Search

The fixed-time control problem for a class of interconnected systems is studied in this article via an asynchronous event-triggered control strategy, in which all subsystems are interconnected by discontinuous interactions. Especially, due to the discontinuity of interactions, the existence of solutions for the concerned systems is solved via the framework of differential inclusion. Unlike the common ones, the asynchronous event-triggered mechanism in this article generates samplings, triggering events, and control updates asynchronously among multiple subsystems. More significantly, due to the discontinuity of the interactions, a fixed-time discontinuous control law and a specific event-triggered scheme are designed to stabilize this class of interconnected systems in a fixed time. In addition, the interexecution time is lower bounded by a positive constant, and it is assured that the Zeno behavior will not happen. Finally, the effectiveness of the obtained results is illustrated by an example.

The characterizing set-valued functions were introduced for uninorms with continuous underlying functions and these set-valued functions were useful for the complete characterization of such uninorms. In this work we study the characterizing functions of n-uninorms with continuous underlying t-norms and t-conorms. We will show that an n-uninorm with continuous underlying functions possesses n characterizing set-valued functions, where the graphs of these characterizing set-valued functions cover the set of all points of discontinuity of the respective n-uninorm. Moreover, for i=1,…,n, the i-th characterizing set-valued function divides the unit square into the two sets, where below the graph of the i-th characterizing set-valued function the n-uninorm attains values smaller than the local neutral element ei and above the graph of the i-th characterizing set-valued function the n-uninorm attains values greater than the local neutral element ei.

Fast factorized back-projection (FFBP) is a classic fast time-domain algorithm (FTDA), which is not limited by the assumption of azimuth-invariant of echo signal and is suitable for the bistatic synthetic aperture radar (BiSAR) process of arbitrary geometric configuration. However, when the conventional FFBP processing is employed for continuous imaging of multiple full-apertures, the processing efficiency will be decreased significantly, and difficulty will be introduced in motion compensation (MOCO) development. The main contributions in this article include the following two aspects: 1) a new FTDA framework based on FFBP implementation is developed for continuous imaging where echo data are divided into several full-aperture data blocks and then processed separately by FFBP implementation to reduce redundant BP operations for achieving high efficiency and 2) an efficient and effective data-driven MOCO methodology is developed based on the new FTDA framework for high focusing quality. In MOCO, because the phase error functions of subimages are estimated in the phase history domain from different local polar coordinate systems, these phase error functions are actually discontinuous in the spatial domain, which will bring significant discontinuity and defocusing into the final image. To address this problem, the correspondence of error functions between the spatial domain and the wavenumber domain is revealed based on which the phase error functions are reconstructed to remove the discontinuity for high focusing quality. Promising results from both simulation and raw data experiments are provided and analyzed to validate the high performance of the proposed algorithm.

Phase unwrapping is a critical step of interferometric synthetic aperture radar (InSAR) processing, and its accuracy directly determines the reliability of subsequent applications. Many phase unwrapping methods have been proposed, most of which assume that the phase has spatial continuity, while decorrelation noise and aliasing fringes invalidate the assumptions, resulting in poor performance of these methods. To obtain more reliable unwrapping results, in this paper, a deep convolutional neural network, called DENet, is proposed for predicting the probabilities of phase discontinuities in interferograms. The main advantages of DENet are: (1) using branching structure to extract detailed and high-level features separately, to retain details while making full use of contextual information; (2) using multi-channel input, including interferogram, range/azimuthal phase gradients, and residues map, to provide effective guidance for discontinuity prediction; and (3) using a single network to estimate phase discontinuities in both range and azimuth directions simultaneously. To train the network, a data set simulation strategy is proposed to generate enough training samples. The strategy considers a variety of phase components such as terrain-related phase, random deformation, atmospheric turbulence, and noise. The phase discontinuity estimated by DENet is then converted to costs in the minimum cost flow solver of SNAPHU to obtain the final unwrapped phase. Based on validations of simulated and real interferograms, the proposed method exhibits excellent performance compared to traditional and deep learning unwrapping methods. The proposed method can effectively unwrap large-scale, low-quality interferograms, which is expected to significantly improve the accuracy of InSAR applications.

In this paper, a new method for controlling battery emulators in the shape of bidirectional step-down converters driving constant power loads (CPL) is presented. The CPL introduces nonlinear behavior into the system and causes unstable system dynamics. This property and the discontinuity introduced by the switches makes it challenging to develop a suitable control strategy. Usually, switching frequencies are assumed to be fast enough for the controller to neglect the fact that the switches are either on or off. As the desired dynamics of the system approaches the switching frequency of the converter, the discontinuity of the switches can no longer be ignored and the controller has to generate a suitable piecewise constant control input. A novel approach for arriving at a piecewise constant control input is presented and compared to state of the art approaches. The advantages of the new control method are demonstrated with simulations as well as measurements from a hardware-in-the-loop testbed.

This article aims to solve the nonsmooth resource allocation problem in the presence of a global network resource constraint and local set constraints in the framework of multiagent system optimization. It is assumed that multiagent systems are subject to some external disturbances, and the control inputs of the agents satisfy Lispchitz continuity. These two distinguished features render the existing distributed optimization algorithms, especially the subgradient-based algorithms inapplicable due to the employment of discontinuity of subgradients. To solve such a challenging resource allocation problem, a new kind of continuous-time proximal algorithm is designed with the aid of convex optimization theory and the internal-model technique. The proximal algorithm is further augmented by introducing an event-based communication scheme such that the continuous-time communication among the agents is avoided successfully. The theoretical analysis shows that the multiagent systems under the proposed algorithms can converge to the optimal solution of the considered problem, while the external disturbances are rejected. Besides, the Zeno behavior can be excluded for the proximal algorithm with event-based communication. Finally, the numerical simulations are given to verify the established theoretical results.

