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In this paper, a new feedback control design for an isolated freeway ramp is presented utilizing hybrid dynamics based on Godunov's numerical technique. Previous feedback ramp metering designs have been mainly based on either discretized linearized methods such as ALINEA or nonlinear feedback designs based on ordinary differential equations for the traffic model. These models use lumped parameters, which fail to represent some details of the rarefaction wave phenomenon of the distributed model. Godunov's condi-tions employ the data known on both sides of each boundary in order to determine the characteristics of the boundary conditions. This paper uses Godunov's hybrid lumped model based on which feedback control design is proposed and simulation results for the model are presented. Real data is collected on one of the major freeway on-ramps in the Las Vegas area. The roadway parameters are estimated using least squares estimator then are used in the proposed Godunov based hybrid model. The proposed feedback ramp control design is compared with the actual ramp control algorithm. Self-tuning adaptive control is also performed using recursive parameter updating with and without exponential forgetting. [ABSTRACT FROM AUTHOR]

Abstract: Numerous studies have focused on the problem of wellbore instability or enlargement; however, most have focused on the physical–chemical interactions between the rock (especially shales) and the drilling fluid and have ignored the effects of drill string impacts. Drill string impacts on the wellbore wall often have important effects on wellbore instability. This paper presents a model for calculating drill string impacts on a wellbore wall based on an experimental study, principles of rock mechanics and rock damage mechanics and the Drucker–Prager yield criterion. The law of rock fragmentation during drill string impacts is investigated using simulations; later, relationships between the rock fragmentation volume and the drill string impact are developed under different conditions (contact lengths of the drill string, impact speeds, rotation speeds, well depths and rock softening). Moreover, formulae describing the drill string′s critical speed and the rock fragmentation volume when the wellbore rock fails are developed based on laboratory experiments and simulations. The results show that drill string impacts greatly influence wellbore instability or enlargement. In particular, shallower formations are affected more by drill string impacts than deeper ones. After rock softening, the drill string′s critical speed decreases, whereas the wellbore rock fragmentation volume increases; compared to a radial impact by the drill string, the drill string′s rotation speed plays only a secondary role in rock failure. The two formulae can be used directly in engineering problems because they provide relevant preventive measures during drilling. The conclusions of this paper will help drilling engineers understand the relationship between drill string vibrations and wellbore instability. [Copyright &y& Elsevier]

This paper presents a method to estimate the inverter lifetime so that we can predict a failure prior to it actually happening. The key contribution of this study is to link the physics of the power devices to a large scale system simulation within a reasonable framework of time. By configuring this technique to a real system, it can be used as a converter design tool or online lifetime estimation tool. In this paper, the presented method is applied to the grid side inverter to show its validity. A power cycling test is designed to gather the lifetime data of a selected insulated gate bipolar transistor (IGBT) module (SKM50GB123D). Die-attach solder fatigue is found out to be the dominant failure mode of this IGBT module under the designed accelerated tests. Furthermore, the crack initiation is found to be highly stress dependent while the crack propagation is almost independent with stress level. Two different damage accumulation methods are used and the estimation results are compared. [ABSTRACT FROM AUTHOR]

Background: The validity of studies describing clinicians' judgements based on their responses to paper cases is questionable, because - commonly used - paper case simulations only partly reflect real clinical environments. In this study we test whether paper case simulations evoke similar risk assessment judgements to the more realistic simulated patients used in high fidelity physical simulations. Methods: 97 nurses (34 experienced nurses and 63 student nurses) made dichotomous assessments of risk of acute deterioration on the same 25 simulated scenarios in both paper case and physical simulation settings. Scenarios were generated from real patient cases. Measures of judgement 'ecology' were derived from the same case records. The relationship between nurses' judgements, actual patient outcomes (i.e. ecological criteria), and patient characteristics were described using the methodology of judgement analysis. Logistic regression models were constructed to calculate Lens Model Equation parameters. Parameters were then compared between the modeled paper-case and physical-simulation judgements. Results: Participants had significantly less achievement (ra) judging physical simulations than when judging paper cases. They used less modelable knowledge (G) with physical simulations than with paper cases, while retaining similar cognitive control and consistency on repeated patients. Respiration rate, the most important cue for predicting patient risk in the ecological model, was weighted most heavily by participants. Conclusions: To the extent that accuracy in judgement analysis studies is a function of task representativeness, improving task representativeness via high fidelity physical simulations resulted in lower judgement performance in risk assessments amongst nurses when compared to paper case simulations. Lens Model statistics could prove useful when comparing different options for the design of simulations used in clinical judgement analysis. The approach outlined may be of value to those designing and evaluating clinical simulations as part of education and training strategies aimed at improving clinical judgement and reasoning. [ABSTRACT FROM AUTHOR]

Abstract: In this paper a laboratory-scale model for prediction of the voltage–current characteristics of wire–plate electrostatic precipitators under clean air conditions is presented and experimentally validated. The model investigates the effect of electrode configurations, wire diameter, spacing between wire electrodes, number of discharge wires and distance between collecting plates that on voltage–current characteristic of wire–plate electrostatic precipitators. Also, this paper presents a simulation model, based on the Finite Difference Method (FDM), to simulate electric conditions of wire–plate electrostatic precipitators under clean air conditions. The experimental results of some models are compared with those obtained from the simulation models. [Copyright &y& Elsevier]

In the present paper has been analyzed the effect of the heat transfer coefficient on the cylinder combustion pressure. For carry out the analysis has been used a simulation model. This model has been used for the research into the influence of multiple injections on the combustion processes and products in the cylinder of slow-speed marine diesel engines. The combustion nul-dimensional mathematical model was validated by comparing the actual data measured on board a ship and the results obtained from simulations. The paper purpose is to presents the results of the heat transfer influence comparison obtained by applying formulas for the heat transfer used by Woschni, Annand and Eichelberg. The results are statistically analyzed and graphically presented. [ABSTRACT FROM AUTHOR]

