The use of x-ray scattering to study the anomalous elastic properties of fe-ni alloys

X-ray scattering technique for study of elastic properties of nickel-iron allo

On satellite meteorology studies Final report

Satellite meteorology research on polar energy budget, atmospherics detection, and Mars atmospheric circulatio

On the Evolutionary History of Stars and their Fossil Mass and Light

The total extragalactic background radiation can be an important test of the global star formation history (SFH). Using direct observational estimates of the SFH, along with standard assumptions about the initial mass function (IMF), we calculate the total extragalactic background radiation and the observed stellar density today. We show that plausible SFHs allow a significant range in each quantity, but that their ratio is very tightly constrained. Current estimates of the stellar mass and extragalactic background are difficult to reconcile, as long as the IMF is fixed to the Salpeter slope above 1 Msun. The joint confidence interval of these two quantities only agrees with that determined from the allowed range of SFH fits at the 3-sigma level, and for our best-fit values the discrepancy is about a factor of two. Alternative energy sources that contribute to the background, such as active galactic nuclei (AGN), Population III stars, or decaying particles, appear unlikely to resolve the discrepancy. However, changes to the IMF allow plausible solutions to the background problem. The simplest is an average IMF with an increased contribution from stars around 1.5--4 Msun. A ``paunchy'' IMF of this sort could emerge as a global average if low mass star formation is suppressed in galaxies experiencing rapid starbursts. Such an IMF is consistent with observations of star-forming regions, and would help to reconcile the fossil record of star formation with the directly observed SFH.Comment: 21 pages, 7 figures, 3 tables; submitted to Monthly Notice

Accurate determination of the Lagrangian bias for the dark matter halos

We use a new method, the cross power spectrum between the linear density field and the halo number density field, to measure the Lagrangian bias for dark matter halos. The method has several important advantages over the conventional correlation function analysis. By applying this method to a set of high-resolution simulations of 256^3 particles, we have accurately determined the Lagrangian bias, over 4 magnitudes in halo mass, for four scale-free models with the index n=-0.5, -1.0, -1.5 and -2.0 and three typical CDM models. Our result for massive halos with $M \ge M_*$ ($M_*$ is a characteristic non-linear mass) is in very good agreement with the analytical formula of Mo & White for the Lagrangian bias, but the analytical formula significantly underestimates the Lagrangian clustering for the less massive halos $M < M_*. Our simulation result however can be satisfactorily described, with an accuracy better than 15%, by the fitting formula of Jing for Eulerian bias under the assumption that the Lagrangian clustering and the Eulerian clustering are related with a linear mapping. It implies that it is the failure of the Press-Schechter theories for describing the formation of small halos that leads to the inaccuracy of the Mo & White formula for the Eulerian bias. The non-linear mapping between the Lagrangian clustering and the Eulerian clustering, which was speculated as another possible cause for the inaccuracy of the Mo & White formula, must at most have a second-order effect. Our result indicates that the halo formation model adopted by the Press-Schechter theories must be improved.Comment: Minor changes; accepted for publication in ApJ (Letters) ; 11 pages with 2 figures include

The growth of galaxies in cosmological simulations of structure formation

We use hydrodynamic simulations to examine how the baryonic components of galaxies are assembled, focusing on the relative importance of mergers and smooth accretion in the formation of ~L_* systems. In our primary simulation, which models a (50\hmpc)^3 comoving volume of a Lambda-dominated cold dark matter universe, the space density of objects at our (64-particle) baryon mass resolution threshold, M_c=5.4e10 M_sun, corresponds to that of observed galaxies with L~L_*/4. Galaxies above this threshold gain most of their mass by accretion rather than by mergers. At the redshift of peak mass growth, z~2, accretion dominates over merging by about 4:1. The mean accretion rate per galaxy declines from ~40 M_sun/yr at z=2 to ~10 M_sun/yr at z=0, while the merging rate peaks later (z~1) and declines more slowly, so by z=0 the ratio is about 2:1. We cannot distinguish truly smooth accretion from merging with objects below our mass resolution threshold, but extrapolating our measured mass spectrum of merging objects, dP/dM ~ M^a with a ~ -1, implies that sub-resolution mergers would add relatively little mass. The global star formation history in these simulations tracks the mass accretion rate rather than the merger rate. At low redshift, destruction of galaxies by mergers is approximately balanced by the growth of new systems, so the comoving space density of resolved galaxies stays nearly constant despite significant mass evolution at the galaxy-by-galaxy level. The predicted merger rate at z<~1 agrees with recent estimates from close pairs in the CFRS and CNOC2 redshift surveys.Comment: Submitted to ApJ, 35 pp including 15 fig

Gravitational energy

Observers at rest in a stationary spacetime flat at infinity can measure small amounts of rest-mass+internal energies+kinetic energies+pressure energy in a small volume of fluid attached to a local inertial frame. The sum of these small amounts is the total "matter energy" for those observers. The total mass-energy minus the matter energy is the binding gravitational energy. Misner, Thorne and Wheeler evaluated the gravitational energy of a spherically symmetric static spacetime. Here we show how to calculate gravitational energy in any static and stationary spacetime for isolated sources with a set of observers at rest. The result of MTW is recovered and we find that electromagnetic and gravitational 3-covariant energy densities in conformastatic spacetimes are of opposite signs. Various examples suggest that gravitational energy is negative in spacetimes with special symmetries or when the energy-momentum tensor satisfies usual energy conditions.Comment: 12 pages. Accepted for publication in Class. Quantum Gra

Plasmarings as dual black rings

We construct solutions to the relativistic Navier-Stokes equations that describe the long wavelength collective dynamics of the deconfined plasma phase of N=4 Yang Mills theory compactified down to d=3 on a Scherk-Schwarz circle and higher dimensional generalisations. Our solutions are stationary, axially symmetric spinning balls and rings of plasma. These solutions, which are dual to (yet to be constructed) rotating black holes and black rings in Scherk-Schwarz compactified AdS(5) and AdS(6), and have properties that are qualitatively similar to those of black holes and black rings in flat five dimensional supergravity.Comment: 40 pages, 40 figures. (v2) Correction to black brane equation of state, additional reference

Generalized mean-field study of a driven lattice gas

Generalized mean-field analysis has been performed to study the ordering process in a half-filled square lattice-gas model with repulsive nearest neighbor interaction under the influence of a uniform electric field. We have determined the configuration probabilities on 2-, 4-, 5-, and 6-point clusters excluding the possibility of sublattice ordering. The agreement between the results of 6-point approximations and Monte Carlo simulations confirms the absence of phase transition for sufficiently strong fields.Comment: 4 pages (REVTEX) with 4 PS figures (uuencoded

Mass and angular momenta of Kerr anti-de Sitter spacetimes in Einstein-Gauss-Bonnet theory

We compute the mass and angular momenta of rotating anti-de Sitter spacetimes in Einstein-Gauss-Bonnet theory of gravity using a superpotential derived from standard Noether identities. The calculation relies on the fact that the Einstein and Einstein-Gauss-Bonnet vacuum equations are the same when linearized on maximally symmetric backgrounds and uses the recently discovered D-dimensional Kerr-anti-de Sitter solutions to Einstein's equations