13,177 research outputs found
H2 Formation on Interstellar Grains in Different Physical Regimes
An analysis of the kinetics of H2 formation on interstellar dust grains is
presented using rate equations. It is shown that semi-empirical expressions
that appeared in the literature represent two different physical regimes. In
particular, it is shown that the expression given by Hollenbach, Werner and
Salpeter [ApJ, 163, 165 (1971)] applies when high flux, or high mobility, of H
atoms on the surface of a grain, makes it very unlikely that H atoms evaporate
before they meet each other and recombine. The expression of Pirronello et al.\
[ApJ, 483, L131 (1997)] -- deduced on the basis of accurate measurements on
realistic dust analogue -- applies to the opposite regime (low coverage and low
mobility). The implications of this analysis for the understanding of the
processes dominating in the Interstellar Medium are discussed.Comment: 4 pages, MN styl
Investigation of light scattering in highly reflecting pigmented coatings. Volume 2 - Classical investigations, theoretical and experimental Final report, 1 May 30 Sep. 1966
Light scattering theory applied to particle arrays to explain scattering in highly reflecting paint coating
When hot water freezes before cold
I suggest that the origin of the Mpemba effect (the freezing of hot water
before cold) is freezing-point depression by solutes, either gaseous or solid,
whose solubility decreases with increasing temperature so that they are removed
when water is heated. They are concentrated ahead of the freezing front by zone
refining in water that has not been heated, reduce the temperature of the
freezing front, and thereby reduce the temperature gradient and heat flux,
slowing the progress of the front. I present a simple calculation of this
effect, and suggest experiments to test this hypothesis.Comment: 7 pages, 1 figur
Investigation of light scattering in high reflecting pigmented coatings quarterly report, 1 may - 1 aug. 1965
Application of light scattering theories to highly pigmented coating
Plasmarings as dual black rings
We construct solutions to the relativistic Navier-Stokes equations that
describe the long wavelength collective dynamics of the deconfined plasma phase
of N=4 Yang Mills theory compactified down to d=3 on a Scherk-Schwarz circle
and higher dimensional generalisations. Our solutions are stationary, axially
symmetric spinning balls and rings of plasma. These solutions, which are dual
to (yet to be constructed) rotating black holes and black rings in
Scherk-Schwarz compactified AdS(5) and AdS(6), and have properties that are
qualitatively similar to those of black holes and black rings in flat five
dimensional supergravity.Comment: 40 pages, 40 figures. (v2) Correction to black brane equation of
state, additional reference
Implications of the Visible and X-Ray Counterparts to GRB970228
The gamma-ray burst source GRB970228 has been observed after a delay of 8--12
hours in X-rays and after one day in visible and near infrared light. This
marks the first detection of emission at lower frequencies following the
gamma-ray observation of a GRB and the first detection of any visible
counterpart to a GRB. We consider possible delayed visible and X-ray emission
mechanisms, and conclude that the intrinsic gamma-ray activity continued at a
much reduced intensity for at least a day. There are hints of such continued
activity in other GRB, and future observations can decide if this is true of
GRB in general. The observed multi-band spectrum of GRB970228 agrees with the
predictions of relativistic shock theory when the flux is integrated over a
time longer than that required for a radiating electron to lose its energy.Comment: 5 pp., tex, 1 figur
A Survey for Transient Astronomical Radio Emission at 611 MHz
We have constructed and operated the Survey for Transient Astronomical Radio
Emission (STARE) to detect transient astronomical radio emission at 611 MHz
originating from the sky over the northeastern United States. The system is
sensitive to transient events on timescales of 0.125 s to a few minutes, with a
typical zenith flux density detection threshold of approximately 27 kJy. During
18 months of around-the-clock observing with three geographically separated
instruments, we detected a total of 4,318,486 radio bursts. 99.9% of these
events were rejected as locally generated interference, determined by requiring
the simultaneous observation of an event at all three sites for it to be
identified as having an astronomical origin. The remaining 3,898 events have
been found to be associated with 99 solar radio bursts. These results
demonstrate the remarkably effective RFI rejection achieved by a coincidence
technique using precision timing (such as GPS clocks) at geographically
separated sites. The non-detection of extra-solar bursting or flaring radio
sources has improved the flux density sensitivity and timescale sensitivity
limits set by several similar experiments in the 1970s. We discuss the
consequences of these limits for the immediate solar neighborhood and the
discovery of previously unknown classes of sources. We also discuss other
possible uses for the large collection of 611 MHz monitoring data assembled by
STARE.Comment: 24 pages, 6 figures; to appear in PAS
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