Combined effects of anisotropy and tension-compression asymmetry on the torsional response of AZ31 Mg

In this paper it is demonstrated that only by accounting for the combined effects of anisotropy and tension-compression asymmetry at polycrystal level, it is possible to explain and accurately predict the room-temperature torsional response of a strongly textured AZ31 Mg material. This is shown by using two modeling frameworks, namely: a viscoplastic self-consistent (VPSC) polycrystal model, and a macroscopic plasticity model based on an yield criterion, developed by Cazacu et al. (2006), that accounts for both orthotropy and tension-compression asymmetry in plastic flow. It is shown that unlike Hill's (1948) criterion, the latter macroscopic criterion quantitatively predicts the experimental results, namely: that the sample with axial direction along the rolling direction contracts, while the sample with axial direction along the normal direction elongates. Moreover, it is demonstrated that these experimentally observed axial strain effects can be quantitatively predicted with the VPSC polycrystal model, only if both slip and twinning are considered operational at single crystal level. On the other hand, if it is assumed that the plastic deformation is fully accommodated by crystallographic slip, the axial strains predicted by VPSC are very close with that predicted with Hill (1948) criterion, which largely underestimates the measured axial strain in the rolling direction, and predicts zero axial strain in the normal direction. (C) 2015 Elsevier Ltd. All rights reserved.X111513Ysciescopu

High-Resolution X-Ray Structure of the Trimeric Scar/WAVE-Complex Precursor Brk1

The Scar/WAVE-complex links upstream Rho-GTPase signaling to the activation of the conserved Arp2/3-complex. Scar/WAVE-induced and Arp2/3-complex-mediated actin nucleation is crucial for actin assembly in protruding lamellipodia to drive cell migration. The heteropentameric Scar/WAVE-complex is composed of Scar/WAVE, Abi, Nap, Pir and a small polypeptide Brk1/HSPC300, and recent work suggested that free Brk1 serves as a homooligomeric precursor in the assembly of this complex. Here we characterized the Brk1 trimer from Dictyostelium by analytical ultracentrifugation and gelfiltration. We show for the first time its dissociation at concentrations in the nanomolar range as well as an exchange of subunits within different DdBrk1 containing complexes. Moreover, we determined the three-dimensional structure of DdBrk1 at 1.5 Å resolution by X-ray crystallography. Three chains of DdBrk1 are associated with each other forming a parallel triple coiled-coil bundle. Notably, this structure is highly similar to the heterotrimeric α-helical bundle of HSPC300/WAVE1/Abi2 within the human Scar/WAVE-complex. This finding, together with the fact that Brk1 is collectively sandwiched by the remaining subunits and also constitutes the main subunit connecting the triple-coil domain of the HSPC300/WAVE1/Abi2/ heterotrimer to Sra1(Pir1), implies a critical function of this subunit in the assembly process of the entire Scar/WAVE-complex

Complementary and alternative medicine: attitudes, knowledge and use among surgeons and anaesthesiologists in Hungary

BACKGROUND: Despite their worldwide popularity the question of using non-conventional treatments is a source of controversy among medical professionals. Although these methods may have potential benefits it presents a problem when patients use non-conventional treatments in the perioperative period without informing their attending physician about it and this may cause adverse events and complications. To prevent this, physicians need to have a profound knowledge about non-conventional treatments. METHODS: An anonymous questionnaire was distributed among surgeons and anaesthesiologists working in Hungarian university clinics and in selected city or county hospitals. Questionnaires were distributed by post, online or in person. Altogether 258 questionnaires were received from 22 clinical and hospital departments. RESULTS: Anaesthesiologists and surgeons use reflexology, Traditional Chinese Medicine, herbal medicine and manual therapy most frequently in their clinical practice. Traditional Chinese Medicine was considered to be the most scientifically sound method, while homeopathy was perceived as the least well-grounded method. Neural therapy was the least well-known method among our subjects. Among the subjects of our survey only 3.1 % of perioperative care physicians had some qualifications in non-conventional medicine, 12.4 % considered themselves to be well-informed in this topic and 48.4 % would like to study some complementary method. Women were significantly more interested in alternative treatments than men, p = 0.001427; OR: 2.2765. Anaesthesiologists would be significantly more willing to learn non-conventional methods than surgeons. 86.4 % of the participants thought that non-conventional treatments should be evaluated from the point of view of evidence. Both surgeons and anaesthesiologists accept the application of integrative medicine and they also approve of the idea of teaching these methods at universities. CONCLUSIONS: According to perioperative care physicians, non-conventional methods should be evaluated based on evidence. They also expressed a willingness to learn about those treatments that meet the criteria of evidence and apply these in their clinical practice

