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1.
A mesoporous silica-supported uranyl material (U(aq)O(2)(2+)-silica) was prepared by a co-condensation method. Our approach involves an I(-)M(+)S(-) scheme, where the electrostatic interaction between the anionic inorganic precursor (I(-)), surfactant (S(-)), and cationic mediator (M(+)) provides the basis for the stability of the composite material. The synthesis was carried out under acidic conditions, where the anionic sodium dodecyl sulfate provided the template for the uranyl cation and silicate to condense. Excitation with visible or near-UV light of aqueous suspensions of U(aq)O(2)(2+)-silica generates an excited state that decays with k(0) = 1.5 x 10(4) s(-1). The reaction of the excited state with aliphatic alcohols exhibits kinetic saturation and concentration-dependent kinetic isotope effects. For 2-propanol, the value of k(C)3(H)7(OH)/k(C)()3(D)7(OH) decreases from 2.0 at low alcohol concentrations to 1.0 in the saturation regime at high alcohol concentrations. Taken together, the data describe a kinetic system controlled by chemical reaction at one extreme and diffusion at the other. At low [alcohol], the second-order rate constants for the reaction of silica-U(aq)O(2)(2+) with methanol, 2-propanol, 2-butanol, and 2-pentanol are comparable to the rate constants obtained for these alcohols in homogeneous aqueous solutions containing H(3)PO(4). Under slow steady-state photolysis in O(2)-saturated suspensions, U(aq)O(2)(2+)-silica acts as a photocatalyst for the oxidation of alcohols with O(2). 相似文献
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Waleligne Molla Salilew Zainal Ambri Abdul Karim Tamiru Alemu Lemma Amare Desalegn Fentaye Konstantinos G. Kyprianidis 《Entropy (Basel, Switzerland)》2022,24(8)
The gas turbine was one of the most important technological developments of the early 20th century, and it has had a significant impact on our lives. Although some researchers have worked on predicting the performance of three-shaft gas turbines, the effects of the deteriorated components on other primary components and of the physical faults on the component measurement parameters when considering the variable inlet guide valve scheduling and secondary air system for three-shaft gas turbine engines have remained unexplored. In this paper, design point and off-design performance models for a three-shaft gas turbine were developed and validated using the GasTurb 13 commercial software. Since the input data were limited, some engineering judgment and optimization processes were applied. Later, the developed models were validated using the engine manufacturer’s data. Right after the validation, using the component health parameters, the physical faults were implanted into the non-linear steady-state model to investigate the performance of the gas turbine during deterioration conditions. The effects of common faults, namely fouling and erosion in primary components of the case study engine, were simulated during full-load operation. The fault simulation results demonstrated that as the severity of the fault increases, the component performance parameters and measurement parameters deviated linearly from the clean state. Furthermore, the sensitivity of the measurement parameters to the fault location and type were discussed, and as a result they can be used to determine the location and kind of fault during the development of a diagnosis model. 相似文献
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Olaf Kunert Ernst Haslinger Martin G. Schmid Josef Reiner Franz Bucar Efrem Mulatu Dawit Abebe Asfaw Debella 《Monatshefte für Chemie / Chemical Monthly》2000,131(2):195-204
Summary. Three bisdesmosidic saponins, 20-hydroxyecdysone, and quercetin-3-O-β-D-galactoside were isolated from the methanol extract of the aerial parts of Achyranthes aspera L. (Amaranthaceae). Their structures were established on the basis of NMR spectroscopic analysis; the complete 1H and 13C assignments of the compounds were achieved by means of 2D NMR studies.
Received July 21, 1999. Accepted August 26, 1999 相似文献
5.
