1,957 research outputs found
Space shuttle orbit maneuvering engine reusable thrust chamber program
Tests were conducted on the regenerative cooled thrust chamber of the space shuttle orbit maneuvering engine. The conditions for the tests and the durations obtained are presented. The tests demonstrated thrust chamber operation over the nominal ranges of chamber pressure mixture ratio. Variations in auxiliary film coolant flowrate were also demonstrated. High pressure tests were conducted to demonstrate the thrust chamber operation at conditions approaching the design chamber pressure for the derivative space tug application
A Late-Time Flattening of Afterglow Light Curves
We present a sample of radio afterglow light curves with measured decay
slopes which show evidence for a flattening at late times compared to optical
and X-ray decay indices. The simplest origin for this behavior is that the
change in slope is due to a jet-like outflow making a transition to
sub-relativistic expansion. This can explain the late-time radio light curves
for many but not all of the bursts in the sample. We investigate several
possible modifications to the standard fireball model which can flatten
late-time light curves. Changes to the shock microphysics which govern particle
acceleration, or energy injection to the shock (either radially or azimuthally)
can reproduce the observed behavior. Distinguishing between these different
possibilities will require simultaneous optical/radio monitoring of afterglows
at late times.Comment: ApJ, submitte
The Ursinus Weekly, December 7, 1936
John Porambo, varsity center, is elected captain of 1937 gridmen by 21 lettermen • Articles by Groff and Yoh are Lantern prize winners • Xmas celebration is two nights • Ursinus rec center to open after Xmas • Y groups to present speaker on cooperative consumers plan • McClure, Sheeder, attend Association of Colleges meeting • Freshman gridders banquet in initial frosh grid fete • Bothell and Garber star in The Dark Tower; record crowd dances to Jan\u27s Tophatters • Dr. Meredith to address physical education group • Interfraternity council issues member list for new students • Students hear economist in talk on natural resources • Debating teams release schedules; women will meet Bucknell this Thursday; men to hold radio debate • Stevens new wrestling coach; good year expected; 27 candidates report for practice • Officials select all-dorm team; five frosh picked • Guest elected soccer captain, bear manager, by 11 lettermen • Costello and Heiges on conference team • Co-ed basketeers participate in new rules exhibition game • Snell\u27s belles end season with six wins, 3 losses • 15 basketballers report; 4 lettermen lead struggle • McAvoy\u27s bears end season in second place, F & M winners in conference; Captain Costello outstanding through season; twelve lettermen leave squadhttps://digitalcommons.ursinus.edu/weekly/1915/thumbnail.jp
The Thermodynamic Properties of Phosphorus, Phosphine, and Some Phosphorus Halides
A critical study of the equilibrium and molecular data for phosphorus and some of its compounds has been made and is described. The data are used to calculate the entropies and free energies of the substances considered
Cosmological Uses of Gamma-Ray Bursts
Studies of the cosmic gamma-ray bursts (GRBs) and their host galaxies are
starting to provide interesting or even unique new insights in observational
cosmology. GRBs represent a new way of identifying a population of star-forming
galaxies at cosmological redshifts. GRB hosts are broadly similar to the normal
field galaxy populations at comparable redshifts and magnitudes, and indicate
at most a mild luminosity evolution out to z ~ 1.5 - 2. GRB optical afterglows
seen in absorption provide a powerful new probe of the ISM in dense, central
regions of their host galaxies, complementary to the traditional studies using
QSO absorbers. Some GRB hosts are heavily obscured, and provide a new way to
select a population of cosmological sub-mm sources, and a novel constraint on
the total obscured fraction of star formation over the history of the universe.
Finally, detection of GRB afterglows at z > 6 may provide a unique way to probe
the primordial star formation, massive IMF, early IGM, and chemical enrichment
at the end of the cosmic reionization era.Comment: An invited review, to appear in: "Gamma-Ray Bursts in the Afterglow
Era: 3rd Workshop", ASPCS, in press; LaTeX file, 8 pages, 1 eps figure, style
files include
XUV Frequency Combs via Femtosecond Enhancement Cavities
We review the current state of tabletop extreme ultraviolet (XUV) sources
based on high harmonic generation (HHG) in femtosecond enhancement cavities
(fsEC). Recent developments have enabled generation of high photon flux (1014
photons/sec) in the XUV, at high repetition rates (>50 MHz) and spanning the
spectral region from 40 nm - 120 nm. This level of performance has enabled
precision spectroscopy with XUV frequency combs and promises further
applications in XUV spectroscopic and photoemission studies. We discuss the
theory of operation and experimental details of the fsEC and XUV generation
based on HHG, including current technical challenges to increasing the photon
flux and maximum photon energy produced by this type of system. Current and
future applications for these sources are also discussed.Comment: invited review article, 38 page
Discovery of Early Optical Emission from GRB 021211
We report our discovery and early time optical, near-infrared, and radio
wavelength follow-up observations of the afterglow of the gamma-ray burst GRB
021211. Our optical observations, beginning 21 min after the burst trigger,
demonstrate that the early afterglow of this burst is roughly three magnitudes
fainter than the afterglow of GRB 990123 at similar epochs, and fainter than
almost all known afterglows at an epoch of 1d after the GRB. Our near-infrared
and optical observations indicate that this is not due to extinction. Combining
our observations with data reported by other groups, we identify the signature
of a reverse shock. This reverse shock is not detected to a 3-sigma limit of
110 uJy in an 8.46-GHz VLA observation at t=0.10d, implying either that the
Lorentz factor of the burst gamma <~ 200, or that synchrotron self-absorption
effects dominate the radio emission at this time. Our early optical
observations, near the peak of the optical afterglow (forward shock), allow us
to characterize the afterglow in detail. Comparing our model to flux upper
limits from the VLA at later times, t >~ 1 week, we find that the late-time
radio flux is suppressed by a factor of two relative to the >~ 80 uJy peak flux
at optical wavelengths. This suppression is not likely to be due to synchrotron
self-absorption or an early jet break, and we suggest instead that the burst
may have suffered substantial radiative corrections.Comment: 13 pages, 2 figures, ApJL accepted; edits for lengt
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