Destruction of Interstellar Dust in Evolving Supernova Remnant Shock Waves

Supernova generated shock waves are responsible for most of the destruction of dust grains in the interstellar medium (ISM). Calculations of the dust destruction timescale have so far been carried out using plane parallel steady shocks, however that approximation breaks down when the destruction timescale becomes longer than that for the evolution of the supernova remnant (SNR) shock. In this paper we present new calculations of grain destruction in evolving, radiative SNRs. To facilitate comparison with the previous study by Jones et al. (1996), we adopt the same dust properties as in that paper. We find that the efficiencies of grain destruction are most divergent from those for a steady shock when the thermal history of a shocked gas parcel in the SNR differs significantly from that behind a steady shock. This occurs in shocks with velocities >~ 200 km/s for which the remnant is just beginning to go radiative. Assuming SNRs evolve in a warm phase dominated ISM, we find dust destruction timescales are increased by a factor of ~2 compared to those of Jones et al. (1996), who assumed a hot gas dominated ISM. Recent estimates of supernova rates and ISM mass lead to another factor of ~3 increase in the destruction timescales, resulting in a silicate grain destruction timescale of ~2-3 Gyr. These increases, while not able resolve the problem of the discrepant timescales for silicate grain destruction and creation, are an important step towards understanding the origin, and evolution of dust in the ISM.Comment: 30 pages, 8 figures, accepted for publication in the Astrophysical Journa

Orphans : childhood alienation and the idea of the self in Rousseau, Wordsworth and Mary Shelley

This thesis explores representations of the self in Rousseau's Émile (1762). Wordsworth's The Prelude (1805) and Mary Shelley's Frankenstein (1818). It uses the idea of 'the orphan' not in a strictly literal sense, but in order to explore representations of the self that stress an individual's autonomy, and thus tend to minimise the importance of society and cultural inheritance to the formation of the self. Crucial to understanding this model of the self is the idea found in Émile of autonomous natural growth: the idea that a child brought up in relative seclusion in the countryside, and offered the minimum of assistance from its adult carers, is capable of developing naturally, seemingly under its own volition. Rousseau believed that such a child would have an authenticity lacking in those children unduly contaminated by external cultural factors. The model of autonomous growth proposed by Rousseau relates to the discourse of possessive individualism and to the idea of the self-made man, beholden to no one, and free to make his own way in the world. This model of the self influenced Wordsworth and Mary Shelley, who both respond to and react against Rousseau's thinking. The thesis explores the contradictions implicit in this model of self-formation. It stresses the impossibility of keeping children free from external human factors, looking at the way that physical and mental development is necessarily accompanied by a child's acculturation, for example in relation to language acquisition. It explores the complications that arise from this in relation to questions of autonomy. The thesis highlights the sense of alienation and the emotional cost experienced by the child who is brought up to perceive itself as set apart from 'others', as exemplified by the loneliness felt by the most isolated of the 'children' under discussion, Victor Frankenstein's creation. In contrast to the discourse of possessive individualism this study persists in treating the self as historically situated, and inhabited by the culture that surrounds it

Money Growth, Inflation, and Causality (Empirical Evidence for Pakistan, 1973-1985)

This paper uses the Granger direct test to evaluate the causal relationship between growth in money supply and inflation in Pakistan. The historical period investigated extends from 1973 to 1985. The results of the test show that money growth had a significant impact on inflation during the period considered. In addition, there is some evidence at hand showing that inflation, too, affected money growth over the 1973- 1985 period. The empirical issue of the impact of money supply on rate of inflation continues to be a much debated topic. For example, Tumovsky and Wohar (1984) do not find any identifiable relationship between money supply and prices over the 1929- 1978 period in the U.S., while Benderly and Zwick (1985) find money supply affecting prices in the U,S, over the 1955-1982 period. Jones and Uri (1986) also find evidence of money supply influencing price level in the U.S. during the 1953- 1984 period. Studies• for other countries, e,g. Driscoll, Ford, and Mullineux (1985) for the U.K., invariably report similar conflicting results about the relationship between money supply and prices. While there are numerous empirical studies that have examined the causal relationship .between money supply and prices in developed countries, there are also several recent studies that have addressed this particular issue for developing countries. In one such study, Aghevli and Khan (1978) use the Haugh-Pierce test to investigate the causal relationship between money growth and inflation in Brazil, Colombia. the Dominican Republic, and Thailand. t The results of the tests show a feedback or bidirectional causality between money and inflation in all the four developing countries over the 1964-1974 period

Error tolerance in an NMR Implementation of Grover's Fixed-Point Quantum Search Algorithm

We describe an implementation of Grover's fixed-point quantum search algorithm on a nuclear magnetic resonance (NMR) quantum computer, searching for either one or two matching items in an unsorted database of four items. In this new algorithm the target state (an equally weighted superposition of the matching states) is a fixed point of the recursive search operator, and so the algorithm always moves towards the desired state. The effects of systematic errors in the implementation are briefly explored.Comment: 5 Pages RevTex4 including three figures. Changes made at request of referees; now in press at Phys Rev

