4,618 research outputs found
Cavitation in liquid cryogens
Cavitation in liquid hydrogen and nitrogen flowing in transparent plastic ventur
Incipient and developed cavitation in liquid cryogens
Cavitational flow of liquid nitrogen and liquid hydrogen in Venturi tub
Thermodynamic depressions within cavities and cavitation inception in liquid hydrogen and liquid nitrogen Final report, 15 Jul. 1964 - 15 Dec. 1967
Thermodynamic depressions within cavities and cavitation inception in liquid hydrogen and nitrogen in transparent plastic venturi tube
Cavitation inception in liquid nitrogen and liquid hydrogen flowing in a venturi Interim report, 15 Jul. 1964 - 15 Jul. 1967
Cavitation characteristics of liquid hydrogen, and liquid nitrogen flow in plastic ventur
X-ray Studies of Two Neutron Stars in 47 Tucanae: Toward Constraints on the Equation of State
We report spectral and variability analysis of two quiescent low mass X-ray
binaries (X5 and X7, previously detected with the ROSAT HRI) in a Chandra
ACIS-I observation of the globular cluster 47 Tuc. X5 demonstrates sharp
eclipses with an 8.666+-0.01 hr period, as well as dips showing an increased
N_H column. The thermal spectra of X5 and X7 are well-modeled by unmagnetized
hydrogen atmospheres of hot neutron stars. No hard power law component is
required. A possible edge or absorption feature is identified near 0.64 keV,
perhaps an OV edge from a hot wind. Spectral fits imply that X7 is
significantly more massive than the canonical 1.4 \Msun neutron star mass, with
M>1.8 \Msun for a radius range of 9-14 km, while X5's spectrum is consistent
with a neutron star of mass 1.4 \Msun for the same radius range. Alternatively,
if much of the X-ray luminosity is due to continuing accretion onto the neutron
star surface, the feature may be the 0.87 keV rest-frame absorption complex (O
VIII & other metal lines) intrinsic to the neutron star atmosphere, and a mass
of 1.4 \Msun for X7 may be allowed.Comment: 16 pages, 7 figures, accepted by Ap
Response of river-dominated delta channel networks to permanent changes in river discharge
Using numerical experiments, we investigate how river-dominated delta channel networks are likely to respond to changes in river discharge predicted to occur over the next century as a result of environmental change. Our results show for a change in discharge up to 60% of the initial value, a decrease results in distributary abandonment in the delta, whereas an increase does not significantly affect the network. However, an increase in discharge beyond a threshold of 60% results in channel creation and an increase in the density of the distributary network. This behavior is predicted by an analysis of an individual bifurcation subject to asymmetric water surface slopes in the bifurcate arms. Given that discharge in most river basins will change by less than 50% in the next century, our results suggest that deltas in areas of increased drought will be more likely to experience significant rearrangement of the delta channel network. Copyright 2010 by the American Geophysical Union
Hypergraphic LP Relaxations for Steiner Trees
We investigate hypergraphic LP relaxations for the Steiner tree problem,
primarily the partition LP relaxation introduced by Koenemann et al. [Math.
Programming, 2009]. Specifically, we are interested in proving upper bounds on
the integrality gap of this LP, and studying its relation to other linear
relaxations. Our results are the following. Structural results: We extend the
technique of uncrossing, usually applied to families of sets, to families of
partitions. As a consequence we show that any basic feasible solution to the
partition LP formulation has sparse support. Although the number of variables
could be exponential, the number of positive variables is at most the number of
terminals. Relations with other relaxations: We show the equivalence of the
partition LP relaxation with other known hypergraphic relaxations. We also show
that these hypergraphic relaxations are equivalent to the well studied
bidirected cut relaxation, if the instance is quasibipartite. Integrality gap
upper bounds: We show an upper bound of sqrt(3) ~ 1.729 on the integrality gap
of these hypergraph relaxations in general graphs. In the special case of
uniformly quasibipartite instances, we show an improved upper bound of 73/60 ~
1.216. By our equivalence theorem, the latter result implies an improved upper
bound for the bidirected cut relaxation as well.Comment: Revised full version; a shorter version will appear at IPCO 2010
Imaginary in all directions: an elegant formulation of special relativity and classical electrodynamics
A suitable parameterization of space-time in terms of one complex and three
quaternionic imaginary units allows Lorentz transformations to be implemented
as multiplication by complex-quaternionic numbers rather than matrices.
Maxwell's equations reduce to a single equation.Comment: 8 page
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