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Gaussian
Kinds of Gaussian Terms modified by Gaussian Selected AbstractsDirect ab initio dynamics calculations of the rate constants for the reaction of CHF2CF2OCH3 with ClINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 4 2007Lei Yang A dual-level direct dynamics method is employed to reveal the dynamical properties of the reaction of CHF2CF2OCH3 (HFE-254pc) with Cl atoms. The optimized geometries and frequencies of the stationary points and the minimum energy path (MEP) are calculated at the B3LYP/6-311G(d,p) level by using GAUSSIAN 98 program package, and energetic information is further refined by the G3(MP2) method. Two H-abstraction channels have been identified. For the reactant CHF2CF2OCH3 and the two products, CHF2CF2OCH2 and CF2CF2OCH3, the standard enthalpies of formation are evaluated with the values of ,256.71 ± 0.88, ,207.79 ± 0.12, and ,233.43 ± 0.88 kcal/mol, respectively, via group-balanced isodesmic reactions. The rate constants of the two reaction channels are evaluated by means of canonical variational transition-state theory (CVT) including the small-curvature tunneling (SCT) correction over a wide range of temperature from 200 to 2000 K. The calculated rate constants agree well with the experimental data, and the Arrhenius expressions for the title reaction are fitted and can be expressed as k1 = 9.22 × 10,19 T2.06 exp(219/T), k2 = 4.45 × 10,14T0.90 exp(,2220/T), and k = 4.71 × 10,22 T3.20) exp(543/T) cm3 molecule,1 s,1. Our results indicate that H-abstraction from CH3 group is the main reaction pathway in the lower temperature range, while H-abstraction from CHF2 group becomes more competitive in the higher temperature range. © 2007 Wiley Periodicals, Inc. 39: 221,230, 2007 [source] Theoretical study of the reactions BF3 + BX, where X = H or NINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 5 2005Patrícia R. P. Barreto Abstract This work presents the rate constant for the gas-phase reaction BF3 + BX, where X = H or N, over the temperature range of 200,4,000 K. Conventional transition state theory (TST) is used to study these reactions. Geometries, frequencies, and the potential energy for reactant, products, and saddle point are obtained from accurate electronic structure calculations performed with the GAUSSIAN 98 program. The reaction rate for these reactions are determined using a simple code developed for this task. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 [source] Motion visualization of human left ventricle with a time-varying deformable model for cardiac diagnosisCOMPUTER ANIMATION AND VIRTUAL WORLDS (PREV: JNL OF VISUALISATION & COMPUTER ANIMATION), Issue 2 2001Soo-Mi Choi Abstract We present a time-varying deformable model to visualize and analyze the motion of the left ventricle from a time series of 3-D images. The model is composed of a non-rigid body that deforms around a reference shape obtained from the previous time step. At each time step, the position and orientation of the left ventricle are extracted from the feature points of images. This information gives the position and orientation of the coordinate system attached to the non-rigid body. To compute a dense non-rigid motion field over the entire endocardial wall of the left ventricle, we introduce a 3-D blob finite element and Galerkin interpolants based on 3-D Gaussian, and use a physically based finite element method and a modal analysis. Then, cinematic attributes are visualized in pseudo colors on the reconstructed surface in order to help medical doctors in their interpretation of the data. Using the presented model, we estimate clinically useful quantitative parameters such as regional wall motion and ejection fraction. Experimental results are shown in a time series of X-ray angiographic images. Copyright ©2001 John Wiley & Sons, Ltd. [source] Probabilistic Approach for Nonlinear Modal Control of MDOF Structures Subjected to Multiple ExcitationsCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 1 2005Kyung-Won Min For the modal control of the MDOF structure, a new eigenvalue assignment algorithm that modifies the dynamic characteristics of only the specific mode is proposed. For the probabilistic evaluation of the proposed nonlinear modal control, the joint probability density function (PDF) of the equivalent nonlinearly controlled single-degree-of-freedom (SDOF) system is obtained by the solution of the reduced Fokker,Planck equation for the equivalent nonlinear system. To overcome the difficulty in the application of the joint PDF to the MDOF structure controlled by the hybrid mass damper (HMD) system and subjected to multiple excitations, the equivalent damping ratio is proposed. The results of the analysis indicate that the proposed nonlinear modal control strategy is effective for the control of MDOF structures requiring a significantly smaller peak control force than the linear quadratic Gaussian (LQG) controller to produce a similar control performance level. [source] Estimation of erosion and deposition volumes in a large, gravel-bed, braided river using synoptic remote sensingEARTH SURFACE PROCESSES AND LANDFORMS, Issue 3 2003Stuart N. Lane Abstract System-scale detection of erosion and deposition is crucial in order to assess the transferability of findings from scaled laboratory and small field studies to larger spatial scales. Increasingly, synoptic remote sensing has the potential to provide the necessary data. In this paper, we develop a methodology for