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Simulation Methods (simulation + methods)
Selected AbstractsSearching Inhibitors of Adenosine Kinase by Simulation MethodsCHINESE JOURNAL OF CHEMISTRY, Issue 11 2006Rui-Xin Zhu Abstract Searching new inhibitors of adenosine kinase (AK) is still drawing attention of experimental scientists. A better and solid model is here proposed by means of simulation methods from different ways, the direct analysis of receptor itself, the conventional 3D-QSAR methods and the integration of docking method and the conventional QSAR analysis. [source] A perturbation analysis of harmonic generation from saturated elements in power systemsELECTRICAL ENGINEERING IN JAPAN, Issue 4 2010Teruhisa Kumano Abstract Nonlinear phenomena such as saturation of magnetic flux have considerable effects in power systems analysis. It is reported that a failure in a real 500-kV system triggered islanding operation, where resultant even harmonics caused malfunctions in protective relays. It is also reported that the major origin of this wave distortion is nothing but unidirectional magnetization of the transformer iron core. Time simulation is widely used today to analyze phenomena of this type, but it has basically two shortcomings. One is that the time simulation takes too much computing time in the vicinity of inflection points in the saturation characteristic curve because certain iterative procedures such as N-R (Newton,Raphson) must be used and such methods tend to be caught in an ill-conditioned numerical hunting. The other is that such simulation methods sometimes do not aid an intuitive understanding of the studied phenomenon because all of the nonlinear equations are treated in matrix form and are not properly divided into understandable parts, as is done in linear systems. This paper proposes a new computation scheme that is based on the so-called perturbation method. Magnetic saturation of iron cores in a generator and a transformer are taken into account. The proposed method has a special feature to deal with the first shortcoming of the N-R-based time simulation method stated above. The proposed method does not use an iterative process to reduce the equation residue, but uses perturbation series, so that it is free of the ill-conditioning problem. The user need only calculate the perturbation terms one by one until the necessary accuracy is attained. In a numerical example treated in the present paper, first-order perturbation can achieve reasonably high accuracy, which means very fast computing time. In a numerical study, three nonlinear elements are considered. The calculation results are almost identical to the conventional N-R-based time simulation, which shows the validity of the method. The proposed method can be effectively used in screening where many case studies are needed. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 170(4): 35,42, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20895 [source] A study on a new AVR parameter tuning concept using on-line measured data with the real-time simulatorEUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 3 2006Joong-Moon Kim Abstract Automatic voltage regulator (AVR) parameter tuning for voltage control of power system generators has generally been performed with the analytic methods and the simulation methods, which mostly depend on off-line linear mathematical models of power system. However, due to the nonlinear nature of power system, the mathematical models of the excitation system may not be correct. So the excitation control system performances with the parameter set that is tuned by using the mathematical model, may not be appropriate for some operating conditions. This paper presents an AVR parameter tuning method using on-line measured data of the excitation control system with parameter optimization technique. As this method utilizes on-line operating data, it can overcome the limitation of model uncertainty problems of conventional method. To validate the proposed tuning concept, a scaled model excitation system is connected to the real-time power system simulator, and the proposed tuning concept is tested. Copyright © 2006 John Wiley & Sons, Ltd. [source] Uncertainty about estimating total returns of Atlantic salmon, Salmo salar to the Gander River, Newfoundland, Canada, evaluated using a fish counting fenceFISHERIES MANAGEMENT & ECOLOGY, Issue 1 2003M. F. O'Connell Abstract ,For a number of rivers in Newfoundland, Atlantic salmon, Salmo salar L., is managed in relation to river-specific conservation spawning requirements. One such river is the Gander River, where between 1989 and 1999, the escapement of Atlantic salmon, a major factor in assessing the status of stock, was determined using a fish counting fence. In 2000, the counting fence was discontinued and alternative means of calculating total returns were explored. Regression and simulation methods, using