degree, a weaker DIB at 9348 Angstrom) suggests C60+ as a promising carrier. However, arguments against the C60+ identification remain and are mostly concerned with the large variation in the intensity ratios of the 9632 and 9577 DIBs. In this work, we search for these DIBs in the ESO VLT/X-shooter archival data and identify the 9632, 9577, 9428 and 9365 Angstrom DIBs in a sample of 25 stars. While the 9428 and 9365 Angstrom DIBs are too noisy to allow any reliable analysis, the 9632 and 9577 Angstrom DIBs are unambiguously detected and, after correcting for telluric water vapor absorption, their correlation can be used to probe their origin. To this end, we select a sub-sample of nine hot, O- or B0-type stars of which the stellar Mg II contamination to the 9632 Angstrom DIB is negligibly small. We find their equivalent widths, after normalized by reddening to eliminate their common correlation with the density of interstellar clouds, exhibit a tight, positive correlation. This supports C60+ as the carrier of the 9632 and 9577 Angstrom DIBs.

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T. Nie, F. Xiang and A. Li
Thu, 11 Nov 21
51/60

Comments: 8 pages, 4 figures, 2 tables; accepted for publication in the Monthly Notices of the Royal Astronomical Society

Where have all the interstellar silicon carbides gone? [GA]

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http://arxiv.org/abs/2111.03920


The detection of the 11.3-micron emission feature characteristic of the Si–C stretch in carbon-rich evolved stars reveals that silicon carbide (SiC) dust grains are condensed in the outflows of carbon stars. SiC dust could be a significant constituent of interstellar dust since it is generally believed that carbon stars inject a considerable amount of dust into the interstellar medium (ISM). The presence of SiC dust in the ISM is also supported by the identification of presolar SiC grains of stellar origin in primitive meteorites. However, the 11.3-micron absorption feature of SiC has never been seen in the ISM and oxidative destruction of SiC is often invoked. In this work we quantitatively explore the destruction of interstellar SiC dust through oxidation based on molecular dynamics simulations and density functional theory calculations. We find that the reaction of an oxygen atom with SiC molecules and clusters is exothermic and could cause CO-loss. Nevertheless, even if this is extrapolable to bulk SiC dust, the destruction rate of SiC dust through oxidation could still be considerably smaller than the (currently believed) injection rate from carbon stars. Therefore, the lack of the 11.3-micron absorption feature of SiC dust in the ISM remains a mystery. A possible solution may lie in the currently believed stellar injection rate of SiC (which may have been overestimated) and/or the size of SiC dust (which may actually be considerably smaller than submicron in size).

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T. Chen, C. Xiao, A. Li, et. al.
Tue, 9 Nov 21
41/102

Comments: 7 pages, 5 figures; accepted for publication in MNRAS

Study of spectrally resolved thermoluminescence in Tsarev and Chelyabinsk chondrites with a versatile high-sensitive setup [EPA]

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http://arxiv.org/abs/2111.01405


Thermoluminescence (TL) research provides a powerful tool for characterizing radiation-induced processes in extraterrestrial matter. One of the challenges in studying the spectral features of the natural TL of stony meteorites is its weak intensity. The present work showcases the capabilities of a high-sensitive original module for measuring the spectrally resolved TL characteristics of the Chelyabinsk and Tsarev chondrites. We have analyzed the emission spectra and glow curves of natural and induced TL over the 300 – 650 nm and RT – 873 K ranges. A quasi-continuous distribution of traps active within the 350 – 650 K range was found in the silicate substructure of both meteorites under study. Based on the general order kinetic formalism and using the natural TL data, we also estimated the activation energies of 0.86 and 1.08 eV for the Chelyabinsk and Tsarev chondrites, respectively.

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A. Vokhmintsev, A. Henaish, T. Sharshar, et. al.
Wed, 3 Nov 21
74/106

Comments: 7 pages, 4 figures, 2 tables, 18 references; Keywords: TL spectroscopy; ordinary chondrite; Chelyabinsk LL5; Tsarev L5; activation energy

Hydrogenated Amorphous Silicon Carbide: A Low-loss Deposited Dielectric for Microwave to Submillimeter Wave Superconducting Circuits [CL]

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http://arxiv.org/abs/2110.03500


Low-loss deposited dielectrics will benefit superconducting devices such as integrated superconducting spectrometers, superconducting qubits and kinetic inductance parametric amplifiers. Compared with planar structures, multi-layer structures such as microstrips are more compact and eliminate radiation loss at high frequencies. Multi-layer structures are most easily fabricated with deposited dielectrics, which typically exhibit higher dielectric loss than crystalline dielectrics. We measured the sub-kelvin and low-power microwave and mm-submm wave dielectric loss of hydrogenated amorphous silicon carbide (a-SiC:H), using a superconducting chip with NbTiN/a-SiC:H/NbTiN microstrip resonators. We deposited the a-SiC:H by plasma-enhanced chemical vapor deposition at a substrate temperature of 400{\deg}C. The a-SiC:H has a mm-submm loss tangent ranging from $0.80 \pm 0.01 \times 10^{-4}$ to $1.43 \pm 0.04 \times 10^{-4}$ in the range of 270 to 385 GHz. The microwave loss tangent is $3.2 \pm 0.2 \times 10^{-5}$. These are the lowest low-power sub-kelvin loss tangents that have been reported for microstrip resonators at mm-submm and microwave frequencies. We observe that the loss tangent increases with frequency. The a-SiC:H films are free of blisters and have low stress: $-$20 MPa compressive at 200 nm thickness to 60 MPa tensile at 1000 nm thickness.

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B. Buijtendorp, S. Vollebregt, K. Karatsu, et. al.
Fri, 8 Oct 21
49/70

Comments: N/A

Directional Detection of Light Dark Matter in Superconductors [CL]

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http://arxiv.org/abs/2109.04473


Superconducting detectors have been proposed as outstanding targets for the direct detection of light dark matter scattering at masses as low as a keV. We study the prospects for directional detection of dark matter in isotropic superconducting targets from the angular distribution of excitations produced in the material. We find that dark matter scattering produces initial excitations with an anisotropic distribution, and further show that this directional information can be preserved as the initial excitations relax. Our results demonstrate that directional detection is possible for a wide range of dark matter masses, and pave the way for light dark matter discovery with bulk superconducting targets.

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Y. Hochberg, E. Kramer, N. Kurinsky, et. al.
Mon, 13 Sep 21
33/52

Comments: 5 pages + references, 2 figures. Includes supplementary material (11 pages, 5 figures). Code available at this https URL

Experimentally measuring rolling and sliding in three-dimensional dense granular packings [CL]

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http://arxiv.org/abs/2108.11975


Understanding granular materials’ aging poses a substantial challenge: Grain contacts form networks with complex topologies, and granular flow is far from equilibrium. In this letter, we experimentally measure a three-dimensional granular system’s reversibility and aging under cyclic compression. We image the grains using a refractive-index-matched fluid, then analyze the images using the artificial intelligence of variational autoencoders. These techniques allow us to track all the grains’ translations and three-dimensional rotations with accuracy sufficient to infer contact-point sliding and rolling. Our observations reveal unique roles played by three-dimensional rotations in granular flow, aging, and energy dissipation. First, we find that granular rotations dominate the bulk dynamics, penetrating more deeply into the granular material than translations do. Second, sliding and rolling do not exhibit aging across the experiment, unlike translations. Third, aging appears not to minimize energy dissipation, according to our experimental measurements of rotations, combined with soft-sphere simulations. The experimental tools, analytical techniques, and observations that we introduce expose all the degrees of freedom of the far-from-equilibrium dynamics of granular flow.

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Z. Benson, A. Peshkov, N. Halpern, et. al.
Mon, 30 Aug 21
30/38

Comments: N/A

Searches for light dark matter using condensed matter systems [CL]

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http://arxiv.org/abs/2108.03239


Identifying the nature of dark matter (DM) has long been a pressing question for particle physics. In the face of ever-more-powerful exclusions and null results from large-exposure searches for TeV-scale DM interacting with nuclei, a significant amount of attention has shifted to lighter (sub-GeV) DM candidates. Direct detection of the light dark matter in our galaxy by observing DM scattering off a target system requires new approaches compared to prior searches. Lighter DM particles have less available kinetic energy, and achieving a kinematic match between DM and the target mandates the proper treatment of collective excitations in condensed matter systems, such as charged quasiparticles or phonons. In this context, the condensed matter physics of the target material is crucial, necessitating an interdisciplinary approach. In this review, we provide a self-contained introduction to direct detection of keV-GeV DM with condensed matter systems. We give a brief survey of dark matter models and basics of condensed matter, while the bulk of the review deals with the theoretical treatment of DM-nucleon and DM-electron interactions. We also review recent experimental developments in detector technology, and conclude with an outlook for the field of sub-GeV DM detection over the next decade.

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Y. Kahn and T. Lin
Tue, 10 Aug 21
17/84

Comments: 89 pages, 19 figures, 2 tables. Submitted as an invited review to Reports on Progress in Physics

Quantum Induced Broadening- A Challenge For Cosmic Neutrino Background Discovery [CL]

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http://arxiv.org/abs/2108.03695


A recent preprint by Cheipesh {\it et al.} pointed out that the zero-point motion of Tritium atoms bound to Graphene may blur the measured energies of $\beta$ electrons. Smearing due to zero point motion is well known. Such an effect features in studies of the $\beta$ spectrum expected in experiments like KATRIN using diatomic Tritium. The recent preprint may, however, challenge new planned experiments seeking to discover the Cosmic Neutrino Background (CNB) neutrinos (and/or other neutrinos of masses smaller than $0.1$ eV) which plan to use Tritium adsorbed onto Graphene or other materials. Our paper clarifies these issues and examines the more general problem of smearing induced by quantum uncertainty. We find that the effect of Cheipesh {\it et al.} is reduced considerably. The importance of the chemical evolution of the $^{3}$H atom hosting the Tritium nucleus into a tightly bound neutral $^{3}$He atom is emphasized. We estimate the excess blurring caused by the dense spectrum near the lowest state of the Graphene or other hosts of the Tritium atom, generated by the electronic response to the “sudden” escape of the $\beta$ electron. Our analysis suggests yet larger effects and difficulties facing many experiments searching for small mass neutrinos. We speculate on a possible experimental setup which could minimize quantum broadening.

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S. Nussinov and Z. Nussinov
Tue, 10 Aug 21
30/84

Comments: 13 pages, 1 figure

Partially Diffusive Helium-Silica Compound in the Deep Interiors of Giant Planets [CL]

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http://arxiv.org/abs/2107.14416


Helium is the second most abundant element in the universe, and together with silica, they are major components of giant planets. Exploring the reactivity and state of helium and silica under high pressure is of fundamental importance for developing and understanding of the evolution and internal structure of giant planets. Here, using first-principles calculations and crystal structure predictions, we identify four stable phases of a helium-silica compound with seven/eight-coordinated silicon atoms at pressure range of 600-4000 GPa, corresponding to the interior condition of the outer planets in the solar system. The density of HeSiO2 agrees with current structure models of the planets. This helium-silica compound exhibits a superionic-like helium diffusive state at the high pressure and high temperature conditions along the isentropes of Saturn, a metallic fluid state in Jupiter, and a solid state in the deep interiors of Uranus and Neptune. The reaction of helium and silica may lead to the erosion of the rocky core of giant planets and form a diluted core region. These results highlight the reactivity of helium under high pressure to form new compounds, and also provides evidence to help build more sophisticated interior models of giant planets.

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C. Liu, J. Wang, X. Deng, et. al.
Mon, 2 Aug 21
49/82

Comments: 20 pages, 5 figures

Superionic silica-water and silica-hydrogen compounds under high pressure [CL]

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http://arxiv.org/abs/2107.13728


Silica, water and hydrogen are known to be the major components of celestial bodies, and have significant influence on the formation and evolution of giant planets, such as Uranus and Neptune. Thus, it is of fundamental importance to investigate their states and possible reactions under the planetary conditions. Here, using advanced crystal structure searches and first-principles calculations in the Si-O-H system, we find that a silica-water compound (SiO2)2(H2O) and a silica-hydrogen compound SiO2H2 can exist under high pressures above 450 and 650 GPa, respectively. Further simulations reveal that, at high pressure and high temperature conditions corresponding to the interiors of Uranus and Neptune, these compounds exhibit superionic behavior, in which protons diffuse freely like liquid while the silicon and oxygen framework is fixed as solid. Therefore, these superionic silica-water and silica-hydrogen compounds could be regarded as important components of the deep mantle or core of giants, which also provides an alternative origin for their anomalous magnetic fields. These unexpected physical and chemical properties of the most common natural materials at high pressure offer key clues to understand some abstruse issues including demixing and erosion of the core in giant planets, and shed light on building reliable models for solar giants and exoplanets.

