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排序方式: 共有620条查询结果,搜索用时 15 毫秒
141.
Palhares Hugo Guimarães Nunes Eduardo Henrique Martins Houmard Manuel 《Journal of Sol-Gel Science and Technology》2021,99(1):188-197
Journal of Sol-Gel Science and Technology - Most studies related to the synthesis of TiO2–SiO2 composites for photocatalytic applications did not systematically evaluate the textural and... 相似文献
142.
I.A.A. Terra L.J. Borrero-González T.R. Figueredo J.M.P. Almeida A.C. Hernandes L.A.O. Nunes O.L. Malta 《Journal of luminescence》2012,132(7):1678-1682
The down-conversion process in Tb3+–Yb3+ co-doped Calibo glasses was studied. The emission, excitation and time-resolved measurements indicated the existence of an energy conversion through the excitation of Tb3+ ions to near-infrared emission by Yb3+ ions. The emission intensity dependence on excitation power confirms that the one-photon process is responsible for the Yb3+ emission. An enhanced Yb3+ emission was observed with Yb3+ doping and an optimal energy transfer efficiency of 32% was obtained before reaching near-infrared emission quenching. The mechanism of the non-resonant energy transfer from Tb3+ to Yb3+ is discussed in terms of the Tb3+–Yb3+ cross-relaxation and multiphonon decay processes. 相似文献
143.
Matheus Nunes da Rocha Márcia Machado Marinho Alexandre Magno Rodrigues Teixeira Emmanuel Silva Marinho Hélcio Silva dos Santos 《印度化学会志》2022,99(7):100535
Considered one of the chronic diseases in a global state of emergency, diabetes mellitus (DM) may cover an area of 629 million people affected by 2045. The main route of hyperglycemia in the human body is associated with the action of the enzyme aldose reductase on glucose molecules, resulting in the accumulation of sorbitol in blood and tissue cells. Thus, the present study is a high-throughput virtual screening (HTS) of the various molecular datasets available online, as well as an investigation of the pharmacokinetic properties of absorption, distribution, metabolism, excretion, and toxicity (ADMET) and enzyme inhibition aldose reductase from a series of derivatives of rhodanine-3-acetic acid chalcones (D1-8). Four derivatives (D1-4) showed greater oral bioavailability, as they are anions of low relative polarity, showing better viability to interact with the aldose reductase target with a low toxic response to the host. 相似文献
144.
Heitor Fernando Nunes de Oliveira Christophe Farès Roberto Rinaldi 《Chemical science》2015,6(9):5215-5224
In this report, 1-butyl-3-methylimidazolium chloride ([C4C1im]Cl) is demonstrated to enhance the kinetics of acid-catalysed hydrolysis of 1,4-β-glucans in binary solvent mixtures. [C4C1im]Cl plays other roles in the reaction beyond acting as a solvent for cellulose, as currently accepted. In fact, the presence of the IL increases the Hammett acidity of the catalyst dissolved in the reaction medium. The kinetic data from cellobiose and cellulose hydrolysis directly correlate with the acid strength found for p-toluenesulfonic acid in the different reaction media studied here. The current report identifies neglected, but yet very important phenomena occurring in cellulose depolymerisation. 相似文献
145.
C. Lucas I. Eiroa M. R. Nunes P. A. Russo M. M. L. Ribeiro Carrott M. I. da Silva Pereira M. E. Melo Jorge 《Journal of Solid State Electrochemistry》2009,13(6):943-950
The electrochemical properties of Ca1 − x
Ce
x
MnO3 perovskite-type oxide electrode have been investigated by cyclic voltammetry in Na2SO4 aqueous solutions with pH 14. The structural and morphological characterizations have also been investigated and the information
used to interpret the electrochemical behavior. An estimation of the electrode’s capacitance and roughness factor has been
obtained by means of cyclic voltammetry. The specific capacitance and consequently the roughness factor values are affected
by the presence of Ce ions in the oxide. These findings are in agreement with the increase of the oxide-specific surface area
by the introduction of Ce ion. The open-circuit potential and the voltammetric patterns are dependent on the presence of Ce
ion in the electrodes and support that the surface electrochemistry of the perovskite oxide electrodes is governed by the
Mn4+–Mn3+ redox couple. 相似文献
146.