Recurrent neural network (RNN) has become popular for human motion prediction thanks to its ability to capture temporal dependencies. However, it has limited capacity in modeling the complex spatial relationship in the human skeletal structure. In this work, we present a novel diffusion convolutional recurrent predictor for spatial and temporal movement forecasting, with multi-step random walks traversing bidirectionally along an adaptive graph to model interdependency among body joints. In the temporal domain, existing methods rely on a single forward predictor with the produced motion deflecting to the drift route, which leads to error accumulations over time. We propose to supplement the forward predictor with a forward discriminator to alleviate such motion drift in the long term under adversarial training. The solution is further enhanced by a backward predictor and a backward discriminator to effectively reduce the error, such that the system can also look into the past to improve the prediction at early frames. The two-way spatial diffusion convolutions and two-way temporal predictors together form a quadruple network.\ud \ud Furthermore, we train our framework by modeling the velocity from observed motion dynamics instead of static poses to predict future movements that effectively reduces the discontinuity problem at early prediction. Our method outperforms the state of the arts on both 3D and 2D datasets, including the Human3.6M, CMU Motion Capture and Penn Action datasets. The results also show that our method correctly predicts both high-dynamic and low-dynamic moving trends with less motion drift.

Modal network theory has proven to be a useful tool in analyzing waveguide discontinuities. Ports of a modal network correspond to waveguide eigenmodes on either side of the discontinuity. In this work, modal network theory is extended beyond conventional/geometrical waveguide discontinuities. We use the modal network formulation to analyze discontinuities resulting from metasurfaces. Specifically, we analyze azimuthally invariant cascaded sheet metasurfaces placed in a cylindrical waveguide excited by ${\text {TM}}_{0n}$ modes. The metasurface comprises multiple radially varying electric admittance sheets separated by dielectric spacers. We derive the modal representation of a single inhomogeneous, electric sheet admittance using two approaches: a conventional numerical integration approach and a discrete Hankel transform (DHT) approach. We show that the DHT approach is more efficient. Subsequently, the modal matrices of cascaded sheet metasurfaces are derived using the DHT. Finally, we propose an optimization-based procedure to synthesize transparent metasurface-based mode converters. The mode converters transform a set of incident modes on one side to another set of desired modes on the opposite side of the metasurface. Two designs are synthesized at 10 GHz: a single-mode converter, and a mode splitter. The designs are verified using the commercial finite element electromagnetic solvers.

Dynamic electromagnetic characteristics is significant for the design and operation of superconducting (SC) electrodynamic suspension (EDS) train. This paper established a three-dimensional transient numerical model in COMSOL. The current density excitation comes from the homogenized model of the superconducting magnet. In order to decrease the computing time, periodic boundary is introduced taking the place of finitely long route. Mapping operator is adopted to ensure the continuity of physical quantities in the case of geometric discontinuity in the process of motion. Induced current and magnetic force at different operation velocity and different structure are simulated. In general, this model could be applied to simulate long term operation. It is also suited for the simulation of propulsion systems for EDS systems. In addition, this model provides electromagnetic environment intuitively that would be helpful for the stability analysis and design of onboard SC magnets during long term operation.

Broadband impedance spectroscopy (BIS) provides a new method for cable fault location, however, this method has not been properly used in locating cable fault of cross-bonded (CB) cables due to the geometric discontinuity of impedance spectroscopy measurement loop. This study addresses the possibility of fault location by BIS in CB cables. First, this paper proposes a fault location method by transforming BIS in frequency domain into the location function in space domain with the aid of integral transformation (IT). The kernel function $\mathrm{e}^{j{2}\beta x}$ is used to obtain fault location function. Second, this paper demonstrates an impedance spectroscopy measurement loop in CB cables. BIS in CB cables is observed having a generalized orthogonality with the kernel function $\mathrm{e}^{j{2}\beta x}$ . Given this, the IT method is applicable for fault location of CB cables. Finally, this study carries out the location experiment of cable joints on a 110 kV CB cable in cable trench. The experiment shows that BIS in CB cables could be obtained by the loop proposed in this paper. Besides, the results verify the possibility of fault location in CB cables by IT method using BIS.

In this paper, the usability of the classical Harmonic Balancing method (cHB) to calculate the weakly nonlinear motion of phase- and amplitude controlled MEMS resonators is demonstrated. A polynomial mechanical stiffness description and linearized electrostatic effects are considered, which allow determining the Jacobian analytically. The effects of amplitude and phase control are taken into account by applying boundary conditions in the iteration process. With a customized cHB, it is possible to efficiently simulate the behavior of a MEMS gyroscope undergoing nonlinear resonance with higher parasitic modes. The presented results of a virtual model compare very well with solutions obtained with the Shooting method. Furthermore, we compare the measurement of a drive frequency discontinuity, taken from a different prototype, with the prediction from our linear extrapolated model and from a model with artificially fitted parameters. The cHB approach yields an order of magnitude speed-up in comparison to the transient simulation method. Besides some restrictions, customized cHB methods are interesting candidates for fast system-type simulation considering the MEMS-ASIC interface. [2021-0028]

