Increase In Spatial Heterogeneity Research Articles

Effects of increasing spatial resolution on the spatial information content and accuracy of downward surface shortwave radiation

Downward Surface Shortwave Radiation (DSSR) plays a crucial role in ecological, hydrological, and solar photovoltaic studies. The estimation of DSSR at higher spatial resolutions is increasingly popular. However, the impact of increasing spatial resolution on spatial information content and accuracy of DSSR estimates is not well understood. Addressing this knowledge gap, an all-sky DSSR dataset at varying spatial resolutions (0.8° to 0.01°) in China was estimated using MODIS top-of-atmosphere reflectance data. Subsequently, the spatial heterogeneity and accuracy of the DSSR dataset as well as its driving factors were analyzed. The results indicate that the magnitude of the increase in spatial heterogeneity varies across different regions as the spatial resolution increases. On the edge of the Qinghai-Tibet Plateau, the spatial heterogeneity experiences the most significant increase. To quantify the factors driving the spatial heterogeneity of DSSR, the Correlation Coefficients (CC) were calculated between the Coefficient Of Variation (COV) of DSSR and the COVs of relevant factors. In cloudy-sky conditions, the CC between the COV of DSSR and cloud optical thickness ranged from 0.54 to 0.62, whereas the CC between DSSR COV and Column Water Vapor (CWV) COV was between 0.72 and 0.78. Under clear-sky conditions, the COV of CWV, aerosol optical depth, and PM2.5 showed more significant correlations with DSSR COV compared to altitude COV. Validation using ground-based measurements revealed that the accuracy of DSSR decreased at coarser spatial resolutions due to the presence of mixed pixel samples. Moreover, it was demonstrated that a spatial resolution of 0.05° offered the highest cost-effectiveness when estimating DSSR. These insights significantly advance our understanding of the role of spatial resolutions in DSSR estimation and are instrumental in guiding the selection of optimal resolutions for such studies.

Spatiotemporal Evolution and Mechanisms of Habitat Quality in Nature Reserve Land: A Case Study of 18 Nature Reserves in Hubei Province

The contribution of biodiversity to the global economy, human survival, and welfare has been significantly increasing. However, nature reserves have long been subject to a sequence of ecological environmental issues caused by human activities. Therefore, quantitatively assessing the spatiotemporal evolution characteristics of habitat quality due to land use changes and exploring the mechanisms of potential influencing factors can provide a scientific basis for the stable and sustainable development of natural ecosystems. This study aims to analyze 18 nature reserves in Hubei Province to identify the spatiotemporal evolution of habitat quality within these reserves and to explore the influence of multifactorial dynamics from nature, humanity, and policy on this evolution. Initially, the study utilizes land use transition matrices and land use dynamic degree methods to understand the spatiotemporal characteristics of land conversion within the study area. Subsequently, it analyzes the spatiotemporal changes in habitat quality from 2000–2020 based on the InVEST model and tools like spatial autocorrelation (Moran’s I) in ArcGIS. Finally, 14 potential influencing factors are selected from natural environment, socio-human, and policy regulation aspects and analyzed in the Geodetector software to understand the factors affecting the spatiotemporal evolution of habitat quality. The results show that, during the study period, the land area of 18 nature reserves in Hubei Province increased from 2000 to 2020, while the water area decreased. There were slight increases in farmland, construction land, and forest land, with significant decreases in grassland and water areas. This reveals the erosion of water bodies due to artificial lake filling during rapid urbanization, leading to a decline in overall habitat quality within the reserves and a gradual increase in spatial heterogeneity. Among the influencing factors, single-factor influences such as land use intensity and distance to county roads and slopes have a strong negative linear relationship with habitat quality, with land use intensity being the most significant human activity factor. The interaction strength among different types of influencing factors in the bivariate interaction detection results is ranked as follows: the interaction between natural geographical and socio-human factors > the interaction within socio-human factors > the interaction within natural geographical factors. This study has diverged from the past focus on the selection of a single continuous natural reserve as the empirical subject. Consequently, it allows for an integrated analysis of physical geographical dimensions such as locational topography with socio-cultural and policy elements including land use and transportation facilities, thereby facilitating a multifactorial assessment of the interactive impacts on habitat quality.

