5,315 research outputs found
The systemic velocities of four long-period cataclysmic variable stars
Although a large number of orbital periods of cataclysmic variable stars
(CVs) have been measured, comparison of period and luminosity distributions
with evolutionary theory is affected by strong selection effects. A test has
been discovered which is independent of these selection effects and is based
upon the kinematics of CVs (Kolb & Stehle, 1996). If the standard models of
evolution are correct then long-period (P_orb > 5 hrs) CVs should be typically
less than 1.5 Gyr old, and their line-of-sight velocity dispersion
() should be small. We present results from a pilot study which
indicate that this postulate is indeed true. Four long-period dwarf novae (EM
Cyg, V426 Oph, SS Cyg and AH Her) were observed over a complete orbit, in order
that accurate radial velocities be obtained. We find values of -1.7, 5.4, 15.4
and 1.8 km/s with uncertainties of order 3 km/s, referred to the dynamical
Local Standard of Rest (LSR), leading to a dispersion of ~ 8 km/s. Calculation
of a 95 per cent confidence interval gives the result 4 < \sigma_\gamma < 28
km/s compared to a prediction of 15 km/s. We also have an improved
determination of mass donor spectral type, K_2 and q for the four systems.Comment: To appear in MNRA
Quantifying the prediction accuracy of a 1-D SVAT model at a range of ecosystems in the USA and Australia: evidence towards its use as a tool to study Earth's system interactions
This paper describes the validation of the SimSphere SVAT (Soil–Vegetation–Atmosphere Transfer) model conducted at
a range of US and
Australian ecosystem types. Specific focus was given to examining the models' ability
in predicting shortwave incoming solar radiation (Rg), net radiation
(Rnet), latent heat (LE), sensible heat (H), air temperature at 1.3 m
(Tair 1.3 m) and air temperature at 50 m (Tair 50 m). Model
predictions were compared against corresponding in situ measurements acquired for a
total of 72 selected days of the year 2011 obtained from eight sites belonging
to the AmeriFlux (USA) and OzFlux (Australia) monitoring networks. Selected
sites were representative of a variety of environmental, biome and climatic
conditions, to allow for the inclusion of contrasting conditions in the
model evaluation.
Overall, results showed a good agreement between the model predictions and
the in situ measurements, particularly so for the Rg, Rnet, Tair
1.3 m and Tair 50 m parameters. The simulated Rg parameter exhibited
a root mean square deviation (RMSD) within 25 % of the observed fluxes for
58 of the 72 selected days, whereas an RMSD within
~ 24 % of the observed fluxes was reported for the Rnet
parameter for all days of study (RMSD = 58.69 W m−2). A systematic
underestimation of Rg and Rnet (mean bias error (MBE) = −19.48
and −16.46 W m−2) was also found. Simulations for the
Tair 1.3 m and Tair 50 m showed good agreement with the
in situ observations, exhibiting RMSDs of 3.23 and
3.77 °C (within ~ 15 and ~ 18 %
of the observed) for all days of analysis, respectively. Comparable, yet
slightly less satisfactory simulation accuracies were exhibited for the H
and LE parameters (RMSDs = 38.47 and 55.06 W m−2, ~ 34 and ~ 28 % of the
observed). Highest simulation accuracies were obtained for the open woodland
savannah and mulga woodland sites for most of the compared parameters.
The Nash–Sutcliffe efficiency index for all parameters ranges from 0.720 to
0.998, suggesting a very good model representation of the observations.
To our knowledge, this study presents the most detailed evaluation of
SimSphere done so far, and the first validation of it conducted
in Australian ecosystem types. Findings are important and timely, given the
expanding use of the model both as an educational and research tool today.
This includes ongoing research by different space agencies examining its
synergistic use with Earth observation data towards the development of
global operational products
Incidence of diabetic retinopathy in people with type 2 diabetes mellitus attending the Diabetic Retinopathy Screening Service for Wales: retrospective analysis
Objectives To determine the incidence of any and referable diabetic retinopathy in people with type 2 diabetes mellitus attending an annual screening service for retinopathy and whose first screening episode indicated no evidence of retinopathy
Interactions between vaccinia virus and sensitized macrophages in vitro
The action of peritoneal exudate cells (PEC) from normal and vaccinia virus infected mice on infectious vaccinia virus particles was investigatedin vitro. PEC from immune mice showed a significantly higher infectivity titre reduction (virus clearance, VC) than normal cells. This effect could be clearly attributed to the macrophage. Vaccinia virus multiplied in PEC from normal animals while there was no virus propagation in cells from immunized mice. The release of adsorbed or engulfed virus was reduced significantly in PEC from immunized animals. Anti-vaccinia-antibodies seem to activate normal macrophages to increased virus clearance. This stimulating effect was demonstrable only in the IgG fraction of the antiserum.
