cometadata/datacite-rtg-text-other-reclassification-records huggingface dataset:
Native defects in the Co$_2$Ti$Z$ ($Z=$ Si, Ge, Sn) full Heusler alloys: formation and influence on the thermoelectric properties
Creators: name: Popescu, Voicu
name: Kratzer, Peter
name: Wimmer, Sebastian
name: Ebert, Hubert
Publisher: name: arXiv
Year: 2017
Subjects: subject: Materials Science (cond-mat.mtrl-sci)
subject: FOS: Physical sciences

description: We have performed first-principles investigations on the native defects in the full Heusler alloys Co$_2$Ti$Z$ ($Z$ one of the group IV elements Si, Ge, Sn), determining their formation energies and how they influence the transport properties. We find that Co vacancies (Vc) in all compounds and the Ti$_\text{Sn}$ anti-site exhibit negative formation energies. The smallest positive values occur for Co in excess on anti-sites (Co$_Z$ or Co$_\text{Ti}$) and for Ti$_Z$. The most abundant native defects were modeled as dilute alloys, treated with the coherent potential approximation in combination with the multiple-scattering theory Green function approach. The self-consistent potentials determined this way were used to calculate the residual resistivity via the Kubo-Greenwood formula and, based on its energy dependence, the Seebeck coefficient of the systems. The latter is shown to depend significantly on the type of defect, leading to variations that are related to subtle, spin-orbit coupling induced, changes in the electronic structure above the half-metallic gap. Two of the systems, Vc$_\text{Co}$ and Co$_Z$, are found to exhibit a negative Seebeck coefficient. This observation, together with their low formation energy, offers an explanation for the experimentally observed negative Seebeck coefficient of the Co$_2$Ti$Z$ compounds as being due to unintentionally created native defects.
The $b$ quark fragmentation fractions at LHCb and meson decays with heavy quark spectators
Creators: name: Dib, C. O.
name: Kim, C. S.
name: Neill, N. A.
Publisher: name: arXiv
Year: 2023
Subjects: subject: High Energy Physics - Phenomenology (hep-ph)
subject: FOS: Physical sciences

description: We study the current estimates of $B_c\to B_s π$ to extract the fragmentation fraction $f_c/f_s$ at the LHCb. A rather robust estimate of $Br(B_c\to B_s π)$ based on factorization and lattice results for the form factor gives $f_c/f_s \sim 0.056$ with a $16\%$ error. We also revisit the extraction of $f_s/f_d$ using $B\to Dπ$ instead of the theoretical cleaner but more suppressed channel $B\to DK$. We also find a tension on the predictions of $Br(B_c\to J/ψπ)$ and $Br(B_c\to B_sπ)$ considering the measurements of these modes at LHCb, and find that, within a $23\%$ uncertainty, only the lower end of the current prediction range $Br(B_c\to J/ψ)\sim 0.4\% - 1.7\%$ would be consistent with the LHCb measurements.
description: 11 pages, 2 figures
Import options for chemical energy carriers from renewable sources to Germany
Creators: name: Hampp, Johannes
name: Düren, Michael
name: Brown, Tom
Publisher: name: arXiv
Year: 2021
Subjects: subject: Physics and Society (physics.soc-ph)
subject: FOS: Physical sciences

description: Import and export of fossil energy carriers are cornerstones of energy systems world-wide. If energy systems are to become climate neutral and sustainable, fossil carriers need to be substituted with carbon neutral alternatives or electrified if possible. We investigate synthetic chemical energy carriers, H2, CH4, MeOH, NH3 and Fischer-Tropsch fuels (FTF), produced using electricity from RES as fossil substitutes. [...] We model the sourcing of feedstock chemicals, synthesis and transport along nine different Energy Supply Chains to Germany (DE) and compare import options for seven locations around the world against each other and with domestically sourced alternatives on the basis of their respective cost per unit of H2 and energy delivered. We find that for each type of chemical energy carrier, there is an import option with lower costs compared to domestic production in DE. No single exporting country or energy carrier has a unique cost advantage, since for each energy carrier and country there are cost-competitive alternatives. This allows exporter and infrastructure decisions to be made based on other criteria than energy and cost. The lowest cost means for importing of energy and H2 are by H2 pipeline from Denmark, Spain and Western Asia and Northern Africa starting at 36 EUR/MWhLHV to 42 EUR/MWh-LHV or 1.0 EUR/kg-H2 to 1.3 EUR/kg-H2 (in 2050, assuming 5 % p.a. capital cost). For complex energy carriers derived from H2 like CH4, NH3, MeOH or FTF, imports from Argentina by ship to DE are lower cost than closer exporters in the European Union or Western Asia and Northern Africa. For meeting H2 demand, direct H2 imports are more attractive than indirect routes using CH4, MeOH or NH3 imports and subsequent decomposition to H2 because of high capital investment costs and energetic losses. We make our model and data available under open licenses for adaptation and reuse.
Stellarator bootstrap current and plasma flow velocity at low collisionality
Creators: name: Helander, P.
name: Parra, F. I.
name: Newton, S. L.
Publisher: name: arXiv
Year: 2017
Subjects: subject: Plasma Physics (physics.plasm-ph)
subject: FOS: Physical sciences

