524 research outputs found
Hydrogen-Helium Mixtures in the Interiors of Giant Planets
Equilibrium properties of hydrogen-helium mixtures under conditions similar
to the interior of giant gas planets are studied by means of first principle
density functional molecular dynamics simulations. We investigate the molecular
and atomic fluid phase of hydrogen with and without the presence of helium for
densities between gcm and gcm and
temperatures from K to . Helium has a crucial influence on
the ionic and electronic structure of the liquid. Hydrogen molecule bonds are
shortened as well as strengthened which leads to more stable hydrogen molecules
compared to pure hydrogen for the same thermodynamic conditions. The {\it ab
initio} treatment of the mixture enables us to investigate the validity of the
widely used linear mixing approximation. We find deviations of up to 8% in
energy and volume from linear mixing at constant pressure in the region of
molecular dissociation.Comment: 13 pages, 18 figures, submitted to PR
Twin Neural Network Regression is a Semi-Supervised Regression Algorithm
Twin neural network regression (TNNR) is a semi-supervised regression
algorithm, it can be trained on unlabelled data points as long as other,
labelled anchor data points, are present. TNNR is trained to predict
differences between the target values of two different data points rather than
the targets themselves. By ensembling predicted differences between the targets
of an unseen data point and all training data points, it is possible to obtain
a very accurate prediction for the original regression problem. Since any loop
of predicted differences should sum to zero, loops can be supplied to the
training data, even if the data points themselves within loops are unlabelled.
Semi-supervised training improves TNNR performance, which is already state of
the art, significantly
The Calibration of the HST Kuiper Belt Object Search: Setting the Record Straight
The limiting magnitude of the HST data set used by Cochran et al. (1995) to
detect small objects in the Kuiper belt is reevaluated, and the methods used
are described in detail. It is shown, by implanting artificial objects in the
original HST images, and re-reducing the images using our original algorithm,
that the limiting magnitude of our images (as defined by the 50% detectability
limit) is . This value is statistically the same as the value found in
the original analysis. We find that of the moving Kuiper belt objects
with are detected when trailing losses are included. In the same data
in which these faint objects are detected, we find that the number of false
detections brighter than is less than one per WFPC2 image. We show
that, primarily due to a zero-point calibration error, but partly due to
inadequacies in modeling the HST'S data noise characteristics and Cochran et
al.'s reduction techniques, Brown et al. 1997 underestimate the SNR of objects
in the HST dataset by over a factor of 2, and their conclusions are therefore
invalid.Comment: Accepted to ApJ Letters; 10 pages plus 3 figures, LaTe
Twin Neural Network Regression
We introduce twin neural network (TNN) regression. This method predicts
differences between the target values of two different data points rather than
the targets themselves. The solution of a traditional regression problem is
then obtained by averaging over an ensemble of all predicted differences
between the targets of an unseen data point and all training data points.
Whereas ensembles are normally costly to produce, TNN regression intrinsically
creates an ensemble of predictions of twice the size of the training set while
only training a single neural network. Since ensembles have been shown to be
more accurate than single models this property naturally transfers to TNN
regression. We show that TNNs are able to compete or yield more accurate
predictions for different data sets, compared to other state-of-the-art
methods. Furthermore, TNN regression is constrained by self-consistency
conditions. We find that the violation of these conditions provides an estimate
for the prediction uncertainty
CaractĂ©ristiques des mĂ©decins prescrivant des psychotropes davantage aux femmes quâaux hommes
Les différences observées dans l'état de santé et l'utilisation des services médicaux, selon le sexe, se sont avérées insuffisantes pour expliquer une plus grande consommation de psychotropes chez les femmes que chez les hommes dans les pays industrialisés. Nous avons testé l'hypothÚse selon laquelle les habitudes de prescription des médecins expliquent une partie importante de cette observation. Nous démontrons, à l'aide des données de la Régie de l'assurance-maladie du Québec pour les personnes ùgées de 65 ans et plus, que le profil socio-démographique et le style de gestion des médecins prescripteurs sont associés de façon significative au pourcentage d'hommes et de femmes ayant obtenu une ordonnance de psychotrope dans leurs pratiques.In industrialized countries, gender differences observed in health condition and the use of medical services appear insufficient to explain a greater consumption of psychotropic drugs in women than men. The authors have tested the hypothesis that physician prescribing patterns largely explains this observation. They demonstrate, using data from the Régie de l'assurance maladie du Québec for people aged 65 and over, that physicians' sociodemographic and practice characteristics are significantly associated with the percentage of men and women who receive a psychotropic drug prescription in their practice
The Resolved Asteroid Program - Size, shape, and pole of (52) Europa
With the adaptive optics (AO) system on the 10 m Keck-II telescope, we
acquired a high quality set of 84 images at 14 epochs of asteroid (52) Europa
on 2005 January 20. The epochs covered its rotation period and, by following
its changing shape and orientation on the plane of sky, we obtained its
triaxial ellipsoid dimensions and spin pole location. An independent
determination from images at three epochs obtained in 2007 is in good agreement
with these results. By combining these two data sets, along with a single epoch
data set obtained in 2003, we have derived a global fit for (52) Europa of
diameters (379x330x249) +/- (16x8x10) km, yielding a volume-equivalent
spherical-diameter of 315 +/- 7 km, and a rotational pole within 7 deg of [RA;
Dec] = [257,+12] in an Equatorial J2000 reference frame (ECJ2000: 255,+35).
