5,921 research outputs found
The bias-extension test for the analysis of in-plane shear properties of textile composite reinforcements and prepregs: a review
The bias-extension test is a rather simple experiment aiming to determine in-plane shear properties of textile composite reinforcements. However the mechanics during the test involves fibrous material at large shear strains and large rotations of the fibres. Several aspects are still being studied and are not yet modeled in a consensual manner. The standard analysis of the test is based on two assumptions: inextensibility of the fibers and rotations at the yarn crossovers without slippage. They lead to the development of zones with constant fibre orientations proper to the bias-extension test. Beyond the analysis of the test within these basic assumptions, the paper presents studies that have been carried out on the lack of verification of these hypothesis (slippage, tension in the yarns, effects of fibre bending). The effects of temperature, mesoscopic modeling and tension locking are also considered in the case of the bias-extension test
Dependence of the Fundamental Plane Scatter on Galaxy Age
The fundamental plane (FP) has an intrinsic scatter that can not be explained
purely by observational errors. Using recently available age estimates for
nearby early type galaxies, we show that a galaxy's position relative to the FP
depends on its age. In particular, the mean FP corresponds to ellipticals with
an age of ~10 Gyr. Younger galaxies are systematically brighter with higher
surface brightness relative to the mean relation. Old ellipticals form an
`upper envelope' to the FP. For our sample of mostly non-cluster galaxies, age
can account for almost half of the scatter in the B band FP. Distance
determinations based on the FP may have a systematic bias, if the mean age of
the sample varies with redshift.
We also show that fundamental plane residuals, B-V colors and Mg_2 line
strength are consistent with an ageing central burst superposed on an old
stellar population. This reinforces the view that these age estimates are
tracing the last major episode of star formation induced by a gaseous merger
event. We briefly discuss the empirical `evolutionary tracks' of
merger-remnants and young ellipticals in terms of their key observational
parameters.Comment: 14 pages, Latex, 2 figures, accepted by ApJ Letter
Probing the Super Star Cluster Environment of NGC 1569 Using FISICA
We present near-IR JH spectra of the central regions of the dwarf starburst
galaxy NGC 1569 using the Florida Image Slicer for Infrared Cosmology and
Astrophysics (FISICA). The dust-penetrating properties and available spectral
features of the near-IR, combined with the integral field unit (IFU) capability
to take spectra of a field, make FISICA an ideal tool for this work. We use the
prominent [He I] (1.083\mu m) and Pa\beta (1.282 \mu m) lines to probe the
dense star forming regions as well as characterize the general star forming
environment around the super star clusters (SSCs) in NGC 1569. We find [He I]
coincident with CO clouds to the north and west of the SSCs, which provides the
first, conclusive evidence for embedded star clusters here.Comment: 6 pages, 3 figures, accepted for publication in the MNRA
Comparing Strategies to Prevent Stroke and Ischemic Heart Disease in the Tunisian Population: Markov Modeling Approach Using a Comprehensive Sensitivity Analysis Algorithm.
