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Computer Simulations (computer + simulation)
Kinds of Computer Simulations Terms modified by Computer Simulations Selected AbstractsProceedings of the Third International Workshop on Computer Simulation and Experimental Assessment of Cardiac Electrical FunctionJOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 2003ANDRÉ KLÉBER M.D., Ph.D. No abstract is available for this article. [source] Computer Simulation of Dissociative Adsorption of Water on the Surfaces of Spinel MgAl2O4JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2001Chang Ming Fang Atomistic simulation techniques have been used to model the dissociative adsorption of water onto the low-index {100}, {110}, and {111} surfaces of spinel MgAl2O4. The Born model of solids and the shell model for oxygen polarization have been used. The resulting structures and chemical bonding on the clean and hydrated surfaces are described. The calculations show that the dissociative adsorption of water on the low-index surfaces is generally energetically favorable. For the {110} and {111} orientations, the surfaces cleaved between oxygen layers show high absorption and stability. The calculations also show that, for the {111} orientation, the surfaces may absorb chemically water molecules up to ,90% coverage and have the highest stability. It is suggested that, during fracture, only partial hydration occurs, leading to cleavage preferentially along the {100} orientation. [source] Computer Simulation and the Philosophy of SciencePHILOSOPHY COMPASS (ELECTRONIC), Issue 5 2009Eric Winsberg There are a variety of topics in the philosophy of science that need to be rethought, in varying degrees, after one pays careful attention to the ways in which computer simulations are used in the sciences. There are a number of conceptual issues internal to the practice of computer simulation that can benefit from the attention of philosophers. This essay surveys some of the recent literature on simulation from the perspective of the philosophy of science and argues that philosophers have a lot to learn by paying closer attention to the practice of simulation. [source] The interactive effects of personal traits and guided practices on preservice teachers' changes in personal teaching efficacyBRITISH JOURNAL OF EDUCATIONAL TECHNOLOGY, Issue 4 2006Yu-Chu Yeh Personal teaching efficacy is associated with a teacher's effectiveness in the classroom. To enhance this efficacy in a computer-simulated training program, both personal traits and guided practices need to be considered concurrently. In this study, it was hypothesised that the interactive effects from the coupling of personal traits with guided practices would be a reliable predictor of the degree of improvement in personal teaching efficacy during computer-simulated training. One hundred and seventy-eight preservice teachers completed an interactive teaching experience via the Computer Simulation for Teaching General Critical-thinking Skills in which guided practices were integrated via specially designed teaching sequences and loops. The findings suggest that intrapersonal intelligence, critical-thinking dispositions and a judicial thinking style are related to self-awareness, analytical learning and reflective thinking and that in this study, these personal qualities seemingly interacted with guided practices, which resulted in reflective teaching and mastery experience. This, in turn, may very well have brought about improvement in the preservice teachers' personal teaching efficacy during the computer-simulated teaching. [source] Hypothetical Uninodal Zeolite Structures: Comparison of AlPO4 and SiO2 Compositions Using Computer Simulation.CHEMINFORM, Issue 13 2004Alexandra Simperler No abstract is available for this article. [source] Computer Simulation of Long Side-Chain Substituted Poly(phenylene vinylene) PolymersCHEMPHYSCHEM, Issue 3 2004Hsiao-Ching Yang Abstract A molecular dynamics (MD) simulation was employed to investigate structure features and segment orientation of four poly(phenylene vinylene) (PPV) derivatives with long, flexible side chains at room temperature. In the simulations, the main chains of the polymers were found to be semirigid and exhibit a tendency to coil into ellipsoidal helices or form zigzag conformations of limited regularity. The simulations show that continuous quasi-coplanar segments along the backbone are in a range of ,2,4 repeat units. The ordered orientation and coupling distance of interchain aromatic rings can be correlated with optical properties of materials. A simplified quantum-mechanical method was