Ultrasound image of B-mode is reconstructed by DC(Direct Current) removal, quadrature demodulation, low-pass filtering, envelope detection and scanning conversion. Demodulation is the most important of the above. Because of the diversity of human organs and their corresponding acoustic properties, the shift frequency of echo signal changes as the depth increases. For a more accurate recovery signal, segmented function is used to describe the process. Traditionally, polynomial fitting or smooth spline was used to eliminate the discontinuity between the neighbor segment. In this brief, a phase-based quick-fitting method is proposed to optimize the step. Experimental investigation revealed that the phase fitting is applied to the linear array, and the mean-variance is 0.0002( $MHz^{2}$ ) compared with the smooth spline( $0.0033MHz^{2}$ ). For convex probe, the mean-variance( $0.0005MHz^{2}$ ) is also smaller than that of polynomial fitting( $0.0046MHz^{2}$ ). Otherwise, this algorithm can overcome the boundary oscillation caused by frequency fitting. Especially, the results are stable even if the number of segments is large. Complex calculations are not required, the process can be implemented regardless of software and hardware.

This article presents a theoretical time-domain analysis of lightning surge propagation on a multistage and multi-conductor tower. An extended traveling wave theory using electric scalar potential is introduced. The non-TEM wave propagation in the tower is characterized by time/position-variant transient impedance. The analytical formulas of the transient impedance are presented for any position/time in the tower, as well as those of the reflection coefficient at a discontinuity. The concept of primary and secondary waves is introduced to depict the multiple reflections in the tower. It is found that the primary current wave attenuates during its propagation in the tower, and is corrected by a factor when crossing over the discontinuity. A pair of secondary waves is generated at the discontinuity, similar to a center-fed dipole. The proposed method is applied to evaluate the lightning current in a two-stage tower. The result of the proposed method is of high consistency with the FDTD result. It is also observed that the secondary waves could be neglected if the reflection coefficient is small. The traditional transmission line theory could lead to a significant error of the current in the tower.

There are some special phenomena like longitudinal end effect, saturation effect, skin effect, edge effect, and half-filled slots which make the single-sided linear induction motor (SSLIM) analysis more complicated compared to its rotary counterparts. Finite element method (FEM) can be the best choice for complete modeling of SSLIM considering all phenomena. But it is not possible to include the non-linear magnetization curve of iron into the time-harmonic FEM analysis. Thus, this article proposes a 2-D time-harmonic FEM considering all phenomena as well as the non-linear magnetization characteristics of iron using appropriate approximation. In order to overcome the Lorentz method calculation error of vertical force caused by inherent discontinuity of magnetic field intensity at the boundaries of elements, a combined Lorentz–Maxwell method is presented. Validity of the methods and final results is proved by comparing the results with analytical results and experimental measurements.

This brief proposes a proportional-type angle filter with the variable feedback gain mechanism for motor drives using the encoder for angle feedback. In this case, the angle measurement suffers from discontinuity that has to be made continuous through low-pass filters and observers. There are three features. The first designs a real-time feedback gain update rule to improve the closed-loop filtering performance by magnifying the feedback gain in transient periods. The second introduces the disturbance observer (DOB) in the resultant proportional-type feedback filter for enhanced disturbance attenuation against the speed variations. The third proves the useful properties of the filtering error convergence and performance recovery by investigating the filtering error dynamics. A prototype 500-W permanent-magnet synchronous motor (PMSM) drive system validates the practical advantages of the proposed technique.

Metasurface technology has become one of the promising structures for controlling and manipulating of the phase and amplitude characteristics of the electromagnetic waves in recent years. For this reason, the determination of the exact diffracted fields is also crucial especially in the edge or discontinuity points of these types of materials. In the paper, the discontinuity problem by the junction between the layers of an anomalously reflecting metasurface and an impedance half-screen is taken into consideration. These two planar layers have a common edge discontinuity where the diffracted waves occur. The scattered waves from the structure are obtained by the novel technique of the method of transition boundary, which especially offers the relation between the diffracted and scattered geometrical optical waves at the transition boundaries. The diffracted wave expressions are derived by the technique of the method of transition boundary and the uniform wave expressions are obtained by the method of uniform geometrical theory of diffraction. The diffracted and total wave results of the method of transition boundary are also compared and verified by the well-known theory of physical optics. The behaviors of the total wave and its components are analyzed numerically.

Altres ajuts: Universidad Politécnica de Madrid Young Researchers (Grant Number: VJIDOCUPM18MGB) i ICREA This article presents an exhaustive study of the sensitivity in reflective-mode phase-variation sensors based on an open-ended transmission line with a step-impedance discontinuity. Such discontinuity delimits the sensing region (which extends up to the open end of the so-called sensing line), from the transmission line section connected to the input port (design line), which is used to enhance the sensitivity. The theoretical analysis provides the design guidelines to achieve a sensor with high sensitivity compared with the one based on an ordinary (uniform) line with a similar length. In particular, it is shown that for sensitivity optimization, the electrical length of the design line must be set to 90° (or an odd multiple), whereas either a 90° (or an odd multiple) or a 180° (or an even or odd multiple) sensing line can be alternatively used in order to maximize the sensitivity. It is shown that the impedance contrast, defined as the ratio between the characteristic impedances of the design and sensing line, is a key parameter for sensitivity enhancement, and it must be as low or as high as possible for the 90° or 180° sensing lines, respectively. For validation purposes, two prototype devices (one with a 90° and the other one with a 180° sensing line) have been designed and fabricated following the design guidelines. Such devices have been tested by loading the sensing region with several materials with different dielectric constants. Compared with the ordinary line-based sensors, it is found that the maximum sensitivity is enhanced by a factor of 19.7 and 11.4 in the phase-variation sensor based on a 90° and 180° sensing line, respectively. Finally, the sensor concept is generalized to a multisection step-impedance transmission line as a means of further increasing the sensitivity, and a prototype device exhibiting 528.7° maximum sensitivity is implemented.

