Spatial Dispersion Research Articles

Spatio-temporal higher-order finite-difference solution for the scalar acoustic wave equation based on the global difference coefficient

The partial derivatives obtained through the difference approximation in the finite-difference method for solving the scalar acoustic wave equation may give rise to computational errors, which have the potential to induce numerical dispersion. Typically, the temporal or spatial higher-order difference format is employed, whereby the difference order between the computational region and the perfectly matched layer (PML) boundaries can result in boundary reflections. In this study, we derive the acoustic wave equation and its PML boundary conditions in the finite difference format of the temporal fourth-order and the spatial 2Nth-order, based on the Lax-Wendroff method. Subsequently, the stability conditions of the two finite difference formats are presented and analyzed under different parameters. This effectively addresses the issue of temporal dispersion. Furthermore, the high-order PML temporal boundary conditions effectively suppress the boundary reflection phenomenon generated by the computational regions and the different difference orders of the PML boundaries. Moreover, the time-space dispersion relation of the acoustic wave equation is employed to globally optimize the difference coefficients via the least-squares method, thereby suppressing the spatial dispersion. The numerical solution experiments of the acoustic wave equation for the horizontal laminar model and the Marmousi model demonstrate the efficacy of the presented algorithm.

Exploring the Enigmatic Spread and Spatial Dynamics of Bursatella leachii in the Mediterranean Sea

The invasion history of the gastropod mollusk Bursatella leachii in the Mediterranean Sea demonstrates a dynamic progression through distinct phases, comprising arrival, establishment, and expansion phases. Initial records in the 1930s trace its entry through the Suez Canal, likely followed by larval transport to the Aegean Sea facilitated by natural currents. The subsequent spread to Maltese and Italian waters suggests secondary dispersion favored by maritime traffic or aquaculture activities. The establishment phase shows a significant increase in occurrences and spatial dispersion, with aggregated nuclei in the central Mediterranean. The expansion phase was characterized by rapid dispersal and intensified densities, particularly in the Aegean, Adriatic, and Spanish coasts. These findings underscore the species’ capability to invade from multiple fronts, driven by both natural and human-mediated processes. A new location in the Strait of Sicily, i.e., the island of Lampedusa, is reported in the present paper for the species. Given the low number of observations, its establishment with a viable population on the island is not confirmed, although its detection validates the Straits of Sicily as a key area of intense settlement of the species.

Competition, capital accumulation, and the geographical organization of production in the North Atlantic offshore wind energy industry

As offshore wind energy development expands throughout the advanced industrial world, the wind turbine manufacturing industry has been passing through a process of organizational and geographical restructuring. In terms of the dynamics of industrial organization, highly concentrated industrial conglomerates have gained a stronger position within the industry as the ownership of capital has been centralized through bankruptcies, mergers and acquisitions. Geographically, some regions are maintaining their pre-eminence within the international division of labour while other longstanding industrial clusters are being dismantled as production processes are being fragmented, transformed and dispersed to new regions. This article illuminates these dynamics of geographical organization through an analysis of (offshore) wind turbine manufacturing in Europe for deployment in Europe and the United States, advancing a unified approach to understanding changing modes of industrial organization and the development of the spatial division of labour. This unified approach is rooted in the examination of material transformations in the process of production, with attention to the specificities of wind energy as a natural resource. Taking up scientific advances made by Marx, radical industrial geographers and contemporary critics of political economy, the article demonstrates that the centralization of capital and the simultaneous spatial consolidation and dispersal of production have been necessary concrete forms of the development of the productive forces of social labour. The article concludes by reflecting on some of the barriers to the increasing fragmentation of wind turbine manufacturing and the potentialities for working-class organization borne by the centralization of capital and the consolidation of production.

