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321.
322.
Silicon is an essential trace element and is found in vegetables, fruits, cereals, water, pasta and rice (Oryza sativa). In this work, the silica content of different types of rice grains were measured. Here, we used the heteropoly blue photometric method with a double beam UV-vis spectrophotometer to determine the amount of silicon in rice samples (n = 7) that were collected in the north of Iran. The samples were digested with wet-ashing method by microwave-assisted heating and then treated with ammonium molybdate to produce a yellow color compound in acidic solution (ca. pH 1.2) and then reduced to give a heteropoly compound with a blue color. Analyses were performed using standard addition method and absorbance values were measured with double beam UV-vis spectrophotometer at λmax = 815 nm. Results indicated that the silica content was 307-451 mg/kg for the samples. X-ray diffraction patterns and infra-red spectra were obtained from rice samples without any sample treatment. 相似文献
323.
SHAABANI Ahmad SOLEIMANI Ebrahim SARVARY Afshin REZAYAN Ali Hossein MALEKI Ali 《中国化学》2009,27(2):369-371
The ability of tin(II) chloride dihydrate as a catalyst to promote the three-component condensation reaction from a diversity of aromatic aldehydes, 2-aminopyridines and isonitriles at room temperature is described. This methodology affords a number of 3-aminoimidazo[1,2-a]pyridines in the presence of tin(II) chloride dihydrate as a new and mild Lewis acid catalyst in the multi-component reaction in reasonable yields and short reaction time without any significant optimization of the reaction conditions. 相似文献
324.
Preparation and characterization of novel semi‐interpenetrating polymer network (semi‐IPN) hydrogels based on partially hydrolyzed polyacrylamide (HPAM) and scleroglucan solution crosslinked with chromium triacetate are described. Effects of scleroglucan concentration on the gelation process and swelling behavior of synthesized hydrogels in different media were investigated using dynamic rheometery and swelling tests, respectively. Oscillatory shear rheology showed that the limiting storage modulus of the semi‐IPN gels increased with increase in scleroglucan concentration. It was also found that the viscous energy dissipating properties of the semi‐IPN gels decreased with increase in the crosslinker concentration of the gelation system. In addition, the loss factor slightly decreased by increasing the scleroglucan content, indicating that the viscous properties of this gelling system decreased more than its elastic properties. The swelling tests showed that the equilibrium swelling ratio (ESR) of the semi‐IPN networks decreased with increase in scleroglucan content, due to the decrease of ionic groups of polyelectrolyte hydrogel. However, the semi‐IPN gels showed lower salt sensitivity in synthetic oil reservoir water as compared with HPAM gels. Therefore, these semi‐IPN hydrogels may be considered potentially good candidates for enhanced oil recovery (EOR) applications. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
325.
Mehrorang Ghaedi Ardeshir Shokrollahi Khodabakhsh Niknam Ebrahim Niknam Mustafa Soylak 《Central European Journal of Chemistry》2009,7(1):148-154
A cloud point extraction procedure for the preconcentration of copper, nickel, iron and zinc ions in various samples has been
described. Analyte ions in aqueous phase are complexed with 3-((indolin-3-yl)(phenyl)methyl)indoline (IYPMI) and following
centrifugation quantitatively extracted to the aqueous phase rich in Triton X-114. The surfactant-rich phase was dissolved
in 2.0 mol L−1 HNO3 in methanol prior to metal content determination by flame atomic absorption spectrometry (FAAS). The effects of some parameters
including, the concentrations of IYPMI, Triton X-114 and HNO3, bath temperature, centrifuge rate and time were investigated on the recoveries of analyte ions. At optimum conditions, the
detection limits of (3 SDb m−1) of 1.6, 2.8, 2.1 and 1.1 ng mL−1 for Cu2+, Fe3+, Ni2+ and Zn2+ along with preconcentration factors of 30 and enrichment factor of 48, 39, 34 and 52 for Cu2+, Ni2+, Fe3+ and Zn2+ respectively, were obtained. The proposed cloud point extraction has been successfully applied for the determination of metal
ions in real samples with complicated matrix such as biological, soil and blood samples with high efficiency.
相似文献
326.
