512 research outputs found
Horizontal and vertical movements of starry smooth-hound Mustelus asterias in the northeast Atlantic
Commercial landings of starry smooth-hound Mustelus asterias in northern European seas are increasing, whilst our knowledge of their ecology, behaviour and population structure remains limited. M. asterias is a widely distributed demersal shark, occupying the waters of the southern North Sea and Irish Sea in the north, to at least the southern Bay of Biscay in the south, and is seasonally abundant in UK waters. There are no species-specific management measures for the northeast Atlantic stock, and the complexity of its population structure is not yet fully understood. To address this issue, we deployed both mark-recapture and electronic tags on M. asterias to gain novel insights into its horizontal and vertical movements. Our data suggest that the habitat use of M. asterias changes on a seasonal basis, with associated changes in geographical distribution, depth utilisation and experienced temperature. We report the first direct evidence of philopatry for this species, and also provide initial evidence of sex-biased dispersal and potential metapopulation-like stock structuring either side of the UK continental shelf. Investigations of finer-scale vertical movements revealed clear diel variation in vertical activity. The illustrated patterns of seasonal space-use and behaviour will provide important information to support the stock assessment process and will help inform any future management options
Uncertainties in the --decay nuclear matrix elements
The nuclear matrix elements of the neutrinoless double beta decay
() of most nuclei with known -decay rates are
systematically evaluated using the Quasiparticle Random Phase Approximation
(QRPA) and Renormalized QRPA (RQRPA). The experimental -decay
rate is used to adjust the most relevant parameter, the strength of the
particle-particle interaction. With such procedure the values become
essentially independent on single-particle basis size, the axial vector
quenching factor, etc. Theoretical arguments in favor of the adopted way of
determining the interaction parameters are presented. It is suggested that most
of the spread among the published 's can be ascribed to the choices
of implicit and explicit parameters, inherent to the QRPA method.Comment: 9 pages, 1 figure. Contribution to MEDEX'05, Corfu, Greece, September
26 - 29, 2005. A short version of nucl-th/0503063, to be published in Czech.
J. Phy
Obtaining a class of Type O pure radiation metrics with a cosmological constant, using invariant operators
Using the generalised invariant formalism we derive a class of conformally
flat spacetimes whose Ricci tensor has a pure radiation and a Ricci scalar
component. The method used is a development of the methods used earlier for
pure radiation spacetimes of Petrov types O and N respectively. In this paper
we demonstrate how to handle, in the generalised invariant formalism,
spacetimes with isotropy freedom and rich Killing vector structure. Once the
spacetimes have been constructed, it is straightforward to deduce their
Karlhede classification: the Karlhede algorithm terminates at the fourth
derivative order, and the spacetimes all have one degree of null isotropy and
three, four or five Killing vectors.Comment: 29 page
Type O pure radiation metrics with a cosmological constant
In this paper we complete the integration of the conformally flat pure
radiation spacetimes with a non-zero cosmological constant , and , by considering the case . This is a
further demonstration of the power and suitability of the generalised invariant
formalism (GIF) for spacetimes where only one null direction is picked out by
the Riemann tensor. For these spacetimes, the GIF picks out a second null
direction, (from the second derivative of the Riemann tensor) and once this
spinor has been identified the calculations are transferred to the simpler GHP
formalism, where the tetrad and metric are determined. The whole class of
conformally flat pure radiation spacetimes with a non-zero cosmological
constant (those found in this paper, together with those found earlier for the
case ) have a rich variety of subclasses with zero,
one, two, three, four or five Killing vectors
Prediction of 30-day mortality after hip fracture surgery by the Nottingham Hip Fracture Score and the Surgical Outcome Risk Tool
The care of the elderly with hip fractures and their outcomes might be improved with resources targeted by the accurate calculation of risks of mortality and morbidity. We used a multicentre national dataset to evaluate and recalibrate the Nottingham Hip Fracture Score and Surgical Outcome Risk Tool. We split 9,017 hip fracture cases from the Anaesthesia Sprint Audit of Practice into derivation and validation data sets and used logistic regression to derive new model co-efficients for death at 30 postoperative days. The area (95% CI) under the receiver operator characteristic curve of 0.71 (0.67 0.75) indicated acceptable discrimination by the Nottingham Hip Fracture Score and acceptable calibration fit (Hosmer–Lemeshow test), p = 0.23, with a similar discrimination by the Surgical Outcome Risk Tool, 0.70 (0.66–0.74), which was miscalibrated to the observed data, p = 0.001. We recommend that studies test these scores for patients with hip fractures in other countries. We also recommend these models are compared with case-mix adjustment tools used in the UK
