Spatiotemporal Coupling Effect Research Articles

Spatio-temporal heterogeneity and coupling effect of mining economy, social governance and environmental conservation: Evidence from Guangxi Zhuang Autonomous Region, China.

In order to solve the problem of coordinated development among mining economy, social governance and environmental conservation in global resource-based cities, we choose Guangxi Zhuang Autonomous Region as the research area. The advantage of resource endowment and resource industry was measured by location quotient and input-output method. The panel data related to mining governance from 2010 to 2021 were selected to build the evaluation and coupling analysis model between mining economic, social governance and environmental conservation, and the spatial-temporal heterogeneity and coupling effect of them were analyzed by comprehensive empowerment evaluation, spatial autocorrelation analysis and barrier degree methods. The results show that: (1) Except for the overall upward trend of social governance, the development level of mining economy and environmental conservation are basically stable; (2) The resource-rich areas have obvious mining economic advantages, and the central cities have good social governance capabilities, and the environmental conservation effectiveness is uncertain; (3) The coupling effect between mining economy and social governance is stronger than that between mining economy and environment conservation, and the synergistic coupling effect of the three is relatively random. Finally, we put forward some policy response strategies to Guangxi, and theoretical and practical reference would be provided for resource-based cities around the world.

Efficient and high-spatiotemporal-quality terawatt-class mid-infrared optical parametric amplifiers by spatially shaped pumping

We propose a method to efficiently generate terawatt (TW)-class mid-infrared (MIR) femtosecond laser pulses with high spatiotemporal quality through optical parametric chirped-pulse amplification (OPCPA). By transforming the pump-beam profile for the OPCPA from Gaussian to flat-top using a designed field mapping optics consisting of two aspherical lenses, we obtain a TW-class femtosecond laser pulse at 2 µm with a conversion efficiency of over 36% according to our simulations. Furthermore, the spatiotemporal coupling effects are greatly suppressed in our method compared to an OPCPA system that is pumped by a widely employed Gaussian profile beam. Our work provides a simple and robust method for developing OPCPA systems with high efficiency and high pulse quality.

Spatiotemporal response of concave VLS grating to ultra-short X-ray pulses.

In soft X-ray free-electron laser (FEL) beamlines, variable-line-spacing (VLS) gratings are often used as dispersive components of monochromators and spectrometers due to their combined dispersion and focusing properties. X-ray FEL pulses passing through the VLS grating can result in not only transverse focusing but also spatiotemporal coupling effects, such as pulse front tilt, pulse front rotation, and pulse stretching. In this paper, we present a theoretical study of the spatiotemporal response of concave VLS gratings to ultra-short X-ray pulses. The theoretical analysis indicates that the tilt angle of the non-zero diffraction orders varies with the propagation distance, and disappears at the focus, where the focal lengths and pulse stretching differ for different diffraction orders. The model demonstrates the pulse duration after the concave VLS grating is the convolution of the initial pulse duration and the stretching term induced by dispersion, while the beam size at the focus in x dimension is the convolution of the geometric scaling beam size and the dispersion term. This work provides a mathematical explanation for the spatiotemporal response of concave VLS grating to ultra-short X-ray pulses and offers valuable insights into the design of FEL grating monochromators, spectrometers, pulse compressors, and pulse stretchers.

Coupling effect of freeze–thaw cycles and multiaxial compression on concrete-filled steel tube (CFST): Insights from simplified meso-scale axisymmetric finite element model

