4,957 research outputs found
Real-Time Operating System/360
RTOS has a cost savings advantage for real-time applications, such as those with random inputs requiring a flexible data routing facility, display systems simplified by a device independent interface language, and complex applications needing added storage protection and data queuing
Cool Companions to White Dwarf Stars from the Two Micron All Sky Survey All Sky Data Release
We present the culmination of our near-infrared survey of the optically spectroscopically identified white dwarf stars from the McCook and Sion catalog, conducted using photometric data from the Two Micron All Sky Survey final All Sky Data Release. The color selection technique, which identifies candidate binaries containing a white dwarf and a low-mass stellar (or substellar) companion via their distinctive locus in the near-infrared color-color diagram, is demonstrated to be simple to apply and to yield candidates with a high rate of subsequent confirmation. We recover 105 confirmed binaries, and identify 27 firm candidates (19 of which are new to this work) and 21 tentative candidates (17 of which are new to this work) from the 2MASS data. Only a small number of candidates from our survey have likely companion spectral types later than M5, none of which is an obvious L-type (i.e., potential brown dwarf) companion. Only one previously known white dwarf + brown dwarf binary is detected. This result is discussed in the context of the 2MASS detection limits, as well as other recent observational surveys that suggest a very low rate of formation (or survival) for binary stars with extreme mass ratios
VLA Observations of the "Eye of the Tornado"- the High Velocity \HII Region G357.63-0.06
The unusual supernova remnant candidate G357.7-0.1 and the compact source
G357.63-0.06 have been observed with the Very Large Array at 1.4 and 8.3 GHz.
The H92 line (8.3 GHz) was detected from the compact source with a
surprising velocity of about -210 km/s indicating that this source is an \HII
region, is most likely located at the Galactic center, and is unrelated to the
SNR. The \HI absorption line (1.4 GHz) data toward these sources supports this
picture and suggests that G357.7-0.1 lies farther away than the Galactic
center.Comment: Latex, 14 pages including 4 figures. Accepted to A
Can the United States Afford a “No-Fault” System of Compensation for Medical Injury?
One of the key issues separating US critics of a no-fault alternative to the tort system for compensating victims of medical injury from supporters is its anticipated cost. Results from a study are presented that estimate the costs of a no-fault system, one that is similar to the system now in operation in Sweden, within the context of the US health care system
Vortex Formation by Interference of Multiple Trapped Bose-Einstein Condensates
We report observations of vortex formation as a result of merging together
multiple Rb Bose-Einstein condensates (BECs) in a confining potential.
In this experiment, a trapping potential is partitioned into three sections by
a barrier, enabling the simultaneous formation of three independent,
uncorrelated condensates. The three condensates then merge together into one
BEC, either by removal of the barrier, or during the final stages of
evaporative cooling if the barrier energy is low enough; both processes can
naturally produce vortices within the trapped BEC. We interpret the vortex
formation mechanism as originating in interference between the initially
independent condensates, with indeterminate relative phases between the three
initial condensates and the condensate merging rate playing critical roles in
the probability of observing vortices in the final, single BEC.Comment: 5 pages, 3 figure
The Radio Evolution of SN 2001gd
We present the results of observations of the radio emission from Supernova
2001gd in NGC 5033 from 2002 February 8 through 2006 September 25. The data
were obtained using the Very Large Array at wavelengths of 1.3 cm (22.4 GHz), 2
cm (14.9 GHz), 3.6 cm (8.4 GHz), 6 cm (4.9 GHz), and 20 cm (1.5 GHz), with one
upper limit at 90 cm (0.3 GHz). In addition, one detection has been provided by
the Giant Metrewave Radio Telescope at 21 cm (1.4 GHz). SN 2001gd was
discovered in the optical well past maximum light, so that it was not possible
to obtain many of the early radio "turn-on" measurements which are important
for estimating the local circumstellar medium (CSM) properties. Only at 20 cm
were turn-on data available. However, our analysis and fitting of the radio
light curves, and the assumption that the Type IIb SN 2001gd resembles the much
better studied Type IIb SN 1993J, enables us to describe the radio evolution as
being very regular through day ~550 and consistent with a nonthermal-emitting
model with a thermal absorbing CSM. The presence of synchrotron-self absorption
(SSA) at early times is implied by the data, but determination of the exact
relationship between the SSA component from the emitting region and the
free-free absorption component from the CSM is not possible as there are
insufficient early measurements to distinguish between models. After day ~550,
the radio emission exhibits a dramatically steeper decline rate which, assuming
similarity to SN 1993J, can be described as an exponential decrease with an
e-folding time of 500 days. We interpret this abrupt change in the radio flux
density decline rate as implying a transition of the shock front into a more
tenuous region of circumstellar material. A similar change in radio evolution
has been seen earlier in other SNe such as SN 1988Z, SN 1980K, and SN 1993J.Comment: 3 tables, 2 figures, To appear in the Astrophysical Journa
A New Test of the Einstein Equivalence Principle and the Isotropy of Space
Recent research has established that nonsymmetric gravitation theories like
Moffat's NGT predict that a gravitational field singles out an orthogonal pair
of polarization states of light that propagate with different phase velocities.
