1,943 research outputs found
Polyx multicrystalline silicon solar cells processed by PF+ 5 unanalysed ion implantation and rapid thermal annealing
Rapid thermal annealing of damage induced by implantation in silicon can be a cost effective technology for the processing of terrestrial solar cells as compared to classical furnace or pulsed laser annealing. Unfortunately, drawbacks as poor bulk lifetime or low open-circuit-voltage occur as well. We have attempted to overcome these limitations for POLYX multicrystalline cast silicon grown by CGE (France) by keeping the annealing temperature of the phosphorus doped layer as high as 800 °C (to ensure a good crystalline quality and a high dopant activation) while being less than 900 °C (to minimize the effect of degradation of the base properties). The purpose of the present work is to investigate the I-V characteristics of the cells and to compare to those obtained with classical furnace annealing or with classical diffusion process
Characterisation of heat transfer in high thermal conductivity graphite foam
Paper presented at the 5th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 1-4 July, 2007.This paper presents the results of an experimental
investigation of forced convection heat transfer in microcellular
graphite foam of high thermal conductivity. The test section
was designed to be adiabatic with constant heat flux supplied at
the bottom of the channel. The graphite foam heat sinks were
fabricated into different structures and compared with
conventional aluminum heat sinks of the same configurations.
Heat transfer characteristics including local temperature and
Nusselt number distributions for steady flow through the tested
heat sinks were measured and discussed. The results show that
graphite foam heat sinks give better heat transfer performance
as compared to conventional aluminum heat sinks for different
configurations. The highest heat transfer rate is obtained by the
graphite foam heat sink with a fin structure. The study implies
that graphite foam material can offer a combination of
properties ideally suited for applications in high heat flux
thermal management applications where conventional materials
and products are not adequate.cs201
Ambient particulate matter (PM10) concentrations in major urban areas of Korea during 1996â2010
AbstractIn this study, ambient particulate matter pollution was investigated using monthly PM10 concentration data collected from seven major cities in Korea from 1996 to 2010. The highest mean value for the whole study period is seen from the capital city, Seoul (63.2±17.9ÎŒg mâ3), while the lowest is from Ulsan (46.7±14.8ÎŒg mâ3). The concentrations of PM10 in all cities exhibited seasonal variations with the peak values occurring consistently in spring (March or April). The PM10 data in each city consistently exhibited strong correlations (p<0.01) with gaseous pollutants (SO2, NO2, and CO), except for O3 (p>0.05). The analysis of long term trends of PM10 levels indicates a weak but consistent decline in concentrations in most cities with the relative average annual reductions of between 0.4 and 2.8% yâ1
Towards unified understanding of conductance of stretched monatomic contacts
When monatomic contacts are stretched, their conductance behaves in
qualitatively different ways depending on their constituent atomic elements.
Under a single assumption of resonance formation, we show that various
conductance behavior can be understood in a unified way in terms of the
response of the resonance to stretching. This analysis clarifies the crucial
roles played by the number of valence electrons, charge neutrality, and orbital
shapes.Comment: 2 figure
Hexatic-Herringbone Coupling at the Hexatic Transition in Smectic Liquid Crystals: 4- Renormalization Group Calculations Revisited
Simple symmetry considerations would suggest that the transition from the
smectic-A phase to the long-range bond orientationally ordered hexatic
smectic-B phase should belong to the XY universality class. However, a number
of experimental studies have constantly reported over the past twenty years
"novel" critical behavior with non-XY critical exponents for this transition.
