Low thrust viscous nozzle flow fields prediction

A Navier-Stokes code was developed for low thrust viscous nozzle flow field prediction. An implicit finite volume in an arbitrary curvilinear coordinate system lower-upper (LU) scheme is used to solve the governing Navier-Stokes equations and species transportation equations. Sample calculations of carbon dioxide nozzle flow are presented to verify the validity and efficiency of this code. The computer results are in reasonable agreement with the experimental data

The Structure and Clustering of Lyman Break Galaxies

The number density and clustering properties of Lyman-break galaxies (LBGs) are consistent with them being the central galaxies of the most massive dark halos present at z~3. This conclusion holds in all currently popular hierarchical models for structure formation, and is almost independent of the global cosmological parameters. We examine whether the sizes, luminosities, kinematics and star-formation rates of LBGs are also consistent with this identification. Simple formation models tuned to give good fits to low redshift galaxies can predict the distribution of these quantities in the LBG population. The LBGs should be small (with typical half-light radii of 0.6-2 kpc/h), should inhabit haloes of moderately high circular velocity (180-290 km/s) but have low stellar velocity dispersions (70-120 km/s) and should have substantial star formation rates (15-100 Msun/yr). The numbers here refer to the predicted median values in the LBG sample of Adelberger et al. (1998); the first assumes an Omega=1 universe and the second a flat universe with Omega=0.3. For either cosmology these predictions are consistent with the current (rather limited) observational data. Following the work of Kennicutt (1998) we assume stars to form more rapidly in gas of higher surface density. This predicts that LBG samples should preferentially contain objects with low angular momentum, and so small size, for their mass. In contrast, samples of damped Lyman alpha systems (DLSs), should be biased towards objects with large angular momentum. Bright LBGs and DLSs may therefore form distinct populations, with very different sizes and star formation rates, LBGs being smaller and more metal-rich than DLSs of similar mass and redshift.Comment: 27 pages, 9 figures, MNRAS submitte

Observational evidence for stochastic biasing

We show that the galaxy density in the Las Campanas Redshift Survey (LCRS) cannot be perfectly correlated with the underlying mass distribution since various galaxy subpopulations are not perfectly correlated with each other, even taking shot noise into account. This rules out the hypothesis of simple linear biasing, and suggests that the recently proposed stochastic biasing framework is necessary for modeling actual data.Comment: 4 pages, with 2 figures included. Minor revisions to match accepted ApJL version. Links and color fig at http://www.sns.ias.edu/~max/r_frames.html or from [email protected]

Two Aspects of the Mott-Hubbard Transition in Cr-doped V_2O_3

The combination of bandstructure theory in the local density approximation with dynamical mean field theory was recently successfully applied to V$_2$O$_3$ -- a material which undergoes the f amous Mott-Hubbard metal-insulator transition upon Cr doping. The aim of this sh ort paper is to emphasize two aspects of our recent results: (i) the filling of the Mott-Hubbard gap with increasing temperature, and (ii) the peculiarities of the Mott-Hubbard transition in this system which is not characterized by a diver gence of the effective mass for the $a_{1g}$-orbital.Comment: 2 pages, 3 figures, SCES'04 conference proceeding

Unusually Large Fluctuations in the Statistics of Galaxy Formation at High Redshift

We show that various milestones of high-redshift galaxy formation, such as the formation of the first stars or the complete reionization of the intergalactic medium, occurred at different times in different regions of the universe. The predicted spread in redshift, caused by large-scale fluctuations in the number density of galaxies, is at least an order of magnitude larger than previous expectations that argued for a sharp end to reionization. This cosmic scatter in the abundance of galaxies introduces new features that affect the nature of reionization and the expectations for future probes of reionization, and may help explain the present properties of dwarf galaxies in different environments. The predictions can be tested by future numerical simulations and may be verified by upcoming observations. Current simulations, limited to relatively small volumes and periodic boundary conditions, largely omit cosmic scatter and its consequences. In particular, they artificially produce a sudden end to reionization, and they underestimate the number of galaxies by up to an order of magnitude at redshift 20.Comment: 8 ApJ pages, 4 figures, ApJ. Minor changes in revised version. Originally first submitted for publication on Aug. 29, 200

The Radial Distribution of Galaxies in LCDM clusters

We study the radial distribution of subhalos and galaxies using high-resolution cosmological simulations of galaxy clusters formed in the concordance LCDM cosmology. In agreement with previous studies, we find that the radial distribution of subhalos is significantly less concentrated than that of the dark matter, when subhalos are selected using their present-day gravitationally bound mass. We show that the difference in the radial distribution is not a numerical artifact and is due to tidal stripping. The subhalos in the cluster core lose more than 70% of their initial mass since accretion, while the average tidal mass loss for halos near the virial radius is ~30%. This introduces a radial bias in the spatial distribution of subhalos when they are selected using their tidally truncated mass. We demonstrate that the radial bias disappears almost entirely if subhalos are selected using their mass or circular velocity at the accretion epoch. The comparisons of the results of dissipationless simulations to the observed distribution of galaxies in clusters are therefore sensitive to the selection criteria used to select subhalo samples. Using the simulations that include cooling and starformation, we show that the radial distribution of subhalos is in reasonable agreement with the observed radial distribution of galaxies in clusters for 0.1<R/R200<2.0, if subhalos are selected using the stellar mass of galaxies. The radial bias is minimized in this case because the stars are located in the centers of dark matter subhalos and are tightly bound. The stellar mass of an object is therefore approximately conserved as the dark matter is stripped from the outer regions. Nevertheless, the concentration of the radial distribution of galaxies is systematically lower than that of the dark matter.Comment: submitted to ApJ, 12 pages, 12 figure

The Effect of Radiative Cooling on the Sunyaev-Zel'dovich Cluster Counts and Angular Power Spectrum: Analytic Treatment

Recently, the entropy excess detected in the central cores of groups and clusters has been successfully interpreted as being due to radiative cooling of the hot intragroup/intracluster gas. In such a scenario, the entropy floors $S_{\rm floor}$ in groups/clusters at any given redshift are completely determined by the conservation of energy. In combination with the equation of hydrostatic equilibrium and the universal density profile for dark matter, this allows us to derive the remaining gas distribution of groups and clusters after the cooled material is removed. Together with the Press-Schechter mass function we are able to evaluate effectively how radiative cooling can modify the predictions of SZ cluster counts and power spectrum. It appears that our analytic results are in good agreement with those found by hydrodynamical simulations. Namely, cooling leads to a moderate decrease of the predicted SZ cluster counts and power spectrum as compared with standard scenario. However, without taking into account energy feedback from star formation which may greatly suppress cooling efficiency, it is still premature to claim that this modification is significant for the cosmological applications of cluster SZ effect.Comment: 16 pages, 3 figures, uses aastex.cls. ApJ accepte