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At least 145 records · Page 8Linked to original sources
PubMed1987

Relation of olfactory EEG to behavior: spatial analysis.

The hypothesis that odor-specific patterns of mitral cell activity during odor discrimination might be found in the corresponding spatial patterns of electroencephalogram (EEG) amplitude over a surgically accessible segment of the bulbar surface was tested in rabbits with chronically implanted electrode arrays. The spatial spectrum of the bulbar EEG was derived and compared with the spectrum predicted for the granule cell generator. Spatial filters were devised to identify, enhance, or remove the granule cell contribution to the EEG. Spatial deconvolution was applied to the filtered granule cell activity patterns to correct for distortion caused by volume conduction. The results indicated that the bulb generated odor-specific spatial patterns in rabbits trained to discriminate between two odors. The odor-specific information was not localizable to subsets of channels. This suggested that the discriminative output of the bulb involved the entire structure, even though the receptor input was delivered to limited subsets of mitral cells.

Animals↗
PubMed2005

Spatial analysis of the distribution of leprosy in the State of Ceará, Northeast Brazil.

The aim of this study was to describe spatial patterns of the distribution of leprosy and to investigate spatial clustering of incidence rates in the state of Ceará, Northeast Brazil. The average incidence rate of leprosy for the period of 1991 to 1999 was calculated for each municipality of Ceará. Maps were used to describe the spatial distribution of the disease, and spatial statistics were applied to explore large- and small-scale variations of incidence rates. Three regions were identified in which the incidence of leprosy was particularly high. A spatial gradient in the incidence rates was identified, with a tendency of high rates to be concentrated on the North-South axis in the middle region of the state. Moran's I statistic indicated that a significant spatial autocorrelation also existed. The spatial distribution of leprosy in Ceará is heterogeneous. The reasons for spatial clustering of disease rates are not known, but might be related to an heterogeneous distribution of other factors such as crowding, social inequality, and environmental characteristics which by themselves determine the transmission of Mycobacterium leprae.

Brazil↗
PubMed2004

Spatial analysis of 3' phosphoinositide signaling in living fibroblasts: I. Uniform stimulation model and bounds on dimensionless groups.

Fluorescent protein probes now permit spatial distributions of specific intracellular signaling molecules to be observed in real time. Mathematical models have been used to simulate molecular gradients and other spatial patterns within cells, and the output of such models may be compared directly with experiments if the binding of the fluorescent probe and the physics of the imaging technique are each incorporated. Here we present a comprehensive model describing the dynamics of 3' phosphoinositides (PIs), lipid second messengers produced in the plasma membrane in response to stimulation of the PI 3-kinase signaling pathway, as monitored in the cell-substratum contact area using total internal reflection fluorescence microscopy. With this technique it was previously shown that uniform stimulation of fibroblasts with platelet-derived growth factor elicits the formation of axisymmetric 3' PI gradients, which we now characterize in the context of our model. We find that upper and lower bounds on the relevant dimensionless model parameter values for an individual cell can be calculated from four well-defined fluorescence measurements. Based on our analysis, we expect that the key dimensionless group, the ratio of 3' PI turnover and diffusion rates, can be estimated within approximately 20% or less.

Animals↗
PubMed2004

Spatial analysis of extreme precipitation in Sweden 1961-2000.

Extreme daily precipitation in Sweden for the years 1961-2000 is analyzed with respect to spatial scale, regional variations and associated weather types. Correlograms based on a lag distance of 30 km estimated the spatial scale of variation of the annual mean precipitation, the 99th percentile of daily precipitation and the average of annual maximum daily precipitation to 100 km, 60-100 km and 40-70 km, respectively. Regions of correlation with respect to precipitation at 82 stations during days of extreme events are identified through Maximum-Likelihood Factor Analysis. Eleven factors are found to provide the optimum factor solution. Weather types for the days of extreme events are determined by an objective classification scheme, based on daily sea level pressure, which is modified by subjective inclusion of fronts. In total, 63% of the extreme events occurred during cyclonic weather types, 32% during frontal, 3% during directional and 2% during anticyclonic types. The frequency of the weather types during extreme events varied between the regions however.

