Spatial Coupling Effect Research Articles

Analysis of the dynamic contact behaviour of high-speed train transmission gear excited by wheel defects

Studies on wheel flatness and polygonal wear have demonstrated that wheel defects cause severe impact forces at the wheel–rail interfaces. This study investigated the dynamic contact mechanical behaviour of high–speed train transmission gears when subjected to wheel defects. First, a train-track coupling dynamics model was established, considering the localized contact characteristics of transmission gears. This model was developed using the slice method and the Hertz contact model, exploring the spatial coupling effects between the gear contact interface and the train–track interface. Subsequently, the dynamic model was employed to extract essential contact mechanical parameters of the transmission gear under the influence of wheel defects, including gear meshing load, gear contact stress, and sliding velocity. Furthermore, an analysis was conducted to uncover and elucidate the mechanism by which wheel flatness and polygonal wear impact the dynamic contact behaviour of the transmission gear. This study underscores the importance of considering wheel defects when assessing the contact fatigue and wear performance of high-speed train transmission gears.

Consideration of Multi-Objective Stochastic Optimization in Inter-Annual Optimization Scheduling of Cascade Hydropower Stations

There exists a temporal and spatial coupling effect among the hydropower units in cascade hydropower stations which constitutes a complex planning problem. Researching the multi-objective optimization scheduling of cascade hydropower stations under various spatiotemporal inflow impacts is of significant importance. Previous studies have typically only focused on the economic dispatch issues of cascade hydropower stations, with little attention given to their coupling mechanism models and the uncertainty impacts of inflows. Firstly, this paper establishes a coupled optimization scheduling model for cascade hydropower stations and elaborates on the operational mechanism of cascade hydropower stations. Secondly, according to the needs of actual scenarios, two types of optimization objectives are set, considering both the supply adequacy and peak-shaving capacity as indicators, with the total residual load and the peak-valley difference of the residual load as comprehensive optimization objectives. Subsequently, considering the uncertainty impact of the inflow side, a stochastic optimization model for inflow is established based on a normal distribution probability. Finally, case study analyses demonstrate that the proposed model not only effectively achieves supply stability but also reduces the peak-valley difference in load, and can achieve optimized scheduling under the uncertain environment of inflow.

Future Land Use Spatial Conflicts and Habitat Quality Impacts Based on SSPs-RCPs Scenarios—Qin-Ba Mountain City

In the future, the pursuit of high-quality economic development and a focus on ecological environmental protection in China will inevitably result in significant conflicts between land use and ecological land use. Land use conflicts primarily occur in peri-urban areas characterized by prominent economic development and urban agglomeration. As a municipality situated in the Qin-Ba mountainous region, Ankang has been promoting ecological preservation for a span of two decades. The allocation of construction areas primarily focuses on the proximity of watersheds, while the northern and southern regions are predominantly characterized by mountainous and hilly terrain, thus exhibiting distinct regional attributes. Previous studies have mainly focused on analyzing the effects of land use on habitat quality during intense urbanization, with fewer studies focusing on integrating eco-regions with urbanization to assess changes in habitat quality. However, it is important to recognize that land pressure encompasses economic, ecological, and social aspects. Additionally, it aims to provide insights for the harmonious development of land use in eco-region-oriented cities. Using the SSPs-RCPs scenarios provided by the sixth phase of the Coupled Model Intercomparison Project (CMIP6), this paper employs a system analysis method, the emerging Patch-Generating Land Use Simulation model (PLUS) model, Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) model, and Land Use Conflict Measurement model to dynamically simulate the future habitat quality and spatial conflict patterns of land use in Ankang City. The study explores the spatial coupling effect of both factors under different scenarios. The results indicate the following: (1) The overall development trend reveals an intensification of land use conflicts and a decrease in habitat quality. The expansion rate of construction land is increasing and exhibiting aggregation, while agricultural land area is expanding, and forest land area is continuously decreasing. (2) Land use intensity exhibits a significant positive correlation with land conflict levels, while land conflict levels demonstrate a significant negative correlation with habitat quality. (3) Under different future shared socioeconomic path scenarios, land use intensity, and land conflict levels follow the order of SSP585 (high forcing scenario), SSP370 (medium to high forcing scenario), SSP245 (medium forcing scenario), and SSP126 (low forcing scenario), with intensity and conflict decreasing accordingly. These findings suggest that land use has had some impact on the ecological environment, with indications of habitat degradation. Even in Ankang, where ecological development is highly valued, the city will gradually face conflicts between ecological protection and economic development in future scenarios. The city already has the environment at heart, so it will be worse in cities where the priority is economic development. Therefore, it is crucial to allocate sufficient space for economic development while simultaneously prioritizing ecological protection. The results of the study can provide a reference for analyzing the trade-offs between land development and habitat protection in eco-mountainous cities and for eco-cities to avoid falling into the conflict dilemma of economic cities.

