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PubMed2004

Distance measurement by circular scanning of the excitation beam in the two-photon microscope.

We developed a method to measure relative distances with nanometer accuracy of fluorescent particles of different color in a two-photon scanning fluorescence microscope, with two-channel photon counting detection. The method can be used in the 10-500 nm range, for distances below the resolution limit of standard far field microscopy. The proposed technique is more efficient than the methods using raster scanning. To achieve maximum sensitivity in the radial direction, the excitation beam is moved periodically in a circular orbit with a radius of the size of the point spread function. The phase and the modulation of the periodic fluorescence signal, calculated by fast Fourier transform, gives the phase and the radial distance of the particle from the center of scanning. The coordinates of particles are recovered simultaneously in the two channels and the relative distance is calculated in real time. Particles can be tracked by moving the center of scanning to the recovered position, while measuring the distance from the second particle. Intensity data are saved and fitted later by a model accounting for light leakage between the channels. The total number of detected photons limited the accuracy of the position and distance measurement. Experiments demonstrating the advantages of the method were performed on fluorescent spheres and single dye molecules immobilized on quartz surface.

Algorithms↗
PubMed2004

Precision 1H-1H distance measurement via 13C NMR signals: utilization of 1H-1H double-quantum dipolar interactions recoupled under magic angle spinning conditions.

We applied the POST-C7 DQ-dipolar recoupling pulse sequence to the measurement of (1)H-(1)H distances with high precision. The spectral resolution is enhanced by detecting the (1)H magnetization via (13)C signals. A least-squares fitting of the build-up curve of the transferred magnetization to the exact numerical simulations yielded a (1)H(alpha)-(1)H(beta) distance of 248 +/- 4 pm for fully (13)C-labeled L-valine. This distance agrees with the neutron diffraction study. The negative transferred magnetization clearly indicates that the direct DQ (1)H-(1)H dipolar couplings have the largest effect. The signal for the magnetization transfer builds up rapidly by the direct (1)H-(1)H dipolar coupling, and decreases to zero at longer mixing time when the relayed magnetization transfer becomes significant. This large intensity change of the signal leads to the high precision in the distance measurement. We inspected factors that limit the effective bandwidth of the POST-C7 recoupling for the (1)H and (13)C homonuclear spin systems. The spin interactions at times shorter than the cycle time of the C7 sequence were also evaluated to measure the distances. The carbon-detected 2D (1)H DQ mixing experiment was demonstrated for the measurement of multiple (1)H-(1)H distances.

Carbon Isotopes↗
PubMed2005

Waiting times for cancer care in Canadian children: impact of distance, clinical, and demographic factors.

BACKGROUND: The objective of this study was to evaluate the impact of distance from residence to pediatric oncology centers on waiting times to diagnostic assessment and treatment in Canadian children with cancer. PROCEDURE: Two thousand three hundred sixteen children (< 15 years of age) captured by the Canadian Childhood Cancer Surveillance and Control Program's (CCCSCP) Treatment and Outcome Surveillance (TOS) system were included in the analysis. The number of days between onset of symptoms and first anti-cancer therapy was compared for those living less than 25, 25-99, and more than 100 kilometers from their treating center. For each time period, the adjusted odds of falling into the longest time quartiles were estimated using logistic regression analysis. RESULTS: Thirty-four percent (n = 786) of children lived more than 100 kilometers from their treating center. There were no significant differences in age at diagnosis (P = 0.33), sex (P = 0.68), or ICCC diagnosis (P = 0.02) by distance from center, though there was a significant difference in region of residence (P < 0.01) and the first health care professional contacted (P < 0.01). Except for waiting time from first health care contact to first assessment by treating oncologist which increased with increasing distance (P < 0.01), there were no significant differences in waiting times by distance. When adjusted for important demographic and clinical characteristics, distance to center did not affect the odds of waiting longer for any event. CONCLUSIONS: Distance to treating center had no significant impact on waiting times for important diagnostic and treatment events, when adjusted for age at diagnosis, diagnosis, region, and first health care professional seen.

Adolescent↗
PubMed1999

Travel distance and mass gain in wintering blackbirds.

