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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Der Nervenarzt 70 (1999), S. 517-521 
    ISSN: 1433-0407
    Keywords: Schlüsselwörter Neuronavigation ; Computer-assistierte Neurochirurgie ; Bildgestütztes Operieren ; Rahmenlose Stereotaxie ; Gliomchirurgie ; Key words Neuronavigation ; Computer-assisted neurosurgery ; Image-guided surgery ; Frameless stereotaxy ; Glioma surgery
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Summary The use of stereotactic methods for the resection of subcortical lesions is heavily advoacted in clinical neurosurgery introducing the term „neuronavigation”. Though being an unequivacally elegant technique for the localisation and delineation of pathological lesions in the central nervous system neuronavigation has not been validated by any prospective randomized controlled trial. The method is prone to significant errors as to the intraoperative localisation based upon preoperative threedimensional images. The maximum error can be up to 2.6 cm depending on the extent of the so-called brain shift. In comparison classical frame based stereotaxy has a mean error of ±1 mm and remains the gold standard for the exact threedimensional localisation of a given lesion. The value of neuronavigation is evident for small deep seated vascular lesions. For metastatic tumors or skull base tumors the usefullness is rather marginal because alternative therapies are available with proven and equivalent efficacy and reduced morbidity on one hand, and because of the anatomy of the tumor which makes neuronavigation unnecessary. For the currently most common application of neuronavigation, i.e. surgery of gliomas, no significant improvements of therapeutic results can be expected from neuronavigation. The biology of gliomas limits any mechanical approaches.
    Notes: Zusammenfassung Die Anwendung der stereotaktischen Methode für die Resektion von tiefliegenden Prozessen wird unter dem Begriff „Neuronavigation” in der klinischen Neurochirurgie vehement propagiert. Der Wert dieses unstrittig eleganten Verfahrens zur Lokalisation und Abgrenzung pathologischer Prozesse im ZNS ist bislang nicht durch prospektiv-kontrollierte, randomisierte Studien belegt. Die Methode ist mit einer erheblichen Fehlerbreite bzgl. der intraoperativen Lokalisation auf der Basis präoperativer dreidimensionaler Bilder behaftet („brain shift”). Dem gegenüber ist die klassische rahmengeführte Stereotaxie mit einer Genauigkeit von ±1 mm weiterhin der Gold-Standard für die exakte dreidimensionale Lokalisation eines Prozesses. Wenngleich der Wert der Neuronavigation für kleine, tiefsitzende, insbesondere vaskuläre Prozesse einleuchtet, ist der Wert bei Metastasen und Schädelbasistumoren nur sehr relativ, da hier entweder alternative Therapieverfahren mit gleicher Effizienz bei geringer Morbidität vorliegen oder weil aufgrund anatomischer Gegebenheiten die Neuronavigation entbehrlich ist. Für die derzeit häufigste Anwendung der Neuronavigation, der Gliomchirurgie, ist aus bekannten Gründen, die in der Biologie der Gliome liegen, keine Verbesserung der Operations-ergebnisse zu erwarten.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    World journal of urology 17 (1999), S. 123-125 
    ISSN: 1433-8726
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Angiomyolipoma (AML) is a benign mesenchymal tumor predominantly occurring in the kidney. Despite its low incidence of 0.07–0.3% in an unselected population, this tumor is well known, because the typical AML can be diagnosed without histological confirmation by a combination of ultrasound (US) and computerized tomography (CT) imaging in up to 95% of cases. In contrast, simultaneous involvement of the kidney and the regional lymph nodes is less known and might be confused with metastasizing malignant tumor. We report a case of the very uncommon simultaneous involvement of the kidney and the lymph nodes in AML.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Oecologia 121 (1999), S. 564-573 
    ISSN: 1432-1939
    Keywords: Key words Fertilization ; Lignin-to-nitrogen ratios ; Metrosideros polymorpha ; Nutrient accumulation ; Nutrient limitation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  We examined the effects of soil nutrient availability and tissue chemistry on decomposition of both fine roots (〈2 mm diameter) and leaves in three sites along a forest chronosequence in the Hawaiian Islands. These sites form a natural fertility gradient, with the youngest and oldest sites having lower nutrient availability than the intermediate-aged site. Nitrogen (N) limits aboveground net primary productivity (ANPP) in the youngest site, while phosphorus (P) limits ANPP in the oldest site. Both root and leaf litter decomposed most slowly in the 4.1-Myear-old site. We also investigated root decomposition in fertilized plots at the youngest and oldest sites; when roots were produced and decomposed in fertilized plots, root decomposition rates increased with N and P additions at the 4.1-Myear-old site. At the 300-year-old site, however, root decomposition rates did not respond to N or P additions. Roots decomposed faster than leaves at the more infertile sites, in part because of lower lignin-to-nitrogen ratios in roots than in leaf litter. Decomposing roots immobilized more nutrients than did decomposing leaves, and may serve an important role in retaining nutrients in these forests.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Philosophical studies 96 (1999), S. 123-146 
    ISSN: 1573-0883
    Source: Springer Online Journal Archives 1860-2000
