Neutron Stars and Nuclei in the Modified Relativistic Hartree Approximation

We have examined the properties of neutron-rich matter and finite nuclei in the modified relativistic Hartree approximation for several values of the renormalization scale, $\mu$, around the standard choice of $\mu$ equal to the nucleon mass $M$. Observed neutron star masses do not effectively constrain the value of $\mu$. However for finite nuclei the value $\mu/M=0.79$, suggested by nuclear matter data, provides a good account of the bulk properties with a sigma mass of about 600 MeV. This value of $\mu/M$ renders the effective three and four body scalar self-couplings to be zero at 60\% of equilibrium nuclear matter density, rather than in the vacuum. We have also found that the matter part of the exchange diagram has little impact on the bulk properties of neutron stars.Comment: 33 pages, Latex, 8 figures (available from authors by fax), Minnesota preprint NUC-MINN-93/7-

Gravitational Radiation from Compact Binary Pulsars

An outstanding question in modern Physics is whether general relativity (GR) is a complete description of gravity among bodies at macroscopic scales. Currently, the best experiments supporting this hypothesis are based on high-precision timing of radio pulsars. This chapter reviews recent advances in the field with a focus on compact binary millisecond pulsars with white-dwarf (WD) companions. These systems - if modeled properly - provide an unparalleled test ground for physically motivated alternatives to GR that deviate significantly in the strong-field regime. Recent improvements in observational techniques and advances in our understanding of WD interiors have enabled a series of precise mass measurements in such systems. These masses, combined with high-precision radio timing of the pulsars, result to stringent constraints on the radiative properties of gravity, qualitatively very different from what was available in the past.Comment: Short review chapter to appear in "Gravitational Wave Astrophysics" by Springer-Verlag, edited by Carlos F. Sopuerta; v3: a few major corrections and updated references. Comments are welcome

Antikaon condensation and the metastability of protoneutron stars

We investigate the condensation of $\bar K^0$ meson along with $K^-$ condensation in the neutrino trapped matter with and without hyperons. Calculations are performed in the relativistic mean field models in which both the baryon-baryon and (anti)kaon-baryon interactions are mediated by meson exchange. In the neutrino trapped matter relevant to protoneutron stars, the critical density of $K^-$ condensation is shifted considerably to higher density whereas that of $\bar K^0$ condensation is shifted slightly to higher density with respect to that of the neutrino free case. The onset of $K^-$ condensation always occurs earlier than that of $\bar K^0$ condensation. A significant region of maximum mass protoneutron stars is found to contain $\bar K^0$ condensate for larger values of the antikaon potential. With the appearance of $\bar K^0$ condensation, there is a region of symmetric nuclear matter in the inner core of a protoneutron star. It is found that the maximum mass of a protoneutron star containing $K^-$ and $\bar K^0$ condensate is greater than that of the corresponding neutron star. We revisit the implication of this scenario in the context of the metastability of protoneutron stars and their evolution to low mass black holes.Comment: 26 pages; Revtex; 8 figures include

Topographic Context of the Burn Edge Influences Postfire Recruitment of Arid Land Shrubs

Although fire is becoming frequent in arid lands throughout the world, little is known about the recruitment pattern of many arid land shrub species after fire. We explored topographic and edaphic correlates of postfire recruitment for four shrub species 6 years following wildfire in central Nevada, United States. We hypothesized that the spatial pattern of shrub recruitment varies with fire-related species traits according to the topographic position of the burn edge, which correlated with postfire seed sources. Where the burn edge fell on a ridge, the frequency of the colonizing shrub, Artemisia tridentata ssp. vaseyana, decreased with distance from the burn edge, whereas the frequency of facultative resprouting specieswas independent or increased with distance. Where the burn edge fell behind a ridge, there were fewer shrubs overall and a greater proportion of resprouting species. Most individuals of resprouting species were adults, suggesting immediate, fire-stimulated recruitment. Interactions among topographic position and distance from the burn edge influence the recruitment patterns of shrub species and have implications for the postfire species assemblage that are predictable on the basis of firerelated plant traits. We demonstrate how the topographic position of the burn edge influences postfire recovery trajectories of the shrub community. © 2016 The Society for Range Management. Published by Elsevier Inc. All rights reserved.The Rangeland Ecology & Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information

Fire dating from tree rings in Western Cascades Douglas-fir forests: an error analysis

Cross dating, the matching of tree-ring patterns to determine absolute dates or tree-ring series, is a valuable technique for dating wildfires. However, most recent fire history studies conducted in Pacific Northwest Douglas-fir (Pseudotsuga menziesii) forests have not employed cross dating. The error associated with non-cross-dated, field-counted, fire history data was assessed at four sites in Douglas-fir forests of the western Cascades, Oregon, USA. Fire scar and tree origin years were dated in the field by counting tree rings on minimally prepared stump surfaces. Wood samples from these same stumps were then prepared in the laboratory, where tree rings were recounted and cross dated. Fire histories from field-counted, laboratory-counted, and cross-dated efforts were compared. Cross dating required 22 times the effort of the field-counted fire history reconstruction, and 87% of fire-scarred samples could be cross dated. The field-counted data generally underestimated ages of fire scar and tree origin years, and fires reconstructed from field-counted data were estimated as having occurred from 1 to 16 years more recently than they actually did. Field-counted scar years were within 10 years of their true values for about 75%, and within 20 years for about 87% of observed cases. Errors in fire frequency estimates were small unless an incorrect number of fires was reconstructed. Also, the error associated with careful laboratory counts on well-prepared surfaces was minimal (mean error of 1.5 years) even when cross dating was not conducted. We recommend that future fire history studies in the Pacific Northwest employ cross dating.Weisberg and Swanson "Fire dating from tree rings in Western Cascades Douglas-fir forests: an error analysis." Northwest Science. 2001; 75(2): 145-15