Climate↗
PubMed2006

Spatial analysis of potential carcinogenic risks associated with ingesting arsenic in aquacultural tilapia (Oreochromis mossambicus) in blackfoot disease hyperendemic areas.

This work analyzed spatially potential carcinogenic risks associated with ingesting arsenic (As) contents in aquacultural tilapia (Oreochromis mossambicus) in coastal regions of southwestern Taiwan, where the blackfoot disease prevails. Sequential indicator simulation (SIS) was used to reproduce As exposure distributions in groundwater based on their three-dimensional variability. A target cancer risk (TR) associated with ingesting As in aquacultural tilapia was calculated to evaluate the potential risk to human health. Owing to sparse measured data, Monte Carlo simulation and SIS properly accounted for the uncertainty of assessed parameters. The probabilistic risk assessment formulated suitable strategies under various remedial stages. Aquacultural regions with high risks were mapped to elucidate the safety of groundwater use at different depths. Many TRs determined from the risks at the 75th and 95th percentiles exceed one millionth in the regions, indicating that ingesting tilapia farmed in the highly As-polluted regions poses potential cancer threats to human health. The 75th percentile of TR is considered in formulating a remedial strategy for the aquacultural use of groundwater in the preliminary stage. Additionally, this study suggests reducing the use of groundwater in aquaculture or changing the depths from which groundwater is withdrawn in the areas with high risks of cancer.

Animals↗
PubMed1991

Temporal and spatial analysis of fields generated by eddy currents in superconducting magnets: optimization of corrections and quantitative characterization of magnet/gradient systems.

We propose methods for the spatial and temporal characterization of time-dependent magnetic fields generated by eddy currents after switching gradients. For an on-line determination of the temporal variations of the fields, we extract two terms from the unresolved signal of an extended sample, describing the time evolution of a frequency shift gamma delta Bz(t) and of a decay constant k(t). This procedure allows us to optimize interactively the multiexponential pre-emphasis as well as any spectral volume selection method with respect to eddy currents. Additionally, we suggest an imaging sequence which allows us to determine the spatial distribution of eddy current fields at a chosen time-point after any gradient sequence to be tested. Expansion of these eddy currents fields into spherical harmonic functions proves the existence of a higher order terms, which cannot be corrected by a standard pre-emphasis device, where time constants and amplitudes are adjusted on the X, Y, Z, and Z0 coils. The proposed numerical analysis gives a tool to characterize any magnet/gradient system quantitatively with respect to eddy current performance.

Magnetic Resonance Imaging↗
PubMed1998

Dynorphin mRNA expression in dorsal horn neurons after traumatic spinal cord injury: temporal and spatial analysis using in situ hybridization.

Dynorphin, an endogenous opioid, may contribute to secondary nervous tissue damage following spinal cord injury. The temporal and spatial distribution of preprodynorphin (PPD) mRNA expression in the injured rat spinal cord was examined by in situ hybridization. Rats were subjected to traumatic spinal cord injury at the T13 spinal segment using the weight-drop method. Motor function of these rats was evaluated by their ability to maintain their position on an inclined plane. Two double-labeling experiments revealed that increased PPD mRNA and dynorphin peptide expression were found exclusively in dorsal horn neurons. Neurons exhibiting an increase in the level of PPD mRNA were concentrated in the superficial laminae and the neck of dorsal horn within several spinal segments from the epicenter of the injury at 24 and 48 h after injury. A number of neurons showing increased PPD mRNA were found in gray matter adjacent to the injury areas. Segments caudal to the injury site exhibited a long-lasting elevation of PPD mRNA in neurons, compared to the rostral segments. The number of neurons expressing PPD mRNA in each rat was significantly positively correlated with its motor dysfunction. These findings suggest that increased expression of dynorphin mRNA and peptide in dorsal horn neurons occurs after traumatic spinal cord injury. This also supports the hypothesis that the dynorphin has a pathological role in secondary tissue damage and neurological dysfunction after spinal cord injury.