With increasing applications in cold regions, concrete-filled steel tube (CFST) has become one of the favorite structural types due to the prompting load-carrying capacity and construction efficiency, where the core concrete is generally under multiaxial stress states. However, the damage mechanism for the coupling effect of freeze–thaw (FT) cycles and multiaxial stress states on the core concrete has not been yet distinctly clarified. This may be attributed to the difficulties in explaining the macro-scale (>10 mm) structural phenomenon (i.e., strength reduction) through efficiently modeling the corresponding micro-scale (10-3–1 mm) damage process considering the spatiotemporal coupling effect. To overcome this limitation, a simplified meso-scale axisymmetric finite element (FE) model has been firstly developed through the rational exploitation of pore expansion-shrink cycles under external multiaxial loads and proved capable of efficiently simulating the concrete damage under the coupling effect. The FT damage evaluations of concrete under various types of multiaxial active compressions have been comprehensively analyzed. The direction of the FT damage distribution proved being consistent with that of external load, and the stress states combining high axial compression with low radial compression show an adverse effect on the FT resistance. On this basis, a multiaxial compression-dependent FT damage model has been proposed and verified against experimental results. Thereafter, the FT resistance of CFST under external load and its corresponding confinement effect have been studied. The results show that, similar to plain concrete, the FT resistance of CFST will firstly increase and then decrease with the increasing axial compression. Meanwhile, the promoting FT resistance mechanism of CFST has been clarified, which originates from two stages as the FT damage mitigation during FT cycles and the damage effect reduction after FT cycles. This analytical method for the coupling effect is also beneficial for other types of confined concretes.

Spatiotemporal Coupling Effect of Regional Economic Development and De-Carbonisation of Energy Use in China: Empirical Analysis Based on Panel and Spatial Durbin Models

The synergistic development of economic construction and low-carbon transformation of energy systems must be promoted for building a green, low-carbon, and cyclic economic system and achieving the “double carbon” goal in China. Based on the panel data of 30 provincial-level administrative regions in China from 2015 to 2019, the global entropy method, coupling coordination degree model, and spatial statistical analysis methods are applied to analyse the factors affecting the coupling effect. The coordination degree increased in the study period, with Beijing, Shanghai, Tianjin, Jiangsu, and Zhejiang being the regions with the highest values. The spatial distribution of the coupling coordination degree is strongly positively correlated with the eastern provincial-level administrative regions located in the high–high concentration area of the Moran scatterplot and western provincial-level administrative regions concentrated in the low–low concentration area. The spatial association pattern is stable in the study period, with only two provinces exhibiting a transition: Shandong province made the transition to high–high agglomeration areas, and Liaoning province made the transition to low–low agglomeration areas. The level of regional economy, urbanization process, energy consumption structure, and level of investment in science and innovation enhance the coupling coordination degree, whereas the industrial structure deteriorates this degree.

Analysis and Detection of Rotor Eccentricity in Permanent Magnet Synchronous Machines Based on Linear Hall Sensors

Rotor eccentricity commonly exists in permanent magnet synchronous machines (PMSMs) due to improper assembly, excessive vibration, and continuous operation. Consequently, the unbalanced magnetic pull, introduced by rotor eccentricity, may lead to unfavorable noise, vibration, and even bear damage, which makes the detection of eccentricity meaningful. Although motor current signal analysis is the most popular method to diagnose eccentricity based on the amplitudes of sideband component, it is a big challenge to classify different types of eccentricities and quantify the eccentric ratio due to the spatiotemporal coupling effect. In this article, by installing a set of Hall sensors at stator slots of PMSMs to measure the magnetic flux density in time domain, the static eccentricity and dynamic eccentricity can be easily separated. This article provides a novel complex-analytical model to reveal the single side band modulation effect in air-gap filed due to dynamic eccentricity. Moreover, a diagnosis algorithm based on frequency-adaptive notch filter is designed to identify the eccentricity type and the corresponding degree. The effectiveness of the novel diagnosis method is validated by both simulations and experiments.

The Spatiotemporal Characteristics of Coupling Effect between Roof and Backfill Body in Dense Backfill Mining

Backfill mining has become an important part of coal mine green mining technology. In this paper, the spatiotemporal characteristics of coupling effect between the roof and dense backfill body were analyzed by theoretical analysis and similar simulation test, and Xingtai Mine in China was taken as an engineering case for verification. The results show that the larger subsidence of the roof is, the stronger the supporting capacity of the backfill body is, and the interaction between the two is more obvious, thus showing a coupling effect. This coupling effect presents a regular variation with the increase of backfill distance and time, that is, the coupling degree of roof and backfill body is high in the middle of goaf and low in the vicinity of the coal pillar in spatial distribution, and the coupling behavior of roof and backfill body continues to occur slowly with time. Through the monitoring of stress and displacement in the engineering site and the analysis of borehole observation results, the spatiotemporal coupling effect between roof subsidence and backfill support is fully verified. The research results are of great significance to the control of surrounding rock in backfill mining, the study of the mechanical aging characteristics of backfilling materials, and the optimization of backfill body support performance.

