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At least 1,405 records · Page 78Linked to original sources
PubMed1988

Genetic, geographic, and linguistic distances in Europe.

Genetic and taxonomic distances were computed for 3466 samples of human populations in Europe based on 97 allele frequencies and 10 cranial variables. Since the actual samples employed differed among the genetic systems studied, the genetic distances were computed separately for each system, as were matrices of geographic distances and of linguistic distances based on membership in the same language family or phylum. Significant matrix correlations between genetics and geography were found for the majority of systems; somewhat less frequent are significant correlations between genetics and language. The effects of the two factors can be separated by means of partial matrix correlations. These show significant values for both genetics and geography, language kept constant, and genetics and language, geography kept constant, with a tendency for the former to be higher. These findings demonstrate that speakers of different language families in Europe differ genetically and that this difference remains even after geographic differentiation is allowed for. The greater effect of geography than of language may be due to the several factors that bring about spatial differentiation in human populations.

Europe↗
PubMed1992

Domain motions in phosphoglycerate kinase: determination of interdomain distance distributions by site-specific labeling and time-resolved fluorescence energy transfer.

3-Phosphoglycerate kinase is composed of two globular domains separated by a wide cleft. The substrate binding sites are situated on the inner surfaces of the two domains. By analogy to other kinases, it has been postulated that the catalytic mechanism of phosphoglycerate kinase involves a hinge bending domain motion that brings the substrates together to allow phosphoryl transfer. To characterize this large-scale conformational change, as well as the dynamics of the unliganded enzyme in solution, we have applied site-directed mutagenesis and time-resolved nonradiative energy transfer techniques. Two genetically engineered cysteines (Cys-135 and Cys-290), one in each of the two domains, were covalently labeled with a donor and acceptor pair of fluorescent probes. Analysis of subnanosecond fluorescence decay curves yielded the equilibrium distribution of interdomain distances. In the absence of substrates, the distribution of distances between the two labeled sites was very broad, with a full width at half maximum estimated as 20 A or broader, indicative of a large number of conformational substates in solution. The mean distance, 31.5 +/- 1 A, was 8 A smaller than in the crystal structure. Upon addition of ATP alone or of ATP and 3-phosphoglycerate, the average distance increased to 38 +/- 1 A and the width of the distribution decreased. Addition of 3-phosphoglycerate alone induced a similar but smaller change. The rate of conformational state fluctuations (interconversion between states) was found to be slow on the nanosecond time scale, as expected for a protein with a relatively large interdomain contact area.

Crystallography↗
PubMed1993

Tests of the long and short extragalactic distance scales.

Distances on the short and long scales of 12 nearby galaxies, one group, and three clusters are compared with recent estimates by independent methods and researchers. All comparisons show a close agreement [within 0.3 magnitude (mag) in the distance modulus (DM)] between the short-scale moduli and the new estimates by others at all distances from the Large Magellanic Cloud [Delta (distance) = 0.05 megaparsec (Mpc); 1 pc = 3.09 x 10(16) m] to the Coma cluster (Delta = 83 Mpc). The mean systematic difference (short - others) is only -0.04 mag with no evidence for a significant Malmquist bias in the short scale. The long scale differs systematically from all the others by about +0.25 mag within the Local Group (DM < 26) and by +1.1 outside (26 < DM < 35). Accidental errors are also much larger in the long-scale moduli (0.5 mag) than in the other two scales (0.1 mag). The mean value of the Hubble expansion ratio for the test objects is = 86 +/- 1 km.sec-1. Mpc-1.

Journal Article↗
PubMed1998

Estimation of evolutionary distances under stationary and nonstationary models of nucleotide substitution.

Estimation of evolutionary distances has always been a major issue in the study of molecular evolution because evolutionary distances are required for estimating the rate of evolution in a gene, the divergence dates between genes or organisms, and the relationships among genes or organisms. Other closely related issues are the estimation of the pattern of nucleotide substitution, the estimation of the degree of rate variation among sites in a DNA sequence, and statistical testing of the molecular clock hypothesis. Mathematical treatments of these problems are considerably simplified by the assumption of a stationary process in which the nucleotide compositions of the sequences under study have remained approximately constant over time, and there now exist fairly extensive studies of stationary models of nucleotide substitution, although some problems remain to be solved. Nonstationary models are much more complex, but significant progress has been recently made by the development of the paralinear and LogDet distances. This paper reviews recent studies on the above issues and reports results on correcting the estimation bias of evolutionary distances, the estimation of the pattern of nucleotide substitution, and the estimation of rate variation among the sites in a sequence.

