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At least 37 records · Page 2Linked to original sources

PubMed2001

Midpedicular distance: an alternative pedicular distance measurement.

OBJECTIVES: 1. To introduce the measurement of midpedicular distance (MPD). 2. To study the correlation of the MPD measured on AP plain film and CT scan film and compared with the correlation of the interpedicular distance (IPD) measurement. MATERIAL AND METHOD: The MPD, the distance between intersection point of midvertical and midhorizontal lines drawn on the two pedicles of the same vertebra, was measured on lumbar spine (L1, L2) AP plain film. The IPD, the distance between the inner cortical shadow of the pedicles, was also measured on the same film. The measurements of MPD and IPD were then carried out on the same individual's CT scan film (which had an imprint scale). The study was performed on 35 subjects (20 males, 15 females) with an average age of 48.2 years (range 19-81 years). The correlation of the value measured on plain film and CT scan film was studied using Pearson's correlation test. RESULT: The MPD measurement on plain film had higher correlation with MPD measurement on CT scan film (L1 level: r = 0.778, L2 level: r = 0.732, p<0.001) compared with the IPD measurement (L1 level: r = 0.672, L2 level: r = 0.604, p<0.001). CONCLUSION: The midpedicular distance measurement on lumbar spine AP plain film can better be used to reflect the pedicular distance than the interpedicular distance.

Adult↗

PubMed1998

Fixation disparity at different viewing distances and the preferred viewing distance in a laboratory near-vision task.

Previous research has shown that subjects with normal binocular vision differ reliably in the extent to which their fixation disparity changes in the exo direction when the viewing distance is shortened from 100 to 20 cm. Since fixation disparity can lead to asthenopic complaints, the present study investigates whether an exo fixation disparity induced by proximity may cause subjects to move to a longer viewing distance during a near-vision task in order to reduce exo fixation disparity. In two optometric sessions, fixation disparity and accommodation were tested at 60, 40, and 30 cm viewing distance. In a further session, subjects were required to begin a one-hour near-vision task at about 40 cm viewing distance, at which the text characters subtended a comfortable visual angle of 21 min arc. Later, the subjects were free to adopt any viewing distance. In the initial phase of the task, subjects moved back from the screen to a greater or lesser extent that was correlated with the amount of proximal exo fixation disparity: the more a subject's fixation disparity changed to exo when the viewing distance had been shortened from 60 to 30 cm the more he or she moved to longer viewing distances in the course of the near-vision task. Further, the more distant the resting position of vergence (dark vergence), the more visual complaints the subjects indicated after the task relative to before.

Accommodation, Ocular↗

PubMed2003

Anaphor resolution as a function of spatial distance and priming: exploring the spatial distance effect in situation models.

Anaphor resolution has been found to depend on the spatial distance between the reader's focus of attention and the location of the anaphor referent in a spatially organized situation model (spatial distance effect; Rinck & Bower, 1995). This effect implies that a) the situation model is spatially organized and b) spatial distance has a stronger effect on the resolution of anaphoric reference than the text priming the anaphor referent. In three experiments, adult participants read 12 short narratives about protagonists moving around a building. Mentionning the location of the anaphor referent in text prior to the anaphoric sentence facilitated anaphor resolution. Decreased spatial distance consistently facilitated anaphor resolution, even when priming the anaphor referent affected anaphor resolution more strongly than spatial distance. Results are discussed with regard to the interpretation and reliability of the spatial distance effect and the interaction of different representational levels in the context of multi-level theories of text comprehension.

Adult↗

PubMed2004

Integration of retinal disparity and fixation-distance related signals toward an egocentric coding of distance in the posterior parietal cortex of primates.

For those movements that are directed toward objects located in extrapersonal space, it is necessary that visual inputs are first remapped from a retinal coordinate system to a body-centered one. The posterior parietal cortex (PPC) most likely integrates retinal and extraretinal information to determine the egocentric distance of an object located in three-dimensional (3-D) space. This determination requires both a retinal disparity signal and a parallel estimate of the fixation distance. We recorded from the lateral intraparietal area (LIP) to see if single neurons respond to both vergence angle and retinal disparity and if these two signals are integrated to encode egocentric distance. Monkeys were trained to make saccades to real targets in 3-D space. When both fixation distance and disparity of visual stimuli were varied, the disparity tuning of individual neurons display a fixation-distance modulation. We propose that the observed modulation contributes to a spatial coding domain intermediate between retinal and egocentric because the disparity tuning shifts in a systematic way with changes in fixation distance.

Action Potentials↗

PubMed1991

Distance-constraint approach to higher-order structures of globular proteins with empirically determined distances between amino acid residues.

