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At least 1,045 records · Page 58Linked to original sources
PubMed2003

Chernobyl 137Cs deposition in Austria: analysis of the spatial correlation of the deposition levels.

The semivariogram can provide a description of the spatial correlation of a variable that represents a continuous function of space co-ordinates. Therefore, it is not only useful to improve sampling strategies and validate the collected data, but it can also define the main parameters that are involved in most mapping algorithms. The spatial correlation may, however, change depending on the values of the variable, which is not without consequences on the quality of the maps of radioactive deposition. This work investigates the spatial correlation for different levels of 137Cs deposited in Austria. It is shown that low levels (< 5 kBq/m2) and high levels (> 40 kBq/m2) of radioactivity present less correlation in space than the mid-levels (5-40 kBq/m2). As a result, maps establishing the probabilities to be under or above a specific deposition threshold will have an uncertainty associated to the estimated values that is directly correlated to the different levels of radioactivity.

Air Movements↗
PubMed2003

Spatial and temporal analysis of second-generation anticoagulant rodenticide residues in polecats (Mustela putorius) from throughout their range in Britain, 1992-1999.

Polecats (Mustela putorius) in Britain are currently expanding their range eastwards from Wales to reoccupy central and eastern areas of England. Second-generation anticoagulant rodenticides (SGARs), to which polecats are exposed by eating contaminated prey, are used more extensively in these central and eastern regions, leading to fears of increased exposure, and possible resultant mortality. We measured bromadiolone, difenacoum, flocoumafen and brodifacoum concentrations in the livers of 50 polecats from areas that included newly recolonised habitats and found that at least one SGAR was detected in the livers of 13 out of 37 (35.1%) male and 5 out of 13 (38.5%) female polecats. Difenacoum and bromadiolone were detected most frequently. We then combined these data with measurements on another 50 individuals from earlier studies to create a dataset for 100 polecats collected throughout the 1990s from across the whole of their current range. Using this dataset, we determined if there was any evidence that contamination in polecats had increased during the 1990s and whether animals from England were more contaminated than those from Wales, as might be expected given regional differences in the patterns of SGAR use. Overall, 31 of the 100 polecats analysed to date contained SGAR residues. The incidence was a little higher (40%) in animals that died between January and June and this probably better reflects the overall proportion of animals that are sub-lethally exposed. There was no statistically significant change during the 1990s in the proportion of polecats exposed to SGARs nor any evidence that greater use of SGARs in England resulted in more contamination of polecats. Contrary to expectation, the proportion of animals that contained difenacoum was marginally higher in Wales than elsewhere.

4-Hydroxycoumarins↗
PubMed1998

Regional analysis of the spatial patterns of Fos induction in brain following flurothyl kindling.

We have recently demonstrated that eight, daily flurothyl-induced generalized clonic seizures, followed by a four week stimulus-free interval, results in a long-lasting reduction in generalized seizure threshold and a change in the type of seizure expressed in response to flurothyl from clonic to tonic. There is a progressive increase in the probability that a mouse will express a tonic seizure during the four week interval, suggesting that prior flurothyl seizures initiate a proepileptogenic process that requires time to develop. In this study, the immunohistochemical detection of the c-fos protein (Fos) was used to evaluate whether seizure-induced epileptogenesis resulted in regional differences in the degree of neuronal activation. Fos immunoreactivity was examined 1.5 h following either a single generalized seizure, the last of eight consecutive daily seizures or a retest seizure evoked two weeks after the last of eight seizures. In each condition, generalized seizure behaviours were elicited in C57BL/6 mice using flurothyl and classified as either "forebrain" (face and forelimb clonus) or "brainstem" (running/bouncing, treading, tonic extension). The spatial distribution of Fos induction was compared on the basis of the seizure phenotype and the seizure history. The predominant differences in Fos distribution were found to be related to the type of seizure expressed regardless of the seizure history. Furthermore, the different motor components that make up a "brainstem" seizure could not be distinguished by the pattern of Fos labelling suggesting that multiple convulsive behaviours are mediated by one anatomical system. Finally, Fos induction in the ventromedial hypothalamic nucleus preceded and predicted the change in seizure type from "forebrain" to "brainstem". These data support the concept that separate anatomical systems mediate the expression of the two generalized seizure phenotypes. In addition, the ventromedial nucleus of the hypothalamus may be a point of interaction between the systems and may play a role in seizure-induced neural reorganization.

Animals↗
PubMed1999

A behavioral analysis of the spatial learning deficit induced by the NMDA receptor antagonist MK-801 (dizocilpine) in the rat.

