4,224 research outputs found
Debye Sources and the Numerical Solution of the Time Harmonic Maxwell Equations, II
In this paper, we develop a new integral representation for the solution of
the time harmonic Maxwell equations in media with piecewise constant dielectric
permittivity and magnetic permeability in R^3. This representation leads to a
coupled system of Fredholm integral equations of the second kind for four
scalar densities supported on the material interface. Like the classical Muller
equation, it has no spurious resonances. Unlike the classical approach,
however, the representation does not suffer from low frequency breakdown. We
illustrate the performance of the method with numerical examples.Comment: 36 pages, 5 figure
An Anomalous UV Extension in NGC6251
Deep U-band FOC images of the nuclear region of NGC6251 have revealed a
region of extended emission which is most probably radiation scattered from a
continuum source in the nucleus. This radiation lies interior to a dust ring,
is nearly perpendicular to the radio jet axis, and is seen primarily in the FOC
U and b filters. The extension has a low observed polarization(), and
is unlikely to arise from line emission. We know of no other examples similar
to what we have found in NGC 6251, and we offer some tentative explanations.
The nuclear morphology shows clear similarities to that seen in the nucleus of
NGC 4261 except for the extended U-band radiation.Comment: 14 pages AAStex format + 4 figures; accepted for publication in ApJ
Letter
Do the Poor Pay More for Healthy Food? An Empirical Economic Analysis
Food Consumption/Nutrition/Food Safety,
Improving retention and performance in civil society in Uganda
This article is the second article in the Human Resources for Health journal's first quarterly feature. The series of seven articles has been contributed by Management Sciences for Health (MSH) under the theme of leadership and management in public health and will be published article-by-article over the next few weeks. The journal invited Dr Manuel M. Dayrit, Director of the WHO Department of Human Resources for Health and former Minister of Health for the Philippines to launch the feature with an opening editorial to be found in the journal's blog
Low Surface Brightness Galaxies around the HDF-S: II. Distances and volume densities
With this study we aim at the spectroscopic verification of a photometrically
selected sample of Low Surface Brightness (LSB) galaxy candidates in a field
around the Hubble Deep Field-South (HDF-S). The sample helps to extend the
parameter space for LSB galaxies to lower central surface brightnesses and to
provide better estimates on the volume densities of these objects. To derive
redshifts for the LSB candidates, long-slit spectra were obtained covering a
spectral range from 3400{\AA} to 7500{\AA}. The observations have been obtained
using the ESO 3.6m telescope, equipped with the EFOSC2 spectrograph. From the
measured radial velocities, distances could be estimated. With this distance
information, it is possible to differentiate between true LSB galaxies and
higher redshift High Surface Brightness (HSB) galaxies which may contaminate
the sample. A correction for the surface brightnesses can then be applied,
accounting for the cosmological dimming effect (``Tolman Dimming''). We show
that ~70% of the LSB candidates, selected based on their location in the
color-color space, are real LSB galaxies. Their position in the color-color
diagrams, therefore, indicate that the LSB galaxies have a different stellar
population mix resulting from a different star formation history compared to
HSBs. Our LSB galaxy sample consists only of large disk galaxies with
scale-length between 2.5kpc and 7.3kpc. We confirm the flat central surface
brightness distribution of previous surveys and extend this distribution down
to central surface brightnesses of 27 B mag arcsec^-2.Comment: 12 pages, 20 figures, accepted by A&
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