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At least 919 records · Page 51Linked to original sources
PubMed2000

Absence of evidence for isolation by distance in an expanding cane toad (Bufo marinus) population: an individual-based analysis of microsatellite genotypes.

The cane toad (Bufo marinus) was introduced in 1935 in Australia, where it spread rapidly. We have tested for isolation by distance by analysing at a local geographical scale a continuous population using seven microsatellite markers and an individual-based method. The matrix of pairwise individual differentiation was not significantly correlated with that of geographical distance. Regression analyses gave a low positive slope of 0.00072 (all individuals) or a negative slope of 0.0017 (individuals with a distance higher than the previously estimated mean dispersal distance). The absence of evidence for isolation by distance favours the hypothesis that the substantial differentiation and autocorrelation previously observed at enzyme loci, mainly results from discontinuities in the colonization process with founder effects occurring at the time of the establishment of new populations.

Animals↗
PubMed2002

Evolutionary and statistical properties of three genetic distances.

Many genetic distances have been developed to summarize allele frequency differences between populations. I review the evolutionary and statistical properties of three popular genetic distances: DS, DA, and theta;, using computer simulation of two simple evolutionary histories: an isolation model of population divergence and an equilibrium migration model. The effect of effective population size, mutation rate, and mutation mechanism upon the parametric value between pairs of populations in these models explored, and the unique properties of each distance are described. The effect of these evolutionary parameters on study design is also investigated and similar results are found for each genetic distance in each model of evolution: large sample sizes are warranted when populations are relatively genetically similar; and loci with more alleles produce better estimates of genetic distance.

Computer Simulation↗
PubMed1996

Estimation of fetal shoulder width by measurement of the humerospinous distance by ultrasound.

The present study was undertaken to find a practical method for estimating the fetal shoulder width by ultrasound. Sixty pregnant women at term were included in the study. The distance between the lateral margin of the fetal cartilaginous caput humeri and the processus spinosus of the cervical vertebra C7 (humerospinous distance) was measured by ultrasound. The neonatal shoulder width was measured with a craniometer during the first postnatal day. Linear regression analysis was used to calculate the correlation between the humerospinous distance and the shoulder width, and a significant linear correlation (r = 0.612, p < 0.001) was shown. Although, in this small study, we could not show a relationship between humerospinous distance and dystocia, we feel a clinical study of humerospinous distance as a predictor of shoulder dystocia is indicated.

Adult↗
PubMed2002

Normal values and standard deviations for pupil diameter and interpupillary distance in subjects aged 1 month to 19 years.

Normal values of pupil diameters and interpupillary distances (PDs) were measured in a population of 1311 subjects (in 4294 visits) ranging from 1 month of age to slightly over 19 years of age. Subjects in this study were recruited from birth announcements in a local newspaper for a developmental vision project. Pupil sizes were measured photographically when the corneas were illuminated by 15.9 +/- 0.5 lux ambient illumination (i.e. under mesopic conditions). Interpupillary distance was measured with an interocular distance rule while the subject fixated an object at 0.66 m distance. These PD measurements were corrected for systematic measurement errors and to an infinite viewing distance using radii of ocular rotation based on age-dependent axial lengths. Means and S.D. were calculated for age, pupil diameter and PD for each 1-year group of male and female subjects. The second order regression equation for average pupil size as a function of age was determined: [males pupil diameter (in mm) = 5.83 +/- 0.181*age in years - 0053*age in years2, r2 = 0.897; female pupil diameter = 5.40 + 0.285*age in years - 0.0109*age in years2, r2 = 0.945]. The dierence between male and female pupil sizes (mean male - female = 0.13 mm) was marginally not significant (p < 0.054). The average corrected PDs as a function of age were found to approximate another second-order regression equation: (males PD = 43.36 + 1.663*age in years - 0.034*age in years2, r2 = 0.986; females PD = 41.76 + 1.891 *age in years - 0.052*age in years2, r2 = 0.986). Male PD was wider than female PD by an average of 1.58 mm (p < 0.0003). As expected, the results of this study were similar to a preliminary investigation conducted by Thunyalukul et al. [Invest. Ophthalmol. Vis. Sci. 37 (1996) S731] on a portion of the present data set, and also very similar to data from another study of comparable racial composition using a different measurement method [Pryor, Pediatrics 44 (1969) 973]. It was concluded that pupil diameter and PD increase more gradually than axial length of the eye in the first few years of life. The normal values and S.D. for both pupil size and PD determined in this study have important clinical implications as well as applications in the optical industry.

