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  • 1
    ISSN: 1433-0423
    Keywords: Schlüsselwörter 3-D-Kapselsackmodell ; Intraokularlinsen ; Kapselsackverformung ; Keywords Three-dimensional capsular bag model ; Intraocular lenses ; Capsular bag distortion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Abstract Background. This study quantified the geometric deformation of the capsular bag following implantation of various intraocular lenses (IOL) using a three-dimensional capsular bag model made of silicone caoutchouc. Methods. After implantation of 13 different IOLs (polymethylmethacrylate, silicone acrygel) into the artificial bag, the induced capsular bag deformation was measured and analyzed. The posterior space between IOL and capsule was examined by ultrasonographic biomicroscopy. Results. Polymethylmethacrylate IOLs with C-haptic design induced a greater deformation of the capsular bag than silicone lenses; however, both types showed a larger gap posterior to the IOL than acrygel lenses. Acrygel IOLs with different haptic design revealed only minimal deformation with close contact posteriorly. Conclusions. The presented three-dimensional model simulates the biomechanical and geometrical parameters of the vital capsular bag. Further investigations may determine a correlation of close posterior IOL contact and lens epithelial cell progression.
    Notes: Zusammenfassung Hintergrund. Zur Bestimmung einer eventuellen Verformung des Kapselsackes nach Implantation von. Intraokularlinsen (IOL) aus unterschiedlichem Material und Design wurde mit Hilfe einer geeigneten Preßvorrichtung aus Silikonkautschuck ein 3-dimensionales Modell des Kapselsackes hergestellt. Material und Methode. Nach Einsetzen von 13 verschiedenen Intraokularlinsen aus PMMA, Silikon und Acrygel in den künstlichen Kapselsack wurden die Verformungsgrade mit Hilfe von Deformierungsquotienten und -faktoren bestimmt. Mit Hilfe des Ultraschallbiomikroskopes (UBM) wurde die Größe des Spaltes zur Kapselsackrückwand ermittelt. Ergebnisse. Intraokularlinsen aus PMMA mit C-Haptik-Design bewirkten eine relativ stärkere Verformung des Kapselsackes als Linsen aus Silikon. Beide Linsentypen zeigten einen relativ breiten Spalt zwischen Optik und Kapselsackrückwand. Intraokularlinsen aus Acrygel mit atypischen Haptikkonfigurationen oder C-Haptik erzielten bessere Ergebnisse hinsichtlich der Verformung und spaltfreier Lage der Optik zur Kapselsackrückwand. Schlussfolgerungen. Ein 3-D-Silikonkautschuckmodell ist geeignet, eine mögliche Verformung des Kapselsackes nach der Implantation einer IOL und die Lage der Optik zur Kapselsackrückwand außerhalb des Auges zu simulieren. Aus den gewonnenen Ergebnissen hinsichtlich der spaltfreien Lage der Optik zur Kapselsackrückwand könnte man Rückschlüsse auf die zu erwartende Nachstarentwicklung ziehen.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1998
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Objective. To examine the extent to which intracranial pressure (ICP) in children after severe brain trauma can be determined by cranial CT.¶Materials and methods. Two experienced paediatric radiologists, without any knowledge of the clinical symptoms, evaluated 124 CT scans from 65 children (average age 5.4 years) who underwent intracranial measurement of their cerebral pressure.¶Results. CT had high sensitivity (99.1 %) for ’high cerebral pressure' but a much lower specificity (78.1 %). The examiners tended to estimate ICP as ’high' even when actual ICP was low. Since therapy for lowering cerebral pressure involves potential risks, actual cerebral pressure measurement, particularly in children, should be considered before intervention (e. g. hyperventilation or trepanation). We report the change in different intracerebral fluid compartments with varying cerebral pressure and modifications of the density of the brain tissue in an inter- and intraobserver comparison.¶Conclusion. The radiologist cannot differentiate, for methodological reasons, between a change in the intracranial fluid compartments not associated with a change in ICP and one in which it is critically elevated. Before any interventional treatments such as decompression-trepanation or hyperventilation are instituted, measurement of ICP should be considered, especially in children.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1434-601X
    Keywords: PACS. 13.60.Le Meson production – 25.20.Lj Photoproduction reactions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: Double neutral pion photoproduction from the proton has been measured at MAMI for photon energies between threshold and 820 MeV. The reaction was identified by an invariant mass and missing mass analysis. From threshold up to 370 MeV the total cross-section does not exceed 30 nb. For higher energies it shows a smooth rise until it reaches a maximum of about 10 μb at E γ = 740 MeV. Dalitz plots of m 2(π0π0) versus m 2(p,π0) for seven bins of incident photon energy have been analysed. For E γ 〉 610 MeV, a strong contribution of a sequential decay is observed with the Δ(1232)-resonance as intermediate state. A comparison to model calculations shows that these sequential decays presumably originate from the D 13(1520) and also the P 11(1440)-resonance.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1434-601X
    Keywords: PACS. 13.60.Le Meson production – 25.20.Lj Photoproduction reactions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: The photoproduction of two neutral pions from the deuteron has been studied for incident photon energies from 200 MeV to 820 MeV with the TAPS spectrometer at MAMI (Mainz Microtron). The total cross-section was determined and used to deduce the cross-section from the neutron. Due to the good statistical quality of the data Dalitz plots for the three particles in the exit channel (π0π0 N) could be constructed. The invariant mass distributions derived from them are presented in this paper. They indicate that the important reaction mechanism in the second resonance region is a sequential decay pattern involving the population of the Δ(1232)-resonance as an intermediate state.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1434-601X
    Keywords: PACS. 13.60.Le Meson production – 14.20.Pt Dibaryons – 25.20.Lj Photoproduction reactions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: The reaction γd↦π0 X has been measured with TAPS at MAMI in the energy range E γ = 140-300 MeV. Using the Glasgow tagging spectrometer a photon energy resolution of 0.8 MeV was achieved. The energy excitation functions of integral and differential total cross-sections show no structures of statistical significance 〉 2σ. Upper limits for the production of narrow isoscalar or isovector dibaryons with masses m? 2100 MeV/c2 were deduced. They are in the range 2-5 μb averaged over the 0.8 MeV energy resolution.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1435-1536
    Keywords: Key words Small vesicles ; Phase behaviour ; Small-angle neutron scattering ; Charged surfactants
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract  The phase behaviour and properties of the tetradecyldimethylamine oxide/HCl/hexanol/water quaternary surfactant system have been studied by means of electric conductivity, rheology, freeze-fracture transmission electron microscopy (FF-TEM) and small-angle neutron scattering (SANS). In this system the originally zwitterionic surfactant can become increasingly charged by protonation through the addition of HCl, i.e. the degree of charging can be changed continuously. An interesting, isotropic phase (L1 * phase) of low viscosity was observed for intermediate degrees of charging. From viscosity and conductivity measurements this phase can clearly be distinguished from the conventional L1 phase that is composed of micelles. Investigation of the structures present by means of FF-TEM and SANS showed that the L1 * phase is made up of unilamellar vesicles of extremely small diameter of 8–10 nm. Evidently such highly curved structures are stabilized by the electrostatic conditions in this system.
    Type of Medium: Electronic Resource
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