Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Spatial Distribution”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,477 records · Page 82Linked to original sources
PubMed2006

Speciation and quantitative mapping of metal species in microbial biofilms using scanning transmission X-ray microscopy.

A scanning transmission X-ray microscope illuminated with synchrotron light was used to investigate the speciation and spatial distributions of metals in a microbial biofilm cultivated from river water. Metal 2p absorption edge signals were used to provide metal speciation (through shapes of the absorption spectra) and quantitative spatial distributions of the metal species. This paper presents sample data and describes methods for extracting quantitative maps of metal species from image sequences recorded in the region of the metal 2p edges. Comparisons were made with biochemical characterization of the same region using images recorded at the C 1s and O 1s edges. The method is applied to detailed quantitative analysis of ferrous and ferric iron in a river biofilm, in concert with mapping Ni(II) and Mn(II) species in the same region. The distributions of the metal species are discussed in the context of the biofilm structure. These results demonstrate that soft X-ray STXM measurements at the metal 2p absorption edges can be used to speciate metals and to provide quantitative spatial distribution maps for metal species in environmental samples with 50 nm spatial resolution.

Biofilms↗
PubMed1999

Isolation of epileptiform discharges from unaveraged EEG by independent component analysis.

OBJECTIVE: We propose a method that allows the separation of epileptiform discharges (EDs) from the EEG background, including the ED's waveform and spatial distribution. The method even allows to separate a spike in two components occurring at approximately the same time but having different waveforms and spatial distributions. METHODS: The separation employs independent component analysis (ICA) and is not based on any assumption regarding generator model. A simulation study was performed by generating ten EEG data matrices by computer: each matrix included real background activity from a normal subject to which was added an array of simulated unaveraged EDs. Each discharge was a summation of two transients having slightly different potential field distributions and small jitters in time and amplitude. Real EEG data were also obtained from three epileptic patients. RESULTS: Through ICA, we could isolate the two epileptiform transients in every simulation matrix, and the retrieved transients were almost identical as the originals, especially in their spatial distributions. Two epileptic components were isolated by ICA in all patients. Each estimated epileptic component had a consistent time course. CONCLUSION: ICA appears promising for the separation of unaveraged spikes from the EEG background and their decomposition in independent spatio-temporal components.

Algorithms↗
PubMed1975

[A way to spatial irradiation planning. II. Vectorial demonstration of spatial dose distribution within a single-ray beam and 1st consequences for the practice].

Spatial irradiation planning among other things demands spatial consideration of the dose distribution within the single useful ray beam. From this point of view, the vectorial dose quantities introduced in part I of this paper are reviewed, their correlations are examined as well as their dependences on different influencing quantities e.g. on the rotational position of the wedge filter with the central ray as an axis of rotation. The vectorial description of dose distribution used in this paper, additionally offers information on the total effect upon the inclination of isodose surfaces or curves respectively, caused either simultaneously by different influences (simultaneous effect) or in temporal succession by separate influences (succession effect). The correlations observed can be verified diagrammatically or dosimetrically using simple practical examples. Thus, it is possible for instance to obtain a continuous defined variation of the isodose inclination by varying the weights of the partial doses with successive irradiation with or without a wedge filter.

Humans↗
PubMed1998

Resource distribution, female home range dispersion and male spatial interactions: group structure in a solitary carnivore.

We monitored 74 (41 male, 33 female) radiocollared raccoons (Procyon lotor) from February 1990 to July 1992 on the Welder Wildlife Refuge, Texas, to relate male and female space use to each other and to the spatial distribution of water, a critical resource for raccoons. Female home ranges were spatially aggregated early in the study, when standing water occurred in only a few, widely separated patches on the study site, but were randomly distributed during seasons when water was more widely distributed. Adult females generally foraged and rested independently of other adults. Most adult males were arranged in spatial groups whose home ranges overlapped little with those of adjacent groups. These groups were usually composed of three to four individuals; Doncaster's (1990, J. theor. Biol., 143, 431-443) test for dynamic interaction and visual observations showed that group members tended to associate positively during resting and foraging activities in all seasons. Among raccoons, as among many other mammals, female spatial patterns are apparently determined primarily by resource distribution, whereas male patterns are influenced by the distribution of females. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed2005

Variation of microbiological parameters within planted soil filter for domestic wastewater treatment.

