Questions tagged [transport-phenomena]
Transport phenomenon are mechanisms by which particles or quantities move from one place to another. For example, this could be electrical transport (where electrical charge moves), thermal transport (where thermal energy moves), or molecular diffusion (where mass moves).
70 questions
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Form of wide-band limit for the broadening
When considering the Green's function (GF) of a system coupled to a reservoir, the wide-band limit (WBL) is often assumed to simplify the discussion.
For instance, the reservoir retarded GF reads $g_k(...
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Nusselt number for developing turbulent flow
I need to develop a uniform method to cool a plate 1 degree, our idea was to let helium flow under it to transfer heat via convection. I concluded by some calculations that the Nusselt number for ...
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Spatially Varying Energy Gap in a Superconductor
The energy of a quasiparticle in a superconductor is given by
$$E_k=\sqrt{\Delta_k^2 + \epsilon_k^2} \approx \sqrt{\Delta^2 + \epsilon_k^2}$$
Where $\epsilon$ is the kinetic-energy of the would-be ...
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Underlying Approximations Leading to the Vlasov Equation?
In classical gas theory, as taught in statistical mechanics classes, we learn that the statistical distribution function for each particle is described by the Boltzmann equation:
$$
\frac{\partial f}{\...
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Deriving the general energy balance equation of an open system from Reynold's Transport Theorem applied for energy
The general energy balance equation for open systems is as follows:
$$\frac{\mathrm{d}(mu)_{cv}}{\mathrm{d}t} + \Delta \left(u + \frac{1}{2} v^2 + gz\right)\dot{m}_{fs} = \dot Q + \dot W,$$
and the ...
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Transmission probability under spatial symmetry
Consider a simple two-band tight-binding system given in momentum space $$H=f_1(k_x)\sigma_x+f_2(k_y)\sigma_y+f_3(k_x,k_y,k_z)\sigma_z$$ where $\sigma_{x,y,z}$ are Pauli matrices, say, for some ...
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Can shot noise in a multi-species system always be expressed in terms of a Fano factor?
Consider a simple model of a two-species system of charge carriers $c$ and $d$ (say, both fermionic, with potentially different masses and dispersions but the same charge). Can the shot noise of such ...
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What is the meaning of the temperature dependence of the Hall coefficient?
I would like to know the physical meaning of investigating the temperature dependence of the Hall coefficient.
It is known that the Hall coefficient is used to investigate charge carriers in a ...
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Transformation to replace a Material derivative with a spatial derivative
In the technical paper referenced below, Gringarten et al. claim that the transient energy transport equation in a planar conduit (Eq. 1 in their paper)
$$
\rho c \Bigg[ \frac{\partial T(z,t)}{\...
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The roles of convection and advection in the absolute flux for species $i$ in mass transfer
I am confused as I have been reading on mass transport on multiple sources and they seem to use "advection" and "convection" interchangeably in the equation for the absolute flux ...
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Is it possible to say that entropy would affect the charge transportation?
I noticed there are a few papers from Dr. Karuppuchamy Navamani, for example:
Generalization on Entropy-Ruled Charge and Energy Transport for Organic Solids and Biomolecular Aggregates
Theoretical ...
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Green Kubo Relation for viscosity
I am calculating viscosity of WCA fluid using the Green Kubo relation. I am also following the paper of Zhang et al. for the Time decomposition method https://doi.org/10.1021/acs.jctc.5b00351 where, ...
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Why there is steady DC current in a metal under static $E$ field in the presence of Bloch oscillation?
Background: This is a question regarding the Bloch oscillation and the solid state description of shifted Fermi sphere under static electric field.
Question:
One explanation for a steady current ...
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Carrier Recombination Lifetime in Thermal Equilibrium
All the books I read talk about carrier recombination lifetime when the semiconductor material is pushed out of equilibrium. But let's say the material is in equilibrium ( where generation and ...
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Confusion regarding quantum point contact conductance
In the Wikipedia Quantum Point Contact (QPC) page the conductance is described as a function if the gate voltage, and has discrete jumps of the size of the conductance quantum $G_0 = 2 e^2/h$. In this ...
