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.

Single-shot characterisation of independent femtosecond extreme ultraviolet free electron andf infrared laser pulses

Two-color above threshold ionization of helium and xenon has been used to analyze the synchronization between individual pulses of the femtosecond extreme ultraviolet (XUV) free electron laser in Hamburg and an independent intense 120 fs mode-locked Ti:sapphire laser. Characteristic sidebands appear in the photoelectron spectra when the two pulses overlap spatially and temporally. The cross-correlation curve points to a 250 fs rms jitter between the two sources at the experiment. A more precise determination of the temporal fluctuation between the XUV and infrared pulses is obtained through the analysis of the single-shot sideband intensities. ©2007 American Institute of Physics

Operation of a free-electron laser from the extreme ultraviolet to the water window

We report results on the performance of a free-electron laser operating at a wavelength of 13.7 nm where unprecedented peak and average powers for a coherent extreme-ultraviolet radiation source have been measured. In the saturation regime, the peak energy approached 170 J for individual pulses, and the average energy per pulse reached 70 J. The pulse duration was in the region of 10 fs, and peak powers of 10 GW were achieved. At a pulse repetition frequency of 700 pulses per second, the average extreme-ultraviolet power reached 20 mW. The output beam also contained a significant contribution from odd harmonics of approximately 0.6% and 0.03% for the 3rd (4.6 nm) and the 5th (2.75 nm) harmonics, respectively. At 2.75 nm the 5th harmonic of the radiation reaches deep into the water window, a wavelength range that is crucially important for the investigation of biological samples.

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.

Iron abundances of B-type post-asymptotic giant branch stars in globular clusters: Barnard29 in M13 and ROA5701 in ωCen

High-resolution optical and ultraviolet (UV) spectra of two B-type post-asymptotic giant branch (post-AGB) stars in globular clusters, Barnard29 in M13 and ROA5701 in ?Cen, have been analysed using model atmosphere techniques. The optical spectra have been obtained with FEROS on the ESO 2.2-m telescope and the 2d-Coudé spectrograph on the 2.7-m McDonald telescope, while the UV observations are from the Goddard high-resolution spectrograph on the Hubble Space Telescope (HST). Abundances of light elements (C, N, O, Mg, Al and S) plus Fe have been determined from the optical spectra, while the UV data provide additional Fe abundance estimates from FeIII absorption lines in the 1875-1900 Å wavelength region. A general metal underabundance relative to young B-type stars is found for both Barnard29 and ROA5701. These results are consistent with the metallicities of the respective clusters, as well as with previous studies of the objects. The derived abundance patterns suggest that the stars have not undergone a gas-dust separation, contrary to previous suggestions, although they may have evolved from the AGB before the onset of the third dredge-up. However, the Fe abundances derived from the HST spectra are lower than those expected from the metallicities of the respective clusters, by 0.5 dex for Barnard29 and 0.8 dex for ROA5701. A similar systematic underabundance is also found for other B-type stars in environments of known metallicity, such as the Magellanic Clouds. These results indicate that the FeIII UV lines may yield abundance values which are systematically too low by typically 0.6 dex and hence such estimates should be treated with caution.