117,515 research outputs found
KINETIC EFFECT OF RADIATION INTENSITY AND THERMAL AFTER-TREATMENT IN THE PHOTOPOLYMERIZATION OF DIALLYL OXYDIETHYLENE DICARBONATE
No full textThe influence of radiation intensity (from 1.08 × 10-7 to 2.48 × 10-4 einstein s-1 L-1) on the photopolymn. of diallyl oxydiethylene dicarbonate was investigated systematically not only in the initial stages of reaction, but also at high monomer conversion (x), in order to detect possible variations in the polymn. mechanism. In some of the runs irradn. was stopped at x = 0.55-0.65 and thermal after-treatments were carried out both in the presence and absence of air by following kinetically x-values during the self-decelerating crosslinking. To rationalize exptl. data a model is proposed which assumes two basically different mechanisms occurring simultaneously (bimol. termination and radical trapping), but with different "wts." as a function of time. Long living radicals produced by irradn. continue to react in the dark. The rate of this reaction, which is enhanced in the presence of O, is fitted by a relaxation model that considers double bonds, particularly of pendant groups, as traps, with increasing lifetimes, able to transfer to radical sites
Deep learning improves macromolecule identification in 3d cellular cryo-electron tomograms
No full textVéase "author correction" en la versión del editor.Moebel, E., Martinez-Sanchez, A., Lamm, L., Righetto, R.D., Wietrzynski, W., Albert, S., Larivière, D., Fourmentin, E., Pfeffer, S., Ortiz, J., Baumeister, W., Peng, T., Engel, B.D., Kervrann, C
Second-order nonlinear optical properties of cyclometallated Ir(III) and Pt(II) complexes
No full textThe second-order NLO properties of various cyclometallated cationic Ir(III) and neutral Pt(II) complexes were determined by both Electric Field Induced Second Harmonic generation (EFISH) and Harmonic Light Scattering (HLS) techniques.
Cationic 1,10-phenanthroline and bipyridine iridium(III) complexes (1, 2) are characterized by high negative EFISH β values which decrease when the ion-pair strength between the cation and the counterion (PF6–, C12H25SO3–) increases. Neutral Pt(II) complexes (3, 4) are also characterized by a good to high negative NLO response.
For all these cyclometallated complexes, the EFISH response is mainly controlled by MLCT/L'LCT processes. Interestingly, a combination of HLS and EFISH techniques, used to evaluate both the dipolar and octupolar contributions to the total quadratic hyperpolarizability, shows that the major contribution is controlled by the octupolar part. [...]
1. V. Aubert, L. Ordronneau, M. Escadeillas, J. A. G. Williams, A. Boucekkine, E. Coulaud, C. Dragonetti, S. Righetto, D. Roberto, R. Ugo, A. Valore, A. Singh, J. Zyss, I. Ledoux-Rak, H. Le Bozec, V. Guerchais, Inorg. Chem. 2011. ASA
Influence of photocatalytic systems on the photo-cross-linking of diallyl oxydiethylene dicarbonate grafted onto cellulose
No full textThe photo-cross-linking of 18.4-20.0 μmol of diallyl oxydiethylene dicarbonate (I) grafted onto cellulose (per square contimetre of apparent cellulose surface) was examined kinetically at 30±2 °C, on exposure to an incident polychromatic radiation flux of (2.05±0.08) × 10-7 einstein s-1 cm-2, in the presence of catalytic amounts (20-200 ppm) of three vanadium- (V) organometallic compounds. As with the diacrylate systems studied previously, the kinetics of photo-cross-linking of grafted I followed a multi-relaxation spectrum in terms of two parameters (width of spectrum β and mean lifetime τ). The β values (0.42±0.04) were almost the same in all experiments and were similar to that (0.44±0.02) observed for the thermal decay of double bonds of pre-irradiated I in bulk. The β parameter therefore seems to reflect the cross-linked character of the linear polymer pattern, rather than the cross-linking process, either thermal or photocatalytic. In contrast, the τ values reflect, in a very sensitive manner, the effect of the concentration and type of photocatalytic system employed. An acceleration factor of about 190 was reached with 200 ppm vanadium (synergic mixture of vanadium (V) isopropoxide and isobutoxide). Some relevant features of the photo-cross-linking mechanism are discussed in the light of the proposed kinetic model
Connected from the outside: The role of u.s. regions in promoting the integration of the european research system
No full textConsiderable efforts have been deployed by the European Union to create an integrated Research & Development area. In this paper, we focus on the structure and evolution of the European collaboration network as reflected by patent data. We study patent networks representing collaborations between inventors located in different geographic areas. Existing studies seem to indicate an increasing integration of the European research system, but none of them has investigated which regions contribute most to this integration. We analyze the patent coinventorship network to measure network-based distances between regions through multiple metrics, in order to evaluate the role of different areas for the integration of the EU R&D system. We study changes of the average closeness between European regions belonging to different countries. In particular, we perform a counterfactual exercise, simulating the impact on EU integration of the removal of countries and individual regions. Our findings reveal an important contribution from U.S. regions in favoring EU integration. In particular, the size and the density of the U.S. system, together with the presence of a few regional hubs, play a key role in reducing the distances between European regions