Birds that range over a large area will have a greater mass-dependent risk of predation than more sedentary birds. Birds that travel more may then reduce winter mass gain to compensate for the increased predation risk that greater travelling entails. I tested whether European blackbirds, Turdus merula, that travelled more in winter had a lower mass than more sedentary birds, independently of any confounding effects of food supply on both ranging behaviour and mass gain. I measured change in winter mass and amount of food eaten in conjunction with the distance that blackbirds travelled to a randomly sited mobile feeder. Blackbirds that travelled shorter distances (per trip and in total) and less often to the feeder had the highest mass midwinter relative to their spring mass. Blackbirds with a higher mean mass midwinter also travelled, on average, shorter distances to the feeder. The distance an individual blackbird travelled to the feeder at any one time was probably independent of the state of its daily energy reserves (how much of its daily total mass gain it had achieved at that point). The relationship between distance travelled and mass was probably independent of food supply because distances actually increased at the end of the winter and the amount of food eaten per individual changed little. More mobile blackbirds were therefore likely to have compensated for any increases in predation risk associated with their greater ranges by decreasing winter mass gain, but will have had an increased risk of starvation because of their lower mass. Copyright 1999 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed2000

Avian dependence on sound pressure level as an auditory distance cue.

Sound pressure level (SPL) has received little attention as a distance cue or signal for communication because of the methodological difficulty of determining source SPL from free-ranging signallers and because SPL is presumed to be unreliable as a distance cue. Eastern towhees, Pipilo erythrophthalmus (Emberizidae, Passeriformes), in south-central Florida give a simple call during territorial interactions. I obtained measurements of call-source SPL with a calibrated microphone positioned 100+/-10 cm from caged male eastern towhees. Measurements of source SPL were highly variable, but much of this variation can be predicted from measurements of call duration or call frequency variables (spectrotemporal variables). Male towhees accurately perceived the distance of a speaker after it played synthetic calls that matched the amplitude and structure of natural 84-dB and 78-dB call types. Subjects flew further in response to an attenuated (-6 or -12 dB) version of an otherwise identical 84-dB call and flew shorter in response to an amplified (+6 dB) version of this same call. Towhees misjudged speaker distance in approximately half of the trials that included a discrepancy (-6, -12 or +6 dB SPL) between playback source SPL and predicted spectrotemporal variables. These distance errors suggest that towhees assess auditory distance partly from the difference between perceived SPL and source SPL, determined from spectrotemporal variables. Copyright 2000 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed1999

Distance measures in terms of substitution processes.

Phylogenetic reconstruction from DNA or amino acid sequences relies heavily on suitable distance measures. A number of new distance measures (asynchronous, LogDet, and paralinear distances) which possess the desired property of tree additivity under fairly general models of sequence evolution have been proposed recently, but they are not well understood from a mechanistic point of view. We review them here in a unifying framework, which is the substitution process in continuous time. The emerging interpretation will also clarify the relationship among these distance measures. We also tackle situations with site-to-site variation of substitution rates which is well known to cause non-additive distances and inconsistent branch lengths. For homogeneous, stationary, time-reversible models, this may be repaired provided that the distribution of rates is known. In contrast, we will show that, for non-stationary models, different tree topologies may produce identical joint distributions of letters in pairs of sequences, given the same distribution of rates. This precludes the existence of any tree-additive pairwise distance measure.

Genetic Heterogeneity↗
PubMed1996

Distance distributions from the tyrosyl to disulfide residues in the oxytocin and [Arg8]-vasopressin measured using frequency-domain fluorescence resonance energy transfer.

We have examined the fluorescence intensity decays of oxytocin and [Arg8]-vasopressin resulting from the single tyrosyl residue in each peptide, and the intensity decay of the Asu1,6-analogues in which the disulfide bridge is substituted by a CH2-CH2 bridge. Viscosity-dependent steady state and intensity decay measurements indicated that fluorescence resonance energy transfer (FRET) from tyrosyl phenol to the disulfide bridge is responsible for the decrease in fluorescence relative to the Asu-analogues. The frequency-domain phase and modulation data for the tyrosyl donor were interpreted in terms of fluorescence resonance energy transfer (FRET) to the weakly absorbing disulfide bridge and a distribution of donor-to-acceptor distances. Energy transfer efficiencies were determined from both time-resolved and steady-state measurements. Fitting the frequency-domain phase and modulation data to a Gaussian distance distribution indicated that the average inter-chromophoric distance (Rav) is similar in both compounds, Rav = 7.94 A for oxytocin and Rav = 8.00 A for vasopressin. However, the width of the distance distribution is narrower for vasopression (hw = 2.80 A) than for oxytocin (hw = 3.58 A), which is consistent with restriction of the tyrosine phenol motion due to its stacking wih the Phe3 side chain of vasopressin. Finally, the recovered distance distribution functions are compared with histograms describing the distance between the chromophores during the course of long, in vacuo, molecular dynamics runs using the computer program CHARMm and the QUANTA 3.0 parameters.

