Spatial Heterogeneity In Structure Research Articles

Chain-like Structures Facilitate Li+ Transport in Concentrated Aqueous Electrolytes: Insights from Ultrafast Infrared Spectroscopy and Molecular Dynamics Simulations.

Highly concentrated aqueous electrolytes have attracted attention due to their unique applications in lithium ion batteries (LIBs). However, the solvation structure and transport mechanism of Li+ cations at concentrated concentrations remain largely unexplored. To address this gap in knowledge, we employ ultrafast infrared spectroscopy and molecular dynamics (MD) simulations to reveal the dynamic and spatial structural heterogeneity in aqueous lithium chloride (LiCl) solutions. The coupling between the reorientation dynamics of the extrinsic probe and the macroscopic viscosity in aqueous LiCl solutions was analyzed using the Stokes-Einstein-Debye (SED) equations. MD simulations reveal that the Cl- and Li+ form chain-like structures through electrostatic interactions, supporting the vehicular migration of Li+ through the chain-like structure. The concentration dependent conductivity of the LiCl solution is well reproduced, where Li(H2O)2+ and Li(H2O)3+ are the dominant species that contribute to the conduction of Li+. This study is expected to establish correlations between ion pair structures and macroscopic properties.

Revealing the structural heterogeneity of metallic glass: Mechanical spectroscopy and nanoindentation experiments

Microstructural heterogeneity is an important issue in understanding the mechanical and physical properties of metallic glasses (MGs). Theoretically, physical aging below the glass transition temperature relax the MGs systems to a lower potential energy state on the potential landscape (PEL) while the cold rolling rejuvenates MGs to a higher potential energy state. In the current work, we systemically turned the structural heterogeneity through dynamic mechanical relaxation and rejuvenation. Correlations among the structural heterogeneity, internal friction, and shear transformation zones (STZs) of the model alloy was connected. Based on the cooperative shear model and statistical analysis, the scale variation of the STZs was revealed. This study demonstrated that the spatial structural heterogeneity can be enhanced by severe plastic deformation which can reduce the energy barrier for STZs activation. And we proposed the barriers decrease and more nucleation sites of STZs from physical aging to rejuvenation, which may be potential mechanism for improving the plasticity in MGs.

Analysing the spatial structure of urban growth across the Yangtze River Middle reaches urban agglomeration in China using NPP-VIIRS night-time lights data

The spatial structure of urban agglomeration reveals the self-organization process of internal factors from the outside. As China ushers into a critical stage with the boosting of urbanization and the booming of the economy, measuring the spatial structure of urban agglomerations is vital to urban planning, regional development, etc. Nighttime stable light data from the National Polar–Orbiting Partnership-Visible Infrared Imaging Radiometer Suite (NPP-VIIRS) night-time light (NTL) series dataset offers a novel source that potentially simulates spatial variations in socio-economic activities. The present study aimed to scientifically guide wide applications of the NPP-VIIRS data to define and measure the evolution of urban agglomeration from a spatial–temporal perspective. Yangtze River Middle Reaches (YRMR) Urban Agglomeration (UA) in Central China was taken as the case study region to systematically identify and measure its spatial configuration of urban growth. The light index model and the method of the rank clock were performed to quantify the dynamics of rank-order distributions. In the meantime, spatial statistics and location coefficient index were used to identify the nature and heterogeneity of spatial structure. According to our findings, NPP-VIIRS data can offer insights into the applications to analyze urbanization processes and reveal the dynamics of urban expansion. The proposed framework will help understand the nature and unbalance of spatial configurations of urban economic growth within urban agglomeration and lay a theoretical basis for the policy-making of regional spatial planning.

