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Results for “Spatial Distribution”

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At least 19 recordsLinked to original sources

PubMed2001

Determination of the pore connectivity and pore size distribution and pore spatial distribution of porous chromatographic particles from nitrogen sorption measurements and pore network modelling theory.

The pore connectivity, pore size distribution and pore spatial distribution of the porous structure of native and silanized silica particles were determined by matching the experimental nitrogen sorption data with the theoretical results obtained from pore network model simulations. The agreement between theory and experiment is found to be good. The results clearly indicate that the deposition of the silane layer to the pore surfaces of the native silica particles produces a silanized silica particle with a mean pore diameter and pore connectivity smaller than that of the native silica particle. Furthermore, the evaluation of the pore diffusivity of ribonuclease under unretained conditions shows that the lower values of the pore connectivity found in the samples of silanized silica particles, when compared with the values of the pore connectivity obtained for the native silica particles, increase the diffusional mass transfer resistance within the porous structure of the silanized silica particles.

Chromatography, Liquid↗

PubMed2002

Spatial distribution of myosin heavy-chain isoforms in mouse masseter.

There is a paucity of information regarding the anatomy and muscle fiber phenotype of the masseter. The objective of this study was to characterize the distribution of each myosin heavy-chain (MyHC) isoform within different anatomical regions of male and female mouse masseters. Masseters from male and female CD-1 mice (2-4 months old) were examined for description of the anatomical partitioning of muscle fibers and endplate distribution. The spatial distribution of MyHC isoforms--embryonic, neonatal, slow, alpha-cardiac, IIa, and IIb--was determined within the defined masseter partitions by means of Western blot analysis and immunofluorescent localization. Types IIa, IIx, and IIb were the predominant MyHC isoforms observed. Distinct differences in the spatial distribution of these MyHC isoforms were found between muscle regions and varied between sexes. The regionalization of muscle fiber types in the mouse masseter is consistent with the functional compartmentalization of the masseter observed in other species.

Animals↗

PubMed1999

Effects of local tissue environment on the differentiation of neural crest cells in turtle, with special reference to understanding the spatial distribution of pigment cells.

The spatial distribution of neural crest-derived pigment cells in turtles differs markedly from those found in chickens and mice. One hypothesis to explain such differences in the spatial distribution of pigment cells is that local tissue factors interact with neural crest cells, thereby determining their differentiation into pigment-synthesizing cells. It is reported here that local tissue factors in the soft-shell turtle (Trionyx sinensis japonicus) play a critical role in the development of melanophores from neural crest cells during embryogenesis. Undifferentiated neural crest cells derived from trunk neural tubes were co-cultured in vitro with homochronous somites, or with heterochronous dermis, lung or liver for 14 days. Melanophore differentiation from neural crest cells was significantly promoted when co-cultured with cells from lung, somites or dermis, but not when co-cultured with liver cells. These results suggest that local tissue factors stimulate the differentiation of pluripotent neural crest derivatives toward pigment cells. It is proposed that specific environmental cues play an important role in the spatial distribution of pigment cells in a variety of vertebrate species.

Animals↗

PubMed1999

Mechanisms of the spatial distribution of QT intervals on the epicardial and body surfaces.

INTRODUCTION: The role of QT dispersion as a predictor of arrhythmia vulnerability has not been consistently confirmed in the literature. Therefore, it is important to identify the electrophysiologic mechanisms that affect QT duration and distribution. We compared the spatial distributions of QT intervals (QTI) with potential distributions on cardiac and body surfaces and with recovery times on the cardiac surface. We hypothesized that the measure of QTI is affected by the presence of the zero potential line in the potential distribution, as well as the sequence of recovery. We also investigated use of the STT area as a possible indicator of recovery times on the cardiac surface. METHODS AND RESULTS: High-resolution spatial distributions of QTI and potentials were determined on the body surface of human subjects and on the surface of a torso-shaped tank containing an isolated canine heart. Additionally, spatial distributions of QTI, recovery times, and STT areas were determined on the surface of exposed canine hearts. Unipolar electrograms were recorded during atrial and ventricular pacing for normal hearts and cases of myocardial infarction. Regions of shortest QTI always coincided with the location of the zero potential line on the cardiac and body surfaces. On the cardiac surface, in regions away from the zero line, similarities were observed between the patterns of QTI and the sequence of recovery. STT areas and recovery times were highly correlated on the cardiac surface. CONCLUSION: QTI is not a robust index of local recovery time on the cardiac surface. QTI distributions were affected by the position of the zero potential line, which is unrelated to local recovery times. However, similarities in the patterns of QTI and recovery times in some regions may help explain the frequently reported predictive value of QT dispersion. Preliminary results indicate STT area may be a better index of recovery time and recovery time dispersion on the epicardium than QTI.