channel change detection, coupled to the use of synoptic remote sensing, for erosion and deposition estimation, and apply it to a wide, braided, gravel-bed river. This is based upon construction of digital elevation models (DEMs) using digital photogrammetry, laser altimetry and image processing. DEMs of difference were constructed by subtracting DEM pairs, and a method for propagating error into the DEMs of difference was used under the assumption that each elevation in each surface contains error that is random, independent and Gaussian. Data were acquired for the braided Waimakariri River, South Island, New Zealand. The DEMs had a 1·0 m pixel resolution and covered an area of riverbed that is more than 1 km wide and 3·3 km long. Application of the method showed the need to use survey-specific estimates of point precision, as project design and manufacturer estimates of precision overestimate a priori point quality. This finding aside, the analysis showed that even after propagation of error it was possible to obtain high quality DEMs of difference for process estimation, over a spatial scale that has not previously been achieved. In particular, there was no difference in the ability to detect erosion and deposition. The estimates of volumes of change, despite being downgraded as compared with traditional cross-section survey in terms of point precision, produced more reliable erosion and deposition estimates as a result of the large improvement in spatial density that synoptic methods provide. Copyright © 2003 John Wiley & Sons, Ltd. [source] Efficiency of base isolation systems in structural seismic protection and energetic assessmentEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 10 2003Giuseppe Carlo Marano Abstract This paper concerns the seismic response of structures isolated at the base by means of High Damping Rubber Bearings (HDRB). The analysis is performed by using a stochastic approach, and a Gaussian zero mean filtered non-stationary stochastic process is used in order to model the seismic acceleration acting at the base of the structure. More precisely, the generalized Kanai,Tajimi model is adopted to describe the non-stationary amplitude and frequency characteristics of the seismic motion. The hysteretic differential Bouc,Wen model (BWM) is adopted in order to take into account the non-linear constitutive behaviour both of the base isolation device and of the structure. Moreover, the stochastic linearization method in the time domain is adopted to estimate the statistical moments of the non-linear system response in the state space. The non-linear differential equation of the response covariance matrix is then solved by using an iterative procedure which updates the coefficients of the equivalent linear system at each step and searches for the solution of the response covariance matrix equation. After the system response variance is estimated, a sensitivity analysis is carried out. The final aim of the research is to assess the real capacity of base isolation devices in order to protect the structures from seismic actions, by avoiding a non-linear response, with associated large plastic displacements and, therefore, by limiting related damage phenomena in structural and non-structural elements. In order to attain this objective the stochastic response of a non-linear n -dof shear-type base-isolated building is analysed; the constitutive law both of the structure and of the base devices is described, as previously reported, by adopting the BWM and by using appropriate parameters for this model, able to suitably characterize an ordinary building and the base isolators considered in the study. The protection level offered to the structure by the base isolators is then assessed by evaluating the reduction both of the displacement response and the hysteretic dissipated energy. Copyright © 2003 John Wiley & Sons, Ltd. [source] Closed-form solution for seismic response of adjacent buildings with linear quadratic Gaussian controllersEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 2 2002Y. L. Xu Abstract Closed-form solution for seismic response of adjacent buildings connected by hydraulic actuators with linear quadratic Gaussian (LQG) controllers is presented in this paper. The equations of motion of actively controlled adjacent buildings against earthquake are first established. The complex modal superposition method is then used to determine dynamic characteristics, including modal damping ratio, of actively controlled adjacent buildings. The closed-form solution for seismic response of the system is finally derived in terms of the complex dynamic characteristics, the pseudo-excitation method and the residue theorem. By using the closed-form solution, extensive parametric studies can be carried out for the system of many degrees of freedom. The beneficial parameters of LQG controllers for achieving the maximum response reduction of both buildings using reasonable control forces can be identified. The effectiveness of LQG controllers for this particular application is evaluated in this study. The results show that for the adjacent buildings of different dynamic properties, if the parameters of LQG controllers are selected appropriately, the modal damping ratios of the system can be significantly increased and the seismic responses of both buildings can be considerably reduced. Copyright © 2001 John Wiley & Sons, Ltd. [source] Extreme value predictions based on nonstationary time series of wave dataENVIRONMETRICS, Issue 1 2006Christos