Abstract: Pedestrian speed in a transfer station corridor is faster than usual and sometimes running can be found among some of them. In this paper, pedestrians are divided into two categories. The first one is aggressive, and the other is conservative. Aggressive pedestrians weaving their way through crowd in the corridor are the study object of this paper. During recent decades, much attention has been paid to the pedestrians’ behavior, such as overtaking (also deceleration) and collision avoidance, and that continues in this paper. After sufficiently analyzing the characteristics of pedestrian flow in transfer station corridor, a cell-based model is presented in this paper, including the acceleration (also deceleration) and overtaking analysis. Acceleration (also deceleration) in a corridor is fixed according to Newton’s Law and then speed calculated with a kinematic formula is discretized into cells based on the fuzzy logic. After the speed is updated, overtaking is analyzed based on updated speed and force explicitly, compared to rule-based models, which herein we call implicit ones. During the analysis of overtaking, a threshold value to determine the overtaking direction is introduced. Actually, model in this paper is a two-step one. The first step is to update speed, which is the cells the pedestrian can move in one time interval and the other is to analyze the overtaking. Finally, a comparison between the rule-based cellular automata, the model in this paper and data in HCM 2000 is made to demonstrate our model can be used to achieve reasonable simulation of acceleration (also deceleration) and overtaking among pedestrians. [Copyright &y& Elsevier]

Abstract: In this paper, we consider the problem of estimating the direction-of-arrival (DOA) of code-division multiple access (CDMA) signals. It has been shown that the searching complexity and estimating accuracy of the conventional spectral searching methods strictly depend on the number of search grids used during the search. It is time consuming and the required number of search grids is not easy to determine. For the purpose of efficient estimation, a highly efficient approach has been proposed that is implemented on polynomial rooting rather than spectral searching. However, this rooting method is suboptimal in the presence of the noise and multiple access interference (MAI). As proposed in this paper, a novelty particle swarm optimization (PSO) with the proposed techniques offers a much faster convergence compared to the PSO with hard-constraints. In conjunction with a modified PSO for angle searching, the proposed approach can achieve the advantages of reducing search complexity and more accurate estimate over existing conventional spectral searching method. Finally, several computer simulation examples are provided for illustration and comparison. [Copyright &y& Elsevier]

Over the past few years, the concept of cluster has been regarded and adopted as a useful policy tool in analyzing maritime industry development. However, there is a lack of studies on the theoretical development of maritime cluster evolution in the existing literature. This paper aims to investigate the dynamic symbiosis derived from maritime cluster evolution. The research leads to a new path to investigate maritime cluster by employing the symbiosis theory in ecology and the Lotka–Volterra model. The paper first develops the concept of maritime cluster classification and evolution. Then, it analyses the compatibility and analogy of biotic community with maritime cluster. In order to study the interaction relationships among maritime sectors, the Lotka–Volterra model is introduced. The model is used to group the revenues of maritime sectors in pairs. These revenues are in turn grouped into a number of comparative pairs accordingly. The model is further advanced to forecast the trend of maritime clusters by studying the existence of an equilibrium point and its stability with the estimated functions. The original approach would deepen the understanding on maritime cluster and stimulate future research. The study also draws insights for policy makers in maritime nations. [ABSTRACT FROM AUTHOR]

Abstract: THEATRe is a real time thermal hydraulic simulation code specifically for the pin type fuel element. In this paper, a research focused on the development of THEATRe code for the plate type fuel nuclear reactor is presented. For this purpose, first a mathematical study for the plate type fuel was completed and was followed by the development of a computer program in FORTRAN language. This program was then coupled with the source code of THEATRe code. The modified code has been verified by comparing its predictions with RELAP5 code. The verification studies were performed by considering a small nuclear reactor, which has the power output of 220MW and is designed by Nuclear Power Simulation and Research Centre (NPS&RC), China. In this paper, comparisons between simulation results from both codes are presented, which verify that the modification of the THEATRe code for the plate type fuel nuclear reactor has been successful. [Copyright &y& Elsevier]

This paper presents a new three-phase phase-locked loop (PLL) system that primarily estimates the phase angles, frequency, and magnitudes of the a three-phase input signal and also provides a filtered version of the input. It is then extended to the estimation of sequence components, their magnitudes, and phase angles. As compared with the conventional three-phase PLL, this method does not suffer from errors that are caused by signal unbalance and dc offset. It also provides estimate for several other variables which are not included in the conventional three-phase PLL. As compared with the method of using three independent single-phase enhanced PLLs, the proposed method offers a simpler structure. Moreover, the estimated frequency is more accurate and smoother because it uses the information from all three phases to estimate a single value for frequency. The paper also presents a modification that makes the PLL parameters independent from the input signal amplitude. The same modification is applicable to existing methods such as conventional three-phase PLL. Simulation and experimental results are presented to confirm desirable performance of the proposed method. [ABSTRACT FROM AUTHOR]

Abstract: When engineers create a safety-critical system, they need to perform an adequate hazard analysis. For Systems of Systems (SoSs), however, hazard analysis is difficult because of the complexity of SoS and the environments they inhabit. Traditional hazard analysis techniques often rely upon static models of component interaction and have difficulties exploring the effects of multiple coincident failures. They cannot be relied on, therefore, to provide adequate hazard analysis of SoS. This paper presents a hazard analysis technique (SimHAZAN) that uses multi-agent modelling and simulation to explore the effects of deviant node behaviour within a SoS. It defines a systematic process for developing multi-agent models of SoS, starting from existing models in the MODAF architecture framework and proceeding to implemented simulation models. It then describes a process for running these simulations in an exploratory way, bounded by estimated probability. This process generates extensive logs of simulated events; in order to extract the causes of accidents from these logs, this paper presents a tool-supported analysis technique that uses machine learning and agent behaviour tracing. The approach is evaluated by comparison to some explicit requirements for SoS hazard analysis, and by applying it to a case study. Based on the case study, it appears that SimHAZAN has the potential to reveal hazards that are difficult to discover when using traditional techniques. [Copyright &y& Elsevier]

