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 1,765 records · Page 98Linked to original sources
PubMed1958

The topography of tip growth in a plant cell.

Tips of young Phycomyces sporangiophores were dusted with starch grains, and growth photographically recorded. Rates of longitudinal displacement from the cell tip of individual markers were determined, also corresponding rates of change of cell diameter. From these the magnitude and spatial distribution of "relative elemental growth rates" along both longitudinal and circumferential axes of the cell were obtained. Growth rates in these two directions are functions of distance from the cell apex, and have different spatial distributions. In particular, rates of growth in cell circumference are complexly patterned. Relative elemental growth rates in length and in girth are approximately equal and maximal at the cell's apex, with a value of 2.4 mm. mm.(-1) hr.(-1). The characteristic shape of the tip is maintained constant in the face of its changing substance and position. This shape reflects a steady state of the cell's constituent growth patterns. At every point the growing membrane simultaneously expands in the two dimensions of its surface. The degree of polarization or directional preference of growth is measured by the ratio of longitudinal to circumferential relative elemental growth rate at any point. The ratio is not constant, but changes with position along the tip. This fact does not support the idea that membrane growth is based upon a quantal "growth event." Possible causal factors in oriented membrane growth are discussed.

Plant Cells↗
PubMed2006

Clustering of cyclic-nucleotide-gated channels in olfactory cilia.

Olfactory cilia contain the known components of olfactory signal transduction, including a high density of cyclic-nucleotide-gated (CNG) channels. CNG channels play an important role in mediating odor detection. The channels are activated by cAMP, which is formed by a G-protein-coupled transduction cascade. Frog olfactory cilia are 25-200 microm in length, so the spatial distribution of CNG channels along the length should be important in determining the sensitivity of odor detection. We have recorded from excised cilia and modeled diffusion of cAMP into a cilium to determine the spatial distribution of the CNG channels along the ciliary length. The proximal segment, which in frog is the first 20% of the cilium, appears to express a small fraction of the CNG channels, whereas the distal segment contains the majority, mostly clustered in one region.

Animals↗
PubMedDate not supplied

Thyroid imaging.

Four modalities are being used to image the thyroid gland: (1) scintigraphy ("scanning"), employing one of several currently available radiopharmaceuticals, (2) ultrasound (US), (3) computed tomography (CT, "CAT" scan), and (4) magnetic resonance imaging (MRI). The first method, scintigraphy, provides an image of the spatial distribution of thyroid functional attributes, the nature of which are dependent on the interaction between the particular radiopharmaceutical employed and the tissue in question, whereas the latter three modalities provide an image of the spatial distribution of structural attributes such as the varying degrees of echogenicity of the tissues examined or the differential tissue attenuation of an x-ray beam, which permits visualization of the structures. A fifth modality, fluorescent thyroid scanning, in which fluorescence of the iodide within the thyroid gland is induced by low-dose external radiation and which gives an image of iodine distribution, is generally unavailable and only rarely used. For most patients, the combination of careful history, skilled physical examination, tests of thyroid function (and serum thyroglobulin and calcitonin for cancer evaluation), fine needle aspiration biopsy, and scintigraphy provide the most cost-effective means of evaluating the thyroid gland and its diseases. Of the four modalities currently used to image the thyroid gland--scintigraphy, ultrasound, computerized tomography, and magnetic resonance imaging--only scintigraphy has the widest application. It is employed to determine gland size, locate thyroid tissue, evaluate nodules and masses, determine the cause of a painful tender gland, differentiate various forms of goiter, detect differentiated thyroid carcinoma and gland remnants, assess suppressibility or stimulatability of the gland, and identify nonfunctioning cancers. Ultrasonography, computed tomography, and magnetic resonance imaging are not useful in differentiating between benign and malignant nodules, and their sensitivity in detecting impalpable nodules is not clinically useful, because nodules less than 1 to 1.5 cm in diameter are only rarely clinically significant. These modalities have limited utility in the evaluation of the thyroid gland: they are useful in sizing known lesions and for the detection of cervical lymphadenopathy in thyroid cancer cases.