A common defect found when reproducing old vinyl and gramophone recordings with mechanical devices are the long pulses with significant low-frequency content caused by the interaction of the arm-needle system with deep scratches or even breakages on the media surface. Previous approaches to their suppression on digital counterparts of the recordings depend on a prior estimation of the pulse location, usually performed via heuristic methods. This paper proposes a novel Bayesian approach capable of jointly estimating the pulse location; interpolating the almost annihilated signal underlying the strong discontinuity that initiates the pulse; and also estimating the long pulse tail by a simple Gaussian Process, allowing its suppression from the corrupted signal. The posterior distribution for the model parameters as well for the pulse is explored via Markov-Chain Monte Carlo (MCMC) algorithms. Controlled experiments indicate that the proposed method, while requiring significantly less user intervention, achieves perceptual results similar to those of previous approaches and performs well when dealing with naturally degraded signals.

This article proposes a novel decomposition technique to address the challenges of electromagnetic (EM) parametric modeling, where the values of geometrical parameters change in a large range. In this method, a systematic and automated algorithm based on second-order derivative information is proposed to decompose the overall geometrical range into a set of subranges. Using the proposed technique, a smooth region is decomposed into a few large subregions, while a highly nonlinear region is decomposed into many small subregions. The proposed technique provides an efficient mathematical methodology to perform the decomposition in a systematic and automated process. An artificial neural network (ANN) model with a simple structure, hereby referred to as a submodel, is developed with geometrical parameters as variables in each subregion. When the values of geometrical parameters change from the region of one submodel to another submodel, the discontinuity of the EM responses is observed at the boundary between the adjacent submodels. There are many submodel boundaries in the overall model resulting in the complex multidimensional discontinuity problem. A submodel modification process is proposed to solve this multidimensional discontinuity problem to obtain a continuous model over the entire region. Parallel data generation, parallel submodel training, and parallel submodel modification are proposed to speed up the modeling development process. Compared with standard modeling methods using a single model to cover the entire wide geometrical range, the proposed method can obtain better model accuracy with short model-development time. Two microwave filter examples are used to illustrate the validity of the proposed technique.

This paper is concerned with the distributed control of vehicle platoons. The dynamics of each vehicle are nonlinear and heterogeneous. The control objective is to regulate vehicles to travel at a common speed while maintaining desired intervehicle gaps. The information flow topology dictates the pattern of communication between vehicles in the platoon. This information is essential to effective platoon control and, therefore, plays a central role in affecting the design and performance of platoon control strategies. Our key contribution is a unified distributed control framework that explicitly incorporates and supports a diversity of information flow topologies. Specifically, we propose a distributed sliding mode control (DSMC) framework for a class of generic topologies. The DSMC constructs the topological sliding surface and reaching law via a so-called “topologically structured function.” The control law obtained by matching the topological sliding surface and topological reaching law is naturally distributed. The Lyapunov stability analysis is carried out for the closed-loop system in the sense of Filippov to cope with the discontinuity originated from switching terms. Moreover, a tradeoff between tracking precision and chattering elimination is discussed with a continuous approximation of the switching control law. The effectiveness of the DSMC for platoons is verified under four different topologies through numerical simulation.

i»?When the first commercial electromagnetic (EM) simulators appeared in the late 1980s and early 1990s, we were thrilled to be able to accurately simulate a single microstrip discontinuity, even if the simulation ran overnight. Today, computer hardware is cheaper and much faster, and EM simulation software is more efficient and sophisticated. Even so, putting an EM simulator inside an optimization loop is still not practical in most cases. Even our simple N = 5 hairpin filter example does not lend itself to directly driven EM optimization. The desire to efficiently optimize microwave filters using accurate EM simulation data led us to the port-tuning concept [1].

Neuro-transfer function (neuro-TF) approaches have become more and more popular in parametric modeling for electromagnetic (EM) behavior of microwave components. Existing pole-residue-based neuro-TF approach has better capability of dealing with high-order problem than the rational-based neuro-TF approach, but has the discontinuity issue and the associated non-smoothness issue of the poles/residues when the geometrical variations become large while the rational-based neuro-TF approach does not have. This paper addresses this situation and presents a novel hybrid-based neuro-TF technique which systematically combines both pole-residue and rational formats of the transfer functions. Starting with the pole-residue-based transfer functions, we propose a novel technique to automatically identify the poles/residues that are smooth-continuous and the poles/residues that have the discontinuity and non-smoothness issues. The proposed technique converts the poles/residues that have those issues into the coefficients of the rational-based transfer function to solve the discontinuity and non-smoothness issues in the existing pole-residue-based neuro-TF approach. The proposed technique remains the smooth-continuous poles/residues in the pole-residue format of the transfer function to maintain the capability of handling high-order problem. Compared with the existing neuro-TF modeling methods, the proposed technique can obtain better accuracy in challenging applications of large geometrical variations and high order. The proposed technique is illustrated by two examples of parametric modeling of microwave components.