Abstract: In this paper, we propose a new method for reversible data hiding by employing the hierarchical relationships of original images. There are many parameters for accessing the performances of reversible data hiding algorithms, including the output image quality, the hiding capacity, and the overhead for decoding. Considering the ease of implementation and the little overhead needed for decoding, we employ modification of difference values between pixels by using histogram-based scheme with extensions to pyramidal structure by utilizing inherent characteristics of original images. By doing so, global and local characteristics of original images can be utilized for hiding more capacity with acceptable quality of output image. With our method, better performances can be obtained with enhanced image quality, the more embedding capacity, and comparable amount of side information for decoding. More importantly, the reversibility of our method is guaranteed, meaning that original image and hidden message can both be perfectly recovered at the decoder. Simulation results demonstrate that proposed method in this paper outperforms those in conventional algorithms. [Copyright &y& Elsevier]

In this paper, a new active grounded inductor controlled in current is described. This structure is realized using negative second generation current controlled conveyors and a single grounded capacitor, with no external resistance. The proposed circuit offers many advantages, such as: operation at high frequencies, simple circuit, tuning by the bias current, low power dissipation, etc. Comparison between this topology and those presented in literature is done to highlight the benefits of our structure. As an application, a bandpass filter based on the proposed active inductance is constructed to confirm the usability of the circuit and illustrate these performances. The filter center frequency and quality factor can be tuned independently. Simulation results, given under PSPICE software, present good agreement with the theoretical ones. [ABSTRACT FROM AUTHOR]

In the paper we compare several parameterized estimators for the positive extreme value index, which is a very important parameter appearing in the estimation of the probability of rare events. Firstly, asymptotic comparison at optimal levels of the corresponding tail index estimators is performed. Secondly, the practical validation of asymptotic results for moderate finite samples is done by means of Monte-Carlo simulations. We demonstrate that theoretical domination of the positive extreme value index estimators, which are asymptotically normal with a null asymptotic bias, is not reflected in Monte-Carlo simulations. Moreover, the estimators of such type do not demonstrate stability in the sense of empirical mean-squared error. [ABSTRACT FROM AUTHOR]

Background: When developing a prediction model for survival data it is essential to validate its performance in external validation settings using appropriate performance measures. Although a number of such measures have been proposed, there is only limited guidance regarding their use in the context of model validation. This paper reviewed and evaluated a wide range of performance measures to provide some guidelines for their use in practice.Methods: An extensive simulation study based on two clinical datasets was conducted to investigate the performance of the measures in external validation settings. Measures were selected from categories that assess the overall performance, discrimination and calibration of a survival prediction model. Some of these have been modified to allow their use with validation data, and a case study is provided to describe how these measures can be estimated in practice. The measures were evaluated with respect to their robustness to censoring and ease of interpretation. All measures are implemented, or are straightforward to implement, in statistical software.Results: Most of the performance measures were reasonably robust to moderate levels of censoring. One exception was Harrell's concordance measure which tended to increase as censoring increased.Conclusions: We recommend that Uno's concordance measure is used to quantify concordance when there are moderate levels of censoring. Alternatively, Gönen and Heller's measure could be considered, especially if censoring is very high, but we suggest that the prediction model is re-calibrated first. We also recommend that Royston's D is routinely reported to assess discrimination since it has an appealing interpretation. The calibration slope is useful for both internal and external validation settings and recommended to report routinely. Our recommendation would be to use any of the predictive accuracy measures and provide the corresponding predictive accuracy curves. In addition, we recommend to investigate the characteristics of the validation data such as the level of censoring and the distribution of the prognostic index derived in the validation setting before choosing the performance measures. [ABSTRACT FROM AUTHOR]

This paper presents a comparative analysis on the off-design performance of a gas turbine and organic Rankine cycle (GT-ORC) combined cycle under different operation approaches. A new solving procedure for off-design performance evaluation of the GT-ORC combined cycle was proposed and optimal design parameters for this GT-ORC combined cycle were given. Then simulations were conducted based on the mathematical model and assumptions. The inlet guide vane (IGV) control was applied to regulate the topping GT cycle. Results showed that the sliding pressure operation had an optimal sliding condition to make the GT-ORC combined cycle have the best off-design performance. This condition was a fixed superheat degree of 0.1 K for organic vapor, and the operation approach under such condition was named modified sliding pressure operation (MSPO). Simulation results showed the MSPO performed better than the constant pressure operation and bivariate operation under off-design conditions. Therefore, the MSPO might be more suitable for the off-design operation of the GT-ORC combined cycle. Finally, the sensitivity analysis indicated that the MSPO was more favorable for the GT-ORC combined cycle to reduce the influence of ambient temperature. [ABSTRACT FROM AUTHOR]

The aberrations in microscope system and polarization of the input light beam directly determine the quality of the depletion patterns, which mainly affect the resolution improvement of Stimulated Emission Depletion (STED) microscopy. In the paper, the influences of combining Seidel aberrations and light polarization on the depletion patterns were analyzed comprehensively. And a comparative study about the effects on the resolution was conducted. Simulation results show that the right-handed circularly polarization is the best choice for the depletion patterns in the same condition. And the serious aberration will influence the realization of super-resolution. This study could provide a reliable theoretical basis for a realization of a STED super-resolution system with less aberration. [ABSTRACT FROM AUTHOR]

In this paper it is performed a comparative analysis of the variation of the motor moment in the case of a quadrilateral mechanism when this mechanism is total statically balanced and when it does not contain balancing masses. It is considered the case where the balancing masses are attached in the prolonging of the crank and of the rocker of the quadrilateral mechanism. Some interesting simulation results that highlight the influence of the balancing masses are finally presented. [ABSTRACT FROM AUTHOR]

