scholarly journals A Rigorous Scattering Approach to Quasifree Fermionic Systems out of Equilibrium

2019 ◽  
Vol 44 (3) ◽  
pp. 261-275
Author(s):  
Walter H. Aschbacher
Keyword(s):  
First Principles ◽  
Degrees Of Freedom ◽  
Entropy Production Rate ◽  
Finite Sample ◽  
Fermionic System ◽  
Fermionic Systems ◽  
Different Temperatures ◽  
Xy Chain ◽  
Quantum Mechanical Systems ◽  
Stationary Scattering

Abstract Within the rigorous axiomatic framework for the description of quantum mechanical systems with a large number of degrees of freedom, we construct the so-called nonequilibrium steady state for the quasifree fermionic system corresponding to the isotropic XY chain in which a finite sample, subject to a local gauge breaking anisotropy perturbation, is coupled to two thermal reservoirs at different temperatures. Using time dependent and stationary scattering theory, we rigorously prove, from first principles, that the nonequilibrium system under consideration is thermodynamically nontrivial, i. e., that its entropy production rate is strictly positive.

scholarly journals Heat flux in general quasifree fermionic right mover/left mover systems

2021 ◽  
pp. 2150018
Author(s):  
Walter H. Aschbacher
Keyword(s):  
Heat Flux ◽  
Scattering Theory ◽  
Nonequilibrium Steady States ◽  
Entropy Production Rate ◽  
Translation Invariance ◽  
Finite Sample ◽  
Systematic Analysis ◽  
Gauge Invariant ◽  
Point Operator ◽  
Different Temperatures

With the help of time-dependent scattering theory on the observable algebra of infinitely extended quasifree fermionic chains, we introduce a general class of so-called right mover/left mover states which are inspired by the nonequilibrium steady states for the prototypical nonequilibrium configuration of a finite sample coupled to two thermal reservoirs at different temperatures. Under the assumption of spatial translation invariance, we relate the 2-point operator of such a right mover/left mover state to the asymptotic velocity of the system and prove that the system is thermodynamically nontrivial in the sense that its entropy production rate is strictly positive. Our study of these not necessarily gauge-invariant systems covers and substantially generalizes well-known quasifree fermionic chains and opens the way for a more systematic analysis of the heat flux in such systems.

scholarly journals Temperature Effects on the Elastic Constants, Stacking Fault Energy and Twinnability of Ni3Si and Ni3Ge: A First-Principles Study

Crystals ◽  
2018 ◽  
Vol 8 (9) ◽  
pp. 364 ◽  
Author(s):  
Lili Liu ◽  
Liwan Chen ◽  
Youchang Jiang ◽  
Chenglin He ◽  
Gang Xu ◽  
...  
Keyword(s):  
Elastic Constants ◽  
First Principles ◽  
Antiphase Boundary ◽  
Stacking Fault ◽  
First Principles Calculations ◽  
Planar Fault ◽  
Different Temperatures ◽  
Generalized Stacking Fault ◽  
Increasing Temperature ◽  
Stacking Fault Energies

The volume versus temperature relations for Ni 3 Si and Ni 3 Ge are obtained by using the first principles calculations combined with the quasiharmonic approach. Based on the equilibrium volumes at temperature T, the temperature dependence of the elastic constants, generalized stacking fault energies and generalized planar fault energies of Ni 3 Si and Ni 3 Ge are investigated by first principles calculations. The elastic constants, antiphase boundary energies, complex stacking fault energies, superlattice intrinsic stacking fault energies and twinning energy decrease with increasing temperature. The twinnability of Ni 3 Si and Ni 3 Ge are examined using the twinnability criteria. It is found that their twinnability decrease with increasing temperature. Furthermore, Ni 3 Si has better twinnability than Ni 3 Ge at different temperatures.

scholarly journals Learning the non-equilibrium dynamics of Brownian movies

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Federico S. Gnesotto ◽  
Grzegorz Gradziuk ◽  
Pierre Ronceray ◽  
Chase P. Broedersz
Keyword(s):  
Degrees Of Freedom ◽  
Time Lapse ◽  
Direct Access ◽  
Dynamical Analysis ◽  
Entropy Production Rate ◽  
Microscopy Imaging ◽  
Time Resolved ◽  
Equilibrium Dynamics ◽  
Many Body Systems ◽  
Non Equilibrium

