scholarly journals Irreversible thermodynamics of transport across interfaces

2011 ◽  
Vol 89 (10) ◽  
pp. 1041-1050 ◽  
Author(s):  
Matthew R. Sears ◽  
Wayne M. Saslow
Keyword(s):  
Entropy Production ◽  
Electric Current ◽  
Heating Rate ◽  
Chemical Potential ◽  
Magnetic Semiconductors ◽  
Spin Current ◽  
Irreversible Thermodynamics ◽  
Heat Current ◽  
Bulk Heating ◽  
Current Production

With spintronics applications in mind, we use irreversible thermodynamics to derive the rates of entropy production and heating near an interface when heat current, electric current, and spin current cross it. Associated with these currents are apparent discontinuities in temperature (ΔT), electrochemical potential (Δ[Formula: see text]), and spin-dependent “magnetoelectrochemical potential” (Δ[Formula: see text]). This work applies to magnetic semiconductors and insulators as well as metals, because of the inclusion of the chemical potential, μ, which is usually neglected in works on interfacial thermodynamic transport. We also discuss the (nonobvious) distinction between entropy production and heat production. Heat current and electric current are conserved, but spin current is not, so it necessitates a somewhat different treatment. At low temperatures or for large differences in material properties, the surface heating rate dominates the bulk heating rate near the surface. We also consider the case where bulk spin currents occur in equilibrium. Although a surface spin current (in A/m2) should yield about the same rate of heating as an equal surface electric current, production of such a spin current requires a relatively large “magnetization potential” difference across the interface.

scholarly journals Evidence for spin current driven Bose-Einstein condensation of magnons

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
B. Divinskiy ◽  
H. Merbouche ◽  
V. E. Demidov ◽  
K. O. Nikolaev ◽  
L. Soumah ◽  
...  
Keyword(s):  
Room Temperature ◽  
Chemical Potential ◽  
Spin Current ◽  
Einstein Condensation ◽  
Electronic Control ◽  
Spintronic Devices ◽  
Bose Einstein Condensation ◽  
Magnetic Insulators ◽  
Spatially Extended ◽  
Bose Einstein

AbstractThe quanta of magnetic excitations – magnons – are known for their unique ability to undergo Bose-Einstein condensation at room temperature. This fascinating phenomenon reveals itself as a spontaneous formation of a coherent state under the influence of incoherent stimuli. Spin currents have been predicted to offer electronic control of Bose-Einstein condensates, but this phenomenon has not been experimentally evidenced up to now. Here we show that current-driven Bose-Einstein condensation can be achieved in nanometer-thick films of magnetic insulators with tailored nonlinearities and minimized magnon interactions. We demonstrate that, above a certain threshold, magnons injected by the spin current overpopulate the lowest-energy level forming a highly coherent spatially extended state. We quantify the chemical potential of the driven magnon gas and show that, at the critical current, it reaches the energy of the lowest magnon level. Our results pave the way for implementation of integrated microscopic quantum magnonic and spintronic devices.

scholarly journals Nonequilibrium Thermodynamics Based on the Distributions Containing Lifetime as a Thermodynamic Parameter

2011 ◽  
Vol 2011 ◽  
pp. 1-10 ◽  
Author(s):  
Vasiliy Vasiliy Ryazanov
Keyword(s):  
Stochastic Processes ◽  
Entropy Production ◽  
Thermodynamic Parameter ◽  
Nonequilibrium Thermodynamics ◽  
Irreversible Thermodynamics ◽  
Statistical Distributions ◽  
Extended Irreversible Thermodynamics ◽  
Nonequilibrium Entropy ◽  
Nonequilibrium States ◽  
Explicit Expressions

To describe the nonequilibrium states of a system, we introduce a new thermodynamic parameter—the lifetime of a system. The statistical distributions which can be obtained out of the mesoscopic description characterizing the behaviour of a system by specifying the stochastic processes are written down. The change in the lifetime values by interaction with environment is expressed in terms of fluxes and sources. The expressions for the nonequilibrium entropy, temperature, and entropy production are obtained, which at small values of fluxes coincide with those derived within the frame of extended irreversible thermodynamics. The explicit expressions for the lifetime of a system and its thermodynamic conjugate are obtained.

scholarly journals Entropy production of soil hydrological processes and its maximisation

