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 1,099 records · Page 61Linked to original sources
PubMed2003

Spatial distribution of high-energy electron emission from water plasmas produced by femtosecond laser pulses.

High energy electrons emitted by water plasmas produced by a single or a multiple laser pulse are investigated. The multipulse mode greatly enhances the generation and the temperature of hot electrons. Directional emission of high energy electrons over 25 keV is observed in two symmetric directions with respect to the laser axis and at 46 degrees from the directions of the laser electric field. Two-dimensional particle-in-cell simulations reproduce well the experimental results and indicate that the acceleration mechanism of the high energy electrons is due mainly to the resonance absorption at the edge of the spherical droplets formed by the leading pulse.

Journal Article↗
PubMed2004

Spatial distribution of competing ions around DNA in solution.

The competition of monovalent and divalent cations for proximity to negatively charged DNA is of biological importance and can provide strong constraints for theoretical treatments of polyelectrolytes. Resonant x-ray scattering experiments have allowed us to monitor the number and distribution of each cation in a mixed ion cloud around DNA. These measurements provide experimental evidence to support a general theoretical prediction: the normalized distribution of each ion around polyelectrolytes remains constant when ions are mixed at different ratios. In addition, the amplitudes of the scattering signals throughout the competition provide a measurement of the surface concentration parameter that predicts the competition behavior of these cations. The data suggest that ion size needs to be taken into account in applying Poisson-Boltzmann treatments to polyelectrolytes such as DNA.

Cations↗
PubMed1979

Spatial Distribution of Circadian Clock Phase in Aging Cultures of Neurospora crassa.

Neurospora crassa has been utilized extensively in the study of circadian clocks. Previously, the clock in this organism has been monitored by observing the morphological and biochemical changes occurring at the growing front of cultures grown on solid medium. A method has been developed for assaying the clock in regions of the culture behind the growing front, where no apparent morphological changes occur during the circadian cycle. Using this assay with Petri dish cultures that were 2 to 7 days old, the presence of a functional circadian clock not only at the growing front but in all other regions of the culture as well was demonstrated. Furthermore, the entire culture is not in the same phase, but shows a gradient of phases which is a function of the length of time the clock in a given part of the culture has been free-running. This gradient may be the result of a somewhat longer period of the oscillator behind the growing front compared to that at the growing front. The phase differences within a single culture of interconnected mycelium demonstrate the absence of total internal synchronization between adjacent regions of the hyphae under these conditions.

Journal Article↗
PubMed1986

Spatial distributions of potassium, solutes, and their deposition rates in the growth zone of the primary corn root.

Densities of osmoticum and potassium were measured as a function of distance from the tip of the primary root of Zea mays L. (cv WF9 x mo17). Millimeter segments were excised and analyzed for osmotic potential by a miniaturized freezing point depression technique, and for potassium by flame spectrophotometry. Local deposition rates were estimated from the continuity equation with values for density and growth velocity. Osmotic potential was uniform, -0.73 +/- 0.05 megapascals, throughout the growth zone of well-watered roots. Osmoticum deposition rate was 260 muosmoles per gram fresh weight per hour. Potassium density fell from 117 micromoles per gram in the first mm region to 48 micromoles per gram at the base of the growth zone. Potassium deposition rates had a maximum of 29 micromoles per gram per hour at 3.5 millimeters from the tip and were positive (i.e. potassium was being added to the tissue) until 8 millimeters from the tip. The results are discussed in terms of ion relations of the growing zone and growth physics.

Journal Article↗
PubMed1991

opaque-2 modifiers increase gamma-zein synthesis and alter its spatial distribution in maize endosperm.

