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Purpose The purpose of this paper is to examine the convergence, offered accuracy and efficiency of the bisectional adaptive frequency sampling (AFS) scheme combined with the Stöer-Bulirsch (SB) algorithm as a tool for supporting frequency-domain method-of-moments (MoM) in broadband electromagnetic (EM) simulations.Design/methodology/approach The AFS and SB procedures have been interfaced with the MoM code, and then, an extensive parametric study has been carried out to explore the performance of the numerical solution for the test problems of reconstructing frequency responses of the wire radiator and scatterer, respectively, over at least a decade bandwidth.Findings The results give evidence for the efficiency of the overall approach and its capability of constructing the approximation of multi-resonant responses with sharp resonant peaks from a substantially reduced number of EM samples (data points) compared to that of conventional uniform sampling.Originality/value Results of the study offer thorough insight into the performance of the AFS-SB technique, and the data given in this paper may be helpful in selecting the convergence criterion and the tolerance for the AFS-SB algorithm to achieve a possibly economical broadband simulation technique. [ABSTRACT FROM AUTHOR]

This paper addresses the problem of identifiability of dynamical networks in the case where the vector of noises on the nodes does not have full rank. In the full-rank noise case, network identifiability is defined as the capability of uniquely identifying the transfer function matrices describing the network from informative data. This includes the noise model, which can be uniquely defined when the noise vector has full rank. When the noise vector has a singular spectrum, it admits an infinite number of different noise models and the definition of network identifiability must be adapted to demand that the correct noise spectrum be identified from informative data rather than a specific noise model. With this new definition, we show that a network with rank reduced noise is identifiable under the same conditions that apply to a network with full-rank noise. [ABSTRACT FROM AUTHOR]

Frequency-domain analysis of dynamic systems is important across many areas of engineering. However, while there are many analysis methods for linear systems, the problem is much less widely studied for nonlinear systems. Frequency-domain analysis of nonlinear systems using frequency response functions (FRFs) is particularly important to reveal resonances, super/subh-armonics, and energy transfer across frequencies. In this paper, the novel contribution is a time-domain, model-based approach to describing the uncertainty of nonlinear systems in the frequency domain. The method takes a nonlinear input–output time-domain model that has normally distributed parameters and propagates that uncertainty into the frequency domain using analytic expressions based on FRFs. We demonstrate the approach on both synthetic examples of nonlinear systems and a real-world nonlinear system identified from experimental data. We benchmark the proposed approach against a brute-force technique based on Monte Carlo sampling and show that there is good agreement between the methods. [ABSTRACT FROM AUTHOR]

The circle formation problem for a group of mobile agents with limited interaction range is addressed in this paper. Distributed switching control laws are developed for multiagent systems to form prescribed formations from any initial configurations on a circle. It is shown that the desired circle formation can be achieved if a parameter depending on the agents’ interaction range is larger than the prescribed angular distance from each agent to its immediate counterclockwise agent. When the agents’ interaction range is not sufficiently large, the formation error of each agent converges to a limit, and an upper bound and a lower bound on the limit value are provided. It is also shown that under the proposed control laws, the mobile agents’ spatial order on the circle is always preserved and thus collision between mobile agents is avoided. [ABSTRACT FROM AUTHOR]

Highlights • A novel model predictive control algorithm is proposed for pre-compensated power converters. • The proposed approach does not modify the original controller, fulfilling production requirements. • Model predictive control improves transient response and load variation sensitivity of current model control. • Simulation and experimental results, together with statistic analysis confirm the benefits and robustness of the algorithm. Abstract Current Mode Control (CMC) is the standard approach to regulate DC-DC power converters in high performance applications, allowing to obtain a faster time-response and better closed-loop stability if compared to Voltage Mode Control (VMC). In the last decade, several algorithms have been proposed to improve standard CMC, most of them requiring to replace the original controller. However, it is common to have either analog or embedded CMC controllers which cannot be replaced easily in commercial power converters. Inspired by very recent results in the topic, this paper proposes a Model Predictive Control (MPC) external loop aimed at optimally modifying the set-point of a CMC loop to improve converter performance. The proposed configuration is directly applicable to any pre-compensated converter as it does not require changes on the already-in-place controller. Moreover, by leveraging a multi-rate implementation, the benefits of MPC are introduced in power conversion without affecting much the computational cost of the over-all control system, contrary to what would happen for a direct MPC implementation. Simulation and experimental results on a synchronous DC-DC buck converter, controlled by a standard CMC algorithm, confirm the benefits of the approach. [ABSTRACT FROM AUTHOR]

In this paper, we study the interacting multiple model (IMM) estimator for networked control systems with packet loss but without packet acknowledgment (ACK). The ACK is a signal sent by the actuator to inform the estimator of whether control packets are lost or not. A system with ACK is usually called a transmission control protocol (TCP) like system; otherwise, it is called a user datagram protocol (UDP) like system. We show that the stability of the IMM estimator for UDP-like systems is determined by the observation packet arrival rate (p.a.r.) and is independent of the control p.a.r. and control inputs. The IMM estimator is stable if the observation p.a.r. is greater than a critical value. We show that this critical value is the same as the critical value for the stability of the optimal estimator for its corresponding TCP-like system. If control inputs eventually tend to zero, the error covariance of the IMM estimator converges to that of the optimal estimator for TCP-like systems. We characterize the impact of the control/observation p.a.r. and the control input on estimation performance. Finally, we prove that the average estimation performance of the IMM estimator approximates that of the optimal estimator within a finite bound, and is superior to that of the linear minimum mean square error estimator. [ABSTRACT FROM AUTHOR]

Abstract This paper explores the application of the parareal algorithm to simulations of ELMs in ITER plasma. The primary focus of this research is identifying the parameters that lead to optimum performance. Since the plasma dynamics vary extremely fast during an ELM cycle, a straightforward application of the algorithm is not possible and a modification to the standard parareal correction is implemented. The size of the time chunks also have an impact on the performance and needs to be optimized. A computational gain of 7.8 is obtained with 48 processors to illustrate that the parareal algorithm can be successfully applied to ELM plasma. [ABSTRACT FROM AUTHOR]

