Helen G. Richter

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Due to their excellent mechanical properties, Yttria-stabilized Tetragonal Zirconia Polycrystal ceramics (Y-TZP) are used in ball heads for Total Hip Replacements. It is known that Y-TZP materials may show strength degradation due to ageing or to hydrothermal treatment. Also high wear of UHMWPE sockets coupled to steam sterilized Y-TZP ball heads after a(More)
Subject The causes of the exceptionally low natural durability of one individual plantation-grown teak tree from Panama were investigated. In durability tests with Coriolus versicolor (Leithoff et al. 2001) the heartwood of this tree had shown a mass loss between 32% und 43% while the reference material of a durable teak from Myanmar revealed only 2.3% up(More)
Crystalline inclusions were observed in more than 50%, silica in nearly 20% of about 1500 wood specimens representing ±750 species from 40 genera of the laurel family. Both types of inorganic cell deposits are described and classified with regard to composition, habit, size, degree of isolation and location. Their diagnostic value and taxonomic implications(More)
It is desired to make a preliminary report of certain experimental evidence that respiratory and other gases may enter one lobule from another in the lung without resort to known anatomical passageways. This was found in vivo and in vitro in work with dogs. In vitro observations. A single lung lobe, freshly secured, was prepared by dissection at the hilus(More)
Y-TZP ball heads were introduced into the market in 1985. Since then these components have had wide diffusion in hip replacements, due to their good mechanical performance and reliability. Namely, only a few papers were published up to year 2000 reporting failures of Y-TZP ball heads. The worldwide recall in August 2001 of some Y-TZP batches changed this(More)
There is interest in using zirconia for biomedical applications as ball heads for total hip prostheses. Two potential types are under discussion: partially stabilized zirconia (PSZ) and tetragonal zirconia polycrystals (TZP) materials. Because of its enhanced material properties, TZP stabilized with yttria is favourable. To eliminate high amounts of natural(More)
It is believed that the sympathetic nervous system through its peripheral distribution, and possibly through central connections, exerts, at least' in part, a control on vasomotor tonus. In recent years, several series of experiments on dogs have been conducted in this laboratory to determine the course of vasomotor fibers as measured by thermic changes in(More)
Since 1974 Biolox ceramic femoral ball heads have been used successfully for artificial modular hip joints. The revision rate due to ball head fracture is lower than 0.02%. This is an extremely low value. In this article it is shown how the safety of a ceramic ball head can be improved using the procedures of HIPing, engraving by laser technique, and 100%(More)
To ensure the stability of ceramic ball heads of hip joint prostheses over the long term, both standards for the material and FDA-regulations for the components have been established. In this paper the philosophy underlying design and reliability is discussed. On the basis of fracture loads determined for Biolox ball heads the high level of stability and(More)
Der zunehmende Bedarf von Handel und Industrie nach holzartenspezifischen Informationen und die entsprechend steigende Nachfrage nach Holzartenbestimmung machen es notwendig, hierfür computergestützte Systeme einzusetzen. Am Institut für Holzbiologie und Holzschutz der Bundesforschungsanstalt, für Forst und Holzwirtschaft, Hamburg, sowie am Ordinariat für(More)