This study analyzes whether the disruptive effects of the noncompetitive NMDA receptor antagonist MK-801 (0.01-0.1 mg/kg s.c.) on spatial learning can be dissociated from sensorimotor disturbances in the rat. Two different modifications of the Morris swim maze task with a hidden underwater platform were used: with or without local cue. Retention was tested either 24 h or 7 days after training as a probe trial (without platform). The present data indicate that MK-801 produces an impairment of spatial learning that cannot be dissociated from motor or sensory mechanisms. These findings support the view that NMDA receptors probably contribute to, but are not essential for, spatial learning in the water maze.

Animals↗
PubMed2002

Size-class differences in genetic structure and individual distribution of Camellia japonica L. in a Japanese old-growth evergreen forest.

Size-class differences in genetic structure and individual spatial distribution were investigated for Camellia japonica within a 1-ha plot in a Japanese old-growth evergreen forest using microsatellite markers. Three size-classes were considered containing plants that were: 30-32.5 cm tall, 103.8 cm-200 cm tall and those that had a diameter at breast height > or =5 cm, designated JV1, JV2, and ADL, respectively. Each size-class contained 174 individuals. Morisita's index of dispersion indicated clumping of individuals was present within all size-classes, with JV2 displaying the highest level. The clumped distribution of JV1 individuals may be a result of limited seed dispersal, while that of JV2 may be attributed to heterogenieties of favourable microsites, such as canopy gaps. There were no significant differences in allele frequencies among size-classes. There were, however, some differences in spatial genetic structure among them. Moran's I spatial autocorrelation analysis revealed clear spatial genetic structure in class JV1 probably due to limited seed dispersal. In class JV2, genetic structure was not observed. Overlapping seed shadows, probably in canopy gaps, may lead to blurred genetic structure in JV2.

Camellia↗
PubMed2003

Analysis of the spatial distribution of cryptosporidiosis in AIDS patients in San Francisco using density equalizing map projections (DEMP).

Environmental transmission of cryptosporidiosis has occurred repeatedly in defined spatial areas during outbreaks of disease attributed, for example, to drinking water contamination. Little work has been done to investigate the possibility of cryptosporidiosis infection in defined spatial areas in non-outbreak (i.e., endemic) settings. This study applies a novel approach to the investigation of the spatial distribution of cryptosporidiosis in AIDS patients in San Francisco. Density equalizing map projection (DEMP) maps were created for nine race/ethnicity-age groups of AIDS patients based on census tract of residence. Additionally, census tracts with a "high density" of cryptosporidiosis cases were identified by applying smoothing techniques to the DEMP maps, and included as a covariate in multivariate Poisson regression analyses of other known risk factors for cryptosporidios. These analyses suggest: (1) cases of cryptosporidiosis among Black and Hispanic AIDS patients, but not among Whites, show a statistically significant non-random spatial distribution (p < 0.05) even after adjustment for the underlying spatial distribution of AIDS patients for these demographic groups, and (2) the risk of residence in these high density census tracts, adjusted for other known risk factors, was not statistically significant (relative risk = 1.27, 95% confidence interval 0.15, 10.53). These results do not support an independent effect of spatial distribution on the transmission of cryptosporidiosis among AIDS patients.

AIDS-Related Opportunistic Infections↗
PubMed1986

Analysis of the spatial organization of microtubule-associated proteins.

We have developed microdensitometer-computer correlation techniques to analyze the arrangement of microtubule arms and bridges (i.e., microtubule-associated proteins [MAPs]). A microdensitometer was used to scan immediately adjacent to the wall of longitudinally sectioned microtubules in positive transparency electron micrographs. Signal enhancement procedures were applied to the digitized densitometer output to produce a binary sequence representing the apparent axial spacing of MAP projections. These enhanced records were analyzed in two ways. (a) Autocorrelograms were formed for each record and correlogram peaks from a group of scans were pooled to construct a peak frequency histogram. (b) Cross-correlation was used to optimize the match between each enhanced record and templates predicted by different models of MAP organization. Seven symmetrical superlattices were considered as well as single axial repeats. The analyses were repeated with randomly generated records to establish confidence levels. Using the above methods, we analyzed the intrarow bridges of the Saccinobaculus axostyle and the MAP2 projections associated with brain microtubules synthesized in vitro. We confirmed a strict 16-nm axial repeat for axostyle bridges. For 26 MAP2 records, the only significant match was to a 12-dimer superlattice model (P less than 0.002). However, we also found some axial distances between MAP2 projections which were compatible with the additional spacings predicted by a 6-dimer superlattice. Therefore, we propose that MAP2 projections are arranged in a "saturated 12-dimer, unsaturated 6-dimer" superlattice, which may be characteristic of a wide variety of MAPs.