An analysis of higher-order structures of globular proteins by means of a distance-constraint approach is presented. Conformations are generated for each of 21 test proteins of small and medium sizes by optimizing an objective function f = sigma sigma wij(dij - (dij]2, where dij is a distance between residues i and j in a calculated conformation, (dij) is an assigned distance to the (ij) pair of residues which is determined based on the statistics of known three-dimensional structures of 14 proteins in the earlier study, and wij is a weighting factor. (dij) involves information about hydrophobicity and hydrophilicity of each amino acid residue and about connectivity of a polypeptide chain. In these calculations, only the amino acid sequence is used as input data specific to a calculated protein. With respect to higher-order structures regenerated in the optimized conformations, the following properties are analyzed: (a) N14 of a residue, defined as the number of residues surrounding the residue located within a sphere of radius of 14 A; (b) root-mean-square differences of the global and local conformations from the corresponding X-ray conformations; (c) distance profiles in the short and medium ranges; and (d) distance maps. The effects of supplementary information about locations of secondary structures and disulfide bonds are also examined to discuss the potential ability of this methodology to predict the three-dimensional structures of globular proteins.

Amino Acids↗

PubMed1988

Resolution of end-to-end distance distributions of flexible molecules using quenching-induced variations of the Forster distance for fluorescence energy transfer.

We describe a new method to recover the distribution of donor-to-acceptor (D-A) distances in flexible molecules using steady-state measurements of the efficiency of fluorescence energy transfer. The method depends upon changes in the Forster distance (Ro) induced by collisional quenching of the donor emission. The Ro-dependent transfer efficiencies are analyzed using nonlinear least squares to recover the mean D-A distance and the width of the distribution. The method was developed and tested using three synthetic D-A pairs, in which the chromophores were separated by alkyl chains of varying lengths. As an example application we also recovered the distribution of distances from the single tryptophan residue in troponin I (trp 158) to acceptor-labeled cysteine 133. The half-width of the distribution increases from 12 A in the native state to 53 A when unfolded by guanidine hydrochloride. For both TnI and the three model compounds the distance distributions recovered from the steady-state transfer efficiencies were in excellent agreement with the distributions recovered using the more sophisticated frequency-domain method (Lakowicz, J.R., M.L. Johnson, W. Wiczk, A. Bhat, and R.F. Steiner. 1987. Chem. Phys. Lett. 138:587-593). The method was found to be reliable and should be generally useful for studies of conformational distributions of macromolecules.

Energy Transfer↗

PubMed1984

The distance between S1, S21, and the 3' end of 16S RNA in 30S ribosomal subunits. The effect of poly(uridylic acid) and 50S subunits on these distances.

The apparent distances between probes covalently attached to the cysteine thiols of S1 or S21 and the 3' end of 16S RNA in Escherichia coli 30S ribosomal subunits were determined by non-radiative energy transfer to be: S21-16S RNA, 5.1 nm; S21-S1, 6.9 nm; S1-16S RNA, 6.8 nm. Binding of poly(uridylic acid) to 30S subunits causes the apparent distances between S1 and 16S RNA or S21 and 16S RNA to increase by more than 1.2 nm and 0.5 nm, respectively, but has little or no effect on the S1-S21 distance. Binding of 50S subunits causes an apparent increase in the S21-16S RNA and S21-S1 distances by 1.0 nm and 0.8 nm, respectively, but has little or no effect on the S1-16S-RNA distance.

Coumarins↗

PubMed1978

Genetical distance and dermatoglyphic characters. II. Intrapopulation distance coefficients.

This paper attempts to evaluate the dermatoglyphic (genetical) distance between two Polish population samples in relation to the intrapopulation distance coefficients estimated within each sample. All the coefficients have been based, in turn, on frequencies of fingertip, palmar and sole pattern elements, separately and for all characters combined. The results of a comparison of various combinations of dermatoglyphic characters with one another in respect of all successive values of a distance coefficient indicate that, if populations of mostly related individuals were compared, sole patterns have been the most efficient ones in differentiating between the two normal population samples. The values of inter- and intrapopulation distance coefficients obtained from samples consisting mostly of family units have been compared with those estimated in samples of non-related individuals. The limitations and difficulties in the interpretation of the values of a distance coefficient related both to the material used and statistical procedures are discussed.

Dermatoglyphics↗

PubMed2001

Anthropometric and demographic factors affecting distance hopped and limb symmetry index for the crossover hop-for-distance test in high school athletes.

