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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Mathematische Zeitschrift 28 (1928), S. 654-676 
    ISSN: 1432-1823
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract The biological reactions to polyethylene wear debris have been shown to result in osteolysis and loosening of total hip arthroplasties. This has led to renewed interest in the use of metal on metal bearings in hip prostheses. This study employed uniaxial and biaxial multistation pin on plate reciprocators to assess how the carbon content of the cobalt chrome alloy and the types of motion affected the wear performance of the bearing surfaces and the morphology of the wear debris generated. The low carbon specimens demonstrated higher wear factors than both the mixed carbon pairings and the high carbon pairings. The biaxial motion decreased the wear rates of all specimens. Plate wear was significantly reduced by the biaxial motion, compared to pin wear. The metal wear particles isolated were an order of magnitude smaller than polyethylene particles, at 60–90 nm, and consequently, 100-fold more particles were produced per unit volume of wear compared to polyethylene. The low carbon specimens produced significantly larger particles than the other material combinations, although it is thought unlikely that the difference would be biologically significant in vivo. The volumetric wear rates were affected by the carbon content of the cobalt chrome alloy, the material combination used and type of motion applied. However, particle morphology was not affected by the carbon content of the alloy or the type of motion applied. ©©1999©Kluwer Academic Publishers
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  • 3
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Counterface damage in the form of scratches, caused by bone cement, bone or metallic particles, has been cited as a cause of increased wear of ultra-high molecular weight polyethylene (UHMWPE) acetabular cups. It is known that high levels of particulate wear debris lead to osteolysis. Surface damage was characterized in a series of explanted Charnley femoral heads. The heads had a mean scratch height of 1 μm with a mean aspect ratio (defined as height divided by half width) of 0.1. Wear discs were artificially scratched using these scratch geometries as a guide. In addition, the scratch geometries were incorporated into a finite element model of a stainless steel asperity repeatedly sliding over UHMWPE under conditions similar to those in an artificial hip joint. Wear tests showed a strong correlation between the average cross-sectional area of the scratch lip above the mean zero line and the measured wear factor. The finite element model predicted increases in the area of UHMWPE suffering plastic strain with increases in the cross-sectional area of the asperity above the mean line. Analysis of the wear debris showed the mode of the particle size was 0.01–0.5 μm for all cases. The morphology of the particles varied with aspect ratio of the asperity, with an increased percentage mass of submicrometer-sized debris with increased scratch lip aspect ratio. The finite element results predicted that the maximum surface strains would increase with increasing asperity aspect ratio. Examination of the worn UHMWPE pin surfaces showed an association between increased surface damage, probably due to high surface strains, and increased aspect ratio. The large areas of surface plastic strain predicted for asperities with high cross-sectional areas above the mean line offer an explanation for the positive correlation between wear rate and the average cross-sectional area of the scratch lip material. The higher surface strains predicted for the higher aspect ratios may explain the increased percentage mass of biologically active submicrometer-sized wear particles found for scratch lips with higher aspect ratios. ©©2000 Kluwer Academic Publishers
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  • 4
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Submicrometer- and micrometer-sized ultra-high molecular weight polyethylene (UHMWPE) wear particles have been associated with osteolysis and failure of total artificial joints. Previous studies have isolated predominantly submicrometer-sized particles at the expense of larger particles (〉10 μm). This study aimed to isolate and characterize quantitatively all sizes of UHMWPE wear particles generated in 18 Charnley hip prostheses. In addition, to analyze the wear debris with respect to the total volumetric wear of the cup and damage to the femoral head. Particle size distributions ranged from 0.1 to -〉1000 μm. A significant proportion (3–82%) of the mass of the wear debris isolated was〉10 μm. The mode of the frequency distribution of the particles was in the range 0.1–0.5 μm for all patients. However, analysis of the mass of wear debris as a function of its size allowed differentiation of the wear debris from different patients. Femoral head damage was associated with high volumetric wear and increased numbers of biologically active submicrometer-sized particles.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Annali di matematica pura ed applicata 29 (1949), S. 25-30 
    ISSN: 1618-1891
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Sunto Allo scopo di svolgere una teoria astratta degli insiemi convessi, vengono introdotti ed utilizzati opportuni postulati, su cui può basarsi un calcolo baricentrico.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Plant and soil 46 (1977), S. 633-636 
    ISSN: 1573-5036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Treatment of a commercial sample of vermiculite (1–2 mm grade) in its natural (non-exfoliated) state with ammonia gas gave a product which nitrified more slowly than ammonium sulphate. The product has potential as a slow-acting fertilizer although its maximum nitrogen content is only 5–6 per cent. The product formed from exfoliated vermiculite and ammonia gas should be useful as a medium for plant growth because it combines good physical properties with a high rate of nitrogen release. re]19760730
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 11 (2000), S. 569-578 
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Numerous small scratches and some larger scratches have been observed on metallic femoral heads of explanted hip prostheses, with the larger scratches believed to be a major contributor to increased wear of the polyethylene acetabular cups. Previous work in our group has shown that smaller scratches, with a mean lip height up to 0.35 μm, can be caused by bone cement and bone particles up to 500 μm in size [1]. However, the larger scratches were not readily replicated with these particles. Therefore in this study experimental and theoretical models have been developed to investigate the damage caused by harder metallic and ceramic particles. Small 10 μm diameter spherical metallic particles were also found to produce small fine scratches on the metallic counterface. However larger diameter spherical metal particles greater than 100 μm in diameter, which were embedded in polyethylene pins, caused severe sharp scratching of the metallic counterface with scratch lips greater than 0.5 μm. This level of damage, which was comparable to the severe damage found in vivo, was also simulated by a three body finite element model. Thus the larger metal particles led to the type of damage which was predicted to increase wear dramatically. This technique for simulating severe in vivo third body damage using spherical metal particles was found to be reproducible and reliable and will be used in the future in hip simulator testing to replicate third body damage and wear.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Acta mathematica 57 (1931), S. 459-463 
    ISSN: 1871-2509
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Type of Medium: Electronic Resource
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  • 9
    Publication Date: 1940-04-15
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
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  • 10
    Publication Date: 1941-01-15
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
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