relationships between total returns and salmon counts at an upstream tributary during 1989,99, formed the basis for estimates of returns for 2000, and the uncertainty around estimates. The accuracy of methods is evaluated by retrospective comparisons with actual total returns between 1989 and 1999. Estimates of total returns deviated from the actual by as much as 50,60%, depending on the method. Management implications of the approach are discussed. [source] Issues concerning association studies for fine mapping a susceptibility gene for a complex disease,GENETIC EPIDEMIOLOGY, Issue 4 2001Norman Kaplan Abstract The usefulness of association studies for fine mapping loci with common susceptibility alleles for complex genetic diseases in outbred populations is unclear. We investigate this issue for a battery of tightly linked anonymous genetic markers spanning a candidate region centered around a disease locus, and study the joint behavior of chi-square statistics used to discover and to localize the disease locus. We used simulation methods based on a coalescent process with mutation, recombination, and genetic drift to examine the spatial distribution of markers with large noncentrality parameters in a case-control study design. Simulations with a disease allele at intermediate frequency, presumably representing an old mutation, tend to exhibit the largest noncentrality parameter values at markers near the disease locus. In contrast, simulations with a disease allele at low frequency, presumably representing a young mutation, often exhibit the largest noncentrality parameter values at markers scattered over the candidate region. In the former cases, sample sizes or marker densities sufficient to detect association are likely to lead to useful localization, whereas, in the latter case, localization of the disease locus within the candidate region is much less likely, regardless of the sample size or density of the map. The effects of increasing sample size or marker density are also investigated. Based upon a single marker analysis, we find that a simple strategy of choosing the marker with the smallest associated P value to begin a laboratory search for the disease locus performs adequately for a common disease allele. We also investigated a strategy of pooling nearby sites to form multiple allele markers. Using multiple degree of freedom chi-square tests for two or three nearby sites, we found no clear advantage of this form of pooling over a single marker analysis. Genet. Epidemiol. 20:432,457, 2001. Published by Wiley-Liss, 2001. [source] Characterization and reconstruction of a rock fracture surface by geostatisticsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 9 2002A. Marache Abstract It is well understood that, in studying the mechanical and hydromechanical behaviour of rock joints, their morphology must be taken into account. A geostatistical approach has been developed for characterizing the morphology of fracture surfaces at a decimetre scale. This allows the analysis of the spatial variability of elevations, and their first and second derivatives, with the intention of producing a model that gives a numerical three-dimensional (3D) representation of the lower and upper surfaces of the fracture. Two samples (I and II) located close together were cored across a natural fracture. The experimental data are the elevations recorded along profiles (using recording steps of 0.5 and 0.02 mm, respectively, for the samples I and II). The goal of this study is to model the surface topography of sample I, so getting estimates for elevations at each node of a square grid whose mesh size will be, for mechanical purposes, no larger than the recording step. Since the fracture surface within the sample core is not strictly horizontal, geostatistical methods are applied to residuals of elevations of sample I. Further, since structural information is necessary at very low scale, theoretical models of variograms of elevations, first and second derivatives are fitted using data of both that sample I and sample II. The geostatistical reconstructions are computed using kriging and conditional simulation methods. In order to validate these reconstructions, variograms and distributions of experimental data are compared with variograms and distributions of the fitted data. Copyright © 2002 John Wiley & Sons, Ltd. [source] Higher-resolution convection schemes for flow in porous media on highly distorted unstructured gridsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 8 2008Sadok Lamine Abstract Higher-resolution schemes are presented for convective flow approximation on highly distorted unstructured grids. The schemes are coupled with continuous full-tensor Darcy-flux approximations. A sequence of non-uniform and distorted grid formulations are developed and compared for a range of unstructured meshes with variable grid spacing. The higher-order schemes are constructed