964 research outputs found
Abelian Higgs Cosmic Strings: Small Scale Structure and Loops
Classical lattice simulations of the Abelian Higgs model are used to
investigate small scale structure and loop distributions in cosmic string
networks. Use of the field theory ensures that the small-scale physics is
captured correctly. The results confirm analytic predictions of Polchinski &
Rocha [1] for the two-point correlation function of the string tangent vector,
with a power law from length scales of order the string core width up to
horizon scale with evidence to suggest that the small scale structure builds up
from small scales. An analysis of the size distribution of string loops gives a
very low number density, of order 1 per horizon volume, in contrast with
Nambu-Goto simulations. Further, our loop distribution function does not
support the detailed analytic predictions for loop production derived by Dubath
et al. [2]. Better agreement to our data is found with a model based on loop
fragmentation [3], coupled with a constant rate of energy loss into massive
radiation. Our results show a strong energy loss mechanism which allows the
string network to scale without gravitational radiation, but which is not due
to the production of string width loops. From evidence of small scale structure
we argue a partial explanation for the scale separation problem of how energy
in the very low frequency modes of the string network is transformed into the
very high frequency modes of gauge and Higgs radiation. We propose a picture of
string network evolution which reconciles the apparent differences between
Nambu-Goto and field theory simulations.Comment: 16 pages, 17 figure
Thermal design of the space shuttle external tank
The shuttle external tank thermal design presents many challenges in meeting the stringent requirements established by the structures, main propulsion systems, and Orbiter elements. The selected thermal protection design had to meet these requirements, and ease of application, suitability for mass production considering low weight, cost, and high reliability. This development led to a spray-on-foam (SOFI) which covers the entire tank. The need and design for a SOFI material with a dual role of cryogenic insulation and ablator, and the development of the SOFI over SLA concept for high heating areas are discussed. Further issuses of minimum surface ice/frost, no debris, and the development of the TPS spray process considering the required quality and process control are examined
Salinity effects on biodegradation of Reactive Black 5 for one stage and two stages sequential anaerobic aerobic biological processes employing different anaerobic sludge
In this study the effect of NaCl, normally found in dye bath wastewaters employing reactive azo dyes, on the performance of sequential anaerobic-aerobic processes for treatment of Reactive Black 5 (RB5) containing media, with concentration in the range 100-500mgL-1, was investigated. Three possible scenarios of the sequential anaerobic-aerobic process, namely two stage process and one stage processes employing either anaerobic or activated sludge, were considered. The results showed a statistically significant enhancement of the anaerobic decolourisation efficiency as a result of the addition of 30gL-1 NaCl to the RB5 containing media for two stage processes and one stage processes employing anaerobic sludge. NaCl at 30gL-1 concentration also inhibited aerobic colour formation during two stage processes whereas it prevented aerobic decolourisation during one stage processes. HPLC and UV Vis analysis indicated that during anaerobic phase/stage the majority of azo bonds in RB5 molecules cleave whereas the hydrophobicity/MW of the resulting dye reduction metabolites decreases. The same analysis revealed partial mineralisation of RB5 reduction metabolites under aerobic conditions. The results of the present work also showed that the effect of salt on anaerobic decolourisation efficiency, TVFA and methane production was dependent on the exposure history of anaerobic sludge
Candidatus Bartonella merieuxii, a potential new zoonotic Bartonella species in canids from Iraq.
Bartonellae are emerging vector-borne pathogens infecting erythrocytes and endothelial cells of various domestic and wild mammals. Blood samples were collected from domestic and wild canids in Iraq under the United States Army zoonotic disease surveillance program. Serology was performed using an indirect immunofluorescent antibody test for B. henselae, B. clarridgeiae, B. vinsonii subsp. berkhoffii and B. bovis. Overall seroprevalence was 47.4% in dogs (n = 97), 40.4% in jackals (n = 57) and 12.8% in red foxes (n = 39). Bartonella species DNA was amplified from whole blood and representative strains were sequenced. DNA of a new Bartonella species similar to but distinct from B. bovis, was amplified from 37.1% of the dogs and 12.3% of the jackals. B. vinsonii subsp. berkhoffii was also amplified from one jackal and no Bartonella DNA was amplified from foxes. Adjusting for age, the odds of dogs being Bartonella PCR positive were 11.94 times higher than for wild canids (95% CI: 4.55-31.35), suggesting their role as reservoir for this new Bartonella species. This study reports on the prevalence of Bartonella species in domestic and wild canids of Iraq and provides the first detection of Bartonella in jackals. We propose Candidatus Bartonella merieuxii for this new Bartonella species. Most of the Bartonella species identified in sick dogs are also pathogenic for humans. Therefore, seroprevalence in Iraqi dog owners and bacteremia in Iraqi people with unexplained fever or culture negative endocarditis requires further investigation as well as in United States military personnel who were stationed in Iraq. Finally, it will also be essential to test any dog brought back from Iraq to the USA for presence of Bartonella bacteremia to prevent any accidental introduction of a new Bartonella species to the New World
Adaptively Weighted Audits of Instant-Runoff Voting Elections: AWAIRE
An election audit is risk-limiting if the audit limits (to a pre-specified
threshold) the chance that an erroneous electoral outcome will be certified.
