Anisotropy of the mean free path length in stationary gas flows

1970 ◽  
Vol 18 (4) ◽  
pp. 459-463 ◽  
Author(s):  
A. L. Stasenko
Keyword(s):  
Free Path ◽  
Path Length ◽  
Free Path Length ◽  
Mean Free Path ◽  
Gas Flows ◽  
The Mean

Applying the mean free-path length model to juvenile Chinook salmon migrating in the Sacramento River, California

2020 ◽  
Vol 103 (12) ◽  
pp. 1603-1617
Author(s):  
Anna E. Steel ◽  
James J. Anderson ◽  
Brian Mulvey ◽  
David L. Smith
Keyword(s):  
Free Path ◽  
Chinook Salmon ◽  
Path Length ◽  
Free Path Length ◽  
Mean Free Path ◽  
Sacramento River ◽  
Juvenile Chinook Salmon ◽  
The Mean ◽  
Juvenile Chinook

Lattice Boltzmann Simulation of Rarefied Gas Flow Along Moving Rigid Objects in Micro-Cavities

2015 ◽  
Author(s):  
Weilin Yang ◽  
Hongxia Li ◽  
TieJun Zhang ◽  
Ibrahim M. Elfadel
Keyword(s):  
Free Path ◽  
Lattice Boltzmann ◽  
Path Length ◽  
Gas Flow ◽  
Rarefied Gas ◽  
Free Path Length ◽  
Mean Free Path ◽  
Fluid Simulation ◽  
Transition Flow ◽  
Rarefied Gas Flow

Rarefied gas flow plays an important role in the design and performance analysis of micro-electro-mechanical systems (MEMS) under high-vacuum conditions. The rarefaction can be evaluated by the Knudsen number (Kn), which is the ratio of the molecular mean free path length and the characteristic length. In micro systems, the rarefied gas flow usually stays in the slip- and transition-flow regions (10−3 < Kn < 10), and may even go into the free molecular flow region (Kn > 10). As a result, conventional design tools based on continuum Navier-Stokes equation solvers are not applicable to analyzing rarefaction phenomena in MEMS under vacuum conditions. In this paper, we investigate the rarefied gas flow by using the lattice Boltzmann method (LBM), which is suitable for mesoscopic fluid simulation. The gas pressure determines the mean free path length and Kn, which further influences the relaxation time in the collision procedure of LBM. Here, we focus on the problem of squeezed film damping caused by an oscillating rigid object in a cavity. We propose an improved LBM with an immersed boundary approach, where an adjustable force term is used to quantify the interaction between the moving object and adjacent fluid, and further determines the slip velocity. With the proposed approach, the rarefied gas flow in MEMS with squeezed film damping is characterized. Different factors that affect the damping coefficient, such as pressure of gas and frequency of oscillation, are investigated in our simulation studies.

scholarly journals Investigating the Effect of Solid Boundaries on the Gas Molecular Mean-Free-Path

2009 ◽  
Author(s):  
Erik J. Arlemark ◽  
Jason M. Reese
Keyword(s):  
Molecular Dynamics ◽  
Boundary Conditions ◽  
Free Path ◽  
Mean Free Path ◽  
Gas Flows ◽  
Standard Temperature ◽  
Binary Collisions ◽  
The Mean ◽  
Temperature And Pressure ◽  
Definition Of

A key parameter for micro-gas-flows, the mean free path, is investigated in this paper. The mean free path is used in various models for predicting micro gas flows, both in the governing equations and their boundary conditions. The conventional definition of the mean free path is based on the assumption that only binary collisions occur and is commonly described using the macroscopic quantities density, viscosity and temperature. In this paper we compare the prediction by this definition of the mean free paths for helium, neon and argon gases under standard temperature and pressure conditions, with the mean free paths achieved by measurements of individual molecules using the numerical simulation technique of molecular dynamics. Our simulation using molecular dynamics consists of a cube with six periodic boundary conditions, allowing us to simulate an unconfined gas “package”. Although, the size of this package is important, since its impact on computational cost is considerable, it is also important to have enough simulated molecules to average data from. We find that the molecular dynamics method using 20520 simulated molecules yields results that are within 1% accuracy from the conventional definition of the mean free paths for neon and argon and within 2.5% for helium. We can also conclude that the normal approximation of only considering binary collisions is seemingly adequate for these gases under standard temperature and pressure conditions. We introduce a single planar wall and two parallel planar walls to the simulated gas of neon and record the mean free paths at various distances to the walls. It is found that the mean free paths affected by molecular collisions with the walls corresponds well with theoretical models up to Knudsen numbers of 0.2.

