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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Journal of neurochemistry 70 (1998), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: We have previously developed an in vitro model for traumatic brain injury that simulates a major component of in vivo trauma, that being tissue strain or stretch. We have validated our model by demonstrating that it produces many of the posttraumatic responses observed in vivo. Sustained elevation of the intracellular free calcium concentration ([Ca2+]i) has been hypothesized to be a primary biochemical mechanism inducing cell dysfunction after trauma. In the present report, we have examined this hypothesis in astrocytes using our in vitro injury model and fura-2 microphotometry. Our results indicate that astrocyte [Ca2+]i is rapidly elevated after stretch injury, the magnitude of which is proportional to the degree of injury. However, the injury-induced [Ca2+]i elevation is not sustained and returns to near-basal levels by 15 min postinjury and to basal levels between 3 and 24 h after injury. Although basal [Ca2+]i returns to normal after injury, we have identified persistent injury-induced alterations in calcium-mediated signal transduction pathways. We report here, for the first time, that traumatic stretch injury causes release of calcium from inositol trisphosphate-sensitive intracellular calcium stores and may uncouple the stores from participation in metabotropic glutamate receptor-mediated signal transduction events. We found that for a prolonged period after trauma astrocytes no longer respond to thapsigargin, glutamate, or the inositol trisphosphate-linked metabotropic glutamate receptor agonist trans-(1S,3R)-1-amino-1,3-cyclopentanedicarboxylic acid with an elevation in [Ca2+]i. We hypothesize that changes in calcium-mediated signaling pathways, rather than an absolute elevation in [Ca2+]i, is responsible for some of the pathological consequences of traumatic brain injury.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 1820-1822 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We observe a light-induced on–off switching of the selective donor–acceptor pair excitation in bulk-grown semi-insulating GaAs. The spectral dependence of the switching process is related to the metastability of the EL2 defect. In the ground state, this As-antisite related midgap donor compensates the shallow acceptors and is responsible for the semi-insulating properties of the material. The loss of the shallow acceptor compensation, that accompanies the transfer of the EL2 to its metastable state leads to the observed absorption and luminescence quench of the shallow donor–acceptor pairs. We exploit these effects in demonstrating optical data storage in semi-insulating GaAs. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new levitation apparatus coupled to a synchrotron-derived x-ray source has been developed to study the structure of liquids at temperatures up to 3000 K. The levitation apparatus employs conical nozzle levitation using aerodynamic forces to stably position solid and liquid specimens at high temperatures. A 270 W CO2 laser was used to heat the specimens to desired temperatures. Two optical pyrometers were used to record the specimen temperature, heating curves, and cooling curves. Three video cameras and a video recorder were employed to obtain and record specimen views in all three dimensions. The levitation assembly was supported on a three-axis translation stage to facilitate precise positioning of the specimen in the synchrotron radiation beam. The levitation system was enclosed in a vacuum chamber with Be windows, connections for vacuum and gas flow, ports for pyrometry, video, and pressure measurements. The vacuum system included automatic pressure control and multi-channel gas flow control. A phosphor screen coupled to a high-resolution video microscope provided images of the x-ray beam and specimen shadow which were used to establish the specimen position. The levitation apparatus was integrated with x-ray diffractometers located at X-6B and X-25 beamlines at the National Synchrotron Light Source. X-ray structural measurements have been obtained on a number of materials including Al2O 3, Ni, Si, Ge, and other metallic and ceramic materials in the liquid state. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 1379-1381 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Palladium is known to exhibit an acceptor state at EC−0.22 eV in n-type Si and a donor state at EV+0.31 eV in p-type Si. We have identified a third level at EV+(0.140±0.005) eV and attribute it to the double donor state of substitutional Pd. The Pd level positions are very similar to the corresponding levels for Pt. The double donor states of both metals show an electric field dependence of the emission rates and a thermal activation of the hole capture cross sections. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 70 (1997), S. 1584-1586 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The midgap level in platinum doped n-type silicon, which was proposed to be the dominant recombination center, is identified as a platinum-hydrogen complex. Hydrogenation of the samples is achieved by wet-chemical etching at room temperature. Defect profiles, determined by deep level transient spectroscopy, clearly associate the level with the concentration profile of atomic hydrogen. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 1425-1434 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The ground- and excited-state properties of both gas phase and crystalline ruthenocene, Ru(cp)2, are investigated using density functional theory. A symmetry-based technique is employed to calculate the energies of the multiplet splittings of the singly excited triplet states. For the crystalline system, a Buckingham potential is introduced to describe the intermolecular interactions between a given Ru(cp)2 molecule and its first shell of neighbors. The overall agreement between experimental and calculated ground- and excited-state properties is very good as far as absolute transition energies, the Stokes shift and the geometry of the excited states are concerned. An additional energy lowering in the 3B2 component of the 5a1′→4e1″ excited state is obtained when the pseudolinear geometry of Ru(cp)2 is relaxed along the low-frequency bending vibration. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    [s.l.] : Macmillan Magazines Ltd.
