1,157 research outputs found
Justification of the symmetric damping model of the dynamical Casimir effect in a cavity with a semiconductor mirror
A "microscopic" justification of the "symmetric damping" model of a quantum
oscillator with time-dependent frequency and time-dependent damping is given.
This model is used to predict results of experiments on simulating the
dynamical Casimir effect in a cavity with a photo-excited semiconductor mirror.
It is shown that the most general bilinear time-dependent coupling of a
selected oscillator (field mode) to a bath of harmonic oscillators results in
two equal friction coefficients for the both quadratures, provided all the
coupling coefficients are proportional to a single arbitrary function of time
whose duration is much shorter than the periods of all oscillators. The choice
of coupling in the rotating wave approximation form leads to the "mimimum
noise" model of the quantum damped oscillator, introduced earlier in a pure
phenomenological way.Comment: 9 pages, typos corrected, corresponds to the published version,
except for the reference styl
Vacuum Stability, Perturbativity, and Scalar Singlet Dark Matter
We analyze the one-loop vacuum stability and perturbativity bounds on a
singlet extension of the Standard Model (SM) scalar sector containing a scalar
dark matter candidate. We show that the presence of the singlet-doublet quartic
interaction relaxes the vacuum stability lower bound on the SM Higgs mass as a
function of the cutoff and lowers the corresponding upper bound based on
perturbativity considerations. We also find that vacuum stability requirements
may place a lower bound on the singlet dark matter mass for given singlet
quartic self coupling, leading to restrictions on the parameter space
consistent with the observed relic density. We argue that discovery of a light
singlet scalar dark matter particle could provide indirect information on the
singlet quartic self-coupling.Comment: 25 pages, 10 figures; v2 - fixed minor typos; v3 - added to text
discussions of other references, changed coloring of figures for easier black
and white viewin
An Infinite-Dimensional Family of Black-Hole Microstate Geometries
We construct the first explicit, smooth, horizonless black-hole microstate
geometry whose moduli space is described by an arbitrary function of one
variable and is thus infinite-dimensional. This is achieved by constructing the
scalar Green function on a simple D6 anti-D6 background, and using this Green
function to obtain the fully back-reacted solution for a supertube with varying
charge density in this background. We show that this supertube can store
parametrically more entropy than in flat space, confirming the entropy
enhancement mechanism that was predicted using brane probes. We also show that
all the local properties of the fully back-reacted solution can, in fact, be
obtained using the DBI action of an appropriate brane probe. In particular, the
supergravity and the DBI analysis yield identical functional bubble equations
that govern the relative locations of the centers. This indicates that there is
a non-renormalization theorem that protects these functional equations as one
moves in moduli space. Our construction creates configurations that are beyond
the scope of recent arguments that appear to put strong limits on the entropy
that can be found in smooth supergravity solutions.Comment: 46 pages, 1 figure, LaTe
Viral population estimation using pyrosequencing
The diversity of virus populations within single infected hosts presents a
major difficulty for the natural immune response as well as for vaccine design
and antiviral drug therapy. Recently developed pyrophosphate based sequencing
technologies (pyrosequencing) can be used for quantifying this diversity by
ultra-deep sequencing of virus samples. We present computational methods for
the analysis of such sequence data and apply these techniques to pyrosequencing
data obtained from HIV populations within patients harboring drug resistant
virus strains. Our main result is the estimation of the population structure of
the sample from the pyrosequencing reads. This inference is based on a
statistical approach to error correction, followed by a combinatorial algorithm
for constructing a minimal set of haplotypes that explain the data. Using this
set of explaining haplotypes, we apply a statistical model to infer the
frequencies of the haplotypes in the population via an EM algorithm. We
demonstrate that pyrosequencing reads allow for effective population
reconstruction by extensive simulations and by comparison to 165 sequences
obtained directly from clonal sequencing of four independent, diverse HIV
populations. Thus, pyrosequencing can be used for cost-effective estimation of
the structure of virus populations, promising new insights into viral
evolutionary dynamics and disease control strategies.Comment: 23 pages, 13 figure
The feasibility of collecting information from people with Multiple Sclerosis for the UK MS Register via a web portal: characterising a cohort of people with MS.