Adolescent↗
PubMed2001

Validity of pulp-to-palm distance as a measure of finger flexion.

This study investigated the validity of pulp-to-palm distance measures as clinical indicators of finger flexion capacity. Pulp-to-palm distance and goniometry of the metacarpophalangeal, proximal interphalangeal and distal interphalangeal joints were measured by a single tester in 50 patients with abnormal digital flexion using a computerized hand assessment system. The correlation between pulp-to-palm distance measurements and total finger flexion measures obtained by goniometry, was moderate (r=-0.46 and -0.51). This indicates that the measures are not interchangeable. The relationship between an upper extremity disability score (DASH) and restricted motion was stronger for the goniometric measurements (r=0.45, P<0.01) than for the pulp-to-palm distance measurements (r<0.30, P>0.01). Both types of range of motion measurements were able to discriminate between minimal and substantial upper extremity disability. Further methodological evaluation is required to support the use of pulp-to-palm distance measures as an outcome indicator.

Adult↗
PubMed2002

Influence of body mass and height on the energy cost of running in highly trained middle- and long-distance runners.

Previous studies about the influence of body dimensions on running economy have not compared athletes specialized in different competition events. Therefore, the purpose of the present study was to assess the influence of body mass (m(b)) and height (h) on the energy cost of running (Cr) in 38 highly trained male runners, specialized in either marathon (M, n = 12), long middle-distance (5000 - 10000 m, LMD, n = 14) or short middle-distance (800 - 1500 m, SMD, n = 12), and to assess possible differences in body dimensions for each event. Subjects performed a progressive maximal exercise on the treadmill to determine oxygen uptake VO(2)) at different submaximal velocities and maximal oxygen uptake VO(2)max). Cr was calculated from VO(2) measurements. LMD runners had significantly higher mean Cr (0.192 +/- 0.007, 0.182 +/- 0.009, and 0.180 +/- 0.009 ml O(2) x kg(-1) x m(-1) for LMD, M and SMD, respectively) and VO(2)max (74.1 +/- 3.7, 68.5 +/- 2.9 and 69.7 +/- 3.4 ml x kg (-1) x min (-1)). Cr correlated with h (r = -0.86, p < 0.001) and m(b) (r = -0.77, p < 0.01) only in the SMD group. In conclusion, these data suggest that highly trained distance runners tend to show counterbalancing profiles of running economy and VO(2)max (the higher Cr, the higher VO(2) max and vice versa), and that anthropometric characteristics related with good performance are different in long-distance and middle-distance events.

Adult↗
PubMed1989

Longitudinal changes in distance-running performance of young males.

Longitudinal studies of adolescent males have shown that absolute maximal aerobic power (VO2max) and distance-running performance improve with age, while VO2max expressed relative to body mass remains stable. These earlier studies used subjects that were engaged in distance-run training; therefore, it was not possible to assess the relative importance of growth and/or run training to improved performance. The purpose of this study, therefore, was to quantify longitudinal changes in VO2max, running economy (RE), and distance-running performance in non-run-trained young males. Six subjects were tested at mean ages of 9.9 (T1) and 16.8 years (T2). Statistical tests of mean values revealed that over the 7-year period, relative VO2max remained unchanged (T1, 48.9 ml.kg-1.min-1; T2, 47.8 ml.kg-1.min-1) and RE improved (T1, 234.2; T2, 202.8 ml.kg-1.km-1), 9-min run distance increased (T1, 1637 m; T2, 2115 m), and the estimated percent of VO2max incurred during the 9-min run increased from 85.8% (T1) to 99.5% (T2). It was concluded that the improvement in distance-running performance observed in adolescent boys was not dependent upon run training. In view of the fact that maximal aerobic power remained stable, this change appears to be attributable to better running economy and an ability in runs of a fixed duration to perform at a higher relative work load.

Adolescent↗
PubMed1989

Structural and ultrastructural changes in skeletal muscle associated with long-distance training and running.

The histological and ultrastructural features of 21 males and 8 females were monitored during an 18- to 20-month training period, during which the training distance was gradually increased. The training period was divided into three periods of 6, 5, and 7 months, respectively. The first, second, and third periods were concluded with a 15-, 25-, 42-km road race, respectively. The competitive distance always exceeded the maximal distance covered in any previous training session. Percutaneous biopsies were taken from the vastus lateralis muscle 5 days before each contest as well as 0.5-6 h post-contest and 8-9 days post-contest. No shift in fiber type was observed during the training period from the 15-km contest until the 42-km contest nor were any changes in fiber diameter observed. Histological examination demonstrated a gradual increase in degenerative changes during the training period, which occurred in type I as well as in type II fibers. Ultrastructural examination revealed irregular Z-lines and hypercontraction immediately after exercise. No damage to the sarcolemma was detected. The number of degenerative changes after each contest was not higher than before each race. It is concluded that long-distance running is associated with transient minor pathological changes in skeletal muscle, which are related to the total distance covered per week rather than the intensity of the exercise.