N. Stefanakos Abstract A new method for calculating return periods of various level values from nonstationary time series data is presented. The key idea of the method is a new definition of the return period, based on the MEan Number of Upcrossings of the level x* (MENU method). In the present article, the case of Gaussian periodically correlated time series is studied in detail. The whole procedure is numerically implemented and applied to synthetic wave data in order to test the stability of the method. Results obtained by using several variants of traditional methods (Gumbel's approach and the POT method) are also presented for comparison purposes. The results of the MENU method showed an extraordinary stability, in contrast to the wide variability of the traditional methods. The predictions obtained by means of the MENU method are lower than the traditional predictions. This is in accordance with the results of other methods that also take into account the dependence structure of the examined time series. Copyright © 2005 John Wiley & Sons, Ltd. [source] Nitroamino Triazoles: Nitrogen-Rich Precursors of Stable Energetic SaltsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 16 2008Yangen Huang Abstract 1-Nitroamino-1,2,3-triazole (5) was synthesized and its zwitterionic structure was established using single-crystal X-ray diffraction. The calculated detonation properties for 4-nitroamino-1,2,4-triazole (2) (P = 33.4 GPa, vD = 8793 m/s) and 1-nitroamino-1,2,3-triazole (5) (P = 33.0 GPa, vD = 8743 m/s) are comparable with RDX. A new family of energetic salts 7,21 based on either the 1-nitroamino-1,2,3-triazolate or the 4-nitroamino-1,2,4-triazolate anion were prepared and characterized by vibrational spectroscopy (IR), multinuclear NMR spectra, elemental analyses, density, TGA and DSC. The heats of formation (,fH°298) and detonation properties for these stable salts were calculated using Gaussian 03 and Cheetah 4.0, respectively. Comparison of the properties of the 1,2,3- and 1,2,4-triazolate salts indicates that while the 1,2,4-derivatives are more stable thermally, the 1,2,3-analogs invariably have higher heats of formation. In contrast to its salts, 1-nitroamino-1,2,3-triazole (5) is extremely shock-sensitive with an impact sensitivty of <1 J. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] A Haigh,Mallion-Based Approach for the Evaluation of the Intensity Factors of Aromatic RingsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 2 2006Cristiano Zonta Abstract A novel method for the determination of intensity factors of benzenoid systems based on the Haigh,Mallion (HM) theory has been developed. In this paper, the magnetic anisotropy generated by the ring-current effect in polycondensed arenes has been quantitatively calculated as nuclear independent chemical shieldings (NICSs) in a three-dimensional grid of points using the B3LYP/6-31G(d) method implemented in the Gaussian 98 program. The fitting of the calculated values to the HM model gives intensity factors for each ring. A comparison of the obtained values with Schleyer's NICS0 is given. The obtained intensity factors may find application in software using 1H NMR chemical shifts for structure determination.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] The 15N-CPMAS spectra of simazine and its metabolites: measurements and quantum chemical calculationsEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 4 2007A. E. Berns Summary DFT calculations are a powerful tool to support NMR studies of xenobiotics such as decomposition studies in soil. They can help interpret spectra of bound residues, for example, by predicting shifts for possible model bonds. The described bound-residue models supported the hypothesis of a free amino side chain already suspected by comparison with the experimental data of the standards. No match was found between the calculated shifts of amide bondings of the amino side chains (free or substituted) and the experimental NMR shifts of a previous study. In the present paper, first-principles quantum chemical calculations were used to support and check the interpretation of the 15N cross polarization-magic angle spinning nuclear magnetic resonance (15N-CPMAS NMR) spectra of simazine and its metabolites. Density functional theory (DFT) calculations were performed using Gaussian 03 and the nuclear magnetic shielding tensors were calculated using the Gauge-Independent Atomic Orbital (GIAO) method and B3LYP/6,311+G(2d,p) model chemistry. Good agreement was reached between the calculated and measured chemical shifts of the core nitrogens and the lactam and lactim forms of the hydroxylated metabolites could be clearly distinguished. The calculated spectra showed that these metabolites exist preferentially in the lactam form, an important fact when considering the possible interactions of such hydroxylated metabolites with the soil matrix. Although the calculated bound-residue models in the present study only partly matched the experimental data, they were nevertheless useful in helping to interpret the experimental NMR results of a previous study. To get a better match between the calculated and the measured shifts of the side-chain nitrogens the calculations need to be further developed, taking into account the influence of neighbouring molecules in the solid state. Altogether, quantum chemical calculations are very helpful in the interpretation of NMR spectra. In the future, they can also be very useful for the prediction of NMR shifts, in particular