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At least 55 records · Page 3Linked to original sources

PubMed2003

Long-distance colonization, isolation by distance, and historical demography in a relictual Mexican pinyon pine (Pinus nelsonii Shaw) as revealed by paternally inherited genetic markers (cpSSRs).

Pinus nelsonii is a relictual pinyon pine distributed across a wide altitudinal range in semiarid zones in Mexico near the border between the States of Nuevo León and Tamaulipas. It also occurs in small patches in the State of San Luis Potosí. Pinus nelsonii is classified in the monotypic subsection Nelsoniae, separated from other pinyon pines (subsection Cembroides), because it possesses several distinctive characters including persistent fascicle sheaths, connate needles, and a distinctive wood anatomy. In the present study, chloroplast simple sequence repeats (cpSSRs) were used to estimate genetic variation in most known populations (nine) of P. nelsonii. The genetic variation (HT = 0.73; 27 haplotypes in 256 individuals) is moderate when compared to other pine species. Population differentiation ranged between low and moderate (FST = 0.13 and RST = 0.05), as did the Nei and Goldstein genetic distances between populations. However, this pattern varied depending on whether the infinite alleles or stepwise mutation model was used. In the former case a significant isolation by distance was found, but not in the latter. A significant association between geographical and genetic structure in one clade, through a nested clade analysis, was found, which suggested long-distance colonization between 125000 and 309000 years ago. We found weak evidence for a population expansion. A mismatch distribution suggests that P. nelsonii populations underwent an expansion 4.25 times their size between 59000 and 146000 years ago. On the other hand, the populations' star-like phylogeny and a slight parabolic relationship between coalescence times and lineage number also suggest weak population expansion. Overall, this species appears to have been in demographic stasis for a large proportion of the time detected by the markers used.

Cluster Analysis↗

PubMed2000

[The measurement of normal values of exophthalmos, interpupillary distance and interorbital distance of children and adolescence in Xiamen and the rule of their development].

OBJECTIVE: To investigate the developing rhythm of children and adolescent exophthalmos, interorbital distance (IOD) and interpupillary distance (IPD) and their mutual relationships. The study will provide biometry data for formulating juvenile criteria of correcting spectacles. METHODS: Random sampling was performed among children and adolescence aged 5 - 17 years in Xiamen. Adopting epidemic survey, we measured the biometry values of IOD, IPD and exophthalmos with a sliding gauge and exophthalmometer. RESULTS: The average value of exophthalmos was (14.48 +/- 1.71) mm. For the 5 - 8 years old children, the value of exophthalmos trended to increase with the increase of age, meanwhile the value of exophthalmos of adolescence aged 9 - 17 years old tended to be stabilized. The average value of IOD was (95.55 +/- 5.32) mm and the average value of IPD was (56.99 +/- 3.93) mm. Both the values of the IOD and IPD of the male were higher than that of the female. The results of the IOD and IDP distance increased with the increase of age and it trended to be periodic. There was positive correlation between the development of IOD and that of IPD, and it could be described by a linear equation. CONCLUSIONS: There is only one rush-increase stage of ocular development which is before the 8 years old in children. The rule of its development is in accordance with the growing and developing mode of neurological system.

Adolescent↗

PubMed1990

[Determining gunshot distance without bullet entry--a new source of error in determining gunshot distance from point of entry].

A court case lead to a quantitative determination of lead and antimony by atomic-absorption at distances 10 to 20 cm from the bullet hole. As a surprising result at first the area-concentrations of lead and antimony increased with rising distance from the muzzle and reached a maximum, after that maximum like expected a decrease was found. The phenomena is of general interest because otherwise misinterpretations in chemical determination of gunshot firing distances would be possible.

Antimony↗

PubMedDate not supplied

Distance learning and distance education: a personal perspective.

During 50 years of service, the Centers for Disease Control and Prevention has made important contributions to U.S. public health, particularly in the area of training, an essential CDC activity. I summarize some of CDC's experiences with distance learning and distance education, describe the need for public health education and training, and consider how distance education can fill that need.

Centers for Disease Control and Prevention, U.S.↗

PubMed1998

Effect of distance traveled and speed of racing on body weight and serum enzyme activity of sled dogs competing in a long-distance race.

