Black hole neutron star coalescence as a source of gamma-ray bursts

We present the results of hydrodynamic (SPH) simulations showing the coalescence of a black hole with a neutron star to be a promising theoretical source of short duration gamma-ray bursts. The favorable features of the process include rapid onset, millisecond variability, a duration much longer than the dynamical timescale, and a range of outcomes sufficient to allow variety in the properties of individual gamma-ray bursts. Interestingly, the process of coalescence differs rather markedly from past predictions.Comment: 6 pages, 4 Postscript figures, uses aipproc.sty . To appear in 4th Gamma Ray Bursts Symposium, C.A. Meegan and P. Cushman, ed

Reduction of porosity in aluminum weldments

Method is described for elimination of porosity of aluminum weldments by replacing polyvinyl chloride tubing (used to connect welder to gas source, and is permeable to moisture at high humidity) with copper tubing. In addition liquid argon gas is used at weld stations

Epilogue

Factors that may have been decisive in turning Rancho Santa Ana Botanic Garden into a successful establishment of botanical teaching and a garden devoted to the conservation and showcasing of the native California flora are put forward. In addition to the enthusiasm and tenacity of its founder, Susanna Bixby Bryant, inspiration and advice came from several other key figures, notably Carl Brandt Wolf, Ernest Braunton, Willis Linn Jepson, and Theodore Payne

Sweeping the cd-Index and the Toric h-Vector

We derive formulas for the cd-index and the toric h-vector of a convex polytope P from a sweeping by a hyperplane. These arise from interpreting the corresponding S-shelling of the dual of P. We describe a partition of the faces of the complete truncation of P to reflect explicitly the nonnegativity of its cd-index and what its components are counting. One corollary is a quick way to compute the toric h-vector directly from the cd-index. We also propose an "extended toric" h-vector that fully captures the information in the flag h-vector.Comment: 23 page

On the Profiles and Polarization of Raman Scattered Emission Lines in Symbiotic Stars:II. Numerical Simulations

A Monte Carlo method is used to calculate the profiles and the polarization of the Raman scattered O VI lines(lambda lambda 6827,7088) in symbiotic stars. A point-like isotropic UV radiation source is assumed and a simple spherical wind model is adopted for the kinematics of the scattering material from the cool giant. We first investigate the case where the incident line photons are described by a Gaussian profile having a width of 10^4 K. We subsequently investigate the effects of the extended ionized region and non-spherical wind models including a disk-type wind and a bipolar wind. The cases where the emissin source is described by non-Gaussian profiles are briefly studied. Finally, as an additional component for the kinematics of symbiotic stars the orbital motion of the hot component around the cool giant is included and the effect on the spectropolarimetry is investigated. In this case the polarization direction changes around the red part of the Raman-scattered emission lines, when the observer's line of sight is perpendicular to the orbital plane, and no such effect is seen when the line of sight lies in the orbital plane. Furthermore, complex peak structures are seen in the degree of polarization and polarized flux, which have often been observed in several symbiotic systems including RR Tel. Brief observational consequences and preditions are discussed in relation to the present and future spectropolarimetry for symbiotic stars. It is concluded that spectropolarimetry may provide a powerful diagnostic of the physical conditions of symbiotic stars.Comment: 22 pages, Tex, 15 postscript figuer