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871.
L. C. R. Andrade J. A. Paixo M. J. M. de Almeida R. M. L. M. Martins H. I. M. Soares G. J. R. Morais M. J. S. M. Moreno M. L. S e Melo A. S. Campos Neves 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(5):587-589
The title compound, C23H32O4, has a 3β configuration, with the epoxy O atom at 16α,17α. Rings A and C have slightly distorted chair conformations. Because of the presence of the C5=C6 double bond, ring B assumes an 8β,9α‐half‐chair conformation slightly distorted towards an 8β‐sofa. Ring D has a conformation close to a 14α‐envelope. The acetoxy and acetyl substituents are twisted with respect to the average molecular plane of the steroid. The conformation of the molecule is compared with that given by a quantum chemistry calculation using the RHF–AM1 (RHF = Roothaan Hartree–Fock) Hamiltonian model. Cohesion of the crystal can be attributed to van der Waals interactions and weak intermolecular C—H?O interactions, which link the molecules head‐to‐tail along [101]. 相似文献
872.
Jorge L. Bali o Axel E. Larreteguy Alicia C. Lorenzo Alberto Gallardo Padilla Fernando R. de Andrade Lima 《Applied Mathematical Modelling》2001,25(12):1117-1138
The differential perturbative method was applied to the sensitivity analysis for waterhammer problems in hydraulic networks. Starting from the classical waterhammer equations in a single-phase liquid with friction (the direct problem) the state vector comprising the piezometric head and the velocity was defined. Applying the differential method the adjoint operator, the adjoint equations with the general form of their boundary conditions, and the general form of the bilinear concomitant were calculated for a single pipe. Considering that any hydraulic network can be built by connecting different components (reservoirs, valves, pumps, tees, etc.) through pipes, the adjoint relationships for any component, as well as the final contribution to the bilinear concomitant, were calculated. Moreover, an analogy was established in which transmission and reflection coefficients can be derived for any adjoint component. The importance or adjoint function was analyzed when the piezometric head or velocity at a given position and time is chosen as the response functional. In this case, it is shown that the importance function is represented by delta-functions travelling along the hydraulic network with the propagation speed. The calculation of the sensitivity coefficients takes into account the cases in which the parameters under consideration influence the initial condition. For these cases, the calculation can be performed by solving sequentially two perturbative problems: the first one is non-steady, while the second one is steady, with an appropriate selection of a weight function coming from the unsteady perturbative problem. The discretized adjoint equations and the corresponding boundary conditions were programmed and solved by using the method of characteristics. As an example, a constant-level tank connected through a pipe to a valve discharging to atmosphere was considered. The corresponding sensitivity coefficients due to the variation of different parameters by using both the differential method and the response surface generated by the computer code WHAT, solver of the direct problem, were also calculated. The results obtained with these methods show excellent agreement. 相似文献
873.
Leida M. Pretto Mateus Mittersteiner Valquiria P. Andrade Helio G. Bonacorso Marcos A.P. Martins Nilo Zanatta 《Tetrahedron letters》2019,60(52):151336
The synthetic versatility of ethyl 2-(2-ethoxy-3,4-dihydro-2H-pyran-5-yl)-2-oxoacetate for the synthesis of ethyl 2-oxo-2-(1-alkyl/aryl-6-(amino/ethoxy)-1,4,5,6-tetrahydropyridin-3-yl)acetates, from the reaction with primary amines, is presented. The methodology proposed herein is highly chemoselective, and twenty products were obtained in moderate to good yields (up to 87%). 相似文献
874.
Rossana M. S. M. Thiré Taíla O. Meiga Sabrina Dick Leonardo R. Andrade 《Macromolecular Symposia》2007,258(1):38-44
Summary: Chemical modification of polymer surface may potentially be used to create smart materials that can guide cellular adhesion, proliferation and maintenance of specific expression of molecules. The microbial polyester poly (3-hydroxybutyrate) (PHB) has been attracted attention as promising material for applications in tissue engineering. In this work, a wet-chemical method, base ethylenediamine aminolysis, was performed to improve the adhesion of chondrocytes isolated from human articular cartilage to PHB films. The effects of chemical treatment on PHB films was evaluated by following changes in morphology and surface chemical composition using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS), respectively. While the effect on cells morphology was studied by scanning electron microscopy (SEM). The treatment with ethylenediamine did not change significantly the morphology of the structures of PHB films surface. However, the roughness of the aminolyzed films was slightly higher. The introduction of nitrogen-containing groups was confirmed by XPS. In vitro experiments indicated that the surface modification did not have toxic effects in cells, since they could adhere and proliferate on modified PHB films. It was observed that long-time treatment improved ability of PHB films to support cell growth, which could be accounted to physicochemical and topological effects. 相似文献
875.