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What are the benefits/weaknesses of different diffusion models in radiation transport?
Can anyone summarize or point me toward references for why someone would choose one diffusion model over another, particularly in relation to radiation transport during a nuclear blast? The diffusion ...
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Confusion about Luttinger's transport coefficients
I've started reading three papers, one by Luttinger, one by Eich and by Tatara, and I'm confused to how they relate to one another.
My understanding is that in Luttinger's paper a "gravitational&...
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Does theory impose a limitation on the size of the sample to be used for measuring permeability?
Theory imposes no limitation on the size of the sample to be used but
it is evident that in order to minimize effects due to local
inhomogeneities in the material such as concretions, small shale
...
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$p$-like or $s$-like bands
What do people mean by $p$-like or $s$-like band structures? I know that d- or f-type electrons are typically more localized, while p and s-type electrons are typically more delocalized, but how would ...
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Superconductivity vs. energy gap
Many textbooks derive the single-particle excitation energy gap from the BCS mean-field hamiltonian, and then stop there, implying that this gap is sufficient for superconductivity.
To be frank, I ...
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Is there specific form of Navier-Stokes equation for which mass can cross bounding surface?
In my textbook, we learned that Navier-Stokes (NS) equations can be derived from Reynolds transport theorem where the control volume is assumed to be fixed. But when the control volume is moving, can ...
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Drude model for electron-hole gas
The Drude formula for the conductivity of the electron gas reads:
$$\sigma=\frac{\sigma_0}{1-i\omega \tau}.$$
How should it be modified when the hole or electron-hole gas is under the consideration? ...
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Does momentum transport occur via diffusion (or random walks)?
Consider a simple gas (or fluid) within a box at thermal equilibrium. I manage to give a kick to one particle within the gas, such that it acquires some momentum. After some time, it should be ...
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How does evaopration and diffusion affect concentration of solute at the solvent surface?
Imagine a long, thin tube with one end sealed and the other end open. It is filled with a volatile solvent with a dissolved non-volatile solute. As the solvent evaporates at the liquid surface, the ...
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What physical property does the crossover frequency in an ionic conductor represent; why is conductivity constant below and increasing above it?
After reading an article about ionic transport1, I remain confused about why the behavior illustrated in Fig. 1 of the article happens. (Figure 1 is shown below.)
Specifically, why is the conductivity ...
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How to show that the diffusion of a species is given by $\frac{\dot{m}}{A}=-\rho_i D \ln(C_i)$?
I'm reading a textbook on viscous flow which says that you can go from Fick's Law for the diffusion of a species
$$\dot{m_i}/A = -D \nabla \rho_i$$
to an equivalent formulation using the species ...
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Scattering processes in $\rm Au$ and $\rm AuPd$
I'm learning about the transport of electrons in solids (especially based on the Drude model), and I was wondering how the different scattering processes that take place in metals vary with ...
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What is the relation between Kubo's formula and the Green-Kubo relations?
In one hand, Kubo's formula is used in linear response quantum mechanics to obtain response functions (conductivity, magnetic susceptibility, dielectric function) and so on in terms of correlation ...
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On Euler: the vorticity vector is not invariant, but vorticity over density is
I've been reading Frankel's Geometry of Physics but I'm struggling to understand a section devoted to "Additional problems on fluid flow" (Sec. 4.3c in my edition).
Consider a fluid flow in $...
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Does the Hagen–Poiseuille equation apply to inviscid core/entrance lengt regions?
Does the Hagen–Poiseuille equation apply within the entrance length region of Incompressible, Newtonian fluid flow in a perfect tube?
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Onsager relations in Hall conductivity
For Onsager relation $\sigma_{ij}(B)=\sigma_{ji}(-B)$, why should one flip the sign of the $B$-field for reciprocity?
In the case of antiferromagnetism, with zero net magnetic moment, can the Onsager ...
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How does heat transfer depend on fluid viscosity
I’ve been dealing with a forced convection internal flow (regular vertical pipe) system where viscosity grows significantly through time.
The flow is way within laminar region, and I want to predict ...