Restoring spatiotemporal variability to enhance the capacity for dispersal-limited species to track climate change.

Climate refugia are areas where species can persist through climate change with little to no movement. Among the factors associated with climate refugia are high spatial heterogeneity, such that there is only a short distance between current and future optimal climates, as well as biotic or abiotic environmental factors that buffer against variability in time. However, these types of climate refugia may be declining due to anthropogenic homogenization of environments and degradation of environmental buffers. To quantify the potential for restoration of refugia-like environmental conditions to increase population persistence under climate change, we simulated a population's capacity to track their temperature over space and time given different levels of spatial and temporal variability in temperature. To determine how species traits affected the efficacy of restoring heterogeneity, we explored an array of values for species' dispersal ability, thermal tolerance, and fecundity. We found that species were more likely to persist in environments with higher spatial heterogeneity and lower environmental stochasticity. When simulating a management action that increased the spatial heterogeneity of a previously homogenized environment, species were more likely to persist through climate change, and population sizes were generally higher, but there was little effect with mild temperature change. The benefits of heterogeneity restoration were greatest for species with limited dispersal ability. In contrast, species with longer dispersal but lower fecundity were more likely to benefit from a reduction in environmental stochasticity than an increase in spatial heterogeneity. Our results suggest that restoring environments to refugia-like conditions could promote species' persistence under the influence of climate change in addition to conservation strategies such as assisted migration, corridors, and increased protection.

Etching-Engineered Low-Voltage Dielectrophoretic Nanotweezers for Trapping of Single Molecules.

Understanding the functions of biomolecules at the single-molecule level is crucial due to their important and diverse roles in cell regulation. Recently, nanotweezers made of dual carbon nanoelectrodes have been developed for single-cell biopsies by applying a high alternating voltage. However, high electric voltage can induce Joule heating, water electrolysis, and other side effects on cell activity, which may be unfavorable for cellular applications. Here, we report a low-voltage nanotweezer for trapping of single DNA molecules using etching-engineered nanoelectrodes which effectively reduce the minimum trapping voltage by six times. Meanwhile, the low-voltage nanotweezer displays an improved trapping stiffness. Based on the finite element method simulations, we attribute the mechanism for the low-voltage nanotweezers to the increase in spatial heterogeneity and nonuniformity of electric field by etching of quartz near the nanoelectrodes. This work opens a new dimension for noninvasive single-molecule manipulation in solution and potential applications in single-cell biopsies.

Four species of bacteria deterministically assemble to form a stable biofilm in a millifluidic channel

Multispecies microbial adherent communities are widespread in nature and organisms, although the principles of their assembly and development remain unclear. Here, we test the possibility of establishing a simplified but relevant model of multispecies biofilm in a non-invasive laboratory setup for the real-time monitoring of community development. We demonstrate that the four chosen species (Bacillus thuringiensis, Pseudomonas fluorescens, Kocuria varians, and Rhodocyclus sp.) form a dynamic community that deterministically reaches its equilibrium after ~30 h of growth. We reveal the emergence of complexity in this simplified community as reported by an increase in spatial heterogeneity and non-monotonic developmental kinetics. Importantly, we find interspecies interactions consisting of competition for resources—particularly oxygen—and both direct and indirect physical interactions. The simplified experimental model opens new avenues to the study of adherent bacterial communities and their behavior in the context of rapid global change.