developed to investigate optical properties based on MD trajectories. The method was tested to simulate the absorption spectra of four PPV derivatives. The absorption maxima of the calculated spectra are in reasonable agreement with experimental data. This work implies that long-range electron transfer along the backbones of these polymers may not occur, but may be mediated by interchain interactions. [source] Grafted Polymer Chains Interacting with Substrates: Computer Simulations and ScalingMACROMOLECULAR THEORY AND SIMULATIONS, Issue 9 2008Radu Descas Abstract We review scaling methods and computer simulations used in the study of the static and dynamic properties of polymer chains tethered to adsorbing surfaces under good solvent conditions. By varying both the grafting density and the monomer/surface interactions a variety of phases can form. In particular, for attractive interactions between the chains and the surface the classical mushroom-brush transition known for repulsive substrates splits up into an overlap transition and a saturation transition which enclose a region of semidilute surface states. At high grafting densities oversaturation effects and a transition to a brush state can occur. We emphasize the role of the critical adsorption parameters for a correct description and understanding of such polymer adsorption phenomena. [source] Electrokinetic partial filling technique as a powerful tool for enantiomeric separation of DL -lactic acid by CE with contactless conductivity detectionELECTROPHORESIS, Issue 11 2007zslav Maier Dr. Abstract A modified partial filling method for chiral separation of DL -lactic acid as the model chiral compound with vancomycin chloride as the chiral selector was developed by CE with contactless conductivity detection. Electrokinetic partial filling technique (EK-PFT) was used as an alternative method to the conventional hydrodynamic partial filling method. EK-PFT, in contrast to the hydrodynamic partial filling technique, allowed the removal of the chloride counterions from the chiral selector which otherwise led to poor sensitivity in conductivity detection. The baseline separation of DL -lactic acid as the model analyte was achieved in 5,min in a polyacrylamide-coated capillary. The best resolution was achieved by electrokinetic partial filling of vancomycin cations from the injection solution containing 5,mmol/L oxalate L -histidinium at pH,4.5 with 10,mmol/L vancomycin chloride. Computer simulation was used to explain the observed phenomena in the boundary between the inject vial and the capillary during the EK-PFT of vancomycin cations. [source] Clustering composition vectors using uncertainty informationENVIRONMETRICS, Issue 8 2007William F. Christensen Abstract In the biological and environmental sciences, interest often lies in using multivariate observations to discover natural clusters of objects. In this manuscript, the incorporation of measurement uncertainty information into a cluster analysis is discussed. This study is motivated by a problem involving the clustering of composition vectors associated with each of several chemical species. The observed abundance of each component is available along with its estimated uncertainty (measurement error standard deviation). An approach is proposed for converting the abundance vectors into composition (relative abundance) vectors, obtaining the covariance matrix associated with each composition vector, and defining a Mahalanobis distance between composition vectors that are suitable for cluster analysis. The approach is illustrated using particle size distributions obtained near Houston, Texas in 2000. Computer simulation is used to compare the performance of Mahalanobis-distance-based and Euclidean-distance-based clustering approaches. The use of a modified Mahalanobis distance along with Ward's method is recommended for use. Copyright © 2007 John Wiley & Sons, Ltd. [source] Computer simulation of the population dynamics of Panonychus ulmi and applications to integrated pest management,EPPO BULLETIN, Issue 1 2000M. Sobala Panonychus ulmi is a serious pest of apple orchards, especially in hot dry years. To improve quantitative insight into its population dynamics, and as a tool for forecasting optimal dates for visual assessment of abundance and of integrated pest management strategies, an age- and stage-structured temperature-dependent predator,prey model for P. ulmi and two of its natural enemies, Typhlodromus pyri and Amblyseius potentillae, has been developed. [source] Adaptive transfer function-based control of nonlinear process.INTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 