Controlling plastic flow in brittle structures

In most oxidation resistant materials, the predominant obstacle to dislocation motion is due to the changes in misfit energy as a dislocation moves, causing them to be brittle. However, at present, there is little understanding of how to design crystal structures to give easy plastic flow. Surprisingly, some hard materials deform readily, but only on a limited number of crystal planes, including ternary carbides and nitrides, such as Ti3SiC2, and compounds such as Nb2Co7, W2B5 and ζ-Ta4C3-x. Using ternary carbides as an example, it is shown that electronegativity differences within a crystal\u27s unit cell enable dislocation line defects to move much more easily, consistent with observations in other structures. Substantial changes appear possible, suggesting that such an approach might be used as a general way of to tailoring plasticity in crystals

Measuring crack initiation and the plastic deformation behaviour of titanium aluminides under compressive and tensile uniaxial loading

At temperatures of the order of 700 °C, suitable for the operation of low and intermediate pressure turbines and compressors in gas turbine engines, gamma titanium aluminides possess a higher specific strength than nickel superalloys. However, γ-TiAl suffers from a sufficiently reduced plasticity for a threshold approach to fatigue lifing to be necessary. Improving the fatigue behaviour of γ-TiAl requires an understanding of crack nucleation and how this is related to the detailed microstructure. Towards this, the monotonic compressive and tensile deformation behaviour of this two-phase lamellar composite alloy, Ti-45Al-2Nb-2Mn(at.%)-0.8vol%TiB2, currently undergoing engine tests by Rolls Royce, has therefore been measured at both room temperature and at 700°C. Both colony and lamellar-scale deformation features of the material have been investigated. Microstructural conditions with varying lamellar thicknesses were characterised by scanning electron microscopy and transmission Kikuchi diffraction. The near-surface plastic strain field and the build-up of local strains have been measured, using digital image correlation, with a remodelled gold speckle pattern, and compared with misorientation mapping using electron backscatter diffraction, both before and after testing. Temperature was found to have a significant impact on the active deformation mechanisms and their directions relative to the lamellae; this affects the ability of the material to provide compatible deformation. At high temperature, the shear generated upon twinning was found to be closely associated to debonding at colony boundaries. This is related to the possible accumulation of damage in cyclic loading

Music in advertising and consumer identity: The search for Heideggerian authenticity

This study discusses netnographic findings involving 472 YouTube postings categorized to identify themes regarding consumers’ experience of music in advertisements. Key themes relate to musical taste, musical indexicality, musical repetition and musical authenticity. Postings reveal how music conveys individual taste and is linked to personal memories and Heidegger’s coincidental time where moments of authenticity may be triggered in a melee of emotions, memories and projections. Identity protection is enabled as consumers frequently resist advertisers’ attempts to use musical repetition to impose normative identity. Critiques of repetition in the music produce Heideggerian anxiety leading to critically reflective resistance. Similarly, where advertising devalues the authenticity of iconic pieces of music, consumers often resist such authenticity transgressions as a threat to their own identity. The Heideggerian search for meaning in life emphasizes the significance of philosophically driven ideological authenticity in consumers’ responses to music in advertisements

Anomalous yielding in the complex metallic alloy Al13Co4

The single crystal deformation behaviour of orthorhombic Al13Co4 hasbeen studied below the brittle-ductile transition temperature observedin bulk material from room temperature to 600 degrees C, usingindentation, microcompression and transmission electron microscopy. Atroom temperature, slip occurred most easily by dislocation motion on the(0 0 1)[0 1 0] slip system, as observed in the ductile regime at hightemperatures. However, as the temperature was increased towards 600degrees C, the slip pattern changed to one consisting of linear defectsrunning perpendicular to the loading axis. Serrated flow was observed atall temperatures, although at 600 degrees C the magnitude of theserrations decreased. Anomalous yielding behaviour was also observedabove 226 degrees C, where both the yield and the 2\% flow stressincreased with temperature, almost doubling between 226 and 600 degreesC. It has been suggested that this might arise due to the increasingstability of orthorhombic Al13Co4 with respect to the monoclinic formwith increasing temperature. This is shown to be consistent with thetheoretical predictions that exist