Adult↗
PubMed1991

The temperature for fusing blood vessels using a copper vapour laser.

Specimens of canine femoral or carotid artery were preserved at the temperature of liquid nitrogen and restored to room temperature before use. Fusing experiments were performed by repeatedly scanning along cuts of 1.0 cm long using a copper vapour laser at a power level of 500 mW. The laser was delivered via a 0.2 mm diameter optical fibre, 10 cm from the specimen, providing a beam spot area of 0.125 mm2 (a power density of 400 W cm-2). Drops of saline solution were applied to the irradiated areas for cooling at a rate of one drop every five seconds. At a scanning rate of 1 cm s-1, about 300 s were taken to successfully fuse a cut of 1 cm long with minimum tissue damage. Direct measurement of tissue temperatures whilst the beam was applied was not possible because of the interference of the laser, therefore the fusing temperature was estimated by the method of extrapolation. Time dependence of the surface temperature at the centre of the target area immediately after exposure and the spatial distribution of the surface temperature around the target area during exposures were measured using a thermocouple thermometer. The fusing temperature was estimated to be 62 degrees C by extrapolation of the time dependence and spatial distributions.

Anastomosis, Surgical↗
PubMed2000

Phenology and spatial pattern of Typhaea stercorea (Coleoptera: Mycetophagidae) infesting stored grain: estimation by pitfall trapping.

The hairy fungus beetle, Typhaea stercorea (L.), occurs frequently in stored grain, often in large numbers. Populations infesting stored barley in Minnesota, corn in South Carolina, and wheat in Florida were sampled by means of grain probe traps. Spatial distribution of the species was examined by contour analysis of trap catch. In South Carolina, corn was sampled at 2 locations over 2 storage seasons, and temperature, moisture content, and malathion residues were measured. These data were used to examine phenology as well as spatial distribution, and showed peak trap catch shortly after harvest in the fall, and in the spring. This pattern followed seasonal changes in grain temperature, but there was no apparent relationship of trap catch to either grain moisture content or malathion residue. The populations of T. stercorea were not distributed randomly, but were largely concentrated in 1 or very few aggregations associated with the "spoutline," a region high in foreign material and broken grain that forms near the center of a bin as it is loaded. However, the spatial patterns were dynamic, even on a very small time scale (week to week). Numbers of insects in aggregations rose and fell, the areas involved expanded and contracted, the centers shifted, and secondary centers appeared and disappeared. These changes were apparently in response to changing patterns of grain temperature and moisture content. Secondary centers of aggregation often formed in warmer grain along bin walls.

Animals↗
PubMed2003

Distribution of deciduous stands in villages located in coniferous forest landscapes in Sweden.

Termination of fire along with active removal of deciduous trees in favor of conifers together with anthropogenic transformation of productive forest into agricultural land, have transformed northern European coniferous forests and reduced their deciduous component. Locally, however, in the villages, deciduous trees and stands were maintained, and have more recently regenerated on abandoned agricultural land. We hypothesize that the present distribution of the deciduous component is related to the village in-field/out-field zonation in different regions, which emerges from physical conditions and recent economic development expressed as land-use change. We analyzed the spatial distribution of deciduous stands in in-field and out-field zones of villages in 6 boreal/hemiboreal Swedish regions (Norrbotten, Angermanland, Jämtland, Dalarna, Bergslagen, Småland). In each region 6 individual quadrates 5 x 5 km centered on village areas were selected. We found significant regional differences in the deciduous component (DEC) in different village zones. At the scale of villages Angermanland had the highest mean proportion of DEC (17%) and Jämtland the lowest (2%). However, the amounts of the DEC varied systematically in in-field and out-field zones. DEC was highest in the in-field in the south (Småland), but generally low further north. By contrast, the amount of DEC in the out-field was highest in the north. The relative amount of DEC in the forest edge peaked in landscapes with the strongest decline in active agriculture (Angermanland, Dalarna, Bergslagen). Because former and present local villages are vital for biodiversity linked to the deciduous component, our results indicate a need for integrated management of deciduous forest within entire landscapes. This study shows that simplified satellite data are useful for estimating the spatial distribution of deciduous trees and stands at the landscape scale. However, for detailed studies better thematic resolution is needed to determine biologically relevant differences in quality of deciduous stands.

