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At least 1,621 records · Page 90Linked to original sources
PubMed2005

[A new method of visual exploration analysis].

The term visual field corresponds to the angular field of view that is seen by the eyes when they are fixed on a point straight-ahead. In neurological patients--e.g. stroke, trauma, or tumour patients--visual field function can be restricted, depending on lesion site and size. In contrast, the term "functional visual field" describes the area of visual field responsiveness under more ordinary viewing conditions. The visual exploration, i.e. the capacity to explore and analyze our visual world, is dependent on the integrity of the visual system and the oculomotor system which has to move the fovea from one object of interest to the next. In this paper, we present a new method to assess the functional visual field, conceptualized as the area that a patient actively scans with eye movements to detect predefined targets placed on everyday scenes. This method allows us to compare three levels of visual field function: (a) the spatial distribution of successful search (hits, i.e. which targets did the patient find?), (b) the spatial distribution of fixations (i.e. where did the patient preferentially search for targets?), and (c) the retinotopic level (i.e. the visual field assessed by perimetry). By integrating these three levels, one can evaluate functional outcomes of visual field disorders. Of particular importance is the question of how a patient compensates for a visual field loss with appropriate eye movements. A further clinical application of this method is the comparison of pre- with post-treatment data. Patients with visual field disorders usually undergo specific exploration trainings, aimed at enhancing the number and amplitude of saccades towards the region of the visual field deficit. The first experiences and clinical application with this method are presented here.

Eye Movements↗
PubMed1998

A large terrestrial carbon sink in north america implied by atmospheric and oceanic carbon dioxide data and models

Atmospheric carbon dioxide increased at a rate of 2.8 petagrams of carbon per year (Pg C year-1) during 1988 to 1992 (1 Pg = 10(15) grams). Given estimates of fossil carbon dioxide emissions, and net oceanic uptake, this implies a global terrestrial uptake of 1.0 to 2. 2 Pg C year-1. The spatial distribution of the terrestrial carbon dioxide uptake is estimated by means of the observed spatial patterns of the greatly increased atmospheric carbon dioxide data set available from 1988 onward, together with two atmospheric transport models, two estimates of the sea-air flux, and an estimate of the spatial distribution of fossil carbon dioxide emissions. North America is the best constrained continent, with a mean uptake of 1.7 +/- 0.5 Pg C year-1, mostly south of 51 degrees north. Eurasia-North Africa is relatively weakly constrained, with a mean uptake of 0.1 +/- 0.6 Pg C year-1. The rest of the world's land surface is poorly constrained, with a mean source of 0.2 +/- 0.9 Pg C year-1.

Journal Article↗
PubMed2003

Models of the mechanical sensitivity and growth of otoliths in fish.

It has been suggested that, in the fish, the change of otolith mass during development under altered gravity conditions and the growth of otoliths in normal conditions, are determined by feedback between otolith dynamics and the processes that regulate otolith growth. The hypothesis originates from an oscillator model of the otolith in which otolith mass is one of the parameters. However, the validity of this hypothesis is not obvious and has not been experimentally verified. We tested this hypothesis by comparing the oscillator model with a simplified spatially distributed model of the otolith. It was shown that in the case of a spatially distributed fixation of the otolith plate (otoconial layer) to the macular surface, the mechanical sensitivity of the otolith does not depend on the total otolith mass nor on its longitudinal size. It is determined by otolith thickness, the Young's modulus and viscosity of gel layer of the growing otolith. These parameters may change in order to maintain otolith sensitivity under conditions (such as growth or altered gravity) that change the dynamics of otolith movement.

Aging↗
PubMed2003

[Analysis on factors affecting net primary productivity distribution in Changbai Mountain based on process model for landscape scale].

