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91.
We propose that the dissipative dynamics of topological defects in a spiral state is responsible for the transport properties in the spin-glass phase of cuprates. Using the collective-coordinate method, we show that topological defects are coupled to a bath of magnetic excitations. By integrating out the bath degrees of freedom, we find that the dynamical properties of the topological defects are dissipative. The calculated damping matrix is related to the in-plane resistivity, which exhibits an anisotropy and linear temperature dependence in agreement with experimental data. 相似文献
92.
Amoureux JP Morais C Trebosc J Rocha J Fernandez C 《Solid state nuclear magnetic resonance》2003,23(4):213-223
In complement to the previously proposed multiple-quantum magic-angle-spinning (MQMAS) and satellite transition MAS (STMAS) sequences, we describe a new two-dimensional high-resolution method, inverse-STMAS (I-STMAS) that allows second-order quadrupolar averaging. Like STMAS, I-STMAS correlates second-order quadrupole dephasing occurring on coherences related to the central transition (CT) and satellite transitions (STs), but does it in a reverse manner: CT evolves during the t1 period while STs are detected during t2. Although STMAS and I-STMAS are symmetric, there are some interesting and useful differences between the two methods. For example, we show that during the acquisition time t2, it is possible to over-sample the data and then to process them to suppress the CT–CT correlation resonance. 相似文献
93.
Iuga D Morais C Gan Z Neuville DR Cormier L Massiot D 《Journal of the American Chemical Society》2005,127(33):11540-11541
We show for the first time that it is possible to acquire high-resolution heteronuclear NMR correlation experiments in solid state between second-order-broadened half integer quadrupolar nuclei (i.e., 27Al and 17O) using the scalar J-coupling. The sensitivity of the experiment is dramatically improved at high fields (gain proportional to the fourth power of the principal field) with a combination of signal enhancement techniques. This turns a challenging experiment into a real tool. We apply this experiment to characterize a calcium aluminate glass in which we prove the presence of tricluster mu3 oxygen sites and describe the signature of their directly bonded aluminum sites. Applications involve a large range of possible pairs of quadrupolar nuclei in different materials, such as glasses, porous or mesoporous framework materials, zeolites, hybrid organic-inorganic, and bioinvolved materials. 相似文献
94.
Da Silva Perez D Ruggiero R Morais LC Machado AE Mazeau K 《Langmuir : the ACS journal of surfaces and colloids》2004,20(8):3151-3158
The adsorption of several aromatic compounds over microcrystalline cellulose was studied by molecular modeling and experimentally using gas chromatography. Experimental adsorption enthalpies were obtained from an equation based on Clausius-Clapeyron formalism and the temperature dependence of retention volume at infinite dilution. Four different cellulose surfaces (three crystalline (110, 100, and 010) and one amorphous) were modeled. Overall strong agreement was observed between the experimental and theoretical work with 84% of the adsorbate-cellulose systems having differences between measured and predicted values of less than 20%. Based on both calculated and experimental data, a morphology for the microcrystalline cellulose as a weighted combination of the four surfaces was proposed: 39% (110), 28% (100), 10% (010), and 23% amorphous. By adopting this distribution, differences between experimental and weighted average predicted adsorption energies were 10% or less for 14 out of 17 compounds; a maximum of 15% was observed for guaiacol. Experimental results for monosubstituted aromatic compounds revealed that adsorption enthalpies are related to the hydrophilic/hydrophobic character of the substituent groups: 3.5 kJ mol(-1) for a methyl group, 15.7 kJ mol(-1) for a double bond, 21.0 kJ mol(-1) for a methoxyl group, 22.8 kJ mol(-1) for a carbonyl group, and 27.6 kJ mol(-1) for a hydroxyl group. These tendencies were confirmed by modeling, except for the aldehyde carbonyl group, where an overestimation of 10.8 kJ mol(-1) was observed. Analysis of experimental and predicted adsorption enthalpies of multisubstituted aromatic compounds suggests that the efficiency of their interaction with cellulose depends on a compromise between the roughness of the cellulose surface and their conformational adaptability. 相似文献
95.
