25,037 research outputs found
The Late Time Light Curve of SN 1998bw Associated with GRB980425
We report 139 photometric observations through the B, V, and I filters of the
supernova SN 1998bw, an object which is associated with the Gamma-Ray Burst GRB
980425. Detailed light curves of this unique supernova can be compared to
theoretical models, so we report here our light curve for 123 days between 27
June 1998 and 28 October 1998. The light curve of SN 1988bw is consistent with
those of the Type Ic class. We find that the magnitude-versus-time relation for
this supernova is linear to within 0.05 mags in all colors over the entire
duration of our study. Our measured uniform decline rates are , , and magnitudes per day in the
B, V, and I bands. The linear decline and the rate of that decline suggest that
late time light curve is powered by the radioactive decay of cobalt with some
leakage of the gamma rays.Comment: 15 pages, 1 figure, 1 table, Accepted for publication in PAS
A -adic RanSaC algorithm for stereo vision using Hensel lifting
A -adic variation of the Ran(dom) Sa(mple) C(onsensus) method for solving
the relative pose problem in stereo vision is developped. From two 2-adically
encoded images a random sample of five pairs of corresponding points is taken,
and the equations for the essential matrix are solved by lifting solutions
modulo 2 to the 2-adic integers. A recently devised -adic hierarchical
classification algorithm imitating the known LBG quantisation method classifies
the solutions for all the samples after having determined the number of
clusters using the known intra-inter validity of clusterings. In the successful
case, a cluster ranking will determine the cluster containing a 2-adic
approximation to the "true" solution of the problem.Comment: 15 pages; typos removed, abstract changed, computation error remove
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Ertel potential vorticity, Bernoulli streamfunction, planetary-scale hydraulic jumps, and transonic jet-streaks in a re-analysis of the Martian atmosphere
Conceptual design of an orbital propellant transfer experiment. Volume 2: Study results
The OTV configurations, operations and requirements planned for the period from the 1980's to the 1990's were reviewed and a propellant transfer experiment was designed that would support the needs of these advanced OTV operational concepts. An overall integrated propellant management technology plan for all NASA centers was developed. The preliminary cost estimate (for planning purposes only) is 31.8 M is for shuttle user costs
Exact Dynamics of Multicomponent Bose-Einstein Condensates in Optical Lattices in One, Two and Three Dimensions
Numerous exact solutions to the nonlinear mean-field equations of motion are
constructed for multicomponent Bose-Einstein condensates on one, two, and three
dimensional optical lattices. We find both stationary and nonstationary
solutions, which are given in closed form. Among these solutions are a
vortex-anti-vortex array on the square optical lattice and modes in which two
or more components slosh back and forth between neighboring potential wells. We
obtain a variety of solutions for multicomponent condensates on the simple
cubic lattice, including a solution in which one condensate is at rest and the
other flows in a complex three-dimensional array of intersecting vortex lines.
A number of physically important solutions are stable for a range of parameter
values, as we show by direct numerical integration of the equations of motion.Comment: 22 pages, 9 figure
Odd Parity and Line Nodes in Non-Symmorphic Superconductors
Group theory arguments have been invoked to argue that odd parity order
parameters cannot have line nodes in the presence of spin-orbit coupling. In
this paper we show that these arguments do not hold for certain non-symmorphic
superconductors. Specifically, we demonstrate that when the underlying crystal
has a twofold screw axis, half of the odd parity representations vanish on the
Brillouin zone face perpendicular to this axis. Many unconventional
superconductors have non-symmorphic space groups, and we discuss implications
for several materials, including UPt3, UBe13, Li2Pt3B and Na4Ir3O8.Comment: 4 page
Severe New Limits on the Host Galaxies of Gamma Ray Bursts
The nature of Gamma Ray Bursts (GRBs) remains a complete mystery, despite the
recent breakthrough discovery of low energy counterparts, although it is now
generally believed that at least most GRBs are at cosmological distances.
Virtually all proposed cosmological models require bursters to reside in
ordinary galaxies. This can be tested by looking inside the smallest GRB error
boxes to see if ordinary galaxies appear at the expected brightness levels.