Imaging of Metal/Semiconductor Interface by Ballistic-Electron-Emission Microscopy (Beem)

1992 ◽  
Vol 295 ◽  
Author(s):  
E. Y. Lee ◽  
B. R. Turnew ◽  
J. R. Jimenez ◽  
L. J. Schowalter
Keyword(s):  
Free Path ◽  
Spatial Resolution ◽  
Electron Emission ◽  
Path Length ◽  
Free Path Length ◽  
Mean Free Path ◽  
Ballistic Electron Emission Microscopy ◽  
Semiconductor Interface ◽  
Ballistic Electron ◽  
Emission Microscopy

AbstractStudies in ballistic-electron-emission spectroscopy (BEES) have enabled precise energy measurements of Schottky barrier heights with excellent spatial resolution and, more recently, it was shown that even scattering at the metal/semiconductor interface affects the BEES spectrum [1]. Monte Carlo simulations have been done to predict the spatial resolution of ballistic-electron-emission microscopy (BEEM) [2]. In this paper, we will discuss the experimental spatial resolution of BEEM, and we will also give some of our BEES results for Au/Si and for Au/PtSi/Si. Our experimental BEEM studies indicate that, for Au/Si, hot electron transport is diffusive rather than ballistic, because the inelastic mean free path length (∼100 nm) is much larger than the elastic mean free path length (∼10 nm). This is in agreement with existing theories and with the literature on the internal photoemission method of studying the transport. Even in this diffusive regime, the spatial resolution of BEEM is still expected to be very good, being on the order of 10 nm [2]. Our preliminary work on PtSi shows that it has an attenuation length of 4 nm, which differs significantly from that of Au.

A STUDY ON PENETRATION DEPTH OF POLARIZATION IMAGING

2010 ◽  
Vol 03 (03) ◽  
pp. 177-181 ◽  
Author(s):  
RAN LIAO ◽  
NAN ZENG ◽  
DONGZHI LI ◽  
TIANLIANG YUN ◽  
YONGHONG HE ◽  
...  
Keyword(s):  
Penetration Depth ◽  
Free Path ◽  
Path Length ◽  
Free Path Length ◽  
Mean Free Path ◽  
Optical Measurements ◽  
Degree Of Polarization ◽  
Polarization Imaging ◽  
Optical Clearing ◽  
Different Response

Optical clearing improves the penetration depth of optical measurements in turbid tissues. Polarization imaging has been demonstrated as a potentially promising tool for detecting cancers in superficial tissues, but its limited depth of detection is a major obstacle to the effective application in clinical diagnosis. In the present paper, detection depths of two polarization imaging methods, i.e., rotating linear polarization imaging (RLPI) and degree of polarization imaging (DOPI), are examined quantitatively using both experiments and Monte Carlo simulations. The results show that the contrast curves of RLPI and DOPI are different. The characteristic depth of DOPI scales with transport mean free path length, and that of RLPI increases slightly with g. Both characteristic depths of RLPI and DOPI are on the order of transport mean free path length and the former is almost twice as large as the latter. It is expected that they should have different response to optical clearing process in tissues.