description: The bootstrap current and flow velocity of a low-collisionality stellarator plasma are calculated. As far as possible, the analysis is carried out in a uniform way across all low-collisionality regimes in general stellarator geometry, assuming only that the confinement is good enough that the plasma is approximately in local thermodynamic equilibrium. It is found that conventional expressions for the ion flow speed and bootstrap current in the low-collisionality limit are accurate only in the $1/ν$-collisionality regime and need to be modified in the $\sqrtν$-regime. The correction due to finite collisionality is also discussed and is found to scale as $ν^{2/5}$.
Performance improvement of three-body radiative diode driven by graphene surface plasmon polaritons
Creators: name: He, Ming-Jian
name: Guo, Xue
name: Qi, Hong
name: Zheng, Zhi-Heng
name: Antezza, Mauro
name: Tan, He-Ping
Publisher: name: arXiv
Year: 2023
Subjects: subject: Optics (physics.optics)
subject: Applied Physics (physics.app-ph)
subject: FOS: Physical sciences

description: As an analogue to electrical diode, a radiative thermal diode allows radiation to transfer more efficiently in one direction than in the opposite direction by operating in a contactless mode. In this study, we demonstrated that, within the framework of three-body photon thermal tunneling, the rectification performance of three-body radiative diode can be greatly improved by bringing graphene into the system. The system is composed of three parallel slabs, with the hot and cold terminals of the diode coated with graphene films, and the intermediate body made of vanadium dioxide (VO2). The rectification factor of the proposed radiative thermal diode reaches 300 % with a 350 nm separation distance between the hot and cold terminals of the diode. With the help of graphene, the rectification performance of the radiative thermal diode can be improved by over 11 times. By analyzing the spectral heat flux and energy transmission coefficients, it was found that the improved performance is primarily attributed to the surface plasmon polaritons (SPPs) of graphene. They excite the modes of insulating VO2 in the forward-biased scenario by forming strongly coupled modes between graphene and VO2, and thus dramatically enhance the heat flux. While, for the reverse-biased scenario, the VO2 is at its metallic state and thus graphene SPPs cannot work by three-body photon thermal tunneling. Furthermore, the improvement was also investigated for different chemical potentials of graphene, and geometric parameters of the three-body system. Our findings demonstrate the feasibility of using thermal-photon-based logical circuits, creating radiation-based communication technology, and implementing thermal management approaches at the nanoscale.
Beamforming Technologies for Ultra-Massive MIMO in Terahertz Communications
Creators: name: Ning, Boyu
name: Tian, Zhongbao
name: Mei, Weidong
name: Chen, Zhi
name: Han, Chong
name: Li, Shaoqian
name: Yuan, Jinhong
name: Zhang, Rui
Publisher: name: arXiv
Year: 2021
Subjects: subject: Information Theory (cs.IT)
subject: Signal Processing (eess.SP)
subject: FOS: Computer and information sciences
subject: FOS: Electrical engineering, electronic engineering, information engineering

description: Terahertz (THz) communications with a frequency band $0.1-10$ THz are envisioned as a promising solution to future high-speed wireless communication. Although with tens of gigahertz available bandwidth, THz signals suffer from severe free-spreading loss and molecular-absorption loss, which limit the wireless transmission distance. To compensate for the propagation loss, the ultra-massive multiple-input-multiple-output (UM-MIMO) can be applied to generate a high-gain directional beam by beamforming technologies. In this paper, a review of beamforming technologies for THz UM-MIMO systems is provided. Specifically, we first present the system model of THz UM-MIMO and identify its channel parameters and architecture types. Then, we illustrate the basic principles of beamforming via UM-MIMO and discuss the far-field and near-field assumptions in THz UM-MIMO. Moreover, an important beamforming strategy in THz band, i.e., beam training, is introduced wherein the beam training protocol and codebook design approaches are summarized. The intelligent-reflecting-surface (IRS)-assisted joint beamforming and multi-user beamforming in THz UM-MIMO systems are studied, respectively. The spatial-wideband effect and frequency-wideband effect in the THz beamforming are analyzed and the corresponding solutions are provided. Further, we present the corresponding fabrication techniques and illuminate the emerging applications benefiting from THz beamforming. Open challenges and future research directions on THz UM-MIMO systems are finally highlighted.
description: This paper has been published: B. Ning et al., "Beamforming Technologies for Ultra-Massive MIMO in Terahertz Communications," in IEEE Open Journal of the Communications Society, vol. 4, pp. 614-658, 2023, doi: 10.1109/OJCOMS.2023.3245669. URL:https://ieeexplore.ieee.org/document/10045774
Atomically flat single terminated oxide substrate surfaces
Creators: name: Biswas, Abhijit
name: Yang, Chan Ho
name: Ramesh, Ramamoorthy
name: Jeong, Yoon H
Publisher: name: arXiv
Year: 2017
Subjects: subject: Materials Science (cond-mat.mtrl-sci)
subject: FOS: Physical sciences