A solid-state nuclear magnetic resonance (NMR) experiment, which provides high-resolution two-dimensional heteronuclear correlation (HETCOR) spectra between 27Al and 31P, is described. The first part of the experiment uses triple-quantum or quintuple-quantum magic-angle spinning (MQMAS) NMR of spin-5/2 nuclei (27Al) to produce an isotropic echo that is unaffected by the second-order quadrupolar broadening. The magnetization is then transferred to the spin-1/2 (31P) nuclei via cross-polarization (CP), resulting in isotropic resolution in both spectral dimensions. To illustrate its usefulness, this method (referred to as MQHETCOR) is applied to two important microporous framework aluminophosphates, hydrated VPI-5 and AIPO4-40. 相似文献
96.
97.
Jacqueline Moreira de Morais Orlando David Henrique dos Santos Tatiani Delicato Pedro Alves da Rocha‐Filho 《Journal of Dispersion Science and Technology》2013,34(7):1009-1014
Emulsion stability is controlled by the physicochemical properties of the adsorbed layers formed on the surface of the droplets. Zeta potential and droplet size measured initially and during storage can estimate O/W emulsion stability. The aim of this study was to characterize and evaluate the effects of different hydrolyzable compounds employed in pharmaceutical and cosmetic preparations on the zeta potential and droplet size of canola O/W nano‐emulsions and, consequently, the emulsion stability. The samples containing additives demonstrated significant change in zeta potential, but in spite of that, no macroscopic instability was observed. Yet the droplet size values did not undergo significant change. 相似文献
98.
Daiane Cristina Sass Vladimir Constantino Gomes Heleno Jader da Silva Barbosa Gustavo Oliveira Morais Fernando Batista Da Costa Mauricio Gomes Constantino 《Tetrahedron letters》2013,54(7):625-627
The conversion of a germacranolide structure (tagitinin C) into a furanoheliangolide one (diversifolin) was achieved by hydride conjugate addition using Stryker’s reagent. 相似文献
99.
Frida Mariana Morais Friederike Buchholz Tom Hartmann Johannes Lerchner Thomas R. Neu Bärbel Kiesel Hauke Harms Thomas Maskow 《Journal of Thermal Analysis and Calorimetry》2014,115(3):2203-2210
Bacteriophages or phage-derived biological structures are a promising alternative to the application of antibiotics to eradicate biofilms. These countermeasures are highly cell specific. For a better understanding of the sequence of the underlying processes (attachment, infection, multiplication, phage release), for optimization of phage applications, or simply for screening of suitable phages or phage-derived enzymes, real-time monitoring devices are urgently required. Calorimetry is promising because it is non-invasive and quantitatively connected to the metabolic fluxes. Chip-calorimetry provides real-time information about biofilm eradication by phages. This was confirmed by comparison with reference analyses (i.e., confocal laser scanning microscopy, colony plate counts, or phage titre determination). Furthermore, chip-calorimetry provides additional information which was not captured by the reference methods such as the enhanced cell-specific heat production caused by the infection process and a residual activity of seemingly persistent bacteria. 相似文献
100.
M. A. González-Martínez S. Morais R. Puchades A. Maquieira M. P. Marco D. Barceló 《Fresenius' Journal of Analytical Chemistry》1998,361(2):179-184
Intensive agriculture associated with the use of large amounts of different pesticides, together with the growing concern
about the potential contamination of ground water, have brought about the need for developing fast screening methods. This
work presents the automation of an enzyme-linked immunosorbent assay for atrazine by means of a flow-through system. Three
different solid supports for antibody immobilization were compared in a direct competitive assay format. Sensitivity reached
in all cases was below the maximum level allowed in the EU (100 ng L–1). Cross-reactivity of atrazine-related compounds was also studied. The performance of the different supports is discussed
regarding sensitivity and immunosurface regeneration.
Received: 21 July 1997 / Revised: 7 November 1997 / Accepted: 11 November 1997 相似文献