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121.
Aline R. Passos Leandro Martins Sandra H. Pulcinelli Celso V. Santilli 《Journal of Sol-Gel Science and Technology》2012,63(2):242-250
Hierarchical aluminas with pore sizes ranging from a few nanometers to micrometers were obtained using an one-pot sol?Cgel synthesis. The aluminas were synthesized under acid conditions from aluminum isopropoxide in presence of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer template and decahydronaphthalene as emulsifier agent. High-resolution transmission electron microscopy, small-angle X-ray scattering, nitrogen physisorption isotherms and mercury intrusion porosimetry provided evidences of porous structure at different hierarchical levels. The produced aluminas possess hierarchical structure composed of different family of pores that coexist in form of cylinders, pyramids and stacking of platelets. The morphology observed by electron microscopy suggests that the cylindrical pores result from the stacking platelets and that the cylinders and pyramidal pores form the walls of macropores of circular section. These aluminas with hierarchical porous architecture present large surface areas (ca. 435?m2 g?1) and pore volumes (ca. 2.1?cm3 g?1), tunable pore-size distributions and good thermal stability. 相似文献
122.
Julio Belmar Leandro OrtizDenis Ramírez Fabiola FuentesMaría Parra Verónica A. JiménezClaudio A. Jiménez 《Tetrahedron letters》2012,53(37):4984-4988
Three compounds containing two β-keto ester units and one containing three were obtained in good yields from sebacyl, terepthaloyl, isophthaloyl, and trimesoyl chlorides. In this one pot procedure the acid chlorides were first treated with ethyl acetoacetate and barium oxide and then with ethyl alcohol. The aliphatic ester exists mainly as keto ester with a very small amount of the enol tautomer. In the case of aromatic esters, all possible tautomers were found in considerable concentrations in deuterochloroform solution. Theoretical chemical shifts were estimated from GIAO/WP04/aug—cc-pVDZ/SCRF calculations, for a probable signal assignation for the corresponding tautomeric species. Our theoretical results are in agreement with experimental findings and account for negligible stability differences between the tautomers of each aromatic compound. 相似文献
123.
Shengda?HuEmail author Eduardo?Leandro Manuele?Santoprete 《Regular and Chaotic Dynamics》2012,17(1):36-53
This paper studies the topology of the constant energy surfaces of the double spherical pendulum. 相似文献
124.
Capillary zone electrophoresis (CZE) was used for the separation of the sulfur species SO3
2–, SO4
2–, S2O3
2– and S2O8
2–. Using an electrolyte system with 9.5 mmol L–1 potassium chromate as UV-absorbing probe and 1 mmol L–1 diethylenetriamine (DETA) as electroosmotic flow modifier, various possibilities for the stabilization of sulfite and electrophoretic
separation of the sulfur anions were investigated. By adding 5% propanol as a stabilizer to both the working electrolyte and
the sample solution, a good stabilization for sulfite and a separation of the sulfur anions in a short analysis time (4 min)
was achieved. The advantages by using propanol instead of other stabilizers often used in analytical techniques are discussed.
The electrophoretic separation of the sulfur anions was optimized with respect to the pH of the working electrolyte and concentration
of the electroosmotic flow modifier (DETA). The detection limits achieved for SO3
2–, SO4
2–, S2O3
2– and S2O8
2– were 0.35, 0.25, 0.78 and 0.80 mg L–1, respectively.
Received: 16 December 1999 / Revised: 7 March 2000 / Accepted: 14 March 2000 相似文献
125.
Gisele C. X. Valle Maria I. B. Tavares Leandro Luetkmeyer Giovanni C. Stael 《Macromolecular Symposia》2007,258(1):113-118
Summary: In the last decades, the growing environmental awareness has resulted in a renewed interest in the use of natural materials for different applications. In this context, the use of wood in plastic to obtain composites has grown significantly. In the present work, heartwood and sapwood from Angelim Pedra (Hymenolobiun petraeum) were used to prepare PVC/wood composites. To study the composites with different wood types and filler contents the molecular dynamic was investigated through low field NMR by poton spin- lattice relaxation time measurements (T1H) and the thermal behavior was characterized by means of differential scanning calorimetry (DSC) focusing the glass transition temperature and thermogravimetric analyses (TGA) observing the changes in the thermal stability. It was found that increasing addition of wood flour (sapwood and heartwood) caused a small but progressive improvement of the decomposition temperature of the composites, whereas the glass transition temperature remains practically unchanged. In the molecular dynamic behavior, a gradual decrease in T1H values was observed with increasing sapwood and heartwood content, indicating that the composites became less rigid. The distribution curves of the domains showed a better interaction and phase dispersion between the composite components with higher filler content. 相似文献
126.
A.F.D. Loula M.R. Correa J.N.C. Guerreiro E.M. Toledo 《International Journal of Solids and Structures》2008,45(25-26):6436-6450
Dealing with variational formulations of second order elliptic problems with discontinuous coefficients, we recall a single field minimization problem of an extended functional presented by Bevilacqua et al. [Bevilacqua, L., Feijóo, R.A., Rojas, L.F., 1974. A variational principle for the Laplace operator with application in the torsion of composite rods. International Journal of Solids Structuring 10, 1091–1102], which we associate with the basic idea supporting discontinuous Galerkin finite element methods. We review residual based stabilized mixed methods applied to Darcy flow in homogeneous porous media and extend them to heterogeneous media with an interface of discontinuity. For smooth interfaces, the proposed formulations preserve the continuity of the flux and exactly imposes the constraint between the tangent components of Darcy velocity on the interface. Convergence studies for a heterogeneous and anisotropic porous medium confirm the same rates of convergence predicted for homogeneous problem with smooth solutions. 相似文献
127.
128.
Journal of Radioanalytical and Nuclear Chemistry - Based on the newly-developed techniques, the transfer behaviors of 90Sr and 137Cs under natural conditions were studied. The concentrations of... 相似文献
129.
Neves Junior Alex Dweck Jo Filho Romildo Dias Toledo Ellis Brian Li Victor 《Journal of Thermal Analysis and Calorimetry》2019,135(1):97-109
Journal of Thermal Analysis and Calorimetry - The present study has evaluated the rheological behavior of an oil-based (5W50) hybrid nanofluid [magnesium oxide (65%)–multi-walled carbon... 相似文献
130.
Dr. Leandro Trupp Dr. Andrea C. Bruttomesso Dr. Svetlana V. Eliseeva Dr. Stéphane Petoud Dr. Javier A. Ramírez Dr. Beatriz C. Barja 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(55):12645-12653
Herein, the design, synthesis, and characterization of a phenhomazine ligand are described. The ligand has six pendant acetate arms designed for the combined coordination of copper(II) and lanthanide(III) ions, with the perspective of developing a “turn-off” copper sensor. The key step for the ligand preparation was the one-step endomethylene bridge fission of a diamino Tröger's base with a concomitant alkylation. Fluorescence and absorption spectroscopies as well as nuclear magnetic resonance (NMR) experiments were performed to analyze and understand the coordination properties of the ligand. Transition metal coordination was driven by the synergistic effect of the free nitrogen atoms of the diazocinic core and the two central acetate arms attached to those nitrogen atoms, whereas lanthanide coordination is performed by the external acetate arms, presumably forming a self-assembled 2:2 metallosupramolecular structure. The terbium complex shows the typical green emission with narrow bands and long luminescence lifetimes. The luminescence quenching produced by the presence of copper(II) ions was analyzed. This work sets, therefore, a starting point for the development of a phenhomazine-based “turn-off” copper(II) sensor. 相似文献