Adaptation, Physiological↗
PubMed1984

Maximal and submaximal oxygen uptakes and blood lactate levels in elite male middle- and long-distance runners.

Physiological characteristics of elite runners from different racing events were studied. Twenty-seven middle- and long-distance runners and two 400-m runners belonging to the Swedish national team in track and field were divided, according to their distance preferences, into six groups from 400 m up to the marathon. The maximal oxygen uptake (VO2 max, ml X kg-1 X min-1) on the treadmill was higher the longer the main distance except for the marathon runners (e.g., 800-1500-m group, 72.1; 5000-10,000-m group, 78.7 ml X kg-1 X min-1). Running economy evaluated from oxygen uptake measurements at 15 km/h (VO2 15) and 20 km/h (VO2 20) did not differ significantly between the groups even though VO2 15 tended to be lower in the long-distance runners. The running velocity corresponding to a blood lactate concentration of 4 mmol/l (vHla 4.0) differed markedly between the groups with the highest value (5.61 m/s) in the 5000-10,000-m group. The oxygen uptake (VO2) at vHla 4.0 in percentage of VO2 max did not differ significantly between the groups. The blood lactate concentration after exhaustion (VO2 max test) was lower in the long-distance runners. In summary, the present study demonstrates differences in physiological characteristics of elite runners specializing in different racing events. The two single (but certainly inter-related) variables in which this was most clearly seen were the maximal oxygen uptake (ml X kg-1 X min-1) and the running velocity corresponding to a blood lactate concentration of 4 mmol/l.

Adult↗
PubMed1981

Skeletal muscle and physiologic characteristics of a world champion masters distance runner: a case study.

Physiologic and skeletal muscle characteristics of a world champion and world record holder Masters distance runner were evaluated in the context of his race performances at age 50 and 51. Comparisons were made to data on other middle-aged runners and on younger, elite distance runners. The subject had a VO2 max of 62.6 mL.kg-1.min-1, an average value for elite, middle-aged runners, but a low value compared to elite, younger distance runners. The subject had a smaller proportion of ST fibers in his gastrocnemius muscle (51.9%) compared to elite distance runners (mean 70.7%) However, the subject had a higher phosphorylase activity and a succinate dehydrogenase activity that was in the same range for younger, elite distance runners. In addition, the subject's gastrocnemius muscle was characterized by small ST and FT fibers with a large capillary density, favoring oxygen diffusion. Despite a relatively modest VO2 max value, the subject has demonstrated superior performance criteria in races from 3 to 42.2 km and an apparent ability to run for several hours at a high percentage of his VO2 max. These capabilities correspond to his large muscle metabolic capacity and enhanced muscle capillarization.

Age Factors↗
PubMed1996

[Effect of interpupillary distance on acuity of depth perception].

BACKGROUND: Until today it is not really known, what kind of influence the interpupillary distance (IPD) has on depth perception. Actual literature says that haploscopic separation of pictures is of disadvantage for subjects with small IPD. This study intended to verify the influence of IPD on stereopsis in order to get valid and comparable results when testing the depth perception of different subjects. SUBJECTS AND METHODS: We examined 58 normosensoric soldiers for their stereoscopic sensation while changing their individual IPD. By using flexible flat plates of glass, the subjects' IPD could be changed infinitely variable to fix depth perception in haploscopic stereotesting. RESULTS: The variety of the interpupillary distance (IPD) of different people has to be strictly differentiated from the intraindividual changes of interpupillary distance, which, by a change of convergence, lead to a change of depth perception. A decrease in intraindividual IPD reveals an increase of depth perception. This change of perception follows, in mathematical terms, the law of logarithm. In case of intraindividual change of IPD the size of objects is also influenced. CONCLUSIONS: Using conventional stereotests, the IPD of different subjects has negligible influence on the depth perception. Different results of depth perception obtained with the help of stereoscopic examination of normosensoric subjects probably correspond with an individual and egocentric dealing with the visual localization of distances (distance between objects, size of objects, depth of objects).

Adult↗
PubMed2005

The perception of distances and spatial relationships in natural outdoor environments.