In minimally invasive surgery, one of the main objectives is to ensure safety and target reaching accuracy during needle steering inside the target organ. In this research work, the needle steering approach is determined using a robust control algorithm namely the Integral sliding mode control &#x0028 ISMC &#x0029 strategy to eliminate the chattering problem associated with the general clinical scenario. In general, the discontinuity component of feedback control input is not appropriate for the needle steering methodology due to the practical limitations of the driving actuators. Thus in ISMC, we have incorporated the replacement of the discontinuous component using a super twisting control &#x0028 STC &#x0029 input due to its unique features of chattering elimination and disturbance observation characteristics. In our study, the kinematic model of an asymmetric flexible bevel-tip needle in a soft-tissue phantom is used to evaluate stability analysis. A comparative study based on the analysis of chattering elimination is executed to determine the performance of the proposed control strategy in real-time needle steering with conventional sliding mode control using vision feedback through simulation and experimental results. This validates the efficacy of the proposed control strategy for clinical needle steering.

Cost and other practically related reasons can mean that velocity sensors are not available on an underwater vehicle. For such cases, the results in this brief are developed on an observer-based fault-tolerant control for underwater vehicles in the presence of external disturbances and unknown thruster faults. An adaptive sliding mode observer is developed to achieve finite-time convergence where, in comparison to a high-gain-based design for the observer, a nonlinear feedback is constructed based on the position estimation error. Unlike alternatives, a discontinuity term in the developed fault tolerant controller is avoided, and the stability of the controlled dynamics is characterized using the Lyapunov theory. Finally, these new results are supported by both a simulation-based study and experimental verification.

A novel method for computing reachable sets is proposed in this paper. In the proposed method, a Hamilton-Jacobi-Bellman equation with running cost function is numerically solved and the reachable sets of different time horizons are characterized by a family of non-zero level sets of the solution of the Hamilton-Jacobi-Bellman equation. In addition to the classical reachable set, by setting different running cost functions and terminal conditions of the Hamilton-Jacobi-Bellman equation, the proposed method allows to compute more generalized reachable sets, which are referred to as cost-limited reachable sets. In order to overcome the difficulty of solving the Hamilton-Jacobi-Bellman equation caused by the discontinuity of the solution, a method based on recursion and grid interpolation is employed. At the end of this paper, some examples are taken to illustrate the validity and generality of the proposed method.

This work validates cylindrical IE-GSTC by applying it to physical metasurfaces, i.e. metasurfaces defined by material properties and dimensions rather than by susceptibility tensor components. Previously reported IE-GSTC which was formulated for zero thickness GSTC discontinuity is extended to handle finite thickness of physical metasurfaces. A simple analytical approach is used to extract the bianisotropic susceptibility tensor of concentric, multilayered, magneto-dielectric shell. Plane wave scattering by a physical metasurface constructed of four segments of multilayered, magneto-dielectric metasurface scatterers is used as an example problem to validate cylindrical IEGSTC. A second example considers an opening on the cylindrical metasurface, confirming IE-GSTC can handle metasurfaces with openings. Good agreement is obtained between IE-GSTC results and full wave simulation results for both cases.

This paper studies the consensus problem of nonidentical Euler–Lagrange systems with parametric uncertainties, under switching directed graphs. We present an adaptive distributed control algorithm that solves this problem in the leaderless scenario, under weak assumptions on the switching interconnection between agents. It is shown that the proposed consensus protocol achieves consensus without using neighbor's velocity information and accounts for the discontinuity of the input torque that results from the switching interaction between agents. Simulation results are given to illustrate the effectiveness of the proposed control schemes.

A novel approximate method based on the Kirchhoff-type circuit for frequency-selective surface (FSS) analysis is presented in this paper. Instead of splitting up the array element and solving a higher order impedance/admittance matrix equation in the periodic moment method, the equivalent transmission line method is adopted to obtain analytical solutions of the normalized receiving current (or magnetic current) distribution for pattern functions. The impedance/admittance elements and transmission coefficients can then be analytically calculated using Munk’s scheme. The proposed method can be applied to generic FSS elements composed of relatively narrow straight slots/strips. The revision scheme of the equivalent transmission line lengths is proposed to account for discontinuity effects at corners of the element. The transmission coefficients of the six biplanar symmetric hybrid radomes are computed to verify the accuracy and efficiency of the presented method.

Spectral unmixing is an important technique for remotely sensed hyperspectral image interpretation, of which the goal is to decompose the image into a set of pure spectral components (endmembers) and their abundance fractions in each pixel of the scene. Sparse-representation-based approaches have been widely studied for remotely sensed hyperspectral unmixing. A recent trend is to incorporate the spatial information to improve the spectral unmixing results. Those methods generally assume that the abundances of the pixels are piecewise smooth and fall into a homogeneous region occupied by the same endmembers and their corresponding fractional abundances. However, in real scenarios, abundances may vary abruptly from pixel to pixel. Therefore, the former assumption in most spatial models does not hold. To address this limitation, we propose a new strategy to preserve the spatial details in the abundance maps via a spatial discontinuity weight. Our experimental results, conducted with both simulated and real hyperspectral data sets, illustrate the good potential of our discontinuity-preserving strategy for sparse unmixing, which can greatly improve the abundance estimation results.

