4,928 research outputs found
A robust method for measuring the Hubble parameter
We obtain a robust, non-parametric, estimate of the Hubble constant from
galaxy linear diameters calibrated using HST Cepheid distances. Our method is
independent of the parametric form of the diameter function and the spatial
distribution of galaxies and is insensitive to Malmquist bias. We include
information on the galaxy rotation velocities; unlike Tully-Fisher, however, we
retain a fully non-parametric treatment. We find km/s/Mpc,
somewhat larger than previous results using galaxy diameters.Comment: 4 pages, 1 figure, Cosmic Flows Workshop, Victoria B.C. Canada, July
1999, ed. S. Courteau, M. Strauss & J. Willick, ASP conf. serie
Microlensing of Extended Stellar Sources
We investigate the feasibility of reconstructing the radial intensity profile
of extended stellar sources by inverting their microlensed light curves. Using
a simple, linear, limb darkening law as an illustration, we show that the
intensity profile can be accurately determined, at least over the outer part of
the stellar disc, with realistic light curve sampling and photometric errors.
The principal requirement is that the impact parameter of the lens be less than
or equal to the stellar radius. Thus, the analysis of microlensing events
provides a powerful method for testing stellar atmosphere models.Comment: 4 pages LaTeX, to appear in New Astronomy Reviews - proceedings of
the Oxford Workshop `Gravitational Lensing: Nature's Own Weighing Scales'.
Uses elsart.cls. Paper also available at
ftp://info.astro.gla.ac.uk/pub/martin/extended.p
The Corralitos Observatory program for the detection of lunar transient phenomena
This is a final report on the establishment, observing procedures, and observational results of a survey program for the detection of lunar transient phenomena (LTP's) by electro-optical image conversion means. For survey, a unique detection system with an image orthicon was used as the primary element in conjunction with a 24-in. f/20 Cassegrainian telescope. Observations in three spectral ranges, with 6,466 man-hours of observing, were actually performed during the period from October 27, 1965, to April 26, 1972. Within this entire period, no color or feature change within the detection capabilities of the instrumentation was observed, either independently or in follow up of amateur LTP reports, with the exception of one general bluing and several localized bluings (probably ascribable to the effects of the terrestrial atmosphere) that were observed solely by the Corralitos system. A table is presented indicating amateur and professional reports of LTP's and the results of efforts to confirm these reports through the Corralitos system
Non-linear resistivity and heat dissipation in monolayer graphene
We have experimentally studied the nonlinear nature of electrical conduction
in monolayer graphene devices on silica substrates. This nonlinearity manifests
itself as a nonmonotonic dependence of the differential resistance on applied
DC voltage bias across the sample. At temperatures below ~70K, the differential
resistance exhibits a peak near zero bias that can be attributed to
self-heating of the charge carriers. We show that the shape of this peak arises
from a combination of different energy dissipation mechanisms of the carriers.
The energy dissipation at higher carrier temperatures depends critically on the
length of the sample. For samples longer than 10um the heat loss is shown to be
determined by optical phonons at the silica-graphene interface.Comment: 4 pages, 4 figure
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