Radiation studies of optical and electronic components used in astronomical satellite studies

The synchronous orbit of the IUE carries the satellite through Earth's outer electron belt. A 40 mCi Sr90 source was used to simulate these electrons. A 5 mCi source of Co60 was used to simulate bremmstrahlung. A 10 MeV electron Linac and a 1.7 MeV electron Van de Graaf wer used to investigate the energy dependence of radiation effects and to perform radiations at a high flux rate. A 100 MeV proton cyclotron was used to simulate cosmic rays. Results are presented for three instrument systems of the IUE and measurements for specific components are reported. The three instrument systems were the ultraviolet converter, the fine error sensor (FES), and the SEC vidicon camera tube. The components were optical glasses, electronic components, silicon photodiodes, and UV window materials

Radiation effects induced in pin photodiodes by 40- and 85-MeV protons

PIN photodiodes were bombarded with 40- and 85-MeV protons to a fluence of 1.5 x 10 to the 11th power p/sq cm, and the resulting change in spectral response in the near infrared was determined. The photocurrent, dark current and pulse amplitude were measured as a function of proton fluence. Changes in these three measured properties are discussed in terms of changes in the diode's spectral response, minority carrier diffusion length and depletion width. A simple model of induced radiation effects is presented which is in good agreement with the experimental results. The model assumes that incident protons produce charged defects within the depletion region simulating donor type impurities

Conceptualising and historicising the US foreign policy establishment in a racialised class structure

In recent years critical scholars of U.S. foreign policy have challenged the mainstream paradigm that fails to account for the racial dimensions of international relations. This article introduces a conceptual and historical analysis of the US foreign policy establishment that posits race and racism at its centre. While alluding to conventional theories of American power such as pluralism and statism, the article also highlights classical Marxism’s failure to acknowledge that US exceptionalism and racism conjoined in a manner that conferred a racial dimension to class politics. The article argues that the U.S. foreign policy establishment has been presided over by an elite or ruling elite; and irrespective of challenges from below, increasing diversity, or the insistence that America is a meritocratic classless society, the U.S establishment is at heart, elitist, racialised and generally Anglo-centric. The article identifies links between the racial dimensions of U.S. foreign policy and the identity profile of the power elite. The paper extends and critiques C. Wright Mills’ definition of the power elite by mapping its racial dimension. Finally the article argues that although the election of Obama represented a more inclusive and cosmopolitan version of the establishment, Obama’s presence has helped to consolidate the status quo as the structural constraints on the executive branch and symbolism associated with the election of the first African-American president has generally silenced the Left and quietly fostered the suggestion that an unconventional identity profile will not necessarily result in the change we can believe in

A Conditioning Lesion Provides Selective Protection in a Rat Model of Amyotrophic Lateral Sclerosis

Amyotrophic Lateral Sclerosis (ALS) is neurodegenerative disease characterized by muscle weakness and atrophy due to progressive motoneuron loss. The death of motoneuron is preceded by the failure of neuromuscular junctions (NMJs) and axonal retraction. Thus, to develop an effective ALS therapy you must simultaneously preserve motoneuron somas, motor axons and NMJs. A conditioning lesion has the potential to accomplish this since it has been shown to enhance neuronal survival and recovery from trauma in a variety of contexts. rats that received a conditioning lesion was delayed and less severe. These improvements in motor function corresponded to greater motoneuron survival, reduced motor axonopathy, and enhanced NMJ maintenance at disease end-stage. Furthermore, the increased NMJ maintenance was selective for muscle compartments innervated by the most resilient (slow) motoneuron subtypes, but was absent in muscle compartments innervated by the most vulnerable (fast fatigable) motoneuron subtypes.These findings support the development of strategies aimed at mimicking the conditioning lesion effect to treat ALS as well as underlined the importance of considering the heterogeneity of motoneuron sub-types when evaluating prospective ALS therapeutics