3,867 research outputs found
Remote sensing and field assessment of tsunami effects on coastal pond aquaculture in northern Sumatra
An attempt was made to conduct spatial assessment of the pattern and extent of damage to coastal aquaculture ponds along the east coast of Aceh province in Sumatra, Indonesia, resulting from the tsunami event of 26 December 2004. High-resolution satellite imagery, i.e., SPOT-5 multispectral scenes covering the 700 km stretch of the coast, acquired before and after the tsunami, were digitally enhanced and visually interpreted to delineate pockets of aquaculture ponds that were discerned to be damaged and relatively intact. Field checks were conducted at 87 sites in the four eastern coastal districts. The results indicate that SPOT-5 multispectral imagery was minimally sufficient to detect areas of damaged and relatively intact aquaculture ponds, but the 10-m spatial resolution poses limitations to evaluating the extent of pond damage. Nevertheless, the 60 km swath of the imagery makes it reasonably affordable for large-area assessment to identify pockets of severe damage for targeting more detailed assessments. The image maps produced from a mosaic of the SPOT-5 scenes can also serve as base maps for spatial planning in the challenging task of reconstruction and rehabilitation of the disrupted livelihoods of the coastal communities.Remote sensing, Disasters, Spatial analysis, Coastal zone, ISEW, Indonesia, Aceh,
Transmission channels for light in absorbing random media: from diffusive to ballistic-like transport
While the absorption of light is ubiquitous in nature and in applications,
the question remains how absorption modifies the transmission channels in
random media. We present a numerical study on the effects of optical absorption
on the maximal transmission and minimal reflection channels in a
two-dimensional disordered waveguide. In the weak absorption regime, where the
system length is less than the diffusive absorption length, the maximal
transmission channel is dominated by diffusive transport and it is equivalent
to the minimal reflection channel. Its frequency bandwidth is determined by the
underlying quasimode width. However, when the absorption is strong, light
transport in the maximal transmission channel undergoes a sharp transition and
becomes ballistic-like transport. Its frequency bandwidth increases with
absorption, and the exact scaling varies with the sample's realization. The
minimal reflection channel becomes different from the maximal transmission
channel and becomes dominated by absorption. Counterintuitively, we observe in
some samples that the minimum reflection eigenvalue increases with absorption.
Our results show that strong absorption turns open channels in random media
from diffusive to ballistic-like.Comment: 11 pages, 7 figure
Stochastic polarization formation in exciton-polariton Bose-Einstein condensates
We demonstrate theoretically the spontaneous formation of a stochastic
polarization in exciton-polariton Bose-Einstein condensates in planar
microcavities under pulsed excitation. Below the threshold pumping intensity
(dependent on the polariton life-time) the average polarization degree is close
to zero, whilst above threshold the condensate acquires a polarization
described by a (pseudospin) vector with random orientation, in general. We
establish the link between second order coherence of the polariton condensate
and the distribution function of its polarization. We examine also the
mechanisms of polarization dephasing and relaxation.Comment: 4 pages, 3 figure
Oxoglutarate receptor (version 2019.4) in the IUPHAR/BPS Guide to Pharmacology Database
Nomenclature as recommended by NC-IUPHAR [2]
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
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
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
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
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