using non-uniform grid slope limiters such that they are stable with a local maximum principle, ensuring that solutions are free of spurious oscillations. Benefits of the resulting schemes are demonstrated for classical test problems in reservoir simulation including cases with full-tensor permeability fields. The test cases involve a range of unstructured grids with variations in grid spacing, orientation and permeability that lead to flow fields that are poorly resolved by standard simulation methods. The higher-order formulations are shown to effectively reduce numerical diffusion, leading to improved resolution of concentration and saturation fronts. Copyright © 2008 John Wiley & Sons, Ltd. [source] Application of the TLM technique to integrated optic component modellingINTERNATIONAL JOURNAL OF NUMERICAL MODELLING: ELECTRONIC NETWORKS, DEVICES AND FIELDS, Issue 2 2001O. Jacquin The TLM algorithm is of high interest to simulate new integrated optical devices as a ,photonic band gap' (PBG) structures. These components are realized with semiconductor material and constituted by a set of abrupt optical discontinuities. The electromagnetic behaviour of these structures does not allow the use of usual simulation methods of integrated optics. Indeed, their validity conditions are not satisfied. Then, we have to use unusual simulation method for integrated optics as TLM software which allows the visualization and understanding of the behaviour of electromagnetic field in the PBG structures. In this paper, the simulation results of different optical devices made from the TLM method are presented. Copyright © 2001 John Wiley & Sons, Ltd. [source] Nonlinear simulation of mixers for assessing system-level performanceINTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING, Issue 4 2005Nuno B. Carvalho Abstract This article deals with nonlinear simulation methods intended to evaluate the impact of mixer nonidealities on the performance of a wireless system. Behavioral models capable of accurately describing the mixer's nonlinear dynamic features at the system level are currently unavailable. The possibility of using alternative circuit analysis techniques to reach this goal is discussed. After a brief review of existing mixer analysis methods, the focus is directed to the techniques amenable to efficiently handling periodic carriers modulated by complex stochastic signals. In particular, it is shown how multi-envelope transient methods coupled with a three-dimensional harmonic-balance engine can model a nonlinear dynamic mixer excited by a modulated RF signal accompanied by a strong adjacent channel interferer and with a local oscillator corrupted by phase noise. © 2005 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2005. [source] Discrete thermodynamics of chemical equilibria and classical limit in thermodynamic simulationISRAEL JOURNAL OF CHEMISTRY, Issue 3-4 2007Boris Zilbergleyt This article sets forth comprehensive basic concepts of the discrete thermodynamics of chemical equilibrium as balance between internal and external thermodynamic forces. Conditions of chemical equilibrium in the open chemical system are obtained in the form of a logistic map, containing only one new parameter that defines the chemical system's resistance to external impact and its deviation from thermodynamic equilibrium. Solutions to the basic map are bifurcation diagrams that have quite traditional shape but the diagram areas feature specific meanings for chemical systems and constitute the system's domain of states. The article is focused on two such areas: the area of "true" thermodynamic equilibrium and the area of open chemical equilibrium. The border between them represents the classical limit, a transition point between the classical and newly formulated equilibrium conditions. This limit also separates regions of the system ideality, typical for isolated classical systems, and non-ideality due to the limitations imposed on the open system from outside. Numerical examples illustrating the difference between results of classical and discrete thermodynamic simulation methods are presented. The article offers an analytical formula to find the classical limit, compares analytical results with these obtained by simulation, and shows the classical limit dependence upon the chemical reaction stoichiometry and robustness. [source] Evaluation of numerical simulation methods in reactive extrusionADVANCES IN POLYMER TECHNOLOGY, Issue 3 2005Linjie Zhu Abstract Reactive extrusion is a complex process, and numerical simulation is an important method in optimizing operational parameters. In the current work, two different simulation methods, one-dimensional (1D) model and three-dimensional (3D) model, were introduced to predict the polymerization of ,-caprolactone in fully filled screw elements. The predicted results of polymerization progression under different simulation conditions based on these two methods were compared. The simulation results show that the simplifications and assumptions in 1D model make it difficult to capture the complex mixing mechanism, heat generation, and heat loss in reactive extrusion. 