Indirect Effects of Grazing on Wind-Dispersed Elm Seeds in Sparse Woodlands of Northern China

Grazing leads to the reduction of biomass and plays a critical role in land degradation in arid and semiarid lands. However, the indirect effects of grazing on the ecosystem, e.g., the effect on seed dispersal, have not been well understood. In this study, we built an agent-based model (ABM) to simulate how grazing intensity affects the seed dispersal of elm trees, one of the native vegetation species of temperate woodlands in semiarid lands. The simulated results from the ABM and observed data from the real world were compared to assess the accuracy and validity of the ABM. The results show that elm seed densities in non-grazing, light, moderate, and heavy grazing lands were 74.97 ± 1.44, 57.63 ± 0.89, 37.73 ± 0.95, and 0.97 ± 0.05 seeds m−2, respectively—an apparently decreasing trend. Moreover, as grazing intensity increased, the values of nugget, sill, and partial sill decreased and the value of the ratio of nugget to sill increased. This study indicates that the grazing indirectly leads to the reduction of elm seed density and the increase of spatial heterogeneity of elm seed on the ground in sparse elm woodlands. Moreover, values of geostatistical indices from the ABM were not significantly different from field observation data except for the ratio of nugget to sill. It shows that ABMs can reasonably replicate the spatial pattern of elm seed densities in the field and thus are useful for simulating long-distance seed dispersal in sandy lands. This finding suggests that the indirect effects of grazing should be considered to effectively protect sparse elm woodlands.

POPULATION DYNAMICS, AGGLOMERATION ECONOMIES AND MUNICIPAL SIZE: A LONG-TERM ANALYSIS

Under the hypothesis that modifications in municipal boundaries and creation (or suppression) of new administrative units reflect a progressive adjustment toward a more balanced distribution of population over space, the present study investigates the long-term relationship (1928-2012) between urban expansion, population dynamics and municipal area in a growing metropolitan region (Athens, Greece). In expanding regions, municipal size is a key variable outlining the amount and spatial concentration of services and infrastructures, resulting to be functionally related to population density, agglomeration factors, land availability to building and characteristic socioeconomic profiles of local communities. A statistical analysis of the relationship between population density and municipal area provides basic knowledge to policy and planning adjustments toward a more balanced spatial distribution of population and land among the local government units. Descriptive statistics, mapping, correlation analysis and linear regressions were used to assess the evolution of such relationship over a sufficiently long time period. The average municipal area in Athens decreased moderately over time, with a slight increase in spatial heterogeneity. Conversely, the average population density per municipality increased more rapidly, with a considerable reduction in spatial heterogeneity. The observed goodness-of-fit of the linear relationship between population density and municipal area increased significantly over time. The empirical results of our study indicate that municipal size has progressively adjusted to population density across metropolitan areas, determining a more balanced spatial distribution of the resident population, which was consolidated by the recent administrative reform of the local authorities in Greece (the so called ‘Kallikratis’ law). Such conditions represent a base for the informed analysis of the spatial structure of local administrative units and they contribute to the debate on the optimal size of municipalities and other administrative districts with relevant impact on both urban and metropolitan scales of governance.

Using in vivo multiphoton fluorescence lifetime imaging to unravel disease-specific changes in the liver redox state

Multiphoton fluorescence lifetime microscopy has revolutionized studies of pathophysiological and xenobiotic dynamics, enabling the spatial and temporal quantification of these processes in intact organs in vivo. We have previously used multiphoton fluorescence lifetime microscopy to characterise the morphology and amplitude weighted mean fluorescence lifetime of the endogenous fluorescent metabolic cofactor nicotinamide adenine dinucleotide (phosphate) (NAD(P)H) of mouse livers in vivo following induction of various disease states. Here, we extend the characterisation of liver disease models by using nonlinear regression to estimate the unbound, bound fluorescence lifetimes for NAD(P)H, flavin adenine dinucleotide (FAD), along with metabolic ratios and examine the impact of using multiple segmentation methods. We found that NAD(P)H amplitude ratio, and fluorescence lifetime redox ratio can be used as discriminators of diseased liver from normal liver. The redox ratio provided a sensitive measure of the changes in hepatic fibrosis and biliary fibrosis. Hepatocellular carcinoma was associated with an increase in spatial heterogeneity and redox ratio coupled with a decrease in mean fluorescence lifetime. We conclude that multiphoton fluorescence lifetime microscopy parameters and metabolic ratios provided insights into the in vivo redox state of diseased compared to normal liver that were not apparent from a global, mean fluorescence lifetime measurement alone.

