30 research outputs found
Interference of a first-order transition with the formation of a spin-Peierls state in alpha'-NaV2O5?
We present results of high-resolution thermal-expansion and specific-heat
measurements on single crystalline alpha'-NaV2O5. We find clear evidence for
two almost degenerate phase transitions associated with the formation of the
dimerized state around 33K: A sharp first-order transition at T1=(33+-0.1)K
slightly below the onset of a second-order transition at T2onset around
(34+-0.1)K. The latter is accompanied by pronounced spontaneous strains. Our
results are consistent with a structural transformation at T1 induced by the
incipient spin-Peierls (SP) order parameter above T2=TSP.Comment: 5 pages, 7 figure
Interference of a first-order transition with the formation of a spin-Peierls state in alpha'-NaV2O5
Solitary magnetic excitations in the low-carrier density, one-dimensional S=1/2 antiferromagnet Yb4As3
Aggregatibacter aphrophilus chronic lacrimal canaliculitis: a case report
International audienceBackground: Chronic canaliculitis is often misdiagnosed as conjunctivitis, delaying proper documentation and management. Aggregatibacter aphrophillus has not been implicated in chronic canaliculitis. Case presentation: We report a case of unilateral chronic epiphora associated with chronic lacrimal canaliculitis resistant to prolonged topical antibiotic treatment in a 65-year-old woman without notable medical history. Canaculotomy, curettage with removal of concretions and tubing with silicone stent for six weeks resolved this chronic infection. Culturing lacrimal secretions and concretions yielded Aggregatibacter aphrophilus in pure culture. Histological analyses showed elongated seed clusters surrounded by neutrophils. Fluorescence in Situ Hybridization confirmed the presence of bacteria in two distinctive concretions. Conclusion: This first documented case of A. aphrophilus chronic lacrimal canaliculitis illustrates that optimal surgical management of chronic lacrimal canaliculitis allows for both accurate microbiological diagnosis and treatment
Analyse génétique et moléculaire de stress arsenic de souches bactériennes isolées d'environnements contaminés par l'arsenic
L'arsenic est un métalloïde présent dans différents compartiments de l'environnement, provenant de sources naturelles ou de sources anthropiques. Les formes inorganiques, l'arsénite (As[III]) et l'arséniate (As[V]), sont les plus abondantes et aussi les plus toxiques. La proportion relative de ces états d'oxydation dans un environnement donné sera fonction de transformations chimiques spontanées, et surtout de biotransformations liées aux métabolismes bactériens, tels que la réduction et l'oxydation.Ce travail de thèse a eu comme objectif principal l'étude moléculaire et génétique de l'arsénite oxydase d'une ß-protéobactérie, Cenibacterium arsenoxidans. L'analyse de mutants obtenus par transposition aléatoire d'un mini-Tn5 a conduit à l'identification de deux gènes aoxA et aoxB, organisés en opéron et codant les deux sous-unités de l'arsénite oxydase. L'analyse phylogénétique des deux sous-unités de cette enzyme a révélé que celle-ci possède des homologues dans d'autres familles enzymatiques assurant des fonctions diverses. La comparaison entre ces différentes familles suggère une apparition très ancienne des enzymes de type arsénite oxydase (pré-LUCA). Par ailleurs nous avons étudié la réponse globale des bactéries se trouvant en contact avec l'arsenic. Pour ce faire, nous avons combiné deux approches, d'une part l'analyse des mutants dont le gène rapporteur est induit par l'arsenic, d'autre part l'étude des protéines dont la synthèse est régulée par l'arsenic. Nous avons montré que les gènes régulés par l'arsenic interviennent dans une grande variété de fonctions incluant l'information, le métabolisme intermédiaire, la structure des enveloppes, la transformation de différentes formes d'arsenic. Cette étude suggère, que la bactérie C. arsenoxidans, est capable de réaliser également la réduction de l'arséniate en arsénite en plus de l'oxydation de l'arsénite en arséniate. Au moins trois opérons de type ars (réduction de l'As[V]) seraient présents dans cette souche.Arsenic is ubiquitous in the biosphere and frequently reported as an environmental pollutant. Many studies have shown that arsenic is cytotoxic at micromolar concentrations. Bacteria overcome the toxic effects of arsenic