Energy and Momentum of a Class of Rotating Gravitational Waves

We calculate energy and momentum for a class of cylindrical rotating gravitational waves using Einstein and Papapetrou's prescriptions. It is shown that the results obtained are reduced to the special case of the cylindrical gravitational waves already available in the literature.Comment: 11 pages, no figure, Late

Energy and momentum of cylindrical gravitational waves. II

Recently Nathan Rosen and the present author obtained the energy and momentum densities of cylindrical gravitational waves in Einstein's prescription and found them to be finite and reasonable. In the present paper we calculate the same in prescriptions of Tolman as well as Landau and Lifshitz and discuss the results.Comment: 8 pages, LaTex, To appear in Pramana- J. Physic

X-ray Light Curves and Accretion Disk Structure of EX Hydrae

We present X-ray light curves for the cataclysmic variable EX Hydrae obtained with the Chandra High Energy Transmission Grating Spectrometer and the Extreme Ultraviolet Explorer Deep Survey photometer. We confirm earlier results on the shape and amplitude of the binary light curve and discuss a new feature: the phase of the minimum in the binary light curve, associated with absorption by the bulge on the accretion disk, increases with wavelength. We discuss several scenarios that could account for this trend and conclude that, most likely, the ionization state of the bulge gas is not constant, but rather decreases with binary phase. We also conclude that photoionization of the bulge by radiation originating from the white dwarf is not the main source of ionization, but that it is heated by shocks originating from the interaction between the inflowing material from the companion and the accretion disk. The findings in this paper provide a strong test for accretion disk models in close binary systems.Comment: 19 pages, 4 figures, accepted for publication in the Ap

Nonet Symmetry and Two-Body Decays of Charmed Mesons

The decay of charmed mesons into pseudoscalar (P) and vector (V) mesons is studied in the context of nonet symmetry. We have found that it is badly broken in the PP channels and in the P sector of the PV channels as expected from the non-ideal mixing of the \eta and the \eta'. In the VV channels, it is also found that nonet symmetry does not describe the data well. We have found that this discrepancy cannot be attributed entirely to SU(3) breaking at the usual level of 20--30%. At least one, or both, of nonet and SU(3) symmetry must be very badly broken. The possibility of resolving the problem in the future is also discussed.Comment: 9 pages, UTAPHY-HEP-

Charged Condensate and Helium Dwarf Stars

White dwarf stars composed of carbon, oxygen or heavier elements are expected to crystallize as they cool down below certain temperatures. Yet, simple arguments suggest that the helium white dwarf cores may not solidify, mostly because of zero-point oscillations of the helium ions that would dissolve the crystalline structure. We argue that the interior of the helium dwarfs may instead form a macroscopic quantum state in which the charged helium-4 nuclei are in a Bose-Einstein condensate, while the relativistic electrons form a neutralizing degenerate Fermi liquid. We discuss the electric charge screening, and the spectrum of this substance, showing that the bosonic long-wavelength fluctuations exhibit a mass gap. Hence, there is a suppression at low temperatures of the boson contribution to the specific heat -- the latter being dominated by the specific heat of the electrons near the Fermi surface. This state of matter may have observational signatures.Comment: 10 pages; v2: to appear in JCAP, brief comments and section titles added, typos correcte

On the Asserted Clash between the Freud and the Bianchi Identities

Through a constructive method it is shown that the claim advanced in recent times about a clash that should occur between the Freud and the Bianchi identities in Einstein's general theory of relativity is based on a faulty argument.Comment: 4 pages, plain Te

Energy-momentum Density of Gravitational Waves

In this paper, we elaborate the problem of energy-momentum in general relativity by energy-momentum prescriptions theory. Our aim is to calculate energy and momentum densities for the general form of gravitational waves. In this connection, we have extended the previous works by using the prescriptions of Bergmann and Tolman. It is shown that they are finite and reasonable. In addition, using Tolman prescription, exactly, leads to same results that have been obtained by Einstein and Papapetrou prescriptions.Comment: LaTeX, 9 pages, 1 table: added reference

The measurement errors in the Swift-UVOT and XMM-OM

The probability of photon measurement in some photon counting instrumentation, such as the Optical Monitor on the XMM-Newton satellite, and the UVOT on the Swift satellite, does not follow a Poisson distribution due to the detector characteristics, but a Binomial distribution. For a single-pixel approximation, an expression was derived for the incident countrate as a function of the measured count rate by Fordham, Moorhead and Galbraith (2000). We show that the measured countrate error is binomial, and extend their formalism to derive the error in the incident count rate. The error on the incident count rate at large count rates is larger than the Poisson-error of the incident count rate.Comment: 4 pages, 2 postscript figures, submitted to MNRA

Searching for the MSW Enhancement

We point out that the length scale associated with the MSW effect is the radius of the Earth. Therefore to verify matter enhancement of neutrino oscillations, it will be necessary to study neutrinos passing through the Earth. For the parameters of MSW solutions to the solar neutrino problem, the only detectable effects occur in a narrow band of energies from 5 to 10 MeV. We propose that serious consideration be given to mounting an experiment at a location within 9.5 degrees of the equator.Comment: 10 pages, RevTe

Fatigue of notched fiber composite laminates. Part 1: Analytical model

A description is given of a semi-empirical, deterministic analysis for prediction and correlation of fatigue crack growth, residual strength, and fatigue lifetime for fiber composite laminates containing notches (holes). The failure model used for the analysis is based upon composite heterogeneous behavior and experimentally observed failure modes under both static and fatigue loading. The analysis is consistent with the wearout philosophy. Axial cracking and transverse cracking failure modes are treated together in the analysis. Cracking off-axis is handled by making a modification to the axial cracking analysis. The analysis predicts notched laminate failure from unidirectional material fatique properties using constant strain laminate analysis techniques. For multidirectional laminates, it is necessary to know lamina fatique behavior under axial normal stress, transverse normal stress and axial shear stress. Examples of the analysis method are given