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Enthalpy of formation of CsSn(Clx(Br,I)1-x)3 and CsPb(Clx(Br,I)1-x)3

Journal of physics: Conference Series 2018年第1期1144卷

作者： Nontapat Wanwieng Yongyut Laosiritaworn Atchara Punya Jaroenjittichai Department of Physics and Materials Science Faculty of Science Chiang Mai University 239 Huay Kaew Road Muang Chiang Mai 50200 Thailand Graduate Program in Physics Faculty of Science Chiang Mai University 239 Huay Kaew Road Muang Chiang Mai 50200 Thailand Center of Excellence in Materials Science and Technology Chiang Mai University Chiang Mai Thailand 50200 Thailand

Organic-inorganic hybrid halide perovskites, e.g., MAPbI3, have revolutionized the field of solution-processable photovoltaic applications. However, due to organic cation, they are found to be unstable under external environment such as moisture and high temperature. Moreover, the toxicity of lead (Pb) in their structure is harmful for human health and hurdle for commercialization. These inspire us to pursue for families of perovskites structure with the formula CsSn(Clx(Br,I)1-x)3 with x = 1/3, 2/3, 1, which are nontoxic and could have better structural stability under ambient conditions. We have investigated the enthalpy of formation of CsSn(Clx(Br,I)1-x )3 and in based on the density functional theory (DFT) with the generalized gradient approximation (GGA). The main objective is to seek for structural stability with respect to the composition x's. We found that the structural stability increases linearly with composition x's of halide atom from I to Br to Cl. We also calculate enthalpy of formation of CsPb(Cix(Br,I)1-x)3 perovskites for comparative purpose, and found that the structural stability of CsSn(Clx(Br,I)1-x)3 is slightly lower than its Pb-counterpart. Thus CsSn(Clx(Br,I)1-x)3 is still the promise candidate for photovoltaics. These studies could serve as a guidance to compromise the stability, by varying composition of halide atoms, with the optimal band gap or other solar-cell-desired properties.

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Orbital migration of interacting stellar mass black holes in disks around supermassive black holes

arXiv

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arXiv 2018年

作者： Secunda, Amy Bellovary, Jillian Low, Mordecai-Mark Mac Ford, K.E. Saavik McKernan, Barry Leigh, Nathan Lyra, Wladimir Department of Astrophysics American Museum of Natural History Central Park West at 79th Street New YorkNY10024 United States Department of Physics Queensborough Community College BaysideNY11364 United States Department of Science Borough of Manhattan Community College City University of New York New YorkNY10007 United States Physics Program Graduate Center CUNY New YorkNY10016 United States Department of Physics and Astronomy Stony Brook University Stony BrookNY11794-3800 United States Center for Computational Astrophysics Flatiron Institute New YorkNY10010 United States Department of Physics and Astronomy California State University Northridge 18111 Nordhoff Street NorthridgeCA91330 United States Jet Propulsion Laboratory California Institute of Technology 4800 Oak Grove Drive PasadenaCA91109 United States

The merger rate of stellar mass black holes binaries (sBHBs) inferred by the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) suggests the need for an efficient source of sBHB formation. Active galactic nucleus (AGN) disks are a promising location for the formation of these sBHBs, as well as binaries of other compact objects, because of powerful torques exerted by the gas disk. These gas torques cause orbiting compact objects to migrate towards regions in the disk where inward and outward torques cancel, known as migration traps. We simulate the migration of stellar mass black holes (sBHs) in an analytically modeled AGN disk using an augmented N-body code that includes migration torques, a stochastic gravitational force exerted by turbulent density fluctuations in the disk, and inclination and eccentricity dampening produced by passages through the gas disk, in addition to the standard gravitational forces between objects. We find that sBHBs form rapidly in the disk as sBHs migrate towards the migration trap. These sBHBs are likely to subsequently merge on short time-scales. The process continues, leading to the build up of a population of over-massive sBHs. sBHBs that form in AGN disks could contribute significantly to the sBHB merger rate inferred by LIGO. Copyright © 2018, The Authors. All rights reserved.

