Hydrogen-Poor Circumstellar Shells from Pulsational Pair-Instability Supernovae with Rapidly Rotating Progenitors

In certain mass ranges, massive stars can undergo a violent pulsation triggered by the electron/positron pair instability that ejects matter, but does not totally disrupt the star. After one or more of these pulsations, such stars are expected to undergo core-collapse to trigger a supernova explosion. The mass range susceptible to this pulsational phenomena may be as low as 50-70 Msun if the progenitor is of very low metallicity and rotating sufficiently rapidly to undergo nearly homogeneous evolution. The mass, dynamics, and composition of the matter ejected in the pulsation are important aspects to determine the subsequent observational characteristics of the explosion. We examine the dynamics of a sample of stellar models and rotation rates and discuss the implications for the first stars, for LBV-like phenomena, and for superluminous supernovae. We find that the shells ejected by pulsational pair-instability events with rapidly rotating progenitors (>30% the critical value) are hydrogen-poor and helium and oxygen-rich.Comment: 14 pages, 2 figure

Annual Report on Cotton Economics Research 2001/02

Crop Production/Industries,

Launch vehicle wind and turbulence response by nonstationary statistical methods

Nonstationary adjoint algorithm for determining launch vehicle flight loads due to winds and turbulenc

Multidimensional Simulations of Rotating Pair Instability Supernovae

We study the effects of rotation on the dynamics, energetics and Ni-56 production of Pair Instability Supernova explosions by performing rotating two-dimensional ("2.5-D") hydrodynamics simulations. We calculate the evolution of eight low metallicity (Z = 10^-3, 10^-4 Zsun) massive (135-245 Msun) PISN progenitors with initial surface rotational velocities 50% that of the critical Keplerian value using the stellar evolution code MESA. We allow for both the inclusion and the omission of the effects of magnetic fields in the angular momentum transport and in chemical mixing, resulting in slowly-rotating and rapidly-rotating final carbon-oxygen cores, respectively. Increased rotation for carbon-oxygen cores of the same mass and chemical stratification leads to less energetic PISN explosions that produce smaller amounts of Ni-56 due to the effect of the angular momentum barrier that develops and slows the dynamical collapse. We find a non-monotonic dependence of Ni-56 production on rotational velocity in situations when smoother composition gradients form at the outer edge of the rotating cores. In these cases, the PISN energetics are determined by the competition of two factors: the extent of chemical mixing in the outer layers of the core due to the effects of rotation in the progenitor evolution and the development of angular momentum support against collapse. Our 2.5-D PISN simulations with rotation are the first presented in the literature. They reveal hydrodynamic instabilities in several regions of the exploding star and increased explosion asymmetries with higher core rotational velocity.Comment: 31 pages, 23 figures, accepted for publication in the Ap

Hidden Dirac Monopoles

Dirac showed that the existence of one magnetic pole in the universe could offer an explanation of the discrete nature of the electric charge. Magnetic poles appear naturally in most grand unified theories. Their discovery would be of greatest importance for particle physics and cosmology. The intense experimental search carried thus far has not met with success. I proposed a universe with magnetic poles which are not observed free because they hide in deeply bound monopole--anti-monopole states named monopolium. I discuss the realization of this proposal and its consistency with known cosmological features. I furthermore analyze its implications and the experimental signatures that confirm the scenario.Comment: Comments: 15 pages, 3 figure

Product Liability Aspects of the Risks of Technological Change--A U.S. Perspective

The Impact of Technological Change in the Canada/U.S. Contex

Ultrastructural Characteristics of Red Maple (Acer Rubrum L.) Wood

The anatomy of red maple (Acer rubrum L.) was examined using the transmission electron microscope. Direct carbon replicas and ultrathin sections of inner and outer sapwood and inner and outer heartwood were prepared. In cross-sectional view sapwood intervessel pit membranes appear thin; in surface views of air-dried and extracted samples of the second sapwood ring and inner sapwood, openings in the intervessel pit membranes are visible. Intervessel pit membranes are permeated with extractives in the heartwood. Vessel-ray parenchyma pits have been described as similar to intervessel pits; but differences in shape, apertures, and pit membranes were detected in this study. The ray parenchyma cells appear different in ultrastructural details from those in species that have been studied with the transmission electron microscope as they do not have well-defined protective layers in the sapwood when they are adjacent to vessels, plasmodesmata channels are not apparent in the parenchyma-parenchyma pits, and there are no pits to the intercellular spaces in the rays. Red maple is an unusual hardwood as it has longitudinal intercellular spaces adjacent to the fibers; the appearance of these spaces is similar to that of the longitudinal intercellular spaces in members of the conifer family, Araucariaceae