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H. Gao, C. Liu, J. Shi, et. al.
Fri, 30 Jul 21
34/71

Comments: 13 pages, 4 figures

The vibrational properties of benzene on an ordered water ice surface [CL]

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http://arxiv.org/abs/2107.08826


We present a hybrid CCSD(T)+PBE-D3 approach to calculating the vibrational signatures for gas phase benzene and benzene adsorbed on an ordered water-ice surface. We compare the results of our method against experimentally recorded spectra and calculations performed using PBE-D3-only approaches (harmonic and anharmonic). Calculations use a proton ordered XIh water-ice surface consisting of 288 water molecules, and results are compared against experimental spectra recorded for an ASW ice surface. We show the importance of including a water ice surface into spectroscopic calculations, owing to the resulting differences in vibrational modes, frequencies and intensities of transitions seen in the IR spectrum. The overall intensity pattern shifts from a dominating $\nu_{11}$ band in the gas-phase to several high-intensity carriers for an IR spectrum of adsorbed benzene. When used for adsorbed benzene, the hybrid approach presented here achieves an RMSD for IR active modes of 21~cm$^{-1}$, compared to 72~cm$^{-1}$ and 49~cm$^{-1}$ for the anharmonic and harmonic PBE-D3 approaches, respectively. Our hybrid model for gaseous benzene also achieves the best results when compared to experiment, with an RMSD for IR active modes of 24~cm$^{-1}$, compared to 55~cm$^{-1}$ and 31~cm$^{-1}$ for the anharmonic and harmonic PBE-D3 approaches, respectively. To facilitate assignment, we generate and provide a correspondence graph between the normal modes of the gaseous and adsorbed benzene molecules. Finally, we calculate the frequency shifts, $\Delta\nu$, of adsorbed benzene relative to its gas phase to highlight the effects of surface interactions on vibrational bands and evaluate the suitability of our chosen dispersion-corrected density functional theory.

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V. Clark and D. Benoit
Wed, 21 Jul 21
77/83

Comments: N/A

Magnetism of Fullerene C60 Compared with Graphene Molecule by DFT Calculation, Laboratory Experiment and Astronomical Observation [GA]

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http://arxiv.org/abs/2107.04725


Magnetism of fullerene C60 was studied by three methods of the density functional theory (DFT) calculation, laboratory experiment and astronomical observation. DFT revealed that the most stable spin state was non-magnetic one of Sz=0/2. This is contrary to our recent study on void induced graphene molecules of C23 and C53 to be magnetic one of Sz=2/2. Two graphene molecules combined model suggested that two up-spin at every carbon pentagon ring may cancel each other to bring Sz=0/2. Similar cancelation may occur on C60. Molecular vibrational infrared spectrum of C60 show four major bands, which coincide with gas-phase laboratory experiment, also with astronomically observed one of carbon rich planetary nebula Tc1 and Lin49. However, there remain many unidentified bands on astronomical one. We supposed multiple voids on graphene sheet, which may create both C60 and complex graphene molecules. It was revealed that spectrum of two voids induced graphene molecule coincident well with major astronomical bands. Simple sum of C60 and graphene molecules could successfully reproduce astronomical bands in detail.

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N. Ota, A. Li, L. Nemes, et. al.
Tue, 13 Jul 21
1/79

Comments: 10 pages, 11 figures, 2 tables. arXiv admin note: text overlap with arXiv:2104.09745

Atom-in-jellium predictions of the shear modulus at high pressure [CL]

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http://arxiv.org/abs/2105.12303


Atom-in-jellium calculations of the Einstein frequency in condensed matter and of the equation of state were used to predict the variation of shear modulus from zero pressure to $\sim 10^7$ g/cm$^3$, for several elements relevant to white dwarf (WD) stars and other self-gravitating systems. This is by far the widest range reported electronic structure calculation of shear modulus, spanning from ambient through the one-component plasma to extreme relativistic conditions. The predictions were based on a relationship between Debye temperature and shear modulus which we assess to be accurate at the $o(10\%)$ level, and is the first known use of atom-in-jellium theory to calculate a shear modulus. We assessed the overall accuracy of the method by comparing with experimental measurements and more detailed electronic structure calculations at lower pressures.

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D. Swift, T. Lockard, S. Hamel, et. al.
Thu, 27 May 21
33/62

Comments: N/A

Extended Calculation of Dark Matter-Electron Scattering in Crystal Targets [CL]

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http://arxiv.org/abs/2105.05253


We extend the calculation of dark matter direct detection rates via electronic transitions in general dielectric crystal targets, combining state-of-the-art density functional theory calculations of electronic band structures and wave functions near the band gap, with semi-analytic approximations to include additional states farther away from the band gap. We show, in particular, the importance of all-electron reconstruction for recovering large momentum components of electronic wave functions, which, together with the inclusion of additional states, has a significant impact on direct detection rates, especially for heavy mediator models and at $\mathcal{O}(10\,\text{eV})$ and higher energy depositions. Applying our framework to silicon and germanium (that have been established already as sensitive dark matter detectors), we find that our extended calculations can appreciably change the detection prospects. Our calculational framework is implemented in an open-source program $\texttt{EXCEED-DM}$ (EXtended Calculation of Electronic Excitations for Direct detection of Dark Matter), to be released in an upcoming publication.

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S. Griffin, K. Inzani, T. Trickle, et. al.
Thu, 13 May 21
21/60

Comments: 34 pages, 15 figures

Void defect induced magnetism and structure change of carbon materials-1, Graphene nano ribbon [CL]

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http://arxiv.org/abs/2104.09740


Void defect is a possible origin of ferromagnetic like feature of pure carbon material. Applying density functional theory to void defect induced graphene nano ribbon (GNR), a detailed relationship between multiple spin state and structure change was studied. An equitorial triangle of an initial initial void having six electrons is distorted to isosceles triangle by rebonding carbon atoms. Among possible spin states, the most stable state was Sz=2/2. The case of Sz=4/2 is remarkable that initial flat ribbon turned to three dimentional curled one having highly polarized spin configuration at ribbon edges. Total energy of Sz=4/2 was very close to that of Sz=2/2, which suggests coexistence of flat and curled ribbons. As a model of three dimensional graphite, bilayered AB stacked GNR was analyzed. Spin distribution was limited to the void created layer. Distributed void triangle show 60 degree clockwise rotation for differrent site void, which was consistent with experimental observation using the scanning tunneling microscope. (To be published on Journal of the Magnetic Society of Japan, 2021 )

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N. Ota and L. Nemes
Wed, 21 Apr 2021
12/72

Comments: 7 pages, 7 figures, 2 tables

Void defect induced magnetism and structure change of carbon material-3, Polycyclic aromatic hydrocarbon [GA]

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http://arxiv.org/abs/2104.09747


Void-defect induced magnetism of graphene molecule was recently reported in our previous paper of this series study. This paper investigated the case of hydrogenated graphene molecule, in chemical term, polycyclic aromatic hydrocarbon (PAH). Molecular infrared spectrum obtained by density functional theory was compared with astronomical observation. Void-defect on PAH caused serious structure change. Typical example of C23H12 had two carbon pentagon rings among hexagon networks. Stable spin state was non-magnetic singlet state. This is contrary to pure carbon case of C23, which show magnetic triplet state. It was discussed that Hydrogen played an important role to diminish magnetism by creating an SP3-bond among SP2-networks. Such a structure change affected molecular vibration and finally to photoemission spectrum in infrared region. The dication-C23H12 showed featured bands at 3.2, 6.3, 7.7, 8.6, 11.2, and 12.7 micrometer. It was surprising that those calculated bands coincided well with astronomically observed bands in many planetary nebulae. To confirm our study, large size molecule of C53H18 was studied. Calculation reproduced again similar astronomical bands. Also, small size molecule of C12H8 showed good coincidence with the spectrum observed for young stars. This paper would be the first report to indicate the specific PAH in space.

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N. Ota, A. Li and L. Nemes
Wed, 21 Apr 2021
38/72

Comments: 10 pages, 14 figures, 1 table

Void defect induced magnetism and structure change of carbon material-2, Graphene molecules [GA]

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http://arxiv.org/abs/2104.09745


Void-defect is a possible origin of ferromagnetic feature on pure carbon materials. In our previous paper, void-defect on graphene-nanoribbon show highly polarized spin configuration. In this paper, we studied cases for graphene molecules by quantum theory, by astronomical observation and by laboratory experiment. Model molecules for the density functional theory are graphene molecules of C23 and C53 induced by a void-defect. They have carbon pentagon ring within a hexagon network. Single void has three radical carbons, holding six spins. Those spins make several spin-states, which affects to molecular structure and molecular vibration, finally to infrared spectrum. The stable spin state was triplet, not singlet. This suggests magnetic pure carbon molecule. It was a surprise that those molecules show close infrared spectrum with astronomically observed one, especially observed on carbon rich planetary nebulae. We could assign major band at 18.9 micrometer, and sub-bands at 6.6, 7.0, 7.6, 8.1, 8.5, 9.0 and 17.4 micrometer. Also, calculated spectrum roughly coincides with that of laboratory experiment by the laser-induced carbon plasma, which is an analogy of cosmic carbon creation in interstellar space.

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N. Ota, A. Li, L. Nemes, et. al.
Wed, 21 Apr 2021
64/72

Comments: 9 pages, 6 figures, 1 table. arXiv admin note: text overlap with arXiv:2007.03862

Critical processing temperature for high performance protected silver thin film mirrors [IMA]

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http://arxiv.org/abs/2104.08233


Silver (Ag) mirrors for astronomical telescopes consist of multiple metallic and dielectric thin films. Furthermore, the topmost surface of such Ag mirrors needs to be covered by a protection coating. While the protection coating is often deposited at room temperature and the entire mirrors are also handled at room temperature, various thin film deposition techniques offer protection coatings with improved characteristics when carried out at elevated temperatures. Thus, in this work, high-performance Ag mirrors were designed and fabricated with a new benchmark. The resulting Ag mirrors were annealed (i.e., post-fabrication annealing) at various temperatures to investigate the viability of introducing thermal processes during and/or after fabrication in improving overall optical performance and durability of protected silver mirrors. In our experiments, Ag mirror samples were deposited by electron-beam evaporation and subsequently annealed at various temperatures in the range from 60 °C to 300 °C, and then the mirror samples underwent an environmental stress test at 80 °C and 80% humidity for 10 days. While all the mirror samples annealed below 200 °C showed negligible corrosion after undergoing the stress testing, those annealed below 160 °C presented spectral reflectivity comparable to or higher than that of as-deposited reference samples. In contrast, the mirror samples annealed above 200 °C exhibited significant degradation after the stress testing. The comprehensive analysis indicated that delamination and voids caused by the growth of Ag grains during the annealing are the primary mechanisms of the degradation.

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D. Fryauf, A. Phillips and N. Kobayashi
Mon, 19 Apr 2021
12/74

Comments: 18 pages, 7 figures

Binary and ternary ionic compounds in the outer crust of a cold nonaccreting neutron star [CL]

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http://arxiv.org/abs/2103.06073


The outer crust of a cold nonaccreting neutron star has been generally assumed to be stratified into different layers, each of which consists of a pure body-centered cubic ionic crystal in a charge compensating background of highly degenerate electrons. The validity of this assumption is examined by analyzing the stability of multinary ionic compounds in dense stellar matter. It is thus shown that their stability against phase separation is uniquely determined by their structure and their composition irrespective of the stellar conditions. However, equilibrium with respect to weak and strong nuclear processes imposes very stringent constraints on the composition of multinary compounds, and thereby on their formation. By examining different cubic and noncubic lattices, it is found that substitutional compounds having the same structure as cesium chloride are the most likely to exist in the outer crust of a nonaccreting neutron star. The presence of ternary compounds is also investigated. Very accurate analytical expressions are obtained for the threshold pressure, as well as for the densities of the different phases irrespective of the degree of relativity of the electron gas. Finally, numerical calculations of the ground-state structure and of the equation of state of the outer crust of a cold nonaccreting neutron star are carried out using recent experimental and microscopic nuclear mass tables.

