26,704 research outputs found
Coupling iterated Kolmogorov diffusions
The Kolmogorov (1934) diffusion is the two-dimensional diffusion generated by real Brownian motion B and its time integral integral B d t. In this paper we construct successful co-adapted couplings for iterated Kolmogorov diffusions defined by adding iterated time integrals integral integral B d s d t,... as further components to the original Kolmogorov diffusion. A Laplace-transform argument shows it is not possible successfully to couple all iterated time integrals at once; however we give an explicit construction of a successful co-adapted coupling method for (B, integral B d t, integral integral B d s d t); and a more implicit construction of a successful co-adapted coupling method which works for finite sets of iterated time integrals
Photoproduction of Xi off nucleons
The photoproduction reaction is investigated based on
a relativistic meson-exchange model of hadronic interactions. The production
amplitude is calculated in the tree-level approximation from relevant effective
Lagrangians, whose (coupling constant) parameters are mostly fixed from the
empirical data and/or quark models together with SU(3) symmetry considerations.
Gauge invariance of the resulting amplitude is maintained by introducing the
contact currents by extending the gauge-invariant approach of Haberzettl for
one-meson photoproduction to two-meson photoproduction. The role of the
intermediate low-lying hyperons and of the intermediate higher-mass hyperon
resonances are analyzed in detail. In particular, the basic features of the
production of in and their possible
manifestations in the forthcoming experimental data are discussed.Comment: 18 pages, 17 figures, REVTeX, 1 figure added, to appear in Phys. Rev.
Molecules, ices and astronomy
Molecules in interstellar gas and in interstellar ices play a fundamental role in astronomy. However, the formation of the simplest molecule, molecular hydrogen, is still not fully understood. Similarly, although interstellar ice analogues have received much attention in the laboratory, the evolution of ices in the interstellar medium still requires further study. At UCL we have developed two separate experiments to address these issues and explore the following questions: How is H formed on dust-grain surfaces? What is the budget between internal, kinetic and surface energies in the formation process? What are the astronomical consequences of these results? For ices, we ask: How do molecules desorb from pure and from mixed ices in regions warmed by newly formed stars? What can molecules released from ices tell us about the star-formation process? We put our results in the context of other laboratory work and we describe their application to current problems in astronomy
Pre- and Post-selection paradoxes and contextuality in quantum mechanics
Many seemingly paradoxical effects are known in the predictions for outcomes
of intermediate measurements made on pre- and post-selected quantum systems.
Despite appearances, these effects do not demonstrate the impossibility of a
noncontextual hidden variable theory, since an explanation in terms of
measurement-disturbance is possible. Nonetheless, we show that for every
paradoxical effect wherein all the pre- and post- selected probabilities are 0
or 1 and the pre- and post-selected states are nonorthogonal, there is an
associated proof of contextuality. This proof is obtained by considering all
the measurements involved in the paradoxical effect -- the pre-selection, the
post-selection, and the alternative possible intermediate measurements -- as
alternative possible measurements at a single time.Comment: 5 pages, 1 figure. Submitted to Phys. Rev. Lett. v2.0 revised in the
light of referee comments, results unchange
Periodic Solutions of the Einstein Equations for Binary Systems
This revision includes clarified exposition and simplified analysis.
Solutions of the Einstein equations which are periodic and have standing
gravitational waves are valuable approximations to more physically realistic
solutions with outgoing waves. A variational principle is found which has the
power to provide an accurate estimate of the relationship between the mass and
angular momentum of the system, the masses and angular momenta of the
components, the rotational frequency of the frame of reference in which the
system is periodic, the frequency of the periodicity of the system, and the
amplitude and phase of each multipole component of gravitational radiation.