when it is not possible to measure the metabolites due to a lack of material or in cases where practical experiments cannot be conducted. [source] Gaussian inputs: performance limits over non-coherent SISO and MIMO channelsEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 3 2007Rasika R. Perera Performance limits of information transfer over a discrete time memoryless Rayleigh fading channel with neither the receiver nor the transmitter knowing the fading coefficients except its statistics is an important problem in information theory. We derive closed form expressions for the mutual information of single input single output (SISO) and multiple input multiple output (MIMO) Rayleigh fading channels for any antenna number at any signal to noise ratio (SNR). Using these expressions, we show that the maximum mutual information of non-coherent Rayleigh fading MIMO channels is achieved with a single transmitter and multiple receivers when the input distribution is Gaussian. We show that the addition of transmit antennas for a fixed number of receivers result in a reduction of mutual information. Furthermore, we argue that the mutual information is bounded by the SNR in both SISO and MIMO systems showing the sub-optimality of Gaussian signalling in non-coherent Rayleigh fading channels. Copyright © 2006 AEIT [source] Frequency-based fatigue analysis of non-stationary switching random loadsFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 11 2007D. BENASCIUTTI ABSTRACT The service loadings in real systems are not only random, but also non-stationary. The spectral methods based on a frequency-domain characterization of random loads, which have been used in alternative to classical time-domain approaches, cannot be applied to non-stationary loads, because the conventional spectral density spectrum is not able to capture the evolutionary frequency characteristics of non-stationary loads. This clearly restricts the applicability of the existing frequency-based methods only to loads which are stationary. At the same time, it is also very difficult to propose general models valid for all types of load non-stationarity encountered in practice. Therefore, a practical approach is to restrict the analysis to a specific class of non-stationary loads; in this work, we consider particular non-stationary loads (i.e. switching loads), which are piecewise stationary in their variance. A frequency-domain analysis of such loads is proposed, which is based on a combination of the frequency-based analysis of each adjacent stationary segment, which can be either Gaussian or non-Gaussian. Numerically simulated load histories, as well as loads measured on mountain bikes in special tracks, are analysed to validate the proposed methodology. The presented results also show the correlation between load non-stationarity and non-Gaussianity. [source] Impact of the timing of stocking on growth and allometric index in aquaculture-based fisheriesFISHERIES MANAGEMENT & ECOLOGY, Issue 2 2004A. L. Ibáńez Abstract The impact of tilapia stocking on fisheries production in Lake Metztitlán was determined through progression analysis of modes obtained from (Gaussian) kernel density estimators (KDEs) of size frequency distributions of juvenile tilapia stocked after a period of total desiccation. The relationship between the allometric index of four cohorts and water temperature and variation in the volume of the basin was analysed. The use of KDEs was found to be a useful technique for the recognition and progression analysis of modes. The reasons for the low yields from the tilapia fishery of Lake Metztitlán are poor growth rate, low water temperature, which is manifest in low allometric indices, and the use of small mesh size nets. Yields can be sustained by improving fishery management; otherwise it is necessary to continue stocking. [source] Geostatistical Prediction and Simulation of Point Values from Areal DataGEOGRAPHICAL ANALYSIS, Issue 2 2005Phaedon C. Kyriakidis The spatial prediction and simulation of point values from areal data are addressed within the general geostatistical framework of change of support (the term support referring to the domain informed by each measurement or unknown value). It is shown that the geostatistical framework (i) can explicitly and consistently account for the support differences between the available areal data and the sought-after point predictions, (ii) yields coherent (mass-preserving or pycnophylactic) predictions, and (iii) provides a measure of reliability (standard error) associated with each prediction. In the case of stochastic simulation, alternative point-support simulated realizations of a spatial attribute reproduce (i) a point-support histogram (Gaussian in this work), (ii) a point-support semivariogram model (possibly including anisotropic nested structures), and (iii) when upscaled, the available areal data. Such point-support-simulated realizations can be used in a Monte Carlo framework to assess the uncertainty in spatially distributed model outputs operating at a fine spatial resolution because of uncertain input parameters inferred from coarser spatial resolution data. Alternatively, such simulated realizations can be used in a model-based hypothesis-testing context to approximate the sampling distribution of, say, the correlation coefficient between two spatial data sets, when one is available at a point support and the other at an areal support. A case study using synthetic data illustrates the application of the proposed