225 research outputs found
On the role of the quark mass thresholds in extrapolations of the running \alpha_s
The accuracy of the conventional treatment of quark mass thresholds in the
QCD running coupling constant , based on the step approximation to
the --function, is investigated. The errors of extrapolating \ase(\mu)
from low energies to , implied by this approximation, are shown to be
of the same magnitude as the typical next--to--next--to--leading order
contributions to \as and tend to increase the resulting \as. The importance of
the proper choice of matching points is emphasized.Comment: latex, 7 pages, 2 uuencoded figure
The Rhode Island Stormwater Management and Treatment Demonstration Facility
The occurrence of toxic heavy metals from Rhode Island highways, verified in a report completed by Thiem, Bade & Alkhatibe in 1998, showed that cadmium, chromium, copper, lead, nickel and zinc exceeded EPAâs acute and/or chronic water quality criteria. Besides toxic metals, stormwater also contains petroleum hydrocarbons, nutrients, and microbial matter as well as many other chemical compounds (Goebel et al., 2007). These toxic stormwater constituents are easily washed into water bodies, causing a decrease in overall stream diversity. The selection of the various, commercially available stormwater runoff commercial systems relies mostly on unverified manufacturerâs data or is based on performance reports from other parts of the country where local environmental conditions are much different than those in Rhode Island. The focus of this joint-research effort is to provide state agencies and the URI transportation community with a new facility where BMP structures can be evaluated against the manufacturerâs claims and under environmental conditions prevailing in our state. This facility will be known as the âRhode Island Stormwater Management and Treatment Demonstration Facilityâ (RI SDF). Our research efforts can be groups in three major research taks. Task I revolves around the set-up of the RI SDF facility. Task II focuses the contaminant removal efficiencies of a commercial hydrodynamic separator unit, while the Task III seeks to evaluate the performance of pervious concrete amended with organo-soils. Task II and III will be the first projects to take advantage of the newly built RI SDF site
The Provision of Urban Ecosystem Services Throughout the Private-Social-Public Domain: A Conceptual Framework
As cities are largely private systems, recent investigations have assessed the provision of ecosystem services from the private realm. However, these assessments are largely based on the concept of ownership and fail to capture the complexity of service provision mediated by interactions between people and ecological structures. In fact, people interact with ecological structures in their role of land tenants and stewards, further modulating the provision of ecosystem services. We devise a theoretical framework based on the concepts of ownership, tenancy, and stewardship, in which people, as mediators of ecosystem services, regulate the provision of services throughout the private-social-public domain. We survey relevant literature describing these dimensions and propose a comprehensive framework focused on the private-social-public domain. Our framework can advance ecosystem service research and enhance the provision of ecosystems services. The inclusion of peopleâs individual, social and public roles in the mediation of ecosystem services could improve how benefits are planned for, prioritized, and optimized across cities
Black hole pair creation in de Sitter space: a complete one-loop analysis
We present an exact one-loop calculation of the tunneling process in
Euclidean quantum gravity describing creation of black hole pairs in a de
Sitter universe. Such processes are mediated by gravitational
instantons giving an imaginary contribution to the partition function. The
required energy is provided by the expansion of the universe. We utilize the
thermal properties of de Sitter space to describe the process as the decay of a
metastable thermal state. Within the Euclidean path integral approach to
gravity, we explicitly determine the spectra of the fluctuation operators,
exactly calculate the one-loop fluctuation determinants in the -function
regularization scheme, and check the agreement with the expected scaling
behaviour. Our results show a constant volume density of created black holes at
late times, and a very strong suppression of the nucleation rate for small
values of .Comment: 63 pages, 4 eps figures, references and thanks added, to appear in
Nucl.Phys.
Off-Diagonal Elements of the DeWitt Expansion from the Quantum Mechanical Path Integral
The DeWitt expansion of the matrix element M_{xy} = \left\langle x \right|
\exp -[\case{1}{2} (p-A)^2 + V]t \left| y \right\rangle, in
powers of can be made in a number of ways. For (the case of interest
when doing one-loop calculations) numerous approaches have been employed to
determine this expansion to very high order; when (relevant for
doing calculations beyond one-loop) there appear to be but two examples of
performing the DeWitt expansion. In this paper we compute the off-diagonal
elements of the DeWitt expansion coefficients using the Fock-Schwinger gauge.
