A study on the orientation effects in polyethylene in the light of crystalline texture

Special sample types established and characterised in Parts 1 and 2 [1,2] were examined systematically under different modes of external deformation at constant temperatures. The structural changes recorded by means of wide- and low-angle X-ray patterns fully substantiated the bodily rotation of the otherwise unaltered crystallites in accordance with the interlamellar slip mechanism postulated in Parts 1 and 2, both in tension and under two modes of compression. Dimensional changes, however, were significantly in excess of those expected from the rotation of crystallites, but were uniquely correlated with this relation in the different samples under different conditions of deformation. This points to a unique structural and mechanistic interrelation between the crystallites and more compliant amorphous regions. As the X-ray long periods were unaffected by the deformation, the more extensible material cannot be identical to that associated with the lamellar periodicity, a fact which points to a previously unsuspected superlamellar regularity in the texture. A simple structural suggestion is made.     

Intracondylar knee joint prosthesis with rotation capacity- Endo model

The St. Georg total knee prosthesis has been modified to incorporate axial rotation of the tibial component. The kinematics approximate more those of the normal knee and the stress imposed at the bone-cement interface are attenuated, thus reducing the risk of mechanical failure. The construction and laboratory testing are described.     

Lymphography in testicular tumors (author's transl)

Results of lymphography in 101 cases of testicular tumor are described. Secondaries could be shown in 43% of seminomas and 46% of teratomas. Examples show the criteria of lymphographic diagnosis of secondaries. Lymphography permits a) more exact classification of stages b) better planning and control of treatment and c) prognosis.     

Formation and properties of single texture polyethylene produced by rolling

The formation of single textured low density polyethylene by unidirectional rolling has been investigated. It was found to be associated with the shear of the sample during annealing, which is a reversal of the shear imparted by the rolling process. Single texture could be produced from double texture by compressing it obliquely in such a way as to simulate this shear. It is concluded that the material probably contains another component besides the single orientation of lamellae which would need to be taken into account when using it as a model for the study of lamellar properties.     

Superconductors with crystalline-field split impurities: Upper critical field and specific heat

We continue the investigation of crystalline-field effects on the properties of superconductors containing rare-earth impurities. Attention is focused on impurities with a nonmagnetic ground state. We calculate the upper critical fieldH _{c 2} and the jump of the specific heat at the phase transition.     

Tracer diffusivity of Ca45and electrical conductivity in CaO-SiO2 melts

The tracer diffusivity of Ca⁴⁵ has been measured in CaO-SiO₂ melts in the temperature range 1500 to 1700°C. In addition the electrical conductivity has been determined. Both properties decrease with increasing silica content. The activation energies (~30 kcal g-atom−1) are of the same order of magnitude. The electrical conductivity as computed from the diffusivity on the assumption that the total current is transported exclusively by divalent calcium ions and that the usual Nernst-Einstein relationship is valid, is somewhat lower than the measured electrical conductivity with the difference increasing with increasing silica content.     

Sliding mode closed-loop control of FES: controlling the shank movement

Functional electrical stimulation (FES) enables restoration of movement in individuals with spinal cord injury. FES-based devices use electric current pulses to stimulate and excite the intact peripheral nerves. They produce muscle contractions, generate joint torques, and thus, joint movements. Since the underlying neuromuscular-skeletal system is highly nonlinear and time-varying, feedback control is necessary for accurate control of the generated movement. However, classical feedback/closed-loop control algorithms have so far failed to provide satisfactory performance and were not able to guarantee stability of the closed-loop system. Because of this, only open-loop controlled FES devices are in clinical use in spite of their limitations. The purpose of the reported research was to design a novel closed-loop FES controller that achieves good tracking performance and guarantees closed-loop stability. Such a controller was designed based on a mathematical neuromuscular-skeletal model and is founded on a sliding mode control theory. The controller was used to control shank movement and was tested in computer simulations as well as in actual experiments on healthy and spinal cord injured subjects. It demonstrated good robustness, stability, and tracking performance properties.