10 2007Case study: Control of temperature in industrial methane tank Abstract The state model-based transfer function models are applied for adaptation of linear controller and disturbance compensator in a feedback/feed-forward control system of nonlinear process. An advantage of the presented adaptation method is the avoidance of artificial disturbances or iterative identification procedures for on-line estimation of process dynamic parameters. The adaptation is based on linearization of the process model at each sampling time about the current state point, independent of the process being at steady-state or transient conditions. The linear time-varying dynamics model is updated on-line using measured values of process variables and reduced to the first-order plus time delay transfer function models in order to directly apply well-developed controller tuning rules. Computational aspects of the adaptation method are discussed and computation algorithms are presented. The adaptive feedback/feed-forward control system was applied for controlling temperature in industrial methane tank, dynamic parameters of which vary in a wide range due to variations of methane-tank process load and external conditions. The heat balance-based process state model is developed and validated using observation data of real plant. Computer simulation of the proposed control system performance under extreme operating conditions demonstrates fast adaptation of controller parameters, robust behaviour and significant improvement in the controllers' performance compared to that of fixed-gain controllers. Copyright © 2007 John Wiley & Sons, Ltd. [source] Computer simulation of flow-sheets for the solvent extraction of uranium: a new route to delay the effect of chemical degradation of the organic phase during uranium recovery from acidic sulfate mediaJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 12 2009Alexandre Chagnes Abstract BACKGROUND: The extractants used in solvent extraction processes undergo degradation under thermal, chemical and radiolytical stresses. In the case of uranium plants, tri- n -octylamine, used as an extractant, slowly degrades into di- n -octylamine. Such degradation causes a gradual depletion of the uranium extraction isotherms and as a result, of the efficiency of uranium recovery from feed solutions. The present work highlights a new route to delay this depletion of the extraction efficiency, merely by optimizing the flow-sheets involved in the process. Five flow-sheets have been compared for uranium recovery from acidic sulfate media by a solution of 0.146 mol L,1 tri- n -octylamine in kerosene modified with 5% w/w 1-tridecanol and stripping with a 199 g L,1 Na2CO3 solution. These five flow-sheets include the classical counter-current flow-sheet with four mixers,settlers in extraction and three mixers,settlers in stripping and four unusual combined solvent extraction flow-sheets with two independent extraction stripping loops and with one or two feed inlets. RESULTS: Computer simulation supplied evidence of the strong influence of the studied flow-sheets on the sturdiness of the process. More precisely, the unusual combined solvent extraction flow-sheets appeared to be significantly more efficient than the classical counter-current one and it is shown that an advantage of this can be to delay the negative impact of gradual degradation of tri- n -octylamine on uranium recovery efficiency from acidic sulfate media. CONCLUSION: The replacement of classical counter-current flow-sheets with a unique extraction-stripping loop in unusual combined flow-sheets with two or more independent extraction-stripping loops and with one or more feed inlets is a fruitful approach to delay the periodic addition of fresh tri- n -octylamine necessary for counter-balancing the progressive degradation of the extraction solvent and, as a result, to delay the gradual depletion of the efficiency of uranium recovery. Copyright © 2009 Society of Chemical Industry [source] SODOCK: Swarm optimization for highly flexible protein,ligand dockingJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 2 2007Hung-Ming Chen Abstract Protein,ligand docking can be formulated as a parameter optimization problem associated with an accurate scoring function, which aims to identify the translation, orientation, and conformation of a docked ligand with the lowest energy. The parameter optimization problem for highly flexible ligands with many rotatable bonds is more difficult than that for less flexible ligands using genetic algorithm (GA)-based approaches, due to the large numbers of parameters and high correlations