43,788 research outputs found
Spacecraft charging: incoming and outgoing electrons
This paper presents an overview of the roles played by incoming and outgoing
electrons in spacecraft surface and stresses the importance of surface
conditions for spacecraft charging. The balance between the incoming electron
current from the ambient plasma and the outgoing currents of secondary
electrons, backscattered electrons, and photoelectrons from the surfaces
determines the surface potential. Since surface conditions significantly affect
the outgoing currents, the critical temperature and the surface potential are
also significantly affected. As a corollary, high level differential charging
of adjacent surfaces with very different surface conditions is a space hazard.Comment: 4 pages, contribution to the Joint INFN-CERN-EuCARD-AccNet Workshop
on Electron-Cloud Effects: ECLOUD'12; 5-9 Jun 2012, La Biodola, Isola d'Elba,
Ital
Computation of H2/air reacting flowfields in drag-reduction external combustion
Numerical simulation and analysis of the solution are presented for a laminar reacting flowfield of air and hydrogen in the case of external combustion employed to reduce base drag in hypersonic vehicles operating at transonic speeds. The flowfield consists of a transonic air stream at a Mach number of 1.26 and a sonic transverse hydrogen injection along a row of 26 orifices. Self-sustained combustion is computed over an expansion ramp downstream of the injection and a flameholder, using the recently developed RPLUS code. Measured data is available only for surface pressure distributions and is used for validation of the code in practical 3D reacting flowfields. Pressure comparison shows generally good agreements, and the main effects of combustion are also qualitatively consistent with experiment
Optimization of synchronization in gradient clustered networks
We consider complex clustered networks with a gradient structure, where sizes
of the clusters are distributed unevenly. Such networks describe more closely
actual networks in biophysical systems and in technological applications than
previous models. Theoretical analysis predicts that the network
synchronizability can be optimized by the strength of the gradient field but
only when the gradient field points from large to small clusters. A remarkable
finding is that, if the gradient field is sufficiently strong,
synchronizability of the network is mainly determined by the properties of the
subnetworks in the two largest clusters. These results are verified by
numerical eigenvalue analysis and by direct simulation of synchronization
dynamics on coupled-oscillator networks.Comment: PRE, 76, 056113 (2007
Surface temperature distribution along a thin liquid layer due to thermocapillary convection
The surface temperature distributions due to thermocapillary convections in a thin liquid layer with heat fluxes imposed on the free surface were investigated. The nondimensional analysis predicts that, when convection is important, the characteristics length scale in the flow direction L, and the characteristic temperature difference delta T sub o can be represented by L and delta T sub o approx. (A2Ma)/1/4 delta T sub R, respectively, where L sub R and delta sub R are the reference scales used in the conduction dominant situations with A denoting the aspect ratio and Ma the Marangoni number. Having L and delta sub o defined, the global surface temperature gradient delta sub o/L, the global thermocapillary driving force, and other interesting features can be determined. Numerical calculations involving a Gaussian heat flux distribution are presented to justify these two relations
Insights into the pulmonary vascular complications of heart failure with preserved ejection fraction
Pulmonary hypertension in the setting of heart failure with preserved ejection fraction (PH-HFpEF) is a growing public health problem that is increasing in prevalence. While PH-HFpEF is defined by a high mean pulmonary artery pressure, high left ventricular end-diastolic pressure and a normal ejection fraction, some HFpEF patients develop PH in the presence of pulmonary vascular remodelling with a high transpulmonary pressure gradient or pulmonary vascular resistance. Ageing, increased left atrial pressure and stiffness, mitral regurgitation, as well as features of metabolic syndrome, which include obesity, diabetes and hypertension, are recognized as risk factors for PH-HFpEF. Qualitative studies have documented that patients with PH-HFpEF develop more severe symptoms than those with HFpEF and are associated with more significant exercise intolerance, frequent hospitalizations, right heart failure and reduced survival. Currently, there are no effective therapies for PH-HFpEF, although a number of candidate drugs are being evaluated, including soluble guanylate cyclase stimulators, phosphodiesterase type 5 inhibitors, sodium nitrite and endothelin receptor antagonists. In this review we attempt to provide an updated overview of recent findings pertaining to the pulmonary vascular complications in HFpEF in terms of clinical definitions, epidemiology and pathophysiology. Mechanisms leading to pulmonary vascular remodelling in HFpEF, a summary of pre-clinical models of HFpEF and PH-HFpEF, and new candidate therapeutic strategies for the treatment of PH-HFpEF are summarized
Evaluating probability forecasts
Probability forecasts of events are routinely used in climate predictions, in
forecasting default probabilities on bank loans or in estimating the
probability of a patient's positive response to treatment. Scoring rules have
long been used to assess the efficacy of the forecast probabilities after
observing the occurrence, or nonoccurrence, of the predicted events. We develop
herein a statistical theory for scoring rules and propose an alternative
approach to the evaluation of probability forecasts. This approach uses loss
functions relating the predicted to the actual probabilities of the events and
applies martingale theory to exploit the temporal structure between the
forecast and the subsequent occurrence or nonoccurrence of the event.Comment: Published in at http://dx.doi.org/10.1214/11-AOS902 the Annals of
Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical
Statistics (http://www.imstat.org
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