21,453 research outputs found

    Gamma-Ray Bursts and Cosmology

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    The unrivalled, extreme luminosities of gamma-ray bursts (GRBs) make them the favored beacons for sampling the high redshift Universe. To employ GRBs to study the cosmic terrain -- e.g., star and galaxy formation history -- GRB luminosities must be calibrated, and the luminosity function versus redshift must be measured or inferred. Several nascent relationships between gamma-ray temporal or spectral indicators and luminosity or total energy have been reported. These measures promise to further our understanding of GRBs once the connections between the luminosity indicators and GRB jets and emission mechanisms are better elucidated. The current distribution of 33 redshifts determined from host galaxies and afterglows peaks near z ~ 1, whereas for the full BATSE sample of long bursts, the lag-luminosity relation predicts a broad peak z ~ 1-4 with a tail to z ~ 20, in rough agreement with theoretical models based on star formation considerations. For some GRB subclasses and apparently related phenomena -- short bursts, long-lag bursts, and X-ray flashes -- the present information on their redshift distributions is sparse or entirely lacking, and progress is expected in Swift era when prompt alerts become numerous.Comment: Invited talk given at the JENAM 2003 Minisymposium on Physics of Gamma-Ray Bursts, August 29-30, 2003, Budapest, Hungary; 6 pages, 1 figur

    “Little Soldiers with Big Guns”: The Language of Child-Soldiering in Africa

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    This project examines the language of child-soldiering in Africa, specifically in Sierra Leone, Rwanda, and Uganda, comparing its use between Western observers and the Africans who experienced the conflict first hand. It concludes that Westerners unilaterally display ethnocentric conceptions of the sanctity of childhood in their admonitions of child-soldiering, while former child-soldiers, perpetrators, victims and local aid workers exhibit more diverse perspectives that more accurately reflect the complexity of the conflicts. Furthermore, it concludes that the use of rhetorical, monolithic language regarding child-soldiering perpetuates stereotypes about African conflict and state-failure while diverting attention from underlying root causes of conflict, and overlooks government corruption and human rights abuses that have gone largely unchecked by Western nations despite their condemnation of the violence

    The Effects of American Involvement in Northern Uganda\u27s Conflict with the Lord\u27s Resistance Army

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    This project explores the impact of American governmental and non-governmental actors in the Lord\u27s Resistance Army (LRA) conflict in northern Uganda and southern Sudan, particularly the U.S. military, United States Agency for International Development (USAID), and various non-governmental organizations (NGOs). It also examines the efficacy of these various forms of intervention, specifically the deployment of U.S. Special Forces tracking the LRA, and the initiation of various soldier reintegration, governance, and sustainability programs organized by USAID and NGOs such as Invisible Children. Additionally, this project seeks to uncover underlying geopolitical objectives, such as gaining alliances in the \u27Global War on Terror\u27 and protecting regional oil interests, that have motivated these U.S. government policies. Overall, this project has sought to critically examine the impact of American involvement in the northern Uganda conflict, both positive and negative, and evaluate the human impact of these international geopolitical influences on the people of northern Uganda, southern Sudan, and beyond

    Proton-Electron Hyperfine Coupling Constants of the Chlorophyll a Cation Radical by ENDOR Spectroscopy

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    In this paper we describe the assignment of the major coupling constants in monomer chlorophyll a cation free radical by ENDOR spectroscopy. To facilitate chemical manipulation methylpyrochlorophyllide a has been used as a stand-in, and a suite of six selectively deuterated derivatives have been subjected to ENDOR investigation. Details of the synthesis of these compounds are described. To study the effect of structural features on the spin distribution in the free radicals, six additional chlorophyll derivatives have been studied. Five coupling constants have been assigned, which account for about 80% of the observed electron spin resonance line width in the chlorophyll a monomer cation radical. The spin distribution appears to be highly asymmetric
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