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N. Chamel and A. Fantina
Thu, 11 Mar 21
44/62

Comments: 34 pages, 10 figures

Atom-in-jellium equations of state and melt curves in the white dwarf regime [SSA]

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http://arxiv.org/abs/2103.03371


Atom-in-jellium calculations of the electron states, and perturbative calculations of the Einstein frequency, were used to construct equations of state (EOS) from around $10^{-5}$ to $10^7$g/cm$^3$ and $10^{-4}$ to $10^{6}$eV for elements relevant to white dwarf (WD) stars. This is the widest range reported for self-consistent electronic shell structure calculations. Elements of the same ratio of atomic weight to atomic number were predicted to asymptote to the same $T=0$ isotherm, suggesting that, contrary to recent studies of the crystallization of WDs, the amount of gravitational energy that could be released by separation of oxygen and carbon is small. A generalized Lindemann criterion based on the amplitude of the ion-thermal oscillations calculated using atom-in-jellium theory, previously used to extrapolate melt curves for metals, was found to reproduce previous thermodynamic studies of the melt curve of the one component plasma with a choice of vibration amplitude consistent with low pressure results. For elements for which low pressure melting satisfies the same amplitude criterion, such as Al, this melt model thus gives a likely estimate of the melt curve over the full range of normal electronic matter; for the other elements, it provides a useful constraint on the melt locus.

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D. Swift, T. Lockard, S. Hamel, et. al.
Mon, 8 Mar 21
17/65

Comments: N/A

Fabrication of astronomical x-ray reflection gratings using thermally activated selective topography equilibration [IMA]

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http://arxiv.org/abs/2102.12359


Thermally activated selective topography equilibration (TASTE) enables the creation of 3D structures in resist using grayscale electron-beam lithography followed by a thermal treatment to induce a selective polymer reflow. A blazed grating topography can be created by reflowing repeating staircase patterns in resist into wedge-like structures. Motivated by astronomical applications, such patterns with periodicities 840 nm and 400 nm have been fabricated in 130 nm-thick PMMA using TASTE to provide a base for X-ray reflection gratings. A path forward to integrate this alternative blazing technique into grating fabrication recipes is discussed.

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J. McCoy, R. McEntaffer and C. Eichfeld
Thu, 25 Feb 21
22/50

Comments: 21 pages, 8 figures, from a special edition of JVST B for the 62nd International Conference on Electron, Ion, and Photon Beam Technology and Nanofabrication (EIPBN)

Directional Detectability of Dark Matter With Single Phonon Excitations: Target Comparison [CL]

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http://arxiv.org/abs/2102.09567


Single phonon excitations are sensitive probes of light dark matter in the keV-GeV mass window. For anisotropic target materials, the signal depends on the direction of the incoming dark matter wind and exhibits a daily modulation. We discuss in detail the various sources of anisotropy, and carry out a comparative study of 26 crystal targets, focused on sub-MeV dark matter benchmarks. We compute the modulation reach for the most promising targets, corresponding to the cross section where the daily modulation can be observed for a given exposure, which allows us to combine the strength of DM-phonon couplings and the amplitude of daily modulation. We highlight Al$_2$O$_3$ (sapphire), CaWO$_4$ and h-BN (hexagonal boron nitride) as the best polar materials for recovering a daily modulation signal, which feature $\mathcal{O}(1 – 100)\%$ variations of detection rates throughout the day, depending on the dark matter mass and interaction. The directional nature of single phonon excitations offers a useful handle to mitigate backgrounds, which is crucial for fully realizing the discovery potential of near future experiments.

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A. Coskuner, T. Trickle, Z. Zhang, et. al.
Mon, 22 Feb 21
32/51

Comments: 13 pages, 11 figures

PTAL multi-spectral database of planetary terrestrial analogues: Raman data overview [EPA]

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http://arxiv.org/abs/2101.08305


The multi analytical study of terrestrial analogues is a useful strategy to deepen the knowledge about the geological and environmental evolution of Mars and other extraterrestrial bodies. In spite of the increasing importance that LIBS, NIR and Raman techniques are acquiring in the field of space exploration, there is a lack web-based platform providing free access to a wide multi-spectral database of terrestrial analogue materials. The Planetary Terrestrial Analogue Library (PTAL) project aims at responding to this critical need by developing and providing free web accessibility to LIBS, NIR and Raman data from more than 94 terrestrial analogues selected according to their congruence with Martian geological contexts. In this framework, the present manuscript provides the scientific community with a complete overview of the over 4500 Raman spectra collected to feed the PTAL database. Raman data, obtained through the complementary use of laboratory and spacecraft-simulator systems, confirmed the effectiveness of this spectroscopic technique for the detection of major and minor mineralogical phases of the samples, the latter being of critical importance for the recognition of geological processes that could have occurred on Mars and other planets. In light of the forthcoming missions to Mars, the results obtained through the RLS ExoMars Simulator offer a valuable insight on the scientific outcome that could derive from the RLS spectrometer that will soon land on Mars as part of the ExoMars rover payload.

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M. Veneranda, J. Saiz, A. Sanz-Arranz, et. al.
Fri, 22 Jan 21
33/69

Comments: N/A

A New Method for Simulating Photoprocesses in Astrochemical Models [GA]

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http://arxiv.org/abs/2101.01209


We propose a new model for treating solid-phase photoprocesses in interstellar ice analogues. In this approach, photoionization and photoexcitation are included in more detail, and the production of electronically-excited (suprathermal) species is explicitly considered. In addition, we have included non-thermal, non-diffusive chemistry to account for the low-temperature characteristic of cold cores. As an initial test of our method, we have simulated two previous experimental studies involving the UV irradiation of pure solid O$_2$. In contrast to previous solid-state astrochemical model calculations which have used gas-phase photoabsorption cross-sections, we have employed solid-state cross-sections in our calculations. This method allows the model to be tested using well-constrained experiments rather than poorly constrained gas-phase abundances in ISM regions. Our results indicate that inclusion of non-thermal reactions and suprathermal species allows for reproduction of low-temperature solid-phase photoprocessing that simulate interstellar ices within cold ($\sim$ 10 K) dense cores such as TMC-1.

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E. Mullikin, H. Anderson, N. O’Hern, et. al.
Wed, 6 Jan 21
35/82

Comments: ApJ, accepted: 15 pages, 3 figures

On stable H-C-N-O compounds at high pressure [CL]

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http://arxiv.org/abs/2011.13285


The make-up of the outer planets, and many of their moons, are dominated by matter from the H-C-N-O chemical space, commonly assumed to originate from mixtures of hydrogen and the planetary ices H$_2$O, CH$_4$, and NH$_3$. In their interiors, these ices experience extreme pressure conditions, around 5 Mbar at the Neptune mantle-core boundary, and it is expected that they undergo phase transitions, decompose, and form entirely new compounds. In turn, this determines planets’ interior structure, thermal history, magnetic field generation, etc. Despite its importance, the H-C-N-O space has not been surveyed systematically. Asked simply: at high-pressure conditions, what compounds emerge within this space, and what governs their stability? Here, we report on results from an unbiased crystal structure search amongst H-C-N-O compounds at 5 Mbar to answer this question.

Read this paper on arXiv…

L. Conway, C. Pickard and A. Hermann
Mon, 30 Nov 20
67/117

Comments: N/A

Measurements of Optical Scatter Versus Annealing Temperature for Amorphous Ta2O5 and TiO2:Ta2O5 Thin Films [CL]

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http://arxiv.org/abs/2011.14013


Optical coatings formed from amorphous oxide thin films have many applications in precision measurements. The Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) and Advanced Virgo use coatings of SiO$_2$ (silica) and TiO$_2$:Ta$_2$O$_5$ (titania doped tantala) and post-deposition annealing to 500$^\circ$C to achieve low thermal noise and low optical absorption. Optical scattering by these coatings is a key limit to the detectors’ sensitivity. This paper describes optical scattering measurements for single-layer ion-beam-sputtered thin films on fused silica substrates: two samples of Ta$_2$O$_5$ and two of TiO$_2$:Ta$_2$O$_5$. Using an imaging scatterometer at a fixed scattering angle of 12.8$^\circ$, in-situ changes in the optical scatter of each sample were assessed during post-deposition annealing to 500$^\circ$C in vacuum. The scatter of three of the four coated optics was observed to decrease during the annealing process, by 25-30$\%$ for tantala and up to 74$\%$ for titania-doped tantala, while scatter from the fourth sample held constant. Angle-resolved scatter measurements performed before and after vacuum annealing suggests some improvement in three of four samples. These results demonstrate that post-deposition high-temperature annealing of single-layer tantala and titania-doped tantala thin films in vacuum does not lead to an increase in scatter, and may actually improve their scatter.

Read this paper on arXiv…

E. Capote, A. Gleckl, J. Guerrero, et. al.
Tue, 1 Dec 20
49/108

Comments: 12 pages, 7 figures, research paper

Unusual chemistry of the C-H-N-O system under pressure and implications for giant planets [CL]

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http://arxiv.org/abs/2011.12803


C-H-N-O system is central for organic chemistry and biochemistry, and plays a major role in planetary science (dominating the composition of “ice giants” Uranus and Neptune). The inexhaustible chemical diversity of this system at normal conditions explains it as the basis of all known life, but the chemistry of this system at high pressures and temperatures of planetary interiors is poorly known. Using ab initio evolutionary algorithm USPEX, we performed an extensive study of the phase diagram of the C-H-N-O system at pressures of 50, 200, and 400 GPa and temperatures up to 3000 K. Eight novel thermodynamically stable phases were predicted, including quaternary polymeric crystal C2H2N2O2 and several new N-O and H-N-O compounds. We describe the main patterns of changes in the chemistry of the C-H-N-O system under pressure and confirm that diamond should be formed at conditions of the middle-ice layers of Uranus and Neptune. We also provide the detailed CH4-NH3-H2O phase diagrams at high pressures, which are important for a further improvement of the models of ice giants – and point out that current models are clearly deficient. In particular, in existing models Uranus and Neptune are presented to have identical composition, nearly identical pressure-temperature profiles, and a single convecting middle layer (“mantle”) made of a mixture H2O : CH4 : NH3 = 56.5 : 32.5 : 11. Here we provide new insights shedding light into the difference of heat flows from Uranus and Neptune, which require them to have different compositions, pressure-temperature conditions, and a more complex internal structure.

Read this paper on arXiv…

A. Naumova, S. Lepeshkin, P. Bushlanov, et. al.
Thu, 26 Nov 20
46/65

Comments: N/A

Unusual chemistry of the C-H-N-O system under pressure and implications for giant planets [CL]

Posted on by

http://arxiv.org/abs/2011.12803


C-H-N-O system is central for organic chemistry and biochemistry, and plays a major role in planetary science (dominating the composition of “ice giants” Uranus and Neptune). The inexhaustible chemical diversity of this system at normal conditions explains it as the basis of all known life, but the chemistry of this system at high pressures and temperatures of planetary interiors is poorly known. Using ab initio evolutionary algorithm USPEX, we performed an extensive study of the phase diagram of the C-H-N-O system at pressures of 50, 200, and 400 GPa and temperatures up to 3000 K. Eight novel thermodynamically stable phases were predicted, including quaternary polymeric crystal C2H2N2O2 and several new N-O and H-N-O compounds. We describe the main patterns of changes in the chemistry of the C-H-N-O system under pressure and confirm that diamond should be formed at conditions of the middle-ice layers of Uranus and Neptune. We also provide the detailed CH4-NH3-H2O phase diagrams at high pressures, which are important for a further improvement of the models of ice giants – and point out that current models are clearly deficient. In particular, in existing models Uranus and Neptune are presented to have identical composition, nearly identical pressure-temperature profiles, and a single convecting middle layer (“mantle”) made of a mixture H2O : CH4 : NH3 = 56.5 : 32.5 : 11. Here we provide new insights shedding light into the difference of heat flows from Uranus and Neptune, which require them to have different compositions, pressure-temperature conditions, and a more complex internal structure.

