27,796 research outputs found
Simplified half-life methods for the analysis of kinetic data
The analysis of reaction rate data has as its goal the determination of the order rate constant which characterize the data. Chemical reactions with one reactant and present simplified methods for accomplishing this goal are considered. The approaches presented involve the use of half lives or other fractional lives. These methods are particularly useful for the more elementary discussions of kinetics found in general and physical chemistry courses
Cosmic microwave background multipole alignments in slab topologies
Several analyses of the microwave sky maps from the Wilkinson Microwave
Anisotropy Probe (WMAP) have drawn attention to alignments amongst the
low-order multipoles. Amongst the various possible explanations, an effect of
cosmic topology has been invoked by several authors. We focus on an alignment
of the first four multipoles (\ell = 2 to 5) found by Land and Magueijo (2005),
and investigate the distribution of their alignment statistic for a set of
simulated cosmic microwave background maps for cosmologies with slab-like
topology. We find that this topology does offer a modest increase in the
probability of the observed value, but that even for the smallest topology
considered the probability of the observed value remains below one percent.Comment: 6 pages RevTex with 6 figures included. Minor changes to match
version accepted as Physical Review D Rapid Communicatio
Signature for the Shape of the Universe
If the universe has a nontrivial shape (topology) the sky may show multiple
correlated images of cosmic objects. These correlations can be couched in terms
of distance correlations. We propose a statistical quantity which can be used
to reveal the topological signature of any Robertson-Walker (RW) spacetime with
nontrivial topology. We also show through computer-aided simulations how one
can extract the topological signatures of flat, elliptic, and hyperbolic RW
universes with nontrivial topology.Comment: 11 pages, 3 figures, LaTeX2e. This paper is a direct ancestor of
gr-qc/9911049, put in gr-qc archive to make it more accessibl
Evolution of the bursting-layer wave during a Type 1 X-ray burst
In a popular scenario due to Heyl, quasi periodic oscillations (QPOs) which
are seen during type 1 X-ray bursts are produced by giant travelling waves in
neutron-star oceans. Piro and Bildsten have proposed that during the burst
cooling the wave in the bursting layer may convert into a deep crustal
interface wave, which would cut off the visible QPOs. This cut-off would help
explain the magnitude of the QPO frequency drift, which is otherwise
overpredicted by a factor of several in Heyl's scenario. In this paper, we
study the coupling between the bursting layer and the deep ocean. The coupling
turns out to be weak and only a small fraction of the surface-wave energy gets
transferred to that of the crustal-interface wave during the burst. Thus the
crustal-interface wave plays no dynamical role during the burst, and no early
QPO cut-off should occur.Comment: 8 pages, submitted to MNRA
Kinetic Inflation in Stringy and Other Cosmologies
An inflationary epoch driven by the kinetic energy density in a dynamical
Planck mass is studied. In the conformally related Einstein frame it is easiest
to see the demands of successful inflation cannot be satisfied by kinetic
inflation alone. Viewed in the original Jordan-Brans-Dicke frame, the obstacle
is manifest as a kind of graceful exit problem and/or a kind of flatness
problem. These arguments indicate the weakness of only the simplest
formulation. {}From them can be gleaned directions toward successful kinetic
inflation.Comment: 26 pages, LaTeX, CITA-94-2
Normal zone in -coated conductors
We consider the distribution of an electric field in YBCO-coated conductors
for a situation in which the DC transport current is forced into the copper
stabilizer due to a weak link -- a section of the superconducting film with a
critical current less than the transport current. The electric field in the
metal substrate is also discussed. The results are compared with recent
experiments on normal zone propagation in coated conductors for which the
substrate and stabilizer are insulated from each other. The potential
difference between the substrate and stabilizer, and the electric field in the
substrate outside the normal zone can be accounted for by a large screening
length in the substrate, comparable to the length of the sample. During a
quench, the electric field inside the interface between YBCO and stabilizer, as
well as in the buffer layer, can be several orders of magnitude greater than
the longitudinal macroscopic electric field inside the normal zone. We
speculate on the possibility of using possible microscopic electric discharges
caused by this large (kV/cm) electric field as a means to detect a
quench.Comment: 8 pages, 4 figure
Use of 2G coated conductors for efficient shielding of DC magnetic fields
This paper reports the results of an experimental investigation of the
performance of two types of magnetic screens assembled from YBa2Cu3O7-d (YBCO)
coated conductors. Since effective screening of the axial DC magnetic field
requires the unimpeded flow of an azimuthal persistent current, we demonstrate
a configuration of a screening shell made out of standard YBCO coated conductor
capable to accomplish that. The screen allows the persistent current to flow in
the predominantly azimuthal direction at a temperature of 77 K. The persistent
screen, incorporating a single layer of superconducting film, can attenuate an
external magnetic field of up to 5 mT by more than an order of magnitude. For
comparison purposes, another type of screen which incorporates low critical
temperature quasi-persistent joints was also built. The shielding technique we
describe here appears to be especially promising for the realization of large
scale high-Tc superconducting screens.Comment: 8 pages, 3 figure
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