This paper proposes a design flow for channel design by a fast hierarchical optimization method based on Channel Operating Margin (COM). Unlike the common design of experiment (DOE), the method performs the design by a hierarchical flow in the level of electrical characteristic while not the usual horizontal structure of physical parameters. It significantly reduces the number of huge samples used in DOE, and thus is able to offer a fast estimation approach for channel in the early design period. In each stage of the vertical flow, the electrical properties of component are extracted by 2.5D or 3D full wave simulator, and thus ensure the accuracy of the channel design. Design strategy for the most crucial discontinuity, Via, to achieve an impedance matching is addressed. Package effect on the COM is also discussed as a reference for adjusting the 3dB criterion of COM in the future.

We demonstrate a new fuzzing tool for the Robotic Operating System (ROS), which exploits the physical nature of robotic systems to detect a novel class of bugs.

Persistent scatterer interferometry that overcomes the spatial and temporal problems is an effective technique for measuring the surface deformation. The main issue of the technique, however, is unwrapping the persistent scatterers’ phases that are irregularly spaced. The problem is even more challenging when the deformation rate is too high. In this paper, a phase unwrapping method based on an extended Kalman filter as a path-following method is presented. Mean fringe frequency as the phase slope, which is to be used in the extended Kalman filter, is estimated within a local window. The most proper paths for unwrapping are identified by a proposed hybrid cost map, which is a combination of the scaled phase derivative variance, the distances between the persistent scatterer pixels, and the discontinuity locations. The presented method is applied to ENVISAT ASAR images acquired over southwestern Tehran for subsidence monitoring. The maximum displacement rate estimated from the proposed method is about 18 cm/year. Moreover, the results are then validated using a continuous GPS station and leveling measurements acquired over a different time interval. The difference between the rates estimated from the GPS measurements and the proposed method is 0.2 cm/year. It was found that the proposed method makes a significant improvement over the unwrapping problem.

Inventory inaccuracy has significant negative impact on the performance of production control. In this paper, we investigate the robust production control problem for a multiple-stage production system with inventory inaccuracy and time delay between stages. The objective of this problem is to minimize the average production cost. The problem is solved in two steps. First, an approximate optimal production control policy is developed for a multiple-stage production system with time delay but without inventory inaccuracy. Second, we reveal that the discontinuity of the controls makes the policy sensitive to the error of inventory data, and then propose a robust production control policy to eliminate this sensitivity, in which the control variables change smoothly when state variables cross boundaries between different domains in the state space. We also prove that the robustness of the proposed robust policy is better than that of the approximate optimal policy. Finally, numerical experiments are conducted to examine the performance of the proposed robust policy for hedging against inventory inaccuracy.

Rock detachment events along roadways pose public safety concerns but can be predicted and safely handled using geological measurements of discontinuities. With modern sensing technology, these measurements can be taken on 3-D point clouds and 2-D optical images that provide a high level of structural accuracy and visual detail. Doing so allows engineers to obtain the needed data with relative ease while eliminating the biases and hazards inherent in taking manual measurements. This letter presents an approach for fusing the 2-D and 3-D data in natural and unstructured scenes. This includes a novel method for visualizing imagery obtained with very different sensors to maximize their visual similarity making registration a more tangible task. To show the effectiveness of our registration methodology, we evaluate measurements taken manually and digitally on rock facet and cut discontinuity orientations in Rolla, MO. Our method is able to align the 2-D and 3-D data with an accuracy of under 2 cm. The median difference between measurements manually obtained by a geological engineer and those obtained with our proposed software is 3.65.

This paper presents the numerical short–open calibration (SOC) method in the full-wave finite-element method (FEM) algorithm for accurate de-embedding of equivalent circuit parameters of a variety of 3-D nonplanar periodic guided-wave and discontinuity structures. It holds its attractive features in high efficiency and good accuracy as demonstrated in the method of moments algorithm, and further allows itself to be capable of characterization of 3-D nonplanar structures. By setting the reference plane along each feeding line as the perfect electric and magnetic conductors, i.e., PEC and PMC, the entire error box involved in each feeding line and impressed source can be characterized by using these two calibration standards, namely, short- and open-ended circuits. Formulation of ABCD matrix of this error box is described under the introduction of an impressed voltage at each port. Then, ABCD matrix of the core circuit structure can be effectively de-embedded or extracted. Finally, a few numerical examples are given to demonstrate the efficiency and accuracy of our proposed full-wave 3-D FEM-SOC approach in numerical de-embedding of 3-D nonplaner structures.

Several error estimators suitable for use with the adaptive refinement solution of the electric field integral equation (EFIE) are investigated. The estimators are evaluated using a series of test problems for which correlation coefficients and scatter plots are computed. In addition, two new discontinuity estimators are introduced based on the combination of the charge discontinuity with the current or current discontinuity. The evaluations show that simple discontinuity estimators are as accurate for adaptive refinement as the EFIE residual estimator, and are far more computationally efficient.

Crossing strip junctions form an important discontinuity problem in differential signaling an pose a major challenge for signal integrity modeling throughout an analysis in high-speed designs. An analytical framework is proposed to characterize differential transmission lines including the effect of crossing strip junctions for broadband circuit analysis. A new analytical model is proposed to include the finite thickness in the existing models for characterization of asymmetric striplines. The proposed modular representation of the differential line segments with discontinuity effects allows for an entire high-speed transmission channel with crossing lines to be modeled in a cascaded fashion for efficient signal integrity analysis.