methodology in a remote sensing context, whereby areal data are available on a regular pixel support. It is demonstrated that point-support (sub-pixel scale) predictions and simulated realizations can be readily obtained, and that such predictions and realizations are consistent with the available information at the coarser (pixel-level) spatial resolution. [source] A Computational Study of the Sub-monolayer Growth of PentaceneADVANCED FUNCTIONAL MATERIALS, Issue 13 2006D. Choudhary Abstract A computational study of organic thin-film growth using a combination of ab,initio based energy calculations and kinetic Monte Carlo (KMC) simulations is provided. A lattice-based KMC model is used in which binding energies determine the relative rates of diffusion of the molecules. This KMC approach is used to present "landscapes" or "maps" that illustrate the possible structural outcomes of growing a thin film of small organic molecules, represented as a two-site dimer, on a substrate in which the strength of organic,substrate interactions is allowed to vary. KMC provides a mesoscopic-scale view of sub-monolayer deposition of organic thin films on model substrates, mapped out as a function of the flux of depositing molecules and the temperature of the substrate. The morphology of the crystalline thin films is shown to be a strong function of the molecule,molecule and molecule,substrate interactions. A rich variety of maps is shown to occur in which the small organic molecules either stand up or lie down in a variety of different patterns depending on the nature of the binding to the surface. In this way, it is possible to suggest how to tailor the substrate or the small organic molecule in order to create a desired growth habit. In order to demonstrate how this set of allowable maps is reduced in the case where the set of energy barriers between substrate and organic molecule are reliably known, we have used Gaussian,98 calculations to establish binding energies for the weak van der Waals interactions between a),pairs of pentacene molecules as a function of orientation and b),pentacene and two substrates, silicon surfaces passivated with cyclopentene molecules and a crystalline model of silicon dioxide. The critical nucleation size and the mode of diffusion of this idealized two-site dimer model for pentacene molecules are found to be in good agreement with experimental data. [source] Demand for traditional medicine in Taiwan: a mixed Gaussian,Poisson model approachHEALTH ECONOMICS, Issue 3 2001Steven T. Yen Abstract Hurdle count models are used to examine the participation and consumption decisions in Chinese medicine use. Motivated by a household production model, a second censoring mechanism is introduced into existing single-hurdle models, and the resulting specification accommodates conscientious abstainers, as well as economic non-consumers, and admits excessive zeros in the sample. In contrast to previous studies that found few predictors, empirical results based on a Taiwanese national sample suggest that Western medicine is a gross substitute to Chinese medicine, and both time price and money price play more important roles than income. Insurance, lifestyle and demographics also determine the use of Chinese medicine. Copyright © 2001 John Wiley & Sons, Ltd. [source] New aluminum-based ionic liquids: Synthesis, characterization, and theoretical studyHETEROATOM CHEMISTRY, Issue 7 2009Hossein Tavakol Synthesis, characterization, spectral and molecular parameters of some new room-temperature ionic liquids (tetraalkylammonium bromotrichloro aluminum [R4N]+[AlCl3Br],) have been studied in the present study. All synthesized ionic liquids were characterized by IR, 1H, 13C, and 81Br-NMR. In addition, synthesized structures were optimized at the B3LYP/LANL2DZ level of theory and then the structures, molecular specifications, and infrared spectra of these were extracted using Gaussian 03 program. Theoretical data show good agreement with the experimental results. © 2010 Wiley Periodicals, Inc. Heteroatom Chem 20:398,404, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20564 [source] Permutation tests for factorially designed neuroimaging experimentsHUMAN BRAIN MAPPING, Issue 3 2004John Suckling Abstract Permutation methods for analysis of functional neuroimaging data acquired as factorially designed experiments are described and validated. The F ratio was estimated for main effects and interactions at each voxel in standard space. Critical values corresponding to probability thresholds were derived from a null distribution sampled by appropriate permutation of observations. Spatially informed, cluster-level test statistics were generated by applying a preliminary probability threshold to the voxel F maps and then computing the sum of voxel statistics in each of the resulting three-dimensional clusters, i.e., cluster "mass." Using simulations comprising two between- or within-subject factors each with two or three levels, contaminated by Gaussian and non-normal noise, the voxel-wise permutation test was compared to the standard parametric F test and to the performance of the spatially informed statistic using receiver operating characteristic (ROC) curves. Validity of the permutation-testing algorithm and software is endorsed by almost identical performance of parametric and permutation tests of the voxel-level F statistic. Permutation testing of suprathreshold voxel cluster mass, however, was found to provide consistently superior sensitivity to detect simulated