2,859 research outputs found
Cardiovascular risk scores do not account for the effect of treatment: a review
OBJECTIVE: To compare the strengths and limitations of cardiovascular risk scores available for clinicians in assessing the global (absolute) risk of cardiovascular disease. DESIGN: Review of cardiovascular risk scores. DATA SOURCES: Medline (1966 to May 2009) using a mixture of MeSH terms and free text for the keywords 'cardiovascular', 'risk prediction' and 'cohort studies'. ELIGIBILITY CRITERIA FOR SELECTING STUDIES: A study was eligible if it fulfilled the following criteria: (1) it was a cohort study of adults in the general population with no prior history of cardiovascular disease and not restricted by a disease condition; (2) the primary objective was the development of a cardiovascular risk score/equation that predicted an individual's absolute cardiovascular risk in 5-10 years; (3) the score could be used by a clinician to calculate the risk for an individual patient. RESULTS: 21 risk scores from 18 papers were identified from 3536 papers. Cohort size ranged from 4372 participants (SHS) to 1591209 records (QRISK2). More than half of the cardiovascular risk scores (11) were from studies with recruitment starting after 1980. Definitions and methods for measuring risk predictors and outcomes varied widely between scores. Fourteen cardiovascular risk scores reported data on prior treatment, but this was mainly limited to antihypertensive treatment. Only two studies reported prior use of lipid-lowering agents. None reported on prior use of platelet inhibitors or data on treatment drop-ins. CONCLUSIONS: The use of risk-factor-modifying drugs-for example, statins-and disease-modifying medication-for example, platelet inhibitors-was not accounted for. In addition, none of the risk scores addressed the effect of treatment drop-ins-that is, treatment started during the study period. Ideally, a risk score should be derived from a population free from treatment. The lack of accounting for treatment effect and the wide variation in study characteristics, predictors and outcomes causes difficulties in the use of cardiovascular risk scores for clinical treatment decision
Polariton Condensate Transistor Switch
A polariton condensate transistor switch is realized through optical
excitation of a microcavity ridge with two beams. The ballistically ejected
polaritons from a condensate formed at the source are gated using the 20 times
weaker second beam to switch on and off the flux of polaritons. In the absence
of the gate beam the small built-in detuning creates potential landscape in
which ejected polaritons are channelled toward the end of the ridge where they
condense. The low loss photon-like propagation combined with strong
nonlinearities associated with their excitonic component makes polariton based
transistors particularly attractive for the implementation of all-optical
integrated circuits
Operation speed of polariton condensate switches gated by excitons
We present a time-resolved photoluminescence (PL) study in real- and
momentum-space of a polariton condensate switch in a quasi-1D semiconductor
microcavity. The polariton flow across the ridge is gated by excitons inducing
a barrier potential due to repulsive interactions. A study of the device
operation dependence on the power of the pulsed gate beam obtains a
satisfactory compromise for the ON/OFF-signal ratio and -switching time of the
order of 0.3 and ps, respectively. The opposite transition is
governed by the long-lived gate excitons, consequently the OFF/ON-switching
time is ps, limiting the overall operation speed of the device
to GHz. The experimental results are compared to numerical
simulations based on a generalized Gross-Pitaevskii equation, taking into
account incoherent pumping, decay and energy relaxation within the condensate.Comment: 11 pages, 11 figure
Optical control of spin textures in quasi-one-dimensional polariton condensates
We investigate, through polarization-resolved spectroscopy, the spin
transport by propagating polariton condensates in a quasi one-dimensional
microcavity ridge along macroscopic distances. Under circularly polarized,
continuous-wave, non-resonant excitation, a sinusoidal precession of the spin
in real space is observed, whose phase depends on the emission energy. The
experiments are compared with simulations of the spinor-polariton condensate
dynamics based on a generalized Gross-Pitaevskii equation, modified to account
for incoherent pumping, decay and energy relaxation within the condensate.Comment: 10 pages, 9 figure
Spin Selective Filtering of Polariton Condensate Flow
Spin-selective spatial filtering of propagating polariton condensates, using
a controllable spin-dependent gating barrier, in a one-dimensional
semiconductor microcavity ridge waveguide is reported. A nonresonant laser beam
provides the source of propagating polaritons while a second circularly
polarized weak beam imprints a spin dependent potential barrier, which gates
the polariton flow and generates polariton spin currents. A complete spin-based
control over the blocked and transmitted polaritons is obtained by varying the
gate polarization.Comment: 5 pages, 4 figure
Energy relaxation of exciton-polariton condensates in quasi-1D microcavities
We present a time-resolved study of energy relaxation and trapping dynamics
of polariton condensates in a semiconductor microcavity ridge. The combination
of two non-resonant, pulsed laser sources in a GaAs ridge-shaped microcavity
gives rise to profuse quantum phenomena where the repulsive potentials created
by the lasers allow the modulation and control of the polariton flow. We
analyze in detail the dependence of the dynamics on the power of both lasers
and determine the optimum conditions for realizing an all-optical polariton
condensate transistor switch. The experimental results are interpreted in the
light of simulations based on a generalized Gross-Pitaevskii equation,
including incoherent pumping, decay and energy relaxation within the
condensate.Comment: 15 pages, 20 figure
Dynamics of a polariton condensate transistor switch
We present a time-resolved study of the logical operation of a polariton
condensate transistor switch. Creating a polariton condensate (source) in a
GaAs ridge-shaped microcavity with a non-resonant pulsed laser beam, the
polariton propagation towards a collector, at the ridge edge, is controlled by
a second weak pulse (gate), located between the source and the collector. The
experimental results are interpreted in the light of simulations based on the
generalized Gross-Pitaevskii equation, including incoherent pumping, decay and
energy relaxation within the condensate.Comment: 4 pages, 2 figure
Towards optimising distributed data streaming graphs using parallel streams
Modern scientific collaborations have opened up the op-portunity of solving complex problems that involve multi-disciplinary expertise and large-scale computational experi-ments. These experiments usually involve large amounts of data that are located in distributed data repositories running various software systems, and managed by different organi-sations. A common strategy to make the experiments more manageable is executing the processing steps as a work-flow. In this paper, we look into the implementation of fine-grained data-flow between computational elements in a scientific workflow as streams. We model the distributed computation as a directed acyclic graph where the nodes rep-resent the processing elements that incrementally implement specific subtasks. The processing elements are connected in a pipelined streaming manner, which allows task executions to overlap. We further optimise the execution by splitting pipelines across processes and by introducing extra parallel streams. We identify performance metrics and design a mea-surement tool to evaluate each enactment. We conducted ex-periments to evaluate our optimisation strategies with a real world problem in the Life Sciences—EURExpress-II. The paper presents our distributed data-handling model, the op-timisation and instrumentation strategies and the evaluation experiments. We demonstrate linear speed up and argue that this use of data-streaming to enable both overlapped pipeline and parallelised enactment is a generally applicable optimisation strategy
On the unique possibility to increase significantly the contrast of dark resonances on D1 line of Rb
We propose and study, theoretically and experimentally, a new scheme of
excitation of a coherent population trapping resonance for D1 line of alakli
atoms with nuclear spin by bichromatic linearly polarized light ({\em
lin}{\em lin} field) at the conditions of spectral resolution of the
excited state. The unique properties of this scheme result in a high contrast
of dark resonance for D1 line of Rb.Comment: 9 pages, 7 figures. This material has been partially presented on
ICONO-2005, 14 May 2005, St. Petersburg, Russia. v2 references added; text is
changed a bi
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