919 research outputs found
Heat resistant protective hand covering
The heat resistant, protective glove is made up of first and second shell sections which define a palm side and a backside, respectively. The first shell section is made of a twill wave fabric of a temperature-resistant aromatic polyamide fiber. The second shell section is made of a knitted fabric of a temperature-resistant aromatic polyamide fiber. The first and second shell sections are secured to one another, e.g., by sewing, to provide the desired glove configuration and an opening for insertion of the wearer's hand. The protective glove also includes a first liner section which is secured to and overlies the inner surface of the first shell section and is made of a felt fabric of a temperature-resistant aromatic polyamide fiber and has a flame resistant, elastomenic coating on the surface facing and overlying the inner surface of the first shell section
Discovery of kHz Fluctuations in Centaurus X-3: Evidence for Photon Bubble Oscillations (PBO) and Turbulence in a High Mass X-ray Binary Pulsar
We report the discovery of kHz fluctuations, including quasi-periodic
oscillations (QPO) at ~330 Hz and ~760 Hz and a broadband kHz continuum in the
power density spectrum of the high mass X-ray binary pulsar Centaurus X-3.
These observations of Cen X-3 were carried out with the Rossi X-ray Timing
Explorer (RXTE). The fluctuation spectrum is flat from mHz to a few Hz, then
steepens to behavior between a few Hz and ~100 Hz. Above a hundred Hz,
the spectrum shows the QPO features, plus a flat continuum extending to ~1200
Hz and then falling out to ~1800 Hz. These results, which required the
co-adding three days of observations of Cen X-3, are at least as fast as the
fastest known variations in X-ray emission from an accreting compact object
(kHz QPO in LMXB sources) and probably faster since extension to ~1800 Hz is
indicated by the most likely parameterization of the data.
Multi-dimensional radiation hydrodynamics simulations of optically thick
plasma flow onto the magnetic poles of an accreting neutron star show that the
fluctuations at frequencies above 100 Hz are consistent with photon bubble
turbulence and oscillations (PBO) previously predicted to be observable in this
source. For a polar cap opening angle of 0.25 radians, we show that the
spectral form above 100 Hz is reproduced by the simulations, including the
frequencies of the QPO and the relative power in the QPO and the kHz continuum.
This has resulted in the first model-dependent measurement of the polar cap
size of an X-ray pulsar.Comment: received ApJ: April 1, 1999 accepted ApJ: September 1, 199
Heat resistant protective hand covering
A heat-resistant aromatic polyamide fiber is described. The outer surface of the shell is coated with a fire-resistant elastomer and liner. Generally conforming and secured to the shell and disposed inwardly of the shell, the liner is made of a felt fabric of temperature-resistant aromatic polymide fiber
Current Flow and Pair Creation at Low Altitude in Rotation Powered Pulsars' Force-Free Magnetospheres: Space-Charge Limited Flow
(shortened) We report the results of an investigation of particle
acceleration and electron-positron plasma generation at low altitude in the
polar magnetic flux tubes of Rotation Powered Pulsars, when the stellar surface
is free to emit whatever charges and currents are demanded by the force-free
magnetosphere. We observe novel behavior. a) When the current density is less
than the Goldreich-Julian (GJ) value (0<j/j_{GJ}<1), space charge limited
acceleration of the current carrying beam is mild, with the full GJ charge
density being comprised of the charge density of the beam, co-existing with a
cloud of electrically trapped particles with the same sign of charge as the
beam. The voltage drops are on the order of mc^2/e, and pair creation is
absent. b) When the current density exceeds the GJ value (j/j_{GJ}>1), the
system develops high voltage drops, causing emission of gamma rays and intense
bursts of pair creation. The bursts exhibit limit cycle behavior, with
characteristic time scales somewhat longer than the relativistic fly-by time
over distances comparable to the polar cap diameter (microseconds). c) In
return current regions, where j/j_{GJ}<0, the system develops similar bursts of
pair creation. In cases b) and c), the intermittently generated pairs allow the
system to simultaneously carry the magnetospherically prescribed currents and
adjust the charge density and average electric field to force-free conditions.
We also elucidate the conditions for pair creating beam flow to be steady,
finding that such steady flows can occupy only a small fraction of the current
density parameter space of the force-free magnetospheric model. The generic
polar flow dynamics and pair creation is strongly time dependent. The model has
an essential difference from almost all previous quantitative studies, in that
we sought the accelerating voltage as a function of the applied current.Comment: 35 pages, 29 figures. Accepted for publication in MNRAS. Added new
appendix, several minor changes in the tex
Computer simulations of cosmic-ray diffusion near supernova remnant shock waves
A plasma simulation model was used to study the resonant interactions between streaming cosmic-ray ions and a self-consistent spectrum of Alfven waves, such as might exist in the interstellar medium upstream of a supernova remnant shock wave. The computational model is a hybrid one, in which the background interstellar medium is an MHD fluid and the cosmic-rays are discrete kinetic particles. The particle sources for the electromagnetic fields are obtained by averaging over the fast cyclotron motions. When the perturbed magnetic field is larger than 10 percent of the background field, the macro- and microphysics are no longer correctly predicted by quasi-linear theory. The particles are trapped by the waves and show sharp jumps in their pitch-angles relative to the background magnetic field, and the effective ninety-degree scattering time for diffusion parallel to the background magnetic field is reduced to between 5 and 30 cyclotron periods. Simulation results suggest that Type 1 supernova remnants may be the principal sites of cosmic ray acceleration
Relativistic Jets and Long-Duration Gamma-ray Bursts from the Birth of Magnetars
We present time-dependent axisymmetric magnetohydrodynamic simulations of the
interaction of a relativistic magnetized wind produced by a proto-magnetar with
a surrounding stellar envelope, in the first seconds after core
collapse. We inject a super-magnetosonic wind with ergs
s into a cavity created by an outgoing supernova shock. A strong
toroidal magnetic field builds up in the bubble of plasma and magnetic field
that is at first inertially confined by the progenitor star. This drives a jet
out along the polar axis of the star, even though the star and the magnetar
wind are each spherically symmetric. The jet has the properties needed to
produce a long-duration gamma-ray burst (GRB). At s after core bounce,
the jet has escaped the host star and the Lorentz factor of the material in the
jet at large radii cm is similar to that in the magnetar wind
near the source. Most of the spindown power of the central magnetar escapes via
the relativistic jet. There are fluctuations in the Lorentz factor and energy
flux in the jet on second timescale. These may contribute to
variability in GRB emission (e.g., via internal shocks).Comment: 5 pages, 3 figures, accepted in MNRAS letter, presented at the
conference "Astrophysics of Compact Objects", 1-7 July, Huangshan, Chin
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