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At least 73 records · Page 4Linked to original sources

PubMed1999

The spatial distribution of larvae of Culicoides impunctatus biting midges.

The spatial distribution of Culicoides impunctatus Goetghebuer (Diptera: Ceratopogonidae) larvae was sampled at a site in western Scotland, and geostatistical analyses were used to quantify spatial dependencies. Nested sampling and analysis indicated that most of the spatial variance occurred within distances of 160-640 cm, levelling off at distances >640 cm. Semivariograms for transformed data from three 100 m x 100 m grids showed similar, isotropic patterns for larval counts, soil organic content, soil water content and the distribution of Juncus spp. rushes, with the variance increasing with separation distance. High levels of significance were associated with power models used to describe the semivariograms, which was indicative of the absence of a plateau (or 'sill') in the respective data. Correlation analysis of transformed data revealed significantly positive relationships between larval counts and soil pH, soil percentage organic content, soil percentage water content and also the distribution of Sphagnum spp., Juncus spp. and Myrica gale. There were also significantly negative relationships between larval counts and the distribution of Pteridium aquilinum and all mosses other than Sphagnum spp. The results suggest a far more structured and predictable pattern of C. impunctatus larval sites than previous studies and are discussed in relation to their application in localized Culicoides control and to studies of the mechanisms determining the spatial distribution of C. impunctatus larvae.

Animals↗

PubMed1996

Spatial distribution of visual attention: perceptual sensitivity and response latency.

Studies of the spatial distribution of visual attention have shown that attentional facilitation monotonically decreases in a graded fashion with increasing distance from an attended location. However, reaction time (RT) measures have typically shown broader gradients than have signal detection (SD) measures of perceptual sensitivity. It is not clear whether these differences have arisen because the stages of information processing indexed by RT measures are different from those indexed by SD measures, or whether these differences are due to methodological confounds in the SD studies. In the present set of experiments, the spatial distribution of attention was studied by using a luminance detection task in an endogenous cuing paradigm that was designed to permit accurate calculations of SD and RT measures for targets at cued and uncued locations. Subjects made target-present/absent decisions at one of six possible cued or uncued upper visual hemifield locations on each trial. The results from three experiments suggest that the differences between broad and focal attentional distributions are not the result of different stages of information processing indexed by RT measures as opposed to SD measures. Rather, the differing distributions appear to reflect variations in attentional allocation strategies induced by the perceptual requirements typical of RT paradigms as opposed to SD paradigms. These findings support numerous prior studies showing that spatial attention affects perceptual sensitivity and that the strategic allocation of attention is a highly flexible process.

Adolescent↗

PubMed2003

[Reserves and spatial distribution characteristics of soil organic carbon in Guangdong Province].

Soil organic carbon is the main part of terrestrial carbon reservoir and important part of soil fertility. The spatial distribution and reserves of soil organic carbon are very important for studying soil carbon cycle. According to the data from the second soil survey, soil organic carbon reserves was estimated and its spatial distribution was analysed by using GIS technique. The results showed that the total amount of soil organic carbon is about 17.52 x 10(8) t. The carbon density of laterite, lateritic red soil and red soil in Guangdong Province is 8.83, 10.31, 9.15 kg.m-2, respectively; lower than the mean carbon density of China. The carbon density of yellow soil and rice soil is 12.08, 12.17 kg.m-2, respectively; higher than the mean carbon density of China. Soil carbon density is about 10.44 kg.m-2 in Guangdong. The spatial distribution characteristic of soil organic carbon density in Guangdong is that the carbon density in south Guangdong Province is higher than that in north Guangdong Province, in that soil organic carbon density in north and middle Guangdong Province is 5-10 kg.m-2 and in east Guangdong Province is 10-15 kg.m-2. Soil organic carbon density mostly vary among 5-15 kg.m-2.

Carbon↗

PubMed2005

Expression and spatial distribution of secretin and secretin receptor in human cerebellum.

The expression and spatial distribution of secretin and its receptor in human cerebellum were investigated by in situ hybridization and immunohistochemical techniques. Secretin mRNAs are found in Purkinje cells whereas secretin receptor transcripts are present in Purkinje cells and basket cells in the molecular cell layer. In addition, secretin-immunoreactivities are localized in both the soma and dendrites of Purkinje cells. These data are the first demonstration of the spatial distribution of secretin and its receptor in distinct neurons within the human cerebellum. The cellular localizations of this ligand-receptor pair are consistent with the proposed actions of secretin in the cerebellum of rodents and hence suggest that secretin also serves specific neural functions in the human cerebellum.

