Structure In Time Domain Research Articles

Deferred correction neural network techniques for solving ordinary differential equations

Neural network technology is widely used to solve problems across science and engineering fields. In this paper, a neural network technique is applied to solve ordinary differential equations (ODEs), instead of using conventional time marching techniques with discretization for ODEs. A numerical solution to ODEs is defined with polynomial basis, and each coefficient of the expansion is calculated through an unsupervised neural network structure in the entire time domain. To make the calculated solution more accurate, we consider the deferred correction technique for calculating a numerical residual with a physics-informed neural network. The empirical results show that the proposed scheme with polynomial basis can influence calculation accuracy depending on the order of basis polynomials, providing the possibility of improving accuracy and efficiency by increasing the order of basis. Several numerical tests confirm that the proposed deferred correction network (DCNet) model has an accuracy approximately 100 and 10 times higher than that of the learning polynomial neural network (LPNet) and the standard existing method, physics-informed neural network (PINN), respectively. Additionally, the proposed schemes generate stable results even for stiff problems and preserve the conservation property for Hamiltonian systems.

Robust Predictive Control of Grid-Connected Converters: Sensor Noise Suppression With Parallel-Cascade Extended State Observer

Model predictive control (MPC) is a constrained optimization control method with superior performance than linear methods for multi-variable and multi-objective control of power converters. Nonetheless, its performance is limited by model uncertainties and measurement noise. This study tackles this challenge by proposing a new hybrid parallel-cascade extended state observer (PC-ESO) with two key advantages, viz.: (i) higher disturbance rejection than the conventional linear ESO and cascade ESO (CESO) at low bandwidth, and (ii) better noise suppression than the conventional ESO. PC-ESO's time-domain structure, and comprehensive frequency-domain analysis are presented. Furthermore, PC-ESO is applied to improve the transient disturbance rejection of CESO through a novel structurally-adaptive ESO (SAESO) algorithm. The proposed SAESO provides both high-frequency noise-suppression and better disturbance rejection than CESO and cascade-parallel ESO. Finally, the proposed methods are experimentally validated by the model-free predictive control of a grid-connected power converter.

Calculation and Uncertainty of Fast Radio Burst Structure Based on Smoothed Data

Studies of the time-domain structure of fast radio bursts (FRBs) require an accurate estimate of the FRB dispersion measure in order to recover the intrinsic burst shape. Furthermore, the exact dispersion measure is itself of interest when studying the time evolution of the medium through which multiple bursts from repeating FRBs propagate. A commonly used approach to obtain the dispersion measure is to take the value that maximizes the FRB structure in the time domain. However, various authors use differing methods to obtain this structure parameter and do not document the smoothing method used. Furthermore, there are no quantitative estimates of the error in this procedure in the FRB literature. In this article, we present a smoothing filter based on the discrete cosine transform, and show that computing the structure parameter by summing the squares of the derivatives and taking the square root (that is, the 2-norm, ) immediately lends itself to the calculation of the uncertainty of the structure parameter. We illustrate this with FRB 20181112A and FRB 20210117A data, which were detected by the Australian Square Kilometre Array Pathfinder, and for which high-time-resolution data are available.

Electromagnetic Interference Cancellation for RIS-Assisted Communications

Reconfigurable intelligent surface (RIS)-empowered communication is an emerging technology that has recently received growing attention as a potential candidate for next-generation wireless communications. Although RISs have shown the potential of manipulating the wireless channel through passive beamforming, it is shown that they can also bring undesired side effects, such as reflecting the electromagnetic interference (EMI) from the surrounding environment to the receiver side. In this study, we propose a novel EMI cancellation scheme to mitigate the impact of the EMI by exploiting its special time-domain structure and considering a clever passive beamforming method at the RIS. Compared to its benchmark, computer simulations show that the proposed scheme achieves superior performance in terms of the average signal-to-interference-plus-noise ratio (SINR) and outage probability (OP), especially when the EMI power is comparable to the power of the information signal impinging on the RIS surface.