Abstract Time-lapse microscopy imaging provides direct access to the dynamics of soft and living systems. At mesoscopic scales, such microscopy experiments reveal intrinsic thermal and non-equilibrium fluctuations. These fluctuations, together with measurement noise, pose a challenge for the dynamical analysis of these Brownian movies. Traditionally, methods to analyze such experimental data rely on tracking embedded or endogenous probes. However, it is in general unclear, especially in complex many-body systems, which degrees of freedom are the most informative about their non-equilibrium nature. Here, we introduce an alternative, tracking-free approach that overcomes these difficulties via an unsupervised analysis of the Brownian movie. We develop a dimensional reduction scheme selecting a basis of modes based on dissipation. Subsequently, we learn the non-equilibrium dynamics, thereby estimating the entropy production rate and time-resolved force maps. After benchmarking our method against a minimal model, we illustrate its broader applicability with an example inspired by active biopolymer gels.

scholarly journals ROTATING FERMIONS IN TWO DIMENSIONS: A THOMAS–FERMI APPROACH

2001 ◽  
Vol 15 (19n20) ◽  
pp. 2799-2810
Author(s):  
SANKALPA GHOSH ◽  
M. V. N. MURTHY ◽  
SUBHASIS SINHA
Keyword(s):  
Ground State ◽  
Analytical Approach ◽  
State Energy ◽  
Critical Size ◽  
Energy Functional ◽  
Two Dimensions ◽  
Fermionic System ◽  
Thomas Fermi ◽  
Fermionic Systems ◽  
Analytical Expressions

Properties of confined mesoscopic systems have been extensively studied numerically over recent years. We discuss an analytical approach to the study of finite rotating fermionic systems in two dimension. We first construct the energy functional for a finite fermionic system within the Thomas–Fermi approximation in two dimensions. We show that for specific interactions the problem may be exactly solved. We derive analytical expressions for the density, the critical size as well as the ground state energy of such systems in a given angular momentum sector.

Effect of Mild Sway on the Interfacial Mass Transfer Rate of Stored Liquids

2015 ◽  
Vol 137 (11) ◽  
Author(s):  
Dibakar Rakshit ◽  
K. P. Thiagarajan ◽  
R. Narayanaswamy
Keyword(s):  
Mass Transfer ◽  
Transfer Rate ◽  
Degrees Of Freedom ◽  
Mass Transfer Rate ◽  
Constant Amplitude ◽  
Two Phase ◽  
Interfacial Mass Transfer ◽  
Different Temperatures ◽  
Slow Moving ◽  
Liquid Vapor

An exploratory study of two-phase physics was undertaken in a slow moving tank containing liquid. This study is under the regime of conjugate heat and mass transfer phenomena. An experiment was designed and performed to estimate the interfacial mass transfer characteristics of a slowly moving tank. The tank was swayed at varying frequencies and constant amplitude. The experiments were conducted for a range of liquid temperatures and filling levels. The experimental setup consisted of a tank partially filled with water at different temperatures, being swayed using a six degrees-of-freedom (DOF) motion actuator. The experiments were conducted for a frequency range of 0.7–1.6 Hz with constant amplitude of 0.025 m. The evaporation of liquid from the interface and the gaseous condensation was quantified by calculating the instantaneous interfacial mass transfer rate of the slow moving tank. The dependence of interfacial mass transfer rate on the liquid–vapor interfacial temperature, the fractional concentration of the evaporating liquid, the surface area of the liquid vapor interface and the filling level of the liquid was established. As sway frequency, filling levels, and liquid temperature increased, the interfacial mass transfer rate also increased. The interfacial mass transfer rate estimated for the swaying tank compared with the interfacial mass transfer rate of stationary tank shows that vibration increases the mass transfer.

