Sollecitazioni termiche nelle roccie attraversate da gallerie in pressione

Sunto. Si determinano gli spostamenti e le tensioni interne di un ammasso roccioso omogeneo, indefinito, attraversato da una galleria cilindrica a sezione retta circolare, soggetto per tale motivo a variazioni termiche stazionarie. Si considera anche il caso della esistenza, a non grande distanza dall'asse della galleria, di un vincolo rigido, simmetrico, che impedisce qualsiasi spostamento.     

PEEK–WC-Based Mixed Matrix Membranes Containing Polyimine Cages for Gas Separation

Membrane-based processes are taking a more and more prominent position in the search for sustainable and energy-efficient gas separation applications. It is known that the separation performance of pure polymers may significantly be improved by the dispersion of suitable filler materials in the polymer matrix, to produce so-called mixed matrix membranes. In the present work, four different organic cages were dispersed in the poly(ether ether ketone) with cardo group, PEEK-WC. The m-xylyl imine and furanyl imine-based fillers yielded mechanically robust and selective films after silicone coating. Instead, poor dispersion of p-xylyl imine and diphenyl imine cages did not allow the formation of selective films. The H₂, He, O₂, N₂, CH₄, and CO₂ pure gas permeability of the neat polymer and the MMMs were measured, and the effect of filler was compared with the maximum limits expected for infinitely permeable and impermeable fillers, according to the Maxwell model. Time lag measurements allowed the calculation of the diffusion coefficient and demonstrated that 20 wt % of furanyl imine cage strongly increased the diffusion coefficient of the bulkier gases and decreased the diffusion selectivity, whereas the m-xylyl imine cage slightly increased the diffusion coefficient and improved the size-selectivity. The performance and properties of the membranes were discussed in relation to their composition and morphology.     

NMR spectroscopy investigation of the cooperative nature of the internal rotational motions in acetophenone.

The proton NMR spectrum of the doubly enriched acetophenone-carbonyl,methyl-13C2 isotopomer dissolved in a liquid-crystalline solvent (LXNMR) was analyzed to yield a data set of 19 dipolar couplings. The presence of so many couplings, and in particular the dependence of some of them on the acetyl carbons enabled the investigation of the structure of the acetyl moiety and of possible cooperative motions about the aryl-carbonyl and carbonyl-methyl bonds. Methodological aspects, and approximations relating to the application of the vibrational correction procedure in the presence of large-amplitude torsional motions, are discussed. Results show that it is possible to discriminate between a continuous and a discrete conformer distribution about the angle phi(1) but not among a few proposed continuous shapes of U(iso)({phi}). In this study, the use of dipolar couplings with a non-negligible contribution from the indirect spin-spin coupling tensor J, (D(C8C9) in our case), for structural determination is extended from rigid to flexible molecules. The 1/2J(aniso)(C8C9) contribution was derived theoretically using the density functional theory linear response (DFT-LR) first-principles calculation of the J(C8C9) spin-spin coupling tensor.     

Influence of cardiolipin on the functionality of the Q(a) site of the photosynthetic bacterial reaction center

The effect of cardiolipin on the functionality of the Q(A) site of a photosynthetic reaction center (RC) was studied in RCs from the purple non-sulfur bacterium Rhodobacter sphaeroides by means of time-resolved absorbance measurements. The binding of the ubiquinone-10 to the Q(A) site of the RC embedded in cardiolipin or lecithin liposomes has been followed at different temperatures and phospholipid loading. A global fit of the experimental data allowed us to get quite reliable values of the thermodynamic parameters joined to the binding process. The presence of cardiolipin does not affect the affinity of the Q(A) site for ubiquinone but has a marked influence on the rate of P+QA(-) --> PQA electron transfer. The P+QA(-) charge recombination kinetics has been examined in liposomes made of cardiolipin/lecithin mixtures and in detergent (DDAO) micelles doped with cardiolipin. The electron-transfer rate constant increases upon cardiolipin loading. It appears that the main effect of cardiolipin on the electron transfer can be ascribed to a destabilization of the charge-separated state. Results obtained in micelles and vesicles follow the same titration curve when cardiolipin concentration evaluated with respect to the apolar phase is used as a relevant variable. The dependence of the P+QA(-) recombination rate on cardiolipin loading suggests two classes of binding sites. In addition to a high-affinity site (compatible with previous crystallographic studies), a cooperative binding, involving about four cardiolipin molecules, takes place at high cardiolipin loading.     

Exploratory analysis of simultaneous degradation of anthocyanins in the calyces of flowers of the Hibiscus sabdariffa species by PARAFAC model.

A three-way resolution method based on PARAFAC model was applied for the UV-Vis spectra to study the simultaneous degradation of anthocyanins extracted from fresh calyces of flowers of the Hibiscus sabdariffa. This methodology was used to resolve a chemical system, for which there was no a priori information about the composition or the pure spectra, a so-called black system. In the pH range from 1 to 13, seven species were identified: flavylium cation, carbinol, quinoidal base, E- and Z-chalcones and E- and Z-ionized chalcones. The concentration changes were determined as functions of pH at different wavelengths. The pK values for the acidity constants as well as tautomeric constant were estimated as 2.70, 3.54 and 0.14, respectively. The spectral profiles recovered by the chemometric methods are in excellent agreement with bands of experimental spectra reported in the literature for the species measured at specific pH values.     

Large eddy simulation of turbulent flows via domain decomposition techniques. Part 1: theory

The present paper discusses large eddy simulations of incompressible turbulent flows in complex geometries. Attention is focused on the application of the Schur complement method for the solution of the elliptic equations arising from the fractional step procedure and/or the semi‐implicit discretization of the momentum equations in velocity–pressure representation. Fast direct and iterative Poisson solvers are compared and their global efficiency evaluated both in serial and parallel architecture environments for model problems of physical relevance. Copyright © 2005 John Wiley & Sons, Ltd.