Through the action of opaque-2 modifier genes, the soft, floury endosperm of opaque-2 mutants is converted to a vitreous phenotype. This change in endosperm texture is associated with a twofold to threefold increase in gamma-zein content. To investigate the effect of opaque-2 modifiers on the expression of gamma-zein genes, we analyzed the synthesis and distribution of gamma-zein protein and the level of gamma-zein mRNAs in developing endosperms of the inbreds W64A and W64Ao2, a modified opaque-2 mutant Pool 34 QPM, and their reciprocal F1 hybrids. We also characterized the number and organization of gamma-zein genes in these and related maize genotypes. Our studies show that opaque-2 modifiers are semidominant genes, resulting in a twofold to threefold increase in gamma-zein gene expression in both opaque-2 and normal genetic backgrounds. The increase in gene expression appears to be a consequence of enhanced mRNA transcription or stability rather than gene amplification because gamma-zein genes occur in one or two copies in modified as well as nonmodified genetic backgrounds. Ultrastructural studies showed that gamma-zein occurs in high concentrations in the first few subaleurone cells of nonmodified endosperms, but high concentrations of gamma-zein occur in the subaleurone and central endosperm cells of modified opaque-2 mutants. The increased concentration and distribution of gamma-zein in modified endosperms are highly correlated with the activity of opaque-2 modifier genes.

Microscopy, Immunoelectron↗
PubMed1996

Spatial distribution of high-frequency electromagnetic energy in human head during MRI: numerical results and measurements.

Finite Element Method (FEM) using 26-node isoparametric finite elements was applied for modeling saddle-shaped head coils used in Magnetic Resonance Imaging (MRI) generating linearly polarized radiofrequency (RF) pulses at 64 MHz. The human head was modeled from MR scans of a volunteer and additional information were taken from Atlas of Sectional Human Anatomy. The physical dimensions of the head coil and the head permit a calculation of the outside magnetic field by a quasistatic approach. Of course, a full-wave approach was applied within the head. Values of specific energy--specific absorption (SA)--as well as of specific power--specific absorption rate (SAR)--were calculated by the method, simulating the real exposure conditions during MRI. Although the results of the used numerical method were compared previously to the results of the analytical solution with homogeneous sphere and to the results of RF measurements on heterogeneous phantom, a comparison between the numerical results of the modeled human head and in vivo measurements performed on the human head of the volunteer was made once more. Since the results are in excellent agreement, they argue for the correctness of the numerical method. The "worst-case" temperature elevations delta theta of the "hot-spots" were calculated, as well. Finally, the results of SA, SAR, and delta theta are compared to the existing recommendations.

Body Composition↗
PubMed1982

The relative spatial distribution of erythroid progenitor cells (BFUe and CFUe) in the normal mouse femur.

Femoral mouse bone marrow cells were separated into axial and marginal fractions, in order to investigate the relative concentration of erythroid progenitor cells (BFUe and CFUe) with respect to their location across the diameter of the femur. Two areas of high incidence of early progenitor cells (BFUe) were identified: one lying near the bone surface with a peak at about 410 micrometers radial distance from the axis of the bone; the other nearer the centre of the bone with a peak at about 270 micrometers. The more immature BFUe were found in higher proportion in the marginal peak. In contrast, CFUe, apart from very low concentration values in the vicinity of the bone surface, demonstrated a fairly uniform distribution throughout the marrow. The present results indicate that the distribution of erythroid progenitor cells within the bone marrow is not random. The haemopoietic tissue seems to exhibit a well-defined structure that may be relevant in regulating proliferation and differentiation processes.

Animals↗
PubMed2005

Airway generation-specific differences in the spatial distribution of immune cells and cytokines in allergen-challenged rhesus monkeys.

BACKGROUND: Accumulation of immune cell populations and their cytokine products within tracheobronchial airways contributes to the pathogenesis of allergic asthma. It has been postulated that peripheral regions of the lung play a more significant role than proximal airways with regard to inflammatory events and airflow obstruction. OBJECTIVE: To determine whether immune cell populations and associated cytokines are uniformly distributed throughout the conducting airway tree in a non-human primate model of allergic asthma. METHODS: We used a stereologic approach with a stratified sampling scheme to measure the volume density of immune cells within the epithelium and interstitium of trachea and 4-5 intrapulmonary airway generations from house dust mite (HDM) (Dermatophagoides farinae)-challenged adult monkeys. In conjunction with immune cell distribution profiles, mRNA levels for 21 cytokines/chemokines and three chemokine receptors were evaluated at four different airway generations from microdissected lungs. RESULTS: In HDM-challenged monkeys, the volume of CD1a+ dendritic cells, CD4+ T helper lymphocytes, CD25+ cells, IgE+ cells, eosinophils, and proliferating cells were significantly increased within airways. All five immune cell types accumulated within airways in unique patterns of distribution, suggesting compartmentalized responses with regard to trafficking. Although cytokine mRNA levels were elevated throughout the conducting airway tree of HDM-challenged animals, the distal airways (terminal and respiratory bronchioles) exhibited the most pronounced up-regulation. CONCLUSION: These findings demonstrate that key effector immune cell populations and cytokines associated with asthma differentially accumulate within distinct regions and compartments of tracheobronchial airways from allergen-challenged primates.