signals than either of the voxel-level tests. The methods are also illustrated by application to an experimental dataset designed to investigate effects of antidepressant drug treatment on brain activation by implicit sad facial affect perception in patients with major depression. Antidepressant drug effects in left amygdala and ventral striatum were detected by this software for an interaction between time (within-subject factor) and group (between-subject factor) in a representative two-way factorial design. Hum. Brain Mapping 22:193,205, 2004. © 2004 Wiley-Liss, Inc. [source] Assessment of rainfall-runoff models based upon wavelet analysisHYDROLOGICAL PROCESSES, Issue 5 2007Stuart N. Lane Abstract A basic hypothesis is proposed: given that wavelet-based analysis has been used to interpret runoff time-series, it may be extended to evaluation of rainfall-runoff model results. Conventional objective functions make certain assumptions about the data series to which they are applied (e.g. uncorrelated error, homoscedasticity). The difficulty that objective functions have in distinguishing between different realizations of the same model, or different models of the same system, is that they may have contributed in part to the occurrence of model equifinality. Of particular concern is the fact that the error present in a rainfall-runoff model may be time dependent, requiring some form of time localization in both identification of error and derivation of global objective functions. We explore the use of a complex Gaussian (order 2) wavelet to describe: (1) a measured hydrograph; (2) the same hydrograph with different simulated errors introduced; and (3) model predictions of the same hydrograph based upon a modified form of TOPMODEL. The analysis of results was based upon: (a) differences in wavelet power (the wavelet power error) between the measured hydrograph and both the simulated error and modelled hydrographs; and (b) the wavelet phase. Power difference and wavelet phase were used to develop two objective functions, RMSE(power) and RMS(phase), which were shown to distinguish between simulated errors and model predictions with similar values of the commonly adopted Nash-Sutcliffe efficiency index. These objective functions suffer because they do not retain time, frequency or time-frequency localization. Consideration of wavelet power spectra and time- and frequency-integrated power spectra shows that the impacts of different types of simulated error can be seen through retention of some localization, especially in relation to when and the scale over which error was manifest. Theoretical objections to the use of wavelet analysis for this type of application are noted, especially in relation to the dependence of findings upon the wavelet chosen. However, it is argued that the benefits of localization and the qualitatively low sensitivity of wavelet power and phase to wavelet choice are sufficient to warrant further exploration of wavelet-based approaches to rainfall-runoff model evaluation. Copyright © 2006 John Wiley & Sons, Ltd. [source] Experimental study of stick-slip behaviourINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 6 2004Florence Adjemian Abstract Simple axi-symmetric uni-axial compression tests have been realized on dry loose samples of glass beads (diameters d: d=0.2 ± 0.05 mm, 0.75 ± 0.1 mm, or 3 mm) and on Hostun sand under small lateral confinement, ,3<60 kPa, using different sample sizes. The experiments with the two smallest spheres (d=0.2 and 0.75 mm) exhibit stick-slips, which are characterized by (i) a rapid release ,q of the deviatoric stress q and by (ii) the strain ,,1 separating two events. The samples which exhibit stick-slip also present a weakening of strength q(,1) as the rate of deformation d,1/dt is increased. No stick-slip is generated during the first part of the q,,1 curve, i.e. when q grows fast with ,1. Four different parameters helped us determine the statistics of ,q and ,,: the lateral pressure ,3,, the rate of deformation d,1/dt, the sample height H, and the diameter D. The statistics do not depend on rate history. They look like exponentials in small samples and/or in (large sample+fast d,1/dt), and they look like Poissonian or Gaussian in (Large sample+small d,1/dt). This change in statistics is attributed to a varying of triggering process starting from a single random event in small samples to multiple random events. We have interpreted this change of statistics as due to some finite size effect so that the representative elementary volume shall contain at least (200)3 grains. Localization of deformation is visible at the end of compression but cannot be detected from stick-slip statistics nor from q vs , curve. Copyright © 2004 John Wiley & Sons, Ltd. [source] An EM-like reconstruction method for diffuse optical tomographyINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 9 2010*Article first published online: 28 JUN 2010, Caifang Wang Abstract Diffuse optical tomography (DOT) is an optical imaging modality which provides the spatial distributions of optical parameters inside an object. The forward model of DOT is described by the diffusion approximation of radiative transfer equation, while the DOT is to reconstruct the optical parameters from boundary measurements. In this paper, an EM-like iterative reconstruction method specifically for the steady state DOT problem is developed. Previous iterative reconstruction methods are mostly based on the assumption that the measurement noise is Gaussian, and