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When incidents happen with the positioning spud of a backhoe dredger, the hull loses stability, heels significantly, and may even capsize under extreme conditions. Coupling the hydrodynamics and spud vibrations, this paper investigates the dynamic stability of a backhoe dredger after spud failure based on the time domain method. The maximum dynamic heeling angle verifies the stability of the backhoe dredger. To identify the influences of environmental load, operating conditions, and spud-soil interactions, numerical motion simulations were conducted in the time domain. The main conclusions on dynamic stability consider the influences of relative environmental and operational factors. This study provides a powerful and efficient approach to analyze the dynamic stability of backhoe dredgers and to design flooding angles. [ABSTRACT FROM AUTHOR]

Acoustic detection technology is a new method for early monitoring of wood-boring pests, and the effective denoising methods are the premise of acoustic detection in forests. This paper used sensors to record Semanotus bifasciatus larval feeding sounds and various environmental noises, and two kinds of sounds were mixed to obtain the noisy feeding sounds with controllable noise intensity. Then, the time domain denoising models and frequency domain denoising models were designed, and the denoising effects were compared using the metrics of a signal-to-noise ratio (SNR), a segment signal-noise ratio (SegSNR), and log spectral distance (LSD). In the experiments, the average SNR increment could achieve 17.53 dB and 11.10 dB using the in the test data using the time domain features and frequency domain features, respectively. The average SegSNR increment achieved 18.59 dB and 12.04 dB, respectively, and the average LSD between pure feeding sounds and denoised feeding sounds were 0.85 dB and 0.84 dB, respectively. The experimental results demonstrated that the denoising models based on artificial intelligence were effective methods for S. bifasciatus larval feeding sounds, and the overall denoising effect was more significant, especially at low SNRs. In view of that, the denoising models using time domain features were more suitable for the forest area and quarantine environment with complex noise types and large noise interference. [ABSTRACT FROM AUTHOR]

To assess the dynamic stiffness of shallow foundations, as an alternative to the existing rigorous approaches, it is convenient to idealize the soil as some semifinite truncated cones representing the infinite nature of the supporting soil. The one-dimensional wave equation for cones which is usually defined in frequency domain has been extended to be solved directly in the time domain. The recently streamlined strength of materials using cones has been developed in the time domain to calculate the response of shallow foundations on a layered half-space for translational degrees of freedom, while the wave pattern in the time domain is not studied for a rocking degree of freedom. The concept of echoes which converts the response of the footing on homogenous half-space to that of the footing on layered site is still applicable when the layered system excited by rocking moments. The echo constants are derived in the current research for rotational degrees of freedom in either the flexibility or stiffness formulation. In this paper, using the theory of cones, equations for direct analysis of soil-structure interaction in the time domain are obtained for the rocking degrees of freedom. The results, calculated exclusively in the familiar time domain, are in remarkable agreement with the results obtained in the frequency domain. [ABSTRACT FROM AUTHOR]

With the increasing demand for convolutional neural networks (CNNs) in many edge computing scenarios and resource-limited settings, researchers have made efforts to apply lightweight neural networks on hardware platforms. While binarized neural networks (BNNs) perform excellently in such tasks, many implementations still face challenges such as an imbalance between accuracy and computational complexity, as well as the requirement for low power and storage consumption. This paper first proposes a novel binary convolution structure based on the time domain to reduce resource and power consumption for the convolution process. Furthermore, through the joint design of binary convolution, batch normalization, and activation function in the time domain, we propose a full-BNN model and hardware architecture (Model I), which keeps the values of all intermediate results as binary (1 bit) to reduce storage requirements by 75%. At the same time, we propose a mixed-precision BNN structure (model II) based on the sensitivity of different layers of the network to the calculation accuracy; that is, the layer sensitive to the classification result uses fixed-point data, and the other layers use binary data in the time domain. This can achieve a balance between accuracy and computing resources. Lastly, we take the MNIST dataset as an example to test the above two models on the field-programmable gate array (FPGA) platform. The results show that the two models can be used as neural network acceleration units with low storage requirements and low power consumption for classification tasks under the condition that the accuracy decline is small. The joint design method in the time domain may further inspire other computing architectures. In addition, the design of Model II has certain reference significance for the design of more complex classification tasks. [ABSTRACT FROM AUTHOR]

This article presents a pulse-amplitude-modulated (PAM)-8 wireline transceiver with receiver-side pulsewidth-modulated (PWM) or time-domain-based feedforward equalization (FFE) technique. The receiver converts the voltage-modulated signals or PAM signals into PWM signals and processes them using inverter-based delay elements having a rail-to-rail voltage swing. Time-to-voltage and voltage-to-time converters are designed to have non-linearity with opposite signs with the aim of achieving higher front-end linearity on the receiver. The proposed PAM-8 transceiver can operate from 12.0 to 39.6 Gb/s and compensates 14-dB loss at 6.6 GHz with an efficiency of 8.66 pJ/bit in 65-nm CMOS. [ABSTRACT FROM AUTHOR]