Animals↗
PubMed1979

Application of cluster analysis for characterization of spatial distribution of particles by stereological methods.

A method for the detection and characterization of clusters of particles observed in section with the electron microscope is presented. Cluster analysis is performed by the division method described by Berthet et al. (1976). Starting from a single cluster, profiles from each electron micrograph are successively classified in sets containing an increasing number of clusters. The decrease in the mean free distance, lambda, between profiles in the clusters, is used for terminating the subdivision procedure. The function relating the mean free distance with the number of clusters is evaluated in each subdivision set. The actual number of clusters is selected on the basis of the slope of that function, at a point where lambda has a value close to the average profile diameter. The method assumes a convex shape for the clusters; the salient feature is that it provides a physical delineation of clusters in the section. Hence, an evaluation of some characteristics of clusters in the three-dimensional sample may be obtained by using standard stereological procedures. Characterization of the volume to which the individual particles of a population are eventually restricted can as a result be performed. Practical problems in the acquisition of the data needed for cluster analysis are discussed and a system using for that purpose a Quantimet 720 image analyser in a basic configuration, connected on line with a PDP 11/10 minicomputer, is presented. Application of the method is illustrated by the analysis of lysosomes in cultured hepatoma (HTC) cells, at the end of mitosis and during the S phase. Cluster analysis shows that in cells actively synthesizing DNA they are grouped in clusters representing 5.7% of the cellular volume. Moreover, the average number of particles per cluster falls from a minimum of thirteen at mitosis to only six at the S phase.

Cells, Cultured↗
PubMed1993

Spatial distribution of curve length: concept and estimation.

The length of a curvilinear feature, such as a dendrite tree of a neuron, can, in principle, be estimated by the recent, non-invasive method of total vertical projections (TVPs). Curve length is a measure of size, but it reports nothing about curve shape. The shape of a tree-like structure can be described to some extent by the distribution of branch length in properly defined regions of three-dimensional (3-D) space. A definition of curve length distribution in three dimensions is proposed and implemented here on a human neuron. The relevant 3-D regions overlap after projection, and therefore the TVPs method cannot be used directly to estimate the corresponding feature lengths. However, using the ANALYZE software system running on a SUN SPARC workstation, dendrite subsets sitting in predefined regions of space were rendered in different colours and measured separately by the TVPs method using a cycloid test system. In combination with non-invasive image acquisition and processing techniques, the length distribution concept is likely to be useful in the metrical analysis of either microscopic or macroscopic arborizations in a wide variety of contexts, including living cells and organisms.

Dendrites↗
PubMed1992

cDNA cloning and deduced amino acid sequence of a major, glycine-rich cuticular protein from the coleopteran Tenebrio molitor. Temporal and spatial distribution of the transcript during metamorphosis.

In Coleoptera, the elytra (forewings), with a very hard and thick cuticle, protect the membranous and delicate hindwings against mechanical stress. We have isolated and characterized a cDNA encoding a major cuticle protein in Tenebrio molitor, named ACP-20. The deduced amino acid sequence is roughly tripartite, with two terminal glycine-rich domains and a central region showing pronounced similarities with some other hard cuticle proteins. Northern blot and in situ hybridization analyses reveal that ACP-20 gene expression is developmentally regulated since transcript accumulation occurs only in epidermal regions synthesizing hard cuticle and is restricted to the period of preecdysial adult cuticle deposition. Moreover, application of a juvenile hormone analogue prevents the appearance of the transcript, indicating that juvenile hormone, a key molecule involved in the control of insect metamorphosis, negatively regulates the expression of the ACP-20 gene.

Amino Acid Sequence↗