Critical Phenomena Associated with Boson Stars

We present a brief synopsis of related work (gr-qc/0007039), describing a study of black hole threshold phenomena for a self-gravitating, massive complex scalar field in spherical symmetry. We construct Type I critical solutions dynamically by tuning a one-parameter family of initial data consisting of a boson star and a massless real scalar field, and numerically evolving this data. The resulting critical solutions appear to correspond to boson stars on the unstable branch, as we show via comparisons between our simulations and perturbation theory. For low-mass critical solutions, we find small ``halos'' of matter in the tails of the solutions, and these distort the profiles which otherwise agree with unstable boson stars. These halos seem to be artifacts of the collisions between the original boson stars and the massless fields, and do not appear to belong to the true critical solutions. From this study, it appears that unstable boson stars are unstable to dispersal (``explosion'') in addition to black hole formation. Given the similarities in macroscopic stability between boson stars and neutron stars, we suggest that similar phenomena could occur in models of neutron stars.Comment: 6 Pages, 5 Figures, LaTeX. To appear in Proceedings of the 20th Texas Symposium on Relativistic Astrophysics (Dec 9-15, 2000

Atmospheric contaminant sensor. Book 2: Appendices

Appendices containing equipment specifications and performance test data of the atmospheric contaminant sensor for submarines are presented

NMR Probing Spin Excitations in the Ring-Like Structure of a Two-Subband System

Resistively detected nuclear magnetic resonance (NMR) is observed inside the ring-like structure, with a quantized Hall conductance of 6e^2/h, in the phase diagram of a two subband electron system. The NMR signal persists up to 400 mK and is absent in other states with the same quantized Hall conductance. The nuclear spin-lattice relaxation time, T1, is found to decrease rapidly towards the ring center. These observations are consistent with the assertion of the ring-like region being a ferromagnetic state that is accompanied by collective spin excitations.Comment: 4 pages, 4 figure

Cosmic Microwave Background Observations as a Way to Discriminate Among Inflation Models

The upcoming satellite missions MAP and Planck will measure the spectrum of fluctuations in the Cosmic Microwave Background with unprecedented accuracy. We discuss the prospect of using these observations to distinguish among proposed models of inflationary cosmology.Comment: To appear in the proceedings of the XXXIIIrd Rencontres de Moriond, "Fundamental Parameters in Cosmology", 17-24 January, Les Arcs, France. 6 Pages, 2 figures, uses moriond.st

Planetary Transits Toward the Galactic Bulge

The primary difficulty with using transits to discover extrasolar planets is the low probability a planet has of transiting its parent star. One way of overcoming this difficulty is to search for transits in dense stellar fields, such as the Galactic bulge. Here I estimate the number of planets that might be detected from a monitoring campaign toward the bulge. A campaign lasting 10 nights on a 10 meter telescope (assuming 8 hours of observations per night and a 5'x5' field of view) would detect about 100 planets with radius \rp=1.5 \rjup, or about 30 planets with \rp=1.0 \rjup, if the frequency and distribution of planets in the bulge is similar to that in the solar neighborhood. Most of these planets will be discovered around stars just below the turn-off, i.e. slightly evolved G-dwarfs. Campaigns involving 1- or 4-m class telescopes are unlikely to discover any planets, unless there exists a substantial population of companions with \rp > 1.5 \rjup.Comment: 4 pages, 4 figures. Submitted to ApJ Letter

Introducing Variable Cell Shape Methods in Field Theory Simulations of Polymers

We propose a new method for carrying out field-theoretic simulations of polymer systems under conditions of prescribed external stress, allowing for shape changes in the simulation box. A compact expression for the deviatoric stress tensor is derived in terms of the chain propagator, and is used to monitor changes in the box shape according to a simple relaxation scheme. The method allows fully relaxed, stress free configurations to be obtained even in non trivial morphologies, and enables the study of morphology transitions induced by external stresses

Long-term Effects of Tillage on the Retention and Transport of Soil Water

Quantitative measurements were made of the physical and chemical properties of two virgin prairie soils, Crowley and Jay, that remain in their native Arkansas environments and of similar soils that had been tilled extensively. Comparisons were made of soil properties at several depths. When compared with the tilled soils the virgin soils had higher organic matter contents, saturated hydraulic conductivities and water retained at several applied pressures. Bulk densities and hydraulic resistances were lower in the virgin soils. For the Crowley silt loam, values of pH and elemental contents of the virgin soil were higher than those of the tilled soil. Determinations also were made of the effects of a 14-year addition of winter cover crops on a Dubbs-Dundee soil in continuous cotton production. In general, the winter cover crops tended to increase hydraulic conductivity~. ·porosity and organic matter content. These results indicated that the detrimental effects of long-term tillage on soil hydraulic properties could partially be overcome with the planting of these crops during the winter. However, the rate of improvement in the hydraulic properties was not dramatic

Viscous Hydrodynamics and Relativistic Heavy Ion Collisions

The matter created in relativistic heavy ion collisions is fairly well described by ideal hydrodynamics, and somewhat better described by viscous hydrodynamics. To this point, most viscous calculations have been two-dimensional, based on an assumption of Bjorken boost invariance along the beam axis. Here, first results are presented for a fully three-dimensional viscous model. The model is described and tests of the numerical accuracy of the code are presented. Two- and three-dimensional runs are compared, and modest changes are observed for mid-rapidity observables at the highest RHIC (Relativistic Heavy Ion Collider) energies.Comment: 23 pages, 7 figure

On the Electronic Spectroscopy of Closed Shell Cations Derived From Resonance Stabilized Radicals: Insights From Theory and Franck-Condon Analysis

Context. Recent attention has been directed on closed-shell aromatic cations as potential carriers of the diffuse interstellar bands. The spectra of mass-selected, matrix-isolated benzylium, and tropylium cations were recently reported. The visible spectrum of benzylium exhibits a large Franck-Condon (FC) envelope, inconsistent with diffuse interstellar band carriers. Aims. We perform a computational analysis of the experimentally studied benzylium spectrum before extending the methods to a range of larger, closed-shell aromatic cations to determine the potential for this class of systems as diffuse interstellar band carriers. Methods. Density functional theory (DFT), time-dependant ((TD)DFT), and multi-configurational self-consistent field second-order perturbation theory (MRPT2) methods in concert with multidimensional FC analysis is used to model the benzylium spectrum. These methods are extended to larger closed-shell aromatic hydrocarbon cations derived from resonance-stabilized radicals, which are predicted to show strong S0 → Sn transitions in the visible region. The ionization energies of a range of these systems are also calculated by DFT. Results. The simulated benzylium spectrum was found to yield excellent agreement with the experimental spectrum showing an extended progression in a low frequency (510 cm-1) ring distortion mode. The FC progression was found to be significantly quenched in the larger species: 1-indanylium, 1-naphthylmethylium, and fluorenium. Excitation and ionization energies of the closed-shell cations were found to be consistent with diffuse interstellar band carriers, with the former lying in the visible range and the latter straddling the Lyman limit in the 13−14 eV range. Conclusions. Large closed-shell polycyclic aromatic hydrocarbon cations remain viable candidate carriers of the diffuse interstellar bands