Ductile-Regime Machining of Germanium and Silicon

Precision machining of germanium and silicon was studied using single-point diamond turning. Special attention was directed to the so-called ductile regime wherein optical quality surface finishes can be machined directly on brittle materials. A novel interrupted-cutting test and a new model of the machining process were used to measure a critical-depth parameter experimentally. This parameter governs the transition from plastic flow to fracture along the tool nose. The critical-depth parameter can be used to provide physical insight into the effect of various machining parameters such as tool rake angle or tool clearnace angle. Because of a complex interplay between tool geometry, machining parameters, and material response, a large fraction of material removal occurs by fracture even when ductile-regime conditions are achieved.     

Testing for antibody to human immunodeficiency virus type 1 in a population in which mycobacterial diseases are endemic

During a large epidemiologic study in the Karonga District of northern Malawi, serum samples from 139 patients with incident leprosy, 124 with newly diagnosed leprosy, 277 patients with incident tuberculosis, and 2296 controls were tested for antibodies to human immunodeficiency virus. Sera were tested according to a four-test protocol using two ELISAs and two particle agglutination assays. Overall, 188 samples were considered positive, 2634 were considered negative, and 14 were indeterminate. All 18 available positive specimens from leprosy patients, a random sample of 14 positive specimens from tuberculosis patients, and 15 positive specimens from controls were tested by Western blot. There was no evidence of substantial numbers of ELISA false-positives in any patient group or among controls.     

Port-wine stains. An assessment of 5 years of treatment

OBJECTIVE: To assess objectively the results of flashlamp-pumped dye laser treatment of port-wine stains (PWS). DESIGN: Pretreatment and posttreatment photographs were compared with the appearance of the lesion at follow-up examination. Clinical response was determined by assigning a percentage of lesional lightening score by 2 physicians and the patient, and by reflectance spectrophotometric measurements. SETTING: University and university-affiliated health center. PATIENTS: One hundred two patients (118 PWS) aged 1 month to 66 years (mean, 20 years; median, 16 years) treated from July 1, 1989, to June 30, 1994. RESULTS: Eighteen (15.3%) of the 118 PWS had more than 90% lesional lightening (complete or almost complete response), 77 (65.3%) had lightening from 50% to 90% (good response), 21 (17.8%) had lightening from 11% to 49% (poor response), and 2 (1.7%) had lightening less than 10% (no response). Clinical response did not vary among age groups, but showed statistically significant differences between anatomical locations. A return of PWS after initial response was observed in patients who were seen more than 1 year following completion of treatment. CONCLUSIONS: Treatment of PWS by flashlamp-pumped dye laser results in a good to complete response in most patients. Anatomical location of the lesion is a valuable prognostic indicator of response to treatment. The initially impressive results of flashlamp-pumped dye laser treatment of PWS may be tempered by the gradual return of the vascular lesion as time elapses after completion of therapy. Our experience indicates that PWS show a tendency to recur at a rate approaching 50% between 3 and 4 years after completion of treatment.     

Exercise in an hypoxic environment as a screening test for ischaemic heart disease

Submaximal and maximal exercise testing have been used to predict coronary events but these tests do not give reliable information regarding employability of subjects with abnormal electrocardiogram. In 30 subjects with stabilized ischaemic heart disease (Group A) and 70 subjects with abnormal resting electrocardiogram (Group B), resting electrocardiograms--at ground level and at a simulated height of 4592 m (15000 ft)--after 40-min exposures were recorded. The double Master's two-step exercise test (DM) was performed at ground level as well as at stimulated height (DMH). In the ischaemic group, exercise combined with hypoxia did not yield better results than exercise alone; but among the asymptomatic subjects, exercise in an hypoxic environment gave significantly better results than exercise alone (p less than 0.005) or hypoxia alone (p less than 0.01). Those with negative responses to the test have been employed on strenous duties, including employment at high altitude for the last 3 years. None of them have manifested any objective or subjective evidence of ischaemic heart disease. DM exercise testing in an hypoxic environment is a reliable method to assess subjects with abnormal electrocardiogram and evaluate their functional status.     

Effects of pinealectomy on the rat oestrous cycle and pituitary gonadotrophin release

Two new cases of the syndrome described by Kaplan, Grumbach and Hoyt are reported. The two children were hypopituitary dwarfs, with congenital nystagmus and small optic discs with double border. Pneumoencephalography showed malformations of the median structures, with trans-sphenoidal encephalocele in one case. The definition of this syndrome and its relation to De Morsier's septooptical dysplasia are briefly discussed.     

Sedimentation: A comparison between theory and experiment

A semi-empirical approach using Darcy's law for flow in a porous medium is applied to the problem of a sedimenting column of particles. Application of the mass continuity equations for the moisture ratio, ?, leads to a non-linear Fokker-Planck equation with non-linear boundary conditions in the material coordinate system. The governing equations and boundary conditions are suitably linearised to predict volume outflows (or volume of clear liquid at the top), and concentration and equilibrium profiles.Experiments were carried out on two columns of different length to record both the volume concentration profiles of particles and volume outflow. The particle concentrations were obtained by a γ-ray attenuation method. Theoretical and experimental determinations of volume outflows agree well, and for early times the profiles for the volume concentration as a function of height are similar. However, near equilibrium the two profiles do not compare so favourably, this being attributed to the limitations of the linear analysis at this stage of the sedimentation process.