Antiferromagnetic Zigzag Spin Chain in Magnetic Fields at Finite Temperatures
We study thermodynamic behaviors of the antiferromagnetic zigzag spin chain
in magnetic fields, using the density-matrix renormalization group method for
the quantum transfer matrix. We focus on the thermodynamics of the system near
the critical fields in the ground-state magnetization process(- curve):
the saturation field, the lower critical field associated with excitation gap,
and the field at the middle-field cusp singularity. We calculate magnetization,
susceptibility and specific heat of the zigzag chain in magnetic fields at
finite temperatures, and then discuss how the calculated quantities reflect the
low-lying excitations of the system related with the critical behaviors in the
- curve.Comment: accepted for publication in Physical Review
Low-temperature dynamics of the Curie-Weiss Model: Periodic orbits, multiple histories, and loss of Gibbsianness
We consider the Curie-Weiss model at a given initial temperature in vanishing
external field evolving under a Glauber spin-flip dynamics corresponding to a
possibly different temperature. We study the limiting conditional probabilities
and their continuity properties and discuss their set of points of
discontinuity (bad points). We provide a complete analysis of the transition
between Gibbsian and non-Gibbsian behavior as a function of time, extending
earlier work for the case of independent spin-flip dynamics. For initial
temperature bigger than one we prove that the time-evolved measure stays Gibbs
forever, for any (possibly low) temperature of the dynamics. In the regime of
heating to low-temperatures from even lower temperatures, when the initial
temperature is smaller than the temperature of the dynamics, and smaller than
1, we prove that the time-evolved measure is Gibbs initially and becomes
non-Gibbs after a sharp transition time. We find this regime is further divided
into a region where only symmetric bad configurations exist, and a region where
this symmetry is broken. In the regime of further cooling from low-temperatures
there is always symmetry-breaking in the set of bad configurations. These bad
configurations are created by a new mechanism which is related to the
occurrence of periodic orbits for the vector field which describes the dynamics
of Euler-Lagrange equations for the path large deviation functional for the
order parameter. To our knowledge this is the first example of the rigorous
study of non-Gibbsian phenomena related to cooling, albeit in a mean-field
setup.Comment: 31 pages, 24 figure
Classical A_n--W-Geometry
This is a detailed development for the case, of our previous article
entitled "W-Geometries" to be published in Phys. Lett. It is shown that the
--W-geometry corresponds to chiral surfaces in . This is comes out
by discussing 1) the extrinsic geometries of chiral surfaces (Frenet-Serret and
Gauss-Codazzi equations) 2) the KP coordinates (W-parametrizations) of the
target-manifold, and their fermionic (tau-function) description, 3) the
intrinsic geometries of the associated chiral surfaces in the Grassmannians,
and the associated higher instanton- numbers of W-surfaces. For regular points,
the Frenet-Serret equations for --W-surfaces are shown to give the
geometrical meaning of the -Toda Lax pair, and of the conformally-reduced
WZNW models, and Drinfeld-Sokolov equations. KP coordinates are used to show
that W-transformations may be extended as particular diffeomorphisms of the
target-space. This leads to higher-dimensional generalizations of the WZNW and
DS equations. These are related with the Zakharov- Shabat equations. For
singular points, global Pl\"ucker formulae are derived by combining the
-Toda equations with the Gauss-Bonnet theorem written for each of the
associated surfaces.Comment: (60 pages
Spacetime Coarse Grainings in the Decoherent Histories Approach to Quantum Theory
We investigate the possibility of assigning consistent probabilities to sets
of histories characterized by whether they enter a particular subspace of the
Hilbert space of a closed system during a given time interval. In particular we
investigate the case that this subspace is a region of the configuration space.
This corresponds to a particular class of coarse grainings of spacetime
regions. We consider the arrival time problem and the problem of time in
reparametrization invariant theories as for example in canonical quantum
gravity. Decoherence conditions and probabilities for those application are
derived. The resulting decoherence condition does not depend on the explicit
form of the restricted propagator that was problematic for generalizations such
as application in quantum cosmology. Closely related is the problem of
tunnelling time as well as the quantum Zeno effect. Some interpretational
comments conclude, and we discuss the applicability of this formalism to deal
with the arrival time problem.Comment: 23 pages, Few changes and added references in v
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