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Three dimensional finite element simulations of fracture tests using the Craft concrete model
A.D. Jefferson,B.I.G. Barr,T. Bennett,S.C. Hee 한국계산역학회 2004 Computers and Concrete, An International Journal Vol.1 No.3
Two enhancements to a recently developed plastic-damage-contact model for concrete are presented. The model itself, which uses planes of degradation that can undergo damage and separation but that can regain contact according to a contact law, is described. The first enhancement is a new damage evolution function which provides a completely smooth transition from the undamaged to the damaged state and from pre-peak to post-peak regions. The second is an improved contact function that governs thepotential degree of contact with increasing opening on a crack plane. The use of a damage evolution function with a pre-peak has implications for the consistent tangent matrix/stress recovery algorithm developed for the model implementation, and amendments to this algorithm to accommodate the new function are described. A series of unpublished experimental tests on notched specimens undertaken in Cardiff in the mid 1990s are then described. These include notched beam tests as well as prismatic and cylindrical torsion tests. The tests are then considered in three dimensional finite element analyses using the modified Craft model implemented in the finite element program LUSAS. Comparisons between experimental and numerical data show reasonable agreement except that the numerical simulations do not fully describe the latter stages of the softening responses for the torsion examples. Finally, it is concluded that the torsion tests described provide useful benchmark examples for the validation of three-dimensional numerical models for concrete.
Ab-Initio Studies of Electronic and Spectroscopic Properties of MgO, ZnO and CdO
A. Schleife,C. R¨odl,J. Furthmuller,F. Bechstedt,P. H. Jefferson,T. D. Veal,C. F. McConville,L. F. J. Piper,A. DeMasi,K. E. Smith,H. Losch,R. Goldhahn,C. Cobet,J. Zuniga-Perez,V. Munoz-Sanjose 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.5
We present ab-initio calculations of excited-state properties within single-particle and two-particle approaches in comparison with corresponding experimental results. For the theoretical treatment of the electronic structure, we compute eigenvalues and eigenfunctions by using a spatially nonlocal exchange-correlation potential. From this starting point, quasiparticle energies within the fully frequency-dependent G0W0 approximation are obtained. By solving the Bethe-Salpeter equation, we evaluate optical properties, including the electron-hole attraction and the local-field effects. The results are compared with experimental spectra from soft X-ray emission, as well as from X-ray photoelectron spectroscopy or ellipsometry measurements. In more detail, we compute the valenceband densities of states, bound excitons, and the dielectric function. For the latter, we discuss both the absorption edge and higher critical points.
Shinozuka, Y.,Clarke, A. D.,Nenes, A.,Jefferson, A.,Wood, R.,McNaughton, C. S.,Strö,m, J.,Tunved, P.,Redemann, J.,Thornhill, K. L.,Moore, R. H.,Lathem, T. L.,Lin, J. J.,Yoon, Y. J. Copernicus GmbH 2015 Atmospheric chemistry and physics Vol.15 No.13
<P>Abstract. We examine the relationship between the number concentration of boundary-layer cloud condensation nuclei (CCN) and light extinction to investigate underlying aerosol processes and satellite-based CCN estimates. For a variety of airborne and ground-based observations not dominated by dust, regression identifies the CCN (cm−3) at 0.4 ± 0.1% supersaturation with 100.3α +1.3σ0.75 where σ (Mm−1) is the 500 nm extinction coefficient by dried particles and α is the Angstrom exponent. The deviation of 1 km horizontal average data from this approximation is typically within a factor of 2.0. ∂logCCN / ∂logσ is less than unity because, among other explanations, growth processes generally make aerosols scatter more light without increasing their number. This, barring special meteorology-aerosol connections, associates a doubling of aerosol optical depth with less than a doubling of CCN, contrary to previous studies based on heavily averaged measurements or a satellite algorithm. </P>