Environmental Monitoring↗
PubMed1993

Cruciferin gene families are expressed coordinately but with tissue-specific differences during Brassica napus seed development.

The major storage protein in seeds of Brassica napus, the 12S globulin cruciferin, is composed of three different groups of subunits; cru1, cru2/3 and cru4. By using gene family-specific probes, we have investigated the accumulation, rate of synthesis and spatial distribution of transcripts corresponding to the different groups of cruciferin subunits in developing seeds. Cruciferin transcripts derived from different gene families accumulate coordinately to comparable amounts during seed development. The corresponding gene families are, however, transcribed at different rates. Investigation of the spatial distribution of transcripts corresponding to each group of cruciferin subunits in the developing seed by in situ hybridization, revealed that mRNAs of all three types accumulate in both axis and cotyledons. Transcripts derived from cru1 and cru4 gene families show a similar cell specificity and accumulate in a similar spatial manner during seed development. In contrast, mRNAs corresponding to the cru2/3 gene family are expressed with a partly different cell specificity and show a slightly different pattern of accumulation in the axis and cotyledons, with a delayed accumulation in epidermal cells. In the cotyledons, the initial accumulation of this type of cruciferin mRNAs is also distinguished from the two other types. The differences in cell specificity are seen in the root cap and in provascular cells, where mRNAs belonging to the cru2/3 family are absent.

Allergens↗
PubMed1998

ON and OFF channels of the frog optic tectum revealed by current source density analysis.

The spatiotemporal patterns of excitatory synaptic activity in response to diffuse lightON and OFF stimuli were examined by means of current source density (CSD) analysis. The qualitative and quantitative analyses obtained from 24 depth profiles for each stimulus revealed obviously different distributions of synaptic activity in the laminar structure. Two or three dominant current sinks I, II, and III were evoked in response to diffuse light ON stimulation. Sink I was observed at the bottom of the retinorecipient layer. Both sinks II and III, showing an identical spatial pattern, were observed just above sink I. On the other hand, diffuse light OFF stimulation elicited up to six current sinks IV, V, VI, VII, VIII, and IX. Sink IV was observed at the bottom of the retinorecipient layer. Sink V was observed in the most superficial layer. Both sinks VI and VIII were located between the two preceding sinks. Finally, sinks VII and IX occurred below the retinorecipient layer. Five electrically evoked current sinks A, B, C, D, and E, characterized in our previous study, were also recognized in the present quantitative analysis. A statistical analysis revealed that, in visually evoked responses, statistical differences in the spatial distribution were not present between sinks I and IV, and sinks II and VIII (P < 0.05). The analysis also showed that, in electrically evoked responses, only a pair of sinks C and E exhibit virtually identical spatial distribution (P < 0.05). Based on well-known properties of the retinal ganglion cells, possible neuronal mechanisms underlying each of current sinks in the ON and OFF channels and their functional meanings were considered. Sink I reflects the excitatory monosynaptic activity derived from R3 retinal ganglion cells. Sink IV reflects the excitatory monosynaptic activity derived from both R3 and R4 cells. Sinks V, VI, VII, and IX may be composed of successive polysynaptic excitatory potentials derived from convergence of inputs from both R3 and R4 cells. We concluded that the early four sinks play in particular an important role in eliciting avoidance behavior. On the other hand, sinks II, III, and VIII reflect excitatory synaptic activities derived from - retinal fibers of another type having slow conduction velocity. These late current sinks were suggested to mediate prey catching and its facilitation.

Animals↗
PubMed2002

Linear spatial integration for single-trial detection in encephalography.

