210 research outputs found
A New Look at Mode Conversion in a Stratified Isothermal Atmosphere
Recent numerical investigations of wave propagation near coronal magnetic
null points (McLaughlin and Hood: Astron. Astrophys. 459, 641,2006) have
indicated how a fast MHD wave partially converts into a slow MHD wave as the
disturbance passes from a low-beta plasma to a high-beta plasma. This is a
complex process and a clear understanding of the conversion mechanism requires
the detailed investigation of a simpler model. An investigation of mode
conversion in a stratified, isothermal atmosphere, with a uniform, vertical
magnetic field is carried out, both numerically and analytically. In contrast
to previous investigations of upward-propagating waves (Zhugzhda and Dzhalilov:
Astron. Astrophys. 112, 16, 1982a; Cally: Astrophys. J. 548, 473, 2001), this
paper studies the downward propagation of waves from a low-beta to high-beta
environment. A simple expression for the amplitude of the transmitted wave is
compared with the numerical solution.Comment: 14 pages, 6 figure
Macro and micro diversity of Clostridium difficile isolates from diverse sources and geographical locations.
Clostridium difficile has emerged rapidly as the leading cause of antibiotic-associated diarrheal disease, with the temporal and geographical appearance of dominant PCR ribotypes such as 017, 027 and 078. Despite this continued threat, we have a poor understanding of how or why particular variants emerge and the sources of strains that dominate different human populations. We have undertaken a breadth genotyping study using multilocus sequence typing (MLST) analysis of 385 C. difficile strains from diverse sources by host (human, animal and food), geographical locations (North America, Europe and Australia) and PCR ribotypes. Results identified 18 novel sequence types (STs) and 3 new allele sequences and confirmed the presence of five distinct clonal lineages generally associated with outbreaks of C. difficile infection in humans. Strains of animal and food origin were found of both ST-1 and ST-11 that are frequently associated with human disease. An in depth MLST analysis of the evolutionary distant ST-11/PCR ribotype 078 clonal lineage revealed that ST-11 can be found in alternative but closely related PCR ribotypes and PCR ribotype 078 alleles contain mutations generating novel STs. PCR ribotype 027 and 017 lineages may consist of two divergent subclades. Furthermore evidence of microdiversity was present within the heterogeneous clade 1. This study helps to define the evolutionary origin of dominant C. difficile lineages and demonstrates that C. difficile is continuing to evolve in concert with human activity
Loss of 5-hydroxymethylcytosine is a frequent event in peripheral T-cell lymphomas.
International audienc
Role of surface roughness in hard x-ray emission from femtosecond laser produced copper plasmas
The hard x-ray emission in the energy range of 30-300 keV from copper plasmas
produced by 100 fs, 806 nm laser pulses at intensities in the range of
10 W cm is investigated. We demonstrate that surface
roughness of the targets overrides the role of polarization state in the
coupling of light to the plasma. We further show that surface roughness has a
significant role in enhancing the x-ray emission in the above mentioned energy
range.Comment: 5 pages, 4 figures, to appear in Phys. Rev.
Apparatus for investigating non-linear microwave interactions in magnetised plasma
Plasma, as a non-linear medium supporting a rich and diverse range of electromagnetic and electrostatic oscillations, can enable a range of multi-wave interactions when excited by multiple injected propagating electromagnetic waves. Electromagnetic wave injection plays a dominant role in the introduction of energy in laser plasma interactions and in the heating of magnetically confined fusion reactors. In magnetically confined plasma, the EM waves tend to fall in the RF to microwave range, whilst in laser plasma interactions the signals are typically near the optical part of the spectrum
The rate of colonization by macro-invertebrates on artificial substrate samplers
The influence of exposure time upon macro-invertebrate colonization on modified Hester-Dendy substrate samplers was investigated over a 60-day period. The duration of exposure affected the number of individuals, taxa and community diversity. The numbers of individuals colonizing the samplers reached a maximum after 39 days and then began to decrease, due to the emergence of adult insects. Coefficients of variation for the four replicate samples retrieved each sampling day fluctuated extensively throughout the study. No tendencies toward increasing or decreasing coefficients of variation were noted with increasing time of sampler exposure. The number of taxa colonizing the samplers increased throughout the study period. The community diversity index was calculated for each sampling day and this function tended to increase throughout the same period. This supports the hypothesis that an exposure period of 6 weeks, as recommended by the United States Environmental Protection Agency, may not always provide adequate opportunity for a truly representative community of macro-invertebrates to colonize multiplate samplers. Many of the taxa were collected in quite substantial proportions after periods of absence or extreme sparseness. This is attributed to the growth of periphyton and the collection of other materials that created food and new habitats suitable for the colonization of new taxa. Investigation of the relationship between âequitabilityâ and length of exposure revealed that equitability did not vary like diversity with increased time of exposure.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72073/1/j.1365-2427.1979.tb01522.x.pd
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