STUDY DESIGN: Prospective cohort study using a random selection from an accessible population. OBJECTIVES: We examined anthropometric and demographic characteristics affecting distance hopped (DH) and limb symmetry index (LSI) in the crossover hop-for-distance test in uninjured high school athletes. BACKGROUND: Between-subject comparisons of hop test results described by DH and LSI are common in the literature and clinical practice. The effect that anthropometric traits and demographic characteristics have on these measures is uncertain but must be known to correctly interpret hop-for-distance test results in research or to determine suitability of return to sports. METHODS AND MEASURES: For 201 high school athletes (age = 15.15+/-1.45 years, mean weight = 63.67+/-14.02 kg, mean height = 167.92+/-9.58 cm) completing the crossover hop-for-distance test, we recorded maximum DH for each leg and calculated the LSI of each subject. We performed 2 separate step-wise regression analysis models to develop predictive equations for DH and LSI. RESULTS: Age (r = 0.36), weight r = 0.41), and body fat percentage (r = 0.58) were significant predictors of DH, with the regression model explaining 59% of the variability. None of the measured variables were significant predictors of LSI (r = 0.03). The regression model explained only 3% of the variability of LSI. CONCLUSIONS: The LSI for the crossover hop-for-distance test can be compared among all individuals without subdividing into groups. Subject characteristics should be as homogeneous as possible when comparing DH among subjects or groups.

Adipose Tissue↗

PubMed2003

Developing interactive course Web sites for distance education and characteristics of students enrolled in distance learning courses.

The ubiquity of the Internet has made disseminating information across geographical boundaries a relatively easy task. Apart from text-based materials, the Internet provides an easy means to transmit images, sound, video, and other multimedia content to a global audience, making it an ideal medium for establishing distance learning programs. Two Internet-based distance learning courses were developed to teach animal physiology to veterinary technicians in the School of Veterinary Medicine at Purdue University. These distance learning course sites are designed to take advantage of multimedia technology to enhance students' learning experiences. Multimedia has been used in education to make the learning process more engaging and interactive. The two course sites have a number of multimedia features that complement the textual subject matter. This article describes the features of the course Web sites and summarizes our experiences in designing and conducting Web-based physiology courses to distance learners. In addition, we describe the characteristics of our distance learning students.

Adolescent↗

PubMed1990

Isolation by distance and correlation analysis of distance measures in the study of population structure: example from the Island of Hvar.

Assessment of the population structure on the island of Hvar is based on the analysis of Malécot's isolation by distance model. We have tested the fit of the model by regression analysis of different measures of similarity (genetic kinship) and distance [Hamming's HSM distance for linguistic data; Mahalanobis's D2 distances for anthropometric head and body dimensions, radiogrammetric dimensions of metacarpal bones, physiological (cardiorespiratory) traits, and quantitative dermatoglyphic properties of the digitopalmar complex; and Edwards's E2 for frequencies of erythrocyte antigens]. Good fit of the model for linguistic and anthropometric data, which was demonstrated in previous studies on other eastern Adriatic populations, is confirmed. We compared parameters of the model with those already published for various populations in the eastern Adriatic and other parts of the world. We also evaluated the pattern of correlations between different measures of geographic, biological, and sociocultural distances through principal components analysis and interpreted the results within the context of microevolutionary theory and the population's ethnohistorical background.

Adult↗

PubMed1998

The necessity of a perception-action approach to definite distance perception: monocular distance perception to guide reaching.

In this investigation of monocular perception of egocentric distance, the authors advocate the necessity of a perception-action approach because calibration is intrinsic to definite distance perception. A helmet-mounted camera and display were used to isolate optic flow generated by participants' head movements toward a target, and participants' reaches to place a stylus either in a target hole (Experiments 1, 2, and 4) or aligned under a target surface (Experiment 3) were analyzed. Conclusions are that binocular distance perception is accurate, monocular distance perception yields compression that is not eliminated by feedback, but feedback is used to eliminate underestimation generated by restriction of the size of the visual field.

Adult↗

PubMed1988

Determination of three-dimensional structures of proteins from interproton distance data by hybrid distance geometry-dynamical simulated annealing calculations.

A new hybrid distance space-real space method for determining three-dimensional structures of proteins on the basis of interproton distance restraints is presented. It involves the following steps: (i) the approximate polypeptide fold is obtained by generating a set of substructures comprising only a small subset of atoms by projection from multi-dimensional distance space into three-dimensional cartesian coordinate space using a procedure known as 'embedding'; (ii) all remaining atoms are then added by best fitting extended amino acids one residue at a time to the substructures; (iii) the resulting structures are used as the starting point for real space dynamical simulated annealing calculations. The latter involve heating the system to a high temperature followed by slow cooling in order to overcome potential barriers along the pathway towards the global minimum region. This is carried out by solving Newton's equations of motion. Unlike conventional restrained molecular dynamics, however, the non-bonded interactions are represented by a simple van der Waals repulsion term. The method is illustrated by calculations on crambin (46 residues) and the globular domain of histone H5 (79 residues). It is shown that the hybrid method is more efficient computationally and samples a larger region of conformational space consistent with the experimental data than full metric matrix distance geometry calculations alone, particularly for large systems.

