1,223 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
Cosmological Models with Shear and Rotation
Cosmological models involving shear and rotation are considered, first in the
General Relat ivistic and then in the Newtonian framework with the aim of
investigating singularities in them by using numerical and analytical
techniques. The dynamics of these rotating models ar e studied. It is shown
that singularities are unavoidable in such models and that the centr ifugal
force arising due to rotation can never overcome the gravitational and shearing
forc e over a length of time.Comment: 17 pages, 6 figures Journal Ref: J. Astrophys. Astr. (1999) 20, 79-8
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
Removing epoxy underfill between neighbouring components using acid for component chip-off
International audienc
On Shear-Free perturbations of FLRW Universes
A surprising exact result for the Einstein Field Equations is that if
pressure-free matter is moving in a shear-free way, then it must be either
expansion-free or rotation-free. It has been suggested this result is also true
for any barotropic perfect fluid, but a proof has remained elusive. We consider
the case of barotropic perfect fluid solutions linearized about a
Robertson-Walker geometry, and prove that the result remains true except for
the case of a specific highly non-linear equation of state. We argue that this
equation of state is non-physical, and hence the result is true in the
linearized case for all physically realistic barotropic perfect fluids. This
result, which is not true in Newtonian cosmology, demonstrates that the
linearized solutions, believed to result in standard local Newtonian theory, do
not always give the usual behaviour of Newtonian solutions
Evaluation of renal Kt/V as a marker of renal function in predialysis patients
Evaluation of renal Kt/V as a marker of renal function in predialysis patients.BackgroundThe use of renal Kt/V (r-Kt/V) as an indicator for the need of dialysis initiation has been recommended in the NKF-DOQI guidelines. In analogy to clinical practice in peritoneal dialysis, a fall of r-Kt/V below a threshold of 2.0 per week may indicate inadequate renal toxin elimination. However, there are no studies linking r-Kt/V with other parameters of glomerular filtration rate (GFR) in predialysis patients, and the validity of r-Kt/V as parameter for timing of dialysis initiation is unknown.MethodsRenal function was assessed repeatedly in 125 patients (N = 465 measurements). In predialysis patients (r-Kt/V <2.5 per week) r-Kt/V was compared with creatinine [CCr], urea [CUr], averaged creatinine/urea clearance [CCr/Ur], Cockcroft-Gault formula [CCG], and MDRD prediction equation 6 (MDRD6-GFR). The diagnostic performance of r-Kt/V as a parameter for timing the initiation of dialysis was evaluated.ResultsRenal Kt/V <2.5 was prevalent in 24.9% of cases (N = 116, mean 1.92 ± 0.34). In this group mean CCr was 13.8 ± 4.9, mean CUr 6.7 ± 1.3, and CCr/Ur 10.2 ± 2.9mL/min/1.73m2. There was no correlation of r-Kt/V with serum creatinine and MDRD6-GFR, but a significantly positive correlation with CCr/Ur (r2 = 0.3382, P < 0.001). Sensitivity of r-Kt/V to detect CCr/Ur < 10.5mL/min/1.73m2, defined as the threshold for dialysis initiation, was 73.6% with a specificity of 91.9%.ConclusionsThese results suggest that r-Kt/V is a parameter of acceptable specificity but poor sensitivity for the timing of dialysis initiation. Additional measures of renal function, such as the average of measured creatinine and urea clearance, also should be taken into consideration when deciding on the timing of dialysis initiation prior to the development of clinical signs of uremia and malnutrition
Tachyonic potential in Bianchi type-I universe
Motivated from recent string theoretic results, a tachyonic potential is
constructed for a spatially homogeneous and anisotropic background cosmology.Comment: 5 pages,LATEX,Typos in the text corrected, more references adde
Newtonian nonlinear hydrodynamics and magnetohydrodynamics
We use covariant methods to analyse the nonlinear evolution of
self-gravitating, non-relativistic media. The formalism is first applied to
imperfect fluids, aiming at the kinematic effects of viscosity, before extended
to inhomogeneous magnetised environments. The nonlinear electrodynamic formulae
are derived and successively applied to electrically resistive and to highly
conductive fluids. By nature, the covariant equations isolate the magnetic
effects on the kinematics and the dynamics of the medium, combining
mathematical transparency and physical clarity. Employing the Newtonian
analogue of the relativistic 1+3 covariant treatment, also facilitates the
direct comparison with the earlier relativistic studies and helps to identify
the differences in an unambiguous way. The purpose of this work is to set the
framework and take a first step towards the detailed analytical study of
complex nonlinear systems, like non-relativistic astrophysical plasmas and
collapsing protogalactic clouds.Comment: Typos corrected, references added and updated (MNRAS in press
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
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