Characterizing wind-structure interaction for performance-based wind design of tall buildings

Performance-based wind design (PBWD) has been receiving a great deal of attention from the wind and structural engineering communities. This is specifically highlighted with the release of the ASCE pre-standard for PBWD (2019). The PBWD of tall building requires a series of steps one of which is the interaction parameter, i.e. characterizing the interaction of the tall building with the wind field. In the studies involving slender structures-such as tall buildings, it is essential to consider this interaction parameter which is a function of the time-varying aerodynamic loads. The aerodynamic loads consist of the turbulent loads due to fluctuating wind, known as buffeting loads, and the self-excited loads resulting from the interaction of the structural motions with wind, referred as aeroelastic loads. Flexible structures can become unstable at a critical wind speed, known as flutter speed, wherein a diverging motion of the structure occurs. Aerodynamic instability that is caused by self-excited loads generally doesn’t occur in tall buildings within their design wind speeds but certainly needs to be considered in a wind-structure interaction analysis, particularly when tall buildings become increasingly slender and are allowed to enter post-elastic region. This study aims to characterize the interaction parameter in the PBWD of tall buildings by including the self-excited loads in its response analysis corresponding to the three-degree-of-freedom response motions of the building in along-wind, across-wind, and torsional directions. For this purpose, the flutter derivatives that are used to represent the self-excited loads in frequency domain are first obtained from wind tunnel tests of scaled section models of the structure and then converted into approximate coefficients known as Rational Function Coefficients (RFC) as part of Rational Function Approximations (RFA) of the self-excited loads in Laplace or time domain. The wind loads on a structure in time domain are calculated by combining both the buffeting loads and self-excited loads associated with the calculated RFC. The non-linear structural behavior of a 44-story and a 60-story tall building each is studied using nonlinear dynamic time-history analysis in extreme wind conditions and then observed for any flutter-like instabilities. The concept PBWD is applied considering the performance objective involving those associated with occupant comfort and structural or non-structural damages.

Human Action Recognition for Dynamic Scenes of Emergency Rescue Based on Spatial-Temporal Fusion Network

Targeting the problems of the insufficient utilization of temporal and spatial information in videos and a lower accuracy rate, this paper proposes a human action recognition method for dynamic videos of emergency rescue based on a spatial-temporal fusion network. A time domain segmentation strategy based on random sampling maintains the overall time domain structure of the video. Considering the spatial-temporal asynchronous relationship, multiple asynchronous motion sequences are increased as input of the temporal convolutional network. spatial-temporal features are fused in convolutional layers to reduce feature loss. Because time series information is crucial for human action recognition, the acquired mid-layer spatial-temporal fusion features are sent into Bidirectional Long Short-Term Memory (Bi-LSTM) to obtain the human movement features in the whole video temporal dimension. Experiment results show the proposed method fully fuses spatial and temporal dimension information and improves the accuracy of human action recognition in dynamic scenes. It is also faster than traditional methods.

Prediction of Vibration-Mode-Induced Noise of Structure–Acoustic Coupled Systems

The exposure of a structure to an acoustic domain induces a sound field owing to the interaction of the air-fluid and structure at the acoustic–structure boundaries. It is difficult to predict sound pressure level through vibration mode, due to the acoustic mode of the coupling effect between vibration and sound in addition to the acoustic mode induced by vibration mode generated by external force. In this study, the acoustic mode induced by structural vibration modes were predicted through a numerical analysis. A finite element model of a reverberation chamber with a shell at one side was constructed, and modal parameters of the vibration and acoustic modes were evaluated through an eigenvalue analysis. In addition, the sound pressure generated by impact loading of the shell were predicted by vibration mode through a time-domain structure–acoustic coupling analysis. The vibration and acoustic modal responses were identified from the measured responses, and the acoustic mode associated with a specific vibration mode was examined. The results showed that the acoustic mode from the coupling effect was verified, and sound pressure prediction from vibration mode was possible if considered as the coupling effect. The proposed approach can be applied to predict the heavy-weight floor impact sound from the vibration of slabs in apartments.