Detection of spatial-temporal variations in forest canopy surface temperature in response to urbanization: a case study from Longyan, China

Urban forests are fundamental components of localized surface energy budgets. Understanding the factors controlling urban forest surface temperatures (UFSTs) should be helpful in mitigating the negative effects of urbanization on urban energy budgets. This study aimed to identify the factors controlling the spatial-temporal pattern of UFSTs by utilizing a variety of data layers and spatial statistical analysis methods. Our results showed that UFST values become more spatially heterogeneous as urbanization progresses. Elevation and degree of slope were the main factors explaining the increase in spatial heterogeneity. Human activities were also significantly related to variations in UFST. Interactions between human activities and almost all environmental factors were related to higher UFST values. Therefore, human activity directly impacts on the spatial heterogeneity of UFST and indirectly affects variations in landscape patterns. Human activities compatible with ecologically sustainable development should be considered for mitigating the deterioration of urban thermal environments.

Factors influencing exotic species richness in Argentina's national parks.

Exotic species introductions are a global phenomenon and protected areas are susceptible to them. Understanding the drivers of exotic species richness is vital for prioritizing natural resource management, particularly in developing countries with limited resources. We analyzed the influence of coarse resolution factors on exotic species richness (plants, mammals, and birds) in Argentina’s National Parks System. We collected data on native species richness, year of park formation, park area, region, elevation range, number of rivers crossing area boundaries, roads entering area, mean annual rainfall, mean annual temperature, mean annual number of visitors, and Human Influence Index within and surrounding each park. We compiled 1,688 exotic records in 36 protected areas: 83% plants and 17% animals (9.5% mammals, 5.5% birds, 1.5% fishes, 0% amphibians, 0% reptiles). The five parks with the most exotic species (all taxa combined) were in north Patagonia. Exotic grasses were the most common exotic plants, and within animals, lagomorphs and feral ungulates were remarkably widespread. Exotic plant richness was mostly influenced by temperature and native plant richness, while exotic mammal and bird richness was driven mostly by anthropogenic variables, with models explaining 36–45% of data deviance. Most variables that positively influenced exotic taxa were indirectly related to an increase in spatial heterogeneity (natural or anthropogenic), suggesting greater niche space variability as facilitators of exotic richness increase. Additional data are needed to further investigate the patterns and mechanisms of exotic species richness in protected areas, which will help to prioritize the greatest needs of monitoring and management.

Non‐interacting impacts of fertilization and habitat area on plant diversity via contrasting assembly mechanisms

AbstractAimThe local‐ and regional‐based forms of anthropogenic change reducing grassland diversity are generally identified, but these scale‐dependent processes tend to co‐occur with unclear interactive effects. Here, we explicitly test how common local and regional perturbations simultaneously affect plant alpha and beta diversity in a multiyear community assembly experiment using fragments of grassland habitat of various sizes. We hypothesized that local disturbances and decreasing patch size would interact, suppressing local diversity while homogenizing composition among patches.LocationNorth America.MethodsWe conducted a three‐year grassland assembly experiment, factorially manipulating local perturbation (nitrogen addition and mowing) and patch area for 36 patches over 13 ha. We quantified the individual and interactive effects of these local and regional factors on plant alpha and beta diversity within (quadrat scale) and among patches (patch scale). We also used a null model approach to disentangle between stochastic‐ and niche‐based assembly mechanisms.ResultsWe detected a gradient of assembly outcomes driven by two non‐interacting factors—the effects of N fertilization on alpha (negative) and beta (positive) diversity regardless of spatial scale and the scale‐dependant effect of increasing patch size on alpha (positive) and beta (positive) diversity. These effects unfolded over time, with the constraints on richness and composition shifting from dispersal‐based during the first sampling year to perturbation‐and size‐based factors at year two and three. Fertilization effects were driven by a mixture of deterministic (i.e., selection at the species level) and stochastic (i.e., random extinctions) processes resulting in a decline in local richness but an increase in spatial heterogeneity in species composition. Area appeared to influence alpha diversity mainly via stochastic “sampling effect”—larger patches represented a larger sample of the regional pool. Niche‐based processes, however, led to convergence in beta diversity among smaller patches driving a positive overall effect of area on beta diversity.Main conclusionOur results illustrate how diversity regulation in contemporary grasslands can be simultaneously shaped by local and regional factors acting additively but via contrasting assembly mechanisms that operate at different spatial and temporal scales.