This paper describes the application of the combined finite-discrete element method (FDEM) for the simulation of two different rock slides observed at the Alpetto Mine in Cesana Brianza (Italy). Previous numerical modeling conducted to study the stability conditions of the high rock cut are used as comparison for the results obtained. The paper presents how the FDEM simulation was performed and discusses the ability and limits of the currently available combined method to simulate rock slide problems for practical purposes. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a comparison of the results of numerical simulations obtained by two different numerical methods for one specific case of stably stratified incompressible flow. The focus in this paper is on the numerical results obtained using some of the compact finite-difference discretizations introduced in the paper [1]. The numerical scheme itself follows the principle of semi-discretisation, with high order compact discretisation in space, while the time integration is carried out by the Strong Stability Preserving Runge–Kutta scheme. Results are compared against the reference solution obtained by the AUSM finite volume method. The test case used to demonstrate the capabilities of selected numerical methods represents the flow of stably stratified fluid over low, smooth, hill-like wall mounted obstacle. [Copyright &y& Elsevier]

Abstract: Sediments of the Marano and Grado Lagoon (Adriatic Sea, Italy) represent one of the world’s most major repositories of mercury (Hg). Its presence is a direct consequence of the historical mining activity in nearby Idrjia (Slovenia), as well as significant discharges from a chlor-alkali plant into the Aussa–Corno river system, which connects to the lagoon. Previous studies have shown that sediment acts as secondary source of Hg species to the overlying water column in natural conditions. However, evidence for the effects of resuspension on the dynamics of Hg species is still lacking. The work reported in this paper formed part of the multidisciplinary “MIRACLE” project, aimed at identifying areas at low risk of Hg bioaccumulation in commercial Manila Clams, an important part of the local economy in this region. The effect of resuspension on the cycling of inorganic mercury (IHg), reactive mercury (RHg) and methylmercury (MeHg) between the sediment and water column was investigated in a mesocosm study. Two experiments were conducted in October 2009 and September 2010 based on material collected from sites heavily impacted by Hg and periodically subjected to dredging activities. Designed to mimic the resuspension of particles, both experiments revealed that the release of Hg species from the solid to the dissolved phase became negligible quickly after the event. MeHg values did not change according to total mercury (THg), suggesting that the enhancement of methylation processes may occur. The findings reported in this paper may be useful for the local management of dredging and fishing activities, although mass balance calculations showed that the total flux of Hg species are trivial compared to lagoon-wide processes. [Copyright &y& Elsevier]

Abstract: Chinese export restrictions already reduced the planning reliability for investments in permanent magnet wind turbines. Today the production of permanent magnets consumes the largest proportion of rare earth elements, with 40% of the rare earth-based magnets used for generators and other electrical machines. The cost and availability of NdFeB magnets will likely determine the production rate of permanent magnet generators. The high volatility of rare earth metals makes it very difficult to quote a price. Prices may also vary from supplier to supplier to an extent of up to 50% for the same size, shape and quantity with a minor difference in quality. The paper presents the analysis and the comparison of salient pole with field winding and of peripheral winding synchronous electrical machines, presenting important advantages. A neodymium alloy magnet rotor structure has been considered and compared to the salient rotor case. The Salient Pole Synchronous Machine and the Permanent Magnet Synchronous Machine were designed so that the plate values remain constant. The Eddy current effect on the windings is taken into account during the design, and the efficiency, output power and the air-gap flux density obtained after the simulation were compared. The analysis results clearly indicate that Salient Pole Synchronous Machine designs would be attractive to wind power companies. Furthermore, the importance of the design of electrical machines and the determination of criteria are emphasized. This paper will be a helpful resource in terms of examination and comparison of the basic structure and magnetic features of the Salient Pole Synchronous Machine and Permanent Magnet Synchronous Machine. Furthermore, an economic analysis of the designed machines was conducted. [Copyright &y& Elsevier]

Abstract: This short communication analyzes the results recently presented in the paper “On a novel dead time compensator for stable processes with long dead times” published in the Journal of Process Control. In the mentioned paper it is argued that the proposed strategy, called modified Smith predictor (MSP), gives better performance than the filtered Smith predictor (FSP) dead-time compensator for stable processes with dead time. In fact MSP has the same structure as FSP and only some specific tuning rules of the filters are proposed. Therefore, in this work some aspects of the comparative analysis and tuning rules presented in the referred paper are discussed to show that MSP is a particular case of FSP and that for some particular cases its tuning rule does not allow for a good closed-loop response. Some simulation case studies are used to illustrate these aspects. [Copyright &y& Elsevier]

The continual reassessment method is a model-based procedure, described in the literature, used to determine the maximum tolerated dose in phase I clinical trials. The maximum tolerated dose can also be found under the framework of D-optimum design, where information is gathered in such a way so that asymptotic variability in the parameter estimates in minimised. This paper investigates the two methods under some realistic settings to explore any potential differences between them. Simulation studies for six plausible dose-response scenarios show that D-optimum design can work well in comparison with the continual reassessment method in many cases. The D-optimum design is also found to allocate doses from the extremes of the design region to the patients in a trial. [ABSTRACT FROM AUTHOR]

The growing demand for the use of biofuels for decentralized power generation initiates new research in gas turbine technology. However, development of new combustors for low calorific fuels is costly in terms of time and money. To give momentum to biofuels application for power generation robust numerical models for multicomponent biofuels must be developed. This paper discusses the use of CFD techniques for modeling the combustion of pyrolysis oil in a new burner geometry from OPRA Turbines. Pyrolysis oil contains many different compounds, which are represented by a discrete fuel model consisting of seven components. The components and their initial fractions approximate the volatility, water content, elemental composition and heating value of a typical fast pyrolysis oil. Simulations have been carried out for both the multicomponent pyrolysis oil and, as a reference, ethanol, a single-component biofuel with a higher volatility. Comparative simulations have been performed to examine the influence of the initial droplet size and to evaluate different combustion models. The results were compared to available experimental data for pyrolysis oil and ethanol combustion. A qualitatively good agreement was achieved. [ABSTRACT FROM AUTHOR]

