5,089,757 research outputs found
Effects on Amorphous Silicon Photovoltaic Performance from High-temperature Annealing Pulses in Photovoltaic Thermal Hybrid Devices
There is a renewed interest in photovoltaic solar thermal (PVT) hybrid
systems, which harvest solar energy for heat and electricity. Typically, a main
focus of a PVT system is to cool the photovoltaic (PV) cells to improve the
electrical performance, however, this causes the thermal component to
under-perform compared to a solar thermal collector. The low temperature
coefficients of amorphous silicon (a-Si:H) allow for the PV cells to be
operated at higher temperatures and are a potential candidate for a more
symbiotic PVT system. The fundamental challenge of a-Si:H PV is light-induced
degradation known as the Staebler-Wronski effect (SWE). Fortunately, SWE is
reversible and the a-Si:H PV efficiency can be returned to its initial state if
the cell is annealed. Thus an opportunity exists to deposit a-Si:H directly on
the solar thermal absorber plate where the cells could reach the high
temperatures required for annealing.
In this study, this opportunity is explored experimentally. First a-Si:H PV
cells were annealed for 1 hour at 100\degreeC on a 12 hour cycle and for the
remaining time the cells were degraded at 50\degreeC in order to simulate
stagnation of a PVT system for 1 hour once a day. It was found that, when
comparing the cells after stabilization at normal 50\degreeC degradation, this
annealing sequence resulted in a 10.6% energy gain when compared to a cell that
was only degraded at 50\degreeC
Precision Measurement of sin^2 theta_W at a Reactor
This paper presents a strategy for measuring sin^2 theta_W to ~1% at a
reactor-based experiment, using antineutrinos electron elastic scattering. This
error is comparable to the NuTeV, SLAC E158, and APV results on sin^2 theta_W,
but with substantially different contributions to the systematics. An improved
method for identifying antineutrino proton events, which serve both as a
background and as a normalization sample, is described. The measurement can be
performed using the near detector of the presently proposed reactor-based
oscillation experiments. We conclude that an absolute error of delta(sin^2
theta_W)=0.0019 may be achieved.Comment: To be Submitted to Phys. Rev.
On the energy deposited by a quark moving in an N=4 SYM plasma
We evaluate the energy momentum tensor of a massive quark as it moves through
an N=4 SYM quark gluon plasma at constant velocity. We find that in the
near-quark region, where the dynamics is expected to be dominated by
dissipative behavior, the energy density may be quantitatively characterized by
a transient at velocities above the speed of sound of the plasma.Comment: 19 pages, 1 figure; Typos corrected, references adde
A boundary element regularised Stokeslet method applied to cilia and flagella-driven flow
A boundary element implementation of the regularised Stokeslet method of
Cortez is applied to cilia and flagella-driven flows in biology.
Previously-published approaches implicitly combine the force discretisation and
the numerical quadrature used to evaluate boundary integrals. By contrast, a
boundary element method can be implemented by discretising the force using
basis functions, and calculating integrals using accurate numerical or analytic
integration. This substantially weakens the coupling of the mesh size for the
force and the regularisation parameter, and greatly reduces the number of
degrees of freedom required. When modelling a cilium or flagellum as a
one-dimensional filament, the regularisation parameter can be considered a
proxy for the body radius, as opposed to being a parameter used to minimise
numerical errors. Modelling a patch of cilia, it is found that: (1) For a fixed
number of cilia, reducing cilia spacing reduces transport. (2) For fixed patch
dimension, increasing cilia number increases the transport, up to a plateau at
cilia. Modelling a choanoflagellate cell it is found that the
presence of a lorica structure significantly affects transport and flow outside
the lorica, but does not significantly alter the force experienced by the
flagellum.Comment: 20 pages, 7 figures, postprin
Rescattering in Meson Photoproduction off Few Body Systems
Exclusive reactions induced at high momentum transfer in few body systems
provide us with an original way to study the production and propagation of
hadrons in cold nuclear matter. In very well defined parts of the phase space,
the reaction amplitude develops a logarithmic singularity. It is on solid
ground since it depends only on on-shell elementary amplitudes and on low
momentum components of the nuclear wave function. This is the best window to
study the propagation of exotic configurations of hadrons such as, for
instance, the onset of color transparency. It may appear earlier in meson
photo-production reactions, more particularly in the strange sector, than in
more classical quasi elastic scattering of electrons. More generally, those
reactions provide us with the best tool to determine the cross section of the
scattering of various hadrons (strange particles, vector mesons) from the
nucleon and to access the production of possible exotic states.Comment: 15 pages; 11 figures During the review process of the paper, the
following changes have been implemented: 1- The title has been changed, 2-
The abstact and the first paragraph of the introduction have been rephrased
for consistency; 3- Figure 10 has been added; 4- The Appedix has been
considerably expanded: it gives the full expressions of the elementary
photoproduction amplitudes in terms of Pauli spinors and matrice
Estimating the causal effect of a time-varying treatment on time-to-event using structural nested failure time models
In this paper we review an approach to estimating the causal effect of a
time-varying treatment on time to some event of interest. This approach is
designed for the situation where the treatment may have been repeatedly adapted
to patient characteristics, which themselves may also be time-dependent. In
this situation the effect of the treatment cannot simply be estimated by
conditioning on the patient characteristics, as these may themselves be
indicators of the treatment effect. This so-called time-dependent confounding
is typical in observational studies. We discuss a new class of failure time
models, structural nested failure time models, which can be used to estimate
the causal effect of a time-varying treatment, and present methods for
estimating and testing the parameters of these models
Holding Dissapearance in RTD-based Quantizers
Multiple-valued Logic (MVL) circuits are one of the most attractive
applications of the Monostable-to-Multistable transition Logic (MML), and they
are on the basis of advanced circuits for communications. The operation of such
quantizer has two steps : sampling and holding. Once the quantizer samples the
signal, it must maintain the sampled value even if the input changes. However,
holding property is not inherent to MML circuit topologies. This paper analyses
the case of an MML ternary inverter used as a quantizer, and determines the
relations that circuit representative parameters must verify to avoid this
malfunction.Comment: Submitted on behalf of TIMA Editions
(http://irevues.inist.fr/tima-editions
Bosonic Partition Functions at Nonzero (Imaginary) Chemical Potential
We consider bosonic random matrix partition functions at nonzero chemical
potential and compare the chiral condensate, the baryon number density and the
baryon number susceptibility to the result of the corresponding fermionic
partition function. We find that as long as results are finite, the phase
transition of the fermionic theory persists in the bosonic theory. However, in
case that bosonic partition function diverges and has to be regularized, the
phase transition of the fermionic theory does not occur in the bosonic theory,
and the bosonic theory is always in the broken phase.Comment: 30 pages, 6 figure
- …