description: To achieve high quality epitaxial thin films and heterostructures of transition metal oxides with atomically controlled interfaces, one critical requirement is the use of atomically flat single terminated oxide substrates since the atomic arrangements and the reaction chemistry of the topmost surface layer of substrates determine the growth and consequent properties of the overlying films. Achieving the atomically flat and chemically single terminated surface state of commercially available substrates, however, requires judicious efforts because the surface of as-received substrates is of chemically mixed nature and also often polar. In this review, we summarize the surface treatment procedures to accomplish atomically flat surfaces with single terminating layer for various metal oxide substrates. We particularly focus on the substrates with lattice constant ranging from 4.00 to 3.70 angstrom, as the lattice constant of most perovskite materials falls into this range. For materials outside the range, one can utilize the substrates to induce compressive or tensile strain on the films and explore new states not available in bulk. The substrates covered in this review, which have been chosen with commercial availability and, most importantly, experimental practicality as a criterion, are KTaO3, REScO3 (RE = Rare-earth elements), SrTiO3, La0.18Sr0.82Al0.59Ta0.41O3 (LSAT), NdGaO3, LaAlO3, SrLaAlO4, and YAlO3. Analyzing all the established procedures, we conclude that atomically flat surfaces with selective A- or B-site single termination would be obtained for most commercially available oxide substrates. We further note that this topmost surface layer selectivity would provide an additional degree of freedom in searching for unforeseen emergent phenomena and functional applications in epitaxial oxide thin films and heterostructures with atomically controlled interfaces.
description: A review article
Strong spin-exchange recombination of three weakly interacting $^7$Li atoms
Creators: name: Li, J. -L.
name: Secker, T.
name: Mestrom, P. M. A.
name: Kokkelmans, S. J. J. M. F.
Publisher: name: arXiv
Year: 2021
Subjects: subject: Quantum Gases (cond-mat.quant-gas)
subject: FOS: Physical sciences

description: We reveal a significant spin-exchange pathway in the three-body recombination process for ultracold lithium-7 atoms near a zero-crossing of the two-body scattering length. This newly discovered recombination pathway involves the exchange of spin between all three atoms, which is not included in many theoretical approaches with restricted spin structure. Taking it into account, our calculation is in excellent agreement with experimental observations. To contrast our findings, we predict the recombination rate around a different zero-crossing without strong spin-exchange effects to be two orders of magnitude smaller, which gives a clear advantage to future many-body experiments in this regime. This work opens new avenues to study elementary reaction processes governed by the spin degree of freedom in ultracold gases.
Multiple magnetoplasmon polaritons of magneto-optical graphene in near-field radiative heat transfer
Creators: name: He, Ming-Jian
name: Qu, Lei
name: Ren, Ya-Tao
name: Qi, Hong
name: Antezza, Mauro
name: Tan, He-Ping
Publisher: name: arXiv
Year: 2023
Subjects: subject: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
subject: Applied Physics (physics.app-ph)
subject: FOS: Physical sciences

description: Graphene, as a two-dimensional magneto-optical material, supports magnetoplasmon polaritons (MPP) when exposed to an applied magnetic field. Recently, MPP of a single-layer graphene has shown an excellent capability in the modulation of near-field radiative heat transfer (NFRHT). In this study, we present a comprehensive theoretical analysis of NFRHT between two multilayered graphene structures, with a particular focus on the multiple MPP effect. We reveal the physical mechanism and evolution law of the multiple MPP, and we demonstrate that the multiple MPP allow one to mediate, enhance, and tune the NFRHT by appropriately engineering the properties of graphene, the number of graphene sheets, the intensity of magnetic fields, as well as the geometric structure of systems. We show that the multiple MPP have a quite significant distinction relative to the single MPP or multiple surface plasmon polaritons (SPPs) in terms of modulating and manipulating NFRHT.
How many mutually unbiased bases are needed to detect bound entangled states?
Creators: name: Bae, Joonwoo
name: Bera, Anindita
name: Chruściński, Dariusz
name: Hiesmayr, Beatrix C.
name: McNulty, Daniel
Publisher: name: arXiv
Year: 2021
Subjects: subject: Quantum Physics (quant-ph)
subject: FOS: Physical sciences

description: From a practical perspective it is advantageous to develop methods that verify entanglement in quantum states with as few measurements as possible. In this paper we investigate the minimal number of mutually unbiased bases (MUBs) needed to detect bound entanglement in bipartite $(d\times d)$-dimensional states, i.e. entangled states that are positive under partial transposition. In particular, we show that a class of entanglement witnesses composed of mutually unbiased bases can detect bound entanglement if the number of measurements is greater than $d/2+1$. This is a substantial improvement over other detection methods, requiring significantly fewer resources than either full quantum state tomography or measuring a complete set of $d+1$ MUBs. Our approach is based on a partial characterisation of the (non-)decomposability of entanglement witnesses. We show that non-decomposability is a universal property of MUBs, which holds regardless of the choice of complementary observables, and we find that both the number of measurements and the structure of the witness play an important role in the detection of bound entanglement.
description: 11 pages, identical to published version
Profits from Farm Power
Creators: name: Rural Electrification Administration
name: Rural Electrification Administration
Publisher: name: Unknown
Year: 1940
Subjects: Community/Rural/Urban Development
Crop Production/Industries
Farm Management
Livestock Production/Industries

description: Contents: Electricity Aids the Poultry Industry; Dairying Profits Stimulated; A New Approach to Farm Grinding: The Portable Farm Motor; Electricity and Two Special Crops; Electrical Refrigeration on the Farm; Electrical Irrigation for the Kitchen and Market Garden; Six New Aids to Farming; Farmers Themselves Build Some Equipment
Large Inflationary Logarithms in a Nontrivial Nonlinear Sigma Model
Creators: name: Litos, C.
name: Woodard, R. P.
name: Yesilyurt, B.
Publisher: name: arXiv
Year: 2023
Subjects: subject: General Relativity and Quantum Cosmology (gr-qc)
subject: High Energy Physics - Theory (hep-th)
subject: FOS: Physical sciences