Animals↗

PubMedDate not supplied

[Optimal strategies of spatial distribution: the Olli effect].

The selection of strategies of spatial distribution of individuals has been studied. In case of non-monotonous dependence of reproduction coefficient on the mean population density, a cluster formation is possible. At low mean densities, parity strategies of spatial distribution are realized, and at high densities, non-parity ones. A generalized notion of parity strategy of spatial distribution has been proposed. It includes such expenditures as expenditure for the movement of an individual, defense of the territory etc. A problem of evolutionary stability of different strategies of spatial distribution has been discussed.

Animals↗

PubMedDate not supplied

A study on the spatial distribution of nitrogen and phosphorus balance, and regional nitrogen flow through crop production.

The spatial distribution patterns of the nitrogen and phosphorus input/intake amounts in crop production within two small basins are examined, based upon a cropping unit distribution map that is obtained from remote sensing data analysis. Firstly, we examine the availability and suitability of approaches to the spatial distribution analysis of cultivation patterns classified from material flow characteristics of crop production using seasonal remote-sensing data. Secondly, material flow units in crop production are grouped according to the cultivation patterns obtained from the remote-sensing data analysis. Consequently, the spatial patterns of the amounts of both nitrogen and phosphorus inputs/intakes through crop production on farmland are examined and their spatial distribution maps are prepared according to the material flow units. In addition, we developed a nitrogen flow and runoff model and the model is simulated based on the examination of the results of spatial distribution patterns of the material flow units. The annual nitrogen runoff from small catchments, where various crops are cultivated, varies from 2.7 kg ha(-1) year(-1) to 108 kg ha(-1) year(-1) and the annual balanced losses of nitrogen in small catchments varied from -30 kg ha(-1) year(-1) to 101 kg ha(-1) year(-1). Also, the monthly changes in soil nitrogen of each material flow unit is estimated at -55 kg ha(-1) as a maximum decrease and 114 kg ha(-1) as a maximum increase. These results indicate that the spatial distribution patterns of nutrient input and intake through agricultural activities should be considered when analyzing the material flows and nutritient movement in soil-water systems in rural areas for watershed environmental control and regional agricultural management.

Agriculture↗

PubMed2003

Integrating the roles of information and competitive ability on the spatial distribution of social foragers.

Understanding and predicting the spatial distribution of social foragers among patchily distributed resources is a problem that has been addressed with numerous approaches over the 30 yr since the ideal free distribution (IFD) was first introduced. The two main approaches involve perceptual constraints and unequal competitors. Here we present a model of social foragers choosing among resource patches. Each forager makes a probabilistic choice on the basis of the information acquired through past foraging experiences. Food acquisition is determined by the forager's competitive ability. This model predicts that perceptual constraints have a greater influence on the spatial distribution of foragers than unequal competitive abilities but that competitive ability plays an important role in determining an individual's information state and behavior. Better competitors have access to more information; consequently, we find that competitive abilities and perceptual constraints are integrated through the social environment occupied by individual foragers. Relative competitive abilities influence the forager's information state, and the ability to use information determines the resulting spatial distribution.

Animals↗

PubMed2004

[Effect of land use change on spatial distribution pattern of soil total nitrogen in Keerqin sandy land].

By using statistics and geostatistics, this paper studied the content and spatial pattern of soil total nitrogen (TN) in a glassland and an arable land of southeast Keerqin sandy land. The TN content in 0-10 cm soil layer of the arable land reclaimed from a glassland 8 years ago was not different from that of the virgin grassland, but the TN content in 10-20 cm soil layer was higher than that in the grassland (P < 0.05). The soil TN storage in the grassland was 262.36 g x hm(-2) higher than that in the arable land, and its spatial pattern was significantly different between arable land and grassland. The heterogeneity and spatial dependence of TN in each soil layer (0-10 cm and 10-20 cm) of the arable land were larger than those of the grassland, and the ranges and fractal dimensions of TN in each soil layer of the arable land were larger than those of the grassland. There existed a clear horizontal spatial structure heterogeneity and spatial distribution pattern in the arable land, while in the grassland, the horizontal spatial structure heterogeneity was very low, and the horizontal spatial distribution pattern was random and uniform. The TN content in the 0-10 cm and 10-20 cm soil layers of the arable land had no difference (P < 0.05), its spatial structure characters had some difference (P < 0.05), and its spatial distribution pattern was very similar (r = 0.683, P < 0.05). The TN content and its spatial structure characters between two soil layers of the grassland had remarkable difference (P < 0.05), but its spatial distribution pattern in the two layers was relatively similar (r = 0.395, P < 0.05). In conclusion, agricultural activity could not only influence soil TN content, but also influence its spatial structure characteristics and spatial distribution pattern. Therefore, our study might promote the further study on the effect of land use change on soil nitrogen distribution pattern and its cycling in ecosystems.

