Low-Energy Spectral Features in GRBs

I discuss low-energy lines in gamma-ray bursts. The process of deconvolving gamma-ray spectral data and the steps needed to demonstrate the existence of a line are explained. Previous observations and the current status of the analysis of the BATSE data are described.Comment: 10 pages, LaTex using Revtex macro aipbook.sty and psfig. To appear in the Proceedings of the 3rd Huntsville Symposium on Gamma-Ray Bursts, AIP, eds. C. Kouveliotou, M. S. Briggs, G. J. Fishma

Search for Supergalactic Anisotropies in the 3B Catalog

The angular distribution of GRBs is isotropic, while the brightness distribution of bursts shows a reduced number of faint events. These observations favor a cosmological burst origin. If GRBs are indeed at cosmological distances and if they trace luminous matter, we must eventually find an anisotropic distribution of bright bursts. If a significant number of bursts originate at redshifts less than z~1, the concentration of nearby galaxies towards the supergalactic plane is pronounced enough that we could discover the corresponding clustering of burst locations. We used the 3B catalog to search for a pattern visible in supergalactic coordinates. No compelling evidence for anisotropies was found. The absence of anisotropies in SG coordinates implies a minimum sampling distance of 200h^-1 Mpc.Comment: 5 pages, uuencoded postscript, to appear in the Proceedings of the Huntsville Conference on Gamma Ray Burst

Spherical Harmonic Analysis of the Angular Distribution of Gamma-Ray Bursts

We compute the angular power spectrum C_l of the BATSE 3B catalog, and find no evidence for clustering on any scale. These constraints bridge the entire range from small scales, probing source clustering and repetition, to large scales constraining possible Galactic anisotropies, or those from nearby cosmological large scale structures.Comment: 5 page conf. proceedings, with one figure included. Postscript. More detailed version at http://astro.berkeley.edu/~max/bursts.html (faster from the US), from http://www.mpa-garching.mpg.de/~max/bursts.html (faster from Europe) or from [email protected]

Bond Strength of ASTM A 1035 Grade 100 Reinforcing Steel

The bond strength of ASTM A 1035 Grade 100 reinforcing steel is evaluated relative to the values predicted using the development expressions in ACI 318-05 and ACI 408R-03. Sixty-nine beam-splice specimens were tested at the University of Kansas, North Carolina State University, and the University of Texas, of which 64 failed in bond. Specimens contained bottom-cast lap-splices of No. 5, No. 8, and No. 11 Grade 100 reinforcement. Parameters studied include splice length, bar size, concrete compressive strength, cover, and the amount of confining transverse reinforcement. Lap splices developed bar stresses varying from 68 ksi to 155 ksi prior to splitting bond failure. Results indicate that the ACI 318-05 development expression is unconservative. Inclusion of a high strength reinforcement factor ψh = 1.48 is recommended for use with Grade 100 steel. The ACI 408R-03 development expression is conservative. Both expressions underestimate the contribution to bond strength of transverse reinforcement

Wafer-bonded single-crystal silicon slot waveguides and ring resonators

We fabricated horizontal Si slot waveguides with a 25 nm SiO2 slot layer by bonding thin Si-on-insulator wafers. After removing the Si substrate and buried oxide from one side of the bonded structure, grating-coupled waveguides and ring resonators were partially etched into the Si/SiO2/Si device layers. The gratings exhibit efficiencies of up to 23% at 1550 nm and the ring resonators were measured to have loaded quality factors near 42 000 for the lowest-order transverse-electric mode, corresponding to a propagation loss of 15 dB/cm. The leaky lowest-order transverse-magnetic mode was also observed with a propagation loss of 44 dB/cm

Improved limits on gamma ray burst repetition

We tighten previous upper limits on gamma ray burst repetition by analyzing the angular power spectrum of the BATSE 3B catalog of 1122 bursts. At 95% confidence, we find that no more than 2% of all observed bursts can be labeled as repeaters, even if no sources are observed to repeat more than once. If a fraction f of all observed bursts can be labeled as repeaters that are observed to burst v times each, then all models with (v-1)f>0.05 are ruled out at 99% confidence, as compared to the best previous 99% limit (v-1)f>0.27. At 95% confidence, our new limit is (v-1)f>0.02. Thus even a cluster of 6 events from a single source would have caused excess power above that present in the 3B catalog. We conclude that the current BATSE data are consistent with no repetition of classical gamma ray bursts, and that any repeater model is severely constrained by the near perfect isotropy of their angular distribution.Comment: 18 pages, with 2 figures included. Postscript. Submitted to ApJL. Latest version at http://astro.berkeley.edu/~max/repeaters.html (faster from the US), from http://www.mpa-garching.mpg.de/~max/repeaters.html (faster from Europe) or from [email protected]

On the Outside Looking In: A Qualitative Study of Southern Appalachian First-Generation Students\u27 Perceptions of Higher Education.

This study was designed to investigate Southern Appalachian, first-generation students\u27 expectations of higher education. Research indicates that many first-generation students drop out of college after only 1 semester; however, little research exists concerning the expectations and experiences of first-generation college students from Southern Appalachia. The study employs a qualitative methodology based in the tradition of grounded theory to highlight students\u27 experiences while encouraging the emergence of data-driven theory based on what the researcher heard. Thus, the entire study is couched in the interpretivist philosophy of research. Eleven full-time university students were interviewed for the study. They were asked to identify their perceptions of college and the effect of parents, friends, and culture on their decision to attend college. Students talked about their life goals and how a university education has helped them move toward those goals. Ultimately, students commented on the transformational aspects of higher education in their lives and how they have begun a life journey that will transform their lives for the better. The primary significance of this study lies in the fact that it addresses first-generation students from Southern Appalachia, a group of students that has been ignored by most research dealing with the issue of first-generation students generally. This study highlights issues related to first-generation students\u27 college experiences and how institutions of higher education might better serve those students and keep them engaged in the educational process through to graduation