Microbial community structure was assessed in a horizontal subsurface flow planted sand filter treating domestic wastewater with molecular and culture-based methods. The diversity and spatial distribution of the microbial community was investigated using a PCR-DGGE (eubacterial and archaeal primers, ammonia-oxidizing bacteria, and ammonium monooxygenase specific primers), and spread plate and MPN counts. Significant differences were found in the spatial distribution of the microbial community structure. Data analysis revealed that different components of the microbial community possessed different spatial distribution patterns within the filter bed and depending on community type, relationships with soil chemical, and microbiological parameters varied. The most important spatial pattern in microbial community structure within the constructed wetland was related to the depth gradient, followed by differences between inflow and outflow. A comparison of a number of heterotrophic bacteria between inlet and outlet pipes as well as between two sampling depths showed no significant differences. In addition, the variation of the abundance of ammonia-oxidizing bacteria demonstrated no clear spatial pattern.

Bacteria↗
PubMed1992

Body surface Laplacian ECG mapping.

A new noninvasive approach has been developed to resolve spatially distributed cardiac electrical activity by measuring the surface Laplacian of the body surface potential. Computer simulations demonstrate the ability of the Laplacian map compared with the potential map to image spatially distributed dipole sources embedded in a semi-infinite volume conductor. Body surface Laplacian mapping has been implemented in human subjects utilizing dry bipolar Laplacian electrodes and compared with potential maps obtained using the central terminal of each bipolar Laplacian electrode. The body surface Laplacian ECG distribution was found to provide better spatial resolution than the body surface potential distribution. The body surface Laplacian map appears to resolve depolarization and repolarization of different regions of the heart. Further improvements of the body surface Laplacian mapping may permit noninvasive mapping of spatially distributed intracardiac events.

Body Surface Area↗
PubMed2005

Impact of the microscale distribution of a Pseudomonas strain introduced into soil on potential contacts with indigenous bacteria.

Soil bioaugmentation is a promising approach in soil bioremediation and agriculture. Nevertheless, our knowledge of the fate and activity of introduced bacteria in soil and thus of their impact on the soil environment is still limited. The microscale spatial distribution of introduced bacteria has rarely been studied, although it determines the encounter probability between introduced cells and any components of the soil ecosystem and thus plays a role in the ecology of introduced bacteria. For example, conjugal gene transfer from introduced bacteria to indigenous bacteria requires cell-to-cell contact, the probability of which depends on their spatial distribution. To quantitatively characterize the microscale distribution of an introduced bacterial population and its dynamics, a gfp-tagged derivative of Pseudomonas putida KT2440 was introduced by percolation in repacked soil columns. Initially, the introduced population was less widely spread at the microscale level than two model indigenous functional communities: the 2,4-dichlorophenoxyacetic acid degraders and the nitrifiers (each at 10(6) CFU g(-1) soil). When the soil was percolated with a substrate metabolizable by P. putida or incubated for 1 month, the microscale distribution of introduced bacteria was modified towards a more widely dispersed distribution. The quantitative data indicate that the microscale spatial distribution of an introduced strain may strongly limit its contacts with the members of an indigenous bacterial community. This could constitute an explanation to the low number of indigenous transconjugants found most of time when a plasmid-donor strain is introduced into soil.

Agriculture↗
PubMed1989

The generation of spatial population distributions from census centroid data.

"Census data are commonly used in geographical analysis and to inform planning purposes, though at the disaggregate level the basis of enumeration poses difficulties. In this paper an approach to surface generation is described that offers the prospect of revealing an underlying population distribution from centroid-based data which is independent of zonal geography. It is suggested that this can serve a wide variety of analytical, cartographic, and policy purposes, including the creation of spatial indicators of economic and social conditions and enhancing the value of census data. The approach is illustrated by reference to an analysis of part of the valleys of South Wales, in the United Kingdom."

Censuses↗
PubMed2006

Estimated distribution of specific membrane resistance in hippocampal CA1 pyramidal neuron.