Crops, Agricultural↗

PubMed1983

Spatial distribution of pain: a descriptive characteristic of chronic pain.

Self-report of spatial distribution of pain has been employed to assess anatomic accuracy of pain description. To date, there is little information on behavioral or psychological characteristics of chronic pain patients as a function of spatial distribution of pain sites. In the present study, 92 patients presenting to a multidisciplinary pain clinic with chronic facial, back, or extremity pain enumerated total sites of pain throughout the body. Responses were categorized into low (1-2), moderate (3-5) and high (6-18) discrete sites of pain. Patients completed self-report scales assessing various activity abilities and health behaviors, a measure of pain description (McGill Pain Language Questionnaire, MPQ), and health related measures of personality (Illness Behavior Questionnaire, IBQ) and cognitive style (Multifactorial Health Locus of Control, MHLC). One-way ANOVAs revealed significant differences as a function of spatial distribution on a number of behavioral (down-time, walking, recreational, vocational and social abilities; total drug use, number of health professionals consulted), pain description (Total Words Chosen-MPQ, Sum of Ranks-MPQ, and Sensory-MPQ) and psychological variables (Disease Conviction-IBQ and Affective Disturbance-IBQ). Results suggest spatial distribution of pain site to be a useful clinical diagnostic indicator of psychological disturbance in chronic pain patients.

Adult↗

PubMed1995

Asymmetric spatial distributions of motion vectors yield characteristic errors in direction judgements.

For a continuous flow field depicting a combined translation and expansion, there exists a natural distribution of local motion directions whose mean direction corresponds to the direction of translation. A random sampling of this distribution may introduce spatial asymmetries and thus alter the mean direction. This statistical phenomenon has a perceptual parallel: the spatial distribution of the dots becomes relevant with respect to the perceived global direction. The perceived direction of motion corresponds to the mean direction, not to the actual direction of translation.

Humans↗

PubMed2007

Soil nutrients influence spatial distributions of tropical tree species.

The importance of niche vs. neutral assembly mechanisms in structuring tropical tree communities remains an important unsettled question in community ecology [Bell G (2005) Ecology 86:1757-1770]. There is ample evidence that species distributions are determined by soils and habitat factors at landscape (<10(4) km(2)) and regional scales. At local scales (<1 km(2)), however, habitat factors and species distributions show comparable spatial aggregation, making it difficult to disentangle the importance of niche and dispersal processes. In this article, we test soil resource-based niche assembly at a local scale, using species and soil nutrient distributions obtained at high spatial resolution in three diverse neotropical forest plots in Colombia (La Planada), Ecuador (Yasuni), and Panama (Barro Colorado Island). Using spatial distribution maps of >0.5 million individual trees of 1,400 species and 10 essential plant nutrients, we used Monte Carlo simulations of species distributions to test plant-soil associations against null expectations based on dispersal assembly. We found that the spatial distributions of 36-51% of tree species at these sites show strong associations to soil nutrient distributions. Neutral dispersal assembly cannot account for these plant-soil associations or the observed niche breadths of these species. These results indicate that belowground resource availability plays an important role in the assembly of tropical tree communities at local scales and provide the basis for future investigations on the mechanisms of resource competition among tropical tree species.

Ecosystem↗

PubMed1984

Spatial distributions of phrenic and medial gastrocnemius motoneurons in the cat spinal cord.