Solid molecular phases of Hydrogen via constant-pressure first-principles Molecular Dynamics

1997 ◽  
Vol 499 ◽  
Author(s):  
Jorge Kohanoff ◽  
Sandro Scandolo
Keyword(s):  
Molecular Dynamics ◽  
First Principles ◽  
Degrees Of Freedom ◽  
Constant Pressure ◽  
Phase Iii ◽  
Orthorhombic Structure ◽  
Lattice Constants ◽  
Symmetry Phase ◽  
Dynamics Simulations ◽  
Zone Sampling

ABSTRACTBy performing constant pressure ab initio molecular dynamics simulations we analyse the high pressure phases of molecular solid hydrogen. We use a gradient corrected LDA, and a freshly implemented efficient technique for Brillouin zone sampling. An extremely good k-point sampling turns out to be crucial for obtaining the correct ground state. Our constant pressure approach allows us to optimize simultaneously the ori-entational degrees of freedom, the lattice constants, and the space group. This can be done either by a local optimization tehcnique, or by running molecular dynamics (MD) trajectories. The MD allows for the system to undergo structural transformations spontaneously. In the lower pressure, namely for the broken symmetry phase (BSP or phase II), we find a quadrupolar orthorhombic structure, of Pca21 symmetry. By means of an MD investigation, we find, at higher pressures, a slightly distorted orthorhombic structure of Cmc21 symmetry. This structure cannot be straightforwardly identified with the H-A phase (or phase III) because: 1) it is metallic, and 2) the Raman vibron discontinuity would be far too large compared to experiment. In fact, we argue that this phase is the first metallic molecular phase of hydrogen. Metallization would happen then, not via a band-overlap mechanism, but due to a structural transformation. By comparing total enthalpies, we also give suggestions for the structure of phase III.

FIRST-PRINCIPLES CALCULATIONS OF STRUCTURE, STABILITY AND THERMODYNAMIC PROPERTIES OF fcc-6LiT UNDER HIGH TEMPERATURES AND PRESSURES

2011 ◽  
Vol 25 (05) ◽  
pp. 333-344 ◽  
Author(s):  
CHENGHUA HU ◽  
FENG WANG ◽  
CHUANHUI XIA ◽  
ZHOU ZHENG ◽  
WEIYI REN
Keyword(s):  
Heat Capacity ◽  
Melting Point ◽  
Thermodynamic Properties ◽  
Debye Temperature ◽  
High Temperatures ◽  
First Principles ◽  
Critical Pressure ◽  
Structure Stability ◽  
First Principles Calculations ◽  
Different Temperatures

We perform first-principles calculations for fcc-6 LiT in order to study its structure, stability and thermodynamic properties under high temperatures and pressures. We find that melting point of 6 LiT (0 GPa) is about 680 K, and rise with the pressures. Reverse equivalent pressure P r and critical pressure P c of different temperatures are predicted from [Formula: see text] or [Formula: see text], and they are found to increase with temperature. 6 LiT should be stable under the condition of P < 80 GPa and T < 680 K . We also find that pressure and temperature will cause different effect of shear on the {100} and {110} planes. Heat capacity of different pressures increase with temperature and closes to the Dulong–Petit limit at higher temperatures. Debye temperature decreases with temperature, and increases with pressure.

scholarly journals Computationally accelerated discovery of high entropy pyrochlore oxides

2021 ◽  
Author(s):  
Krishna Chaitanya Pitike ◽  
Antonio Macias ◽  
Markus Eisenbach ◽  
Craig Bridges ◽  
Valentino Cooper
Keyword(s):  
Monte Carlo ◽  
Oxygen Vacancy ◽  
First Principles ◽  
Degrees Of Freedom ◽  
Vacancy Concentration ◽  
Oxygen Vacancy Concentration ◽  
High Entropy ◽  
Impurity Phases ◽  
Wide Range ◽  
Pyrochlore Oxides

Abstract High entropy ceramics provide enhanced flexibility for tailoring a wide range of physical properties, emerging from the diverse chemical and configurational degrees of freedom. Expanding upon the endeavors of recently synthesized high entropy ceramics in rock salt, fluorite, spinel and perovskite structures, we explore the relative feasibility of formation of high entropy pyrochlore oxides, A2B2O7, with multi-cation occupancy of the B-site, estimated from first principles based thermodynamic descriptors. Subsequently, we used Monte Carlo simulations to estimate the phase composition, oxygen vacancy concentration and local ionic segregation as a function of temperature and oxygen partial pressure. In parallel, we have investigated the synthesis of several multicomponent oxides with a pyrochlore composition, related to our computational investigations, resulting in several high purity pyrochlore oxides, in some cases with minor impurity phases. Ultimately, our approach allows us to evaluate potential impurity phases, ionic disorder and oxygen vacancy concentration in response to the experimental variables, thereby making realistic predictions that can direct and accelerate experimental synthesis of novel multicomponent ceramics.

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