104,112 research outputs found
Masses, Beaming and Eddington Ratios in Ultraluminous X-ray Sources
I suggest that the beaming factor in bright ULXs varies as , where is the Eddington ratio for accretion. This is required
by the observed universal relation between
soft--excess luminosity and temperature, and is reasonable on general physical
grounds. The beam scaling means that all observable properties of bright ULXs
depend essentially only on the Eddington ratio , and that these systems
vary mainly because the beaming is sensitive to the Eddington ratio. This
suggests that bright ULXs are stellar--mass systems accreting at Eddington
ratios of order 10 -- 30, with beaming factors b \ga 0.1. Lower--luminosity
ULXs follow bolometric (not soft--excess) correlations and
probably represent {\it sub}--Eddington accretion on to black holes with masses
\sim 10\msun. High--mass X-ray binaries containing black holes or neutron
stars and undergoing rapid thermal-- or nuclear--timescale mass transfer are
excellent candidates for explaining both types. If the
scaling for bright ULXs can be extrapolated to the Eddington ratios found in
SS433, some objects currently identified as AGN at modest redshifts might
actually be ULXs (`pseudoblazars'). This may explain cases where the active
source does not coincide with the centre of the host galaxy.Comment: MNRAS Letters, in pres
Relationships of Job and Family Involvement, Family Social Support, and Work–Family Conflict with Job and Life Satisfaction
A model of the relationship between work and family that incorporates variables from both the work-family conflict and social support literatures was developed and empirically tested. This model related bidirectional work-family conflict, family instrumental and emotional social support, and job and family involvement to job and life satisfaction. Data came from 163 workers who were living with at least 1 family member. Results suggested that relationships between work and family can have an important effect on job and life satisfaction and that the level of involvement the worker assigns to work and family roles is associated with this relationship. The results also suggested that the relationship between work and family can be simultaneously characterized by conflict and support. Higher levels of work interfering with family predicted lower levels of family emotional and instrumental support. Higher levels of family emotional and instrumental support were associated with lower levels of family interfering with work. (PsycINFO Database Record (c) 2013 APA, all rights reserved)
Black-Hole Transients and the Eddington Limit
I show that the Eddington limit implies a critical orbital period P_crit(BH)
= 2d beyond which black-hole LMXBs cannot appear as persistent systems. The
unusual behaviour of GRO J1655-40 may result from its location close to this
critical period.Comment: 3 pages, no figures; to appear in MNRA
Magnetic Fields, Accretion, and the Central Engine of Gamma-Ray Bursts
I briefly review magnetic effects in accretion physics, and then go on to
discuss a possible central engine for gamma-ray bursts. A rotating black hole
immersed in a non-axisymmetric magnetic field experiences a torque trying to
align spin and field. I suggest that gamma-ray burst hosts may provide
conditions where this effect allows rapid extraction of a significant fraction
of the hole's rotational energy. I argue that much of the electromagnetic
emission is in two narrow beams parallel and antiparallel to the asymptotic
field direction. This picture suggests that only a mass 10^-5 Msun is expelled
in a relativistic outflow, as required by the fireball picture.Comment: 8 pages, Invited talk to appear in the Proceedings of Magnetic Fields
in the Universe, Angra dos Reis, Brazil, November 28 - December 3 200
Minimal generating sets of non-modular invariant rings of finite groups
It is a classical problem to compute a minimal set of invariant polynomial
generating the invariant ring of a finite group as an algebra. We present here
an algorithm for the computation of minimal generating sets in the non-modular
case. Apart from very few explicit computations of Groebner bases, the
algorithm only involves very basic operations, and is thus rather fast.
As a test bed for comparative benchmarks, we use transitive permutation
groups on 7 and 8 variables. In most examples, our algorithm implemented in
Singular works much faster than the one used in Magma, namely by factors
between 50 and 1000. We also compute some further examples on more than 8
variables, including a minimal generating set for the natural action of the
cyclic group of order 11 in characteristic 0 and of order 15 in characteristic
2.
We also apply our algorithm to the computation of irreducible secondary
invariants.Comment: 14 pages v3: Timings updated. One example adde
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