Ploughing force is a parasitic force induced by the blunt cutting edge and the contact at flank face. Investigation on the ploughing force is necessary for the cutting mechanism understanding, the tool wear monitoring, and the tool sharpness evaluation. In this paper, a new comparison method to determine the ploughing force is developed by considering the cutting edge radius. This method is verified in the FEM simulation. Cutting experiments are performed to investigate the ploughing force in microcutting. Not only the cutting edge radius but also the uncut chip thickness is found to have great effects on the ploughing force. The nonlinear increase of the total specific cutting energy is also attributed to the ploughing force. [ABSTRACT FROM AUTHOR]

Frost growth modeling based on heat and mass diffusion through a porous media is studied in this paper. First, the basic set of equations is established. Then, the main different assumptions used to handle this basic set are presented. Thus, different models, including models found in the literature, are developed. Simulation results from the models are compared to each other and to experimental data. Impacts of each assumption are analyzed. It appears that several assumptions have dramatic impacts on the predictions. Frost thicknesses can be tripled from one model to another one. The effects of the different assumptions are explained, and recommendations to select proper assumptions are made. It appears that simple and reliable frost growth models exist. Those models are particularly suitable for applications requiring low frost growth model complexity (system modeling for instance). On the other hand, the pathway to improve predictions is also pointed out. [ABSTRACT FROM AUTHOR]

This paper deals with the optimum design focused on an LHS (Latin hypercube sampling) experiment with the many design variables of a developed motor and comparison of the optimum algorithm. The effective design variables are selected by screening and analysis of means (ANOM). In this paper, the optimum design is achieved by using the comparison response surface methodology (RSM) with the genetic algorithm (GA) method as the multiobjective optimum design. The torque ripple ratio is satisfied with a design goal within 3%. Therefore, multiobjective optimum design is considered between average torque and efficiency. The simulation results are compared with the experiment and show a deviation below 5%. [ABSTRACT FROM AUTHOR]

Abstract: This paper proposes a Takagi–Sugeno (TS) fuzzy gain-scheduling PI stabilizer to damp the power system low-frequency oscillations and enhance power system stability. The work describes the construction of appropriate fuzzy membership functions and rules for a Power System Stabilizer (PSS) so that its proportional and integral gains can be automatically tuned in real-time to react to changes in the system operating conditions. To find the optimal number and locations of required stabilizers, this paper uses the participation factor method. Simulation results on a practical power system demonstrate that the proposed stabilizer is effective in damping low-frequency oscillations as well as improving system dynamic stability and voltage profile. In addition, the proposed approach provides superior performance when compared to a conventional PI PSS. [Copyright &y& Elsevier]

In this paper, we used a 3-D discrete-element model, Grains3D, which allows the simulation of unsteady granular flows of monodisperse soft spherical particles in a common situation (i.e., down a rectangular channel). A series of numerical dam-break experiments was performed to predict the behavior of granular columns that propagate down a rough horizontal surface from different initial conditions (varying the initial aspect ratio). Numerical results were compared to those obtained experimentally by Lajeunesse et al. (Phys Fluids 17:103302, ) from a similar configuration. Runout distance, temporal flow evolution, deposit morphology and internal flow structures of similar laboratory experiments were quantitatively reproduced as well as prediction of empirical and theoretical scaling laws. This paper highlights that such fully 3-D simulations of soft-spheres can remarkably capture dam-break collapses performed in a rectangular channel. Moreover, Grains3D can provide a complete physical description of such complex unsteady systems which will be the topic of future on-going studies. [ABSTRACT FROM AUTHOR]

Abstract: The paper proposes an IPv6 address configuration scheme for wireless sensor networks. The paper creates an IPv6 address structure for sensor nodes, and based on the proposed IPv6 address structure, the paper proposes an IPv6 address auto-configuration scheme. In the scheme, the transmission scope of the control packets is controlled within one-hop scope and the scheme neither records the address allocation status nor performs the duplicate address detection, so the address configuration cost is reduced and the address configuration delay is shortened. In addition, based on the proposed IPv6 address structure, the paper proposes the address recovery algorithm. From the perspectives of the address configuration cost and address configuration delay, the paper analyzes and compares the performance parameters of the proposed scheme and the existing schemes, including MANETConf, Strong DAD, LISAA and IAC. The analytical and simulative results show that the performance of the proposed scheme is better. [Copyright &y& Elsevier]

Abstract: A recent study () proposed a describing-function approach (DFA) to analytically predict oscillation propagation properties (i.e., dominating frequency and amplitude growth) for a general class of nonlinear car-following laws. This paper presents a new graphic solution approach to DFA and proposes a systematic framework to validate DFA using observed vehicle trajectory data. A set of new empirical measures are defined to extract steady-state traffic properties and oscillation characteristics from vehicle trajectory data. A frequency-domain calibration approach based on DFA is developed to construct a proper nonlinear car-following model that fits these empirical measurements. The analytical DFA predictions of oscillation propagation patterns of the calibrated car-following law are then compared with (i) the observed oscillation properties, and (ii) the simulated oscillation characteristics from the same car-following law. Empirical experiments with real-world trajectory data show that the prediction, the simulation, and the field observation typically match very nicely. This not only validates the analytical prediction approach in the previous study, but also shows that the framework proposed in this paper is capable of calibrating a realistic nonlinear car-following law that reproduces the observed oscillation propagation phenomenon. Our proposed modeling method also brings theoretical analyses and empirical observations into one integrated framework that potentially lays the foundation to understand how nonlinearities in a car-following law affect traffic oscillation evolution, and develop possible counteracting strategies. [Copyright &y& Elsevier]