Animals↗
PubMed2001

Patterns of spread in biological invasions dominated by long-distance jump dispersal: Insights from Argentine ants.

Invading organisms may spread through local movements (giving rise to a diffusion-like process) and by long-distance jumps, which are often human-mediated. The local spread of invading organisms has been fit with varying success to models that couple local population growth with diffusive spread, but to date no quantitative estimates exist for the relative importance of local dispersal relative to human-mediated long-distance jumps. Using a combination of literature review, museum records, and personal surveys, we reconstruct the invasion history of the Argentine ant (Linepithema humile), a widespread invasive species, at three spatial scales. Although the inherent dispersal abilities of Argentine ants are limited, in the last century, human-mediated dispersal has resulted in the establishment of this species on six continents and on many oceanic islands. Human-mediated jump dispersal has also been the primary mode of spread at a continental scale within the United States. The spread of the Argentine ant involves two discrete modes. Maximum distances spread by colonies undergoing budding reproduction averaged 150 m/year, whereas annual jump-dispersal distances averaged three orders of magnitude higher. Invasions that involve multiple dispersal processes, such as those documented here, are undoubtedly common. Detailed data on invasion dynamics are necessary to improve the predictive power of future modeling efforts.

Animals↗
PubMed1998

Molecular distance measurements reveal an (alpha beta)2 dimeric structure of Na+/K+-ATPase. High affinity ATP binding site and K+-activated phosphatase reside on different alpha-subunits.

ATP hydrolysis by Na+/K+-ATPase proceeds via the interaction of simultaneously existing and cooperating high (E1ATP) and low (E2ATP) substrate binding sites. It is unclear whether both ATP sites reside on the same or on different catalytic alpha-subunits. To answer this question, we looked for a fluorescent label for the E2ATP site that would be suitable for distance measurements by Förster energy transfer after affinity labeling of the E1ATP site by fluorescein 5'-isothiocyanate (FITC). Erythrosin 5'-isothiocyanate (ErITC) inactivated, in an E1ATP site-blocked enzyme (by FITC), the residual activity of the E2ATP site, namely K+-activated p-nitrophenylphosphatase in a concentration-dependent way that was ATP-protectable. The molar ratios of FITC/alpha-subunit of 0.6 and of ErITC/alpha-subunit of 0.48 indicate 2 ATP sites per (alpha beta)2 diprotomer. Measurements of Förster energy transfer between the FITC-labeled E1ATP and the ErITC-labeled or Co(NH3)4ATP-inactivated E2ATP sites gave a distance of 6.45 +/- 0.64 nm. This distance excludes 2 ATP sites per alpha-subunit since the diameter of alpha is 4-5 nm. Förster energy transfer between cardiac glycoside binding sites labeled with anthroylouabain and fluoresceinylethylenediamino ouabain gave a distance of 4.9 +/- 0.5 nm. Hence all data are consistent with the hypothesis that Na+/K+-ATPase in cellular membranes is an (alpha beta)2 diprotomer and works as a functional dimer (Thoenges, D., and Schoner, W. (1997) J. Biol. Chem. 272, 16315-16321).

Adenosine Triphosphate↗
PubMed2005

Sequence, distance, and accessibility are determinants of 5'-end-directed cleavages by retroviral RNases H.

The RNase H activity of reverse transcriptase is essential for retroviral replication. RNA 5'-end-directed cleavages represent a form of RNase H activity that is carried out on RNA/DNA hybrids that contain a recessed RNA 5'-end. Previously, the distance from the RNA 5'-end has been considered the primary determinant for the location of these cleavages. Employing model hybrid substrates and the HIV-1 and Moloney murine leukemia virus reverse transcriptases, we demonstrate that cleavage sites correlate with specific sequences and that the distance from the RNA 5'-end determines the extent of cleavage. An alignment of sequences flanking multiple RNA 5'-end-directed cleavage sites reveals that both enzymes strongly prefer A or U at the +1 position and C or G at the -2 position, and additionally for HIV-1, A is disfavored at the -4 position. For both enzymes, 5'-end-directed cleavages occurred when sites were positioned between the 13th and 20th nucleotides from the RNA 5'-end, a distance termed the cleavage window. In examining the importance of accessibility to the RNA 5'-end, it was found that the extent of 5'-end-directed cleavages observed in substrates containing a free recessed RNA 5'-end was most comparable to substrates with a gap of two or three bases between the upstream and downstream RNAs. Together these finding demonstrate that the selection of 5'-end-directed cleavage sites by retroviral RNases H results from a combination of nucleotide sequence, permissible distance, and accessibility to the RNA 5'-end.

