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PubMed1990

Spatial distribution and temporal changes of pulmonary thallium uptake in myocardial perfusion studies.

Spatial distribution and temporal changes in pulmonary thallium uptake were assessed in 24 normal subjects and 35 patients with coronary artery disease (CAD). In studies carried out directly after stress and 3 h later, pulmonary Tl uptake was assessed as body surface area corrected absolute pulmonary uptake in the upper, middle and lower right lung regions, and in the total right lung and upper left lung. Pulmonary/myocardial (PM) uptake ratios for these 5 regions were calculated as mean pulmonary/mean background-corrected myocardial uptake. Additionally, wash-out was assessed for each region and for the myocardium. In normal subjects, the initial pulmonary Tl uptake, the PM ratios and Tl wash-out were greater in the lower lung regions than in the upper. In the late studies, no significant differences in Tl content or PM ratios were found among the regions. In patients with CAD, initial pulmonary Tl uptake and PM ratios were greater in the lower than in the upper regions, and higher than for the normal subjects in all pulmonary regions (P less than 0.001). Tl wash-out was significantly higher in the low and middle regions versus the upper region (P less than 0.001) and higher in all regions than in normal subjects (P less than 0.001). In the late studies no significant differences in Tl content or PM ratios were found between any pulmonary regions. Pulmonary Tl content was, in all regions, higher in CAD than in normal subjects (P less than 0.01), as were the PM ratios (P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Coronary Disease↗
PubMed2005

Spatial distributions of Cryptosporidium oocysts in porous media: evidence for dual mode deposition.

Spatial distributions of Cryptosporidium parvum oocysts in columns packed with uniform glass-bead collectors were measured over a broad range of physicochemical conditions. Oocyst deposition behavior is shown to deviate from predictions based on classical colloid filtration theory (CFT) in the presence of repulsive (unfavorable) colloidal interactions. Specifically, CFT tends to predict greater removal of oocysts (less transport) than that observed in controlled laboratory experiments. Comparison of oocyst retention with results obtained using polystyrene latex particles of similar size suggests that mechanisms controlling particle deposition are the same in both systems. At a given ionic strength, the deposition of Cryptosporidium oocysts is generally greater than that of the microspheres; however, this discrepancy is partly attributable to large differences in oocyst and microsphere zeta potentials. A dual deposition mode (DDM) model is applied which considers the combined influence of "fast" and "slow" oocyst deposition due to the concurrent existence of favorable and unfavorable oocyst-collector interactions. Model simulations of retained oocyst profiles and suspended oocyst concentration at the column effluent are consistent with experimental data. Because classic CFT does not account for the effect of dual mode deposition (i.e., simultaneous "fast" and "slow" oocyst deposition), these observations have important implications for predictions of oocyst transport in subsurface environments, where repulsive electrostatic interactions predominate. Supporting elution experiments further suggest that specific surface interactions between oocyst wall macromolecules and the glass bead collectors could retard or even completely inhibit oocyst release upon perturbation in solution chemistry.

Animals↗
PubMed2004

Phenology, sex ratio, and spatial distribution among dioecious species of Trichilia (Meliaceae).

The flowering, sex ratio, and spatial distribution of four dioecious species of Trichilia (Meliaceae) were studied in a semi-deciduous forest in southeastern Brazil. All reproductive trees (T. clausseni, T. pallida and T. catigua) with dbh > or = 5 cm within a 1-ha plot were collected, sexed, mapped and, for individuals of each species, the distances to the nearest neighbour of the same and opposite sex were measured. For the shrub species T. elegans (dbh < 5 cm), all reproductive individuals were sampled randomly in 10 samples of 10 x 10 m. The reproductive phenology was observed at weekly to monthly intervals from May 1988 to January 1990. The species are strictly dioecious, did not present any sex-mixed trees or sex switching during the study, and sex ratio did not differ significantly from 1 : 1. The size distributions and the relative size variation were not significantly different between sexes. There was no significant segregation or clumping between individuals of either sex and no fruit production without pollination. Onset of flowering and flowering peak were synchronous between male and female plants for all species studied. Flower synchrony was related to outcrossing and pollinator attraction rather than climatic factors.

