Mean Nearest-neighbor Distance Research Articles

Small Catchment Runoff Sensitivity to Station Density and Spatial Interpolation: Hydrological Modeling of Heavy Rainfall Using a Dense Rain Gauge Network

Precipitation is the most important input to hydrological models, and its spatial variability can strongly influence modeled runoff. The highly dense station network WegenerNet (0.5 stations per km2) in southeastern Austria offers the opportunity to study the sensitivity of modeled runoff to precipitation input. We performed a large set of runoff simulations (WaSiM model) using 16 subnetworks with varying station densities and two interpolation schemes (inverse distance weighting, Thiessen polygons). Six representative heavy precipitation events were analyzed, placing a focus on small subcatchments (10–30 km2) and different event durations. We found that the modeling performance generally improved when the station density was increased up to a certain resolution: a mean nearest neighbor distance of around 6 km for long-duration events and about 2.5 km for short-duration events. However, this is not always true for small subcatchments. The sufficient station density is clearly dependent on the catchment area, event type, and station distribution. When the network is very dense (mean distance < 1.7 km), any reasonable interpolation choice is suitable. Overall, the station density is much more important than the interpolation scheme. Our findings highlight the need to study extreme precipitation characteristics in combination with runoff modeling to decompose precipitation uncertainties more comprehensively.

Proximity model of perceived numerosity.

The occupancy model (OM) was proposed to explain how the spatial arrangement of dots in sparse random patterns affects their perceived numerosity. The model's central thesis maintained that each dot seemingly fills or occupies its surrounding area within a fixed radius ro and the total area collectively occupied by all the dots determines their apparent number. Because the perceptual system is not adapted for the precise estimation of area, it looks likely that the OM is just a convenient computational algorithm that does not necessarily correspond to the processes that actually take place in the perceptual system. As an alternative, the proximity model (PM) was proposed, which instead relies on a binomial function with the probability β characterizing the perceptual salience with which each element can be registered by the perceptual system. It was also assumed that the magnitude of β is proportional to the distance between a dot and its nearest neighbor. A simulation experiment demonstrated that the occupancy area computed according to the OM can almost perfectly be replicated by the mean nearest neighbor distance. It was concluded that proximity between elements is a critical factor in determining their perceived numerosity, but the exact algorithm that is used for the measure of proximities is yet to be established.

Evaluating restoration outcomes through assessment of pollen dispersal, mating system, and genetic diversity

Ecological genetics can provide a novel contribution to assessing the achievement of restoration objectives. We used paternity assignment to infer realized pollen dispersal within, and pollen immigration into, a restoration population of Hakea nitida, a common near‐coastal shrub or small tree in southwest Australia. We compared mating system parameters and genetic diversity with a nearby remnant reference population and assessed genetic divergence among the restoration and reference populations. We found realized pollen dispersal events closely tracked the frequency distributions of the distances between all plants within the restoration focus area. Mean realized pollen dispersal distance (359 m) approached the mean of the distances between all plants (407 m), far exceeding mean nearest neighbor distance (12 m). Maximum realized pollen dispersal distance (869 m) approached the maximum distance between all plants in the study area (1,033 m). Pollen immigration into the restoration study area was limited (4%). The mating system revealed moderate outcrossing rates (tm = 0.861 restoration and tm = 0.745 reference population), with significant and similar biparental inbreeding (tm − ts = 0.180, tm− ts = 0.186) but greater correlated paternity (rpm) in the restoration (0.519) than in the reference (0.188) population. Genetic divergence among the restoration and reference remnant population was moderate (FST = 0.094, DST = 0.239). Patterns of pollen dispersal and mating system parameters imply the attraction of pollinators within the restoration population as a key factor in progressing towards the establishment of self‐sustaining populations.

