Diffusivity 208 - generation

The quantity k is related to the intensity of the turbulent fluctuations in the three directions, k = 0.5 u u. Equation 41 is derived from the Navier-Stokes equations and relates the rate of change of k to the advective transport by the mean motion, turbulent transport by diffusion, generation by interaction of turbulent stresses and mean velocity gradients, and destmction by the dissipation S. One-equation models retain an algebraic length scale, which is dependent only on local parameters. The Kohnogorov-Prandtl model (21) is a one-dimensional model in which the eddy viscosity is given by... 

G.A. Eiceman, D. Preston, G. Tiano, J. Rodriguez and J.E. Parmeter, Quantitative calibration of vapor levels of TNT, KDX, and PETN using a diffusion generator with gravimetry and ion mobility spectrometry, Talanta 45(1) (1997) 57—74. 

Figure 5.66 Elemental concentration profiles in a thermometric couple. (A) Ideal case elemental concentration is constant from interface to nucleus of crystal. (B) Nonideal case slow diffusivity generates concentration gradients from interface to nucleus of crystal.

The addition of valinomycin, a K+ ionophore, leads to generation of a diffusion potential through efflux of K+ down its concentration gradient. The F protein permits uptake of H+ by the vesicles (which are impermeable to H+ in the absence of F ) in response to this diffusion-generated gradient. 

Find the expression for the modified Onsager equations to describe reciprocal influence of the given stepwise reactions in the presence of the chemical components diffusion generated by the system nonunifor mity. The diffusion coefficient is the same for aU of the components. 

A consideration of all the factors influencing should include not only diffusion, but also differences in mobility or diffusion generated by Joule heating, the reahty that the sample is not introduced... 

There a particle reaches the surface as in the random deposition model, but then is allowed to diffuse on the surface. The diffusion continues until the particle finds the colunm of minimum height inside a domain of finite size around the initial contact. A schematic view of the model and an example of the resulting interface for d = 2 is shown in Fig. 31.9. The surface diffusion generates a nontrivial... 

The delta tube behaves similarly to the diffusion generator except that it has a more positively controlled carrier fiow that can overcome the generator s internal system pressure. A diffusion system, which the vapor from the substance passively diffuses depending on flow dynamics of the system, can be quite unpredictable due... 

At steady state, for the interface, the following mass balance for component A is valid [incoming A due to diffusion] + [generated A] = 0. (8.45)... 

Ambipolar diffusion Generation of drift cnrrents, dne to differences in mass between ions and electrons, by charge separation. 

ERP is a capacitative signal — an AC-coupled electric signal. In contrast, most diffusion-generated bioelectric signals are DC-coupled electric signals. (However, the weU-known gating current detected in a squid axon is a voltage-induced displacement current.)... 

The statement by Maxwell quoted earlier suggests that diffusion and convection always occur together, that one cannot occur without the other. This fact sets diffusion apart from many other phenomena. For example, thermal conduction can certainly occur without convection. In contrast, diffusion generates its own convection, so that understanding the process can be much more complicated, especially in concentrated solutions. 

Zhu X D, Rasing T H and Shen Y R 1988 Surface diffusion of CO on Ni(111) studied by diffraction of optical second-harmonic generation off a monolayer grating Phys. Rev. Lett. 61 2883-5... 

In HMC the momenta are constantly being refreshed with the consequence that the accompanying dynamics will generate a spatial diffusion process superposed on the ini rtial dynamics, as in BGK or Smoluchowski dynamics. It is well known from the theory of barrier crossing that this added spatial... 

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