Search results for " value"
showing 10 items of 3662 documents
Zero-range model of traffic flow.
2005
A multi--cluster model of traffic flow is studied, in which the motion of cars is described by a stochastic master equation. Assuming that the escape rate from a cluster depends only on the cluster size, the dynamics of the model is directly mapped to the mathematically well-studied zero-range process. Knowledge of the asymptotic behaviour of the transition rates for large clusters allows us to apply an established criterion for phase separation in one-dimensional driven systems. The distribution over cluster sizes in our zero-range model is given by a one--step master equation in one dimension. It provides an approximate mean--field dynamics, which, however, leads to the exact stationary s…
Non-uniform Sediment Transport Estimation in Non-equilibrium Situations: Case Studies
2014
Abstract Quantitative estimate of sediment transport in alluvial channels is one of the most important task in river engineering. Even today, numerical models of sediment transport processes are confronted with some difficulties, often of conceptual nature. One of these difficulties is the simulation of non-uniform sediment transport in non-equilibrium situations, which requires the characterization of the ability of the alluvial system to immediately overcome the variations of the sediment boundary conditions. In this work a 1-D numerical model, which includes a new expression of the so-called “adaptation coefficient”, has been applied to test its capability to simulate the transient bed p…
The Many Faces of Interactivity in Convergent Media Environments. Assessing Uses and Effects of Interactivity from a User and Management Perspective
2013
Digitization has blurred the distinctions between producers and audiences. Thus, research on interactivity as a key element of convergent media environments has grown dramatically over the past three decades. However, despite this strong research interest there is currently no consensus about the multi-faced and hard-to-grasp concept. Obviously, interactivity is used to describe numerous processes in convergent media environments that are related to communication in general, and online communication and practices like online journalism in particular. This article highlights the main strands in the conceptual development of interactivity and explores some of the effects of interactivity by s…
Measuring Child-Rearing Values. A Research Note
2012
Abstract Large scale comparative studies, such as the value surveys (EVS and WVS) or the Eurobarometer, include measurements for parental/child-rearing values. This reflects a persistent interest for the topic, which produced salient studies starting with the first half of the twentieth century (Lynd and Lund 1929; Duvall 1946). Various scholars report data on parental values which use versions of the Q-sort methodology (Kohn 1977), ranking variables (Alwin 1990; Lenski 1961), scale indicators (Tulviste et al. 2007). Q-sort methodology remains the most widely employed. One of its versions is included in the value surveys as well. However, it fails to produce comparable indicators in differe…
A Shock to the System: HIV among Older African Women in Zimbabwe
2018
HIV remains a threat to the ordinary everyday life of older woman in African society. In what can be called “a reality shock,” HIV challenges most of the ordinary everyday endeavors in conservative African societies as it imposes new Western prevention, treatment, and health-management methods over long-held African traditions. The reality of the “Western” HIV epidemic, and its impact on the “African” ordinary everyday life, demands that the infected undergo a paradigm shift in order for them to live harmoniously within their society. This calls for a re-examination of traditional values and a strong sense of responsibility, courage, and determination to remain relevant and not be considere…
Optimal control of the atmospheric arc of a space shuttle and numerical simulations with multiple-shooting method
2005
This article, continuation of previous works, presents the applications of geometric optimal control theory to the analysis of the Earth re-entry problem for a space shuttle where the control is the angle of bank, the cost is the total amount of thermal flux, and the system is subject to state constraints on the thermal flux, the normal acceleration and the dynamic pressure. Our analysis is based on the evaluation of the reachable set using the maximum principle and direct computations with the boundary conditions according to the CNES research project\footnote{The project is partially supported by the Centre National d'Etude Spatiales.}. The optimal solution is approximated by a concatenat…
Optimal control of an ensemble of Bloch equations with applications in MRI
2016
International audience; The optimal control of an ensemble of Bloch equations describing the evolution of an ensemble of spins is the mathematical model used in Nuclear Resonance Imaging and the associated costs lead to consider Mayer optimal control problems. The Maximum Principle allows to parameterize the optimal control and the dynamics is analyzed in the framework of geometric optimal control. This lead to numerical implementations or suboptimal controls using averaging principle.
Minimum fuel control of the planar circular restricted three-body problem
2012
The circular restricted three-body problem is considered to model the dynamics of an artificial body submitted to the attraction of two planets. Minimization of the fuel consumption of the spacecraft during the transfer, e.g. from the Earth to the Moon, is considered. In the light of the controllability results of Caillau and Daoud (SIAM J Control Optim, 2012), existence for this optimal control problem is discussed under simplifying assumptions. Thanks to Pontryagin maximum principle, the properties of fuel minimizing controls is detailed, revealing a bang-bang structure which is typical of L1-minimization problems. Because of the resulting non-smoothness of the Hamiltonian two-point bound…
Recent changes in measured wind in the NE Atlantic and variability of correlation with NAO
2010
The paper deals with wind measurements, recorded since the 1950s, at twelve meteorological stations along a transect near the westernmost European border, between 64° and 44° N. Extreme wind speed tends to decrease sharply near the northern boundary (at Reykjavick), near the middle of the study area (at Shannon and Valentia) and near the southern boundary (at Brest and Cap Ferret), to increase at Thorshavn, with less significant trends at the other stations. Average wind speeds confirm the above tendencies, with an additional increasing speed at Lerwick, Kirkwall, Malin Head, Belle-Ile and Cap Ferret. To compare changes in wind activity, the data have been subdivided into three periods: unt…
Functional ecology for evaluating and predicting the aptitude of permanent grassland to provide services
2013
National audience; Applying the principles of functional ecology helps better predict the services which can be provided by permanent grassland. Farming practices and environmental characteristics influence the functional composition of grassland. Functional plant types have a generic effect on forage services which can be assessed. 13 types of grassland composed of distinct functional types were defined based on 1,283 sample grassland fields located on 8 sites. This approach was validated by checking 8 Ellenberg indicator values (used to evaluate environmental characteristics and farming practices) against climatic data and descriptive data for farming practices. The interest of a function…