Mean free-path length theory of predator–prey interactions: Application to juvenile salmon migration

2005 ◽  
Vol 186 (2) ◽  
pp. 196-211 ◽  
Author(s):  
James J. Anderson ◽  
Eliezer Gurarie ◽  
Richard W. Zabel
Keyword(s):  
Free Path ◽  
Path Length ◽  
Free Path Length ◽  
Mean Free Path ◽  
Juvenile Salmon ◽  
Predator Prey

Variation of mean free path length over time and its effect on room impulse response

2008 ◽  
Vol 123 (5) ◽  
pp. 3769-3769 ◽  
Author(s):  
Miomir Mijic ◽  
Dragana Sumarac Pavlovic
Keyword(s):  
Free Path ◽  
Impulse Response ◽  
Path Length ◽  
Free Path Length ◽  
Mean Free Path ◽  
Over Time

ALTERNATIVE EXPERIMENTAL DETERMINATION OF WEAK LOCALIZATION OF LIGHT IN NANOSTRUCTURED MATERIALS

2002 ◽  
Vol 11 (03) ◽  
pp. 261-274 ◽  
Author(s):  
KOEN CLAYS ◽  
KURT WOSTYN ◽  
YUXIA ZHAO ◽  
ANDRÉ PERSOONS
Keyword(s):  
Random Walk ◽  
Free Path ◽  
Nanostructured Materials ◽  
Path Length ◽  
Dwell Time ◽  
Colloidal Crystals ◽  
Weak Localization ◽  
Free Path Length ◽  
Mean Free Path

An alternative experimental technique for the determination of weak localization of light in partially ordered nanostructured materials is proposed. The technique is based on the criterion for weak localization of light that the transport mean free path length of multiply scattered photons is reduced down to shorter than the wavelength of the light. This mean free path is calculated from the experimental dwell time of the photons in the scattering structure and by applying the photon random walk model using the diffusion approximation. The dwell time is experimentally determined by multifrequency phasefluorimetry. This technique is capable of providing corroborative intensity demodulation data that can be linked to the wavelength dependent transmission (optical bandgap) of colloidal crystals.

scholarly journals Simulation of Z-Shaped Graphene Geometric Diodes Using Particle-In-Cell Monte Carlo Method in theQuasi-Ballistic Regime

Nanomaterials ◽  
2021 ◽  
Vol 11 (9) ◽  
pp. 2361
Author(s):  
John Stearns ◽  
Garret Moddel
Keyword(s):  
Monte Carlo ◽  
Free Path ◽  
Path Length ◽  
Ballistic Transport ◽  
Free Path Length ◽  
Simulation Method ◽  
Mean Free Path ◽  
Device Performance ◽  
Ballistic Regime ◽  
Particle In Cell

Geometric diodes are planar conductors patterned asymmetrically to provide electrical asymmetry, and they have exhibited high-frequency rectification in infrared rectennas. These devices function by ballistic or quasi-ballistic transport in which the transport characteristics are sensitive to the device geometry. Common methods for predicting device performance rely on the assumption of totally ballistic transport and neglect the effects of electron momentum relaxation. We present a particle-in-cell Monte Carlo simulation method that allows the prediction of the current–voltage characteristics of geometric diodes operating quasi-ballistically, with the mean-free-path length shorter than the critical device dimensions. With this simulation method, we analyze a new diode geometry made from graphene that shows an improvement in rectification capability over previous geometries. We find that the current rectification capability of a given geometry is optimized for a specific mean-free-path length, such that arbitrarily large mean-free-path lengths are not desirable. These results present a new avenue for understanding geometric effects in the quasi-ballistic regime and show that the relationship between device dimensions and the carrier mean-free-path length can be adjusted to optimize device performance.

scholarly journals From diffusive to ballistic Stefan–Boltzmann heat transport in thin non-crystalline films

RSC Advances ◽  
2016 ◽  
Vol 6 (96) ◽  
pp. 94193-94199 ◽  
Author(s):  
A. Makris ◽  
T. Haeger ◽  
R. Heiderhoff ◽  
T. Riedl
Keyword(s):  
Thin Films ◽  
Heat Transport ◽  
Free Path ◽  
Path Length ◽  
Theoretical Models ◽  
Free Path Length ◽  
Mean Free Path ◽  
Crystalline Films

Today, different theoretical models exist to describe heat transport in ultra-thin films with a thickness approaching the phonon mean free path length.

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