Read this paper on arXiv…

A. Naumova, S. Lepeshkin, P. Bushlanov, et. al.
Thu, 26 Nov 20
25/65

Comments: N/A

Neutron star crust in Voigt approximation: general symmetry of the stress-strain tensor and an universal estimate for the effective shear modulus [HEAP]

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http://arxiv.org/abs/2010.08398


I discuss elastic properties of neutron star crust in the framework of static Coulomb solid model when atomic nuclei are treated as non-vibrating point charges; electron screening is neglected. The results are also applicable for solidified white dwarf cores and other materials, which can be modeled as Coulomb solids (dusty plasma, trapped ions, etc.). I demonstrate that the Coulomb part of the stress-strain tensor has additional symmetry: contraction $B_{ijil}=0$. It does not depend on the structure (crystalline or amorphous) and composition. I show as a result of this symmetry the effective (Voigt averaged) shear modulus of the polycrystalline or amorphous matter to be equal to $-2/15$ of the Coulomb (Madelung) energy density at undeformed state. This result is general and exact within the model applied. Since the linear mixing rule and the ion sphere model are used, I can suggest a simple universal estimate for the effective shear modulus: $\sum_Z 0.12\, n_Z Z^{5/3}e^2 /a_\mathrm{e}$. Here summation is taken over ion species, $n_Z$ is number density of ions with charge $Ze$. Finally $a_\mathrm{e}=(4 \pi n_\mathrm{e}/3)^{-1/3}$ is electron sphere radius. Quasineutrality condition $n_\mathrm{e}=\sum_Z Z n_Z$ is assumed.

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A. Chugunov
Mon, 19 Oct 20
15/44

Comments: 5 pages, accepted for publication in MNRAS:Letters

SiC Detectors for Sub-GeV Dark Matter [CL]

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http://arxiv.org/abs/2008.08560


We propose the use of silicon carbide (SiC) for direct detection of sub-GeV dark matter. SiC has properties similar to both silicon and diamond, but has two key advantages: (i) it is a polar semiconductor which allows sensitivity to a broader range of dark matter candidates; and (ii) it exists in many stable polymorphs with varying physical properties, and hence has tunable sensitivity to various dark matter models. We show that SiC is an excellent target to search for electron, nuclear and phonon excitations from scattering of dark matter down to 10 keV in mass, as well as for absorption processes of dark matter down to 10 meV in mass. Combined with its widespread use as an alternative to silicon in other detector technologies and its availability compared to diamond, our results demonstrate that SiC holds much promise as a novel dark matter detector.

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S. Griffin, Y. Hochberg, K. Inzani, et. al.
Thu, 20 Aug 20
-1110/48

Comments: 28 pages, 11 figures

Prediction of Tunable Spin-Orbit Gapped Materials for Dark Matter Detection [CL]

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http://arxiv.org/abs/2008.05062


New ideas for low-mass dark matter direct detection suggest that narrow band gap materials, such as Dirac semiconductors, are sensitive to the absorption of meV dark matter or the scattering of keV dark matter. Here we propose spin-orbit semiconductors – materials whose band gap arises due to spin-orbit coupling – as low-mass dark matter targets owing to their ~10 meV band gaps. We present three material families that are predicted to be spin-orbit semiconductors using Density Functional Theory (DFT), assess their electronic and topological features, and evaluate their use as low-mass dark matter targets. In particular, we find that that the tin pnictide compounds are especially suitable having a tunable range of meV-scale band gaps with anisotropic Fermi velocities allowing directional detection. Finally, we address the pitfalls in the DFT methods that must be considered in the ab initio prediction of narrow-gapped materials, including those close to the topological critical point.

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K. Inzani, A. Faghaninia and S. Griffin
Thu, 13 Aug 20
-893/67

Comments: 10 pages, 7 figures + SI 6 pages, 5 figures

Sticky or not sticky? Measurements of the tensile strength of micro-granular organic materials [EPA]

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http://arxiv.org/abs/2007.07538


Knowledge of the mechanical properties of protoplanetary and cometary matter is of key importance to better understand the activity of comets and the early stages of planet formation. The tensile strength determines the required pressure to lift off grains, pebbles and agglomerates from the cometary surface and also describes how much strain a macroscopic body can withstand before material failure occurs. As organic materials are ubiquitous in space, they could have played an important role during the planet formation process. This work provides new data on the tensile strength of five different micro-granular organic materials, namely, humic acid, paraffin, brown coal, charcoal and graphite. These materials are investigated by the so-called Brazilian Disc Test and the resulting tensile strength values are normalised to a standard grain size and volume filling factor. We find that the tensile strength of these materials ranges over four orders of magnitude. Graphite and paraffin possess tensile strengths much higher than silica, whereas coals have very low tensile strength values. This work demonstrates that organic materials are not generally stickier than silicates, or water ice, as often believed.

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D. Bischoff, C. Kreuzig, D. Haack, et. al.
Thu, 16 Jul 20
-229/56

Comments: N/A

Detectability of Axion Dark Matter with Phonon Polaritons and Magnons [CL]

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http://arxiv.org/abs/2005.10256


Collective excitations in condensed matter systems, such as phonons and magnons, have recently been proposed as novel detection channels for light dark matter. We show that excitation of i) optical phonon polaritons in polar materials in an ${\mathcal O}$(1 T) magnetic field (via the axion-photon coupling), and ii) gapped magnons in magnetically ordered materials (via the axion wind coupling to the electron spin), can cover the difficult-to-reach ${\mathcal O}$(1-100) meV mass window of QCD axion dark matter with less than a kilogram-year exposure. Finding materials with a large number of optical phonon or magnon modes that can couple to the axion field is crucial, suggesting a program to search for a range of materials with different resonant energies and excitation selection rules; we outline the rules and discuss a few candidate targets, leaving a more exhaustive search for future work. Ongoing development of single photon, phonon and magnon detectors will provide the key for experimentally realizing the ideas presented here.

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A. Mitridate, T. Trickle, Z. Zhang, et. al.
Fri, 22 May 20
38/64

Comments: 35 pages, 5 figures

Superconducting Materials for Microwave Kinetic Inductance Detectors [IMA]

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http://arxiv.org/abs/2004.14576


The superconducting materials that make up an MKID have a significant effect on its performance. The $T_\textrm{c}$ and normal state resistivity $\rho_\textrm{N}$ of the film determine the penetration depth $\lambda$ and therefore how much kinetic inductance it has. The ratio of kinetic inductance to total inductance ($\alpha$), the volume of the inductor, and $Q_\textrm{m}$ determines the magnitude of the response to incoming energy. The quasiparticle lifetime $\tau_\textrm{qp}$ is the characteristic time during which the MKID’s surface impedance is modified by the incoming energy. Many materials have been explored for use in superconducting resonators and MKIDs, but that information is often not published or scattered around the literature. This chapter contains information and references on the work that has been done with thin film lithographed circuits for MKIDs over the last two decades. Note that measured material properties such as the internal loss quality factor $Q_\textrm{i}$ and quasiparticle lifetime $\tau_\textrm{qp}$ vary significantly depending on how the MKID superconducting thin film is made and the system they are measured in, so it is best to interpret all stated values as typical but not definitive. Values are omitted in cases when there aren’t enough measurements or there is too much disagreement in the literature to estimate a typical value. In order to be as complete as possible some unpublished results from the author’s lab are included and can be identified by the lack of a reference. Unless noted all films are polycrystalline or amorphous.

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B. Mazin
Fri, 1 May 20
16/54

Comments: 19 pages, 4 figures. To appear in the Handbook of Superconducting Materials

Thermodynamic anomalies and three distinct liquid-liquid transitions in warm dense liquid hydrogen [CL]

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http://arxiv.org/abs/2003.06629


The properties of hydrogen at high pressure have wide implications in astrophysics and high-pressure physics. Its phase change in the liquid is variously described as a metallization, H2-dissociation, density discontinuity or plasma phase transition. It has been tacitly assumed that these phenomena coincide at a first-order liquid-liquid transition (LLT). In this work, the relevant pressure-temperature conditions are thoroughly explored with first-principles molecular dynamics. We show there is a large dependency on exchange-correlation functional and significant finite size effects. We use hysteresis in a number of measurable quantities to demonstrate a first-order transition up to a critical point, above which molecular and atomic liquids are indistinguishable. At higher temperature beyond the critical point, H2-dissociation becomes a smooth cross-over in the supercritical region that can be modelled by a pseudo-transition, where the H2-2H transformation is localized and does not cause a density discontinuity at metallization. Thermodynamic anomalies and counter-intuitive transport behavior of protons are also discovered even far beyond the critical point, making this dissociative transition highly relevant to the interior dynamics of Jovian planets. Below the critical point, simulation also reveals a dynamic H2-2H chemical equilibrium with rapid interconversion, showing that H2 and H are miscible. The predicted critical temperature lies well below the ionization temperature. Our calculations unequivocally demonstrate that there are three distinct regimes in the liquid-liquid transition of warm dense hydrogen.

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H. Geng, Q. Wu, M. Marqués, et. al.
Tue, 17 Mar 20
10/63

Comments: 34 pages, 7 figures, with Supplementary Material

Planetary Felsic Crust Formation at Shallow Depth [EPA]

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http://arxiv.org/abs/2003.01508


Current theories suggest that on Earth and, possibly, on other terrestrial planets early in their history, the first continental crust may has been produced by direct melting of hydrated peridotite. However, the conditions, mechanisms and necessary ingredients of such production remain elusive. To fill this gap, we have conducted experiments of serpentinite melting in the presence of variable proportions of basaltic melt, at typical conditions of the shallow lithosphere and asthenosphere. These experiments revealed formation of silica-rich liquids, which are similar to tonalite-trondhjemite-granodiorite magmas (TTG) identified in modern terrestrial oceanic mantle settings. Our results suggest a new mechanism of aqueous fluid-assisted partial melting of peridotite that may have operated on the early Earth and Mars just after the solidification of an ultramafic-mafic magma ocean, leading to the formation of the first embryos of continental crust. The proposed mechanism of the continental crust formation may have been predominant before the onset of plate tectonics.

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A. Borisova, N. Zagrtdenov, M. Toplis, et. al.
Wed, 4 Mar 20
32/51

Comments: 62 pages, 9 figures, submitted to Frontiers in Earth Science

Reply to Robinson and Michaud, arXiv:2002.08893 [CL]

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http://arxiv.org/abs/2003.00101


We respond to Robinson and Michaud’s (RM) comment (arXiv:2002.08893) on our recent preprint arXiv:2002.06937, in which we discuss recent excesses in low-threshold dark matter searches, and offer a potential unifying dark matter interpretation. We thank RM for their feedback, which highlights the critical need for future measurements to directly calibrate plasmon charge yields for low $\sim$ 10 eV energy depositions. RM objected to our assertion that plasmons generated at energy scales below 100~eV may have a large branching fraction into phonons. As we argue below, the points raised by RM do not invalidate our primary conclusions, as they pertain to a much different energy scale than we discuss in our paper.

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N. Kurinsky, D. Baxter, Y. Kahn, et. al.
Tue, 3 Mar 20
25/68

Comments: 4 Pages

Separate silicate and carbonaceous solids formed from mixed atomic and molecular species diffusing in neon ice [GA]

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http://arxiv.org/abs/2002.10728


The formation and growth of refractory matter on pre-existing interstellar dust grain surfaces was studied experimentally by annealing neon-ice matrices in which potential precursors of silicate grains (Mg and Fe atoms, SiO and SiO$_2$ molecules) and of solid carbon (C$_n$ molecules, $n$ = 2-10) were initially isolated. Other molecules, mainly O$_3$, CO, CO$_2$, C$_3$O, and H$_2$O, were embedded at the same time in the matrices. The annealing procedure caused the cold dopants to diffuse and interact in the neon ice. Monitoring the procedure in situ with infrared spectroscopy revealed the disappearance of the silicon oxide and carbon molecules at temperatures lower than 13 K, and the rise of the Si-O stretching band of silicates. Ex situ electron microscopy confirmed the formation of silicate grains and showed that their structure was amorphous. It also showed that amorphous carbon matter was formed simultaneously next to the silicate grains, the two materials being chemically separated. The results of the experiments support the hypothesis that grains of complex silicates and of carbonaceous materials are re-formed in the cold ISM, as suggested by astronomical observations and evolution models of cosmic dust masses. Moreover, they show that the potential precursors of one material do not combine with those of the other at cryogenic temperatures, providing us with a clue as to the separation of silicates and carbon in interstellar grains.

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G. Rouillé, C. Jäger and T. Henning
Wed, 26 Feb 20
54/72

Comments: 20 pages, 9 figures, accepted for publication in The Astrophysical Journal

Comment on A dark matter interpretation of excesses in multiple direct detection experiments [arXiv:2002.06937] [CL]

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http://arxiv.org/abs/2002.08893


In their recent preprint [arXiv:2002.06937], Kurinsky, Baxter, Kahn, and Krnjaic assume an unphysical ionization yield for plasmon excitations in order to claim a possible dark matter signal. Their proposed signal is not possible based on known physics, but their proposed detection method warrants further investigation.

