Atomistic mechanisms of fatigue in nanocrystalline metals

We investigate the mechanisms of fatigue behavior in nanocrystalline metals at the atomic scale using empirical force laws and molecular level simulations. A combination of molecular statics and molecular dynamics was used to deal with the time scale limitations of molecular dynamics. We show that the main atomistic mechanism of fatigue crack propagation in these materials is the formation of nanovoids ahead of the main crack. The results obtained for crack advance as a function of stress intensity amplitude are consistent with experimental studies and a Paris law exponent of about 2.

Marcasite and Pyrite (FeS2)

We first describe the structures of FeS2-marcasite and FeS2-pyrite, and the way in which they are related. It is then explained how this relationship can successfully account for several phenomena: pyrite- marcasite intergrowths, the reported anisotropy of (nominally cubic, and therefore isotropic) FeS2-pyrite, stacking and deformation faults in pyrite parallel to {100}, and the observed structure of the pararammelsbergite polymorph of NiAs2.

The Crystal Chemistry of Moganite and Amethyst

The crystal structure of moganite , SiO2, is described, analysed, and shown to be (mimetic) Brazil-twinned α-quartz: it consists of {1101} layers of the latter, one tetrahedron thick, coherently joined at composition planes, with left- and right-handed quartz layers alternating. The structure of the region immediately adjacent to a composition plane is identical to that found in macroscopically twinned quartz, e.g. in amethyst. Thus the 'defect' structure in the latter is the total structure of the former-a classic example of Wadsley's idea that, in crystals, 'defects' are stable structural entities.

Smith-Lemli-Opitz syndrome: biochemical before clinical diagnosis; early dietary management

Pursuit of a possible metabolic basis for an unrecognized pattern of multiple congenital anomalies in a newborn girl led to the detection of a huge elevation of plasma 7-dehydrocholesterol at age 8 months. The biochemical findings and the evolving clinical picture led to the diagnosis of Smith-Lemli-Opitz syndrome at age 11 months. High cholesterol diet may have improved the rate of developmental progress.

Modularity in health visitor education

This examination of curriculum innovation in health visitor education suggests proposals requiring an appreciation of changing health visiting practice, Project 2000 and developments in higher and further education.

Complete, circular papovavirus genomes in the cells of hamsters exposed to a horizontally transmitted lymphomagenic agent

Contagious lymphomas were produced in a colony of Syrian golden hamsters by an unknown agent that also caused fatal ulcerative bowel disease (UBD) lesions prior to lymphoma development. A low percentage of these animals developed epitheliomas of the skin independently of the UBD or lymphomas. Previous work has shown that the epitheliomas contain numerous hamster papovavirus (HaPV) particles, whereas lymphomas do not. Cells from both kinds of tumors do contain HaPV DNA sequences, however. In this study, Southern blot hybridization showed that complete, circular HaPV genomes were present in these cells. Complete, circular HaPV genomes also were found in the cells of animals with UBD. Electron microscopy revealed the presence of HaPV particles in UBD lesions. These results, together with previous data, indicate that in the hamster, lymphomas contain complete, circular papovavirus genomes in the absence of virus particles, whereas epitheliomas and UBD lesions contain these genomes in the presence of virus particles.

An interview study of pregnant women's attitudes to ultrasound scanning

404 pregnant women were interviewed, in the ante-natal clinics of two hospitals, concerning their attitudes to ultrasound scanning, which is routine at one of these hospitals, selective at the other. It was found at the hospital where scanning is selective, that women who had not been examined by ultrasound were less likely to regard a scan as an additional source of reassurance, and to approve of routine scanning, than were those who had yet to be scanned at the other hospital, or any of those who had experienced the procedure. A majority of the women interviewed were enthusiastic about the method, but an important source of dissatisfaction was failure of the operator to reveal and/or explain the foetal image.

A solid-phase fluoroimmunoassay for the quantitation of antibodies to Toxoplasma gondii

A solid-phase fluoroimmunoassay (FIAX¿) for the detection and quantitation of human antibodies to Toxoplasma gondii is described. The method is a modification of the procedure of Walls and Barnhart [1] which differs from the earlier test in that it uses a dual rather than single surface StiQTM Sampler, having both an antigen and a control surface. Each sampler is carried through four steps: reaction with diluted serum, a buffer wash, reaction with FITC-labeled goat anti-human IgG, and a final buffer wash. The fluorescence of each surface is measured using a dedicated surface-reading fluorometer. Serum titers are interpolated from a standard curve. The antibody titers of 233 sera were determined by both the indirect immunofluorescent antibody (IFA) and the FIAX¿ assays. The titers determined by the two tests agreed within one four-fold dilution for 226 (97%) of the sera. For replicates (n = 21) of the sera with low, mid and high antibody titers the coefficients of variation were 13.6, 10.0, and 12.3% respectively.

Method for differentiation of nonspecific from specfic toxoplasma IgM fluorescent antibodies in patients with rheumatoid factor

In a study performed to define the prevalence of false positive toxoplasma IgM-IFA test results in sera containing RF, 8 (19.5%) of 41 sera which were positive for RF were positive in the toxoplasma DT and conventional toxoplasma IFA test. Three of these eight were also positive in the toxoplasma IgM-IFA test and in two, the results were considered to be false positives. Of the 33 sera remaining which were positive for RF but negative in both the DT and conventional IFA test, three were positive in the toxoplasma IgM-IFA test. Of 51 sera from patients with suspected rheumatoid arthritis or other collagen vascular disorders, all of which were negative when tested for RF, none was positive for toxoplasma IgM antibodies in the IgM-IFA test. Sera from 15 adults with the acute lymphadenopathic form of toxoplasmosis and 13 infants with congenital toxoplasmosis were tested for the presence of RF. Whereas none of the sera from the acquired cases had demonstrable RF, two of the congenital cases had RF, and their titers were both 1:320. False positive IgM-IFA test results became negative after treatment of sera with heat-aggregated IgG. In contrast, IgM-IFA test titers in cases of acute congenital or acquired toxoplasmosis were unaffected by this treatment. Thus, treatment with heat-aggregated IgG can be used to differentiate false positive IgM-IFA test titers due to RF from those due to specific IgM toxoplasma antibody.

Physiological Effects of Gibberellic Acid. VII. Electron Microscopy of Barley Aleurone Cells

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