are of least-squares type. In this paper, with the assumption that the boundary measurements have independent and identical Poisson distributions, the inverse problem of DOT is solved by maximizing a log-likelihood functional with inequality constraints, and then an EM-like reconstruction algorithm is developed according to the Kuhn,Tucker condition. The proposed algorithm is a variant of the well-known EM algorithm. The performance of the proposed algorithm is tested with three-dimensional numerical simulation. Copyright © 2010 John Wiley & Sons, Ltd. [source] Linear random vibration by stochastic reduced-order modelsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 12 2010Mircea Grigoriu Abstract A practical method is developed for calculating statistics of the states of linear dynamic systems with deterministic properties subjected to non-Gaussian noise and systems with uncertain properties subjected to Gaussian and non-Gaussian noise. These classes of problems are relevant as most systems have uncertain properties, physical noise is rarely Gaussian, and the classical theory of linear random vibration applies to deterministic systems and can only deliver the first two moments of a system state if the noise is non-Gaussian. The method (1) is based on approximate representations of all or some of the random elements in the definition of linear random vibration problems by stochastic reduced-order models (SROMs), that is, simple random elements having a finite number of outcomes of unequal probabilities, (2) can be used to calculate statistics of a system state beyond its first two moments, and (3) establishes bounds on the discrepancy between exact and SROM-based solutions of linear random vibration problems. The implementation of the method has required to integrate existing and new numerical algorithms. Examples are presented to illustrate the application of the proposed method and assess its accuracy. Copyright © 2009 John Wiley & Sons, Ltd. [source] Development of a genetic algorithm-based lookup table approach for efficient numerical integration in the method of finite spheres with application to the solution of thin beam and plate problemsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 12 2006Suleiman BaniHani Abstract It is observed that for the solution of thin beam and plate problems using the meshfree method of finite spheres, Gaussian and adaptive quadrature schemes are computationally inefficient. In this paper, we develop a novel technique in which the integration points and weights are generated using genetic algorithms and stored in a lookup table using normalized coordinates as part of an offline computational step. During online computations, this lookup table is used much like a table of Gaussian integration points and weights in the finite element computations. This technique offers significant reduction of computational time without sacrificing accuracy. Example problems are solved which demonstrate the effectiveness of the procedure. Copyright © 2006 John Wiley & Sons, Ltd. [source] Application of model-free LQG subspace predictive control to TCP congestion controlINTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 6 2008Belinda A. Chiera Abstract We investigate the application of a model-free linear quadratic Gaussian (LQG) subspace-based predictive controller to Internet congestion control. Specifically, we consider a classically designed LQG linear congestion controller with a non-standard performance index and determine whether a model-free controller is a viable alternative in this instance. We employ the model-free subspace predictive controller methodology which we customize for end-to-end transmission control protocol (TCP) congestion control. A series of network simulations support the use of the more easily implementable model-free controller over its classical analogue. We further demonstrate that the model-free controller provides increased stability under transient network conditions when compared with the first feedback congestion controller, TCP Vegas. Copyright © 2007 John Wiley & Sons, Ltd. [source] Optimality for the linear quadratic non-Gaussian problem via the asymmetric Kalman filterINTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 1 2004Rosario Romera Abstract In the linear non-Gaussian case, the classical solution of the linear quadratic Gaussian (LQG) control problem is known to provide the best solution in the class of linear transformations of the plant output if optimality refers to classical least-squares minimization criteria. In this paper, the adaptive linear quadratic control problem is solved with optimality based on asymmetric least-squares approach, which includes least-squares criteria as a special case. Our main result gives explicit solutions for this optimal quadratic control problem for partially observable dynamic linear systems with asymmetric observation errors. The main difficulty is to find the optimal state estimate. For this purpose, an asymmetric version of the Kalman filter based on asymmetric least-squares estimation is used. We illustrate the applicability of our approach with numerical results. Copyright © 2004 John Wiley & Sons, Ltd. [source] Theoretical analysis of iterative signal reconstruction for impulsive noise mitigation in OFDM systemsINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 3 2010Nikola Rozic Abstract In this paper a theoretical analysis of the iterative signal reconstruction algorithm for impulsive noise mitigation in orthogonal