Dynamics in Land Cover and Landscape Patterns of Myanmar: A Three-Decade Perspective (1990–2020)

A comprehensive scientific assessment of the dynamic changes in land cover and landscape patterns in Myanmar, considering both human activities and natural factors such as climate change, is essential for a thorough understanding of the transformations in the country’s ecological environment. This assessment also provides data-driven insights into the complex interactions between humans, climate, and the environment. This study aims to examine the dynamic changes in land cover in Myanmar over a thirty-year period from a comprehensive perspective. This paper, based on the MLC30 land cover dataset for Myanmar from 1990 to 2020, employs land use dynamic degree and land use transition matrix to analyze the extent and process of land cover changes in Myanmar. Furthermore, using landscape pattern indicators, the paper explores the changes in the spatial structural characteristics of land cover in Myanmar at both the patch scale and the landscape scale. The results indicate the following: (a) Areas with significant land cover changes are primarily located in the eastern, southeastern, and southwestern regions bordering China, Laos, and Thailand, as well as the coastal areas, with the change intensity from 2000 to 2020 being notably higher than before 2000. (b) Myanmar’s cultivated land, artificial surfaces, and water bodies show an expanding trend, with cultivated land expansion mainly at the expense of forests, while the increase in artificial surfaces and water bodies is through the conversion of the existing cultivated land. (c) Myanmar’s landscape patterns remained stable from 1990 to 2000. However, after 2000, the land cover has shown a clear trend towards fragmentation and spatial distribution dispersion, especially for the dominant forest and cultivated land types. Despite Myanmar’s rapid economic development, the trend toward the fragmentation and irregularization of cultivated land patches indicates a lack of attention to cultivated land use and planning. The reduction and fragmentation of forest areas have led to a decline in ecological connectivity, posing risks of ecological environment deterioration. Consequently, Myanmar must prioritize scientific land use planning and the rational allocation of land resources to foster the sustainable development of agriculture and the protection of natural ecosystems.

Lesson for the future climate migration. A study of relocation and development of new settlements in urban peripheries based on spatial dispersion of forced migrants in Serbia between 1991 and 2021

Climate migrations are going to affect the spatial structure in many regions of the world. We are now able to research long-term displacement and its spatial effects. Using the example of Serbia and the 30-year history of migration after the conflicts connected with the collapse of the former Yugoslavia, the article analyses the accompanying processes. The aim of this article is to study the spatial effects of long-term (forced) migration. The research is based on sociological and spatial planning methods, i.e. statistical data, geospatial information and institutional document analysis. The analyses show social and spatial trends in migration and settlement formation in Serbia between 1991 and 2021.

How penetration of e-commerce in rural areas drives consumption in China

PurposeThis paper explores how rural e-commerce drives consumption in both urban and rural residents; further, it presents evidence from the perspective of e-commerce penetration in rural areas and among farmers to assess the contribution of e-commerce to China’s economic strategy goal of fostering an economy driven by domestic demand.Design/methodology/approachData of Taobao villages from 2014 to 2021 are matched with data on prefecture-level cities. A two-way fixed effect model, instrumental variable model and group comparison method are employed to explore the role and mechanism of e-commerce penetration in rural areas in stimulating residents’ consumption through consumption propensity, purchasing power and consumer population.FindingsThe findings confirm that e-commerce penetration of rural areas can stimulate residential consumption, and residents generally adhere to the consumption concept of “living within their means.” The driving effect on residents’ consumption is achieved by expanding the urban consumer population and improving the purchasing powers of both urban and rural residents. The spatial dispersion of e-commerce villages strengthens the positive impact of e-commerce penetration in rural areas on consumption; this strengthening is caused by the increasing consumer population of urban residents and the purchasing power of both urban and rural residents. The agriculture-oriented e-commerce penetration of rural areas negatively impacts residents’ consumption, consumption propensity and consumer population; however, industrial-oriented penetration positively affects residents’ consumption, consumption propensity, purchasing power and consumer population.Originality/valueTo the best of our knowledge, this paper is the first to analyze the role and mechanism of e-commerce penetration in rural areas in stimulating residents’ consumption through consumption propensity, purchasing power and consumer population. This study contributes to advancing e-commerce and consumer theory by exploring the realm of rural e-commerce while also presenting empirical evidence from China.

