Calculation of wear (f.i. wear modulus) in the plastic cup of a hip joint prosthesis

The wear equation is applied to the wear process in a hip joint prosthesis and a wear modulus is defined. The sliding distance, wear modulus, wear volume, wear area, contact angle and the maximum normal stress were calculated and the theoretical calculations applied to test results.\ud \ud During the wear process the increase of the wear modulus is about 100 Nmm−2 per mm sliding distance in the Charnley and the Charnley-Muller hip joint prosthesis. From the wear volume point of view the Charnley prosthesis is probably superior to the Charnley-Muller prosthesis if run-in before implantation

Friction of Teflon-S-coated Ti-6Al-4V under conditions of oscillatory relative motion

An extendable prosthesis for implantation in a human leg has been developed. The friction forces during extension of the prosthesis must be low, so a coating of Teflon-S was applied to the sliding surfaces. During walking, damage can occur as a result of oscillatory relative motion. Therefore experiments were performed with an apparatus which simulated this type of motion. It was found that the coefficient of friction reached a maximum value within one million movement cycles. This maximum value of the coefficient of friction increased with decreasing coating thickness. Even at an initial coating thickness of less than 1 μm, coating with Teflon-S was found to be very effective in reducing friction

Wear numbers for ball cup and journal bearings

A wear number is defined for ball cup bearings and for journal bearings where the cup and the cylindrical bearing are made of soft material. This dimensionless wear number provides a relation between the following five quantities: the radius of the ball or the length of the journal bearing in millimetres, the wear modulus in newtons per square millimetre, the maximum wear depth rate of the cup or the cylindrical bearing in millimetres per second, the force between the mating surfaces in newtons and the angular angular speed of the ball or the journal in radians per second. The wear volume of the plastic cup of a hip joint prosthesis was calculated and from the point of view of wear the Charnley prosthesis is probably superior to the Charnley-Muller prosthesis

Heavy baryon properties with NLO accuracy in perturbative QCD

We present an analysis of the static properties of heavy baryons at next-to-leading order in the perurbative expansion of QCD. We obtain analytical next-to-leading order three-loop results for the two-point correlators of baryonic currents with one finite mass quark field for a variety of quantum numbers of the baryonic currents. We consider both the massless limit and the HQET limit of the correlator as special cases of the general finite mass formula and find agreement with previous results. We present closed form expressions for the moments of the spectral density. We determine the residues of physical baryon states using sum rule techniques.Comment: 43 pages in LaTeX, including 3 figure

Grain Surface Models and Data for Astrochemistry

AbstractThe cross-disciplinary field of astrochemistry exists to understand the formation, destruction, and survival of molecules in astrophysical environments. Molecules in space are synthesized via a large variety of gas-phase reactions, and reactions on dust-grain surfaces, where the surface acts as a catalyst. A broad consensus has been reached in the astrochemistry community on how to suitably treat gas-phase processes in models, and also on how to present the necessary reaction data in databases; however, no such consensus has yet been reached for grain-surface processes. A team of ∼25 experts covering observational, laboratory and theoretical (astro)chemistry met in summer of 2014 at the Lorentz Center in Leiden with the aim to provide solutions for this problem and to review the current state-of-the-art of grain surface models, both in terms of technical implementation into models as well as the most up-to-date information available from experiments and chemical computations. This review builds on the results of this workshop and gives an outlook for future directions

Measurement of Wear in Radial Journal Bearings

this article, the measurement of wear in radial journal bearings is discussed, where a distinction is made between stationary and non-stationary contact conditions. Starting with Holm/Archard's wear law, equations are derived for the calculation of the specific wear rate k of the bearing material as a function of the wear depth d, measured after an experiment or a period of use in practice. It is also possible to calculate a value for the maximum allowable apparent pressure pa at given values of k, required lifetime and maximum allowable wear depth d, or a value of d at a given value of pa. In order to facilitate the use of the equations mentioned above, non-dimensional diagrams are presented. Two examples are given to explain the use of these diagrams