We show that a much wider class of nonmetric theories encompassed by the formalism predict such violations of the Einstein equivalence principle.
This gravity-induced birefringence of space implies that propagation through a
gravitational field can alter the polarization of light. We use data from
polarization measurements of extragalactic sources to constrain birefringence
induced by the field of the Galaxy. Our new constraint is times sharper
than previous ones.Comment: 21 pages, Latex, 3 Postscript figure
OH Zeeman Magnetic Field Detections Toward Five Supernova Remnants Using the VLA
We have observed the OH (1720 MHz) line in five galactic SNRs with the VLA to
measure their magnetic field strengths using the Zeeman effect. We detected all
12 of the bright ( mJy) OH (1720 MHz) masers previously detected
by Frail et al. (1996) and Green et al. (1997) and measured significant
magnetic fields (i.e. ) in ten of them. Assuming that the
``thermal'' Zeeman equation can be used to estimate for OH
masers, our estimated fields range from 0.2 to 2 mG. These magnetic field
strengths are consistent with the hypothesis that ambient molecular cloud
magnetic fields are compressed via the SNR shock to the observed values.
Magnetic fields of this magnitude exert a considerable influence on the
properties of the cloud with the magnetic pressures ( erg
cm) exceeding the pressure in the ISM or even the thermal pressure of
the hot gas interior to the remnant. This study brings the number of galactic
SNRs with OH (1720 MHz) Zeeman detections to ten.Comment: 23 pages, 14 figures, accepted to ApJ, for higher resolution images
of Figs 4,11, and 12 see http://www.pa.uky.edu/~brogan/brog_publ.htm
Multi-Wavelength Properties of the Type IIb SN 2008ax
We present the UV, optical, X-ray, and radio properties of the Type IIb SN
2008ax discovered in NGC 4490. The observations in the UV are one of the
earliest of a Type IIb supernova (SN). On approximately day four after the
explosion, a dramatic upturn in the u and uvw1 (lambda_c = 2600 Angstroms)
light curves occurred after an initial rapid decline which is attributed to
adiabatic cooling after the initial shock breakout. This rapid decline and
upturn is reminiscent of the Type IIb SN 1993J on day six after the explosion.
Optical/near-IR spectra taken around the peak reveal prominent H-alpha, HeI,
and CaII absorption lines. A fading X-ray source is also located at the
position of SN 2008ax, implying an interaction of the SN shock with the
surrounding circumstellar material and a mass-loss rate of the progenitor of
M_dot = (9+/-3)x10^-6 solar masses per year. The unusual time evolution (14
days) of the 6 cm peak radio luminosity provides further evidence that the
mass-loss rate is low. Combining the UV, optical, X-ray, and radio data with
models of helium exploding stars implies the progenitor of SN 2008ax was an
unmixed star in an interacting-binary. Modeling of the SN light curve suggests
a kinetic energy (E_k) of 0.5x10^51 ergs, an ejecta mass (M_ej) of 2.9 solar
masses, and a nickel mass (M_Ni) of 0.06 solar masses.Comment: Accepted to ApJ Letters, 14 pages, 3 figures, 2 table
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