Animals↗
PubMed2006

Spatial analysis of fatal and injury crashes in Pennsylvania.

Using injury and fatal crash data for Pennsylvania for 1996-2000, full Bayes (FB) hierarchical models (with spatial and temporal effects and space-time interactions) are compared to traditional negative binomial (NB) estimates of annual county-level crash frequency. Covariates include socio-demographics, weather conditions, transportation infrastructure and amount of travel. FB hierarchical models are generally consistent with the NB estimates. Counties with a higher percentage of the population under poverty level, higher percentage of their population in age groups 0-14, 15-24, and over 64 and those with increased road mileage and road density have significantly increased crash risk. Total precipitation is significant and positive in the NB models, but not significant with FB. Spatial correlation, time trend, and space-time interactions are significant in the FB injury crash models. County-level FB models reveal the existence of spatial correlation in crash data and provide a mechanism to quantify, and reduce the effect of, this correlation. Addressing spatial correlation is likely to be even more important in road segment and intersection-level crash models, where spatial correlation is likely to be even more pronounced.

Accidents, Traffic↗
PubMed2006

Spatial analysis of campylobacter infection in the Canadian province of Manitoba.

BACKGROUND: The study describes population level variations in campylobacter incidence within the Canadian province of Manitoba, and the relationship to sociodemographic and landscape related characteristics. Using data derived from the Manitoba Health Public Health Branch communicable disease surveillance database, the study applied a number of spatial and ecological techniques to visualize, explore and model campylobacter incidence for the years 1996 to 2004. Analytical techniques used in the study included spatial smoothing, the spatial scan statistic, the Gini coefficient, and Poisson regression analysis. RESULTS: The study demonstrated marked and statistically significant geographic variability in the rates of campylobacter incidence in Manitoba.. The incidence of campylobacter was observed to be significantly higher in populations living in rural and agricultural areas of the province, with the highest rates occurring in populations living in proximity to high densities of farm animals (cows, pigs, chickens). The study also observed that the age specific pattern of campylobacter incidence in rural Manitoba was very different than the urban pattern, with the incidence rate in the 0-4 year age group seven times higher in rural Manitoba than in the City of Winnipeg. CONCLUSION: The study demonstrates the value of a deploying a diverse set of spatial techniques to better understand the dynamics of an enteric disease such as campylobacter infection. The study concludes that there may be three distinct mechanisms for the transmission of campylobacter in Manitoba which are operating simultaneously. These include broad population exposure to a centralized food system endemically infected with the campylobacter organism, exposure to local level factors such as farm animals or contaminated water, and exposure to campylobacter infection through foreign travel.

Adolescent↗
PubMed2003

A spatial analysis of county-level variation in hospitalization rates for low back problems in North Carolina.

Hospitalization rates for low back problems vary widely. In previous non-spatial analyses, population-level socioeconomic and health resource characteristics have explained little of the variation in rates. This study examines geographic variation in hospitalization rates for low back problems while controlling for spatial dependence in the data. County-level surgical and medical hospitalization rates were calculated using North Carolina hospital (USA) discharge data from 1990-92. Non-spatial and spatial regression models were estimated using socioeconomic and health resource predictors. Both surgical and medical rates varied significantly among the 100 counties. Non-spatial models explained 62% of variation in log-transformed surgical rates and 66% of variation in log-transformed medical rates; however, residuals showed significant spatial dependence. Spatial lag models were therefore applied. Using simple contiguity spatial weights, surgery rates increased with higher percent urban population, primary care physician density, and discharge rate for other causes, and decreased with higher percent college graduates, percent disabled, occupied hospital bed density, and unoccupied hospital bed density. There was a nonlinear relationship between surgery rates and percent employed in heavy lifting/transportation industries. Medical rates increased with higher other-cause discharge rate and with MRI/CT scanner availability, and decreased with higher percent urban population, percent nonwhite population, percent in heavy lifting/transportation industries, and unoccupied hospital bed density. The results show that population-level socioeconomic and health resource characteristics are important determinants of variation in low back hospitalization rates. Independent of these variables, a separate spatial process produces geographic clustering of high-rate counties. Spatial effects are important and should be considered in small area analyses.