description: Loops of inflationary gravitons are known to induce large temporal and spatial logarithms which can cause perturbation theory to break down. Nonlinear sigma models possess the same kind of derivative interactions and induce the same sorts of large logarithms, without the complicated index structure and potential gauge problem. Previous studies have examined models with zero field space curvature which can be reduced to free field theories by local, invertible field redefinitions. Here we study a model which cannot be so reduced and still shows the same sorts of large logarithms. We compute the evolution of the background at 1-loop and 2-loop orders, and we find the 1-loop $β$ and $γ$ functions.
description: 17 pages, 7 figures, uses LaTex 2e, Version 2 revised for publication with 7 figures and length of 19 pages
Fourier Neural Operator Networks: A Fast and General Solver for the Photoacoustic Wave Equation
Creators: name: Guan, Steven
name: Hsu, Ko-Tsung
name: Chitnis, Parag V.
Publisher: name: arXiv
Year: 2021
Subjects: subject: Image and Video Processing (eess.IV)
subject: Computer Vision and Pattern Recognition (cs.CV)
subject: FOS: Electrical engineering, electronic engineering, information engineering
subject: FOS: Computer and information sciences

description: Simulation tools for photoacoustic wave propagation have played a key role in advancing photoacoustic imaging by providing quantitative and qualitative insights into parameters affecting image quality. Classical methods for numerically solving the photoacoustic wave equation relies on a fine discretization of space and can become computationally expensive for large computational grids. In this work, we apply Fourier Neural Operator (FNO) networks as a fast data-driven deep learning method for solving the 2D photoacoustic wave equation in a homogeneous medium. Comparisons between the FNO network and pseudo-spectral time domain approach demonstrated that the FNO network generated comparable simulations with small errors and was several orders of magnitude faster. Moreover, the FNO network was generalizable and can generate simulations not observed in the training data.
Hybrid deep learning methods for phenotype prediction from clinical notes
Creators: name: Khalafi, Sahar
name: Ghadiri, Nasser
name: Moradi, Milad
Publisher: name: arXiv
Year: 2021
Subjects: subject: Computation and Language (cs.CL)
subject: Information Retrieval (cs.IR)
subject: FOS: Computer and information sciences
subject: J.3; I.2.7; I.2.1
subject: 68T50, 68T07

description: Identifying patient cohorts from clinical notes in secondary electronic health records is a fundamental task in clinical information management. However, with the growing number of clinical notes, it becomes challenging to analyze the data manually for phenotype detection. Automatic extraction of clinical concepts would helps to identify the patient phenotypes correctly. This paper proposes a novel hybrid model for automatically extracting patient phenotypes using natural language processing and deep learning models to determine the patient phenotypes without dictionaries and human intervention. The model is based on a neural bidirectional sequence model (BiLSTM or BiGRU) and a CNN layer for phenotypes identification. An extra CNN layer is run parallel to the hybrid model to extract more features related to each phenotype. We used pre-trained embeddings such as FastText and Word2vec separately as the input layers to evaluate other embedding's performance. Experimental results using MIMIC III database in internal comparison demonstrate that the proposed model achieved significant performance improvement over existing models. The enhanced version of our model with an extra CNN layer obtained a relatively higher F1-score than the original hybrid model. We also showed that BiGRU layer with FastText embedding had better performance than BiLSTM layer to identify patient phenotypes.
Nonmaximal $θ_{23}$ mixing at NOvA from neutrino decoherence
Creators: name: Coelho, Joao A. B.
name: Mann, W. Anthony
name: Bashar, Saqib S.
Publisher: name: arXiv
Year: 2017
Subjects: subject: High Energy Physics - Phenomenology (hep-ph)
subject: High Energy Physics - Experiment (hep-ex)
subject: FOS: Physical sciences

description: In study of muon neutrino disappearance at 810 km, the NOvA experiment finds flavor mixing of the atmospheric sector to deviate from maximal ($\sin^2θ_{23} = 0.5$) by 2.6 $σ$. The result is in tension with the 295-km baseline measurements of T2K which are consistent with maximal mixing. We propose that $θ_{23}$ is in fact maximal, and that the disagreement is harbinger of environmentally-induced decoherence. The departure from maximal mixing can be accounted for by an energy-independent decoherence of strength $Γ= (2.3 \pm 1.1) \times 10^{-23}$ GeV.
description: 5 pages, 2 figures, accepted for publication in Physical Review Letters
SDSS-IV MaNGA: Ionization sources of diffuse extra-planar galactic medium
Creators: name: Postnikova, Vera K.
name: Bizyaev, Dmitry
Publisher: name: arXiv
Year: 2023
Subjects: subject: Astrophysics of Galaxies (astro-ph.GA)
subject: FOS: Physical sciences

description: We explore sources of ionization of diffuse gas at different altitudes in galaxies in dependence of their stellar mass, \Ha\ luminosity, and specific star formation rate. We use the MaNGA data from SDSS-IV data release DR16 together with photoionization and shock ionization models provided by the 3MdB database. Our sample comprises 239 edge-on galaxies, which makes our results statistically valuable. We reach very high galactic altitudes with the help of spectra stacking. We demonstrate that models of the gas photoionization in a combination of young OB-stars and hot low-mass evolved stars (HOLMES) describes the gas ionization state in the galaxies of all types on diagnostic diagrams. Nevertheless, the shock waves may contribute to the gas ionization in massive galaxies with passive star formation. We observe a general trend of decreasing the fraction of the ionizing flux from OB-stars and the ionization parameter with the altitude, while the role of the ionization by the HOLMES increases. The biggest difference in the contribution from these types of ionizing sources correlates with the specific star formation rate and with stellar masses of galaxies. The HOLMES are the principal gas ionization sources in massive galaxies with passive star formation, while OB-stars dominate the gas ionization in low-mass galaxies with active star formation.
description: 14 pages, 9 figures. Published in Astronomy Letters
Flaviol (flûte à bec) à quatre trous antérieurs. Vue générale de dos
Creators: name: Musée National Des Arts Et Traditions Populaires (Paris)
name: Centre D'ethnologie Française
Publisher: name: École des Hautes Études en Sciences Sociales; Institut  interdisciplinaire d'anthropologie du contemporain (Paris); Laboratoire d'anthropologie et d'histoire de l'institution de la culture (Paris)
Year: 2022