It has been suggested that dendritic membrane properties play an important role in a synaptic integration. In particular, the specific membrane resistance, one of membrane properties, has been reported to be non-uniformly distributed in a single neuron, although the spatial distribution of the specific membrane resistance is still unclear. To reveal its non-uniformity in dendrite, we estimated the spatial distribution of specific membrane resistance in a single neuron, based on voltage imaging data, observed optically in hippocampal CA1 slices. As the optically recorded data, we used bi-directional propagations of subthreshold excitatory postsynaptic potentials in dendrite, which were not be reproduced numerically with uniform-specific membrane resistance. By numerical simulations for multi-compartment models with non-uniformity of specific membrane resistance, we estimated that the distribution obeys a step function; the optically recorded data were consistently reproduced for the distribution with a steep decrease in the specific membrane resistance at the distal apical dendrite, which occurs 300-500 microm away from the soma. In the estimated distribution, the specific membrane resistance at the distal side is less than about 10(3) Omegacm(2), whereas the resistance at the proximal side is greater than about 10(4) Omegacm(2). This result implies that the specific membrane resistance decreases drastically at the distal apical dendrite in hippocampal CA1 pyramidal neuron.

2-Amino-5-phosphonovalerate↗
PubMed2000

A dendritic cable model for the amplification of synaptic potentials by an ensemble average of persistent sodium channels.

The persistent sodium current density (I(NaP)) at the soma measured with the 'whole-cell' patch-clamp recording method is linearized about the resting state and used as a current source along the dendritic cable (depicting the spatial distribution of voltage-dependent persistent sodium ionic channels). This procedure allows time-dependent analytical solutions to be obtained for the membrane depolarization. Computer simulated response to a dendritic current injection in the form of synaptically-induced voltage change located at a distance from the recording site in a cable with unequally distributed persistent sodium ion channel densities per unit length of cable (the so-called 'hot-spots') is used to obtain conclusions on the density and distribution of persistent sodium ion channels. It is shown that the excitatory postsynaptic potentials (EPSPs) are amplified if hot-spots of persistent sodium ion channels are spatially distributed along the dendritic cable, with the local density of I(NaP) with respect to the recording site shown to specifically increase the peak amplitude of the EPSP for a proximally placed synaptic input, while the spatial distribution of I(NaP) serves to broaden the time course of the amplified EPSP. However, in the case of a distally positioned synaptic input, both local and nonlocal densities yield an approximately identical enhancement of EPSPs in contradiction to the computer simulations performed by Lipowsky et al. [J. Neurophysiol. 76 (1996) 2181]. The results indicate that persistent sodium channels produce EPSP amplification even when their distribution is relatively sparse (i.e. , approximately 1-2% of the transient sodium channels are found in dendrites of CA1 hippocampal pyramidal neurons). This gives a strong impetus for the use of the theory as a novel approach in the investigation of synaptic integration of signals in active dendrites represented as ionic cables.

Animals↗
PubMed2006

Dynamic distribution of Spatial during mouse spermatogenesis and its interaction with the kinesin KIF17b.

The Spatial gene is expressed in highly polarized cell types, such as epithelial cells in the thymus, neurons in the brain and germ cells in the testis. In this study, we report the characterization and distribution of Spatial proteins during mouse spermatogenesis. Besides Spatial-epsilon and -delta, we show that the newly described short isoform Spatial-beta is expressed specifically in round spermatids. Using indirect immunofluorescence, we detected Spatial in the cytosol of the early round spermatid. By the end stages of round spermatids, Spatial is concentrated at the opposite face of the acrosome near the nascent flagellum and in the manchette during the elongation process. Finally in mature sperm, Spatial persists in the principal piece of the tail. Moreover, we found that Spatial colocalizes with KIF17b, a testis-specific isoform of the brain kinesin-2 motor KIF17. This colocalization is restricted to the manchette and the principal piece of the sperm tail. Further, coimmunoprecipitation experiments of native proteins from testis lysates confirmed Spatial-KIF17b association through the long Spatial-epsilon isoform. Together, these findings imply a function of Spatial in spermatid differentiation as a new cargo of kinesin KIF17b, in a microtubule-dependent mechanism specific to the manchette and the principal piece of the sperm tail.

Animals↗
PubMed1983

Propagation through electrically coupled cells. Effects of regional changes in membrane properties.