Based on the data received from remote sensing images, the spatial distribution of annual net primary productivity (NPP) was simulated by the process model (EPPML), and the relationships between annual NPP and environmental conditions were analyzed. The results showed that NPP in 1995 was 0.680 kg C.m-2.yr.-1, mostly ranging from 0.105 to 1.241 kg C.m-2.yr.-1, accounting for 82.1%. The highest NPP (1.084 kg C.m-2.yr.-1) appears in mixed broad-leaved and Korean pine forest. Environmental conditions decide the main trend of the spatial distribution of annual NPP (Carbon) in Changbai Mountain. Soil water content had a negative correlativity with NPP, and the correlation coefficient (R) was -0.65. Therefore, water was sufficient for the growth of plants in Changbai Mountain. NPP was highly correlated with LAI (R = 0.81). When LAI was greater than 4-5 m2.m-2, NPP became saturated. NPP was also highly correlated with canopy transpiration (R = 0.77). The response of NPP on environmental conditions, LAI and canopy transpiration in Betula ermanii and broad-leaved forests were different from those in other vegetation.

Conservation of Natural Resources↗
PubMed1994

Cardiovascular and pulmonary responses to breath-hold diving in humans.

Cardiovascular and pulmonary responses to breath-hold diving (breath holding, submersion, and compression) were investigated. In addition, the effects of transitions between dry conditions and head-out immersion during eupnea were studied. Surface breath holds at a large lung volume with relaxed respiratory muscles resulted in a positive esophageal (transthoracic) pressure and a reduced cardiac output. In contrast, the esophageal pressure (relative to ambient pressure) was decreased, and cardiac output was at least partially restored, when lung gas volume was reduced by compression during breath-hold diving. The increased cardiac output that accompanied eupneic transition from dry to immersed conditions was associated with a short-lasting increase of alveolar gas exchange, whereas the decreased cardiac output during immersion-to-dry transition was associated with a long-lasting decrease of alveolar gas exchange, both reflecting changes in the tissue gas stores of the body. Surface breath holds were associated with a decreased O2 uptake from the lung to the blood, and breath-hold dives were associated with a large transient increase of O2 uptake at depth which resulted in a restoration of the time-averaged O2 uptake to the eupneic control level: these changes reflected changes in tissue O2 stores. Compared to surface breath holds, breath-hold dives were associated with larger tissue retention of CO2 during breath holds, and prolonged recovery for CO2 elimination after breath holds. The distribution of pulmonary perfusion, as indicated by expirograms obtained immediately after breath holds, was made more homogeneous by submersion and the distribution was further improved by compression during breath-hold dives. All of these different effects on the gas exchange in breath-hold diving and in eupneic headout immersion can to a large extent be explained by associated changes in cardiac output in combination with redistributions of peripheral blood flow and venous blood volume. Thus, the different components of breath-hold diving have profound cardiovascular and pulmonary effects. Changes in the intrathoracic pressure and in the distribution of venous blood volume induce changes in cardiac output. All of these changes affect the temporal and spatial distributions of pulmonary perfusion and peripheral blood flow. Also, the circulatory changes affect the temporal and spatial distributions of alveolar gas exchange and of tissue gas stores of the body.

Adolescent↗
PubMed2004

Nano-optics with single quantum systems.

This paper reviews the recent progress in using single quantum systems, here mainly single fluorescent molecules, as local probes for nano-optical field distributions. We start by discussing the role of the absorption cross-section for the spatial resolution attainable in such experiments and its behaviour for different environmental conditions. It is shown that the spatial distribution of field components in a high-numerical aperture laser focus can be mapped with high precision using single fluorescent molecules embedded in a thin polymer film on glass. With this proof-of-principle experiment as a starting point, the possibility of mapping strongly confined and enhanced nano-optical fields close to material structures, e.g. sharp metal tips, is discussed. The mapping of the spatial distribution of the enhanced field at an etched gold tip using a single molecule is presented as an example. Energy transfer effects and quenching are identified as possible artefacts in this context. Finally, it is demonstrated that the local quenching at a sharp metal structure nevertheless can be exploited as a novel contrast mechanism for ultrahigh-resolution optical microscopy with single-molecule sensitivity.

Fluorescence Resonance Energy Transfer↗
PubMed2001

Mapping continued brain growth and gray matter density reduction in dorsal frontal cortex: Inverse relationships during postadolescent brain maturation.