Flowers↗
PubMed1997

Spatial distribution of synaptically activated sodium concentration changes in cerebellar Purkinje neurons.

The spatial distribution of Na(+)-dependent events in guinea pig Purkinje cells was studied with a combination of high-speed imaging and simultaneous intracellular recording. Individual Purkinje cells in sagittal cerebellar slices were loaded with either fura-2 or the Na+ indicator sodium binding benzofuran isophthalate (SBFI) with sharp electrodes or patch electrodes on the soma or dendrites. [Na+]i changes were detected in response to climbing fiber and parallel fiber stimulation. These changes were located both at the anatomically expected sites of synaptic contact in the dendrites and in the somatic region. The variation in time course of these [Na+]i changes in different locations implies that Na+ enters at the synapse and diffuses rapidly to locations of lower initial [Na+]i. The synaptically activated somatic [Na+]i changes probably reflect Na+ entry through voltage-sensitive Na+ channels because they were detected only when regenerative potentials were recorded in the soma. [Na+]i changes in response to antidromically or intrasomatically evoked Na+ action potentials also were confined to the cell body. These observations are in agreement with other evidence that Na+ spikes are generated in the somatic region of the Purkinje neuron and spread passively into the dendrites. Plateau potentials, evoked by depolarizing pulses to the soma or dendrites, caused [Na+]i changes only in the soma, indicating that the noninactivating Na+ channels contributing to this potential also were concentrated in this region. The climbing fiber-activated [Na+]i changes were blocked by the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione, indicating that these changes were not due to direct stimulation of the Purkinje neuron or activation of metabotropic receptors. Direct depolarization of the soma or dendrites never caused dendritic [Na+]i increases, suggesting that the climbing fiber-activated [Na+]i changes in the dendrites are due to Na+ entry through ligand-gated channels. A climbing fiber-like regenerative potential could be recorded in the soma after anode break stimulation, parallel fiber activation, or depolarizing pulses to the soma. The [Na+]i changes evoked by all of these potentials were confined to the cell body region of the Purkinje cell. [Ca2+]i changes in the dendrites evoked by the anode break potential were small relative to climbing fiber-activated changes, suggesting that a Ca2+ spike was not evoked by this response. The anode break and directly responses were blocked by tetrodotoxin. These results suggest that the somatically recorded climbing fiber response is predominantly a Na(+)-dependent event, consisting of a few fast action potentials and a slower regenerative response activating the same channels as the Na+ plateau potential.

Animals↗
PubMed1992

[Spatial distribution of the action potentials of the sural nerve].

We investigated the spatial distribution of the sural nerve sensory nerve action potential (SNAP) in 25 healthy subjects between 21 and 50 years. Stimulation was achieved through surface electrodes at the lateral malleolus. Recordings were made 15-18 cm proximal to the site of the stimulation from different positions on a line perpendicular to the sural nerve using needle electrodes insulated except for the tip. The amplitude of the SNAP decreased on both sides of the potential of highest amplitude. 10 mm lateral to the potential of highest amplitude the mean amplitude was reduced to 55%. The latency of the first positive phase decreased within increasing distance from the largest SNAP. We explained this with different influence of more distal, earlier depolarized nerve segments on the locally generated SNAP. In 20 subjects we performed an additional recording using an uninsulated needle electrode that was placed 3-4 cm subcutaneously perpendicular to the sural nerve. The latency of the SNAP recorded in this way was similar to the latency of the largest SNAP using the insulated needle electrode; however, the amplitude was smaller by 19%. We recommend for clinical practice to use the uninsulated needle in case the SNAP is smaller than 4 microV.

Action Potentials↗
PubMed2000

Spatial distribution of protists in the presence of macroaggregates in a marine system.