Variability of isotopic partitioning between sympatric brown trout (Salmo trutta) and European grayling (Thymallus thymallus) in the Loue River (France)

AbstractTrophic partitioning, defining how individuals or populations differ in their resource use, is expected to promote coexistence of sympatric species by reducing resource overlap. We used stable isotope measurements (δ13C and δ15N) to address niche characteristics (δ13C and δ15N ranges, isotope convex hull and standard ellipse areas, mean nearest neighbour distances and trophic positions) and trophic partitioning of sympatric brown trout (Salmo trutta,n = 110) and European grayling (Thymallus thymallus,n = 63) in two sampling locations of a French river. Aquatic resources predominantly fuelled both species, yet both terrestrial resources (TER) and trophic positions (TP) were higher for trout (~36 ± 13% TER, 3.6 ± 0.7 TP) than grayling (~26 ± 9% TER, 2.7 ± 0.6 TP) supporting difference in their trophic niches. Isotope analyses showed that trout had a larger isotope niche than grayling suggesting more opportunistic trophic behaviour. Their isotopic overlapping was higher at the upstream site (isotopic nestedness = 0.8 ± 0.1) than that at the downstream site (isotopic nestedness = 0.4 ± 0.2). Euclidian distances of stable isotopes and TP for the two species increased with salmonid size, while aquatic resource use decreased with salmonid size. These results demonstrate an increase in isotopic niche partitioning and change in trophic attributes with ontogeny. Our study showed that despite relying on similar resources, these two sympatric salmonids exhibited clear trophic differences that were amplified with ontogeny. The consideration of fish ontogenetic dietary shift would hence be a determinant driver of the trophic niche partitioning for these sympatric salmonids.

Assessing the effect of water scarcity on crop selection and spatial pattern of croplands in central Iran

Farming and food production for the increasing world’s population require proper preparation of a diverse range of environmental parameters especially water availability and accessibility. This study investigated the effect of water scarcity on crop selection and spatial pattern of croplands in an agricultural landscape in central Iran. Towards this aim, the main crops including wheat, alfalfa, potato, fruit trees, rice and vegetables were mapped using a combination of decision tree and object-based classifiers and four Landsat 8 images acquired from March 2015 to June 2015 with Kappa Coefficient and Overall Accuracy of 80.16 and 85.37 percent, respectively. Groundwater depth as an indicator of water availability was mapped by interpolating over 13 thousand wells and, according to the ability of farmers and available technologies to extract water, classified into four groundwater level areas (GLA). Finally, spatial pattern of crops in each GLA was investigated using four landscape-level metrics including Mean Patch Size (MPS), Mean Nearest-Neighbor distance (MNN), Contagion index (CONTAG) and Shannon's diversity (SHDI). The results of this study showed that cropping system in drier areas has shifted towards monoculture (crops with fewer water requirements such as wheat) and led to a fragmented and homogeneous landscape with large and low dispersed agricultural units. It was finally concluded that changes in crop selection and spatial pattern of croplands could be considered and applied as a precise and fast indicator of determining water availability and accessibility over large geographical regions in Iran.

Random forest machine learning models for interpretable X-ray absorption near-edge structure spectrum-property relationships

X-ray absorption spectroscopy (XAS) produces a wealth of information about the local structure of materials, but interpretation of spectra often relies on easily accessible trends and prior assumptions about the structure. Recently, researchers have demonstrated that machine learning models can automate this process to predict the coordinating environments of absorbing atoms from their XAS spectra. However, machine learning models are often difficult to interpret, making it challenging to determine when they are valid and whether they are consistent with physical theories. In this work, we present three main advances to the data-driven analysis of XAS spectra: we demonstrate the efficacy of random forests in solving two new property determination tasks (predicting Bader charge and mean nearest neighbor distance), we address how choices in data representation affect model interpretability and accuracy, and we show that multiscale featurization can elucidate the regions and trends in spectra that encode various local properties. The multiscale featurization transforms the spectrum into a vector of polynomial-fit features, and is contrasted with the commonly-used “pointwise” featurization that directly uses the entire spectrum as input. We find that across thousands of transition metal oxide spectra, the relative importance of features describing the curvature of the spectrum can be localized to individual energy ranges, and we can separate the importance of constant, linear, quadratic, and cubic trends, as well as the white line energy. This work has the potential to assist rigorous theoretical interpretations, expedite experimental data collection, and automate analysis of XAS spectra, thus accelerating the discovery of new functional materials.

