261 research outputs found
Helical liquid of snake states
We derive an exact solution to the problem of spin snake states induced in a
nonhomogeneous magnetic field by a combined action of the Rashba spin-orbit and
Zeeman fields. In an antisymmetric magnetic field the spin snake states are
nonlocal composite particles, originating from spatially separated entangled
spins. Adding an external homogeneous magnetic field breaks the spin-parity
symmetry gapping out the spectral branches, which results in a regular beating
pattern of the spin current. These new phenomena in a helical liquid of snake
states are proposed for an experimental realization.Comment: 5 pages, 3 figure
Superdiffusive heat conduction in semiconductor alloys -- II. Truncated L\'evy formalism for experimental analysis
Nearly all experimental observations of quasi-ballistic heat flow are
interpreted using Fourier theory with modified thermal conductivity. Detailed
Boltzmann transport equation (BTE) analysis, however, reveals that the
quasi-ballistic motion of thermal energy in semiconductor alloys is no longer
Brownian but instead exhibits L\'evy dynamics with fractal dimension . Here, we present a framework that enables full 3D experimental analysis by
retaining all essential physics of the quasi-ballistic BTE dynamics
phenomenologically. A stochastic process with just two fitting parameters
describes the transition from pure L\'evy superdiffusion as short length and
time scales to regular Fourier diffusion. The model provides accurate fits to
time domain thermoreflectance raw experimental data over the full modulation
frequency range without requiring any `effective' thermal parameters and
without any a priori knowledge of microscopic phonon scattering mechanisms.
Identified values for InGaAs and SiGe match ab initio BTE predictions
within a few percent. Our results provide experimental evidence of fractal
L\'evy heat conduction in semiconductor alloys. The formalism additionally
indicates that the transient temperature inside the material differs
significantly from Fourier theory and can lead to improved thermal
characterization of nanoscale devices and material interfaces
PERSIAN CUED SPEECH: THE EFFECT ON PHONOLOGICAL COMBINATION AND SEGMENTATION SKILLS OF CHILDREN WITH INTELLECTUAL DISABILITY
The aim of this paper was to study the effect of a Persian Cued Speech training program for increasing the phonological combination and segmentation skills of intellectually disabled children. This study was a quasi–experimental study. A convenience sample was selected and divided in two groups, namely an experimental group and a control group (n = 5). The study used the Phonological Awareness Questionnaire as the tool of analysis. The Cued Speech training is a forty 90-minute session program, which was implemented on the experimental group. At the end of the program, they were again assessed with the questionnaire. The findings from the study show the efficacy of our intervention on increasing the Phonological Combination and Segmentation skills (P < 0/10, P < 0/05). Using Cued Speech with the intellectually disabled children can be helpful to develop their pre reading skills such as phonological awareness
Impact of Atlantic salmon cage culture on sediment chemistry in Mjoifjordur, Iceland
Impact of Atlantic salmon (Salmo salar) cage culture in Mjoifjordur, Eastern Iceland on the chemistry of the sediment was investigated. Sediment samples were collected using a Shipek grab in December 2003. A core sub-sample was taken from each grab for analyzing total organic matter, total organic carbon, total nitrogen and phosphorus in different depths from three stations at various distances from the cage. These parameters were analyzed in the top layer of additional four stations. The results showed significant increase in all analyzed parameters in station 1, at 5m from the cage (p0.05), indicating localized impact of cage farming to the vicinity of cage. The analyzed parameters in various depth did not show significant differences (p>0.05). The value of analyzed parameters in the perimeter of the cage and their differences with reference stations showed small magnitude and localized impact on the chemistry of sediment. It might be due to deep water and moderate velocity of water current in this fjord. The magnitude of impact may differ during the summer season when biomass and feeding rate would be at the maximum level
Monte Carlo Simulation of Electron Transport in Degenerate Semiconductors
A modified algorithm is proposed to include Pauli exclusion principle in
Monte-Carlo simulations. This algorithm has significant advantages to implement
in terms of simplicity, speed and memory storage. We show that even in
moderately high applied fields, one can estimate electronic distribution with a
shifted Fermi sphere without introducing significant errors. Furthermore, the
free-flights must be coupled to state availability constraints; this leads to
substantial decrease in carrier heating at high fields. We give the correct
definition for electronic temperature and show that in high applied fields, the
quasi Fermi level is valley dependent. The effect of including Pauli exclusion
principle on the band profile; electronic temperature and quasi Fermi level for
inhomogeneous case of a single barrier heterostructure is illustrated
Method of Images for the Fast Calculation of Temperature Distributions in Packaged VLSI Chips
Thermal aware routing and placement algorithms are important in industry.
Currently, there are reasonably fast Green's function based algorithms that
calculate the temperature distribution in a chip made from a stack of different
materials. However, the layers are all assumed to have the same size, thus
neglecting the important fact that the thermal mounts which are placed
underneath the chip can be significantly larger than the chip itself. In an
earlier publication, we showed that the image blurring technique can be used to
calculate quickly temperature distribution in realistic packages. For this
method to be effective, temperature distribution for several point heat sources
at the center and at the corner and edges of the chip should be calculated
using finite element analysis (FEA) or measured. In addition, more accurate
results require correction by a weighting function that will need several FEA
simulations. In this paper, we introduce the method of images that take the
symmetry of the thermal boundary conditions into account. Thus with only "two"
finite element simulations, the steady-state temperature distribution for an
arbitrary complex power dissipation profile in a packaged chip can be
calculated. Several simulation results are presented. It is shown that the
power blurring technique together with the method of images can reproduce the
temperature profile with an error less than 0.5%.Comment: Submitted on behalf of TIMA Editions
(http://irevues.inist.fr/tima-editions
Efficiency in nanostructured thermionic and thermoelectric devices
Advances in solid-state device design now allow the spectrum of transmitted
electrons in thermionic and thermoelectric devices to be engineered in ways
that were not previously possible. Here we show that the shape of the electron
energy spectrum in these devices has a significant impact on their performance.
We distinguish between traditional thermionic devices where electron momentum
is filtered in the direction of transport only and a second type, in which the
electron filtering occurs according to total electron momentum. Such 'total
momentum filtered' kr thermionic devices could potentially be implemented in,
for example, quantum dot superlattices. It is shown that whilst total momentum
filtered thermionic devices may achieve efficiency equal to the Carnot value,
traditional thermionic devices are limited to efficiency below this. Our second
main result is that the electronic efficiency of a device is not only improved
by reducing the width of the transmission filter as has previously been shown,
but also strongly depends on whether the transmission probability rises sharply
from zero to full transmission. The benefit of increasing efficiency through a
sharply rising transmission probability is that it can be achieved without
sacrificing device power, in contrast to the use of a narrow transmission
filter which can greatly reduce power. We show that devices which have a
sharply-rising transmission probability significantly outperform those which do
not and it is shown such transmission probabilities may be achieved with
practical single and multibarrier devices. Finally, we comment on the
implications of the effect the shape of the electron energy spectrum on the
efficiency of thermoelectric devices.Comment: 11 pages, 15 figure
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