Base Sequence↗
PubMedDate not supplied

Comparison of pitot traverses taken at varying distances downstream of obstructions.

This study determined the deviations between pitot traverses taken under "ideal" conditions--at least seven duct diameter's lengths (i.e., distance = 7D) from obstructions, elbows, junction fittings, and other disturbances to flows--with those taken downstream from commonplace disturbances. Two perpendicular 10-point, log-linear velocity pressure traverses were taken at various distances downstream of tested upstream conditions. Upstream conditions included a plain duct opening, a junction fitting, a single 90 degrees elbow, and two elbows rotated 90 degrees from each other into two orthogonal planes. Airflows determined from those values were compared with the values measured more than 40D downstream of the same obstructions under ideal conditions. The ideal measurements were taken on three traverse diameters in the same plane separated by 120 degrees in honed drawn-over-mandrel tubing. In all cases the pitot tubes were held in place by devices that effectively eliminated alignment errors and insertion depth errors. Duct velocities ranged from 1500 to 4500 ft/min. Results were surprisingly good if one employed two perpendicular traverses. When the averages of two perpendicular traverses was taken, deviations from ideal value were 6% or less even for traverses taken as close as 2D distance from the upstream disturbances. At 3D distance, deviations seldom exceeded 5%. With single diameter traverses, errors seldom exceeded 5% at 6D or more downstream from the disturbance. Interestingly, percentage deviations were about the same at high and low velocities. This study demonstrated that two perpendicular pitot traverses can be taken as close as 3D from these disturbances with acceptable (< or = 5%) deviations from measurements taken under ideal conditions.

Air Movements↗
PubMed2005

The effect of pallet distance on torso kinematics and low back disorder risk.

Intervention research for prevention of occupational low back injuries has focused on the effects of reducing extreme torso flexion and the external moment. Little is known about prevention strategies for torso twisting and lateral bending. The objective of this study was to assess the effect of pallet distance with regard to a constant lift origin on the torso kinematics and a measure of low back disorder risk. Fifteen male participants transferred 11.3 kg boxes from a constant origin to six different regions on a pallet. Two pallet distances with regard to the lift origin were investigated. ANOVA indicated that increasing the pallet distance resulted in increases in torso kinematics (velocities and accelerations) as well as a measure of risk of low back disorder. The increases in torso kinematics (e.g. twisting and lateral awkward postures and bending velocities) occurred mostly at the lower height regions on the pallet. It is concluded that increasing the pallet distance with regard to the lifting origin, with the intention to influence the participant to take a step during a palletizing task does not appear to be an effective intervention strategy to reduce the risk of low back disorder associated with torso kinematics.

Adult↗
PubMed1990

Change in visual function and viewing distance during work with VDTs.

Seven female volunteer bank clerks aged between 24 and 32 yr were selected for a laboratory trial after a preliminary ocular examination which showed them to be emmetropic or slightly myopic (less than or equal to 1D) and to have normal ocular motility or only minor deficiencies. Near and far point refraction and phorias and near point fusional vergences were measured before and immediately after a 6 h workday at a PC workstation. Eye screen distance (viewing distance) was monitored. Near and far distance refraction showed an increase and a decrease of accommodation in 13 out of 14 eyes respectively. Fusional convergence decreased in six out of seven cases: a smaller decrease in divergence was recorded in all subjects. These changes were statistically significant. Viewing distance, though showing some interindividual differences, increased considerably during the last 2 h of the trial, without reaching statistical significance.

Adult↗
PubMed1981

Imagery ability in recall of distance and location information.

The role of visual imagery in short-term retention of movement end locations and distances was examined by comparing performances of subjects with extreme scores on the space relations section of the Differential Aptitude Test. Twelve HIGHS and twelve LOWS were tested on reproduction accuracy of six distances and six end locations immediately following presentation a 30-sec rest, a 30 sec imaginal rehearsal condition, and a 30-sec imaginal distraction condition. Initial analysis of the data provided little support for the hypothesis that HIGHS would reproduce criterion locations with more accuracy than LOWS. However, when scores of HIGHS reporting use of an imaginal coding strategy (HIGHS) were compared with LOWS who did not (LOWS), several expected findings were disclosed. HIGHS reproduced end locations with significantly less error in the immediate and imaginal rehearsal conditions, and as expected, accuracy scores for HIGHS and LOWS did not differ for the distance task. The findings suggest that when subjects employ an imaginal coding strategy, visual imagery ability may be an important factor in the retention of location information, but of little functional significance in the recall of distance.

Journal Article↗
PubMed1996

Response Timing Accuracy as a Function of Movement Velocity and Distance.