关键词： Merging

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Non-reciprocal willis coupling in zero-index moving media

arXiv

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arXiv 2018年

作者： Quan, Li Sounas, Dimitrios L. Alù, Andrea Department of Electrical and Computer Engineering University of Texas at Austin AustinTX78712 United States Department of Electrical and Computer Engineering Wayne State University DetroitMI48202 United States Photonics Initiative Advanced Science Research Center City University of New York New YorkNY10031 United States Physics Program Graduate Center City University of New York New YorkNY10016 United States Department of Electrical Engineering City College of The City University of New York NY10031 United States

Mechanical motion can break the symmetry in which sound travels in a medium, but significant non-reciprocity is typically achieved only for very large motion speeds. Here we combine moving media with zero-index acoustic propagation, yielding extreme non-reciprocity and induced bianisotropy for modest applied speeds. The metamaterial is formed by an array of waveguides loaded by Helmholtz resonators, and it exhibits opposite signs of the refractive index sustained by asymmetric Willis coupling for propagation in opposite directions. We use this response to design a nonreciprocal acoustic lens focusing only when excitation from one side, with applications for imaging and ultrasound technology. Copyright © 2018, The Authors. All rights reserved.

关键词： Refractive index

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A chromaticity analysis and PSF subtraction techniques for SCExAO/CHARIS data

arXiv

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arXiv 2019年

作者： Gerard, Benjamin L. Marois, Christian Currie, Thayne Brandt, Timothy Chilcote, Jeffrey K. Draper, Zachary H. Groff, Tyler Guyon, Olivier Hayashi, Masahiko Jovanovic, Nemanja Knapp, Gillian R. Kudo, Tomoyuki Kwon, Jungmi Lozi, Julien Martinache, Frantz McElwain, Michael Tamura, Motohide Uyama, Taichi University of Victoria Department of Physics and Astronomy 3800 Finnerty Rd VictoriaV8P 5C2 Canada National Research Council of Canada Astronomy & Astrophysics Program 5071 West Saanich Rd VictoriaV9E 2E7 Canada NASA-Ames Research Center Moffett FieldCA United States Subaru Telescope National Astronomical Observatory of Japan 650 North A’ohōkū Place HiloHI96720 United States Eureka Scientific 2452 Delmer Street Suite 100 OaklandCA United States Department of Physics University of California-Santa Barbara Santa BarbaraCA United States Department of Physics University of Notre Dame 225 Nieuwland Science Hall Notre DameIN46556 United States NASA-Goddard Space Flight Center GreenbeltMD United States Steward Observatory University of Arizona TucsonAZ85721 United States Astrobiology Center National Institutes of Natural Sciences 2-21-1 Osawa Mitaka Tokyo Japan NAOJ 2-21-1 Osawa Mitaka Tokyo181-8588 Japan Department of Astronomy California Institute of Technology 1200 E. California Blvd. PasadenaCA91125 United States Department of Astrophysical Science Princeton University Peyton Hall Ivy Lane PrincetonNJ08544 United States ISAS JAXA 3-1-1 Yoshinodai Chuo-ku Sagamihara Kanagawa252-5210 Japan Université Côte d’Azur Observatoire de la Côte d’Azur CNRS Laboratoire Lagrange France Department of Astronomy Graduate School of Science University of Tokyo 7-3-1 Hongo Bunkyo-ku Tokyo113-0033 Japan

We present an analysis of instrument performance using new observations taken with the Coronagraphic High Angular Resolution Imaging Spectrograph (CHARIS) instrument and the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) system. In a correlation analysis of our datasets (which use the broadband mode covering J through K band in a single spectrum), we find that chromaticity in the SCExAO/CHARIS system is generally worse than temporal stability. We also develop a point spread function (PSF) subtraction pipeline optimized for the CHARIS broadband mode, including a forward modelling-based exoplanet algorithmic throughput correction scheme. We then present contrast curves using this newly developed pipeline. An analogous subtraction of the same datasets using only the H band slices yields the same final contrasts as the full JHK sequences;this result is consistent with our chromaticity analysis, illustrating that PSF subtraction using spectral differential imaging (SDI) in this broadband mode is generally not more effective than SDI in the individual J, H, or K bands. In the future, the data processing framework and analysis developed in this paper will be important to consider for additional SCExAO/CHARIS broadband observations and other ExAO instruments which plan to implement a similar integral field spectrograph broadband mode. Copyright © 2019, The Authors. All rights reserved.

关键词： Optical transfer function

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Silicon waveguide modulator with embedded phase change material

arXiv

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arXiv 2017年

作者： Miller, Kevin J. Hallman, Kent A. Haglund, Richard F. Weiss, Sharon M. Interdisciplinary Graduate Program in Materials Science Vanderbilt University NashvilleTN37235 United States Department of Physics and Astronomy Vanderbilt University NashvilleTN37235 United States Department of Electrical Engineering and Computer Science Vanderbilt University NashvilleTN37235 United States

Phase-change materials (PCMs) have emerged as promising active elements in silicon (Si) photonic systems. In this work, we design, fabricate, and characterize a hybrid Si-PCM optical modulator. By integrating vanadium dioxide (a PCM) within a Si photonic waveguide, in a non-resonant geometry, we demonstrate ~ 10 dB broadband modulation with a PCM length of 500 nm. Copyright © 2017, The Authors. All rights reserved.

