Very High Energy Gamma Rays from Supernova Remnants and Constraints on the Galactic Interstellar Radiation Field

The large-scale Galactic interstellar radiation field (ISRF) is the result of stellar emission and dust re-processing of starlight. Where the energy density of the ISRF is high (e.g., the Galactic Centre), the dominant gamma-ray emission in individual supernova remnants (SNRs), such as G0.9+0.1, may come from inverse Compton (IC) scattering of the ISRF. Several models of the ISRF exist. The most recent one, which has been calculated by us, predicts a significantly higher ISRF than the well-used model of Mathis, Mezger, and Panagia. However,comparison with data is limited to local observations. Based on our current estimate of the ISRF we predict the gamma-ray emission in the SNRs G0.9+0.1 and RXJ1713, and pair-production absorption features above 20 TeV in the spectra of G0.9+0.1, J1713-381, and J1634-472. We discuss how GLAST, along with current and future very high energy instruments, may be able to provide upper bounds on the large-scale ISRF.Comment: To appear in the proceedings of the 1st GLAST Symposiu

A Comprehensive Four-Quark Interpretation of D_s(2317), D_s(2457) and D_s(2632)

The recently observed new member of the charm-strange family D_s(2632) which has a surprisingly narrow width is challenging our theory. D_s(2317) and D_s(2457) which were observed earlier have similar behaviors and receive various theoretical explanations. Some authors use the heavy hadron chiral effective theory to evaluate heavy-light quark systems and obtain a reasonable evaluation on the masses of D_s(2317) and D_s(2457). An alternative picture is to interpret them as four-quark or molecular states. In this work, we are following the later and propose a unitive description for all the three new members D_s(2632), D_s(2317) and D_s(2457) and at least, so far our picture is consistent with the data.Comment: 6 page

Hadronic Gamma Rays from Supernova Remnants

A gas cloud near a supernova remnant (SNR) provides a target for pp-collisions leading to subsequent gamma-ray emission through neutral pion decay. The assumption of a power-law ambient spectrum of accelerated particles with index near -2 is usually built into models predicting the spectra of very-high energy (VHE) gamma-ray emission from SNRs. However, if the gas cloud is located at some distance from the SNR shock, this assumption is not necessarily correct. In this case, the particles which interact with the cloud are those leaking from the shock and their spectrum is approximately monoenergetic with the injection energy gradually decreasing as the SNR ages. In the GLAST energy range the gamma-ray spectrum resulting from particle interactions with the gas cloud will be flatter than expected, with the cutoff defined by the pion momentum distribution in the laboratory frame. We evaluate the flux of particles escaping from a SNR shock and apply the results to the VHE diffuse emission detected by the HESS at the Galactic centre.Comment: 4 pages, 3 figures. Contribution to the 30th ICRC, Merida, Mexico, 2007 (final version

Between the classroom and the field: An examination of the experiences of black male football student-athletes

This study is concerned with the fact that numerous Black student-athletes that play football at Division 1 predominantly White institutions (PWIs) are graduating at the lowest rates of all student and student-athlete groups on college campuses nationwide. An intercollegiate athletics system acts as the commercial arm of the university and is designed to ensure the sustainability and viability of football by creating contradictory athletic and academic pressures that the student-athletes must navigate. Despite the intentional obstacles that Black student athletes encounter, there are many that do graduate from their institution and transition into a professional career. Therefore, the guiding research question was: How did Black male football student-athletes manage to graduate while being part of a Division 1 team at a research-intensive institution? Purposeful sampling was used to select participants who met the criteria defined by the researcher. This study utilized a qualitative case study method to examine the experiences of the selected participants. Primary data were collected through interviews from five Black football players and seven current and former university faculty and staff members. Secondary data were collected from participant questionnaires and cross-referenced with media guides and player profiles. The study revealed three central findings. First, the data disproved the common notion that Black football student-athletes are from inner city, poor socioeconomic backgrounds and attended failing high schools that did not adequately prepare them for college. Second, the participants in this study navigated contradictory athletic and academic pressures when they utilized their strong social support network of people who provided advice, guidance, and a safe space to process feelings. The function of the support was to strengthen their motivation to graduate. Last, the organizational system which these student-athletes had to navigate, influenced all facets of their lives and dictated the degree programs they pursued. The student-athletes that managed to graduate from the institution did so from a degree program that was accommodating to their football related schedules. Implications and suggestions from the author for future research are also discussed

Global Maps of Science based on the new Web-of-Science Categories

In August 2011, Thomson Reuters launched version 5 of the Science and Social Science Citation Index in the Web of Science (WoS). Among other things, the 222 ISI Subject Categories (SCs) for these two databases in version 4 of WoS were renamed and extended to 225 WoS Categories (WCs). A new set of 151 Subject Categories (SCs) was added, but at a higher level of aggregation. Since we previously used the ISI SCs as the baseline for a global map in Pajek (Rafols et al., 2010) and brought this facility online (at http://www.leydesdorff.net/overlaytoolkit), we recalibrated this map for the new WC categories using the Journal Citation Reports 2010. In the new installation, the base maps can also be made using VOSviewer (Van Eck & Waltman, 2010).Comment: Scientometrics, in pres