OBJECTIVE: To determine the relationship of serum biochemical values and change in body weight with finishing status (retired from or finished the race), finishing order of a team, and distance traveled for dogs participating in a long-distance sled dog race. ANIMALS: 262 of 848 dogs that participated in the 1995 Iditarod Trail sled dog race. DESIGN: Prospective study. PROCEDURE: Body weight was recorded for 261 dogs before the race and again when these dogs retired from or completed the race. Using a nonrandom convenience sample of participating dogs, blood samples were obtained from 151 dogs that retired from the race and 111 dogs that completed the race. RESULTS: Serum biochemical indices of skeletal muscle damage were significantly higher in dogs retiring during the first 500 miles of the race than in dogs retiring in the last 638 miles or finishing the race. Serum sodium concentration was less than the reference range in a significantly greater proportion of dogs that retired from the race than of dogs that completed the race. There was little relationship between finishing order and serum biochemical values. Dogs completing the race lost a mean of 8.9% of body weight, and amount of weight lost was not related to finishing order. CLINICAL IMPLICATIONS: Results indicated that exertional rhabdomyolysis develops more often in dogs that retire during the initial 500 miles of a long-distance race, compared with dogs that complete the race. There is no detectable relationship between the speed with which the race is run (finishing order) and body weight loss or serum biochemical values.

Animals↗

PubMed2000

Distance education. Part 4. Supervision of family medicine research at a distance. A formative evaluation.

INTRODUCTION: A survey on supervision of research projects was undertaken among current general practitioner students, recent graduates and supervisors of a Masters of Family Medicine degree. The aim was to describe and compare the experience of the three groups and, in particular, to identify the problems associated with distance supervision. METHODS: A self-administered questionnaire survey was distributed to current students (n = 21), graduates (n = 16) and current supervisors (n = 7). RESULTS: Forty out of 44 doctors returned completed questionnaires. Distance was a relatively minor barrier to successful supervision, provided that the student and supervisor established good communication patterns and were able to respond to each other with minimal delay. The commencement of the study and its final write-up were critical phases in the supervision process. DISCUSSION: Communication, including emotional and psychological support, was at least as important as expert opinion in helping Masters students to successfully complete their research projects. Attention must be paid to establishing good understanding and regular means of communication at the beginning of the supervisory process.

Data Collection↗

PubMed2000

Distance education. Part 5. Family medicine research at a distance. Guidelines for supervisors.

INTRODUCTION: This paper recommends guidelines for the supervision of Masters degrees or similar postgraduate courses, in which research projects are supervised at a distance. METHODS: The guidelines are based on the experiences of the authors with a five year old Masters of Family Medicine degree and a formative evaluation conducted by questionnaire survey among its students, graduates and supervisors. RESULTS: It is important to establish ground rules for communication at an early point in the supervisory process. Supervisors need to take into account psychosocial, pedagogical and organisational aspects of their mentorship of students. DISCUSSION: These guidelines are relevant to courses where there remains a strong one-to-one relationship between supervisors and students. In these cases, 'distance' need not be a barrier provided that both sides are aware of and committed to maintaining good patterns of communications with each other.

Communication↗

PubMed1988

Isolation by distance on the Island of Korcula: correlation analysis of distance measures.

Within the framework of holistic anthropological investigations of the rural populations on the Island of Korcula, various measures of biological distances between eight villages were estimated (Mahalanobis' D2 for anthropometric, physiological, and dermatoglyphic traits); socio-cultural similarities and distances were determined (kinship coefficient estimated from migrational data and Hemming similarity measure estimated from linguistic data). A matrix of Spearman's rank correlation coefficients among these measures demonstrated a pattern of interdependencies, which we analysed further by principal components analysis. The first component reflects the cumulative effect of different processes acting on the initial gene distribution over a long period of time; the second component represents initial population structure; and the third component reflects recent migration influences.

Anthropometry↗

PubMed1993

Use of hybridization for distance measurement by fluorescence energy transfer in oligomeric proteins: distance between two functional sites in aspartase.