Recent in vivo structural imaging studies have shown spatial and temporal patterns of brain maturation between childhood, adolescence, and young adulthood that are generally consistent with postmortem studies of cellular maturational events such as increased myelination and synaptic pruning. In this study, we conducted detailed spatial and temporal analyses of growth and gray matter density at the cortical surface of the brain in a group of 35 normally developing children, adolescents, and young adults. To accomplish this, we used high-resolution magnetic resonance imaging and novel computational image analysis techniques. For the first time, in this report we have mapped the continued postadolescent brain growth that occurs primarily in the dorsal aspects of the frontal lobe bilaterally and in the posterior temporo-occipital junction bilaterally. Notably, maps of the spatial distribution of postadolescent cortical gray matter density reduction are highly consistent with maps of the spatial distribution of postadolescent brain growth, showing an inverse relationship between cortical gray matter density reduction and brain growth primarily in the superior frontal regions that control executive cognitive functioning. Inverse relationships are not as robust in the posterior temporo-occipital junction where gray matter density reduction is much less prominent despite late brain growth in these regions between adolescence and adulthood. Overall brain growth is not significant between childhood and adolescence, but close spatial relationships between gray matter density reduction and brain growth are observed in the dorsal parietal and frontal cortex. These results suggest that progressive cellular maturational events, such as increased myelination, may play as prominent a role during the postadolescent years as regressive events, such as synaptic pruning, in determining the ultimate density of mature frontal lobe cortical gray matter.

Adolescent↗
PubMed1995

Distribution and spatial geometry of dopamine interplexiform cells in the retina. II. External arborizations in the adult rat and monkey.

The morphology and distribution of dopaminergic interplexiform cells in adult rat and monkey retinas were analyzed to determine any correlation with the function of dopamine in the outer retinal layers. The retinas were processed as whole mounts for tyrosine hydroxylase immunohistochemistry. There was a network formed by the sclerally directed processes of interplexiform cells in the inner nuclear, outer plexiform, and outer nuclear layers running throughout the retina. Their density was higher in the superior retina than in the inferior retina of the rat and was especially high in the superior temporal quadrant. The external network in this quadrant was significantly less dense in the monkey than in the rat, as are the interplexiform cells. The somata of interplexiform and other dopaminergic cells were about the same size in both rats and monkeys. Computer-assisted reconstruction of external arborizations of individual cells showed that external processes lay very close to horizontal and photoreceptor cells and also to blood capillaries. Because they were long, thin, and highly varicose; branched at right angles; and often arose from an axon hillock, the external processes were identified as axons. Therefore, we define the dopaminergic interplexiform cells as multiaxonal neurons, with at least one outwardly directed axon that reaches the outer plexiform layer. The function of the network of external processes from the interplexiform dopaminergic cells is discussed in terms of modulating the release of dopamine to external layers.

Animals↗
PubMed2001

The effect of electrode configuration and duration of deafness on threshold and selectivity of responses to intracochlear electrical stimulation.

This report examines the effects of intracochlear electrode configuration and mode of stimulation (bipolar or monopolar) on neural threshold and spatial selectivity in the inferior colliculus (IC) of the cat. Single and multiunit IC recordings were made in three groups of animals; acutely deafened adults (controls), neonatally deafened animals studied at 6 to 18 months of age and neonatally deafened cats studied at 2.5 to 6.5 years. Response thresholds were plotted versus IC depth to measure the spatial distribution of responses. The response selectivity for each stimulating configuration was defined as the width of the resulting spatial tuning curve (STC) measured at 6 dB above threshold. Spiral ganglion cell (SG) survival was examined histologically in all neonatally deafened animals and correlated with physiological results. Animals studied at less than 1.5 years had SG densities of 23.5%-64.4% of normal (mean=42.7%) while animals studied at greater than 2.5 years had densities of 5.1%-18.3% of normal (mean=9.9%). Electrophysiological results include the following. (1) Monopolar thresholds were 7-8 dB lower than bipolar thresholds in the same animals. (2) Varying the configuration of bipolar contacts (measured as radial, offset radial and longitudinal pairs) did not systematically affect IC threshold in either controls or short-term neonatally deafened animals. In contrast, the long-term neonatally deafened animals showed a difference in threshold with each configuration. (3) The spatial distributions (Q(6 dB)) of responses to bipolar stimulation were approximately 40% more restricted than those for monopolar stimulation. (4) The spatial selectivity of neonatally deafened animals studied at ages up to 1.5 years was equal to that of control animals with normal auditory experience. However, selectivity was degraded in the older animals. (5) Selectivity was decreased in some animals with the longitudinal bipolar configuration and multiple response peaks were seen in several cases using this stimulus configuration.

