7,613 research outputs found
Black Hole Motion as Catalyst of Orbital Resonances
The motion of a black hole about the centre of gravity of its host galaxy
induces a strong response from the surrounding stellar population. We treat the
case of a harmonic potential analytically and show that half of the stars on
circular orbits in that potential shift to an orbit of lower energy, while the
other half receive a positive boost and recede to a larger radius. The black
hole itself remains on an orbit of fixed amplitude and merely acts as a
catalyst for the evolution of the stellar energy distribution function f(E). We
show that this effect is operative out to a radius of approx 3 to 4 times the
hole's influence radius, R_bh. We use numerical integration to explore more
fully the response of a stellar distribution to black hole motion. We consider
orbits in a logarithmic potential and compare the response of stars on circular
orbits, to the situation of a `warm' and `hot' (isotropic) stellar velocity
field. While features seen in density maps are now wiped out, the kinematic
signature of black hole motion still imprints the stellar line-of-sight mean
velocity to a magnitude ~18% the local root mean-square velocity dispersion
sigma.Comment: revised version, typos fixed, added references, 20 pages MN styl
Polymers near Metal Surfaces: Selective Adsorption and Global Conformations
We study the properties of a polycarbonate melt near a nickel surface as a
model system for the interaction of polymers with metal surfaces by employing a
multiscale modeling approach. For bulk properties a suitably coarse grained
bead spring model is simulated by molecular dynamics (MD) methods with model
parameters directly derived from quantum chemical calculations. The surface
interactions are parameterized and incorporated by extensive quantum mechanical
density functional calculations using the Car-Parrinello method. We find strong
chemisorption of chain ends, resulting in significant modifications of the melt
composition when compared to an inert wall.Comment: 8 pages, 3 figures (2 color), 1 tabl
Public Sector Bargaining in a Democracy - An Assessment of the Ohio Public Employee Collective Bargaining Law
The purpose of this Article is to examine the Ohio Act in terms of its accommodation of the major theoretical considerations in favor of, or opposed to, public sector collective bargaining. In other words, is the Ohio Act structured so as to maximally achieve the benefits asserted to be available from collective bargaining and to avoid the costs asserted to arise from it? In order to accomplish this task, this Article will briefly summarize major provisions of the Act. An overview of some of the major arguments for and against public sector unionization will then be provided. Once this background has been established, the Act will be analyzed, focusing upon its effect upon individual employees, labor organizations, and the democratic process. The conclusions reached are that the Act is not structured so as to protect public employees to the degree that private sector employees are protected, that the Act will assist labor organizations, and that the Act strikingly fails to provide a structure that can minimize damage to the processes of democracy
Public Sector Bargaining in a Democracy - An Assessment of the Ohio Public Employee Collective Bargaining Law
The purpose of this Article is to examine the Ohio Act in terms of its accommodation of the major theoretical considerations in favor of, or opposed to, public sector collective bargaining. In other words, is the Ohio Act structured so as to maximally achieve the benefits asserted to be available from collective bargaining and to avoid the costs asserted to arise from it? In order to accomplish this task, this Article will briefly summarize major provisions of the Act. An overview of some of the major arguments for and against public sector unionization will then be provided. Once this background has been established, the Act will be analyzed, focusing upon its effect upon individual employees, labor organizations, and the democratic process. The conclusions reached are that the Act is not structured so as to protect public employees to the degree that private sector employees are protected, that the Act will assist labor organizations, and that the Act strikingly fails to provide a structure that can minimize damage to the processes of democracy
Maximum gravitational recoil
Recent calculations of gravitational radiation recoil generated during
black-hole binary mergers have reopened the possibility that a merged binary
can be ejected even from the nucleus of a massive host galaxy. Here we report
the first systematic study of gravitational recoil of equal-mass binaries with
equal, but anti-aligned, spins parallel to the orbital plane. Such an
orientation of the spins is expected to maximize the recoil. We find that
recoil velocity (which is perpendicular to the orbital plane) varies
sinusoidally with the angle that the initial spin directions make with the
initial linear momenta of each hole and scales up to a maximum of ~4000 km/s
for maximally-rotating holes. Our results show that the amplitude of the recoil
velocity can depend sensitively on spin orientations of the black holes prior
to merger.Comment: 4 pages, 4 figs, revtex
115 DEGRADATION TO SYNTHESIS RATIOS OF TYPE II COLLAGEN BIOMARKERS IN SYNOVIAL FLUID AND SERUM IN THOROUGHBRED RACEHORSES
Spin Flips and Precession in Black-Hole-Binary Mergers
We use the `moving puncture' approach to perform fully non-linear evolutions
of spinning quasi-circular black-hole binaries with individual spins not
aligned with the orbital angular momentum. We evolve configurations with the
individual spins (parallel and equal in magnitude) pointing in the orbital
plane and 45-degrees above the orbital plane. We introduce a technique to
measure the spin direction and track the precession of the spin during the
merger, as well as measure the spin flip in the remnant horizon. The former
configuration completes 1.75 orbits before merging, with the spin precessing by
98-degrees and the final remnant horizon spin flipped by ~72-degrees with
respect to the component spins. The latter configuration completes 2.25 orbits,
with the spins precessing by 151-degrees and the final remnant horizon spin
flipped ~34-degrees with respect to the component spins. These simulations show
for the first time how the spins are reoriented during the final stage of
binary black hole mergers verifying the hypothesis of the spin-flip phenomenon.
We also compute the track of the holes before merger and observe a precession
of the orbital plane with frequency similar to the orbital frequency and
amplitude increasing with time.Comment: Revtex4, 17 figures, 14 pages. Accepted for publication in PR
Is there a Supermassive Black Hole at the Center of the Milky Way?
This review outlines the observations that now provide an overwhelming
scientific case that the center of our Milky Way Galaxy harbors a supermassive
black hole. Observations at infrared wavelength trace stars that orbit about a
common focal position and require a central mass (M) of 4 million solar masses
within a radius of 100 Astronomical Units. Orbital speeds have been observed to
exceed 5,000 km/s. At the focal position there is an extremely compact radio
source (Sgr A*), whose apparent size is near the Schwarzschild radius
(2GM/c^2). This radio source is motionless at the ~1 km/s level at the
dynamical center of the Galaxy. The mass density required by these observations
is now approaching the ultimate limit of a supermassive black hole within the
last stable orbit for matter near the event horizon.Comment: Invited review submitted to International Journal of Modern Physics
D; 23 pages; 10 figure
Scientific Visualization Using the Flow Analysis Software Toolkit (FAST)
Over the past few years the Flow Analysis Software Toolkit (FAST) has matured into a useful tool for visualizing and analyzing scientific data on high-performance graphics workstations. Originally designed for visualizing the results of fluid dynamics research, FAST has demonstrated its flexibility by being used in several other areas of scientific research. These research areas include earth and space sciences, acid rain and ozone modelling, and automotive design, just to name a few. This paper describes the current status of FAST, including the basic concepts, architecture, existing functionality and features, and some of the known applications for which FAST is being used. A few of the applications, by both NASA and non-NASA agencies, are outlined in more detail. Described in the Outlines are the goals of each visualization project, the techniques or 'tricks' used lo produce the desired results, and custom modifications to FAST, if any, done to further enhance the analysis. Some of the future directions for FAST are also described
- …