Bostonia. Volume 13

Founded in 1900, Bostonia magazine is Boston University's main alumni publication, which covers alumni and student life, as well as university activities, events, and programs

Self-energy Effects in the Superfluidity of Neutron Matter

The superfluidity of neutron matter in the channel $^1 S_0$ is studied by taking into account the effect of the ground-state correlations in the self-energy. To this purpose the gap equation has been solved within the generalized Gorkov approach. A sizeable suppression of the energy gap is driven by the quasi-particle strength around the Fermi surface.Comment: 8 pages and 3 figure

Systematic thermal reduction of neutronization in core-collapse supernovae

We investigate to what extent the temperature dependence of the nuclear symmetry energy can affect the neutronization of the stellar core prior to neutrino trapping during gravitational collapse. To this end, we implement a one-zone simulation to follow the collapse until beta equilibrium is reached and the lepton fraction remains constant. Since the strength of electron capture on the neutron-rich nuclei associated to the supernova scenario is still an open issue, we keep it as a free parameter. We find that the temperature dependence of the symmetry energy consistently yields a small reduction of deleptonization, which corresponds to a systematic effect on the shock wave energetics: the gain in dissociation energy of the shock has a small yet non-negligible value of about 0.4 foe (1 foe = 10^51 erg) and this result is almost independent from the strength of nuclear electron capture. The presence of such a systematic effect and its robustness under changes of the parameters of the one-zone model are significative enough to justify further investigations with detailed numerical simulations of supernova explosions.Comment: 15 pages, 2 tables, 3 figure

Final fate of the spherically symmetric collapse of a perfect fluid

The final fate of the spherically symmetric collapse of a perfect fluid which follows the $\gamma$-law equation of state and adiabatic condition is investigated. Full general relativistic hydrodynamics is solved numerically using a retarded time coordinate, the so-called observer time coordinate. Thanks to this coordinate, the causal structure of the resultant space-time is automatically constructed. Then, it is found that a globally naked, shell-focusing singularity can occur at the center from relativistically high-density, isentropic and time symmetric initial data if \gamma \alt 1.01 within the numerical accuracy. The result is free from the assumption of self-similarity. The upper limit of $\gamma$ with which a naked singularity can occur from generic initial data is consistent with the result of Ori and Piran based on the assumption of self-similarity.Comment: 17 pages, including 21 ps figures. Accepted for publication in Physical Review D, Typos corrected, References update

Geography of Spring Landbird Migration Through Riparian Habitats in Southwestern North America

Migration stopover resources, particularly riparian habitats, are critically important to landbirds migrating across the arid southwestern region of North America. To explore the effects of species biogeography and habitat affinity on spring migration patterns, we synthesized existing bird abundance and capture data collected in riparian habitats of the borderlands region of the U.S. and Mexico. We determined the importance of geographic factors (longitude and latitude) in explaining variation in abundances and capture rates of 32 long-distance and three short-distance migrant species. Abundances and capture rates of 13 and 11 species, respectively, increased with increasing longitude, and four species\u27 abundance and capture rates decreased with increasing longitude. Riparian associates, but not nonriparian species, were more abundant in western sites. Their abundance patterns were only weakly influenced by species biogeography. In contrast, biogeography did influence abundance patterns of nonriparian birds, suggesting that they choose the shortest, most direct route between wintering and breeding areas. We hypothesize that riparian obligate birds may, to some degree, adjust their migration routes to maximize time spent in high-quality riparian zones, but they are able to find suitable habitat opportunistically when crossing more hostile landscapes. In contrast, nonriparian birds adhere more closely to a hierarchical model in which the migratory route is determined by biogeographic constraints. Conservation of riparian habitats is necessary to meet future habitat stopover requirements of many western Neotropical migrant birds. We advocate a coordinated research effort to further elucidate patterns of distribution and habitat use so that conservation activities can be focused effectively

Web-Based Depression Treatment for Type 1 and Type 2 Diabetic Patients: A randomized, controlled trial

OBJECTIVE - Comorbid depression is common in patients with type 1 and type 2 diabetes, adversely affecting quality of life, diabetes outcomes, and mortality. Depression can be effectively treated with cognitive behavior therapy (CBT). The Internet is a new and attractive method for delivering CBT intervention on a large scale at relatively low costs. This study evaluated the effectiveness of Web-based CBT for depression treatment in adults with type 1 or type 2 diabetes, with minimal guidance. RESEARCH DESIGN ANDMETHODS - A randomized controlled trial was conducted in the Netherlands in 255 adult diabetic patients with elevated depressive symptoms. Primary outcomes were depressive symptoms. Secondary outcomes were diabetes-specific emotional distress and glycemic control. Assessments were at baseline, after treatment, and at the 1-month follow-up. RESULTS - The Web-based CBT was effective in reducing depressive symptoms by intention-to-treat analyses (P = 0.04, d = 0.29; clinical improvement 41% vs. 24% P 0.05). CONCLUSIONS - Web-based CBT depression treatment is effective in reducing depressive symptoms in adults with type 1 and type 2 diabetes. In addition, the intervention reduces diabetes-specific emotional distress in depressed patients. © 2011 by the American Diabetes Association

General Relativistic Effects in the Core Collapse Supernova Mechanism

We apply our recently developed code for spherically symmetric, fully general relativistic (GR) Lagrangian hydrodynamics and multigroup flux-limited diffusion neutrino transport to examine the effects of GR on the hydrodynamics and transport during collapse, bounce, and the critical shock reheating phase of core collapse supernovae. Comparisons of models computed with GR versus Newtonian hydrodynamics show that collapse to bounce takes slightly less time in the GR limit, and that the shock propagates slightly farther out in radius before receding. After a secondary quasistatic rise in the shock radius, the shock radius declines considerably more rapidly in the GR simulations than in the corresponding Newtonian simulations. During the shock reheating phase, core collapse computed with GR hydrodynamics results in a substantially more compact structure from the center out to the stagnated shock. The inflow speed of material behind the shock is also increased. Comparisons also show that the luminosity and rms energy of any neutrino flavor during the shock reheating phase increases when switching from Newtonian to GR hydrodynamics, and decreases when switching from Newtonian to GR transport. This latter decrease in neutrino luminosities and rms energies is less in magnitude than the increase that arise when switching from Newtonian to GR hydrodynamics, with the result that a fully GR simulation gives higher neutrino luminosities and harder neutrino spectra than a fully Newtonian simulation of the same precollapse model.Comment: 35 pages, 23 figure