3,559 research outputs found
Cluster mergers, core oscillations, and cold fronts
We use numerical simulations with hydrodynamics to demonstrate that a class
of cold fronts in galaxy clusters can be attributed to oscillations of the dark
matter distribution. The oscillations are initiated by the off-axis passage of
a low-mass substructure. From the simulations, we derive three observable
morphological features indicative of oscillations: 1) The existence of
compressed isophotes; 2) The regions of compression must be alternate (opposite
and staggered) and lie on an axis passing through the center of the cluster; 3)
The gradient of each compression region must pass through the center of the
cluster. Four of six clusters reported in the literature to have cold fronts
have morphologies consistent with the presence of oscillations. The clusters
with oscillations are A496, A1795, A2142, and RX J1720.1+2638. Galaxy clusters
A2256 and A3667 are not consistent so the cold fronts are interpreted as group
remnants. The oscillations may be able to provide sufficient energy to solve
the cooling-flow problem and, importantly, provide it over an extended
duration.Comment: Submitted to ApJ. 11 pages, 9 figure
Recommendations to the formulation of EU regulation 2092/91 on livestock production
Within the SAFO network, the workpackage on standard development has focussed on the topic, on how and to what degree the EU-Regulations con-tribute to the objective of a high status of anima health and food safety in organic livestock production. Results and conclusions from the discussions at 5 SAFO workshops are presented
Fluctuation spectrum of quasispherical membranes with force-dipole activity
The fluctuation spectrum of a quasi-spherical vesicle with active membrane
proteins is calculated. The activity of the proteins is modeled as the proteins
pushing on their surroundings giving rise to non-local force distributions.
Both the contributions from the thermal fluctuations of the active protein
densities and the temporal noise in the individual active force distributions
of the proteins are taken into account. The noise in the individual force
distributions is found to become significant at short wavelengths.Comment: 9 pages, 2 figures, minor changes and addition
New Velocity Distribution in the Context of the Eddington Theory
Exotic dark matter together with the vacuum energy (associated with the
cosmological constant) seem to dominate the Universe. Thus its direct detection
is central to particle physics and cosmology. Supersymmetry provides a natural
dark matter candidate, the lightest supersymmetric particle (LSP). One
essential ingredient in obtaining the direct detection rates is the density and
velocity distribution of the LSP. The detection rate is proportional to this
density in our vicinity. Furthermore, since this rate is expected to be very
low, one should explore the two characteristic signatures of the process,
namely the modulation effect, i.e. the dependence of the event rate on the
Earth's motion and the correlation of the directional rate with the motion of
the sun. Both of these crucially depend on the LSP velocity distribution. In
the present paper we study simultaneously density profiles and velocity
distributions based on the Eddington theory.Comment: 40 LaTex pages, 19 figures and one table. The previous version was
expanded to include new numerical solutions to Poisson's equation. Sheduled
to appear in vol. 588, ApJ, May 1, 300
An X-ray Survey of Galaxies in Pairs
Results are reported from the first survey of X-ray emission from galaxies in
pairs. The sample consists of fifty-two pairs of galaxies from the Catalog of
Paired Galaxies Karachentsev (1972) whose coordinates overlap ROSAT Position
Sensitive Proportional Counter pointed observations. The mean observed log l_x
for early-type pairs is 41.35 +/-0.21 while the mean log l_x predicted using
the l_x-l_b relationship for isolated early-type galaxies is 42.10 +/-0.19.
With 95% confidence, the galaxies in pairs are underluminous in the X-ray,
compared to isolated galaxies, for the same l_b. A significant fraction of the
mixed pair sample also appear similarly underluminous. A spatial analysis shows
that the X-ray emission from pairs of both types typically has an extent of ~10
- 50 kpc, much smaller than group intergalactic medium and thus likely
originates from the galaxies. CPG 564, the most X-ray luminous early-type pair,
4.7x10^42 ergs/sec, is an exception. The extent of it's X-ray emission, >169
kpc, and HWHM, ~80 kpc, is comparable to that expected from an intergalactic
medium. The sample shows only a weak correlation, ~81% confidence, between l_x
and l_b, presumably due to variations in gas content within the galaxies. No
correlation between l_x and the pair velocity difference, separation, or
far-infrared luminosity is found though the detection rate is low, 22%.Comment: 40 pages, 6 jpg figures, ApJ (in press
Mothers of Sons with Substance Use Disorders: A Grounded Theory Approach Revealing Maternal Expectations and Three Stages of Change
Addiction problems in a family present challenges in coping with the addicted family member\u27s behaviors are often described in terms of the psychopathology of the interactions of the family members. The present article describes a qualitative study of the lived experiences of mothers whose male children have struggled or currently are struggling with chemical dependence. Our overall aim in the study was to explore critical stages or events in the experiences of these mothers relevant to their chemically dependent sons. As such, our research question was: What are the lived experiences of mothers of substance abusing sons who are either in recovery or are still using substances? Results of the interviews of nine mothers indicated that regardless of age, ethnicity, social status, education, or career, they experienced a process highlighted by maternal expectations and consisting of three stages: (a) the pre-addiction stage in which mother and son did not experience abnormal relational stress or conflict, (b) the addiction stage in which mother and son experienced extreme relational stress and conflict, and (c) the mother\u27s recovery stage in which the mother experienced a confusion in her relationship with her son and his addiction leading to her own recovery and wellness
Disorder mediated splitting of the cyclotron resonance in two-dimensional electron systems
We perform a direct study of the magnitude of the anomalous splitting in the
cyclotron resonance (CR) of a two-dimensional electron system (2DES) as a
function of sample disorder. In a series of AlGaAs/GaAs quantum wells,
identical except for a range of carbon doping in the well, we find the CR
splitting to vanish at high sample mobilities but to increase dramatically with
increasing impurity density and electron scattering rates. This observation
lends strong support to the conjecture that the non-zero wavevector, roton-like
minimum in the dispersion of 2D magnetoplasmons comes into resonance with the
CR, with the two modes being coupled via disorder.Comment: accepted to PRB Rapid Com
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