Exploiting universal nonlocal dispersion in optically active materials for spectro-polarimetric computational imaging

Recent years have seen significant advancements in exploring novel light-matter interactions such as hyperbolic dispersion within natural crystals. However, current studies have predominantly concentrated on local optical response of materials characterized by a dielectric tensor without spatial dispersion. Here, we investigate the nonlocal response in optically-active crystals with screw symmetries, revealing their lossless, super-dispersive properties compared to traditional optical response functions. We leverage this universal nonlocal dispersion, i.e. the dispersion of optical rotatory power, to explore a novel spectral de-multiplexing scheme compared to conventional gratings, prisms and metasurfaces. We design and demonstrate an ‘Nonlocal-Cam’ - a camera that exploits nonlocal dispersion through sampling of polarized spectral states and the application of computational spectral reconstruction algorithms. The Nonlocal-Cam captures information in both laboratory and outdoor field experiments which is unavailable to traditional intensity cameras - the spectral texture of polarization. Merging the fields of nonlocal electrodynamics and computational imaging, our work paves the way for exploiting nonlocal optics of optically active materials in a variety of applications, from biological microscopy to physics-driven machine vision and remote sensing.

A Hydrodynamic Finite-Difference Time-Domain Model of Spatial Dispersion and Surface Modes in Metallic Thin Films

A Hydrodynamic Finite-Difference Time-Domain Model of Spatial Dispersion and Surface Modes in Metallic Thin Films

A robust seismic wavefield modeling method based on minimizing spatial simulation error using L2-norm cost function

To reduce the spatial simulation error generated by the finite difference method, previous researchers compute the optimal finite-difference weights always by minimizing the error of spatial dispersion relation. However, we prove that the spatial simulation error of the finite difference method is associated with the dot product of the spatial dispersion relation of the finite-difference weights and the spectrum of the seismic wavefield. Based on the dot product relation, we construct a norm cost function to minimize spatial simulation error. For solving this optimization problem, the seismic wavefield information in wavenumber region is necessary. Nevertheless, the seismic wavefield is generally obtained by costly forward modeling techniques. To reduce the computational cost, we substitute the spectrum of the seismic wavelet for the spectrum of the seismic wavefield, as the seismic wavelet plays a key role in determining the seismic wavefield. In solving the optimization problem, we design an exhaustive search method to obtain the solution of the norm optimization problem. After solving the optimization problem, we are able to achieve the finite-difference weights that minimize spatial simulation error. In theoretical error analyses, the finite-difference weights from the proposed method can output more accurate simulation results compared to those from previous optimization algorithms. Furthermore, we validate our method through numerical tests with synthetic models, which encompass homogenous/inhomogeneous media as well as isotropic and anisotropic media.

Managing tourism pressure: Exploring tourist traffic patterns and seasonality in mountain national parks to alleviate overtourism effects

Overtourism results in pressure exerted on the natural environment, negative impacts on local communities and lower tourist satisfaction in many protected areas (PAs). This phenomenon has become an increasingly important issue in the management of national parks (NPs) in Poland, especially the mountain ones. Countering and alleviating the effects of overtourism requires developing appropriate management strategies based on the detailed analysis of tourism monitoring data. Having recognized this need, a research was conducted to develop methodology for analyzing daily visitors in NPs (methodological objective), to identify regularities characteristic for visitor flow in mountain NPs in Poland (cognitive objective), and to present the usefulness of monitoring studies in developing effective strategies aimed at tourist traffic management in NPs and their surrounding areas (application objective). The availability of data allowed conducting analyses for three national parks: The Pieniny NP (PNP), The Stołowe Mountains NP (SMNP) and The Tatra NP (TNP).The analyses covering the period 2017–2022 revealed a strong intensification of visitor flow and a growing problem of overtourism in the analyzed areas, primarily in TNP. An increase in maximum daily values, the number of days showing these values, and intensified tourist traffic off-high season were found. Using Daily Visitor Index and Seasonality Index, high-, mid-, and low seasons were identified, including the similarities in traffic seasonality between PNP and SMNP, along with the different nature of TNP, where the winter season was additionally separated. Using the Monthly Visitor Index and Gini coefficient, the long-term variation analysis revealed a reduction in the seasonality of tourism resulting from higher intensity of visits off summer season, in particular the extension of mid-seasons. Due to the growing number of high season visitors and the increasing visitor flow, it is necessary to implement time-limit measures at specific locations and activities aimed at temporal and spatial tourist traffic dispersion. The study shows the development process of overtourism in NPs. It also gives indications that the uneven spatial distribution of visitor flow determines the need for diagnosing overtourism in places and periods with the highest visitation intensity. Such a diagnosis is essential for effective tourism management in NPs and supports decision-making processes for the development of surrounding localities.