    Nature 393 (1998), S. 769-771 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Optical fibres doped with lanthanide or transition-metal elements can serve as in-line lasers and amplifiers for fibre-optic telecommunications systems. In general, most such fibre lasers use conventional silica-glass fibres doped with erbium or neodymium. But silicon dioxide absorbs strongly ...
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1433-0407
    Keywords: Schlüsselwörter Magnetresonanztomographie ; Diffusion ; Echo-planar ; Zerebrale Ischämie ; Key words MRI ; Diffusion ; Echo - planar ; Cerebral ischemia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Summary Magnetic resonance imaging represents today the most important tool in neuroradiology for both clinical pratice and research. MRI allows imaging of the human body in 2 or 3 dimensions with variable tissue contrast. The natural diffusion of tissue protons can now be used as a supplementary contrast mechanism. Different MRI techniques can be used to obtain clinically useful diffusion-weighted images. These techniques all require the use of strong gradient pulses in order to obtain the diffusion contrast. In the current article, the most important physical principles of diffusion measurement are presented. After a short introduction into the basic physical principles, we will present the prerequisites and limitations of clinically relevant applications today. Finally a few select examples of clinical use of these techniques in the acute diagnosis of stroke will be presented.
    Notes: Zusammenfassung Die Kernspintomographie (Magnetresonanztomographie, MRT) ist das zentrale diagnostische Instrument der Neuroradiologie für die Routinediagnostik, aber auch für Fragestellungen, die Forschung und Lehre betreffen, geworden. Zu den bereits bekannten und erprobten MR-Bildkontrasten ist die Diffusion der Protonen als neuer zusätzlicher Kontrastmechanismus hinzugekommen. In letzter Zeit wurden verschiedene kernspintomographische Techniken beschrieben, die zur Diffusionsbildgebung herangezogen werden können. Dabei verlangen MR-Diffusionssequenzen den Einsatz starker Gradientenpulse, die den Diffusionskontrast erzeugen. Andere, weniger bekannte Techniken lassen sich aber auch auf MR-Geräten mit schwächeren Gradienten einsetzen. Untersuchungen die belegen, daß Art und Ausmaß eines Schlaganfalls mit der MR-Diffusionsbildgebung sehr früh mit hoher Sensitivität nachzuweisen ist, haben diese neue MR-Bildgebungstechnik in das Zentrum von Therapiestrategien für diese häufige Erkrankung gerückt. In der vorliegenden Arbeit werden die wichtigsten physikalischen Grundlagen der MR-Diffusionsmessung vorgestellt. Die heute klinisch einsetzbaren Techniken, deren technische Voraussetzungen und Einschränkungen werden erläutert. Im abschließenden Teil wird die klinische Anwendung dieser neuen Bildgebungstechnik zur Diagnostik von akuten Hirninfarkten anhand einiger Beispiele beschrieben.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract A search for an abundant and economical source of isoflavones, particularly genistein, led to the discovery that the erythromycin-producing organism Saccharopolyspora erythraea also produces this promising new cancer-prevention agent. Erythromycin fermentation is a large-scale, soybean-based process used world-wide for the commercial production of this medically important antibiotic. Results from this study indicate that genistin (the glucoside form of genistein), which is added to the fermentation in the soybean media, was converted to genistein through the action of a β-glucosidase produced by the organism. Genistein was co-extracted with erythromycin from the fermentation broth, then separated from erythromycin during the second step of the purification process for the production of erythromycin.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1432-1262