A reduced-order model of finite periodic structures with absorbing boundary conditions (ABCs) and localized time-dependent excitations is proposed. 1D-periodic structures whose cells can represent any 2D or 3D arbitrary substructures are considered. The key steps for modeling an ABC in the time domain are: (i) expression of the impedance matrix with the wave finite element (WFE) method; (ii) partial rational decomposition of the impedance matrix; (iii) introduction of vectors of supplementary variables to describe the ABC in the time domain. In this paper, a model reduction approach is proposed to speed up the computation of the ABCs. The focus is on the reduction of the number of internal degrees of freedom of substructures, and the reduction of the number of degrees of freedom at the substructure interfaces. The approach allows the consideration of complex substructures with large FE models, and the computation of the time response of periodic structures at a low computational cost. Numerical experiments are carried out to highlight the relevance of the proposed approach. Specifically, the analysis of a metamaterial structure containing nonlinear resonant substructures is carried out with the proposed approach. Results show that, when compared to the linear case, band gaps in periodic structures with nonlinear substructures can be significantly improved. • The time response of periodic structures with localized excitations is computed. • Absorbing boundaries are built using supplementary variables and reduced DOFs. • Solutions are obtained by time integration of a finite element dynamic system. • Examples of infinite periodic structures with a large number of DOFs are given. • The influence of nonlinearities on band gaps effects is illustrated. [ABSTRACT FROM AUTHOR]

The linear forced vibration characteristics of viscoelastic variable stiffness laminated composite plates (VVSLC) are studied using a generalized Maxwell model and finite element method. The integral form of the viscoelastic constitutive relation is converted to the incremental form for finite element formulation based on the Reissner–Mindlin plate theory. The recursive relations are developed to compute the current time-step solution using only the previous time-step solution. The periodic response directly in the time domain is obtained using shooting technique coupled with Newmark's time integration method. The implementation of shooting technique for Boltzmann integral-based viscoelasticity for curvilinear fibre composite plates is done for the first time in this study. For the comparison purpose, the response/resonance frequency/modal loss factor is also obtained using equivalent complex modulus based viscoelastic correspondence principle. It is observed that the variation in fibre orientation and boundary conditions leads to significant variations in response, stress/moment resultant amplitude and the damping factor of the VVSLC plates. Further, the present time domain based approach is capable of predicting damping factor at all forcing frequencies whereas complex eigenvalue analysis can predict damping factor only at discrete resonance frequency. Based on the detailed studies, it is found that the curvilinear fibre composite plates depict a significant reduction in response/moment resultants compared to straight fibre composite plates. • Dynamic response of viscoelastic variable stiffness laminated composite plates. • Spatial and temporal variations of stiffness. • Effect of different parameters on response amplitude and damping factor. • Significant reduction in response amplitude with appropriate fibre path. [ABSTRACT FROM AUTHOR]

Asymptotic homogenization (AH) is a rigorous method used for modeling multiscale mechanical behavior in periodic composites. Unlike conventional AH methods, which predict the effective viscoelasticity using the elastic–viscoelastic correspondence principle, an AH method was proposed to directly calculate the effective material properties in the time domain, thereby enabling the complex transform to be omitted between the time and Laplace domains. This time-domain AH method is reformulated based on the integral form rather than the differential form of the Kelvin–Voigt viscoelastic model. Thus, multiple time-domain-based characteristic elasticity and viscosity displacement tensors are replaced by one integral form characteristic displacement tensor in the polymer matrix composite. Using mathematical formulae, a numerical implementation method was then developed by establishing location- and time-related stress loads. An in-house Python subroutine was also programmed to compute the effective viscoelastic properties from the finite element implementation results. Unidirectional and woven fabric composite homogenization results were comparable to those obtained using the conventional representative volume element method, indicating high effectiveness and accuracy. The results suggest that the proposed time-domain AH method is a powerful tool for modeling the two-scale mechanical behavior of viscoelastic composites and is compatible with the existing commercial software.

One way to recognize hand gestures is to use signal electromyography (EMG). The processed signal can use the time domain, frequency domain, or a mixture of the two domains. Meanwhile, the classification method that is widely used recently is the classification of Artificial Neural Networks (ANN). This paper presents a comparison study between time domains with frequency domain for EMG signals using ANN classification. This comparison aims to find out a better method for controlling the hand robot. The time domain features are root mean square (RMS) of the signal, while the signal’s octave band becomes a feature of the frequency domain. The EMG signals were obtained from the subject with eight fingers gestures. The results of this classification are used to control the robot’s hand. The success of each method in recognizing hand movements was counted. In addition, the response speed of the robot in changing positions is measured. The results showed that features using the frequency domain had a higher percentage of success than another domain. But the speed and memory used then the system using signals in the time domain is better.

• Performance evaluation procedure for tall buildings using database assisted design approach is proposed. • Three performance levels of occupant comfort, operational, and continued occupancy with limited interruption are considered. • Wind directionality analysis using local climatological data. In recent years, performance-based design (PBD) has gained attention and is sought to be the benchmark approach in the field of wind engineering. While the concept of performance-based design is well-accepted in earthquake engineering, it is yet to be embraced for the design of buildings to resist severe wind loads. This paper introduces a framework for the performance-based wind design (PBWD) of tall steel buildings using a time domain analysis that keeps the process of wind effects and the structural design process integrated, transparent, and fully auditable. From the perspective of PBWD, the main objective is to achieve a desirable performance level for a given hazard level, i.e., mean recurrence interval of extreme wind. The wind effects are directly related to the mean annual return of wind through a well-accepted simulation approach. A 180 m tall standard CAARC building is used for the case study to illustrate the proposed methodology. The wind load time histories are determined using the pressure tap data on exterior faces of the building measured in the wind tunnel. With the calculated wind loads, nonlinear dynamic analysis is conducted with various wind directions and mean wind speeds based on database-assisted design (DAD) approach. The key performance measures such as demand-to-capacity indices, inter-story drift, damage deformation index, and floor accelerations are calculated as a function of wind directions and mean wind speed. The obtained responses are used in conjunction with a local wind climatological database to determine the extreme wind effects for any specific mean recurrence interval. The performance of the steel building is evaluated for three performance criteria, including occupant comfort, operational, and continuous occupancy. The conducted performance assessment reveals that building fails to satisfy the serviceability requirement of drifts. However, the building satisfies the requirements for the occupant comfort and operational performance levels for strength design, while it also satisfies the continuous occupancy, limited interruption in Risk category II. The result reveals that the proposed framework provides realistic assessment of performance of the building incorporating the wind directionality and return period of the wind speeds. [ABSTRACT FROM AUTHOR]