Structure evolution of pullulan–alginate edible films during drying studied by low‐field NMR

AbstractThe evolutions of spatial structure for pullulan, alginate, and pullulan–alginate blend aqueous solutions during drying were investigated by low‐field nuclear magnetic resonance. For pullulan solutions, during the first 1,320 min of drying, NMR signal intensity in profiles did not vary with position. Thereafter, the apparent shift of the air–pullulan interface began at 1,440 min, indicating the onset of progressive shrinkage of pullulan samples. Similar shrinkage phenomena were observed for alginate and pullulan–alginate blend solutions. In contrast, spatial structural heterogeneity was observed for alginate solution during drying time from 1,200 to 1,560 min, due to the formation of a skin layer near the air–alginate interface. Based on the change of polymer solutions during drying, two‐stage evaporation process was detected in the aqueous pullulan, alginate, and their blend solutions. Moreover, the evaporation rate of water during the second stage of drying was significantly lower than that of the first stage.Practical applicationsEdible films have emerged as an alternative to synthetic petroleum‐based polymers for food packaging. The evolutions of spatial structure of pullulan–alginate solutions during drying were studied by monitoring of their NMR profiles. Information shown in this study would provide some scientific basis for studying film‐forming mechanism of edible films and their applications in the food field.

Forecasting Urban Forest Ecosystem Structure, Function, and Vulnerability

The benefits derived from urban forest ecosystems are garnering increasing attention in ecological research and municipal planning. However, because of their location in heterogeneous and highly-altered urban landscapes, urban forests are vulnerable and commonly suffer disproportionate and varying levels of stress and disturbance. The objective of this study is to assess and analyze the spatial and temporal changes, and potential vulnerability, of the urban forest resource in Toronto, Canada. This research was conducted using a spatially-explicit, indicator-based assessment of vulnerability and i-Tree Forecast modeling of temporal changes in forest structure and function. Nine scenarios were simulated for 45 years and model output was analyzed at the ecosystem and municipal scale. Substantial mismatches in ecological processes between spatial scales were found, which can translate into unanticipated loss of function and social inequities if not accounted for in planning and management. At the municipal scale, the effects of Asian longhorned beetle and ice storm disturbance were far less influential on structure and function than changes in management actions. The strategic goals of removing invasive species and increasing tree planting resulted in a decline in carbon storage and leaf biomass. Introducing vulnerability parameters in the modeling increased the spatial heterogeneity in structure and function while expanding the disparities of resident access to ecosystem services. There was often a variable and uncertain relationship between vulnerability and ecosystem structure and function. Vulnerability assessment and analysis can provide strategic planning initiatives with valuable insight into the processes of structural and functional change resulting from management intervention.

The bivariate distribution characteristics of spatial structure in natural Korean pine broad‐leaved forest

AbstractAimsSpatial structure is important in describing forest stand structure and change. We present a new method for the quantitative analysis of forest spatial structure based on the relationship of nearest neighbour tree groups.LocationSix hundred m a.s.l., Dongdapo Natural Reserve, Jiaohe, Jilin Province, ChinaMethodsSix plots in three common stand types of natural Korean pine broad‐leaved forest in northeast China were used to validate the method. Each plot measured 100 × 100 m, and all trees with DBH ≥5 cm were marked and located using a Total Station. We calculated bivariate distribution of the structural parameters, uniform angle index, mingling and dominance using Winkelmass and Excel software.ResultsMost trees in the forest were highly mixed by species and randomly distributed. Individuals with high DBH values were typically surrounded by other species; trees within stochastic distribution patterns were usually surrounded by different species; and medium‐sized trees were randomly distributed.ConclusionsThe bivariate distribution of structural parameters can provide more direct and useful information about the heterogeneity of spatial structure than can univariate distributions or other conventional stand descriptors. This could be helpful for selective thinning in continuous cover forest management and in modelling and restoring forests.