Our previous studies suggested that in a tetrameric enzyme aspartase, Cys-140 and Trp-430 are located at or near the catalytic and activator sites, respectively. To estimate the distance between these two sites, fluorescence energy transfer between a single tryptophan (Trp-430) and a fluorescent group specifically attached to Cys-140 has been measured. From the fluorescence spectra of the enzyme, the distance was calculated to be 22.2 A according to the Förster's theory. To estimate the contribution of energy transfer between subunits, we prepared hybrids composed of non-fluorescent and fluorescent subunits and showed that the energy transfer occurred mainly within one subunit in the tetramer. These results indicate that the use of hybridization is very effective as a general method for evaluation of intersubunit energy transfer in oligomeric proteins.

Aspartate Ammonia-Lyase↗

PubMed1995

Helical parameters, fluctuations, alternative hydrogen bonding, and bending in oligonucleotides containing a mistmatched base-pair by NOESY distance restrained and distance free molecular dynamics.

We have analysed and compared the molecular structures and dynamics of the DNA duplex, that corresponds to the sequence 29 to 39 of the K-ras gene, where the central base-pair is the normal C.G base or a mismatch base-pair C.A, C.A+, A.G and A+.G. Molecular dynamics runs of 100 picoseconds without or with distance restraints derived from NOE measurements are analysed and compared in all cases. (1) The EMBO convention of helical parameters for nucleic acids is extended to account for the construction and the description of any DNA mismatched base-pair. (2) Both types of MD runs reproduce very well all NMR data, except the H8 H2 inter-residue distances where agreement is not as good. (3) Average parameter values and fluctuations are in good agreement with results derived from persistence length and torsion modulus measurements. (4) Our molecular dynamics suggest the presence, in certain cases, of three-centred hydrogen bonds, which should be viewed as an equilibrium between hydrogen-bonding alternatives. In the case of the C.A mismatch, we observe the correlation between transient DNA bending and possible hydrogen bonding between a base and its 5' neighbour on the opposite strand in the sequence CCA. (5) These molecular dynamics analyses and observations provide a coherent view for the results obtained from recent DNA crystal structures and for results derived from other techniques such as gel electrophoresis at C.A steps.

Base Sequence↗

PubMed1983

The Hellinger distance as used for the representation of serological ABO distances among earlier human populations.

The Hellinger (arccos) distance is examined for the purpose of demonstrating to what extent it represents the differences among populations. When the Hellinger distance is employed to estimate gene frequencies, a result very similar to that of the maximum likelihood (Bernstein) method can be gained. It is pointed out that in palaeoserological examinations the Dobson/Ikin method usually mentioned as Fisher method is not equivalent to the Bernstein method.

ABO Blood-Group System↗

PubMed1988

Obtaining oblique technique source-to-skin distances for irregular field (Clarkson) calculations: the Mayo Off-axis Distance Indicator.

Significant dose inhomogeneities may exist between the supraclavicular fossa (SCF) and the internal mammary chain (IMC) regions in the irregular L-shaped (hockey stick) field associated with breast cancer treatments. This dose inhomogeneity exists, in part, because of a positive air gap in the SCF and a negative air gap in the IMC locations. Independent of treatment technique, [i.e., whether anterior-posterior (AP) or oblique fields are used], accurate source-to-skin distance (SSD) values for the SCF, IMC, and axilla are necessary when doing an irregular field (Clarkson) dose calculation. However, when an oblique technique is used to treat the hockey stick field, obtaining non-central-axis SSDs is not as straightforward as when an AP technique is employed. The "Mayo Off-axis Distance Indicator" was constructed to slide into the blocking tray slot of the simulator or treatment machine. This mechanical measuring device provides quick and accurate SSD measurements for non-central-axis points under either AP or, more importantly, oblique treatment conditions.

Breast Neoplasms↗

PubMed1999

The bioenergetics of optimal performances in middle-distance and long-distance track running.

