4,638 research outputs found
Enhanced nasopharyngeal infection and shedding associated with an epidemic lineage of emm3 group A Streptococcus
Background:
A group A Streptococcus (GAS) lineage of genotype emm3, sequence type 15 (ST15) was
associated with a six month upsurge in invasive GAS disease in the UK. The epidemic lineage
(Lineage C) had lost two typical emm3 prophages, Φ315.1 and Φ315.2 associated with the
superantigen ssa, but gained a different prophage (ΦUK-M3.1) associated with a different
superantigen, speC and a DNAse spd1.
Methods and Results:
The presence of speC and spd1 in Lineage C ST15 strains enhanced both in vitro mitogenic
and DNAse activities over non-Lineage C ST15 strains. Invasive disease models in Galleria
mellonella and SPEC-sensitive transgenic mice, revealed no difference in overall invasiveness
of Lineage C ST15 strains compared to non-Lineage C ST15 strains, consistent with clinical
and epidemiological analysis. Lineage C strains did however markedly prolong murine nasal
infection with enhanced nasal and airborne shedding compared to non-Lineage C strains.
Deletion of speC or spd1 in two Lineage C strains identified a possible role for spd1 in airborne
shedding from the murine nasopharynx.
Conclusions:
Nasopharyngeal infection and shedding of Lineage C strains was enhanced compared to nonLineage
C strains and this was, in part, mediated by the gain of the DNase spd1 through prophage acquisition
Sampling Effects on Gene Expression Data from a Human Tumour Xenograft
Human tumour tissue transplanted to and passed through immunodeficient mice as xenografts make powerful model systems to study tumour biology, in particular to investigate the dynamics of treatment responses, e.g. to chemotherapeutic agents. Before embarking on large-scale gene expression analysis of chemotherapy response in human sarcoma xenografts, we investigated the reproducibility of expression patterns derived from such samples. We compared expression profiles from tumours from the same or different mice and of various sizes, as well as central and peripheral parts of the same tumours. Twenty-three microarray hybridisations were performed on cDNA arrays representing 13000 genes, using direct labelling of target cDNAs. An ANOVA-based linear mixed-effects model was constructed, and variances of experimental and biological factors contributing to variability were estimated. With our labelling procedure used, the effect of switching the dyes was pronounced compared to all other factors. We detected a small variation in gene expression between two tumours in the same mouse as well as between tumours from different mice. Furthermore, central or peripheral position in the tumour had only moderate influence on the variability of the expression profiles. The biological variability was comparable to experimental variability caused by labelling, confirming the importance of both biological and technical replicates. We further analysed the data by pair-wise Fisher’s linear discriminant method and identified genes that were significantly differentially expressed between samples taken from peripheral or central parts of the tumours. Finally, we evaluated the result of pooling biological samples to estimate the recommended number of arrays and hybridisations for microarray experiments in this model.
A comparative study of different integrate-and-fire neurons: spontaneous activity, dynamical response, and stimulus-induced correlation
Stochastic integrate-and-fire (IF) neuron models have found widespread
applications in computational neuroscience. Here we present results on the
white-noise-driven perfect, leaky, and quadratic IF models, focusing on the
spectral statistics (power spectra, cross spectra, and coherence functions) in
different dynamical regimes (noise-induced and tonic firing regimes with low or
moderate noise). We make the models comparable by tuning parameters such that
the mean value and the coefficient of variation of the interspike interval
match for all of them. We find that, under these conditions, the power spectrum
under white-noise stimulation is often very similar while the response
characteristics, described by the cross spectrum between a fraction of the
input noise and the output spike train, can differ drastically. We also
investigate how the spike trains of two neurons of the same kind (e.g. two
leaky IF neurons) correlate if they share a common noise input. We show that,
depending on the dynamical regime, either two quadratic IF models or two leaky
IFs are more strongly correlated. Our results suggest that, when choosing among
simple IF models for network simulations, the details of the model have a
strong effect on correlation and regularity of the output.Comment: 12 page
Building professional discourse in emerging markets: Language, context and the challenge of sensemaking