Noise from rail transit viaducts often has a negative effect on surrounding buildings and nearby residents. To reduce the bridge vibration and radiated noise, floating slab tracks have been widely adopted in rail transit viaducts. To calculate the vibration of coupled track-bridge systems, both time-domain and frequency-domain methods can be applied although their relative performance is not very clear. This study aims to compare the two approaches and then provide some guidelines in choosing the appropriate method for predicting the vibration. The principle and methodology of the two calculation methods are firstly introduced, and the models for the train, floating slab track and bridge are developed using similar parameters. To further improve the efficiency and accuracy of the frequency-domain method, a half period method and a weighted average method are proposed to calculate the average responses of a certain point on the rail, floating slab and bridge to approximate the response during the pass-by. An indirect method is used to estimate the wheel–rail combined roughness from the measured rail acceleration when the train is running on the bridge, and compared with the direct measurement rail roughness. For the vibration of the bridge and floating slab, comparisons are made between results obtained from the time-domain and frequency-domain methods with different train speeds, and between results from experiment and simulation with different roughness. It is found that the wheel–rail contact forces and other structural responses from the two approaches show good consistency in the frequency region above 20 Hz. It is shown that a good approximation of the response during the pass-by can be obtained using the frequency-domain method by adopting the half period average or a simplified weighted average of two wheel position cases. When using the measured roughness and estimated roughness, the simulated vibration of the floating slab and bridge match well with the experimental results, and the indirect method can be used to modify direct measurement roughness in lower frequency regions. In the vibration prediction, the rail vibration or roughness, and other parameters in the vehicle–track–bridge system, should be measured accurately to ensure high reliability. • The train-induced vibration characteristics of floating slab and bridge coupled system are summarized. • A comparison of time-domain and frequency-domain methods in predicting dynamic response of coupled system is developed. • Two simplified frequency-domain methods with different wheel arrangement cases is proposed and verified. • A field test is carried out to validate the numerical prediction. [ABSTRACT FROM AUTHOR]

This paper proposes a concurrent topology optimization method for optimizing the structures that are periodically filled with multiple microstructures excited by dynamic response in the time domain. At the macroscale, different microstructures are considered as different materials. To generate the various distribution of different microstructures, a multi-material interpolation approach based on the Solid Isotropic Material with Penalization (SIMP) is integrated. At the microscale, the energy-based homogenization method (EBHM) is employed to determine the macroscopic effective properties of the microstructures. All macroscale elements with identical material are represented by a distinct microstructure. For the proportional damping model, the HHT- α is implemented as a time integration technique to obtain the dynamic response of multi-scale and assumed multi-material structures. The objective function of the topology optimization problem is to minimize the mean dynamic compliance. Combined differentiate-then-discretize method with the adjoint variable method, the sensitivity analysis applies the gradient-based Zhang-Paulino-Ramos Jr. (ZPR) algorithm or Method of Moving Asymptotes (MMA) to update the design variables under multiple constraints in the time and space-discretized system. The proposed approach is numerically performed through 2D and 3D examples to demonstrate its effectiveness. [ABSTRACT FROM AUTHOR]

This paper presents a stability-preserving model reduction approach for a vibro-acoustic finite element model including poroelastic materials. Most of the research on these systems in the past was conducted in the frequency domain and there were less focus on the stability properties. However, with the increasing of interest in time-domain auralization and virtual sensing, stability-preserving model order reduction is becoming essential for efficient time-domain simulations. The original finite element models for such systems are already well established but not extended to the time domain because of its high computational demand. Therefore, this paper proposes a method to generate stable reduced-order models. The solid displacement–total displacement ( u s − u t ) formulation of the Biot's model is used to describe the poroelastic media. This formulation leads to a set of positive and symmetric system matrices with passive transfer functions. Applying the Kalman–Yakubovich–Popov lemma and the Cholesky/LDL decomposition, this formulation is modified to satisfy the previously proven stability-preserving conditions under one-sided model order reduction. Furthermore, the coupling conditions between the poroelastic media, air, and structure are also investigated. It is finally shown that the stability-preserving property is kept for the coupled models with appropriate variables. The proposed method is verified by several numerical simulations. • A time-domain formulation of Biot's equations is derived. • The time-domain Biot's model is stability-preserving under one-sided model order reduction methods. • The coupling models between the proposed time-domain Biot's model and vibro-acoustic systems are still stability-preserving. • The reduced order model enables efficient time-domain simulations of the vibro-acoustic system with the Biot's model. [ABSTRACT FROM AUTHOR]

