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131.
Linping Mu Zhiqun He Prof. Xiangfei Kong Guanbao Hui Min Xu Chunjun Liang Dr. Xiping Jing Dr. Andrzej Danel Dr. Ewa Kulig Dr. 《Chemphyschem》2010,11(12):2623-2629
Pyrazolo[3,4‐b]quinoline derivatives are reported to be highly efficient organic fluorescent materials suitable for applications in light‐emitting devices. Although their fluorescence remains stable in organic solvents or in aqueous solution even in the presence of H2O, halide salts (LiCl), alkali (NaOH) and weak acid (acetic acid), it suffers an efficient quenching process in the presence of protic acid (HCl) in aqueous or ethanolic solution. This quenching process is accompanied by a change in the UV spectrum, but it is reversible and can be fully recovered. Both steady‐state and transient fluorescence spectra of 1‐phenyl‐3,4‐dimethyl‐1H‐pyrazolo‐[3,4‐b]quinoline (PAQ5) during quenching are measured and analyzed. It is found that a combined dynamic and static quenching mechanism is responsible for the quenching processes. The ground‐state proton‐transfer complex [PAQ5 ??? H+] is responsible for static quenching. It changes linearly with proton concentration [H+] with a bimolecular association constant KS=1.95 M ?1 controlled by the equilibrium dissociation of HCl in ethanol. A dynamic quenching constant KD=22.4 M ?1 is obtained by fitting to the Stern–Volmer equation, with a bimolecular dynamic quenching rate constant kd=1.03×109 s?1 M ?1 under ambient conditions. A change in electron distribution is simulated and explains the experiment results. 相似文献
132.
The Diels-Alder reaction between cyclopentadiene and dienophiles in deanol derivatives containing bis(trifluoromethylsulfonyl)imide
anion as media have been studied. The effect of the substituents attached to the cation on the endo:exo selectivity as well
as the reaction yield have been evaluated in the absence and presence of Lewis acid catalyst - Y(OTf)3. Catalytic activity of metal triflates and the recycling of chosen catalytic systems have also been investigated
相似文献
133.
Luke Chimuka Titus A.M. Msagati Ewa Cukrowska Hlanganani Tutu 《Journal of chromatography. A》2010,1217(16):2318-2325
The reviews cover important critical parameters that are often optimized in a supported liquid membrane extraction technique in both flat sheet and hollow fibre designs for ionizable organic molecules. Understanding of these parameters can enable one to predict the behavior of the compound before hand and thus reduce the number of optimization experiments. Moreover, less number of experiments can be also generated using statistical techniques which are now becoming more commonly used. Supported liquid membrane extraction optimal parameters such as the conditions of the pH of the acceptor and donor phases should easily be fixed from the pKa values of the compounds. Other parameters, including the polarity of the compound can help to predict the partitioning into the membrane and the behavior of the compound. The influence of parameters such as temperature on the mass transfer in supported liquid membrane depends on the design of the module, experimental design and type of mass transfer controlling the extraction process. 相似文献
134.
Ewa M. Bednarczuk Enrico Miglierina Elena Molho 《Set-Valued and Variational Analysis》2011,19(4):569-587
The mountain pass theorem for scalar functionals is a fundamental result of the minimax methods in variational analysis. In this work we extend this theorem to the class of \(\mathcal{C}^{1}\) functions \(f:\mathbb{R}^{n}\rightarrow\mathbb{R}^{m}\), where the image space is ordered by the nonnegative orthant \(\mathbb{R}_{+}^{m}\). Under suitable geometrical assumptions, we prove the existence of a critical point of f and we localize this point as a solution of a minimax problem. We remark that the considered minimax problem consists of an inner vector maximization problem and of an outer set-valued minimization problem. To deal with the outer set-valued problem we use an ordering relation among subsets of \(\mathbb{R}^{m}\) introduced by Kuroiwa. In order to prove our result, we develop an Ekeland-type principle for set-valued maps and we extensively use the notion of vector pseudogradient. 相似文献
135.
