6,294 research outputs found
Tool pre-tensions covers prior to lacing
In securing a bulky object in a storage compartment, a cinching or tightening tool is used to draw two opposing cover halves together at a predetermined tension to permit quick lacing to retain the stored object. This tool is also useful in fabrication industries to draw components together during assembly or treating
Particle acceleration in solar flares
The most direct signatures of particle acceleration in flares are energetic particles detected in interplanetary space and in the Earth atmosphere, and gamma rays, neutrons, hard X-rays, and radio emissions produced by the energetic particles in the solar atmosphere. The stochastic and shock acceleration theories in flares are reviewed and the implications of observations on particle energy spectra, particle confinement and escape, multiple acceleration phases, particle anistropies, and solar atmospheric abundances are discussed
Detection of ocean color changes from high altitudes
The detection of ocean color changes, thought to be due to chlorophyll concentrations and gelbstoffe variations, is attempted from high altitude (11.3km) and low altitude (0.3km). The atmospheric back scattering is shown to reduce contrast, but not sufficiently to obscure color change detection at high altitudes
Morse matchings on polytopes
We show how to construct homology bases for certain CW complexes in terms of
discrete Morse theory and cellular homology. We apply this technique to study
certain subcomplexes of the half cube polytope studied in previous works. This
involves constructing explicit complete acyclic Morse matchings on the face
lattice of the half cube; this procedure may be of independent interest for
other highly symmetric polytopes
Viscous Kelvin-Helmholtz instabilities in highly ionised plasmas
Transport coefficients in highly ionised plasmas like the intra-cluster
medium (ICM) are still ill-constrained. They influence various processes, among
them the mixing at shear flow interfaces due to the Kelvin-Helmholtz
instability (KHI). The observed structure of potential mixing layers can be
used to infer the transport coefficients, but the data interpretation requires
a detailed knowledge of the long-term evolution of the KHI under different
conditions. Here we present the first systematic numerical study of the effect
of constant and temperature-dependent isotropic viscosity over the full range
of possible values. We show that moderate viscosities slow down the growth of
the KHI and reduce the height of the KHI rolls and their rolling-up.
Viscosities above a critical value suppress the KHI. The effect can be
quantified in terms of the Reynolds number Re = U{\lambda}/{\nu}, where U is
the shear velocity, {\lambda} the perturbation length, and {\nu} the kinematic
viscosity. We derive the critical Re for constant and temperature dependent,
Spitzer-like viscosities, an empirical relation for the viscous KHI growth time
as a function of Re and density contrast, and describe special behaviours for
Spitzer-like viscosities and high density contrasts. Finally, we briefly
discuss several astrophysical situations where the viscous KHI could play a
role, i.e., sloshing cold fronts, gas stripping from galaxies, buoyant
cavities, ICM turbulence, and high velocity clouds.Comment: Accepted by MNRAS. 22 pages, 21 figure
The Disturbed 17 keV Cluster Associated with the Radio Galaxy 3C 438
We present results from a {\em Chandra} observation of the cluster gas
associated with the FR II radio galaxy 3C 438. This radio galaxy is embedded
within a massive cluster with gas temperature 17 keV and bolometric
luminosity of 6 ergs s. It is unclear if this high
temperature represents the gravitational mass of the cluster, or if this is an
already high ( 11 keV) temperature cluster that has been heated
transiently. We detect a surface brightness discontinuity in the gas that
extends 600 kpc through the cluster. The radio galaxy 3C 438 is too small
(110 kpc across) and too weak to have created this large disturbance in
the gas. The discontinuity must be the result of either an extremely powerful
nuclear outburst or the major merger of two massive clusters. If the observed
features are the result of a nuclear outburst, it must be from an earlier epoch
of unusually energetic nuclear activity. However, the energy required
( ergs) to move the gas on the observed spatial scales strongly
supports the merger hypothesis. In either scenario, this is one of the most
extreme events in the local Universe.Comment: 13 pages, 4 figures, 1 table - accepted for publication in the
Astrophysical Journal Letter
Interstellar extinction and the distribution of stellar populations in the direction of the ultra-deep Chandra Galactic field
We studied the stellar population in the central 6.6x6.6arcmin,region of the
ultra-deep (1Msec) Chandra Galactic field - the "Chandra bulge field" (CBF)
approximately 1.5 degrees away from the Galactic Center - using the Hubble
Space Telescope ACS/WFC blue (F435W) and red (F625W) images. We mainly focus on
the behavior of red clump giants - a distinct stellar population, which is
known to have an essentially constant intrinsic luminosity and color. By
studying the variation in the position of the red clump giants on a spatially
resolved color-magnitude diagram, we confirm the anomalous total-to-selective
extinction ratio, as reported in previous work for other Galactic bulge fields.
We show that the interstellar extinction in this area is = 4 on
average, but varies significantly between ~3-5 on angular scales as small as 1
arcminute. Using the distribution of red clump giants in an
extinction-corrected color-magnitude diagram, we constrain the shape of a
stellar-mass distribution model in the direction of this ultra-deep Chandra
field, which will be used in a future analysis of the population of X-ray
sources. We also show that the adopted model for the stellar density
distribution predicts an infrared surface brightness in the direction of the
"Chandra bulge field" in good agreement (i.e. within ~15%) with the actual
measurements derived from the Spitzer/IRAC observations.Comment: 9 pages, 9 figures. Accepted for publication in A&
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