Our technique is based on representing by a quantum mechanical path
integral. We also generalize our method to the case of curved space, allowing
us to determine the DeWitt expansion of \tilde M_{xy} = \langle x| \exp
\case{1}{2} [\case{1}{\sqrt {g}} (\partial_\mu - i
A_\mu)g^{\mu\nu}{\sqrt{g}}(\partial_\nu - i A_\nu) ] t| y \rangle by use of
normal coordinates. By comparison with results for the DeWitt expansion of this
matrix element obtained by the iterative solution of the diffusion equation,
the relative merit of different approaches to the representation of as a quantum mechanical path integral can be assessed. Furthermore, the
exact dependence of on some geometric scalars can be
determined. In two appendices, we discuss boundary effects in the
one-dimensional quantum mechanical path integral, and the curved space
generalization of the Fock-Schwinger gauge.Comment: 16pp, REVTeX. One additional appendix concerning end-point effects
for finite proper-time intervals; inclusion of these effects seem to make our
results consistent with those from explicit heat-kernel method
Large-momentum convergence of Hamiltonian bound-state dynamics of effective fermions in quantum field theory
Contributions to the bound-state dynamics of fermions in local quantum field
theory from the region of large relative momenta of the constituent particles,
are studied and compared in two different approaches. The first approach is
conventionally developed in terms of bare fermions, a Tamm-Dancoff truncation
on the particle number, and a momentum-space cutoff that requires counterterms
in the Fock-space Hamiltonian. The second approach to the same theory deals
with bound states of effective fermions, the latter being derived from a
suitable renormalization group procedure. An example of two-fermion bound
states in Yukawa theory, quantized in the light-front form of dynamics, is
discussed in detail. The large-momentum region leads to a buildup of
overlapping divergences in the bare Tamm-Dancoff approach, while the effective
two-fermion dynamics is little influenced by the large-momentum region. This is
illustrated by numerical estimates of the large-momentum contributions for
coupling constants on the order of between 0.01 and 1, which is relevant for
quarks.Comment: 22 pages, 9 figure
Skin preparation with alcohol versus alcohol followed by any antiseptic for preventing bacteraemia or contamination of blood for transfusion (Review)
Background: Blood for transfusion may become contaminated at any point between collection and transfusion and may result in bacteraemia (the presence of bacteria in the blood), severe illness or even death for the blood recipient. Donor arm skin is one potential source of blood contamination, so it is usual to cleanse the skin with an antiseptic before blood donation. One-step and two-step alcohol based antiseptic regimens are both commonly advocated but there is uncertainty as to which is most effective. Objectives: To assess the effects of cleansing the skin of blood donors with alcohol in a one-step compared with alcohol in a two-step procedure to prevent contamination of collected blood or bacteraemia in the recipient. Search methods: For this second update we searched the Cochrane Wounds Group Specialised Register (searched 20 November 2012); The Cochrane Central Register of Controlled Trials (CENTRAL) The Cochrane Library 2012, Issue 11; Ovid MEDLINE (20011 to November Week 2 2012); Ovid MEDLINE (In-Process & Other Non-Indexed Citations November 20, 2012); Ovid EMBASE ( 20011 to 2012 Week 46); and EBSCO CINAHL ( 2008 to 15 November 2012). Selection criteria: All randomised trials (RCTs) comparing alcohol based donor skin cleansing in a one-step versus a two-step process that includes alcohol and any other antiseptic for pre-venepuncture skin cleansing were considered. Quasi randomised trials were to have been considered in the absence of RCTs. Data collection and analysis: Two review authors independently assessed studies for inclusion. Main results: No studies (RCTs or quasi RCTs) met the inclusion criteria. Authors' conclusions: We did not identify any eligible studies for inclusion in this review. It is therefore unclear whether a two-step, alcohol followed by antiseptic skin cleansing process prior to blood donation confers any reduction in the risk of blood contamination or bacteraemia in blood recipients, or conversely whether a one-step process increases risk above that associated with a two-step process
Variation in the Neisseria lactamica porin, and its relationship to meningococcal PorB
One potential vaccine strategy in the fight against meningococcal disease involves the exploitation of outer-membrane components of Neisseria lactamica, a commensal bacterium closely related to the meningococcus, Neisseria meningitidis. Although N. lactamica shares many surface structures with the meningococcus, little is known about the antigenic diversity of this commensal bacterium or the antigenic relationships between N. lactamica and N. meningitidis. Here, the N. lactamica porin protein (Por) was examined and compared to the related PorB antigens of N. meningitidis, to investigate potential involvement in anti-meningococcal immunity. Relationships among porin sequences were determined using distance-based methods and FST, and maximum-likelihood analyses were used to compare the selection pressures acting on the encoded proteins. These analyses demonstrated that the N. lactamica porin was less diverse than meningococcal PorB and although it was subject to positive selection, this was not as strong as the positive selection pressures acting on the meningococcal porin. In addition, the N. lactamica porin gene sequences and the protein sequences of the loop regions predicted to be exposed to the human immune system were dissimilar to the corresponding sequences in the meningococcus. This suggests that N. lactamica Por, contrary to previous suggestions, may have limited involvement in the development of natural immunity to meningococcal disease and might not be effective as a meningococcal vaccine component
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