Systematic search for high-energy gamma-ray emission from bow shocks of runaway stars

Context. It has been suggested that the bow shocks of runaway stars are sources of high-energy gamma rays (E > 100 MeV). Theoretical models predicting high-energy gamma-ray emission from these sources were followed by the first detection of non-thermal radio emission from the bow shock of BD+43^\deg 3654 and non-thermal X-ray emission from the bow shock of AE Aurigae. Aims. We perform the first systematic search for MeV and GeV emission from 27 bow shocks of runaway stars using data collected by the Large Area Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope (Fermi). Methods. We analysed 57 months of Fermi-LAT data at the positions of 27 bow shocks of runaway stars extracted from the Extensive stellar BOw Shock Survey catalogue (E-BOSS). A likelihood analysis was performed to search for gamma-ray emission that is not compatible with diffuse background or emission from neighbouring sources and that could be associated with the bow shocks. Results. None of the bow shock candidates is detected significantly in the Fermi-LAT energy range. We therefore present upper limits on the high-energy emission in the energy range from 100 MeV to 300 GeV for 27 bow shocks of runaway stars in four energy bands. For the three cases where models of the high-energy emission are published we compare our upper limits to the modelled spectra. Our limits exclude the model predictions for Zeta Ophiuchi by a factor $\approx$ 5.Comment: 5 pages, 5 figures, 1 table, accepted by A&

Solar Activation of Molecular Water Oxidation Catalysts Using Semiconductors.

Water splitting has been proposed as a viable route toward the renewable production of hydrogen. However, this approach is limited by the water oxidation half-reaction due to the large energy input needed the reaction is sluggish. Sunlight has been used to create excited state electron/hole pairs that are thermodynamically capable of generating H2 and O2. Molecular (homogeneous) and heterogeneous catalysts have been developed to oxidize water efficiently under illumination. The focus of this dissertation is to anchor molecular catalysts onto heterogeneous light absorbers (semiconductors) to more efficiently oxidize water using sunlight. The most significant discovery is that when a molecular Fe water oxidation catalyst is anchored to WO3, a 60% increase in the rate of oxygen evolution and a 40% increase in selectivity towards water oxidation is achieved. Additionally, when different tsemiconductors are used, the reaction rate is dependent on the energy of the conduction band edge and the band gap. For instance, when the conduction band potential energy is held constant and the band gap is decreased from 2.7 eV (WO3) to 2.1 eV (Fe2O3) the rate enhancement with the Fe catalyst increases from 60% to 273%. In addition to the role of the semiconductor on the photoelectrochemical performance, the molecular species also plays an important role in the photoelectrochemical rate enhancement. The most significant development using various molecular species is that replacing iron with other first-row transition metals (Mn-Zn) results in complexes that are only active toward water oxidation when anchored to WO3. And, the corresponding nickel and copper complexes increase the selectivity towards water oxidation up to 99% compared to bare WO3 (56%). Unfortunately, when the best-performing ruthenium catalyst is anchored to various semiconductors, the rate enhancement for solar water oxidation is negligible compared to the other molecular species used in this work. This work demonstrates for the first time that photoelectrochemically generated minority carriers (holes) from semiconductors can be used directly as oxidants to activate molecular oxidation complexes under solar irradiation. Furthermore, this work is the first to quantify the increase in selectivity towards water oxidation directly for WO3 when modified with molecular species.PHDChemistryUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/111517/1/bklepser_1.pd

Phase-resolved Crab pulsar measurements from 25 to 400 GeV with the MAGIC telescopes

We report on observations of the Crab pulsar with the MAGIC telescopes. Our data were taken in both monoscopic (> 25GeV) and stereoscopic (> 50GeV) observation modes. Two peaks were detected with both modes and phase-resolved energy spectra were calculated. By comparing with Fermi- LAT measurements, we find that the energy spectrum of the Crab pulsar does not follow a power law with an exponential cutoff, but has an additional hard component, extending up to at least 400 GeV. This suggests that the emission above 25 GeV is not dominated by curvature radiation, as suggested in the standard scenarios of the OG and SG models.Comment: 4 pages, 2 figures, Proc. TAUP 2011, submitted for publication in JCP

A major electronics upgrade for the H.E.S.S. Cherenkov telescopes 1-4

The High Energy Stereoscopic System (H.E.S.S.) is an array of imaging atmospheric Cherenkov telescopes (IACTs) located in the Khomas Highland in Namibia. It consists of four 12-m telescopes (CT1-4), which started operations in 2003, and a 28-m diameter one (CT5), which was brought online in 2012. It is the only IACT system featuring telescopes of different sizes, which provides sensitivity for gamma rays across a very wide energy range, from ~30 GeV up to ~100 TeV. Since the camera electronics of CT1-4 are much older than the one of CT5, an upgrade is being carried out; first deployment was in 2015, full operation is planned for 2016. The goals of this upgrade are threefold: reducing the dead time of the cameras, improving the overall performance of the array and reducing the system failure rate related to aging. Upon completion, the upgrade will assure the continuous operation of H.E.S.S. at its full sensitivity until and possibly beyond the advent of CTA. In the design of the new components, several CTA concepts and technologies were used and are thus being evaluated in the field: The upgraded read-out electronics is based on the NECTAR readout chips; the new camera front- and back-end control subsystems are based on an FPGA and an embedded ARM computer; the communication between subsystems is based on standard Ethernet technologies. These hardware solutions offer good performance, robustness and flexibility. The design of the new cameras is reported here.Comment: Proceedings of the 34th International Cosmic Ray Conference, 30 July- 6 August, 2015, The Hague, The Netherland

Midwest Pharmacists\u27 Familiarity, Experience, and Willingness to Provide Pre-Exposure Prophylaxis (PrEP) for HIV

INTRODUCTION: Pharmacist provision of pre-exposure prophylaxis (PrEP) through collaborative practice agreements with physicians could expand access to people at risk for HIV. We characterized pharmacists\u27 familiarity with and willingness to provide PrEP services in Nebraska and Iowa. METHODS: An invitation to complete an 18-question survey was emailed to 1,140 pharmacists in Nebraska and Iowa in June and July of 2016. Descriptive analyses and Pearson chi-square tests were used to determine to what extent demographics, familiarity and experience were associated with respondent willingness to provide PrEP. Wilcoxon rank-sum tests compared ages and years of experience between groups of respondents. RESULTS: One hundred forty pharmacists (12.3%) responded. Less than half were familiar with the use of PrEP (42%) or the CDC guidelines for its use (25%). Respondents who were older (p = .015) and in practice longer (p = .005) were less likely to be familiar with PrEP. Overall, 54% indicated they were fairly or very likely to provide PrEP services as part of a collaborative practice agreement and after additional training. While familiarity with PrEP use or guidelines did not affect respondents\u27 willingness to provide PrEP, respondents were more likely to provide PrEP with prior experience counseling HIV-infected patients on antiretroviral therapy (OR 2.43; p = 0.023) or PrEP (OR 4.67; p = 0.013), and with prior HIV-related continuing education (OR 2.77; p = 0.032). CONCLUSIONS: Pharmacist respondents in Nebraska and Iowa had limited familiarity and experience with PrEP, but most indicated willingness to provide PrEP through collaborative practice agreements after additional training. Provision of PrEP-focused continuing education may lead to increased willingness to participate in PrEP programs