• We have explored a well-justified approach to effectively simulate neutron noise induced by fluctuations in thermal–hydraulic parameters. • DYNOSIM, a time-domain simulator tailored for WWER-type reactors, has been enhanced to model these phenomena. • Our study systematically addresses key inlet coolant parameters: flow rate, temperature, and boric acid concentration. • A CFD-based "coolant mixing matrix" has been integrated into DYNOSIM for realistic modeling of both uniform and non-uniform distributions of thermal–hydraulic parameters among coolant loops. • The analysis includes both symmetric and asymmetric scenarios of neutron noise triggered by the fluctuation of thermal–hydraulic parameters. The neutron noise phenomenon, occurring in all types of nuclear reactors, provides valuable insights into the dynamic behavior of these reactors. In this work, a well-justified approach for modeling neutron noise induced by thermal–hydraulic sources in a hexagonal reactor core is presented in detail. These sources encompass fluctuations in key features of the inlet coolant, including flow rate, temperature, and boric acid concentration. Our proposed approach touches on various aspects of the distribution of thermal–hydraulic parameters among coolant loops, accounting for both uniform and non-uniform distributions. The latter allows for the asymmetric and asynchronous distribution of their fluctuating component among the coolant loops. To manage such complexity, it becomes imperative to determine the contribution of each fuel assembly based on each coolant loop. To achieve this, CFD simulations are conducted for the downcomer and lower plenum of the reactor pressure vessel. These simulations provide essential data to establish the coolant mixing matrix, which accounts for non-uniform distributions. The obtained mixing matrix is subsequently integrated into our neutron noise simulator, DYNOSIM, ensuring the faithful reproduction of neutron noise. Our study comprehensively analyzes both uniform and non-uniform scenarios. The radial and axial distributions of neutron noise amplitude and phase are examined for these scenarios. Their qualitative verifications are conducted by prior works in this field. Furthermore, we compare one of the uniform scenarios with reference results obtained using a frequency domain simulator. Notably, our CFD simulation results closely match the experimental data. Our findings demonstrate the effectiveness and efficiency of this methodology in modeling and understanding neutron noise in hexagonal reactor cores. [ABSTRACT FROM AUTHOR]

• A novel nonlinear system identification method is proposed based on OKID. • Nonlinear coefficients can be estimated without system order determination. • Combined with ERA, nature frequencies of the system can be identified accurately. In this paper, a novel time-domain method for identifying nonlinear structural dynamical system with explicit model is proposed. By exploiting the observer/Kalman filter identification (OKID) and nonlinear feedback interpretation, the nonlinear parameters of the system are estimated accurately. The effectiveness of the proposed nonlinear OKID (NOKID) method is demonstrated through three numerical examples, namely a five degree-of-freedom system with one nonlinear spring, a three degree-of-freedom system with three nonlinear springs and a nonlinear rectangular membrane structure with all edges clamped. Comparing with the time-domain nonlinear subspace identification (TNSI) method, the proposed NOKID method can identify the nonlinear parameters without system order determination, and the identification results obtained by the proposed method are real numbers and have no dependency on frequency. [ABSTRACT FROM AUTHOR]

An assessment is made of the stress distribution and the hydrodynamic response of the preliminary structural design of the tension leg platform of a 10 MW wind turbine. The platform supporting a 10 MW turbine is modelled and analysed by the finite element method. The stress distribution of the platform is determined in still water with the turbine at above-rated conditions, and the response of the tension leg platform is estimated in the time domain. The results of the time domain analysis show reasonable agreement between the present results and the available data. To check the design stiffener dimensions, span, and spacing against stress distribution, classification societies’ recommendations are used. The results of the stress distribution analysis indicate that the critical locations of the platform are the interaction of the lower columns with the upper columns and the connection of the tower of the turbine.

Electroporation is a biophysical phenomenon involving an increase in cell membrane permeability to molecules after a high-pulsed electric field is applied to the tissue. Currently, electroporation is being developed for non-thermal ablation of cardiac tissue to treat arrhythmias. Cardiomyocytes have been shown to be more affected by electroporation when oriented with their long axis parallel to the applied electric field. However, recent studies demonstrate that the preferentially affected orientation depends on the pulse parameters. To gain better insight into the influence of cell orientation on electroporation with different pulse parameters, we developed a time-dependent nonlinear numerical model where we calculated the induced transmembrane voltage and pores creation in the membrane due to electroporation. The numerical results show that the onset of electroporation is observed at lower electric field strengths for cells oriented parallel to the electric field for pulse durations ≥10 µs, and cells oriented perpendicular for pulse durations ~100 ns. For pulses of ~1 µs duration, electroporation is not very sensitive to cell orientation. Interestingly, as the electric field strength increases beyond the onset of electroporation, perpendicular cells become more affected irrespective of pulse duration. The results obtained using the developed time-dependent nonlinear model are corroborated by in vitro experimental measurements. Our study will contribute to the process of further development and optimization of pulsed-field ablation and gene therapy in cardiac treatments.

