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The effect of grinding on new types of advanced ceramics have been studied experimentally, a series of grinding tests having been undertaken where three process variables; wheel speed, depth of cut and workpiece in-feed rate; were investigated to ascertain their influence on the strength of the ceramic samples. Grinding forces generated under the various conditions were obtained. Residual stresses introduced into the samples were measured using an X-ray diffraction technique. The wheel surface was monitored during its preparation and during the test. The strengths of the samples were found using a 3-point bend test. The ground surfaces were observed with a scanning electron microscope and their Ra values obtained. Results from comparable vitrified and resin-bond diamond grinding wheels were examined.

Three hundred and fifty New Zealand children with occult tuberculous infection are reviewed. Ninety four had received BCG vaccine previously. Three hundred and forty were admitted to hospital and 3 gastric aspirations were obtained from each child and cultured for tubercle bacilli. Mycobacterium tuberculosis was isolated from 1 or more aspirates in 29 (8.5 %) of the children. Excluding those who had received BCG the isolation rate was 10.9 %. Mycobacterium bovis was not cultured from any child. X-rays of the chest which were initially normal showed calcification after 2 to 5 years in 73 (20.8 %) cases. The 350 children were treated with 2 drugs, during the early years isoniazid and PAS and in the past 3 years isoniazid and rifampicin in standard dosage for either 12 or 18 months. The reasons for treating these children are discussed.

Light scattering determinations of molecular weight and coil size made at room temperature with three different cells at two wavelengths of incident light and in two solvents (acetone and acetonitrile) on fourteen fractions and six whole polymers of polymethyl methacrylate ranging in molecular weight from 2.7 × 103 to 2.5 × 106 provide a basis for estimation of the validity and reliability of such measurements. It is concluded that the absolute scale for Mw may be high by a factor of 1.05 ± 0.05. Values of Φ × 10−21 of 2.3 ± 0.2 and 2.6 ± 0.4 obtained in acetone and acetonitrile, respectively, agree with the ‘best value’ of 2.1 suggested earlier, within the uncertainty (ca. 15 to 20 per cent) arising from the experimental uncertainty in [η], M and ( r 2 ) 3 2 . The close agreement between [η] M w relationships established herein for conventional polymethyl methacrylate fractions at 30° in benzene, for M from 200 to 2.5 × 106, and in eight other solvents, with similar results from other laboratories demonstrates that reliable and reproducible dilute solution measurements of [η] and of Mw are indeed possible.

High resolution n.m.r. spectra are readily obtained at room temperature on ten per cent solutions of polymethyl methacrylate in chloroform. For polymers prepared by free radical polymerization, the tacticity parameter β (the probability that neighbouring asymmetric carbon atoms in the chain are in syndiotactic placement) computed accurately (±2 per cent) from the relative areas of the α-methyl magnetic resonance peaks, is observed to obey Bernoulli trial statistics (as reported by others), to increase from 0·64 to 0·86 as the temperature chosen for polymerization ranges from 250° to −40°, and to be unaffected by other polymerization variables such as the initiator, the conversion, the molecular weight of the product, and the presence of any of a variety of solvents. Accordingly, the reaction producing an isotactic placement occurs with an Arrhenius factor 1·65-fold greater, and an activation energy 1·07 kcal larger, than the corresponding variables for the competing syndiotactic addition, a result somewhat different from that found in Bovey's pioneering investigation. Speculations on correlations between sequence length distributions and the diffraction pattern and solubility of partially crystalline polymers are included.

Intrinsic viscosity/temperature relationships from 0° to 120°C determined in a variety of solvents on sixteen fractions of conventional polymethyl methacrylate ranging in molecular weight from 105 to 2.6 × 106 yield, through comparison with existing theory, information on both the intrachain forces and the thermodynamic interactions with the solvent, and their effect on the average dimensions of the polymer coil. The observation that the viscosity at the critical miscibility temperature Θ is 4.8 × 10 −4 M 1 2 independent of temperature, from 30° to 70° at least, indicates an average linear dimension for the polymer coil twice that expected for free rotation about the chain bonds; the observed temperature independence indicates that the trans and gauche minima in the potential energy profile on rotation have the same energy. The heat of mixing and the Θ-temperature for polyisobutylene, polystyrene, and polymethyl methacrylate in different solvents are shown to be generally related to (and to increase with) the difference between the Hildebrand solubility parameters for the polymer and the solvent, and other unknown factors which in specific instances play a dominant role. The abnormally low entropy of mixing observed for these solutions indicates a high degree of local order in the packing of solvent molecules and polymer segments as a result of specific interactions dependent on the chemical and geometrical structure of the polymer-solvent pair.

This is the first report of a series on the properties of dilute solutions of conventional polymethyl methacrylate designed to characterize the chain length and its distribution, the intramolecular chain interactions and the thermodynamic interactions with solvent and their effects on the chain dimensions, and to establish the accuracy and reproducibility of such data. Herein [η] M n relations in benzene at 30° are established for both fractionated and unfractionated polymers from ebulliometric determinations in benzene for Mn from 200 to 6 × 103 and from osmotic pressure measurements in two or more solvents for Mn from 104 to 7 × 105. Evidence is presented that the values of Mn so obtained are generally accurate and reproducible within an uncertainty of three per cent. The observed curvature and its molecular weight dependence in osmotic pressure/concentration relations is in general accord with theoretical expectation. The identity of [η] M n relationships found for unfractionated polymers prepared both with and without added chain transfer agent indicates that both have the same molecular weight distribution and that disproportionation is the predominant mode of termination of methyl methacrylate radicals at 60°.

The present paper represents a summary of the findings of a six month study of health care in the western Pennsylvania region, conducted by the Biotechnology Program of Carnegie-Mellon University during 1968. The study, one of six, was commissioned by the Committee on Engineering in Medicine and Biology of the National Academy of Engineering. A parallel study of Bioengineering in Pennsylvania, sponsored by the Pennsylvania Science and Engineering Foundation of the Department of Commerce, Commonwealth of Pennsylvania, was conducted simultaneously with the NAE study. Major conclusions of this paper center about the need for introduction of modern technology into the health care industry.