BACKGROUND: A UK Register of people with Multiple Sclerosis has been developed to address the need for an increased knowledge-base about MS. The Register is being populated via: a web-based portal; NHS neurology clinical systems; and administrative data sources. The data are de-identified and linked at the individual level. At the outset, it was not known whether people with MS would wish to participate in the UK MS Register by personally contributing their data to the Register via a web-based system. Therefore, the research aim of this work was to build an internet-mounted recruitment and consenting technology for people with Multiple Sclerosis, and to assess its feasibility as a questionnaire delivery platform to contribute data to the UK MS Register, by determining whether the information provided could be used to describe a cohort of people with MS. METHODS: The web portal was developed using VB.net and JQuery with a Microsoft SQL 2008 database. UK adults with MS can self-register and enter data about themselves by completing validated questionnaires. Descriptive statistics were used to characterise the respondents. RESULTS: The web portal was launched in May 2011, and in first three months 7,279 individuals registered on the portal. The ratio of men to women was 1:2.4 (n = 5,899), the mean self-reported age at first symptoms was 33.8 (SD 10.5) years, and at diagnosis 39.6 (SD 10.3) years (n = 4,401). The reported types of MS were: 15% primary progressive, 63% relapsing-remitting, 8% secondary progressive, and 14% unknown (n = 5,400). These characteristics are similar to those of the prevalent MS population. Employment rates, sickness/disability rates, ethnicity and educational qualifications were compared with the general UK population. Information about the respondents' experience of early symptoms and the process of diagnosis, plus living arrangements are also reported. CONCLUSIONS: These initial findings from the MS Register portal demonstrate the feasibility of collecting data about people with MS via a web platform, and show that sufficient information can be gathered to characterise a cohort of people with MS. The innovative design of the UK MS register, bringing together three disparate sources of data, is creating a rich resource for research into this condition
A systematic review of strategies to recruit and retain primary care doctors
Background There is a workforce crisis in primary care. Previous research has looked at the reasons underlying recruitment and retention problems, but little research has looked at what works to improve recruitment and retention. The aim of this systematic review is to evaluate interventions and strategies used to recruit and retain primary care doctors internationally. Methods A systematic review was undertaken. MEDLINE, EMBASE, CENTRAL and grey literature were searched from inception to January 2015.Articles assessing interventions aimed at recruiting or retaining doctors in high income countries, applicable to primary care doctors were included. No restrictions on language or year of publication. The first author screened all titles and abstracts and a second author screened 20%. Data extraction was carried out by one author and checked by a second. Meta-analysis was not possible due to heterogeneity. Results 51 studies assessing 42 interventions were retrieved. Interventions were categorised into thirteen groups: financial incentives (n=11), recruiting rural students (n=6), international recruitment (n=4), rural or primary care focused undergraduate placements (n=3), rural or underserved postgraduate training (n=3), well-being or peer support initiatives (n=3), marketing (n=2), mixed interventions (n=5), support for professional development or research (n=5), retainer schemes (n=4), re-entry schemes (n=1), specialised recruiters or case managers (n=2) and delayed partnerships (n=2). Studies were of low methodological quality with no RCTs and only 15 studies with a comparison group. Weak evidence supported the use of postgraduate placements in underserved areas, undergraduate rural placements and recruiting students to medical school from rural areas. There was mixed evidence about financial incentives. A marketing campaign was associated with lower recruitment. Conclusions This is the first systematic review of interventions to improve recruitment and retention of primary care doctors. Although the evidence base for recruiting and care doctors is weak and more high quality research is needed, this review found evidence to support undergraduate and postgraduate placements in underserved areas, and selective recruitment of medical students. Other initiatives covered may have potential to improve recruitment and retention of primary care practitioners, but their effectiveness has not been established
The holographic principle
There is strong evidence that the area of any surface limits the information
content of adjacent spacetime regions, at 10^(69) bits per square meter. We
review the developments that have led to the recognition of this entropy bound,
placing special emphasis on the quantum properties of black holes. The
construction of light-sheets, which associate relevant spacetime regions to any
given surface, is discussed in detail. We explain how the bound is tested and
demonstrate its validity in a wide range of examples.
