Investigation of Shallow Sedimentary Structure of the Anchorage Basin, Alaska, Using Simulated Annealing Inversion of Site Response

This study deals with shallow sedimentary structure of the Anchorage basin in Alaska. For this purpose, inversion of site response [SR(f)] data in the frequency range 0.5-11.0 Hz from various sites of the basin has been performed using the simulated annealing method to compute subsurface layer thickness, shear-wave velocity (beta), density, and shear-wave quality factor. The one-dimensional (1D) models for the aforementioned parameters were obtained with preset bounds on the basis of available geological information such that the L-2 norm error between the observed and computed site response attained a global minimum. Next, the spatial distribution of the important parameter beta was obtained by interpolating values yielded by the 1D models. The results indicate the presence of three distinct velocity zones as the source of spatial variation of SR(f) in the Anchorage basin. In the uppermost part of the basin, the beta values of fine-grain Quaternary sediments mainly lie in the range of 180-500 m/sec with thickness varying from 15 to 50 m. This formation overlies relatively thick (80-200 m) coarse-grain Quaternary sediments with beta values in the range of 600-900 m/sec. These two Quaternary units are, in turn, overlain on Tertiary sediments with beta > 1000 m/sec located at depths of 100 and 250 m, respectively, in the central and western side along the Knik Arm parts of the basin. The important implication of the result is that the sources of spatial variation of SR(f) in the Anchorage basin for the frequency band 0.5-11 Hz, besides in the uppermost 30 m, are found to be deeper than this depth. Thus, use of commonly considered geological formations in the depth intervals from 0 to 30 m for the ground-motion interpretation will likely yield erroneous results in the Anchorage basin.GIEnvironment and Natural Resources InstituteSchool of Engineering of the University of Alaska, AnchorageGeological Science

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

Periodic Orbits in Polygonal Billiards

We review some properties of periodic orbit families in polygonal billiards and discuss in particular a sum rule that they obey. In addition, we provide algorithms to determine periodic orbit families and present numerical results that shed new light on the proliferation law and its variation with the genus of the invariant surface. Finally, we deal with correlations in the length spectrum and find that long orbits display Poisson fluctuations.Comment: 30 pages (Latex) including 11 figure

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

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

The CWKB Method of Particle Production in Periodic Potential

In this work we study the particle production in time dependent periodic potential using the method of complex time WKB (CWKB) approximation. In the inflationary cosmology at the end of inflationary stage, the potential becomes time dependent as well as periodic. Reheating occurs due to particle production by the oscillating inflaton field. Using CWKB we obtain almost identical results on catastrophic particle production as obtained by others.Comment: 17 pages, latex, 2 figure

Abundance of low energy (50-150 MeV) antiprotons in cosmic rays

The progress is presented of the nuclear emulsion experiment to determine abundance of low energy antiprotons in cosmic rays. No antiprotons have been detected so far at upper limit of p/p less than or similar to 4 x .0001 in the energy range 50 MeV to 15 MeV

Low-energy quenching of positronium by helium

Very low-energy scattering of orthopositronium by helium has been investigated for simultaneous study of elastic cross section and pick-off quenching rate using a model exchange potential. The present calculational scheme, while agrees with the measured cross section of Skalsey et al, reproduces successfully the parameter ^ 1Z_{\makebox{eff}}, the effective number of electrons per atom in a singlet state relative to the positron. Together with the fact that this model potential also leads to an agreement with measured medium energy cross sections of this system, this study seems to resolve the long-standing discrepancy at low energies among different theoretical calculations and experimental measurements.Comment: 4 latex pages, 3 postscript figure