4,147 research outputs found
Critical Phenomena Associated with Boson Stars
We present a brief synopsis of related work (gr-qc/0007039), describing a
study of black hole threshold phenomena for a self-gravitating, massive complex
scalar field in spherical symmetry. We construct Type I critical solutions
dynamically by tuning a one-parameter family of initial data consisting of a
boson star and a massless real scalar field, and numerically evolving this
data. The resulting critical solutions appear to correspond to boson stars on
the unstable branch, as we show via comparisons between our simulations and
perturbation theory. For low-mass critical solutions, we find small ``halos''
of matter in the tails of the solutions, and these distort the profiles which
otherwise agree with unstable boson stars. These halos seem to be artifacts of
the collisions between the original boson stars and the massless fields, and do
not appear to belong to the true critical solutions. From this study, it
appears that unstable boson stars are unstable to dispersal (``explosion'') in
addition to black hole formation. Given the similarities in macroscopic
stability between boson stars and neutron stars, we suggest that similar
phenomena could occur in models of neutron stars.Comment: 6 Pages, 5 Figures, LaTeX. To appear in Proceedings of the 20th Texas
Symposium on Relativistic Astrophysics (Dec 9-15, 2000
Omnidirectional acceleration device Patent
Omnidirectional liquid filled accelerometer design with liquid and housing temperature compensatio
NITRATE REDUCTION PROGRAM AT THE LINE CREEK OPERATION
Blasting activities at the Line Creek operation are releasing oxides of nitrogen and arecontributing to chemical changes in the surrounding watersheds. Through analysis of themechanisms of nitrogen release, history of explosive usage, historical nitrate release, changingregulatory requirements, strategy analysis and social impacts associated with the release ofnitrates a nitrate reduction plan will be established.The paper develops the framework for engineering groups, operations groups andmanagers to make decisions around the development of a sustainable and achievablecommunication and monitoring plan for nitrate release while working to meeting the regulatory,social, and stakeholder requirements to continue efficient and effective mining operations.The strategy recommended within this document is to develop practices around nitratemanagement through effective operational practices, introduction of high stability emulsion andemulsion contact with water. The effective operational controls will provide the mechanisms forreduction of oxides of nitrogen rather than through capital projects
A Commonwealth of Hope: The New Deal Response to Crisis
Review of: "A Commonwealth of Hope: The New Deal Response to Crisis," by Alan Lawson
Gaining Access: Congress and the Farm Lobby, 1919-1981
Review of: Gaining Access: Congress and the Farm Lobby, 1919-1981. Hansen, John Mark
Laser diode initiated detonators for space applications
Ensign Bickford Aerospace Company (EBAC) has over ten years of experience in the design and development of laser ordnance systems. Recent efforts have focused on the development of laser diode ordnance systems for space applications. Because the laser initiated detonators contain only insensitive secondary explosives, a high degree of system safety is achieved. Typical performance characteristics of a laser diode initiated detonator are described in this paper, including all-fire level, function time, and output. A finite difference model used at EBAC to predict detonator performance, is described and calculated results are compared to experimental data. Finally, the use of statistically designed experiments to evaluate performance of laser initiated detonators is discussed
Transition from collisionless to collisional MRI
Recent calculations by Quataert et al. (2002) found that the growth rates of
the magnetorotational instability (MRI) in a collisionless plasma can differ
significantly from those calculated using MHD. This can be important in hot
accretion flows around compact objects. In this paper we study the transition
from the collisionless kinetic regime to the collisional MHD regime, mapping
out the dependence of the MRI growth rate on collisionality. A kinetic closure
scheme for a magnetized plasma is used that includes the effect of collisions
via a BGK operator. The transition to MHD occurs as the mean free path becomes
short compared to the parallel wavelength 2\pi/k_{\Par}. In the weak magnetic
field regime where the Alfv\'en and MRI frequencies are small compared
to the sound wave frequency k_{\Par} c_0, the dynamics are still effectively
collisionless even if , so long as the collision frequency \nu
\ll k_{\Par} c_{0}; for an accretion flow this requires \nu \lsim \Omega
\sqrt{\beta}. The low collisionality regime not only modifies the MRI growth
rate, but also introduces collisionless Landau or Barnes damping of long
wavelength modes, which may be important for the nonlinear saturation of the
MRI.Comment: 20 pages, 4 figures, submitted to ApJ with a clearer derivation of
anisotropic pressure closure from drift kinetic equatio
The Unknown, or Lays of the Forest
https://commons.und.edu/settler-literature/1133/thumbnail.jp
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