1D model is feasible only under particular conditions, such as low screw rotating speed, small heat from reaction, and small screw diameter, whereas 3D model is a more powerful simulation tool for much wider processing conditions. © 2005 Wiley Periodicals, Inc. Adv Polym Techn 24: 183,193, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20041 [source] MDLab: A molecular dynamics simulation prototyping environmentJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 7 2010Trevor Cickovski Abstract Molecular dynamics (MD) simulation involves solving Newton's equations of motion for a system of atoms, by calculating forces and updating atomic positions and velocities over a timestep ,t. Despite the large amount of computing power currently available, the timescale of MD simulations is limited by both the small timestep required for propagation, and the expensive algorithm for computing pairwise forces. These issues are currently addressed through the development of efficient simulation methods, some of which make acceptable approximations and as a result can afford larger timesteps. We present MDLab, a development environment for MD simulations built with Python which facilitates prototyping, testing, and debugging of these methods. MDLab provides constructs which allow the development of propagators, force calculators, and high level sampling protocols that run several instances of molecular dynamics. For computationally demanding sampling protocols which require testing on large biomolecules, MDL includes an interface to the OpenMM libraries of Friedrichs et al. which execute on graphical processing units (GPUs) and achieve considerable speedup over execution on the CPU. As an example of an interesting high level method developed in MDLab, we present a parallel implementation of the On-The-Fly string method of Maragliano and Vanden-Eijnden. MDLab is available at http://mdlab.sourceforge.net. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010 [source] Complex molecular assemblies at hand via interactive simulationsJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 15 2009Olivier Delalande Abstract Studying complex molecular assemblies interactively is becoming an increasingly appealing approach to molecular modeling. Here we focus on interactive molecular dynamics (IMD) as a textbook example for interactive simulation methods. Such simulations can be useful in exploring and generating hypotheses about the structural and mechanical aspects of biomolecular interactions. For the first time, we carry out low-resolution coarse-grain IMD simulations. Such simplified modeling methods currently appear to be more suitable for interactive experiments and represent a well-balanced compromise between an important gain in computational speed versus a moderate loss in modeling accuracy compared to higher resolution all-atom simulations. This is particularly useful for initial exploration and hypothesis development for rare molecular interaction events. We evaluate which applications are currently feasible using molecular assemblies from 1900 to over 300,000 particles. Three biochemical systems are discussed: the guanylate kinase (GK) enzyme, the outer membrane protease T and the soluble N -ethylmaleimide-sensitive factor attachment protein receptors complex involved in membrane fusion. We induce large conformational changes, carry out interactive docking experiments, probe lipid,protein interactions and are able to sense the mechanical properties of a molecular model. Furthermore, such interactive simulations facilitate exploration of modeling parameters for method improvement. For the purpose of these simulations, we have developed a freely available software library called MDDriver. It uses the IMD protocol from NAMD and facilitates the implementation and application of interactive simulations. With MDDriver it becomes very easy to render any particle-based molecular simulation engine interactive. Here we use its implementation in the Gromacs software as an example. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009 [source] ,-Dynamics free energy simulation methodsJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 11 2009Jennifer L. Knight Abstract Free energy calculations are fundamental to obtaining accurate theoretical estimates of many important biological phenomena including hydration energies, protein-ligand binding affinities and energetics of conformational changes. Unlike traditional free energy perturbation and thermodynamic integration methods, ,-dynamics treats the conventional "," as a dynamic variable in free energy simulations and simultaneously evaluates thermodynamic properties for multiple states in a single simulation. In the present article, we provide an overview of the theory of ,-dynamics, including the use of biasing and restraining potentials to facilitate conformational sampling. We review how ,-dynamics has been used to rapidly and reliably compute relative hydration free energies and binding affinities for series of ligands, to accurately identify crystallographically observed binding modes starting from incorrect orientations, and to model the effects of mutations upon protein stability. Finally, we suggest how ,-dynamics may be extended to facilitate modeling efforts in structure-based drug design. © 2009 Wiley Periodicals, Inc. J Comput Chem 2009 [source] Introduction to the special issue "small farms: decline or persistence?"AGRICULTURAL ECONOMICS, Issue 2009A. Bailey Agricultural diversification; Food chains; Globalization; Transition economies Abstract This issue of,Agricultural Economics,contains articles from a seminar entitled "Small Farms: Decline or Persistence?" held at the University of Kent. This issue includes nine papers selected from more than 50 papers presented at the seminar. Articles published use a range of econometric and simulation methods to provide a suite of case studies. Topics studied range from such fundamental issues as what constitutes a small farm to recent trends in the diversification of small farms and their integration into modern globalized food chains. Several papers emphasize the link between agricultural policy development and the future of small farms. [source] Introduction to the special issue on the world food crisisAGRICULTURAL ECONOMICS, Issue 2008William A. Masters Food prices; Food markets; Food policy; Poverty Abstract This issue of Agricultural Economics contains articles on the causes and effects of rising food prices. All papers were subject to full, double-blind peer review on an accelerated basis, in an effort to publish the best new research as quickly as possible. We received more than 60 submissions; referees were given three weeks to respond, and authors of candidate papers had an additional week to revise their work before final acceptance. Articles published use descriptive, econometric, and simulation methods for both global overviews and case studies. [source] A Comparison of Two Quadratic Approaches to Hedging in Incomplete MarketsMATHEMATICAL FINANCE, Issue 4 2001David Heath This paper provides comparative theoretical and numerical results on risks, values, and hedging strategies for local risk-minimization versus mean-variance hedging in a class of stochastic volatility models. We explain the theory for both hedging approaches in a general framework, specialize to a Markovian situation, and analyze in detail variants of the well-known Heston (1993) and Stein and Stein (1991) stochastic volatility models. Numerical results are obtained mainly by PDE and simulation methods. In addition, we take special care to check that all of our examples do satisfy the conditions required by the general theory. [source] Lineage diversification in a widespread species: roles for niche divergence and conservatism in the common kingsnake, Lampropeltis getulaMOLECULAR ECOLOGY, Issue 16 2009R. ALEXANDER PYRON Abstract Niche conservatism and niche divergence are both important ecological mechanisms associated with promoting allopatric speciation across geographical barriers. However, the potential for variable responses in widely distributed organisms has not been fully investigated. For allopatric sister lineages, three patterns for the interaction of ecological niche preference and geographical barriers are possible: (i) niche conservatism at a physical barrier; (ii) niche divergence at a physical barrier; and (iii) niche divergence in the absence of a physical barrier. We test for the presence of these patterns in a transcontinentally distributed snake species, the common kingsnake (Lampropeltis getula), to determine the relative frequency of niche conservatism or divergence in a single species complex inhabiting multiple distinct ecoregions. We infer the phylogeographic structure of the kingsnake using a range-wide data set sampled for the mitochondrial gene cytochrome b. We use coalescent simulation methods to test for the presence of structured lineage formation vs. fragmentation of a widespread ancestor. Finally, we use statistical techniques for creating and evaluating ecological niche models to test for conservatism of ecological niche preferences. Significant geographical structure is present in the kingsnake, for which coalescent tests indicate structured population division. Surprisingly, we find evidence for all three patterns of conservatism and divergence. This suggests that ecological niche preferences may be labile on recent phylogenetic timescales, and that lineage formation in widespread species can result from an interaction between inertial tendencies of niche conservatism and natural selection on