Flexible Liquid Crystal Cascade Dielectric Metasurface for Dynamically Controlling Terahertz Beam Deflection

AbstractTerahertz (THz) beam deflection devices with tunable capabilities are highly desired in future wireless communication and radar systems. In this work, a cascaded metadevice is constructed by integrating liquid crystal (LC) into a dielectric metasurface, and then the phase of each meta‐atom is designed to achieve different polarization conversions and spatial phase gradient distributions. Therefore, by changing the polarization of the incident wave or the LC optical axis orientation, an active THz beam deflection device that can actively and independently control the spin state and deflection angle of the output wave can be obtained. Specifically, the output right circularly polarized (RCP) wave is deflected to the +1st diffraction order, and the output left circularly polarized (LCP) wave is deflected to the +2nd diffraction order. The experimental results indicate that the cascaded metadevice exhibits a large angular spatial dispersion in the frequency angle scanning range of +25°–+17.5° (+1st order) and +52.5°–+35° (+2nd order) corresponding to the broadband range of 0.6–0.83 THz. The spin isolation of all diffraction order channels can reach over 10 dB and the maximum diffraction efficiency of 56% can be obtained. In addition, the universality of the proposed LC‐cascaded metasurface design concept has also been verified, providing a feasible path for complex, multifunctional, and active THz wavefront manipulation, thereby exploring more possible application scenarios.

Electron confinement-induced plasmonic breakdown in metals.

Plasmon resonance represents the collective oscillation of free electron gas density and enables enhanced light-matter interactions in nanoscale dimensions. Traditionally, the classical Drude model describes plasmonic excitation, wherein plasma frequency exhibits no spatial dispersion. Here, we show conclusive experimental evidence of the breakdown of plasmon resonance and a consequent metal-insulator transition in an ultrathin refractory plasmonic material, hafnium nitride (HfN). Epitaxial HfN thick films exhibit a low-loss and high-quality Drude-like plasmon resonance in the visible spectral range. However, as the film thickness is reduced to nanoscale dimensions, Coulomb interaction among electrons increases because of electron confinement, leading to the spatial dispersion of plasma frequency. With a further decrease in thickness, electrons lose their ability to shield the incident electric field, turning the medium into a dielectric. The observed metal-insulator transition might carry some signatures of Wigner crystallization and indicates that such transdimensional, between 2D and 3D, films can serve as a promising playground to study strongly correlated electron systems.

Search, transport costs and labour markets in South Africa

AbstractSouth Africa's labour market exhibits a unique equilibrium with one of the highest unemployment rates in the world and yet a low level of informal employment. The unemployment rate has remained high and persistent over recent decades, in spite of the formal demise of the apartheid regime and subsequent transition to democracy in 1994. This paper uses a matching model of the labour market to argue that spatial considerations combined with low productivity of informal work may be responsible for such an outcome. Spatial dispersion inherited from the apartheid regime thins the labour market, creating exclusion and perpetuating spatial segregation. In most developing countries, the result would be higher informal employment. However, spatial dispersion also reduces productivity in the informal sector so that workers prefer to look for a low probability job in the formal sector rather than move to informality. This produces high and persistent unemployment rates. As a result, transportation costs and housing deregulation may become the key factors in improving the working of the labour market in South Africa.

Influence of seasonal variation on spatial distribution of PM2.5 concentration using low-cost sensors.

