3,907 research outputs found
Communications technology satellite output-tube design and development
The design and development of a 200-watt-output, traveling-wave tube (TWT) for the Communications Technology Satellite (CTS) is discussed, with emphasis on the design evolution during the manufacturing phase of the development program. Possible further improvements to the tube design are identified
ROSAT PSPC Observations of the Richest () ACO Clusters
We have compiled an X-ray catalog of optically selected rich clusters of
galaxies observed by the PSPC during the pointed GO phase of the ROSAT mission.
This paper contains a systematic X-ray analysis of 150 clusters with an optical
richness classification of from the ACO catalog (Abell, Corwin, and
Olowin 1989). All clusters were observed within 45' of the optical axis of the
telescope during pointed PSPC observations. For each cluster, we calculate: the
net 0.5-2.0 keV PSPC count rate (or upper limit) in a 1 Mpc radius
aperture, 0.5-2.0 keV flux and luminosity, bolometric luminosity, and X-ray
centroid. The cluster sample is then used to examine correlations between the
X-ray and optical properties of clusters, derive the X-ray luminosity function
of clusters with different optical classifications, and obtain a quantitative
estimate of contamination (i.e, the fraction of clusters with an optical
richness significantly overestimated due to interloping galaxies) in the ACO
catalog
Learning and interaction in groups with computers: when do ability and gender matter?
In the research reported in this paper, we attempt to identify the background and process factors influencing the effectiveness of groupwork with computers in terms of mathematics learning. The research used a multi-site case study design in six schools and involved eight groups of six mixed-sex, mixed-ability pupils (aged 9-12) undertaking three research tasks â two using Logo and one a database. Our findings suggest that, contrary to other recent research, the pupil characteristics of gender and ability have no direct influence on progress in group tasks with computers. However, status effects â pupils' perceptions of gender and ability â do have an effect on the functioning of the group, which in turn can impede progress for all pupils concerned
RELATIONSHIP BETWEEN ATOPIC DERMATITIS AND IMMUNOGLOBULIN E
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66225/1/j.1365-4362.1976.tb00705.x.pd
Functional determinants for general Sturm-Liouville problems
Simple and analytically tractable expressions for functional determinants are
known to exist for many cases of interest. We extend the range of situations
for which these hold to cover systems of self-adjoint operators of the
Sturm-Liouville type with arbitrary linear boundary conditions. The results
hold whether or not the operators have negative eigenvalues. The physically
important case of functional determinants of operators with a zero mode, but
where that mode has been extracted, is studied in detail for the same range of
situations as when no zero mode exists. The method of proof uses the properties
of generalised zeta-functions. The general form of the final results are the
same for the entire range of problems considered.Comment: 28 pages, LaTe
Chandra Observations of NGC 4438: An Environmentally Damaged Galaxy in the Virgo Cluster
We present results from a 25 ksec CHANDRA ACIS-S observation of galaxies
NGC4438 and NGC4435 in the Virgo Cluster. X-ray emission in NGC4438 is observed
in a ~700 pc nuclear region, a 2.3 kpc spherical bulge, and a network of
filaments extending 4-10 kpc to the W and SW of the galaxy. The X-ray emission
in all 3 regions is highly correlated to similar features observed in Halpha.