Harmonic estimation is essential for mitigating or suppressing harmonic distortions in power systems. The most important idea is that spectrum analysis, waveform estimation, harmonic source classification, source location, the determination of harmonic source contributions, data clustering, and filter-based harmonic elimination capacity are also considered. The feature extraction method is a fundamental component of the optimization that improves the effectiveness of the Harmonic Mitigation method. In this study, techniques to extract fundamental frequencies and harmonics in the frequency domain, the time domain, and the spatial domain include 67 literature reviews and an overall assessment. The combinations of signal processing with artificial intelligence (AI) techniques are also reviewed and evaluated in this study. The benefit of the feature extraction methods is that the analysis extracts the powerful basic information of the feedback signals from the sensors with the most redundancy, ensuring the highest efficiency for the next sampling process of algorithms. This study provides an overview of the fundamental frequency and harmonic extraction methods of recent years, an analysis, and a presentation of their advantages and limitations.

The numerically simulated method of using electromagnetic field from an alternating current is a patented method to create in liquid metal, under the conditions of resonance, acoustic waves of sufficient strength to cause cavitation and implosion of gas bubbles, leading to beneficial degassing and grain refinement. The modelling stages of electromagnetics are described below along with acoustics in liquids, bubble dynamics, and their interactions. Sample results are presented for a cylindrical container with liquid aluminium surrounded by an induction coil. The possibility of establishing acoustic resonance and sustaining the bubble oscillation at a useful level is demonstrated. Limitations of the time-dependent approach to this multi-physics modelling problem are also discussed.

A thorough study of the literature suggests that greater attention has to be paid to power line noise measurements, characterization, and modeling. Several studies show that significant differences do exist, and the findings are somewhat conflicting. This may be attributed to the diverse environment under investigation, which includes volatile noise sources, differences in electrical grid structure from country to country, topology, and unknown power cable characteristics. An in-depth analysis of the approaches for measuring, characterizing, and modeling noise, as well as the descriptions of relevant components, and the environment needed to carry out the measurements, is presented. This review serves as a roadmap for academics and engineers in the deployment of power line communication systems.

Nowadays, the Earth observation based on the Moon has attracted attention from many researchers and relevant departments. There also exists a considerable amount of interest in monitoring large-scale and long-term geoscience phenomena using the Moon-based SAR (MBS). However, the Earth's observation from MBS has long transmission time, and the relative motion of MBS with its Earth ground target (EGT) is much different to the space-borne SAR, the above reasons indicate that the traditional stop-and-go model is no longer suitable for MBS in frequency domain imaging. Here a dual-path separate calculation method for single pulse is presented in this paper for a better match of a real scenario, and then the slant range is fitted to a high-order polynomial series. The MBS's location, the synthetic aperture time and other factors have effects on length of the dual- path and fit bias. Without thoroughly investigated phase de-correlation processing in frequency domain, and to avoid computational costs in traditional back-projection (BP) algorithm, the paper first proposes a fast back-projection (FBP) algorithm in time domain for MBS, a platform that has long transmission time and long synthetic aperture time. In the FBP algorithm, the original method, that projected echo on all pixels in the imaging area, is changed to projected echo on a centerline instead. A suitable interpolation for points on the centerline is adopted to reduce the projected error; the synthetic aperture length and imaging area are also divided into subsections to reduce computation cost. The formula indicates that the range error could be control once the product of sub-imaging area's length and sub-aperture's length stay constant. Through the theoretical analysis, the detailed range difference mainly at apogee, perigee, ascending, and descending nodes indicate the necessity to separately calculate the dual-path for MBS's single pulse transmission in Earth-Moon motion, with real ephemeris been adopted; then, the high-order polynomial fitting will better describe the motion trajectory. Lastly, the FBP algorithm proposed is simulated in a specific scenario under acceptable resolution, and the result shows its feasibility for image compression. [ABSTRACT FROM AUTHOR]

This paper concerns an inverse elastic scattering problem which is to determine a rigid obstacle from time domain scattered field data for a single incident plane wave. By using the Helmholtz decomposition, we reduce the initial-boundary value problem for the time domain Navier equation to a coupled initial-boundary value problem for wave equations, and prove the uniqueness of the solution for the coupled problem by employing the energy method. The retarded single layer potential is introduced to establish a set of coupled boundary integral equations, and uniqueness is discussed for the solution of these boundary integral equations. Based on the convolution quadrature method for time discretization, the coupled boundary integral equations are reformulated into a system of boundary integral equations in the s -domain, and then a convolution quadrature based nonlinear integral equation method is proposed for the inverse problem. Numerical experiments are presented to show the feasibility and effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

In this paper, we propose a fully convolutional neural network based on recursive recurrent convolution for monaural speech enhancement in the time domain. The proposed network is an encoder-decoder structure using a series of hybrid dilated modules (HDM). The encoder creates low-dimensional features of a noisy input frame. In the HDM, the dilated convolution is used to expand the receptive field of the network model. In contrast, the standard convolution is used to make up for the under-utilized local information of the dilated convolution. The decoder is used to reconstruct enhanced frames. The recursive recurrent convolutional network uses GRU to solve the problem of multiple training parameters and complex structures. State-of-the-art results are achieved on two commonly used speech datasets. [ABSTRACT FROM AUTHOR]

