398 research outputs found
Late Holocene Toolstone Procurement and Land-Use Strategies in the Black Rock Desert and High Rock Country of Northwest Nevada
This thesis tests current interpretations of Late Holocene (5,000 cal BP to present) archaeology for the Black Rock Desert and High Rock Country (BRD/HRC) through an assessment of the toolstone procurement and land-use strategies of the region's prehistoric occupants. This is achieved through: lithic analysis from Paiute Creek Shelter (PCS), a recently excavated rock shelter with stratified cultural remains spanning the Late Holocene; X-ray fluorescence analysis of artifacts from PCS, Hanging Rock Shelter, Silent Snake Springs, and Smokey Creek Cave; and spatial analysis of 623 archaeological sites in the BRD/HRC. Results indicate that no changes occurred in how obsidian toolstone was procured between the Middle Archaic (5,000-1,500 cal BP) and Late Archaic (1,500 cal BP to contact), while residential mobility intensified during the Late Archaic, likely promoting increased trade in the region
Systematic differences between Cochrane and non-Cochrane meta-analyses on the same topic: a matched pair analysis
BACKGROUND: Meta-analyses conducted via the Cochrane Collaboration adhere to strict methodological and reporting standards aiming to minimize bias, maximize transparency/reproducibility, and improve the accuracy of summarized data. Whether this results in differences in the results reported by meta-analyses on the same topic conducted outside the Cochrane Collaboration is an open question.
METHODS: We conducted a matched-pair analysis with individual meta-analyses as the unit of analysis, comparing Cochrane and non-Cochrane reviews. Using meta-analyses from the cardiovascular literature, we identified pairs that matched on intervention and outcome. The pairs were contrasted in terms of how frequently results disagreed between the Cochrane and non-Cochrane reviews, whether effect sizes and statistical precision differed systematically, and how these differences related to the frequency of secondary citations of those reviews.
RESULTS: Our search yielded 40 matched pairs of reviews. The two sets were similar in terms of which was first to publication, how many studies were included, and average sample sizes. The paired reviews included a total of 344 individual clinical trials: 111 (32.3%) studies were included only in a Cochrane review, 104 (30.2%) only in a non-Cochrane review, and 129 (37.5%) in both. Stated another way, 62.5% of studies were only included in one or the other meta-analytic literature. Overall, 37.5% of pairs had discrepant results. The most common involved shifts in the width of 95% confidence intervals that would yield a different statistical interpretation of the significance of results (7 pairs). Additionally, 20% differed in the direction of the summary effect size (5 pairs) or reported greater than a 2-fold difference in its magnitude (3 pairs). Non-Cochrane reviews reported significantly higher effect sizes (P < 0.001) and lower precision (P < 0.001) than matched Cochrane reviews. Reviews reporting an effect size at least 2-fold greater than their matched pair were cited more frequently.
CONCLUSIONS: Though results between topic-matched Cochrane and non-Cochrane reviews were quite similar, discrepant results were frequent, and the overlap of included studies was surprisingly low. Non-Cochrane reviews report larger effect sizes with lower precision than Cochrane reviews, indicating systematic differences, likely reflective of methodology, between the two types of reviews that could generate different interpretations of the interventions under question
Systematic differences between Cochrane and non-Cochrane meta-analyses on the same topic: a matched pair analysis
BACKGROUND: Meta-analyses conducted via the Cochrane Collaboration adhere to strict methodological and reporting standards aiming to minimize bias, maximize transparency/reproducibility, and improve the accuracy of summarized data. Whether this results in differences in the results reported by meta-analyses on the same topic conducted outside the Cochrane Collaboration is an open question.
METHODS: We conducted a matched-pair analysis with individual meta-analyses as the unit of analysis, comparing Cochrane and non-Cochrane reviews. Using meta-analyses from the cardiovascular literature, we identified pairs that matched on intervention and outcome. The pairs were contrasted in terms of how frequently results disagreed between the Cochrane and non-Cochrane reviews, whether effect sizes and statistical precision differed systematically, and how these differences related to the frequency of secondary citations of those reviews.
