7,266 research outputs found
Floristic links between the West Coast and South Coast (South Africa) - is the Breede River Valley a migration route?
The bacteriology of sheep periodontitis with special reference to Actinobacillus actinomycetemcomitans
P
Phase I of the DiaVACCS screening trial: Study design, methods, population demographics and baseline results
Background. Human papillomavirus (HPV)-based primary screening guidelines are based on screening test performance and prevalence data generated in high-resource areas with low HIV infection rates. There is an urgent need for local data on infection and disease prevalence, as well as screening test performance, among both HIV-positive and HIV-negative South African (SA) women, in order to inform updated screening guidelines. Objectives. This study describes the baseline characteristics of participants in the cross-sectional phase of the multicentric DIAgnosis in Vaccine And Cervical Cancer Screen (DiaVACCS) screening trial. The objective was to determine the prevalence of positive screening and pre-invasive disease using different tests and strategies in the SA HIV-positive and HIV-negative population.Methods. A total of 1 104 women aged 25 - 65 years and eligible for screening were included, 465 HIV positive and 639 HIV negative. Visual inspection and molecular and cytological screening tests were done on self-sampled and healthcare worker-collected specimens. All participants who screened positive and 49.1% of those who screened negative were invited for colposcopy and biopsy, and those qualifying for treatment were recalled for large loop excision of the transformation zone as part of the trial. The worst histology result for each participant was used, and for untested women, multiple imputation was used to estimate verification biasadjusted histology values.Results. Visual inspection was positive in 50.4% of HIV-positive v. 20.9% of HIV-negative women, cytology (atypical squamous cells of undetermined significance) in 39.9% v. 17.0%, and high-risk HPV DNA in 41.2% v. 19.6%. Overall, high-grade squamous intraepithelial lesion-positive cytology peaked in the age group 30 - 39 years at 16.7%. After adjustment for verification bias, histological diagnosis of cervical intraepithelial neoplasia (CIN)2+ was suspected in 44.7% v. 23.5% and CIN3+ in 23.3% v. 10.2% of HIV-positive and negative women, respectively. Invasive cancer was diagnosed in 15 women (1.95% of histological studies performed), and verification bias adjustment suggested 20 cases (1.8% of the study population).Conclusion. The baseline findings from the DiaVACCS trial confirm a high prevalence of HPV-related cervical pathology in the SA HIV-negative screening population, showing a clear need to reach these women with a screening programme. Among HIV-positive women, prevalence values were almost doubled. The prevalence of existing invasive cervical cancer was 1 - 2% of all women. Further analysis of the performance of single and multiple screening tests between the two subgroups will contribute to the choice of the most effective strategies to identify women at risk of developing invasive cancer
Chandra Observations of Extended X-ray Emission in Arp 220
We resolve the extended X-ray emission from the prototypical ultraluminous
infrared galaxy Arp 220. Extended, faint edge-brightened, soft X-ray lobes
outside the optical galaxy are observed to a distance of 10 to 15 kpc on each
side of the nuclear region. Bright plumes inside the optical isophotes coincide
with the optical line emission and extend 11 kpc from end to end across the
nucleus. The data for the plumes cannot be fit by a single temperature plasma,
and display a range of temperatures from 0.2 to 1 keV. The plumes emerge from
bright, diffuse circumnuclear emission in the inner 3 kpc centered on the
Halpha peak, which is displaced from the radio nuclei. There is a close
morphological correspondence between the Halpha and soft X-ray emission on all
spatial scales. We interpret the plumes as a starburst-driven superwind, and
discuss two interpretations of the emission from the lobes in the context of
simulations of the merger dynamics of Arp 220.Comment: Accepted for publication in ApJ; see also astro-ph/0208477 (Paper 1
M/L, H-alpha Rotation Curves, and HI Measurements for 329 Nearby Cluster and Field Spirals: II. Evidence for Galaxy Infall
We have conducted a study of optical and HI properties of spiral galaxies
(size, luminosity, H-alpha flux distribution, circular velocity, HI gas mass)
to explore the role of gas stripping as a driver of morphological evolution in
clusters. We find a strong correlation between the spiral and S0 fractions
within clusters, and the spiral fraction scales tightly with cluster X-ray gas
luminosity. We explore young star formation and identify spirals that are (1)
asymmetric, with truncated H-alpha emission and HI gas reservoirs on the
leading edge of the disk, on a first pass through the dense intracluster medium
in the cores of rich clusters; (2) strongly HI deficient and stripped, with
star formation confined to the inner 5 kpc/h and 3 disk scale lengths; (3)
reddened, extremely HI deficient and quenched, where star formation has been
halted across the entire disk. We propose that these spirals are in successive
stages of morphological transformation, between infalling field spirals and
cluster S0s, and that the process which acts to remove the HI gas reservoir
suppresses new star formation on a similarly fast timescale. These data suggest
that gas stripping plays a significant role in morphological transformation and
rapid truncation of star formation across the disk.Comment: 24 pages, 12 figures; accepted for publication in AJ;
higher-resolution figures available at http://astronomy.nmsu.edu/nicol
On the emergence of Lorentzian signature and scalar gravity
In recent years, a growing momentum has been gained by the emergent gravity
framework. Within the latter, the very concepts of geometry and gravitational
interaction are not seen as elementary aspects of Nature but rather as
collective phenomena associated to the dynamics of more fundamental objects. In
this paper we want to further explore this possibility by proposing a model of
emergent Lorentzian signature and scalar gravity. Assuming that the dynamics of
the fundamental objects can give rise in first place to a Riemannian manifold
and a set of scalar fields we show how time (in the sense of hyperbolic
equations) can emerge as a property of perturbations dynamics around some
specific class of solutions of the field equations. Moreover, we show that
these perturbations can give rise to a spin-0 gravity via a suitable
redefinition of the fields that identifies the relevant degrees of freedom. In
particular, we find that our model gives rise to Nordstrom gravity. Since this
theory is invariant under general coordinate transformations, this also shows
how diffeomorphism invariance (albeit of a weaker form than the one of general
relativity) can emerge from much simpler systems.Comment: 10 pages, revtex4. Replaced with the published versio
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