Phosphorus in land-water systems

Analyses were made to obtain information on distribution of different forms of phosphate in different environmental media, including soils, eroding material, and bottom sediment. Major emphasis was placed on determining several forms of inorganic phosphate in each media. Results show that eroding material can transport significant quantities of phosphates from soils

Black hole solutions in 2+1 dimensions

We give circularly symmetric solutions for null fluid collapse in 2+1-dimensional Einstein gravity with a cosmological constant. The fluid pressure $P$ and energy density $\rho$ are related by $P=k\rho$ $(k\le 1)$. The long time limit of the solutions are black holes whose horizon structures depend on the value of $k$. The $k=1$ solution is the Banados-Teitelboim-Zanelli black hole metric in the long time static limit, while the $k<1$ solutions give other, `hairy' black hole metrics in this limit.Comment: 8 pages, RevTeX (to appear in Phys. Rev. D) References to Mann and Ross, and Mann, Chan and Chan adde

Diffusion Enhances Chirality Selection

Diffusion effect on chirality selection in a two-dimensional reaction-diffusion model is studied by the Monte Carlo simulation. The model consists of achiral reactants A which turn into either of the chiral products, R or S, in a solvent of chemically inactive vacancies V. The reaction contains the nonlinear autocatalysis as well as recycling process, and the chiral symmetry breaking is monitored by an enantiomeric excess $\phi$. Without dilution a strong nonlinear autocatalysis ensures chiral symmetry breaking. By dilution, the chiral order $\phi$ decreases, and the racemic state is recovered below the critical concentration $c_c$. Diffusion effectively enhances the concentration of chiral species, and $c_c$ decreases as the diffusion coefficient $D$ increases. The relation between $\phi$ and $c$ for a system with a finite $D$ fits rather well to an interpolation formula between the diffusionless(D=0) and homogeneous ($D=\infty$) limits.Comment: 7 pages, 6 figure

PON1 status does not influence cholinesterase activity in Egyptian agricultural workers exposed to chlorpyrifos.

Animal studies have shown that paraoxonase 1 (PON1) genotype can influence susceptibility to the organophosphorus pesticide chlorpyrifos (CPF). However, Monte Carlo analysis suggests that PON1 genotype may not affect CPF-related toxicity at low exposure conditions in humans. The current study sought to determine the influence of PON1 genotype on the activity of blood cholinesterase as well as the effect of CPF exposure on serum PON1 in workers occupationally exposed to CPF. Saliva, blood and urine were collected from agricultural workers (n=120) from Egypt's Menoufia Governorate to determine PON1 genotype, blood cholinesterase activity, serum PON1 activity towards chlorpyrifos-oxon (CPOase) and paraoxon (POase), and urinary levels of the CPF metabolite 3,5,6-trichloro-2-pyridinol (TCPy). The PON1 55 (P≤0.05) but not the PON1 192 genotype had a significant effect on CPOase activity. However, both the PON1 55 (P≤0.05) and PON1 192 (P≤0.001) genotypes had a significant effect on POase activity. Workers had significantly inhibited AChE and BuChE after CPF application; however, neither CPOase activity nor POase activity was associated with ChE depression when adjusted for CPF exposure (as determined by urinary TCPy levels) and stratified by PON1 genotype. CPOase and POase activity were also generally unaffected by CPF exposure although there were alterations in activity within specific genotype groups. Together, these results suggest that workers retained the capacity to detoxify chlorpyrifos-oxon under the exposure conditions experienced by this study population regardless of PON1 genotype and activity and that effects of CPF exposure on PON1 activity are minimal

The Origin of Primordial Dwarf Stars and Baryonic Dark Matter

I present a scenario for the production of low mass, degenerate dwarfs of mass $>0.1 M_{\odot}$ via the mechanism of Lenzuni, Chernoff & Salpeter (1992). Such objects meet the mass limit requirements for halo dark matter from microlensing surveys while circumventing the chemical evolution constraints on normal white dwarf stars. I describe methods to observationally constrain this scenario and suggest that such objects may originate in small clusters formed from the thermal instability of shocked, heated gas in dark matter haloes, such as suggested by Fall & Rees (1985) for globular clusters.Comment: TeX, 4 pages plus 2 postscript figures. To appear in Astrophysical Journal Letter

Neutrons and Gamma Rays from the Alpha-Particle Bombardment of Be9, B10, B11, C13, and O18

Excitation curves at 0° and 90° were studied for neutrons and γ rays produced in bombardment of thin targets of Be9, B10, B11, C13, and O18 by α particles with energies of from 1.8 to 5.3 Mev. Resonances were observed in the Be9(α, n)C12 reaction at bombarding energies of 1.9, 2.3, 2.6, 3.98, 4.4, and 5.0 Mev. The C13(α, n)O16 reaction showed resonances at 2.09, 2.25, 2.42, 2.605, 2.69, 2.775, 2.825, 3.09, 3.33, 3.42, 3.67, 3.73, 4.125, 4.42, 4.50, 4.63, 4.75, and 5.05 Mev. The B10(α, n)N13 excitation curve has resonances at 2.16, 2.25, 2.90, 4.53, 4.85, and 5.36 Mev, while the γ-ray yield from the B10(α, pγ)C13 reaction showed all these as well as resonances at 3.6 and 3.95 Mev. The B11(α, n)C13 reaction has resonances at bombarding energies of 2.06, 2.60, 2.93, 2.97, 3.23, 3.54, 3.72, 3.92, 4.25, 4.34, and 5.00 Mev. The O18(α, n)Ne21 reaction was studied with a thicker target (90-130 kev). Resonances in the neutron yield were resolved at 2.21, 2.47, 2.57, 2.72, 2.94, 3.24, 3.63, 3.91, 4.12, 4.22, 4.33, 4.52, and 4.82 Mev. Cross sections and widths of the resonances in the various reactions were determined