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Calculating the power received by a pixel from a set of rays
I've written a path tracer and am now working on implementing a physically accurate way of simulating the actual sensor response for a given wavelength$^*$, given an exposure time, aperture size, ...
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Numerically solving Navier-Stokes-Darcy (Brinkman) equation
I'm trying to learn fluid dynamics in porous media and I need to solve Navier-Stokes-Darcy (Brinkman) equation numerically but I'm not sure how to do that (I was trying to use method of lines for ...
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How to define the surface current operator of a bulk system?
Consider a bulk uniform system with a boundary (edge, surface, etc.) and we want to study some transport effects mainly due to some boundary states. One possible experimental scenario might be to ...
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Is it possible that the scattering matrix is the minus identity matrix $S=-\mathbb{I}$?
We know that if the scattering matrix is an identity matrix ($S=+\mathbb{I}$), it means that transmission is zero and there is full reflection.
My question:
Is it possible that the scattering matrix ...
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Which is uniform at steady state: flux or flow rate?
Background
My initial focus was on heat transport, but I tried to gain insight by working with the analogous mass transport equations and I realized my confusion isn't necessary specific to heat ...
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Confused about flux transport
I am confused about a very simple thing:
Let's assume you have a 1D flow (fluid), where your flow velocity v$_x (x)$ = -$\frac{1}{x} \hat{x}$, i.e. your speed (= |velocity|) increases as you approach ...
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When are Dufour and Soret effects non-negligible?
Dufour effect is often times excluded from energy equations without mentioning. But there are many papers (out of my iq-league) which study effects of these phenomena in chemically reacting flows. ...
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Mass flux in a multicomponent mixture with a concentration-dependent density
This question concerns how to properly calculate the change in mass in a multicomponent mixture when the mass density is concentration-dependent.
For a 1D rod of length $L$ that has a mass density $\...
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Fick's Law dependency on concentration or pressure gradients
The question is about the Fick's law dependency on pressure. Would the gas molecules still flow through a membrane in case there is no concentration gradient but still a pressure gradient (e.g. ...
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Transport of energy in DC current
In alternating current (AC), electrons barely move a few centimeters along the conductor, with the usual frequencies and intensities in electric lines. That fact, together with Maxwell's equations, ...
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Doubts about how to apply Fick's law to gas
According to Fick's law the flux of gas through a membrane depends on the concentration gradient and then on the pressure gradient:
$$\Delta P = P_a - P_b$$
where $P_a$ is the pressure of container $A$...
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Transport Phenomena, question on statement in Wikipedia article
The Wikipedia article on Transport Phenomena contains the following statement:
Transport phenomena encompass all agents of physical change in the universe. Moreover, they are considered to be ...
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QED in 1+1 dimensions | Transport equation with an imaginary (reaction) source term
I would like to know what is the contribution of the right source term to this fermion component equation of motion:
\begin{equation}
i(\partial_0+\partial_1)\psi_R= a \psi_R
\end{equation} where $a$ ...
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The superconductor's electromagnetic response and Meissner current
We know
"In the superconducting state, the DC electrical resistivity is zero."
But other situations has confused me a bit. There are several situations that superconductors interact with ...
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What is the difference between Collective excitations and quasiparticle in superconductor? How to consider superconductors' optical response?
In the BCS theory, superconductors can be seen as Cooper pair condensates and quasiparticle excitations (Bogoliubov quasiparticle). But in Ginzburg-Landau's theory of superconductivity phenomenology, ...
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Effect of changing $\rm CO_2$-levels on cooling the desert at night
It is known (e.g. as mentioned in this popular article) that the reason why deserts cool down at night so much (to temperature below zero degrees celsius) is that there is much less humidity in the ...
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In Reynolds transport theorem, is the integral region simply-connected?
Reynolds transport theorem for a material element (parcels of fluids or solids which no material enters or leaves) reads $^1$
$$
(1):\frac{d}{dt}\left(\int_{\Omega(t)} \mathbf{f}\,dV\right) = \int_{\...
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An Exotic Transport Phenomena with Zero-Current at Different Voltage Values
I am a researcher working with active matters, and in one of my experiment I've seen a very exotic transport phenomena which we obtain zero-current for many different values of voltage (those values ...
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