22 research outputs found
Performance of a commercial polymerase chain reaction test for endocervical Chlamydia trachomatis infection in a university hospital population.
OBJECTIVES: To examine the accuracy of a commercial polymerase chain reaction (PCR) test (Amplicor CTR, Roche Diagnostic Systems, Branchburg NJ) for identification of endocervical chlamydial infections through both laboratory evaluation and among a diverse teaching hospital patient population. METHODS: Testing of reliable threshold inocula and reproducibility were carried out using laboratory stock organisms. Paired endocervical samples from patients with a wide range of indications were tested by PCR and an established culture procedure, and discrepant pairs were further analyzed to determine true results. RESULTS: Laboratory evaluation suggested that one copy of target DNA from a viable organism consistently yielded a positive result, and test reproducibility was very good, with an overall coefficient of variation of 15%. Compared to true results in 1,588 paired clinical samples from 1,489 women with a 10% prevalence of infection, the PCR test and culture yielded respective sensitivities of 87.4% and 78.0%, and negative predictive values of 98.6% and 97.6%. Specificity and positive predictive value for both tests were 100%. Cost per specimen was nearly identical at 18.88 respectively. Polymerase inhibitors and organisms lacking target DNA were not found in false-negative PCR samples. CONCLUSION: This commercial PCR test is accurate, cost-competitive, and much faster than culture for diagnosis of endocervical chlamydia infections in our population of intermediate prevalence of chlamydial infection
Singular Isothermal Disks: II. Nonaxisymmetric Bifurcations and Equilibria
We review the difficulties of the classical fission and fragmentation
hypotheses for the formation of binary and multiple stars. A crucial missing
ingredient in previous theoretical studies is the inclusion of dynamically
important levels of magnetic fields. As a minimal model for a candidate
presursor to the formation of binary and multiple stars, we therefore formulate
and solve the problem of the equilibria of isopedically magnetized, singular
isothermal disks, without the assumption of axial symmetry. Considerable
analytical progress can be made if we restrict our attention to models that are
scale-free, i.e., that have surface densities that vary inversely with distance
from the rotation axis of the system. In agreement with earlier analysis by
Syer and Tremaine, we find that lopsided (M=1) configurations exist at any
dimensionless rotation rate, including zero. Multiple-lobed (M = 2, 3, 4, ...)
configurations bifurcate from an underlying axisymmetric sequence at
progressively higher dimensionless rates of rotation, but such nonaxisymmetric
sequences always terminate in shockwaves before they have a chance to fission
into M=2, 3, 4, ... separate bodies. On the basis of our experience in this
paper, and the preceding Paper I, we advance the hypothesis that binary and
multiple star-formation from smooth (i.e., not highly turbulent) starting
states that are supercritical but in unstable mechanical balance requires the
rapid (i.e., dynamical) loss of magnetic flux at some stage of the ensuing
gravitational collapse.Comment: 49 pages, 11 figures, LaTeX, needs aaspp4.sty. The Astrophysical
Journal, in pres
Optical polarimetry toward the Pipe nebula: Revealing the importance of the magnetic field
Magnetic fields are proposed to play an important role in the formation and
support of self-gravitating clouds and the formation and evolution of
protostars in such clouds. We use R-band linear polarimetry collected for about
12000 stars in 46 fields with lines of sight toward the Pipe nebula to
investigate the properties of the polarization across this dark cloud complex.
Mean polarization vectors show that the magnetic field is locally perpendicular
to the large filamentary structure of the Pipe nebula (the `stem'), indicating
that the global collapse may have been driven by ambipolar diffusion. The
polarization properties clearly change along the Pipe nebula. The northwestern
end of the nebula (B59 region) is found to have a low degree of polarization
and high dispersion in polarization position angle, while at the other extreme
of the cloud (the `bowl') we found mean degrees of polarization as high as
15% and a low dispersion in polarization position angle. The plane of
the sky magnetic field strength was estimated to vary from about 17 G in
the B59 region to about 65 G in the bowl. We propose that three distinct
regions exist, which may be related to different evolutionary states of the
cloud; this idea is supported by both the polarization properties across the
Pipe and the estimated mass-to-flux ratio that varies between approximately
super-critical toward the B59 region and sub-critical inside the bowl. The
three regions that we identify are: the B59 region, which is currently forming
stars; the stem, which appears to be at an earlier stage of star formation
where material has been through a collapsing phase but not yet given birth to
stars; and the bowl, which represents the earliest stage of the cloud in which
the collapsing phase and cloud fragmentation has already started.Comment: 4 pages, 2 figure
Control of star formation by supersonic turbulence
Understanding the formation of stars in galaxies is central to much of modern
astrophysics. For several decades it has been thought that stellar birth is
primarily controlled by the interplay between gravity and magnetostatic
support, modulated by ambipolar diffusion. Recently, however, both
observational and numerical work has begun to suggest that support by
supersonic turbulence rather than magnetic fields controls star formation. In
this review we outline a new theory of star formation relying on the control by
turbulence. We demonstrate that although supersonic turbulence can provide
global support, it nevertheless produces density enhancements that allow local
collapse. Inefficient, isolated star formation is a hallmark of turbulent
support, while efficient, clustered star formation occurs in its absence. The
consequences of this theory are then explored for both local star formation and