Abstract In this paper, we present an efficient algorithm for identifying and tracking the impulse response of a sparse system that exhibits time varying sparseness and is driven by correlated input. The proposed method convexly combines the outputs of two filters, namely, the sparsity unaware affine projection algorithm (APA), and the sparsity aware zero attracting affine projection algorithm (ZA-APA), each trying to identify the same system using the same input. The combining parameter is adapted by following a steepest descent of the error variance at the convex combination output. A detailed performance analysis of the proposed combination is carried out, which reveals that while for highly non-sparse and highly sparse systems, the proposed combination converges respectively to the APA and ZA-APA (i.e., better of the two filters under the given levels of sparsity), for certain sparsity ranges, it leads to a combination filter that performs better than both the constituent filters. The claims made are validated by exhaustive simulation studies using white, colored as well as speech inputs. [ABSTRACT FROM AUTHOR]

Highlights • This paper proposes a diffusion generalized maximum correntropy criterion. • The D-GMCC algorithm is adjusted for multitask estimation. • Mean and mean-square performance analysis of the D-GMCC algorithm are provided. Abstract Adopting mean-square error (MSE) criterion, distributed estimation algorithms achieve desirable performance if the background noise is drawn from the Gaussian distribution. However, these algorithms may degrade considerably in non-Gaussian situations, especially for the impulsive-noise. The diffusion generalized maximum correntropy criterion (D-GMCC) algorithm is proposed in this article to address this problem. Furthermore, we contribute in multiple tasks problem, which differs from single-task estimation problem. The relatedness of tasks among nodes is also studied to uncover its impact on estimation performance. Simulations illustrate that the proposed algorithm achieves desirable performance and outperforms other related methods. The results on the mean and mean square stability analysis of the proposed algorithm are also provided. [ABSTRACT FROM AUTHOR]

Time and state descriptions form the core of a simulation model representation. The historical influence of initial application areas and the exigencies of language implementations have created a muddled view of the time and state relationships. As a consequence, users of simulation programming languages work in relative isolation; model development, simulation application, model portability, and the communication of results are inhibited and simulation practice fails to contribute to the recognition of an underlying foundation or integrating structure. A model representation structure has been forged from a small set of basic definitions which carefully distinguish the state and time relationships. This paper focuses on the coordination of the time and state concepts using "object" as the link. In addition to clarifying the relationships, the structure relates the concept of ""state-sequenced simulation" to the variations in time flow mechanisms. In conclusion, some speculations are offered regarding alternative algorithms for time flow mechanisms. [ABSTRACT FROM AUTHOR]

This paper presents a model of an I/O subsystem in which devices can be accessed from multiple CPUs and/or via alternative channel and control unit paths. The model estimates access response times, given access rates for all CPU-device combinations. Central to the model's algorithm is the estimation of the rotational position sensing (RPS) miss probabilities by means of the maximum entropy principle. [ABSTRACT FROM AUTHOR]

This paper investigates the performance of 35 dynamic memory allocation algorithms when used to service simulation programs as represented by 18 test cases. Algorithm performance was measured in terms of processing time, memory usage, and external memory fragmentation. Algorithms maintaining separate free space lists for each size of memory block used tended to perform quite well compared with other algorithms. Simple algorithms operating on memory ordered lists (without any free list) performed surprisingly well. Algorithms employing power-of-two block sizes had favorable processing requirements hut generally unfavorable memory usage. Algorithms employing LIFO, FIFO, or memory ordered free lists generally performed poorly compared with others. [ABSTRACT FROM AUTHOR]

Improvements to the exhaustive search method of best-match file searching have previously been achieved by doing a preprocessing step involving the calculation of distances from a reference point. This paper discusses the proper choice of reference points and extends the previous algorithm to use more than one reference point. It is shown that reference points should be located outside of data clusters. The results of computer simulations are presented which show that large improvements can be achieved by the proper choice and location of multiple reference points. [ABSTRACT FROM AUTHOR]

Consider a connected network of agents endowed with local cost functions representing private objectives. Agents seek to find an agreement on some minimizer of the aggregate cost, by means of repeated communications between neighbors. Consensus on the average over the network, usually addressed by gossip algorithms, is a special instance of this problem, corresponding to quadratic private objectives. Consensus on the median, or more generally, consensus on a given quantile, is also a special instance of this problem. In this paper we show that optimizing the aggregate cost function regularized by a total variation (TV) term has appealing properties. First, it can be done very naturally in a distributed way, yielding algorithms that are efficient on numerical simulations. Secondly, the optimum for the regularized cost is shown to be also the optimum for the initial aggregate cost function under assumptions that are simple to state. Finally, these algorithms are robust to unreliable agents that keep injecting some false value in the network. This is remarkable enough, and is not the case, for instance, of gossip algorithms that are entirely ruled by unreliable agents as detailed in the paper. [ABSTRACT FROM PUBLISHER]