Massive Grant-Free Access With Massive MIMO and Spatially Coupled Replicas

Massive multiple access schemes, capable of serving a large number of uncoordinated devices while fulfilling reliability and latency constraints, are proposed. The schemes belong to the class of grant-free coded random access protocols and are tailored to massive multiple input multiple output (MIMO) base station processing. High reliability is obtained owing to an intra-frame spatial coupling effect, triggered by a simple device access protocol combined with acknowledgements (ACKs) from the base station. To provide system design guidelines, analytical bounds on error floor and latency are also derived. The proposed schemes are particularly interesting to address the challenges of massive machine-type communications in the framework of next generation massive multiple access systems.

Distributed Electro-Mechanical Coupling Effects in a Dielectric Elastomer Membrane Array

BackgroundDielectric elastomer (DE) transducers permit to effectively develop large-deformation, energy-efficient, and compliant mechatronic devices. By arranging many DE elements in an array-like configuration, a soft actuator/sensor system capable of cooperative features can be obtained. When many DE elements are densely packed onto a common elastic membrane, spatial coupling effects introduce electro-mechanical interactions among neighbors, which strongly affect the system actuation and sensing performance. To effectively design cooperative DE systems, those coupling effects must be systematically characterized and understood first.ObjectiveAs a first step towards the development of complex cooperative DE systems, in this work we present a systematic characterization of the spatial electro-mechanical interactions in a 1-by-3 array of silicone DEs. More specifically, we investigate how the force and capacitance characteristics of each DE in the array change when its neighbors are subject to different types of mechanical or electrical loads. Force and capacitance are chosen for this investigation, since those quantities are directly tied to the DE actuation and sensing behaviors, respectively.MethodsAn electro-mechanical characterization procedure is implemented through a novel experimental setup, which is specifically developed for testing soft DE arrays. The setup allows to investigate how the force and capacitance characteristics of each DE are affected by static deformations and/or electrical voltages applied to its nearby elements. Different combinations of electro-mechanical loads and DE neighbors are considered in an extensive experimental campaign.ResultsThe conducted investigation shows the existence of strong electro-mechanical coupling effects among the different array elements. The interaction intensity depends on multiple parameters, such as the distance between active DEs or the amount of deformation/voltage applied to the neighbors, and provides essential information for the design of array actuators. In some cases, such coupling effects may lead to changes in force up to 9% compared to the reference configuration. A further coupling is also observed in the DE capacitive response, and opens up the possibility of implementing advanced and/or distributed self-sensing strategies in future applications.ConclusionBy means of the conducted experiments, we clearly show that the actuation and sensing characteristics of each DE in the array are strongly influenced by the electro-mechanical loading state of its neighbors. The coupling effects may significantly affect the overall cooperative system performance, if not properly accounted for during the design. In future works, the obtained results will allow developing cooperative DE systems which are robust to, and possibly take advantage of, such spatial coupling effects.

Seismic response of the long-span steel truss arch bridge with the thrust under multidimensional excitation

PurposeUnder different ground motion excitation modes, the spatial coupling effect of seismic response for the arch bridge with thrust, seismic weak parts and the internal force components of the control section of main arch ribs are analyzed.Design/methodology/approachTaking a 490 m deck type railway steel truss arch bridge as the background, the dynamic calculation model of the whole bridge was established by SAP2000 software. The seismic response analyses under one-, two- and three-dimension (1D, 2D and 3D) uniform ground motion excitations were carried out.FindingsFor the steel truss arch bridge composed of multiple arch ribs, any single direction ground motion excitation will cause large axial force in the chord of arch rib. The axial force caused by transverse and vertical ground motion excitation in the chord of arch crown area is 1.4–3.6 times of the corresponding axial force under longitudinal seismic excitation. The in-plane bending moment caused by the lower chord at the vault is 4.2–5.5 times of the corresponding bending moment under the longitudinal seismic excitation. For the bottom chord of arch rib, the arch foot is the weak part of earthquake resistance, but for the upper chord of arch rib, the arch foot, arch crown and the intersection of column and upper chord can all be the potential earthquake-resistant weak parts. The normal stress of the bottom chord of the arch rib under multidimensional excitation is mainly caused by the axial force, but the normal stress of the upper chord of the arch rib is caused by the axial force, in-plane and out of plane bending moment.Originality/valueThe research provides specific suggestions for ground motion excitation mode and also provides reference information for the earthquake-resistant weak part and seismic design of long-span deck type railway steel truss arch bridges.