The negative group delay (NGD) is one of less familiar electronic functions. So far, the time domain (TD) experimentation of NGD circuits remains a challenging task. This paper investigates an innovative TD measurement of a band‐pass (BP) NGD passive circuit. The topology of the considered BP NGD distributed circuit constituted by transmission line structure having a 101O‐geometrical shape is introduced. After the design description of the 101O‐structure, the NGD response illustrates from simulation and measurement based on S‐parameters. The NGD center frequency, bandwidth, and value are approximately 3.6 GHz, 33 MHz, and −4.9 ns, respectively. The TD measurement experimentation is based on the sine carrier‐modulated microwave signal generation with 50‐ns duration. The 101O‐NGD circuit input and output signals are plotted with innovative synchronization. It was shown from the TD‐simulated and measured results that the BP NGD effect induces an output envelope about 4.2 ns advanced of the test signal input. Key Points: This study investigates a band‐pass (BP) negative group delay (NGD)The topology of the considered BP NGD distributed circuit is constituted by transmission line structure having a 101O‐geometrical shapeThe circuit behaves as a BP NGD function with center frequency of about 3.6 GHz and NGD value of about −3.6 ns [ABSTRACT FROM AUTHOR]

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Fetal heart rate variability (FHRV) reflects autonomic cardiac regulation. The autonomic nervous system constantly adjusts the heart rate to maintain homeostasis. By providing insight into the fetal autonomic state, FHRV has the potential to become an investigational and clinical instrument. However, the method needs standardization and the influence of fetal movements, including fetal respiratory movements, is not well explored. Therefore, in a highly standardized setting, the aim was to evaluate the association between fetal movements and fetal heart rate variability (FHRV) including their impact on reliability. Fetal heart rate was obtained by noninvasive fetal electrocardiography (NI‐FECG) and fetal movements by simultaneous ultrasound scanning in 30 healthy singleton pregnant women on two occasions with a maximum interval of 7 days. The standard deviation of normal‐to‐normal RR‐intervals (SDNN), root mean square of successive RR‐interval differences (RMDDS), high‐frequency power (HF‐power), low‐frequency power (LF‐power), and LF/HF were measured. A multivariate mixed model was used and reliability was defined as acceptable by a coefficient of variance (CV) ≤15% and an intraclass correlation coefficient (ICC) ≥0.80. During time periods with fetal respiratory movements, the highest reliability was achieved. Intra‐ and inter‐observer reliability measurements were very high (CV: 0–9%; ICC ≧ 0.86). Within the same recording, SDNN and RMSSD achieved acceptable reliability (CV: 14–15%; ICC ≧ 0.80). However, day‐to‐day reliability displayed high CV's. In time periods with fetal respiratory movements, as compared to periods with quiescence RMSSD and HF‐power were higher (Ratio: 1.33–2.03) and LF/HF power lower (Ratio: 0.54). In periods with fetal body movements SDNN, RMSSD and HF‐power were higher (Ratio: 1.27–1.65). In conclusion, time periods with fetal respiratory movements were associated with high reliability of FHRV analyses and the highest values of parameters supposed to represent vagal activity. [ABSTRACT FROM AUTHOR]

• A non-local absorbing boundary conditions is constructed in peridynamic theory. • Motion equation of peridynamic theory is re-derived considering material damping. • Algorithm to realize the non-local absorbing boundary conditions in peridynamics is proposed. • Elastic wave propagation in semi-unbounded and unbounded solids are simulated. In order to simulate the elastic wave propagation in unbounded solids, this paper introduces a non-local method to construct absorbing boundary conditions in the bond-based peridynamic theory. To construct non-local absorbing boundary conditions in the form of absorbing layers with increasing damping, we first re-derived the particle motion equilibrium equation of the bond-based peridynamic theory, based on the principle of virtual work and Lagrange's equation on the premise of considering material damping. We also give the expression for the inter-particle damping force density which satisfies the balance laws of linear momentum and angular momentum. This paper also provides a process and algorithm for realizing the non-local absorbing boundary conditions in the bond-based peridynamic theory, and adopts the Fortran language for computer program compilation. Finally, we simulate the elastic wave propagation in semi-unbounded and unbounded solids as numerical examples. The results show that such non-local absorbing boundary conditions can stably absorb and attenuate incident elastic waves. Since it is derived in the time domain, this method does not require frequency-domain operations, such as Fourier and Laplace transformations, nor does it require wave field splitting. [ABSTRACT FROM AUTHOR]

We propose a new approach based on the multicarrier system, in which multiple narrowband pulses emit toward a chipless RFID tag in the UWB, to decode the tag in the time domain. The multicarrier system is known to be able to reduce complexity and interference, and also increase spectrum efficiency and flexibility. In this study, we not only experimentally investigate the backscattered signal of a frequency-coded chipless RFID tag interrogated by narrowband pulses, but we have also derived mathematical equations to describe the tag responses. We have found that the shape of the reflected response from the tag is determined by the emitted signal multiplied by a distortion factor. The distortion amount depends on transmitted signal bandwidth, tag quality factor, and resonance frequency. We further use the distorted tag response as a tag signature in the time domain for decoding purposes, eliminating the signal transformation to the frequency spectrum, which is one of the most time-consuming post-processing algorithms. To further demonstrate the performance of the proposed approach in a more realistic scenario, we have developed a customized multicarrier transceiver to decode a four-bit cross-polarized tag in the time domain. We have demonstrated that the proposed analytical approach can also enhance tag detection in a realistic environment with multiple parasitic reflections. [ABSTRACT FROM AUTHOR]