Graph attention temporal convolutional network for traffic speed forecasting on road networks

Traffic speed forecasting plays an increasingly essential role in successful intelligent transportation systems. However, this still remains a challenging task when the accuracy requirement is demanding. To improve the prediction accuracy and achieve a timely performance, the capture of the intrinsically spatio-temporal dependencies and the creation of a parallel model architecture are required. Accordingly, we propose a novel end-to-end deep learning framework named Graph Attention Temporal Convolutional Network (GATCN). The proposed model employs the graph attention network to mine the complex spatial correlations within the traffic network and temporal convolution operation to capture temporal dependencies. In addition, the multi-head self-attention mechanism is incorporated into the model to extract the spatio-temporal coupling effects. Experiments show that the proposed model consistently outperforms other state-of-the-art baselines for various prediction intervals on two real-world datasets. Moreover, we reveal that the proposed model can effectively distinguish the sophisticated traffic patterns of ramps on expressways by analyzing the graph attention heatmap.

Effect of object thickness on ultrashort pulse diffraction.

When calculated in the spectral domain, the propagation of an ultrashort optical pulse may suffer from inaccuracy due to the finite thickness of the object it diffracts on. Unlike monochromatic radiation, ultrashort pulse interaction with an object in the time domain depends on the pulse longitudinal coordinate. Here, we propose an algorithm to study the effect of the object thickness on ultrashort pulse diffraction on amplitude, phase, and three-dimensional highly scattering objects. The algorithm comprises a stepwise approach to simulating the diffraction of ultrashort pulses on apertures or scatterers having a finite thickness. We confirm the applicability of the approach and convergence of the result upon reducing the simulation step. We compare the simulation results obtained with traditionally calculated wavefields and the updated results obtained with the proposed approach. We reveal a discrepancy of about 7% for pulsed radiation with λ=800nm on a 1 mm thick object. Then, we demonstrate the dependence of this mismatch on the object thickness and show that for non-Gaussian vortex beams, this effect is even more pronounced. We reveal that spatiotemporal coupling effects depend on the pulse-object interaction simulation approach as well. The obtained results demonstrate that applicability of the single-layer representation of the simulated object strongly depends on its specific features, and inaccuracy of such an approach strongly depends on individual characteristics of the object.

Investigation of temporal evolution of picosecond laser pulse by synchronized femtosecond laser pulse

In this paper, we theoretically and experimentally investigate the initial temporal characterization and the temporal evolution of a picosecond laser pulse by a synchronized femtosecond laser pulse. After theoretically analyzing the measurement principle, we experimentally measure the initial temporal characterization of the picosecond laser pulse. Further, the temporal evolution of the picosecond laser pulse propagating in different lengths of a carbon disulfide (CS2) is measured. We find that the initial temporal shape of the picosecond laser pulse is smooth and clean. As increasing of the CS2 length, the pulse width of the picosecond laser pulse has a trend of slight narrow owing to the spatiotemporal coupling effect.

On terahertz pulsed broadband Gauss-Bessel beam free-space propagation

Terahertz pulse time-domain holography is the ultimate technique allowing the evaluating a propagation of pulse broadband terahertz wavefronts and analyze their spatial, temporal and spectral evolution. We have numerically analyzed pulsed broadband terahertz Gauss-Bessel beam’s both spatio-temporal and spatio-spectral evolution in the non-paraxial approach. We have characterized two-dimensional spatio-temporal beam behavior and demonstrated all stages of pulse reshaping during the propagation, including X-shape pulse forming. The reshaping is also illustrated by the energy transfer dynamics, where the pulse energy flows from leading edge to trailing edge. This behavior illustrates strong spatio-temporal coupling effect when spatio-temporal distribution of Bessel beam’s wavefront depends on propagation distance. The spatio-temporal and spatio-spectral profiles for different spectral components clearly illustrate the model where the Bessel beam’s wavefront at the exit from the axicon can be divided into radial segments for which the wave vectors intersect. Phase velocity via propagation distance is estimated and compared with existing experimantal results. Results of the phase velocity calculation depend strongly on distance increment value, thus demonstrating superluminal or subluminal behavior.

