1,032 research outputs found
Derivation of a tangent function using an integrated circuit four-quadrant multiplier
A tangent function generator is provided which utilizes input signals proportionate to the sine and cosine of a given angle. The equipment accomplishes a trigonometric manipulation which forms an output signal substantially independent of the input reference voltage but proportional to the tangent of the angle. The device uses a multiplier and operational amplifier
The Dependence of the Soft X-ray Properties of LMXBs on the Metallicity of Their Environment
We determine the X-ray spectral properties of a sample of low-mass X-ray
binaries (LMXBs) which reside in globular clusters of M31, as well as five
LMXBs in Galactic globular clusters and in the Large Magellanic Cloud using the
ROSAT PSPC. We find a trend in the X-ray properties of the LMXBs as a function
of globular cluster metallicity. The spectra of LMXBs become progressively
softer as the metallicity of its environment increases. The one M31 globular
cluster LMXB in our sample which has a metallicity greater than solar has
spectral properties similar to those of LMXBs in the bulge of M31, but markedly
different from those which reside in low metallicity globular clusters, both in
M31 and the Galaxy. The spectral properties of this high metallicity LMXB is
also similar to those of X-ray faint early-type galaxies. This lends support to
the claim that a majority of the X-ray emission from these X-ray faint
early-type galaxies results from LMXBs and not hot gas, as is the case in their
X-ray bright counterparts.Comment: 5 pages, 2 embedded Postscript figures, uses emulateapj.sty,
Astrophysical Journal Letters, in pres
Multifrequency observations of the superluminal quasar 3C 345
We have investigated the continuum properties of the superluminal quasar 3C 345 with monitoring studies at radio, optical, infrared, and X-ray frequencies as well as with simultaneous multifrequency spectra extending from the radio through the X-ray bands. Variability occurs more rapidly and with greater amplitude toward shorter wavelengths in the infrared-optical region (0.4-100 μm). Radio outbursts, which appear to follow infrared-optical outbursts by about a year, occur first at the highest frequencies, as expected from optical depth effects, although the peak flux is often reached at several frequencies at once. The beginning of outbursts as defined by millimeter measurements corresponds to the appearance of the three known "superluminal" components. An increase in the X-ray flux during 1979-1980 corresponds to increased radio flux, while the infrared flux changes in the opposite sense. The multifrequency spectra show that the nearly flat radio continuum steepens at 10^(11)-10^(12) Hz and has a power-law slope of -0.91 ± 0.04 from 350 to 20 μm that steepens to -1.40 ± 0.02 at 20 μm-1200 A. A "blue bump" is detected at rest wavelengths 4000-1500 A. The X-ray emission has a flatter slope (-0.7) than the infrared-ultraviolet continuum and lies above an extrapolation of that continuum to X-ray energies. This supports the finding from variability that the X-ray emission is not simply connected to the optical emission. Although the shape of the infrared-ultraviolet continuum is generally preserved during flux variations, slope variations occur and are most common in the ultraviolet region. Most of the total power (3 x 10^(47) ergs s ^(-1)) emerges in the submillimeter-optical region but about one-sixth of the power is emitted at X-ray and radio
Mass Loss From Evolved Stars in Elliptical Galaxies
Most of the X-ray emitting gas in early-type galaxies probably originates
from red giant mass loss and here we model the interaction between this stellar
mass loss and the hot ambient medium. Using two-dimensional hydrodynamic
simulations, we adopt a temperature for the ambient medium of 3E6 K along with
a range of ambient densities and stellar velocities. When the stellar velocity
is supersonic relative to the ambient medium, a bow shock occurs, along with a
shock driven into the stellar ejecta, which heats only a fraction of the gas.
Behind the bow shock, a cool wake develops but the fast flow of the hot medium
causes Kelvin-Helmholtz instabilities to grow and these fingers are shocked and
heated (without radiative cooling). Along with the mixing of this wake material
with the hot medium, most of the stellar ejecta is heated to approximately the
temperature of the hot ambient medium within 2 pc of the star. With the
addition of radiative cooling, some wake material remains cool (< 1E5 K),
accounting for up to 25% of the stellar mass loss. Less cooled gas survives
when the ambient density is lower or when the stellar velocity is higher than
in our reference case. These results suggest that some cooled gas should be
present in the inner part of early-type galaxies that have a hot ambient
medium. These calculations may explain the observed distributed optical
emission line gas as well as the presence of dust in early-type galaxies.Comment: 57 pages, which includes 27 figures; ApJ, in press. A version with
full-resolution figures can be found at
http://www.astro.lsa.umich.edu/~jbregman/public/ms.ps.g
Radial Temperature Profiles of X-Ray--Emitting Gas Within Clusters of Galaxies
Previous analyses of ASCA data of clusters of galaxies have found conflicting
results regarding the slope of the temperature profile of the hot X-ray gas
within clusters, mainly because of the large, energy-dependent point spread
function (PSF) of the ASCA mirrors. We present a summary of all ASCA-determined
cluster temperature profiles found in the literature, and find a discrepancy in
the radial temperature trend of clusters based on which PSF-correction routine
is used. This uncertainty in the cluster temperature profile in turn can lead
to large uncertainties in the amount of dark matter in clusters. In this study,
we have used ROSAT PSPC data to obtain independent relative temperature
profiles for 26 clusters, most of which have had their temperature profiles
determined by ASCA. Our aim is not to measure the actual temperature values of
the clusters, but to use X-ray color profiles to search for a hardening or
softening of the spectra with radius for comparison to ASCA-derived profiles.