Amino Acid Sequence↗
PubMed1993

Do frogs use retinal elevation to measure the distance of a barrier?

Grass frogs, Rana pipiens, will detour around a barrier to reach prey on the other side. However, if the distance between prey and barrier is short, frogs attempt to push through the barrier and reach the prey directly. The relationship between the probability of detouring and the distance between prey and barrier is the same whether the frog's starting position is 4 cm or 8 cm from the barrier. This suggests that frogs measure the absolute separation between the two objects. To discover whether the retinal elevation of the bottom of the barrier contributes to measuring this distance, the relationship between the frequency of detouring and barrier-prey distance was examined in several experiments in which the retinal position of the bottom of the barrier was manipulated. No evidence was obtained that the barrier's retinal elevation helps in gauging distance. On the other hand, retinal elevation influences strongly how far a frog lunges to reach its prey. It is suggested that different cues to distance are applied to the two classes of object because, under natural circumstances, it is difficult to judge where a barrier emerges from the ground. A barrier may be hard to detect below the horizon because of the low contrast between it and the ground, or because vegetation and ground litter mask where the barrier meets the ground. In contrast, the prey's movements make it easily detectable against a stationary background and the prey's short height means that partial occlusion will have little effect on its apparent vertical position in the visual field.

Animals↗
PubMed1994

The effects of practice on movement distance and final position reproduction: implications for the equilibrium-point control of movements.

Predictions of two views on single-joint motor control, namely programming of muscle force patterns and equilibrium-point control, were compared with the results of experiments with reproduction of movement distance and final location during fast unidirectional elbow flexions. Two groups of subjects were tested. The first group practiced movements over a fixed distance (36 degrees), starting from seven different initial positions (distance group, DG). The second group practiced movements from the same seven initial positions to a fixed final location (location group, LG). Later, all the subjects were tested at the practiced task with their eyes closed, and then, unexpectedly for the subjects, they were tested at the other, unpracticed task. In both groups, the task to reproduce final position had lower indices of final position variability than the task to reproduce movement distance. Analysis of the linear regression lines between initial position and final position (or movement distance) also demonstrated a better (more accurate) performance during final position reproduction than during distance reproduction. The data are in a good correspondence with the predictions of the equilibrium-point hypothesis, but not with the predictions of the force-pattern control approach.

Adult↗
PubMed1982

Evolutionary genetics of birds. V. Genetic distances within Mimidae (mimic thrushes) and vireonidae (Vireos).

Genetic distances (D's) between five species within each of the families Mimidae and Vireonidae were estimated from frequencies of protein electromorphs at 23 loci. For three mimid species in the genus Toxostoma, D equals 0.084 (range, 0.069-0.104); and among three mimid genera, D equals 0.223 (0.167-0.278). These distances typify values previously reported in other birds at comparable levels of taxonomic recognition. In sharp contrast, the mean genetic distance among five congeneric species of Vireonidae is far higher, D = 0.360 (0.027-0.578). One possible explanation for these results is that Vireo species are considerably older, on the average, than are species of Toxostoma or than are members of several other avain genera assayed to date. Conventional thought about the origin and relative age of the Vireonidae appears compatible with this explanation. Although genetic distances in the Vireonidae are large by "avian standards," they remain modest or even small in comparison with distances between many nonavian vertebrate congeners. Results for the Mimidae and the Vireonidae are directly contrasted with genetic distances in well-known genera of Amphibia and Reptilia.

Animals↗
PubMed1993

Metabolic consequences of repeated exercise in long distance runners.