Skrodzka E Łapa A Linde BB Rosenfeld E 《The Journal of the Acoustical Society of America》2011,130(4):2186-2194
Similarities and differences in vibrational behavior of two guitars having a symmetric Torres bracing pattern and an asymmetric pattern forming a lattice on a soundboard are investigated by means of the modal analysis technique and laser Doppler vibrometry (LDV) measurements. Instruments are investigated before and after a bridge and strings assembling (i.e., they are incomplete or complete). The bracing pattern and the absence/presence of the bridge and strings have some effect on modal frequencies and mode shapes. The bracing pattern does not affect the sequence of at least first three low frequency mode shapes of incomplete/complete instruments but affects their modal frequencies. Depending on frequency, the bridge behaves either as a rigid or a flexible structure. 相似文献
136.
Beata Zielińska Ewa Borowiak-Palen Ryszard J. Kalenczuk 《Journal of Physics and Chemistry of Solids》2011,72(2):117-123
Fe-, Ni-, Co- and Ag- loaded NaNbO3 catalysts were prepared and their activities have been investigated in the reaction of photocatalytic hydrogen generation. Me/NaNbO3 were synthesized by impregnation of NaNbO3 in an aqueous solution of metal nitrates and then by calcination at the temperature of 400 °C. The crystallographic phases and optical and vibronic properties were examined by X-ray diffraction (XRD) and diffuse reflectance (DR) UV-vis and resonance Raman spectroscopic methods, respectively. Morphology and chemical composition of the produced samples were studied using a high-resolution transmission electron microscope (HR-TEM) and an energy dispersive X-Ray spectrometer (EDX) as its mode. The detailed analysis has revealed that all the investigated catalysts exhibit high crystallinity and the presence of Fe2O3, NiO, Co3O4 and Ag2O oxides on Me/NaNbO3 was confirmed. Finally, the influence of different metal loadings (Fe, Ni, Co and Ag) on the photocatalytic activity of NaNbO3 for photocatalytic hydrogen generation has been investigated. Here we report that among all the Me/NaNbO3 photocatalysts Ag-loaded NaNbO3 exhibited higher photocatalytic efficiency for photocatalytic hydrogen generation than NaNbO3. 相似文献
137.
In this paper we propose a new method for estimating parameters in a single-index model under censoring based on the Beran estimator for the conditional distribution function. This, likelihood-based method is also a useful and simple tool used for bandwidth selection. Additionally, we perform an extensive simulation study comparing this new Beran-based approach with other existing method based on Kaplan–Meier integrals. Finally, we apply both methods to a primary biliary cirrhosis data set and propose a bootstrap test for the parameters. 相似文献
138.
I. O. B. Ewa 《光谱学快报》2013,46(5):885-900
Fast (14 MeV) neutrons have been successfully used in investigating the protein content of different food grains (Soya Beans, Sorghum, Maize and Beans) locally grown and consumed in Nigeria. Protein was estimated via nitrogen using the 14N(n, 2n)13N reaction. Quantification of nitrogen was achieved through a γ-γ coincidence counting of 511 keV positron emissions from the decaying 13N. The implication of the use of the emitted annihilation positrons, the interference introduced in the analytical energy spectra from other activated target nuclides present in the sample, as well as possible proton “knock on” reactions anticipated from cellulose in grain matrix were assessed, and their contributions to the 511 keV gamma energy resolved. For comparative purposes, replicates of samples analyzed through Fast Neutron Activation Analysis (FNAA) were investigated using the Kjeldahl method. The samples were carried through the Kjeldahl process of pre-digestion (with appropriate catalysts), digestion and titration. The results obtained through the Kjeldahl process were found to be in good agreement with those obtained using FNAA although slightly lower. Protein content (%) of Nigerian grains analyzed varied from a low 8.75 ± 2.96 for sorghum to 35.93 ± 0.31 for soya beans. 相似文献
139.
Conditions for a gas-chromatographic determination of vapors and aerosols of p-chlorostyrene and 2,6-dichlorostyrene contained in workplace air samples were determined. The method is based on the adsorption
of p-chlorostyrene and 2,6-dichlorostyrene on activated charcoal and fiberglass, desorption with toluene and analysis of the obtained
solution by capillary gas chromatography with flame ionization detection (FID). The determination limit of the method is 5
mg m–3 for each substance.
Received: 13 December 1999 / Revised: 6 March 2000 / Accepted: 7 March 2000 相似文献
140.