Tunable spatial heterogeneity in structure and composition within aqueous microfluidic droplets

In this paper, we demonstrate biphasic microfluidic droplets with broadly tunable internal structures, from simple near-equilibrium drop-in-drop morphologies to complex yet uniform non-equilibrium steady-state structures. The droplets contain an aqueous mixture of poly(ethylene glycol) (PEG) and dextran and are dispensed into an immiscible oil in a microfluidic T-junction device. Above a certain well-defined threshold droplet speed, the inner dextran-rich phase is "stirred" within the outer PEG-rich phase. The stirred polymer mixture is observed to exhibit a near continuum of speed and composition-dependent phase morphologies. There is increasing interest in the use of such aqueous two-phase systems in microfluidic devices for biomolecular applications in a variety of contexts. Our work presents a method to go beyond equilibrium phase morphologies in generating microfluidic "multiple" emulsions and at the same time raises the possibility of biochemical experimentation in benign yet complex biomimetic milieus.

An Official Research Policy Statement of the American Thoracic Society/European Respiratory Society: Standards for Quantitative Assessment of Lung Structure

Keywords: morphometry; stereology; unbiased sampling; reference lung volume; cell volume; surface area; cell size; cell number; in vivo imaging

Spatial dispersion of trees in an old-growth temperate hardwood forest over 60 years of succession

An analysis of spatial dispersion was conducted for individual tree species in the old-growth forest at the Davis-Purdue Research Forest in Indiana. This 20.6 ha stand has been left largely undisturbed by exogenous factors since its acquisition by Purdue in 1917. It is the only long-term study plot of its size for a temperate hardwood forest with x– y coordinates (rectangular plot) for all species above 10 cm diameter. Full censuses have been conducted spanning 60 years (1926, 1976 and 1986). Ripley’s L( t) function revealed that most species are characterized by some form of aggregation, agreeing with a prior evaluation from 1981. Heterogeneity of spatial structure was evident between two large plots, indicating that differences in site quality and history had influenced spatial structure. Shade-intolerant species were numerically dominant and spatially aggregated in 1926 but have declined over the 60-year interval and become more random in spatial dispersion. Shade-tolerant species have increased in number and become more aggregated over time, or they exhibit little change in spatial structure. Examples of the latter include Acer saccharum and Ulmus americana, species that experienced explosive population growth. These contrasting patterns are masked by stand-level patterns that show a trend toward uniformity over the same time frame. These data reveal that changes in dispersion accompany the demographic failure experienced by numerous tree species in Central Hardwood old-growth stands, and these changes may feed back into a negative population cycle and further impede regeneration. The simultaneous manipulation of dispersion and density should be considered as a tool for influencing forest succession and promoting regeneration of desired tree species.

Variation in overstory nitrogen uptake in a small, high-elevation southern Appalachian spruce-fir watershed

High-elevation red spruce (Picea rubens Sarg.) – Fraser fir (Abies fraseri (Pursh) Poir.) forests of the southern Appalachians exhibit considerable spatial heterogeneity in structure, and possibly in N uptake, because of a combination of natural disturbances and heavy fir mortality caused by infestations of the exotic balsam woolly adelgid (Adelges piceae Ratz). The objectives of this study are to determine spatial variability in tree N uptake in a small high-elevation catchment in the Great Smoky Mountains National Park, compare outcomes among calculation methods, and assess the influence of stand and landscape properties on N uptake. Tree N uptake is estimated for fifty 20 × 20 m plots in the Noland Divide Watershed (NDW). Components considered in the calculations are stem growth, foliage increment, and mortality of spruce, fir, and yellow birch (Betula alleghaniensis Britt.) from 1993 and 1998 stand inventories; throughfall N flux measured in summers 1998 and 1999; litterfall N return for 1 year in a subset of 12 plots; tissue N analyses; and atmospheric N deposition and root turnover estimates from the literature. Overstory N uptake varies spatially within NDW, with a CV of 9–41% depending on the calculation method. Variability among methods is even higher, with an almost 15-fold difference between the smallest and largest average overstory uptake estimate (5 vs. 74 kg·ha–1·year–1). Only 5 and 3 kg·ha–1·year–1of N is sequestered in wood and foliar increment, respectively, while 36 kg·ha–1of N returns annually as aboveground litterfall. Uptake and its components are correlated with measures of stand structure but not with elevation or aspect.