The spatial coupling effect between urban street network's centrality and collection & delivery points: A spatial design network analysis-based study.

The sustainable development of collection and delivery points and urban street network is an important consideration of logistic planners. Urban street networks have a significant impact on collection and delivery points’ location, but the spatial relationship between the centrality of urban street network and collection and delivery points has not been studied using spatial design network analysis. In a multiple centrality assessment model, we used point of interest and street network data to evaluate the location of two types of collection and delivery points and the centrality of streets in Nanjing city, based on four indicators: closeness, betweenness, severance, and efficiency. Then, kernel density estimation and spatial autocorrelation are used to study spatial patterns of distribution and centrality coupling effects of urban street network and collection and delivery points. The results show that the centrality of Nanjing streets has a big influence on the location of the collection and delivery points, and the directions of different types of centrality also vary. The location of the Cainiao Stations are largely related to closeness, followed by betweenness, severance, and efficiency. China Post Stations and street centrality have a weak correlation between efficiency and severance, but no correlation between closeness and betweenness. Our results can help logistics enterprises and urban planners to develop collection and delivery points’ network based on the urban street network.

Asymmetric diffraction mechanism induced by inclined all-dielectric nanostructure

3D asymmetric structure could induce asymmetric diffraction with spatial coupling behavior for various optical applications, but the study still faces challenges due to the complicated local-field coupling mechanism within structures. In this study, the spatial asymmetry based on inclined all-dielectric structure was theoretically modeled. The normal reflection of the 2D array shows that the increasing structural inclination selectively enhances the Fano resonance between different polarization directions which is mainly due to the oriented spatial coupling effect by increasing structural asymmetry, proved with the near-field distribution. The angular-resolved reflection shows the selected enhancement of first-order diffraction even over that of zero order by combining the structural asymmetry and oblique incidence. Our study provides a new insight for exploring asymmetric photonic structures and relative devices in practical applications.

The spatial coupling effect between urban public transport and commercial complexes: A network centrality perspective

The sustainable development of urban public transport (UPTN) and commercial complexes is an important consideration of city planners. This study examined the coordinated coupling development between the UPTN and urban commercial complexes using the network centrality as a bridge variable. After constructing the model of UPTN, we used multiple centrality assessment and urban network analysis models to measure the UPTN’s centrality. Thereafter, we gathered the latitude and longitude coordinates of commercial complexes and depicted their spatial distribution. Then, we studied the spatial distribution pattern and coupling effect of the UPTN’s centrality and the commercial complexes using Kernel Density Estimation and spatial autocorrelation. Finally, a case study based on Xi'an City, China was conducted. The results show that the UPTN possesses multi-center characteristics of closeness, betweenness and straightness; the distribution of urban commercial complexes is mainly concentrated in the existing commercial circles of the city; there is a positive linear correlation between the UPTN’s centrality and the distribution of commercial complexes. This study provides a basis for optimizing decision-making related to the sustainable planning and site-selection of urban public transport and commercial complexes.

Spatially Coupled Turbo-Like Codes: A New Trade-Off Between Waterfall and Error Floor

Spatially coupled turbo-like codes (SC-TCs) have been shown to have excellent decoding thresholds due to the threshold saturation effect. Furthermore, even for moderate block lengths, the simulation results demonstrate a very good bit error rate performance in the waterfall region. In this paper, we discuss the effect of spatial coupling on the performance of TCs in the finite block-length regime. We investigate the effect of coupling on the error floor performance of SC-TCs by establishing conditions under which the spatial coupling either preserves or improves the minimum distance of TCs. This allows us to investigate the error floor performance of SC-TCs by performing a weight enumerator function analysis of the corresponding uncoupled ensembles. Our results demonstrate that the spatial coupling changes the design trade-off between the waterfall and error floor performance. Instead of optimizing the belief propagation (BP) threshold of uncoupled TCs, which in turn leads to a higher error floor, we can take advantage of the threshold saturation property of the SC-TCs. Choosing strong ensembles, characterized by good maximum-a-posteriori (MAP) thresholds and low error floors, the corresponding SC-TCs are then able to simultaneously approach capacity and achieve very low error floor.