Abstract: The performance of a newly developed three dimensional (3-D) reactor kinetic model for CANDU reactor is evaluated in this paper. The evaluation is carried out in a closed-loop environment with the help of an existing reactor regulating system (RRS). The 3-D model is obtained based on a modal synthesis method, which represents the neutron flux distribution inside the reactor in both time and space. Throughout this paper, a special attention has been paid to compare the performance of the developed 3-D model with that of traditional coupled point kinetic models. The dynamic behavior of the reactor model in a practical load-following mode has also been examined. The accuracy of the model has been validated against actual plant measurements under both transient and steady-state conditions. Through the analysis and the simulation studies, it has convincingly demonstrated that the developed 3-D model has significant advantages over traditional coupled point kinetic models in terms of the improved accuracy and the higher resolution in modeling the reactor internal dynamics. [Copyright &y& Elsevier]

Purpose: The recent introduction of a specific electronic readout chip, designed for the processing of the same signal pulses from an x-ray sensor in one integrating and one counting channel in each pixel E. Kraft et al., [IEEE Trans. Nucl. Sci. 54, 383-390 (2007)]; E. Kraft, 'Counting and integrating microelectronics development for direct conversion X-ray imaging,' Ph.D. thesis, 2007; J. Fink, 'Characterization of the imaging performance of the simultaneously counting and integrating X-ray detector CIX,' Ph.D. thesis, 2010, enables an alternative to conventional dual-energy imaging methods. As shown in a previous paper, the proposed alternative benefits from positively correlated noise in the raw data, inherent to the counting-integrating readout (CIX), which results in a reduction of basis image noise after dual-energy decomposition. In the present paper, the authors compare the new approach to dual-energy imaging to two conventional dual-energy techniques, the dual-kV technique and the dual-crystal technique and to a photon-counting technique based on two energy windows. Methods: The study is based on x-ray computed tomography (CT) simulations of an anthropomorphic head phantom, where the signal-to-noise ratios and the contrast-to-noise ratios in basis material images and quasi-monochromatic images at 60 keV are compared. Moreover, a simple pictorial illustration of the relevance of input noise correlations in the noise-propagation process during the dual-energy basis material decomposition are presented, as well as measurement data for the correlation obtained as a function of the x-ray flux rate. Results: Under the idealized assumptions of the absence of scatter and detector imperfections like K-escape, crosstalk and detector noise, our comparison shows that among the dual-energy techniques investigated, the CIX concept together with the dual-kV technique performs best, confirming the mitigating effect of correlated measurement data on the dual-energy basis material decomposition. Conclusions: The novel concept of simultaneous counting of photons and integrating the x-ray energy flux has a large potential for dual-energy applications in both projection and tomographic x-ray imaging. Future work will have to focus on the sensitivity of the CIX dual-energy concept to scattered radiation, detector imperfections and high x-ray fluxes. [ABSTRACT FROM AUTHOR]

Abstract: In a dynamically changing environment, the manager of a maintenance and remodeling (M/R) program is confronted with an increasing complexity of coordinating and cooperating multi-resource constrained multiple projects. Uncertainty and interdependence are sources of the complexity, and cause an internal disruption of an activity and chain reactions of disturbance propagation that deteriorate the stability and manageability of the program. This paper evaluates previous endeavors to apply production control and management techniques to the construction industry, and investigates the possibility of applying other production concepts and theories to organizational program management. In particular, this paper proposes a buffer allocation strategy by which periodic buffers are allocated in the flows of program constraint resources (PCRs) to stabilize a master construction schedule instead of protecting individual activities. Comparative experiments by Monte Carlo simulations illustrate better performance of the proposed strategy in terms of program goals: productivity, flexibility, and long-term stability. [Copyright &y& Elsevier]

This paper deals with a new family of high boost voltage inverters called switched-inductor quasi-Z-source inverters (SL-qZSIs). The proposed SL-qZSI is based on the well-known qZSI topology and adds only one inductor and three diodes. In comparison to the SL-ZSI, for the same input and output voltages, the proposed SL-qZSI provides continuous input current, a common ground with the dc source, reduced the passive component count, reduced voltage stress on capacitors, lower shoot-through current, and lower current stress on inductors and diodes. In addition, the proposed SL-qZSI can suppress inrush current at startup, which might destroy the devices. This paper presents the operating principles, analysis, and simulation results, and compares them with those of the SL-ZSI. To verify the performance of the proposed converter, a laboratory prototype was constructed with 48 Vdc input and an ac output line-to-line voltage of 120 Vrms. The simulation and experimental results verified that the converter has high step-up inversion ability. [ABSTRACT FROM AUTHOR]

Abstract: The trend of using floating structures with cage aquaculture is becoming more popular in the open sea. The purpose of this paper is to investigate the dynamic properties of a dual pontoon floating structure (DPFS) when attached to a fish net by using physical and numerical models. A two-dimensional (2-D) fully nonlinear numerical wave tank (NWT), based on the boundary element method (BEM), is developed to calculate the wave forces on the DPFS. The wave forces on a fish net system are then evaluated using a modified Morison equation. The comparisons of dynamic behaviors between numerical simulations and experimental measurements on the DPFS show good agreement. Results also display that a fish net system causes the resonant response of body motions and mooring forces to be slightly lower due to the net''s damping effect. Finally, for designing the rearing space of cage aquaculture, the influences which net depth and net width have on the DPFS dynamic responses are also presented in this paper. [Copyright &y& Elsevier]