Propagation and spatiotemporal coupling characteristics of ultra-short Gaussian vortex pulse

Based on Collins diffraction integral formula, the propagation equation of ultra-short Gaussian vortex pulse beam has been derived. Using the equation, the intensity distribution variations of vortex pulse in the propagation process are calculated. Specially, the spatiotemporal coupling characteristics of ultra-short vortex beams are discussed in detail. The results show that some key parameters, such as transverse distance, transmission distance, pulse width and topological charge number will influence the spatiotemporal coupling characteristics significantly. With the increasing of transverse distance, the waveforms of the pulses distort obviously. And when transmission distance is far than 50 mm, the distribution curve of transverse intensity gradually changes into a Gaussian type. In addition, initial pulse width will affect the distribution of light field, however, when initial pulse width is larger than 3 fs, the spatiotemporal coupling effect will be insignificant. Topological charge number does not affect the time delay characteristics, since with the increasing of topological charge number, the waveform of the pulse distorts gradually but the time delay does not occur.

Study on spatiotemporal evolution of chirped femtosecond laser pulses at specific spatial position during small-scale self-focusing

We experimentally study the spatiotemporal evolution of chirped femtosecond laser pulses at a specific spatial position, such as the modulation peak position (MPP), during small-scale self-focusing (SSSF). It is found that the spatial peak intensity at the MPP increases rapidly initially with increment of input power due to the effect of SSSF, however it becomes saturated at the higher power because the finite energy of the beam restraints increasing of the peak intensity at the MPP. The pulse width at the MPP is compressed gradually with rising power owing to the spatiotemporal coupling effect, which will reach the narrowest when the spatial peak intensity at the MPP reaches the maximum. Further, the influence of chirp on the pulse width evolution at the MPP is discussed theoretically. We find that the negative chirp accelerates the pulse width compression because the negative chirp enhances the process of SSSF, but the positive chirp is counterproductive. Our results may provide some helps for propagation and amplification of broadband laser pulses.

Degradation of femtosecond petawatt laser beams: Spatio-temporal/spectral coupling induced by wavefront errors of compression gratings

Recently, several petawatt (PW, 1015 W) lasers with pulse duration of ∼20–30 fs have been introduced throughout the world, pushing the upper limit on laser peak power. However, besides well-known spatio-temporal coupling effects, such as residual spatial/angular chirps and pulsefront tilt/curvature, the spatio-temporal/spectral coupling in compressors induced by wavefront errors of gratings, which could dramatically distort ultra-intense pulses, has been neglected. In this work, for the first time we analyzed this phenomenon and the peak power/intensity degradation induced by it. Our results suggest that the actual performance of femtosecond PW lasers may be worse than previously estimated.

Measuring the temporal evolution characteristics of picosecond pulses based on cross-correlation during nonlinear propagation

When the picosecond pulse with a initial temporal modulation propagates and amplifies in the large-scale Nd:glass laser system, the temporal modulation will be accumulated and enhanced, which causes serious temporal distortion in the output picosecond pulse. The output beam quality of the whole Nd:glass laser system will become very poor due to the spatiotemporal coupling effect. So measuring the initial temporal structure and temporal evolutions of the picosecond pulse after nonlinear propagation is necessary. We propose a method of measuring the temporal characteristics of a picosecond pulse by a synchronized femtosecond pulse. This method has advantages of simple operation, convenient and high resolution. The initial temporal fine structure and temporal evolutions of the picosecond pulse passing through different lengths of CS2 nonlinear medium are measured. The results show that the initial temporal shape of the picosecond pulse is very clean and smooth. When the picosecond pulse propagates in CS2 nonlinear medium, the pulse width has a trend of slight narrow with increasing the length of CS2 nonlinear medium due to the spatiotemporal coupling effect.

