A variational principle of steady-state transport processes

AIAA Journal ◽  
1970 ◽  
Vol 8 (2) ◽  
pp. 335-338 ◽  
Author(s):  
C. F. WANG
Keyword(s):  
Steady State ◽  
Variational Principle ◽  
Transport Processes

scholarly journals Stable intracellular acidification upon polyamine depletion induced by α-difluoromethylornithine or N1,N12-bis(ethyl)spermine in L1210 leukaemia cells

1995 ◽  
Vol 312 (3) ◽  
pp. 749-756 ◽  
Author(s):  
R Poulin ◽  
A E Pegg
Keyword(s):  
Steady State ◽  
Acid Stress ◽  
Weak Acid ◽  
Transport Processes ◽  
Set Point ◽  
L1210 Cells ◽  
Acid Load ◽  
Mouse Leukaemia ◽  
A Minor ◽  
Steady State Control

Polyamines play major roles in ionic and osmotic regulation, but their exact involvement in specific ion transport processes is poorly defined. Treatment of L1210 mouse leukaemia cells with either 5 mM alpha-difluoromethylornithine (DFMO), a suicide substrate of ornithine decarboxylase, or 25 microM N1,N12-bis(ethyl)spermine (BE-3-4-3), a dysfunctional polyamine analogue, caused a stable decreased in intracellular pH (pHi) by 0.1-0.4 unit from steady-state control values between 7.4 and 7.6, as measured either by partition of a weak acid or with a fluorescent pH-sensitive probe. This effect was not related to cell growth status or differences in metabolic acid generation, and was observed in either the presence or absence of HCO3-. Exogenous spermidine (10-25 microM) or putrescine (25-50 microM) fully reversed DFMO- or BE-3-4-3-induced acidification within 2 and 8 h respectively. Recovery of pHi in L1210 cells after a nigericin- or NH4(+)-mediated acid load in HCO3(-)-free buffers was mediated by Na+/H+ antiporter activity, in addition to a minor Na(+)-independent and amiloride-insensitive pathway. Decreased steady-state pHi was maintained in polyamine-depleted L1210 cells after recovery from acid stress. Moreover, the pHi-dependence of the rate of Na(+)-dependent H+ extrusion after an acid stress was altered by DFMO and BE-3-4-3, resulting in a set-point which was lower by 0.25-0.30 pH unit in polyamine-depleted cells. On the other hand, neither the rate nor the magnitude of Na+/H(+)-exchanger-mediated alkalinization induced by hypertonic shock was decreased by polyamine depletion. Thus polyamine depletion induces a persistent defect in pHi homeostasis which is due, at least in part, to a stable decrease in the pHi set-point of the Na+/H+ exchanger.

Modeling of Transient Moisture Diffusion in Wood below the Fiber Saturation Point

2011 ◽  
Vol 312-315 ◽  
pp. 455-459
Author(s):  
Johannes Eitelberger ◽  
Karin Hofstetter
Keyword(s):  
Steady State ◽  
Moisture Diffusion ◽  
Transport Processes ◽  
Fiber Saturation Point ◽  
Saturation Point ◽  
Transient Transport ◽  
Fiber Saturation ◽  
Physical Background ◽  
The Difference ◽  
Near Future

During the last two decades the macroscopic formulation of moisture transport in wood below the fiber saturation point has motivated many research efforts. From experiments the difference in steady-state and transient transport processes is well known, but could not be explained in a fully physically motivated manner. In the following article, first the microstructure of wood is depicted, followed by a description of the physical background of steady-state and transient transport processes in wood, and thereon based mathematical formulations. For a correct macroscopic description of transient transport processes, three coupled differential equations have to be solved in parallel, which is done using the finite element method. The validation of the whole model by comparison of model predictions with experimentally derived values is currently in progress and will be published in near future.

CRYSTAL GROWTH AND THE THERMODYNAMICS OF IRREVERSIBLE PROCESSES

1959 ◽  
Vol 37 (6) ◽  
pp. 739-754 ◽  
Author(s):  
J. S. Kirkaldy
Keyword(s):  
Free Energy ◽  
Steady State ◽  
Entropy Production ◽  
Dendritic Growth ◽  
Transport Processes ◽  
Irreversible Processes ◽  
Interface Morphology ◽  
Crystal Face ◽  
Thermodynamics Of Irreversible Processes ◽  
Alloy Crystal

The principle of minimum rate of entropy production is applied to steady-state transport processes in the neighborhood of an alloy crystal face growing into its melt. The procedure gives a satisfactory rationale of observed interface morphology. It is noted that segregation, which occurs in cellular or dendritic growth of alloys, is a direct manifestation of the system's attempt to minimize entropy production by conserving free energy. The general problems of growth of pure and impure single crystals from the melt and vapor are discussed.

scholarly journals Fluctuation–response inequality out of equilibrium

2020 ◽  
Vol 117 (12) ◽  
pp. 6430-6436 ◽  
Author(s):  
Andreas Dechant ◽  
Shin-ichi Sasa
Keyword(s):  
Steady State ◽  
Uncertainty Relation ◽  
Stochastic Dynamics ◽  
Direct Consequence ◽  
Transport Processes ◽  
Unperturbed System ◽  
Mean Velocity ◽  
Leibler Divergence ◽  
Probability Densities ◽  
Local Mean

We present an approach to response around arbitrary out-of-equilibrium states in the form of a fluctuation–response inequality (FRI). We study the response of an observable to a perturbation of the underlying stochastic dynamics. We find that the magnitude of the response is bounded from above by the fluctuations of the observable in the unperturbed system and the Kullback–Leibler divergence between the probability densities describing the perturbed and the unperturbed system. This establishes a connection between linear response and concepts of information theory. We show that in many physical situations, the relative entropy may be expressed in terms of physical observables. As a direct consequence of this FRI, we show that for steady-state particle transport, the differential mobility is bounded by the diffusivity. For a “virtual” perturbation proportional to the local mean velocity, we recover the thermodynamic uncertainty relation (TUR) for steady-state transport processes. Finally, we use the FRI to derive a generalization of the uncertainty relation to arbitrary dynamics, which involves higher-order cumulants of the observable. We provide an explicit example, in which the TUR is violated but its generalization is satisfied with equality.