Spectra of the filaments and bulge are well represented by a 0.4 keV MEKAL
model with combined 0.3-2 keV intrinsic luminosity of 1.24x10^{40}erg/s,
electron densities ~ 0.02-0.04 cm^{-3}, cooling times of 400-700 Myr and X-ray
gas mass <~ 3.7x10^8 Msolar. In the nuclear region of NGC4438 X-ray emission is
seen from the nucleus and from two outflow bubbles extending 360(730) pc to the
NW(SE) of the nucleus. The spectrum of the NW outflow bubble plus nucleus is
well fitted by an absorbed (n_H=1.9x10^{21} cm^{-2}) 0.58 keV MEKAL plasma
model plus a heavily absorbed (n_H = 2.9 x10^{22} cm^{-2}) Gamma = 2, power law
component. The electron density, cooling time, and X-ray gas mass in the NW
outflow are ~0.5 cm^{-3}, 30 Myr and 3.5x10^6 Msolar. Weak X-ray emission is
observed in the central region of NGC4435 with the peak of the hard emission
coincident with the galaxy's optical center; while the peak of the soft X-ray
emission is displaced 316 pc to the NE. The spectrum of NGC 4435 is well fitted
by a non-thermal power law plus a thermal component from 0.2-0.3 keV diffuse
ISM gas. We argue that the X-ray properties of gas outside the nuclear region
in NGC4438 and in NGC4435 favor a high velocity, off-center collision between
these galaxies ~ 100 Myr ago; while the nuclear X-ray emitting outflow gas in
NGC4438 has been heated only recently (within ~ 1-2 Myr) by shocks (v_s ~ 600
kms^{-1}) possibly powered by a central AGN.Comment: 40 pages, 7 figures; minor changes to conform to published version,
improved spectral fits to NGC 4435, improved figures 3,5; new figures 6b,
A Richness Study of 14 Distant X-ray Clusters From the 160 Square Degree Survey
We have measured the surface density of galaxies toward 14 X-ray-selected
cluster candidates at redshifts greater than z=0.46, and we show that they are
associated with rich galaxy concentrations. We find that the clusters range
between Abell richness classes 0-2, and have a most probable richness class of
one. We compare the richness distribution of our distant clusters to those for
three samples of nearby clusters with similar X-ray luminosities. We find that
the nearby and distant samples have similar richness distributions, which shows
that clusters have apparently not evolved substantially in richness since
redshift z =0.5. We compare the distribution of distant X-ray clusters in the
L_x--richness plane to the distribution of optically-selected clusters from the
Palomar Distant Cluster Survey. The optically-selected clusters appear overly
rich for their X-ray luminosities when compared to X-ray-selected clusters.
Apparently, X-ray and optical surveys do not necessarily sample identical mass
concentrations at large redshifts. This may indicate the existence of a
population of optically rich clusters with anomalously low X-ray emission. More
likely, however, it reflects the tendency for optical surveys to select
unvirialized mass concentrations, as might be expected when peering along
large-scale filaments.Comment: The abstract has been abridged. Accepted for publication in the
Astrophysical Journa
Using Synthetic Spacecraft Data to Interpret Compressible Fluctuations in Solar Wind Turbulence
Kinetic plasma theory is used to generate synthetic spacecraft data to
analyze and interpret the compressible fluctuations in the inertial range of
solar wind turbulence. The kinetic counterparts of the three familiar linear
MHD wave modes---the fast, Alfven, and slow waves---are identified and the
properties of the density-parallel magnetic field correlation for these kinetic
wave modes is presented. The construction of synthetic spacecraft data, based
on the quasi-linear premise---that some characteristics of magnetized plasma
turbulence can be usefully modeled as a collection of randomly phased, linear
wave modes---is described in detail. Theoretical predictions of the
density-parallel magnetic field correlation based on MHD and Vlasov-Maxwell
linear eigenfunctions are presented and compared to the observational
determination of this correlation based on 10 years of Wind spacecraft data. It
is demonstrated that MHD theory is inadequate to describe the compressible
turbulent fluctuations and that the observed density-parallel magnetic field
correlation is consistent with a statistically negligible kinetic fast wave
energy contribution for the large sample used in this study. A model of the
solar wind inertial range fluctuations is proposed comprised of a mixture of a
critically balanced distribution of incompressible Alfvenic fluctuations and a
critically balanced or more anisotropic than critical balance distribution of
compressible slow wave fluctuations. These results imply that there is little
or no transfer of large scale turbulent energy through the inertial range down
to whistler waves at small scales.Comment: Accepted to Astrophysical Journal. 28 pages, 7 figure
Confined two-dimensional fermions at finite density
We introduce the chemical potential in a system of two-dimensional massless
fermions, confined to a finite region, by imposing twisted boundary conditions
in the Euclidean time direction. We explore in this simple model the
application of functional techniques which could be used in more complicated
situations.Comment: 15 pages, LaTe
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