The normal process of excitation of the heart involves propagation of action potentials through cardiac regions of different anatomy and different intrinsic membrane properties. Although our understanding of these properties is still incomplete, it is well accepted that the parameters measured from a single cell penetration in an electrical syncytium (e.g., action potential duration, rate of rise, and velocity) reflect not only the properties of that cell but also the electrotonic interactions with other cells to which the recorded cell is electrically coupled. We have used simulation techniques to predict the spatial distribution of action potential parameters resulting from discretely localized alterations in the intrinsic membrane properties of some of the cells of an electrical syncytium. We have shown that the resulting spatial distribution is markedly different for alterations in plateau and pacemaker currents vs. rising phase currents, and that other factors, such as the site of stimulation and the underlying spatial pattern of cell-cell coupling resistance, also modify the spatial distribution of action potential properties resulting from a discrete regional change in intrinsic membrane properties.

Action Potentials↗
PubMed1995

The spatial accuracy of cellular dose estimates obtained from 3D reconstructed serial tissue autoradiographs.

In order to better predict and understand the effects of radiopharmaceuticals used for therapy, it is necessary to determine more accurately the radiation absorbed dose to cells in tissue. Using thin-section autoradiography, the spatial distribution of sources relative to the cells can be obtained from a single section with micrometre resolution. By collecting and analysing serial sections, the 3D microscopic distribution of radionuclide relative to the cellular histology, and therefore the dose rate distribution, can be established. In this paper, a method of 3D reconstruction of serial sections is proposed, and measurements are reported of (i) the accuracy and reproducibility of quantitative autoradiography and (ii) the spatial precision with which tissue features from one section can be related to adjacent sections. Uncertainties in the activity determination for the specimen result from activity losses during tissue processing (4-11%), and the variation of grain count per unit activity between batches of serial sections (6-25%). Correlation of the section activity to grain count densities showed deviations ranging from 6-34%. The spatial alignment uncertainties were assessed using nylon fibre fiduciary markers incorporated into the tissue block, and compared to those for alignment based on internal tissue landmarks. The standard deviation for the variation in nylon fibre fiduciary alignment was measured to be 41 microns cm-1, compared to 69 microns cm-1 when internal tissue histology landmarks were used. In addition, tissue shrinkage during histological processing of up to 10% was observed. The implications of these measured activity and spatial distribution uncertainties upon the estimate of cellular dose rate distribution depends upon the range of the radiation emissions. For long-range beta particles, uncertainties in both the activity and spatial distribution translate linearly to the uncertainty in dose rate of < 15%. For short-range emitters (< 100 microns), such as alpha particle sources, the magnitude of the uncertainty in serial section alignment is comparable with the particle track length. Under these circumstances, dosimetric errors are introduced in proportion to the serial section alignment inaccuracy.

Animals↗
PubMed1990

Influence of crown structural properties on PAR absorption, photosynthesis, and transpiration in Sitka spruce: application of a model (MAESTRO).

The structure of a tree crown can be described by the spatial distribution, inclination, and orientation of all the phytoelements (leaves, twigs, branches, trunk, etc.), and their geometric properties. The following four structural properties have been studied in relation to radiation absorption, photosynthesis, and transpiration using a simulation model named MAESTRO: crown shape, total area of leaves and their spatial distribution within the tree crown, and the leaf inclination angle distribution. It was found that the total area of leaves and their spatial distribution within the tree crown are far more important than the other two properties for radiation absorption, photosynthesis, and transpiration.

Journal Article↗
PubMed1989

Aspects of the lognormal function in the analysis of regional population distribution.

"The spatial structure of population within a metropolitan-area-based region is approached via the population density function, in much the same way as has been undertaken for a city or metropolitan area.... The concern in the balance of the paper is with certain properties lognormal form.... Consideration is given first to properties based on density. The population form of the lognormal function is then derived, and properties based on population are examined. Attention is also given to relationships among density-based and population-based properties." The approach is illustrated using data for London, England, for the period 1971-1981.

Demography↗
PubMed1989

Empirical Bayes procedures for stabilizing maps of U.S. cancer mortality rates.