Catchment Area, Health↗
PubMed1978

The social behavior of a marmoset (Saguinus fuscicollis) group III. Spatial analysis of social structure.

The social behavior, and particularly the spacing patterns, of a marmoset (Saguinus fuscicollis) group in a semi-naturalistic enclosure were observed for 14 months. Data analysis revealed various changes as the group grew in size from four to eventually six members. Weekly mean distances between the adult pair supported a spatial measure for estrus for the female. Group dispersion, mean squared distance between all possible pairs, seemed to vary with the age composition of the group. Factor analysis of location correlation matrices by 4-week blocks resulted in age-related subgroupings. Each of the adult pair formed an independent subgroup except for behavioral estrus and early infant care periods when they formed one subgroup. The offspring, initially attached to the adults, gradually moved into juvenile/subadult subgroups. Increasing spatial independence was shown as an animal approached adulthood at 24 months of age.

Animals↗
PubMed2005

Plasmodium falciparum spatial analysis, western Kenya highlands.

We carried out a population-based study to determine the unbiased, age-specific Plasmodium falciparum prevalence, asexual and sexual parasite density, and spatial distribution to establish rates of infection at a site in western Kenya. Three cross-sectional surveys were carried out in western Kenya highlands. Blood samples were taken from 1,388 persons from 6 months to 75 years of age. Parasite prevalence and densities in the population decreased with age and distance from valley bottoms. Children from 1 to 4 years of age had the highest parasite prevalence (38.8%-62.8%); in adults, prevalence declined to 2.9%-24.1%. Malaria prevalence declined by an average of 19% from July to December 2002 across age groups. These observations suggest that parasite transmission is intense at this altitude. Asexual parasite density indicated clustering near major vector breeding habitats. Variability in seasonal prevalence indicates transmission instability and susceptibility to epidemics.

Adolescent↗
PubMed2006

Spatial analysis and mapping of malaria risk in Malawi using point-referenced prevalence of infection data.

BACKGROUND: Current malaria control initiatives aim at reducing malaria burden by half by the year 2010. Effective control requires evidence-based utilisation of resources. Characterizing spatial patterns of risk, through maps, is an important tool to guide control programmes. To this end an analysis was carried out to predict and map malaria risk in Malawi using empirical data with the aim of identifying areas where greatest effort should be focussed. METHODS: Point-referenced prevalence of infection data for children aged 1-10 years were collected from published and grey literature and geo-referenced. The model-based geostatistical methods were applied to analyze and predict malaria risk in areas where data were not observed. Topographical and climatic covariates were added in the model for risk assessment and improved prediction. A Bayesian approach was used for model fitting and prediction. RESULTS: Bivariate models showed a significant association of malaria risk with elevation, annual maximum temperature, rainfall and potential evapotranspiration (PET). However in the prediction model, the spatial distribution of malaria risk was associated with elevation, and marginally with maximum temperature and PET. The resulting map broadly agreed with expert opinion about the variation of risk in the country, and further showed marked variation even at local level. High risk areas were in the low-lying lake shore regions, while low risk was along the highlands in the country. CONCLUSION: The map provided an initial description of the geographic variation of malaria risk in Malawi, and might help in the choice and design of interventions, which is crucial for reducing the burden of malaria in Malawi.