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A. Robinson and &. Michaud
Fri, 21 Feb 20
47/67

Comments: 2 pages

A Dark Matter Interpretation of Excesses in Multiple Direct Detection Experiments [CL]

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http://arxiv.org/abs/2002.06937


We present a novel unifying interpretation of excess event rates observed in several dark matter direct-detection experiments that utilize single-electron threshold semiconductor detectors. Despite their different locations, exposures, readout techniques, detector composition, and operating depths, these experiments all observe statistically significant excess event rates of $\sim$ 10 Hz/kg. However, none of these persistent excesses has yet been reported as a dark matter signal because their common spectral shapes are inconsistent with dark matter particles scattering elastically off detector nuclei or electrons. We show that these results can be reconciled if the semiconductor detectors are seeing a collective inelastic process known as a plasmon. We further show that plasmon excitation could arise in two compelling dark matter scenarios, both of which can explain rates of existing signal excesses in germanium and, at least at the order of magnitude level, across several traditional WIMP searches and single-electron threshold detectors. Both dark matter scenarios motivate a radical rethinking of the standard interpretations of dark matter-electron scattering from recent experiments.

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N. Kurinsky, D. Baxter, Y. Kahn, et. al.
Tue, 18 Feb 20
49/72

Comments: 20 pages, 7 figures. Preparing for journal submission

On Carbon Nanotubes in the Interstellar Medium [GA]

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http://arxiv.org/abs/2002.05588


Since their discovery in 1991, carbon nanotubes (CNTs) — a novel one-dimensional carbon allotrope — have attracted considerable interest worldwide because of their potential technological applications such as electric and optical devices. In the astrophysical context, CNTs may be present in the interstellar space since many of the other allotropes of carbon (e.g., amorphous carbon, fullerenes, nanodiamonds, graphite, polycyclic aromatic hydrocarbons, and possibly graphene as well) are known to be widespread in the Universe, as revealed by presolar grains in carbonaceous primitive meteorites and/or by their fingerprint spectral features in astronomical spectra. In addition, there are also experimental and theoretical pathways to the formation of CNTs in the interstellar medium (ISM). In this work, we examine their possible presence in the ISM by comparing the observed interstellar extinction curve with the ultraviolet/optical absorption spectra experimentally obtained for single-walled CNTs of a wide range of diameters and chiralities. Based on the absence in the interstellar extinction curve of the ~4.5 and 5.25 eV $\pi$-plasmon absorption bands which are pronounced in the experimental spectra of CNTs, we place an upper limit of ~10 ppm of C/H (i.e., ~4% of the total interstellar C) on the interstellar CNT abundance.

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Q. Li, A. Li, B. Jiang, et. al.
Fri, 14 Feb 20
43/51

Comments: 7 pages, 2 figures; accepted for publication in MNRAS

Crystal Defects: A Portal To Dark Matter Detection [CL]

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http://arxiv.org/abs/2002.03525


We propose to use the defect creation energy loss in commonly used high energy physics solid state detectors as a tool to statistically identify dark matter signal from background. We simulate the energy loss in the process of defect creation using density functional theory and molecular dynamics methods and calculate the corresponding expected dark matter spectra. We show that in phonon-mediated solid state detectors, the energy loss due to defect creation convolved with the expected dark matter interaction signal results in a significant change in the expected spectra for common detector materials. With recent progress towards $\sim$10 eV threshold low-mass dark matter searches, this variation in expected dark matter spectrum can be used as a direct signature of dark matter interactions with atomic nuclei.

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F. Kadribasic, N. Mirabolfathi, K. Nordlund, et. al.
Tue, 11 Feb 20
39/81

Comments: N/A

A method for the experimental measurement of bulk and shear loss angles in amorphous thin films [CL]

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http://arxiv.org/abs/1911.12277


Brownian thermal noise is a limiting factor for the sensitivity of many high precision metrology applications, among other gravitational wave detectors. The origin of Brownian noise can be traced down to internal friction in the amorphous materials that are used for the high reflection coatings. To properly characterize the internal friction in an amorphous material, one needs to consider the energy losses in the bulk and shear modes. In most of previous works the two loss angles were considered equal, although without any first principle motivation. In this work we show how it is possible to use current state-of-the-art coating ring-down measurement systems to extract the material bulk and shear loss angles. We also show that for titania-doped-tantala, a material commonly used in gravitational wave detector coatings, the experimental data strongly favor a model with two different and distinct loss angles, over the simpler case of one single loss angle.

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G. Vajente, M. Fazio, L. Yang, et. al.
Thu, 28 Nov 19
52/70

Comments: N/A

A method for the experimental measurement of bulk and shear loss angles in amorphous thin films [CL]

Posted on by

http://arxiv.org/abs/1911.12277


Brownian thermal noise is a limiting factor for the sensitivity of many high precision metrology applications, among other gravitational wave detectors. The origin of Brownian noise can be traced down to internal friction in the amorphous materials that are used for the high reflection coatings. To properly characterize the internal friction in an amorphous material, one needs to consider the energy losses in the bulk and shear modes. In most of previous works the two loss angles were considered equal, although without any first principle motivation. In this work we show how it is possible to use current state-of-the-art coating ring-down measurement systems to extract the material bulk and shear loss angles. We also show that for titania-doped-tantala, a material commonly used in gravitational wave detector coatings, the experimental data strongly favor a model with two different and distinct loss angles, over the simpler case of one single loss angle.

Read this paper on arXiv…

G. Vajente, M. Fazio, L. Yang, et. al.
Thu, 28 Nov 19
46/70

Comments: N/A

Laser-Driven High-Velocity Microparticle Launcher In Atmosphere And Under Vacuum [IMA]

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http://arxiv.org/abs/1911.11572


This paper presents a novel approach to launch single microparticles at high velocities under low vacuum conditions. In an all-optical table-top method, microparticles with sizes ranging from a few microns to tens of microns are accelerated to supersonic velocities depending on the particle mass. The acceleration is performed through a laser ablation process and the particles are monitored in free space using an ultra-high-speed multi-frame camera with nanosecond time resolution. Under low vacuum, we evaluate the current platform performance by measuring particle velocities for a range of particle types and sizes, and demonstrate blast wave suppression and drag reduction under vacuum. Showing an impact on polyethylene, we demonstrate the capability of the experimental setup to study materials behavior under high-velocity impact. The present method is relevant to space applications, particularly to rendezvous missions where velocities range from tens of m/s to a few km/s, as well as to a wide range of terrestrial applications including impact bonding and impact-induced erosion.

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D. Veysset, Y. Sun, S. Kooi, et. al.
Wed, 27 Nov 19
50/59

Comments: 13 pages, 9 figures, keywords: high-velocity launcher; microparticle impact; high-speed imaging; low vacuum; laser-based method; table-top system; ejecta; drag; blast; ballistic limit

Graphene-based Josephson junction microwave bolometer [CL]

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http://arxiv.org/abs/1909.05413


Sensitive microwave detectors are critical instruments in radioastronomy, dark matter axion searches, and superconducting quantum information science. The conventional strategy towards higher-sensitivity bolometry is to nanofabricate an ever-smaller device to augment the thermal response. However, this direction is increasingly more difficult to obtain efficient photon coupling and maintain the material properties in a device with a large surface-to-volume ratio. Here we advance this concept to an ultimately thin bolometric sensor based on monolayer graphene. To utilize its minute electronic specific heat and thermal conductivity, we develop a superconductor-graphene-superconductor (SGS) Josephson junction bolometer embedded in a microwave resonator of resonant frequency 7.9 GHz with over 99\% coupling efficiency. From the dependence of the Josephson switching current on the operating temperature, charge density, input power, and frequency, we demonstrate a noise equivalent power (NEP) of 7 $\times 10^{-19}$ W/Hz$^{1/2}$, corresponding to an energy resolution of one single photon at 32 GHz and reaching the fundamental limit imposed by intrinsic thermal fluctuation at 0.19 K.

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G. Lee, D. Efetov, L. Ranzani, et. al.
Fri, 13 Sep 19
58/70

Comments: 8 pages, 4 figures

Material Science and Impact Crater Formation [EPA]

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http://arxiv.org/abs/1909.00842


The surfaces of solid objects in our planetary system are dappled with craters. Some of them are due to impacts of various solid projectiles into the surfaces of the objects. A smaller part of these craters is of volcanic origin. %Some of these are of volcanic origin, but others are consequences of impacts of various projectiles into the objects concerned On the Earth,two most often mentioned such events are the “Tunguska event” of 1908. and the impact which led to the formation of the Barringer crater in Arizona. Impact craters are frequently analyzed within the “scaling theory”, which is founded on dimensional analysis. The same problem can be treated by using standard laws of material science and condensed matter physics. In this chapter the two approaches will be compared and possibilities for future work indicated to some extent. Some preliminary conclusions concerning an impact into a granular target will be presented.

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V. V.Celebonovic
Wed, 4 Sep 19
112/146

Comments: 12 pages,LaTeX,published in 2017 in a book. The reference is given on the first page

Bond strengthening in dense H2O and implications to planetary composition [CL]

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http://arxiv.org/abs/1906.11990


H2O is an important constituent in planetary bodies, controlling habitability and, in geologically-active bodies, plate tectonics. At pressures within the interior of many planets, the H-bonds in H2O collapse into stronger, ionic bonds. Here we present agreement between X-ray diffraction and Raman spectroscopy for the transition from ice-VII to ice-X occurring at a pressure of approximately 30.9 GPa by means of combining grain normalizing heat treatment via direct laser heating with static compression. This is evidenced by the emergence of the characteristic Raman mode of cuprite-like ice-X and an abrupt 2.5-fold increase in bulk modulus, implying a significant increase in bond strength. This is preceded by a transition from cubic ice-VII to a structure of tetragonal symmetry, ice-VIIt at 5.1 GPa. Our results significantly shift the mass/radius relationship of water-rich planets and define a high-pressure limit for release of chemically-bound water within the Earth, making the deep mantle a potential long-term reservoir of ancient water.

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Z. Grande, C. Huang, D. Smith, et. al.
Tue, 2 Jul 19
65/79

Comments: N/A

Evidence for supercritical behavior of high-pressure liquid hydrogen [CL]

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http://arxiv.org/abs/1906.03341


Hydrogen exhibits unusual behaviors at megabar pressures, with consequences for planetary science, condensed matter physics and materials science. Experiments at such extreme conditions are challenging, often resulting in hard-to-interpret and controversial observations. We present a theoretical study of the phase diagram of dense hydrogen, using machine learning to overcome time and length scale limitations while describing accurately interatomic forces. We reproduce the re-entrant melting behavior and the polymorphism of the solid phase. In simulations based on the machine learning potential we find evidence for continuous metallization in the liquid, as a first-order liquid-liquid transition is pre-empted by freezing. This suggests a smooth transition between insulating and metallic layers in giant gas planets, and reconciles existing discrepancies between experiments as a manifestation of supercritical behavior.

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B. Cheng, G. Mazzola and M. Ceriotti
Tue, 11 Jun 19
60/60

Comments: N/A

Direct Detection of Light Dark Matter with Magnons [CL]

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http://arxiv.org/abs/1905.13744


Scattering of light dark matter with sub-eV energy deposition can be detected with collective excitations in condensed matter systems. When dark matter has spin-independent couplings to atoms or ions, it has been shown to efficiently excite phonons. Here we show that, if dark matter couples to the electron spin, magnon excitations in materials with magnetic dipole order offer a promising detection path. We derive general formulae for single magnon excitation rates from dark matter scattering, and demonstrate as a proof of principle the projected reach of a yttrium iron garnet target for several dark matter models with spin-dependent interactions. This highlights the complementarity of various collective excitations in probing different dark matter interactions.

