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PubMed1976

Species-distance relation for birds of the Solomon Archipelago, and the paradox of the great speciators.

For scattered remote islands and for likely forms of immigration and extinction curves, the equilibrium theory of island biogeography leads to the prediction [unk](2) log S/[unk]A[unk]D > 0, where S is the number of species on an island, A island area, and D island distance from the colonization source. This prediction is confirmed for birds of the Solomon Archipelago. Bird species can be classified into three types according to how distance affects their distributions: non-water-crossers, which are stopped completely (usually for psychological reasons) by water gaps of even 1 mile; short-distance colonists, successful at colonizing close but not remote islands; and long-distance colonists, successful at colonizing remote as well as close islands. Almost all of the "great speciators", the species for whose inter-island geographic variation the Solomons are famous, prove to be short-distance colonists. Lack's interpretation of the decrease in S with D is shown to rest on incorrect assumptions.

Journal Article↗

PubMed1987

Iron distances in hemoglobin: comparison of x-ray crystallographic and extended x-ray absorption fine structure studies.

A comparison is presented of the structures obtained around the iron atom in deoxyhemoglobin (Hb). The data come from extended x-ray absorption fine structure (EXAFS) studies of the iron, which gave Fe-porphyrin nitrogen distances of 2.06 +/- 0.01 A, and from the most recent high-resolution x-ray crystallographic study, which gave exactly the same distance--2.06 +/- 0.02 A. The distance of Fe above the plane of the porphyrin nitrogens was 0.38 +/- 0.04 A from the crystallographic study; this value is not far from the upper limit of the distances 0.20 +/- (0.10)0.20 A calculated from the EXAFS experiment by triangulation. These distances above the nitrogen plane are shorter than those estimated in the earliest x-ray structures.

Hemoglobins↗

PubMed1994

Reconstructing evolutionary trees from DNA and protein sequences: paralinear distances.

The reconstruction of phylogenetic trees from DNA and protein sequences is confounded by unequal rate effects. These effects can group rapidly evolving taxa with other rapidly evolving taxa, whether or not they are genealogically related. All algorithms are sensitive to these effects whenever the assumptions on which they are based are not met. The algorithm presented here, called paralinear distances, is valid for a much broader class of substitution processes than previous algorithms and is accordingly less affected by unequal rate effects. It may be used with all nucleic acid, protein, or other sequences, provided that their evolution may be modeled as a succession of Markov processes. The properties of the method have been proven both analytically and by computer simulations. Like all other methods, paralinear distances can fail when sequences are misaligned or when site-to-site sequence variation of rates is extensive. To examine the usefulness of paralinear distances, the "origin of the eukaryotes" has been investigated by the analysis of elongation factor Tu sequences with a variety of sequence alignments. It has been found that the order in which sequences are pairwise aligned strongly determines the topology which is reconstructed by paralinear distances (as it does for all other reconstruction methods tested). When the parts of the alignment that are unaffected by alignment order are analyzed, paralinear distances strongly select the eocyte topology. This provides evidence that the eocyte prokaryotes are the closest prokaryotic relatives of the eukaryotes.

Algorithms↗

PubMed1996

A general additive distance with time-reversibility and rate variation among nucleotide sites.

As additivity is a very useful property for a distance measure, a general additive distance is proposed under the stationary time-reversible (SR) model of nucleotide substitution or, more generally, under the stationary, time-reversible, and rate variable (SRV) model, which allows rate variation among nucleotide sites. A method for estimating the mean distance and the sampling variance is developed. In addition, a method is developed for estimating the variance-covariance matrix of distances, which is useful for the statistical test of phylogenies and molecular clocks. Computer simulation shows (i) if the sequences are longer than, say, 1000 bp, the SR method is preferable to simpler methods; (ii) the SR method is robust against deviations from time-reversibility; (iii) when the rate varies among sites, the SRV method is much better than the SR method because the distance is seriously underestimated by the SR method; and (iv) our method for estimating the sampling variance is accurate for sequences longer than 500 bp. Finally, a test is constructed for testing whether DNA evolution follows a general Markovian model.