This paper describes the main features of a state-of-the-art Monte Carlo solver for radiation transport which has been implemented within COOLFluiD, a world-class open source object-oriented platform for scientific simulations. The Monte Carlo code makes use of efficient ray tracing algorithms (for 2D, axisymmetric and 3D arbitrary unstructured meshes) which are described in detail. The solver accuracy is first verified in testcases for which analytical solutions are available, then validated for a space re-entry flight experiment (i.e. FIRE II) for which comparisons against both experiments and reference numerical solutions are provided. Through the flexible design of the physical models, ray tracing and parallelization strategy (fully reusing the mesh decomposition inherited by the fluid simulator), the implementation was made efficient and reusable. Program summary Program title: COOLFluiD-MC Catalogue identifier: AEZG_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AEZG_v1_0.html Program obtainable from: CPC Program Library, Queen’s University, Belfast, N. Ireland Licensing provisions: GNU General Public License, version 3 No. of lines in distributed program, including test data, etc.: 1990165 No. of bytes in distributed program, including test data, etc.: 149533288 Distribution format: tar.gz Programming language: C++. Computer: From desktops to large HPC distributed systems. Operating system: Mac OS X, Linux. Has the code been vectorized or parallelized?: Parallelized through MPI RAM: Depending on the problem size from a few Megabytes to several Gigabytes. Classification: 21.2. External routines: MPI, boost, PETSc, ParMETIS, cmake Nature of problem: Radiative processes play a fundamental role in countless science and engineering contexts, including combustion, astrophysics, atmospheric space re-entry, experiments in plasma facilities (e.g. shock tubes, arc jets). The problem we are interested in is the computation of radiative heat transfer on arbitrarily complex geometries, in particular to characterize thermal loads acting on the surface of space vehicles. Solution method: Our C++ code implements a flexible and efficient Monte Carlo algorithm making use of state-of-the-art ray tracing techniques designed for and validated on arbitrary unstructured meshes. The code is organized as a collection of dynamically linked libraries connected to the computational kernel of the open source COOLFluiD platform. The Monte Carlo method is parallelized through mesh decomposition, while reusing the same partitioned mesh (and associated data structures) on which fluid dynamics equations are solved. Unusual features: The radiation transfer code of COOLFluiD-MC offers a unique combination of ray tracing algorithms suitable for handling 2D, 2D axisymmetric and 3D simulations on arbitrary unstructured grids. The parallelization strategy is scalable and based on domain decomposition. The overall object-oriented design allows for easy integration of new models and algorithms which can be plugged in dynamically through self-registration techniques. Additional comments: The code is part of a much larger set of COOLFluiD libraries, which are fully available on Github at https://github.com/andrealani/COOLFluiD and include multiple numerical solvers, physico-chemical models, processing algorithms and interfaces to third party scientific software. The CPC distribution also includes a state-of-the-art fully implicit Finite Volume solver for Euler and Navier–Stokes systems which is used to produce the flow solution for the radiative transport algorithm described in the paper. The aerothermodynamic solver, which is used for the final testcase (FIREII) in our paper, is based on the same core Finite Volume modules but on different physico-chemical and radiation models. The latter cannot be made available through the CPC library since they rely on third party libraries (MUTATION version 2.0 and PARADE version 3.1) which cannot be distributed due to NDA. !!!!! The distribution file for this program is over 149 Mbytes and therefore is not delivered directly when download or Email is requested. Instead a html file giving details of how the program can be obtained is sent. !!!!! Running time: Depending on the size of the computational grid, if it is 2D or 3D, on the number of processors used, the running time can vary from a few seconds up to hours or days. The testcases that are included with this version of the code, all using relatively small 2D or 3D meshes, run in 1–10 s each on 8 CPU-cores. The user is, however, totally free to run the same cases on a different number of cores (more or less, according to his/her convenience). [ABSTRACT FROM AUTHOR]

This paper presents novel design procedures for class E switching circuits allowing implicit circuit equations. Because of the allowance, circuit simulators can be used in the proposed design procedures. Moreover, the proposed design procedures also allow any conditions considered until now. The proposed design algorithms are implemented by using PSpice and OPTIMUS. This paper shows the design examples of two kinds of class E switching circuits. In particular, the design example of the class E oscillator shows the benefit of the proposed design procedure eminently, i.e., it is unnecessary to make an equivalent model of the semiconductor devices for the design. These design examples show the validity and effectiveness of the proposed design procedures. [ABSTRACT FROM AUTHOR]

Current transformer (CT) saturation can cause protective relay mal-operation or even prevent tripping. The wave shape of the secondary current is severely distorted as the CT is forced into deep saturation when the residual flux in the core adds to the flux change caused by faults. In this paper, a morphological lifting scheme is proposed to extract features contained in the waveform of the signal. The detection of the CT saturation is accurately achieved and the points of the inflection, where the saturation begins and ends, are found with the scheme used. This paper also presents a compensation algorithm, based upon the detection results, to reconstruct healthy secondary currents. The proposed morphological lifting scheme and compensation algorithm are demonstrated on a sample power system. The simulation results clearly indicate that they can successfully detect and compensate the distorted secondary current of a saturated CT with residual flux. [ABSTRACT FROM AUTHOR]

This paper presents a new approach to blind source extraction from convolutive mixtures in multi-input multi-output (MIMO) channels. Two ill-conditioned cases are considered: the number of sensors is less than the number of sources and the number of sensors is greater than or equal to the number of sources but the system is noninvertible. Although there exist several works related to ill-conditioned dynamic MIMO channels, especially on blind channel identification, how to obtain a true source Only from observable convolutive mixtures is still an open problem. In this paper, beginning with introducing two blind ex- traction models for blind deconvolution in ill-conditioned MIMO channels, we discuss the extractability issue. Results from our extractability analysis (a necessary and sufficient condition) show that it is possible to extract individual sources from the outputs. Furthermore, all potentially separable sources (at most equal to the number of sensors) can be extracted sequentially based on these extraction models. A cost function based on cross cumulant is discussed along with the Gauss-Newton algorithm. Finally, a simulation example is presented for illustration. [ABSTRACT FROM AUTHOR]

Purpose – The purpose of this paper is to propose a method to reduce the non-linear distortion of a transistor to its input and output ports to aid distortion contribution analysis (DCA). This is especially needed when the internal structure of a device model is complex. Design/methodology/approach – The non-linear distortion generated by all non-linear sources inside a device model are reduced to transistor i/o ports by LMSE fitting techniques. Simulations of an LDMOS power transistor are used to compare the reduced distortion results with the actual non-linear sources. Findings – It is shown, that device models where the current sources are split by intermediate nodes cause superficial results, when distortion contributions are calculated as a superposition of contributions from individual non-linear sources. The proposed iterative fitting technique works. Research limitations/implications – Some non-quasistatic effects and the transfer functions from external terminals to internal controlling nodes are not covered. Practical implications – The analysis is a step toward a generic non-linear distortion contribution simulation tool that would aid the designers to develop more linear analog circuits. Originality/value – The concept of DCA itself is fairly new. This paper makes a step to represent the distortion sources in a canonical way. [ABSTRACT FROM AUTHOR]

