102 research outputs found
Atherosclerosis and calcium signalling in endothelial cells
The link between atherosclerosis and regions of disturbed flow and low wall shear
stress is now firmly established, but the causal mechanisms underlying the link are not
yet understood. It is now recognised that the endothelium is not simply a passive barrier
between the blood and the vessel wall, but plays an active role in maintaining vascular
homeostasis and participates in the onset of atherosclerosis. Calcium signalling is one of
the principal intracellular signalling mechanisms by which endothelial cells (EC) respond
to external stimuli, such as fluid shear stress and ligand binding. Previous studies have
separately modelled mass transport of chemical species in the bloodstream and calcium
dynamics in EC via the inositol triphosphate (IP₃) signalling pathway. In this study, we
integrate these two important components to provide an inclusive model for the calcium
response of the endothelium in an arbitrary vessel geometry. This enables the combined
effects of fluid flow and biochemical stimulation on EC to be investigated. Model results
show that low endothelial calcium levels in the area of disturbed flow at an arterial
widening may be one contributing factor to the onset of vascular disease
Spatial Point Processes and Moment Dynamics in the Life Sciences: A Parsimonious Derivation and Some Extensions
Mathematical models of dynamical systems in 6 the life sciences typically assume that biological systems are spatially well mixed (the mean-field assumption). Even spatially explicit differential equation models typically make a local mean-field assumption. In effect, the assumption is that diffusive movement is strong enough to destroy spatial structure, or that interactions between individuals are sufficiently long-ranged that the effects of spatial structure are weak. However, many important biophysical processes, such as chemical reactions of biomolecules within cells, disease transmission among humans, and dispersal of plants, have characteristic spatial scales that can generate strong spatial structure at the scale of individuals, with important effects on the behaviour of biological systems. This calls for mathematical methods that in corporate spatial structure. Here we focus on one method, spatial-moment dynamics, which is based on the idea that important information about a spatial point process is held in its low-order spatial moments. The method goes beyond dynamics of the first moment, i.e. the mean density or concentration of agents in space, in which no information about spatial structure is retained. By including the dynamics of at least the second moment, the method retains some information about spatial structure. Whereas mean-field models effectively use a closure assumption for the second moment, spatial-moment models use a closure assumption for the third (or a higher-order) moment. The aim of the paper is to provide a parsimonious and intuitive derivation of spatial-moment dynamic equations that is accessible to non-specialists. The derivation builds naturally from the first moment to the second and we show how it can be extended to higher-order moments. Rather than tying the model to a specific biological example, we formulate a general model of movement, birth and death of multiple types of interacting agents. This model can be applied to problems from a range of disciplines, some of which we discuss. The derivation is performed in a spatially non-homogeneous setting, to facilitate future investigations of biological scenarios, such as invasions, in which the spatial patterns are non-stationary over space
The ZEPLIN II dark matter detector: data acquisition system and data reduction
ZEPLIN-II is a two-phase (liquid/gas) xenon dark matter detector searching
for WIMP-nucleon interactions. In this paper we describe the data acquisition
system used to record the data from ZEPLIN-II and the reduction procedures
which parameterise the data for subsequent analysis.Comment: 11 pages, 10 figure
The ZEPLIN II dark matter detector: data acquisition system and data reduction
ZEPLIN-II is a two-phase (liquid/gas) xenon dark matter detector searching
for WIMP-nucleon interactions. In this paper we describe the data acquisition
system used to record the data from ZEPLIN-II and the reduction procedures
which parameterise the data for subsequent analysis.Comment: 11 pages, 10 figure
Balanced harvest: concept, policies, evidence, and management implications
Balanced harvest has been proposed to reduce fishing impact on ecosystems while simultaneously maintaining or even increasing fishery yield. The concept has attracted broad interest, but also received criticisms. In this paper, we examine the theory, modelling studies, empirical evidence, the legal and policy frameworks, and management implications of balanced harvest. The examination reveals unresolved issues and challenges from both scientific and management perspectives. We summarize current knowledge and address common questions relevant to the idea. Major conclusions include: balanced harvest can be expressed in several ways and implemented on multiple levels, and with different approaches e.g. métier based management; it explicitly bridges fisheries and conservation goals in accordance with international legal and policy frameworks; modelling studies and limited empirical evidence reveal that balanced harvest can reduce fishing impact on ecosystem structure and increase the aggregate yield; the extent of balanced harvest is not purely a scientific question, but also a legal and social choice; a transition to balanced harvest may incur short-term economic costs, while in the long-term, economic results will vary across individual fisheries and for society overall; for its application, balanced harvest can be adopted at both strategic and tactical levels and need not be a full implementation, but could aim for a “partially-balanced” harvest. Further objective discussions and research on this subject are needed to move balanced harvest toward supporting a practical ecosystem approach to fisheries
The ZEPLIN-III dark matter detector: performance study using an end-to-end simulation tool
We present results from a GEANT4-based Monte Carlo tool for end-to-end
simulations of the ZEPLIN-III dark matter experiment. ZEPLIN-III is a two-phase
detector which measures both the scintillation light and the ionisation charge
generated in liquid xenon by interacting particles and radiation. The software
models the instrument response to radioactive backgrounds and calibration
sources, including the generation, ray-tracing and detection of the primary and
secondary scintillations in liquid and gaseous xenon, and subsequent processing
by data acquisition electronics. A flexible user interface allows easy
modification of detector parameters at run time. Realistic datasets can be
produced to help with data analysis, an example of which is the position
reconstruction algorithm developed from simulated data. We present a range of
simulation results confirming the original design sensitivity of a few times
pb to the WIMP-nucleon cross-section.Comment: Submitted to Astroparticle Physic
A EXPERIÊNCIA DE HOSPITALIZAÇÃO EXPLICADA PELA PRÓPRIA CRIANÇA
O presente estudo foi realizado com 20 crianças, em idade escolar, internadas em unidades pediátricas. Teve como objetivos identificar: como as crianças expressam a percepção de sua doença e hospitalização; os recursos de 'que elas dispõem para obter conhecimento sobre sua experiência de doença e hospitalização; e seus interesses e preocupações
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