Human immunodeficiency virus (HIV) infection and arthritis

A variety of inflammatory arthritic conditions are observed in the setting of HIV infection. The epidemiology of these disorders is a point of current controversy, although it appears that several unique syndromes are clinically associated. The pathogenesis of these disorders remains unclear, but we hope that further work in this area will lend important insights into the mechanisms of both HIV-associated and non-HIV associated rheumatic disease. The overall management of such patients is based on recognizing the underlying HIV infection and the judicious use of antirheumatic drug therapy. Rheumatologists need to be aware of the natural history of HIV infection and its clinical manifestations.     

Effects of growth hormone in osteoporosis

The effect of chronic administration of growth hormone (GH) to osteoporotic patients was studied using the techniques of total body neutron activation analysis, whole body counting, calcium tracer kinetics, photon absorptiometry, quantitative microradiography, and urinary hydroxyproline. Two dosage schedules were utilized for six months each: 2 units daily and 0.2 w3/4 units of GH daily (where W represents body weight expressed in kg). The lower dosage (2 units) did not produce any appreciable change in the indices studied. Following the higher dose, no evidence of any anabolic effect was apparent in most patients (i.e., no increase in total body levels of Ca, Na, K, P, or Cl). Increases were noted in the urinary calcium excretion rate and in the urinary hydroxyproline excretion. Bone mineral content decreased. The bone biopsies displayed an increase in bone formation and resorption surfaces in response to treatment, but these changes were not statistically significant. It may be concluded that under the conditions of this study, GH administration did not result in an increment in skeletal mass. Several side effects that are characteristic of acromegaly were observed, including hyperglycemia, hypertension, arthralgia, and the carpal tunnel syndrome. Because of the lack of demonstrated benefit and the associated complications of therapy, GH administration does not appear to be of value in the treatment of osteoporosis.     

Anisotropic hygroelastic behaviour of oriented poly(methyl methacrylate)

A series of samples of oriented poly(methyl methacrylate) was prepared by drawing at a range of temperatures above T_g to a constant extension ratio. The birefringence was used as a measure of orientation. The specimens were immersed in water at 21°C and the coefficients of hygroelasticity were calculated from the dimensional change and weight gain data. Two coefficients, namely the longitudinal and the transverse, were measured for each sample. The longitudinal coefficients of hygroelasticity exhibit a linear decrease and the transverse exhibit an increase as the birefringence increases from zero. The results are analogous to those obtained for thermoelasticity (Wilson, J. D. and Treloar, L. R. G. J. Phys. (D) 1972, 5, 1614).     

Recollections of the evolution of realtime control applications to power systems

Paralleling the extensive growth and expansion of interconnected electric power systems in the United States and Canada during the past 60 years, has been the related need to regulate generation in the constituent areas, and the power flow between them, to achieve equitable, reliable and economic system and area operation. Many individuals and groups have made contributions to these objectives. These contributions constitute the evolution of the system and area realtime control art from modest, tentative beginnings to the comprehensive, broadly scoped and highly capable present day on-line digital control systems. This paper presents one individual's view, based largely on personal experience and observation, of significant steps in this evolutionary process. The paper deals primarily with the analog phases of these developments, many of the philosophies and techniques of which remain basic to current digital executions.