Generalized eigendecomposition problem has been widely employed in many signal processing applications. In this paper, we propose a unified and self-stabilizing algorithm, which is able to extract the first principal and minor generalized eigenvectors of a matrix pencil of two vector sequences adaptively. Furthermore, we extend the proposed algorithm to extract multiple generalized eigenvectors. The performance analysis shows that only the desired equilibrium point of the proposed algorithm is stable and all others are (unstable) repellers or saddle points. Convergence analysis based on the deterministic discrete-time approach shows that, for a step size within a certain range, the norm of the principal/minor state vector converges to a fixed value that relates to the corresponding principal/minor generalized eigenvalue. Thus, the proposed algorithm is a generalized eigenpairs (eigenvectors and eigenvalues) extraction algorithm. Finally, the simulation experiments are carried to further demonstrate the efficiency of the proposed algorithm. [ABSTRACT FROM PUBLISHER]

This paper considers the problem of the leader-following consensus of generally nonlinear discrete-time multi-agent systems with limited communication channel capacity over directed fixed communication networks. The leader agent and all follower agents are with multi-dimensional nonlinear dynamics. We propose a novel kind of consensus algorithm for each follower agent based on dynamic encoding and decoding algorithms and conduct a rigorous analysis for consensus convergence. It is proved that under the consensus algorithm designed, the leader-following consensus is achievable and the quantizers equipped for the multi-agent systems can never be saturated. Furthermore, we give the explicit forms of the data transmission rate for the connected communication channel. By properly designing the system parameters according to restriction conditions, we can ensure the consensus and communication efficiency with merely one bit information exchanging between each pair of adjacent agents per step. Finally, simulation example is presented to verify the validity of results obtained. [ABSTRACT FROM AUTHOR]

Purpose – An axisymmetric shock-tube model of the high-pressure shock-tube facility at the Texas A&M University has been developed. The shock tube is non-conventional with a non-uniform cross-section and features a driver section with a smaller diameter than the driven section. The paper aims to discuss these issues. Design/methodology/approach – Computations were carried out based on the finite volume approach and the AUSM+ flux-differencing scheme. The adaptive mesh refinement algorithm was applied to the time-dependent flow fields to accurately capture and resolve the shock and contact discontinuities as well as the very fine scales associated with the viscous effects. The incorporation of a conjugate heat transfer model enhanced the credibility of the results. Findings – The shock-tube model is validated with simulation of the bifurcation phenomenon and with experimental data. The model is shown to be capable of accurately simulating the shock and expansion wave propagations and reflections as well as the flow non-uniformities behind the reflected shock wave as a result of reflected shock/boundary layer interaction or bifurcation. The pressure profiles behind the reflected shock wave agree with the experimental results. Originality/value – This paper presents one of the first studies to model the entire flow field history of a non-uniform diameter shock tube with a conjugate heat transfer model beginning from the bursting of the diaphragm while simultaneously resolving the fine features of the reflected shock-boundary layer interaction and the post-shock region near the end-wall, at conditions useful for chemical kinetics experiments. An important discovery from this study is the possible existence of hot spots in the end-wall region that could lead to early non-homogeneous ignition events. More experimental and numerical work is needed to quantify the hot spots. [ABSTRACT FROM AUTHOR]

In all presented analyses of the normalized subband adaptive filter (NSAF) algorithm, there is a common assumption that the length of the adaptive filter is equal to that of the unknown system. In many practices, however, the adaptive filter usually works in an under-modeling situation. Namely, the length of the adaptive filter is less than that of the unknown system. Therefore, for this case, the existing analysis results for the NSAF algorithm are not applicable. In this paper, we analyze the performance of the deficient length NSAF algorithm based on some reasonable assumptions and approximations. More precisely, the expressions that characterize the transient-state and steady-state mean-square behavior of the algorithm are presented. Simulation results in various scenarios support our theoretical expressions. In addition, based on our analyses, a variable step size NSAF algorithm suitable for the under-modeling case is developed, which improves the performance. [ABSTRACT FROM AUTHOR]

In the paper, a problem of improving efficiency of the particle–particle– particle-mesh (P 3 M) algorithm in computing the inter-particle electrostatic forces is considered. The particle-mesh (PM) part of the algorithm is modified in such a way that the space field equation is solved by the direct method of summation of potentials over the ensemble of particles lying not too close to a reference particle. For this purpose, a specific matrix “pattern” is introduced to describe the spatial field distribution of a single point charge, so the “pattern” contains pre-calculated potential values. This approach allows to reduce a set of arithmetic operations performed at the innermost of nested loops down to an addition and assignment operators and, therefore, to decrease the running time substantially. The simulation model developed in C++ substantiates this view, showing the descent accuracy acceptable in particle beam calculations together with the improved speed performance. [ABSTRACT FROM AUTHOR]

According to the special requirements of the acquisition time and carrier frequency for strapdown inertial navigation system (SINS)/BeiDou tightly integrated navigation system under high dynamic environment, an algorithm based on zoom-fast Fourier transformation (Zoom-FFT) that receiver captures BeiDou B1 signal with SINS is put forward in this paper. The algorithm optimizes the traditional algorithm, the parallel code phase acquisition method based on fast Fourier transformation(FFT). Then, it designs a high dynamic source for simulation and verifies the algorithm. The simulation results show that this method reduces 50% cold start-time than that without aid, the warm start-time is only about 2%, and the sensitivity of the system is improved. At the same time, the estimated carrier frequency resolution increases by more than 50 times, and the error is less than 10Hz. The optimized algorithm can meet the requirements of tracking loop in the deeply integrated navigation system under high-dynamic environment, and improve the system acquisition performance. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, a scheme for the canonical ensemble simulation of the coarse-grained articulated polymers is discussed. In this coarse-graining strategy, different subdomains of the system are considered as rigid and/or flexible bodies connected to each other via kinematic joints instead of stiff, but elastic bonds. Herein, the temperature of the simulation is controlled by a Nosé–Hoover thermostat. The dynamics of this feedback control system in the context of multibody dynamics may be represented and solved using traditional methods with computational complexity of where denotes the number of degrees of freedom of the system. In this paper, we extend the divide-and-conquer algorithm (DCA), and apply it to constant temperature molecular simulations. The DCA in its original form uses spatial forces to formulate the equations of motion. The Generalized-DCA applied here properly accommodates the thermostat generalized forces (from the thermostat), which control the temperature of the simulation, in the equations of motion. This algorithm can be implemented in serial and parallel with computational complexity of and , respectively. [Copyright &y& Elsevier]