Conventional analysis of electroencephalography (EEG) and magnetoencephalography (MEG) often relies on averaging over multiple trials to extract statistically relevant differences between two or more experimental conditions. In this article we demonstrate single-trial detection by linearly integrating information over multiple spatially distributed sensors within a predefined time window. We report an average, single-trial discrimination performance of Az approximately 0.80 and faction correct between 0.70 and 0.80, across three distinct encephalographic data sets. We restrict our approach to linear integration, as it allows the computation of a spatial distribution of the discriminating component activity. In the present set of experiments the resulting component activity distributions are shown to correspond to the functional neuroanatomy consistent with the task (e.g., contralateral sensorymotor cortex and anterior cingulate). Our work demonstrates how a purely data-driven method for learning an optimal spatial weighting of encephalographic activity can be validated against the functional neuroanatomy.

Algorithms↗
PubMed1999

Three-dimensional filtering approach to brain potential mapping.

The spatial distribution of electroencephalogram (EEG) features on the scalp surface, both in time or frequency, is of great importance in clinical applications and medical research. Traditionally, mathematical methods based on interpolation algorithms have been widely applied to obtain the EEG mappings. This paper presents an innovative approach to reconstructing the brain potential mappings from multichannel EEG's. The three-dimensional (3-D) filtering approach, differing from the numerical interpolating methods, considers the spatial distribution of brain potentials as a 3-D signal, which is processed and interpolated according to its spatial frequency characteristics. The performance of the 3-D filtering method evaluated on simulated brain potentials is shown to be comparable to the four-nearest-neighbors method. Moreover, the 3-D filtering method is superior to the spherical splines method in efficiency. Two main advantages of this method are: the prospect of developing real-time, animated EEG mappings utilizing powerful digital signal processors and its capability of processing and interpolating the brain potentials on the realistic irregular scalp surface.

Brain Mapping↗
PubMed2000

Computer-assisted 3D mapping and morphometry of dysplastic zones in endoscopically resected colonic adenomas.

Three-dimensional (3D) reconstruction and morphometry of resected colonic adenomas were undertaken to extend current knowledge of clinically significant features such as the frequency of occurrence of cancer, and the size and spatial distribution of dysplastic zones in these tumours. Fifty endoscopically resected colonic adenomas were serially sectioned at intervals of 0.2 mm and the sectional images were loaded into a computer system in order to visualize the spatial distribution of dysplastic zones. These were graded into five groups according to the criteria of Morson and Dawson: normal mucosa, mild dysplasia, moderate dysplasia, severe dysplasia, and cancer. The way in which zones of different grades are distributed in a polyp was visualized in a computer display and the volume of each dysplastic zone was estimated by the Cavalieri principle. In five polyps, adenocarcinoma was found growing in an adenoma. In all of these, the cancer was surrounded by less dysplastic zones, in the form of 'cancer in adenoma'. In pedunculated polyps, submucosal invasion could occur even if the volume percent of severe dysplasia was less than 10%. In such a case, multiple biopsy specimens are advisable. Semipedunculated polyps smaller than 200 mm(3) can also harbour submucosal invasion. In this study it was found that if the adenomas had been examined by only a single section, as many as one in five of the cases in which submucosal invasion had already developed would have escaped microscopic confirmation. To prevent such diagnostic failure, it is advisable to add a few deeper sections. Thus, 3D reconstruction and morphometry have been helpful in establishing a better standard for the diagnostic histopathology of colonic tumours.

Adenocarcinoma↗
PubMed1982

Ganglion cells of the cat accessory optic system: morphology and retinal topography.

The ganglion cells of the cat's retina form classes that are distinct in their cell morphology, retinal distribution, central projections, and functional properties. By means of the retrograde transport of horseradish peroxidase injected into the accessory optic nuclei of the cat midbrain, we have characterized the retinal ganglion cells projecting to these nuclei. The retinal projection is virtually completely crossed to the medial terminal nucleus and to the lateral terminal nucleus. This appears to be true for the dorsal terminal nucleus as well, although difficulties of the technique limit our findings for this region. No differences were found in either the spatial distribution, or the somal size distribution, or the morphological characteristics of the ganglion cells projecting to these three nuclei. In spatial distribution, these cells are concentrated in the area centralis and visual streak and show no evidence of a nasotemporal division. Morphologically, they have small to medium-sized somas and delicate, sparsely branching dendrites. They do not appear to belong to any of the morphological cell type thus far identified.