2011 ◽  
Vol 2 (2) ◽  
pp. 179-190 ◽  
Author(s):  
P. Porada ◽  
A. Kleidon ◽  
S. J. Schymanski
Keyword(s):  
Entropy Production ◽  
Land Surface ◽  
Chemical Potential ◽  
Hydrological Cycle ◽  
Promising Result ◽  
Hydrological Processes ◽  
Unknown Parameters ◽  
Hydrological System ◽  
Entropy Budget ◽  
Principle Of Maximum

Abstract. Hydrological processes are irreversible and produce entropy. Hence, the framework of non-equilibrium thermodynamics is used here to describe them mathematically. This means flows of water are written as functions of gradients in the gravitational and chemical potential of water between two parts of the hydrological system. Such a framework facilitates a consistent thermodynamic representation of the hydrological processes in the model. Furthermore, it allows for the calculation of the entropy production associated with a flow of water, which is proportional to the product of gradient and flow. Thus, an entropy budget of the hydrological cycle at the land surface is quantified, illustrating the contribution of different processes to the overall entropy production. Moreover, the proposed Principle of Maximum Entropy Production (MEP) can be applied to the model. This means, unknown parameters can be determined by setting them to values which lead to a maximisation of the entropy production in the model. The model used in this study is parametrised according to MEP and evaluated by means of several observational datasets describing terrestrial fluxes of water and carbon. The model reproduces the data with good accuracy which is a promising result with regard to the application of MEP to hydrological processes at the land surface.

scholarly journals QUADRATIC REHEATING

1999 ◽  
Vol 08 (03) ◽  
pp. 307-323 ◽  
Author(s):  
LUIS P. CHIMENTO ◽  
ALEJANDRO S. JAKUBI
Keyword(s):  
Entropy Production ◽  
Linear Model ◽  
Particle Number ◽  
Equilibrium Mixture ◽  
Irreversible Thermodynamics ◽  
Decay Rates ◽  
Inflaton Field ◽  
Inflationary Scenario ◽  
Self Consistent ◽  
Reheating Process

The reheating process for the inflationary scenario is investigated phenomenologically. The decay of the oscillating massive inflaton field into light bosons is modeled after an out of equilibrium mixture of interacting fluids within the framework of irreversible thermodynamics. Self-consistent, analytic results for the evolution of the main macroscopic magnitudes like temperature and particle number densities are obtained. The models for linear and quadratic decay rates are investigated in the quasiperfect regime. The linear model is shown to reheat very slowly while the quadratic one is shown to yield explosive particle and entropy production. The maximum reheating temperature is reached much faster and its magnitude is comparable with the inflaton mass.

scholarly journals It is not the entropy you produce, rather, how you produce it

2010 ◽  
Vol 365 (1545) ◽  
pp. 1317-1322 ◽  
Author(s):  
Tyler Volk ◽  
Olivier Pauluis
Keyword(s):  
Entropy Production ◽  
Production Rate ◽  
Thought Experiment ◽  
Biological Evolution ◽  
Irreversible Thermodynamics ◽  
Entropy Production Rate ◽  
Chemical Systems ◽  
Principle Of Maximum Entropy ◽  
Relative Contribution ◽  
Principle Of Maximum

The principle of maximum entropy production (MEP) seeks to better understand a large variety of the Earth's environmental and ecological systems by postulating that processes far from thermodynamic equilibrium will ‘adapt to steady states at which they dissipate energy and produce entropy at the maximum possible rate’. Our aim in this ‘outside view’, invited by Axel Kleidon, is to focus on what we think is an outstanding challenge for MEP and for irreversible thermodynamics in general: making specific predictions about the relative contribution of individual processes to entropy production. Using studies that compared entropy production in the atmosphere of a dry versus humid Earth, we show that two systems might have the same entropy production rate but very different internal dynamics of dissipation. Using the results of several of the papers in this special issue and a thought experiment, we show that components of life-containing systems can evolve to either lower or raise the entropy production rate. Our analysis makes explicit fundamental questions for MEP that should be brought into focus: can MEP predict not just the overall state of entropy production of a system but also the details of the sub-systems of dissipaters within the system? Which fluxes of the system are those that are most likely to be maximized? How it is possible for MEP theory to be so domain-neutral that it can claim to apply equally to both purely physical–chemical systems and also systems governed by the ‘laws’ of biological evolution? We conclude that the principle of MEP needs to take on the issue of exactly how entropy is produced.