Aspects of anaerobic and aerobic energy conversion are investigated using a mathematical model of running in conjunction with world-record statistics. Analysis of the data shows that over distances from 1500 to 10,000 m the anaerobic energy utilised is constant and independent of running distance. This result is consistent with the view that the full potential of the anaerobic capacity is available for conversion during extended periods of running; the opinions of Gollnick and Hermansen (1973) and Peronnet and Thibault (1989) that the anaerobic energy contribution declines with race duration are not corroborated. The analysis supports the finding of Peronnet and Thibault (1989) that, for running times below about T = 420 s, the maximum sustainable aerobic power is constant, and that for larger T it then declines progressively. The present analysis shows it falls by some 4.5% over 10,000 m, T approximately 1600 s, indicating that in establishing current world records at 5000 and 10,000 m athletes did not rely solely on glycogen as the source of aerobic metabolism; limited use was made of free fatty acids. For elite male runners, the anaerobic capacity and maximal aerobic power are evaluated as 1570 J/kg and 27.1 W/kg, respectively.

Aerobiosis↗

PubMed2002

The impact of central lung distance, maximal heart distance, and radiation technique on the volumetric dose of the lung and heart for intact breast radiation.

PURPOSE: To investigate the impact of radiographic parameter and radiation technique on the volumetric dose of lung and heart for intact breast radiation. METHODS AND MATERIALS: Forty patients with both two-dimensional (2D) and computed tomographic (CT) simulations were enrolled in the study. Central lung distance (CLD), maximal heart distance (MHD), and maximal heart length (MHL) were measured under virtual simulation. Four plans were compared for each patient. Plan A used a traditional 2D tangential setup. Plan B used clinical target volume (CTV) based three-dimensional (3D) planning. Both plans C and D used a combination of a medial breast field with shallow tangents. Plan D is a further modification of plan C. RESULTS: Under the traditional tangential setup, the mean ipsilateral lung dose and volume at 20, 30, and 40 Gy correlated linearly with CLD (R = 0.85 approximately 0.91). The mean ipsilateral lung dose (Gy) approximated 4 times the CLD value (cm), whereas the percentage volume (%) of ipsilateral lung at 20, 30, and 40 Gy was about 10 times the CLD (cm). The mean heart dose and percentage volume at 20, 30, and 40 Gy correlated with MHD (R = 0.76 approximately 0.80) and MHL (R = 0.65 approximately 0.75). The mean heart dose (Gy) approximated 3 times the MHD value (cm), and the percentage volume (%) of the heart at 10, 20, 30, and 40 Gy was about 6 times MHD (cm). Radiation technique impacted lung and heart dose. The 3D tangential plan (plan B) failed to reduce the volumetric dose of lung and heart from that of the 2D plan (plan A). The medial breast techniques (plans C and D) significantly decreased the volume of lung and heart receiving high doses (30 and 40 Gy). Plan D further decreased the 20 Gy volumes. By use of the medial breast technique, the lung and heart dose were not impacted by original CLD and MHD/MHL. Therefore, the improvement from the tangential technique was more remarkable for patients with CLD >or= 3.0 cm (p < 0.001). CONCLUSIONS: The CLD and MHD impact the volumetric dose of lung and heart. The application of 3D planning for tangential breast irradiation does not decrease heart and lung dose. Adding a medial breast port significantly decreases percentage volume (PV) of lung and heart receiving high doses, especially when the CLD is excessive.

Breast Neoplasms↗

PubMed1991

The solution structure of motilin from NMR distance constraints, distance geometry, molecular dynamics, and an iterative full relaxation matrix refinement.

A model of the structure of the 22 amino acid residue gastrointestinal peptide hormone motilin in 30% hexafluoro-2-propanol has been obtained by using distance constraints obtained from two-dimensional nuclear Overhauser enhancements. A set of initial structures have been generated by using the distance geometry program DIANA, and 10 of these structures have been refined by using restrained molecular dynamics (AMBER). The resulting structures are virtually indistinguishable in terms of constraint violations and energies and display less than 0.5-A root mean square deviations (RMSD) of the backbone atom positions from Tyr7 to Lys20. A comparison of back-calculated and experimental NOE intensities indicates that RMSD's are not the best indicators of the goodness of fit or of the precision with which the structure is defined. The structure was further refined by fitting the experimental NOE data using an iterative full relaxation matrix analysis. The mean error between the observed and calculated backbone NOE intensities for the final refined structure was 0.23 for the full length of the molecule, 0.18 for the region from Glu9 to Lys20, and 0.29 for the region from Phe1 to Gly8. R factors for the same regions were 0.27, 0.19, and 0.43, respectively. All of the NOE-determined structures consistently display an alpha-helix which extends from Glu9 to Lys20. Considerable lack of definition of structure exists at the amino and carboxyl ends of the molecule and also in the vicinity of Thr6-Tyr7-Gly8. A tendency to form a wide turn appears to exist over the sequence Pro3-Ile4-Phe5-Thr6, but the structure in this region is not well defined by the NOE data.