The ability of observers to perceive distances and spatial relationships in outdoor environments was investigated in two experiments. In experiment 1, the observers adjusted triangular configurations to appear equilateral, while in experiment 2, they adjusted the depth of triangles to match their base width. The results of both experiments revealed that there are large individual differences in how observers perceive distances in outdoor settings. The observers' judgments were greatly affected by the particular task they were asked to perform. The observers who had shown no evidence of perceptual distortions in experiment 1 (with binocular vision) demonstrated large perceptual distortions in experiment 2 when the task was changed to match distances in depth to frontal distances perpendicular to the observers' line of sight. Considered as a whole, the results indicate that there is no single relationship between physical and perceived space that is consistent with observers' judgments of distances in ordinary outdoor contexts.

Humans↗
PubMed2006

Phylogenetic comparisons suggest that distance from the locus control region guides developmental expression of primate beta-type globin genes.

Phylogenetic inferences drawn from comparative data on mammalian beta-globin gene clusters indicate that the ancestral primate cluster contained a locus control region (LCR) and five paralogously related beta-type globin loci (5'-LCR-epsilon-gamma-psieta-delta-beta-3'), with epsilon and gamma expressed solely during embryonic life. A gamma locus tandem duplication (5'-gamma(1)-gamma(2)-3') triggered gamma's evolution toward fetal expression but by a different trajectory in platyrrhines (New World monkeys) than in catarrhines (Old World monkeys and apes, including humans). In platyrrhine (e.g., Cebus) fetuses, gamma(1) at the ancestral distance from epsilon is down-regulated, whereas gamma(2) at increased distance is up-regulated. Catarrhine gamma(1) and gamma(2) acquired longer distances from epsilon (14 and 19 kb, respectively), and both are up-regulated throughout fetal life with gamma(1)'s expression predominating over gamma(2)'s. On enlarging the platyrrhine expression data, we find Aotus gamma is embryonic, Alouatta gamma is inactive at term, and in Callithrix, gamma(1) is down-regulated fetally, whereas gamma(2) is up-regulated. Of eight mammalian taxa now represented per taxon by embryonic, fetal, and postnatal beta-type globin gene expression data, four taxa are primates, and data for three of these primates are from this laboratory. Our results support a model in which a short distance (<10 kb) between epsilon and the adjacent gamma is a plesiomorphic character that allows the LCR to drive embryonic expression of both genes, whereas a longer distance (>10 kb) impedes embryonic activation of the downstream gene.

Animals↗
PubMed2006

End-to-end distance distributions and intrachain diffusion constants in unfolded polypeptide chains indicate intramolecular hydrogen bond formation.

Characterization of the unfolded state is essential for the understanding of the protein folding reaction. We performed time-resolved FRET measurements to gain information on the dimensions and the internal dynamics of unfolded polypeptide chains. Using an approach based on global analysis of data obtained from two different donor-acceptor pairs allowed for the determination of distance distribution functions and diffusion constants between the chromophores. Results on a polypeptide chain consisting of 16 Gly-Ser repeats between the FRET chromophores reveal an increase in the average end-to-end distance from 18.9 to 39.2 Angstrom between 0 and 8 M GdmCl. The increase in chain dimensions is accompanied by an increase in the end-to-end diffusion constant from (3.6 +/- 1.0) x 10(-7) cm(2) s(-1) in water to (14.8 +/- 2.5) x 10(-7) cm(2) s(-1) in 8 M GdmCl. This finding suggests that intrachain interactions in water exist even in very flexible chains lacking hydrophobic groups, which indicates intramolecular hydrogen bond formation. The interactions are broken upon denaturant binding, which leads to increased chain flexibility and longer average end-to-end distances. This finding implies that rapid collapse of polypeptide chains during refolding of denaturant-unfolded proteins is an intrinsic property of polypeptide chains and can, at least in part, be ascribed to nonspecific intramolecular hydrogen bonding. Despite decreased intrachain diffusion constants, the conformational search is accelerated in the collapsed state because of shorter diffusion distances. The measured distance distribution functions and diffusion constants in combination with Szabo-Schulten-Schulten theory were able to reproduce experimentally determined rate constants for end-to-end loop formation.

Fluorescence Resonance Energy Transfer↗
PubMed2002

Donor-bridge-acceptor energetics determine the distance dependence of electron tunneling in DNA.