In the present paper, we discuss algorithms of record generation when records are taken from a Gamma population. We develop such generation algorithms and study their asymptotic performance. [ABSTRACT FROM AUTHOR]

Purpose – Conventional rule-based systems are insufficient for description of complex dynamic systems requiring nontrivial decision procedures. Fuzzy cognitive maps seem to be convenient to overcome these limitations. However, they lack ability of self-learning and therefore some adaptation approaches are needed. The purpose of this paper is both to show the use of fuzzy cognitive maps for such systems and to present migration algorithms as convenient adaptation means. Design/methodology/approach – Some problems of a complex dynamic system description by knowledge-based means are discussed. Fuzzy cognitive maps are presented as a possible way to solve these problems followed by description of migration algorithms as their adaptation means. Their use is clarified on an example of the so-called parking problem based on path planning using a graph search algorithm and a traffic simulation system. Findings – After series of simulations the reality of the proposed system and selected methods with their modifications was proved. It has shown the robustness of the presented solution under circumstances of uncertainty, too. Research limitations/implications – The paper points to stability investigation of the proposed approach introducing uncertainties into the traffic simulation system to take into account, e.g. unexpected events. Further, a possibility of developing a linguistic information retrieval system is mentioned. Practical implications – The proposed approach can find various implementations not only in planning tasks but also in robotic navigation and multi-agent applications in general. In addition, it suggests possibilities of knowledge-based systems, directly using human-like approaches, to areas of decision making under uncertainties and contradictories. Originality/value – An new modification of migration algorithms for adaptation of parameters for fuzzy cognitive maps is introduced and compared to other known self-learning methods. Further, the concept of a traffic simulation system for path planning is presented. [ABSTRACT FROM AUTHOR]

This paper discusses consensus problems for multiagent networks under directed communication graphs. The motions of agents are described by impulsive differential equations, and thus, consensus algorithms can be designed in terms of impulsive systems. Different from the standard consensus algorithms which rely on continuous-time or discrete-time models, the proposed algorithms based on impulsive systems take advantages of instantaneous information. It is shown that the proposed algorithms have a faster convergence speed than the standard consensus algorithms. Moreover, conditions under which all agents reach consensus with the desired performance are presented for the multiagent networks with external disturbances. Simulation results demonstrate the effectiveness of the proposed algorithms. [ABSTRACT FROM AUTHOR]

Abstract: The generalized difference methods (GDM) have been successfully used in numerical simulations of unsaturated soil water flow problems. The object of this paper is to extend applications of the GDM, that is, apply GDM to numerically solve one-dimensional coupled transport models of unsaturated soil water flow and solute. The semi-discrete and fully discrete generalized difference schemes are established, and the detailed algorithm of numerical approximation schemes is provided. Moreover, some numerical examples illustrate that the generalized difference methods are feasible and efficient to find the numerical solutions of one-dimensional coupled transport models in this paper. Finally, satisfactory results and some other significant and valuable conclusions are obtained from studies. [Copyright &y& Elsevier]

Abstract: Sparsified Randomization Monte Carlo (SRMC) algorithms introduced in our recent paper for solving systems of linear algebraic equations are extended to construct the SVD-based randomized low rank approximations for large matrices. We suggest some efficient implementations of SRMC based on low rank approximations, and give different applications. In particular, an important application we present in this paper is a fast simulation algorithm for a randomized approximation of non-homogeneous random fields based on a discrete version of the Karhunen-Loéve expansion. We present two examples of non-homogeneous random field simulation which include a long-correlated Lorenzian random field and the fractional Wiener process. Another application we deal in this paper concerns the randomized solvers for large linear systems. We suggest a hybrid method which combines SRMC with an algorithm for solving boundary integral equations based on a separation representation of the kernel. This method is illustrated in this paper by solving a 2D boundary integral equation from potential theory governing the Dirichlet problem for the Laplace equation. [Copyright &y& Elsevier]

Abstract: Digital watermarking is a useful solution for digital rights management systems, and it has been a popular research topic in the last decade. Most watermarking related literature focuses on how to resist deliberate attacks by applying benchmarks to watermarked media that assess the effectiveness of the watermarking algorithm. Only a few papers have concentrated on the error-resilient transmission of watermarked media. In this paper, we propose an innovative algorithm for vector quantization (VQ) based image watermarking, which is suitable for error-resilient transmission over noisy channels. By incorporating watermarking with multiple description coding (MDC), the scheme we propose to embed multiple watermarks can effectively overcome channel impairments while retaining the capability for copyright and ownership protection. In addition, we employ an optimization technique, called tabu search, to optimize both the watermarked image quality and the robustness of the extracted watermarks. We have obtained promising simulation results that demonstrate the utility and practicality of our algorithm. [Copyright &y& Elsevier]

Abstract: The steady flow of new research results and developments in the field of adaptive equalization that was witnessed for at least the last four decades is clearly evidenced by the many footprints of success it left behind and shows no sign of ending. The thrust of research and implementation in this field is mainly powered by the use of the well-known mean-square cost function upon which relies the ubiquitous least-mean square (LMS) algorithm. However, such an algorithm is well-known to lead to sub-optimal solutions in the real world that is largely dominated by non-Gaussian interference signals. The use of a non-mean-square cost function would successfully tackle these types of interference signals but would invariably involve a higher computational cost. To address these important practical issues, this paper proposes a new adaptive equalization technique that combines both the least-mean-fourth (LMF) algorithm, which is governed by a non-mean-square cost function, with a power-of-two quantizer (PTQ) in the coefficient update process, which greatly reduces the computational cost involved and which therefore makes the proposed technique applicable to time-varying environments. This paper not only elaborates on the basic idea behind the proposed technique but also defines the necessary assumptions and provides a thorough statistical performance analysis (including a study of the convergence behavior) of the combined algorithm LMF-PTQ that is at the core of the proposed technique. An extensive simulation work was carried out and showed that the theoretical predictions are very well substantiated. [Copyright &y& Elsevier]