Animals↗
PubMed2004

Analysis of the spatial expression pattern of seven Kip related proteins (KRPs) in the shoot apex of Arabidopsis thaliana.

BACKGROUND AND AIMS: Kip-related-proteins (KRPs), negative regulators of cell division, have recently been discovered in plants but their in planta function is as yet unclear. In this study the spatial expression of all seven KRP genes in shoot apices of Arabidopsis thaliana were compared. METHODS: In situ hybridization analyses were performed on longitudinal sections of shoot apices from 2-month-old Arabidopsis plants. KEY RESULTS: The study provides evidence for different expression pattern groups. KRP1 and KRP2 expression is restricted to the endoreduplicating tissues. In contrast, KRP4 and KRP5 expression is mainly restricted to mitotically dividing cells. KRP3, KRP6 and KRP7 can be found in both mitotically dividing and endoreduplicating cells. CONCLUSION: The results suggest differential roles for the distinct KRPs. KRP1 and KRP2 might specifically be involved in the establishment of polyploidy. In contrast, KRP4 and KRP5 might be involved in regulating the progression through the mitotic cell cycle. KRP3, KRP6 and KRP7 might have a function in both types of cell cycle.

Arabidopsis↗
PubMed1999

Spatial and temporal analysis of Ross River virus disease patterns at Maroochy Shire, Australia: association between human morbidity and mosquito (Diptera: Culicidae) abundance.

Notifications of Ross River (RR) virus disease in Maroochy Shire were mapped according to the patient's place of residence, and standardized morbidity ratios were calculated for each of 11 census districts, with 4 areas having higher than average overall rates of RR virus disease notification. Temporal analysis of RR virus disease notifications from each of the 11 areas indicated that epidemics of RR virus disease either were widespread, resulting in higher than average numbers of cases from the majority of areas, or limited to only certain areas. Mosquitoes were collected in CO2 light traps, and the numbers analyzed to determine whether there was any association between mosquito abundance and disease incidence. Seasonal light trap indices for the fresh water-breeding Culex annulirostris Skuse and brackish water-breeding Aedes funereus (Theobald) were correlated positively with disease incidence. There was no apparent association between Aedes vigilax (Skuse) or Aedes procax (Skuse) light trap indices and disease incidence. Identification of human subpopulations with higher than average rates of RR virus disease, and the mosquito vectors associated with virus transmission, should provide a framework for the development of focused and therefore more effective control programs.

Aedes↗
PubMed2005

An ES cell system for rapid, spatial and temporal analysis of gene function in vitro and in vivo.

We describe a versatile genetic system for rapid analysis of mammalian gene function. In this, loss of reporter activity in a novel embryonic stem (ES) cell line enables rapid identification of targeting to the ubiquitously expressed Rosa26 locus. Subsequent regulation of gene activity is governed by a dual regulatory strategy utilizing two drugs, Tamoxifen and Doxycycline. To illustrate this approach, a dominant allele of Smoothened was introduced into this cell line, enabling regulated activation of Hedgehog signaling. By coupling Cre-loxP dependent activation with tetracycline dependent transcription in a single allele, we established a conditional method to control Smoothened activity and neural progenitor specification in differentiating ES cells in vitro and in chimeric embryos in vivo When crossed to an appropriate Cre driver strain, gene activity can also be temporally regulated within a specific cell lineage. This platform will facilitate rapid analysis of gene function in the mouse.

Alleles↗
PubMed2005

Analysis of the spatial distribution between successive earthquakes.

Spatial distances between subsequent earthquakes in southern California exhibit scale-free statistics, with a critical exponent delta approximately 0.6, as well as finite size scaling. The statistics are independent of the threshold magnitude as long as the catalog is complete, but depend strongly on the temporal ordering of events, rather than the geometry of the spatial epicenter distribution. Nevertheless, the spatial distance and waiting time between subsequent earthquakes are uncorrelated with each other. These observations contradict the theory of aftershock zone scaling with main shock magnitude.

Journal Article↗
PubMed1981

Analysis of the spatial organization of the cell: a statistical method for revealing the non-random location of an organelle.

A method is proposed for testing the randomness of the location of an organelle within a given area of a cell section. The approach chosen is to analyse the distance between this organelle and a specific point considered as a point of reference. The method consists of converting this distance into the ratio of one given area to another and comparing the statistical distribution of the converted values to the uniform distribution. This method has the advantage of being valid in the absence of any restrictive assumptions concerning the heterogeneity in size and/or shape of the collection of sections sampled. Detailed examples are given to illustrate the practical use of the method, and its possible extensions are discussed.

