Structural and chemical embrittlement of grain boundaries by impurities: A general theory and first-principles calculations for copper

First-principles calculations of the Sigma 5(310)[001] symmetric tilt grain boundary in Cu with Bi, Na, and Ag substitutional impurities provide evidence that in the phenomenon of Bi embrittlement of Cu grain boundaries electronic effects do not play a major role; on the contrary, the embrittlement is mostly a structural or "size" effect. Na is predicted to be nearly as good an embrittler as Bi, whereas Ag does not embrittle the boundary in agreement with experiment. While we reject the prevailing view that "electronic" effects (i.e., charge transfer) are responsible for embrittlement, we do not exclude the role of chemistry. However, numerical results show a striking equivalence between the alkali metal Na and the semimetal Bi, small differences being accounted for by their contrasting "size" and "softness" (defined here). In order to separate structural and chemical effects unambiguously if not uniquely, we model the embrittlement process by taking the system of grain boundary and free surfaces through a sequence of precisely defined gedanken processes; each of these representing a putative mechanism. We thereby identify three mechanisms of embrittlement by substitutional impurities, two of which survive in the case of embrittlement or cohesion enhancement by interstitials. Two of the three are purely structural and the third contains both structural and chemical elements that by their very nature cannot be further unraveled. We are able to take the systems we study through each of these stages by explicit computer simulations and assess the contribution of each to the net reduction in intergranular cohesion. The conclusion we reach is that embrittlement by both Bi and Na is almost exclusively structural in origin; that is, the embrittlement is a size effect.

After Housing Policy: Housing and the UK General Election 2001

This paper describes the results of a review of the housing content of UK General Election 2001 manifestos. Housing policy was of little importance during the election campaign. The main British political parties had, essentially, a shared housing agenda - to promote and facilitate home ownership, support area and community regeneration, tackle homelessness, improve the private rented sector, and prevent building on greenfield sites. Many issues of importance to housing specialists received little or no attention, most notably that of low demand. Some policy variations within the UK were evident, for example in attitudes towards greenfield development, home ownership and stock transfer. The paper concludes that differences in housing policy are emerging within the UK as part of a new politics of devolution and that the days of a single housing policy approach for the UK are over.

Perceived and reported access to the general practitioner: an international comparison of universal access and mixed private/public systems.

Timely and convenient access to primary healthcare is essential for the health of the population as delays can incur additional health and financial costs. Access to health care is under increasing scrutiny as part of the drive to contain escalating costs, while attempting to maintain equity in service provision. The objective was to compare primary care services in Republic of Ireland and Northern Ireland, and to report on perceived and reported access to GP services in universal access and mixed private/public systems. A questionnaire study was performed in Northern Ireland (NI) and the Republic of Ireland (ROI). Patients of 20 practices in the ROI and NI were contacted (n = 22,796). Main outcome measures were overall satisfaction and the access to GP services. Individual responses and scale scores were derived using the General Practice Assessment Questionnaire (G-PAQ). The response rate was 52% (n = 11,870). Overall satisfaction with GP practices was higher in ROI than in NI (84.2% and 80.9% respectively). Access scores were higher in ROI than in NI (69.2% and 57.0% respectively) Less than 1 in 10 patients in ROI waited two or more working days to see a doctor of choice (8.1%) compared to almost half (45.0%) in NI. In NI overall satisfaction decreased as practice size increased; 82.8%, 80.4%, and 75.8%. In both systems, in large practices, accessibility is reduced when compared to smaller practices. The faster access to GP services in ROI may be due to the deterrent effect of the consultation charge freeing up services although, as it is the poorest and sickest who are deterred by the charge this improved accessibility may come at a significant cost in terms of equity. The underlying concern for policy makers centres around provision of equitable services.