Formation of Al2O3 grains with different sizes and morphologies during the pulse electric current sintering process

2001 ◽  
Vol 16 (12) ◽  
pp. 3514-3517 ◽  
Author(s):  
S. W. Wang ◽  
L. D. Chen ◽  
T. Hirai ◽  
Jingkun Guo
Keyword(s):  
Electric Current ◽  
Heating Rate ◽  
Cross Sections ◽  
Mechanical Pressure ◽  
Pulse Electric Current ◽  
Side Edge ◽  
Microstructure Observation ◽  
Different Temperatures ◽  
Powder Compacts ◽  
Pulse Electric

Commercial micrometer Al2O3 powder was sintered at 1550 °C under a mechanical pressure of 30 MPa by pulse electric current sintering (PECS). Microstructure observation was performed on polished, thermal-etched cross sections parallel to the direction of mechanical pressure. Platelike Al2O3 grains formed when the powder was heated at a heating rate of 5 °C/min, while a heating rate of 200 °C/min resulted in equiaxed grains. These results indicated that PECS is an effective approach to hinder grain growth by application of a higher heating rate. However, Al2O3 grains at the upper edge were larger than those at the side edge of the samples in both cases. It implied that there were different temperatures at the upper edge and the side edge of the Al2O3 powder compacts during the PECS process.

scholarly journals ENTROPY PRODUCTION OF ENTIRELY DIFFUSIONAL LAPLACIAN TRANSFER AND THE POSSIBLE ROLE OF FRAGMENTATION OF THE BOUNDARIES

Fractals ◽  
2015 ◽  
Vol 23 (03) ◽  
pp. 1550026 ◽  
Author(s):  
K. KARAMANOS ◽  
S. I. MISTAKIDIS ◽  
T. J. MASSART ◽  
I. S. MISTAKIDIS
Keyword(s):  
Entropy Production ◽  
Active Zone ◽  
Numerical Study ◽  
Near Field ◽  
Irreversible Thermodynamics ◽  
Koch Curve ◽  
Variational Functional ◽  
Numerical Resolution ◽  
New Interpretation

The entropy production and the variational functional of a Laplacian diffusional field around the first four fractal iterations of a linear self-similar tree (von Koch curve) is studied analytically and detailed predictions are stated. In a next stage, these predictions are confronted with results from numerical resolution of the Laplace equation by means of Finite Elements computations. After a brief review of the existing results, the range of distances near the geometric irregularity, the so-called "Near Field", a situation never studied in the past, is treated exhaustively. We notice here that in the Near Field, the usual notion of the active zone approximation introduced by Sapoval et al. [M. Filoche and B. Sapoval, Transfer across random versus deterministic fractal interfaces, Phys. Rev. Lett. 84(25) (2000) 5776;1 B. Sapoval, M. Filoche, K. Karamanos and R. Brizzi, Can one hear the shape of an electrode? I. Numerical study of the active zone in Laplacian transfer, Eur. Phys. J. B. Condens. Matter Complex Syst. 9(4) (1999) 739-753.]2 is strictly inapplicable. The basic new result is that the validity of the active-zone approximation based on irreversible thermodynamics is confirmed in this limit, and this implies a new interpretation of this notion for Laplacian diffusional fields.

scholarly journals Attempts to Measure the Inductive Element Associated with the Natural Convection of Heat

1960 ◽  
Vol 13 (1) ◽  
pp. 84
Author(s):  
RCL Bosworth
Keyword(s):  
Natural Convection ◽  
Kinetic Energy ◽  
Electric Current ◽  
Heating Rate ◽  
Heat Input ◽  
Inductive Element ◽  
Heated Wire ◽  
The Wire ◽  
Inductive Elements

A study has been made of the variation in time of the temperature of a wire immersed in a fluid and heated by a constant electric current. For a given fluid the curve obtained by plotting the ratio of the temperature of the wire to the heat input versus the time is initially the same shape for all rates �of heat input. Divergences from the lowest heating rate set in only when the system of convection currents sets in. This occurs at earlier times after the commencement of heating the higher the heating rate. Expressions already developed are used to evaluate the resistive, capacitive, and inductive elements required to fit the observed transient curves. The values of the former two types of element are consistent with an assumed stagnant film of a thickness the order of 1 mm around the heated wire, but the value of the deduced inductive element is some 10--106 greater than that associated with the kinetic energy belonging to the system of convection currents.

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