To assess the rates of change in muscle metabolites such as phosphocreatine (PCr) and inorganic phosphate (Pi) during repeated exercise sessions with rest periods, 31-phosphorus nuclear magnetic resonance spectroscopy was used for continuous and noninvasive measurements. Five long-distance runners and six healthy male subjects as controls performed a 2-min femoral flexion exercise at 20 kg.m.min-1 in a 2.1 T superconducting magnet with a 67-cm bore; they repeated this exercise four times with a 2-min rest period. At the beginning of exercise, PCr decreased exponentially; at the end, it increased. During exercise and in the early phase of the recovery in every exercise session, the PCr values were significantly higher in the long-distance runners than in the control subjects (P < 0.05). The Pi increases and decreases involved with exercise also revealed exponential changes. The Pi values did not significantly differ during exercise; however, Pi recovery was faster in the long-distance runners than in the control subjects (P < 0.05). The Pi:PCr ratio during exercise increased linearly with exercise; and Pi:PCr during recovery was smaller in the long-distance runners than in the control subjects (P < 0.05). In conclusion, the long-distance runners revealed faster PCr and Pi kinetics after exercise and a smaller Pi:PCr during exercise than did the control subjects. It is suggested that these results were attributable to a greater oxidative capacity of muscles in the long-distance runners.

Adult↗
PubMed1985

A prediction equation for indirect assessment of anaerobic threshold in male distance runners.

The predictability of anaerobic threshold (AT) from maximal aerobic power, distance running performance, chronological age, and total running distance achieved on the treadmill (TRD) was investigated in a sample of 53 male distance runners, 17-23 years of age. The dependent variable was oxygen uptake (Vo2) at which AT was detected (i.e. Vo2 @ AT). A regression analysis of the data indicated Vo2 @ AT could be predicted from the following four measurements with a multiple R = 0.831 and a standard error of the estimate of 2.66 ml . min-1 . kg-1: Vo2max (67.9 +/- 5.7 ml . min-1 . kg-1), 1,500-m running performance (254.5 +/- 14.2 s), TRD (6.82 +/- 1.13 km), and age (19.4 +/- 2.2 years). When independent variables were limited to Vo2max (X1) and 1,500-m running performance (X2) for simpler assessment, a multiple R = 0.806 and a standard error of the estimate of 2.76 ml . min-1 . kg-1 were computed. A useful prediction equation with this predictive accuracy was considered to be Vo2 @ AT = 0.386X1 - 0.128X2 + 57.11. To determine if the prediction equation developed for the 53 male distance runners could be generalized to other samples, cross-validation of the equation was tested, using 21 different distance runners, 17-22 years of age. A high correlation (R = 0.927) was obtained between Vo2 AT predicted from the above equation and directly measured Vo2 @ AT. It is concluded that the generalized equation may be applicable to young distance runners for indirect assessment of Vo2 @ AT.

Adolescent↗
PubMed1984

Assessment of resolution by half distance values for tritium and radioiodine in electron microscopic radioautographs using Ilford L4 emulsion developed by "solution physical" or D-19b methods.

Half distance values for electron microscopic (EM) radioautographs with the isotopes 3H and 125I were determined using Ilford L4 emulsion processed with either fine grain, solution physical development, or filamentous grain, chemical development with D-19b. 3H- and 125I-line sources, obtained by cutting perpendicular sections from sections of 3H-labeled methacrylate or 125I-labeled thyroid glands, were processed for EM radioautography. The distribution of silver grains around a line source was determined by measuring their distance from the source in photographs of EM radioautographs. The number of silver grains per unit distance from the line source was plotted on graphs and half distance values were calculated. With solution physical development, the half distance value was 74 nm for 3H and 80 nm for 125I; whereas with D-19 b development it was 187 nm for 3H and 157 nm for 125I. Since solution physical development produced a reduction of about 50% in the half distance values for both isotopes, it is concluded that the production of fine grain by this method provides better resolution for EM radioautography than filamentous grain development with D-19b.

Autoradiography↗
PubMed1998

Utilization of the psychiatric emergency service in Mannheim: ecological and distance-related aspects.

