7,006 research outputs found
Pore opening effects and transport diffusion in the Knudsen regime in comparison to self- (or tracer-) diffusion
We study molecular diffusion in linear nanopores with different types of
roughness in the so-called Knudsen regime. Knudsen diffusion represents the
limiting case of molecular diffusion in pores, where mutual encounters of the
molecules within the free pore space may be neglected and the time of flight
between subsequent collisions with the pore walls significantly exceeds the
interaction time between the pore wall and the molecules. We present an
extension of a commonly used procedure to calculate transport diffusion
coefficients. Our results show that using this extension, the coefficients of
self- and transport diffusion in the Knudsen regime are equal for all regarded
systems, which improves previous literature data.Comment: 5 pages, 7 figure
A renormalization approach for the 2D Anderson model at the band edge: Scaling of the localization volume
We study the localization volumes (participation ratio) of electronic
wave functions in the 2d-Anderson model with diagonal disorder. Using a
renormalization procedure, we show that at the band edges, i.e. for energies
, is inversely proportional to the variance \var of the
site potentials. Using scaling arguments, we show that in the neighborhood of
, scales as V=\var^{-1}g((4-\ve E\ve)/\var) with the scaling
function . Numerical simulations confirm this scaling ansatz
Rule-based Modelling and Tunable Resolution
We investigate the use of an extension of rule-based modelling for cellular
signalling to create a structured space of model variants. This enables the
incremental development of rule sets that start from simple mechanisms and
which, by a gradual increase in agent and rule resolution, evolve into more
detailed descriptions
A full field, 3-D velocimeter for microgravity crystallization experiments
The programming and algorithms needed for implementing a full-field, 3-D velocimeter for laminar flow systems and the appropriate hardware to fully implement this ultimate system are discussed. It appears that imaging using a synched pair of video cameras and digitizer boards with synched rails for camera motion will provide a viable solution to the laminar tracking problem. The algorithms given here are simple, which should speed processing. On a heavily loaded VAXstation 3100 the particle identification can take 15 to 30 seconds, with the tracking taking less than one second. It seeems reasonable to assume that four image pairs can thus be acquired and analyzed in under one minute
Scaling of the localization length in linear electronic and vibrational systems with long-range correlated disorder
The localization lengths of long-range correlated disordered chains are
studied for electronic wavefunctions in the Anderson model and for vibrational
states. A scaling theory close to the band edge is developed in the Anderson
model and supported by numerical simulations. This scaling theory is mapped
onto the vibrational case at small frequencies. It is shown that for small
frequencies, unexpectateley the localization length is smaller for correlated
than for uncorrelated chains.Comment: to be published in PRB, 4 pages, 2 Figure
Scaling behavior of a one-dimensional correlated disordered electronic System
A one-dimensional diagonal tight binding electronic system with correlated
disorder is investigated. The correlation of the random potential is
exponentially decaying with distance and its correlation length diverges as the
concentration of "wrong sign" approaches to 1 or 0. The correlated random
number sequence can be generated easily with a binary sequence similar to that
of a one-dimensional spin glass system. The localization length (LL) and the
integrated density of states (IDOS) for long chains are computed. A comparison
with numerical results is made with the recently developed scaling technique
results. The Coherent Potential Approximation (CPA) is also adopted to obtain
scaling functions for both the LL and the IDOS. We confirmed that the scaling
functions show a crossover near the band edge and establish their relation to
the concentration. For concentrations near to 0 or 1 (longer correlation length
case), the scaling behavior is followed only for a very limited range of the
potential strengths.Comment: will appear in PR
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