Animals↗
PubMed2000

[Vertical distribution and quantitative dynamics of dominant functional groups of arthropod community in rice fields and estimation of natural enemy effects].

The study showed that Lycosid (wolf spider) mainly distributed in the basal part of rice plants, not as wide as we know in past. Tetragnathid did not limited in the upper part of plants, but might translate to middle or lower part when affected by insecticide. The relationship between the vertical distributions of top and basal species was not significant. Besides the amount of natural enemies, the spatial distribution characteristics of natural enemies and brownplanthopper, and the proportion of brownplanthopper to total preys of natural enemies were the factors affecting the role of natural enemies on the population dynamics of brownplanthopper in rice fields. A model to evaluate the effect of natural enemies to brownplanthopper was put forward, which included the message of quantitative dynamics, spatial distribution and feeding characteristics of natural enemies, brownplanthopper and neutral insects.

Animals↗
PubMed2006

Femtosecond two-photon high-resolution 3D imaging, spatial-volume rendering and microspectral characterization of immunolocalized MHC-II and mLangerin/CD207 antigens in the mouse epidermis.

Langerhans cells (LCs) play a sentinel role by initiating both adaptive and innate immune responses to antigens pertinent to the skin. With the discovery of various LCs markers including antibodies to major histocompatibility complex class II (MHC-II) molecules and CD1a, intracellular presence of racket-shaped "Birbeck granules," and very recently Langerin/CD207, LCs can be readily distinguished from other subsets of dendritic cells. Femtosecond two-photon laser scanning microscopy (TPLSM) in recent years has emerged as an alternative to the single photon-excitation based confocal laser scanning microscope (CLSM), particularly for minimally-invasive deep-tissue 3D and 4D vital as well as nonvital biomedical imaging. We have recently combined high resolution two-photon immunofluorescence (using anti MHC-II and Langerin/CD207 antibodies) imaging with microspectroscopy and advanced image-processing/volume-rendering modalities. In this work, we demonstrate the use of this novel state-of-the-art combinational approach to characterize the steady state 3D organization and spectral features of the mouse epidermis, particularly to identify the spatial distribution of LCs. Our findings provide unequivocal direct evidence that, in the mouse epidermis, the MHC-II and mLangerin/CD207 antigens do indeed manifest a high degree of colocalization around the nucleus of the LCs, while in the distal dendritic processes, mLangerin/CD207 antigens are rather sparsely distributed as punctuate structures. This unique possibility to simultaneously visualize high resolution 3D-resolved spatial distributions of two different immuno-reactive antigens, namely MHC-II and mLangerin/CD207, along with the nuclei of LCs and the adjacent epidermal cells can find interesting applications. These could involve aspects associated with pragmatic analysis of the kinetics of LCs migration as a function of immuno-dermatological responses during (1) human Immunodeficiency virus disease progression, (2) vaccination and targeted gene therapy, (3) skin transplantation/plastic surgery, (4) ultraviolet and other radiation exposure, (5) tissue-engineering of 3D skin constructs, as well as in (6) cosmetic industry, to unravel the influence of cosmeceuticals.

Animals↗
PubMedDate not supplied

Method for quantitative analysis of glycosaminoglycan distribution in cultured natural and engineered cartilage.

Cartilage tissue engineering can provide a valuable tool for controlled studies of tissue development. As an example, analysis of the spatial distribution of glycosaminoglycans (GAG) in sections of cartilaginous tissues engineered under different culture conditions could be used to correlate the effects of environmental factors with the structure of the regenerated tissue. In this paper we describe a computer-based technique for quantitative analysis of safranin-O stained histological sections, using low magnification light microscopy images. We identified a parameter to quantify the intensity of red color in the sections, which in turn was proportional to the biochemically determined wet weight fraction of GAG in corresponding tissue samples, and to describe the spatial distribution of GAG as a function of depth from the section edge. A broken line regression model was then used to determine the thickness of an external region, with lower GAG fractions, and the spatial rate of change in GAG content. The method was applied to the quantitation of GAG distribution in samples of natural and engineered cartilage, cultured for 6 weeks in three different vessels: static flasks, mixed flasks, and rotating bioreactors.