Ecologically oriented research of psychiatric service utilization has almost exclusively dealt with regular in- and out-patient services. There are hardly any results on the ecological distribution of utilization rates of psychiatric emergency services. This study aims at investigating the topographic distribution of utilization rates of the psychiatric emergency service out of office hours at the Central Institute of Mental Health (CIMH, Mannheim) from 1982 to 1993. Within this period of time 6463 patients with a total of 14,628 contacts were registered at the CIMH. In order to explain topographic differences in the utilization rates, ecological variables, the distance between patients' residence and service location, and diagnosis were taken into account. The study shows that ecological, distance-related and diagnostic factors all influence the utilization of the psychiatric emergency service in Mannheim. First contact and contact rates decrease from the city centre toward the outskirts. There was a strong general effect of ecological variables: the utilization rates were higher for districts with worse ecological conditions and specific for some diagnostic groups. The greatest difference in utilization rates between the city centre and the outskirts was found for schizophrenia and psychoactive substance use disorders, whereas there was no difference with regard to organic and symptomatic mental disorders. With increasing spatial and time-related distance between residence and service location, the utilization rate decreases. No relation was found between diagnosis and distance. The study also shows an interaction between time-related distance and the ecological variables. The influence of the ecological factors on service utilization is amplified with decreasing distance.

Ambulatory Care↗
PubMed1998

Canal-otolith interactions in the squirrel monkey vestibulo-ocular reflex and the influence of fixation distance.

Natural head movements include angular and linear components of motion. Two classes of vestibulo-ocular reflex (VOR), mediated by the semicircular canals and otoliths (the angular and linear VOR, or AVOR and LVOR, respectively), compensate for head movements and help maintain binocular fixation on targets in space. In this study, AVOR/LVOR interactions were quantified during complex head motion over a broad range of fixation distances at a fixed stimulus frequency of 4.0 Hz. Binocular eye movements were recorded (search-coil technique) in squirrel monkeys while fixation distance (assessed by vergence) was varied using brief presentations of earth-fixed targets at various distances. Stimuli consisted of rotations around an earth-vertical axis and therefore always activated the AVOR. Horizontal and vertical AVORs were assessed when the head was centered over the axis of rotation and oriented upright (UP) and right-side-down (RD), respectively. AVOR gains increased slightly with increasing vergence in darkness, as expected given the small anterior position of the eyes in the head. Combined AVOR/LVOR responses were recorded when subjects were displaced eccentrically from the rotation axis. Eccentric rotations activated the AVOR just as when the head was centered, but added a translational stimulus which generated an LVOR component in response to interaural (IA) or dorsoventral (DV) tangential accelerations, depending on whether the head was UP or RD, respectively. When the head was eccentric and facing nose-out, the AVOR and LVOR produced ocular responses in the same plane and direction (coplanar and synergistic), and response magnitudes increased with increasing vergence. With the head facing nose-in, AVOR and LVOR response components were oppositely directed (coplanar and antagonistic). The AVOR dominated the response when fixation distance was far, and phase was compensatory for head rotation. As fixation distance decreased toward the rotation axis, responses declined to near zero, and when fixation distance approached even closer, the LVOR component dominated and response phase inverted. The same pattern was observed for both horizontal (head UP) and vertical (head RD) responses. The LVOR was recorded directly by rotating subjects eccentrically but in the nose-up (NU) orientation. The AVOR then generated torsional responses to head roll, coexistent with either horizontal or vertical LVOR responses to tangential acceleration when the subject was oriented head-out or right-side-out, respectively. Only the LVOR response components were modulated by vergence. A vectorial analysis of AVOR, LVOR, and combined responses supports the conclusion that AVOR and LVOR response components combine linearly during complex head motion.

Animals↗
PubMed1999

Effect of viewing distance on the generation of vertical eye movements during locomotion.

