1,585 research outputs found
Multivariate Nonparametric Estimation of the Pickands Dependence Function using Bernstein Polynomials
Many applications in risk analysis, especially in environmental sciences,
require the estimation of the dependence among multivariate maxima. A way to do
this is by inferring the Pickands dependence function of the underlying
extreme-value copula. A nonparametric estimator is constructed as the sample
equivalent of a multivariate extension of the madogram. Shape constraints on
the family of Pickands dependence functions are taken into account by means of
a representation in terms of a specific type of Bernstein polynomials. The
large-sample theory of the estimator is developed and its finite-sample
performance is evaluated with a simulation study. The approach is illustrated
by analyzing clusters consisting of seven weather stations that have recorded
weekly maxima of hourly rainfall in France from 1993 to 2011
Quantification of the contribution of cardiac and arterial remodeling to hypertension.
The study aim was to quantify the individual and combined contributions of both the arterial system and the heart to systolic blood pressure in hypertension. We assessed the parameters of a heart-arterial model for normotensive control subjects and hypertensive patients with left ventricular adaptation patterns classified as normal, concentric remodeling, concentric hypertrophy, or eccentric hypertrophy. The present simulations show that vascular stiffening alone increases the pulse pressure without increasing systolic blood pressure. It is only in combination with an increased peripheral resistance that arterial stiffening leads to systolic hypertension in concentric remodeling and concentric hypertrophy. The contribution of cardiac pump function to the increase in blood pressure depends on cardiac remodeling, hypertrophy, or both. In hypertensive patients with a normal left ventricle, the heart is responsible for 55% of the increase in systolic blood pressure. In concentric remodeling, concentric hypertrophy, and eccentric hypertrophy, the cardiac contribution to the increase in systolic blood pressure is 21%, 65%, and 108%, respectively. We conclude that along with arterial changes, cardiac remodeling and hypertrophy contribute to hypertension
On the use of mass-conserving wind fields in chemistry-transport models
A new method has been developed that provides mass-conserving wind fields for global chemistry-transport models. In previous global Eulerian modeling studies a mass-imbalance was found between the model mass transport and the surface pressure tendencies. Several methods have been suggested to correct for this imbalance, but so far no satisfactory solution has been found. Our new method solves these problems by using the wind fields in a spherical harmonical form (divergence and vorticity) by mimicing the physics of the weather forecast model as closely as possible. A 3-D chemistry-transport model was used to show that the calculated ozone fields with the new processing method agree remarkably better with ozone observations in the upper troposphere and lower stratosphere. In addition, the calculated age of air in the lower stratosphere show better agreement with observations, although the air remains still too young in the extra-tropical stratosphere
Does Self-directedness in Learning and Careers Predict the Employability of Low-Qualified Employees?
Employability has become a key element in sustaining successful vocational careers. The role of self-directedness is considered paramount in maintaining one's employability. However, it also requires certain competences on part of employees to invest in learning and career development. This study examines the influence of self-directedness in learning and career of low-qualified employees on their employability. In a follow-up study of 284 low-qualified employees, we find that higher levels of self-directedness in learning and career of employees corresponds with higher chance to be promoted to higher-level job positions (vertical job mobility). However, no relationship was found between different formats of self-directedness and job retention or horizontal job mobility of lower qualified personnel.</p
A 3D porous media liver lobule model: the importance of vascular septa and anisotropic permeability for homogeneous perfusion
Forces on a boiling bubble in a developing boundary layer, in microgravity with g-jitter and in terrestrial conditions
Terrestrial and microgravity flow boiling experiments were carried out with the same test rig, comprising a locally heated artificial cavity in the center of a channel near the frontal edge of an intrusive glass bubble generator. Bubble shapes were in microgravity generally not far from those of truncated spheres,which permitted the computation of inertial lift and drag from potential flow theory for truncated spheres approximating the actual shape. For these bubbles, inertial lift is counteracted by drag and both forces are of the same order of magnitude as g-jitter. A generalization of the Laplace equation is found which applies to a deforming bubble attached to a plane wall and yields the pressure difference between the hydrostatic pressures in the bubble and at the wall, p. A fully independent way to determine the overpressure p is given by a second Euler-Lagrange equation. Relative differences have been found to be about 5% for both terrestrial and microgravity bubbles. A way is found to determine the sum of the two counteracting major force contributions on a bubble in the direction normal to the wall from a single directly measurable quantity. Good agreement with expectation values for terrestrial bubbles was obtained with the difference in radii of curvature averaged over the liquid-vapor interface, (1/R2 − 1/R1), multiplied with the surface tension coefficient, σ. The new analysis methods of force components presented also permit the accounting for a surface tension gradient along the liquid-vapor interface. No such gradients were found for the present measurements
Learning under pressure: Learning strategies, workplace climate, and leadership style in the hospitality industry.
Gedragsveranderingen bij leerlingen en hun lerare
Evolutionary Dynamics of Pathoadaptation Revealed by Three Independent Acquisitions of the VirB/D4 Type IV Secretion System in Bartonella.
The α-proteobacterial genus Bartonella comprises a group of ubiquitous mammalian pathogens that are studied as a model for the evolution of bacterial pathogenesis. Vast abundance of two particular phylogenetic lineages of Bartonella had been linked to enhanced host adaptability enabled by lineage-specific acquisition of a VirB/D4 type IV secretion system (T4SS) and parallel evolution of complex effector repertoires. However, the limited availability of genome sequences from one of those lineages as well as other, remote branches of Bartonella has so far hampered comprehensive understanding of how the VirB/D4 T4SS and its effectors called Beps have shaped Bartonella evolution. Here, we report the discovery of a third repertoire of Beps associated with the VirB/D4 T4SS of B. ancashensis, a novel human pathogen that lacks any signs of host adaptability and is only distantly related to the two species-rich lineages encoding a VirB/D4 T4SS. Furthermore, sequencing of ten new Bartonella isolates from under-sampled lineages enabled combined in silico analyses and wet lab experiments that suggest several parallel layers of functional diversification during evolution of the three Bep repertoires from a single ancestral effector. Our analyses show that the Beps of B. ancashensis share many features with the two other repertoires, but may represent a more ancestral state that has not yet unleashed the adaptive potential of such an effector set. We anticipate that the effectors of B. ancashensis will enable future studies to dissect the evolutionary history of Bartonella effectors and help unraveling the evolutionary forces underlying bacterial host adaptation
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