Fine particulate matter (PM2.5) is one of the major airborne pollutants in urban environments and is associated with severe health impacts. In this study, a dense network of low-cost sensor (LCS) is used to cover large spatial area and detect ambient PM2.5 concentration in Guwahati city. The measurements were conducted at multiple sites in different seasons between July 2022 and June 2023. Seasonal variability significantly influences regional meteorology, aerosol optical depth (AOD), and PM2.5 concentration. The seasonal average PM2.5 concentration was highest during winter (113.05µgm -3), followed by post-monsoon (56.11µgm-3), then pre-monsoon (46.60µgm-3), and least for monsoon (32.36µgm-3) season. The elevated PM2.5 concentrations may be attributed to environmental conditions (low ambient temperature, calm wind, and low planetary boundary layer height) that resulted in the least dispersion of PM2.5. The concentration-weighted trajectory (CWT) analysis identifies the effect of regional (Indo-Gangetic Plain and northeast region) and transboundary (Bay of Bengal, Bangladesh, and northwest Asian countries) transported air masses on urban air quality. Post-monsoon and winter season has a high influence on long-range transported aerosols, whereas the monsoon and pre-monsoon seasons are affected by ocean and land air masses. Changes in surrounding activities and meteorology influence spatial distribution of PM2.5 particles. Elevated PM2.5 concentrations were recorded at in-city and outskirt sites because of the nearby activities (industry and traffic) and build-up area. In meteorology, wind significantly affects spatial dispersion of PM2.5 concentration to the sites located in upwind and downwind directions.

The Influence of Temperature on Charging Effects in Mask During Plasma Etching

ABSTRACTThis research examines the correlation between temperature effects and surface charging problems on a silicon dioxide mask using simulation techniques. The findings of this study validate the significance of considering electron–solid interactions, especially when influenced by varying temperatures. The impacts of temperature changes on the spatial distributions of net charge deposition, electric potential, and electric field are examined. It was noted that the temperature rise leads to an increase in the concentration of positively charged holes near the surface of the mask, thereby diminishing the spatial dispersion of positive potential. This results in a less conspicuous alteration of the mask profile as the temperature increases. This investigation is anticipated to possess substantial significance and offer valuable insights for optimizing mask design.

Efficient Simultaneous Second Harmonic Generation and Dispersive Wave Generation in Lithium Niobate Thin Film

AbstractLithium niobate thin film (LNTF) is a promising platform for ultra‐low loss nonlinear integrated photonics. Here, the simultaneous generation of second harmonic wave (SHW) and dispersive wave (DW) are demonstrated in a single LNTF under the pump of a femtosecond pulse laser, with a conversion efficiency exceeding 25%. The second harmonic generation (SHG) uses the modal phase matching mechanism based on the second‐order nonlinear effect, while the DW generation is based on the perturbations of soliton dynamics caused by self‐phase modulation and higher‐order dispersion. Notably, significant and symmetrical SHW and DW patterns are observed, which exhibit strong spatial dispersion properties. A comprehensive analysis of the phase‐matching conditions are conducted for SHG and DW generation and provide a clear elucidation of the spectral properties of different regions of the emitted light patterns. Additionally, the evolution of the pump light in LNTF is thoroughly investigated, and the solutions of the generalized Schrödinger equation are in good agreement with these experimental results. This work sheds new light on the rich physics of nonlinear optical interactions on LNTF, and by utilizing the synergistic effect of second‐order and third‐order nonlinear effects, this study anticipates achieving efficient and high energy on‐chip broadband frequency conversion and supercontinuum generation across octaves.

Citrus Industry Agglomeration and Citrus Green Total Factor Productivity in China: An Empirical Analysis Utilizing a Dynamic Spatial Durbin Model