In this paper, a numerical short-open calibration (SOC) technique is presented to numerically model and de-embed a variety of non-planar periodic guided-wave structures based on the 3-D full-wave finite element method (FEM). A simple current source or lumped-port model is introduced in formulation of a determinant FEM algorithm. By incorporating the SOC in the FEM solver, the intrinsic port discontinuity caused by this port model is then fully removed or calibrated out of the core non-planar periodic guided-wave structure during the calibration process. Because of the 3-D nature of FEM, the effective per-unit-length parameters of the core periodic guided-wave structure, i.e., effective propagation constant and effective characteristic impedance, are extracted successfully. Two numerical examples, including microstrip line with periodical loading of shorting pins and metal–insulator–metal composite right/left handed structure, are numerically modeled for demonstration and verification. Extracted results have validated the feasibility and accuracy of the presented FEM-SOC, thereby exhibiting its advanced capability in numerical modeling and de-embedding of non-planar structures with complicated configurations.

As a promising signal processing technique, a joint sparse model (JSM) has been used to integrate spatial and spectral information in the classification of remotely sensed images. This technique defines a local region of a fixed window size and assumes an equal contribution from each neighborhood pixel in the classification process of the test pixel. However, equal weighting is less reasonable for heterogeneous pixels, especially around class boundaries. Hence, a discontinuity preserving relaxation (DPR) method can be used to locally smooth the results without crossing the boundaries by detecting the discontinuities of an image in advance. In this letter, we developed a novel strategy that combines these two methods to improve the hyperspectral image classification. A JSM is first applied to obtain a posteriori probability distribution of pixels and then a DPR method is used to further improve the classification results. Experiments conducted on two benchmark data sets demonstrate that the proposed method leads to superior performance when compared with several popular algorithms.

This paper is concerned with obtaining closed-form exact solution for the 2-D canonical problem of the reflected field from a moving planar discontinuity of a dielectric–magnetic medium that is excited by an impulsive line current. The spectral theory of transient (STT) that originally deals with nondispersive frequency-domain plane-wave spectra is used in this paper for addressing a time-variant scattering problem. The scattering from a moving object yields dispersive and anisotropic PW spectra. Nevertheless, we demonstrate that the STT is capable of dealing with these types of spectra and obtain the desired exact time-dependent solutions. The unique wave phenomena that are associated with the medium and scatterer velocity are explored.

Under constant stress accelerated test, we analyze the masked data from hybrid systems including series–parallel system and parallel–series system. The Bayesian posterior distribution and estimates of components’ subsurvival functions are obtained by assuming a prior of the multivariate Dirichlet process. By establishing a relationship between subsurvival and survival functions of components, the estimates of reliabilities for components and system are derived from the estimates of subsurvival functions. It is not confined to the common restriction that the sets of discontinuity points of the survival functions have to be disjointed. For a complex system, we represent it to the proposed series–parallel system or parallel–series system. Thus, the nonparametric Bayesian approach is also applicable for the complex system with s-independent components. A simulated example is presented to demonstrate the efficiency of the method. Finally, the method is applied to a real data of coal wine monitoring power.

Error-free temperature measurement by Raman scattering based optical fiber distributed temperature sensor (OFDTS) is possible if the sensing fiber has no sharp bend. However, in real life applications, the sensing fiber might have sharp bend that may cause discontinuity in the profiles of Raman anti-Stokes (AS) and Stokes (St) signals resulting in erroneous distributed temperature measurement by OFDTS. In such a case, it is necessary to detect the presence and location of the bend. For a human operator using OFDTS, it is difficult to detect the presence of bend and locate it by visually observing AS and St signals. In this article, an online automated technique based on measurement of a new parameter called the instantaneous area of analytic intrinsic mode functions (IMFs) of St signals is presented to serve the purpose. The proposed technique is more automation friendly than earlier reported technique where area corresponding to IMF of complete duration of St signal was considered. The instantaneous area parameter alone is able to detect both the bend induced malfunctioning of OFDTS and the location of bend.

Only with 1-D Green function for 1-D elliptic differential operator, we can solve 2-D/3-D general elliptic problems by applying the axial Green function method (AGM). An extension of AGM is proposed to enforce Neumann boundary conditions. This extension is directly available for 2-D problems with straight boundaries parallel to axes on which Neumann boundary conditions are assigned. It is thoroughly attributed to the specific axial Green functions associated with the Neumann conditions. Moreover, since this extended AGM (XAGM) in 1-D satisfies the transmission condition across an interface along which the permittivity is discontinuous, it can be applied to 2-D problems with interfaces parallel to axes without loss of accuracy. Finally, we apply the XAGM in 2-D to 3-D axisymmetric electric potential problems with variable and/or even discontinuous permittivities along interfaces. Owing to the cylindrical coordinate transform, the transformed problem is tractable to solve using this XAGM. Arbitrary distribution of axial lines is available, which must be a marked advantage of XAGM compared to other methods.

Deembedding a device mounted between a pair of identical transitions requires the transition two-port parameters. These can be obtained using the through-line (TL) deembedding method requiring only through and uniform line deembedding standards. Other related deembedding methods introduce factors to scale a pair of eigenvectors to obtain the transition two-port parameters. In this paper, it is shown that these scaling factors are interdependent and provide a corrective reference plane adjustment. Moreover, the transition wave-transmission matrix can be factored into two wave-transmission matrices with one encapsulating the transition discontinuity and the other of a matched line to provide a corrective reference plane shift. This factorization permits incorporation of desired and corrective reference plane shifts, using data from a second matched line standard. With an emphasis on substrate-integrated waveguide, the proposed TL deembedding method is verified.