Bruinsma and Aeppli argued in Physical Review Letters {\bf 48}, 1625 (1982),
using a renormalization-group calculation, that short-range
molecular herringbone correlations coupled to the hexatic ordering drive this
transition first order via thermal fluctuations, and that the critical behavior
observed in real systems is controlled by a `nearby' tricritical point. We have
revisited the model of Bruinsma and Aeppli and present here the results of our
study. We have found two nontrivial strongly-coupled herringbone-hexatic fixed
points apparently missed by those authors. Yet, those two new nontrivial
fixed-points are unstable, and we obtain the same final conclusion as the one
reached by Bruinsma and Aeppli, namely that of a fluctuation-driven first order
transition. We also discuss the effect of local two-fold distortion of the bond
order as a possible missing order parameter in the Hamiltonian.Comment: 1 B/W eps figure included. Submitted to Physical Review E. Contact:
[email protected]
Search for Invisible Decays of and in and
Using a data sample of decays collected with the BES
II detector at the BEPC, searches for invisible decays of and
in to and are performed.
The signals, which are reconstructed in final states, are used
to tag the and decays. No signals are found for the
invisible decays of either or , and upper limits at the 90%
confidence level are determined to be for the ratio
and for . These are the first
searches for and decays into invisible final states.Comment: 5 pages, 4 figures; Added references, Corrected typo
Time-Dependent Spintronic Transport and Current-Induced Spin Transfer Torque in Magnetic Tunnel Junctions
The responses of the electrical current and the current-induced spin transfer
torque (CISTT) to an ac bias in addition to a dc bias in a magnetic tunnel
junction are investigated by means of the time-dependent nonquilibrium Green
function technique. The time-averaged current (time-averaged CISTT) is
formulated in the form of a summation of dc current (dc CISTT) multiplied by
products of Bessel functions with the energy levels shifted by . The tunneling current can be viewed as to happen between the photonic
sidebands of the two ferromagnets. The electrons can pass through the barrier
easily under high frequencies but difficultly under low frequencies. The tunnel
magnetoresistance almost does not vary with an ac field. It is found that the
spin transfer torque, still being proportional to the electrical current under
an ac bias, can be changed by varying frequency. Low frequencies could yield a
rapid decrease of the spin transfer torque, while a large ac signal leads to
both decrease of the electrical current and the spin torque. If only an ac bias
is present, the spin transfer torque is sharply enhanced at the particular
amplitude and frequency of the ac bias. A nearly linear relation between such
an amplitude and frequency is observed.Comment: 13 pages,8 figure
Probing the energy bands of a Bose-Einstein condensate in an optical lattice
We simulate three experimental methods which could be realized in the
laboratory to probe the band excitation energies and the momentum distribution
of a Bose-Einstein condensate inside an optical lattice. The values of the
excitation energies obtained in these different methods agree within the
accuracy of the simulation. The meaning of the results in terms of density and
phase deformations is tested by studying the relaxation of a phase-modulated
condensate towards the ground state.Comment: 5 pages, 5 figure
Charged Higgs Boson Production in Bottom-Gluon Fusion
We compute the complete next-to-leading order SUSY-QCD corrections for the
associated production of a charged Higgs boson with a top quark via
bottom-gluon fusion. We investigate the applicability of the bottom parton
description in detail. The higher order corrections can be split into real and
virtual corrections for a general two Higgs doublet model and into additional
massive supersymmetric loop contributions. We find that the perturbative
behavior is well under control. The supersymmetric contributions consist of the
universal bottom Yukawa coupling corrections and non-factorizable diagrams.
Over most of the relevant supersymmetric parameter space the Yukawa coupling
corrections are sizeable, while the remaining supersymmetric loop contributions
are negligible.Comment: 18 pages, v2: some discussions added, v3: published versio
Collective excitations of trapped Bose condensates in the energy and time domains
A time-dependent method for calculating the collective excitation frequencies
and densities of a trapped, inhomogeneous Bose-Einstein condensate with
circulation is presented. The results are compared with time-independent
solutions of the Bogoliubov-deGennes equations. The method is based on
time-dependent linear-response theory combined with spectral analysis of
moments of the excitation modes of interest. The technique is straightforward
to apply, is extremely efficient in our implementation with parallel FFT
methods, and produces highly accurate results. The method is suitable for
general trap geometries, condensate flows and condensates permeated with vortex
structures.Comment: 6 pages, 3 figures small typos fixe
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