Web strategy and intelligent software agents in decision process for networks knowledge based
No full textFlow dynamical characterization of sorbents immobilized as composites in membranes prepared by photochemical grafting onto polymers
No full textPermeability measurements of water and n-hexane were carried out at 20°C through membranes prepared by photochemically grafting an epoxy-diacrylate copolymer or its composites onto cellulose. Composite membranes immobilizing 30.0 wt.% of calcite, seven calcium oxide samples obtained from calcination of calcite in different experimental conditions, α-iron(III) oxide and cobalt peroxide were thus tested. Hydraulic resistances as a function of membrane thickness were studied. Experimental results in the Poiseuille 's laminar flow regime are compatible with a normal Kozeny-Carman constant and a porosity of nominally 50%, indicating a regular packing of isometrically shaped particles in the microporous medium. Surface areas of membranes, both without additions and in the presence of filler materials, could thus be obtained by liquid permeametry measurements and successive treatment of data by the Kozeny-Carman equation. A general analysis of surface area characterization of immobilized sorbents is presented and compared with experimental values of B.E.T. method (liquid nitrogen adsorption). Results of flow dynamical investigation confirm the peculiar regularity of structure of the dense layer of photosynthetic membranes, as was found from morphology, from correlation between mean pore diameter and water fluxes per unit applied pressure drop, as well as from rejection characteristics in preceding studies
Marketing automation & intelligent agent nelle reti knowledge based: la prospettiva dell'utente
No full textCopper(II) Complexes of salen Analogues with Two Differently Substituted (Push-Pull) Salicylaldehyde Moieties. A Study on the Modulation of Electronic Asymmetry and Nonlinear Optical Properties
No full textThis paper presents some copper(II) complexes of salen analogues in which the two salicylaldehyde moieties carry different (electron donor, D, and acceptor, A) substituents in position 5, producing a push-pull charge asymmetry. The X-ray structures of some compounds show the presence of pairs of stacked molecules with head-to-tail intermolecular associations. The geometries of all complexes have been optimized through density functional theory (DFT) studies, which have shown that a major influence on the coordination bond lengths is given by the presence of the electron acceptor NO2 group. Such an influence operates mainly on the Cu-phenolato bonds: elongation of the Cu-O distance of the 5-nitrosalicylaldehyde moiety, with a concomitant decrease of the other Cu-O distance; the Cu-N bonds are less affected. The D groups have only a minor influence. The nonlinear optical responses, mu(g)beta(vec), of some molecules have been determined by EFISH measurements, and the beta(vec) values have been obtained using the DFT-calculated mu(g) values because solubility problems hampered the experimental measurements of mu(g) of some derivatives; the former, however, have been found to be in agreement with the experimental values that could be obtained. Deconvolution of the absorption bands in the near-UV region has allowed recognition of the charge-transfer (CT) transition, assigned to a ligand-to-metal CT (LMCT) by time-dependent DFT computations; we have then used the solvatochromism of this transition to obtain beta(0) and beta(CT) values using the two-state model. These values were compared with those obtained by computational studies, which have also allowed evaluation of the influence of the substituents on the directions of mu(g) and beta(tot)
Trasport of oxygen facilitated by peroxo[N, N'-ethylene bis-(salicylideneiminato)dimethylformamide-cobalt(III)] embedded in liquid membranes immobilized by photografting onto cellulose
No full textA novel method to prepare liquid membranes, suitable to obtain facilitated transport of oxygen, incorporating the title complex (I) or the same without dimethylformamide (II), is reported. These membranes were obtained by photochemical grafting an epoxy-diacrylate copolymer onto cellulose in the presence of (I) or (II) together with dimethylformamide. Sorption isotherms of oxygen into deoxygenated membranes were obtained by Langmuir plots at 343-373 K. By these isotherms the molar ratio (0.5) between sorbed oxygen and cobalt in the membrane corresponding to saturation was evaluated, and constants K (bar-1) of heterogeneous equilibrium involving (I) and (II) were obtained as a function of temperature. From K values, a mean enthalpy change of -84 kJ mol-1 and entropy change of -220 J mol-1 K-1 were calculated. This latter reflects the high order in binuclear dioxygen complex formation. Permeability coefficients of oxygen and nitrogen from air through the photosynthetic membranes at 343 K were measured. These values show an efficient O2/N2 separation, with a very advantageous ratio (50) between their fluxes
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