关键词： Phase change materials

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Relating braking indices of young pulsars to the dynamics of superfluid cores

arXiv

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arXiv 2018年

作者： Oliveira, H.O. Magalhaes, N.S. Marinho, R.M. Carvalhoa, G.A. Frajuca, C. Graduate Program in Physics Technological Institute of Aeronautics Praça Marechal Eduardo Gomes 50 Sao Jose dos Campos SP12228-900 Brazil Federal University of Sao Paulo Department of Physics Rua Sao Nicolau 210 Diadema SP09913-030 Brazil Dipartimento di Fisica ICRA Sapienza Università di Roma P.le Aldo Moro 5 RomeI-00185 Italy ICRANet P.zza della Repubblica 10 PescaraI-65122 Italy Federal Institute of Education Science and Technology of Sao Paulo R. Pedro Vicente 625 Sao Paulo SP01109-010 Brazil

Pulsars are stars that emit electromagnetic radiation in well-defined time intervals. The frequency of such pulses decays with time as is quantified by the braking index (n). In the canonical model n = 3 for all pulsars, but observational data show that n ≠ 3, indicating a limitation of the model. In this work we present a new approach to study the frequency decay of the rotation of a pulsar, based on an adaptation of the canonical one. We consider the pulsar a star that rotates in vacuum and has a strong magnetic field but, differently from the canonical model, we assume that its moment of inertia changes in time due to a uniform variation of a displacement parameter in time. We found that the braking index results smaller than the canonical value as a consequence of an increase in the star's displacement parameter, whose variation is small enough to allow plausible physical considerations that can be applied to a more complex model for pulsars in the future. In particular, this variation is of the order of neutron vortices' creep in rotating superfluids. When applied to pulsar data our model yielded values for the stars' braking indices close to the observational ones. The application of this approach to a more complex star model, where pulsars are assumed to have superfluid interiors, is the next step in probing it. We hypothesize that the slow expansion of the displacement parameter might mimic the motion of core superfluid neutron vortices in realistic models. Copyright © 2018, The Authors. All rights reserved.

关键词： Pulsars

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On the Yearly Performance of a Bifacial PV Module in Central Anatolia - Turkey

On the Yearly Performance of a Bifacial PV Module in Central...

引用

International Renewable and Sustainable Energy Conference (IRSEC)

作者： Talat Özden Raşit Turan Bülent Gültekin Aklnoğlu Department of Electrical and Electronics Engineering Gumüshane University Gumushane Turkey Department of Physics Middle East Technical University METU Ankara Turkey Earth System Science Program Graduate School of Natural and Applied Sciences Ankara Turkey

With the tremendous increase in the photovoltaic (PV) power plants world-wide remarkable decreases in their installation prices per watt are attained mainly due to economic scale effect. This brings questioning to increase their energy yields by considering any possible way like fabricating bifacial solar modules. Present study is on the performance analysis of a bifacial PV module using one-year outdoor testing results in Ankara-Turkey. The module performed very well and reached a specific yield value of 1750 kWh/kWp. This value for Central Anatolia region is well above the values predicted (and suggested) by the local authorities. The efficiency and performance ratio variation with respect to ambient and module temperature are obtained. The calculated dependence of efficiency on the module temperature is found to be η = -0.073T mod +18.05, and the maximum measured module temperature is about 70 °C. The results show that the bifacial modules have the potential to replace the mono facial modules that are now dominating the PV market.

关键词： Testing Temperature measurement Temperature dependence MONOS devices Meteorology Solar energy

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Ambient-pressure CVD of graphene on low-index Ni surfaces using methane: A combined experimental and first-principles study

引用

Physical Review Materials 2018年第7期2卷 073404-073404页

作者： Daniela L. Mafra Jimena A. Olmos-Asar Fabio R. Negreiros Alfonso Reina Ki Kang Kim Mildred S. Dresselhaus Jing Kong Gary J. Mankey Paulo T. Araujo Department of Electrical Engineering and Computer Sciences Massachusetts Institute of Technology Cambridge Massachusetts 02139 USA Centro de Ciências Naturais e Humanas Universidade Federal do ABC Santo André 09210-580 SP Brazil INFIQC CONICET Departamento de Química Teórcia y Computacional Facultad de Ciencias Químicas Universidad Nacional de Córdoba X5000HUA Argentina Department of Materials Science and Engineering Massachusetts Institute of Technology Cambridge Massachusetts 02139 USA Department of Energy and Materials Engineering Dongguk University-Seoul Seoul 04620 Republic of Korea Department of Physics Massachusetts Institute of Technology Cambridge Massachusetts 02139 USA Department of Physics and Astronomy The University of Alabama Tuscaloosa Alabama 35487 USA Center for Materials for Information Technology (MINT Center) The University of Alabama Tuscaloosa Alabama 35401 USA Natural Sciences Institute Graduate Program in Physics - Federal University of Para Belem PA 66075-110 Brazil