Animals↗
PubMed1988

Dopaminergic neurons in the cat retina.

Dopaminergic neurons have been directly visualized in the flat mount cat retina with an immunohistochemical technique that uses antisera directed to the enzyme tyrosine hydroxylase. In a previous study, three specific neuronal populations--amacrine cells, displaced amacrine (DA) cells, and interplexiform (IP) cells--were identified on the basis of morphology in the flat mount retina. The present study incorporates three-dimensional computer reconstructions and differences in the frequency distributions of some area to support the original cell classification. The three neuronal populations differ in cell numbers and spatial distributions in the retina; quantitative comparison of two cat retinas shows that the total numbers of cells and the spatial distributions of the three cell populations are consistent between retinas. These results suggest that a single neurotransmitter can serve different functions in modifying signals and flow of visual information within the neural networks of the retina.

Animals↗
PubMed2005

Distribution of rare earth elements in an alluvial aquifer affected by acid mine drainage: the Guadiamar aquifer (SW Spain).

This work analyses the spatial distribution, the origin, and the shale-normalised fractionation patterns of the rare earth elements (REE) in the alluvial aquifer of the Guadiamar River (south-western Spain). This river received notoriety in April 1998 for a spill that spread a great amount of slurry (mainly pyrites) and acid waters in a narrow strip along the river course. Groundwaters and surface waters were sampled to analyse, among other elements, the REEs. Their spatial distribution shows a peak close to the mining region, in an area with low values of pH and high concentrations of sulphates and other metals such as Zn, Cu, Co, Ni, Pb, and Cd. The patterns of shale-normalised fractionation at the most-contaminated points show an enrichment in the middle rare earth elements (MREE) with respect to the light (LREE) and heavy (HREE) ones, typical of acid waters. The Ce-anomaly becomes more negative as pH increases, due to the preferential fractionation of Ce in oxyhydroxides of Fe.

Environmental Monitoring↗
PubMed1998

Distribution of scattered radiation during intraoral radiography with the patient in supine position.

OBJECTIVE: The purpose of this study was to investigate the spatial distribution of scattered radiation during intraoral radiography with the patient in a supine position to determine the exposure to an operator without a suitable barrier. STUDY DESIGN: A phantom was placed in the supine position on a dental chair with the occlusal plane perpendicular to the floor, and four intraoral periapical radiographic examinations in the anterior and posterior regions of the maxilla and mandible were performed. The scattered radiation was measured with an ionization chamber at distances ranging from 25 to 200 cm at 25 cm increments and at intervals of 45 degrees. Measurements were made at two different heights: level with the occlusal plane and 30 cm below it. The exposure was converted to an air-kerma/absorbed dose in air. RESULTS: The distribution of scattered radiation was symmetric during examinations of the anterior region. Circular iso-exposure curves of up to 0.5 microGy were observed at the level of the occlusal plane, and curves of up to 0.1 microGy were observed 30 cm below the plane. The lowest exposures were measured 30 cm below the occlusal plane and behind the chair. The distribution of scattered radiation was not symmetric during examinations of the posterior region. Iso-exposure curves of up to 0.25 microGy were observed at the level of the occlusal plane during exposure of the maxilla, and curves of up to 0.5 microGy were observed during exposure of the mandible. Circular iso-exposure curves of up to 0.1 microGy were observed 30 cm below the occlusal plane. Lower values for scattered radiation were observed 30 cm below the occlusal plane between 135 and 180 degrees behind the phantom. CONCLUSION: The spatial distribution of scattered radiation with the patient in a supine position was not the same in eight directions around the chair. Although the preferred position for the operator is behind a suitable barrier, the preferred position in the absence of a barrier is 200 cm behind the patient.

