23,762 research outputs found
September 11: Symbolism And Responses To 9/11
Professors Hopkins and Hopkins review the impact of 9/11 as a symbol in American politics. Following the terrorist attacks, 9/11 became a simple reference condensing wide-ranging events and emotions. Various interpretations emerged about what caused 9/11 and enabled the attacks. The authors claim that 9/11 allowed US leaders to pursue certain policy prescriptions that otherwise would have been blocked. Among four possible prescriptions for responding to the attacks, the Bush administration chose a praetorian policy of preventive war, with Iraq as its first example. In the authorsâ view, by pursuing an expansive but highly militarized response, the US has overlooked the need to alleviate the conditions that made 9/11 possible. The authors recommend that the US, as part of a multilateral effort, allocate major resources to expanding global public goods, including measures that strengthen barriers to proliferation, enhance fighting of global crime, and reduce incentives for terrorism, especially ones arising in failing states where distorted education and weak protection of human rights encourage organized terrorism
Effects of impurities on silicon solar-cell performance
Model analyses indicate that sophisticated solar cell designs (back surface fields, optical reflectors, surface passivation, and double layer antireflective coatings) can produce devices with conversion efficiencies above 20%. To realize this potential, the quality of the silicon from which the cells are made must be improved; and these excellent electrical properties must be maintained during device processing. As the cell efficiency rises, the sensitivity to trace contaminants also increases. For example, the threshold Ti impurity concentraion at which cell performance degrades is more than an order of magnitude lower for an 18% cell than for a 16% cell. Similar behavior occurs for numerous other metal species which introduce deep level traps that stimulate the recombination of photogenerated carriers in silicon. Purification via crystal growth in conjunction with gettering steps to preserve the large diffusion length of the as grown material can lead to the production of devices with efficiencies above 18%, as verified experimentally
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Anti-social behaviour orders: an infringement of the Human Rights Act 1998?
The Economics of Non-Governmental Organisations.
The purpose of this paper is to identify the organisational comparative advantage of NGOs, and to develop a model which explains the set of circumstances uder which they emerge and dominate other types of firms. It is argued that the potential superiority of NGOs derives from two features: (1) the creation of an institutional environment within the firm which selectively attracts altruists, who have a lower supply price of effective labour than egotists, and (2) the ability to develop efficient technologies for converting the relevatory and productive effort of their staff into local outputs which are highly valued by the target group of beneficiaries.miroeconomic analyses of economic development, formal and informal sectors, non-governmental organisations, institutional arrangements, non-profit institutions, altruism
The Transition Town Network: a review of current evolutions and renaissance
The Transition Network started as a movement with Transition Totnes (Devon, UK) in late 2005, with Rob Hopkins as its founder. To date it has grown to encompass 313 official Transition Network initiatives spread across the world from the UK (with roughly 50% of all initiatives) to the USA, Canada, Italy, Japan, Germany, Ireland, New Zealand, Chile, the Netherlands, Brazil and so on (Transition Network, 2010a). For any social movement, this could most certainly be described as something of a success and warrants a closer examination. Indeed, the aim of this profile is to explore the movement's aims and modus operandi, the problematics it has faced and how it is now evolving. The profile draws on my auto-ethnographic encounters with the movement in Transition Nottingham and at the recent Transition Network Conference 2010, whilst also being grounded in the material made publically available on the Transition Network and Transition Culture websites (see Transition Network, 2010b and Transition Culture, 2010a)
Protostellar Feedback in Turbulent Fragmentation: Consequences for Stellar Clustering and Multiplicity
Stars are strongly clustered on both large (~pc) and small (~binary) scales,
but there are few analytic or even semi-analytic theories for the correlation
function and multiplicity of stars. In this paper we present such a theory,
based on our recently-developed semi-analytic framework called MISFIT, which
models gravito-turbulent fragmentation, including the suppression of
fragmentation by protostellar radiation feedback. We compare the results
including feedback to a control model in which it is omitted. We show that both
classes of models robustly reproduce the stellar correlation function at >0.01
pc scales, which is well approximated by a power-law that follows generally
from scale-free physics (turbulence plus gravity) on large scales. On smaller
scales protostellar disk fragmentation becomes dominant over common core
fragmentation, leading to a steepening of the correlation function.
Multiplicity is more sensitive to feedback: we found that a model with the
protostellar heating reproduces the observed multiplicity fractions and mass
ratio distributions for both Solar and sub-Solar mass stars (in particular the
brown dwarf desert), while a model without feedback fails to do so. The model
with feedback also produces an at-formation period distribution consistent with
the one inferred from observations. However, it is unable to produce
short-range binaries below the length scale of protostellar disks. We suggest
that such close binaries are produced primarily by disk fragmentation and
further decrease their separation through orbital decay.Comment: 17 pages, 15 figures, submitted to MNRA
Nonlinear Evolution of Instabilities Between Dust and Sound Waves
We study the non-linear evolution of the acoustic 'Resonant Drag Instability'
(RDI) using numerical simulations. The acoustic RDI is excited in a dust-gas
mixture when dust grains stream through gas, interacting with sound waves to
cause a linear instability. We study this process in a periodic box by
accelerating neutral dust with an external driving force. The instability grows
as predicted by linear theory, eventually breaking into turbulence and
saturating. As in linear theory, the non-linear behavior is characterized by
three regimes - high, intermediate, and low wavenumbers - the boundary between
which is determined by the dust-gas coupling strength and the dust-to-gas mass
ratio. The high and intermediate wavenumber regimes behave similarly to one
another, with large dust-to-gas ratio fluctuations while the gas remains
largely incompressible. The saturated state is highly anisotropic: dust is
concentrated in filaments, jets, or plumes along the direction of acceleration,
with turbulent vortex-like structures rapidly forming and dissipating in the
perpendicular directions. The low-wavenumber regime exhibits large fluctuations
in gas and dust density, but the dust and gas remain more strongly coupled in
coherent 'fronts' perpendicular to the acceleration. These behaviors are
qualitatively different from those of dust 'passively' driven by external
hydrodynamic turbulence, with no back-reaction force from dust onto gas. The
virulent nature of these instabilities has interesting implications for
dust-driven winds in a variety of astrophysical systems, including around
cool-stars, in dusty torii around active-galactic-nuclei, and in and around
giant molecular clouds.Comment: 11 pages, 9 figure
Design and breadboard evaluation of the SPS reference phase control system concept
The total breadboard system includes one pilot transmitter, one pilot receiver, nine phase distribution units, and two power transponders. With this complement of equipment, segments of a typical phase distribution system can be assembled to facilitate the evaluation of significant system parameters. The achievable accuracy of a large phase distribution system, the sensitivity of the system to parameter variations, and the limitations of commercially available components in such applications were determined
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