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Wear debris associated with the polyethylene components of total joint replacements has been shown to induce bone resorption which contributes to implant loosening. In an effort to promote lubrication and reduce wear in artificial hip joints, the use of the cushion bearing concept has been proposed previously; however, an elastomeric material tested as a cushion bearing has been shown to have poor tribological properties during initiation of motion from rest. The goal of this project was to fabricate and characterize an elastomer that has the ability to attract to its surface naturally occurring boundary lubricants from an aqueous solution. The test elastomer and appropriate controls were characterized using fluorescence, electron spin resonance and X-ray photoelectron spectroscopy. The test elastomer was found to have an enhanced ability to attract dipalmitoylphosphatidylcholine, a known physiological boundary lubricant. A cushion bearing that also encourages boundary lubrication represents a potential improvement over currently existing orthopaedic implant-bearing materials.

The trigatron has been in widespread use as a demand-triggered, high-voltage switch for more than 40 years. In spite of the popularity and maturity of the technology, there persists an uncertainty over the basic physical mechanism(s) responsible for triggering breakdown in the devices. We present the results of an empirical study which directly demonstrate that in the normal operating region of the devices breakdown is initiated by streamers launched from the trigger pin before the appearance of the trigger spark. We compare our results with those of previous workers, and discuss the generality of our conclusions. Our results also provide empirical information about the streamers.

Photoconductive and other types of semiconductor switches hold great promise for use in high voltage switching applications requiring reliability, light weight, and system simplicity. At present, the utility of these devices is sharply limited by the occurrence of surface flashover at the semiconductor-ambient interface at voltages roughly an order of magnitude below that expected on the basis of the bulk dielectric strength of the material. The physical mechanisms responsible for this flashover are not understood, but recent empirical evidence suggests that the problem can be overcome, and that although the actual flashover appears to occur in the ambient, the processes responsible for initiating flashover occur inside the semiconductor. We propose a model for surface flashover based on band bending at the semiconductor-ambient interface.

This paper presents a method for verifying that two hierarchical combinational circuits implement the same Boolean functions. The key new feature of the method is its ability to exploit the modularity of the circuits to reuse results obtained from one part of the circuits in other parts. We demonstrate the method on large adder and multiplier circuits.

A two dimensional mathematical model of knee motion in the sagittal plane was developed. The cruciate ligaments were modeled as a crossed four bar linkage. The mathematical model uses a series of vector loops and scalar equations to solve for all linkage parameters. The model requires 11 equations to solve for 11 unknowns. The equations were driven with a linkage angle that is directly related to the flexion angle. The model was used to examine the effect of various geometric parameters on the roll and slip between the articulating surfaces of the medial condyle. A geometric computer model was developed to verify the results. >

Summary We report a case of disseminated histoplasmosis presenting with acute renal impairment due to adrenal insufficiency. The finding of bilateral adrenal gland enlargement on abdominal ultrasound examination led to a diagnostic CT-guided adrenal biopsy. Prolonged therapy with amphotericin and itraconazole resulted in a clinical cure, although the patient still requires adrenal replacement therapy.

Dipalmitoyl phosphatidylcholine (DPPC), the major lipidic component of the synovial fluid (45 per cent), has been implicated in previous studies in synovial joint lubrication as a potential boundary lubricant for articular cartilage. The purpose of this study was to evaluate the effectiveness of DPPC as a boundary lubricant at physiological stresses experienced by weight-bearing joints (up to 7.5 MPa). The sliding coefficients of static and kinetic friction for glass surfaces coated with DPPC layers of physiological thickness (70 nm) were measured as a function of average contact stress, contact geometry (point and line), applied load and relative velocity (from 25 to 0 mm/s) and compared to the coefficient of friction for clean glass in the same conditions. The coefficient of friction for DPPC-lubricated surfaces was dependent on contact geometry, obeyed Amonton's law (not dependent on axial load or contact area), was dependent on relative velocity within the range stated and was an effective lubricant at physiological stresses. This study showed that dipalmitoyl phosphatidylcholine can be an effective boundary lubricant at stresses observed in load-bearing joints. Because of their surface-active nature, these adsorbed molecules might also act as a protective layer for the articular surfaces.

We describe a new algorithm for directly solving Poisson's equation in cylindrically symmetric geometries. It is based on the use of fast Fourier transforms for the axial solution, and a novel expansion in cubic splines for the radial solution. Error and stability analyses of the algorithm are included, and the results of test calculations are presented. The algorithm has proved stable, reasonably fast, and able to handle very stiff driving functions.

Ideas concerning several of the problems associated with the development of foliations are reviewed and discussed. The points are made that an axial plane foliation may locally overprint itself and that axial plane foliations are not always parallel to the axes of associated folds. The relationship between foliations and strain is discussed and it is concluded that many foliations are approximately parallel to the λ 1 λ 2 plane of finite strain, but only because they have been rotated towards that orientation with increasing strain and not because they have formed parallel to the principal plane. This means that shear strains of any magnitude parallel to the foliation are possible. Three models for the development of preferred orientation in layer silicates are discussed: rotation, stress controlled oriented growth, and other growth mechanisms. The conclusion drawn is that both rotation and some form of growth mechanism(s) operate in the development of foliations and that they “compete” with one another for the principal role. Finally, the state of the rock during foliation development is discussed. Development of foliation in soft sediment is accepted as a possibility but this model is not considered to be generally applicable. However, it is concluded that some low grade rocks may be essentially disaggregated, in part at least, so as to give the rock a high permeability during foliation development.

