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Present Simulation (present + simulation)
Selected AbstractsGene-dropping vs. empirical variance estimation for allele-sharing linkage statisticsGENETIC EPIDEMIOLOGY, Issue 8 2006Jeesun Jung Abstract In this study, we compare the statistical properties of a number of methods for estimating P -values for allele-sharing statistics in non-parametric linkage analysis. Some of the methods are based on the normality assumption, using different variance estimation methods, and others use simulation (gene-dropping) to find empirical distributions of the test statistics. For variance estimation methods, we consider the perfect variance approximation and two empirical variance estimates. The simulation-based methods are gene-dropping with and without conditioning on the observed founder alleles. We also consider the Kong and Cox linear and exponential models and a Monte Carlo method modified from a method for finding genome-wide significance levels. We discuss the analytical properties of these various P -value estimation methods and then present simulation results comparing them. Assuming that the sample sizes are large enough to justify a normality assumption for the linkage statistic, the best P -value estimation method depends to some extent on the (unknown) genetic model and on the types of pedigrees in the sample. If the sample sizes are not large enough to justify a normality assumption, then gene-dropping is the best choice. We discuss the differences between conditional and unconditional gene-dropping. Genet. Epidemiol. 2006. © 2006 Wiley-Liss, Inc. [source] Multi-annual dry episodes in Australian climatic variabilityINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 12 2009B. G. Hunt Abstract The output from a 10 000-year simulation with the CSIRO Mark 2 coupled global climatic model has been analysed to investigate the occurrence of multi-year dry episodes for three selected regions of Australia, specifically, the northeast, southeast and southwest of the continent. Results are presented for dry episodes lasting for 8 or more years. An episode is defined as a time interval having consecutive negative rainfall anomalies, but not necessarily a major drought, for each year of the episode. The hydrological consequences of such an episode can persist for over a century. Typically about 30 episodes are found over the 10 000 years of the simulation for each of the three regions. There is little synchronicity between the regions in the occurrence of the dry episodes. While there is an El Nino/Southern Oscillation (ENSO) influence associated with these episodes, it is not continuous over the duration of an episode. Composites of sea surface temperature anomalies over an episode highlight the limited presence of ENSO events. The occurrence of the dry episodes for all three regions is essentially random, with multi-centennial periods without an episode, and episodes at multi-decadal frequency at other times. Following a discussion of possible mechanistic influences, it is concluded that stochastic forcing is responsible for the occurrence of dry episodes. This implies that there is no predictability associated with the initiation, duration or termination of individual dry episodes. This also suggests that the 2000,2007 dry episodes occurring over much of Australia may not be caused by the greenhouse effect. Such an episode has a return period of between 200 and 300 years based on the mean frequency of occurrence in the present simulation. Copyright © 2008 Royal Meteorological Society [source] Perceptual denoising of color imagesINTERNATIONAL JOURNAL OF IMAGING SYSTEMS AND TECHNOLOGY, Issue 3 2010Ilka A. Netravali Abstract Denoising of color images is a trade-off between sharpness of an image and perceived noise. We formulate a novel optimization problem that can maximize sharpness of an image while limiting the perceived noise under a model of visibility of additive random noise. We derive a closed-form expression for an optimal two-dimensional finite impulse response filter, show its uniqueness and existence, and present simulation results for black and white as well as color images. Simulation results show remarkable reduction in perceptibility of noise, while preserving sharpness. The computational burden required for the optimal filter is reduced by a new adhoc filter which is simple but has near optimal performance. © 2010 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 20, 215,222, 2010. [source] The Application of the Sliding Mode Controller on the Ship Roll Reduction in Random Waves Using Genetic AlgorithmNAVAL ENGINEERS JOURNAL, Issue 4 2006Ming-Chung Fang The paper presents the sliding mode controller technique with roll reduction function on the ship rudder to simulate ship motion in random sea. By way of the rudder operation, the trackkeeping ability of the sliding mode controller on the ship is also examined using the line-of-sight (LOS) guidance technique. To reduce computer time consumption, the optimized design parameters of sliding mode controller tuned by genetic algorithm are obtained from ship motion simulation in regular waves. Based on the present simulation results in random waves, the combined heading/roll sliding mode controller including LOS technique developed here works for either roll reduction or track-keeping while the ship is maneuvering in waves. [source] Effects of blood models on flows through a stenosisINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 6-7 2003Panagiotis Neofytou Abstract The paper presents a numerical investigation of non-Newtonian modelling effects on unsteady periodic flows in a two-dimensional (2D) channel with a stenosis. The geometry and boundary conditions were chosen so as to reproduce