GRB990123: Evidence that the Gamma Rays Come from a Central Engine

GRB990123 was a long complex gamma-ray burst with an optical transient that started early within the gamma-ray phase. The peak and power law decay of the early optical emission strongly indicates the presence of a decelerating relativistic shell during that phase. Prior to this burst, it was not known if the shell decelerated during the burst, so an external shock origin for the gamma rays was still possible. If the gamma-rays are produced in the external shock, then the pulse widths should reflect the observed deceleration of the shell and increase by about 2.3. We analyze the fine time structure observed in the gamma-ray data from BATSE and determine that the width of the peaks do not increase as expected for a decelerating shell; the later pulses are, at most, a factor of 1.15 longer than the earlier pulses. We also analyze the variability to determine what fraction of the shell's surface could be involved in the production of the gamma rays, the so-called surface filling factor. For GRB990123 we find a filling factor of 0.008. The lack of pulse width evolution eliminates the only remaining kinematically acceptable external shock explanation for the gamma-ray phase and, thus, the gamma rays must originate at a central engine.Comment: 14 pages, 3 embedded figues, Latex, Submitted to ApJ

Magnetic Structure and Spin Waves in the Kagom\'{e} Jarosite compound KFe3(SO4)2(OH)6{\bf KFe_3(SO_4)_2(OH)_6}

We present a detailed study of the magnetic structure and spin waves in the Fe jarosite compound ${\rm KFe_3(SO_4)_2(OH)_6}$ for the most general Hamiltonian involving one- and two-spin interactions which are allowed by symmetry. We compare the calculated spin-wave spectrum with the recent neutron scattering data of Matan {\it et al.} for various model Hamiltonians which include, in addition to isotropic Heisenberg exchange interactions between nearest ($J_1$) and next-nearest ($J_2$) neighbors, single ion anisotropy and Dzyaloshinskii-Moriya (DM) interactions. We concluded that DM interactions are the dominant anisotropic interaction, which not only fits all the splittings in the spin-wave spectrum but also reproduces the small canting of the spins out of the Kagom\'e plane. A brief discussion of how representation theory restricts the allowed magnetic structure is also given.Comment: 23 pages, 17 figures, submitted to Phys. Rev. B (March 2006

Invasive Rats (\u3ci\u3eRattus\u3c/i\u3e sp.), but not always Mice (\u3ci\u3eMus musculus\u3c/i\u3e), are Ubiquitous at All Elevations and Habitats within the Caribbean National Forest, Puerto Rico

Invasive rodents, particularly rats (Rattus spp.), occupy \u3e80% of the world’s islands and are among the greatest threats to native biodiversity and agriculture on islands. At the time of their introduction in the 1500s, there was at least 1 native rat species in Puerto Rico. Today there are no native rodents remaining in Puerto Rico, but R. norvegicus (Norway Rat) may be found in urban settings, and R. rattus (Black Rat) are the most common rat across the island including within natural areas, and invasive Mus musculus (House Mouse) may also be found in urban and non-urban habitats. The Caribbean National Forest (CNF; locally El Yunque) in northeastern Puerto Rico has some native and endangered species vulnerable to rat predation. The objective of our study was to determine the presence and distribution of invasive rodents (rats and mice) across elevations and habitats within the CNF. We used 104 tracking tunnels, which are baited ink cards placed in tunnels so that foot prints of animal visitors could be identified, to determine presence of invasive rodent species. We placed 3 tracking tunnels at each 50-m elevation-gain (n = 66 total tunnels), on the edge of forest habitat from sea level to 1070 m at El Yunque peak along the main road (Highway 191) through the CNF. We established additional tracking tunnels (n = 38) in the major habitats in the CNF, including treefall and hurricane gaps, landslides, stream edges, and continuous forest. House Mice had not been previously reported in the CNF, and were found only at the forest edge along Highway 191 at elevations of 50–150 m and 300–1070 m, whereas rats (Rattus sp.) were found at all elevations and in all habitat types sampled. Logistic regressions revealed that mice and rat presence each increases with elevation (mice: P = 0.0352, rat: P = 0.0019), though total rodent presence did not. Knowledge of the habitat types and elevations that these invasive rodents occupy can inform management strategies for rodent control and native species protection