In two experiments, patterns of response error during a timing accuracy task were investigated. In Experiment 1, these patterns were examined across a full range of movement velocities, which provided a test of the hypothesis that as movement velocity increases, constant error (CE) shifts from a negative to a positive response bias, with the zero CE point occurring at approximately 50% of maximum movement velocity (Hancock & Newell, 1985). Additionally, by examining variable error (VE), timing error variability patterns over a full range of movement velocities were established. Subjects (N = 6) performed a series of forearm flexion movements requiring 19 different movement velocities. Results corroborated previous observations that variability of timing error primarily decreased as movement velocity increased from 6 to 42% of maximum velocity. Additionally, CE data across the velocity spectrum did not support the proposed timing error function. In Experiment 2, the effect(s) of responding at 3 movement distances with 6 movement velocities on response timing error were investigated. VE was significantly lower for the 3 high-velocity movements than for the 3 low-velocity movements. Additionally, when MT was mathematically factored out, VE was less at the long movement distance than at the short distance. As in Experiment 1, CE was unaffected by distance or velocity effects and the predicted CE timing error function was not evident.

Journal Article↗
PubMed1984

Psychological tension and closeness to others: stress and interpersonal distance preference.

The prediction that increased tension would lead to a preference for greater distance from others was tested on 40 male and 40 female Ss approached in eight natural settings of high or low tension and their distance preference measured. Ss in the four higher-tension situations indicated a preference for significantly more distance. Self-reported tension was correlated significantly and positively with the distance preferred across all eight situations. There was no effect of sex.

Adolescent↗
PubMed2006

A new device for evaluating distance and directional performance of golf putters.

The purpose of this study was to construct and evaluate the reliability of an apparatus for testing golf putters with respect to distance and direction deviation at different impact points on the clubface. An apparatus was constructed based on the pendulum principle that allowed putter golf clubs to swing at different speeds. The mean speed of the club head before ball impact, and of the ball after impact, was calculated from time measurements with photocells. A pin profile rig was used to determine the directional deviation of the golf ball. Three different putters were used in the study, two that are commercially available (toe-heel weighted and mallet types) and one specially made (wing-type) putter. The points of impact were the sweet spot (as indicated by the manufacturer's aim line), and 1, 2 and 3 cm to the left and right of the sweet spot. Calculation of club head speed before impact, and of ball speed after impact (proportional to distance), showed errors < or = 0.5% of interval duration. The variability in ball impacts was tested by measuring time and direction deviations during 50 impacts on the same ball. The mean duration (+/- s) after ball impact in the test interval (1.16 m long) was 206 (0.8) ms and the standard deviation in the perpendicular spreading of the balls in relation to the direction of the test interval was 0.005 m. A test-retest of one putter on two consecutive days after remounting of the putter on the test apparatus showed less than 1% difference in distance deviation. We conclude that the test apparatus enables a precise recording of distance and direction deviation in golf putters as well as comparisons between different putters. The apparatus and set-up can be used in the laboratory as well as outdoors on the putting green.

Equipment Design↗
PubMed1990

Muscular activity of different shooting distances, different release techniques, and different performance levels, with and without stabilizers, in target archery.

The quadruple approach in the title refers to four different studies over a period of 3 years. The common factor in these studies is the methodology of the (Brussels) Electromyographic Signal Processing and Analysis System (ESPAS), a hardware and software EMG data acquisition system that has constantly been improved. Therefore, the ESPAS methodology is described extensively (i.e. the electrodes, amplifier, tape-recorder and processing hardware). Experiment 1 investigated muscular behaviour in target shooting, both indoors (18 and 25 m) and outdoors (50, 70 and 90 m). It was found (via iEMG) that a significant increase in activity only exists between 25 and 50 m, and that there is no linear increase of activity with increased distance. No differences in muscular pattern (IDANCO system: Clarys and Cabri, 1988) or activity between the indoor distances and between the outdoor distances were found. Experiment 2 investigated the muscular economy of four string grips: the three-finger grip, two-finger grip, thumb grip and reversed grip. The largest variations in activity were found for the two most unfamiliar grips, i.e. the thumb and reversed grips; however, low iEMG and the rapid precision improvement (over a limited number of shots) suggest that the thumb grip, if practised long enough, might be the most economical technique. Experiment 3 attempted to differentiate muscular activity and a number of performance variables in three different populations of archers--Olympic athletes, National competitors and beginners--in order to obtain feedback regarding improved performance. Apparently, overall muscle pattern, intensities and arrow speed were not discriminatory. The differences found between the groups (or levels of skill) were affected by the ability to reproduce identical patterns and arrow velocities in consecutive shots and by the constancy of neuromuscular control of the M. trapezius, M. biceps brachii and M. extensor digitorum. Finally, Experiment 4 investigated the muscular activity of elite archers shooting at distances of 70 and 90 m with and without stabilizers. Differences in iEMG were not supported by differences in precision. Over time, the low iEMG in shooting without stabilizers increases precision and delays fatigue.

