The Complex Time WKB Approximation And Particle Production

The complex time WKB (CWKB) approximation has been an effective technique to understand particle production in curved as well as in flat spacetime. Earlier we obtained the standard results on particle production in time dependent gauge in various curved spacetime. In the present work we generalize the technique of CWKB to the equivalent problems in space dependent gauge. Using CWKB, we first obtain the gauge invariant result for particle production in Minkowski spacetime in strong electric field. We then carry out particle production in de-Sitter spacetime in space dependent gauge and obtain the same result that we obtained earlier in time dependent gauge. The results obtained for de-Sitter spacetime has a obvious extension to particle production in black hole spacetime. It is found that the origin of Planckian spectrum is due to repeated reflections between the turning points. As mentioned earlier, it is now explicitly shown that particle production is accompanied by rotation of currents.Comment: 12 pages, Revte

Collapse of the charge ordering gap of Nd_{0.5}Sr_{0.5}MnO_{3} in an applied magnetic field

We report results of tunneling studies on the charge ordering compound Nd_{0.5}Sr_{0.5}MnO_{3} in a magnetic field up to 6T and for temperature down to 25K.We show that a gap (2\Delta_{CO} \approx 0.5eV opens up in the density of state (DOS) at the Fermilevel (E_F) on charge ordering (T_{CO}=150K) which collapses in an applied magnetic field when the charge ordered state melts. There is a clear correspondence between the behavior of the resistivity and the gap formation and its collapse in an applied magnetic field. We conclude that a gap in the DOS at E_F is necessary for the stability of the charge ordered state.Comment: 4 pages REVTeX, 5 postscript figures included, submitted to Phys. Rev. Let

Computer Recognition Method as Applied to Codification Process for Inventory System of a Large Multidisciplined Laboratory

A variety of algorithms are existing to retrieve the information by means of furnished keys'. As suggested by Nakatsu N. et al . algorithm for the LCS problem can be used to find string which contain some given words or words similar to them. Some such LCS algorithms with their time responses are discussed 2-6 This paper also describes an effective method of recognizing the information. The method involves two way search giving the weightages to each. Finally the two values are combined to produce a match factor for recognition of information. Its application to codification in inventory system is discussed

Green synthesis of Ag nanoparticles in large quantity by cryomilling

Most of the synthetic methods for the preparation of Ag nanoparticles (Ag NPs) involve wet chemical synthesis, in which hazardous chemicals are used and the NPs are further stabilized by a surfactant. The presence of a surfactant is detrimental to the purity as well as to the native properties of the Ag NPs. The present study reports a unique technique to prepare ultrapure free-standing Ag NPs in large quantities without the use of any hazardous chemicals. This has been achieved by cryomilling. Note that cryomilling is a cost effective method to prepare metal NPs, involving ball milling below 160 ± 10 °C under a protective Ar atmosphere. The experimental results reveal that it is possible to obtain Ag NPs with a narrow size distribution (4–8 nm). The level of contamination (34 ppb of W) in the nanoparticles was estimated by EPMA, whereas the ultra-high purity of the Ag NPs was confirmed by ICP-OES and XPS. The surfactant-free Ag NPs were also stable at elevated temperatures (400 °C) and exhibited free-standing nature in liquids including ethanol, methanol, and water. The results have been discussed based on the low-temperature deformation behaviour of Ag and the electrostatic stabilization of highly pure Ag NPs in different polar liquids

Semiclassical Inequivalence of Polygonalized Billiards

Polygonalization of any smooth billiard boundary can be carried out in several ways. We show here that the semiclassical description depends on the polygonalization process and the results can be inequivalent. We also establish that generalized tangent-polygons are closest to the corresponding smooth billiard and for de Broglie wavelengths larger than the average length of the edges, the two are semiclassically equivalent.Comment: revtex, 4 ps figure

Gapped tunneling spectra in the normal state of Pr2−x_{2-x}Cex_xCuO4_4

We present tunneling data in the normal state of the electron doped cuprate superconductor Pr$_{2-x}$Ce$_x$CuO$_4$ for three different values of the doping $x$. The normal state is obtained by applying a magnetic field greater than the upper critical field, $H_{c2}$ for $T < T_c$. We observe an anomalous normal state gap near the Fermi level. From our analysis of the tunneling data we conclude that this is a feature of the normal state density of states. We discuss possible reasons for the formation of this gap and its implications for the nature of the charge carriers in the normal and the superconducting states of cuprate superconductors.Comment: 7 pages ReVTeX, 11 figures files included, submitted to PR