RESULTS: Our search yielded 40 matched pairs of reviews. The two sets were similar in terms of which was first to publication, how many studies were included, and average sample sizes. The paired reviews included a total of 344 individual clinical trials: 111 (32.3%) studies were included only in a Cochrane review, 104 (30.2%) only in a non-Cochrane review, and 129 (37.5%) in both. Stated another way, 62.5% of studies were only included in one or the other meta-analytic literature. Overall, 37.5% of pairs had discrepant results. The most common involved shifts in the width of 95% confidence intervals that would yield a different statistical interpretation of the significance of results (7 pairs). Additionally, 20% differed in the direction of the summary effect size (5 pairs) or reported greater than a 2-fold difference in its magnitude (3 pairs). Non-Cochrane reviews reported significantly higher effect sizes (P < 0.001) and lower precision (P < 0.001) than matched Cochrane reviews. Reviews reporting an effect size at least 2-fold greater than their matched pair were cited more frequently.
CONCLUSIONS: Though results between topic-matched Cochrane and non-Cochrane reviews were quite similar, discrepant results were frequent, and the overlap of included studies was surprisingly low. Non-Cochrane reviews report larger effect sizes with lower precision than Cochrane reviews, indicating systematic differences, likely reflective of methodology, between the two types of reviews that could generate different interpretations of the interventions under question
Mechanical cell-matrix feedback explains pairwise and collective endothelial cell behavior in vitro
In vitro cultures of endothelial cells are a widely used model system of the
collective behavior of endothelial cells during vasculogenesis and
angiogenesis. When seeded in an extracellular matrix, endothelial cells can
form blood vessel-like structures, including vascular networks and sprouts.
Endothelial morphogenesis depends on a large number of chemical and mechanical
factors, including the compliancy of the extracellular matrix, the available
growth factors, the adhesion of cells to the extracellular matrix, cell-cell
signaling, etc. Although various computational models have been proposed to
explain the role of each of these biochemical and biomechanical effects, the
understanding of the mechanisms underlying in vitro angiogenesis is still
incomplete. Most explanations focus on predicting the whole vascular network or
sprout from the underlying cell behavior, and do not check if the same model
also correctly captures the intermediate scale: the pairwise cell-cell
interactions or single cell responses to ECM mechanics. Here we show, using a
hybrid cellular Potts and finite element computational model, that a single set
of biologically plausible rules describing (a) the contractile forces that
endothelial cells exert on the ECM, (b) the resulting strains in the
extracellular matrix, and (c) the cellular response to the strains, suffices
for reproducing the behavior of individual endothelial cells and the
interactions of endothelial cell pairs in compliant matrices. With the same set
of rules, the model also reproduces network formation from scattered cells, and
sprouting from endothelial spheroids. Combining the present mechanical model
with aspects of previously proposed mechanical and chemical models may lead to
a more complete understanding of in vitro angiogenesis.Comment: 25 pages, 6 figures, accepted for publication in PLoS Computational
Biolog
The RASSCALS: An X-ray and Optical Study of 260 Galaxy Groups
We describe the ROSAT All-Sky Survey-Center for Astrophysics Loose Systems
(RASSCALS), the largest X-ray and optical survey of low mass galaxy groups to
date. We draw 260 groups from the combined Center for Astrophysics and Southern
Sky Redshift Surveys, covering one quarter of the sky to a limiting Zwicky
magnitude of 15.5. We detect 61 groups (23%) as extended X-ray sources.
The statistical completeness of the sample allows us to make the first
measurement of the X-ray selection function of groups, along with a clean
determination of their fundamental scaling laws. We find robust evidence of
similarity breaking in the relationship between the X-ray luminosity and
velocity dispersion. Groups with sigma < 340 km/s are overluminous by several
orders of magnitude compared to the familiar LX ~ sigma^4 law for higher
velocity dispersion systems. An understanding of this break depends on the
detailed structure of groups with small velocity dispersions sigma < 150 km/s.Comment: 16 pages, including 6 figures. To appear in The Astrophysical Journa
Error Propagation Analysis in the SAE Architecture Analysis and Design Language (AADL) and the EDICT Tool Framework
This report documents the capabilities of the EDICT tools for error modeling and error propagation analysis when operating with models defined in the Architecture Analysis & Design Language (AADL). We discuss our experience using the EDICT error analysis capabilities on a model of the Scalable Processor-Independent Design for Enhanced Reliability (SPIDER) architecture that uses the Reliable Optical Bus (ROBUS). Based on these experiences we draw some initial conclusions about model based design techniques for error modeling and analysis of highly reliable computing architectures
On the Origin of the Eccentricities of Extrasolar Planets
We develop a phenomenological theory that aims to account for the origin of