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T. Trickle, Z. Zhang and K. Zurek
Mon, 3 Jun 19
43/59

Comments: 8 pages, 2 figures, 1 table

On Simulating the Proton-Irradiation of O$_2$ and H$_2$O Ices Using Astrochemical-type Models, with Implications for Bulk Reactivity [GA]

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http://arxiv.org/abs/1904.04143


Many astrochemical models today explicitly consider the species that comprise the bulk of interstellar dust grain ice-mantles separately from those in the top few monolayers. Bombardment of these ices by ionizing radiation – whether in the form of cosmic rays, stellar winds, or radionuclide emission – represents an astrochemically viable means of driving a rich chemistry even in the bulk of the ice-mantle, now supported by a large body of work in laboratory astrophysics. In this study, using an existing rate equation-based astrochemical code modified to include a method of considering radiation chemistry recently developed by us, we attempted to simulate two such studies in which (a) pure O$_2$ ice at 5 K and, (b) pure H$_2$O ice at 16 K and 77 K, were bombarded by keV H$^+$ ions.
Our aims are twofold: (1) to test the capability of our newly developed method to replicate the results of ice-irradiation experiments, and (2) to determine in such a well-constrained system how bulk chemistry is best handled using the same gas-grain codes that are used to model the interstellar medium (ISM). We find that our modified astrochemical model is able to reproduce both the abundance of O$_3$ in the 5 K pure O$_2$ ice, as well as both the abundance of H$_2$O$_2$ in the 16 K water ice and the previously noted decrease of hydrogen peroxide at higher temperatures. However, these results require the assumption that radicals and other reactive species produced via radiolysis react quickly and non-diffusively with neighbors in the ice.

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C. Shingledecker, A. Vasyunin, E. Herbst, et. al.
Tue, 9 Apr 19
82/105

Comments: ApJ, accepted. 30 pages, 5 figures

Modification of Nanodiamonds by Xenon Implantation: A Molecular Dynamics Study [CL]

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http://arxiv.org/abs/1903.10711


Xenon implantation into nanodiamonds is studied using molecular dynamics. The nanodiamonds range in size from 2-10 nm and the primary knock-on (PKA) energy extends up to 40 keV. For small nanodiamonds an energy-window effect occurs in which PKA energies of around 6 keV destroy the nanodiamond, while in larger nanodiamonds the radiation cascade is increasingly similar to those in bulk material. Destruction of the small nanodiamonds occurs due to thermal annealing associated with the small size of the particles and the absence of a heat-loss path. Simulations are also performed for a range of impact parameters, and for a series of double-nanodiamond systems in which a heat-loss path is present. The latter show that the thermal shock caused by the impact occurs on the timescale of a few picoseconds. These findings are relevant to ion-beam modification of nanoparticles by noble gases as well as meteoritic studies where implantation is proposed as the mechanism for xenon incorporation in pre-solar nanodiamonds.

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J. Fogg, A. Aghajamali, J. Hinks, et. al.
Wed, 27 Mar 19
17/74

Comments: N/A

Transparent tiles of silica aerogels for high-energy physics [CL]

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http://arxiv.org/abs/1902.05374


Silica aerogels are important to be used as photon radiators in Cherenkov counters for high-energy-physics experiments because of their optical transparency and intermediate refractive indices between those of gases and liquids or solids. Cherenkov counters that employ silica aerogels as radiators and photodetectors are often used to identify subatomic charged particles (e.g., electrons, protons, and pions) with momenta on the order of sub-GeV/$c$ to GeV/$c$; they are also used to measure particle velocities in accelerator-based particle- and nuclear-physics experiments and in space- and balloon-borne experiments in the field of cosmic-ray physics. Recent studies have demonstrated that it is important for the design of Cherenkov counters that the transparent silica-aerogel tiles comprise solid material with recently improved transparency and a refractive index that can be controlled between 1.003 and 1.26 by varying the bulk density in the range of 0.01$-$1.0 g/cm$^3$. Additionally, a technique for fabricating large-area silica-aerogel tiles without cracking has been developed. In this chapter, we describe advances in the technologies for producing silica aerogels with high optical performances to be used in scientific instruments. We further discuss the principles underlying the operation of detectors based on the Cherenkov effect. We also review applications of silica aerogels in specific high-energy-physics experiments.

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M. Tabata
Fri, 15 Feb 19
11/48

Comments: Contributed chapter submitted to Springer Handbook of Aerogels (2nd ed.)

Developing a silica aerogel radiator for the HELIX ring-imaging Cherenkov system [CL]

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http://arxiv.org/abs/1901.06663


This paper reports the successful fabrication of silica aerogel Cherenkov radiators produced in the first batches from a 96-tile mass production performed using pin-drying technique in our laboratory. The aerogels are to be used in a ring-imaging Cherenkov detector in the spectrometer of a planned balloon-borne cosmic-ray observation program, HELIX (High Energy Light Isotope eXperiment). A total of 36 transparent, hydrophobic aerogel tiles with a high refractive index of 1.16 and dimensions of 10 cm $\times $ 10 cm $\times $ 1 cm will be chosen as the flight radiators. Thus far, 40 out of the 48 tiles fabricated were confirmed as having no tile cracking. In the first screening, 8 out of the first 16 tiles were accepted as flight-qualified candidates, based on basic optical measurement results. To fit the aerogel tiles into a radiator support structure, the trimming of previously manufactured prototype tiles using a water-jet cutting device was successful.

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M. Tabata, P. Allison, J. Beatty, et. al.
Wed, 23 Jan 19
87/111

Comments: Submitted to Nucl. Instrum. Methods Phys. Res. A (NIMA Proc. Special Issue: RICH 2018), 5 pages, 6 figures

Electrostatic energy and phonon properties of Yukawa crystals [CL]

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http://arxiv.org/abs/1901.04427


We study electrostatic and phonon properties of Yukawa crystals. It is shown that in the harmonic approximation these systems which is in use in the theory dusty plasma can be described analytically by the model from the theory of neutron stars and white dwarfs. Using this approximation we consider properties of body-centred cubic (bcc), face-centred cubic (fcc), hexagonal close-packed (hcp), and MgB$_2$ lattices. MgB$_2$ and hcp lattices have never been studied earlier in the context of Yukawa systems. It is shown that they never possess the smallest potential energy and the phase diagram of stable Yukawa crystals contains bcc and fcc lattices only. However, corrections to the charge density $\propto (\kappa a)^4$ can noticeably change the structural diagram of Yukawa systems. The developed analytical model also allows to describe low-temperature effects where numerical simulations are difficult.

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A. Kozhberov
Tue, 15 Jan 19
75/83

Comments: 8 pages, 6 figures

Dielectric Properties of Conductively Loaded Polyimides in the Far Infrared [CL]

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http://arxiv.org/abs/1810.01962


The dielectric properties of selected conductively-loaded polyimide samples are characterized in microwave through far infrared wavebands. These materials, belonging to the Vespel\textsuperscript{\textregistered} family, are more readily formed by direct machining than their ceramic loaded epoxy counterparts and present an interesting solution for realizing absorptive optical control structures. Measurements spanning a spectral range from 1 to 600\,${\rm cm^{-1}}$ (0.03 to 18\,THz) were preformed and used in parametrization of the media’s dielectric function at frequencies below $\approx3\,$THz.

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K. Helson, K. Rostem, M. Quijada, et. al.
Fri, 5 Oct 18
6/53

Comments: 5 pages, 4 figures, 2 tables

The Equation of State of MH-III: a possible deep CH$_4$ reservoir in Titan, Super-Titan exoplanets and moons [EPA]

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http://arxiv.org/abs/1808.07925


We investigate the thermal equation of state, bulk modulus, thermal expansion coefficient, and heat capacity of MH-III (CH$_4$ filled-ice Ih), needed for the study of CH$_4$ transport and outgassing for the case of Titan and super-Titans. We employ density functional theory and ab initio molecular dynamics simulations in the generalized-gradient approximation with a van der Waals functional. We examine the finite temperature range of $300$K-$500$K and pressures between $2$GPa-$7$GPa. We find that in this P-T range MH-III is less dense than liquid water, and may migrate outward during episodic melting events. There is uncertainty in the normalized moment of inertia (MOI) of Titan; it is estimated to be in the range of $0.33-0.34$. If Titan’s MOI is close to $0.34$, MH-III may not be stable at present, yielding an easier path for the outgassing of CH$_4$. However, if its MOI is closer to $0.33$, MH-III is stable at the bottom of a hypothesized ice-rock internal layer, and outgassing would become dependent on the evolution of melt on the mixed ice-rock to core boundary. We further find that the heat capacity of MH-III is higher than measured values for pure water-ice, larger than heat capacity often adopted for ice-rock mixtures, with implications for internal heating of icy moons and ice-rich exoplanets.

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A. Levi and R. Cohen
Mon, 27 Aug 18
28/46

Comments: 14 pages, 13 figures

Materials Informatics for Dark Matter Detection [CL]

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http://arxiv.org/abs/1806.06040


Dark Matter particles are widely assumed to be weakly interacting massive particles (WIMPs) with sub-GeV mass. WIMP detection would require the use of small gap materials in sensors. We propose the use of informatics tools to rapidly assay materials band structures to search for small gap semiconductors and semimetals. Using recent estimates of the WIMP mass, we identify the relevant target space towards small band gap materials (100-10 meV). We use a large dataset search to identify candidate materials, rather than focusing on a few preselected compounds. Dirac Materials, a class of small- or zero-gap materials, emerge as natural candidates for sensors for Dark Matter detection. As a specific example of the proposed search strategy, we use the organic materials database (omdb.diracmaterials.org) to identify few organic candidates for sensors: the narrow band gap semiconductors BNQ-TTF and DEBTTT with gaps of 40 and 38 meV, and the Dirac-line semimetal (BEDT-TTF)$\cdot$B which exhibits a tiny gap of $\approx$ 50 meV when spin-orbit coupling is included. We outline a novel approach to search for sensor materials where a rapid assay of materials using informatics tools yields more candidates and thus provides a useful tool to identify sensor materials for Dark Matter detection.

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R. Geilhufe, B. Olsthoorn, A. Ferella, et. al.
Mon, 18 Jun 18
46/54

Comments: 5 pages, 3 figures

Helium-iron compounds at terapascal pressures [CL]

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http://arxiv.org/abs/1806.03017


We investigate the binary phase diagram of helium and iron using first-principles calculations. We find that helium, which is a noble gas and inert at ambient conditions, forms stable crystalline compounds with iron at terapascal pressures. A FeHe compound becomes stable above 4 TPa, and a FeHe$_2$ compound above 12 TPa. Melting is investigated using molecular dynamics simulations, and a superionic phase with sublattice melting of the helium atoms is predicted. We discuss the implications of our predicted helium-iron phase diagram for interiors of giant (exo)planets and white dwarf stars.

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B. Monserrat, M. Martinez-Canales, R. Needs, et. al.
Tue, 12 Jun 18
30/79

Comments: 5 pages, 3 figures, includes Supplemental Material

Theoretical and experimental investigation of the equation of state of boron plasmas [CL]

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http://arxiv.org/abs/1804.11322


We report a theoretical equation of state (EOS) table for boron across a wide range of temperatures (5.1$\times$10$^4$-5.2$\times$10$^8$ K) and densities (0.25-49 g/cm$^3$), and experimental shock Hugoniot data at unprecedented high pressures (5608$\pm$118 GPa). The calculations are performed with full, first-principles methods combining path integral Monte Carlo (PIMC) at high temperatures and density functional theory molecular dynamics (DFT-MD) methods at lower temperatures. PIMC and DFT-MD cross-validate each other by providing coherent EOS (difference $<$1.5 Hartree/boron in energy and $<$5% in pressure) at 5.1$\times$10$^5$ K. The Hugoniot measurement is conducted at the National Ignition Facility using a planar shock platform. The pressure-density relation found in our shock experiment is on top of the shock Hugoniot profile predicted with our first-principles EOS and a semi-empirical EOS table (LEOS 50). We investigate the self diffusivity and the effect of thermal and pressure-driven ionization on the EOS and shock compression behavior in high pressure and temperature conditions We study the performance sensitivity of a polar direct-drive exploding pusher platform to pressure variations based on comparison of the first-principles calculations with LEOS 50 via 1D hydrodynamic simulations. The results are valuable for future theoretical and experimental studies and engineering design in high energy density research. (LLNL-JRNL-748227)

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S. Zhang, B. Militzer, M. Gregor, et. al.
Tue, 1 May 18
63/78

Comments: 12 pages, 9 figures, 2 tables

Ion implantation in nanodiamonds: size effect and energy dependence [CL]

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http://arxiv.org/abs/1803.09081


Nanoparticles are ubiquitous in nature and are increasingly important for technology. They are subject to bombardment by ionizing radiation in a diverse range of environments. In particular, nanodiamonds represent a variety of nanoparticles of significant fundamental and applied interest. Here we present a combined experimental and computational study of the behaviour of nanodiamonds under irradiation by xenon ions. Unexpectedly, we observed a pronounced size effect on the radiation resistance of the nanodiamonds: particles larger than 8 nm behave similarly to macroscopic diamond (i.e. characterized by high radiation resistance) whereas smaller particles can be completely destroyed by a single impact from an ion in a defined energy range. This latter observation is explained by extreme heating of the nanodiamonds by the penetrating ion. The obtained results are not limited to nanodiamonds, making them of interest for several fields, putting constraints on processes for the controlled modification of nanodiamonds, on the survival of dust in astrophysical environments, and on the behaviour of actinides released from nuclear waste into the environment.

