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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↗
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↗
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↗
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↗
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↗
PubMed1994

Effects of activation sequence on the spatial distribution of repolarization properties.

The electrotonic effects of activation spread on the spatial distribution of repolarization properties were studied in animal experiments and with computer simulations. Refractory periods (RPs) were measured at 36 sites within a 1.0 cm2 region of the epicardial surface of the canine pulmonary conus during 37 drives in 11 experiments. In each experiment three or four sites along the perimeter of the region bounding the RP test sites were driven. Activation propagated uniformly during some and nonuniformly during other drives in the same animals. In general, RPs were distributed uniformly when activation spread uniformly and nonuniformly when activation spread nonuniformly. The authors observed RP differences as large as 16 ms between sites with 2 mm separation during drive from some epicardial sites in these normal canine hearts. Indices of nonuniformity of activation and of relative RP values were used to quantify the relation between nonuniformity of activation spread and the spatial distribution of the RP. There was a significant negative correlation between nonuniformity of activation and RP indices during the 19 drives in which activation spread nonuniformly. This indicated that RPs were relatively long at sites where activation spread decelerated and relatively short at sites where activation spread accelerated. When nonuniform activation spread was simulated by introducing high-resistance barriers in a model with fixed anisotropic conductivities, there were marked spatial variations in action potential duration. The spatial variations in action potential duration were negatively correlated to acceleration and deceleration of activation spread. The major new finding of this study is that the spatial distributions of RPs are markedly affected by activation spread. Since both characteristics of activation sequence and nonuniformity of RP distributions have roles in reentrant arrhythmias, the findings suggest that some sites of origin of premature activity may be more arrhythmogenic than others. The findings may also explain why ventricular tachycardia can sometimes be initiated from one but not from other sites in patients undergoing electrophysiologic testing.

Action Potentials↗
PubMed2000

Evidence for auditory feature integration with spatially distributed items.

Recent auditory research using sequentially presented, spatially fixed tones has found evidence that, as in vision for simultaneous, spatially distributed objects, attention appears to be important for the integration of perceptual features that enable the identification of auditory events. The present investigation extended these findings to arrays of simultaneously presented, spatially distributed musical tones. In the primary tasks, listeners were required to search for specific cued conjunctions of values for the features of pitch and instrument timbre. In secondary tasks, listeners were required to search for a single cued value of either the pitch or the timbre feature. In the primary tasks, listeners made frequent errors in reporting the presence or absence of target conjunctions. Probability modeling, derived from the visual search literature, revealed that the error rates in the primary tasks reflected the relatively infrequent failure to correctly identify pitch or timbre features, plus the far more frequent illusory conjunction of separately presented pitch and timbre features. Estimates of illusory conjunction rate ranged from 23% to 40%. Thus, a process must exist in audition that integrates separately registered features. The implications of the results for the processing of isolated auditory features, as well as auditory events defined by conjunctions of features, are discussed.

Auditory Perception↗
PubMed1984

Nonrandom spatial distribution by mammalian cells in culture.

Quadrat analysis was used to investigate the spatial distribution of seven mammalian cell lines in culture. The number of cells in replicate unit areas of the culture was determined, and the variance to mean ratio used as an index of random and nonrandom spatial distribution. Only mouse SV3T3 cells distributed themselves randomly throughout the entire culture growth cycle. The remaining six lines all assumed a nonrandom distribution at some point in their growth cycles. Mouse L929 cells displayed avoidance behavior, and spaced themselves at regular intervals in a uniform spatial distribution. The five remaining lines (mouse S180, rat C6, hamster CHO, canine MDCK, and human BeWo) formed multicellular clusters, and were distributed aggregatively rather than randomly. Random walk migration can account for the random distribution of SV3T3 cells. Random walk combined with contact inhibition of movement provides a satisfactory explanation for the uniform distribution of L929 cells. Random walk and contact inhibition are incompatible with cell clustering, however. Thus other mechanisms of motility or adhesiveness must contribute to cell clustering. It is possible that random walk and contact inhibition may be less common components of cell movement than generally assumed.