Theory of Acceleration of Decision-Making by Correlated Time Sequences

Photonic accelerators have been intensively studied to provide enhanced information processing capability to benefit from the unique attributes of physical processes. Recently, it has been reported that chaotically oscillating ultrafast time series from a laser, called laser chaos, provides the ability to solve multi-armed bandit (MAB) problems or decision-making problems at GHz order. Furthermore, it has been confirmed that the negatively correlated time-domain structure of laser chaos contributes to the acceleration of decision-making. However, the underlying mechanism of why decision-making is accelerated by correlated time series is unknown. In this study, we demonstrate a theoretical model to account for accelerating decision-making by correlated time sequence. We first confirm the effectiveness of the negative autocorrelation inherent in time series for solving two-armed bandit problems using Fourier transform surrogate methods. We propose a theoretical model that concerns the correlated time series subjected to the decision-making system and the internal status of the system therein in a unified manner, inspired by correlated random walks. We demonstrate that the performance derived analytically by the theory agrees well with the numerical simulations, which confirms the validity of the proposed model and leads to optimal system design. This study paves the way for improving the effectiveness of correlated time series for decision-making, impacting artificial intelligence and other applications.

Dynamic response of a multi-layered pavement structure with subgrade modulus varying with depth subjected to a moving load

The dynamic response of a three-dimensional multi-layered pavement system subjected to a moving load is calculated by an analytical solution method. In this method, the pavement structure is assumed to be a transverse isotropic viscoelastic multi-layered structure with partially bonded interface, and the subgrade is considered to be a transverse isotropic half-space medium with its modulus varying with depth. The load is considered as a three-dimensional elliptical moving load with a constant speed. This study is divided into three key steps. Firstly, the ordinary differential equations of pavement and subgrade structures are obtained via the double Fourier transform, and the general solutions of dynamic response are obtained according to the theory of ordinary differential equations and the Frobenius method. Secondly, combined with the boundary conditions, the method of wave vector matrix, and the inverse Fourier integral transform, the dynamic responses of pavement structure in time domain are calculated. The accuracy of the analytical solution is verified by comparing against the solution from a finite element method. Lastly, the sensitivity analysis is conducted to assess the influence of four parameters on the dynamic response, namely, the horizontal load, the condition of interlayer contact, the transverse isotropy, and the non-uniform distribution of subgrade moduli. The calculation methods and the corresponding results can further develop a theory of the multi-layered system.

Simultaneous View of FRB 180301 with FAST and NICER during a Bursting Phase

FRB 180301 is one of the most actively repeating fast radio bursts (FRBs) that has shown polarization angle changes in its radio burst emission, an indication for their likely origin in the magnetosphere of a highly magnetized neutron star. We carried out a multiwavelength campaign with the FAST radio telescope and NICER X-ray observatory to investigate any possible X-ray emission temporally coincident with the bright radio bursts. The observations took place on 2021 March 4, 9 and 19. We detected five bright radio bursts with FAST, four of which were strictly simultaneous with the NICER observations. The peak flux density of the radio bursts ranged between 28 and 105 mJy, the burst fluence between 27 and 170 mJy ms, and the burst durations between 1.7 and 12.3 ms. The radio bursts from FRB 180301 exhibited a complex time domain structure, and subpulses were detected in individual bursts, with no significant circular polarization. The linear degree of polarization in the L band reduced significantly compared to the 2019 observations. We do not detect any X-ray emission in excess of the background during the 5, 10, 100 ms, 1 and 100 s time intervals at/around the radio-burst barycenter-corrected arrival times, at a > 5σ confidence level. The 5σ upper limits on the X-ray (a) persistent flux is <7.64 × 10−12 erg cm−2 s−1, equivalent to L X < 2.50 × 1045 erg s−1 and (b) 5 ms fluence is <2 × 10−11 erg cm−2, at the radio burst regions. Using the 5 ms X-ray fluence upper limit, we can estimate the radio efficiency η R/X ≡ L radio/L X−ray ≳ 10−8. The derived lower limit on η R/X is consistent with both magnetospheric models and synchrotron maser models involving relativistic shocks.

