1,063 research outputs found
Friction and Surface Damage of Several Corrosion-resistant Materials
Friction and surface damage of several materials that are resistant to corrosion due to liquid metals was studied in air. The values of kinetic friction coefficient at low sliding velocities and photomicrographs of surface damage were obtained. Appreciable surface damage was evident for all materials tested. The friction coefficients for the combinations of steel, stainless steel, and monel sliding against steel, stainless steel, nickel, Iconel, and Nichrome ranged from 0.55 for the monel-Inconel combination to 0.97 for the stainless-steel-nickel combination; for steel, stainless steel, monel, and tungsten carbide against zirconium, the friction coefficient was approximately 0.47. Lower coefficients of friction (0.20 to 0.60) and negligible surface failure at light loads were obtained with tungsten carbide when used in combination with various plate materials
Probable Gravitational Microlensing towards the Galatic Bulge
The MACHO project carries out regular photometric monitoring of millions of
stars in the Magellanic Clouds and Galactic Bulge, to search for very rare
gravitational microlensing events due to compact objects in the galactic halo
and disk. A preliminary analysis of one field in the Galactic Bulge, containing
{} stars observed for 190 days, reveals four stars which show
clear evidence for brightenings which are time-symmetric, achromatic in our two
passbands, and have shapes consistent with gravitational microlensing. This is
significantly higher than the event expected from microlensing by
known stars in the disk. If all four events are due to microlensing, a 95\%
confidence lower limit on the optical depth towards our bulge field is , and a ``best fit" value is ,where is the detection efficiency of the
experiment, and . If the true optical depth is close to the
``best fit" value, possible explanations include a ``maximal" disk which
accounts for most of the galactic circular velocity at the solar radius, a halo
which is centrally concentrated, or bulge-bulge microlensing.Comment: submitted to Astrophysical Journal Letters, 10 pages text as
uuencoded compressed PostScript, 5 figures and paper also available via
anonymous ftp from merlin.anu.edu.au in /pub/kcf/mach
A Spectroscopic and Photometric Study of Short-Timescale Variability in NGC5548
Results of a ground-based optical monitoring campaign on NGC5548 in June 1998
are presented. The broad-band fluxes (U,B,V), and the spectrophotometric
optical continuum flux F_lambda(5100 A) monotonically decreased in flux while
the broad-band R and I fluxes and the integrated emission-line fluxes of Halpha
and Hbeta remained constant to within 5%. On June 22, a short continuum flare
was detected in the broad band fluxes. It had an amplitude of about ~18% and it
lasted only ~90 min. The broad band fluxes and the optical continuum
F_lambda(5100 A) appear to vary simultaneously with the EUV variations. No
reliable delay was detected for the broad optical emission lines in response to
the EUVE variations. Narrow Hbeta emission features predicted as a signature of
an accretion disk were not detected during this campaign. However, there is
marginal evidence for a faint feature at lambda = 4962 A with FWHM=~6 A
redshifted by Delta v = 1100 km/s with respect to Hbeta_narrow.Comment: 12 pages, 7 figures, accepted for publishing in A&
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