Rhombohedral R3c to orthorhombic Pnma phase transition induced by Y-doping in BiFeO3.

In this work we study, by means of ab initio calculations, the structural, electronic and magnetic properties of Y-doped BiFeO3 compounds. We determine that there is a morphotropic phase boundary at an yttrium concentration of [Formula: see text], where the structure changes from R3c to Pnma. This structural transition is driven by the chemical pressure induced by the dopant. By analyzing the evolution of the oxygen octahedral tilts we find an enhanced antiferrodistortive distortion when increasing the Y-doping, together with a reduction of the ferroelectric distorsion, that gives rise to a smaller value of the electric polarization. These cooperative effects should lead to a larger canting of the Fe magnetic moments and to a larger ferromagnetic response in the R3c phase, as it is observed in the experiments.

Effect of magnetism and light sp-dopants on chain creation in Ir and Pt break junctions.

Applying the generalization of the model for chain formation in break-junctions (Di Napoli et al 2012 J. Phys.: Condens. Matter 24 135501), we study the effect of light impurities on the energetics and elongation properties of Pt and Ir chains. Our model enables us to develop a tool ideal for detailed analysis of impurity-assisted chain formation, in which zigzag bonds play an important role. In particular we focus on H (s-like) and O (p-like) impurities and assume, for simplicity, that the presence of impurity atoms in experiments results in a ..M-X-M-X-... (M: metal, X: impurity) chain structure in between the metallic leads. Feeding our model with material-specific parameters from systematic full-potential first-principles calculations, we find that the presence of such impurities strongly affects the binding properties of the chains. We find that, while both types of impurities enhance the probability of chains being elongated, the s-like impurities lower the chain's stability. We also analyze the effect of magnetism and spin-orbit interaction on the growth properties of the chains.

Non-Fermi-liquid behavior in transport through Co-doped Au chains.

We calculate the conductance as a function of temperature G(T) through Au monatomic chains containing one Co atom as a magnetic impurity, and connected to two conducting leads with a fourfold symmetry axis. Using the information derived from ab initio calculations, we construct an effective model H(eff) that hybridizes a 3d(7) quadruplet at the Co site with two 3d(8) triplets through the hopping of 5d(xz) and 5d(yz) electrons of Au. The quadruplet is split by spin anisotropy due to spin-orbit coupling. Solving H(eff) with the numerical renormalization group we find that at low temperatures G(T)=a-b√[T] and the ground state impurity entropy is ln(2)/2, a behavior similar to the two-channel Kondo model. Stretching the chain leads to a non-Kondo phase, with the physics of the underscreened Kondo model at the quantum critical point.

Modeling impurity-assisted chain creation in noble-metal break junctions.

In this work we present the generalization of the model for chain formation in break junctions, introduced by Thiess et al (2008 Nano Lett. 8 2144), to zigzag transition-metal chains with s and p impurities. We apply this extended model to study the producibility trends for noble-metal chains with impurities, often present in break junction experiments, namely, Cu, Ag and Au chains with H, C, O and N adatoms. Providing the material-specific parameters for our model from systematic full-potential linearized augmented plane-wave first-principles calculations, we find that the presence of such impurities crucially affects the binding properties of the noble-metal chains. We reveal that both the impurity-induced bond strengthening and the formation of zigzag bonds can lead to a significantly enhanced probability for chain formation in break junctions.

Correlated dynamics of water and amphiphilic molecules in thin Newton black films.

The dynamical properties of amphiphilics in Newton black films, as well as those of the water confined between the two charged hydrophilic surfaces, have been calculated via a series of molecular dynamic calculations in several films with different water contents. A charged semiflexible amphiphilic model and the TIP5P model of water are used in our simulations [Z. Gamba, J. Chem. Phys. 129, 164901 (2008)]. We calculate the diffusion coefficients, reorientational dynamics, and the atomic density profile of water molecules as a function of the number of water molecules per amphiphilic (n(w)). We also analyze the reorientational motion of the amphiphilics and determine a strong correlation between the dynamics of water molecules and the translational and reorientational dynamics of the amphiphilics, as well as a correlation between the reorientational dynamics of the amphiphilics belonging to the upper and lower halves of the studied thin films.

Elective laparoscopic cholecystectomy.

BACKGROUND: Gallbladder stones are very common in patients with sickle cell disease and are the cause of recurrent abdominal pain. Their management has been highly controversial, especially for children. Nonoperated patients and those treated on an emergency basis have a very high rate of morbidity (>50%). METHODS: We performed a retrospective review of a series of 29 homozygous SS sickle cell children who underwent laparoscopic cholecystectomy between 1991 and April 1998. RESULTS: Only in one case a conversion was necessary (early in the series). Exploration of the common bile duct was done via intraoperative cholangiography. There were no mortalities. The morbidity rate was 17%; (however, of the five patients concerned, four suffered from hyperthermia for 2 days. All of the children were improved and enjoyed resolution of their abdominal pain. CONCLUSIONS: We believe that elective laparoscopic cholecystectomy at the earliest time possible, along with correct perioperative management, is the treatment of choice for cholelithiasis in children with sickle cell disease.