the flow features that are observed in real haemodynamic conditions. Three different non-Newtonian constitutive equations for modelling the shear characteristics of the blood namely the Casson, power-law and Quemada models, are utilized. Similarly with previous studies based on Newtonian modelling, the present simulations show the formation of several vortices downstream of the stenosis, as well as substantial variations of the wall shear stress throughout the unsteady cycle. Additionally, it is shown that: (i) there are substantial differences between the results obtained by Newtonian and non-Newtonian models, and (ii) the prediction of vortex formation, wall shear stress distribution and separation behind the stenosis is strongly dependent on the details of the non-Newtonian model employed in the simulations. Copyright © 2003 John Wiley & Sons, Ltd. [source] Luminescence imaging for the detection of shunts on silicon solar cellsPROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 4 2008M. Kasemann Abstract Luminescence imaging is a non-destructive, fast, and versatile imaging method for spatially resolved solar cell and material characterization. In this paper, we investigate its ability to detect shunts on silicon solar cells. We give a detailed description of the relation between local junction voltage and local luminescence signal. This relation is important because shunts drain majority currents causing voltage drops across the surrounding series resistances and that way affect luminescence images. To investigate effects related to majority currents, we describe and apply a simulation model that allows the simulation of lateral voltage distributions on solar cells. This model, and a comparison to illuminated lock-in thermography, helps to discuss some practical aspects about shunt detection by luminescence imaging. We will discuss a procedure to distinguish between ohmic and diode-like shunts and finally present simulations and measurements showing that luminescence imaging is only weakly sensitive to shunts under the metallization. However, we also show its high sensitivity for remote shunts and propose a possible application where this high sensitivity could be especially helpful. Copyright © 2008 John Wiley & Sons, Ltd. [source] Proton-transfer dynamics in the (HCO3,)2 dimer of KHCO3 from Car,Parrinello and path-integrals molecular dynamics calculationsACTA CRYSTALLOGRAPHICA SECTION B, Issue 2 2010Przemyslaw D. Dopieralski The proton motion in the (HCO)2 dimer of KHCO3 at 298,K has been studied with Car,Parrinello molecular dynamics (CPMD) and path-integrals molecular dynamics (PIMD) simulations. According to earlier neutron diffraction studies at 298,K hydrogen is disordered and occupies two positions with an occupancy ratio of 0.804/0.196. A simulation with only one unit cell is not sufficient to reproduce the disorder of the protons found in the experiments. The CPMD results with four cells, 0.783/0.217, are in close agreement with experiment. The motion of the two protons along the O...O bridge is highly correlated inside one dimer, but strongly uncoupled between different dimers. The present results support a mechanism for the disorder which involves proton transfer from donor to acceptor and not orientational disordering of the entire dimer. The question of simultaneous or successive proton transfer in the two hydrogen bonds in the dimer remains unanswered. During the simulation situations with almost simultaneous proton transfer with a time gap of around 1,fs were observed, as well as successive processes where first one proton is transferred and then the second one with a time gap of around 20,fs. The calculated vibrational spectrum is in good agreement with the experimental IR spectrum, but a slightly different assignment of the bands is indicated by the present simulations. [source] Characterization of flow conditions in 2 L and 20 L wave bioreactors® using computational fluid dynamicsBIOTECHNOLOGY PROGRESS, Issue 1 2010Alper A. Öncül Abstract Characterization of flow conditions is of great importance to control cell growth and cell damage in animal cell culture because cell viability is influenced by the flow properties in bioreactors. Alternative reactor types like Wave Bioreactors® have been proposed in recent years, leading to markedly different results in cell growth and product formation. An advantage of Wave Bioreactors® is the disposability of the Polyethylenterephthalet-bags after one single use (fast setup of new production facilities). Another expected advantage is a lower shear stress compared to classical stirred-tank reactors, due to the gentle liquid motion in the rocking cellbag. This property would considerably reduce possible cell damage. The purpose of the present study is to investigate in a quantitative manner the key flow properties in Wave Bioreactors®, both numerically and experimentally. To describe accurately flow conditions and shear stress in Wave Bioreactors® using numerical simulations, it is necessary to compute the unsteady flow applying Computational Fluid Dynamics (CFD). Corresponding computations for two reactor scales (2 L and 20 L cellbags) are presented using the CFD code ANSYS-FLUENT®. To describe correctly the free liquid surface, the present simulations employ the Volume of Fluid (VOF) method. Additionally, experimental measurements have been carried out to determine liquid level, flow velocity and liquid shear stress, which are used as a validation of the present CFD simulations. It is shown that the obtained flows stay in the laminar regime. Furthermore, the obtained shear stress levels are well below known threshold values leading to damage of animal cells. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2010 [source] | |||||||||||||