frequency-division multiplexing (OFDM) systems is developed. The following main results are developed: first, analytical model for the total noise in the frequency domain, and second the model for the total noise probability density function (pdf) in the frequency domain, both defined for each step of the iterative reconstruction process. Finally, based on the pdf of the total noise, explicit expressions for BER in kth iteration are defined as well. The main intention of the paper is to present the approach to theoretical analysis of the iterative impulsive noise mitigation algorithm that has not yet been appeared in the literature, because the theoretical analysis of the noise pdf during iterations has been considered as too complex a problem. Analyses and analytical results presented in the paper are given for scenario with a fixed number of noise impulses per frame. However, this is not a handicap of the proposed approach, since all presented models can be used as building blocks for scenarios with other impulsive noise distributions including Bernoulli,Gaussian and Middleton's Class A. Copyright © 2009 John Wiley & Sons, Ltd. [source] Nonrelativistic CI calculations for B+, B, and B, ground statesINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 15 2010César X. Almora-Díaz Abstract State of the art configuration interaction (CI) techniques are used to obtain the best possible nonrelativistic CI results for B+, B, and B, ground states using energy-optimized basis sets of 252, 294, and 294 radial Slater-type functions, respectively. For positive boron, E(B+) = ,24.348861 + ,Ebie = ,24.348883(1) a.u.(B) with a basis set incompleteness error ,Ebie = ,0.000022(1), in good agreement with the latest exponentially correlated Gaussian (ECG) result of ,24.348883 a.u.(B) of Komasa et al. (Phys Rev A, 2002, 65, 042507). For neutral B, E(B) = ,24.653837 ,0.000024(2) = ,24.653861(2), which is the most accurate ab initio estimate and lies slightly below a recent (not fully optimized) ECG result of ,24.653840 a.u.(B) of Bubin et al (J Chem Phys, 2009, 131, 044128). For negative boron, E(B,) = ,24.664014 ,0.000024(2) to which an energy error of ,0.000001 must be added to give ,24.664039(2), which is the first fully correlated ab initio result. Comparison with experimental values of ionization energy and electron affinity must await the results of corresponding relativistic calculations, in progress. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [source] Comparative theoretical study of small Rhn nanoparticles (2 , n , 8) using DFT methodsINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 6 2010V. Bertin Abstract This work is aimed at identifying some key characteristics (energy, geometry, and spin) concerning Rhn particles (2 = n , 8) to perform further studies on adsorption and coadsorption sites of pollutants (CO and NO). The DFT methods of the Gaussian 03 program with the LANL2DZ basis set and the LANL2 potential are used. With the purpose to obtain a better nanoparticles definition, five different functionals were tested: B3LYP, O3LYP, BPW91, BP86, and HCTH; and the corresponding results are used to determine which of them best describes distances, spin, and gives acceptable highest vibration frequency and binding energy values, by comparing these results with values measured or calculated by many other authors. For the structure optimization process of the particles, the initial geometric shape was taken mainly from the literature, using the Rh,Rh distance: 2.67 Ĺ, known for the bulk; and doing a complete optimization. We also considered flat nanoparticles structures, which most of them display three-dimensional structures after the optimization process. The few flat shapes are mainly higher in energy than those of three-dimensional structure. For some Rhn particles for different n values, the spin of the ground state present degeneration. In some cases, the optimization process changes the initial geometry, but in most cases, there are only minor changes in bonds and geometry. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [source] MaSK: A visualization tool for teaching and research in computational chemistryINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 1 2009Yevgeniy Podolyan Abstract The number of researchers using computational chemistry tools is growing every year. There are multiple programs used for calculation of various molecular and electronic properties such as optimized geometry, energy, vibrational spectra, and so forth. Another set of programs is used for the visualization of these properties. However, such programs are either too complex for a beginner or too simple for an intermediate user for everyday use. Molecular Modeling and Simulation Kit (MaSK) is designed to fill this gap by presenting an easy-to-use intuitive interface to quantum chemical programs such as GAMESS and Gaussian with an array of advanced tools. The program can be used as a postprocessor to visualize calculated properties or as a preprocessor to prepare the input files for quantum chemical programs. In addition, some properties such as the surfaces of molecular orbitals, electron and spin densities, and molecular electrostatic potentials are actually calculated by MaSK. If MaSK is combined with PC GAMESS, the preparation of the input, running of the calculations, and the display of the results can all be done without leaving the program's interface. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [source] | ||||||||||||||||||||||||||||||||||