Analysis of Variance↗

PubMed2002

Structure of apolipophorin-III in discoidal lipoproteins. Interhelical distances in the lipid-bound state and conformational change upon binding to lipid.

The structure of apolipophorin III in the lipid-bound state and the extent of the conformational change that takes place when the five-helix bundle apolipoprotein binds to a lipoprotein lipid surface were investigated by fluorescence resonance energy transfer in discoidal lipoproteins. Four intramolecular interhelical distances between helix pairs 1-4, 2-4, 3-4, and 5-4 were estimated by fluorescence resonance energy transfer in both the lipid-free and the lipid-bound states. Depending on the helices pairs, the intramolecular interhelical distances increased between 15 and > or = 20 A upon binding of the apolipoprotein to lipid, demonstrating for the first time that binding to lipid is accompanied by a major change in interhelical distances. Using discoidal lipoproteins made with a combination of apolipophorin III molecules containing donor and acceptor groups and apolipophorin III molecules containing neither donor nor acceptor groups, it was possible to obtain information about intermolecular interhelical distances between the helix 4 of one apolipoprotein and the helices 1, 2, 3, and 5 of a second apolipoprotein residing in the same discoidal lipoprotein. Altogether, the estimated intermolecular and intramolecular interhelical distances suggest a model in which the apolipoprotein arranges in pairs of antiparallel and fully extended polypeptide chains surrounding the periphery of the bilayer disc.

Apolipoproteins↗

PubMed2003

Social interaction distance and stratification.

There have been calls from several sources recently for a renewal of class analysis that would encompass social and cultural, as well as economic elements. This paper explores a tradition in stratification that is founded on this idea: relational or social distance approaches to mapping hierarchy and inequality which theorize stratification as a social space. The idea of 'social space' is not treated as a metaphor of hierarchy nor is the nature of the structure determined a priori. Rather, the space is identified by mapping social interactions. Exploring the nature of social space involves mapping the network of social interaction--patterns of friendship, partnership and cultural similarity--which gives rise to relations of social closeness and distance. Differential association has long been seen as the basis of hierarchy, but the usual approach is first to define a structure composed of a set of groups and then to investigate social interaction between them. Social distance approaches reverse this, using patterns of interaction to determine the nature of the structure. Differential association can be seen as a way of defining proximity within a social space, from the distances between social groups, or between social groups and social objects (such as lifestyle items). The paper demonstrates how the very different starting point of social distance approaches also leads to strikingly different theoretical conclusions about the nature of stratification and inequality.

Hierarchy, Social↗

PubMed1982

Distance and movement time effects on the timing of agonist and antagonist muscles: a test of the impulse-timing theory.

The experiment examined the effects of movement time (MT) and distance on the timing at electromyographic (EMG) activity from an agonist and antagonist muscle during rapid, discrete elbow movements in the horizontal plane. According to impulse-timing theory (Wallace, 1981) MT, not distance moved, should have a pronounced effect on the timing of EMG activity (duration of initial agonist and antagonist burst and time to onset of initial antagonist burst). The levels of MT were 100 and 160 msec and the levels of distance were 27 degrees and 45 degrees of elbow flexion. In general support of impulse-timing theory, the results of the three EMG timing measures showed that MT had a more pronounced effect on these measures than distance. In addition, the timing of EMG activity in relation to total MT remained fairly consistent across the four MT-distance conditions.

Journal Article↗

PubMed1992

Interference Between Location and Distance Information in Motor Short-Term Memory: The Respective Roles of Direct Kinesthetic Signals and Abstract Codes.