A universal relation between geometry and information is thus uncovered. It
has yet to be explained. The holographic principle asserts that its origin must
lie in the number of fundamental degrees of freedom involved in a unified
description of spacetime and matter. It must be manifest in an underlying
quantum theory of gravity. We survey some successes and challenges in
implementing the holographic principle.Comment: 52 pages, 10 figures, invited review for Rev. Mod. Phys; v2:
reference adde
Long term extension of a randomised controlled trial of probiotics using electronic health records
Most randomised controlled trials (RCTs) are relatively short term and, due to costs and available resources, have limited opportunity to be re-visited or extended. There is no guarantee that effects of treatments remain unchanged beyond the study. Here, we illustrate the feasibility, benefits and cost-effectiveness of enriching standard trial design with electronic follow up. We completed a 5-year electronic follow up of a RCT investigating the impact of probiotics on asthma and eczema in children born 2005-2007, with traditional fieldwork follow up to two years. Participants and trial outcomes were identified and analysed after five years using secure, routine, anonymised, person-based electronic health service databanks. At two years, we identified 93% of participants and compared fieldwork with electronic health records, highlighting areas of agreement and disagreement. Retention of children from lower socio-economic groups was improved, reducing volunteer bias. At 5 years we identified a reduced 82% of participants. These data allowed the trial's first robust analysis of asthma endpoints. We found no indication that probiotic supplementation to pregnant mothers and infants protected against asthma or eczema at 5 years. Continued longer-term follow up is technically straightforward
Stochastic Gravity: Theory and Applications
Whereas semiclassical gravity is based on the semiclassical Einstein equation
with sources given by the expectation value of the stress-energy tensor of
quantum fields, stochastic semiclassical gravity is based on the
Einstein-Langevin equation, which has in addition sources due to the noise
kernel.In the first part, we describe the fundamentals of this new theory via
two approaches: the axiomatic and the functional. In the second part, we
describe three applications of stochastic gravity theory. First, we consider
metric perturbations in a Minkowski spacetime: we compute the two-point
correlation functions for the linearized Einstein tensor and for the metric
perturbations. Second, we discuss structure formation from the stochastic
gravity viewpoint. Third, we discuss the backreaction of Hawking radiation in
the gravitational background of a quasi-static black hole.Comment: 75 pages, no figures, submitted to Living Reviews in Relativit
Stochastic Gravity: Theory and Applications
Whereas semiclassical gravity is based on the semiclassical Einstein equation
with sources given by the expectation value of the stress-energy tensor of
quantum fields, stochastic semiclassical gravity is based on the
Einstein-Langevin equation, which has in addition sources due to the noise
kernel. In the first part, we describe the fundamentals of this new theory via
two approaches: the axiomatic and the functional. In the second part, we
describe three applications of stochastic gravity theory. First, we consider
metric perturbations in a Minkowski spacetime, compute the two-point
correlation functions of these perturbations and prove that Minkowski spacetime
is a stable solution of semiclassical gravity. Second, we discuss structure
formation from the stochastic gravity viewpoint. Third, we discuss the
backreaction of Hawking radiation in the gravitational background of a black
hole and describe the metric fluctuations near the event horizon of an
evaporating black holeComment: 100 pages, no figures; an update of the 2003 review in Living Reviews
in Relativity gr-qc/0307032 ; it includes new sections on the Validity of
Semiclassical Gravity, the Stability of Minkowski Spacetime, and the Metric
Fluctuations of an Evaporating Black Hol
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