Purpose - The purpose of this paper is to consider the process of design and implementation of an enhanced fuzzy H8 (EFH8) estimation algorithm to determine the attitude and heading angles of ground vehicles, which are frequently affected by considerable exogenous disturbances. To detect the changes of disturbances, a fuzzy system is designed based on expert knowledge and experiences of a navigation engineer. In the EFH8 estimator, the intensity bounds of disturbances affecting the measurements are updated using a heuristic combination of three change-detection indices. Performance of the proposed estimator is evaluated by Monte-Carlo simulations and field tests of three kinds of vehicles using a manufactured attitude-heading reference system (AHRS). In both simulations and real tests, the proposed estimator results in a superior performance compared to those of the recently developed and standard H8 estimators. Design/methodology/approach - Design, implementation and real tests of the EFH8 estimator are considered for an AHRS specialized for vehicular applications. In the AHRS, three-axis accelerometers (TAA) and three-axis magnetometers (TAM) may be affected by large disturbances due to non-gravitational accelerations and local magnetic fields. Therefore, the design parameters of EFH8 estimator including the theoretic bound of disturbance intensity and the attenuation level are adaptively tuned using a fuzzy combination of three change-detection indices. Once a sensor is affected by an exogenous disturbance, the fuzzy system will increase the scale factor of the corresponding measurement disturbance to place more confidence on the data of the AHRS dynamics including measurements of gyros with respect to the data coming from the TAA and TAM. Findings - An intelligent fault detector is proposed for considering changes of disturbances to adjust the upper bounds of the estimator''s disturbances and the length of data to update the fuzzy system inputs. The EFH8 estimator is suitable to attenuate the effects of disturbances changes on accurate estimation of the attitude and heading angles, intelligently. Originality/value - The paper provides a fuzzy state estimator for adaptively adjusting the theoretic disturbance matrices according to the actual intensity of the disturbances affecting the AHRS dynamics and the measurement sensors. [ABSTRACT FROM AUTHOR]

Abstract: Parallel code presents a non-trivial problem of load balancing computational workload throughout a system of hardware and software resources. The task of load balancing is further complicated when the number of allowable processors changes through time. This paper presents a two-component load-balancing mechanism using optimal initial workload distribution and dynamic load maintenance. The initial guess is provided by inversion of the workload distribution function. Workload distribution inversion enables efficient domain decomposition for arbitrary workloads and easily compensates for changes in system resources. Dynamic load balancing is provided by process feedback control as used, for example, in control mechanisms of physical processes. Proportional, integral, and differential (PID) feedback readily allows controls to compensate for runtime-changes of the workload distribution function. This paper demonstrates a one-dimensional realization of the ideas presented here. We apply this load-balancing technique to our gridless direct simulation Monte Carlo algorithm. We demonstrate that the method does indeed maintain uniform workload distribution across available resources as the workload and usable system resources undergo change through time. [ABSTRACT FROM AUTHOR]

Purpose – The purpose of this paper is to propose a novel decoding algorithm, to decrease the complexity in decoding conventional block turbo codes. Design/methodology/approach – In this algorithm, the signal-to-noise ratio (SNR) values of channels are adaptively estimated. After analyzing the relationship between the statistics of the received vectors R and the channel SNR, an adaptive method of tuning the decoding complexity is presented. Findings – Simulation results show that the proposed algorithm has greatly decreased the decoding complexity and sped up the decoding process while achieving better bit error rate performance. Originality/value – Simulation experiments described in this paper show that the proposed algorithm can decrease the decoding complexity, shorten the decoding time and achieve good decoding performance. [ABSTRACT FROM AUTHOR]

Abstract: This paper introduces a novel neural filtered-U recursive least mean square (NFURLMS) algorithm and its corresponding weight updating method to the application of active noise control (ANC) system. Instead of the complex designing procedures, the proposed approach uses few mathematical transfer functions to design the ANC system. The correction terms momentum to avoid the premature saturation of back-propagation algorithm and the way to design the optimal learning rate are also included in the paper to improve the noise reduction performance. In addition, the proposed method protects ANC systems against unstable poles such as occur in conventional filtered-U design. Several simulation results show that the proposed method can effectively cancel the narrowband and broadband noise in an ANC system. [Copyright &y& Elsevier]

Abstract: In this paper, we present a family of complex-valued support vector classifiers (CSVCs) based on the definition of the complex sign inspired by the modulation in digital communications and the complex-valued kernel functions. We also propose a theorem to construct the complex-valued Mercer kernels and the corresponding kernel function groups. CSVC algorithms include binary (2-state) CSVC (BCSVC), quadrature (4-state) CSVC (QCSVC) and some multi-state CSVCs. In this paper, we focus on QCSVC. For a quadrature complex-valued classification problem, QCSVC is identical to the 4-quadrature amplitude modulation demodulation methods in digital communications. Finally, the simulated experiments confirm the validity and the efficiency of CSVCs. [Copyright &y& Elsevier]

Clocked comparators have found widespread use in noise sensitive applications including analog-to-digital converters, wireline receivers, and memory bit-line detectors. However, their nonlinear, time-varying dynamics resulting in discrete output levels have discouraged the use of traditional linear time-invariant (LTI) small-signal analysis and noise simulation techniques. This paper describes a linear, time-varying (LTV) model of clock comparators that can accurately predict the decision error probability without resorting to more general stochastic system models. The LTV analysis framework in conjunction with the linear, periodically time-varying (LPTV) simulation algorithms available from RF circuit simulators can provide insights into the intrinsic sampling and decision operations of clock comparators and the major contribution sources to random decision errors. Two comparators are simulated and compared with laboratory measurements. A 90-nm CMOS comparator is measured to have an equivalent input-referred random noise of 0.73 mVrms for dc inputs, matching simulation results with a short channel excess noise factor γ = 2. [ABSTRACT FROM AUTHOR]

