Origin of the Thermal Radiation in a Solid-State Analog of a Black-Hole

An effective black-hole-like horizon occurs, for electromagnetic waves in matter, at a surface of singular electric and magnetic permeabilities. In a physical dispersive medium this horizon disappears for wave numbers with $k>k_c$. Nevertheless, it is shown that Hawking radiation is still emitted if free field modes with $k>k_c$ are in their ground state.Comment: 13 Pages, 3 figures, Revtex with epsf macro

Human factors in design of passenger seats for commercial aircraft: A review

Seat comfort and safety research since the early part of the century is reviewed. The approach blends empirical and theoretical human factors and technical knowledge of seated humans under static and dynamic conditions experienced on commercial aircraft

Minimal Off-Shell Version of N = 1 Chiral Supergravity

We construct the minimal off-shell formulation of N = 1 chiral supergravity (SUGRA) introducing a complex antisymmetric tensor field $B_{\mu \nu}$ and a complex axial-vector field $A_{\mu}$ as auxiliary fields. The resulting algebra of the right- and left-handed supersymmetry (SUSY) transformations closes off shell and generates chiral gauge transforamtions and vector gauge transformations in addition to the transformations which appear in the case without auxiliary fields.Comment: 9 pages, late

Noncommutative electrodynamics and ultra high energy gamma rays

Plane waves in noncommutative classical electrodynamics (NCED) have a peculiar dispersion relation. We investigate the kinematical conditions on this deformed "mass shell" which come from ultra high energy gamma rays and discuss noncommutative dynamical effects on the gamma absorption by the infrared background and on the intrinsic spectrum. Finally we note that in NCED there is a strong correlation between the modified dispersion relation and the presence of dynamical effects in electromagnetic phenomena such as in the case of the synchrotron radiation. From this point of view, the limits on the typical energy scale of the violation of Lorentz invariance obtained by deformed dispersion relations and by assuming undeformed dynamical effects should be taken with some caution.Comment: Latex file, 7 pages, to be published in Europhysics Letter

Bound on the Dark Matter Density in the Solar System from Planetary Motions

High precision planet orbital data extracted from direct observation, spacecraft explorations and laser ranging techniques enable to put a strong constraint on the maximal dark matter density of a spherical halo centered around the Sun. The maximal density at Earth's location is of the order $10^5$ ${\rm GeV/cm^3}$ and shows only a mild dependence on the slope of the halo profile, taken between 0 and -2. This bound is somewhat better than that obtained from the perihelion precession limits.Comment: 7 pages, 1 figur

The use of VTE prophylaxis in relation to patient risk profiling(TUNE-IN) Wave 2 Study

KMBackground: The TUNE-IN (The Use of VTE prophylaxis in relatioN to patiEnt risk profiling) study evaluated venous thromboembolism (VTE) risk assessment and prophylaxis in private medical and surgical inpatients in Gauteng Province, South Africa. The study concluded that of the 608 patients enrolled, 54.1% were clinically evaluated to be at risk for VTE. A VTE risk assessment model (RAM), the Caprini score, increased the rate to 74.6%. Objectives: TUNE-IN Wave 2, an extension of TUNE-IN, was conducted on a national level including the public sector, focusing on surgical inpatients. Methods. The study was a national, prospective, non-interventional, multisite, epidemiological disease registry enrolling 453 surgical inpatients. The perceived clinical VTE risk, VTE risk score on Caprini RAM, VTE prophylaxis and clinical details were documented during a baseline visit. A bleeding risk score was provided. Results: Of the cohort, 269 patients (59.4%) were assessed to be at risk for VTE before applying the RAM. All patients (100%), however, were at risk on the RAM score. Early mobilisation and assessment of the VTE risk as low were the most frequent reasons for non-prescription of prophylaxis. Only 15 patients in the private and 2 in the public sector were assessed as having a bleeding risk. Chemoprophylaxis differed between the healthcare sectors, with low-molecular-weight heparin predominating in the private sector and unfractionated heparin being prescribed only in the public sector. Conclusion: VTE risk assessment and prophylaxis need to improve in both the public and the private sectors. A formal RAM will improve identification of patients at risk of VTE

Hawking Radiation Without Transplanckian Frequencies

In a recent work, Unruh showed that Hawking radiation is unaffected by a truncation of free field theory at the Planck scale. His analysis was performed numerically and based on a hydrodynamical model. In this work, by analytical methods, the mathematical and physical origin of Unruh's result is revealed. An alternative truncation scheme which may be more appropriate for black hole physics is proposed and analyzed. In both schemes the thermal Hawking radiation remains unaffected even though transplanckian energies no longer appear. The universality of this result is explained by working in momentum space. In that representation, in the presence of a horizon, the d'Alembertian equation becomes a singular first order equation. In addition, the boundary conditions corresponding to vacuum before the black hole formed are that the in--modes contain positive momenta only. Both properties remain valid when the spectrum is truncated and they suffice to obtain Hawking radiation.Comment: 27 pages, latex, includs 5 postscript figures, encoded using uufile

Hawking Radiation and Ultraviolet Regulators

Polchinski has argued that the prediction of Hawking radiation must be independent of the details of unknown high-energy physics because the calculation may be performed using `nice slices', for which the adiabatic theorem may be used. If this is so, then any calculation using a manifestly covariant --- and so slice-independent --- ultraviolet regularization must reproduce the standard Hawking result. We investigate the dependence of the Hawking radiation on such a short-distance regulator by calculating it using a Pauli--Villars regularization scheme. We find that the regulator scale, $\Lambda$, only contributes to the Hawking flux by an amount that is exponentially small in the large variable {\Lambda}/{T_\ssh} \gg 1, where T_\ssh is the Hawking temperature; in agreement with Polchinski's arguments. We also solve a technical puzzle concerning the relation between the short-distance singularities of the propagator and the Hawking effect.Comment: Tex, 11 pages, no figures, new references adde

Causal structure of acoustic spacetimes

The so-called ``analogue models of general relativity'' provide a number of specific physical systems, well outside the traditional realm of general relativity, that nevertheless are well-described by the differential geometry of curved spacetime. Specifically, the propagation of acoustic disturbances in moving fluids are described by ``effective metrics'' that carry with them notions of ``causal structure'' as determined by an exchange of sound signals. These acoustic causal structures serve as specific examples of what can be done in the presence of a Lorentzian metric without having recourse to the Einstein equations of general relativity. (After all, the underlying fluid mechanics is governed by the equations of traditional hydrodynamics, not by the Einstein equations.) In this article we take a careful look at what can be said about the causal structure of acoustic spacetimes, focusing on those containing sonic points or horizons, both with a view to seeing what is different from standard general relativity, and to seeing what the similarities might be.Comment: 51 pages, 39 figures (23 colour figures, colour used to convey physics information.) V2: Two references added, some additional discussion of maximal analytic extension, plus minor cosmetic change