Electron transfer (ET) processes in DNA are of current interest because of their involvement in oxidative strand cleavage reactions and their relevance to the development of molecular electronics. Two mechanisms have been identified for ET in DNA, a single-step tunneling process and a multistep charge-hopping process. The dynamics of tunneling reactions depend on both the distance between the electron donor and acceptor and the nature of the molecular bridge separating the donor and acceptor. In the case of protein and alkane bridges, the distance dependence is not strongly dependent on the properties of the donor and acceptor. In contrast, we show here that the distance decay of DNA ET rates varies markedly with the energetics of the donor and acceptor relative to the bridge. Specifically, we find that an increase in the energy of the bridge states by 0.25 eV (1 eV = 1.602 x 10(-19) J) relative to the donor and acceptor energies for photochemical oxidation of nucleotides, without changing the reaction free energy, results in an increase in the characteristic exponential distance decay constant for the ET rates from 0.71 to 1.1 A(-1). These results show that, in the small tunneling energy gap regime of DNA ET, the distance dependence is not universal; it varies strongly with the tunneling energy gap. These DNA ET reactions fill a "missing link" or transition regime between the large barrier (rapidly decaying) tunneling regime and the (slowly decaying) hopping regime in the general theory of bridge-mediated ET processes.

Biophysical Phenomena↗
PubMed2003

Labeled cortical mantle distance maps of the cingulate quantify differences between dementia of the Alzheimer type and healthy aging.

The cingulate gyri in 37 subjects with and without early dementia of the Alzheimer type (DAT) were studied by using MRI at 1.0 mm3 isotropic resolution. Groups were segregated into young controls (n = 10), age-matched normal controls (n = 10), very mild DAT (n = 8), and mild DAT (n = 9). By using automated Bayesian segmentation of the cortex and gray matter/white matter (GM/WM) isosurface generation, tissue compartments were labeled into gray, white, and cerebrospinal fluid as a function of distance from the GM/WM isosurface. Cortical mantle distance maps are generated profiling the GM volume and cortical mantle distribution as a function of distance from the cortical surface. Probabilistic tests based on generalizations of Wilcoxon-Mann-Whitney tests were applied to quantify cortical mantle distribution changes with normal and abnormal aging. We find no significant change between young controls and healthy aging as measured by the GM volume and cortical mantle distribution as a function of distance in both anterior and posterior regions of the cingulate. Significant progression of GM loss is seen in the very mild DAT and mild DAT groups in all areas of the cingulate. Posterior regions show both GM volume loss as well as significant cortical mantle distribution decrease with the onset of mild DAT. The "shape of the cortical mantle" as measured by the cortical mantle distance profiles manifests a pronounced increase in variability with mild DAT.

Adult↗
PubMed2001

DNA supercoiling allows enhancer action over a large distance.

Enhancers are regulatory DNA elements that can activate their genomic targets over a large distance. The mechanism of enhancer action over large distance is unknown. Activation of the glnAp2 promoter by NtrC-dependent enhancer in Escherichia coli was analyzed by using a purified system supporting multiple-round transcription in vitro. The data suggest that DNA supercoiling is an essential requirement for enhancer action over a large distance (2,500 bp) but not over a short distance (110 bp). DNA supercoiling facilitates functional enhancer-promoter communication over a large distance, probably by bringing the enhancer and promoter into close proximity.

Base Sequence↗
PubMed1975

Energy transfer between terbium (III) and cobalt (II) in thermolysin: a new class of metal--metal distance probes.

The visible fluorescence of terbium(III) when bound to a calcium binding site of thermolysin is greatly enhanced with an excitation maximum at 280 nm but substitution of cobalt(II) for zinc at the active site decreases the intensity by 89.5%. Treatment with N-bromosuccinimide quenches enzyme tryptophan and Tb(III) fluorescence to a similar extent and suggests the operation of tryptophan vector Tb(III) vector Co(II) energy relay system in the enzyme. Dipoledipole radiationless energy transfer between the Tb(III) donor and the Co(II) acceptor can account for this quenching. The inherent characteristics of the metal pair limits the value of the orientation factor, K2, of the Förster equation, thereby reducing uncertainties in distance measurements by energy transfer compared with other systems. A quantum yield of 0.51 yields a value of R0, the distance for 50% energy transfer, of 19.6 A, and a distance, R, between Tb(III) and Co(II) of 13.7 A, a value identical to that measured for the distance between the active site zinc atom and calcium atom number 1 by x-ray analysis in native thermolysin crystals. The limits of confidence of this measurement are discussed. Energy transfer between two different metal atom sites of a protein provides a new class of probes to measure intramolecular distances of biological macromolecules in solution.

Binding Sites↗