The radial color profiles indicate that outside of the cooling flow region, the
temperature profiles of clusters are in general constant. Within 35% of the
virial radius, we find a temperature drop of 20% at 10 keV and 12% at 5 keV can
be ruled out at the 99% confidence level. A subsample of non-cooling flow
clusters shows that the condition of isothermality applies at very small radii
too, although cooling gas complicates this determination in the cooling flow
subsample. The colors predicted from the temperature profiles of a series of
hydrodynamical cluster simulations match the data very well, although they
cannot be used to discriminate among different cosmologies. An additional
result is that the color profiles show evidence for a central peak in
metallicity in low temperature clusters.Comment: 39 pages, 15 embedded Postscript figures, uses aaspp4.sty, accepted
for publication in Astrophysical Journa
Abnormal cingulum bundle development in autism: A probabilistic tractography study
There is now considerable evidence that white matter abnormalities play a role in the neurobiology of autism. Little research has been directed, however, at understanding (a) typical white matter development in autism and how this relates to neurocognitive impairments observed in the disorder. In this study we used probabilistic tractography to identify the cingulum bundle in 21 adolescents and young adults with Autism Spectrum Disorder (ASD), and 21 age- and sex-matched healthy volunteers. We investigated group differences in the relationships between age and fractional anisotropy, a putative measure of white matter integrity, within the cingulum bundle. Moreover, in a preliminary investigation, we examined the relationship between cingulum fractional anisotropy and executive functioning using the Behavior Rating Inventory of Executive Function (BRIEF). The ASD participants demonstrated significantly lower fractional anisotropy within the cingulum bundle compared to the typically developing volunteers. There was a significant group-by-age interaction such that the ASD group did not show the typical age-associated increases in fractional anisotropy observed among healthy individuals. Moreover, lower fractional anisotropy within the cingulum bundle was associated with worse BRIEF behavioral regulation index scores in the ASD group. The current findings implicate a dysregulation in cingulum bundle white matter development occurring in late adolescence and early adulthood in ASD, and suggest that greater disturbances in this trajectory are associated with executive dysfunction in ASD. (C) 2013 Elsevier Ireland Ltd. All rights reserved
New OH Zeeman measurements of magnetic field strengths in molecular clouds
We present the results of a new survey of 23 molecular clouds for the Zeeman
effect in OH undertaken with the ATNF Parkes 64-m radio telescope and the NRAO
Green Bank 43-m radio telescope. The Zeeman effect was clearly detected in the
cloud associated with the HII region RCW 38, with a field strength of 38+/-3
micro-Gauss, and possibly detected in a cloud associated with the HII region
RCW 57, with a field strength of -203+/-24 micro-Gauss. The remaining 21
measurements give formal upper limits to the magnetic field strength, with
typical 1-sigma sensitivities <20 micro-Gauss. For 22 of the molecular clouds
we are also able to determine thecolumn density of the gas in which we have
made a sensitive search for the Zeeman effect. We combine these results with
previous Zeeman studies of 29 molecular clouds, most of which were compiled by
Crutcher (1999), for a comparsion of theoretical models with the data. This
comparison implies that if the clouds can be modeled as initially spherical
with uniform magnetic fields and densities that evolve to their final
equilibrium state assuming flux-freezing then the typical cloud is magnetically
supercritical, as was found by Crutcher (1999). If the clouds can be modeled as
highly flattened sheets threaded by uniform perpendicular fields, then the
typical cloud is approximately magnetically critical, in agreement with Shu et
al. (1999), but only if the true values of the field for the non-detections are
close to the 3-sigma upper limits. If instead these values are significantly
lower (for example, similar to the 1-sigma limits), then the typical cloud is
generally magnetically supercritical.Comment: 39 pages, 7 figures. Accepted for publication in Ap
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