Cerebellum↗

PubMed2006

Spatially distributed stochastic systems: Equation-free and equation-assisted preconditioned computations.

Spatially distributed problems are often approximately modeled in terms of partial differential equations (PDEs) for appropriate coarse-grained quantities (e.g., concentrations). The derivation of accurate such PDEs starting from finer scale, atomistic models, and using suitable averaging is often a challenging task; approximate PDEs are typically obtained through mathematical closure procedures (e.g., mean field approximations). In this paper, we show how such approximate macroscopic PDEs can be exploited in constructing preconditioners to accelerate stochastic computations for spatially distributed particle-based process models. We illustrate how such preconditioning can improve the convergence of equation-free coarse-grained methods based on coarse timesteppers. Our model problem is a stochastic reaction-diffusion model capable of exhibiting Turing instabilities.

Algorithms↗

PubMed2001

Spatial distribution and behaviour of laying hens housed in an alternative system.

The spatial distribution and behaviour of perchery housed laying hens were compared at a constant stocking density (18.5 birds/m(2)) in eight pens with colonies of five different sizes (323 birds (N=1), 374 birds (N=2), 431 birds (N=2), 572 birds (N=1) and 912 birds (N=2)). The birds were placed in the perchery when they were 12 weeks old. Observations began when they were 26 weeks old and continued at 8 week intervals until 61 weeks of age. Colony size did not appear to affect the spatial distribution of birds, but more standing behaviour and less feeding behaviour were observed in the smallest and largest colony sizes. Older birds spent more time on the floor areas and less time on perches. Young birds (26-28 weeks) spent more time feeding, foraging, drinking and preening, and less time standing idle than older birds. In the afternoons, there were fewer birds on the perches and more on the floor levels, corresponding with less time spent resting and more time spent performing active behaviours. Birds did not distribute themselves evenly throughout their pens: within specific areas of pens densities varied between 9 and 41 birds/m(2). This variation, which reflects the flux of birds from one part of the pen to another, was greatest for the larger colony sizes, and may have adverse implications for welfare in terms of crowding and hysteria.

Journal Article↗

PubMed1999

Time trends, cohort effect and spatial distribution of cerebrovascular disease mortality in Spain.

STUDY OBJECTIVE: This study describes mortality due to cerebrovascular disease (CVD) in Spain, based on time-series analysis in the period 1951-1995 by age, sex, and cohort of birth; spatial distribution observed for the five-year period 1991 1995, and time-spatial analysis in the period 1992-1995 vs. 1988-1991. Special attention is paid to risk of medium aged population. DESIGN: Longitudinal and cross-sectional observational study. SETTING AND PARTICIPANTS: Spanish population. All mortality data used were taken from official statistics. Time trends and spatial distribution were analyzed using log-linear Poisson regression models. MAIN RESULTS: CVD mortality declined over the last two decades of the study period (1974-1995) by an annual average of 4.16% (95% CI: 3.95-4.36) and 4.00% (95% CI: 3.77-4.24) in men and women, respectively. The downward trends were accelerated in last decade. An excess of male mortality was in evidence. For all age groups mortality declined with more recent cohorts, but the decline was less marked among ages 35 64. Spatial distribution of CVD mortality revealed a north-south pattern, but this is being difuminated by increasing rates in the lower risk provinces. Internationally, Spain ranks midway to low in terms of its overall CVD mortality. CONCLUSIONS: Efforts to reduce CVD incidence and case fatality are the essential prerequisite for any long-term improvement in mortality. Accordingly, further research is called for into current disease morbidity and the risk factors to be targeted at a general population level, nationwide.

Adult↗

PubMed2006

Temporal and spatial distributions of sediment total organic carbon in an estuary river.