Abstract: The computational costs of calculating the matrix sign function of the overlap operator together with fundamental numerical problems related to the discontinuity of the sign function in the kernel eigenvalues are the major obstacle towards simulations with dynamical overlap fermions using the Hybrid Monte Carlo algorithm. In a previous paper of the present series we introduced optimal numerical approximation of the sign function and have developed highly advanced preconditioning and relaxation techniques which speed up the inversion of the overlap operator by nearly an order of magnitude. In this fourth paper of the series we construct an HMC algorithm for overlap fermions. We approximate the matrix sign function using the Zolotarev rational approximation, treating the smallest eigenvalues of the Wilson operator exactly within the fermionic force. Based on this we derive the fermionic force for the overlap operator. We explicitly solve the problem of the Dirac delta-function terms arising through zero crossings of eigenvalues of the Wilson operator. The main advantage of scheme is that its energy violations scale better than and thus are comparable with the violations of the standard leapfrog algorithm over the course of a trajectory. We explicitly prove that our algorithm satisfies reversibility and area conservation. We present test results from our algorithm on 44, 64, and 84 lattices. [Copyright &y& Elsevier]

Adaptive infinite impulse response (IIR) filters provide significant advantages over equivalent finite impulse response (FIR) implementations because they are able to more accurately model physical plants that have pole-zero structures. Additionally, they are typically capable of meeting performance specifications using fewer filter parameters. This savings in parameters, which can be as much as 5-10 times, leads to the use of fewer multiplier blocks and therefore, lower power consumption. Despite these advantages, adaptive hR filters have not found widespread use because the associated mean squared error (MSE) cost function is multimodal and therefore, significantly difficult to minimize. Additionally, the filter can become unstable during adaptation. These two properties pose several problems for adaptive algorithms, causing them to be sensitive to initial conditions, produce biased solutions, unstable filter configurations or converge to local minima. These problems prevent the widespread use of adaptive hR filters in practice and if such filter structures are to become more practical, new, innovative solutions are required. This paper proposes a new algorithm for minimizing the MSE cost function of adaptive hR filters aimed at addressing some of the aforementioned issues. We adopt the approach of using a Branch-and-Bound algorithm, which is an exhaustive search method, and employ interval arithmetic for all computations. Simulation results show that the resulting algorithm is viable and competitive and, when compared with a number of existing state-of-the-art algorithms, outperforms them in terms of the MSE of the final point. [ABSTRACT FROM AUTHOR]

Communication systems are designed to provide reliable transmission of information and to cope with various channel imperfections. The amplitude of the received signal is attenuated depending on length and type of the transmission channel. Usually, automatic gain control is placed before the clock recovery in the receiver to combat signal power/swing variations. Optical channel impairments caused by chromatic dispersion, polarization mode dispersion, self-phase modulation, etc. can be efficiently compensated by the use of maximum-likelihood sequence estimation receivers. This paper describes an efficient AGC gain adjustment procedure using a gain control parameter that provides almost the optimum MLSE performance. A gradient algorithm is used to minimize the gain control parameter. Simulation results of 10.7 Gb/s intensity-modulated direct-detection nonreturn-to-zero optical channels disturbed by noise and chromatic dispersion show the advantage of the proposed algorithm. [ABSTRACT FROM AUTHOR]

Since multiuser code-division multiple-access (CDMA) communications systems suffer significantly from multiple-access interference (MAI) and from classical white Gaussian noise, it is therefore necessary to consider their impact on the performance of these systems. It is well known that the learning speed of any adaptive filtering algorithm is increased by adding a constraint to it. In this paper, a constrained least-mean-square (LMS) algorithm, which incorporates the. knowledge of the number of users, spreading sequence length, and additive noise variance, is developed subject to the new combined constraint comprising the MAI and noise variance for a synchronous down-link direct-sequence CDMA system. The novelty of this constraint resides in the fact that the MAI variance was never used as a constraint. In our approach, a Robbins-Monro algorithm is used to minimize the conventional mean-square-error criterion subject to the variance of the new constraint (MAI plus noise). This constrained optimization technique results in an (MAI plus noise)-constrained LMS (MNCLMS) algorithm. The MNCLMS algorithm is a type of variable step-size LMS algorithm where the step-size rule arises naturally from the constraints on MAI and noise variance. Convergence and tracking analysis of the proposed algorithm are carried out in the presence of MAT. Finally, a number of simulations are conducted to compare the performance of the MNCLMS algorithm with other adaptive algorithms. [ABSTRACT FROM AUTHOR]

This paper considers blind-channel estimation for multiple-input multiple-output (MIMO) systems with structured transmitter design. First, a structured transmit delay (STD) scheme is proposed for MIMO systems. Unlike existing transmit diversity approaches, in which different antennas transmit delayed, zero padded, or time-reversed versions of the same signal, in the proposed scheme, each antenna transmits an independent data stream, therefore promises higher data rate and more flexibility to transmitter design. Second, second-order statistics based blind-channel estimation algorithms are developed for MIMO systems with STD scheme. Channel identifiability is addressed for both correlation-based and subspace-based approaches. The proposed approaches involve no pre-equalization, have no limitations on channel zero locations, and do not rely on nonconstant modulus precoding. Third, when channel coding is employed, estimation accuracy can be further enhanced through "postprocessing", in which channel estimation is refined by taking the tentative decisions from the channel decoder as pseudo-training symbols. Simulation examples are provided to demonstrate the robustness and effectiveness of the proposed approaches. [ABSTRACT FROM AUTHOR]

This paper presents a new algorithm and circuit implementation for high-speed frequency-to-voltage converters (FVC). The proposed system overcomes the deficiencies of a previously reported converter and can operate about 20 times faster. To validate this FVC and show its usefulness, it was used in the design of a frequency locked loop. For the design of this ioop, it was found that existing analytical models were incomplete in that they neglect the delay associated to frequency measurements. We proposed a new model which, unlike previous work, shows that frequency locked loops can potentially be unstable. Simulations confirm this fact and also show that the proposed implementation can operate at 5 GHz. To validate the results, a prototype circuit has been fabricated in a 0.18-tm CMOS technology. Tests performed on the prototype show that it runs reliably at 3.84 GHz and consumes 77.4 mW with a 1.8-V power supply when biasing circuitry is included. [ABSTRACT FROM AUTHOR]