the large eccentricities of extrasolar planets and that of the small
eccentricities in the solar system, the preference for apsidal alignment in
non-resonant multiplanet systems, and the origin of the similarities in the
eccentricity distribution of extra-solar planets and that of spectroscopic
binary stars. We show that if a physical process is weakly dependent on the
local dynamics of the companion and imparts a small relative acceleration to
the star-companion system, the eccentricity of the companion's orbit is excited
to large values depending on the direction and duration of acceleration. A
natural candidate for such processes are asymmetric stellar jets and star-disk
winds. When the acceleration originates from a precessing jet, large
eccentricities can be excited by the resonance of the jet's precession
frequency with the induced acceleration's excitation frequency even for nearly
perpendicular jets. Precession also reduces the eccentricity amplitude far
inside the resonance radius. The acceleration's strength is best constrained in
multiplanet systems because of the companions' mutual gravitational
perturbations, while the acceleration's duration is bounded by the condition
that the residual velocity imparted to the star is smaller than the stellar
velocity dispersion in the Galaxy. In the outer parts of the star-companion
system where the acceleration excitation time is comparable to or smaller than
the orbital period, significant radial migration takes place which may have
important consequences for the dynamics of the minor body populations in the
solar system. The theory is illustrated with the Andromedae binary
system.Comment: 41 pages, 14 figures, accepted for publication in the Astronomical
Journa
Do HIV treatment eligibility expansions crowd out the sickest? Evidence from rural South Africa
OBJECTIVE: The 2015 WHO recommendation to initiate all HIV patients on antiretroviral therapy (ART) at diagnosis could potentially overextend health systems and crowd out sicker patients, mitigating the policy's impact. We evaluate whether South Africa's prior eligibility expansion from CD4 ≤200 to CD4 ≤350 cells/μL reduced ART uptake in the sickest patients. METHODS: Using data on all patients presenting to the Hlabisa HIV Treatment and Care Program in KwaZulu-Natal from April 2010 - June 2012 (n=13,809), we assessed the impact of the August 2011 eligibility expansion on the number of patients seeking care, number initiating ART, and time from HIV diagnosis to ART initiation among patients always eligible (CD4 0-200), newly eligible (CD4 201-350), and not yet eligible by CD4 count (>350). We used interrupted time series methods to control for long-run trends and isolate the effect of the policy. RESULTS: Expanding ART eligibility led to an increased number of patients initiating ART per month [+95.5; 95% CI (-1.3; 192.3)]. Newly eligible patients (CD4 201-350) initiated treatment 47% faster than before (95% CI 19%; 82%), while the sickest patients (CD4 ≤200) saw no decline in the monthly number of patients initiating treatment or the rate of treatment uptake. CONCLUSION: The Hlabisa program successfully extended ART to patients with CD4 ≤350 cells/μL, while ensuring that the sickest patients did not experience delays in ART initiation. Treatment programs must be vigilant to maintain quality of care for the sickest as countries move to treat all patients irrespective of CD4 count. This article is protected by copyright. All rights reserved
HeI 1.083 micron emission and absorption in DG Tau: line excitation in jet, hot wind, and accretion flow
We present long-slit spectroscopy and spectro-astrometry of HeI 1.083 micron
emission in the T Tauri star, DG Tau. We identify three components in the HeI
feature: (1) a blueshifted emission component atv -200 km s^-1, (2) a bright
emission component at zero-velocity with a FWZI of ~500 km s^-1, and (3) a
blueshifted absorption feature at velocities between -250 and -500 km s^-1. The
position and velocity of the blueshifted HeI emission coincide with a
high-velocity component (HVC) of the [FeII] 1.257 micron emission, which arises
from a jet within an arcsecond of the star. The presence of such a high
excitation line (excitation energy ~ 20 eV) within the jet supports the
scenario of shock heating. The bright HeI component does not show any spatial
extension, and it is likely to arise from magnetospheric accretion columns.
The blueshifted absorption shows greater velocities than that in H-alpha,
suggesting that these absorption features arise from the accelerating wind
close to the star.Comment: 10 pages including 2 figures, accepted for publication in the
Astrophysical Journal Letter
Detection of Excercise-Induced Ischemia by Measurement of NT-proBNP
Electrocardiographic exercise testing is the most widely used non-invasive screening test for coronary artery disease (CAD); however, both positive and negative predictive values for this procedure are hampered by relatively low sensitivity and specificity, leading to significant numbers of false negative and false positive studies. We hypothesized that NT-proBNP, a Neuro hormone secreted by cardiac myocytes in the ventricular wall in response to increased wall stress, would rise as a result of exercise-induced ischemia. If this were true, the enhancement of exercise testing by analysis of this plasma biomarker may offer significant improvement in the diagnostic accuracy of this procedure
- …