This paper presents and discusses different approaches for the measurements of the shielding effectiveness of thick multilayered panels, based on the use of nested reverberation chambers. In particular, it is considered the case of thick multilayered panels, characterized by one highly reflecting face, like a protected composite laminate or a protected glazing window. The paper proposes a novel test procedure, which allows one to estimate from the measurement of a finite dimension panel, the shielding performance of an infinite material sheet against a reverberating field. The method is validated by comparison with the results of analytical simulations and provides accurate results in a wide frequency range, above the lowest-usable frequency of the outer chamber. [ABSTRACT FROM PUBLISHER]

Abstract: The paper deals with modelling of hygro-thermal performance and thermo-chemical degradation of concrete exposed to high temperature. Several possible simplifications in modelling of heat and mass transport phenomena in heated concrete are considered and their effect on the results of numerical simulations is analyzed. In part I of the companion paper, the physical phenomena, and heat and mass flux and sources in a concrete element were studied, both during slow and fast heating process, to examine the relative importance of different flux components. Then, the mathematical model of concrete at high temperature, developed by Authors in the last 10years, was briefly presented and for the first time all the constitutive relationships of the model are summarized and discussed in detail. Finally, the method of numerical solution of the model equations was thoroughly presented. In this part of the paper a brief literature review of the existing mathematical models of concrete at high temperature and a summary of their main features and physical assumptions is presented first. Then, extensive numerical study is performed with several simplified models, neglecting a chosen physical phenomenon or flux component, to evaluate a difference between the results obtained with the simplified models and with the reference model. The study concerns hygric, thermal and degradation performance of 1-D and 2-D axisymmetric concrete elements during fast and slow heating. The analysis will allow us to indicate which simplifications in modeling of concrete at high temperature are practically and physically possible, without generating excessive differences of the results with respect to the full reference model. [Copyright &y& Elsevier]

Abstract: The paper deals with modelling of hygro-thermal performance and thermo-chemical degradation of concrete exposed to high temperature. Several possible simplifications in modelling of heat and mass transport phenomena in heated concrete are considered and their effect on the results of numerical simulations is analyzed. A mathematical model of concrete at high temperature, already extensively validated with respect to experiments, is used as the reference model. It is based on mechanics of multiphase porous media and considers all important couplings and material nonlinearities, as well as different properties of water above the critical point of water, i.e. 647.3K (374.15°C). In this part of the paper, first physical phenomena, as well as heat and mass flux and sources in a concrete element are studied, both during slow and fast heating process, to examine the relative importance of different flux components. Then, the mathematical model of concrete at high temperature, developed by Authors in the last 10years, is briefly presented and for the first time all the constitutive relationships of the model are summarized and discussed in detail. Finally, the method of numerical solution of the model equations is thoroughly presented. In the companion paper (part II) a brief literature review of the existing mathematical models of concrete at high temperature and a summary of their main features and physical assumptions will be presented. Then, extensive numerical studies will be performed with several simplified models, neglecting chosen physical phenomenon or flux components, to evaluate the difference between the results obtained with the simplified models and with the reference model. The study will concern hygric, thermal and degradation performance of 1-D and 2-D axisymmetric concrete elements during fast and slow heating. The analysis will allow us to indicate which simplifications in modeling of concrete at high temperature are practically and physically possible, without generating excessive errors with respect to the full reference model. [Copyright &y& Elsevier]

The west coast and islands of Taiwan have abundant wind resource, which offers a great opportunity for large-scale offshore wind power generation. In Taiwan, the first stage of the offshore wind farms at the Jhang-Bin and Penghu areas has been planned. In particular, the Jhang-Bin wind farm will become the first and one of the largest wind farms in Taiwan. Therefore, its impacts on system operation and security have to be investigated and studied in advance. Following a general connection design discussion, this paper is consist of four major system impact analyses: load flow, fault current, voltage variation, and transient stability. Moreover, three types of typical wind turbines have been adopted in this paper in order to compare their performances on the wind farm integration system. From the simulation results, some significant conclusion and recommendations have been extracted, which would contribute to the first offshore wind farm development in Taiwan. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a new individual based optimization algorithm, which is inspired from asexual reproduction known as a remarkable biological phenomenon, called as asexual reproduction optimization (ARO). ARO can be essentially considered as an evolutionary based algorithm that mathematically models the budding mechanism of asexual reproduction. In ARO, a parent produces a bud through a reproduction operator; thereafter the parent and its bud compete to survive according to a performance index obtained from the underlying objective function of the optimization problem; this leads to the fitter individual. ARO adaptive search ability along with its strength and weakness points are fully described in the paper. Furthermore, the ARO convergence to the global optimum is mathematically analyzed. To approve the effectiveness of the ARO performance, it is tested with several benchmark functions frequently used in the area of optimization. Finally, the ARO performance is statistically compared with that of an improved genetic algorithm (GA). Results of simulation illustrate that ARO remarkably outperforms GA. [ABSTRACT FROM AUTHOR]

This paper explores the social dynamics of so-called intercomparison projects. An intercomparison project is a type of collaborative project that takes place in a number of simulation-based research areas such as astrophysics and climate modelling. Intercomparison projects can be seen as form of metrological practice in which the participants compare the results of numerical simulations of the ‘same’ scientific problem in order to ensure their reliability and validity. The paper is based on case studies of astrophysics, meteorology and oceanography, and the focus is on the organization and coordination of intercomparison projects. I argue that such projects have the effect of defining which scientists work on a particular problem and that they also serve as organizational vehicles for creating and presenting a dominant view of — and a standard result for — that problem. These types of projects are important for understanding numerical simulation-based research, because they show that expectations about desirable results are generated within the group. [ABSTRACT FROM PUBLISHER]

