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

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