50,725 research outputs found
Gauge fixing and equivariant cohomology
The supersymmetric model developed by Witten to study the equivariant
cohomology of a manifold with an isometric circle action is derived from the
BRST quantization of a simple classical model. The gauge-fixing process is
carefully analysed, and demonstrates that different choices of gauge-fixing
fermion can lead to different quantum theories.Comment: 18 pages LaTe
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High intensity x-ray diffraction in transmission mode employing an analog of Poisson's spot
Poisson’s spot is a diffraction phenomenon producing an intensity maximum at the center of the geometric shadow of circular opaque objects. In an analog of the Poisson spot experiment, we show that a tubular cone of x-rays incident upon a crystalline sample produces diffraction spots or foci, corresponding to Bragg maxima within a transmission shadow. We discuss the beam geometry and the intensity gain recorded at the foci in transmission mode. We describe the geometric growth and decay of the foci over a linear axis with the aid of a movie sequence synchronized with the plotting of a diffractogram. The mean signal of a small central area in each successive camera image provides the intensity data for the diffractogram
Central Charge and the Andrews-Bailey Construction
From the equivalence of the bosonic and fermionic representations of
finitized characters in conformal field theory, one can extract mathematical
objects known as Bailey pairs. Recently Berkovich, McCoy and Schilling have
constructed a `generalized' character formula depending on two parameters \ra
and , using the Bailey pairs of the unitary model . By taking
appropriate limits of these parameters, they were able to obtain the characters
of model , model , and the unitary model with
central charge . In this letter we computed the effective
central charge associated with this `generalized' character formula using a
saddle point method. The result is a simple expression in dilogarithms which
interpolates between the central charges of these unitary models.Comment: Latex2e, requires cite.sty package, 13 pages. Additional footnote,
citation and reference
Deep-sea coral distribution on seamounts, oceanic islands, and continental slopes in the Northeast Atlantic
A unified framework for Schelling's model of segregation
Schelling's model of segregation is one of the first and most influential
models in the field of social simulation. There are many variations of the
model which have been proposed and simulated over the last forty years, though
the present state of the literature on the subject is somewhat fragmented and
lacking comprehensive analytical treatments. In this article a unified
mathematical framework for Schelling's model and its many variants is
developed. This methodology is useful in two regards: firstly, it provides a
tool with which to understand the differences observed between models;
secondly, phenomena which appear in several model variations may be understood
in more depth through analytic studies of simpler versions.Comment: 21 pages, 3 figure
Numerical Algorithm for Detecting Ion Diffusion Regions in the Geomagnetic Tail with Applications to MMS Tail Season May 1 -- September 30, 2017
We present a numerical algorithm aimed at identifying ion diffusion regions
(IDRs) in the geomagnetic tail, and test its applicability. We use 5 criteria
applied in three stages. (i) Correlated reversals (within 90 s) of Vx and Bz
(at least 2 nT about zero; GSM coordinates); (ii) Detection of Hall electric
and magnetic field signatures; and (iii) strong (>10 mV/m) electric fields.
While no criterion alone is necessary and sufficient, the approach does provide
a robust, if conservative, list of IDRs. We use data from the Magnetospheric
Multiscale Mission (MMS) spacecraft during a 5-month period (May 1 to September
30, 2017) of near-tail orbits during the declining phase of the solar cycle. We
find 148 events satisfying step 1, 37 satisfying steps 1 and 2, and 17
satisfying all three, of which 12 are confirmed as IDRs. All IDRs were within
the X-range [-24, -15] RE mainly on the dusk sector and the majority occurred
during traversals of a tailward-moving X-line. 11 of 12 IDRs were on the
dusk-side despite approximately equal residence time in both the pre- and
post-midnight sectors (56.5% dusk vs 43.5% dawn). MMS could identify signatures
of 4 quadrants of the Hall B-structure in 3 events and 3 quadrants in 7 of the
remaining 12 confirmed IDRs identified. The events we report commonly display
Vx reversals greater than 400 km/s in magnitude, normal magnetic field
reversals often >10 nT in magnitude, maximum DC |E| which are often well in
excess of the threshold for stage 3. Our results are then compared with the set
of IDRs identified by visual examination from Cluster in the years 2000-2005.Comment: In Submission at JGR:Space Physic
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Research Factsheet: Woodfuel experiment - North Thurlbar, Newton Rigg
An experiment has been set up to assess the economic viability and environmental impacts of woodfuel harvesting in North Thurlbar, a small wood land on the University of Cumbria Newton Rigg campus estate. This factsheet describes the aim of the study and the experiment design
Shock tube instrumentation techniques for study of hypervelocity entry problems
Shock tube instrumentation methods for convective heat transfer study and radiative properties of high temperature gas at conditions simulating hypervelocity entr
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