Ultrafast measurement of a single-photon wave packet using an optical Kerr gate.

Ultrafast quantum optics with time-frequency entangled photons is at the forefront of progress towards future quantum technologies. However, to unravel the time domain structure of entangled photons and exploit fully their rich dimensionality, a single-photon detector with sub-picosecond temporal resolution is required. Here, we present ultrafast single-photon detection using an optical Kerr gate composed of a photonic crystal fiber (PCF) placed inside a Sagnac interferometer. A near-rectangle temporal waveform of a heralded single-photon generated via spontaneous parametric down-conversion is measured with temporal resolution as high as 224 ± 9 fs. The large nonlinearity and long effective interaction length of the PCF enables maximum detection efficiency to be achieved with only 30.5 mW gating pulse average power, demonstrating an order-of-magnitude improvement compared to optical gating with sum-frequency generation. Also, we discuss the trade-off relationship between detection efficiency and temporal resolution.

CBFMCycleGAN-VC: Using the Improved MaskCycleGAN-VC to Effectively Predict a Person’s Voice After Aging

One task of nonparallel speech conversion is to convert the source speaker’s speech samples to the target speaker’s speech samples, keeping the content unchanged. In view of the advantages of MaskCycleGAN-VC in nonparallel speech conversion, such as small model size and superior performance, our paper uses the basic structure of MaskCycleGAN-VC to improve it and proposes a cyclic boundary method filling in the frame MaskCycleGAN-VC (CBFMCycleGAN-VC) model, which predicts the voice of a person as he ages by using voice samples of his younger self. First, this paper adds speech preprocessing modules, including the Chebyshev low-pass filter and adaptive filter, which increases the robustness of the system. Second, our paper considers the time-domain difference in the weight parameters, which makes it easier to grasp the mapping law of the time-domain structure, with a faster convergence speed. Last, the circular boundary method is introduced to avoid the ringing effect, to enhance the connection between the filled frame and the adjacent frame, and to obtain a better generator. The simulation results show that the CBFMCycleGAN-VC model is more suitable for the speech conversion task of predicting the voices of elderly people, and the convergence speed is faster. The converted voice is also closer to the voice of the target speaker in the time domain and frequency domain. Under the condition that the accuracy rate is similar to that of MaskCycleGAN-VC, the MOS score is 17.5% higher than that of MaskCycleGAN-VC.

Self-training dictionary based approximated ℓ0 norm constraint reconstruction for compressed ECG

Compressed sensing provides a sub-Nyquist sampling rate but requires a sparse structure of the signal. Electrocardiogram (ECG) signal expresses no sparse structure in time domain. This study aims to improve the sparse expression based on a self-training dictionary scheme (STDS), to obtain a self-training dictionary. Furthermore, an approximated ℓ0 norm constraint method (AL0CM) is designed for sparse expression by using an accelerated gradient descent method. The reconstruction of the compressed data could be applied by combining the sampling matrix, dictionary, and sparse expression. The ECG experiments are conducted to confirm the superiority of the proposed STDS-AL0CM framework in terms of the recovered signal-to-noise ratio (RSNR), percent norm difference (PND), and running time.

Time correction to eliminate structural ambiguity on velocity anomaly in the upper cibulakan formation of ITEUNG field, northern West Java basin

