2,660,699 research outputs found
Reunion of Vicious Walkers: Results from -Expansion -
The anomalous exponent, , for the decay of the reunion probability
of vicious walkers, each of length , in dimensions,
is shown to come from the multiplicative renormalization constant of a
directed polymer partition function. Using renormalization group(RG) we
evaluate to . The survival probability exponent is
. For , our RG is exact and stops at .
For , the log corrections are also determined. The number of walkers that
are sure to reunite is 2 and has no expansion.Comment: No of pages: 11, 1figure on request, Revtex3,IP/BBSR/929
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
Energy Conditions and Supernovae Observations
In general relativity, the energy conditions are invoked to restrict general
energy-momentum tensors on physical grounds. We show that in the standard
Friedmann-Lemaitre-Robertson-Walker approach to cosmological modelling where
the equation of state of the cosmological fluid is unknown, the energy
conditions provide model-independent bounds on the behavior of the distance
modulus of cosmic sources as a function of the redshift. We use both the gold
and the legacy samples of current type Ia supenovae to carry out a
model-independent analysis of the energy conditions violation in the context of
standard cosmology.Comment: 4 pages, 2 figures; v2: References added, misprints corrected,
published in Phys.Rev.D in the present for
Solar Dynamics, Rotation, Convection and Overshoot
We discuss recent observational, theoretical and modeling progress made in
understanding the Sun's internal dynamics, including its rotation, meridional
flow, convection and overshoot. Over the past few decades, substantial
theoretical and observational effort has gone into appreciating these aspects
of solar dynamics. A review of these observations, related helioseismic
methodology and inference and computational results in relation to these
problems is undertaken here.Comment: 31 pages, 10 figures, Space Science Review
On 2D N=(4,4) superspace supergravity
We review some recent results obtained in studying superspace formulations of
2D N=(4,4) matter-coupled supergravity. For a superspace geometry described by
the minimal supergravity multiplet, we first describe how to reduce to
components the chiral integral by using ``ectoplasm'' superform techniques as
in arXiv:0907.5264 and then we review the bi-projective superspace formalism
introduced in arXiv:0911.2546. After that, we elaborate on the curved
bi-projective formalism providing a new result: the solution of the covariant
type-I twisted multiplet constraints in terms of a weight-(-1,-1) bi-projective
superfield.Comment: 18 pages, LaTeX, Contribution to the proceedings of the International
Workshop "Supersymmetries and Quantum Symmetries" (SQS'09), Dubna, July
29-August 3 200
Why do people live apart together?
Interpretations of living apart together (LAT) have typically counter-posed 'new family form' versus 'continuist' perspectives. Recent surveys, however, construct LAT as a heterogeneous category that supports a 'qualified continuist' position â most people live apart as a response to practical circumstances or as a modern version of 'boy/girlfriend', although a minority represents something new in preferring to live apart more permanently. This article interrogates this conclusion by examining in depth why people live apart together, using a nationally representative survey from Britain and interview accounts from 2011. Our analysis shows that LAT as a category contains different sorts of relationship, with different needs and desires. While overall coupledom remains pivotal and cohabitation remains the goal for most, LAT allows people flexibility and room to manoeuvre in adapting couple intimacy to the demands of contemporary life. Hence, we suggest, LAT is both 'new' and a 'continuation'
Relation between and from QCD
We have studied, using double ratio of QCD (spectral) sum rules, the ratio
between the masses of and X(3872) assuming that they are respectively
described by the and molecular currents. We found
(within our approximation) that the masses of these two states are almost
degenerate. Since the pion exchange interaction between these mesons is exactly
the same, we conclude that if the observed X(3872) meson is a
molecule, then the molecule should also exist with approximately the
same mass. An extension of the analysis to the -quark case leads to the same
conclusion. We also study the SU(3) breakings for the mass
ratios. Motivated by the recent Belle observation of two states, we
revise our determination of by combining results from exponential and
FESR sum rules.Comment: revised version to appear on Phys. Lett.
Line emission from gamma-ray burst environments
The time and angle dependent line and continuum emission from a dense torus
around a cosmological gamma-ray burst source is simulated, taking into account
photoionization, collisional ionization, recombination, and electron heating
and cooling due to various processes. The importance of the hydrodynamical
interaction between the torus and the expanding blast wave is stressed. Due to
the rapid deceleration of the blast wave as it interacts with the dense torus,
the material in the torus will be illuminated by a drastically different photon
spectrum than observable through a low-column-density line of sight, and will
be heated by the hydrodynamical interaction between the blast wave and the
torus. A model calculation to reproduce the Fe K-alpha line emission observed
in the X-ray afterglow of GRB 970508 is presented. The results indicate that ~
10^{-4} solar masses of iron must be concentrated in a region of less than
10^{-3} pc. The illumination of the torus material due to the hydrodynamic
interaction of the blast wave with the torus is the dominant heating and
ionization mechanism leading to the formation of the iron line. These results
suggest that misaligned GRBs may be detectable as X-ray flashes with pronounced
iron emission line features.Comment: Accepted for publication in ApJ. Updated recombination rate data;
discussion on element abundances added; references update
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