Source Model (source + model)

Distribution by Scientific Domains


Selected Abstracts


Stochastic models for simulation of strong ground motion in Iceland

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 9 2001
Símon Ólafsson
Abstract Two types of modelling approaches for simulating ground motion in Iceland are studied and compared. The first type of models, named discrete-time series models (ARMA), are based solely on measured acceleration in earthquakes occurring in Iceland. The second type of models are based on a theoretical seismic source model called the extended Brune model. Based on measured acceleration in Iceland during the period 1986,1996, the parameters for the extended Brune models have been estimated. The seismic source models are presented here as ARMA models, which simplifies the simulation process. A single-layer soil amplification model is used in conjunction with the extended Brune model to estimate local site amplification. Emphasis is put on the ground motion models representing the variability in the measured earthquakes, with respect to energy, duration and frequency content. Demonstration is made using these models for constructing linear and non-linear probabilistic response spectra using a discretised version of the Bouc,Wen model for the hysteresis of the second-order system. Copyright © 2001 John Wiley & Sons, Ltd. [source]


Predicting toxic gas concentrations resulting from enclosure fires using local equivalence ratio concept linked to fire field models

FIRE AND MATERIALS, Issue 1 2007
Z. Wang
Abstract A practical CFD method is presented in this study to predict the generation of toxic gases in enclosure fires. The model makes use of local combustion conditions to determine the yield of carbon monoxide, carbon dioxide, hydrocarbon, soot and oxygen. The local conditions used in the determination of these species are the local equivalence ratio (LER) and the local temperature. The heat released from combustion is calculated using the volumetric heat source model or the eddy dissipation model (EDM). The model is then used to simulate a range of reduced-scale and full-scale fire experiments. The model predictions for most of the predicted species are then shown to be in good agreement with the test results. Copyright © 2006 John Wiley & Sons, Ltd. [source]


Functional source separation applied to induced visual gamma activity

HUMAN BRAIN MAPPING, Issue 2 2008
Giulia Barbati
Abstract Objective of this work was to explore the performance of a recently introduced source extraction method, FSS (Functional Source Separation), in recovering induced oscillatory change responses from extra-cephalic magnetoencephalographic (MEG) signals. Unlike algorithms used to solve the inverse problem, FSS does not make any assumption about the underlying biophysical source model; instead, it makes use of task-related features (functional constraints) to estimate source/s of interest. FSS was compared with blind source separation (BSS) approaches such as Principal and Independent Component Analysis, PCA and ICA, which are not subject to any explicit forward solution or functional constraint, but require source uncorrelatedness (PCA), or independence (ICA). A visual MEG experiment with signals recorded from six subjects viewing a set of static horizontal black/white square-wave grating patterns at different spatial frequencies was analyzed. The beamforming technique Synthetic Aperture Magnetometry (SAM) was applied to localize task-related sources; obtained spatial filters were used to automatically select BSS and FSS components in the spatial area of interest. Source spectral properties were investigated by using Morlet-wavelet time-frequency representations and significant task-induced changes were evaluated by means of a resampling technique; the resulting spectral behaviours in the gamma frequency band of interest (20,70 Hz), as well as the spatial frequency-dependent gamma reactivity, were quantified and compared among methods. Among the tested approaches, only FSS was able to estimate the expected sustained gamma activity enhancement in primary visual cortex, throughout the whole duration of the stimulus presentation for all subjects, and to obtain sources comparable to invasively recorded data. Hum Brain Mapp 29:131,141, 2008. © 2007 Wiley-Liss, Inc. [source]


Intellectual Property in the Context of e-Science

JOURNAL OF COMPUTER-MEDIATED COMMUNICATION, Issue 2 2007
Dan L. Burk
E-science promises to allow globally-distributed collaboration and access to scientific research via computer networks, but e-science development is already encountering difficulty over the intellectual property rights associated with data and networked collaborative activity. The proprietary nature of intellectual property is generally problematic in the practice of science, but such difficulties are likely to be exacerbated in the context of e-science collaboration where the development and use of intellectual resources will likely be distributed among many researchers in a variety of physical locations, often spanning national boundaries. While a potential solution to such problems may reside in the mechanism of "open source" licenses, the organizational structure of scientific research may not map cleanly onto the open source model. Consequently, a firm understanding of not only the technical structure but of the social and communicative structure of e-science will be necessary in order to adapt licensing solutions to the practice of e-science. [source]