among these parameters. This investigation presents a novel optimization algorithm SODOCK based on particle swarm optimization (PSO) for solving flexible protein,ligand docking problems. To improve efficiency and robustness of PSO, an efficient local search strategy is incorporated into SODOCK. The implementation of SODOCK adopts the environment and energy function of AutoDock 3.05. Computer simulation results reveal that SODOCK is superior to the Lamarckian genetic algorithm (LGA) of AutoDock, in terms of convergence performance, robustness, and obtained energy, especially for highly flexible ligands. The results also reveal that PSO is more suitable than the conventional GA in dealing with flexible docking problems with high correlations among parameters. This investigation also compared SODOCK with four state-of-the-art docking methods, namely GOLD 1.2, DOCK 4.0, FlexX 1.8, and LGA of AutoDock 3.05. SODOCK obtained the smallest RMSD in 19 of 37 cases. The average 2.29 Ĺ of the 37 RMSD values of SODOCK was better than those of other docking programs, which were all above 3.0 Ĺ. © 2006 Wiley Periodicals, Inc. J Comput Chem 28: 612,623, 2007 [source] The Reliability of Difference Scores in Populations and SamplesJOURNAL OF EDUCATIONAL MEASUREMENT, Issue 1 2009Donald W. Zimmerman This study was an investigation of the relation between the reliability of difference scores, considered as a parameter characterizing a population of examinees, and the reliability estimates obtained from random samples from the population. The parameters in familiar equations for the reliability of difference scores were redefined in such a way that determinants of reliability in both populations and samples become more transparent. Computer simulation was used to find sample values and to plot frequency distributions of various correlations and variance ratios relevant to the reliability of differences. The shape of frequency distributions resulting from the simulations and the means and standard deviations of these distributions reveal the extent to which reliability estimates based on sample data can be expected to meaningfully represent population reliability. [source] Sexual selection maintains whole-body chiral dimorphism in snailsJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 5 2007M. SCHILTHUIZEN Abstract Although the vast majority of higher animals are fixed for one chiral morph or another, the cause for this directionality is known in only a few cases. In snails, for example, rare individuals of the opposite coil are unable to mate with individuals of normal coil, so directionality is maintained by frequency-dependent selection. The snail subgenus Amphidromus presents an unexplained exception, because dextral (D) and sinistral (S) individuals occur sympatrically in roughly equal proportions (so-called ,antisymmetry') in most species. Here we show that in Amphidromus there is sexual selection for dimorphism, rather than selection for monomorphism. We found that matings between D and S individuals occur more frequently than expected by chance. Anatomical investigations showed that the chirality of the spermatophore and the female reproductive tract probably allow a greater fecundity in such inter-chiral matings. Computer simulation confirms that under these circumstances, sustained dimorphism is the expected outcome. [source] The Effect of Activation/Deactivation Processes on the Microcomposition and Microsequence Structure of Controlled/Living CopolymersMACROMOLECULAR THEORY AND SIMULATIONS, Issue 2-3 2008Ying Shi Abstract A new method is proposed to study the process of controlled/living radical copolymerization as well as the structures of the products. Computer simulation has been carried out to produce this LRP or CRP propagation including the activation/deactivation process. The information about segment distribution was obtained for the first time. The results show that under a stationary condition, controlled/living copolymer's composition and sequence distribution are totally identical to those prepared from the conventional free radical copolymerization (FRcP). In other words, the activation/deactivation process of controlled/living radical copolymerization has no effect on copolymer's microcomposition and microsequence structure. [source] The streak retinoscopy pupil reflex in the presence of astigmatismOPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 4 2003G. Smith Abstract Computer simulation is being increasingly used as a teaching tool. Having developed a computer-generated virtual focimeter, we are now in the process of developing a computer-generated virtual streak retinoscope