COMBINING THE MIE-LENNARD-JONES AND MODEL ATOMIC POTENTIALS IN STUDYING THE ELASTIC DEFORMATION OF INTERSTITIAL ALLOY FeSi WITH BCC STRUCTURE UNDER PRESSURE

The mean nearest neighbor distance between two atoms, the Helmholtz free energy and characteristic quantities for elastic deformation such as elastic moduli E, G, K, and elastic constants C11, C12, C44 for binary interstitial alloys with BCC structure under pressure are derived from the statistical moment method. The numerical calculations for interstitial alloy FeSi are performed by combining the Mie-Lennard-Jones potential and the model atomic potential. Our calculated results are compared with other calculations and the experimental data.

Cluster Formation by Mobile Molecular Communication Systems

This paper considers mobile molecular communication systems where mobile bio-nanomachines release signaling molecules to form a cluster of bio-nanomachines. This paper examines how the sensitivity of bio-nanomachines to detect signaling molecules impacts on cluster formation. When the sensitivity is high, each bio-nanomachine reacts to signaling molecules that it releases. When the sensitivity is low, a bio-nanomachine reacts to signaling molecules only when a group of bio-nanomachines collectively releases signaling molecules. We extend a rotational diffusion model to describe the mobility of bio-nanomachines by considering the sensitivity of bio-nanomachines to detect signaling molecules. We also develop measures to characterize formed clusters. Simulation experiment results are shown to demonstrate how the sensitivity of bio-nanomachine to detect signaling molecules impacts the number of clusters formed, the mean cluster size, the mean cluster diameter, and the mean nearest neighbor distance between clusters.

Thermodynamic properties of interstitial alloy FeC with BCC structure under pressure

The analytic expressions for the thermodynamic quantities such as the mean nearest neighbor distance, the free energy, the isothermal compressibility, the thermal expansion coefficient, the heat capacities at constant volume and at constant pressure of binary interstitial alloy with body-centered cubic (BCC) structure and the small concentration are derived by the statistical moment method. The theoretical results are applied to the interstitial FeC alloy in the interval of temperature from 50 to 1000K and in the interval of interstitial atom concentration from 0 to 5%. In special cases, we obtain the thermodynamic quantities of the main Fe metal. Our calculated results for the thermal expansion coefficient and the heat capacity under constant pressure of main metal Fe are in good agreement with experiments.

The melting temperature of BCC perfect ternary alloy FeCrC under pressure

The analytic expressions of the mean nearest neighbour distance, the free energy, the absolute stabilizing temperature of alloy state and the melting temperature for substitution alloy AB with interstitial atom C and body-cantered cubic structure under pressure are derived by the statistical moment method. The theoretical results are applied to alloy FeCrC. Our calculated results are compared with other calculations and experimental data.

STUDY ON ELASTIC DEFORMATION OF INTERSTITIAL ALLOY FeCWITH BCC STRUCTURE UNDER PRESSURE

The analytic expressions of the free energy, the mean nearest neighbor distance between two atoms, the elastic moduli such as the Young modulus E, the bulk modulus K, the rigidity modulus G and the elastic constants C11, C12, C44 for interstitial alloy AB with BCC structure under pressure are derived from the statistical moment method. The elastic deformations of main metal A is special case of elastic deformation for interstitial alloy AB. The theoretical results are applied to alloy FeC under pressure. The numerical results for this alloy are compared with the numerical results for main metal Fe and experiments.

Effect of MCl3 (M=La, U or Sc) component on the local structures and transport properties of LiCl–KCl–MCl3 eutectic: A molecular dynamics study

LiCl–KCl eutectic material is a crucial waste reprocessing candidate for use in molten salt reactors and the major component of spent nuclear fuel. Investigating the structure and thermodynamic transport properties of this eutectic mixed with fission waste cations will provide a better understanding of the reprocessing progress. In this study, molecular dynamic simulations were performed on the molten salts of a LiCl–KCl eutectic mixed with La3+, U3+, or Sc3+ cations, and the mole fractions of the trivalent cations ranged from 0% to 50% at 773 K, 873 K, and 973 K. The local structures (in nearest neighbor distance and coordination numbers) and macroscopic transport properties (self-diffusion, electrical conductivity, and viscosity coefficients) of the three systems have been studied. When the trivalent cation concentration varied from 0 mol% to 50 mol%, the mean nearest neighbor distance of La3+–Cl- and U3+–Cl- increased and the mean nearest neighbor distance of Sc3+–Cl- decreased, and the coordination numbers of La3+ and U3+ increased while the coordination numbers of Sc3+ decreased as the trivalent cation concentrations increased. The trivalent cations were primarily present in the form of [MClx]3−x in diluted mixtures, and they linked to form a network in the viscous regions. The viscosity was primarily affected by the network and followed by a nearly linear increase with the degree of the network in the arbitrary trivalent mixtures. Additional investigation predicted the electrical conductivity and self-diffusion over a broader range; the results indicated that the electrical conductivities were hardly affected by the radius of the given trivalent cation.

