Proton-neutron quasiparticle RPA and charge-changing transitions

General formulae for a proton-neutron QRPA calculation are presented. All terms in the RPA order are retained, and no specific assumptions on the residual interaction and one-body charge-changing transitions are made. QRPA phonon correlations are introduced in first-order perturbation for quasiparticle transitions from odd-mass and odd-odd parent nuclei.     

An investigation of trivalent substituted M-type hexagonal ferrite using X-ray and Mössbauer spectroscopy

Series of substituted M-type hexagonal ferrite has been synthesized, and studied by means of X-ray diffraction, IR and Mössbauer spectroscopy. The samples have the formula (BaCr _x Fe_12?x O₁₉) (with x = 0.0, 1.0, 2.0, 3.0, 4.0, and 5.0). X-ray diffraction studies prove that all samples has a single phase M-type hexagonal structure. The lattice parameters both a and c were found to be composition dependent. This observation was attributed to the atomic radii of the substituted cations. The Mössbauer spectra change from magnetically ordered (x = 0) toward magnetically ordered with strong line broadening. The broadening increases as the Cr content increase. Measurements at low temperature (80 K) restore the magnetic order. The Mössbauer parameters suggest that Cr³⁺ prefers to occupy the 4f₂ and 2a crystal sites. IR absorption bands were observed between 1,500 and 400 cm^?1, and confirm the structure in coincidence with X-ray results.     

Use of high-speed cineradiography in head-impact experiments

Experimental Techniques -     

Integral equation formulation for buoyancy-driven convection problems

An integral equation formulation for buoyancy-driven convection problems is developed and illustrated. Buoyancy-driven convection in a bounded cylindrical geometry with a free surface is studied for a range of aspect ratios and Nusselt numbers. The critical Rayleigh number, the nature of the cellular motion, and the heat transfer enhancement are computed using linear theory. Green's functions are used to convert the linear problem into linear Fredholm integral equations. Theorems are proved which establish the properties of the eigenvalues and eigenfunctions of the linear integral operator which appears in these equations.     

Phase behaviour of binary systems of lactones in carbon dioxide

Experimental phase equilibrium data for binary systems involving ε-caprolactone, δ-hexalactone, and γ-caprolactone with carbon dioxide have been measured applying the synthetic method using a high-pressure, variable-volume view cell over the temperature range of (303 to 343) K and pressures up to 21 MPa. For the systems investigated, (vapour + liquid) (VLE), (liquid + liquid) (LLE), and (vapour + liquid + liquid) (VLLE) equilibrium were visually recorded. It was observed that an increase in temperature or in carbon dioxide concentration led to a pronounced raise in transition pressure values. The experimental results were modelled using the Peng–Robinson equation of state with the conventional quadratic mixing rule, affording a satisfactory representation of the experimental values.     

Phase behaviour of the ternary system {poly(ε-caprolactone) + carbon dioxide + dichloromethane}

Recently, production of biocompatible and biodegradable polymer microparticles has been a matter of growing interest in pharmaceutical and food areas such as drug or active compounds delivery. To conduct production of microparticles, polymeric particle coating, impregnation of active compounds in polymeric films, the knowledge of phase behaviour involving the biodegradable polymer in supercritical carbon dioxide in the presence of a modifier may be needed to allow developing new industrial applications. In this sense, the aim of this work was to investigate the phase behaviour of the ternary system formed by the biodegradable polymer poly(ε-caprolactone) in (carbon dioxide + dichloromethane). Experimental phase transition (bubble and cloud point) values were obtained by applying the static-synthetic method using a variable-volume view cell over the temperature range of (303 to 343) K and pressures up to 21 MPa, in the CO₂ overall composition range of (25–46) wt%, while polymer concentrations studied were (1, 3, 5, and 7) wt%. For the system investigated, depending on the polymer concentration, vapour–liquid, liquid–liquid, and vapour–liquid–liquid phase transitions were verified.     

Optimized δ-expansion for lattice U(1) and SU(2) with interpolating continuum action

Embedding the lattice gauge theory into a continuum theory allows to use the continuum action as trial action in the variational calculation. Only originally divergent graphs contribute. This leads to a very simple scheme which makes it possible to write down explicit expressions for the plaquette energy E for U(1) in arbitrary space time dimension for the first three orders of the expansion. For dimensions three and four one can even go up to fourth order. This allows a rather thorough empirical investigation of the convergence properties of the δ-expansion, in particular near the phase transition or the transition region, respectively. As already found in previous work, the principle of minimal sensitivity can be only applied for β above a certain value, because otherwise no extremum with respect to the variational parameter exists. One can, however, extend the range of applicability down to small β, by calculating instead of E some power E^κ, or by performing an appropriate Padé transformation. We find excellent agreement with the data for β above the transition region for the second and higher orders. Below the transition region the agreement is rather poor in low orders, but quite impressive in fourth order. For SU(2) we performed the calculation up to second order. The agreement with the data is somewhat worse than in the abelian case.     

Assessment of mismatched epitaxial layers by X-ray rocking curve measurements and simulations

In the design of heteroepitaxial systems the knowledge of composition, strain and thickness of the various layers involved is of great importance. The determination of these structural parameters is among the applications most common in high-resolution X-ray diffraction. Numerical simulation of rocking curves has emerged as an important aid in the determination of the relevant structural parameters. Based upon the dynamical theory of X-ray diffraction a FORTRAN program has been written to simulate and refine structural parameters from rocking curve data. X-ray rocking curve analysis has been used to develop and optimize MOCVD-growth of Ga_xIn_1-xP/GaAs heteroepitaxial systems. We observed superlattice peaks in samples of low misfit. With the aid of computer simulations we attribute these to unintentional periodic compositional fluctuations (Ga/In) of the order of 1%.     

E-FiRST: Electric field responsive shear thickening fluids

A novel electrorheological (ER) effect is presented where the application of an electric field, orthogonal to the vorticity-flow plane, increases the critical hydrodynamic stress required to shear thicken concentrated, colloidal dispersions (the E-FiRST effect). The shear thickening behavior of a Brownian charge stabilized dispersion (226 nm silica in 4-methylcyclohexanol at 53, 50. and 41 vol.%) is studied in the presence of an electric field as a function of the field strength and coupling parameter ( ß) where the latter is a function of a.c. field frequency due to diffusion limitations on the polarization of the particles' double layer. A mechanism is proposed whereby the applied electric field suppresses the formation of the self-organized hydrocluster microstructure responsible for shear thickening, thus delaying the onset of shear thickening to higher applied shear stresses. A Mason-number type scaling law is found to scale the effect, which supports the proposed mechanism.