to teach the principles of retinoscopy and the effect of residual refractive error and mirror movement on the pupil reflex. One of the important requirements was to provide as accurate a simulation as possible for the completely general case of an astigmatic patient and a streak in any orientation being moved also in any orientation. This required a thorough understanding of the optical theory of the retinoscope and equations that describe the behaviour of the pupil reflex. We have taken this opportunity to review the optics of the streak retinoscope and derive equations for the behaviour of the pupil streak reflex. [source] Computer simulation of stress-induced crystallization in injection molded thermoplasticsPOLYMER ENGINEERING & SCIENCE, Issue 11 2001Jianxin Guo Injection molding of semicrystalline plastics was simulated with the proposed stress-induced crystallization model. A pseudo-concentration method was used to track the melt front advancement. Stress relaxation was considered using the WFL model. Simulations were carried out under different processing conditions to investigate the effect of processing parameters on the crystallinity of the final part. The simulation results reproduced most of the experimental results in the literature. Comparison is made between the slow-crystallizing polymer (PET) and fast-crystallizing polymer (PP) to demonstrate the effect of stress on the crystallization kinetics during the injection molding process for materials with different crystallization properties. The results show that for fast-crystallizing plastics, stress has little effect on the final crystallinity in the injection molded parts. [source] Confidence Intervals for Unbalanced Two-factor Gauge R&R StudiesQUALITY AND RELIABILITY ENGINEERING INTERNATIONAL, Issue 8 2005Liyun Gong Abstract We consider methods for constructing confidence intervals in a two-factor gauge repeatability and reproducibility (R&R) study when there are unequal replicates. We consider both random and mixed models and propose a general approach using unweighted sums of squares. Computer simulation is used to determine how well confidence intervals maintain the stated confidence level. The main conclusion is that the method performs well under a variety of conditions typically encountered in gauge R&R studies. The method is simple and the intervals can be computed in a spreadsheet program. Copyright © 2005 John Wiley & Sons, Ltd. [source] Heat opens axon initial segment sodium channels: A febrile seizure mechanism?,ANNALS OF NEUROLOGY, Issue 2 2009Evan A. Thomas PhD Objective A number of hypotheses have been put forward as to why humans respond to fever by seizing. The current leading hypotheses are that respiratory alkalosis produces an as yet unidentified change in neural excitability or that inflammatory mediators potentiate excitatory synaptic transmission. However, it is well known that ion channel gating rates increase with increased temperature. Furthermore, skeletal and cardiac sodium channel activation can be temperature sensitive in some situations. We measured the temperature sensitivity of the brain sodium channel, NaV1.2, to determine whether febrile temperatures might produce a direct increase in neuronal excitability. Methods The effect of temperature on NaV1.2 electrophysiological properties was measured in a transfected mammalian cell line. The subcellular location of NaV1.2 in the mouse brain was ascertained using antibodies against NaV1.2 and ankyrin-G. Computer simulation of a hippocampal granule cell model was used to predict the effect of temperature on action potential firing. Results As well as the expected increase in gating rates, the voltage dependence of activation became 7.6mV more negative when the temperature was increased from 37°C to 41°C. NaV1.2 was localized to the axon initial segment in hippocampal and cortical neurons. Computer simulation showed that increased gating rates and the more negative activation dramatically increase neuronal excitability. Interpretation The direct effect of heat on ion channels localized to the site of action potential initiation potentially causes a profound increase in neuronal excitability. This is likely to contribute to febrile seizure genesis. Ann Neurol 2009;66:219,226 [source] A Review of HNS-32: A Novel Azulene-l-Carboxamidine Derivative with Multiple Cardiovascular Protective ActionsCARDIOVASCULAR THERAPEUTICS, Issue 4 2001Yoshio Tanaka ABSTRACT HNS-32 [N1,N1 -dimethyl- N2 -(2-pyridylmethyl)-5-isopropyl-3,8-dimethylazulene-1-carboxamidine] (CAS Registry Number: 186086-10-2) is a newly synthesized azulene derivative. Computer simulation