Understanding temporal and spatial distributions of naturally occurring total organic carbon (TOC) in sediments is critical because TOC is an important feature of surface water quality. This study investigated temporal and spatial distributions of sediment TOC and its relationships to sediment contaminants in the Cedar and Ortega Rivers, Florida, USA, using three-dimensional kriging analysis and field measurement. Analysis of field data showed that large temporal changes in sediment TOC concentrations occurred in the rivers, which reflected changes in the characteristics and magnitude of inputs into the rivers during approximately the last 100 yr. The average concentration of TOC in sediments from the Cedar and Ortega Rivers was 12.7% with a maximum of 22.6% and a minimum of 2.3%. In general, more TOC accumulated at the upper 1.0 m of the sediment in the southern part of the Ortega River although the TOC sedimentation varied with locations and depths. In contrast, high concentrations of sediment contaminants, that is, total polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs), were found in sediments from the Cedar River. There was no correlation between TOC and PAHs or PCBs in these river sediments. This finding is in contradiction to some other studies which reported that the sorption of hydrocarbons is highly related to the organic matter content of sediments. This discrepancy occurred because of the differences in TOC and hydrocarbon source input locations. It was found that more TOC loaded into the southern part of the Ortega River, while almost all of the hydrocarbons entered into the Cedar River. This study suggested that the locations of their input sources as well as the land use patterns should also be considered when relating hydrocarbons to sediment TOC.

Carbon↗

PubMed1987

Assessment of spatial distribution of growth in the elongation zone of grass leaf blades.

Knowledge about the spatial distribution of growth is essential for understanding the leaf growth process. In grasses the elongation zone is located at the base of the leaf blade and is enclosed by sheaths of older leaves. Assessment of spatial growth distribution, therefore, necessitates use of a destructive method. We used a fine needle to make holes through bases of tillers at the location of the leaf elongation zone of tall fescue (Festuca arundinacea Schreb.), then measured the displacement of the holes after a 6 or 24 h interval. Needle holes caused a 22 to 41% decrease in daily leaf elongation so experiments were conducted to investigate if the spatial distribution of growth in the elongation zone was altered. Leaf elongation rate was reduced similarly when needle holes were made within or above the zone where cell elongation occurs. Distribution of elongation within the zone was the same when estimated by displacement of needle holes or ink marks placed on the epidermis of the elongation zone after surrounding tissue had been removed. Making holes at different locations within the elongation zone did not differentially affect the relative contribution of the damaged or undamaged parts to leaf elongation. These findings demonstrate that needle holes or ink marks in paired leaves can be used to estimate the relative distribution of growth in the elongation zone of undamaged tall fescue leaf blades.

Journal Article↗

PubMed2005

Detection of temporal changes in the spatial distribution of cancer rates using local Moran's I and geostatistically simulated spatial neutral models.

This paper presents the first application of spatially correlated neutral models to the detection of changes in mortality rates across space and time using the local Moran's I statistic. Sequential Gaussian simulation is used to generate realizations of the spatial distribution of mortality rates under increasingly stringent conditions: 1) reproduction of the sample histogram, 2) reproduction of the pattern of spatial autocorrelation modeled from the data, 3) incorporation of regional background obtained by geostatistical smoothing of observed mortality rates, and 4) incorporation of smooth regional background observed at a prior time interval. The simulated neutral models are then processed using two new spatio-temporal variants of the Morany's I statistic, which allow one to identify significant changes in mortality rates above and beyond past spatial patterns. Last, the results are displayed using an original classification of clusters/outliers tailored to the space-time nature of the data. Using this new methodology the space-time distribution of cervix cancer mortality rates recorded over all US State Economic Areas (SEA) is explored for 9 time periods of 5 years each. Incorporation of spatial autocorrelation leads to fewer significant SEA units than obtained under the traditional assumption of spatial independence, confirming earlier claims that Type I errors may increase when tests using the assumption of independence are applied to spatially correlated data. Integration of regional background into the neutral models yields substantially different spatial clusters and outliers, highlighting local patterns which were blurred when local Moran's I was applied under the null hypothesis of constant risk.

Journal Article↗

PubMed2005

Stochastic analysis to assess the spatial distribution of groundwater nitrate concentrations in the Po catchment (Italy).

A large database including temporal trends of physical, ecological and socio-economic data was developed within the EUROCAT project. The aim was to estimate the nutrient fluxes for different socio-economic scenarios at catchment and coastal zone level of the Po catchment (Northern Italy) with reference to the Water Quality Objectives reported in the Water Framework Directive (WFD 2000/60/CE) and also in Italian legislation. Emission data derived from different sources at national, regional and local levels are referred to point and non-point sources. While non-point (diffuse) sources are simply integrated into the nutrient flux model, point sources are irregularly distributed. Intensive farming activity in the Po valley is one of the main Pressure factors Driving groundwater pollution in the catchment, therefore understanding the spatial variability of groundwater nitrate concentrations is a critical issue to be considered in developing a Water Quality Management Plan. In order to use the scattered point source data as input in our biogeochemical and transport models, it was necessary to predict their values and associated uncertainty at unsampled locations. This study reports the spatial distribution and uncertainty of groundwater nitrate concentration at a test site of the Po watershed using a probabilistic approach. Our approach was based on geostatistical sequential Gaussian simulation used to yield a series of stochastic images characterized by equally probable spatial distributions of the nitrate concentration across the area. Post-processing of many simulations allowed the mapping of contaminated and uncontaminated areas and provided a model for the uncertainty in the spatial distribution of nitrate concentrations.