Animals↗
PubMed1997

The role of vitronectin in the attachment and spatial distribution of bone-derived cells on materials with patterned surface chemistry.

In recent years a central objective of tissue engineering has been understanding the interaction of cells with biomaterial surfaces. In this study we examined the protein adsorption events necessary to control the attachment and the subsequent spatial distribution of bone-derived cells exposed to chemically modified surfaces. Silane chemistry and photolithography techniques were used to create substrates with alternating regions of an aminosilane, N-(2-aminoethyl)-3-aminopropyl-trimethoxysilane (EDS), along side an alkylsilane, dimethyldichlorosilane (DMS), on quartz surfaces. Sera depleted of fibronectin (Fn), vitronectin (Vn), or both were used to determine if these proteins were necessary for the initial attachment and spatial distribution of bone-derived cells exposed to modified surfaces in vitro. The kinetics and mechanisms of the spatial distribution of cells were examined using light microscopy and digital image acquisition and subsequently were analyzed. Compared to complete serum, the use of serum depleted of fibronectin with vitronectin included had minimal effect on the cell attachment, spreading, and spatial distribution on the EDS regions of the surface. However, the use of serum depleted of vitronectin with or without fibronectin included resulted in greatly reduced cell attachment and spreading. Thus the presence of vitronectin was required for the attachment, spreading, and spatial distribution of bone-derived cells exposed to EDS/DMS-patterned surfaces.

Adsorption↗
PubMed1988

A general, computer-based method for study of the spatial distribution of muscle fiber types in skeletal muscle.

The present method provides detailed quantitative information on the spatial distribution of the muscle fiber types in skeletal muscle. This is accomplished by comparing the measured spatial distribution of the fiber types with a computer-simulated random pattern. The method is based on a registration of the absolute frequency for six principal categories of fiber contacts (I-I, I-IIA, I-IIB, IIA-IIA, IIA-IIB, IIB-IIB). A computer program was designed to simulate a random pattern of fibers. The simulations were performed with high accuracy with regard to fiber type proportion and the number of neighbouring fibers. The computer then calculated the frequency for each of the different categories of fiber contacts in the simulated random pattern. The measured distribution of fiber contacts could thus be compared to the simulated random pattern. In three bovine muscles studied, the spatial distribution of the muscle fiber types showed a similar pattern. The muscle fibers had a distinct tendency to be surrounded by fibers of a different type. In all three muscles the difference between the measured and the simulated random pattern was statistically significant (p less than 10(-3).

Animals↗
PubMed2001

Reliability of tissue volumes and their spatial distribution for segmented magnetic resonance images.

Before using MRI tissue segmentation in clinical studies as a dependent variable or as a means to correct functional data for differential tissue contribution, we must first establish the volume reliability and spatial distribution reproducibility of the segmentation method. Although several reports of volume reliability can be found in the literature, there are no articles assessing the reproducibility of the spatial distribution of tissue. In this report, we examine the validity, volume reliability, and spatial distribution reproducibility for our K-means cluster segmentation. Validation was examined by classifying gray matter, white matter, and CSF on images constructed using an MRI simulator and digital brain phantom, with percentage volume differences of less than 5% and spatial distribution overlaps greater than 0.94 (1.0 is perfect). We also segmented repeat scan MRIs from 10 healthy subjects, with intraclass correlation coefficients greater than 0.92 for cortical gray matter, white matter, sulcal CSF, and ventricular CSF. The original scans were also coregistered to the repeat scan of the same subject, and the spatial overlap for each tissue was then computed. Our overlaps ranged from 0.75 to 0.86 for these tissues. Our results support the use of K-means cluster segmentation, and the use of segmented structural MRIs to guide the analysis of functional and other images.

Adult↗
PubMed1997

Influence of epinephrine, propranolol, and atrial pacing on spatial distribution of recovery time measured by body surface mapping in congenital long QT syndrome.