Amino Acid Sequence↗

PubMed1975

Role of DNA sequences in genetic recombination in the iso-1-cytochrome c gene of yeast. I. Discrepancies between physical distances and genetic distances determined by five mapping procedures.

Recombination rates have been examined in two-point crosses of various defined cyc1 mutants using five mapping methods. Nucleotide sequences of mutant codons were identified in previous studies from alterations in functional iso-1-cytochromes c produced by intragenic revertants. Heteroallelic diploids were analyzed for rates of mitotic recombination that occurred spontaneously and that were induced with x-rays, ultraviolet light and the near-ultraviolet light emitted by sunlamps, as well as rates of meiotic recombination that occur after sporulation. Frequencies of both mitotic and meiotic recombination do not necessarily correspond with physical distances separating altered nucleotides. The most extreme discrepancy involved two adjacent intervals of thirteen basepairs which differed approximately thirty-fold in their spontaneous and X-ray-induced recombination rates. Marked disproportions between genetic and physical distances appear to be due to the interaction of the two nucleotide sequences in the heteroallelic combination and not to the sequences of the mutant codons alone. Recombination values that were obtained by all five methods could not be used to establish to correct order of mutant sitesmrelationships of the recombination rates for the various pairwise crosses are different after mitosis from those after meiosis, suggesting that these two recombinational processes are to some extent different in their dependence on particular nucleotide configurations. On the other hand, the relationships of the rates induced by UV-, sunlamp- and X-irradiation were identical or very similar. In addition to the intrinsic properties of the alleles affecting frequencies of mitotic and meiotic recombination rates, two- to threefold variations in recombination rates could be attributed to genetic backgrounds.

Base Sequence↗

PubMedDate not supplied

Solution conformations of human growth hormone releasing factor: comparison of the restrained molecular dynamics and distance geometry methods for a system without long-range distance data.

A series of three-dimensional structures of the 1-29 fragment of human growth hormone releasing factor in trifluoroethanol have been determined by molecular dynamics and distance geometry methods. The resulting structures satisfy information from nuclear Overhauser effect (NOE) distance data and an empirical potential energy function. Although the polypeptide was found to have an ordered structure in all simulations, the NOE data were not sufficient for global convergence to a unique three-dimensional geometry. Several satisfactory structures have been determined, all of which are extended conformations consisting of a short beta-strand and two alpha-helices (residues 6-13 and residues 16-29) connected by short segments of less well defined secondary structure. Because of the lack of NOE data connecting the helix segments, their relative orientation is not uniquely determined.

Growth Hormone-Releasing Hormone↗

PubMed1986

Changes in eye position during growth and adult life as based on exophthalmometry, interpupillary distance, and orbital distance measurements.

The association between eye position and age is analysed in a material comprising 267 subjects aged 5-20 years and 187 aged 21-80. The study was prompted by a previous longitudinal finding of a 3 mm increase in exophthalmometry value from age of 10 to 18 years, and by a literature almost devoid of similar investigations in young age groups. The increase in Hertel value during growth could be confirmed. An adult mean value of 16.0 mm in females and 16.6 mm in males was achieved in late teen-age years, the level being stable after that. The adult range was 11-23 mm. After a similar marked increase in the young, interpupillary distance and orbital width also showed some slight trends in adults. A suggested decrease in orbital width towards old age was consistent with a secular trend, while a concomitant increase in interpupillary distance was unexpected, the combined result being a more divergent (relative) eye position with age (P less than 0.01). There was no significant correlation between exophthalmometry and refractive value. Fixed upper Hertel value limits of normal are hard to give; clinically it is the changes that matter. Modelling of facial bony structures and soft tissue contours is discussed.

Adolescent↗