Agriculture↗

PubMed1987

Spatial distribution of twitch and tonic fibres in a snake muscle one myofibre thick.

The spatial distribution of twitch and tonic fibres in a snake muscle one myofibre thick (ventral costocutaneous) has been investigated. It was found that small groups of like fibres were favoured at the expense of larger groups when compared with sequences generated by a computer in which fibres were distributed randomly. The number of times that like fibres occurred next to one another was used as another measure of their spatial distribution. The number of adjacencies of like fibres was less than the expected number of adjacencies determined both by random sequences and by probability theory. The expected number of adjacencies determined by means of random sequences and a priori probability theory were almost identical. This dispersion of like fibres may reflect processes that occur during muscle development and may have functional implications.

Animals↗

PubMed1975

Spatial distribution of rat fungiform papillae.

The objective of this study was to determine the spatial distribution of fungiform papillae on the rat's tongue. Since each fungiform papilla in the rat has a single taste bud, the spatial distribution of fungiform papillae is equivalent to the location of taste buds on the anterior tongue. A mean total number of 187 fungiform papillae per tongue were found which were about equally divided between the two lateral halves of the tongue. Over 50% of the total number of fungiform papillae were located on the tongue tip for an average density of 3.4 papillae/mm2,while the dorsal surface of the tongue had an average density of 1.3 papillae/mm2 of tongue surface. Papillae were absent on the dorsal midline, but a paracentral line of papillae running from anterior to posterior was a consistent finding. Though not identical, the distribution of papillae was essentially the same on different tongues. The functional significance of the papilla distribution is not understood, but electrophysiological experiments show evidence of neural interaction of papillae which are clustered together. The distribution of papillae and the distribution of nerve fibers which innervate them must be evaluated together in order to appreciate the significance of the distribution of fungiform papillae and their associated taste buds.

Animals↗

PubMed1994

[Hyperintensive intramedullary lesions in psychiatric patients. Spatial distribution and psychopathologic symptoms].

In a sample of 130 patients who had undergone MRI (transverse T2-weighted SE sequence) patchy white matter lesions (WML) were documented according to number and spatial distribution in the brain. Ventricle-to-Brain Ratio (VBR) was determined. Configural frequency analysis led to delineation of four patient groups on the basis of WML location: 1. no WML (n = 35), 2. right frontal-temporal WML (n = 23), 3. bifrontal WML (n = 12), 4. WML in all/all but one brain region (n = 16). Psychopathological symptoms reported in the course of a maximum of 3 years were documented by chart review. In the 'pervasive WML' group psychopathological items characteristic of organic brain syndromes prevailed, mean VBR exceeded values in all other groups (ANOVA, p < 0.001). WML spatial distribution accounted for 10.2% of total psychopathological variance. Patient age, but not VBR, had a significant impact on symptom profile (MANCO-VA). When the 'pervasive WML' group was excluded, the finding of a significant effect of WML location on psychopathological symptom profiles was robust. Bifrontal WML were associated with thought incoherence, right frontal-temporal WML with affective symptoms. Findings support an impact of spatial distribution of unspecific WML on psychopathological symptoms in psychiatric patients.

Adult↗

PubMed2001

Infrared microscopic imaging of bone: spatial distribution of CO3(2-).

This article describes a novel technology for quantitative determination of the spatial distribution of CO3(2-) substitution in bone mineral using infrared (IR) imaging at approximately 6 microm spatial resolution. This novel technology consists of an IR array detector of 64 x 64 elements mapped to a 400 microm x 400 microm spot at the focal plane of an IR microscope. During each scan, a complete IR spectrum is acquired from each element in the array. The variation of any IR parameter across the array may be mapped. In the current study, a linear relationship was observed between the band area or the peak height ratio of the CO3(2-) v3 contour at 1415 cm(-1) to the PO4(3-) v1,v3 contour in a series of synthetic carbonated apatites. The correlation coefficient between the spectroscopically and analytically determined ratios (R2 = 0.989) attests to the practical utility of this IR area ratio for determination of bone CO3(2-) levels. The relationship forms the basis for the determination of CO3(2-) in tissue sections using IR imaging. In four images of trabecular bone the average CO3(2-) levels were 5.95 wt% (2298 data points), 6.67% (2040 data points), 6.66% (1176 data points), and 6.73% (2256 data points) with an overall average of 6.38+/-0.14% (7770 data points). The highest levels of CO3(2-) were found at the edge of the trabeculae and immediately adjacent to the Haversian canal. Examination of parameters derived from the phosphate v1,v3 contour of the synthetic apatites revealed that the crystallinity/perfection of the hydroxyapatite (HA) crystals was diminished as CO3(2-) levels increased. The methodology described will permit evaluation of the spatial distribution of CO3(2-) levels in diseased and normal mineralized tissues.

