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  • 23Na+,87Rb+, and14N NMR  (1)
  • Active head tilt  (1)
  • Gallbladder contraction  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Separation of local asymmetry and selective solvation effects using the quadrupole relaxation of the23Na+ and87Rb+ ions in acetonitrile-water mixtures (1983)
    Springer
    Journal of solution chemistry 12 (1983), S. 685-701 
    Details
    ISSN: 1572-8927
    Keywords: Quadrupole relaxation ; 23Na+,87Rb+, and14N NMR ; ion-solvent interaction ; asymmetry effects ; preferential solvation ; acetonitrile-water mixtures
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Nuclear magnetic relaxation rates of23Na+,87Rb+, and14N in acetonitrile-water mixtures have been measured over the complete mixture range. The interaction of the quadrupole moment of ionic nuclei with electric field gradients is an excellent short ranged probe for the direct neighborhood of ions in solution. Thus the23Na+ and87Rb+ relaxation contains information about dynamics composition and symmetry of the inner solvation sphere in the mixed solvent. It was found that the relaxation rate of both ionic nuclei has an unexpected marked maximum in the acetonitrile (AN) rich region. The14N and2H relaxation rates of the solvent molecules revealed that the maximum could not be explained by dynamic effects. Further experimental results showed that it is caused by local symmetry changes. By measuring 1/T1 of the cationic nuclei in AN-H2O and AN-D2O it was possible for the first time to separate quantitatively asymmetry effects from selective solvation effects. It turned out that both cations are strongly preferentially hydrated. Comparison of the results of two approaches for the evaluation of the D2O-H2O isotope effect led to interesting hints concerning the location of the electric point dipole in acetonitrile molecules having contact with cations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00647381
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  • 2
    Electronic Resource
    Electronic Resource
    The influence of head position and head reorientation on the axis of eye rotation and the vestibular time constant during postrotatory nystagmus (1992)
    Springer
    Experimental brain research 91 (1992), S. 121-128 
    Details
    ISSN: 1432-1106
    Keywords: Vestibuloocular reflex ; Velocity storage ; Active head tilt ; Semicircular canals ; Otolith ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Reorienting the head with respect to gravity during the postrotatory period alters the time course of postrotatory nystagmus (PRN), hastening its decline and thereby reducing the calculated vestibular time constant. One explanation for this phenomenon is that the head reorientation results in a corresponding reorientation of the axis of eye rotation with respect to head coordinates. This possibility was investigated in 10 human subjects whose eye movements were monitored with a three-dimensional magnetic field — search — coil technique using a variety of head reorientation paradigms in a randomized order during PRN following the termination of a 90°/s rotation about earth vertical. Average eye velocities were calculated over two time intervals: from 1 s to 2 s and from 7 s to 8 s after cessation of head rotation. The time constant was estimated as one third of the duration of PRN. For most conditions, a reorientation of the head with respect to gravity 2 s after the rotation had stopped did not significantly alter the direction of the eye velocity vector of PRN with respect to head coordinates. This strongly indicates that, in humans, PRN is mainly stabilized in head coordinates and not in space coordinates, even if the otolith input changes. This finding invalidates the notion that the shortening of PRN due to reorientation of the head could be due to a change of the eye velocity vector towards a direction (torsion), which is not detectable with the eye recording methods (electrooculography) used in earlier studies. The results regarding the vestibular time constant basically confirm earlier findings, showing a strong dependence on static head position, with the time constant being lowest if mainly the vertical canals are stimulated (60° nose up and 90° left ear down). In addition, the time constant was drastically shortened for tilts away from upright. The reduction in vestibular time constant with head reorientation cannot be explained solely on the basis of the dependence of the time constant on static head position. A clear example is provided by head reorientations back towards the upright position, which results in a decrease in the time constant, rather than an increase that would be expected on the basis of static head position.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00230020
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  • 3
    Electronic Resource
    Electronic Resource
    Changes in gallbladder motor function during the female cycle — a risk factor leading to gallstone formation? (1982)
    Springer
    Journal of molecular medicine 60 (1982), S. 1357-1362 
    Details
    ISSN: 1432-1440
    Keywords: Gallbladder motor function ; Gallstone formation ; Gallbladder ultrasonography ; Gallbladder contraction ; Gallbladder refilling ; Gallensteinentstehung ; Gallenblasenkontraktion ; Motorische Gallenblasenfunktion ; Gallenblasenfüllung ; Ultraschalldiagnostik
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Zusammenfassung Bei 8 Frauen mit stabilem Zyklus wurden mittels Sonographie das Gallenblasenvolumen bestimmt und in der Progesteron- sowie der Östrogenphase des Zyklus die Gallenblasenkontraktion nach oraler Reizmahlzeit und die spontane Wiederauffüllung der entleerten Gallenblase quantitativ untersucht. Zur Volumenberechnung wurde die Formel eines Drehellipsoids verwandt, die sich im Modellversuch als hinreichend exakt erwiesen hatte. Die intraindividuellen Vergleichsuntersuchungen zeigten in der Progesteronphase (21. oder 22. Tag) gegenüber der östrogenphase (12. oder 13. Tag) statistisch gesicherte größere Nüchternvolumina, höhere Residualvolumina nach Kontraktion und eine langsamere Gallenblasenentleerung sowie eine verzögerte Wiederauffüllung der entleerten Gallenblase. Dem hormonal modifizierten Kontraktionsverhalten und der unterschiedlich ablaufenden Gallenblasenfüllung könnte im Rahmen der Gallensteinentstehung eine wesentliche Bedeutung zukommen.
    Notes: Summary The gallbladder volume of eight women with stable cycles was determined by sonography. Furthermore, gallbladder contraction — following an orally administered fatty meal and the spontaneous refilling of the empty gallbladder — was quantitatively examined. The formula of a rotation ellipsoid, which has been proven to be adequately accurate in in vitro studies, was used for calculating the gallbladder volume. In the gestagen phase (21st or 22nd day) the intraindividual studies showed greater fasting volumes, higher residual volumes after contraction, slower gallbladder emptying, and retarded refilling of the empty gallbladder as compared to the estrogen phase (12th or 13th day). The hormonally modified contraction behavior and the differing course of gallbladder filling may play a major role in the pathogenesis of gallstone formation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01716215
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    Paper (German National Licenses)
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