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Résumé. Le but de cette étude est de déterminer la fiabilité des potentiels évoqués corticaux après stimulation électrique du canal anal. Des potentiels évoqués corticaux ont été enregistrés chez 243 patients se plaignant de douleurs périnéales (28 patients), d'impuissance (55 patients) d'incontinence fécale (52 patients), d'incontinence urinaire (30 patients), de constipation (49 patients), et chez 29 patients neurologiques, par stimulation du sphincter anal externe et du pénis ou du clitoris. La reproductibilité inter- et intra-observateurs a étéétudiée par codage des interprétations données par trois observateurs à l'occasion de deux évaluations distinctes. L'influence des caractéristiques de l'enregistrement et des données cliniques a été déterminée. Afin d'étudier le rôle de l'opérateur, cinq opérateurs ont investigué les patients mais un seul était particulièrement entraîné pour cette investigation. L'interprétation des courbes d'enregistrement par les observateurs était peu reproductible dans 15% des cas, dépendant du temps écoulé entre les deux lectures et dépendant de la qualité de l'enregistrement. L'interprétation de la réponse cérébrale après la stimulation anale est dépendante de l'observateur et influencée par sa connaissance des données cliniques. Ceci a également été observée avec la mesure des potentiels corticaux évoqués après stimulation du pénis ou du clitoris, toutefois dans une moindre mesure. La méthode du potentiel évoqué cérébral est également dépendante de l'opérateur, particulièrement après la stimulation anale. Lorsque une étude des potentiels corticaux évoqués par stimulation périnéale est nécessaire en pratique clinique, il semble logique de préférer la technique des potentiels corticaux évoqués par stimulation du pénis ou du clitoris, car ils semblent plus faciles à obtenir que ceux observés après stimulation anale si les investigateurs ne sont pas particulièrement familiers avec les méthodes électrophysiologiques et, car les premiers sont davantage opérateurs et observateurs dépendants.
    Notes: Abstract. The aim of this study was to assess the reliability of cortical evoked potentials after electrical stimulation of the anal canal. Cortical evoked potentials were recorded on 243 patients presenting with perineal pain (28 patients), impotence (55 patients), anal incontinence (52 patients), urinary continence (30 patients), constipation (49 patients), and on 29 neurological patients, by stimulating the external anal sphincter and penis (or clitoris). The inter- and intra-observer reproducibility was studied by coding recordings interpreted by three different observers on two separate occasions. The influence of recording characteristics and clinical data were assessed. To study operator dependence, five operators investigated the patients. Only one of them was well trained in this technique. The interpretation of the coded curves by the observers was poorly reproducible in about 15% of cases, depending on time between the two readings and the quality of recordings. The interpretation of cerebral responses after anal stimulation were observer-dependent and influenced by the knowledge of clinical data. This was also observed with cortical evoked potentials after electrical stimulation of the penis or clitoris, but to a lesser extent. The cerebral evoked potentials method was also operator-dependent, mainly after anal stimulation. When a study of cortical evoked potentials by perineal stimulation is needed in clinical practice, it seems logical to prefer cortical evoked potentials by penile or clitoral stimulation as they seem easier to obtain than those evoked by anal stimulation if the investigators are not well trained for the performance of electrophysiological studies as the former are much less operator- and observer-dependent.
    Type of Medium: Electronic Resource
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