Mechanisms for Lasing with Cold Atoms as the Gain Medium

We realize a laser with a cloud of cold rubidium atoms as gain medium, placed in a low-finesse cavity. Three different regimes of laser emission are observed corresponding respectively to Mollow, Raman and Four Wave Mixing mechanisms. We measure an output power of up to 300 $\mu$W and present the main properties of these different lasers in each regime

Genetic heterogeneity of hepatitis E virus in Darfur, Sudan, and neighboring Chad.

The within-outbreak diversity of hepatitis E virus (HEV) was studied during the outbreak of hepatitis E that occurred in Sudan in 2004. Specimens were collected from internally displaced persons living in a Sudanese refugee camp and two camps implanted in Chad. A comparison of the sequences in the ORF2 region of 23 Sudanese isolates and five HEV samples from the two Chadian camps displayed a high similarity (>99.7%) to strains belonging to Genotype 1. But four isolates collected in one of the Chadian camps were close to Genotype 2. Circulation of divergent strains argues for possible multiple sources of infection

Short term bioassay and bioassay chemistry of materials related to synthetic fossil fuels

An abstract was prepared for one paper. Abstracts of the five additional papers appeared previously in ERA

Conductance switching at the nanoscale of diarylethene derivatives self-assembled monolayers on La0.7_{0.7}Sr0.3_{0.3}MnO3_3

We report on the phosphonic acid route for the grafting of functional molecules, optical switch (dithienylethene diphosphonic acid, DDA), on La0.7Sr0.3MnO3 (LSMO). Compact self-assembled monolayers (SAMs) of DDA are formed on LSMO as studied by topographic atomic force microscopy (AFM), ellipsometry, water contact angle and X-ray photoemission spectroscopy (XPS). The conducting AFM measurements show that the electrical conductance of LSMO/DDA is about 3 decades below that of the bare LSMO substrate. Moreover, the presence of the DDA SAM suppresses the known conductance switching of the LSMO substrate that is induced by mechanical and/or bias constraints during C-AFM measurements. A partial light-induced conductance switching between the open and closed forms of the DDA is observed for the LSMO/DDA/C-AFM tip molecular junctions (closed/open conductance ratio of about 8). We show that, in the case of long-time exposition to UV light, this feature can be masked by a non-reversible decrease (a factor of about 15) of the conductance of the LSMO electrode.Comment: Full paper with supporting informatio

An operator representation for Matsubara sums

In the context of the imaginary-time formalism for a scalar thermal field theory, it is shown that the result of performing the sums over Matsubara frequencies associated with loop Feynman diagrams can be written, for some classes of diagrams, in terms of the action of a simple linear operator on the corresponding energy integrals of the Euclidean theory at T=0. In its simplest form the referred operator depends only on the number of internal propagators of the graph. More precisely, it is shown explicitly that this \emph{thermal operator representation} holds for two generic classes of diagrams, namely, the two-vertex diagram with an arbitrary number of internal propagators, and the one-loop diagram with an arbitrary number of vertices. The validity of the thermal operator representation for diagrams of more complicated topologies remains an open problem. Its correctness is shown to be equivalent to the correctness of some diagrammatic rules proposed a few years ago.Comment: 4 figures; references added, minor changes in notation, final version accepted for publicatio

The Change in Prevalence of Campylobacter on Chicken Carcasses During Processing: A Systematic Review

A systematic review was conducted to evaluate the change in prevalence of Campylobacter on chicken carcasses during processing. A structured literature search of 8 electronic databases using the key words for Campylobacter, chicken, and processing identified 1,734 unique citations. Abstracts were screened for relevance by 2 independent reviewers. Thirty-two studies described prevalence at more than one stage during processing and were included in this review. Of the studies that described the prevalence of Campylobacter on carcasses before and after specific stages of processing, the chilling stage had the greatest number of studies (9), followed by washing (6), defeathering (4), scalding (2), and evisceration (1). Studies that sampled before and after scalding or chilling, or both, showed that the prevalence of Campylobacter generally decreased immediately after the stage (scalding: 20.0 to 40.0% decrease; chilling: 100.0% decrease to 26.6% increase). The prevalence of Campylobacter increased after defeathering (10.0 to 72.0%) and evisceration (15.0%). The prevalence after washing was inconsistent among studies (23.0% decrease to 13.3% increase). Eleven studies reported the concentration of Campylobacter, as well as, or instead of, the prevalence. Studies that sampled before and after specific stages of processing showed that the concentration of Campylobacter decreased after scalding (minimum decrease of 1.3 cfu/g, maximum decrease of 2.9 cfu/mL), evisceration (0.3 cfu/g), washing (minimum 0.3 cfu/mL, maximum 1.1 cfu/mL), and chilling (minimum 0.2 cfu/g, maximum 1.7 cfu/carcass) and increased after defeathering (minimum 0.4 cfu/g, maximum 2.9 cfu/mL). Available evidence is sparse and suggests more data are needed to understand the magnitude and mechanism by which the prevalence and concentration of Campylobacter changes during processing. This understanding should help researchers and program developers identify the most likely points in processing to implement effective control efforts. For example, if contamination will occur during defeathering and likely during evisceration, critical control points postevisceration are likely to have a greater effect on the end product going to the consumer

A Large Outbreak of Hepatitis E Among a Displaced Population in Darfur, Sudan, 2004: The Role of Water Treatment Methods.

BACKGROUND: The conflict in Darfur, Sudan, was responsible for the displacement of 1.8 million civilians. We investigated a large outbreak of hepatitis E virus (HEV) infection in Mornay camp (78,800 inhabitants) in western Darfur. METHODS: To describe the outbreak, we used clinical and demographic information from cases recorded at the camp between 26 July and 31 December 2004. We conducted a case-cohort study and a retrospective cohort study to identify risk factors for clinical and asymptomatic hepatitis E, respectively. We collected stool and serum samples from animals and performed a bacteriological analysis of water samples. Human samples were tested for immunoglobulin G and immunoglobulin M antibody to HEV (for serum samples) and for amplification of the HEV genome (for serum and stool samples). RESULTS: In 6 months, 2621 hepatitis E cases were recorded (attack rate, 3.3%), with a case-fatality rate of 1.7% (45 deaths, 19 of which involved were pregnant women). Risk factors for clinical HEV infection included age of 15-45 years (odds ratio, 2.13; 95% confidence interval, 1.02-4.46) and drinking chlorinated surface water (odds ratio, 2.49; 95% confidence interval, 1.22-5.08). Both factors were also suggestive of increased risk for asymptomatic HEV infection, although this was not found to be statistically significant. HEV RNA was positively identified in serum samples obtained from 2 donkeys. No bacteria were identified from any sample of chlorinated water tested. CONCLUSIONS: Current recommendations to ensure a safe water supply may have been insufficient to inactivate HEV and control this epidemic. This research highlights the need to evaluate current water treatment methods and to identify alternative solutions adapted to complex emergencies