Abstract
Polymer translocation driven by longitudinal and transversal time-dependent end-pulling forces
Creators: name: Sainz-Agost, Alejandro
name: Falo, Fernando
name: Fiasconaro, Alessandro
Publisher: name: arXiv
Year: 2023
Subjects: subject: Soft Condensed Matter (cond-mat.soft)
subject: Biological Physics (physics.bio-ph)
subject: FOS: Physical sciences

description: Polymer translocation has long been a topic of interest in the field of biological physics given its relevance in both biological (protein and DNA/RNA translocation through nuclear and cell membranes) and technological processes (nanopore DNA sequencing, drug delivery). In this work, we simulate the translocation of a semiflexible homopolymer through an extended pore, driven by both a constant and a time-dependent end-pulled force, employing a model introduced in previous studies. The time dependence is simplistically modeled as a cosine function, and we distinguish between two scenarios for the driving -- longitudinal force and transversal force -- depending on the relative orientation of the force, parallel or perpendicular respectively, with respect to the pore axis. Beside some key differences between the two drivings, the mean translocation times present a large minimum region as function of the frequency of the force that is typical of the Resonant Activation effect. The presence of the minimum is independent on the elastic characteristics of the polymeric chains and reveals a linear relation between the optimum mean translocation time and the corresponding period of the driving. The mean translocation times show different scaling exponent with the polymer length for different flexibilities. Lastly, we derive an analytical expression of the mean translocation time for low driving frequency, which clearly agrees with the simulations.
description: Submitted to Physical Review E
The Characteristic Dimension of Four-dimensional $\mathcal{N} = 2$ SCFTs
Creators: name: Cecotti, Sergio
name: Del Zotto, Michele
name: Martone, Mario
name: Moscrop, Robert
Publisher: name: arXiv
Year: 2021
Subjects: subject: High Energy Physics - Theory (hep-th)
subject: FOS: Physical sciences

description: In this paper we introduce the characteristic dimension of a four dimensional $\mathcal{N}=2$ superconformal field theory, which is an extraordinary simple invariant determined by the scaling dimensions of its Coulomb branch operators. We prove that only nine values of the characteristic dimension are allowed, $-\infty$, 1 ,6/5, 4/3, 3/2, 2, 3, 4, and 6, thus giving a new organizing principle to the vast landscape of 4d $\mathcal N=2$ SCFTs. Whenever the characteristic dimension differs from 1 or 2, only very constrained special Kähler geometries (i.e. isotrivial, diagonal and rigid) are compatible with the corresponding set of Coulomb branch dimensions and extremely special, maximally strongly coupled, BPS spectra are allowed for the theories which realize them. Our discussion applies to superconformal field theories of arbitrary rank, i.e. with Coulomb branches of any complex dimension. Along the way, we predict the existence of new $\mathcal{N}=3$ theories of rank two with non-trivial one-form symmetries.
description: 23 pages, 3 tables
Quantum measurements with prescribed symmetry
Creators: name: Bruzda, W.
name: Goyeneche, D.
name: Życzkowski, K.
Publisher: name: arXiv
Year: 2017
Subjects: subject: Quantum Physics (quant-ph)
subject: FOS: Physical sciences

description: We introduce a method to determine whether a given generalised quantum measurement is isolated or it belongs to a family of measurements having the same prescribed symmetry. The technique proposed reduces to solving a linear system of equations in some relevant cases. As consequence, we provide a simple derivation of the maximal family of Symmetric Informationally Complete measurements (SIC)-POVM in dimension 3. Furthermore, we show that the following remarkable geometrical structures are isolated, so that free parameters cannot be introduced: (a) maximal sets of mutually unbiased bases in prime power dimensions from 4 to 16, (b) SIC-POVM in dimensions from 4 to 16 and (c) contextuality Kochen-Specker sets in dimension 3, 4 and 6, composed of 13, 18 and 21 vectors, respectively.
description: 10 pages, 2 figures
Airfoil's Aerodynamic Coefficients Prediction using Artificial Neural Network
Creators: name: Moin, Hassan
name: Khan, Hafiz Zeeshan Iqbal
name: Mobeen, Surrayya
name: Riaz, Jamshed
Publisher: name: arXiv
Year: 2021
Subjects: subject: Fluid Dynamics (physics.flu-dyn)
subject: Artificial Intelligence (cs.AI)
subject: FOS: Physical sciences
subject: FOS: Computer and information sciences

