344 research outputs found
Cluster states in nuclei as representations of a U(n+1) group
We propose a description of cluster states in nuclei in terms of
representations of unitary algebras U(n+1), where n is the number of space
degrees of freedom. Within this framework, a variety of situations including
both vibrational and rotational spectra, soft and rigid configurations,
identical and non-identical constituents can be described. As an example, we
show how the method can be used to study alpha-clustering configurations in 12C
with point group symmetry D(3h).Comment: 5 pages, 2 figures, Phys. Rev. C, in pres
The Paradox of Virtual Dipoles in the Einstein Action
The functional integral of pure Einstein 4D quantum gravity admits abnormally
large and long-lasting "dipolar fluctuations", generated by virtual sources
with the property Int d^4x Sqrt{g(x)} Tr T(x) = 0. These fluctuations would
exist also at macroscopic scales, with paradoxical consequences. We set out
their general features and give numerical estimates of possible suppression
processes.Comment: LaTeX, 5 pages; reference adde
Pathways into services for offenders with intellectual disabilities : childhood experience, diagnostic information and offence variables
The patterns and pathways into intellectual disability (ID) offender services were studied through case file review for 477 participants referred in one calendar year to community generic, community forensic, and low, medium, and maximum secure services. Data were gathered on referral source, demographic information, index behavior, prior problem behaviors, diagnostic information, and abuse or deprivation. Community referrers tended to refer to community services and secure service referrers to secure services. Physical and verbal violence were the most frequent index behaviors, whereas contact sexual offenses were more prominent in maximum security. Age at first incident varied with security, with the youngest in maximum secure services. Attention-deficit/hyperactivity disorder or conduct disorder was the most frequently recorded diagnosis, and severe deprivation was the most frequent adverse developmental experience. Fire starting, theft, and road traffic offenses did not feature prominently. Generic community services accepted a number of referrals with forensic-type behavior and had higher proportions of both women and people with moderate or severe ID
Quantum measurement as driven phase transition: An exactly solvable model
A model of quantum measurement is proposed, which aims to describe
statistical mechanical aspects of this phenomenon, starting from a purely
Hamiltonian formulation. The macroscopic measurement apparatus is modeled as an
ideal Bose gas, the order parameter of which, that is, the amplitude of the
condensate, is the pointer variable. It is shown that properties of
irreversibility and ergodicity breaking, which are inherent in the model
apparatus, ensure the appearance of definite results of the measurement, and
provide a dynamical realization of wave-function reduction or collapse. The
measurement process takes place in two steps: First, the reduction of the state
of the tested system occurs over a time of order , where
is the temperature of the apparatus, and is the number of its degrees of
freedom. This decoherence process is governed by the apparatus-system
interaction. During the second step classical correlations are established
between the apparatus and the tested system over the much longer time-scale of
equilibration of the apparatus. The influence of the parameters of the model on
non-ideality of the measurement is discussed. Schr\"{o}dinger kittens, EPR
setups and information transfer are analyzed.Comment: 35 pages revte
The Superspace of Geometrodynamics
Wheeler's Superspace is the arena in which Geometrodynamics takes place. I
review some aspects of its geometrical and topological structure that Wheeler
urged us to take seriously in the context of canonical quantum gravity.Comment: 29 pages, 8 figures. To appear in the Wheeler memorial volume of
General Relativity and Gravitatio
OC-0183 Multi-institutional evaluation of a Pareto navigation guided automated planning solution
The Hamiltonian formulation of General Relativity: myths and reality
A conventional wisdom often perpetuated in the literature states that: (i) a
3+1 decomposition of space-time into space and time is synonymous with the
canonical treatment and this decomposition is essential for any Hamiltonian
formulation of General Relativity (GR); (ii) the canonical treatment
unavoidably breaks the symmetry between space and time in GR and the resulting
algebra of constraints is not the algebra of four-dimensional diffeomorphism;
(iii) according to some authors this algebra allows one to derive only spatial
diffeomorphism or, according to others, a specific field-dependent and
non-covariant four-dimensional diffeomorphism; (iv) the analyses of Dirac
[Proc. Roy. Soc. A 246 (1958) 333] and of ADM [Arnowitt, Deser and Misner, in
"Gravitation: An Introduction to Current Research" (1962) 227] of the canonical
structure of GR are equivalent. We provide some general reasons why these
statements should be questioned. Points (i-iii) have been shown to be incorrect
in [Kiriushcheva et al., Phys. Lett. A 372 (2008) 5101] and now we thoroughly
re-examine all steps of the Dirac Hamiltonian formulation of GR. We show that
points (i-iii) above cannot be attributed to the Dirac Hamiltonian formulation
of GR. We also demonstrate that ADM and Dirac formulations are related by a
transformation of phase-space variables from the metric to lapse
and shift functions and the three-metric , which is not canonical. This
proves that point (iv) is incorrect. Points (i-iii) are mere consequences of
using a non-canonical change of variables and are not an intrinsic property of
either the Hamilton-Dirac approach to constrained systems or Einstein's theory
itself.Comment: References are added and updated, Introduction is extended,
Subsection 3.5 is added, 83 pages; corresponds to the published versio
Metal enrichment processes
There are many processes that can transport gas from the galaxies to their
environment and enrich the environment in this way with metals. These metal
enrichment processes have a large influence on the evolution of both the
galaxies and their environment. Various processes can contribute to the gas
transfer: ram-pressure stripping, galactic winds, AGN outflows, galaxy-galaxy
interactions and others. We review their observational evidence, corresponding
simulations, their efficiencies, and their time scales as far as they are known
to date. It seems that all processes can contribute to the enrichment. There is
not a single process that always dominates the enrichment, because the
efficiencies of the processes vary strongly with galaxy and environmental
properties.Comment: 18 pages, 8 figures, accepted for publication in Space Science
Reviews, special issue "Clusters of galaxies: beyond the thermal view",
Editor J.S. Kaastra, Chapter 17; work done by an international team at the
International Space Science Institute (ISSI), Bern, organised by J.S.
Kaastra, A.M. Bykov, S. Schindler & J.A.M. Bleeke
Gravitational Collapse in Generalized Vaidya Space-Time for Lovelock Gravity Theory
In this work, we have assumed the generalized Vaidya solution in Lovelock
theory of gravity in -dimensions. It has been shown that Gauss-Bonnet
gravity, dimensionally continued Lovelock gravity and pure Lovelock gravity can
be constructed by suitable choice of parameters. We have investigated the
occurrence of singularities formed by the gravitational collapse in above three
particular forms of Lovelock theory of gravity. The dependence of the nature of
singularity on the existence of radial null geodesic for Vaidya space-time has
been specially considered. In all the three models, we have shown that the
nature of singularities (naked singularity or black hole) completely depend on
the parameters. Choices of various parameters are shown in tabular form. In
Gauss-Bonnet gravity theory, it can be concluded that the possibility of naked
singularity increases with increase in dimensions. In dimensionally continued
Lovelock gravity, the naked singularity is possible for odd dimensions for
several values of parameters. In pure Lovelock gravity, only black hole forms
due to the gravitational collapse for any values of parameters. It has been
shown that when accretion is taking place on a collapsing object, it is highly
unlikely to get a black hole. Finally on considering the phantom era in the
expanding universe it is observed that there is no possibility of formation of
a black hole if we are in the Gauss-Bonnet gravity considering the accreting
procedure upon a collapsing object.Comment: 11 page
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