Animals↗
PubMed1986

Temporal and spatial dynamics of the periodic increase in intracellular free calcium at fertilization of golden hamster eggs.

A series of periodic increases in intracellular free calcium concentration ([Ca2+]i) occurred upon fertilization in golden hamster eggs. The spatial distribution of the Ca2+ transients was investigated in single zona-free, aequorin-injected eggs, inseminated by single sperm. A supersensitive TV camera system for recording Ca2+-aequorin luminescence enabled us to observe the spatial distribution of the Ca2+ rise. In the first response, which usually occurred 10-30 sec after the sperm attachment, the increase in [Ca2+]i began near the sperm attachment site, and the Ca2+ rise spread over the entire egg within 4-7 sec. The Ca2+ rise attained its peak in 5-8 sec, declined with almost even distribution, and ceased in 12-17 sec. The spreading Ca2+ rise was repeated in the second and sometimes the third response, starting from the same focus, but spreading more rapidly (approximately 2 sec). In succeeding responses [Ca2+]i increased synchronously in the whole cytoplasm within 1 sec. When additional sperm attached to the egg after the occurrence of the first response by the first sperm, the spread of the Ca2+ rise could take place from near the site of additional sperm attachment but only in the second or third response.

Aequorin↗
PubMed2005

Spontaneous polarization in eukaryotic gradient sensing: a mathematical model based on mutual inhibition of frontness and backness pathways.

A key problem of eukaryotic cell motility is the signaling mechanism of chemoattractant gradient sensing. Recent experiments have revealed the molecular correlate of gradient sensing: Frontness molecules, such as PI3P and Rac, localize at the front end of the cell, and backness molecules, such as Rho and myosin II, accumulate at the back of the cell. Importantly, this frontness-backness polarization occurs spontaneously even if the cells are exposed to uniform chemoattractant profiles. The spontaneous polarization suggests that the gradient sensing machinery undergoes a Turing bifurcation. This has led to several classical activator-inhibitor and activator-substrate models which identify the frontness molecules with the activator. Conspicuously absent from these models is any accounting of the backness molecules. This stands in sharp contrast to experiments which show that the backness pathways inhibit the frontness pathways. Here, we formulate a model based on the mutually inhibitory interaction between the frontness and backness pathways. The model builds upon the mutual inhibition model proposed by Bourne and coworkers [Xu et al., 2003. Divergent signals and cytoskeletal assemblies regulate self-organizing polarity in neutrophils. Cell 114, 201-214.]. We show that mutual inhibition alone, without the help of any positive feedback (autocatalysis), can trigger spontaneous polarization of the frontness and backness pathways. The spatial distribution of the frontness and backness molecules in response to inhibition and activation of the frontness and backness pathways are consistent with those observed in experiments. Furthermore, depending on the parameter values, the model yields spatial distributions corresponding to chemoattraction (frontness pathways in-phase with the external gradient) and chemorepulsion (frontness pathways out-of-phase with the external gradient). Analysis of the model suggests a mechanism for the chemorepulsion-to-chemoattraction transition observed in neurons.

Animals↗
PubMed2004

Memoryless control of boundary concentrations of diffusing particles.