description: Figuring out the right airfoil is a crucial step in the preliminary stage of any aerial vehicle design, as its shape directly affects the overall aerodynamic characteristics of the aircraft or rotorcraft. Besides being a measure of performance, the aerodynamic coefficients are used to design additional subsystems such as a flight control system, or predict complex dynamic phenomena such as aeroelastic instability. The coefficients in question can either be obtained experimentally through wind tunnel testing or, depending upon the accuracy requirements, by numerically simulating the underlying fundamental equations of fluid dynamics. In this paper, the feasibility of applying Artificial Neural Networks (ANNs) to estimate the aerodynamic coefficients of differing airfoil geometries at varying Angle of Attack, Mach and Reynolds number is investigated. The ANNs are computational entities that have the ability to learn highly nonlinear spatial and temporal patterns. Therefore, they are increasingly being used to approximate complex real-world phenomenon. However, despite their significant breakthrough in the past few years, ANNs' spreading in the field of Computational Fluid Dynamics (CFD) is fairly recent, and many applications within this field remain unexplored. This study thus compares different network architectures and training datasets in an attempt to gain insight as to how the network perceives the given airfoil geometries, while producing an acceptable neuronal model for faster and easier prediction of lift, drag and moment coefficients in steady state, incompressible flow regimes. This data-driven method produces sufficiently accurate results, with the added benefit of saving high computational and experimental costs.
Radiative grain alignment in protoplanetary disks: Implications for polarimetric observations
Creators: name: Tazaki, Ryo
name: Lazarian, Alexandre
name: Nomura, Hideko
Publisher: name: arXiv
Year: 2017
Subjects: subject: Earth and Planetary Astrophysics (astro-ph.EP)
subject: FOS: Physical sciences

description: We apply the theory of radiative torque (RAT) alignment for studying protoplanetary disks around a T-Tauri star and perform 3D radiative transfer calculations to provide the expected maps of polarized radiation to be compared with observations, such as with ALMA. We revisit the issue of grain alignment for large grains expected in the protoplanetary disks and find that mm-sized grains at midplane do not align with the magnetic field as the Larmor precession timescale for such large grains becomes longer than the gaseous damping timescale. Hence, for these grains the RAT theory predicts that the alignment axis is determined by the grain precession with respect to the radiative flux. As a result, we expect that the polarization will be in the azimuthal direction for a face-on disk. It is also shown that if dust grains have superparamagnetic inclusions, magnetic field alignment is possible for (sub-)micron grains at the surface layer of disks, and this can be tested by mid-infrared polarimetric observations.
description: 17 pages, 12 figures, 1 table, accepted for publication in ApJ
Consistent approach to study gluon quasi-particles
Creators: name: Islam, Chowdhury Aminul
name: Mustafa, Munshi G.
name: Ray, Rajarshi
name: Singha, Pracheta
Publisher: name: arXiv
Year: 2021
Subjects: subject: High Energy Physics - Phenomenology (hep-ph)
subject: High Energy Physics - Lattice (hep-lat)
subject: Nuclear Theory (nucl-th)
subject: FOS: Physical sciences

description: We discuss a novel approach to estimate the partition function in effective model frameworks when the effective potentials have multiple extrema, so that ascertaining a mean field becomes difficult. Using this approach we present a consistent model to study the thermodynamic properties of gluon quasi-particles as a function of temperature, both in the color confined and the color deconfined phases.
description: 8 pages, 9 captioned figures, matches with the published version
Near-wall model for compressible turbulent boundary layers based on an inverse velocity transformation
Creators: name: Griffin, Kevin Patrick
name: Fu, Lin
name: Moin, Parviz
Publisher: name: arXiv
Year: 2023
Subjects: subject: Fluid Dynamics (physics.flu-dyn)
subject: FOS: Physical sciences

description: In this work, a near-wall model, which couples the inverse of a recently developed compressible velocity transformation [Griffin, Fu, & Moin, PNAS, 118:34, 2021] and an algebraic temperature-velocity relation, is developed for high-speed turbulent boundary layers. As input, the model requires the mean flow state at one wall-normal height in the inner layer of the boundary layer and at the boundary-layer edge. As output, the model can predict mean temperature and velocity profiles across the entire inner layer, as well as the wall shear stress and heat flux. The model is tested in an a priori sense using a wide database of direct numerical simulation high-Mach-number turbulent channel flows, pipe flows, and boundary layers (48 cases with edge Mach numbers in the range of 0.77--11 and semi-local friction Reynolds numbers in the range of 170--5700). The present model is significantly more accurate than the classical ordinary differential equation (ODE) model for all cases tested. The model is deployed as a wall model for large-eddy simulations in channel flows with bulk Mach numbers in the range of 0.7--4 and friction Reynolds numbers in the range of 320--1800. When compared to the classical framework, in the a posteriori sense, the present method greatly improves the predicted heat flux, wall stress, and temperature and velocity profiles, especially in cases with strong heat transfer. In addition, the present model solves one ODE instead of two and has a similar computational cost and implementation complexity as the commonly used ODE model.
description: 21 pages, 15 figures, submitted to the Journal of Fluid Mechanics
Monotone-Value Neural Networks: Exploiting Preference Monotonicity in Combinatorial Assignment
Creators: name: Weissteiner, Jakob
name: Heiss, Jakob
name: Siems, Julien
name: Seuken, Sven
Publisher: name: arXiv
Year: 2021
Subjects: subject: Computer Science and Game Theory (cs.GT)
subject: FOS: Computer and information sciences

