5,401 research outputs found
RXTE and BeppoSAX Observations of MCG -5-23-16: Reflection From Distant Cold Material
We examine the spectral variability of the Seyfert 1.9 galaxy MCG -5-23-16
using RXTE and BeppoSAX observations spanning 2 years from April 1996 to April
1998. During the first year the X-ray source brightens by a factor of ~25% on
timescales of days to months. During this time, the reprocessed continuum
emission seen with RXTE does not respond measurably to the continuum increase.
However, by the end of the second year during the BeppoSAX epoch the X-ray
source has faded again. This time, the reprocessed emission has also faded,
indicating that the reprocessed flux has responded to the continuum. If these
effects are caused by time delays due to the distance between the X-ray source
and the reprocessing region, we derive a light crossing time of between ~1
light day and ~1.5 light years. This corresponds to a distance of 0.001 pc to
0.55 pc, which implies that the reprocessed emission originates between 3x10^15
cm and 1.6x10^18 cm from the X-ray source. In other words, the reprocessing in
MCG -5-23-16 is not dominated by the inner regions of a standard accretion
disk.Comment: Accepted for publication in ApJ. 17 pages, 8 figure
Epitaxial Growth of an n-type Ferromagnetic Semiconductor CdCr2Se4 on GaAs(001) and GaP(001)
We report the epitaxial growth of CdCr2Se4, an n-type ferromagnetic
semiconductor, on both GaAs and GaP(001) substrates, and describe the
structural, magnetic and electronic properties. Magnetometry data confirm
ferromagnetic order with a Curie temperature of 130 K, as in the bulk material.
The magnetization exhibits hysteretic behavior with significant remanence, and
an in-plane easy axis with a coercive field of ~125 Oe. Temperature dependent
transport data show that the films are semiconducting in character and n-type
as grown, with room temperature carrier concentrations of n ~ 1 x 10^18 cm-3.Comment: 12 pages, 3 figure
Heat-transfer and pressure drop correlations for hydrogen and nitrogen flowing through tungsten wire mesh at temperatures to 5200 deg r
Heat transfer and friction pressure drop for forced convection of hydrogen and nitrogen through electrically heated tungsten wire mes
A 4500 deg R /2500 deg K/ flowing-gas facility
High temperature flowing gas heater consisting of four stages for heating gase
Nuclei of Double-Charm Hyperons
The ground states of double-charm hyperons form a spin 1/2 isospin 1/2
multiplet analogous to that of nucleons. Their main strong interaction may be
inferred directly from the corresponding nucleon-nucleon interaction by
multiplication of the interaction components by the appropriate fractional
difference between interaction strengths for pairs of light flavor quarks and
pairs of triplets, e.g. nucleons, of light flavor quarks. By construction of
the interaction between the recently discovered double-charm hyperons by this
method from several realistic nucleon-nucleon interaction models it is shown
that double-charm hyperons are likely to form bound (or possibly meta-stable)
states akin to the deuteron in the spin triplet state. Double beauty baryons
would form corresponding deeply bound states. Nucleons and double charm
(beauty) hyperons will also form bound states. The existence of hypernuclei
with double-charm and double-beauty hyperons, which are stable against the
strong decay, is very likely.Comment: Revised version. Conclusions unchange
Bound States of Heavy Flavor Hyperons
Several realistic phenomenological nucleon-nucleon interaction models are
employed to investigate the possibility of bound deuteron-like states of such
heavy flavor hyperons and nucleons, for which the interaction between the light
flavor quark components is expected to be the most significant interaction. The
results indicate that deuteron-like bound states are likely to form between
nucleons and the and charm hyperons as well as between
hyperons and double-charm hyperons. Bound states between two
hyperons are also likely. In the case of beauty hyperons the corresponding
states are likely to be deeply bound.Comment: 25 pages, 3 figures. Accepted Nucl. Phys.
Detector for Particle Surface Contamination
A system and method for detecting and quantizing particle fallout contamination particles which are collected on a transparent disk or other surface employs an optical detector, such as a CCD camera, to obtain images of the disk and a computer for analyzing the images. From the images, the computer detects, counts and sizes particles collected on the disk The computer also determines, through comparison to previously analyzed images, the particle fallout rate, and generates an alarm or other indication if the rate exceeds a maximum allowable value. The detector and disk are disposed in a housing having an aperture formed therein for defining the area on the surface of the disk which is exposed to the particle fallout. A light source is provided for evenly illuminating the disk. A first drive motor slowly rotates the disk to increase the amount of its surface area which is exposed through the aperture to the particle fallout. A second motor is also provided for incrementally scanning the disk in a radial direction back and forth over the camera so that the camera eventually obtains images of the entire surface of the disk which is exposed to the particle fallout
Baryon Magnetic Moments in Relativistic Quark Models
It is shown that the phenomenological description of the baryon magnetic
moments in the quark model carries over to the Poincar\'e covariant extension
of the model. This applies to all the three common forms of relativistic
kinematics with structureless constituent currents, which are covariant under
the corresponding kinematic subgroups. In instant and front form kinematics the
calculated magnetic moments depend strongly on the constituent masses, while in
point form kinematics the magnetic moments are fairly insensitive to both the
quark masses and the wave function model. The baryon charge radii and magnetic
moments are determined in the different forms of kinematics for the
light-flavor, strange and charm hyperons. The wave function model is determined
by a fit to the electromagnetic form factor of the proton.Comment: Six references and one paragraph adde
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