Converting seismic data or structural maps from time to depth domain is very important in the stage of oil and gas exploration. Interpretation in time domain often produce inaccurate interpretation especially in zones under high velocity such as sub-salt or sub-carbonate. Under this zone, there are pull up velocity anomalies or pseudo-anticline. Otherwise in zones under low velocity such as water bottoms with sharp or fluctuating slopes (canyons), loose material overburden or rapid sedimentation, under detached electric normal faults and shale flaps, there are push down velocity anomaly or pseudo-syncline. The study area is in the Main and Massive Formation of ITEUNG Field, Northern West Java Basin where is proven to have petroleum potential. In the study area there are pull-up velocity anomaly or pseudo-anticline even though in reality they are just flat or even syncline due to the location in the zone under high velocity. This study aims to correct velocity anomaly by doing time correction and convert the time domain structure map into depth domain structure map with the time-depth curve method to eliminate structural ambiguity on velocity anomaly. The result shows that the map is obtained in the form of a depth domain structure map which is more accurate than the time domain structure map. Depth structure map make the interpretation more accurate because the structures in depth structure map is more similar to the original sovereignty after correlating with well data. In this present study shows that pull up velocity anomaly can be avoided so that interpretation can be done more accurately.

Conceptual interpretation seismic 3d using rms amplitude and dip-azimuth attribute analysis for identification structure and facies model in physical geographic

Interpretation of seismic 3D data using attributes analysis to determine the condition of the subsurface geology and distribution facies as physical geography study. The results of interpretation formed surface horizon analysis of structures located in the southwest (SW) is the high of the continuous anticline to the northeast (NE) and the structure of the valley are in the south (S) continuously until the northeast (NE). From the results of the RMS amplitude attribute map shows that high amplitude anomalies uneven section southwest (SW). Show areas indicated as coal facies deployment area and assuming a low impedance possibility for the existence of coal facies. The map dip, azimuth, dip-azimuth can be analyzed map depicts stance or azimuth direction and dip (slope) time domain structure with angle pattern shown seismic trace with section 4501 and the arbitrary line a - b and line c - d clarify seen a pattern of fractures (faults) on a small scale where the direction nearly perpendicular to the strike of major fault.

Time-Domain Structure Analysis of a Typical Semisubmersible Drilling Rig

Ye, Q.; Jin, W.-L., and Bai, Y., 2020. Time-domain structure analysis of a typical semisubmersible drilling rig. In: Liu, X. and Zhao, L. (eds.), Today's Modern Coastal Society: Technical and Sociological Aspects of Coastal Research. Journal of Coastal Research, Special Issue No. 111, pp. 118–123. Coconut Creek (Florida), ISSN 0749-0208.This paper evaluates time-domain structure analysis approaches of a semisubmersible drilling rig using a nonlinear finite element method. Hydrodynamic random wave loads are calculated by WVTDUT, which was developed by a research group from the Dalian University of Technology. Time-domain structure analysis of a semisubmersible platform is very time consuming; simplified time-domain analysis approaches are therefore proposed to improve efficiency using equivalent time series. Validity of the approach is tested by a concrete example and simulation results are discussed in detail. The work of this paper can lead to a better understanding of structure behavior of a typical semisubmersible platform under characteristic wave loads. Performing structure analyses in time domain increases the accuracy and reliability of structure performance and the present study may be a benchmark study on time-domain structure analysis of a semisubmersible drilling rig.

Applying PML technique with additional differential equation method in non-uniform mixed-element DGTD method

In discontinuous Galerkin time domain method (DGTD), the computational region is divided into multiple subdomains instead of using a single mesh for the multiscale structure in finite-difference time-domain (FDTD) method. Accordingly, electrically coarse structures are modeled by hexahedral elements with higher interpolation degrees, while electrically fine structures with complex shapes are spatial discretized by tetrahedral elements with lower interpolation degrees. A nonconforming mixed-element DGTD method is implemented to simulate transient electromagnetic response of general 3-D targets in this paper. Perfectly matched layer (PML) boundary condition is utilized to simulate the propagation of electromagnetic waves in infinite space. PML is formulated by auxiliary differential equation with transformed field variables E and H. The numerical flux is employed to communicate fields between adjacent subdomains including physical region and PML region. The accuracy and efficiency of the proposed method is demonstrated by several numerical experiments.

