1,473,745 research outputs found
Expandable coating cocoon leak detection system
Development of system and materials for detecting leaks in cocoon protective coatings are discussed. Method of applying materials for leak determination is presented. Pressurization of system following application of materials will cause formation of bubble if leak exists
A search for thermal X-ray signatures in Gamma-Ray Bursts II: The Swift sample
In several gamma-ray bursts (GRBs) excess emission, in addition to the
standard synchrotron afterglow spectrum, has been discovered in the early time
X-ray observations. It has been proposed that this excess comes from black body
emission, which may be related to the shock break-out of a supernova in the
GRBs progenitor star. This hypothesis is supported by the discovery of excess
emission in several GRBs with an associated supernova. Using mock spectra we
show that it is only likely to detect such a component, similar to the one
proposed in GRB 101219B, at low redshift and in low absorption environments. We
also perform a systematic search for black body components in all the GRBs
observed with the Swift satellite and find six bursts (GRB 061021, 061110A,
081109, 090814A, 100621A and 110715A) with possible black body components.
Under the assumption that their excess emission is due to a black body
component we present radii, temperatures and luminosities of the emitting
components. We also show that detection of black body components only is
possible in a fraction of the Swift bursts.Comment: 11 pages, 8 figures, accepted for MNRA
Granular Flow in a Vertically Vibrating Hopper
The behavior of the flow of glass spheres in a vertically vibrating hopper is examined. A two-dimensional hopper is mounted on a shaker that provides sinusoidal, vertical vibrations. Both the frequency and amplitude of the vibrations are adjustable. Hopper discharge rates and flow patterns are measured as the acceleration amplitude of the vibrations is increased from 0 to 4g's. Comparisons are made with unvibrated hopper flows and with a two-dimensional discrete element simulation model
The Hubble Sequence in Groups: The Birth of the Early-Type Galaxies
The physical mechanisms and timescales that determine the morphological
signatures and the quenching of star formation of typical (~L*) elliptical
galaxies are not well understood. To address this issue, we have simulated the
formation of a group of galaxies with sufficient resolution to track the
evolution of gas and stars inside about a dozen galaxy group members over
cosmic history. Galaxy groups, which harbor many elliptical galaxies in the
universe, are a particularly promising environment to investigate morphological
transformation and star formation quenching, due to their high galaxy density,
their relatively low velocity dispersion, and the presence of a hot intragroup
medium. Our simulation reproduces galaxies with different Hubble morphologies
and, consequently, enables us to study when and where the morphological
transformation of galaxies takes place. The simulation does not include
feedback from active galactic nuclei showing that it is not an essential
ingredient for producing quiescent, red elliptical galaxies in galaxy groups.
Ellipticals form, as suspected, through galaxy mergers. In contrast with what
has often been speculated, however, these mergers occur at z>1, before the
merging progenitors enter the virial radius of the group and before the group
is fully assembled. The simulation also shows that quenching of star formation
in the still star-forming elliptical galaxies lags behind their morphological
transformation, but, once started, is taking less than a billion years to
complete. As long envisaged the star formation quenching happens as the
galaxies approach and enter the finally assembled group, due to quenching of
gas accretion and (to a lesser degree) stripping. A similar sort is followed by
unmerged, disk galaxies, which, as they join the group, are turned into the
red-and-dead disks that abound in these environments.Comment: 12 pages, 12 Figures, 1 Table, accepted for publication in AP
Single-channel digital command-detection system
System, fabricated of highly-reliable digital logic elements, operates on binary pulse-code-modulated signals and derives internal synchronization from data signal. All-digital implementation of detector develops synchronization from data signal by computer cross-correlation of command modulation signal with its expected forms in sequence and adjusts detector phases in accordance with correlation peaks
Simulation and theory of fluid demixing and interfacial tension of mixtures of colloids and non-ideal polymers
An extension of the Asakura-Oosawa-Vrij model of hard sphere colloids and
non-adsorbing polymers, that takes polymer non-ideality into account through a
repulsive stepfunction pair potential between polymers, is studied with grand
canonical Monte Carlo simulations and density functional theory. Simulation
results validate previous theoretical findings for the shift of the bulk fluid
demixing binodal upon increasing strength of polymer-polymer repulsion,
promoting the tendency to mix. For increasing strength of the polymer-polymer
repulsion, simulation and theory consistently predict the interfacial tension
of the free colloidal liquid-gas interface to decrease significantly for fixed
colloid density difference in the coexisting phases, and to increase for fixed
polymer reservoir packing fraction.Comment: 10 pages, 4 figure
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