A Method for Measuring the Pulsewidth at Different Spatial Positions of Ultrashort Laser Pulses

In this letter, we propose a method for measuring the pulsewidths at different spatial positions of ultrashort laser pulses. By measuring the pulsewidths varying with spatial positions of chirped and chirped-free femtosecond laser pulses, it is found that pulsewidths at edge positions are longer than that of central positions due to the effect of residual spatial chirp. Then, we measure the temporal evolutions of pulse at the strongest spatial modulation position after small-scale self-focusing and our results show that the pulsewidths become narrower with increasing spatial contrast due to spatiotemporal coupling effect. We find that the method is reliable and feasible.

超短脉冲径向偏振光束的解析解及时空耦合效应

Based on the propagation equation which governs the propagation of ultra-short pulsed beams,and by utilizing the Fourier transform technique as well as the commutation relation between two mathematical operators,the analytical solution for ultra-short pulsed radially polarized beams is obtained.This solution is applicable to radially polarized beams driven by any pulse.On the basis of the solution,the propagation properties of the ultra-short pulsed radially polarized beams are discussed.It shows that the pulse at the beam periphery is delayed compares to that around the beam center.This effect results in the the varying of transverse intensity distribution of the ultra-short pulsed radially polarized beam at different temporal positions during propagation,and the asymmetric intensity distribution of the vertical profle at the head and the trail of the pulse.The method used in this paper is applicable in obtaining the analytical solution and the propagation properties for the ultra-short pulsed azimuthally polarized beams.

The coupling of fluid flow and uplift since Late Cretaceous in Zoige area, western Sichuan

The uplift indicated by five AFT (apatite fission track) samples is more than 3400 m by multi-episodic uplift since Late Cretaceous in Zoige area; especially the processes of fast uplift in Late Cretaceous and Neogene have important influences on the stress of paleo-fluid. Based on field geology, macroscopic features of fracture, and geochemistry of fluid inclusions, we decipher the paleo-fluid process of episodic migration. In early uplift stage, the temperature of inclusions increased with the constant salinity, whilst both of them proportionally decreased in the mid-late stage, indicating the different tendency of heat-fluid warming and freshwater contamination at different time. Of particular importance are the features of episodic fluid flow, such as ESR ages, and features of multi-episodic migration that correspond well with the process of multi-episodic uplift. Thus, concerning the rock stress-strain behavior responding to uplift, we further discuss the spatio-temporal coupling effect of episodic migration and decompression in multi-episodic uplift, thereby to better understand petroleum geology in the region.

Space–time coupling of shaped ultrafast ultraviolet pulses from an acousto-optic programmable dispersive filter

A comprehensive experimental analysis of spatiotemporal coupling effects inherent to the acousto-optic programmable dispersive filter (AOPDF) is presented. Phase and amplitude measurements of the AOPDF transfer function are performed using spatially and spectrally resolved interferometry. Spatiotemporal and spatio-spectral coupling effects are presented for a range of shaped pulses that are commonly used in quantum control experiments. These effects are shown to be attributable to a single mechanism: a group-delay-dependent displacement of the shaped pulse. The physical mechanism is explained, and excellent quantitative agreement between the measured and calculated coupling speed is obtained. The implications for quantum control experiments are discussed.

Analysis of ultra short pulse propagation in optical directional coupler structures

We employ an efficient time-domain beam propagation technique to study the effect of the propagation of ultra short pulse duration on the behavior of directional coupler operation. The technique used is based on higher order non-paraxial formulation that takes into account the spatiotemporal coupling effect which is crucial for the proper propagation of ultra short optical pulses. In this work the characterization of pulse spread and broad frequency content interactions of short pulse propagation have been analyzed. We validate in this rigorous analysis that the intermodal dispersion of the structure changes the behavior of the well known operation and breaks up the pulse during propagation which gives rise to distortion.