The spatial distribution of marine protistan communities in the presence of organic macroaggregates, formed from natural seawater, was studied in several microcosm experiments. The presence of macroaggregates had two main effects. First, the size of the communities of bacteria, flagellates and ciliates increased, as these communities were three orders of magnitude higher in the aggregates than in the microcosm water. In addition, it brought the diversification on the niches accessible to planktonic microorganisms, as three phases were formed: water, aggregates and aggregate-water interphase. Some of the detected protistan taxa were only found in the water, and therefore they can be considered as truly free-swimming protists. Others quickly colonised the aggregates, and finally, some of them showed a preference for the aggregate-water interphase. We discuss this spatial structuring of the protistan community on the basis of their feeding strategies and structural and behavioural characteristics.

Journal Article↗
PubMed1999

Spatial distribution and spread of sheep biting lice, Bovicola ovis, from point infestations.

The spatial distribution of chewing lice (Bovicola ovis) on their hosts was examined in Polypay and Columbia ewes initially artificially infested on the midside or the neck. Densities of lice were determined at 69 body sites in eight body regions at approximately monthly intervals for 2 years. In the second year, half of the ewes were mated and lice were counted at 26 body sites on the resulting lambs. Polypay ewes had higher densities of lice than Columbias at most inspections but there was little effect of infestation point or mating on either numbers or the distribution of lice. During periods of high louse numbers densities were generally greatest on the sides or the back. Densities on the head were also high at times and peaked later than overall louse densities. Shearing markedly reduced density but increased the proportion of lice found on the neck, belly and lowleg sites. The distribution of lice on the lambs was similar to that on the ewes except that fewer lice were found on the head. Comparisons of lice per part with the numbers of lice extracted from clipped patches indicated that a sheep with wool bearing area of 1 m2 and a mean count of one louse per 10 cm fleece parting carried approximately 2000 lice. At most times of the year inspections for sheep lice should be concentrated on the sides and back, but in recently shorn sheep greater attention should be paid to the lower neck and ventral regions. Implications of the observed distributions of lice for the efficacy of chemical treatments are discussed.

Abdomen↗
PubMed2005

A simple method for measuring thoron spatial distributions.

A simple but effective method that allows the measurement of the 220Rn spatial distribution in working or living environments using a solid-state detector is presented in this paper. The method is based on measurements of the alpha particles emitted by 216Po (the first 220Rn progeny) directly deposited on the detector surface at different distances from a 220Rn exhalation source. The validity of the method is shown by comparing the results of an experiment, where the 220Rn activity concentration is measured under conditions of diffusion at constant temperature, with finite-element calculations.

Air Pollution, Indoor↗
PubMed2000

[The spatial distribution of the horizontal connections in area 18 of the cat cerebral cortex].

Spatial distribution of horizontal inner links in field 18 of cat cerebral cortex was studied after microiontophoretic administration of HRP into a certain cortical column. HRP labelled cell location and their distribution in plane of cortex surface and sagittal and frontal planes were detected. Ellipsoid shape and rostrocaudal direction of the area of labelled cells was demonstrated irrelevant to the column localization in field 18 (stereotaxic coordinates of the columns studied are from P4 to A14). Thus, topography of the field 18 inner links was coordinated with its macrotopography, detect established electrophysiologically.

Animals↗
PubMed1991

Spatial distributions of inelastic events produced by electrons in gaseous and liquid water.

The spatial distributions of ionizations and other inelastic events in charged-particle tracks are important quantities that influence the final outcome of radiation interaction. Calculations of such distributions are presented for the tracks of electrons in the energy range 100 eV to 10 keV in liquid water and water vapor, and the results are compared. The distributions include the frequency of nearest-neighbor distances for all inelastic events, the mean nearest-neighbor distances for ionizations and for all inelastic events as a function of electron energy, the frequency of distances between all ionizations and all inelastic events, and the farthest distances between all inelastic events in electron tracks. The physical differences between liquid water and water vapor are discussed in terms of the respective inverse mean free paths, the collision spectra, and the nonlocalization of energy losses that are likely to occur in the liquid.