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A. Shiryaev, J. Hinks, N. Marks, et. al.
Wed, 28 Mar 18
22/148

Comments: Supplementray information is at: doi:10.1038/s41598-018-23434-y

Tetrahedral hydrocarbon nanoparticles in space: X-ray spectra [SSA]

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http://arxiv.org/abs/1803.01185


It has been proposed, or confirmed, that diamond nanoparticles exist in various environments in space: close to active galactic nuclei, in the vicinity of supernovae and pulsars, in the interior of several planets in the Solar system, in carbon planets and other exoplanets, carbon-rich stars, meteorites, in X-ray active Herbig Ae/Be stars, and in the interstellar medium. Using density functional theory methods we calculate the carbon K-edge X-ray absorption spectrum of two large tetrahedral nanodiamonds: C26H32 and C51H52. We also study and test our methods on the astrophysical molecule CH4, the smallest C-H tetrahedral structure. A possible detection of nanodiamonds from X-ray spectra by future telescopes, such as the project Arcus, is proposed. Simulated spectra of the diffuse interstellar medium using Cyg X-2 as a source show that nanodiamonds studied in this work can be detected by Arcus, a high resolution X-ray spectrometer mission selected by NASA for a Phase A concept study.

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G. Bilalbegovic, A. Maksimovic and L. Valencic
Tue, 6 Mar 2018
18/70

Comments: accepted for publication in MNRAS

Ab initio Simulations of Superionic H2O, H2O2, and H9O4 Compounds [CL]

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http://arxiv.org/abs/1801.06907


Using density functional molecular dynamics simulations, we study the behavior of different hydrogen-oxygen compounds at megabar pressures and several thousands of degrees Kelvin where water has been predicted to occur in superionic form. When we study the close packed hcp and dhcp structures of superionic water, we find that they have comparable Gibbs free energies to the fcc structure that we predicted previously [Phys. Rev. Lett., 110 (2013) 151102]. Then we present a comprehensive comparison of different superionic water candidate structures with P2_1, P2_1/c, P3_121, Pcca, C2/m, and Pa3 symmetry that are based on published ground-state structures. We find that the P2_1 and P2_1/c structures transform into a different superionic structure with P2_1/c symmetry, which at 4000 K has a lower Gibbs free energy than fcc for pressures higher than 22.8 +- 0.5 Mbar. This novel structure may also be obtained by distorting a hcp supercell. Finally we show that H2O2 and H9O4 structures will also assume a superionic state at elevated temperatures. Based on Gibbs free energy calculations at 5000 K, we predict that superionic water decompose into H2O2 and H9O4 at 68.7 +- 0.5 Mbar.

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B. Militzer and S. Zhang
Tue, 23 Jan 18
3/85

Comments: 6 figures, in press at AIP conference proceedings, 2018

Herbig Ae Young Star's Infrared Spectrum Identified By Hydrocarbon Pentagon-Hexagon Combined Molecules [GA]

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http://arxiv.org/abs/1709.04560


Infrared spectrum (IR) of Herbig Ae young stars was reproduced and classified by hydrocarbon pentagon-hexagon combined molecules by the quantum chemical calculation. Observed IR list by B. Acke et al. was categorized to four classes. Among 53 Herbig Ae stars, 26 samples show featured IR pattern named Type-D, which shows common IR peaks at 6.2, 8.3, 9.2, 10.0, 11.3, 12.1, and 14.0 micrometer. Typical star is HD144432. Calculation on di-cation molecule (C12H8)2+ having hydrocarbon one pentagon and two hexagons shows best coincidence at 6.1, 8.2, 9.2, 9.9, 11.3, 12.2, and 14.1 micrometer. There are some variation in Type-D. Spectrum of HD37357 was explained by a mixture with di-cation (C12H8)2+ and tri-cation (C12H8)3+. Ubiquitously observed spectrum Type-B was observed in 12 samples of Acke’s list. In case of HD85567, observed 16 peaks were precisely reproduced by a single molecule (C23H12)2+. There is a mixture case with Type-B and Type-D. Typical example was HD142527. In this study, we could identify hidden carrier molecules for all types of IR in Herbig Ae stars.

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N. Ota
Fri, 15 Sep 17
43/57

Comments: 8 pages,6 figures, 1 table

Pyrite FeO2: material "in between'" oxides and peroxides [CL]

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http://arxiv.org/abs/1705.08085


Recent discovery [Nature 534, 241 (2016)] of FeO$_2$, which can be an important ingredient of the Earth’s lower mantle and which in particular may serve as an extra source of oxygen and water at the Earth’s surface and atmosphere, opens new perspectives for geophysics and geochemistry, but this is also an extremely interesting material from physical point of view. We found that in contrast to naive expectations Fe is nearly 3+ in this material, which strongly affects its magnetic properties and makes it qualitatively different from well known sulfide analogue – FeS$_2$. Doping, which is most likely to occur in the Earth’s mantle, makes FeO$_2$ much more magnetic. In addition we show that unique electronic structure places FeO$_2$ “in between” the usual dioxides and peroxides making this system interesting both for physics and solid state chemistry.

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S. Streltsov, A. Shorikov, S. Skornyakov, et. al.
Wed, 24 May 17
9/70

Comments: N/A

Directional Sensitivity In Light-Mass Dark Matter Searches With Single-Electron Resolution Ionization Detectors [CL]

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http://arxiv.org/abs/1703.05371


We present a method for using solid state detectors with directional sensitivity to dark matter interactions to detect low-mass Weakly Interacting Massive Particles (WIMPs) originating from galactic sources. In spite of a large body of literature for high-mass WIMP detectors with directional sensitivity, there is no available technique to cover WIMPs in the mass range <1 GeV. We argue that single-electron resolution semiconductor detectors allow for directional sensitivity once properly calibrated. We examine commonly used semiconductor material response to these low-mass WIMP interactions.

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F. Kadribasic, N. Mirabolfathi, K. Nordlund, et. al.
Fri, 17 Mar 17
32/50

Comments: N/A

ENDOR study of nitrogen hyperfine and quadrupole tensors in vanadyl porphyrins of heavy crude oil [CL]

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http://arxiv.org/abs/1702.06066


We report the observation of pulsed electron-nuclear double resonance (ENDOR) spectrum caused by interactions of the nitrogen nuclei 14N with the unpaired electron of the paramagnetic vanadyl complexes VO2+ of vanadyl porphyrins in natural crude oil. We provide detailed experimental and theoretical characterization of the nitrogen hyperfine and quadrupole tensors.

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I. Gracheva, M. Gafurov, G. Mamin, et. al.
Tue, 21 Feb 17
29/70

Comments: 6 pages, 2 Figures

The Origins of Asteroidal Rock Disaggregation: Interplay of Thermal Fatigue and Microstructure [EPA]

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http://arxiv.org/abs/1701.03510


The distributions of size and chemical composition in the regolith on airless bodies provides clues to the evolution of the solar system. Recently, the regolith on asteroid (25143) Itokawa, visited by the JAXA Hayabusa spacecraft, was observed to contain millimeter to centimeter sized particles. Itokawa boulders commonly display well-rounded profiles and surface textures that appear inconsistent with mechanical fragmentation during meteorite impact; the rounded profiles have been hypothesized to arise from rolling and movement on the surface as a consequence of seismic shaking. We provide a possible explanation of these observations by exploring the primary crack propagation mechanisms during thermal fatigue of a chondrite. We present the in situ evolution of the full-field strains on the surface as a function of temperature and microstructure, and observe and quantify the crack growth during thermal cycling. We observe that the primary fatigue crack path preferentially follows the interfaces between monominerals, leaving them intact after fragmentation. These observations are explained through a microstructure-based finite element model that is quantitatively compared with our experimental results. These results on the interactions of thermal fatigue cracking with the microstructure may ultimately allow us to distinguish between thermally induced fragments and impact products.

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K. Hazeli, C. Mir, S. Papanikolaou, et. al.
Mon, 16 Jan 17
17/55

Comments: 23 pages, 7 figures

Qualitative observation of reversible phase change in astrochemical ethanethiol ices using infrared spectroscopy [CL]

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http://arxiv.org/abs/1611.08589


Here we report the first evidence for a reversible phase change in an ethanethiol ice prepared under astrochemical conditions. InfraRed (IR) spectroscopy was used to monitor the morphology of the ice using the S-H stretching vibration, a characteristic vibration of thiol molecules. The deposited sample was able to switch between amorphous and crystalline phases repeatedly under temperature cycles between 10 K and 130 K with subsequent loss of molecules in every phase change. Such an effect is dependent upon the original thickness of the ice. Further work on quantitative analysis is to be carried out in due course whereas here we are reporting the first results obtained.

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S. Pavithraa, R. Rajan, P. Gorai, et. al.
Tue, 29 Nov 16
24/77

Comments: 13 pages, 7 figures, submitted to spectrochimica Acta

Predicted reentrant melting of dense hydrogen at ultra-high pressures [CL]

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http://arxiv.org/abs/1611.01418


The phase diagram of hydrogen is one of the most important challenges in high-pressure physics and astrophysics. Especially, the melting of dense hydrogen is complicated by dimer dissociation, metallization and nuclear quantum effect of protons, which together lead to a cold melting of dense hydrogen when above 500 GPa. Nonetheless, the variation of the melting curve at higher pressures is virtually uncharted. Here we report that using ab initio molecular dynamics and path integral simulations based on density functional theory, a new atomic phase is discovered, which gives an uplifting melting curve of dense hydrogen when beyond 2 TPa, and results in a reentrant solid-liquid transition before entering the Wigner crystalline phase of protons. The findings greatly extend the phase diagram of dense hydrogen, and put metallic hydrogen into the group of alkali metals, with its melting curve closely resembling those of lithium and sodium.

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H. Geng and Q. Wu
Mon, 7 Nov 16
43/48

Comments: 27 pages, 10 figures

Missing Fe: hydrogenated iron nanoparticles [SSA]

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http://arxiv.org/abs/1611.00309


Although it was found that the FeH lines exist in the spectra of some stars, none of the spectral features in the ISM have been assigned to this molecule. We suggest that iron atoms interact with hydrogen and produce Fe-H nanoparticles which sometimes contain many H atoms. We calculate infrared spectra of hydrogenated iron nanoparticles using density functional theory methods and find broad, overlapping bands. Desorption of H2 could induce spinning of these small Fe-H dust grains. Some of hydrogenated iron nanoparticles posses magnetic and electric moments and should interact with electromagnetic fields in the ISM. Fe_nH_m nanoparticles could contribute to the polarization of the ISM and the anomalous microwave emission. We discuss the conditions required to form FeH and Fe_nH_m in the ISM.

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G. Bilalbegovic, A. Maksimovic and V. Mohacek-Grosev
Wed, 2 Nov 16
53/55

Comments: accepted for publications in MNRAS Letters

Infrared Opacities in Dense Atmospheres of Cool White Dwarf Stars [SSA]

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http://arxiv.org/abs/1610.07357


Dense, He-rich atmospheres of cool white dwarfs represent a challenge to the modeling. This is because these atmospheres are constituted of a dense fluid in which strong multi-atomic interactions determine their physics and chemistry. Therefore, the ideal-gas-based description of absorption is no longer adequate, which makes the opacities of these atmospheres difficult to model. This is illustrated with severe problems in fitting the spectra of cool, He-rich stars. Good description of the infrared (IR) opacity is essential for proper assignment of the atmospheric parameters of these stars. Using methods of computational quantum chemistry we simulate the IR absorption of dense He/H media. We found a significant IR absorption from He atoms (He-He-He CIA opacity) and a strong pressure distortion of the H$_2$-He collision-induced absorption (CIA). We discuss the implication of these results for interpretation of the spectra of cool stars.