Thermodynamic properties of BCC interstitial alloy FeH under pressure

The analytic expressions of the mean nearest neighbor distance, the free energy and the thermodynamic quantities for interstitial alloy AB with body-centered cubic (BCC) structure under pressure are derived by the statistical moment method. The theoretical results are applied to interstitial alloy FeH. Our calculated results for Fe as main metal are in good agreement with experiments.

Analysis of the spatiotemporal correlation between vegetation pattern and human activity intensity in Yancheng coastal wetland, China

Remote sensing images were used to reproduce the changes in wetland vegetation since 1987, and the potential impact of policy changes and human activities on vegetation restoration and biodiversity conservation in coastal wetlands was explored based on the landscape pattern index and the human disturbance index (HDI). The results showed that the vegetation displayed a zonal distribution pattern in which, perpendicular to the coastline early in the study period, the vegetation type changed from coastal wetland to bare mud flat with Spartina alterniflora, Suaeda glauca, and Phragmites australis as well as to constructed wetlands dominated by rice. Under the influence of human activities, the number of patches (NP) and mean nearest-neighbor distance (MNN) between patches gradually increased during the study period, while the mean patch size gradually decreased. The patch density increased from 179 (1987) to 296 patches per ha (2013). Additionally, human activity in the study area intensified. The HDI increased from 0.353 (1987) to 0.471 (1987) and showed positive correlations (R2 > 80%, p < 0.01) with NP and MNN. Human activity, such as changes in land use, resulted in more fragmented vegetation patterns, and the nonzonal (intrazonal) distribution of the vegetation became more obvious in coastal wetlands.

Surveys reveal increasing and globally important populations of south polar skuas and Antarctic shags in Ryder Bay (Antarctic Peninsula)

Despite their importance in ecosystems, population sizes and trends are unknown for many seabirds, including in the Antarctic. Here we report on the first comprehensive survey of south polar skuas Stercorarius maccormicki and Antarctic shags Leucocarbo bransfieldensis in Ryder Bay, and collate previous count data. In austral summer 2017/18, totals of 259 skuas at club sites and 978 occupied skua territories were counted in 2.3 km2 of suitable habitat at Rothera Point and adjacent islands. Based on the mean nearest neighbour distance (23.2 m), skua nest densities were comparable with colonies elsewhere. Long-term monitoring of skuas at Rothera Point indicated considerable annual variation and overall increases of 1.9 and 1.3% per annum, respectively, in breeding pairs from 1975/76 to 2017/18, and occupied territories from 1988/89 to 2017/18. In total, 405 pairs of Antarctic shags bred at two known and one newly discovered colony in 2017/18. Previous counts at the two known colonies indicated substantial annual variation and increases of 5.5 and 3.3% per annum, respectively, from 1985/86 to 2017/18 and 1989/90 to 2017/18. Factors leading to overall increases in both species, and the intermittent seasons of near-complete failure to breed, are unclear, but likely to reflect impacts of environmental change on their marine prey or sea ice. The breeding populations of south polar skuas and Antarctic shags in Ryder Bay represent 10.3 and 3.5%, respectively, of revised global estimates of 9500 and 11,684 breeding pairs. We recommend that the breeding colonies be included as important bird areas (IBAs) and within the Antarctic Specially Protected Area (ASPA) system, and provision made to conserve foraging areas at sea.

Seasonal variation in trophic structure of fish community in Minjiang Estuary based on stable isotope technique.