A Finite Element Approach Derived From the Simplified Variational Principle

2008 ◽  
Author(s):  
Asher Yahalom
Keyword(s):  
Fluid Dynamics ◽  
Finite Element ◽  
Steady State ◽  
Variational Principle ◽  
Velocity Field ◽  
State Equations ◽  
Finite Element Approach ◽  
Independent Functions ◽  
Element Approach ◽  
Variational Formalism

In previous papers [1–4] we have described how by minimizing the fluid action numerically one can obtain a solution of the fluid steady state equations. The action which was used was the four function action of Seliger & Whitham [5]. In a recent paper [6] we describe how one can improve upon previous art by reducing the number of variables in the action. Three independent functions variational formalism for stationary and non-stationary barotropic flows is introduced. This is less than the four variables which appear in the standard equations of fluid dynamics which are the velocity field ν⃗ and the density ρ. In this paper we will discuss a possible finite element approach related to the usage of the new action principles as basis for a CFD algorithms.

Cytosolic ion exchange dynamics: insights into the mechanisms of component ion fluxes and their measurement

2003 ◽  
Vol 30 (4) ◽  
pp. 355 ◽  
Author(s):  
Dev T. Britto ◽  
Herbert J. Kronzucker
Keyword(s):  
Steady State ◽  
Compartmental Analysis ◽  
Transport Processes ◽  
Ion Fluxes ◽  
Half Time ◽  
Inorganic N ◽  
Cellular Compartment ◽  
Wide Range ◽  
Ion Relations ◽  
Pool Sizes

The quantification of cellular pool sizes of ions is essential for the understanding of the energetics of metabolic and membrane transport processes. No less important is the quantification of ion fluxes into, out of, and within cells. Of the variety of analytical methods available, only one, compartmental analysis by tracer efflux (CATE), can be used to simultaneously determine subcellular ion pool sizes and resolve ion fluxes. Thus, this methodology can be used to provide steady-state isotherms for major flux processes not amenable to direct measurement, such as effluxes or xylem fluxes, and to develop hypotheses about mechanisms underlying them. The exchange half-time for an ion in a cellular compartment emerges as a key CATE parameter that relates pool sizes with fluxes, and is a term that can be used to estimate errors in a wide range of findings in plant ion relations, and verify their plausibility. Case studies involving the flux and compartmentation of Ca2+, K+, and inorganic N are presented.

Transient Axial Free Jet Impinging Over a Flat Uniformly Heated Disk: Solid–Fluid Properties Effects

2000 ◽  
Author(s):  
Antonio J. Bula ◽  
Muhammad M. Rahman ◽  
John E. Leland
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Transfer Process ◽  
Conjugate Heat Transfer ◽  
Finite Thickness ◽  
Heat Transfer Process ◽  
Transport Processes ◽  
Liquid Region ◽  
Free Jet ◽  
Wide Range

Abstract Transient conjugate heat transfer process during axial free jet impingement on a solid disk of finite thickness was considered. As the fluid reached steady state, power was turned on and a uniform heat flux was imposed on the disk at its opposite surface. The numerical model considered both solid and fluid regions. Equations for conservation of mass, momentum, and energy were solved in the liquid region taking into account the transport processes at the inlet and exit boundaries, as well as at the solid-liquid and liquid-gas interfaces. Inside the solid, only the heat conduction equation was solved. The shape and location of the free surface (liquid-gas interface) was determined iteratively as a part of the solution process by satisfying the kinematic condition as well as the balance of normal and shear forces at this interface. A non-uniform grid distribution, captured from a systematic grid-independence study, was used to adequately accommodate large variations near the solid-fluid interface. Computed results include the simulation of six different substrate materials namely, aluminum, constantan, copper, diamond, silicon, and silver, and three different impinging liquids, FC - 77, Mil - 7808, and water. The solids and fluids selected covered a wide range of possibilities of conjugate heat transfer phenomena. The analysis performed showed that the thermal storage capacity, defined as density times specific heat, is an important factor defining which material will attain steady state faster during conjugate heat transfer process, like the thermal diffusivity does it for pure conduction heat transfer.

Transport Processes in Magnetosolidmechanics-Adiabatic Conditions

1969 ◽  
Vol 36 (1) ◽  
pp. 107-112
Author(s):  
O. A. Arnas ◽  
G. T. Craig
Keyword(s):  
Magnetic Field ◽  
Steady State ◽  
Applied Magnetic Field ◽  
Irreversible Thermodynamics ◽  
Transport Processes ◽  
One Dimensional ◽  
Adiabatic Conditions ◽  
Basic Concepts ◽  
General Relations ◽  
State Case

General phenomenological relations describing the interactions between an externally applied magnetic field and thermal and electrical gradients in a solid are formulated from basic concepts of irreversible thermodynamics. Galvanomagnetic and thermomagnetic effects are defined under adiabatic conditions and the results obtained are compared with previous analyses under isothermal conditions. The general relations are applied to a one-dimensional steady-state case.

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