Abstract: In our society the use of hydrogen is continually growing and there will be a widespread installation of plants with high capacity storages in several towns as automotive refueling stations. For this reason, it is necessary to make accurate studies on the safety of these kinds of plants to protect our town inhabitants. Generally several simulation models, whether or not concerned with fluid dynamics, used in safety and risk studies are validated in the past for hydrogen use. However there is a very important need of experimental data covering a broad range of system configurations for strict validation of CFD simulations of hydrogen. This aspect may imply that the results of validation studies can be too accurate and realistic. This paper introduces an experimental activity which was performed by the Department of Energetics of Politecnico of Torino with the collaboration of the University of Pisa. Accidental hydrogen release and dispersion were studied in order to acquire a set of experimental data to validate simulation models for such studies. A pilot plant called Hydrogen Pipe Break Test was built. During the experimental activity, data was acquired regarding hydrogen concentration as a function of distance from the release hole, also lengthwise and vertically. In this paper some of the experimental data acquired during the activity have been compared with the integral models, Effects and Phast. [Copyright &y& Elsevier]

The Bayesian method is widely used to identify a joint distribution, which is modeled by marginal distributions and a copula. The joint distribution can be identified by one-step procedure, which directly tests all candidate joint distributions, or by two-step procedure, which first identifies marginal distributions and then copula. The weight-based Bayesian method using two-step procedure and the Markov chain Monte Carlo (MCMC)-based Bayesian method using one-step and two-step procedures were recently developed. In this paper, the one-step weight-based Bayesian method and two-step MCMC-based Bayesian method using the parametric marginal distributions are proposed. Comparison studies among the Bayesian methods have not been thoroughly carried out. In this paper, the weight-based and MCMC-based Bayesian methods using one-step and two-step procedures are compared to see which Bayesian method accurately and efficiently identifies a correct joint distribution through simulation studies. It is validated that the two-step weight-based Bayesian method has the best performance. [ABSTRACT FROM AUTHOR]

A comparative study of the dynamics of the electron beam-plasma system in two spatial dimensions is carried out by means of particle-in-cell (PIC) simulation and quasilinear theory. In the literature, the beam-plasma instability is usually studied with one-dimensional assumption. Among the few works that include higher-dimensional effects are two- and three-dimensional quasilinear theory and two-dimensional PIC simulations. However, no efforts were made to compare the theory and simulation side by side. The present paper carries out a detailed comparative study of two-dimensional simulation and quasilinear theory. It is found that the quasilinear theory quite adequately accounts for most important features associated with the simulation result. For instance, the particle diffusion time scale, the maximum wave intensity, dynamical development of the electron distribution function, and the change in the wave spectrum all agree quantitatively. However, certain nonlinear effects such as the Langmuir condensation phenomenon are not reproduced by the quasilinear theory. Nevertheless, the present paper verifies that the simple quasilinear theory is quite effective for the study of beam-plasma instability for the present choice of parameters. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents and compares the performance of three popular packet rate estimators used in predicting the rate of incoming traffic to a network host. The paper proposes a fourth and novel packet rate estimator. Unlike other estimators, the proposed estimator is cost effective as its computation is simple and is not performed upon the arrival of every incoming packet. We evaluate and compare the quality and performance of all estimators in terms of accuracy, agility, stability, and cost. The performance evaluation is primarily conducted by using discrete-event simulation. Our simulation accounts for constant traffic as well as synthesized bursty traffic with empirical packet sizes. We also implement and measure the actual computational cost of two time-window based estimators. The cost is measured in terms of consumed CPU cycles for packet and bit rate estimations. In addition, we investigate how to optimize the performance of our proposed estimator by examining the impact of tuning its key configurable estimation parameters. [ABSTRACT FROM AUTHOR]

Abstract: In this work single- and two-phase flow numerical models of a pilot DAF (Dissolved Air Flotation) tank are presented. In the latter framework, the mixture in the tank consists of water and air bubbles. The motion of air bubbles is resolved within the Lagrangian frame of reference. Interaction between bubbles is neglected in the present model. To account for turbulence in the tank, the realizable k–ɛ model is selected as a compromise between a need to correctly resolve the flow and the computational cost of the calculations. To validate the numerical simulations the results are compared with experimental results of an independent research group. The paper discusses the choice between performing two (2D)- or three-dimensional (3D) simulations of a flotation process. Our simulations show that a 3D hydrodynamic model of the flow pattern can well reproduce the single-phase flow in the pilot tank. Despite the major changes in the flow pattern that occur when the second phase (air bubbles) is introduced, the validated single-phase model provides a useful tool in the process of setting up the two-phase model. We show in the paper that a 2D two-phase model cannot resolve successfully the flow in the contact zone, whereas major flow characteristics in the separation zone can, to some extent, be described by a 2D approach (e.g. the stratification of the flow). In addition, two-phase simulations demonstrate that a 3D model is sensitive to the distribution of air and water from the needle valves, which, in turn, influences the stability of the solution obtained. [Copyright &y& Elsevier]

This paper presents a Lebedev finite difference scheme on staggered grids for the numerical simulation of wave propagation in an arbitrary 3D anisotropic elastic media. The main concept of the scheme is the definition of all the components of each tensor (vector) appearing in the elastic wave equation at the corresponding grid points, i.e., all of the stresses are stored in one set of nodes while all of the velocity components are stored in another. Meanwhile, the derivatives with respect to the spatial directions are approximated to the second order on two-point stencils. The second-order scheme is presented for the sake of simplicity and it is easy to expand to a higher order. Another approach, widely-known as the rotated staggered grid scheme, is based on the same concept; therefore, this paper contains a detailed comparative analysis of the two schemes. It is shown that the dispersion condition of the Lebedev scheme is less restrictive than that of the rotated staggered grid scheme, while the stability criteria lead to approximately equal time stepping for the two approaches. The main advantage of the proposed scheme is its reduced computational memory requirements. Due to a less restrictive dispersion condition and the way the media parameters are stored, the Lebedev scheme requires only one-third to two-thirds of the computer memory required by the rotated staggered grid scheme. At the same time, the number of floating point operations performed by the Lebedev scheme is higher than that for the rotated staggered grid scheme. [ABSTRACT FROM AUTHOR]