showed that its three dimensional structure is similar to that of the class Ib antiarrhythmic drugs, e.g., lidocaine or mexiletine. HNS-32 potently suppressed ventricular arrhythmias induced by ischemia due to coronary ligation and/or ischemia-reperfusion in dogs and rats. In the isolated dog and guinea pig cardiac tissues, HNS-32 had negative inotropic and chronotropic actions, prolonged atrial-His and His-ventricular conduction time and increased coronary blood flow. In the isolated guinea pig ventricular papillary muscle, HNS-32 decreased maximal rate of action potential upstroke (V,max) and shortened action potential duration (APD). These findings suggest that HNS-32 inhibits inward Na+ and Ca2+ channel currents. In the isolated pig coronary and rabbit conduit arteries, HNS-32 inhibited both Ca2+ channel-dependent and -independent contractions induced by a wide variety of chemical stimuli. HNS-32 is a potent inhibitor of protein kinase C (PKC)-mediated constriction of cerebral arteries. It is likely to block both, Na+ and Ca2+ channels expressed in cardiac and vascular smooth muscles. These multiple ion channel blocking effects are largely responsible for the antiarrhythmic and vasorelaxant actions of HNS-32. This drug may represent a novel approach to the treatment of arrhythmias. [source] Consistent dynamics suggests tight regulation of biophysical parameters in a small network of bursting neuronsDEVELOPMENTAL NEUROBIOLOGY, Issue 14 2006Attila Szücs Abstract The neuronal firing patterns in the pyloric network of crustaceans are remarkably consistent among animals. Although this characteristic of the pyloric network is well-known, the biophysical mechanisms underlying the regulation of the systems output are receiving renewed attention. Computer simulations of the pyloric network recently demonstrated that consistent motor output can be achieved from neurons with disparate biophysical parameters among animals. Here we address this hypothesis by pharmacologically manipulating the pyloric network and analyzing the emerging voltage oscillations and firing patterns. Our results show that the pyloric network of the lobster stomatogastric ganglion maintains consistent and regular firing patterns even when entire populations of specific voltage-gated channels and synaptic receptors are blocked. The variations of temporal parameters used to characterize the burst patterns of the neurons as well as their intraburst spike dynamics do not display statistically significant increase after blocking the transient K-currents (with 4-aminopyridine), the glutamatergic inhibitory synapses (with picrotoxin), or the cholinergic synapses (with atropine) in pyloric networks from different animals. These data suggest that in this very compact circuit, the biophysical parameters are cell-specific and tightly regulated. © 2006 Wiley Periodicals, Inc. J Neurobiol, 2006 [source] A new type of migrating zone boundary in electrophoresis: 1.ELECTROPHORESIS, Issue 2 2005General description of boundary behavior based on electromigration dispersion velocity profiles Abstract Till now two principal types of electrophoretic boundaries have been recognized: a steady-state one showing self-sharpening properties and an unsteady-state one showing electromigration dispersion (EMD). In this contribution, the existence of a third (hybrid) type of electrophoretic boundary is revealed, that shows simultaneously: (i) steady-state character with self-sharpening properties in a certain part of the boundary, demarcated by a certain range of its composition; (ii) unsteady-state character with EMD in the resting part. A new theoretical approach to the study of the structure and properties of electrophoretic boundaries is presented, based on EMD velocity profiles representing the dependence of the EMD velocity on the composition in any point of the transition region across the boundary. According to this approach, the linearity or nonlinearity of the EMD velocity profile is recommended as the criterion for distinguishing the actual type of the boundary in question. It is shown that the new type of electrophoretic boundary is not an exotic case but may be observed even in simple systems as, e.g., formed by adjacent zones containing mixtures of current species such as picrate and acetate. Computer simulations are presented which confirm the theoretical conclusions and illustrate the three types of electrophoretic boundaries. [source] BALANCING SELECTION, RANDOM GENETIC DRIFT, AND GENETIC VARIATION AT THE MAJOR HISTOCOMPATIBILITY COMPLEX IN TWO WILD POPULATIONS OF GUPPIES (POECILIA RETICULATA)EVOLUTION, Issue 12 2006Cock van Oosterhout