Quantitative simulation of mechanical properties of porous ceramic materials by discrete element method

In this work, the mechanical response of porous ceramic was investigated by performing discrete element method (DEM) simulations. Isotropic packing strategy was adopted to prepare numerical samples with different densities. For each numerical sample, the contact size between particles was calculated using Coble’s sintering model. To account for the spatial coupling effect between solid bonds under multi-contact condition, the classic Hertz contact model was modified by introducing a correct factor which reflects the influences of contact size in-between grains and the geometrical arrangement of grains. The quantitative predicting ability of the built DEM framework was then evaluated by using the partially sintered alumina ceramic as investigated system. It was demonstrated that the predicted effective Young’s modulus and fracture strength are both in quantitative agreement with experimental data. As to partially sintered alumina ceramic containing large pores, both the interaction behavior between pores and the influence of the geometrical arrangements of pores on effective Young’s modulus and fracture strength predicted by the theoretical analyses or finite element method were successfully captured by our DEM simulations. All these quantitative comparisons demonstrate that the built DEM framework can be used to quantitatively model the mechanical properties of porous ceramics.

Multilevel Coding With Spatially Coupled Repeat-Accumulate Codes for High-Order QAM Optical Transmission

We propose multilevel coding (MLC) with spatially coupled codes to increase the net coding gain (NCG) and reduce the power consumption of forward error correction (FEC) codes in high-order quadratic-amplitude modulation (QAM) optical transmissions. We optimized the degree distribution of the spatially coupled repeat-accumulate (SC-RA) codes by using density evolution to enhance the effect of spatial coupling with a limited code length. We constructed multilevel codes with the SC-RA codes and investigated their performance in numerical simulations. NCGs of 12.5, 13.2, and 13.7 dB were obtained for 16, 64, and 256 QAM. We found that MLC is more efficient in terms of circuit size and computational complexity than the conventional FEC configuration of bit-interleaved coded modulation (BICM). Moreover, its efficiency tends to increase as the modulation order increases. Our estimates suggest that the power consumed in the FEC process could be reduced to about half for 16 QAM, 35% for 64 QAM, and 15% for 256 QAM compared with when BICM is used to obtain similar NCG values.

Rotation Stiffness Investigation of Spatial Joints with End‐Plate Connection

Spatial joints with end‐plate connections show significant spatial coupling effects under spatial loading. Mechanical behaviour and failure modes of these spatial joints differ from those of planar joints. This study involved experiments and finite element analyses with respect to planar joints with end‐plate connections under static load. The numerical results agreed well with the experimental data, and this verified the adequacy of the finite element analyses. Then, finite element models of the spatial interior joint, exterior joint, and corner joint were established to analyse the difference between the mechanical behaviour of spatial joints and planar joints. The component method was used to analyse components contributing to the initial stiffness of spatial joints. An initial rotation stiffness calculation model of spatial joints was proposed based on the deformation of joints. The findings indicated that results of the calculation models were in good agreement with those of the finite element analyses, and this proved that the calculation model proposed in this study could act as a reference method.

Comparative epidemiology of poliovirus transmission

Understanding the determinants of polio transmission and its large-scale epidemiology remains a public health priority. Despite a 99% reduction in annual wild poliovirus (WPV) cases since 1988, tackling the last 1% has proven difficult. We identified key covariates of geographical variation in polio transmission patterns by relating country-specific annual disease incidence to demographic, socio-economic and environmental factors. We assessed the relative contributions of these variables to the performance of computer-generated models for predicting polio transmission. We also examined the effect of spatial coupling on the polio extinction frequency in islands relative to larger land masses. Access to sanitation, population density, forest cover and routine vaccination coverage were the strongest predictors of polio incidence, however their relative effect sizes were inconsistent geographically. The effect of climate variables on polio incidence was negligible, indicating that a climate effect is not identifiable at the annual scale, suggesting a role for climate in shaping the transmission seasonality rather than intensity. We found polio fadeout frequency to depend on both population size and demography, which should therefore be considered in policies aimed at extinction. Our comparative epidemiological approach highlights the heterogeneity among polio transmission determinants. Recognition of this variation is important for the maintenance of population immunity in a post-polio era.