Very large floating structure (VLFS) is an environmentally sensitive technology which creates artificial land at sea. Designated for the open sea, the Delta is a new type of VLFS. Formed, inherently, by the innovative geometry, the sheltered basin is a unique feature of the Delta. Its year-round operability as the gateway of the structure directly affects the Delta's utilization. This study examines the basin in terms of its operability as a service port. Relying on potential flow theory and applying the boundary element method, we conducted a nonlinear hydrodynamic analysis of a moored vessel at the basin. It consists of a time-domain simulation of a tanker, berthed via nonlinear mooring system along the Delta's side hull under severe wave conditions typical to the East Mediterranean Sea. The system is evaluated in terms of acceptable motion of the ship and permissible load on the mooring system. The favorable results indicate that the basin enables most cargo handling operations under waves conditions of H mo = 2.5   m , and minimal downtime of less than 6% of the year. In this paper we present the analysis procedure, the evaluation criteria, and the mooring system's design. The study results and their significance are presented and discussed as well. [ABSTRACT FROM AUTHOR]

In this paper, we propose a transmission line model to represent three-phase untransposed transmission lines with vertical symmetry. Here, we decouple a transmission line into its propagation modes using Concordia's matrix, which is the proper orthogonal form of Clarke's matrix that has its columns normalised. Due to the usage of Concordia's matrix, the transmission line is decoupled into two coupled modes and one uncoupled mode. We represent the uncoupled mode by a single-phase transmission line, and the coupled modes by a two-phase transmission line without vertical symmetry. We compute voltages and currents for the single-phase transmission line using the classic Lumped Parameter Model. Voltages and currents in the two-phase transmission line are calculated using a cascade of coupled L circuits pairs. Modal voltages and currents are then transformed back to the phase domain. We compare the results obtained with the proposed model to those obtained with two well-known time domain models, the classic modal lumped parameter model and the lumped parameter model available in the Alternate Transients Program ATP. Results show that the proposed model agrees with time-domain models and has the advantage that is developed in the time domain without needing any inverse transformations. [ABSTRACT FROM AUTHOR]

We propose the multiple changepoint isolation (MCI) method for detecting multiple changes in the mean and covariance of a functional process. We first introduce a pair of projections to represent the variability "between" and "within" the functional observations. We then present an augmented fused lasso procedure to split the projections into multiple regions robustly. These regions act to isolate each changepoint away from the others so that the powerful univariate CUSUM statistic can be applied region‐wise to identify the changepoints. Simulations show that our method accurately detects the number and locations of changepoints under many different scenarios. These include light and heavy tailed data, data with symmetric and skewed distributions, sparsely and densely sampled changepoints, and mean and covariance changes. We show that our method outperforms a recent multiple functional changepoint detector and several univariate changepoint detectors applied to our proposed projections. We also show that MCI is more robust than existing approaches and scales linearly with sample size. Finally, we demonstrate our method on a large time series of water vapor mixing ratio profiles from atmospheric emitted radiance interferometer measurements. [ABSTRACT FROM AUTHOR]

The problem of reducing the measurement errors of the electrodynamic characteristics of antenna radiation using measuring systems in the far zone is considered. The most significant limitations in such measurements are the sphericity of the phase front and multipath reflections. The impossibility of ensuring the specified conditions can lead to unacceptable measurement errors and the need to use complexes of other types. A method is proposed to improve the accuracy of measurements of antenna radiation patterns in the Fresnel zone under conditions of multipath multiple reflections. The method under consideration can be used to expand the range of antennas tested using far-field measuring systems. The implementation of the method can significantly reduce the requirements for the characteristics of measuring systems and, therefore, reduce the cost of testing antenna devices and systems. The essence of the proposed method is to synthesize the spatial (two- or three-dimensional) impulse response of the antenna by transforming the original frequency-angular dependence of the transmission coefficient. The physical meaning of the transformation can be interpreted as the restoration of the distributions of equivalent fields on the plane or in the volume containing the test antenna or its geometric projection onto the plane of rotation. The decrease in the error caused by the multipath propagation of the electromagnetic field occurs due to the filtering of the synthesized spatial impulse response of the antenna from the signals due to multiple reflections outside the allocated volume. The linearity of the transformations used allows the possibility of recalculating the synthesized characteristic to an arbitrary distance. Thus, it is possible to restore the radiation pattern in the Fraunhofer zone and to reduce the error caused by the sphericity of the phase front of the electromagnetic field. A feature of the proposed method is a significant increase in the signal-to-noise ratio. The main theoretical relationships and the results of experimental studies on testing the method are presented. [ABSTRACT FROM AUTHOR]

Static energy meters have shown errors beyond the standards due to conducted electromagnetic interference of pulsed currents. This was observed in several case studies and confirmed by laboratory experiments, which showed errors up to 2675%. The extent of this interference case is unknown, because there is limited information about the waveforms occurring in the real on-site scenarios. This article aims to detect critical waveforms in on-site surveyed data that have similar characteristics as the pulses that resulted in metering errors. The time-domain parameters of the laboratory experiments that show static energy meter interference are compared to the on-site waveform data using an interpolation based on an inverse weighting distance function. Using this approach, the waveform characteristics are compared, and an error is estimated. This approach was satisfactorily validated using data from validation experiments that shows a correct estimation of the actual error according to the permissible limits for energy metering for all validation indices. The performed on-site surveys show the existence of nonlinear waveforms. During the survey of three sites for ten days, 19 531 waveforms were captured, of which 14 487 indicate large nonlinearities and 379 are estimated to produce metering errors up to 925%. [ABSTRACT FROM AUTHOR]