Abstract Our understanding of the evolution of genes of the major histocompatibility complex (MHC) is rapidly increasing, but there are still enigmatic questions remaining, particularly regarding the maintenance of high levels of MHC polymorphisms in small, isolated populations. Here, we analyze the genetic variation at eight microsatellite loci and sequence variation at exon 2 of the MHC class IIB (DAB) genes in two wild populations of the Trinidadian guppy, Poecilia reticulata. We compare the genetic variation of a small (Ne, 100) and relatively isolated upland population to that of its much larger (Ne, 2400) downstream counterpart. As predicted, microsatellite diversity in the upland population is significantly lower and highly differentiated from the population further downstream. Surprisingly, however, these guppy populations are not differentiated by MHC genetic variation and show very similar levels of allelic richness. Computer simulations indicate that the observed level of genetic variation can be maintained with overdominant selection acting at three DAB loci. The selection coefficients differ dramatically between the upland (s 0.2) and lowland (s, 0.01) populations. Parasitological analysis on wild-caught fish shows that parasite load is significantly higher on upland than on lowland fish, which suggests that large differences in selection intensity may indeed exist between populations. Based on the infection intensity, a substantial proportion of the upland fish would have suffered direct or indirect fitness consequences as a result of their high parasite loads. Selection by parasites plays a particularly important role in the evolution of guppies in the upland habitat, which has resulted in high levels of MHC diversity being maintained in this population despite considerable genetic drift. [source] High Quality Factor Metallodielectric Hybrid Plasmonic,Photonic CrystalsADVANCED FUNCTIONAL MATERIALS, Issue 12 2010Xindi Yu Abstract A 2D polystyrene colloidal crystal self-assembled on a flat gold surface supports multiple photonic and plasmonic propagating resonance modes. For both classes of modes, the quality factors can exceed 100, higher than the quality factor of surface plasmons (SP) at a polymer,gold interface. The spatial energy distribution of those resonance modes are carefully studied by measuring the optical response of the hybrid plasmonic,photonic crystal after coating with dielectric materials under different coating profiles. Computer simulations with results closely matching those of experiments provide a clear picture of the field distribution of each resonance mode. For the SP modes, there is strong confinement of electromagnetic energy near the metal surface, while for optical modes, the field is confined inside the spherical particles, far away from the metal. Coating of dielectric material on the crystal results in a large shift in optical features. A surface sensor based on the hybrid plasmonic,photonic crystal is proposed, and it is shown to have atomic layer sensitivity. An example of ethanol vapor sensing based on physisorption of ethanol onto the sensor surface is demonstrated. [source] Adaptive synchronization for nonlinear FitzHugh,Nagumo neurons in external electrical stimulationINTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 9 2008Chung-Wen Lai Abstract This paper investigates the synchronization problem for FitzHugh,Nagumo (FHN) neurons in external electrical stimulations. Using the sliding mode control technique, an adaptive control law is established that guarantees synchronization even when the parameters of the master and slave FHN neurons are fully unknown. A proportional-integral switching surface is introduced to simplify the task of assigning the stability of the closed-loop error system in the sliding mode. Furthermore, the proposed synchronization scheme is then applied to a secure communication system. Computer simulations are provided to verify the effectiveness of the proposed adaptive synchronization scheme. Copyright © 2007 John Wiley & Sons, Ltd. [source] Determination of the rate coefficients of the SO2 + O + M , SO3 + M reactionINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 3 2010S. M. Hwang Rate coefficients of the title reaction R31 (SO2 + O + M , SO3 + M) and R56 (SO2 + HO2, SO3 + OH), important in the conversion of S(IV) to S(VI), were obtained at T = 970,1150 K and ,ave = 16.2 ,mol cm,3 behind reflected shock waves by a perturbation method. Shock-heated H2/O2/Ar mixtures were perturbed by adding small amounts of SO2 (1%, 2%, and 3%) and the OH temporal profiles were then measured using laser absorption