248 research outputs found
Impact of a mass vaccination campaign against a meningitis epidemic in a refugee camp.
Serogroup A meningococcus epidemics occurred in refugee populations in Zaire in August 1994. The paper analyses the public health impact of a mass vaccination campaign implemented in a large refugee camp. We compared meningitis incidence rates from 2 similar camps. In Kibumba camp, vaccination was implemented early in the course of the epidemic whilst in the control camp (Katale), vaccination was delayed. At a threshold of 15 cases per 100 000 population per week an immunization campaign was implemented. Attack rates were 94 and 134 per 100,000 in Kibumba and Katale respectively over 2 months. In Kibumba, one week after crossing the threshold, 121,588 doses of vaccine were administered covering 76% of all refugees. Vaccination may have prevented 68 cases (30% of the expected cases). Despite its rapid institution and the high coverage achieved, the vaccination campaign had a limited impact on morbidity due to meningitis. In the early phase in refugee camps, the relative priorities of meningitis vaccination and case management need to be better defined
Conception et realisation d 'un ordinateur analogique tout optique de type 'reservoir' a l 'aide d'une cavite optique lineaire passive fonctionnant en lumiere coherente
Bilateral symmetry breaking in a nonlinear Fabry-Perot cavity exhibiting optical tristability
We show the existence of a region in the parameter space that defines the
field dynamics in a Fabry-Perot cylindrical cavity, where three output stable
stationary states of the light are possible for a given localized incident
field. Two of these states do not preserve the bilateral (i.e. left-right)
symmetry of the entire system. These broken-symmetry states are the
high-transmission nonlinear modes of the system. We also discuss how to excite
these states.Comment: 5 pages, 5 figure
Experimental quantum key distribution over highly noisy channels
Error filtration is a method for encoding the quantum state of a single
particle into a higher dimensional Hilbert space in such a way that it becomes
less sensitive to phase noise. We experimentally demonstrate this method by
distributing a secret key over an optical fiber whose noise level otherwise
precludes secure quantum key distribution. By filtering out the phase noise, a
bit error rate of 15.3% +/- 0.1%, which is beyond the security limit, can be
reduced to 10.6% +/- 0.1%, thereby guaranteeing the cryptographic security.Comment: 4 pages, 2 figure
Passive Fiber Ring Flip-Flop Memory Based on Polarization Dynamics
Passive fiber ring resonators synchronously pumped by cw trains of ultrashort pulses are shown to exhibit polarization symmetry breaking. Application of this feature to all-optical storage is considered. The proposed storage device operates in the flip-flop mode which makes possible all-optical writing and erasing operations on individual bits. Numerical simulations suggest that a storage capacity of the order of thousand bits could be attainable at bit rates of hundreds of Gb/s with a maximum information processing rate of several Gb/s.Peer Reviewe
Preparatory investigation
A great deal of preparatory investigation preceded the organizational work at Bergenmeersen. This was necessary to gain an insight into soil quality and structure and the archaeological richness of the project area, since these elements influence the design and costs of the project.This chapter describes the results of the environmental, geotechnical and geophysical soil survey and the archaeological survey. It also examines the model trials of the inlet and outlet sluices. It is through these sluices that the Scheldt water will flow into and out of the flood control area with controlled reduced tide (FCA-CRT)
Vector modulation instability induced by vacuum fluctuations in highly birefringent fibers in the anomalous dispersion regime
We report a detailed experimental study of vector modulation instability in
highly birefringent optical fibers in the anomalous dispersion regime. We prove
that the observed instability is mainly induced by vacuum fluctuations. The
detuning of the spectral peaks agrees with linear perturbation analysis. The
exact shape of the spectrum is well reproduced by numerical integration of
stochastic nonlinear Schrodinger equations describing quantum propagation.Comment: 11 pages, 4 figures, to be published in Optics Letter
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