Bose-Einstein Correlations and Sonoluminescence

Sonoluminescence may be studied in detail by intensity correlations among the emitted photons. As an example, we discuss an experiment to measure the size of the light-emitting region by the Hanbury Brown-Twiss effect. We show that single bubble sonoluminescence is almost ideally suited for study by this method and that plausible values for the physical parameters are within easy experimental reach. A sequence of two and higher order photon correlation experiments is outlined.Comment: Latex File, 8 pages, Postscript file with 2 figs. attache

Phase-resolved XMM-Newton and swift observations of WR 25

We present an analysis of long-term X-ray and optical observations of the Wolf-Rayet binary WR 25. Using archival data from observations with the XMM-Newton and the Swift observatories spanning over ~10 yr, we show that WR 25 is a periodic variable in X-rays with a period of $208 \pm 3$ days. X-ray light curves in the 0.5-10.0 keV energy band show phase-locked variability, where the flux increased by a factor of ~2 from minimum to maximum, being maximum near periastron passage. The light curve in the soft energy band (0.5-2.0 keV) shows two minima indicating the presence of two eclipses. However, the light curve in the hard energy band (2.0-10.0 keV) shows only one minimum during the apastron passage. The X-ray spectra of WR 25 were explained by a two-temperature plasma model. Both the cool and the hot plasmas were constant at 0.628+/-0.008 and 2.75+/-0.06 keV throughout an orbital cycle, where the cooler plasma could be due to the small scale shocks in a radiation-driven outflow and the high temperature plasma could be due to the collision of winds. The column density varied with the orbital phase and was found to be maximum after the periastron passage, when the WN star is in front of the O star. The abundances of WR 25 were found to be non-solar. Optical V-band data of WR 25 also show the phase-locked variability, being at maximum near periastron passage. The results based on the present analysis indicate that WR 25 is a colliding wind binary where the presence of soft X-rays is attributed to individual components; however, hard X-rays are due to the collision of winds.Comment: 12 pages, 7 figures, 5 tables, Ap

Operational Trans-Resistance Amplifier Based Tunable Wave Active Filter

In this paper, Operational Trans-Resistance Amplifier (OTRA) based wave active filter structures are presented. They are flexible and modular, making them suitable to implement higher order filters. The circuits implement the resistors using matched transistors, operating in linear region, making them well suited for IC fabrication. They are insensitive to parasitic input capacitances and input resistances due to the internally grounded input terminals of OTRA. As an application, a doubly terminated third order Butterworth low pass filter has been implemented, by substituting OTRA based wave equivalents of passive elements. PSPICE simulations are given to verify the theoretical analysis

Dust modification of the plasma conductivity in the mesosphere

Relative transverse drift (with respect to the ambient magnetic field) between the weakly magnetized electrons and the unmagnetized ions at the lower altitude (80 km) and between the weakly magnetized ions and unmagnetized dust at the higher altitude (90 km) gives rise to the finite Hall conductivity in the Earth's mesosphere. If, on the other hand, the number of free electrons is sparse in the mesosphere and most of the negative charge resides on the weakly magnetized, fine, nanometre sized dust powder and positive charge on the more massive, micron sized, unmagnetized dust, the sign of the Hall conductivity due to their relative transverse drift will be opposite to the previous case. Thus the sign of the Hall effect not only depends on the direction of the local magnetic field but also on the nature of the charge carrier in the partially ionized dusty medium. As the Hall and the Ohm diffusion are comparable below 80 km, the low frequency long wavelength waves will be damped at this altitude with the damping rate typically of the order of few minutes. Therefore, the ultra--low frequency magnetohydrodynamic waves can not originate below 80 km in the mesosphere. However, above 80 km since Hall effect dominates Ohm diffusion the mesosphere can host the ultra--low frequency waves which can propagate across the ionosphere with little or, no damping.Comment: 21 pages, 3 figures; to appear in the Journal of Atmospheric and Solar-Terrestrial Physic