Stability of Dynamically Collapsing Gas Sphere

We discuss stability of dynamically collapsing gas spheres. We use a similarity solution for a dynamically collapsing sphere as the unperturbed state. In the similarity solution the gas pressure is approximated by a polytrope of $P = K \rho ^\gamma$. We examine three types of perturbations: bar ($\ell = 2$) mode, spin-up mode, and Ori-Piran mode. When $\gamma < 1.097$, it is unstable against bar-mode. It is unstable against spin-up mode for any $\gamma$. When $\gamma < 0.961$, the similarity solution is unstable against Ori-Piran mode. The unstable mode grows in proportion to $| t - t_0 | ^{-\sigma}$ while the central density increases in proportion to $\rho_c \propto (t - t_0) ^{-2}$ in the similarity solution. The growth rate, $\sigma$ is obtained numerically as a function of $\gamma$ for bar mode and Ori-Piran mode. The growth rate of the bar mode is larger for a smaller $\gamma$. The spin-up mode has the growth rate of $\sigma = 1/3$ for any $\gamma$.Comment: submitted to PASJ. 7 pages including 6 figures. This paper is also available at http://www.a.phys.nagoya-u.ac.jp/~hanawa/dpnu9922/dpnu9922.htm

Trading Behavior in a Marginal Organized Market

As increasingly more transactions occur away from open markets, the so-called "thin" market issues arise. This paper analyzes unpublished transaction data from Egg Clearinghouse, Inc. (ECI), a marginal marketplace for eggs that trades 4% of all eggs (80% of eggs available for open trading). Results suggest that marginalized markets can serve as an inventory adjustment mechanism while maintaining the role of price discovery as a check for non-market prices. At ECI, most firms both buy and sell regardless of operational types, participation is balanced across all types of firms in the industry, and sellers in general yield to buyers' preferred terms of trade.eggs, inventory adjustment, organized market, price discovery, thin market, Agribusiness,

GEOGRAPHIC CHANGES IN U.S. DAIRY PRODUCTION

Changes in quantities of milk marketed are analyzed by spatial econometrics using the county-level data, to provide statistical explanations of the recent major geographic shifts in U.S. dairy production. (Revised edition posted August 2002)Livestock Production/Industries,

The rp Process Ashes from Stable Nuclear Burning on an Accreting Neutron Star

We calculate the nucleosynthesis during stable nuclear burning on an accreting neutron star. This is appropriate for weakly magnetic neutron stars accreting at near-Eddington rates in low mass X-ray binaries, and for most accreting X-ray pulsars. We show that the nuclear burning proceeds via the rapid proton capture process (rp process), and makes nuclei far beyond the iron group. The final mixture of nuclei consists of elements with a range of masses between approximately A=60 and A=100. The average nuclear mass of the ashes is set by the extent of helium burning via (alpha,p) reactions, and depends on the local accretion rate. Our results imply that the crust of these accreting neutron stars is made from a complex mixture of heavy nuclei, with important implications for its thermal, electrical and structural properties. A crustal lattice as impure as our results suggest will have a conductivity set mostly by impurity scattering, allowing more rapid Ohmic diffusion of magnetic fields than previously estimated.Comment: To appear in the Astrophysical Journal (33 pages, LaTeX, including 11 postscript figures

Superconducting properties of the pyrochlore oxide Cd2Re2O7

We report the superconducting properties of the pyrochlore oxide Cd2Re2O7. The bulk superconducting transition temperature Tc is about 1.0 K, and the upper critical field Hc2 determined by the measurement of specific heat under magnetic fields is 0.29 T. The superconducting coherence length is estimated to be 34 nm. Specific heat data measured on single crystals suggest that the superconducting gap of Cd2Re2O7 is nodeless.Comment: 6 pages, 6 figures, 1 table, to be published in J. Chem. Phys. Solid

Structural Phase Transition in the Superconducting Pyrochlore Oxide Cd2Re2O7

We report a structural phase transition found at Ts = 200 K in a pyrochlore oxide Cd2Re2O7 which shows superconductivity at Tc = 1.0 K. X-ray diffractionexperiments indicate that the phase transition is of the second order, from a high-temperature phase with the ideal cubic pyrochlore structure (space group Fd-3m) to a low-temperature phase with another cubic structure (space group F-43m). It is accompanied by a dramatic change in the resistivity and magnetic susceptibility and thus must induce a significant change in the electronic structure of Cd2Re2O7.Comment: 4 pages, 4figures, proceeding for ISSP