6,623 research outputs found
Handbook of cryogenic data in graphic form
Handbook of Cryogenic Data is written in graphic form and concentrates extensive data on common materials of construction and properties of fluids frequently encountered in designing cryogenic systems. All data are presented in the British system of units
Production of Hypervelocity Stars through Encounters with Stellar-Mass Black Holes in the Galactic Centre
Stars within 0.1 pc of the supermassive black hole Sgr A* at the Galactic
centre are expected to encounter a cluster of stellar-mass black holes (BHs)
that have segregated to that region. Some of these stars will scatter off an
orbiting BH and be kicked out of the Galactic centre with velocities up to
~2000 km/s. We calculate the resulting ejection rate of hypervelocity stars
(HVSs) by this process under a variety of assumptions, and find it to be
comparable to the tidal disruption rate of binary stars by Sgr A*, first
discussed by Hills (1988). Under some conditions, this novel process is
sufficient to account for all of the hypervelocity B-stars observed in the
halo, and may dominate the production rate of all HVSs with lifetimes much less
than the relaxation time-scale at a distance ~2 pc from Sgr A* (>~ 2 Gyr).
Since HVSs are produced by at least two unavoidable processes, the statistics
of HVSs could reveal bimodal velocity and mass distributions, and can constrain
the distribution of BHs and stars in the innermost 0.1 pc around Sgr A*.Comment: 8 pages, 3 figures. Accepted for publication in MNRAS. Some major
changes to text, however conclusions remain the sam
Study made of pneumatic high pressure piping materials /10,000 psi/
Evaluations of five types of steel for use in high pressure pneumatic piping systems include tests for impact strength, tensile and yield strengths, elongation and reduction in area, field weldability, and cost. One type, AISI 4615, was selected as most advantageous for extensive use in future flight vehicles
Cosmological production of H_2 before the formation of the first galaxies
Previous calculations of the pregalactic chemistry have found that a small
amount of H_2, x[H_2]=n[H_2]/n[H] = 2.6e-6, is produced catalytically through
the H^-, H_2^+, and HeH^+ mechanisms. We revisit this standard calculation
taking into account the effects of the nonthermal radiation background produced
by cosmic hydrogen recombination, which is particularly effective at destroying
H^- via photodetachment. We also take into consideration the non-equilibrium
level populations of H_2^+, which occur since transitions among the
rotational-vibrational levels are slow compared to photodissociation. The new
calculation predicts a final H_2 abundance of x[H_2] = 6e-7 for the standard
cosmology. This production is due almost entirely to the H^- mechanism, with ~1
per cent coming from HeH^+ and ~0.004 per cent from H_2^+. We evaluate the
heating of the diffuse pregalactic gas from the chemical reactions that produce
H_2 and from rotational transitions in H_2, and find them to be negligible.Comment: 13 pages, 5 figures, MNRAS submitte
- …