Effects of increasing landscape heterogeneity on local plant species richness: how much is enough?

Contemporary landscape ecology continues to explore the causes and consequences of landscape heterogeneity across a range of scales, and demands for the scientific underpinnings of landscape planning and management still remains high. The spatial distribution of resources can be a key element in determining habitat quality, and that in turn is directly related to the level of heterogeneity in the system. In this sense, forest habitat mosaics may be more affected by lack of heterogeneity than by structural fragmentation. Nonetheless, increasing spatial heterogeneity at a given spatial scale can also decrease habitat patch size, with potential negative consequences for specialist species. Such dual effect may lead to hump-backed shape relationships between species diversity and heterogeneity, leading to three related assumptions: (i) at low levels of heterogeneity, an increase in heterogeneity favours local and regional species richness, (ii) there is an optimum heterogeneity level at which a maximum number of species is reached, (iii) further increase in spatial heterogeneity has a negative effect on local and regional species richness, due to increasing adverse effects of habitat fragmentation. In this study, we investigated the existence of a hump-shaped relationship between local plant species richness and increasing forest landscape heterogeneity on a complex mosaic in the French Alps. Forest landscape heterogeneity was quantified with five independent criteria. We found significant quadratic relationships between local forest species richness and two heterogeneity criteria indicators, showing a slight decrease of forest species richness at very high heterogeneity levels. Species richness–landscape heterogeneity relationships varied according to the heterogeneity metrics involved and the type of species richness considered. Our results support the assumption that intermediate levels of heterogeneity may support more species than very high levels of heterogeneity, although we were not able to conclude for a systematic negative effect of very high levels of heterogeneity on local plant species richness.

Biodiversity of transitional waters: species composition and comparative analysis of hard bottom communities from the south-eastern Italian coast

Numerous studies have focused on the soft bottom macrozoobenthos from Mediterranean transitional environments, pointing out a correlation between the variation in environmental parameters and changes occurring in benthic communities. Less attention has been paid to the study of hard bottom organisms settling on both natural and artificial substrates usually present within the basins and often constituting peculiar communities. The ecological role of such communities is remarkable, since they often reach high values of species richness and include bioconstructor organisms able to build true reefs. These reefs can strongly impact the environment, improving biodiversity through the increase of spatial heterogeneity. The present work aims to supplement new faunistic data on five lagoon systems of the south-eastern Italian coast, integrating the still fragmentary knowledge of their macrozoobenthos through the study of hard substrate communities. Sampling was performed on hard substrates colonized by complex benthic communities. The assemblages recorded were then compared in the light of the study sites’ main ecological traits. Our data highlighted the occurrence of a rich benthic macrofauna, with 100 taxa found. This markedly increases the value of species richness reported in the literature for the macrozoobenthos of the study sites. In particular, the species list provided for the Ugento Basins was the first ever compiled for this site. In spite of their geographical proximity, the investigated sites, according to their diverse environmental conditions, showed substantial differences as regards their respective macrozoobenthic communities.

Shrubs increase soil resources heterogeneity along semiarid grass slopes in the Loess Plateau