Cell Nucleolus↗
PubMed2007

Recent invasion of the mountain birch Betula pubescens ssp. tortuosa above the treeline due to climate change: genetic and ecological study in northern Sweden.

Mountain birch, Betula pubescens ssp. tortuosa, forms the treeline in northern Sweden. A recent shift in the range of the species associated with an elevation of the treeline is commonly attributed to climate warming. Using microsatellite markers, we explored the genetic structure of populations along an altitudinal gradient close to the treeline. Low genetic differentiation was found between populations, whereas high genetic diversity was maintained within populations. High level of gene flow compensated for possible losses of genetic diversity at higher elevations and dissipated the founding effect of newly established populations above the treeline. Spatial autocorrelation analysis showed low spatial genetic structure within populations because of extensive gene flow. At the treeline, significant genetic structure within the juvenile age class at small distances did not persist in the adult age class, indicating recent expansion of young recruits due to the warming of the climate. Finally, seedling performance above the treeline was positively correlated with parameters related to temperature. These data confirm the high migration potential of the species in response to fluctuating environmental conditions and indicate that it is now invading higher altitudes due to the recent warming of the climate.

Age Factors↗
PubMed2002

Analysis of the spatial distribution of polarized light backscattered from layered scattering media.

The scattering of polarized light from a two layer scattering medium is investigated using Monte Carlo simulations. First order and normalized second order moments are used to analyze the spatial properties of the emerging light in different polarization states. Linearly and circularly polarized illumination is used to probe different depths. Absorption and layer thickness are varied and it is demonstrated that the determination of these values is aided by the inclusion of polarization information. The lateral and depth localization of light by polarization subtraction is also quantified. Potential applications of these techniques are burn depth and melanoma thickness measurements.

Biophysical Phenomena↗
PubMed2000

Childhood leukaemia in areas with different radon levels: a spatial and temporal analysis using GIS.

OBJECTIVES: To evaluate the relation between exposure to ground radon levels and leukaemia among children using existing population and disease registers. DESIGN: Ecological correlation study. SETTING: The county of Ostergötland in Sweden. METHODS: Every child born in the county between 1979 and 1992 was mapped to the property centroid coordinates by linking addresses in the population and property registers. Population maps were overlaid with radon maps and exposure at birth and each subsequent year was quantified as high, normal, low or unknown. This was analysed with data from the tumour registry. Standardised mortality ratios (SMRs) were calculated using the age and sex specific rates for Sweden for the year 1995. RESULTS: 90 malignancies occurred among 53 146 children (498 887 person years) who formed the study population. SMRs for acute lymphatic leukaemia (ALL) among children born in high, normal and low risk areas were 1.43, 1.17 and 0.25 respectively. The relative risk for the normal risk group and high risk group as compared with the low risk group was 4.64 (95% CI 1.29, 28.26) and 5. 67 (95% CI 1.06, 42.27). The association between ALL and continued residence at normal or high risk areas showed a similar trend. No association between radon risk levels and any other malignancy was seen. CONCLUSION: Children born in and staying at areas where the risk from ground radon has been classified as low are less likely to develop ALL than those born in areas classified as normal and high risk.

Adolescent↗
PubMed2004

Comparative analysis of the spatial distribution and severity of cerebral microbleeds and old lacunes.

BACKGROUND: Cerebral microbleeds, which result from microangiopathic changes following chronic hypertension, may reflect bleeding-prone microangiopathy. However, the distribution of these lesions has not been compared with that of lacunes, which represent occlusive type microangiopathy. OBJECTIVES: To compare the cerebral distribution of microbleeds and lacunes and correlate their severity. METHODS: The study population comprised 129 hypertensive patients who underwent brain magnetic resonance imaging (MRI), including gradient echo (GE) sequences. Cerebral microbleeds were counted using GE-MRI data, and lacunes were also counted by comparing T1 and T2 weighted MRI. To investigate the distributions, the number of patients with each type of lesion was compared, and the occurrence index (the total number of the specific lesions divided by the total number of patients) was examined statistically. Correlation analyses were done on the relations between the different grades of microbleeds, lacunes, and leukoaraiosis. RESULTS: Cerebral microbleeds and lacunes were found at various foci in the brain, with a preference for the cortico-subcortical region and the deep grey matter. The occurrence index of microbleeds, but not of lacunes, was significantly higher in the cortico-subcortical region than in the deep grey matter. The severity of the microbleeds was positively correlated with the severity of lacunes, and both types of lesion were closely correlated with the degree of leukoaraiosis. CONCLUSIONS: These data suggest that microbleeds and lacunes tend to occur to a similar extent in long standing hypertension, but not necessarily in the same locations.

Aged↗