Interference between location and distance information in motor short-term memory has been hypothesized on the basis of the systematic pattern of undershooting and overshooting in movement reproduction that occurs when the starting position for reproduction movements is shifted. To determine the possible contribution of limb-specific kinesthetic information to this systematic undershooting-overshooting pattern, we compared the reproduction of linear arm positioning movements performed under either same-limb or switched-limb conditions. Ten subjects were assigned to either a location or distance cue condition, and each subject completed a total of 40 trials, 20 under same-limb and 20 under switched-limb conditions. Each trial consisted of criterion and reproduction movements, separated by a 10-s retention interval. The starting position for the reproduction movement was shifted by 0, 2, or 4 cm in either direction from that of the criterion movement. The systematic undershooting-overshooting pattern, which occurs when either the movement location or distance is reproduced, arose under both the same-limb and switched-limb conditions, suggesting that the primary cause of the location-distance interference is not limb-specific kinesthetic information. Rather, more abstract information in the form of a conceptual memory code appears to be the probable cause of the location distance interference phenomenon.

Journal Article↗

PubMed2006

The distance-time relationship over a century of running Olympic performances: A limit on the critical speed concept.

We analyse the evolution of the slope (critical speed) and the y-intercept (anaerobic distance capacity) of the linear distance-time relationship over a century of Olympic running performances. The distance-time relationship of each Olympic Games (1920-2004) was plotted using the performances in the 800-, 1500- and 5000-m track events. Values for critical speed and anaerobic distance capacity were determined by linear modelling. Mean performances for the 800, 1500 and 5000 m were 104.9 +/- 1.5 s (1.4%), 217.2 +/- 2.8 s (1.3%) and 808.9 +/- 18.4 s (2.3%), respectively. Critical speed improved during the first three-quarters of the twentieth century to reach a plateau in 1984. This is in accordance with the literature (Peronnet & Thibault, 1989) and suggests that "human aerobic endurance" has improved within the century (+13.4%) and tends to stabilize. Anaerobic distance capacity was highly variable over the century (coefficient of variation = 9.4%) and did not show a linear improvement over the years as has previously been suggested (Peronnet & Thibault, 1989). This could be due to an artefact in the application of the two-parameter model to only three Olympic performances. A limitation to the use of this linear mathematical model to fit physiological data may have been demonstrated.

Anaerobic Threshold↗

PubMedDate not supplied

Matrimonial distance, inbreeding coefficient and population size: Dhangar data.

Data on the distance between the birthplaces of spouses (matrimonial distance) were collected from 2,260 married individuals belonging to 21 endogamous castes of the Dhangar (shepherd) cast-cluster of Maharashtra, India. The general form of the distribution of matrimonial distances is one which is extremely positively skewed and leptokurtic. The percentage of intra-village marriages generally decreases from the southern areas of Maharashtra to the northern areas of the state, as does the inbreeding coefficient. This situation is in conformity with the socio-cultural norms regulating matrimonial choice in south and north India. An attempt has been made to relate the degree of inbreeding to the mean matrimonial distance and population size. The mean matrimonial distance is more useful in predicting the degree of inbreeding than population size.

Consanguinity↗

PubMedDate not supplied

Effect of average heterozygosity on the genetic distance of several Indian tribes from the Amazon region.

The relationship between average heterozgosity and genetic distance estimates was evaluated among 13 Amazonian Indian tribes, using data of 24 genetic systems. The results showed that the genetic distances were negatively correlated with the average heterozygosity for each pair of tribes. The relationship between genetic and geographic distances was also examined, but no significant correlation was observed between these measures. The negative correlation between genetic distance and average heterozygosity may be attributed to the bottleneck effect or inbreeding due to the small effective size of several tribes, reducing the heterozgosity and increasing the genetic distance between them.

Brazil↗

PubMedDate not supplied

Hindsight bias as a function of anchor distance and anchor plausibility.