In the context of increasingly severe resource and environmental constraints, examining the impact of citrus industry agglomeration on the green total factor productivity (GTFP) of citrus is of great importance for the sustainable development of the citrus industry and is crucial for promoting the green, high-quality growth of China’s agricultural sector. In this study, the global Malmquist–Luenberger productivity index (GMLPI) model was used to measure the GTFP of mandarins and tangerines based on inter-provincial panel data from China’s major citrus-producing regions between 2007 and 2022. The dynamic spatial Durbin model was employed to empirically analyze the effects of citrus industry agglomeration on the GTFP of mandarins and tangerines, including the disaggregation of its spatial spillover effects. The results indicate that, in terms of temporal dynamics, the GTFP, technical progress index (GTC), and technical efficiency index (GEC) of mandarins and tangerines significantly fluctuated, especially during the period from 2007 to 2015. Regional disparities in GTFP and the GTC are more pronounced for mandarins than for tangerines, while the GEC shows greater regional disparities for tangerines than for mandarins. The intensification of citrus industry agglomeration has had a significant positive impact on the GTFP of mandarins and tangerines, both locally and in neighboring regions. The spatial correlation of the green total factor productivity of mandarins and tangerines fluctuated; mandarins showed significant spatial aggregation in some years, while tangerines showed significant spatial dispersion in several years. The local Moran scatterplot further reveals the significant negative spatial autocorrelation of mandarin and tangerine green total factor productivity from 2007 to 2022. The direct, indirect, and total effects of citrus industry agglomeration on the GTFP of mandarins and tangerines are significant and positive in both the short- and long-term, with short-term benefits exceeding long-term effects. Consequently, enhancing regional cooperation and exchange while advancing citrus industry agglomeration is essential for sustained productivity growth.

On the large time behaviour of the solutions of an evolutionary-epidemic system with spatial dispersal.

This paper investigates some properties of the large time behaviour of the solutions of a spatially distributed system of equations modelling the evolutionary epidemiology of a plant-pathogen system. The model takes into account the phenotypic trait and the mutation of the pathogen, which is described by a non-local operator. We roughly speaking prove that the solutions separate the phenotype trait from the spatio-temporal evolution in the large time asymptotic. This feature is obtained by investigating the positive and bounded entire solutions of the problem, that are shown to exhibit such a separation of the variables property, by reformulating them as the positive solutions of suitable integral equations in some ordered Banach space. In addition, some numerical simulations are performed to support our theoretical results.

Genomic epidemiology of early SARS-CoV-2 transmission dynamics in Bangladesh

BackgroundGenomic epidemiology has helped reconstruct the global and regional movement of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). However, there is still a lack of understanding of SARS-CoV-2 spread in some of the world’s least developed countries (LDCs).MethodsTo begin to address this disparity, we studied the transmission dynamics of the virus in Bangladesh during the country’s first COVID-19 wave by analysing case reports and whole-genome sequences from all eight divisions of the country.ResultsWe detected > 50 virus introductions to the country during the period, including during a period of national lockdown. Additionally, through discrete phylogeographic analyses, we identified that geographical distance and population -density and/or -size influenced virus spatial dispersal in Bangladesh.ConclusionsOverall, this study expands our knowledge of SARS-CoV-2 genomic epidemiology in Bangladesh, shedding light on crucial transmission characteristics within the country, while also acknowledging resemblances and differences to patterns observed in other nations.

Microplastics abundance associated with farmland use types and the impact on soil microbial communities: A case study in Southern China

To investigate the impact of various farmland use types on the spatial distribution of microplastics (MPs) and their correlation with microbial communities, 78 soil samples from distinct farmland use types (orchard, paddy field, and vegetable field) in Southern China were examined. Results revealed that the abundance of MPs ranged from 528 to 39,864 items/kg with a mean abundance of 10,562 items/kg, which were primarily 0–30 µm in size. A total of 32 polymer types were identified, with the main polymer being polyethylene terephthalate (PET, 28.8 %), followed by polyvinyl chloride (PVC, 13.5 %) and fluororubber (FKM, 9.5 %). The abundance of MPs was highest in orchard field (8896 ± 5745 items/kg), followed by paddy field (4176 ± 2976 items/kg) and lastly vegetable field (2967 ± 3698 items/kg). Results of 16 S rRNA gene amplicon sequencing showed that the presence of MPs affected the bacterial distribution patterns. Compared with soil bacterial communities, the spatial dispersion and dissimilarity of plasticsphere communities were less variable. Notably, the predicted sequences related to xenobiotics biodegradation and metabolism became more abundant, thereby affecting the ecological function of soil. Overall, this study provides important data for further research on MP ecosystem risks associated with farmland use types.