Damaso Mônica C. T. Andrade Carolina M. M. C. Pereira Nei 《Applied biochemistry and biotechnology》2000,84(1-9):821-834
The production of cellulase-free end oxylanase by the thermophilic fungus Thermomyces lanuginosus was investigated insemisolid fermentation and liquid fermentation. Different process variables were investigated in semisolid
fermentation, employing corncobas the carbon source. The best results were with the following conditions: grain size=4.5 mm,
solid:liquid ratio=1:2, and inoculum size=20% (v/v). Corncob, xylan, and xylose were the best inducers for endoxylanase production.
Additionally, organic nitrogen sources were necessary for the production of high endoxylanase activities. The crude enzyme
had optimum activity at pH 6.0 and 75°C, displaying a high thermostability. The apparent K
25 and V
max were 1.77 mg of xylan/mL and 21.5 U/mg of protein, respectively. 相似文献
876.
This work has two objectives. The first is to begin a mathematical formalism appropriate to treating particles which only interact with each otherindirectly due to hypothesized memory effects in a stochastic medium. More specifically we treat a situation in which a sequence of particles consecutively passes through a region (e.g., a measuring apparatus) in such a way that one particle leaves the region before the next one enters. We want to study a situation in which a particle may interact with other particles that previously passed through the system via disturbances made in the region by these previous particles.Second, we apply the type of stochastic process appearing in this context to the stochastic interpretation of quantum mechanics to obtain a modified version of this interpretation. This version is free of many of the criticisms made against the stochastic interpretation of quantum mechanics. 相似文献
877.
Summary The complex intraparticle structure typical of chromatographic column packings has been analyzed by use of an equivalent network
model which emphasizes pore size distribution and connectivity. Special attention is given as to the way in which diffusion
and adsorption interact and display modified peak spreading characteristics according to the morphology of the pore space.
This study reveals a very significant increase in the column band broadening over that expected from physical adsorption which
can arise from particular distributions of pore sizes. This has implications for designing packings which take advantage of
the separating power due to adsorption but do not compromise the resolution of the chromatographic system. 相似文献
878.
M. S. S. Ferreira A. V. M. De Andrade J. F. Kennedy 《Applied biochemistry and biotechnology》1991,31(1):1-9
Thermostable invertase (E.C. 3.2.1.26) and inulinase 2,1-beta-D-fructan fructanohydrolase (E.C. 3.2.1.7) activities were produced by Cladosporium cladosporioides grown on sucrose, inulin, yam extract, or Jerusalem artichoke. The ratio I (inulinase)/S(invertase) activity was between 0.31 and 0.36. Both activities had high temperature optima (60 degrees C) and were stable during pretreatment for 4.5 h at this temperature. Whole cells of C. cladosporioides were used for batch fructose production from Jerusalem artichoke extract at several concentrations. With the highest extract concentration used (260 g total sugars/L), total hydrolysis was achieved in 150 min at 60 degrees C. Thin-layer chromatography of the enzymatic hydrolysis of inulin and Jerusalem artichoke extract showed that from the beginning of the reaction, fructose was the only product released. This suggests an exoaction mechanism, beta-D-fructofuranoside fructohydrolase [E.C. 3.2.1.2.6]. 相似文献
879.
L. C. Garcia de Andrade 《International Journal of Theoretical Physics》1991,30(2):235-238
A Ricci recurrent space-time with covariantly constant stress tensor is an Einstein space-time. We extend this result to Ricci recurrent space-times with torsion. The result is applied to the case of Riemann-Cartan space-times with spin density. 相似文献
880.
Andrade Plácido do Socorro Pereira Maria 《Bulletin of the Brazilian Mathematical Society》1990,21(1):79-89
We show that the cohomology groupH
1 (M, f) is an infinite dimensional vector space, for a dense set of one dimensional foliations on a closed manifold. In particular we compute this cohomology, for some foliations on the torus T2. 相似文献