Finite-element heat-transfer analysis of a PEEK-steel sliding pair in a pin-on-disc configuration

LUBRICATION SCIENCE, Issue 1 2001
László Kónya
Abstract Finite-element (FE) thermal models have been developed in order to study the temperature distribution in a sliding pair comprising a poly(ether ether ketone) (PEEK) pin and a steel disc in a pin-on-disc configuration. First, a moving heat source model for the disc was created. An alternative distributed heat source model was also produced in order to reduce computing time for the evaluation of the moving heat source model by some orders of magnitude. This latter model gave the same results as the moving heat source model, except for a small region just below the moving heat source. On the basis of the distributed heat source approach, a complete axisymmetric FE model for the disc side (taking the effect of thermal resistance between the assembled components into consideration) and a steady-state quarter model for the pin were developed. Water cooling and air cooling of the steel shaft were also compared. It was found that air cooling allowed a higher temperature in the contact region of the two sliding partners. The experimental results obtained with thermocouples and a thermal camera showed good agreement with the model predictions. [source]


Carbohydrate translocation determines the phenolic content of Populus foliage: a test of the sink,source model of plant defense

NEW PHYTOLOGIST, Issue 1 2004
Tom Arnold
Summary ,,Here, we examine the influence of source-to-sink carbohydrate (CHO) flow on the development of constitutive and inducible levels of phenylpropenoids in hybrid poplar (Populus nigra × P. deltoides) foliage to determine if secondary metabolic processes in plant modules can be inhibited in a predictable manner by events such as herbivory and the development of new leaves and reproductive structures, which alter the path of phloem-borne resources. ,,Phenylpropenoid concentrations were determined for developing foliage after CHO flow, measured as the translocation of 13C from labeled sources was manipulated. ,,Phenylpropenoid metabolism in both unwounded and induced sink leaves was directly and positively linked to rates of CHO import. Alterations in rates of translocation yielded different results, depending on how CHO import was affected: the removal of competing sinks rapidly and dramatically increased leaf phenolic contents, whereas phenolic levels (and their inducibility) tended to be reduced when import was interrupted. ,,High and inducible sink strength in developing poplar leaves provides resources for phenolic biosynthesis and, as a result, restrictions or re-directions of CHOs affect the foliar quality. Sink strength and the vascular architecture of plants, which confer upon them a modular nature, can determine the direction and magnitude of defense responses in trees. [source]


Nondipolar Content of T Wave Derived from a Myocardial Source Simulation with Increased Repolarization Inhomogeneity

ANNALS OF NONINVASIVE ELECTROCARDIOLOGY, Issue 2 2009
Milos Kesek M.D., Ph.D.
Background: Several conditions with repolarization disturbances are associated with increased level of nondipolar components of the T wave. The nondipolar content has been proposed as a measure of repolarization inhomogeneity. This computer simulation study examines the link between increased nondipolar components and increased repolarization inhomogeneity in an established model. Methods: The simulation was performed with Ecgsim software that uses the equivalent double-layer source model. In the model, the shape of transmembrane potential is derived from biological recordings. Increased repolarization inhomogeneity was simulated globally by increasing the variance in action potential duration and locally by introducing changes mimicking acute myocardial infarction. We synthesized surface ECG recordings with 12, 18, and 300 leads. The T-wave residue was calculated by singular value decomposition. The study examined the effects of the number of ECG leads, changes in definition of end of T wave and random noise added to the signal. Results: Normal myocardial source gave a low level of nondipolar content. Increased nondipolar content was observed in the two types of increased repolarization inhomogeneity. Noise gave a large increase in the nondipolar content. The sensitivity of the result to noise increased when a higher number of principal components were used in the computation. Conclusions: The nondipolar content of the T wave was associated with repolarization inhomogeneity in the computer model. The measure was very sensitive to noise, especially when principal components of high order were included in the computations. Increased number of ECG leads resulted in an increased signal-to-noise ratio. [source]