7,224 research outputs found
Dimensional Reduction, Hard Thermal Loops and the Renormalization Group
We study the realization of dimensional reduction and the validity of the
hard thermal loop expansion for lambda phi^4 theory at finite temperature,
using an environmentally friendly finite-temperature renormalization group with
a fiducial temperature as flow parameter. The one-loop renormalization group
allows for a consistent description of the system at low and high temperatures,
and in particular of the phase transition. The main results are that
dimensional reduction applies, apart from a range of temperatures around the
phase transition, at high temperatures (compared to the zero temperature mass)
only for sufficiently small coupling constants, while the HTL expansion is
valid below (and rather far from) the phase transition, and, again, at high
temperatures only in the case of sufficiently small coupling constants. We
emphasize that close to the critical temperature, physics is completely
dominated by thermal fluctuations that are not resummed in the hard thermal
loop approach and where universal quantities are independent of the parameters
of the fundamental four-dimensional theory.Comment: 20 pages, 13 eps figures, uses epsfig and pstrick
Controlled functional expression of the bacteriocins pediocin PA-1 and bactofencin A in Escherichia coli
peer-reviewedThe bacteriocins bactofencin A (class IId) and pediocin PA-1 (class IIa) are encoded by operons with a similarly clustered gene organization including a structural peptide, an immunity protein, an ABC transporter and accessory bacteriocin transporter protein. Cloning of these operons in E. coli TunerTM (DE3) on a pETcoco-2 derived vector resulted in successful secretion of both bacteriocins. A corresponding approach, involving the construction of vectors containing different combinations of these genes, revealed that the structural and the transporter genes alone are sufficient to permit heterologous production and secretion in this host. Even though the accessory protein, usually associated with optimal disulfide bond formation, was not required for bacteriocin synthesis, its presence did result in greater pediocin PA-1 production. The simplicity of the system and the fact that the associated bacteriocins could be recovered from the extracellular medium provides an opportunity to facilitate protein engineering and the overproduction of biologically-active bacteriocins at industrial scale. Additionally, this system could enable the characterization of new bacteriocin operons where genetic tools are not available for the native producers
The Random Walk in Generalized Quantum Theory
One can view quantum mechanics as a generalization of classical probability
theory that provides for pairwise interference among alternatives. Adopting
this perspective, we ``quantize'' the classical random walk by finding, subject
to a certain condition of ``strong positivity'', the most general Markovian,
translationally invariant ``decoherence functional'' with nearest neighbor
transitions.Comment: 25 pages, no figure
Improved ventilatory function associated with relief of chest pain in a patient with Kartagener's syndrome treated by subcutaneous analgesia
Development of a single-tube, low-cost, analytical process to extract, separate and determine efavirenz and rifampicin plasma concentrations in HIV/TB co-infected patients
On the "renormalization" transformations induced by cycles of expansion and contraction in causal set cosmology
We study the ``renormalization group action'' induced by cycles of cosmic
expansion and contraction, within the context of a family of stochastic
dynamical laws for causal sets derived earlier. We find a line of fixed points
corresponding to the dynamics of transitive percolation, and we prove that
there exist no other fixed points and no cycles of length two or more. We also
identify an extensive ``basin of attraction'' of the fixed points but find that
it does not exhaust the full parameter space. Nevertheless, we conjecture that
every trajectory is drawn toward the fixed point set in a suitably weakened
sense.Comment: 22 pages, 1 firgure, submitted to Phys. Rev.
What factors are most influential in increasing cervical cancer screening attendance? An online study of UK-based women1
Objective: Cervical cancer is the fourth most commonly occurring cancer in women worldwide. The UK has one of the highest cervical screening rates in Europe, yet attendance has been decreasing. This study aimed to identify barriers and facilitators to screening attendance and assess the perceived importance of these factors.
Methods: 194 women living in the UK were recruited via an online research recruitment website to an online survey. Most participants (N = 128, 66.0%) were currently up-to-date with cervical screening, 66 participants (34.0%) had never been screened, or were overdue for screening. Participants identified barriers and facilitators to cervical screening attendance via free-text responses and were also asked to rate a list of factors as most to least influential over decision making. Results were analysed using thematic content analysis and ratings analysed using multivariable analyses.
Results: The most commonly reported barriers were: Pain/discomfort; Embarrassment; and Time. These were also rated as most influential for decision making. The most commonly reported facilitators were: Ease of making appointments; Peace of mind; and Fear of cancer/preventing serious illness. While importance rating of barriers did not differ by previous screening behaviour, ratings of some facilitators significantly differed. Up-to-date women rated believing screening is potentially life-saving and part of personal responsibility as significantly more important than overdue/never screened women.
Conclusion: This study confirmed that factors which encourage screening are key to the decision of whether to attend screening. Women suggested several improvements that might make attending easier and improve uptake, including flexibility of screening locations to fit around work hours and childcare arrangements. Psychological facilitators included the peace of mind that screening brings and the belief that cervical cancer screening is potentially life-saving. Public health interventions should target factors which facilitate screening and how these interplay with barriers in order to improve uptake
Lifetime Measurement of the 6s Level of Rubidium
We present a lifetime measurements of the 6s level of rubidium. We use a
time-correlated single-photon counting technique on two different samples of
rubidium atoms. A vapor cell with variable rubidium density and a sample of
atoms confined and cooled in a magneto-optical trap. The 5P_{1/2} level serves
as the resonant intermediate step for the two step excitation to the 6s level.
We detect the decay of the 6s level through the cascade fluorescence of the
5P_{3/2} level at 780 nm. The two samples have different systematic effects,
but we obtain consistent results that averaged give a lifetime of 45.57 +- 0.17
ns.Comment: 10 pages, 9 figure
Atomistic modeling of amorphous silicon carbide: An approximate first-principles study in constrained solution space
Localized basis ab initio molecular dynamics simulation within the density
functional framework has been used to generate realistic configurations of
amorphous silicon carbide (a-SiC). Our approach consists of constructing a set
of smart initial configurations that conform essential geometrical and
structural aspects of the materials obtained from experimental data, which is
subsequently driven via first-principles force-field to obtain the best
solution in a reduced solution space. A combination of a priori information
(primarily structural and topological) along with the ab-initio optimization of
the total energy makes it possible to model large system size (1000 atoms)
without compromising the quantum mechanical accuracy of the force-field to
describe the complex bonding chemistry of Si and C. The structural, electronic
and the vibrational properties of the models have been studied and compared to
existing theoretical models and available data from experiments. We demonstrate
that the approach is capable of producing large, realistic configurations of
a-SiC from first-principles simulation that display excellent structural and
electronic properties of a-SiC. Our study reveals the presence of predominant
short-range order in the material originating from heteronuclear Si-C bonds
with coordination defect concentration as small as 5% and the chemical disorder
parameter of about 8%.Comment: 16 pages, 7 figure
Effective Critical Exponents for Dimensional Ccrossover and Quantum Systems from an Environmentally Friendly Renormalization Group
Series for the Wilson functions of an ``environmentally friendly''
renormalization group are computed to two loops, for an vector model, in
terms of the ``floating coupling'', and resummed by the Pad\'e method to yield
crossover exponents for finite size and quantum systems. The resulting
effective exponents obey all scaling laws, including hyperscaling in terms of
an effective dimensionality, {d\ef}=4-\gl, which represents the crossover in
the leading irrelevant operator, and are in excellent agreement with known
results.Comment: 10 pages of Plain Tex, Postscript figures available upon request from
[email protected], preprint numbers THU-93/18, DIAS-STP-93-1
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