Flux between regions of different concentration occurs in nearly every device involving diffusion, whether an electrochemical cell, a bipolar transistor, or a protein channel in a biological membrane. Diffusion theory has calculated that flux since the time of Fick (1855), and the flux has been known to arise from the stochastic behavior of Brownian trajectories since the time of Einstein (1905), yet the mathematical description of the behavior of trajectories corresponding to different types of boundaries is not complete. We consider the trajectories of noninteracting particles diffusing in a finite region connecting two baths of fixed concentrations. Inside the region, the trajectories of diffusing particles are governed by the Langevin equation. To maintain average concentrations at the boundaries of the region at their values in the baths, a control mechanism is needed to set the boundary dynamics of the trajectories. Different control mechanisms are used in Langevin and Brownian simulations of such systems. We analyze models of controllers and derive equations for the time evolution and spatial distribution of particles inside the domain. Our analysis shows a distinct difference between the time evolution and the steady state concentrations. While the time evolution of the density is governed by an integral operator, the spatial distribution is governed by the familiar Fokker-Planck operator. The boundary conditions for the time dependent density depend on the model of the controller; however, this dependence disappears in the steady state, if the controller is of a renewal type. Renewal-type controllers, however, produce spurious boundary layers that can be catastrophic in simulations of charged particles, because even a tiny net charge can have global effects. The design of a nonrenewal controller that maintains concentrations of noninteracting particles without creating spurious boundary layers at the interface requires the solution of the time-dependent Fokker-Planck equation with absorption of outgoing trajectories and a source of ingoing trajectories on the boundary (the so called albedo problem).

Biological Transport↗
PubMed2002

Benchmarking of the dose planning method (DPM) Monte Carlo code using electron beams from a racetrack microtron.

A comprehensive set of measurements and calculations has been conducted to investigate the accuracy of the Dose Planning Method (DPM) Monte Carlo code for dose calculations from 10 and 50 MeV scanned electron beams produced from a racetrack microtron. Central axis depth dose measurements and a series of profile scans at various depths were acquired in a water phantom using a Scanditronix type RK ion chamber. Source spatial distributions for the Monte Carlo calculations were reconstructed from in-air ion chamber measurements carried out across the two-dimensional beam profile at 100 cm downstream from the source. The in-air spatial distributions were found to have full width at half maximum of 4.7 and 1.3 cm, at 100 cm from the source, for the 10 and 50 MeV beams, respectively. Energy spectra for the 10 and 50 MeV beams were determined by simulating the components of the microtron treatment head using the code MCNP4B. DPM calculations are on average within +/- 2% agreement with measurement for all depth dose and profile comparisons conducted in this study. The accuracy of the DPM code illustrated in this work suggests that DPM may be used as a valuable tool for electron beam dose calculations.

Algorithms↗
PubMedDate not supplied

Amending of fluorescence sensor signal localization in human skin by matching of the refractive index.

Fluorescence diagnostic techniques are notable amongst many other optical methods because they offer high sensitivity and noninvasive measurement of tissue properties. However, a combination of multiple scattering and physical heterogeneity of biological tissues hampers interpretation of the fluorescence measurements. Analyses of the spatial distribution of endogenous and exogenous fluorophores excitation within tissues and their contribution to the detected signal localization are essential for many applications. We have developed a novel Monte Carlo technique that gives a graphical perception of how the excitation and fluorescence detected signal are localized in tissues. Our model takes into account the spatial distribution of fluorophores, the variation of concentrations and quantum yield. We demonstrate that matching the refractive indices of the ambient medium and topical skin layer improves spatial localization of the detected fluorescence signal within the tissues.

Computer Simulation↗
PubMed1974

Spatio-temporal distribution of auditory-evoked far field potentials in rat and cat.

Short latency (less than 5 msec) auditory-evoked 'far field' potentials were mapped over the head of anesthetized rats and cats using a monaural 'click' stimulus. Significant activity was found over most of the head and, in the rat, on other parts of the body. Different components of the observed waveforms have different spatial distributions, supporting earlier evidence that they come from different generators. No area was found on the head which could be considered as an electrically neutral reference point for all the waves. There was considerable asymmetry in the spatial distribution of the early waves, with the area near the contralateral ear showing larger magnitudes than the area near the ipsilateral ear. It was found that most of the head of the rat is not in the far field, as previously defined. Significant activity was found on the tongue in the cat, which tended to increase the apparent magnitude of waves I and II at the vertex when the tongue was used as a reference. The area near the ear canal was also found to show significant activity, raising questions as to the use of the ear lobe as a reference point in human studies. We conclude that the placement of the electrodes can markedly influence the waveforms obtained, in some cases enhancing detection of early components.

Animals↗