Electrons↗
PubMed2004

Application of laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) to investigate trace metal spatial distributions in human tooth enamel and dentine growth layers and pulp.

Human tooth enamel provides a nearly permanent and chronological record of an individual's nutritional status and anthropogenic trace metal exposure during development; it might thus provide an excellent bio archive. We investigated the micro-spatial distribution of trace metals (Cu, Fe, Mg, Sr, Pb, and Zn) in 196 x 339 microm2 raster pattern areas (6.6 x 10(4) microm2) in a deciduous tooth using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). Ablated areas include prenatal and postnatal enamel, the neonatal line, the dentine-enamel junction (DEJ), dentine, and the dentine-pulp junction. Topographic variations in the surface elemental distribution of lead, zinc, strontium, and iron intensities in a deciduous tooth revealed heterogeneous distribution within and among regions. 43Ca normalized elemental intensities showed the following order: Sr>Mg>>Zn>Pb>Fe>Cu. Elevated zinc and lead levels were present in the dental pulp region and at the neonatal line. This study demonstrates the ability of LA-ICP-MS to provide unique elemental distribution information in micro spatial areas of dental hard tissues. Elemental distribution plots could be useful in decoding nutrition and pollution information embedded in their bio apatite structure.

Child↗
PubMed1981

Effects of commune-internal migration in Finland on the spatial distribution of population and on dwelling house utilization.

"The article is based on a programme of research which has been pursued for some years with the purpose of describing the extent and spatial orientation of commune-internal migration [in Finland], a topic about which very little has previously been known, relating this form of migration to total population movement and to dwelling house requirements and utilization. The analysis yields information on the dynamics of population changes occurring in areas on the margins of permanent settlement, while at the same time taking into consideration the effects of regional and in particular housing policy decisions upon the spatial distribution of population."

Demography↗
PubMed1986

The spatial distribution of fiber loss in diabetic polyneuropathy suggests ischemia.

Characterization and quantitation of the spatial distribution of pathological abnormalities along the length of nerves may be helpful in understanding the underlying mechanisms of diabetic polyneuropathy. To this end, by examining transverse sections of nerve roots and proximal-to-distal levels of lower limb nerves in 9 controls and 15 diabetic patients with polyneuropathy, we have determined the myelinated fiber (MF) number, size distribution, median diameter, and variability of density (MFs/mm2) among frames and among fascicles. Even in cases with mild polyneuropathy, fiber loss, a decrease in the median diameter, and an increase in the variability of density among frames and among fascicles began in proximal nerve and extended to distal levels. Multifocal fiber loss along the length of nerves and sprouting provide the best explanation for these findings. The pattern is dissimilar from that observed in diffuse metabolic disease of Schwann cells, neuronal degeneration, and dying-back neuropathy, but like that found in experimental ischemic neuropathy induced by embolization of nerve capillaries.

Adult↗
PubMed1984

Spatial distribution of blastomeres is dependent on cell division order and interactions in mouse morulae.

Spatial distribution of blastomeres was examined in 16- to 30-cell morulae obtained from aggregates of 1/2----1/2 and 1/2----2/4 blastomeres. The advanced blastomeres (2/4) contributed disproportionately more inner cells while there was a corresponding decline in the contribution from the delayed blastomere (1/2) so that a balance between the total number of inner and outer cells was retained. There was, however, no marked change in the relative number of outer cells. It is suggested that once formed, the inner more adhesive cells divide relatively faster than the outer cells whose behaviour is dictated by the inner cells. The outer less adhesive cells spread over the inner cells; cell spreading is incompatible with division. The degree to which cell spreading and retardation of division of outer cells occurs may be dictated by the number of inner cells present at any one time and this partly determines the entry of further cells inside. The suggested mechanism for cell allocation is highly flexible and, indeed, essential to encompass the wide variety of patterns of cell interactions and distribution observed in morulae. It is also proposed that the retardation of division of outer cells may trigger differentiation of trophectoderm by inducing endoreduplication and the blastomeres delayed from dividing for the longest period of time may mark down the abembryonic pole and establish the embryonic-abembryonic axis.