This study explored the influence of anchor distance on hindsight bias and how the subjective plausibility of different anchors moderates this relation. In addition to the standard memory design used in hindsight bias research, participants were asked to indicate the range of values for possible answers to difficult almanac questions. Varying anchor distance on the basis of each participant's individual range of possible answers showed (1) that anchor plausibility decreased with increasing anchor distance following a non-linear monotone function, (2) that size of hindsight bias initially increased with increasing anchor distance but, from a certain distance, started to decrease, and (3) that hindsight bias was found to be always higher for plausible than for implausible anchors.

Adult↗

PubMed2005

Evaluation of a distance-learning immunology and pathology module in a postgraduate biomedical science course.

An electronic presentation of materials for a distance-learning immunology and pathology module from a postgraduate biomedical science course is evaluated. Two different electronic presentation formats for the delivery of the educational material to distance learners are assessed. Responses from users of this material highlighted a preference for a format that has a design tailored to distance learning. There was no significant difference in learning outcome between those taking the module on campus and by distance learning. This suggests that the prerequisites for entry, learning materials and direction given to the students studying by distance learning are adequate for these students to achieve the learning objectives outlined in the course. The evaluation also gave direction for areas within the (CAL) application that can be improved for future students.

Allergy and Immunology↗

PubMed2006

The ancestral distance test: what relatedness can reveal about correlated evolution in large lineages with missing character data and incomplete phylogenies.

The ancestral distance test is introduced to detect correlated evolution between two binary traits in large phylogenies that may lack resolved subclades, branch lengths, and/or comparative data. We define the ancestral distance as the time separating a randomly sampled taxon from its most recent ancestor (MRA) with extant descendants that have an independent trait. The sampled taxon either has (target sample) or lacks (nontarget sample) a dependent trait. Modeled as a Markov process, we show that the distribution of ancestral distances for the target sample is identical to that of the nontarget sample when characters are uncorrelated, whereas ancestral distances are smaller on average for the target sample when characters are correlated. Simulations suggest that the ancestral distance can be estimated using the time, total branch length, taxonomic rank, or number of speciation events between a sampled taxon and the MRA. These results are shown to be robust to deviations from Markov assumptions. A Monte Carlo technique estimates P-values when fully resolved phylogenies with branch lengths are available, and we evaluate the Monte Carlo approach using a data set with known correlation. Measures of relatedness were found to provide a robust means to test hypotheses of correlated character evolution.

Classification↗

PubMed2006

Evaluation of an audiovisual-FM system: speechreading performance as a function of distance.

A research program was undertaken to evaluate the efficacy of an audiovisual-FM system as a speechreading aid. The present study investigated the effects of the distance between the talker and the speechreader on a visual-speech perception task. Sentences were recorded simultaneously with a conventional Hi8 mm video camera, and with the microcamera of an audiovisual-FM system. The recordings were obtained from two talkers at three different distances: 1.83 m, 3.66 m, and 7.32 m. Sixteen subjects completed a visual-keyword recognition task. The main results of the investigation were as follows: For the recordings obtained with the conventional video camera, there was a significant decrease in speechreading performance as the distance between the talker and the camera increased. For the recordings obtained with the microcamera of the audiovisual-FM system, there were no differences in speechreading as a function of the test distances. The findings of the investigation confirm that in a classroom setting the use of an audiovisual-FM system may constitute an effective way of overcoming the deleterious effects of distance on speechreading performance.

Adult↗

PubMed2006

Hybridization among divergent stocks of largemouth bass (Micropterus salmoides) results in altered cardiovascular performance: the influence of genetic and geographic distance.