Dental Auxiliaries↗
PubMed2003

Genetic and clonal diversity for Myrica cerifera along a spatiotemporal island chronosequence.

Changes in genetic diversity and clonal structure were investigated along a spatiotemporal island chronosequence for the shrub Myrica cerifera. On our study site, Hog Island, Virginia, USA, island movement creates a sequence of dune ridges and intervening swales along an east-west axis of the island that produces an age-structured geomorphology. This substrate-mediated age structure, called the chronosequence, superimposes itself upon cohorts of M. cerifera that colonize behind nascent dune ridges as they are formed. This chronosequence allowed comparisons of levels of genetic diversity and clonal structure among different aged cohorts of M. cerifera. We observed little change in allelic diversity along the chronosequence and no evidence for heterosis, although there was moderate change in genotypic diversity. The spatial distribution of individuals within 10 plots established along three transects intersecting the island chronosequence identified a nonrandom spatial distribution of individuals in all cohorts, with increasing aggregation of above-ground stems into multistemmed clusters in the older sites. This aggregation of individuals did not correspond to a significant increase in clonal growth with cohort age, nor was there significant spatial genetic autocorrelation within any of the plots.

Genetic Variation↗
PubMed2006

Geostatistical analysis of disease data: visualization and propagation of spatial uncertainty in cancer mortality risk using Poisson kriging and p-field simulation.

BACKGROUND: Smoothing methods have been developed to improve the reliability of risk cancer estimates from sparsely populated geographical entities. Filtering local details of the spatial variation of the risk leads however to the detection of larger clusters of low or high cancer risk while most spatial outliers are filtered out. Static maps of risk estimates and the associated prediction variance also fail to depict the uncertainty attached to the spatial distribution of risk values and does not allow its propagation through local cluster analysis. This paper presents a geostatistical methodology to generate multiple realizations of the spatial distribution of risk values. These maps are then fed into spatial operators, such as in local cluster analysis, allowing one to assess how risk spatial uncertainty translates into uncertainty about the location of spatial clusters and outliers. This novel approach is applied to age-adjusted breast and pancreatic cancer mortality rates recorded for white females in 295 US counties of the Northeast (1970-1994). A public-domain executable with example datasets is provided. RESULTS: Geostatistical simulation generates risk maps that are more variable than the smooth risk map estimated by Poisson kriging and reproduce better the spatial pattern captured by the risk semivariogram model. Local cluster analysis of the set of simulated risk maps leads to a clear visualization of the lower reliability of the classification obtained for pancreatic cancer versus breast cancer: only a few counties in the large cluster of low risk detected in West Virginia and Southern Pennsylvania are significant over 90% of all simulations. On the other hand, the cluster of high breast cancer mortality in Niagara county, detected after application of Poisson kriging, appears on 60% of simulated risk maps. Sensitivity analysis shows that 500 realizations are needed to achieve a stable classification for pancreatic cancer, while convergence is reached for less than 300 realizations for breast cancer. CONCLUSION: The approach presented in this paper enables researchers to generate a set of simulated risk maps that are more realistic than a single map of smoothed mortality rates and allow the propagation of cancer risk uncertainty through local cluster analysis. Coupled with visualization and querying capabilities of geographical information systems, animated display of realizations can highlight areas that depart consistently from the general behavior observed across the region, guiding further investigation and control activities.

Cluster Analysis↗
PubMed2000

Modeling of the acoustic pressure fields and the distribution of the cavitation phenomena in a dual frequency sonic processor

An attempt has been made to model the acoustic pressure field and the spatial distribution of the cavitation phenomena in a dual frequency sonic processor. A methodology has been presented with numerical simulations to optimize the conditions of the dual frequency acoustic field. The simulations presented in this work reveal that with manipulation of the parameters (viz., frequency ratio and the pressure amplitude ratio of the two acoustic waves and the phase difference between the two waves) of the dual frequency acoustic field it is possible to control the mode (stable or transient) and spatial distribution of the cavitation events in the sonic processor. It has been shown that two major shortcomings of the sonic reactor, viz., directional sensitivity of the cavitation events and erosion of the sonicator surface can be overcome by application of a dual frequency acoustic field.

Journal Article↗