Using ethnographic evidence from the former Soviet republics, this article examines a relatively new and mainly unobserved in the International Business (IB) literature phenomenon of communication disengagement that manifests itself in many emerging markets. We link it to the deficiencies of the local professional business discourse rooted in language limitations reflecting lack of experience with the market economy. This hampers cognitive coherence between foreign and local business entities, adding to the liability of foreignness as certain instances of professional experience fail to find adequate linguistic expression, and complicates cross-cultural adjustments causing multi-national companies (MNCs) financial losses. We contribute to the IB literature by examining cross-border semantic sensemaking through a retrospectively constructed observational study. We argue that a relative inadequacy of the national professional idiom is likely to remain a feature of business environment in post-communist economies for some time and therefore should be factored into business strategies of MNCs. Consequently, we recommend including discursive hazards in the risk evaluation of international projects
A General Organocatalytic System for Enantioselective Radical Conjugate Additions to Enals
Herein, we report a general iminium ion-based catalytic method for the enantioselective conjugate addition of carbon-centered radicals to aliphatic and aromatic enals. The process uses an organic photoredox catalyst, which absorbs blue light to generate radicals from stable precursors, in combination with a chiral amine catalyst, which secures a consistently high level of stereoselectivity. The generality of this catalytic platform is demonstrated by the stereoselective interception of a wide variety of radicals, including non-stabilized primary ones which are generally difficult to engage in asymmetric processes. The system also served to develop organocatalytic cascade reactions that combine an iminium-ion-based radical trap with an enamine-mediated step, affording stereochemically dense chiral products in one-step
Magnetic phase diagram and transport properties of FeGe_2
We have used resistivity measurements to study the magnetic phase diagram of
the itinerant antiferromagnet FeGe_2 in the temperature range from 0.3->300 K
in magnetic fields up to 16 T. In contrast to theoretical predictions, the
incommensurate spin density wave phase is found to be stable at least up to 16
T, with an estimated critical field \mu _0H_c of ~ 30 T. We have also studied
the low temperature magnetoresistance in the [100], [110], and [001]
directions. The transverse magnetoresistance is well described by a power law
for magnetic fields above 1 T with no saturation observed at high fields. We
discuss our results in terms of the magnetic structure and the calculated
electronic bandstructure of FeGe_2. We have also observed, for the first time
in this compound, Shubnikov-de Haas oscillations in the transverse
magnetoresistance with a frequency of 190 +- 10 T for a magnetic field along
[001].Comment: 13 pages, RevTeX, 7 postscript figures, to appear in Journal of
Physics: Condensed Matte
Propagation Failure in Excitable Media
We study a mechanism of pulse propagation failure in excitable media where
stable traveling pulse solutions appear via a subcritical pitchfork
bifurcation. The bifurcation plays a key role in that mechanism. Small
perturbations, externally applied or from internal instabilities, may cause
pulse propagation failure (wave breakup) provided the system is close enough to
the bifurcation point. We derive relations showing how the pitchfork
bifurcation is unfolded by weak curvature or advective field perturbations and
use them to demonstrate wave breakup. We suggest that the recent observations
of wave breakup in the Belousov-Zhabotinsky reaction induced either by an
electric field or a transverse instability are manifestations of this
mechanism.Comment: 8 pages. Aric Hagberg: http://cnls.lanl.gov/~aric; Ehud
Meron:http://www.bgu.ac.il/BIDR/research/staff/meron.htm
Cl 1205+44, a fossil group at z = 0.59
This is a report of Chandra, XMM-Newton, HST and ARC observations of an
extended X-ray source at z = 0.59. The apparent member galaxies range from
spiral to elliptical and are all relatively red (i'-Ks about 3). We interpret
this object to be a fossil group based on the difference between the brightness
of the first and second brightest cluster members in the i'-band, and because
the rest-frame bolometric X-ray luminosity is about 9.2x10^43 h70^-2 erg s^-1.
This makes Cl 1205+44 the highest redshift fossil group yet reported. The
system also contains a central double-lobed radio galaxy which appears to be
growing via the accretion of smaller galaxies. We discuss the formation and
evolution of fossil groups in light of the high redshift of Cl 1205+44.Comment: 21 pages, 13 figures, minor corrections to match published ApJ
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