populations in ecologically divergent habitats. [source] Measurement and analysis of vibration levels for truck transport in Spain as a function of payload, suspension and speedPACKAGING TECHNOLOGY AND SCIENCE, Issue 8 2008Manuel-Alfredo Garcia-Romeu-Martinez Abstract The vibration levels that occur during transportation in vehicles are complex and play a significant role in the level of damage experienced by products when shipped. In the past decade, technology has allowed packaging engineers to measure and analyse the vibration levels in commercial shipments. Recent studies have measured vibration in shipping environments on a global basis to allow packaging designers to develop packaging to meet worldwide distribution challenges. The purpose of this study was to measure and develop simulation methods for truck transport in Spain. The study quantifies vibration characteristics in trucks as a function of speed, payload and suspension type. The shipments were instrumented with vibration data recorders to measure the vibration levels and a global position system to measure the truck speed. The recorders were mounted at the rear and front location of the trailer. Two different trucks, one with leaf spring suspension and the other with air ride suspension were studied using two different load conditions. The road surface was asphalt. The data is presented in the form of power spectral density that can be used to program electrohydraulic vibration tables using ASTM, ISTA and ISO vibration test methods. Results showed that the air ride vibration levels were lower than that of leaf spring suspension trailers. Overall, the vibration intensity was lower for both types of truck as compared with the levels measured in North America, China, India and Southeast Asia. Copyright © 2007 John Wiley & Sons, Ltd. [source] Integral modeling approach to study the phase behavior of complex solids: application to phase transitions in MgSiO3 pyroxenesACTA CRYSTALLOGRAPHICA SECTION A, Issue 5 2010Sandro Jahn A combination of electronic structure calculations, classical molecular dynamics simulations and metadynamics is proposed to study the phase behavior of complex crystals. While the former provide accurate energetics for thermodynamic properties, molecular dynamics and metadynamics simulations may reveal new metastable phases and provide insight into mechanisms and kinetics of the respective structural transformations. Here, different simulation methods are used to investigate the polymorphism of MgSiO3 pyroxenes (enstatites) up to high pressures and temperatures. A number of displacive phase transitions are observed within the three basic structure types clino-, ortho- and protoenstatite using classical molecular dynamics simulations. Transitions between these types require a change of stacking order, which is modeled using a combination of molecular dynamics and metadynamics. [source] Human placental lactogen is a first-trimester maternal serum marker of Down syndromePRENATAL DIAGNOSIS, Issue 1 2007Michael Christiansen Abstract Background Human placental lactogen (hPL) is synthesised by the placenta and found in maternal serum. We analysed the potential of hPL as a first-trimester maternal serum-screening marker for fetal Down syndrome (DS). Materials and Methods hPL was quantified by ELISA in 47 DS pregnancies and 136 controls in gestational weeks 8,13. Distributions of log multiples of the median (MoMs) were established. The quantity of hPL in DS screening was estimated using Monte Carlo simulation methods. Results The mean log10 MoM hPL was , 0.1995 (SD: 0.1993) in affected and 0.0026 (SD: 0.2129) in control pregnancies. This corresponds to a MoM of 0.63 in DS pregnancies. hPL correlated significantly with log10 MoM values of hCG, (r = 0.320) and PAPP-A (r = 0.590) in controls, but not with hCG, (r = 0.228) or PAPP-A (r = 0.090) in DS pregnancies. The inclusion of hPL in the double test (PAPP-A + hCG,) increased the detection rate from 67 to 75% for a false-positive rate of 5%. Conclusion hPL is a DS screening marker that is applicable at weeks 9,13 and could be included in multiple marker first-trimester screening for DS. Copyright © 2007 John Wiley & Sons, Ltd. [source] A Holistic Simulation Approach from a Measured Load to Element Stress Using Combined Multi-body Simulation and Finite Element ModellingPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2009Matthias Harter The design of vehicle bodies requires the knowledge of the vehicle's structural response to external loads and disturbances. In rigid multi-body simulation the dynamic behaviour of complex systems is calculated with rigid bodies and neglect of body elasticity. On the other hand, in finite element models large degree of freedom numbers are used to represent the elastic properties of a single body. Both simulation methods can be combined, if the finite element model size is reduced to a degree of freedom number feasible to multi-body simulation. The application to practical purposes requires the use and interconnection of several different software tools. In this contribution a holistic method is presented, which starts with the measurement or synthesis of loads and excitations, continues with the integration of a reduced finite element model into a multi-body system, the dynamic response calculation of this combined model, and concludes with the result expansion to the full finite element model for calculating strain and stress values at any point of the finite element mesh. The applied software tools are Simpack, Nastran, and Matlab. An example is given with a railway vehicle simulated on measured track geometry. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Measuring business cycles with a dynamic Markov switching factor model: an assessment using Bayesian simulation methodsTHE ECONOMETRICS JOURNAL, Issue 1 2000Sylvia Kaufmann A Markov switching common factor is used to drive a dynamic factor model for important macroeconomic variables in eight countries. Bayesian estimation of the model is based on Markov chain Monte Carlo simulation methods which yield inferences about the unobservable path of the common factor, the latent variable of the state process and all model parameters. Additionally, simulation based filtering provides us with samples from the prediction density that can be used for model diagnostics and specification tests. The mean posterior state probabilities are used to date business cycle turning points that follow quite closely previous datings reported in the literature. Moreover, we test the Markov switching against a no-switching specification by means of a Bayes factor. The evidence proves to be quite favorable for the Markov switching model. [source] Structural elucidation of the Bi2(n,+,2)MonO6(n,+,1) (n = 3, 4, 5 and 6) family of fluorite superstructures by transmission electron microscopyACTA CRYSTALLOGRAPHICA SECTION B, Issue 4 2009Ángel R. Landa-Cánovas The cationic framework structure of a whole new family of compounds with the general formula Bi2(n,+,2)MonO6(n,+,1) (n = 3, 4, 5 and 6) has been elucidated by transmission electron microscopy (TEM) methods. High-resolution transmission electron microscopy (HRTEM) has been used to postulate heavy-atom models based on the known structure of the n = 3 phase, Bi10Mo3O24. These models were tested by HRTEM image simulation, electron diffraction and powder X-ray diffraction simulation methods which agreed with the experimental results. The four known phases of this family correspond to n = 3, 4, 5 and 6 members and all show fluorite superstructures. They consist of a common ,-Bi2O3 fluorite-type framework, inside of which are distributed ribbons of {MoO4} tetrahedra which are infinite along b, one tetrahedron thick along c, and of variable widths of 3, 4, 5 or 6 {MoO4} tetrahedra along a depending on the family member (n value). These {MoO4} tetrahedra are isolated, i.e. without sharing any corner as in the [Bi12O14] columnar structural-type phase Bi[Bi12O14][MoO4]4[VO4]. The structure of all these family members can be described as crystallographic shear derivatives from Aurivillius-type phases such as Bi2MoO6, the n = , end member. All these compounds are good oxygen-ion conductors. [source] Bayesian modeling of financial returns: A relationship between volatility and trading volumeAPPLIED STOCHASTIC MODELS IN BUSINESS AND INDUSTRY, Issue 2 2010Carlos A. Abanto-Valle Abstract The modified mixture model with Markov switching volatility specification is introduced to analyze the relationship between stock return volatility and trading volume. We propose to construct an algorithm based on Markov chain Monte Carlo simulation methods to estimate all the parameters in the model using a Bayesian approach. The series of returns and trading volume of the British Petroleum stock will be analyzed. Copyright © 2009 John Wiley & Sons, Ltd. [source] Minimally invasive surgical technologies: Challenges in education and trainingASIAN JOURNAL OF ENDOSCOPIC SURGERY, Issue 3 2010J Sándor Abstract The laparoscopic revolution has fundamentally changed surgical technology. However, this new technology, with its unique psychomotor adaptations, has been a challenge for both experienced and novice surgeons. This review summarizes the history of practical education and training methods and those currently used to ensure surgeons safely practice these new surgical skills. Traditional training boxes, augmented reality simulators and virtual reality simulators represent recently developed educational tools. There are objective programs that subsequently assess the results of training by these simulation methods. Additionally, the advent of robotics in laparoscopic surgery has been accompanied by the introduction of computer-based robotic surgical simulators. Surgical curricula should also include non-technical skills