To study the trophic structure of fish community in Minjiang Estuary, we measured the carbon and nitrogen stable isotope ratios (δ13C and δ15N) of common fish species sampled in winter (January), spring (May), summer (August) and autumn (November) of 2015 by trawling, as well as seven quantitative metrics (ratios range of δ15N, NR; ratios range of δ13C, CR; total area, TA; standard ellipse area, SEAc; average distance of centroid, CD; mean nearest neighbor distance, MNND; standard deviation of nearest neighbor distance, SDNND). The results showed significant differences of δ13C values among all the seasons except between summer and autumn. There were significant differences of δ15N values between spring and other three seasons but no significant difference among summer, autumn, and winter. According to the results of the seven quantitative metrics, trophic structure of common fish community remarkably varied among the four seasons, as TA, SEAc, CR, NR, CD and MNND increased in succession from summer, autumn, winter to spring. Our results indicated that seasonal differences in trophic structure of common fish community were related to the fish spawning migration and the diversity of food source.

Elastic Moduli and Elastic Constants of Alloy AuCuSi With FCC Structure Under Pressure

Abstract This paper studies on the dependence of the mean nearest neighbor distance, the Young modulus E, the bulk modulus K, the rigidity modulus G and the elastic constants C 11, C 12, C 44 on temperature, pressure, the concentration of substitution atoms and the concentration of interstitial atoms for alloy AuCuSi (substitution alloy AuCu with interstitial atom Si) with FCC structure by the way of the statistical moment method (SMM). The numerical results for alloy AuCuSi are compared with the numerical results for main metal Au, substitution alloy AuCu, interstitial alloy AuSi, other calculated results and experiments.

Spatial assessment of the effects of in situ and neighbourhood factors on urban land surface temperature mitigation in a rapidly developing region

ABSTRACTThis study investigates the effect of a set of in situ and neighbourhood factors on urban land surface temperature (LST) in the city of Sari, northern Iran. 200 urban pixels were randomly selected to investigate how LST values in these points linked to their corresponding normalized difference built-up index (NDBI) values as an in situ factor and the percentage of green pixels (%Green), the mean normalized difference vegetation index (M-NDVI), mean patch size (MPS), mean nearest neighbour distance (MNN), and mean shape index (MSI) of green patches located within a set of circular rings around the sample points as neighbourhood factors. The results showed that M-NDVI in the 150-m-radius ring had the highest impact (r = –0.63), and %Green had the longest distance impact (r = 0.24) on mitigating urban LST. MSI and MNN showed the highest association with LST within 300-m to 1000-m-radius rings with the highest r values of about −0.34 and 0.34, respectively. These results indicate that maximum integration of green cover patches with the least MNN value, and the highest degree of MSI is the most effective approach to alleviate urban LST; however, small but dense green cover patches can be suggested as an alternative approach for areas with restricted availability of open spaces.

Study on elastic deformation of substitution alloy AB with interstitial atom C and BCC structure under pressure

The analytic expressions of the free energy, the mean nearest neighbor distance between two atoms, the elastic moduli such as the Young modulus E, the bulk modulus K, the rigidity modulus G and the elastic constants C11, C12, C44 for substitution alloy AB with interstitial atom C and BCC structure under pressure are derived from the statistical moment method. The elastic deformations of main metal A, substitution alloy AB and interstitial alloy AC are special cases of elastic deformation for alloy ABC. The theoretical results are applied to alloy FeCrSi. The numerical results for alloy FeCrSi are compared with the numerical results for main metal Fe, substitution alloy FeCr, interstitial alloy FeSi and experiments.

Quantitative Analysis of Tissue Damage Evolution in Porcine Liver With Interrupted Mechanical Testing Under Tension, Compression, and Shear.

In this study, the damage evolution of liver tissue was quantified at the microstructural level under tensile, compression, and shear loading conditions using an interrupted mechanical testing method. To capture the internal microstructural changes in response to global deformation, the tissue samples were loaded to different strain levels and chemically fixed to permanently preserve the deformed tissue geometry. Tissue microstructural alterations were analyzed to quantify the accumulated damages, with damage-related parameters such as number density, area fraction, mean area, and mean nearest neighbor distance (NND). All three loading states showed a unique pattern of damage evolution, in which the damages were found to increase in number and size, but decrease in NND as strain level increased. To validate the observed damage features as true tissue microstructural damages, more samples were loaded to the above-mentioned strain levels and then unloaded back to their reference state, followed by fixation. The most major damage-relevant features at higher strain levels remained after the release of the external loading, indicating the occurrence of permanent inelastic deformation. This study provides a foundation for future structure-based constitutive material modeling that can capture and predict the stress-state dependent damage evolution in liver tissue.