description: Many important resource allocation problems involve the combinatorial assignment of items, e.g., auctions or course allocation. Because the bundle space grows exponentially in the number of items, preference elicitation is a key challenge in these domains. Recently, researchers have proposed ML-based mechanisms that outperform traditional mechanisms while reducing preference elicitation costs for agents. However, one major shortcoming of the ML algorithms that were used is their disregard of important prior knowledge about agents' preferences. To address this, we introduce monotone-value neural networks (MVNNs), which are designed to capture combinatorial valuations, while enforcing monotonicity and normality. On a technical level, we prove that our MVNNs are universal in the class of monotone and normalized value functions, and we provide a mixed-integer linear program (MILP) formulation to make solving MVNN-based winner determination problems (WDPs) practically feasible. We evaluate our MVNNs experimentally in spectrum auction domains. Our results show that MVNNs improve the prediction performance, they yield state-of-the-art allocative efficiency in the auction, and they also reduce the run-time of the WDPs. Our code is available on GitHub: https://github.com/marketdesignresearch/MVNN.
Coronal Flux Ropes and their Interplanetary Counterparts
Creators: name: Gopalswamy, N.
name: Akiyama, S.
name: Yashiro, S.
name: Xie, H.
Publisher: name: arXiv
Year: 2017
Subjects: subject: Solar and Stellar Astrophysics (astro-ph.SR)
subject: Space Physics (physics.space-ph)
subject: FOS: Physical sciences

description: We report on a study comparing coronal flux ropes inferred from eruption data with their interplanetary counterparts constructed from in situ data. The eruption data include the source-region magnetic field, post-eruption arcades, and coronal mass ejections (CMEs). Flux ropes were fit to the interplanetary CMEs (ICMEs) considered for the 2011 and 2012 Coordinated Data Analysis Workshops (CDAWs). We computed the total reconnected flux involved in each of the associated solar eruptions and found it to be closely related to flare properties, CME kinematics, and ICME properties. By fitting flux ropes to the white-light coronagraph data, we obtained the geometric properties of the flux ropes and added magnetic properties derived from the reonnected flux. We found that the CME magnetic field in the corona is significantly higher than the ambient magnetic field at a given heliocentric distance. The radial dependence of the flux-rope magnetic field strength is faster than that of the ambient magnetic field. The magnetic field strength of the coronal flux rope is also correlated with that in interplanetary flux ropes constructed from in situ data, and with the observed peak magnetic field strength in ICMEs. The physical reason for the observed correlation between the peak field strength in MCs is the higher magnetic field content in faster coronal flux ropes and ultimately the higher reconnected flux in the eruption region. The magnetic flux ropes constructed from the eruption data and coronagraph observations provide a realistic input that can be used by various models to predict the magnetic properties of ICMEs at Earth and other destination in the heliosphere.
description: 36 pages, 8 figures, 1 table, under review in J. Atmos. Solar-Terr. Phys. May 24, 2017
Atomic Bose-Einstein condensate in a twisted-bilayer optical lattice
Creators: name: Meng, Zengming
name: Wang, Liangwei
name: Han, Wei
name: Liu, Fangde
name: Wen, Kai
name: Gao, Chao
name: Wang, Pengjun
name: Chin, Cheng
name: Zhang, Jing
Publisher: name: arXiv
Year: 2021
Subjects: subject: Quantum Gases (cond-mat.quant-gas)
subject: FOS: Physical sciences

description: Observation of strong correlations and superconductivity in twisted-bilayer-graphene have stimulated tremendous interest in fundamental and applied physics. In this system, the superposition of two twisted honeycomb lattices, generating a Moir$\acute{\mathrm{e}}$ pattern, is the key to the observed flat electronic bands, slow electron velocity and large density of states. Despite these observations, a full understanding of the emerging superconductivity from the coupled insulating layers and the appearance of a small magic angle remain a hot topic of research. Here, we demonstrate a quantum simulation platform to study superfluids in twisted bilayer lattices based on Bose-Einstein condensates loaded into spin-dependent optical lattices. The lattices are made of two sets of laser beams that independently address atoms in different spin states, which form the synthetic dimension of the two layers. The twisted angle of the two lattices is controlled by the relative angle of the laser beams. We show that atoms in each spin state only feel one set of the lattice and the interlayer coupling can be controlled by microwave coupling between the spin states. Our system allows for flexible control of both the inter- and intralayer couplings. Furthermore we directly observe the spatial Moir$\acute{\mathrm{e}}$ pattern and the momentum diffraction, which confirm the presence of atomic superfluid in the bilayer lattices. Our system constitutes a powerful platform to investigate the physics underlying the superconductivity in twisted-bilayer-graphene and to explore other novel quantum phenomena difficult to realize in materials.
description: 6 pages, 5 figures
Tunnel transport and interlayer excitons in bilayer fractional quantum Hall systems
Creators: name: Zhang, Yuhe
name: Jain, J. K.
name: Eisenstein, J. P.
Publisher: name: arXiv
Year: 2017
Subjects: subject: Strongly Correlated Electrons (cond-mat.str-el)
subject: FOS: Physical sciences