Animal populations exhibit wide ranges of divergence associated with both geographic and genetic distances. Here, we examined the role of crossing distance on the cardiovascular response to exhaustive exercise among differentiated stocks of largemouth bass Micropterus salmoides at 10 degrees C and 20 degrees C. Stocks of 2+ fish were produced using adults from three regions in the midwestern United States (southeastern Wisconsin, northwestern Wisconsin, and west central Minnesota) and were crossed with fish from central Illinois. Doppler flow probes were used to quantify cardiac output, heart rate, and stroke volume. Cardiac variables (both resting and maximal) were consistently lowest in pure Illinois fish relative to the F(1) interstock hybrids. Additionally, when exposed to exercise, cardiac variables for F(1) interstock hybrids required approximately 40% longer to return to resting levels compared with the pure Illinois stock. However, the time required to exhaust fish was similar across stocks. Interestingly, all of the stocks (including the interstock hybrids and pure Illinois) maintained cardiac scope. In general, the patterns observed in cardiovascular performance were consistent for both water temperatures. Multiple regression analysis was used to determine which of the divergence metrics contributed to variation in cardiovascular performance in interstock hybrids. Mitochondrial DNA data (genetic distance) were infrequently identified as a significant source of variation in cardiovascular performance. However, genetic distance data for the neutral allozyme markers revealed that these stocks have experienced significant divergence. Latitude (geographic distance) accounted for between 31% and 45% of variation observed in the recovery parameters. This study suggests that the magnitude of stock divergence is an important determinant in the degree to which cardiovascular performance of bass is altered from interstock hybridization and associated breakdown of coadapted gene complexes. Furthermore, these data suggest that translocating bass among even geographically discrete regions or among stocks with reasonable genetic similarity can result in substantial performance alterations at the F(1) generation.

Animals↗

PubMed2004

Monte Carlo investigations of distance-dependent effects on energy deposition in K-shell x-ray fluorescence bone lead measurement.

Radiation energy deposition results are presented from a Monte Carlo code simulating the lower part of a leg during an in vivo 109Cd K-shell x-ray fluorescence (KXRF) bone lead measurement. The simulations were run for a leg phantom model representing an adult subject, assuming concentrations of 10 microg Pb per gram bone mineral and tracing 500 million photons in each simulation. Trials were performed over a range (0.5-6.0 cm) of source-to-sample (S-S) distances. Energies deposited due to Compton and photoelectric processes occurring in the bone and the soft tissue were obtained. The data show an increase in the amount of energy deposited in the bone as the sample is moved closer to the source (from 2.0 cm to 0.5 cm). However, there is a decrease in the amount of energy deposited in the soft tissue as the sample is moved closer to the source over the same distance interval. In decreasing the S-S distance from 2.0 cm to 0.5 cm, the amount of energy deposited in the sample as a whole was found to increase by 11%. By calculating the energy deposition in the bone and in the soft tissue as a fraction of the total energy deposited in the sample, the corresponding changes are quantified as a function of S-S distance. Similarly, the proportions of energy deposited via the photoelectric effect and Compton scattering are presented as a function of S-S distance.

Adult↗

PubMed2004

Simultaneous minimization of leaf travel distance and tongue-and-groove effect for segmental intensity-modulated radiation therapy.

This paper introduces a method to simultaneously minimize the leaf travel distance and the tongue-and-groove effect for IMRT leaf sequences to be delivered in segmental mode. The basic idea is to add a large enough number of openings through cutting or splitting existing openings for those leaf pairs with openings fewer than the number of segments so that all leaf pairs have the same number of openings. The cutting positions are optimally determined with a simulated annealing technique called adaptive simulated annealing. The optimization goal is set to minimize the weighted summation of the leaf travel distance and tongue-and-groove effect. Its performance was evaluated with 19 beams from three clinical cases; one brain, one head-and-neck and one prostate case. The results show that it can reduce the leaf travel distance and (or) tongue-and-groove effect; the reduction of the leaf travel distance reaches its maximum of about 50% when minimized alone; the reduction of the tongue-and-groove reaches its maximum of about 70% when minimized alone. The maximum reduction in the leaf travel distance translates to a 1 to 2 min reduction in treatment delivery time per fraction, depending on leaf speed. If the method is implemented clinically, it could result in significant savings in treatment delivery time, and also result in significant reduction in the wear-and-tear of MLC mechanics.

Algorithms↗