INTRODUCTION: Sympathetic stimulation plays an important role in the genesis of QT(U) prolongation and ventricular arrhythmias in congenital long QT syndrome (LQTS). Permanent pacemaker as well as beta blockers are reported to be effective in the management of this syndrome. The purpose of this study was to examine influence of epinephrine (alpha- and beta-adrenergic stimulation), propranolol (beta blocker), and atrial pacing on the spatial distribution of repolarization using body surface recovery time (RT) in congenital LQTS. METHODS AND RESULTS: Body surface mapping was recorded in 16 patients with congenital LQTS and 20 control patients before and after epinephrine infusion (0.1 microg/kg per min), oral propranolol (1 to 2 mg/kg per day), addition of epinephrine during oral propranolol, atrial pacing at a cycle length of 600 or 750 msec, and addition of epinephrine during atrial pacing. The RT, that is, the interval between the QRS onset and the maximum dV/dt point in the ST-T segment, was measured automatically by a computer from each of the 87 mapping leads, and the corrected RT (RTc) was calculated using Bazett's method. In patients with congenital LQTS, epinephrine markedly changed the T(U) wave morphology and spatial distribution of RT, especially the distribution of maximum RT of the left anterior chest and back. Epinephrine prolonged the maximum RTc and the minimum RTc in 87 leads and increased the RTc dispersion (difference between maximum and minimum RTc in each patient). Neither propranolol nor atrial pacing changed the T(U) wave morphology, spatial distribution of RT, or any RTc parameters at rest. Propranolol prevented the influences of epinephrine on the T(U) wave morphology, spatial distribution of RT, and RTc parameters, whereas atrial pacing did not. In control patients, marked changes of the T(U) wave morphology and RTc parameters were not recognized during the entire protocol. CONCLUSIONS: Our results indicate that epinephrine markedly changes the spatial distribution of repolarization and increases the dispersion of repolarization, which probably are linked to arrhythmogenesis in congenital LQTS. The data suggest that propranolol but not atrial pacing are effective to suppress repolarization abnormalities during sympathetic stimulation.

Adolescent↗
PubMed1985

Spatial distribution of dopamine, methotrexate and antipyrine during continuous intracerebral microperfusion.

The spatial distributions of 3 model drugs, [14C]dopamine hydrochloride (DA), [3H]sodium methotrexate (MTX) and [14C]antipyrine (AP), were determined after 6 days continuous microperfusion of the diencephalon of rabbits. The basic pattern of distribution was the same for each drug: the tissue concentration, expressed as a function of the perfusate concentration, was maximal at the cannula tip, and declined sharply with radial distance from the tip. However, at any given distance, concentrations of radioisotopes derived from DA and MTX, both ionized, lipid-insoluble drugs, were one to two orders of magnitude higher than those derived from AP, a lipid-soluble drug. Although concentrations of isotopes derived from DA and MTX were in the same range, their distribution patterns were consistently different. The results demonstrate that intracerebrally microperfused drugs may have quantitatively different spatial distributions, related to their physicochemical characteristics and/or their binding and metabolism in brain tissue.

Animals↗
PubMed1985

Spatial distribution of immature Culicoides variipennis (Coq.).

Circadian fluctuation in the spatial distribution of immature Culicoides variipennis (Coq.) was studied in Saltville, Virginia, USA during the summer of 1983. Pupae and early instar larvae (1st and 2nd) were localized above the shoreline in the top cm of mud and displayed little migration from this region during the 24 hr sampling period, however, later instar larvae (3rd and 4th) showed marked migration patterns. Most larval movement was horizontal rather than vertical and was confined to the top cm of mud. Late instar larvae moved towards the water during the day but migrated up above shoreline during the night. Seasonal fluctuation in larval spatial distribution was also studied. Larvae appeared to move progressively downward into the mud during the autumn. However, when the site became frozen the majority of larvae occupied a narrow liquid interface between the ice cover and the frozen mud beneath.

Animals↗