by either reducing arsenate (As[V]) to As[III], which is actively exported (ars operon), or by oxidizing As[III] to the lesser toxic form As[V]. In a first part, the effects of arsenic stress on the arsenic oxidizing ß-proteobacterial strain C. arsenoxidans were studied. More than 4000 mutants were generated by random insertion of the lacZ-based reporter gene transposon Tn5lacZ2. Increased gene expression in the presence of As[III] was observed in twenty-two mutants. Two were deficient in As[III] oxidation. Sequence analysis of the DNA flanking the inserted transposon insertions allowed us to characterise for the first time two adjacent genes coding the two subunit of the arsenite oxidase, named aoxA and aoxB, organised in an operonic structure. Phylogenetic analysis for the two constituent subunits of the arsenite oxidase indicate an early origin of this enzyme, before the divergence of Archaea and Bacteria. In a second part, the global response to arsenic stress was studied by combining a proteomic approach with the mutants analysis. Twenty-two proteins and sixteen genes were identified as differentially expressed in cells grown in the presence of As[III]. We identified genes and proteins belonging to various functional classes including information and regulation pathways, intermediary metabolism, cell envelope and cellular processes. Moreover, the presence of As[V] reduction mechanisms in a As[III] oxidizing bacteria was shown for the first time.Our results suggest that the adaptation of C. arsenoxidans to an arsenic-contaminated environment is not limited to transformation of arsenic species, but is rather pleiotropic, since a great variety of biological effects were involved.STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF
Status of Philips' extreme UV source
The paper describes progress of the Philips' hollow cathode triggered (HCT) gas discharge EUV source. The program has been focussed on three major areas: (1) Studying the basic physics of ignition, pinch formation and EUV generation. The paper reports on progress in this area and particularly describes the underlying atomic physics both for Xe and Sn. (2) Discharge based on Sn. Results on overall efficiency more than 5 times the Xe efficiency are reported as well as high frequency operation up to 6.5 kHz. This system shows all the necessary ingredients for scaling to production power levels. (3) Integration of the Xe source in an alpha tool. Results on integration issues like electrode life time, collector life time and dose control will be presented
Integrating Philips' extreme UV source in the alpha-tools
The paper describes recent progress in the development of the Philips's EUV source. Progress has been realized at many frontiers: Integration studies of the source into a scanner have primarily been studied on the Xe source because it has a high degree of maturity. We report on integration with a collector, associated collector lifetime and optical characteristics. Collector lifetime in excess of 1 bln shots could be demonstrated. Next, an active dose control system was developed and tested on the Xe lamp. Resulting dose stability data are less than 0.2% for an exposure window of 100 pulses. The second part of the paper reports on progress in the development of the Philips' Sri source. First, the details of the concept are described. It is based on a Laser triggered vacuum arc, which is an extension with respect to previous designs. The source is furbished with rotating electrodes that are covered with a Sri film that is constantly regenerated. Hence by the very design of the source, it is scalable to very high power levels, and moreover has fundamentally solved the notorious problem of electrode erosion. Power values of 260 W in 2 pi sr are reported, along with a stable, long life operation of the lamp. The paper also addresses the problem of debris generation and mitigation of the Sn-source. The problem is attacked by a combined strategy of protection of the collector by traditional means (e.g. fields, foiltraps,...), and by designing the gas atmosphere according to the principles of the well known halogen cycles in incandescent lamps. These principles have been studied in the Lighting industry for decades and rely on the excessively high vapor pressures of metal halides. Transferred to the Sri source, it allows pumping away tin residues that would otherwise irreversibly deposit on the collector