description: In a bilayer system consisting of a composite-fermion Fermi sea in each layer, the tunnel current is exponentially suppressed at zero bias, followed by a strong peak at a finite bias voltage $V_{\rm max}$. This behavior, which is qualitatively different from that observed for the electron Fermi sea, provides fundamental insight into the strongly correlated non-Fermi liquid nature of the CF Fermi sea and, in particular, offers a window into the short-distance high-energy physics of this state. We identify the exciton responsible for the peak current and provide a quantitative account of the value of $V_{\rm max}$. The excitonic attraction is shown to be quantitatively significant, and its variation accounts for the increase of $V_{\rm max}$ with the application of an in-plane magnetic field. We also estimate the critical Zeeman energy where transition occurs from a fully spin polarized composite fermion Fermi sea to a partially spin polarized one, carefully incorporating corrections due to finite width and Landau level mixing, and find it to be in satisfactory agreement with the Zeeman energy where a qualitative change has been observed for the onset bias voltage [Eisenstein et al., Phys. Rev. B 94, 125409 (2016)]. For fractional quantum Hall states, we predict a substantial discontinuous jump in $V_{\rm max}$ when the system undergoes a transition from a fully spin polarized state to a spin singlet or a partially spin polarized state.
description: 14 pages, 14 figures
Échantillonnage de signaux sur graphes via des processus déterminantaux
Creators: name: Tremblay, Nicolas
name: Barthelme, Simon
name: Amblard, Pierre-Olivier
Publisher: name: arXiv
Year: 2017
Subjects: subject: Data Structures and Algorithms (cs.DS)
subject: Discrete Mathematics (cs.DM)
subject: Machine Learning (cs.LG)
subject: FOS: Computer and information sciences

description: We consider the problem of sampling k-bandlimited graph signals, ie, linear combinations of the first k graph Fourier modes. We know that a set of k nodes embedding all k-bandlimited signals always exists, thereby enabling their perfect reconstruction after sampling. Unfortunately, to exhibit such a set, one needs to partially diagonalize the graph Laplacian, which becomes prohibitive at large scale. We propose a novel strategy based on determinantal point processes that side-steps partial diagonalisation and enables reconstruction with only O(k) samples. While doing so, we exhibit a new general algorithm to sample determinantal process, faster than the state-of-the-art algorithm by an order k.
description: in French
Cosmological perturbations in transient phantom inflation scenarios
Creators: name: Richarte, Martin G.
name: Kremer, Gilberto M.
Publisher: name: arXiv
Year: 2016
Subjects: subject: General Relativity and Quantum Cosmology (gr-qc)
subject: FOS: Physical sciences

description: We present a model of inflation where the inflaton is accommodated as a phantom field which exhibits an initial transient pole behavior and then decays into a quintessence field which is responsible for a radiation era. We must stress that the present unified model only deals with a single field and that the transition between two eras is achieved in a smooth way, so the model does not suffer from the eternal inflation issue. We explore the conditions for the crossing of the phantom divide line within the inflationary era along with the structural stability of several critical points. We study the behavior of the phantom field within the slow climb approximation along with the necessary conditions to have sufficient inflation. We also examine the model at the level of classical perturbations within the Newtonian gauge and determine the behavior of the gravitational potential, contrast density and perturbed field near the inflation stage and the subsequent radiation era.
description: 11pp. Accepted for its publication in EPJC. http://link.springer.com/article/10.1140/epjc/s10052-017-4629-8
The Casimir effect for parallel plates in Friedmann-Robertson-Walker universe
Creators: name: de Mello, E. R. Bezerra
name: Saharian, A. A.
name: Setare, M. R.
Publisher: name: arXiv
Year: 2017
Subjects: subject: High Energy Physics - Theory (hep-th)
subject: General Relativity and Quantum Cosmology (gr-qc)
subject: FOS: Physical sciences

description: We evaluate the Hadamard function, the vacuum expectation values (VEVs) of the field squared and the energy-momentum tensor for a massive scalar field with general curvature coupling parameter in the geometry of two parallel plates on a spatially flat Friedmann-Robertson-Walker background with a general scale factor. On the plates, the field operator obeys the Robin boundary conditions with the coefficients depending on the scale factor. In all the spatial regions, the VEVs are decomposed into the boundary-free and boundary-induced contributions. Unlike to the problem with the Minkowski bulk, in the region between the plates the normal stress is not homogeneous and does not vanish in the geometry of a single plate. Near the plates, it has different signs for accelerated and deccelerated expansions of the universe. The VEV of the energy-momentum tensor, in addition to the diagonal components, has a nonzero off-diagonal component describing an energy flux along the direction normal to the boundaries. Expressions are derived for the Casimir forces acting on the plates. Depending on the Robin coefficients and on the vacuum state, these forces can be either attractive or repulsive. An important difference from the corresponding result in the Minkowski bulk is that the forces on the separate plates, in general, are different if the corresponding Robin coefficients differ. We give the applications of general results for the class of $α$-vacua in the de Sitter bulk. It is shown that, compared with the Bunch-Davies vacuum state, the Casimir forces for a given $α$-vacuum may change the sign.
description: 20 pages, no figure. Version accepted for publication in PRD
Analyticity and spectral properties of noncommutative Ricci flow in a matrix geometry
Creators: name: Duvenhage, Rocco
name: van Staden, Wernd
name: Wuzyk, Jan
Publisher: name: arXiv
Year: 2017
Subjects: subject: Operator Algebras (math.OA)
subject: Classical Analysis and ODEs (math.CA)
subject: Quantum Algebra (math.QA)
subject: FOS: Mathematics
subject: Primary 58B34, Secondary 47A55, 35K55

description: We study a first variation formula for the eigenvalues of the Laplacian evolving under the Ricci flow in a simple example of a noncommutative matrix geometry, namely a finite dimensional representation of a noncommutative torus. In order to do so, we first show that the Ricci flow in this matrix geometry is analytic.
description: 16 pages