Testing linear-theory predictions of galaxy formation

The angular momentum of galaxies is routinely ascribed to a process of tidal torques acting during the early stages of gravitational collapse, and is predicted from the initial mass distribution using second-order perturbation theory and the Zel'dovich approximation. We have tested this theory for a flat hierarchical cosmogony using a large N-body simulation with sufficient dynamic range to include tidal fields, allow resolution of individual galaxies, and thereby expand on previous studies. We find relatively good correlation between the predictions of linear theory and actual galaxy evolution. While structure formation from early times is a complex history of hierarchical merging, salient features are well described by the simple spherical-collapse model. Most notably, we test several methods for determining the turnaround epoch, and find that turnaround is succesfully described by the spherical collapse model. The angular momentum of collapsing structures grows linearly until turnaround, as predicted, and continues quasi-linearly until shell crossing. The predicted angular momentum for well-resolved galaxies at turnaround overestimates the true turnaround and final values by a factor of ~3 with a scatter of ~70 percent, and only marginally yields the correct direction of the angular momentum vector. We recover the prediction that final angular momentum scales as mass to the 5/3 power. We find that mass and angular momentum also vary proportionally with peak height.Comment: 20 pages, 16 figures, Accepted for publication in MNRA

Theoretical and material studies on thin-film electroluminescent devices

A theoretical study of resonant tunneling in multilayered heterostructures is presented based on an exact solution of the Schroedinger equation under the application of a constant electric field. By use of the transfer matrix approach, the transmissivity of the structure is determined as a function of the incident electron energy. The approach presented is easily extended to many layer structures where it is more accurate than other existing transfer matrix or WKB models. The transmission resonances are compared to the bound state energies calculated for a finite square well under bias using either an asymmetric square well model or the exact solution of an infinite square well under the application of an electric field. The results show good agreement with other existing models as well as with the bound state energies. The calculations were then applied to a new superlattice structure, the variablly spaced superlattice energy filter, (VSSEP) which is designed such that under bias the spatial quantization levels fully align. Based on these calculations, a new class of resonant tunneling superlattice devices can be designed

Performance characteristics of high-earning minority banks

An abstract for this article is not available.Banks and banking

Design, fabrication, and bench testing of a solar chemical receiver

Solar thermal energy can be effectively collected, transported, stored, and utilized by means of a chemical storage and transport system employing the reversible SO2 oxidation reaction. A solar chemical receiver for SO3 thermal decomposition to SO2 and oxygen was analyzed. Bench tests of a ten foot section of a receiver module were conducted with dissociated sulfuric acid (SO3 and H2O) in an electrical furnace. Measured percent conversion of SO3 was 85% of the equilibrium value. Methods were developed to fabricate and assemble a complete receiver module. These methods included applying an aluminide coating to certain exposed surfaces, assembling concentric tubes with a wire spacer, applying a platinum catalyst to the tubing wall, and coiling the entire assembly into the desired configuration

Galaxy Tracers and Velocity Bias

This paper examines several methods of tracing galaxies in N-body simulations and their effects on the derived galaxy statistics, especially measurements of velocity bias. Using two simulations with identical initial conditions, one following dark matter only and the other following dark matter and baryons, both collisionless and collisional methods of tracing galaxies are compared to one another and against a set of idealized criteria. None of the collisionless methods proves satisfactory, including an elaborate scheme developed here to circumvent previously known problems. The main problem is that galactic overdensities are both secularly and impulsively disrupted while orbiting in cluster potentials. With dissipation, the baryonic tracers have much higher density contrasts and much smaller cross sections, allowing them to remain distinct within the cluster potential. The question remains whether the incomplete physical model introduces systematic biases. Statistical measures determined from simulations can vary significantly based solely on the galaxy tracing method utilized. The two point correlation function differs most on sub-cluster scales with generally good agreement on larger scales. Pairwise velocity dispersions show less uniformity on all scales addressed here. All tracing methods show a velocity bias to varying degrees, but the predictions are not firm: either the tracing method is not robust or the statistical significance has not been demonstrated. Though theoretical arguments suggest that a mild velocity bias should exist, simulation results are not yet conclusive.Comment: ApJ, in press, 23 pages, plain TeX, 8 of 13 figures included, all PostScript figures (4.8 MB) available via anonymous ftp from ftp://astro.princeton.edu/summers/tracers . Also available as POPe-616 on http://astro.princeton.edu/~library/prep.htm

Galaxy tracers in N-body simulations

Using the method of smoothed particle hydrodynamics, we have modeled the formation of a compact group of galaxies with sufficient resolution to trace galaxies. Radiative cooling allows the baryons to dissipate their thermal energy and collapse to overdensities characteristic of real galaxies. With their cross section greatly reduced, these galaxy tracers remain distinct during cluster formation while their dark matter halos merge. In addition, the number density, the mass distribution function, and even the morphology of these objects are similar to those of observed galaxies. A viable population of galaxy tracers can be unambiguously defined