training, particularly as global certification of technical and non-technical surgical skills is expected in the near future. Ultimately, these new systems of surgical simulation contribute to a decrease in surgical error as well as with reduced morbidity and mortality. [source] AN APPROXIMATION FOR THE OPTIMAL LINEAR INCOME TAX RATEAUSTRALIAN ECONOMIC PAPERS, Issue 3 2009JOHN CREEDY This paper derives a convenient method of calculating an approximation to the optimal tax rate in a linear income tax structure. Individuals are assumed to have Cobb-Douglas preferences and the wage rate distribution is lognormal. First, the optimal tax rate is shown, for a general form of social welfare function, to be the smallest root of a quadratic equation involving a welfare-weighted average wage rate. Second, an approximation to this average is derived for an isoelastic social welfare function. This average depends on the degree of inequality aversion of the welfare function and the coefficient on consumption in individuals' utility functions. Calculations show that the method performs well in comparison with standard simulation methods of computing the optimal tax rate. [source] Advanced Medical Simulation Applications for Emergency Medicine Microsystems Evaluation and TrainingACADEMIC EMERGENCY MEDICINE, Issue 11 2008Leo Kobayashi MD Abstract Participants in the 2008 Academic Emergency Medicine Consensus Conference "The Science of Simulation in Healthcare: Defining and Developing Clinical Expertise" morning workshop session on developing systems expertise were tasked with evaluating best applications of simulation techniques and technologies to small-scale systems in emergency medicine (EM). We collaborated to achieve several objectives: 1) describe relevant theories and terminology for discussion of health care systems and medical simulation, 2) review prior and ongoing efforts employing systems thinking and simulation programs in general medical sectors and acute care medicine, 3) develop a framework for discussion of systems thinking for EM, and 4) explore the rational application of advanced medical simulation methods to a defined framework of EM microsystems (EMMs) to promote a "quality-by-design" approach. This article details the materials compiled and questions raised during the consensus process, and the resulting simulation application framework, with proposed solutions as well as their limitations for EM systems education and improvement. [source] Molecular dynamics calculations on amylose fragments.BIOPOLYMERS, Issue 2 2002Abstract Molecular dynamics simulations (NPT ensembles, 1 atm) using the all atom force field AMB99C (F. A. Momany and J. L. Willett, Carbohydrate Research, Vol. 326, pp 194,209 and 210,226), are applied to a periodic cell containing ten maltodecaose fragments and TIP3P water molecules. Simulations were carried out at 25 K intervals over a range of temperatures above and below the expected glass transition temperature, Tg, for different water concentrations. The amorphous cell was constructed through successive dynamic equilibration steps at temperatures above Tg and the temperature lowered until several points of reduced slope (1/T vs volume) were obtained. This procedure was carried out at each hydration level. Each dynamics simulation was continued until the volume remained constant without up or down drift for at least the last 100 ps. For a given temperature, most simulations required 400,600 ps to reach an equilibrium state, but longer times were necessary as the amount of water in the cell was reduced. A total of more than 30 ns of simulations were required for the complete study. The Tg for each hydrated cell was taken as that point at which a discontinuity in slope of the volume (V), potential energy (PE), or density (,) vs 1/T was observed. The average calculated Tg values were 311, 337, 386, and 477 K for hydration levels of 15.8, 10, 5, and 1%, respectively, in generally good agreement with experimental values. The Tg for anhydrous amylose is above the decomposition temperature for carbohydrates and so cannot be easily measured. However, it has also been difficult to obtain a value of Tg for anhydrous amylose using simulation methods. Other molecular parameters such as end-to-end distances, mean square distributions, and pair distributions are discussed. Published 2002 John Wiley & Sons, Inc. Biopolymers 63: 99,110, 2002 [source] Searching Inhibitors of Adenosine Kinase by Simulation MethodsCHINESE JOURNAL OF CHEMISTRY, Issue 11 2006Rui-Xin Zhu Abstract Searching new inhibitors of adenosine kinase (AK) is still drawing attention of experimental scientists. A better and solid model is here proposed by means of simulation methods from different ways, the direct analysis of receptor itself, the conventional 3D-QSAR methods and the integration of docking method and the conventional QSAR analysis. [source] | |||||||||||||||||||||||||||||||||||||