The achievable payload of a launch vehicle is sensitive to the mass of the terminal stage which injects the payload into orbit, as well as to tracking errors introduced by the autopilot. The system is usually characterized by lightly damped slosh modes with uncertain parameters, whose stabilization is critical, while maintaining the overall performance of the system. Passive slosh stabilization involves introduction of mechanical baffles into the fluid tanks, which impacts the achievable payload mass. Optimal tracking performance along with active slosh stabilization is hence an ideal combination of autopilot design objectives. While optimal control methods are attractive for such systems, the lack of physical insight in the design procedure often limits the usefulness of these methods for launch vehicle autopilot design. A major challenge in stabilizing lightly damped slosh is the necessity to cater to very large mode magnitudes and phase swings exhibited by the system over the range of parameter perturbations. The significant contribution of this paper is the development of a two phase Linear Quadratic Gaussian approach, utilizing the physical insight into the system performance for tuning the weights in the performance index, to satisfy the time domain as well as frequency domain objectives. A robust design which exhibits superior time domain as well as frequency domain performance as compared to the benchmark classical controller is obtained, with near perfect phase stabilization of the lightly damped slosh dynamics. [ABSTRACT FROM AUTHOR]

A resonator is one of the important components in electronic systems. It is often used in an electronic system to give an accurate time reference. But it can also be used as a highly sensitive physical parameter sensor especially with the rapid development of fabrication technology for Micro Electro Mechanic System (MEMS) sensors. One of the parameters used to describe the performance of a resonator is its quality factor, also called Q-factor for short. Knowing the Q-factor of a resonator can make sure the performance of the system in which the resonator will be used. For applications in which a resonator is used as a sensing device, it is crucial for the Q-factor to be surveyed and measured in real time. In this paper, a review of a resonator’s quality factor (Q-factor) measurement is given. Three major approaches can be identified from the literature: frequency domain, time-frequency domain and time domain. Both advantages and limitations of each approach are presented. Based on the published results, a comparison of the three approaches is conducted. As the time-domain measurement is the only way to present the potential for an in-situ Q-factor measurement but it is relatively less exploited compared with others, a special focus on the time-domain measurement is granted with two time-domain circuit designs.

Road condition monitoring is essential for improving traffic safety and reducing accidents. Machine learning methods have recently gained prominence in the practically important task of controlling road surface quality. Several systems have been proposed using sensors, especially accelerometers present in smartphones due to their availability and low cost. However, these methods require practitioners to specify an exact set of features from all the sensors to provide more accurate results, including the time, frequency, and wavelet-domain signal features. It is important to know the effect of these features change on machine learning model performance in handling road anomalies classification tasks. Thus, we address such a problem by conducting a sensitivity analysis of three machine learning models which are Support Vector Machine, Decision Tree, and Multi-Layer Perceptron to test the effectiveness of the model by selecting features. We built a feature vector from all three axes of the sensors that boosts classification performance. Our proposed approach achieved an overall accuracy of 94% on four types of road anomalies. To allow an objective analysis of different features, we used available accelerometer datasets. Our objective is to achieve a good classification performance of road anomalies by distinguishing between significant and relatively insignificant features. Our chosen baseline machine learning models are based on their comparative simplicity and powerful empirical performance. The extensive analysis results of our study provide practical advice for practitioners wishing to select features effectively in real-world settings for road anomalies detection.

Some types of dynamic stiffness, such as the dynamic ground stiffness used in soil-structure interaction analyses and the viscoelastic body used in vibration control systems, have strong frequency dependency. To perform seismic response analysis considering this frequency dependence and the nonlinearity of the model, the dynamic stiffness in the frequency domain must be transformed into the time domain, and a time-history nonlinear response analysis is required. Therefore, many studies on these time-domain transforms have been conducted. One of the present authors has already studied and proposed transform methods for this purpose, and some of their results were used to design new types of damping models. In the present study, the outline and characteristics of the proposed methods (A to C) for this transform are described first. Next, typical problems with strong frequency dependency (i.e., the dynamic soil stiffness, Maxwell element, viscoelastic body, Biot model, and causal hysteretic damping) were transformed into the time domain using these transform methods. The applicability of the transform methods was examined. Subsequently, the characteristics of each problem in the frequency domain and the characteristics of the obtained impulse response in the time domain were analyzed. Finally, it was confirmed that the proposed methods were applicable to all studied problems. These studies are important to understand the physical meaning of these problems, which have strong frequency dependency.

The present work applies singular spectrum analysis (SSA) to the study of macroeconomic fluctuations in three European countries: Italy, The Nether- lands, and the United Kingdom. This advanced spectral method provides valu- able spatial and frequency information for multivariate data sets and goes far beyond the classical forms of time domain analysis. In particular, SSA enables us to identify dominant cycles that characterize the deterministic behavior of each time series separately, as well as their shared behavior. We demonstrate its usefulness by analyzing several fundamental indicators of the three countries’ real aggregate economy in a univariate, as well as a multivariate setting. Since business cycles are international phenomena, which show common characteris- tics across countries, our aim is to uncover supranational behavior within the set of representative European economies selected herein. Finally, the analysis is extended to include several indicators from the U.S. economy, in order to examine its influence on the European economies under study and their inter- relationships.