    Topics: Philosophy
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1434-6036
    Keywords: PACS. 79.60.-i Photoemission and photoelectron spectra - 78.66.-w Optical properties of specific thin films, surfaces, and low-dimensional structures
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: We present investigations of the electronic and magnetic structure of the Rare Earth valence states. In particular, we have examined ultra thin films of the rare earth metals gadolinium and neodymium epitaxially grown on tungsten (110). Various experiments on dichroism in angular resolved photoemission have been performed using circularly as well as linearly polarised light in the VUV-range with photon energies below 40 eV. A special emphasis was placed on the investigation of the surface state, which was observed for both Gd and Nd. A very small magnetic splitting of about 25 meV was observed for the surface state of ferromagnetic Gd. A magnetic ordering of a Nd-monolayer on a remanently magnetised Fe-film is observed. Large dichroism effects are found for the surface state as well as the valence bands of paramagnetic Nd. In the latter case, these are used to determine the dispersion of the valence bands. Different numerical approaches are presented, one based on atomic photoionisation theory, another is based on a one-step model of solid state photoemission. Atomic photoionisation theory is used together with three-step calculations to explain the non-magnetic circular dichroism observed in the Gd 4f emission. The capability of dichroism experiments for resolving details of the electronic structure and for sensitive tests of photoemission calculations is demonstrated.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 34 (1999), S. 557-563 
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The feasibility of using cathodoluminescence (CL) and scanning acoustic microscopy (SAM) to measure residual stresses and to map their spatial distribution was investigated. Both techniques were utilized to obtain qualitative and quantitative information on stresses in the vicinity of fibers in pressureless sintered fiber reinforced composites. Both techniques reveal that the stresses are high in close vicinity with the fiber reinforcements and decrease rapidly with increasing distance from the fiber/matrix interface. CL is a surface technique that requires the fibers to be exposed to the surface. SAM is a bulk technique that gives information on residual stresses when fibers are embedded in the matrix. The former can be applied to nonmetallic materials such as semiconductors, ceramics, and glasses; the latter can be applied to metallic materials as well.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 34 (1999), S. 3883-3891 
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The failure of steel beam-to-column connections during the Northridge earthquake of January 1994 was both surprising and alarming to the structural engineering community. These steel moment resisting frames (SMRFs) are intended to behave in a ductile manner. However, in many steel buildings inspected in the Los Angeles area after the Northridge earthquake the connections exhibited brittle fracture. Despite recent laboratory testing of numerous large and small scale structural connections reasons for brittle fracture are still not clearly understood. Therefore, rational design methods to prevent or control brittle fracture in building structures have not been established. This paper investigates the contribution of the microstructure of welded connections to brittle failure. The various microstructures present in a fractured welded connection were characterized and their influence on crack initiation examined. The predominantly brittle failure is preceded in this case by a ductile crack which initiates in a brittle microstructure in the vicinity of the weld root, adjacent to the unfused backing bar.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 34 (1999), S. 4173-4179 
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Residual stresses which arise from thermal expansion and contraction due to welding may have contributed to the brittle fracture exhibited by welded steel beam-to-column connections during the Northridge Earthquake. These residual stresses have a strong influence on crack initiation and crack propagation in the vicinity of stress concentrations (i.e., unfused backup bar in welded steel beam-to-column connections) and account for changes in the driving force for fracture. They affect material toughness by changing the constraint condition under which fracture occurs. Currently, all methods of dealing with residual stresses are hampered by the lack of a consistent means of measuring the magnitudes and distribution of these stresses. This paper describes a new acoustic microscopy technique that allows the mapping of residual stresses in welded connections with high spatial resolution. The technique is based on the sensitivity of polarized acoustic modes to local elastic anisotropy induced by stress. The technique furthermore allows the mapping of residual stresses in a “tomographic” way by changing the frequencies of the acoustic waves. The results reveal that the magnitude of the residual stresses is influenced by the local microstructure of the steel and the weld metal. Ductile microstructures within the weld and the heat affected zone release residual stresses by yielding, whereas brittle microstructures retain residual stresses.
    Type of Medium: Electronic Resource
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