The longitudinal distributions of both phrenic and medial gastrocnemius motoneurons were quantitatively studied in the cat spinal cord. Both populations of motoneurons were retrogradely labeled by applying horseradish peroxidase (HRP) to the cut central ends of the appropriate peripheral nerves. The longitudinal positions of all labeled motoneurons in each motor column were determined; these data then were used to generate longitudinal distribution histograms and spatial interval distributions (SIDs), the latter being analyzed further by means of power spectra. In three of four cats, longitudinal clustering of phrenic motoneuronal cell bodies was revealed by the presence of a narrow central peak in the SID and the presence of subsidiary peaks. In the fourth cat, only a smaller central peak was observed. Power spectral analysis of the three SIDs having subsidiary peaks revealed that the mean longitudinal distance between clusters was 0.95 mm (range 0.52 to 1.22 mm). The analyses also revealed that on average a phrenic motoneuronal cluster contained 17 motoneurons, and the mean longitudinal length of a cluster was 450 microns. Using single, small-volume injections of HRP into the diaphragm, we concluded that not all the phrenic motoneurons within a single cluster innervate muscle fibers in a discrete region of the diaphragm. Similar quantitative analysis of the distribution of medial gastrocnemius motoneurons did not reveal clustering in this motor column. We suggest that the fundamental differences in the spatial distributions of motoneurons within these two motor columns may be related to differences in the functional organizations of motoneurons innervating axial versus appendicular musculature, i.e., diaphragm versus medial gastrocnemius.

Animals↗

PubMedDate not supplied

Effects of filtration seeding on cell density, spatial distribution, and proliferation in nonwoven fibrous matrices.

The cell seeding density and spatial distribution in a 3-D scaffold are critical to the morphogenetic development of an engineered tissue. A dynamic depth-filtration seeding method was developed to improve the initial cell seeding density and spatial distribution in 3-D nonwoven fibrous matrices commonly used as tissue scaffolds. In this work, trophoblast-like ED27 cells were seeded in poly(ethylene terephthalate) (PET) matrices with various porosities (0.85-0.93). The effects of the initial concentration of cells in the suspension used to seed the PET matrix and the pore size of the matrix on the resulting seeding density and subsequent cell proliferation and tissue development were studied. Compared to the conventional static seeding method, the dynamic depth-filtration seeding method gave a significantly higher initial seeding density (2-4 x 10(7) vs 4 x 10(6) cells/cm3), more uniform cell distribution, and a higher final cell density in the tissue scaffold. The more uniform initial cell spatial distribution from the filtration seeding method also led to more cells in S phase and a prolonged proliferation period. However, both uniform spatial cell distribution and the pore size of the matrices are important to cell proliferation and morphological development in the seeded tissue scaffold. Large-pore matrices led to the formation of cell aggregates and thus might reduce cell proliferation. The dynamic depth-filtration seeding method is better in providing a higher initial seeding density and more uniform cell distribution and is easier to apply to large tissue scaffolds. A depth-filtration model was also developed and can be used to simulate the seeding process and to predict the maximum initial seeding densities in matrices with different porosities.

Biocompatible Materials↗

PubMed2005

Spatial distribution of Dermacentor reticulatus and Ixodes ricinus in Hungary: evidence for change?

A survey was conducted to investigate the spatial distribution of Ixodes ricinus and Dermacentor reticulatus in Hungary and to compare these data with the results of a previous large-scale survey. In the survey conducted in the 1950s, D. reticulatus adults were detected in two isolated areas of two counties, and the presence of these ticks in the collection was explained by accidental introduction. In the present survey, D. reticulatus became the second most common species occurring in all 16 counties involved in the monitoring and showed high prevalence. The change in the spatial distribution of this tick species, the increase of incidence of Babesia canis infection in Hungary, and the increasing number of canine babesiosis case reports from other Central and Central Eastern European countries since the 1970s suggest an expansion of the geographic range of D. reticulatus and intensification of the transmission rate of B. canis and probably other D. reticulatus-borne diseases (e.g. tularemia and tick-borne lymphadenopathy) in the region. The spatial distribution of I. ricinus was roughly in line with the results of the earlier survey. I. ricinus was the most common tick species being present in all 16 counties with the highest prevalence. Nevertheless, the comparison of the data of the previous and current survey cannot be used for fine-scale analysis; thus, it cannot be dismissed that the spatial distribution of I. ricinus also changed during the past decades. The spatial distribution patterns of tick-borne encephalitis in Hungary and other Central Eastern European countries may indicate such a change.

Animals↗

PubMed2004

Spatial distribution of acoustic and elastic properties of human femoral cortical bone.