"The geographic mapping of age-standardized, cause-specific death rates is a powerful tool for identifying possible etiologic factors, because the spatial distribution of mortality risks can be examined for correlations with the spatial distribution of disease-specific risk factors. This article presents a two-stage empirical Bayes procedure for calculating age-standardized cancer death rates, for use in mapping, which are adjusted for the stochasticity of rates in small area populations. Using the adjusted rates helps isolate and identify spatial patterns in the rates. The model is applied to sex-specific data on U.S. county cancer mortality in the white population for 15 cancer sites for three decades: 1950-1959, 1960-1969, and 1970-1979. Selected results are presented as maps of county death rates for white males."

Age Factors↗
PubMed1996

Viability analysis of cryopreserved rat pancreatic islets using laser scanning confocal microscopy.

We have developed a digital image analysis technique to assay the viability of frozen-thawed pancreatic islets by using laser scanning confocal microscopy (LSCM) in conjunction with double fluorescent staining [acridine orange/propidium iodide (AO/PI)]. Freshly isolated rat pancreatic islets were cultured for 18-24 h and then brought to a 2 M concentration of dimethyl sulfoxide (Me2SO) by serial addition at decreasing temperatures. Ice was nucleated in the islet suspension at a defined temperature (-10 degrees C), followed by a controlled period for equilibration and then cooling in a programmable bulk freezer at rates of 0.3, 1, 3, 10 and 30 degrees C/min to -70 degrees C. Samples were then stored in liquid nitrogen. Subsequent to rapid thawing and serial dilution with sucrose solution to remove Me2SO, AO/PI-stained individual islets were prepared for imaging on the LSCM. A series of optical sections through individual stained islets were obtained and processed to obtain high-contrast images at two different wavelengths; 488 nm and 514 nm for viable and damaged tissue, respectively. Image analysis algorithms consisted of template masking, generation of histograms of the pixel intensity profile, and gray level thresholding to obtain binary images. The total percentages of both types of tissue in the islet were computed by summing the two populations in each serial section. The spatial distributions of viable and damaged tissue were calculated from the three-dimensional (3-D) data base for both cultured (control) and cryopreserved islets. The 3-D spatial distributions of damaged and viable tissue in the islets were computed by determining the normalized distance of each viable/damaged voxel from the centroid of the islet volume to a mathematically estimated 3-D superquadric surface used to estimate the outer boundary of the islet. Further, each isolated damaged cell was identified and its volume determined. These studies indicate that cryopreserved islets exhibit shape distortion and a decrease in the numerical density of cells in comparison to unfrozen controls. Maximal survival was observed at the slower cooling rates. Accordingly, damage was found to occur throughout the 3-D islet volume in distinct spatial distributions for islets frozen at the slower and the faster cooling rates. Further, it was found that the volume of the majority of damaged cells identified was consistent with that of cells ranging in diameter from 5 to 9 micrometers.

Algorithms↗
PubMed2003

Membrane-bound stem cell factor is a key regulator in the initial lodgment of stem cells within the endosteal marrow region.

OBJECTIVE: The transmembrane isoform of stem cell factor (tm-SCF) has been implicated in the adhesion of hemopoietic stem cells to the extracellular matrix within the bone marrow microenvironment in vitro. In addition, in vivo SCF has been shown to play a role in cell mobilization and migration. The aim of this study was to determine if SCF is an integral component of the hemopoietic "niche" of the bone marrow in situ. MATERIALS AND METHODS: To analyze the role of tm-SCF in cell lodgment, purified populations of primitive progenitors and hemopoietic stem cells (HSC) were transplanted into a hemopoietic microenvironment devoid of tm-SCF, and the spatial distribution of engrafted cells was analyzed. In addition, populations of HSC were isolated using non-neutralizing and neutralizing antibodies to the SCF receptor c-kit, and their spatial distribution was analyzed post-transplant. RESULTS: The data demonstrated a significant impairment in the lodgment of transplanted cells within the endosteal marrow region in mice lacking tm-SCF, with a reduction of almost 30% by 15 hours post-transplant. The role of tm-SCF was confirmed by analyzing the spatial distribution of HSC isolated using a neutralizing antibody to c-kit. CONCLUSION: The data demonstrate that although tm-SCF does not appear to play a role in the homing of transplanted cells to the bone marrow, it is critical in the lodgment and detainment of HSC within their hemopoietic "niche."

Animals↗