1,594,987 research outputs found
Magnetic Field Limits on SGRs
We measure the period and spin-down rate for SGR 1900+14 during the
quiescient period two years before the recent interval of renewed burst
activity. We find that the spin-down rate doubled during the burst activity
which is inconsistent with both mangetic dipole driven spin down and a magnetic
field energy source for the bursts. We also show that SGRs 1900+14 and 1806-20
have braking indices of 1 which indicate that the spin-down is due to
wind torques and not magnetic dipole radiation. We further show that a
combination of dipole radiation, and wind luminosity, coupled with estimated
ages and present spin parameters, imply that the magnetic fields of SGRs
1900+14 and 1806-20 are less than the critical field of 4 G and
that the efficiency for conversion of wind luminosity to x-ray luminosity is
<2%.Comment: 5 pages, 2 figures submitted to 5th Huntsville GRB Symposium
proceeding
System measures unidirectional forces, excludes extraneous forces
System measures unidirectional force without interference from other directional forces. The measuring apparatus is mounted so that it only moves vertically and is constrained from horizontal and rotational movement. This system can be used to accurately measure small forces in one direction, or as an analytic balance
Convoluting device for forming convolutions and the like Patent
Punch and die device for forming convolution series in thin gage metal hemisphere
Small Gas Turbine Combustor Primary Zone Study
The combustion research program, small gas turbine combustor primary zone study is summarized. The basic elements of a design methodology program to obtain the maximum performance potential of small reverse-flow annular combustors is described. Three preferred combustion design approaches for internal flame stabilization patterns were selected. Design features are incorporated in the combustors to address the performance limiting problem areas associated with smaller annular combustors. Performance is predicted by using a 3-D aerodynamic/chemical kinetic elliptic flow analysis, initially developed by Garrett Corporation for the USARTL. It is shown that the analytical flow field predictive models provide a useful design tool for understanding the combustion performance of a small reverse flow annular combustor
Classical Functional Bethe Ansatz for : separation of variables for the magnetic chain
The Functional Bethe Ansatz (FBA) proposed by Sklyanin is a method which
gives separation variables for systems for which an -matrix is known.
Previously the FBA was only known for and (and associated)
-matrices. In this paper I advance Sklyanin's program by giving the FBA for
certain systems with -matrices. This is achieved by constructing
rational functions \A(u) and \B(u) of the matrix elements of , so
that, in the generic case, the zeros of \B(u) are the separation
coordinates and the P_i=\A(x_i) provide their conjugate momenta. The method
is illustrated with the magnetic chain and the Gaudin model, and its wider
applicability is discussed.Comment: 14pp LaTex,DAMTP 94-1
Is SGR 1900+14 a Magnetar?
We present RXTE observations of the soft gamma--ray repeater SGR 1900+14
taken September 4-18, 1996, nearly 2 years before the 1998 active period of the
source. The pulsar period (P) of 5.1558199 +/- 0.0000029 s and period
derivative (Pdot) of (6.0 +/- 1.0) X 10^-11 s/s measured during the 2-week
observation are consistent with the mean Pdot of (6.126 +/- 0.006) X 10^-11 s/s
over the time up to the commencement of the active period. This Pdot is less
than half that of (12.77 +/- 0.01) X 10^-11 s/s observed during and after the
active period. If magnetic dipole radiation were the primary cause of the
pulsar spindown, the implied pulsar magnetic field would exceed the critical
field of 4.4 X 10^13 G by more than an order of magnitude, and such field
estimates for this and other SGRs have been offered as evidence that the SGRs
are magnetars, in which the neutron star magnetic energy exceeds the rotational
energy. The observed doubling of Pdot, however, would suggest that the pulsar
magnetic field energy increased by more than 100% as the source entered an
active phase, which seems very hard to reconcile with models in which the SGR
bursts are powered by the release of magnetic energy. Because of this, we
suggest that the spindown of SGR pulsars is not driven by magnetic dipole
radiation, but by some other process, most likely a relativistic wind. The
Pdot, therefore, does not provide a measure of the pulsar magnetic field
strength, nor evidence for a magnetar.Comment: 14 pages, aasms4 latex, figures 1 & 2 changed, accepted by ApJ
letter
Abundances and Kinematics of Field Halo and Disk Stars I: Observational Data and Abundance Analysis
We describe observations and abundance analysis of a high-resolution,
high-S/N survey of 168 stars, most of which are metal-poor dwarfs. We follow a
self-consistent LTE analysis technique to determine the stellar parameters and
abundances, and estimate the effects of random and systematic uncertainties on
the resulting abundances. Element-to-iron ratios are derived for key alpha,
odd, Fe-peak, r- and s-process elements. Effects of Non-LTE on the analysis of
Fe I lines are shown to be very small on the average. Spectroscopically
determined surface gravities are derived that are generally close to those
obtained from Hipparcos parallaxes.Comment: 41 pages, 7 Postscript figures. Accepted for publication in the A
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