spectroscopy. Reaction rate coefficients were elucidated by matching the characteristic reaction times acquired from the individual experimental absorption profiles via simultaneous optimization of k31 and k56 values in the reaction modeling (for satisfactory matches to the observed characteristic times, it was necessary to take into account R56). In the experimental conditions of this study, R31 is in the low-pressure limit. The rate coefficient expressions fitted using the combined data of this study and the previous experimental results are k31,0/[Ar] = 2.9 × 1035 T,6.0 exp(,4780 K/T) + 6.1 × 1024 T,3.0 exp(,1980 K/T) cm6 mol,2 s,1 at T = 300,2500 K; k56 = 1.36 × 1011 exp(,3420 K/T) cm3 mol,1 s,1 at T = 970,1150 K. Computer simulations of typical aircraft engine environments, using the reaction mechanism with the above k31,0 and k56 expressions, gave the maximum S(IV) to S(VI) conversion yield of ca. 3.5% and 2.5% for the constant density and constant pressure flow condition, respectively. Moreover, maximum conversions occur at rather higher temperatures (,1200 K) than that where the maximum k31,0 value is located (,800 K). This is because the conversion yield is dependent upon not only the k31,0 and k56 values (production flux) but also the availability of H, O, and HO2 in the system (consumption flux). © 2010 Wiley Periodicals, Inc., Int J Chem Kinet 42: 168,180, 2010 [source] Bifurcation behaviour in parallel-connected boost convertersINTERNATIONAL JOURNAL OF CIRCUIT THEORY AND APPLICATIONS, Issue 3 2001H. H. C. Iu Abstract This paper describes the bifurcation phenomena of a system of parallel-connected d.c./d.c. boost converters. The results provide important information for the design of stable current sharing in a master,slave configuration. Computer simulations and experiments are performed to capture the effects of variation of some chosen parameters on the qualitative behaviour of the system. In particular, it is found that variation of some parameters leads to Neimark,Sacker bifurcation. Analysis is presented to establish the possibility of the bifurcation phenomena. Copyright © 2001 John Wiley & Sons, Ltd. [source] Reconstruction of chaotic signals with application to channel equalization in chaos-based communication systemsINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 3 2004Jiuchao Feng Abstract A number of schemes have been proposed for communication using chaos over the past years. Regardless of the exact modulation method used, the transmitted signal must go through a physical channel which undesirably introduces distortion to the signal and adds noise to it. The problem is particularly serious when coherent-based demodulation is used because the necessary process of chaos synchronization is difficult to implement in practice. This paper addresses the channel distortion problem and proposes a technique for channel equalization in chaos-based communication systems. The proposed equalization is realized by a modified recurrent neural network (RNN) incorporating a specific training (equalizing) algorithm. Computer simulations are used to demonstrate the performance of the proposed equalizer in chaos-based communication systems. The Hénon map and Chua's circuit are used to generate chaotic signals. It is shown that the proposed RNN-based equalizer outperforms conventional equalizers as well as those based on feedforward neural networks for noisy, distorted linear and non-linear channels. Copyright © 2004 John Wiley & Sons, Ltd. [source] A direct conversion receiver for satellite communication systemsINTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 2 2005Xinping Huang Abstract A direct receiver is an alternative to the well-established super-heterodyne receiver. It is especially attractive to highly integrated low-cost terminals since it eliminates the need for components at intermediate frequencies. There is increasingly more interest in using it in various ground/space-based systems. This article presents a new direct quadrature receiver that uses three channels with different phase shifts and a novel technique to derive the in-phase and quadrature baseband signals independent of the actual gains and phases in the receiver chains. The new technique relies on the property that the in-phase and quadrature signals are orthogonal, and its implementation involves the signal subspace decomposition and projection. Computer simulations and a 90 Mbps Ka-band prototype receiver have demonstrated that the performance of the receiver closely matches the theory. Copyright © 2005 John Wiley & Sons, Ltd. [source] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||