28,237 research outputs found
Innermost Stable Circular Orbit of a Spinning Particle in Kerr Spacetime
We study stability of a circular orbit of a spinning test particle in a Kerr
spacetime. We find that some of the circular orbits become unstable in the
direction perpendicular to the equatorial plane, although the orbits are still
stable in the radial direction. Then for the large spin case ($S < \sim O(1)),
the innermost stable circular orbit (ISCO) appears before the minimum of the
effective potential in the equatorial plane disappears. This changes the radius
of ISCO and then the frequency of the last circular orbit.Comment: 25 pages including 8 figure
Interaction between graphene and SiO2 surface
With first-principles DFT calculations, the interaction between graphene and
SiO2 surface has been analyzed by constructing the different configurations
based on {\alpha}-quartz and cristobalite structures. The single layer graphene
can stay stably on SiO2 surface is explained based on the general consideration
of configuration structures of SiO2 surface. It is also found that the oxygen
defect in SiO2 surface can shift the Fermi level of graphene down which opens
out the mechanism of hole-doping effect of graphene absorbed on SiO2 surface
observed in experiments.Comment: 17 pages, 7 figure
Cusp-scaling behavior in fractal dimension of chaotic scattering
A topological bifurcation in chaotic scattering is characterized by a sudden
change in the topology of the infinite set of unstable periodic orbits embedded
in the underlying chaotic invariant set. We uncover a scaling law for the
fractal dimension of the chaotic set for such a bifurcation. Our analysis and
numerical computations in both two- and three-degrees-of-freedom systems
suggest a striking feature associated with these subtle bifurcations: the
dimension typically exhibits a sharp, cusplike local minimum at the
bifurcation.Comment: 4 pages, 4 figures, Revte
Effectiveness of a self-help cognitive behavioural treatment program for problem gamblers: a randomised controlled trial
The study aimed to strengthen the scarce literature on self-help treatments for Problem Gambling (PG) by comparing the effectiveness of a Self-Help Cognitive Behavioral Treatment (SHCBT) program (n\ua0=\ua023) with a 6-week Waitlist condition (n\ua0=\ua032) in problem gamblers. Participants were community volunteers with gambling problems and were randomly allocated to the Waitlist and treatment conditions. Results showed significant improvements at post-treatment in gambling behaviors including frequency of gambling, average amount gambled per day and PG symptoms as well as a number of gambling correlates including psychological states (e.g., depression, anxiety and stress), gambling cognitions, gambling urges, gambling related self-efficacy, satisfaction with life, and quality of life among those who completed the SHCBT program, when compared with the waitlist condition. The effect size (partial η) ranged from .25 to .57 for all assessed outcomes that showed significant improvement from pre- to post-treatment. It was concluded that a self-help CBT program can be beneficial for treating community problem gamblers
General-relativistic coupling between orbital motion and internal degrees of freedom for inspiraling binary neutron stars
We analyze the coupling between the internal degrees of freedom of neutron
stars in a close binary, and the stars' orbital motion. Our analysis is based
on the method of matched asymptotic expansions and is valid to all orders in
the strength of internal gravity in each star, but is perturbative in the
``tidal expansion parameter'' (stellar radius)/(orbital separation). At first
order in the tidal expansion parameter, we show that the internal structure of
each star is unaffected by its companion, in agreement with post-1-Newtonian
results of Wiseman (gr-qc/9704018). We also show that relativistic interactions
that scale as higher powers of the tidal expansion parameter produce
qualitatively similar effects to their Newtonian counterparts: there are
corrections to the Newtonian tidal distortion of each star, both of which occur
at third order in the tidal expansion parameter, and there are corrections to
the Newtonian decrease in central density of each star (Newtonian ``tidal
stabilization''), both of which are sixth order in the tidal expansion
parameter. There are additional interactions with no Newtonian analogs, but
these do not change the central density of each star up to sixth order in the
tidal expansion parameter. These results, in combination with previous analyses
of Newtonian tidal interactions, indicate that (i) there are no large
general-relativistic crushing forces that could cause the stars to collapse to
black holes prior to the dynamical orbital instability, and (ii) the
conventional wisdom with respect to coalescing binary neutron stars as sources
of gravitational-wave bursts is correct: namely, the finite-stellar-size
corrections to the gravitational waveform will be unimportant for the purpose
of detecting the coalescences.Comment: 22 pages, 2 figures. Replaced 13 July: proof corrected, result
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