Examination of the boundary terms of the variational principle leads to
definitions of the effective mass and effective angular momentum of a periodic
geometry which capture the concepts of mass and angular momentum of the source
alone with no contribution from the gravitational radiation. These effective
quantities are surface integrals in the weak-field zone which are independent
of the surface over which they are evaluated, through second order in the
deviations of the metric from flat space.Comment: 18 pages, RevTeX 3.0, UF-RAP-93-1
Tidal interaction in binary black hole inspiral
In rotating viscous fluid stars, tidal torque leads to an exchange of spin
and orbital angular momentum. The horizon of a black hole has an effective
viscosity that is large compared to that of stellar fluids, and an effective
tidal torque may lead to important effects in the strong field interaction at
the endpoint of the inspiral of two rapidly rotating holes. In the most
interesting case both holes are maximally rotating and all angular momenta
(orbital and spins) are aligned. We point out here that in such a case (i) the
transfer of angular momentum may have an important effect in modifying the
gravitational wave ``chirp'' at the endpoint of inspiral. (ii) The tidal
transfer of spin energy to orbital energy may increase the amount of energy
being radiated. (iii) Tidal transfer in such systems may provide a mechanism
for shedding excess angular momentum. We argue that numerical relativity, the
only tool for determining the importance of tidal torque, should be more
specifically focused on binary configurations with aligned, large, angular
momenta.Comment: 5 pages, 2 figure
Formation of a rotating hole from a close limit head-on collision
Realistic black hole collisions result in a rapidly rotating Kerr hole, but
simulations to date have focused on nonrotating final holes. Using a new
solution of the Einstein initial value equations we present here waveforms and
radiation for an axisymmetric Kerr-hole-forming collision starting from small
initial separation (the ``close limit'' approximation) of two identical
rotating holes. Several new features are present in the results: (i) In the
limit of small separation, the waveform is linear (not quadratic) in the
separation. (ii) The waveforms show damped oscillations mixing quasinormal
ringing of different multipoles.Comment: 4 pages, 4 figures, submitted to PR
The Pan-STARRS1 Photometric System
The Pan-STARRS1 survey is collecting multi-epoch, multi-color observations of
the sky north of declination -30 deg to unprecedented depths. These data are
being photometrically and astrometrically calibrated and will serve as a
reference for many other purposes. In this paper we present our determination
of the Pan-STARRS photometric system: gp1, rp1, ip1, zp1, yp1, and wp1. The
Pan-STARRS photometric system is fundamentally based on the HST Calspec
spectrophotometric observations, which in turn are fundamentally based on
models of white dwarf atmospheres. We define the Pan-STARRS magnitude system,
and describe in detail our measurement of the system passbands, including both
the instrumental sensitivity and atmospheric transmission functions.
Byproducts, including transformations to other photometric systems, galactic
extinction, and stellar locus are also provided. We close with a discussion of
remaining systematic errors.Comment: 39 pages, 9 figures, machine readable table of bandpasses, accepted
for publication in Ap
Late-Time Evolution of Realistic Rotating Collapse and The No-Hair Theorem
We study analytically the asymptotic late-time evolution of realistic
rotating collapse. This is done by considering the asymptotic late-time
solutions of Teukolsky's master equation, which governs the evolution of
gravitational, electromagnetic, neutrino and scalar perturbations fields on
Kerr spacetimes. In accordance with the no-hair conjecture for rotating
black-holes we show that the asymptotic solutions develop inverse power-law
tails at the asymptotic regions of timelike infinity, null infinity and along
the black-hole outer horizon (where the power-law behaviour is multiplied by an
oscillatory term caused by the dragging of reference frames). The damping
exponents characterizing the asymptotic solutions at timelike infinity and
along the black-hole outer horizon are independent of the spin parameter of the
fields. However, the damping exponents at future null infinity are spin
dependent. The late-time tails at all the three asymptotic regions are
spatially dependent on the spin parameter of the field. The rotational dragging
of reference frames, caused by the rotation of the black-hole (or star) leads
to an active coupling of different multipoles.Comment: 16 page
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