Quasi-Ballistic Transport in Nano-Scale Devices: Boundary Layer, Potential Fluctuation, and Coulomb Interaction

2011 ◽  
Vol 470 ◽  
pp. 207-213
Author(s):  
Nobuyuki Sano ◽  
Takahiko Karasawa
Keyword(s):  
Boundary Layer ◽  
Coulomb Interaction ◽  
Physical Mechanism ◽  
Layer Structure ◽  
Ballistic Transport ◽  
Boltzmann Transport ◽  
Virtual Source ◽  
Layer Potential ◽  
Nano Scale ◽  
Device Structures

The singular nature of the Boltzmann transport equation leads to the boundary layer structure around the virtual source in nano-scale device structures. We show that the boundary layer is a key concept to understand the physical mechanism behind quasi-ballistic transport in nano-scale devices. The self-consistent 3D Monte Carlo device simulator is constructed by accurately including the full Coulomb interaction. It is explicitly shown that the Coulomb interaction is indeed a key ingredient for any reliable predictions of device characteristics.

Rotationally symmetric flow of Reiner-Rivlin fluid over a heated porous wall using numerical approach

2021 ◽  
pp. 095440622110342
Author(s):  
Talat Rafiq ◽  
M Mustafa ◽  
Junaid Ahmad Khan
Keyword(s):  
Boundary Layer ◽  
Layer Structure ◽  
Full Range ◽  
Porous Wall ◽  
Symmetric Flow ◽  
Axial Velocity Component ◽  
Suction Velocity ◽  
Rotationally Symmetric ◽  
Non Linear System ◽  
Rotationally Symmetric Flow

This research features one parameter family of solutions representing rotationally symmetric flow of non-Newtonian fluid obeying Reiner-Rivlin model. Such flows take place over a revolving plane permeable surface through origin such that fluid at infinity also undergoes uniform rotation about the vertical axis. Heat transfer accompanied with viscous heating effect is also analyzed. A similarity solution is proposed that results into a coupled non-linear system with four unknowns. Boundary layer structure is characterized by a parameter [Formula: see text] that compares angular velocity of external flow with that of the rotating surface. Solutions are developed by a well-known package bvp4c of MATLAB for full range of [Formula: see text]. Flow pattern for different choices of [Formula: see text] is scrutinized by computing both 2 D and 3 D streamlines. It is further noted that value of suction velocity is important with regards to the sign of axial velocity component. Boundary layer suppresses considerably whenever the surface is permeable. For sufficiently high suction velocity with [Formula: see text], entire fluid undergoes rigid body rotation. In no suction case, axially upward flow accelerates for increasing values of parameter [Formula: see text] in the range [Formula: see text], whereas opposite trend is apparent in the case [Formula: see text]. Results for normalized wall shear and Nusselt number are scrutinized for various choices of embedded parameters.

scholarly journals On the boundary layer arising in the spin-up of a stratified fluid in a container with sloping walls

1997 ◽  
Vol 335 ◽  
pp. 233-259 ◽  
Author(s):  
P. W. DUCK ◽  
M. R. FOSTER ◽  
R. E. HEWITT
Keyword(s):  
Boundary Layer ◽  
Layer Structure ◽  
Outer Region ◽  
Stratified Fluid ◽  
Main Body ◽  
Similarity Type ◽  
Cone Apex ◽  
Uniform Solution ◽  
Steady Solutions ◽  
Finite Time Singularity

In this paper we consider the boundary layer that forms on the sloping walls of a rotating container (notably a conical container), filled with a stratified fluid, when flow conditions are changed abruptly from some initial (uniform) state. The structure of the solution valid away from the cone apex is derived, and it is shown that a similarity-type solution is appropriate. This system, which is inherently nonlinear in nature, is solved numerically for several flow regimes, and the results reveal a number of interesting and diverse features.In one case, a steady state is attained at large times inside the boundary layer. In a second case, a finite-time singularity occurs, which is fully analysed. A third scenario involves a double boundary-layer structure developing at large times, most significantly including an outer region that grows in thickness as the square-root of time.We also consider directly the nonlinear fully steady solutions to the problem, and map out in parameter space the likely ultimate flow behaviour. Intriguingly, we find cases where, when the rotation rate of the container is equal to that of the main body of the fluid, an alternative nonlinear state is preferred, rather than the trivial (uniform) solution.Finally, utilizing Laplace transforms, we re-investigate the linear initial-value problem for small differential spin-up studied by MacCready & Rhines (1991), recovering the growing-layer solution they found. However, in contrast to earlier work, we find a critical value of the buoyancy parameter beyond which the solution grows exponentially in time, consistent with our nonlinear results.

Unsteady dynamics of turbulent flow in the wakes of barchan dunes modulated by overlying boundary-layer structure

2021 ◽  
Vol 920 ◽  
Author(s):  
Nathaniel R. Bristow ◽  
Gianluca Blois ◽  
James L. Best ◽  
Kenneth T. Christensen
Keyword(s):  
Boundary Layer ◽  
Turbulent Flow ◽  
Layer Structure ◽  
Boundary Layer Structure ◽  
Barchan Dunes

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