The activity of macrophages from mice injected three times over a period of 14 days with vaccinia virus could be entirely blocked with anti-mouse-IgG, while PEC from mice injected one time six days previously were not inhibited
The Thermonuclear Explosion Of Chandrasekhar Mass White Dwarfs
The flame born in the deep interior of a white dwarf that becomes a Type Ia
supernova is subject to several instabilities. We briefly review these
instabilities and the corresponding flame acceleration. We discuss the
conditions necessary for each of the currently proposed explosion mechanisms
and the attendant uncertainties. A grid of critical masses for detonation in
the range - g cm is calculated and its
sensitivity to composition explored. Prompt detonations are physically
improbable and appear unlikely on observational grounds. Simple deflagrations
require some means of boosting the flame speed beyond what currently exists in
the literature. ``Active turbulent combustion'' and multi-point ignition are
presented as two plausible ways of doing this. A deflagration that moves at the
``Sharp-Wheeler'' speed, , is calculated in one dimension
and shows that a healthy explosion is possible in a simple deflagration if the
front moves with the speed of the fastest floating bubbles. The relevance of
the transition to the ``distributed burning regime'' is discussed for delayed
detonations. No model emerges without difficulties, but detonation in the
distributed regime is plausible, will produce intermediate mass elements, and
warrants further study.Comment: 28 pages, 4 figures included, uses aaspp4.sty. Submitted to Ap
A survey on parallel and distributed Multi-Agent Systems
International audienceSimulation has become an indispensable tool for researchers to explore systems without having recourse to real experiments. Depending on the characteristics of the modeled system, methods used to represent the system may vary. Multi-agent systems are, thus, often used to model and simulate complex systems. Whatever modeling type used, increasing the size and the precision of the model increases the amount of computation, requiring the use of parallel systems when it becomes too large. In this paper, we focus on parallel platforms that support multi-agent simulations. Our contribution is a survey on existing platforms and their evaluation in the context of high performance computing. We present a qualitative analysis, mainly based on platform properties, then a performance comparison using the same agent model implemented on each platform
Diabetic Retinopathy in Newly Diagnosed Subjects With Type 2 Diabetes Mellitus: Contribution of β-Cell Function
Purpose: The association of hyperglycemia and diabetic retinopathy (DR) in established type 2 diabetes mellitus (T2DM) subjects is well accepted. However, the association between β-cell responsiveness and insulin sensitivity leading to fasting and postprandial hyperglycemia with DR in newly diagnosed treatment-naïve T2DM subjects remain unreported. Methods: A total of 544 newly diagnosed treatment-naïve T2DM subjects were screened for DR (digital photography) and underwent a standardized meal tolerance test. Serial plasma glucose and insulin levels were measured, and fasting (M0) and postprandial β-cell responsiveness calculated Calculating Pancreatic Response Program along with homeostasis model assessment-β cell function (HOMA-B) and HOMA-Insulin Sensitivity. A subgroup of 201 subjects also underwent a frequently sampled IV glucose tolerance test and the acute insulin response to glucose, insulin sensitivity, and glucose effectiveness (SG) estimated (MINMOD model). Results: A total of 16.5% (90) subjects had DR at diagnosis. Subjects with DR had significantly reduced M0, HOMA-B and SG leading to higher fasting and postprandial (2 hour) glucose and significantly lower fasting and postprandial (2 hour) insulin. Factors independently associated with DR in multivariate logistic regression analysis were M0, HOMA-B, and SG with fasting and postprandial (2 hour) glucose and insulin. There was no statistical difference in glycated hemoglobin, systolic blood pressure, acute insulin response to glucose, and insulin sensitivity between those with or without DR. Principal Conclusions: In this cohort of newly diagnosed T2DM subjects, DR is associated with reduced β-cell responsiveness, resulting from β-cell failure rather than insulin resistance, leading to fasting and postprandial hyperglycemia and hypoinsulinemi
Contribution of extracellular negatively charged residues to ATP action and zinc modulation of rat P2X 2 receptors
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65506/1/j.1471-4159.2008.05228.x.pd
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