Concerted Determination of the Hydrogen Atom and Electron Transfer Capacity of Lipid Soluble Reducing Agents
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Solomon Mengistu Lemma Matteo Scampicchio Andrea Bulbarello Marco Mason Loni Schweikert 《Electroanalysis》2014,26(7):1582-1587
This paper describes a method based on square wave voltammetry to evaluate either the electron transfer or the hydrogen atom transfer of lipid soluble antioxidants such as dl ‐mix‐tocopherol, BHT, ethoxyquin and retynil acetate. The electron transfer (ET) capacity was evaluated by the peak current, peak potential and the area under the anodic wave, whereas the hydrogen atom transfer (HAT) capacity by the kinetic rate of the reaction between antioxidants and 2,2‐Azobis(2‐methylpropionamidine) dihydrochloride (AAPH). The results indicate that ethoxyquin and tocopherol have the highest ET and HAT capacity. However, HAT capacity of tocopherol, BHT and retinyl acetate depend on the concentration. The approach has the advantage to assess HAT and ET capacity of lipid soluble antioxidant in a single concerted protocol. 相似文献
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Lemma Teshome Tufa Khalid Siraj Tesfaye Refera Soreta 《Russian Journal of Electrochemistry》2013,49(1):59-66
Electrochemical application of bismuth film modified glassy carbon electrode was studied with the objective of lead detection. Bismuth film on glassy carbon substrate was formed in a plating solution of 2 mmol/L Bi(NO3)3, in 1 mol/L HCl at ?1.1 V (vs. Ag/AgCl) for 300 s. Lead was detected by differential pulse anodic voltammetry in acetate buffer of pH 5.0 in the concentration range of 7.5 nmol/L to 12.5 μmol/L. Factors influencing the anodic stripping performance, including deposition time, solution pH, Bi(III) concentration, potential, pulse amplitude, pulse width, have been optimized. Three linear calibration plots in the range 7.5 nmol/L to 0.1 μmol/L, 0.25 to 1 μmol/L, 2.5 to 12.5 μmol/L with regression coefficients of 0.991, 0.986 and 0.978 respectively were obtained. The theoretical detection limit equivalent to three times standard deviation for 7.5 nmol/L lead (n = 5) was calculated to be 5.25 nmol/L utilizing a 5 min deposition time and sensitivity 83.97 A L/mol. The sensitivity and detection limit of the method was compared with reported voltammetric methods for detection of lead and the result obtained was found to be promising for determination of lead. 相似文献
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Mulatu Lemma 《Southeast Asian Bulletin of Mathematics》2002,25(4):643-652
Recently the author introduced the logarithmic matrix Lt and studied as it mappings into l. In this paper, we study Lt as mappings into G. The necessary and sufficient conditions for Lt to be G-G is proved. The strengths of Lt in the G-G is settings is investigated. Also, it is shown that Lt is translative in the G-G senses for certain sequences. 相似文献
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The kinetics and mechanism of the hydrolysis of cysteine sulfenyl thiocyanate (CySSCN) to give cysteine thiosulfinate ester (CyS(=O)SCy) have been investigated between pH 0 and 4. The reaction is reversible. The hydrolysis of CySSCN is second-order in [CySSCN] and inverse first-order in [H+] and [SCN-]. The following mechanism is proposed for the hydrolysis of CySSCN (where the charge depends upon the pH): CySSCN0/+ + H2O <==>CySOH0/+ + SCN- + H+, CySOH0/+ + CySSCN0/+ --> CyS(=O)SCy0/+/2+ + SCN- + H+; k1 = 3.36 +/- 0.01 x 10-3 s-1, K1k2 = 0.13 +/- 0.05 Ms-1 (which yields k2/k-1 = 39 M). The observed rate law rules out alternative mechanisms for 1 0.4 M). The following mechanism is proposed: CyS(=O)SCy2+ + H+ <==> CyS(OH)=SCy3+, Ka; CyS(OH)SCy3+ + SCN- --> CySOH+ + CySSCN+, k-2 = 0.239 +/- 0.007 M-2s-1/Ka M-1. Since cysteine sulfenic acids are known to play an important function in many enzymes, and SCN- exists in abundance in physiologic fluids, we discuss the possible role of sulfenyl thiocyanates in vivo. 相似文献
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An Inexpensive and Recyclable Silver‐Foil Catalyst for the Cyclopropanation of Alkenes with Diazoacetates under Mechanochemical Conditions
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Longrui Chen Mark O. Bovee Betsegaw E. Lemma Kimberlee S. M. Keithley Sara L. Pilson Michael G. Coleman James Mack 《Angewandte Chemie (International ed. in English)》2015,54(38):11084-11087
The diastereoselective cyclopropanation of various alkenes with diazoacetate derivatives can be achieved under mechanochemical conditions using metallic silver foil and a stainless‐steel vial and ball system. This solvent‐free method displays analogous reactivity and selectivity to solution‐phase reactions without the need for slow diazoacetate addition or an inert atmosphere. The heterogeneous silver‐foil catalyst system is easily recyclable without any appreciable loss of activity or selectivity being observed. The cyclopropanation products were obtained with excellent diastereoselectivities (up to 98:2 d.r.) and in high yields (up to 96 %). 相似文献