Extant methods for auditing instant-runoff voting (IRV) elections are either
not risk-limiting or require cast vote records (CVRs), the voting system's
electronic record of the votes on each ballot. CVRs are not always available,
for instance, in jurisdictions that tabulate IRV contests manually.
We develop an RLA method (AWAIRE) that uses adaptively weighted averages of
test supermartingales to efficiently audit IRV elections when CVRs are not
available. The adaptive weighting 'learns' an efficient set of hypotheses to
test to confirm the election outcome. When accurate CVRs are available, AWAIRE
can use them to increase the efficiency to match the performance of existing
methods that require CVRs.
We provide an open-source prototype implementation that can handle elections
with up to six candidates. Simulations using data from real elections show that
AWAIRE is likely to be efficient in practice. We discuss how to extend the
computational approach to handle elections with more candidates.
Adaptively weighted averages of test supermartingales are a general tool,
useful beyond election audits to test collections of hypotheses sequentially
while rigorously controlling the familywise error rate.Comment: 16 pages, 3 figures, accepted for E-Vote-ID 202
Using the Uncharged Kerr Black Hole as a Gravitational Mirror
We extend the study of the possibility to use the Schwarzschild black hole as
a gravitational mirror to the more general case of an uncharged Kerr black
hole. We use the null geodesic equation in the equatorial plane to prove a
theorem concerning the conditions the impact parameter has to satisfy if there
shall exist boomerang photons. We derive an equation for these boomerang
photons and an equation for the emission angle. Finally, the radial null
geodesic equation is integrated numerically in order to illustrate boomerang
photons.Comment: 11 pages Latex, 3 Postscript figures, uufiles to compres
Towards the synthesis of wastewater recovery facilities using enviroeconomic optimization
The wastewater treatment industry is undergoing a major shift towards a proactive interest in recovering materials and energy from wastewater streams, driven by both economic incentives and environmental sustainability. With the array of available treatment technologies and recovery options growing steadily, systematic approaches to determining the inherent trade-off between multiple economic and environmental objectives become necessary, namely enviroeconomic optimization. The main objective of this chapter is to present one such methodology based on superstructure modeling and multi-objective optimization, where the main environmental impacts are quantified using life cycle assessment (LCA). This methodology is illustrated with the case study of a municipal wastewater treatment facility. The results show that accounting for LCA considerations early on in the synthesis problem may lead to dramatic changes in the optimal process configuration, thereby supporting LCA integration into decision-making tools for wastewater treatment alongside economical selection criteria
Auditing Ranked Voting Elections with Dirichlet-Tree Models: First Steps
Ranked voting systems, such as instant-runo voting (IRV)
and single transferable vote (STV), are used in many places around the
world. They are more complex than plurality and scoring rules, pre-
senting a challenge for auditing their outcomes: there is no known risk-
limiting audit (RLA) method for STV other than a full hand count.
We present a new approach to auditing ranked systems that uses a sta-
tistical model, a Dirichlet-tree, that can cope with high-dimensional pa-
rameters in a computationally e cient manner. We demonstrate this ap-
proach with a ballot-polling Bayesian audit for IRV elections. Although
the technique is not known to be risk-limiting, we suggest some strategies
that might allow it to be calibrated to limit risk
Two substrate-targeting sites in the Yersinia protein tyrosine phosphatase co-operate to promote bacterial virulence
YopH is a protein tyrosine phosphatase and an essential virulence determinant of the pathogenic bacterium Yersinia. Yersinia delivers YopH into infected host cells using a type III secretion mechanism. YopH dephosphorylates several focal adhesion proteins including p130Cas in human epithelial cells, resulting in disruption of focal adhesions and cell detachment from the extracellular matrix. How the C-terminal protein tyrosine phosphatase domain of YopH targets specific substrates such as p130Cas in the complex milieu of the host cell has not been fully elucidated. An N-terminal non-catalytic domain of YopH binds p130Cas in a phosphotyrosine-dependent manner and functions as a novel substrate-targeting site. The structure of the YopH protein tyrosine phosphatase domain bound to a model phosphopeptide substrate was solved and the resulting structure revealed a second substrate-targeting site (āsite 2ā) within the catalytic domain. Site 2 binds to p130Cas in a phosphotyrosine-dependent manner, and co-operates with the N-terminal domain (āsite 1ā) to promote efficient recognition of p130Cas by YopH in epithelial cells. The identification of two substrate-targeting sites in YopH that co-operate to promote epithelial cell detachment and bacterial virulence reinforces the importance of proteināprotein interactions for determining protein tyrosine phosphatase specificity in vivo , and highlights the sophisticated nature of microbial pathogenicity factors.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73103/1/j.1365-2958.2005.04477.x.pd
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