Bone and Bones↗

PubMed2001

Age-related accumulation and spatial distribution of lipofuscin in RPE of normal subjects.

PURPOSE: To characterize the age-related accumulation of lipofuscin in a population of normal subjects, resolve differences in estimated accumulation rates obtained in previous studies, and characterize the spatial distribution of lipofuscin in the normal fundus. METHODS: Spectrophotometric measurements were made at the fovea and 7 degrees temporal to the fovea in 145 normal subjects (age range, 15-80 years). Spatial distribution along the four cardinal meridians was measured in selected subjects by both spectrophotometry and autofluorescence imaging. To minimize contributions of extraneous fluorophores, macular pigment, and melanin, all measurements used excitation at 550 nm, integrating emission between 650 and 750 nm. RESULTS: Lipofuscin fluorescence increased linearly until age 70, then declined. The rate of accumulation was significantly slower in the fovea than at the temporal site; accumulation rates in vivo were greater than previously observed in microscopic studies. Fluorescence was approximately 40% lower in the fovea than at 7 degrees eccentricity and was asymmetrically distributed around the fovea. The fluorescence was maximal at approximately 11 degrees temporally, approximately 7 degrees nasally, approximately 13 degrees superiorly, and approximately 9 degrees inferiorly. At the same eccentricity, fluorescence was always less along the inferior meridian than along any other. CONCLUSIONS: Light absorption by RPE melanin can explain differences between the in vivo and ex vivo estimates of the rate of lipofuscin accumulation. Declining fluorescence at old age may represent removal of atrophic RPE cells. The spatial distribution of lipofuscin generally matches that of rods and reflects, rather than predicts, the pattern of age-related loss of rod photoreceptors.

Adolescent↗

PubMed2002

Modelling bovine trypanosomosis spatial distribution by GIS in an agro-pastoral zone of Burkina Faso.

Modelling of the spatial distribution of bovine trypanosomosis prevalence in Sideradougou district Burkina Faso was performed by using a combination of spatial and statistical analysis. Based on a comprehensive and geographically representative census of herds and farms in the area, more than 2000 cattle were randomly chosen and their blood sampled during field survey. Data on livestock farming practices were recorded for each farm. All data were mapped within a GIS to generate new information on spatial constraints in the area. Surveys results were analysed and serological prevalence data were modelled using logistic regression. The model allowed identification and quantification of risk factors. In a second step the statistical model was used predictively on the entire farm population in the area. This method was successful in predicting the serological prevalence for each individual herd in the sample, from their livestock management patterns and spatial location. Predicted prevalences were represented within the GIS, taking daily movements of animals into account. Spatial distribution of prevalence would illustrate specific locations at risk from an epidemiological viewpoint. It gives evidence that the hydrological network and land occupation patterns in the savanna-type countryside are playing an important part when structuring a so-called "trypanosomosis space".

Animals↗

PubMed2002

Frequency-dependent spatial distribution of human somatosensory evoked neuromagnetic fields.

Using synthetic aperture magnetometry (SAM), we examined the spatial distribution of frequency changes in magnetoencephalography signal rhythms on individual magnetic resonance images following somatosensory stimulation. SAM is a novel statistical spatial filtering method that uses an adaptive beamformer. Electrical stimulation of the right median nerve demonstrated high-frequency event-related synchronization (ERS) in the 50-200-Hz range, consistently localized in the contralateral primary sensorimotor area in all subjects (n=7). Event-related desynchronization (ERD) was demonstrated in the 8-13, 13-25 and 25-50-Hz ranges bilaterally in the area surrounding the central sulcus. The differences in the spatial distribution as well as the frequency bands between ERS and ERD suggest that ERS and ERD reflect the responses of different cell assemblies rather than a frequency shift of the same cell assembly.

Adult↗