45,168 research outputs found
Anomalous spin-dependent behaviour of one-dimensional subbands
We report a new electron interaction effect in GaAs/AlGaAs quantum wires.
Using DC-bias spectroscopy, we show that large and abrupt changes occur to the
energies of spin-down (lower energy) states as they populate. The effect is not
observed for spin-up energy states. At B=0, interactions have a pronounced
effect, in the form of the well-known 0.7 Structure. However, our new results
show that interactions strongly affect the energy spectrum at all magnetic
fields, from 0 to 16T, not just in the vicinity of the 0.7 Structure.Comment: 4 pages, 2 figure
Segregation by membrane rigidity in flowing binary suspensions of elastic capsules
Spatial segregation in the wall normal direction is investigated in
suspensions containing a binary mixture of Neo-Hookean capsules subjected to
pressure driven flow in a planar slit. The two components of the binary mixture
have unequal membrane rigidities. The problem is studied numerically using an
accelerated implementation of the boundary integral method. The effect of a
variety of parameters was investigated, including the capillary number,
rigidity ratio between the two species, volume fraction, confinement ratio, and
the number fraction of the more floppy particle in the mixture. It was
observed that in suspensions of pure species, the mean wall normal positions of
the stiff and the floppy particles are comparable. In mixtures, however, the
stiff particles were found to be increasingly displaced towards the walls with
increasing , while the floppy particles were found to increasingly
accumulate near the centerline with decreasing . The origins of this
segregation is traced to the effect of the number fraction on the
localization of the stiff and the floppy particles in the near wall region --
the probability of escape of a stiff particle from the near wall region to the
interior is greatly reduced with increasing , while the exact opposite
trend is observed for a floppy particle with decreasing . Simple model
studies on heterogeneous pair collisions involving a stiff and a floppy
particle mechanistically explain this observation. The key result in these
studies is that the stiff particle experiences much larger cross-stream
displacement in heterogeneous collisions than the floppy particle. A unified
mechanism incorporating the wall-induced migration of deformable particles and
the particle fluxes associated with heterogeneous and homogeneous pair
collisions is presented.Comment: 19 Pages, 16 Figure
Energy-level pinning and the 0.7 spin state in one dimension: GaAs quantum wires studied using finite-bias spectroscopy
We study the effects of electron-electron interactions on the energy levels
of GaAs quantum wires (QWs) using finite-bias spectroscopy. We probe the energy
spectrum at zero magnetic field, and at crossings of opposite-spin-levels in
high in-plane magnetic field B. Our results constitute direct evidence that
spin-up (higher energy) levels pin to the chemical potential as they populate.
We also show that spin-up and spin-down levels abruptly rearrange at the
crossing in a manner resembling the magnetic phase transitions predicted to
occur at crossings of Landau levels. This rearranging and pinning of subbands
provides a phenomenological explanation for the 0.7 structure, a
one-dimensional (1D) nanomagnetic state, and its high-B variants.Comment: 6 pages, 4 figure
Hot forming of silicon sheet, silicon sheet growth development for the large area silicon sheet task of the low cost silicon solar array project
The hot workability of polycrystalline silicon was studied. Uniaxail stress-strain curves are given for strain rates in the range of .0001 to .1/sec and temperatures from 1100 to 1380 C. At the highest strain rates at 1380 C axial strains in excess of 20% were easily obtainable without cracking. After deformations of 36%, recrystallization was completed within 0.1 hr at 1380 C. When the recrystallization was complete, there was still a small volume fraction of unrecyrstallized material which appeared very stable and may degrade the electronic properties of the bulk materials. Texture measurements showed that the as-produced vapor deposited polycrystalline rods have a 110 fiber texture with the 110 direction parallel to the growth direction and no preferred orientation about this axis. Upon axial compression perpendicular to the growth direction, the former 110 fiber axis changed to 111 and the compression axis became 110 . Recrystallization changed the texture to 110 along the former fiber axis and to 100 along the compression axis
Small gaps between products of two primes
Let denote the number that is a product of exactly two
distinct primes. We prove that
This sharpens an earlier result of the authors (arXivMath NT/0506067), which
had 26 in place of 6. More generally, we prove that if is any positive
integer, then
We also prove several other results on the representation of numbers with
exactly two prime factors by linear forms.Comment: 11N25 (primary) 11N36 (secondary
Methods for nanoparticle labeling of ricin and effect on toxicity
The unique optical properties associated with nanostructured materials that support the excitation of surface plasmons offer many new opportunities for the enhanced optical investigation of biological materials that pose a security threat. In particular, ricin is considered a significant bioterrorism risk due to its high toxicity combined with its ready availability as a byproduct in castor oil production. Therefore, the development of optical techniques capable of rapid on-site toxin detection with high molecular specificity and sensitivity continues to be of significant importance. Furthermore, understanding of the ricin cell entry and intracellular pathways remains poor due to a lack of suitable bioanalytical techniques. Initial work aimed at simultaneously tackling both these issues is described where different approaches for the nanoparticle labeling of ricin are investigated along with changes in ricin toxicity associated with the labeling process
Minimax studies
Effect of nonzero initial conditions on selection of minimax controllers for large launch vehicles and extremal bounded amplitude bounded rate inputs to linear system
Coarse Brownian Dynamics for Nematic Liquid Crystals: Bifurcation Diagrams via Stochastic Simulation
We demonstrate how time-integration of stochastic differential equations
(i.e. Brownian dynamics simulations) can be combined with continuum numerical
bifurcation analysis techniques to analyze the dynamics of liquid crystalline
polymers (LCPs). Sidestepping the necessity of obtaining explicit closures, the
approach analyzes the (unavailable in closed form) coarse macroscopic
equations, estimating the necessary quantities through appropriately
initialized, short bursts of Brownian dynamics simulation. Through this
approach, both stable and unstable branches of the equilibrium bifurcation
diagram are obtained for the Doi model of LCPs and their coarse stability is
estimated. Additional macroscopic computational tasks enabled through this
approach, such as coarse projective integration and coarse stabilizing
controller design, are also demonstrated
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