Arm↗
PubMedDate not supplied

The size and distance of the opposite flat applicator change the SAR and thermal distributions of RF capacitive intracavitary hyperthermia.

The variations of the specific absorption rate (SAR) and thermal distributions in the JSHO QA phantom were investigated by using the radiofrequency (RF) capacitive intracavitary hyperthermia (ICHT) applicator (AP-T01, Omron Electric Co., Kyoto, Japan) and the opposite flat applicators of different sizes (AP-75E: 7.5 cm in diameter, AP-100E: 10 cm in diameter, and AP-150E: 15 cm in diameter). The influences of the distance between both applicators were also investigated. Heating of the region between both applicators became weaker with the increase in size of the opposite flat applicator, and it became stronger with the decrease of the distance between both applicators. Heating near the flat applicator became weaker with the increase in size of the flat applicators, and it showed no apparent difference with the increase of the distance between both applicators. The normalized SAR values between AP-T01 and the opposite flat applicator became smaller and its slope became steeper with the increase in size of the opposite flat applicator and in the distance between both applicators. These results suggest that the variability of the specific absorption rate (SAR) and thermal distributions of the region between both applicators may show the potentiality of usefulness for heating the tumours of various sizes, shapes and location.

Humans↗
PubMed1992

The reliability of distance run tests for children in grades K-4.

The purpose of this study was to determine test-retest reliability for the 1-mile, 3/4-mile, and 1/2-mile distance run/alk tests for children in Grades K-4. Fifty-one intact physical education classes were randomly assigned to one of the three distance run conditions. A total of 1,229 (621 boys, 608 girls) completed the test-retests in the fall (October), with 1,050 of these students (543 boys, 507 girls) repeating the tests in the spring (May). Results indicated that the 1-mile run/walk distance, as recommended for young children in most national test batteries, has acceptable intraclass reliability (.83 less than R less than .90) for both boys and girls in Grades 3 and 4, has minimal (fall) to acceptable (spring) reliability for Grade 2 students (.70 less than R less than .83), but is not reliable for children in Grades K and 1 (.34 less than R less than .56). The 1/2 mile was the only distance meeting minimal reliability standards for boys and girls in Grades K and 1 (.73 less than R less than .82). Results also indicated that reliability estimates remained fairly stable across gender and age groups from the fall to spring testing periods, with the exception of the noticeably improved values for Grade 2 students on the 1-mile run/walk test. Criterion-referenced reliability (P, percent agreement) was also estimated relative to Physical Best and Fitnessgram run/walk standards. Reliability coefficients for all age group standards were acceptable to high (.70 less than P less than .95), except for Fitnessgram standards for 5-year-old girls on the 1-mile test for both fall and spring and for 6-year-old boys and girls on the 1-mile test administered in the spring.

Child↗
PubMedDate not supplied

Ovarian impairments of female recreational distance runners during a season of training.

This study was carried out to investigate the relationship between the level of training and the impairment of ovarian function among female recreational distance runners, and its reversibility. Thirty-six female distance runners self-recorded, for 7 consecutive days each month, the duration and distance of daily running from October 1989 to May 1990 in Great Britain. During the last 3 months of the survey, saliva samples were taken for progesterone assay and a subsample was measured for body composition. No trend in weight loss was observed over the season of training. Amenorrheic (AM) and oligomenorrheic (Oligo) runners had a significantly lower body mass index than eumenorrheic (EU) and irregularly menstruating (IM) runners. The amenorrheic and oligomenorrheic subjects did not show any rise in progesterone, at any time, during the 3 months of sampling. The eumenorrheic subjects showed evidence of a rise in progesterone, though the mean level was always significantly lower than that of sedentary controls. The most severely impaired runners (AM and Oligo) ran more than EU or irregularly menstruating runners in this sample, had lower body weight, a younger age and had a significantly lower body mass index (BMI). They tended to run faster during training sessions than those with apparently normal menstrual cycle or just irregular periods. It is suggested that low BMI, which is an indicator of body energy stores, reflects the intensity of regular training runs among female athletes with a stable body weight. It is possible that repeated elevations of beta-endorphins or other suppressors of gonadotropin release, secreted above a level of training commonly exceeded by long distance runners, when concurrent with energy restriction, could contribute to impairment of menstrual cycle.

Adult↗