Some Evidence On The Secondary Market Trading Of Syndicated Loans

An important recent development in U. S. capital markets is the tremendous growth in the secondary market trading of syndicated loans. This paper uses a unique trading data set for syndicated loans over the period 1997 to 2003 to empirically investigate two major issues. First, we present a statistical overview of the recent growth in the secondary market trading of syndicated loans. Second, we examine the determinants of which syndicated loans are most likely to be traded in the secondary market using binomial logistic regression models. We find that syndicated loans that are larger, have longer maturities, are underwritten by larger syndicates, and are used for debt repayment, takeovers, and leveraged buyouts are more likely to be traded. Lender reputation plays an important role as well, with loans originated by very active lenders more likely to be traded.  We also find that syndicated loans made to borrowers with only senior debt ratings are more likely to be traded in the secondary market than loans made to borrowers with both a debt rating and equity that trades in a stock exchange. This result most likely reflects the growing demand of institutional investors for the higher yields of levered and highly levered syndicated loans made to riskier opaque borrowers with less available market information

Geometric quantum computation with NMR

The experimental realisation of the basic constituents of quantum information processing devices, namely fault-tolerant quantum logic gates, requires conditional quantum dynamics, in which one subsystem undergoes a coherent evolution that depends on the quantum state of another subsystem. In particular, the subsystem may acquire a conditional phase shift. Here we consider a novel scenario in which this phase is of geometric rather than dynamical origin. As the conditional geometric (Berry) phase depends only on the geometry of the path executed it is resilient to certain types of errors, and offers the potential of an intrinsically fault-tolerant way of performing quantum gates. Nuclear Magnetic Resonance (NMR) has already been used to demonstrate both simple quantum information processing and Berry's phase. Here we report an NMR experiment which implements a conditional Berry phase, and thus a controlled phase shift gate. This constitutes the first elementary geometric quantum computation.Comment: Minor additions at request of referees. 4 pages revtex including 2 figures (1 eps). Nature in pres

NASA Manned Launch Vehicle Lightning Protection Development

Historically, the National Aeronautics and Space Administration (NASA) relied heavily on lightning avoidance to protect launch vehicles and crew from lightning effects. As NASA transitions from the Space Shuttle to the new Constellation family of launch vehicles and spacecraft, NASA engineers are imposing design and construction standards on the spacecraft and launch vehicles to withstand both the direct and indirect effects of lightning. A review of current Space Shuttle lightning constraints and protection methodology will be presented, as well as a historical review of Space Shuttle lightning requirements and design. The Space Shuttle lightning requirements document, NSTS 07636, Lightning Protection, Test and Analysis Requirements, (originally published as document number JSC 07636, Lightning Protection Criteria Document) was developed in response to the Apollo 12 lightning event and other experiences with NASA and the Department of Defense launch vehicles. This document defined the lightning environment, vehicle protection requirements, and design guidelines for meeting the requirements. The criteria developed in JSC 07636 were a precursor to the Society of Automotive Engineers (SAE) lightning standards. These SAE standards, along with Radio Technical Commission for Aeronautics (RTCA) DO-160, Environmental Conditions and Test Procedures for Airborne Equipment, are the basis for the current Constellation lightning design requirements. The development and derivation of these requirements will be presented. As budget and schedule constraints hampered lightning protection design and verification efforts, the Space Shuttle elements waived the design requirements and relied on lightning avoidance in the form of launch commit criteria (LCC) constraints and a catenary wire system for lightning protection at the launch pads. A better understanding of the lightning environment has highlighted the vulnerability of the protection schemes and associated risk to the vehicle, which has resulted in lost launch opportunities and increased expenditures in manpower to assess Space Shuttle vehicle health and safety after lightning events at the launch pad. Because of high-percentage launch availability and long-term on-pad requirements, LCC constraints are no longer considered feasible. The Constellation vehicles must be designed to withstand direct and indirect effects of lightning. A review of the vehicle design and potential concerns will be presented as well as the new catenary lightning protection system for the launch pad. This system is required to protect the Constellation vehicles during launch processing when vehicle lightning effects protection might be compromised by such items as umbilical connections and open access hatches

Altered synaptic plasticity in the mossy fibre pathway of transgenic mice expressing mutant amyloid precursor protein

Aβ peptides derived from the cleavage of amyloid precursor protein are widely believed to play an important role in the pathophysiology of Alzheimer's disease. A common way to study the impact of these molecules on CNS function is to compare the physiology of transgenic mice that overproduce Aβ with non-transgenic animals. In the hippocampus, this approach has been frequently applied to the investigation of synaptic transmission and plasticity in the perforant and Schaffer collateral commissural pathways, the first and third components of the classical hippocampal trisynaptic circuit, respectively. Similar studies however have not been carried out on the remaining component of the trisynaptic circuit, the mossy fibre pathway. Using transverse hippocampal slices prepared from ~2 year old animals we have compared mossy fibre synaptic function in wild-type mice and their Tg2576 littermates which age-dependently overproduce Aβ. Input-output curves were not altered in slices from Tg2576 mice, but these animals exhibited a significant loss of the prominent frequency-facilitation expressed by the mossy fibre pathway. In addition to this change in short term synaptic plasticity, high frequency stimulation-induced, NMDA-receptor-independent LTP was absent in slices from the transgenic mice. These data represent the first description of functional deficits in the mossy fibre pathway of Aβ-overproducing transgenic mice