The response of soil resources to the introduction of shrubs in semiarid grasslands is essential to the distribution of vegetation and revegetation. To determine how soil resources respond to the introduction of shrubs in semiarid grassland slopes, we investigated in the Loess Plateau of China the spatial patterns of soil organic matter (OM), total and extractable nitrogen (N) and phosphorous (P) in grass slopes with shrubs introduced (SS) and in adjacent native grass slopes without shrub introduction (GS). Three soil types, Loessial, Castanozems and Skeletal, were examined to test the influences of soil type on the effects of shrubs on soil resources. Shrub introduction in grass slopes induced significant increases in soil resources, especially in clay rich soils. The best fit models of spatial structure for soil variables differed with soil types in both GS and SS. A Gaussian model described most of the soil resources in GS, but Spherical and Gaussian models were useful for describing spatial structure in SS. Shrub introduction increased the magnitude of spatial heterogeneity, but reduced the effective range of spatial correlation for most variables (OM, NO3−, total P and extractable P) along grass slopes. The increase of spatial heterogeneity was greater in sandy soil than in clay rich soil. The relationships among OM, N and P were not influenced by shrub introduction. Taken together, the results of this study indicated that shrubs increased soil resources heterogeneity, and these increases varied with soil types in semiarid grass slopes of the Loess Plateau. These changes might cause degradation of the ecosystem in the area, suggesting that shrubs should be avoided in favor of implementing natural rehabilitation with native grasses for the semiarid grass slopes of the Loess Plateau.

Effects of Fiber Type and Size on the Heterogeneity of Oxygen Distribution in Exercising Skeletal Muscle

The process of oxygen delivery from capillary to muscle fiber is essential for a tissue with variable oxygen demand, such as skeletal muscle. Oxygen distribution in exercising skeletal muscle is regulated by convective oxygen transport in the blood vessels, oxygen diffusion and consumption in the tissue. Spatial heterogeneities in oxygen supply, such as microvascular architecture and hemodynamic variables, had been observed experimentally and their marked effects on oxygen exchange had been confirmed using mathematical models. In this study, we investigate the effects of heterogeneities in oxygen demand on tissue oxygenation distribution using a multiscale oxygen transport model. Muscles are composed of different ratios of the various fiber types. Each fiber type has characteristic values of several parameters, including fiber size, oxygen consumption, myoglobin concentration, and oxygen diffusivity. Using experimentally measured parameters for different fiber types and applying them to the rat extensor digitorum longus muscle, we evaluated the effects of heterogeneous fiber size and fiber type properties on the oxygen distribution profile. Our simulation results suggest a marked increase in spatial heterogeneity of oxygen due to fiber size distribution in a mixed muscle. Our simulations also suggest that the combined effects of fiber type properties, except size, do not contribute significantly to the tissue oxygen spatial heterogeneity. However, the incorporation of the difference in oxygen consumption rates of different fiber types alone causes higher oxygen heterogeneity compared to control cases with uniform fiber properties. In contrast, incorporating variation in other fiber type-specific properties, such as myoglobin concentration, causes little change in spatial tissue oxygenation profiles.

Effects of Salsola passerina shrub patches on the microscale heterogeneity of soil in a montane grassland, China

The spatial distributions of water and nutrients were examined in the desert grassland of Helan Mountain to test the hypothesis that the expansion of shrub patches in the grassland is associated with the degree of soil heterogeneity. The results showed that shrub patches significantly increase the water content and nutrient enrichment in surface soil (0–10 cm), and increase the microscale heterogeneity of the soil. Geostatistics analysis indicated that the autocorrelation distances of soil properties, such as water, total nitrogen (TN), organic matter (OM), and pH, are larger than the mean canopy size of Salsola passerina (30±12.3 cm), but less than in the control (enclosed) grassland. This suggests that the spatial distribution of soil properties may be associated with biotic processes in the shrub patch site. Furthermore, the smaller autocorrelation distances (65–382 cm) found for all soil properties indicate an increase in spatial heterogeneity, or potentially degradation, in the enclosed grassland. Based on these results, a conceptual model of montane grassland degradation processes following overgrazing was developed.

Plugging Space into Predator‐Prey Models: An Empirical Approach

Extrapolating ecological processes from small-scale experimental systems to scales of natural populations usually entails a considerable increase in spatial heterogeneity, which may affect process rates and, ultimately, population dynamics. We demonstrate how information on the heterogeneity of natural populations can be taken into account when scaling up laboratory-derived process functions, using the technique of moment approximation. We apply moment approximation to a benthic crustacean predator-prey system, where a laboratory-derived functional response is made spatial by including correction terms for the variance in prey density and the covariance between prey and predator densities observed in the field. We also show how moment approximation may be used to incorporate spatial information into a dynamic model of the system. While the nonspatial model predicts stable dynamics, its spatial equivalent also produces bounded fluctuations, in agreement with observed dynamics. A detailed analysis shows that predator-prey covariance, but not prey variance, destabilizes the dynamics. We conclude that second-order moment approximation may provide a useful technique for including spatial information in population models. The main advantage of the method is its conceptual value: by providing explicit estimates of variance and covariance effects, it offers the possibility of understanding how heterogeneity affects ecological processes.

