29,037 research outputs found
Detector panels-micrometeoroid impact Patent
Development of large area micrometeoroid impact detector panel
System maintains constant penetration during fusion welding
Servo system senses variations in fusion welding process, and adjusts the control parameters to compensate for them. The system assumes a correlation between uniform weld penetration and temperature gradients near the molten puddle. It senses weld properties and makes adjustments to travel speed and weld current
Quasi-circular Orbits for Spinning Binary Black Holes
Using an effective potential method we examine binary black holes where the
individual holes carry spin. We trace out sequences of quasi-circular orbits
and locate the innermost stable circular orbit as a function of spin. At large
separations, the sequences of quasi-circular orbits match well with
post-Newtonian expansions, although a clear signature of the simplifying
assumption of conformal flatness is seen. The position of the ISCO is found to
be strongly dependent on the magnitude of the spin on each black hole. At close
separations of the holes, the effective potential method breaks down. In all
cases where an ISCO could be determined, we found that an apparent horizon
encompassing both holes forms for separations well inside the ISCO.
Nevertheless, we argue that the formation of a common horizon is still
associated with the breakdown of the effective potential method.Comment: 13 pages, 10 figures, submitted to PR
Design and development of a water vapor electrolysis unit
Design and development of water vapor electrolysis unit for oxygen productio
Using rewards and penalties to obtain desired subject performance
Operant conditioning procedures, specifically the use of negative reinforcement, in achieving stable learning behavior is described. The critical tracking test (CTT) a method of detecting human operator impairment was tested. A pass level is set for each subject, based on that subject's asymptotic skill level while sober. It is critical that complete training take place before the individualized pass level is set in order that the impairment can be detected. The results provide a more general basis for the application of reward/penalty structures in manual control research
Towards a wave--extraction method for numerical relativity: III. Analytical examples for the Beetle--Burko radiation scalar
Beetle and Burko recently introduced a background--independent scalar
curvature invariant for general relativity that carries information only about
the gravitational radiation in generic spacetimes, in cases where such
radiation is incontrovertibly defined. In this paper we adopt a formalism that
only uses spatial data as they are used in numerical relativity and compute the
Beetle--Burko radiation scalar for a number of analytical examples,
specifically linearized Einstein--Rosen cylindrical waves, linearized
quadrupole waves, the Kerr spacetime, Bowen--York initial data, and the Kasner
spacetime. These examples illustrate how the Beetle--Burko radiation scalar can
be used to examine the gravitational wave content of numerically generated
spacetimes, and how it may provide a useful diagnostic for initial data sets.Comment: 23 pages, 4 figures; We changed the convention used, corrected typos,
and expanded the discussio
Streamlining the walls of an empty two-dimensional flexible-walled test section
The techniques used to find aerodynamically straight wall contours in a test section of a transonic wind tunnel are discussed. The walls were defined as aerodynamically straight up to Mach 0.9
Excision boundary conditions for black hole initial data
We define and extensively test a set of boundary conditions that can be
applied at black hole excision surfaces when the Hamiltonian and momentum
constraints of general relativity are solved within the conformal thin-sandwich
formalism. These boundary conditions have been designed to result in black
holes that are in quasiequilibrium and are completely general in the sense that
they can be applied with any conformal three-geometry and slicing condition.
Furthermore, we show that they retain precisely the freedom to specify an
arbitrary spin on each black hole. Interestingly, we have been unable to find a
boundary condition on the lapse that can be derived from a quasiequilibrium
condition. Rather, we find evidence that the lapse boundary condition is part
of the initial temporal gauge choice. To test these boundary conditions, we
have extensively explored the case of a single black hole and the case of a
binary system of equal-mass black holes, including the computation of
quasi-circular orbits and the determination of the inner-most stable circular
orbit. Our tests show that the boundary conditions work well.Comment: 23 pages, 23 figures, revtex4, corrected typos, added reference,
minor content changes including additional post-Newtonian comparison. Version
accepted by PR
Improved initial data for black hole binaries by asymptotic matching of post-Newtonian and perturbed black hole solutions
We construct approximate initial data for non-spinning black hole binary
systems by asymptotically matching the 4-metrics of two tidally perturbed
Schwarzschild solutions in isotropic coordinates to a resummed post-Newtonian
4-metric in ADMTT coordinates. The specific matching procedure used here
closely follows the calculation in gr-qc/0503011, and is performed in the so
called buffer zone where both the post-Newtonian and the perturbed
Schwarzschild approximations hold. The result is that both metrics agree in the
buffer zone, up to the errors in the approximations. However, since isotropic
coordinates are very similar to ADMTT coordinates, matching yields better
results than in the previous calculation, where harmonic coordinates were used
for the post-Newtonian 4-metric. In particular, not only does matching improve
in the buffer zone, but due to the similarity between ADMTT and isotropic
coordinates the two metrics are also close to each other near the black hole
horizons. With the help of a transition function we also obtain a global smooth
4-metric which has errors on the order of the error introduced by the more
accurate of the two approximations we match. This global smoothed out 4-metric
is obtained in ADMTT coordinates which are not horizon penetrating. In
addition, we construct a further coordinate transformation that takes the
4-metric from global ADMTT coordinates to new coordinates which are similar to
Kerr-Schild coordinates near each black hole, but which remain ADMTT further
away from the black holes. These new coordinates are horizon penetrating and
lead, for example, to a lapse which is everywhere positive on the t=0 slice.
Such coordinates may be more useful in numerical simulations.Comment: 25 pages, 21 figures. Replaced with accepted versio
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