Background. Mathematical models offer the potential to analyze and compare the effectiveness of very different interventions to prevent future cardiovascular disease. We developed a comprehensive Markov model to assess the impact of three interventions to reduce ischemic heart diseases (IHD) and stroke deaths: (i) improved medical treatments in acute phase, (ii) secondary prevention by increasing the uptake of statins, (iii) primary prevention using health promotion to reduce dietary salt consumption. Methods. We developed and validated a Markov model for the Tunisian population aged 35–94 years old over a 20-year time horizon. We compared the impact of specific treatments for stroke, lifestyle, and primary prevention on both IHD and stroke deaths. We then undertook extensive sensitivity analyses using both a probabilistic multivariate approach and simple linear regression (metamodeling). Results. The model forecast a dramatic mortality rise, with 111,134 IHD and stroke deaths (95% CI 106567 to 115048) predicted in 2025 in Tunisia. The salt reduction offered the potentially most powerful preventive intervention that might reduce IHD and stroke deaths by 27% (−30240 [−30580 to −29900]) compared with 1% for medical strategies and 3% for secondary prevention. The metamodeling highlighted that the initial development of a minor stroke substantially increased the subsequent probability of a fatal stroke or IHD death. Conclusions. The primary prevention of cardiovascular disease via a reduction in dietary salt consumption appeared much more effective than secondary or tertiary prevention approaches. Our simple but comprehensive model offers a potentially attractive methodological approach that might now be extended and replicated in other contexts and populations
Symbiotic Stars in OGLE Data I. Large Magellanic Cloud Systems
Symbiotic stars are long-orbital-period interacting-binaries characterized by
extended emission over the whole electromagnetic range and by complex
photometric and spectroscopic variability. In this paper, the first of a
series, we present OGLE light curves of all the confirmed symbiotic stars in
the Large Magellanic Cloud, with one exception. By careful visual inspection
and combined time-series analysis techniques, we investigate for the first time
in a systematic way the photometric properties of these astrophysical objects,
trying in particular to distinguish the nature of the cool component (e.g.,
Semi-Regular Variable vs. OGLE Small-Amplitude Red Giant), to provide its
first-order pulsational ephemerides, and to link all this information with the
physical parameters of the binary system as a whole. Among the most interesting
results, there is the discovery of a 20-year-long steady fading of Sanduleak's
star, a peculiar symbiotic star known to produce the largest stellar jet ever
discovered. We discuss by means of direct examples the crucial need for
long-term multi-band observations to get a real understanding of symbiotic and
other interacting binary stars. We eventually introduce BOMBOLO, a multi-band
simultaneous imager for the SOAR 4m Telescope, whose design and construction we
are currently leading.Comment: 16 pages, 4 Tables, 12 Figures. Accepted for publication in MNRA
The Stellar Population Histories of Early-Type Galaxies. II. Controlling Parameters of the Stellar Populations
We analyze single-stellar-population (SSP) equivalent parameters for 50 local
elliptical galaxies as a function of their structural parameters. These
galaxies fill a two-dimensional plane in the four-dimensional space of [Z/H],
log t, log , and [E/Fe]. SSP age and velocity dispersion can be taken
as the two independent parameters that specify a galaxy's location in this
``hyperplane.'' The hyperplane can be decomposed into two sub-relations: (1) a
``Z-plane,'' in which [Z/H] is a linear function of log and log t; and
(2) a relation between [E/Fe] and in which [E/Fe] is larger in
high- galaxies. Cluster and field ellipticals follow the same
hyperplane, but their (,t) distributions within it differ. Nearly all
cluster galaxies are old; the field ellipticals span a large range in SSP age.
The tight Mg-- relations of these ellipticals can be understood as
two-dimensional projections of the metallicity hyperplane showing it edge-on;
the tightness of these relations does not necessarily imply a narrow range of
ages at fixed . The relation between [E/Fe] and is consistent
with a higher effective yield of Type II SNe elements at higher . The
Z-plane is harder to explain and may be a powerful clue to star formation in
elliptical galaxies if it proves to be general. Present data favor a
``frosting'' model in which low apparent SSP ages are produced by adding a
small frosting of younger stars to an older base population. If the frosting
abundances are close to or slightly greater than the base population, simple
two-component models run along lines of constant in the Z-plane, as
required. This favors star formation from well-mixed pre-enriched gas rather
than unmixed low-metallicity gas from an accreted object. (Abridged)Comment: To be published in the June 2000 issue of the Astronomical Journal.