The purpose of this study is to quantify the spatial distribution of acoustic velocities and elastic properties (elastic constants) on Human femoral cortical bone. Four cross sections (average thickness of 2.09+/-0.27 mm) have been cut transversally between 40% and 70% of the total length and between them parallelepiped samples in each quadrant have been cut. Ultrasonic technique in transmission with immersion focused transducers at 5 MHz and contact transducers 2.25 MHz were used on the cross sections and parallelepiped samples, respectively. The first technique allows relative spatial distribution of velocities to be obtained, meanwhile the second technique allows the direct assessment of elastic constants. For both techniques, bulk velocities were found to be lower at the posterior side with an increase along the length (from 40% to 70% total length) (p < 0.05). Densities and elastic constants show equivalent pattern of variation. These variations are mainly due the cortical porosity related to vascularisation environment. The spatial distribution of velocities exhibits significant radial variation from the endosteal to the periosteal region. This is in agreement with variation of the porosity at that location. Same range of velocities was obtained with both techniques. The range of longitudinal velocities values varies from 3548 to 3967 m/s and between 18.5 and 33.1 GPa for the bulk velocities and axial elastic constants, respectively. Our results are within the range with those found in the literature. However, it must be noted that the range of acoustic and elastic properties variation is concerning the same bone. So, our new results show the ability of the technique to quantify accurately local variation of acoustic and elastic properties (within the section and along the length) of human cortical bone. Furthermore, our immersion technique could be used to assess the spatial distribution of the elastic constants with the knowledge of spatial distribution of densities.

Acoustics↗

PubMed2006

Optimal movement between patches under incomplete information about the spatial distribution of food items.

If the food distribution contains spatial pattern, the food density in a particular patch provides a forager with information about nearby patches. Foragers might use this information to exploit patchily distributed resources profitably. We model the decision on how far to move to the next patch in linear environments with different spatial patterns in the food distribution (clumped, random, and regular) for foragers that differ in their degree of information. An ignorant forager is uninformed and therefore always moves to the nearest patch (be it empty or filled). In contrast, a prescient forager is fully informed and only exploits filled patches, skipping all empty patches. A Bayesian assessor has prior knowledge about the content of patches (i.e. it knows the characteristics of the spatial pattern) and may skip neighbouring patches accordingly by moving to the patch where the highest gain rate is expected. In most clumped and regular distributions there is a benefit of assessment, i.e. Bayesian assessors achieve substantially higher long-term gain rates than ignorant foragers. However, this is not the case in distributions with less strong spatial pattern, despite the fact that there is a large potential benefit from a sophisticated movement rule (i.e. a large penalty of ignorance). Bayesian assessors do also not achieve substantially higher gain rates in environments that are relatively rich or poor in food. These results underline that an incompletely informed forager that is sensitive to spatial pattern should not always respond to existing pattern. Furthermore, we show that an assessing forager can enhance its long-term gain rate in highly clumped and some specific near-regular food distributions, by sampling the environment in slightly larger spatial units.

Animals↗

PubMed2005

Analysis of the spatial distribution between successive earthquakes.

Spatial distances between subsequent earthquakes in southern California exhibit scale-free statistics, with a critical exponent delta approximately 0.6, as well as finite size scaling. The statistics are independent of the threshold magnitude as long as the catalog is complete, but depend strongly on the temporal ordering of events, rather than the geometry of the spatial epicenter distribution. Nevertheless, the spatial distance and waiting time between subsequent earthquakes are uncorrelated with each other. These observations contradict the theory of aftershock zone scaling with main shock magnitude.

Journal Article↗

PubMedDate not supplied

Effects of spatial distribution on proton relaxation enhancement by particulate iron oxide.

The proton relaxation effect of superparamagnetic iron oxide (SPIO) particles under varying conditions of spatial distribution was investigated with use of phantoms. Agar phantoms containing various concentrations of SPIO or gadopentetate dimeglumine, with and without Sephadex beads, were studied. Phantoms with Sephadex had a heterogeneous spatial distribution of iron oxide, comparable to liver tissue in vivo. Relaxometry at 0.47 T showed decreased T2 relaxivity of SPIO in Sephadex phantoms compared with that in agar phantoms without Sephadex. On T2-weighted images obtained at 1.5 T, the signal intensity of Sephadex phantoms showed less SPIO relaxation effect than that of plain agar phantoms. Unlike SPIO, gadopentetate dimeglumine showed the same relaxivities and signal intensity in plain agar and Sephadex phantoms. The results show that the T2 relaxation effect of iron oxide depends on its spatial distribution. A heterogeneous spatial distribution, as in intact liver tissue, diminishes the T2 relaxivity of iron oxide particles.

Agar↗