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P. Kowalski, S. Blouin and P. Dufour
Tue, 25 Oct 16
54/69

Comments: 6 pages, 5 figures, Proceedings of the EUROWD2016 workshop. To be published in ASPCS

Astromaterial Science and Nuclear Pasta [HEAP]

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http://arxiv.org/abs/1606.03646


The heavens contain a variety of materials that range from conventional to extraordinary and extreme. For this colloquium, we define Astromaterial Science as the study of materials, in astronomical objects, that are qualitatively denser than materials on earth. Astromaterials can have unique properties, related to their density, such as extraordinary mechanical strength, or alternatively be organized in ways similar to more conventional materials. The study of astromaterials may suggest ways to improve terrestrial materials. Likewise, advances in the science of conventional materials may allow new insights into astromaterials. We discuss Coulomb crystals in the interior of cold white dwarfs and in the crust of neutron stars and review the limited observations of how stars freeze. We apply astromaterial science to the generation of gravitational waves. According to Einstein’s Theory of General Relativity accelerating masses radiate gravitational waves. However, very strong materials may be needed to vigorously accelerate large masses in order to produce continuous gravitational waves that are observable in present detectors. We review large-scale molecular dynamics simulations of the breaking stress of neutron star crust that suggest it is the strongest material known, some ten billion times stronger than steel. Nuclear pasta is an example of a soft astromaterial. It is expected near the base of the neutron star crust at densities of ten to the fourteen grams per cubic centimeter. Competition between nuclear attraction and Coulomb repulsion rearrange neutrons and protons into complex non-spherical shapes such as flat plates (lasagna) or thin rods (spaghetti). We review semi-classical molecular dynamics simulations of nuclear pasta. We illustrate some of the shapes that are possible and discuss transport properties including shear viscosity and thermal and electrical conductivities.

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M. Caplan and C. Horowitz
Tue, 14 Jun 16
50/67

Comments: 13 pages, 7 figures

The sequence to hydrogenate coronene cations: A journey guided by magic numbers [CL]

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http://arxiv.org/abs/1603.02593


The understanding of hydrogen attachment to carbonaceous surfaces is essential to a wide variety of research fields and technologies such as hydrogen storage for transportation, precise localization of hydrogen in electronic devices and the formation of cosmic H2. For coronene cations as prototypical Polycyclic Aromatic Hydrocarbon (PAH) molecules, the existence of magic numbers upon hydrogenation was uncovered experimentally. Quantum chemistry calculations show that hydrogenation follows a site-specific sequence leading to the appearance of cations having 5, 11, or 17 hydrogen atoms attached, exactly the magic numbers found in the experiments. For these closed-shell cations, further hydrogenation requires appreciable structural changes associated with a high transition barrier. Controlling specific hydrogenation pathways would provide the possibility to tune the location of hydrogen attachment and the stability of the system. The sequence to hydrogenate PAHs, leading to PAHs with magic numbers of H atoms attached, provides clues to understand that carbon in space is mostly aromatic and partially aliphatic in PAHs. PAH hydrogenation is fundamental to assess the contribution of PAHs to the formation of cosmic H2.

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S. Cazaux, L. Boschman, N. Rougeau, et. al.
Wed, 9 Mar 16
6/71

Comments: Published in Scientific reports from Nature publishing group

A Preliminary Jupiter Model [EPA]

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http://arxiv.org/abs/1602.05143


In anticipation of new observational results for Jupiter’s axial moment of inertia and gravitational zonal harmonic coefficients from the forthcoming Juno orbiter, we present a number of preliminary Jupiter interior models. We combine results from ab initio computer simulations of hydrogen-helium mixtures, including immiscibility calculations, with a new nonperturbative calculation of Jupiter’s zonal harmonic coefficients, to derive a self-consistent model for the planet’s external gravity and moment of inertia. We assume helium rain modified the interior temperature and composition profiles. Our calculation predicts zonal harmonic values to which measurements can be compared. Although some models fit the observed (pre-Juno) second- and fourth-order zonal harmonics to within their error bars, our preferred reference model predicts a fourth-order zonal harmonic whose absolute value lies above the pre-Juno error bars. This model has a dense core of about 12 Earth masses, and a hydrogen-helium-rich envelope with approximately 3 times solar metallicity.

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W. Hubbard and B. Militzer
Wed, 17 Feb 16
41/55

Comments: 18 figures, 3 tables, in press, Astrophysical Journal

CO2 hydrate dissociation at low temperatures – formation and annealing of ice Ic [CL]

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http://arxiv.org/abs/1510.08004


Dissociation of gas hydrates below 240 K leads to the formation of a metastable form of water ice, so called cubic ice (Ic). Through its defective nature and small particle size the surface film composed of such material is incapable of creating any significant diffusion barrier. Above 160 K, cubic ice gradually transforms to the stable hexagonal (Ih) form on laboratory time scales. The annealing, coupled with a parallel decomposition of gas hydrates, accelerates as temperature rises but already above 190 K the first process prevails, transforming cubic stacking sequences in-to ordinary Ih ice within a few minutes. Remaining stacking faults are removed through very slow isothermal annealing or after heating up above 240 K. The role of the proportion of cubic stacking on the decomposition rate is discussed. A better understanding of the dissociation kinetics at low temperatures is particularly im-portant for the critical evaluation of existing hypotheses that consider clathrates as a potential medium that actively participate in geological processes or is able to store gases (e.g. CH4, CO2 or Xe) in environments like comets, icy moons (i. e. Titan, Europa, Enceladus) or on Mars. Here, we present kinetics studies on the dissociation of CO2 clathrates at isothermal and isobaric conditions between 170 and 190K and mean Martian surface pressure. We place special attention to the formed ice and demonstrate its influence on the dissociation rates with a combination of neutron diffraction studies (performed on D20 at ILL/Grenoble) and cryo-SEM. More detailed crystallo-graphic information has been acquired via a flexible stacking-fault model capable of revealing the time evolution of the defect structure of ice Ic in terms of stacking probabilities and crystal size.

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A. Falenty, T. Hansen and W. Kuhs
Wed, 28 Oct 15
57/79

Comments: Unpublished contribution to the 7th International Conference on Gas Hydrates (ICGH-7), Edinburgh, UK, 17-21 July 2011 (was only available to the conference participants)

Towards graphene-based detectors for dark matter directional detection [CL]

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http://arxiv.org/abs/1509.08801


Dark matter detectors with directional sensitivity have the capability to distinguish dark matter induced nuclear recoils from isotropic backgrounds, thus providing a smoking gun signature for dark matter in the Galactic halo. Here we propose a conceptually novel class of high directional sensitivity dark matter detectors utilizing graphene-based van der Waals heterostructures. The advantages over conventional low pressure gas time projection chamber-based directional detectors are discussed in detail. A practical implementation using graphene/hexagonal boron nitride and graphene/molybdenum disulfide heterostructures is presented together with an overwhelming amount of experimental evidence in strong support of its feasibility.

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S. Wang
Wed, 30 Sep 15
38/71

Comments: 5 pages, 1 figure

Microwave Loss Reduction in Cryogenically Cooled Conductors [IMA]

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http://arxiv.org/abs/1509.05273


Measurements of microwave attenuation at room temperature and 4.2 K have been performed on some conductors commonly used in receiver input circuits. The reduction in loss on cooling is substantial, particularly for copper and plated gold, both of which showed a factor of 3 loss reduction. Copper passivated with benzotriazole shows the same loss as without passivation. The residual resistivity ratio between room temperature and 4.2 K, deduced from the measurements using the classical skin effect formula, was smaller than the measured DC value to a degree consistent with conduction in the extreme anomalous skin effect regime at cryogenic temperatures. The measurements were made in the 5-10 GHz range. The materials tested were: aluminum alloys 1100-T6 and 6061-O, C101 copper, benzotriazole treated C101 copper, and brass plated with electroformed copper, Pur-A-Gold 125-Au soft gold, and BDT200 bright gold.

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R. Finger and A. Kerr
Fri, 18 Sep 15
50/71

Comments: 9 pages

Crystal chemistry of three-component white dwarfs and neutron star crusts: phase stability, phase stratification, and physical properties [HEAP]

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http://arxiv.org/abs/1508.05088


A systematic search for multicomponent crystal structures is carried out for five different ternary systems of nuclei in a polarizable background of electrons, representative of accreted neutron star crusts and some white dwarfs. Candidate structures are “bred” by a genetic algorithm, and optimized at constant pressure under the assumption of linear response (Thomas-Fermi) charge screening. Subsequent phase equilibria calculations reveal eight distinct crystal structures in the $T=0$ bulk phase diagrams, five of which are complicated multinary structures not before predicted in the context of compact object astrophysics. Frequent instances of geometrically similar but compositionally distinct phases give insight into structural preferences of systems with pairwise Yukawa interactions, including and extending to the regime of low density colloidal suspensions made in a laboratory. As an application of these main results, we self-consistently couple the phase stability problem to the equations for a self-gravitating, hydrostatically stable white dwarf, with fixed overall composition. To our knowledge, this is the first attempt to incorporate complex multinary phases into the equilibrium phase layering diagram and mass-radius-composition dependence, both of which are reported for He-C-O and C-O-Ne white dwarfs. Finite thickness interfacial phases (“interphases”) show up at the boundaries between single-component bcc crystalline regions, some of which have lower lattice symmetry than cubic. A second application — quasi-static settling of heavy nuclei in white dwarfs — builds on our equilibrium phase layering method. Tests of this nonequilibrium method reveal extra phases which play the role of transient host phases for the settling species.

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T. Engstrom, N. Yoder and V. Crespi
Mon, 24 Aug 15
13/43

Comments: 11 pages, 4 figures, 1 table. Submitted to ApJ

Crossing Statistics of Anisotropic Stochastic Surface [CL]

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http://arxiv.org/abs/1508.01409


We use crossing statistics and its generalization to determine the anisotropic direction imposed on a stochastic fields in $(2+1)$Dimension. This approach enables us to examine not only the rotational invariance of morphology but also we can determine the Gaussianity of underlying stochastic field in various dimensions. Theoretical prediction of up-crossing statistics (crossing with positive slope at a given threshold $\alpha$ of height fluctuation), $\nu^+_{\diamond}(\alpha)$, and generalized roughness function, $N^{\diamond}_{tot}(q)$, for correlation length ($\xi_{\diamond}$) and/with scaling exponent ($\gamma_{\diamond}$) anisotropies are calculated. The strategy to examine the anisotropy nature and to determine its direction is as follows: we consider a set of normal axes, and sign them $||$ (parallel) and $ \bot$ (normal) with respect to unknown anisotropic direction. Then we determine $\nu_{\diamond}^+ (\alpha)$ and $N^{\diamond}_{tot}(q)$ in both directions. The directional dependency of difference between computed results in mentioned directions are clarify. Finally we systematically recognize the anisotropy direction at $3\sigma$ confidence interval using P-value approach. In order to distinguish between nature of anisotropies, after applying a typical method in determining the scaling exponents in both mentioned directions with respect to the recognized anisotropy direction using up-crossing statistics, the kind and the ratio of correlation length anisotropy are specified. Our algorithm can be mounted with a simple software on various instruments for surface analysis, such as AFM, STM and etc.

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M. Nezhadhaghighi, S. Movahed, T. Yasseri, et. al.
Fri, 7 Aug 15
35/51

Comments: 14 pages and 11 figures

High-pressure, temperature elasticity of Fe- and Al-bearing MgSiO3: implications for the Earth's lower mantle [CL]

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http://arxiv.org/abs/1507.05025


Fe and Al are two of the most important rock-forming elements other than Mg, Si, and O. Their presence in the lower mantle’s most abundant minerals, MgSiO_3 bridgmanite, MgSiO_3 post-perovskite and MgO periclase, alters their elastic properties. However, knowledge on the thermoelasticity of Fe- and Al-bearing MgSiO_3 bridgmanite, and post-perovskite is scarce. In this study, we perform ab initio molecular dynamics to calculate the elastic and seismic properties of pure, Fe^{3+}- and Fe^{2+}-, and Al^{3+}-bearing MgSiO_3 perovskite and post-perovskite, over a wide range of pressures, temperatures, and Fe/Al compositions. Our results show that a mineral assemblage resembling pyrolite fits a 1D seismological model well, down to, at least, a few hundred kilometers above the core-mantle boundary, i.e. the top of the D” region. In D”, a similar composition is still an excellent fit to the average velocities and fairly approximate to the density. We also implement polycrystal plasticity with a geodynamic model to predict resulting seismic anisotropy, and find post-perovskite with predominant (001) slip across all compositions agrees best with seismic observations in the D”.

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S. Zhang, S. Cottaar, T. Liu, et. al.
Mon, 20 Jul 15
11/52

Comments: 26 pages, 6 figures; submitted to journal 8 June 2015