galactic scale star formation. (ABSTRACT ABBREVIATED)Comment: Invited review for "Reviews of Modern Physics", 87 pages including 28
figures, in pres
Symposium on the Scottish labour market
In the post-war period, up to the late 1960s, Britain enjoyed a modicum of unemployment and government policies which were geared to producing Full Employment were considered a success. It was simple - boost demand and more people would find work. But the mid 1970s the economic regency enjoyed by those advocating demand sided policies fell into disrepute as the OPEC nations raised prices dramatically and brought in a new era of both rising prices and unemployment. The laws of economics, which previously had viewed policy decisions as the choice between lower unemployment and higher inflation were now redundant. Both unemployment and inflation were moving in the same direction. The era of stagflation had begun
M1T1 group A streptococcal pili promote epithelial colonization but diminish systemic virulence through neutrophil extracellular entrapment
Group A Streptococcus is a leading human pathogen associated with a diverse array of mucosal and systemic infections. Cell wall anchored pili were recently described in several species of pathogenic streptococci, and in the case of GAS, these surface appendages were demonstrated to facilitate epithelial cell adherence. Here we use targeted mutagenesis to evaluate the contribution of pilus expression to virulence of the globally disseminated M1T1 GAS clone, the leading agent of both GAS pharyngitis and severe invasive infections. We confirm that pilus expression promotes GAS adherence to pharyngeal cells, keratinocytes, and skin. However, in contrast to findings reported for group B streptococcal and pneumococcal pili, we observe that pilus expression reduces GAS virulence in murine models of necrotizing fasciitis, pneumonia and sepsis, while decreasing GAS survival in human blood. Further analysis indicated the systemic virulence attenuation associated with pilus expression was not related to differences in phagocytic uptake, complement deposition or cathelicidin antimicrobial peptide sensitivity. Rather, GAS pili were found to induce neutrophil IL-8 production, promote neutrophil transcytosis of endothelial cells, and increase neutrophil release of DNA-based extracellular traps, ultimately promoting GAS entrapment and killing within these structures
Environmental Acidification Drives S. pyogenes Pilus Expression and Microcolony Formation on Epithelial Cells in a FCT-Dependent Manner
Group A Streptococcus (GAS, Streptococcus pyogenes) is a Gram-positive human pathogen responsible for a diverse variety of diseases, including pharyngitis, skin infections, invasive necrotizing fasciitis and autoimmune sequelae. We have recently shown that GAS cell adhesion and biofilm formation is associated with the presence of pili on the surface of these bacteria. GAS pilus proteins are encoded in the FCT (Fibronectin- Collagen-T antigen) genomic region, of which nine different variants have been identified so far. In the present study we undertook a global analysis of GAS isolates representing the majority of FCT-variants to investigate the effect of environmental growth conditions on their capacity to form multicellular communities. For FCT-types 2, 3, 5 and 6 and a subset of FCT-4 strains, we observed that acidification resulting from fermentative sugar metabolism leads to an increased ability of the bacteria to form biofilm on abiotic surfaces and microcolonies on epithelial cells. The higher biofilm forming capacity at low environmental pH was directly associated with an enhanced expression of the genes encoding the pilus components and of their transcription regulators. The data indicate that environmental pH affects the expression of most pilus types and thereby the formation of multicellular cell-adhering communities that assist the initial steps of GAS infection
Early science with the Large Millimetre Telescope: Deep LMT/AzTEC millimetre observations of ϵ Eridani and its surroundings
ϵ Eridani is a nearby, young Sun-like star that hosts a ring of cool debris analogous to the Solar system's Edgeworth-Kuiper belt. Early observations at (sub-)mm wavelengths gave tentative evidence of the presence of inhomogeneities in the ring, which have been ascribed to the effect of a putative low eccentricity planet, orbiting close to the ring. The existence of these structures has been recently challenged by high-resolution interferometric millimetre observations. Here, we present the deepest single-dish image of ϵ Eridani at millimetre wavelengths, obtained with the Large Millimetre Telescope Alfonso Serrano (LMT). The main goal of these LMT observations is to confirm (or refute) the presence of non-axisymmetric structure in the disc. The dusty ring is detected for the first time along its full projected elliptical shape. The radial extent of the ring is not spatially resolved and shows no evidence, to within the uncertainties, of dust density enhancements. Additional features of the 1.1 mm map are: (i) the presence of significant flux in the gap between the ring and the star, probably providing the first exo-solar evidence of Poynting-Robertson drag, (ii) an unambiguous detection of emission at the stellar positionwith a flux significantly above that expected from ϵ Eridani's photosphere, and (iii) the identification of numerous unresolved sources which could correspond to background dusty star-forming galaxies.This work would have not been possible without the long-term financial support from the Mexican Science and Technology Funding Agency, CONACyT (Consejo Nacional de Ciencia y Tecnología) during the construction and operational phase of the Large Millimetre Telescope Alfonso Serrano, as well as support from the US National Science Foundation via the University Radio Observatory program, the Instituto Nacional de Astrofísica, Optica y Electrónica (INAOE) and the University of Massachusetts, Amherst (UMass). MC, EB, FCSM, MO and RLV work was supported by CONACyT research grants SEP-2009-134985 and SEP-2011-169554. GMK is supported by the Royal Society as a Royal Society University Research Fellow. CE is partly supported by Spanish grant AYA2014-55840-P. JPM is supported by a UNSW Vice Chancellor's Postdoctoral Fellowship. SL acknowledges support from CONACyT through grant 238631