Histones↗

PubMed2001

Geographical and genetic distances among zooplankton populations in a set of interconnected ponds: a plea for using GIS modelling of the effective geographical distance.

In systems of interconnected ponds or lakes, the dispersal of zooplankton may be mediated by the active population component, with rivulets and overflows functioning as dispersal pathways. Using a landscape-based approach, we modelled the effective geographical distance among a set of interconnected ponds (De Maten, Genk, Belgium) in a Geographic Information System (GIS) environment. The first model (the Landscape Model; LM) corrects for the presence of direct connections among ponds and was based on the existing landscape structure (i.e. network of connecting elements among ponds, travelling distance and direction of the current). A second model (the Flow Rate Model; FRM) also incorporated field data on flow rates in the connecting elements as the driving force for the passive dispersal of the active zooplankton population component. Finally, the third model (the Dispersal Rate Model; DRM) incorporated field data on zooplankton dispersal rates. An analysis of the pattern of genetic differentiation among Daphnia ambigua populations inhabiting 10 ponds in the pond complex reveals that the effective geographical distance as modelled by the flow rate and the dispersal rate model provide a better approximation of the true rates of genetic exchange among populations than mere Euclidean geographical distances or the landscape model that takes into account solely the presence of physical connections.

Alleles↗

PubMed1998

Comparison of frequency-distance relationship and Gaussian-diffusion-based methods of compensation for distance-dependent spatial resolution in SPECT imaging.

The goal of this investigation was to compare resolution recovery versus noise level of two methods for compensation of distance-dependent resolution (DDR) in SPECT imaging. The two methods of compensation were restoration filtering based on the frequency-distance relationship (FDR) prior to iterative reconstruction, and modelling DDR in the projector/backprojector pair employed in iterative reconstruction. FDR restoration filtering was computationally faster than modelling the detector response in iterative reconstruction. Using Gaussian diffusion to model the detector response in iterative reconstruction sped up the process by a factor of 2.5 over frequency domain filtering in the projector/backprojector pair. Gaussian diffusion modelling resulted in a better resolution versus noise tradeoff than either FDR restoration filtering or solely modelling attenuation in the projector/backprojector pair of iterative reconstruction. For the pixel size investigated herein (0.317 cm), accounting for DDR in the projector/backprojector pair by Gaussian diffusion, or by applying a blurring function based on the distance from the face of the collimator at each distance, resulted in very similar resolution recovery and slice noise level.

Computer Simulation↗

PubMed1976

Genetical distance and dermatoglyphic characters. I. Interpopulation distance coefficients.

The distance coefficients between two relatively isolated population groups in Poland, based on various combinations of dermatoglyphic non-measurable characters were estimated. These were compared with the overall dermatoglyphic distance coefficients estimated separately for left and right, as well as with the serologic distance coefficient, based on ABO, Rh and Duffy blood groups. Dermatoglyphic distance coefficients, estimated from quantitative variables (pattern intensities) using Penrose's C2H analysis of variance method, were also introduced for a comparison. The differences in frequencies between two populations, separately for each character, were also compared with its heritability values.

ABO Blood-Group System↗

PubMed1978

Genetical distance and dermatoglyphic characters. III. Dermatoglyphic distances within twin pairs, between left and right sides and between normals and 21-trisomics.

The dermatoglyphic (genetical) distance coefficients have been estimated within monozygotic and dizygotic twin pairs, between left and right sides of the same individual and between normal subjects and 21-trisomics. All the coefficients have been based, in turn, on frequencies of fingertip, palmar and sole pattern elements, separately and for all characters combined. Quantitative variables (pattern intensities) have also been used for independent evaluation of the C2H distance coefficient in monozygotic and dizygotic twins, and in 21-trisomics as compared with normal individuals. The values of a distance have then been considered in relation to the degree of genetical likeness between the compared items as well as to the relative contribution of each pattern combination to the overall value of a distance. Some limitations in the interpretation of the results, connected mainly with statistical procedures, are also discussed.

Chromosomes, Human, 21-22 and Y↗

PubMed1987

A comparison of the restrained molecular dynamics and distance geometry methods for determining three-dimensional structures of proteins on the basis of interproton distances.

A direct comparison of the metric matrix distance geometry and restrained molecular dynamics methods for determining three-dimensional structures of proteins on the basis of interproton distances is presented using crambin as a model system. It is shown that both methods reproduce the overall features of the secondary and tertiary structure (shape and polypeptide fold). The region of conformational space sampled by the converged structures generated by the two methods is similar in size, and in both cases the converged structures are distributed about mean structures which are closer to the X-ray structure than any of the individual structures. The restrained molecular dynamics structures are superior to those obtained from distance geometry as regards local backbone conformation, side chain positions and non-bonding energies.

Chemical Phenomena↗