1,379 research outputs found
Transport Properties of Strong-Interaction Matter
The properties of strong-interaction matter are probed in ultra-relativistic
heavy-ion collisions. In the context of measurements of the elliptic flow at
RHIC and the LHC the shear viscosity is of particular interest. In this
presentation we discuss recent results for eta/s in hadronic matter at
vanishing baryo-chemical potential within kinetic theory. Using the
Nambu-Jona-Lasinio model, special attention is paid to effects arising from the
restoration of spontaneously broken chiral symmetry with increasing
temperature.Comment: 8 pages, 4 figures, presented at the HIC for FAIR Workshop and XXVIII
Max Born Symposium "Three days on Quarkyonic Island", Wroclaw, May 19-21,
2011; v2: conversion to Pa in fig. 2 correcte
On the Significance of the Weyl Curvature in a Relativistic Cosmological Model
The Weyl curvature includes the Newtonian field and an additional field, the
so-called anti-Newtonian. In this paper, we use the Bianchi and Ricci
identities to provide a set of constraints and propagations for the Weyl
fields. The temporal evolutions of propagations manifest explicit solutions of
gravitational waves. We see that models with purely Newtonian field are
inconsistent with relativistic models and obstruct sounding solutions.
Therefore, both fields are necessary for the nonlocal nature and radiative
solutions of gravitation.Comment: 15 pages, incorporating proof correction
Incidence of seropositive myasthenia gravis in Cape Town and South Africa
Background. Myasthenia gravis (MG) is a treatable autoimmune disease characterised by fatiguable weakness of skeletal muscles. More than 85% of MG patients have antibodies to the acetylcholine receptor (AChR) at the neuromuscular junction or are seropositive for MG (SPMG). In the developed world the incidence of MG has increased, particularly among older individuals, but no epidemiological studies have been done on SPMG in Africa.
Objectives. To determine the annual incidence rate (IR) of SPMG in the Cape Town (CT) municipality, and the crude annual IR of SPMG for the whole of South Africa (SA).
Methods. Positive AChR antibody tests were identified between 1 January 2003 and 1 January 2005 for patients living in CT, and the age- and sex-specific incidences were calculated. To determine the national crude annual IR over the same period, positive assays were identified from the laboratories that process AChR assays for SA. National Census 2001 population statistics formed the denominators.
Results. There were 65 positive assays in CT, and 230 nationwide. Based on these figures the annual IR for CT was 11.2 per million per year (95% confidence interval (CI) 8.7 - 14.3), and for South Africa 2.6 per million / year (95% CI 2.2 - 2.9). After a questionnaire response from CT neurologists regarding the routine use of the AChR antibody assay, the annual IR for CT was adjusted to 12.6 per million (95% CI 9.9 - 15.9) to incorporate those presumed to have SPMG without a confirmatory test. In CT, the IR in females was 15.3 per million / year (95% CI 11.2 - 20.4), and in males, 6.8 per million / year (95% CI 4.1 - 10.7). The CT IRs for blacks, coloureds and whites were not statistically different after adjusting for age and gender. The IR of SPMG in CT was 6 times greater in those presenting after the age of 50 years than in those with earlier disease onset (95% CI 3.7 - 9.7).
Conclusions. The annual IR of SPMG in CT is much the same as rates recorded recently in other developed countries, but the rest of SA has a much lower IR. A preponderance of MG starting after the age of 50 years reflects a worldwide trend, although the CT data showed a relatively lower-than-expected incidence for older males. IRs for SPMG vary widely in different regions in SA; this is likely to be related to differences in regional health care delivery, and underdiagnosis
Can noncommutativity resolve the Big-Bang singularity?
A possible way to resolve the singularities of general relativity is proposed
based on the assumption that the description of space-time using commuting
coordinates is not valid above a certain fundamental scale. Beyond that scale
it is assumed that the space-time has noncommutative structure leading in turn
to a resolution of the singularity. As a first attempt towards realizing the
above programme a modification of the Kasner metric is constructed which is
commutative only at large time scales. At small time scales, near the
singularity, the commutation relations among the space coordinates diverge. We
interpret this result as meaning that the singularity has been completely
delocalized.Comment: Latex, 13 pages, 2 figures, accepted for publication in EPJ
Post-Newtonian Cosmology
Newtonian Cosmology is commonly used in astrophysical problems, because of
its obvious simplicity when compared with general relativity. However it has
inherent difficulties, the most obvious of which is the non-existence of a
well-posed initial value problem. In this paper we investigate how far these
problems are met by using the post-Newtonian approximation in cosmology.Comment: 12 pages, Late
Momentum resolved spin dynamics of bulk and surface excited states in the topological insulator
The prospective of optically inducing a spin polarized current for spintronic
devices has generated a vast interest in the out-of-equilibrium electronic and
spin structure of topological insulators (TIs). In this Letter we prove that
only by measuring the spin intensity signal over several order of magnitude in
spin, time and angle resolved photoemission spectroscopy (STAR-PES) experiments
is it possible to comprehensively describe the optically excited electronic
states in TIs materials. The experiments performed on
reveal the existence of a Surface-Resonance-State in the 2nd bulk band gap
interpreted on the basis of fully relativistic ab-initio spin resolved
photoemission calculations. Remarkably, the spin dependent relaxation of the
hot carriers is well reproduced by a spin dynamics model considering two
non-interacting electronic systems, derived from the excited surface and bulk
states, with different electronic temperatures.Comment: 5 pages and 4 figure
Post-Newtonian extension of the Newton-Cartan theory
The theory obtained as a singular limit of General Relativity, if the
reciprocal velocity of light is assumed to tend to zero, is known to be not
exactly the Newton-Cartan theory, but a slight extension of this theory. It
involves not only a Coriolis force field, which is natural in this theory
(although not original Newtonian), but also a scalar field which governs the
relation between Newtons time and relativistic proper time. Both fields are or
can be reduced to harmonic functions, and must therefore be constants, if
suitable global conditions are imposed. We assume this reduction of
Newton-Cartan to Newton`s original theory as starting point and ask for a
consistent post-Newtonian extension and for possible differences to usual
post-Minkowskian approximation methods, as developed, for example, by
Chandrasekhar. It is shown, that both post-Newtonian frameworks are formally
equivalent, as far as the field equations and the equations of motion for a
hydrodynamical fluid are concerned.Comment: 13 pages, LaTex, to appear in Class. Quantum Gra
Anisotropy and inflation in Bianchi I brane worlds
After a more general assumption on the influence of the bulk on the brane, we
extend some conclusions by Maartens et al. and Santos et al. on the asymptotic
behavior of Bianchi I brane worlds. As a consequence of the nonlocal
anisotropic stresses induced by the bulk, in most of our models, the brane does
not isotropize and the nonlocal energy does not vanish in the limit in which
the mean radius goes to infinity. We have also found the intriguing possibility
that the inflation due to the cosmological constant might be prevented by the
interaction with the bulk. We show that the problem for the mean radius can be
completely solved in our models, which include as particular cases those in the
references above.Comment: 10 pages, improved discussion on the likeliness of
non-isotropization, completed list of references, matches version to appear
in Class. Quantum Gra
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