Adaptive Bootstrap Design for Hybrid Terrestrial Broadcast and Mobile Communication Networks

The bootstrap in ATSC 3.0 is expected to act as a universal wake-up signal for various wireless systems in addition to broadcast network. However, the signaling decoding performance of the standardized bootstrap degrades significantly in channels of fast time-variation and strong multipath. Furthermore, part of available bandwidth is reserved to ensure the compatibility with mobile communication network (MCN), which puts a limitation on the performance improvement. In this paper, to make the best of the available bandwidth, we introduce the bandwidth-concerned version information to enable an adaptive bandwidth configuration for the proposed bootstrap. Moreover, a 2-D signaling scheme is used to increase signaling capacity by selecting different gold sequences in frequency domain (FD) and simultaneously applying cyclic shift in time domain (TD). At the receiver side, we first provide improved estimators of symbol timing offset (STO) and fine frequency offset (FFO) for the bootstrap with special TD structure. Meanwhile, a learning-based binary classifier taking the output of STO estimator as training data is provided to generate an SNR-independent threshold for spectrum sensing without requiring the knowledge of channel conditions nor noise estimator. Afterwards, an inverse fast Fourier transform (IFFT)-based algorithm is used to decode FD signaling in the presence of unknown TD signaling, which allows 3-bit higher signaling capacity. Numerical analysis and simulation results demonstrate that the proposed adaptive bootstrap design as well as corresponding receiver algorithms significantly outperform the standardized one in terms of synchronization, detection and signaling decoding.

Low PAPR Filter Bank Single Carrier for 5G mMTC

Asynchronous transmission for 5G massive machine type communication (mMTC) reduces power consumption and provides longer battery life of mMTC devices compared to synchronous transmission because of less signaling interaction between the base station and mMTC devices. To reduce frequency leakage from other user devices, several waveforms based on modification on orthogonal frequency division multiple (OFDM) with low out-of-band (OOB) emission property has been proposed in 5G new radio. However, those waveforms are typically of high peak to average power ratio (PAPR) and it has been shown for those waveforms there is OOB emission regrowth for mMTC devices caused by nonlinear power amplify (PA). We propose a low PAPR filter bank single carrier frequency division multiple access (SC-FDMA) waveform, called LP-FBSC, which helps to resist OOB emission regrowth caused by nonlinear PA. Two filters are applied in one stream to achieve low PAPR and low OOB emission performance, where one filter is poly phase network (PPN) structure in time domain for low OOB emission purpose, and the other is applied at frequency domain with element-wise multiplication for low PAPR purpose. In addition, the proposed method introduces multiple streams for purpose of even further reduced PAPR, where the modulated data and filter coefficients of the other streams are determined from those of first stream. For Pi/2-BPSK and Pi/4-QPSK modulation, the PAPR for LP-FBSC can be as low as 2.6 dB and 4.2 dB while low OOB emission property being maintained.

A three-scale asymptotic analysis for ageing linear viscoelastic problems of composites with multiple configurations

• A novel three-scale asymptotic analysis is proposed. • Composite materials with multiple periodic configurations are considered. • Ageing linear viscoelastic problems of composites are investigated. • Numerical results are given in detail to validate the proposed method. A novel three-scale asymptotic expansion is proposed in this work to investigate ageing linear viscoelastic problems of composites with multiple periodic configurations. Here, the composite structures are established by periodical distribution of local cells on microscale and mesoscale. The new three-scale asymptotic expansion formulas based on classical homogenized methods in time domain are constructed at first, and the microscale and mesoscale functions are also derived in detail. Further, two distinct homogenized parameters defined on microscale and mesoscale domains are obtained by upscaling methods, and the newly developed homogenized equations are given on whole structure in time domain. Then, the three-scale strain and stress solutions are constructed by assembling the unit cell solutions and homogenized solutions. Also, the efficient finite element algorithms based on the three-scale asymptotic expansion and homogenized method are brought forward. Finally, some representative numerical examples are evaluated to verify the proposed methods. They show that the three-scale asymptotic expansions developed in this work are effective and valid for predicting the ageing linear viscoelastic properties of the composite materials with multiple configurations.