Using the average of all mass determinations available forEuropa, we derive a
density of 1.5 +/- 0.4, typical of C-type asteroids. Comparing our images with
the shape model of Michalowski et al. (A&A 416, 2004), derived from optical
lightcurves, illustrates excellent agreement, although several edge features
visible in the images are not rendered by the model. We therefore derived a
complete 3-D description of Europa's shape using the KOALA algorithm by
combining our imaging epochs with 4 stellar occultations and 49 lightcurves. We
use this 3-D shape model to assess these departures from ellipsoidal shape.
Flat facets (possible giant craters) appear to be less distinct on (52) Europa
than on other C-types that have been imaged in detail. We show that fewer giant
craters, or smaller craters, is consistent with its expected impact history.
Overall, asteroid (52) Europa is still well modeled as a smooth triaxial
ellipsoid with dimensions constrained by observations obtained over several
apparitions.Comment: Accepted for publication in Icaru
Association between risk factors for injurious falls and new benzodiazepine prescribing in elderly persons
<p>Abstract</p> <p>Background</p> <p>Benzodiazepines are frequently prescribed to elderly patients' despite concerns about adverse effects leading to injurious falls. Previous studies have not investigated the extent to which patients with pre-existing risk factors for falls are prescribed benzodiazepines. The objective of this study is to assess if some of the risk factors for falls are associated with new benzodiazepine prescriptions in elderly persons.</p> <p>Methods</p> <p>Using provincial administrative databases, elderly Quebec residents were screened in 1989 for benzodiazepine use and non-users were followed for up to 5 years. Logistic regression models were used to evaluate potential predictors of new benzodiazepine use among patient baseline characteristics.</p> <p>Results</p> <p>In the 252,811 elderly patients who had no benzodiazepine prescription during the baseline year (1989), 174,444 (69%) never filled a benzodiazepine prescription and 78,367 (31%) filled at least one benzodiazepine prescription. In the adjusted analysis, several risk factors for falls were associated with statistically significant increases in the risk of receiving a new benzodiazepine prescription including the number of prescribing physicians seen at baseline (OR: 1.12; 95% CI 1.11â1.13), being female (OR: 1.20; 95% CI 1.18â1.22) or a diagnosis of arthritis (OR: 1.11; 95% CI 1.09â1.14), depression (OR: 1.42; 95% CI 1.35â1.49) or alcohol abuse (OR: 1.24; 95% CI 1.05â1.46). The strongest predictor for starting a benzodiazepine was the use of other medications, particularly anti-depressants (OR: 1.85; 95% CI 1.75â1.95).</p> <p>Conclusion</p> <p>Patients with pre-existing conditions that increase the risk of injurious falls are significantly more likely to receive a new prescription for a benzodiazepine. The strength of the association between previous medication use and new benzodiazepine prescriptions highlights an important medication safety issue.</p
Assessing the accuracy of an inter-institutional automated patient-specific health problem list
<p>Abstract</p> <p>Background</p> <p>Health problem lists are a key component of electronic health records and are instrumental in the development of decision-support systems that encourage best practices and optimal patient safety. Most health problem lists require initial clinical information to be entered manually and few integrate information across care providers and institutions. This study assesses the accuracy of a novel approach to create an inter-institutional automated health problem list in a computerized medical record (MOXXI) that integrates three sources of information for an individual patient: diagnostic codes from medical services claims from all treating physicians, therapeutic indications from electronic prescriptions, and single-indication drugs.</p> <p>Methods</p> <p>Data for this study were obtained from 121 general practitioners and all medical services provided for 22,248 of their patients. At the opening of a patient's file, all health problems detected through medical service utilization or single-indication drug use were flagged to the physician in the MOXXI system. Each new arising health problem were presented as 'potential' and physicians were prompted to specify if the health problem was valid (Y) or not (N) or if they preferred to reassess its validity at a later time.</p> <p>Results</p> <p>A total of 263,527 health problems, representing 891 unique problems, were identified for the group of 22,248 patients. Medical services claims contributed to the majority of problems identified (77%), followed by therapeutic indications from electronic prescriptions (14%), and single-indication drugs (9%). Physicians actively chose to assess 41.7% (n = 106,950) of health problems. Overall, 73% of the problems assessed were considered valid; 42% originated from medical service diagnostic codes, 11% from single indication drugs, and 47% from prescription indications. Twelve percent of problems identified through other treating physicians were considered valid compared to 28% identified through study physician claims.</p> <p>Conclusion</p> <p>Automation of an inter-institutional problem list added over half of all validated problems to the health problem list of which 12% were generated by conditions treated by other physicians. Automating the integration of existing information sources provides timely access to accurate and relevant health problem information. It may also accelerate the uptake and use of electronic medical record systems.</p
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