Cross Section and Angular Distributions of the (d, p) and (d, n) Reactions in C12 from 1.8 to 6.1 Mev

The reaction C12(d, p)C13 has been studied from a deuteron bombarding energy of 1.8 to 6.1 Mev. Resonances were found at 2.47, 2.67, 2.99, 3.39, 4.00, 4.6, 4.8, 5.34, and 5.64 Mev. Angular distributions of protons leaving C13 in the ground state show a pronounced Butler peak at 25° over the entire deuteron energy range. The angular distributions can be explained by assuming small amplitudes for compound nucleus formation interfering with large stripping amplitudes. Angular distributions of the lower energy group of protons leaving C13 excited to 3.09 Mev show a pronounced Butler peak at 0° and an even smaller contribution of compound nucleus formation. The reaction C12(d, n)N13 was also studied, and showed similar resonances and angular distributions. An analysis is made of the phase difference between the resonant and nonresonant parts of the cross section for the (d, p) reaction near the resonance at 4.00 Mev

The Nature of the Dense Core Population in the Pipe Nebula: Thermal Cores Under Pressure

In this paper we present the results of a systematic investigation of an entire population of starless dust cores within a single molecular cloud. Analysis of extinction data shows the cores to be dense objects characterized by a narrow range of density. Analysis of C18O and NH3 molecular-line observations reveals very narrow lines. The non-thermal velocity dispersions measured in both these tracers are found to be subsonic for the large majority of the cores and show no correlation with core mass (or size). Thermal pressure is thus the dominate source of internal gas pressure and support for most of the core population. The total internal gas pressures of the cores are found to be roughly independent of core mass over the entire range of the core mass function (CMF) indicating that the cores are in pressure equilibrium with an external source of pressure. This external pressure is most likely provided by the weight of the surrounding Pipe cloud within which the cores are embedded. Most of the cores appear to be pressure confined, gravitationally unbound entities whose nature, structure and future evolution are determined by only a few physical factors which include self-gravity, the fundamental processes of thermal physics and the simple requirement of pressure equilibrium with the surrounding environment. The observed core properties likely constitute the initial conditions for star formation in dense gas. The entire core population is found to be characterized by a single critical Bonnor-Ebert mass. This mass coincides with the characteristic mass of the Pipe CMF indicating that most cores formed in the cloud are near critical stability. This suggests that the mass function of cores (and the IMF) has its origin in the physical process of thermal fragmentation in a pressurized medium.Comment: To appear in the Astrophysical Journa

The Structure of Isothermal, Self-gravitating Gas Spheres for Softened Gravity

A theory for the structure of isothermal, self-gravitating gas spheres in pressure equilibrium in a softened gravitational field is developed. The one parameter spline softening proposed by Hernquist & Katz (1989) is used. We show that the addition of this extra scale parameter implies that the set of equilibrium solutions constitute a one-parameter family, rather than the one and only one isothermal sphere solution for Newtonian gravity. We demonstrate the perhaps somewhat surprising result that for any finite choice of softening length and temperature, it is possible to deposit an arbitrarily large mass of gas in pressure equilibrium and with a non-singular density distribution inside of r_0 for any r_0 > 0. The theoretical predictions of our models are compared with the properties of the small, massive, quasi-isothermal gas clumps which typically form in numerical Tree-SPH simulations of 'passive' galaxy formation of Milky Way sized galaxies. We find reasonable agreement despite the neglect of rotational support in the models. We comment on whether the hydrodynamical resolution in our numerical simulation of galaxy formation is sufficient, and finally we conclude that one should be cautious, when comparing results of numerical simulations involving gravitational softening and hydrodynamical smoothing, with reality.Comment: 22 pages Latex + 12 figure

Global Nonradial Instabilities of Dynamically Collapsing Gas Spheres

Self-similar solutions provide good descriptions for the gravitational collapse of spherical clouds or stars when the gas obeys a polytropic equation of state, $p=K\rho^\gamma$ (with $\gamma\le 4/3$). We study the behaviors of nonradial perturbations in the similarity solutions of Larson, Penston and Yahil, which describe the evolution of the collapsing cloud prior to core formation. Our global stability analysis reveals the existence of unstable bar-modes ($l=2$) when $\gamma\le 1.09$. In particular, for the collapse of isothermal spheres, which applies to the early stages of star formation, the $l=2$ density perturbation relative to the background, $\delta\rho({\bf r},t)/\rho(r,t)$, increases as $(t_0-t)^{-0.352}\propto \rho_c(t)^{0.176}$, where $t_0$ denotes the epoch of core formation, and $\rho_c(t)$ is the cloud central density. Thus, the isothermal cloud tends to evolve into an ellipsoidal shape (prolate bar or oblate disk, depending on initial conditions) as the collapse proceeds. In the context of Type II supernovae, core collapse is described by the $\gamma\simeq 1.3$ equation of state, and our analysis indicates that there is no growing mode (with density perturbation) in the collapsing core before the proto-neutron star forms, although nonradial perturbations can grow during the subsequent accretion of the outer core and envelope onto the neutron star. We also carry out a global stability analysis for the self-similar expansion-wave solution found by Shu, which describes the post-collapse accretion (``inside-out'' collapse) of isothermal gas onto a protostar. We show that this solution is unstable to perturbations of all $l$'s, although the growth rates are unknown.Comment: 28 pages including 7 ps figures; Minor changes in the discussion; To be published in ApJ (V.540, Sept.10, 2000 issue