EFFECTS OF SPATIAL COUPLING OF WATER AND FERTILIZER APPLICATIONS ON ROOT GROWTH CHARACTERISTICS AND WATER USE OF WINTER WHEAT

□ Root systems play vital roles, inter alia in the acquisition of water and nutrients in all plants, and hence in their growth, physiology and metabolism. However, much remains to be learned about the mechanisms affecting root distributions and uptake efficiencies. These are important aspects to understand in order to optimize water and fertilizer applications, especially in arid areas such as the Loess Plateau of China, where a key crop is winter wheat. Therefore, we have studied the effects of spatial coupling of water, nitrogen and phosphorus applications on winter wheat root growth patterns at different growth stages and in different soil layers in soil columns. Observations by minirhizotrons showed root length, surface area, volume and number to be respectively 18.9, 25.3, 29.8 and 8.0% higher under dry treatments than under wet treatments. Simultaneous application of nitrogen and phosphorus in the 0–90 or 0–30 cm layers promoted extensive spatial distributions of roots, especially in the 0–30 cm layer. In addition, water use efficiency (WUE) was found to be strongly correlated with root length, surface area, volume and number (r 2 = 0.72–0.80, n = 26), but weakly correlated with root biomass (r 2 = 0.3).

Controlling Spatiotemporal Chaos with a Generalized FeedbackMethod

The usual linear variable feedback control method is extended to ageneralized function feedback scheme. The scheme is applied tohigh-dimensional spatiotemporal systems. By a combination of localgeneralized feedback control and the spatial coupling effect amongelements, turbulent motion can be successfully eliminated.

MOSAIC SOLUTIONS AND SPATIAL ENTROPY FOR A CLASS OF NEURAL NETWORK MODELS

In this article, we present a lattice differential equation model for a class of neural networks. A subset of the equilibrium solutions called mosaic equilibrium solutions is defined. Existence and stability theorems are proved for mosaic equilibrium solutions. Regions of stability are defined and spatial entropy calculations, as a measure of the complexity of the system, are presented that give insights into the effects of spatial coupling.

Strain localization and formation of heterogeneous distribution of shearable ordered precipitates: application to an Al–10at.%Li single crystal

A model is established for plastic deformation of crystals containing shearable ordered precipitates. The precipitate structure undergoes an evolution caused by enhanced growth and redissolution of precipitates due to their shearing by dislocations. Opposing the strain hardening of the matrix and the spatial coupling effect between adjacent material elements, such a thermodynamic evolution, in addition to the geometrical effect of the shearing, finally causes strain softening and hence leads to a plastic instability–strain localization with the formation of precipitate-deficit channels. A numerical simulation is carried out taking as an illustrative example the case of an Al–10at.%Li single crystal. The results are compared with some known observations concerning post-yield properties, especially of the plastic instability and the corresponding microstructure.

A new stochastic analysis for multiple supported MDOF secondary systems: II. Tuning and spatial coupling effects

A new stochastic analysis is developed to estimate the response of multiply-supported multi-degree-of-freedom (MDOF) secondary systems to dynamic loading. The preceding paper illustrates how the effect of the dynamic interaction between the secondary and primary systems is included in the proposed stochastic analysis. The effects of both tuning and spatial coupling are covered in this paper. First, the terms associated with the cross correlations are defined. Then, a section is assigned to demonstrate how the tuning character can be accounted for. Subsequently, numerical examples are provided in order to demonstrate the significance of both effects of tuning and spatial coupling in the stochastic analysis of secondary systems.

Frequency-Dependent Nodal Analysis of Boiling Water Reactor Stability

A general spatial kinetics model has been developed for boiling water reactor (BWR) stability analysis utilizing nodal analysis, a commonly used technique for analyzing power distributions in large power reactors. Kinetics parameters for use in the kinetics equations have been derived by utilizing self-consistent nodal data and power distribution. Spatial coupling effects on the stability margin have been analyzed for a typical BWR. Various influences on stability are investigated. Spatial kinetics is found to have substantial effects on the stability margins for density wave oscillations.