Energy Flow in the Hadronic Final State of Diffractive and Non-Diffractive Deep-Inelastic Scattering at HERA

An investigation of the hadronic final state in diffractive and non--diffractive deep--inelastic electron--proton scattering at HERA is presented, where diffractive data are selected experimentally by demanding a large gap in pseudo --rapidity around the proton remnant direction. The transverse energy flow in the hadronic final state is evaluated using a set of estimators which quantify topological properties. Using available Monte Carlo QCD calculations, it is demonstrated that the final state in diffractive DIS exhibits the features expected if the interaction is interpreted as the scattering of an electron off a current quark with associated effects of perturbative QCD. A model in which deep--inelastic diffraction is taken to be the exchange of a pomeron with partonic structure is found to reproduce the measurements well. Models for deep--inelastic $ep$ scattering, in which a sizeable diffractive contribution is present because of non--perturbative effects in the production of the hadronic final state, reproduce the general tendencies of the data but in all give a worse description.Comment: 22 pages, latex, 6 Figures appended as uuencoded fil

A Search for Selectrons and Squarks at HERA

Data from electron-proton collisions at a center-of-mass energy of 300 GeV are used for a search for selectrons and squarks within the framework of the minimal supersymmetric model. The decays of selectrons and squarks into the lightest supersymmetric particle lead to final states with an electron and hadrons accompanied by large missing energy and transverse momentum. No signal is found and new bounds on the existence of these particles are derived. At 95% confidence level the excluded region extends to 65 GeV for selectron and squark masses, and to 40 GeV for the mass of the lightest supersymmetric particle.Comment: 13 pages, latex, 6 Figure

Stellar population synthesis at the resolution of 2003

We present a new model for computing the spectral evolution of stellar populations at ages between 100,000 yr and 20 Gyr at a resolution of 3 A across the whole wavelength range from 3200 to 9500 A for a wide range of metallicities. These predictions are based on a newly available library of observed stellar spectra. We also compute the spectral evolution across a larger wavelength range, from 91 A to 160 micron, at lower resolution. The model incorporates recent progress in stellar evolution theory and an observationally motivated prescription for thermally-pulsing stars on the asymptotic giant branch. The latter is supported by observations of surface brightness fluctuations in nearby stellar populations. We show that this model reproduces well the observed optical and near-infrared colour-magnitude diagrams of Galactic star clusters of various ages and metallicities. Stochastic fluctuations in the numbers of stars in different evolutionary phases can account for the full range of observed integrated colours of star clusters in the Magellanic Clouds. The model reproduces in detail typical galaxy spectra from the Early Data Release (EDR) of the Sloan Digital Sky Survey (SDSS). We exemplify how this type of spectral fit can constrain physical parameters such as the star formation history, metallicity and dust content of galaxies. Our model is the first to enable accurate studies of absorption-line strengths in galaxies containing stars over the full range of ages. Using the highest-quality spectra of the SDSS EDR, we show that this model can reproduce simultaneously the observed strengths of those Lick indices that do not depend strongly on element abundance ratios [abridged].Comment: 35 pages, 22 figures, to appear in MNRAS; version with full resolution figures available at http://www.iap.fr/~charlot/bc2003/pape

A Measurement of the Proton Structure Function F ⁣2(x,Q2)F_{\!2}(x,Q^2)

A measurement of the proton structure function $F_{\!2}(x,Q^2)$ is reported for momentum transfer squared $Q^2$ between 4.5 $GeV^2$ and 1600 $GeV^2$ and for Bjorken $x$ between $1.8\cdot10^{-4}$ and 0.13 using data collected by the HERA experiment H1 in 1993. It is observed that $F_{\!2}$ increases significantly with decreasing $x$, confirming our previous measurement made with one tenth of the data available in this analysis. The $Q^2$ dependence is approximately logarithmic over the full kinematic range covered. The subsample of deep inelastic events with a large pseudo-rapidity gap in the hadronic energy flow close to the proton remnant is used to measure the "diffractive" contribution to $F_{\!2}$.Comment: 32 pages, ps, appended as compressed, uuencoded fil