28 pages, 13 figures, uses emulateap
Structure of the Yersinia pestis tip protein LcrV refined to 1.65 A resolution
This is the publisher's version, also available electronically from http://scripts.iucr.org/cgi-bin/paper?S1744309113008579.The human pathogen Yersinia pestis requires the assembly of the type III secretion system (T3SS) for virulence. The structural component of the T3SS contains an external needle and a tip complex, which is formed by LcrV in Y. pestis. The structure of an LcrV triple mutant (K40A/D41A/K42A) in a C273S background has previously been reported to 2.2 Ã… resolution. Here, the crystal structure of LcrV without the triple mutation in a C273S background is reported at a higher resolution of 1.65 Ã…. Overall the two structures are similar, but there are also notable differences, particularly near the site of the triple mutation. The refined structure revealed a slight shift in the backbone positions of residues Gly28-Asn43 and displayed electron density in the loop region consisting of residues Ile46-Val63, which was disordered in the original structure. In addition, the helical turn region spanning residues Tyr77-Gln95 adopts a different orientation
Worldline master formulas for the dressed electron propagator. Part 2. On-shell amplitudes
In the first part of this series, we employed the second-order formalism and the \u201csymbol\u201d map to construct a particle path-integral representation of the electron propagator in a background electromagnetic field, suitable for open fermion-line calculations. Its main advantages are the avoidance of long products of Dirac matrices, and its ability to unify whole sets of Feynman diagrams related by permutation of photon legs along the fermion lines. We obtained a Bern-Kosower type master formula for the fermion propagator, dressed with N photons, in terms of the \u201cN-photon kernel,\u201d where this kernel appears also in \u201csubleading\u201d terms involving only N 12 1 of the N photons. In this sequel, we focus on the application of the formalism to the calculation of on-shell amplitudes and cross sections. Universal formulas are obtained for the fully polarised matrix elements of the fermion propagator dressed with an arbitrary number of photons, as well as for the corresponding spin-averaged cross sections. A major simplification of the on-shell case is that the subleading terms drop out, but we also pinpoint other, less obvious simplifications. We use integration by parts to achieve manifest transversality of these amplitudes at the integrand level and exploit this property using the spinor helicity technique. We give a simple proof of the vanishing of the matrix element for \u201call +\u201d photon helicities in the massless case, and find a novel relation between the scalar and spinor spin-averaged cross sections in the massive case. Testing the formalism on the standard linear Compton scattering process, we find that it reproduces the known results with remarkable efficiency. Further applications and generalisations are pointed out
Characteristics and monetary compensation of caregivers for patients with rheumatic conditions
Musculoskeletal disorders (MD) are highly prevalent conditions that affect quality of life. MD cause physical and psychological dependence. Usually, the care of a patient with MD is assumed by a caregiver. The aim of this study was to describe the sociodemographic characteristics and the monetary remuneration associated to the care of a patient with MD. A cross sectional study was carried out in order to estimate the monetary remuneration related to the health care of patients with MD. A survey was applied to caregivers of patients with MD. Demographic data was collected. We asked about the relationship with the patient, the time as a caregiver and all data related to the monetary compensation. Descriptive epidemiology was done. We reported monetary data in American Dollars (USD) using the average exchange rate for 2018. We surveyed 132 caregivers. Mean age was 52 years [standard deviation 19], 72% were women, 78% were taking care of a patient with rheumatoid arthritis, 12% osteoarthrosis 2% lupus, and 2% osteoporosis. The remaining 6% were caregivers of patients with ankylosing spondylitis, fibromyalgia and Sjogren syndrome. Regarding the time as a caregiver, 48% had less than a year, 16% between two and three years, 18% more than three years, 13% more than four years, and 5% were temporarily caregivers. In our study, 85% of caregivers were a family member, while 15% a nurse or a non-related person. Regarding the compensation, 97% did not receive any salary or payment for being caregiver, the remaining 3% received between 265 and 530 USD per month. Our study demonstrated that the care for patients with MD is mainly assumed by family members. Our results agree with other studies in chronic conditions where only a small proportion of caregivers is paid. Caregivers should be considered for the health system
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