Effects of Acute Atrial Dilation on Heterogeneity in Conduction in the Isolated Rabbit Heart

Atrial dilation plays an important role in the development and persistence of atrial fibrillation (AF). The mechanisms by which atrial dilation increases the vulnerability to AF are not fully understood. In 11 isolated rabbit hearts, the right atrium was acutely dilated by increasing the intra-atrial pressure from 2 to 9 and 14 cm H2O. A rectangular mapping array of 240 electrodes (spatial resolution 0.5 mm) was positioned on the free wall of the right atrium. The atrium was paced from four different sites at intervals of 240 and 125 msec. At normal atrial pressure (2 cm H2O), conduction was uniform in all directions with an anisotropy ratio between 1.5 and 1.7. Increasing the pressure to 9 cm H2O decreased the normalized conduction velocity during rapid pacing by 18%. The incidence of areas of slow conduction and conduction block increased from 6.6% and 1.6% to 10.2% and 3.3%. At 14 cm H2O, conduction velocity decreased by 31% and the percentage of slow conduction and block further increased to 11.5% and 6.6% (P < 0.001). The appearance of lines of intra-atrial block was largely dependent on the pacing site. Whereas during pacing at the cranial part of the crista terminalis no increase in conduction delays occurred, pacing from the low right atrium unmasked several lines of block oriented parallel to the major trabeculae and the crista terminalis. In an additional series of six hearts the left atrium also was mapped. The effect of dilation of the left atrium was comparable to that of the right atrium. Increasing the atrial pressure to 14 cm H2O increased the amount of intra-atrial conduction block threefold to fourfold. Acute atrial dilation results in slowing of conduction and an increase of the amount of intra-atrial conduction block. The increase in spatial heterogeneity in conduction was related to the anisotropic properties of the atrial wall.

Effect of Pressure on Conformational Dynamics in Polyethylene: A Molecular Dynamics Simulation Study

Molecular dynamics simulations have been used to delineate the pressure dependence of conformational dynamics in polyethylene. Chain dynamics have been studied as a function of pressure (0−25 kbar) at 400 K and as a function of temperature (280−450 K) at an elevated pressure of 10 kbar. The volumetric glass transition is found isobarically (10 kbar) at ∼315 K and is considerably elevated from the ∼220 K atmospheric pressure value. On increasing pressure at constant temperature, the system displays several signatures indicative of the vitrification process that are complementary to those previously found to be associated with lowering of temperature. These include a large increase in autocorrelation function relaxation times, divergence of the relaxation times from conformational transition rates, an increase in spatial heterogeneity of the distribution of conformational transition rates over the various bonds, and an increase in self-correlation of the conformational transitions. Isobarically at high pres...

Risk assessment model for a waterborne outbreak of cryptosporidiosis

Counts of Cryptosporidium oocysts in 100L volumes of treated water are simulated for conditions representative of a waterborne outbreak in a surface water-derived supply. Assuming oocysts act independently during infection, the risk of infection is directly related to the arithmetic mean oocyst density in the water supply, which is in turn related to the total number of oocysts which break through treatment. Spatial/temporal heterogeneity of oocyst concentrations in the treated water contributes to monitoring programmes based on “spot-sampling” underestimating the arithmetic mean oocyst density and hence the risk of infection. This could contribute to the reported lack of a clear association between oocyst concentrations measured in drinking water supplies and the risk of waterborne outbreak of cryptosporidiosis in the population. An increase in spatial heterogeneity of oocysts during treatment could also contribute to an overestimation of the net oocyst removal by treatment.