Purpose - The paper seeks to provide an adaptive fuzzy logic controller for permanent magnet synchronous motor (PMSM) under direct torque control (DTC) algorithm to minimize the torque ripple. Design/methodology/approach - The design methodology is based on vector control analysis. MATLAB simulations supported with experimental study under C++ are used to execute the proposed work. Findings - The results show that considerable torque ripple reduction as well as considerable current ripple reduction can be achieved by utilizing adaptive fuzzy switching algorithm to fire the inverter supplying the PMSM. Research limitations/implications - This research is limited to PMSM, however the research can be extended to include other AC motors as well. In addition, the following points can be studied, the effects of harmonics in control signals on the torque ripple. Digital and active filters as solution to these harmonics can be also addressed. The actual mathematical relation between the torque ripple and flux ripple can be studied to set the flux and torque bands width in reasonable value. Practical implications - Based on existence DTC control system, it is only required to change the software-switching algorithm, to provide smooth torque, given that the switching frequency of the inverter module is more than or equal to 15?kHz and the system is supplied with timers. In addition, a relatively higher DC voltage may be required to achieve higher speed compared with the traditional DTC. Originality/value - In this paper, the stator flux position, and errors due to deviations from reference values of the torque and stator flux are used to select two active vectors while at the same time the absolute value of the torque error and the stator flux position are fuzzified to adapt the switching of the inverter in order to control the applied average voltage level in such a way as to minimize the torque ripple, so instead of fixed time table structure, a fuzzy logic is used to calculate the switching time for the selected vectors and no PI controller is used as the case in the traditional-space vector modulation. This work is directed to motor drive system designers who seek highly smooth torque performance with fast response. [ABSTRACT FROM AUTHOR]

Purpose - This paper sets out to perform a detailed numerical study of turbulent channel flow with strong temperature gradients using large-eddy simulations. Design/methodology/approach - A recently developed time-accurate algorithm based on a predictor-corrector time integration scheme is used in the simulations. Spatial discretization is performed on a collocated grid system using a flux interpolation technique. This interpolation technique avoids the pressure odd-even decoupling problem that is typically encountered in collocated grids. The eddy viscosity is calculated with the extension of the dynamic Smagorinsky model to variable-density flows. Findings - The mean velocity profile at the cold side deviates from the classical isothermal logarithmic law of the wall. Nonetheless, at the hot side, there is a better agreement between the present results and the isothermal law of the wall. Further, the numerical study predicts that the turbulence kinetic energy near the cold wall is higher than near the hot one. In other words heat addition tends to laminarize the channel flow. The temperature fluctuations were also higher in the vicinity of the cold wall, even though the peak of these fluctuations occurs at the side of the hot wall. Practical implications - The findings of the paper have applications in the design and analysis of convective heat transfer equipment such as heat exchangers and cooling systems of nuclear reactors. Originality/value - The paper presents the first numerical results for non-isothermal turbulent channel flow with high wall-temperature ratios (up to 9). These findings can be of interest to scientists carrying out research in turbulent flows. [ABSTRACT FROM AUTHOR]

The two-path algorithm is an adaptive filter algorithm based on a parallel filter structure, which has been found to be useful for line echo cancellation as well as for acoustic echo cancellation. It is well known that in finite precision arithmetic, the adaptation process of adaptive algorithms can be reduced or even halted due to finite precision effects. This paper proposes a variant of the two-path scheme where the effects of quantization are reduced, without any significant increase in complexity. The improvement is shown by simulations using bandlimited flat spectrum noise as well as real speech signals. [ABSTRACT FROM AUTHOR]

This paper proposes new adaptive beamforming algorithms for a class of uniform concentric circular arrays (UCCAs) having near-frequency invariant characteristics. The basic principle of the UCCA frequency invariant beamformer (FIB) is to transform the received signals to the phase mode representation and remove the frequency dependence of individual phase modes through the use of a digital beamforming or compensation network. As a result, the far field pattern of the array is electronic steerable and is approximately invariant over a wider range of frequencies than the uniform circular arrays (UCAs). The beampattern is governed by a small set of variable beamformer weights. Based on the minimum variance distortionless response (MVDR) and generalized sidelobe canceller (GSC) methods, new recursive adaptive beamforming algorithms for UCCA-FIB are proposed. In addition, robust versions of these adaptive beamforming algorithms for mitigating direction-of-arrival (DOA) and sensor position errors are developed. Simulation results show that the proposed adaptive UCCA-FIBs converge much faster and reach a considerable lower steady-state error than conventional broadband UCCA beamformers without using the compensation network. Since fewer variable multipliers are required in the proposed algorithms, it also leads to lower arithmetic complexity and faster tracking performance than conventional methods. [ABSTRACT FROM AUTHOR]

Purpose - This paper aims to develop a numerical method for analysing the time-dependent conjugate heat and fluid flows inside and around single bubbles rising in a hot liquid. Design/methodology/approach - The procedure combines the moving mesh method for flows in time-dependent geometries and the zoned calculation algorithm for conjugate viscous flows. A moving axisymmetric boundary-fitted mesh is used to track the deformable gas-liquid interface, while conjugate flows in both gas and liquid sides are calculated by a two-block zoned method. The interfacial stresses are employed to calculate the velocity value and to decide the time-dependent bubble shape simultaneously. Governing equations for the rising velocity and acceleration of the bubble are derived according to the forces acting on the bubble. Findings - A calculating procedure for time-dependent conjugate heat and fluid flows inside and around a rising single bubble has been developed. The algorithm has been verified, and can be employed for further analysing heat, mass and momentum transfer phenomena and their relevant mechanisms. Originality/value - The paper developed a method to obtain high fidelity results for the heat and fluid flow details in the vicinity of a time-dependent moderately deformable rising bubble; the physically zero-thickness of a gas-liquid interface is guaranteed. The governing equations for the time-dependent rising velocity and acceleration are derived. [ABSTRACT FROM AUTHOR]