Cluster Analysis↗
PubMed1998

Birth profile for the city of rio de janeiro: a spatial analysis

This article analyzes the birth profile by neighborhood in the city of Rio de Janeiro, using data for 1994 from the Data Base on Live Births. Pattern maps were employed in addition to the Moran I statistical test to detect spatial clustering. Proportions of live newborns with an Apgar score of 8-10, cesareans, mothers with greater than a secondary school education, and teenage mothers displayed visually identifiable spatial patterns and significant spatial self-correlation. Low birth weight displayed a random pattern, indicating that on this scale of analysis, this indicator does not distinguish risk groups, despite its unquestionable predictive value for child morbidity/mortality at the individual level. The Apgar score, despite the high number of non-responses in some neighborhoods, showed a pattern more consistent with the distribution of the neighborhoods and should thus be used more extensively. The methodology expanded the available knowledge on the birth profile in the city, showing potential for orienting measures devoted to specific geographic areas.

Journal Article↗
PubMed2006

Secular values and the location of religion: a spatial analysis of an English medical centre.

What do contemporary controversies in healthcare reveal about secular values and the location of religion within an English medical centre? Using a socio-spatial methodology designed to break open ideological perspectives and normative values, we analyse the doctor-patient relationship, complementary and alternative medicine, and an issue that bridges the two, evidence-based medicine. In the physical, social and mental spaces of the medical centre we uncover the traces of religious activity and roles, and of alternative therapeutic regimes often informed by spiritual or religious systems. Furthermore, we disclose the heterogeneity of values that comprise the secular worldview of one group of contemporary general practitioners.

Cluster Analysis↗
PubMed1998

Spatial analysis of lymphatic filariasis distribution in the Nile Delta in relation to some environmental variables using geographic information system technology.

Geographic information system (GIS) was used to analyze the spatial distribution of filariasis in the Nile Delta. The study involved 201 villages belonging to Giza, Qalubiya, Monoufiya, Gharbiya, and Dakahliya governorates. Villages with similar microfilarial (mf) prevalence rates were observed to cluster within 1-2 km distance, then, clustering started to decrease significantly with distance up to 5 km (Pearson correlation coefficient = -0.98). the likelihood of negative and high prevalence villages being contiguous was very low (approximately 1.8%, n = 612 village-pairs) indicating homogeneity in disease processes within the defined spatial scales. Of the villages located within 2 km from the main Nile branches (n = 46), 95% exhibited low prevalence. In addition, the spatial pattern of mf prevalence was shown to be negatively associated with annual rainfall and relative humidity, while it was positively associated with annual daily temperature. Average mf prevalence in warmer, relatively drier areas receiving 25 mm of rain was significantly higher (3.9%) than that in less warmer but more humid areas receiving 50 mm of rain (1.6%) (P < 0.0001). Based on the results of the present study, GIS was used to generate a "filariasis risk map" that could be used by health authorities to efficiently direct surveillance and control efforts. This investigation identified some of the factors underlying filariasis spatial pattern, quantified clustering and demonstrated the potential of GIS application in vector-borne disease epidemiology.

Animals↗
PubMed2004

Spatial analysis and indicator building for metal accumulation in mosses.

Mosses are used as passive accumulation monitors for metal accumulation in terrestrial ecosystems. Under leadership of the Federal Agency for Environmental Protection Germany took part in the previous European-wide moss monitoring campaigns 1990, 1995 and 2000. The investigations accomplished thereby cannot be presented completely in this article. The remarks rather concentrate on methodical aspects of the statistical data analysis. In Chapter 2 the design of data collection is summarized. Chapter 3 treats the geostatistical analysis and transformation of point data to areal information. Chapter 4 describes the aggregation of the element-specific metal concentrations in mosses to a spatially and temporally differentiated indicator of metal accumulation by means of descriptive and multivariate statistics. The work presented is only a small part of geostatistics and multivariate statistics which fit for analysis of moss monitoring data. Taking the results presented here as a basis, the following steps would further be of great importance: cluster-analytic evaluation of the results of the Moss Monitoring 1990 and 1995, detailing the cluster results using additional empirical and location describing information (e.g. moss species, ecoregions, site and species specific variability of metal accumulation) as well as optimizing the indicator buildung by testing of multivariate statistical regression models (e.g. Classification and Regression Trees).

Bryophyta↗