Vertical head and eye coordination was studied as a function of viewing distance during locomotion. Vertical head translation and pitch movements were measured using a video motion analysis system (Optotrak 3020). Vertical eye movements were recorded using a video-based pupil tracker (Iscan). Subjects (five) walked on a linear treadmill at a speed of 1.67 m/s (6 km/h) while viewing a target screen placed at distances ranging from 0.25 to 2.0 m at 0. 25-m intervals. The predominant frequency of vertical head movement was 2 Hz. In accordance with previous studies, there was a small head pitch rotation, which was compensatory for vertical head translation. The magnitude of the vertical head movements and the phase relationship between head translation and pitch were little affected by viewing distance, and tended to orient the naso-occipital axis of the head at a point approximately 1 m in front of the subject (the head fixation distance or HFD). In contrast, eye velocity was significantly affected by viewing distance. When viewing a far (2-m) target, vertical eye velocity was 180 degrees out of phase with head pitch velocity, with a gain of 0. 8. This indicated that the angular vestibulo-ocular reflex (aVOR) was generating the eye movement response. The major finding was that, at a close viewing distance (0.25 m), eye velocity was in phase with head pitch and compensatory for vertical head translation, suggesting that activation of the linear vestibulo-ocular reflex (lVOR) was contributing to the eye movement response. There was also a threefold increase in the magnitude of eye velocity when viewing near targets, which was consistent with the goal of maintaining gaze on target. The required vertical lVOR sensitivity to cancel an unmodified aVOR response and generate the observed eye velocity magnitude for near targets was almost 3 times that previously measured. Supplementary experiments were performed utilizing body-fixed active head pitch rotations at 1 and 2 Hz while viewing a head-fixed target. Results indicated that the interaction of smooth pursuit and the aVOR during visual suppression could modify both the gain and phase characteristics of the aVOR at frequencies encountered during locomotion. When walking, targets located closer than the HFD (1.0 m) would appear to move in the same direction as the head pitch, resulting in suppression of the aVOR. The results of the head-fixed target experiment suggest that phase modification of the aVOR during visual suppression could play a role in generating eye movements consistent with the goal of maintaining gaze on targets closer than the HFD, which would augment the lVOR response.

Adolescent↗
PubMed2002

The lineage-specific base-pair contents in the stem regions of ribosomal RNAs and their influence on the estimation of evolutionary distances.

The base-pair changes in the stem regions of ribosomal RNAs provide a useful measure for resolving the phylogeny of organisms. In the present study, how the biased base-pair content influences the estimation of evolutionary distances is theoretically investigated. By regarding the biased base-pair content as a result of the difference in selective strength between A:U and G:C base pairs, the evolutionary distance empirically obtained by enumerating base-pair changes is theoretically expressed in terms of selective strength, base-pair change rate, and divergence time. Its application to nuclear-coded large subunit ribosomal RNAs (LSU rRNAs) reveals the followings. LSU rRNAs from most organisms have moderate base-pair contents and the empirical evolutionary distances obtained by the comparison of these LSU rRNAs are approximately proportional to their divergence times. In the comparison of these moderate LSU rRNAs with the GC-rich LSU rRNAs such as those from Mycoplasma, Crenarchaeota, and Giardia, however, the empirically calculated distances are considerably smaller than the true evolutionary distances, while the comparison with AU-rich LSU rRNAs from Microsporidia overestimates their distances. With this result in mind, the relative base-pair change probabilities among three kingdoms are carefully estimated from the statistical distribution of base-pair change ratios enumerated for LSU rRNAs showing almost the same base-pair contents, leading to the result that prokaryotes and eukaryotes first diverged and that archaebacteria and eubacteria diverged on the line of prokaryotes slightly later, by about 0.3 billion years.

Animals↗
PubMed2005

Increase in dance imprecision with decreasing foraging distance in the honey bee Apis mellifera L. is partly explained by physical constraints.

Honey bee foragers communicate the direction and distance of both food sources and new nest sites to nest mates by means of a symbolic dance language. Interestingly, the precision by which dancers transfer directional information is negatively correlated with the distance to the advertised food source. The 'tuned-error' hypothesis suggests that colonies benefit from this imprecision as it spreads recruits out over a patch of constant size irrespective of the distance to the advertised site. An alternative to the tuned-error hypothesis is that dancers are physically incapable of dancing with great precision for nearby sources. Here we revisit the tuned-error hypothesis by studying the change in dance precision with increasing foraging distance over relatively short distances while controlling for environmental influences. We show that bees indeed increase their dance precision with the increase in foraging distance. However, we also show that dance performed by swarm-scouts for a nearby (30 m) nest site, where there could be no benefit to imprecision, are either without or with only limited directional information. This result suggests that imprecision in dance communication is caused primarily by physical constraints in the ability of dancers to turn around quickly enough when the advertised site is nearby.

Animal Communication↗