Dislocation interactions in olivine control postseismic creep of the upper mantle

Changes in stress applied to mantle rocks, such as those imposed by earthquakes, commonly induce a period of transient creep, which is often modelled based on stress transfer among slip systems due to grain interactions. However, recent experiments have demonstrated that the accumulation of stresses among dislocations is the dominant cause of strain hardening in olivine at temperatures ≤600 °C, raising the question of whether the same process contributes to transient creep at higher temperatures. Here, we demonstrate that olivine samples deformed at 25 °C or 1150–1250 °C both preserve stress heterogeneities of ~1 GPa that are imparted by dislocations and have correlation lengths of ~1 μm. The similar stress distributions formed at these different temperatures indicate that accumulation of stresses among dislocations also provides a contribution to transient creep at high temperatures. The results motivate a new generation of models that capture these intragranular processes and may refine predictions of evolving mantle viscosity over the earthquake cycle

The influence of grain shape and volume fraction of sheet silicates on elastic properties of aggregates: Biotite platelets in an isotropic matrix

Elastic anisotropy of sheet-silicate-rich rocks such as shalesand slates strongly depends on the orientation distribution ofplatelet-shaped minerals, as well as shape and orientation ofpores. Bulk elastic anisotropy of the rock results in the anisotropywith respect to the propagation of elastic waves, and consequently,the fastest P-waves can travel with velocities exceedingthe slowest velocities by a factor of two or even greater. An importantfactor is the sheet-silicate's grain shapes.We approacheda model system of biotite platelets in an isotropic matrix withdifferent methods: A mean-field self-consistent method thatconsidered ellipsoidal particles in an effective anisotropic matrix,and a full-field method based on fast Fourier transformsthat considered the microstructure, the topology of the polycrystal,and local interactions. Both methods provided numericallyvery close results. Using these results, we predicted that the aggregatewith more oblate grain shape (thinner platelets) waselastically more anisotropic than the material with grains of lessoblate shape, but only for small volume fractions of orientedplatelets. For large fractions of platelets, the opposite was true.This switchover in the elastic anisotropy depended on texturestrength, platelet shape, and elastic properties of the isotropicmatrix

The influence of grain shape and volume fraction of sheet silicates on elastic properties of aggregates: Biotite platelets in an isotropic matrix

Elastic anisotropy of sheet-silicate-rich rocks such as shalesand slates strongly depends on the orientation distribution ofplatelet-shaped minerals, as well as shape and orientation ofpores. Bulk elastic anisotropy of the rock results in the anisotropywith respect to the propagation of elastic waves, and consequently,the fastest P-waves can travel with velocities exceedingthe slowest velocities by a factor of two or even greater. An importantfactor is the sheet-silicate's grain shapes.We approacheda model system of biotite platelets in an isotropic matrix withdifferent methods: A mean-field self-consistent method thatconsidered ellipsoidal particles in an effective anisotropic matrix,and a full-field method based on fast Fourier transformsthat considered the microstructure, the topology of the polycrystal,and local interactions. Both methods provided numericallyvery close results. Using these results, we predicted that the aggregatewith more oblate grain shape (thinner platelets) waselastically more anisotropic than the material with grains of lessoblate shape, but only for small volume fractions of orientedplatelets. For large fractions of platelets, the opposite was true.This switchover in the elastic anisotropy depended on texturestrength, platelet shape, and elastic properties of the isotropicmatrix