Recent work has established a correspondence between the tripartite entanglement measure of three qubits and the macroscopic entropy of the four-dimensional 8-charge STU black hole of supergravity. Here we consider the configurations of intersecting D3-branes, whose wrapping around the six compact dimensions T6 provides the microscopic string-theoretic interpretation of the charges, and associate the three-qubit basis vectors |ABC>, (A, B, C=0 or 1) with the corresponding 8 wrapping cycles. In particular, we relate a well-known fact of quantum information theory, that the most general real three-qubit state can be parameterized by four real numbers and an angle, to a well-known fact of string theory, that the most general STU black hole can be described by four D3-branes intersecting at an angle. 相似文献
327.
Brownmillerite phase is one of the four main phases of Portland cement clinker. It was prepared as pure C4AF1 and C4AF with different amount of SiO2, (5, 10, 15, 20, 25, and 40 mol%) by addition. Pure C4AF was prepared using CaO, Al2O3 and Fe2O3 according to the ratios 4:1:1. Each sample mixture was fired at 1,400°C for 1 h then ground and introduced again to 1,400°C for 1/2 h then quenched in air. The prepared samples were ground and measured using x-ray diffraction, scanning electron microscope, A.C. conductivity and Mössbauer spectroscopy. The results were correlated and discussed. The main finding is the formation of a glassy phase besides the C4AF structure, in addition to the formation of the C2S phase of cement clinker as SiO2 addition was upgraded. The electrical conductivity results showed that the 20 mol% SiO2 sample has the lowest (σ) value. 相似文献
328.
Serhii Shyshkanov Tu N. Nguyen Fatmah Mish Ebrahim Kyriakos C. Stylianou Paul J. Dyson 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(16):5425-5429
Frustrated Lewis pairs (FLPs) consist of sterically hindered Lewis acids and Lewis bases, which provide high catalytic activity towards non‐metal‐mediated activation of “inert” small molecules, including CO2 among others. One critical issue of homogeneous FLPs, however, is their instability upon recycling, leading to catalytic deactivation. Herein, we provide a solution to this issue by incorporating a bulky Lewis acid‐functionalized ligand into a water‐tolerant metal‐organic framework (MOF), named SION‐105 , and employing Lewis basic diamine substrates for the in situ formation of FLPs within the MOF. Using CO2 as a C1‐feedstock, this combination allows for the efficient transformation of a variety of diamine substrates into benzimidazoles. SION‐105 can be easily recycled by washing with MeOH and reused multiple times without losing its identity and catalytic activity, highlighting the advantage of the MOF approach in FLP chemistry. 相似文献
329.
Deependra M. Shakya Otega A. Ejegbavwo Thayalan Rajeshkumar Sanjaya D. Senanayake Amy J. Brandt Sharfa Farzandh Narayan Acharya Amani M. Ebrahim Anatoly I. Frenkel Ning Rui Gregory L. Tate John R. Monnier Konstantinos D. Vogiatzis Natalia B. Shustova Donna A. Chen 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(46):16685-16689
We report the first study of a gas‐phase reaction catalyzed by highly dispersed sites at the metal nodes of a crystalline metal–organic framework (MOF). Specifically, CuRhBTC (BTC3?=benzenetricarboxylate) exhibited hydrogenation activity, while other isostructural monometallic and bimetallic MOFs did not. Our multi‐technique characterization identifies the oxidation state of Rh in CuRhBTC as +2, which is a Rh oxidation state that has not previously been observed for crystalline MOF metal nodes. These Rh2+ sites are active for the catalytic hydrogenation of propylene to propane at room temperature, and the MOF structure stabilizes the Rh2+ oxidation state under reaction conditions. Density functional theory calculations suggest a mechanism in which hydrogen dissociation and propylene adsorption occur at the Rh2+ sites. The ability to tailor the geometry and ensemble size of the metal nodes in MOFs allows for unprecedented control of the active sites and could lead to significant advances in rational catalyst design. 相似文献
330.
Ebrahim Ghaderpour 《Discrete Mathematics》2018,341(1):277-285
Craigen introduced and studied signed group Hadamard matrices extensively and eventually provided an asymptotic existence result for Hadamard matrices. Following his lead, Ghaderpour introduced signed group orthogonal designs and showed an asymptotic existence result for orthogonal designs and consequently Hadamard matrices. In this paper, we construct some interesting families of orthogonal designs using signed group orthogonal designs to show the capability of signed group orthogonal designs in generation of different types of orthogonal designs. 相似文献