Animals↗
PubMed2006

Spatial distribution of polyelectrolyte and counterions in nanocapsules: a computer simulation study.

We study a spatial distribution of polyelectrolyte chains and counterions inside nanometer-size capsules by means of molecular dynamics simulation on the level of a colloidal model in which polyelectrolyte coils are modeled as soft charged spheres. The capsule shell is treated as a semipermeable membrane, impermeable for the polyelectrolyte chains, but allowing free diffusion of solvent molecules and counterions. As a result, counterions leak out from the capsule immersed into a fluid of low ionic strength. This counterion leakage leads to a formation of characteristic polyelectrolyte density profiles with the central plateau and large peaks at the wall. We show that a nonuniform distribution of the inner polyelectrolyte depends on the capsule radius, surface charge, concentration of encapsulated polyelectrolyte, and the volume fraction of capsules.

Adsorption↗
PubMed2006

Spatial distribution of bumblebees foraging on two cultivars of tomato in a commercial greenhouse.

The spatial distribution of foraging bumblebees, Bombus terrestris L. (Hymenoptera: Apidae), was studied in a greenhouse planted with two cultivars of tomato, Lycopersicum esculentum Mill. (Solanaceae), in two patches. In both patches, bumblebee densities per square meter were measured on plots, and the results showed that their densities were nearly similar. The densities of available flowers, their pollen production, and availability also were measured. Our results showed that, although the cultivars greatly differed in flower density, flower morphology, and pollen production, their pollen availability (i.e., pollen actually collected by bumblebees per square meter) was approximately the same. Therefore, the mean quantities of pollen collected per bumblebee were similar in each patch. Knowing that bumblebees do not visit different varieties randomly, our results suggest that the major factor affecting the bumblebee distribution among patches was the density of available resource. Results are discussed both from an applied point of view and in relation to the assumptions of the ideal free distribution theory.

Animals↗
PubMedDate not supplied

[Development of an algorithm for spatial distribution of the radiation intensity from photometric therapeutic devices].

An algorithm for calculating the spatial distribution of radiation intensity from type-transparency matrix therapeutical apparatuses based on superbright light-emitting diodes is considered. The method developed takes into account the geometric and topological features of both radiation sources themselves and irradiated surfaces. The algorithm proposed is important in solving the problems of dosimetry of light therapeutical apparatuses already used in medical practice and those under design.

Algorithms↗
PubMed2000

Spatial distribution and sampling plans for Thrips palmi (Thysanoptera: Thripidae) infesting fall potato in Korea.

The spatial distribution of adult and immature Thrips palmi Karny on fall potato, Solanum tuberosum L., on Cheju Island, Korea, was studied over a 2-yr period by visually inspecting potato leaves. The majority of thrips collected from the leaves were observed in the top one-third of the plant. The within-field spatial patterns of adults and immature thrips were aggregated. The slopes and intercepts of Taylor's power law did not differ among adults and immature thrips. A fixed-precision-level sampling plan was developed using the parameters from Taylor's power law and was tested with resampling simulations using eight independent data sets. Over a wide range of densities, the simulation demonstrated that actual sampling precision (d = SEM/mean) values at d = 0.25 averaged < 0.24 in all cases. A binomial sampling plan for estimating mean density was developed using an empirical model evaluated at tally thresholds (the minimum number of insects present before a leaf is considered infested) of one, three, five, and eight thrips per leaf. Increasing sampling size had little effect on the precision of the estimated mean regardless of tally threshold (T). However, increasing T had a dramatic effect on precision. The best tally threshold for estimating thrips density based on the applicable density ranges and the precision of the model was T = 5. A binomial sampling plan with a tally threshold of five and a fixed sample size of 30 leaves should be an effective replacement for enumerative counts when thrips average < 10 per leaf.

Animals↗