Oswaldo Ludwig Urbano Nunes Rui Araújo Leizer Schnitman Herman Augusto Lepikson 《Communications in Nonlinear Science & Numerical Simulation》2009,14(7):2870-2885
This work introduces a new information-theoretic methodology for choosing variables and their time lags in a prediction setting, particularly when neural networks are used in non-linear modeling. The first contribution of this work is the Cross Entropy Function (XEF) proposed to select input variables and their lags in order to compose the input vector of black-box prediction models. The proposed XEF method is more appropriate than the usually applied Cross Correlation Function (XCF) when the relationship among the input and output signals comes from a non-linear dynamic system. The second contribution is a method that minimizes the Joint Conditional Entropy (JCE) between the input and output variables by means of a Genetic Algorithm (GA). The aim is to take into account the dependence among the input variables when selecting the most appropriate set of inputs for a prediction problem. In short, theses methods can be used to assist the selection of input training data that have the necessary information to predict the target data. The proposed methods are applied to a petroleum engineering problem; predicting oil production. Experimental results obtained with a real-world dataset are presented demonstrating the feasibility and effectiveness of the method. 相似文献
147.
Nunes PM Agapito F Costa Cabral BJ Borges dos Santos RM Martinho Simões JA 《The journal of physical chemistry. A》2006,110(15):5130-5134
The gas-phase C-H bond dissociation enthalpy (BDE) in 1,3-cyclopentadiene has been determined by time-resolved photoacoustic calorimetry (TR-PAC) as 358 +/- 7 kJ mol(-1). Theoretical results from ab initio complete basis-set approaches, including the composite CBS-Q and CBS-QB3 procedures, and basis-set extrapolated coupled-cluster calculations (CCSD(T)) are reported. The CCSD(T) prediction for the C-H BDE of 1,3-cyclopentadiene (353.3 kJ mol(-1)) is in good agreement with the TR-PAC result. On the basis of the experimental and the theoretical values obtained, we recommend 355 +/- 8 kJ mol(-1) for the C-H BDE of 1,3-cyclopentadiene and 271 +/- 8 kJ mol(-1) for the enthalpy of formation of cyclopentadienyl radical. 相似文献
148.
In this paper, the large time decay of the magneto-micropolar fluid equations on \(\mathbb {R}^n\) (\( n=2,3\)) is studied. We show, for Leray global solutions, that \( \Vert ({\varvec{u}},{\varvec{w}},{\varvec{b}})(\cdot ,t) \Vert _{{L^2(\mathbb {R}^n)}} \rightarrow 0 \) as \(t \rightarrow \infty \) with arbitrary initial data in \( L^2(\mathbb {R}^n)\). When the vortex viscosity is present, we obtain a (faster) decay for the micro-rotational field: \( \Vert {\varvec{w}}(\cdot ,t) \Vert _{{L^2(\mathbb {R}^n)}} = o(t^{-1/2})\). Some related results are also included. 相似文献
149.
The chemistry of trifluoromethyl azafulvenium methides was explored leading to a new route to trifluoromethylpyrrole-annulated systems. The first evidence of azafulvenium methides acting as 1,3-dipoles is reported. These azafulvenium methides showed site selectivity in the reaction with strong electron-deficient dipolarophiles leading exclusively to 1,3-cycloadducts. In the cycloaddition with less-activated dipolarophiles 1,7-cycloadducts resulting from [8π+2π] cycloaddition are also formed. FMO analysis of the cycloaddition reactions allowed the rationalization of the observed selectivity. 相似文献
150.
Mário A. P. Nunes Hélder Vila-Real Pedro C. B. Fernandes Maria H. L. Ribeiro 《Applied biochemistry and biotechnology》2010,160(7):2129-2147
A synthetic polymer, polyvinyl alcohol (PVA), a cheap and nontoxic synthetic polymer to organism, has been ascribed for biocatalyst
immobilization. In this work PVA–alginate beads were developed with thermal, mechanical, and chemical stability to high temperatures
(<80 °C). The combination of alginate and bead treatment with sodium sulfate not only prevented agglomeration but produced
beads of high gel strength and conferred enzyme protection from inactivation by boric acid. Naringinase from Penicillium decumbens was immobilized in PVA (10%)–alginate beads with three different sizes (1–3 mm), at three different alginate concentrations
(0.2–1.0%), and these features were investigated in terms of swelling ratio within the beads, enzyme activity, and immobilization
yield during hydrolysis of naringin. The pH and temperature optimum were 4.0 and 70 °C for the PVA–alginate-immobilized naringinase.
The highest naringinase activity yield in PVA (10%)–alginate (1%) beads of 2 mm was 80%, at pH 4.0 and 70 °C. The Michaelis
constant (K
Mapp) and the maximum reaction velocity (V
maxapp) were evaluated for both free (K
Mapp = 0.233 mM; V
maxapp = 0.13 mM min−1) and immobilized naringinase (K
Mapp = 0.349 mM; V
maxapp = 0.08 mM min−1). The residual activity of the immobilized enzyme was followed in eight consecutive batch runs with a retention activity
of 70%. After 6 weeks, upon storage in acetate buffer pH 4 at 4 °C, the immobilized biocatalyst retained 90% of the initial
activity. These promising results are illustrative of the potential of this immobilization strategy for the system evaluated
and suggest that its application may be effectively performed for the entrapment of other biocatalysts. 相似文献