162 research outputs found
Plasma Cleaning of LCLS-II-HE verification cryomodule cavities
Plasma cleaning is a technique that can be applied in superconducting
radio-frequency (SRF) cavities in situ in cryomodules in order to decrease
their level of field emission. We developed the technique for the Linac
Coherent Light Source II (LCLS-II) cavities and we present in this paper the
full development and application of plasma processing to the LCLS-II High
Energy (HE) verification cryomodule (vCM). We validated our plasma processing
procedure on the vCM, fully processing four out of eight cavities of this CM,
demonstrating that cavities performance were preserved in terms of both
accelerating field and quality factor. Applying plasma processing to this
clean, record breaking cryomodule also showed that no contaminants were
introduced in the string, maintaining the vCM field emission-free up to the
maximum field reached by each cavity. We also found that plasma processing
eliminates multipacting (MP) induced quenches that are typically observed
frequently within the MP band field range. This suggests that plasma processing
could be employed in situ in CMs to mitigate both field emission and
multipacting, significantly decreasing the testing time of cryomodules, the
linac commissioning time and cost and increasing the accelerator reliability.Comment: 11 pages, 10 figure
Relapsing tricuspid valve endocarditis by multidrug-resistant Pseudomonas aeruginosa in 11 years: tricuspid valve replacement with an aortic valve homograft
Prolonged outbreak of clonal MDR Pseudomonas aeruginosa on an intensive care unit: contaminated sinks and contamination of ultra-filtrate bags as possible route of transmission?
Extensive recombination events and horizontal gene transfer shaped the Legionella pneumophila genomes
<p>Abstract</p> <p>Background</p> <p><it>Legionella pneumophila </it>is an intracellular pathogen of environmental protozoa. When humans inhale contaminated aerosols this bacterium may cause a severe pneumonia called Legionnaires' disease. Despite the abundance of dozens of <it>Legionella </it>species in aquatic reservoirs, the vast majority of human disease is caused by a single serogroup (Sg) of a single species, namely <it>L. pneumophila </it>Sg1. To get further insights into genome dynamics and evolution of Sg1 strains, we sequenced strains Lorraine and HL 0604 1035 (Sg1) and compared them to the available sequences of Sg1 strains Paris, Lens, Corby and Philadelphia, resulting in a comprehensive multigenome analysis.</p> <p>Results</p> <p>We show that <it>L. pneumophila </it>Sg1 has a highly conserved and syntenic core genome that comprises the many eukaryotic like proteins and a conserved repertoire of over 200 Dot/Icm type IV secreted substrates. However, recombination events and horizontal gene transfer are frequent. In particular the analyses of the distribution of nucleotide polymorphisms suggests that large chromosomal fragments of over 200 kbs are exchanged between <it>L. pneumophila </it>strains and contribute to the genome dynamics in the natural population. The many secretion systems present might be implicated in exchange of these fragments by conjugal transfer. Plasmids also play a role in genome diversification and are exchanged among strains and circulate between different <it>Legionella </it>species.</p> <p>Conclusion</p> <p>Horizontal gene transfer among bacteria and from eukaryotes to <it>L. pneumophila </it>as well as recombination between strains allows different clones to evolve into predominant disease clones and others to replace them subsequently within relatively short periods of time.</p
Gene flow in environmental Legionella pneumophila leads to genetic and pathogenic heterogeneity within a Legionnairesâ disease outbreak
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