Mass enhancement, correlations, and strong coupling superconductivity in the beta-pyrochlore KOs2O6

To assess electron correlation and electron-phonon coupling in the recently discovered beta-pyrochlores KOs2O6 and RbOs2O6, we have performed specific heat measurements in magnetic fields up to 14 T. We present data from high quality single crystalline KOs2O6, showing that KOs2O6 is a strong coupling superconductor with a coupling parameter lambda_ep \approx 1.0 to 1.6 (RbOs2O6: lambda_ep \approx 1). The estimated Sommerfeld coefficient of KOs2O6, gamma=76 to 110 mJ/(mol K^2), is twice that of RbOs2O6 [gamma=44 mJ/(mol K^2)]. Using strong-coupling corrections, we extract useful thermodynamic parameters of KOs2O6. Quantifying lambda_ep allows us to determine the mass enhancement over the calculated band electronic density of states. A significant contribution in addition to the electron-phonon term of lambda_c=1.7 to 4.3 is deduced. In an effort to understand the origin of the enhancement mechanism, we also investigate an unusual energetically low-lying phonon. There are three phonon modes per RbOs2O6, suggestive of the phonon source being the rattling motion of the alkali ion. This dynamic instability of the alkali ions causes large scattering of the charge carriers which shows up in an unusual temperature dependence of the electrical resistivity.Comment: Accepted for publication in PR

A complete devil's staircase in the Falicov-Kimball model

We consider the neutral, one-dimensional Falicov-Kimball model at zero temperature in the limit of a large electron--ion attractive potential, U. By calculating the general n-ion interaction terms to leading order in 1/U we argue that the ground-state of the model exhibits the behavior of a complete devil's staircase.Comment: 6 pages, RevTeX, 3 Postscript figure

Robotic partial nephrectomy for posterior tumors through a retroperitoneal approach offers decreased length of stay compared with the transperitoneal approach: A propensity-matched analysis

INTRODUCTION: We sought to compare surgical outcomes between transperitoneal and retroperitoneal robotic partial nephrectomy (RPN) for posterior tumors. PATIENTS AND METHODS: Using our multi-institutional RPN database, we reviewed 610 consecutive cases for posterior renal masses treated between 2007 and 2015. Primary outcomes were complications, operative time, length of stay (LOS), surgical margin status, and estimated glomerular filtration rate (eGFR) preservation. Secondary outcomes were estimated blood loss, warm ischemia time (WIT), disease recurrence, and disease-specific mortality. Due to significant differences in treatment year and tumor size between approaches, retroperitoneal cases were matched 1:4 to transperitoneal cases based on propensity scores using the greedy algorithm. Outcomes were compared between approaches using the chi-square and Mann-Whitney U tests. RESULTS: After matching, 296 transperitoneal and 74 retroperitoneal cases were available for analysis, and matched groups were well balanced in terms of treatment year, age, gender, race, American Society of Anesthesiologists physical status classification (ASA) score, body mass index, tumor laterality, tumor size, R.E.N.A.L. (radius, exophytic/endophytic properties, nearness of tumor to the collecting system or sinus, anterior/posterior, location relative to polar lines) score, and hilar location. Compared with transperitoneal, the retroperitoneal approach was associated with significantly shorter mean LOS (2.2 vs 2.6 days, p = 0.01), but longer mean WIT (21 vs 19 minutes, p = 0.01). Intraoperative (p = 0.35) and postoperative complications (p = 0.65), operative time (p = 0.93), positive margins (p = 1.0), and latest eGFR preservation (p = 0.25) were not significantly different between approaches. No differences were detected in the other outcomes. CONCLUSIONS: Among high-volume surgeons, transperitoneal and retroperitoneal RPN achieved similar outcomes for posterior renal masses, although with slight differences in LOS and WIT. Retroperitoneal RPN may be an effective option for the treatment of certain small posterior renal masses