Local Lagrangian Approximations for the Evolution of the Density Distribution Function in Large-Scale Structure

We examine local Lagrangian approximations for the gravitational evolution of the density distribution function. In these approximations, the final density at a Lagrangian point q at a time t is taken to be a function only of t and of the initial density at the same Lagrangian point. A general expression is given for the evolved density distribution function for such approximations, and we show that the vertex generating function for a local Lagrangian mapping applied to an initially Gaussian density field bears a simple relation to the mapping itself. Using this result, we design a local Lagrangian mapping which reproduces nearly exactly the hierarchical amplitudes given by perturbation theory for gravitational evolution. When extended to smoothed density fields and applied to Gaussian initial conditions, this mapping produces a final density distribution function in excellent agreement with full numerical simulations of gravitational clustering. We also examine the application of these local Lagrangian approximations to non-Gaussian initial conditions.Comment: LaTeX, 22 pages, and 11 postscript figure

Annual and solar-magnetic-cycle variations in the interplanetary magnetic field, 1926-1971

The analysis of forty-five years of inferred interplanetary magnetic field polarity shows an annual variation and a variation of about twenty years, associated here with the solar magnetic cycle. On the average the phase of the annual variation of the interplanetary field changes about 2 and 2/3 years after sunspot maximum, i.e. for about ten consecutive years the predominant polarity of the interplanetary field is away from the sun during the six-month interval in which the earth is at southern heliographic latitudes. Then a change of phase occurs so that for about the next ten years the predominant polarity is toward the sun, while the earth is at southern heliographic latitudes. The annual variation changes its predominant polarity within a few days of the times when the heliographic latitude of the earth is zero

The rotation of the Sun: Observations at Stanford

Daily observations of the photospheric rotation rate using the Doppler effect made at the Stanford Solar Observatory since May 1976 are analyzed. Results show that these observations show no daily or long period variations in the rotation rate that exceed the observational error of about one percent. The average rotation rate is the same as that of the sunspot and the large-scale magnetic field structures

The equatorial rotation velocity of the photosphere is measured to be the same as sunspots

The equatorial rotation rate of the photosphere was measured at effect data. It was found that scattered light has a large influence and must be taken into account properly. When this was done it was found that the rotation rate from Doppler shifts agreed very well with the rate found for sunspots. Short-term fluctuations in rotation rate (i.e. from day to day) were less than plus or minus 15 m/s and were thus within observational errors

Optical and Electron Paramagnetic Resonance Characterization of Point Defects in Semiconductors

Point defects in two semiconductor materials, both with promising optical properties, are investigated. The first material, CdSiP2, is a nonlinear optical material in which absorption bands due to point defects can hinder performance when used in frequency conversion applications in the infrared. The second material, Sn2P2S6, is a photorefractive material where point defects with specific properties are needed to optimize response in dynamic holography applications. Electron paramagnetic resonance (EPR) spectroscopy is used to identify the electronic structure of defects and their charge states. Correlations between EPR spectra and optical absorption allow assignments for the primary absorption bands in CdSiP2. This research established that singly ionized silicon vacancies in CdSiP2 (VSi-) are responsible for three unwanted absorption bands peaking near 800 nm, 1.0 μm, and 1.9 μm. Two new acceptor defects were identified in CdSiP2: the neutral silicon-on-phosphorus antisite (SiP0) and the neutral copper-on-cadmium (CuCd0). These defects are associated with two additional broad photoinduced optical absorption bands appearing at 0.8 μm and 1.4 μm. A series of new point defects have been identified in tellurium-doped Sn2P2S6 crystals using EPR. An iodine ion on a phosphorous site and a tellurium ion on a Sn site are trapped-electron centers. Five trapped-hole centers involve Te ions replacing sulfur ions. The g-matrix has been determined for each of the new paramagnetic defects in Sn2P2S6 and models are assigned

Radiation can never again dominate Matter in a Vacuum Dominated Universe

We demonstrate that in a vacuum-energy-dominated expansion phase, surprisingly neither the decay of matter nor matter-antimatter annihilation into relativistic particles can ever cause radiation to once again dominate over matter in the future history of the universe.Comment: updated version, as it will appear in Phys. Rev D. Title change, and some other minor alteration