2,066 research outputs found
A solid state light-matter interface at the single photon level
Coherent and reversible mapping of quantum information between light and
matter is an important experimental challenge in quantum information science.
In particular, it is a decisive milestone for the implementation of quantum
networks and quantum repeaters. So far, quantum interfaces between light and
atoms have been demonstrated with atomic gases, and with single trapped atoms
in cavities. Here we demonstrate the coherent and reversible mapping of a light
field with less than one photon per pulse onto an ensemble of 10 millions atoms
naturally trapped in a solid. This is achieved by coherently absorbing the
light field in a suitably prepared solid state atomic medium. The state of the
light is mapped onto collective atomic excitations on an optical transition and
stored for a pre-programmed time up of to 1 mu s before being released in a
well defined spatio-temporal mode as a result of a collective interference. The
coherence of the process is verified by performing an interference experiment
with two stored weak pulses with a variable phase relation. Visibilities of
more than 95% are obtained, which demonstrates the high coherence of the
mapping process at the single photon level. In addition, we show experimentally
that our interface allows one to store and retrieve light fields in multiple
temporal modes. Our results represent the first observation of collective
enhancement at the single photon level in a solid and open the way to multimode
solid state quantum memories as a promising alternative to atomic gases.Comment: 5 pages, 5 figures, version submitted on June 27 200
Adjusting for dependent comorbidity in the calculation of healthy life expectancy
BACKGROUND: Healthy life expectancy – sometimes called health-adjusted life expectancy (HALE) – is a form of health expectancy indicator that extends measures of life expectancy to account for the distribution of health states in the population. The World Health Organization has estimated healthy life expectancy for 192 WHO Member States using information from health interview surveys and from the Global Burden of Disease Study. The latter estimates loss of health by cause, age and sex for populations. Summation of prevalent years lived with disability (PYLD) across all causes would result in overestimation of the severity of the population average health state because of comorbidity between conditions. Earlier HALE calculations made adjustments for independent comorbidity in adding PYLD across causes. This paper presents a method for adjusting for dependent comorbidity using available empirical data. METHODS: Data from five large national health surveys were analysed by age and sex to estimate "dependent comorbidity" factors for pairs of conditions. These factors were defined as the ratio of the prevalence of people with both conditions to the product of the two total prevalences for each of the conditions. The resulting dependent comorbidity factors were used for all Member States to adjust for dependent comorbidity in summation of PYLD across all causes and in the calculation of HALE. A sensitivity analysis was also carried out for order effects in the proposed calculation method. RESULTS: There was surprising consistency in the dependent comorbidity factors across the five surveys. The improved estimation of dependent comorbidity resulted in reductions in total PYLD per capita ranging from a few per cent in younger adult ages to around 8% in the oldest age group (80 years and over) in developed countries and up to 15% in the oldest age group in the least developed countries. The effect of the dependent comorbidity adjustment on estimated healthy life expectancies is small for some regions (high income countries, Eastern Europe, Western Pacific) and ranges from an increase of 0.5 to 1.5 years for countries in Latin America, South East Asia and Sub-Saharan Africa. CONCLUSION: The available evidence suggests that dependent comorbidity is important, and that adjustment for it makes a significant difference to resulting HALE estimates for some regions of the world. Given the data limitations, we recommend a normative adjustment based on the available evidence, and applied consistently across all countries
Prediction of peptide and protein propensity for amyloid formation
Understanding which peptides and proteins have the potential to undergo amyloid formation and what driving forces are responsible for amyloid-like fiber formation and stabilization remains limited. This is mainly because proteins that can undergo structural changes, which lead to amyloid formation, are quite diverse and share no obvious sequence or structural homology, despite the structural similarity found in the fibrils. To address these issues, a novel approach based on recursive feature selection and feed-forward neural networks was undertaken to identify key features highly correlated with the self-assembly problem. This approach allowed the identification of seven physicochemical and biochemical properties of the amino acids highly associated with the self-assembly of peptides and proteins into amyloid-like fibrils (normalized frequency of β-sheet, normalized frequency of β-sheet from LG, weights for β-sheet at the window position of 1, isoelectric point, atom-based hydrophobic moment, helix termination parameter at position j+1 and ΔGº values for peptides extrapolated in 0 M urea). Moreover, these features enabled the development of a new predictor (available at http://cran.r-project.org/web/packages/appnn/index.html) capable of accurately and reliably predicting the amyloidogenic propensity from the polypeptide sequence alone with a prediction accuracy of 84.9 % against an external validation dataset of sequences with experimental in vitro, evidence of amyloid formation
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
Inhibition of PKC activity blocks the increase of ET(B )receptor expression in cerebral arteries
BACKGROUND: Previous studies have shown that there is a time-dependent upregulation of contractile endothelin B (ET(B)) receptors in middle cerebral arteries (MCA) after organ culture. This upregulation is dependent on mitogen-activated protein kinases and possibly protein kinase C (PKC). The aim of this study was to examine the effect of PKC inhibitors with different profiles on the upregulation of contractile ET(B )receptors in rat MCA. Artery segments were incubated for 24 hours at 37°C. To investigate involvement of PKC, inhibitors were added to the medium before incubation. The contractile endothelin-mediated responses were measured and real-time PCR was used to detect endothelin receptor mRNA levels. Furthermore, immunohistochemistry was used to demonstrate the ET(B )receptor protein distribution in the MCA and Western blot to measure which of the PKC subtypes that were affected by the inhibitors. RESULTS: The PKC inhibitors bisindolylmaleimide I, Ro-32-0432 and PKC inhibitor 20–28 attenuated the ET(B )receptor mediated contractions. Furthermore, Ro-32-0432 and bisindolylmaleimide I decreased ET(B )receptor mRNA levels while PKC inhibitor 20–28 reduced the amount of receptor protein on smooth muscle cells. PKC inhibitor 20–28 also decreased the protein levels of the five PKC subtypes studied (α, βI, γ, δ and ε). CONCLUSION: The results show that PKC inhibitors are able to decrease the ET(B )receptor contraction and expression in MCA smooth muscle cells following organ culture. The PKC inhibitor 20–28 affects the protein levels, while Ro-32-0432 and bisindolylmaleimide I affect the mRNA levels, suggesting differences in activity profile. Since ET(B )receptor upregulation is seen in cerebral ischemia, the results of the present study provide a way to interfere with the vascular involvement in cerebral ischemia
Interaction Between Convection and Pulsation
This article reviews our current understanding of modelling convection
dynamics in stars. Several semi-analytical time-dependent convection models
have been proposed for pulsating one-dimensional stellar structures with
different formulations for how the convective turbulent velocity field couples
with the global stellar oscillations. In this review we put emphasis on two,
widely used, time-dependent convection formulations for estimating pulsation
properties in one-dimensional stellar models. Applications to pulsating stars
are presented with results for oscillation properties, such as the effects of
convection dynamics on the oscillation frequencies, or the stability of
pulsation modes, in classical pulsators and in stars supporting solar-type
oscillations.Comment: Invited review article for Living Reviews in Solar Physics. 88 pages,
14 figure
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