The growth of large area single-layer graphene (1-LG) is studied using ambient pressure chemical vapor deposition on single-crystal Ni(111), Ni(110), and Ni(100). By varying both the furnace temperature in the range of 800–1100 °C and the gas flow through the growth chamber, uniform, high-quality 1-LG is obtained for Ni(111) and Ni(110) single crystals and for Ni(100) thin films. Surprisingly, only multilayer graphene growth could be obtained for single-crystal Ni(100). The experimental results are analyzed to determine the optimum combination of temperature and gas flow. Characterization with optical microscopy, Raman spectroscopy, and optical transmission support our findings. Density-functional theory calculations are performed to determine the energy barriers for diffusion, segregation, and adsorption, and model the kinetic pathways for formation of different carbon structures on the low-index surfaces of Ni.

关键词： Growth Synthesis 2-dimensional systems Carbon-based materials Atomic force microscopy Chemical vapor deposition Density functional calculations Density functional theory Raman spectroscopy

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Anomalous and regular transport in spin 1/2 chains: AC conductivity

arXiv

引用

arXiv 2017年

作者： Sánchez, R.J. Varma, V.K. Oganesyan, V. Bethe Center for Theoretical Physics Universität Bonn Germany Department of Engineering Science and Physics College of Staten Island CUNY Staten IslandNY10314 United States Physics program and Initiative for the Theoretical Sciences Graduate Center CUNY New YorkNY10016 United States Department of Physics and Astronomy University of Pittsburgh PittsburghPA15260 United States

We study magnetization transport in anisotropic spin-1/2 chains governed by the integrable XXZ model with and without integrability-breaking perturbations at high temperatures (T → ∞) using a hybrid approach that combines exact sum-rules with judiciously chosen Ansätze. In the integrable XXZ model we find (i) super-diffusion at the isotropic (Heisenberg) point, with frequency dependent conductivity σ′(ω → 0) ∼ |ω|α, where α = −3/7 in close numerical agreement with recent t-DMRG computations;(ii) a continuously drifting exponent from α = −1+ in the XY limit of the model to α > 0 within the Ising regime;and (iii) a diffusion constant saturating in the XY coupling deep in the Ising limit. We consider two kinds of integrability breaking perturbations — a simple next-nearest-neighbor spin-flip term (J2) and a three-spin assisted variant (t2), natural in the fermion particle representation of the spin chain. In the first case we discover a remarkable sensitivity of σ′(ω) to the sign of J2, with enhanced low frequency spectral weight and a pronounced upward shift in the magnitude of α for J2 > 0. Perhaps even more surprising, we find sub-diffusion (α > 0) over a range of J2 Copyright © 2017, The Authors. All rights reserved.

关键词： Diffusion

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Interactions between species introduce spurious associations in microbiome studies

arXiv

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arXiv 2017年

作者： Menon, Rajita Ramanan, Vivek Korolev, Kirill S. Department of Physics Boston University BostonMA United States BRITE Bioinformatics REU Program Boston University BostonMA United States Graduate Program in Bioinformatics Boston University BostonMA United States Department of Biology and Computer Science Swarthmore College SwarthmorePA United States

Microbiota contribute to many dimensions of host phenotype, including disease. To link specific microbes to specific phenotypes, microbiome-wide association studies compare microbial abundances between two groups of samples. Abundance differences, however, reflect not only direct associations with the phenotype, but also indirect effects due to microbial interactions. We found that microbial interactions could easily generate a large number of spurious associations that provide no mechanistic insight. Using techniques from statistical physics, we developed a method to remove indirect associations and applied it to the largest dataset on pediatric inflammatory bowel disease. Our method corrected the inflation of p-values in standard association tests and showed that only a small subset of associations is directly linked to the disease. Direct associations had a much higher accuracy in separating cases from controls and pointed to immunomodulation, butyrate production, and the brain-gut axis as important factors in the inflammatory bowel disease. Copyright © 2017, The Authors. All rights reserved.

关键词： Association reactions

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