Quartz c -axis fabrics are described from a shear zone in a jadeite — garnet bearing meta-granite from Monte Mucrone, in the Sesia-Lanzo Zone of the western Italian Alps. Quartz blebs in the meta-granitoid are progressively deformed into cigar shaped lenses, and are recrystallized. Fabrics measured from individual blebs show considerable variation resulting from an initial orientation effect, and are not very enlightening. A synoptic diagram, however, has a pole-free area which can be correlated with the extension direction, and an asymmetry which is consistent with the known sense of shear operating in the zone. Although the technique of preparing synoptic diagrams is rather painstaking, its use is advocated for complex fabric situations, as it may allow partial removal of problems associated with non-random initial orientation distributions.

We present a novel method for accurately determining repulsive potential functions of diatomic molecules. The method utilizes an analysis of the continuum resonance Raman spectra observed from such molecular vapors. We report the results of applying this method to determine the repulsive 1 Π 1u state potential function of I 2 .

Rotated helicitic garnets, syntectonically overgrowing axial plane crenulation cleavage on the limbs of folds, show the opposite sense of rotation to that undergone by the folded foliation during the development of the fold. The garnet rotation is inconsistent with simple minded shear models, for the development of the crenulation cleavage, and it is useful to consider this problem in order to understand the development of crenulation cleavage better. Various models are considered in an attempt to explain both garnet rotation and cleavage morphology. Earlier models were based on the assumption that garnet rotation is driven by shear parallel to S2. They were mostly unsatisfactory, but one, involving migration of the crenulation hinges, is viable when combined with other models described here. The new models proposed here are based on the assumption that garnet rotation is driven by shear on the crenulated surface (S1); the new foliation (S2) is considered to be a passive structure, at least in the early stages of its development. These models satisfactorily explain garnet rotation and development of the cleavage, including differentiation and they can be used to predict the morphological evolution of the cleavage microstructure as it should be preserved in garnets. Comparison of observed and predicted helicitic structures strongly supports the proposed models. Evidence is presented to show that where a garnet has an Se that is a schistosity and an Si that is a crenulation cleavage, the schistosity can have developed by unfolding of the crenulations.

Multiple samples of eight candidate solar concentrator mirrors, including both first and second-surfaces types, were deployed 2.13 m above ground level. This exposure included the majority of the 1977, 1978 and 1979 dust storm seasons in West Texas. Additional samples were deployed at the 28.96–30.48 m elevation on a radio transmitter tower. The samples were evaluated at regular intervals and after every major dust and hailstorm and after most thunderstorms in the area. All materials tested failed except the Carolina Glass Co. mirrors. Polymeric materials failed due to disintegration of the reflective (second) surface; one first surface material failed due to hailstone pitting. Other materials failed due to blistering of the reflective surface or the inability to withstand 1.27–2.54 cm hail. These results are confirmed by the reflectivity and topographic studies (by scanning electron microscopy) reported here. The effects of different methods used to clean naturally occurring dust deposits from the mirrors is reported in terms of changes in reflectivitity.

The relationship between various types of axial-plane foliation, strain history and finite strain are considered from a theoretical point of view. It is concluded that foliations (including slaty cleavage and schistosity) will not be precisely parallel to a principal plane of finite strain in the general case. There are however, a number of special cases that are geologically feasible and these are discussed.

A group of folds in alternating pelites and cross-laminated siltstones is described. An interpretation of the finite strain state, in the competent silt layers, is proposed on the basis of an analysis of the angle between cross-lamination and the principal surface of accumulation. Strain magnitudes are greatest in the fold hinge where domains of layer parallel shortening and layer parallel extension are separated by a neutral surface. Strain magnitudes in the fold limbs are small and are largely related to the development of the asymmetry of the folds. In the incompetent pelitic layers, strain in the fold limbs has a large, layer parallel shear component. Deformation in the pelites is accompanied by, and presumably partially achieved by, migration of quartz from areas where there is a tendency for volume to decrease, to areas where it is tending to increase. This process involves local increases in volume of more than 50%. A kinematic model is proposed for development of the folds. It involves early development of small symmetrical folds followed by their modification to asymmetrical, parasitic structures on the limbs of later folds. In the late stages of folding, continued shortening perpendicular to the axial surface orientation is achieved by development of a conjugate crenulation cleavage.

Renal impairment in sarcoidosis is usually due to hypercalcaemia and nephrocalcinosis but can also be caused by granulomatous nephritis or interstitial nephritis without sarcoid granulomata. A variety of types of glomerulonephritis have also been described in sarcoidosis but these rarely cause impaired renal function. Renal failure as an isolated manifestation of sarcoidosis is uncommon. A 66-year-old woman presented with a 1-year history of lethargy, polyuria and nocturia. Clinical examination was unremarkable and she had impaired renal function (urea 18 mmol/l (108 mg%) and creatinine 380 mumol/l (4.3 mg%)). As her kidneys were normal in size, she underwent renal biopsy, which revealed granulomatous interstitial nephritis. Reevaluation showed no other evidence of sarcoidosis and she had impaired urinary acidification and concentrating capacities. Therapy with corticosteroids produced a marked improvement in symptoms and renal function. This case confirms the view that granulomatous sarcoid nephritis is steroid sensitive and that full recovery can be expected provided interstitial fibrosis and scarring do not occur.