This letter reports on an analysis of the contents of 26 of the smallest
regions, many from the brightest bursts. These events will have and
small uncertainties about luminosity functions, K corrections and galaxy
evolutions; whereas the recent events with optical transients are much fainter
and hence have high redshifts and grave difficulties in interpretation. This
analysis strongly rejects the many models with peak luminosities of as deduced from the curve with no evolution.
Indeed, the lower limit on acceptable luminosities is . The only possible solution is to either place GRBs at
unexpectedly large distances (with for the faint BATSE bursts) or to
require bursters to be far outside any normal host galaxy.Comment: 17 pages, to be published by ApJ
Low Cost Nuclear Thermal Rocket Cermet Fuel Element Environment Testing
Deep space missions with large payloads require high specific impulse and relatively high thrust to achieve mission goals in reasonable time frames.1,2 Conventional storable propellants produce average specific impulse. Nuclear thermal rockets capable of producing high specific impulse are proposed. Nuclear thermal rockets employ heat produced by fission reaction to heat and therefore accelerate hydrogen, which is then forced through a rocket nozzle providing thrust. Fuel element temperatures are very high (up to 3000 K), and hydrogen is highly reactive with most materials at high temperatures. Data covering the effects of high-temperature hydrogen exposure on fuel elements are limited.3 The primary concern is the mechanical failure of fuel elements that employ high-melting-point metals, ceramics, or a combination (cermet) as a structural matrix into which the nuclear fuel is distributed. The purpose of the testing is to obtain data to assess the properties of the non-nuclear support materials, as-fabricated, and determine their ability to survive and maintain thermal performance in a prototypical NTR reactor environment of exposure to hydrogen at very high temperatures. The fission process of the planned fissile material and the resulting heating performance is well known and does not therefore require that active fissile material be integrated in this testing. A small-scale test bed designed to heat fuel element samples via non-contact radio frequency heating and expose samples to hydrogen is being developed to assist in optimal material and manufacturing process selection without employing fissile material. This paper details the test bed design and results of testing conducted to date
Gamma-Ray Burster Counterparts: HST Blue and Ultraviolet Data
The surest solution of the Gamma Ray Burst (GRB) mystery is to find an
unambiguous low-energy quiescent counterpart. However, to date no reasonable
candidates have been identified in the x-ray, optical, infrared, or radio
ranges. The Hubble Space Telescope (HST) has now allowed for the first deep
ultraviolet searches for quiescent counterparts. This paper reports on
multiepoch ultraviolet searches of five GRB positions with HST. We found no
sources with significant ultraviolet excesses, variability, parallax, or proper
motion in any of the burst error regions. In particular, we see no sources
similar to that proposed as a counterpart to the GRB970228. While this negative
result is disappointing, it still has good utility for its strict limits on the
no-host-galaxy problem in cosmological models of GRBs. For most cosmological
models (with peak luminosity 6X10^50 erg/s), the absolute B magnitude of any
possible host galaxy must be fainter than -15.5 to -17.4. These smallest boxes
for some of the brightest bursts provide the most critical test, and our limits
are a severe problem for all published cosmological burst models.Comment: 15 pages, 2 ps figures, accepted for publication in the Astrophysical
Journa
Feasibility study of the transonic biplane concept for transport aircraft application
Investigations were conducted to evaluate the feasibility of a transonic biplane consisting of a forward-mounted swept-back lower wing, a rear-mounted swept-forward upper wing, and a vertical fin connecting the wings at their tips. This wing arrangement results in significant reductions in induced drag relative to a monoplane designed with the same span, and it allows for a constant-section fuselage shape while closely matching an ideal area distribution curve for M = 0.95 cruise. However, no significant reductions in ramp weight were achieved for the biplane relative to a monoplane with the same mission capability. Flutter analyses of the biplane revealed both symmetric and antisymmetric instabilities that occur well below the required flutter speed. Further studies will be required to determine if acceptable flutter speeds can be achieved through the elimination of the instabilities by passive means or by active controls. Configurations designed for other missions, especially those with lower Mach numbers and lower dynamic pressures, should be examined since the geometries suitable for those design constraints might avoid the weight penalties and flutter instabilities which prevent exploitation of induced drag benefits for the configuration studied
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