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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
Magnetohydrodynamic Simulations of the Atmosphere of HD 209458b
We present the first three-dimensional magnetohydrodynamic (MHD) simulations
of the atmosphere of HD 209458b which self-consistently include reduction of
winds due to the Lorentz force and Ohmic heating. We find overall wind
structures similar to that seen in previous models of hot Jupiter atmospheres,
with strong equatorial jets and meridional flows poleward near the day side and
equatorward near the night side. Inclusion of magnetic fields slows those winds
and leads to Ohmic dissipation. We find wind slowing ranging from 10%-40% for
reasonable field strengths. We find Ohmic dissipation rates ~10^17 W at 100
bar, orders of magnitude too small to explain the inflated radius of this
planet. Faster wind speeds, not achievable in these anelastic calculations, may
be able to increase this value somewhat, but likely will not be able to close
the gap necessary to explain the inflated radius. We demonstrate that the
discrepancy between the simulations presented here and previous models is due
to inadequate treatment of magnetic field geometry and evolution. Induced
poloidal fields become much larger than those imposed, highlighting the need
for a self-consistent MHD treatment of these hot atmospheres.Comment: 6 pages, 4 figures, accepted at ApJ
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
Innovative concepts for aerodynamic control of wind turbine rotors
New systems for the aerodynamic control of wind turbine rotors are being studied in various projects funded by the UK Department of Energy. Results from a current project, ongoing at the National Wind Turbine Test Centre (NWTC) in Scotland are presented. These systems show the promise of much cheaper and more affective active control of horizontal axis wind turbines than has been achieved with full span and partial span pitching systems
Old and New Fields on Super Riemann Surfaces
The ``new fields" or ``superconformal functions" on super Riemann
surfaces introduced recently by Rogers and Langer are shown to coincide with
the Abelian differentials (plus constants), viewed as a subset of the functions
on the associated super Riemann surface. We confirm that, as originally
defined, they do not form a super vector space.Comment: 9 pages, LaTex. Published version: minor changes for clarity, two new
reference
A framework for Multistate Demoeconomic Modeling and Projection, with an Illustrative Application
This paper outlines a theoretical framework for the consistent and policy relevant projection of populations disaggregated by sex, age, marital status, and region. The framework makes use of multistate life table and projection techniques, and a two-sex model of transitions between the married, divorced, and widowed states, to ensure the consistent determination of the future size and structure of the population on the basis of transitions assumed to occur over the projection period. It also uses model schedules to reduce the information load required for projection and to produce descriptive and interpretable parameters which can be explained and projected with the aid of an economic model that relates these parameters of demographic transition to their demographic and economic determinants. An illustrative application of this framework, using Australian data, is included
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