The paper studies plasmonics modeling issues and examines the reasons behind the failure of the field-based methods relying on Padé approximations widely used in the analysis of photonic devices based on dielectric materials. Through a study of evanescent, radiation, guided, and surface modes of a plasmonic structure where the failure appears clearly, we demonstrate the physical explanation of this failure and suggest some remedies. We developed a Bidirectional Beam Propagation Method (BiBPM) by adopting a Blocked Schur (BS) algorithm to introduce an unconditionally stable method for plasmonic structures with strong discontinuities. Central to BiBPMs is the accurate calculation of the square root operators that is very widely performed using Padé approximations. However, recent reports demonstrate convergence of Padé that is too slow to lend itself a stable solver in plasmonics. Moreover, Padé approximations completely fail in handling such a strong discontinuity between dielectric and plasmonic waveguides, where a very-wide spectrum of modes could be excited. Alternatively, we propose calculating these operators by the twice faster BS algorithm. Beyond the computational speed, our suggested approach overbears the Padé-based BiBPMs instability and accuracy problems, thanks to the proper physical treatment of surface and evanescent waves: the notorious sources of instability. Through the plasmonic discontinuity problems, the superiority of BS approach has been determined numerically and explained physically.

The product of exponential model based robot calibration approach eliminates parameter discontinuity and simplifies coordinate frame setup, but demands extra effort to normalize twist coordinates and differentiate parameter-varying exponential maps. In this paper, we show that such an endeavor can be exempted by respecting the nonlinear geometry of the joint axis configuration space (ACS), the set of all possible axis locations. We analyze the geometry of the ACS models for prismatic and revolute joints, and treat the errors as Adjoint transformations on joint twists. We propose a novel robot kinematic calibration algorithm based on the ACS and Adjoint error model. It is geometrically intuitive, computationally efficient, and can easily handle additional assumptions on joint axes relations. We present a comparative study with simulations and experiments to show that our algorithm outperforms the existing ones in various aspects.

The finite-element-based subgridding algorithm for the 3-D finite-difference time-domain method proposed by Chilton and Lee is shown to be closely related to the finite integration technique. This new insight permits the straightforward derivation of coupling coefficients for complex configurations without the need for arduous finite-element preprocessing. The result is a flexible cell-by-cell subgridding algorithm that allows different refinement ratios without buffer zone and that preserves highly desired physical conservation properties on the discrete level. Its accuracy is validated by the S-parameter analysis of a rectangular waveguide with a ridge discontinuity.

The polar format algorithm (PFA) is a frequency-domain algorithm with high computational efficiency especially for the high resolution imaging applications in wide-angle staring synthetic aperture radar (WAS-SAR). Because of the image distortion and defocus caused by plane wave assumption, the effective imaging scene is limited to a small region which is defined as the defocus-negligible region. In this article, a novel sub-block imaging algorithm which first applied to WAS-SAR is proposed. This method combines sub-block imaging and spatially variant post-filtering (SVPF) which can not only effectively extend the depth of focus of PFA but also greatly reduces the computational burden. What's more, the method of mosaic image is proposed in this article which can eliminate discontinuity between adjacent sub-blocks. First, the large scene is segmented into multiple regions along range direction and the size of each region is still larger than that of the defocus-negligible region. Second, refocusing is implemented by a phase compensation of the already de-chirped signal with the center of sub-blocks, respectively, and each sub-block image is formed by PFA. Third, the region in each sub-block that exceeds the defocus-negligible region is corrected by SVPF and the image distortion can be corrected by 2-D interpolation. Finally, the mosaic image method is applied to get the large-scene image with high quality. The algorithm proposed in this article is efficient and solves the problems in the process of SAR image mosaic such as dislocation and grayscale differences. The simulated and experimental data results demonstrate the effectiveness and practicability of the proposed algorithm.

Background completion for consumer videos captured by free-moving cameras is a challenging problem. In this paper, we present a new approach to complete the holes left by removing objects with motion-guided pixels assignment optimization. We first estimate the motion field in the holes by applying a two-step motion propagation method. Then, using estimated motion field as guidance, the missing parts of the video are completed by performing pixels assignment optimization based on the Markov random field, which optimally assigns available pixels from other neighboring video frames to the missing regions. Finally, we present an illumination-adjusting approach to eliminate the illumination inconsistency in the completed holes. We validate our method on a variety of videos captured by free-moving cameras. Compared with previous methods, our method works better to keep the completed background spatiotemporally coherent, to complete video background with much depth discontinuity and to make the illumination consistent in the completed region.

This brief addresses a distributed region formation following problem for multiagent systems with the Euler–Lagrange dynamics. In the region control method, specific orders or positions of the agents are not required, but the main drawback is that a desired reference of the whole group is preplanned and made available to all agents. Here, we present a two-layered framework to achieve the distributed region formation following. In the first layer, we develop a smooth estimator to estimate the global reference information. In the second layer, we propose a control methodology using the estimated desired reference to achieve region formation following in a distributed manner. Unlike most existing methods for distributed tracking, which suffer from discontinuity in the controller, our proposed method is continuous and therefore chattering free. A rigorous Lyapunov-based analysis is utilized to show the stability of the overall system. It is shown that the stability of the overall system can be ensured if the estimation error converges at least exponentially. Finally, the experimental result is presented to illustrate the performance of the proposed methodology.