Cation distribution in Ni-substituted Mn-ferrites by Mössbauer technique

The neutron spectra of one outer (#10) and two inner (#2 and #3) sites of the Dalhousie University SLOWPOKE-2 reactor (DUSR) have been calibrated for the k ₀-based neutron activation analysis (k ₀-NAA). The parameters determined include the cadmium ratio (R _Cd), epithermal neutron flux shape factor (), subcadmium-to-epithermal neutron flux ratio (f), thermal-to-fast neutron flux ratio (f _F), modified spectral index r()(T_n/T₀)^1/2, Westcott g _Lu(T _n)-factor, and absolute neutron temperature (T _n). The a-values of -0.0098±0.0045 and -0.0425±0.0047 and -0.0422±0.0053 and f-values of 57.1±2.2 and 18.8±0.4 and 18.9±0.4 were obtained for the sites #10, #2 and #3, respectively. The modified spectral index (MSI), g _Lu(T _n)-factor, and T _n have been determined for the handling of non 1/v (n,) reactions. The accuracy of the method was evaluated by analyzing reference materials.     

Reactivity of some sulphur- and non-sulphur-containing amino acids towards water soluble colloidal MnO<Subscript>2</Subscript>. A kinetic study

Kinetic data for the oxidation of glutathione (reduced, GSH), cysteine, glycine and glutamic acid by colloidal manganese dioxide, (MnO₂) _n are reported. Colloidal MnO₂, oxidized glutathione to disulphide (glutathione, oxidized), was reduced to manganese (II). Glycine and glutamic acid (structural units of glutathione) are not oxidized by colloidal MnO₂, but the other structural unit, cysteine, is also oxidized by the same oxidant under similar experimental conditions. This is interpreted in terms of the rate-determining colloidal MnO₂-S bonded intermediate. The reactivity of GSH towards colloidal MnO₂ is very much higher than cysteine. Kinetics of oxidation of GSH and cysteine by colloidal MnO₂ were performed spectrophotometrically as a function of [GSH], [cysteine], colloidal [(MnO₂) _n ], [HClO₄], temperature and trapping agents sodium fluoride and manganese (II) (reduction product of colloidal MnO₂). The purpose of this work was to study the role of –NH₂, –COOH, –SH groups present in the carbon chain of the above amino acids. It was found that the reactivity of –SH group is higher than –NH₂ and –COOH groups. The mechanisms, involving a colloidal MnO₂ complex with GSH and cysteine, are proposed. The complexes decompose in a rate-determining step, leading to the formation of free radical and manganese (III), which is also an intermediate. The dimerization of radicals takes place in a subsequent fast step to yield the products.     

Pattern selection in biaxially stressed solids

We analyze the morphological instability of the surface of a solid which is subject to a biaxial stress. The stability calculation reveals a new favored pattern: a diamond morphology. This occurs if the stress is tensile in one direction and compressive in the orthogonal one and the ratio exceeds a certain value. A nonlinear analysis shows that the bifurcation is subcritical and hints to a nontrivial competition between tilted stripes and diamonds. This study opens a new line of inquiries in the field of stress-induced pattern selection.     

Sand ripple dynamics in the case of out-of-equilibrium aeolian regimes

From a phenomenological hydrodynamical model, we analyze the aeolian sand ripple evolution in an out-of-equilibrium aeolian regime where erosion exceeds accretion (and vice versa). We find, in particular, that the ripple structure can be destroyed in favor of a flat sand bed. In the ripple regime we report on a new class of generic dynamics described by the Benney equation. This equation reveals either order or disorder depending on whether wave dispersion is strong or weak. In both cases, the average wavelength of the pattern is fixed in time. This markedly contrasts with the regime of equilibrium aeolian regime -reached when erosion balances deposition- where ripples undergo a coarsening process at long time (i.e., the wavelength increases indefinitely with time).Received: 4 August 2003, Published online: 5 February 2004PACS: 81.05.Rm Porous materials; granular materials     

Vesicle migration and spatial organization driven by flow line curvature

Cross-streamline migration of deformable entities is essential in many problems such as industrial particulate flows, DNA sorting, and blood rheology. Using two-dimensional numerical experiments, we have discovered that vesicles suspended in a flow with curved flow lines migrate towards regions of high flowline curvature, which are regions of high shear rates. The migration velocity of a vesicle is found to be a universal function of the normal stress difference and the flow curvature. This finding quantitatively demonstrates a direct coupling between a microscopic quantity (migration) and a macroscopic one (normal stress difference). Furthermore, simulations with multiple vesicles revealed a self-organization, which corresponds to segregation, in a rim closer to the inner cylinder, resulting from a subtle interaction among vesicles. Such segregation effects could have a significant impact on the rheology of vesicle flows.     

Quantum Teleportation of High-dimensional Atomic Momenta State

Atomic momenta states of the neutral atoms are known to be decoherence resistant and therefore present a viable solution for most of the quantum information tasks including the quantum teleportation. We present a systematic protocol for the teleportation of high-dimensional quantized momenta atomic states to the field state inside the cavities by applying standard cavity QED techniques. The proposal can be executed under prevailing experimental scenario.