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111.
Anita Rani Surender Kumar N. R. Bannerjee 《Fresenius' Journal of Analytical Chemistry》1987,328(1-2):33-36
Summary A Potassium ion-selective electrode based on dibenzo-18-crown-6-tungstophosphoric acid precipitate membrane is prepared and conditions for the best functioning have been investigated. The working concentration and pH-range of the electrode is 2.0×10–2 to 1.3×10–6 mol/l and 2.9–6.5, respectively. The selectivity coefficient values for a large number of cations are quite low except for caesium and ammonium ions. The electrode can tolerate non-aqueous content upto 20%.
Kaliumion-sensitive Membranelektrode auf Basis von Kronenether-Heteropolysäure相似文献
112.
CHANGES IN TRANSMISSION CHARACTERISTICS OF POLYMETHYLMETHACRYLATE AND CELLULOSE (III) ACETATE DURING EXPOSURE TO ULTRAVIOLET LIGHT 总被引:2,自引:0,他引:2
Steef F. Steeneken Anita G. J. Buma Winfried W. C. Gieskes 《Photochemistry and photobiology》1995,61(3):276-280
Abstract— Ultraviolet-transparent polymethylmethacrylate (PMMA) and cellulose (III) acetate (CA) (often used as a cut-off filter in UVB [280–320 nm] biological effect studies) were exposed to a 20 W Philips TL 12 lamp to examine changes in transmission characteristics due to UVB exposure. Transmission of UVB and biologically weighted UVB (UVBE(DNA) ) through PMMA were similar, 88.3 and 83.5%, respectively. The absorption characteristics of PMMA did not change with time at any of the UV irradiance levels applied. However, transmission of UVB and UVBBE(DNA) ) through new CA differed considerably: 59% versus only 11%, respectively. Also, spectral absorption characteristics changed with time due to degradation of CA, at a rate that was dependent on the incident UVB irradiance. The decrease in transmission through CA of both UVB and UVBE(DNA) can be described by exponential functions. The CA that was wrapped around the UV lamp showed dramatic changes in UV absorption over the first few hours of use. However, when CA was placed at a longer distance from the light source initial degradation was less. It is concluded that PMMA can be applied in UV effect studies as a reasonable alternative for quartz. The CA should, however, be used with care, because the large transmission decreases that were observed strongly hamper an accurate calculation of (biologically weighted) UVB dose rates. 相似文献
113.
JPC – Journal of Planar Chromatography – Modern TLC - An HPTLC method has been established for rapid and simple quantitative determination of corosolic acid, a type-II (non-insulin... 相似文献
114.
Tina Brueckner Anita Eberl Sonja Heumann Maike Rabe Georg M. Guebitz 《Journal of polymer science. Part A, Polymer chemistry》2008,46(19):6435-6443
Alkaline and enzymatic hydrolyzes of poly(ethylene terephthalate) fabrics (PET) were mechanistically compared based on released degradation products (HPLC‐UV‐RI) and changes in surface properties [hydrophilicity, cationic dyeing, X‐ray photoelectron spectroscopy (XPS)]. Enzymatic hydrolysis led to an increase in the amount of hydroxyl and carboxyl groups on the surface resulting in an enhanced water absorption and dyeability. Enzymes partially adsorbed to PET fabrics during hydrolysis were completely removed by subsequent extraction according to XPS analysis. In contrast to the enzyme treatment, alkaline hydrolysis did not lead to an increase of hydroxyl and acid groups according to XPS while both treatments caused a substantial increase in hydrophilicity and were more effective on amorphous fibers. Alkaline hydrolysis led to a greater increase in the K/S value after cationic dyeing due to enlarged surface area. Consequently, ESEM‐images demonstrated that alkaline treatment drastically affected the surface morphology of the polymer resulting in crater‐like structures of the fibers, whereas after enzymatic treatment the morphology of the fibers remained unchanged. To reach similar benefits in hydrophilicity, drastically higher amounts of degradation products were released during alkaline hydrolysis as also indicated by >6% weight loss compared to <1% after enzyme treatment. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6435–6443, 2008 相似文献
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The electron affinity and first three ionization potentials of C3 are calculated using the multiconfigurational SCF and configuration interaction methods and by Möller-Plesset perturbation theory. Whereas Koopmans' theorem and SCF calculations indicate that the first cation state is 2Πu, upon inclusion of correlation effects both the 2Σu and 2Σg cation states are found to lie lower in energy. CI calculations indicate that the ground state (2Πg) anion is stable by 1.74 eV. Allowing for the error in the calculated electron affinity of the carbon atom, C3? is estimated to be stable by 2.0 eV, in excellent agreement with the 2.05 eV value determined from recent photodetachment measurements. No excited anion states are found to be bound at the equilibrium geometry of the neutral molecule. 相似文献
117.
A new synthesis of homoisoflavanones (3-benzyl-4-chromanones) 总被引:2,自引:0,他引:2
Two 7-hydroxyhomoisoflavanones (
/
) have been synthesized from corresponding 2'-hydroxydihydrochalcones (
/
) in about 33% overall yields. The stages are : (1) selective protection of C4'-hydroxyl in (
/
) with EtO.CH2Cl (1 molar equiv.) In the presence of dry K2C03 and acetone at r.t.; (ii) reaction with one more molar equiv. of EtO.CH2Cl at 60–70° without Isolating products (
/
) (iii) cyclizatlon of resulting α-hydroxymethyl derivatives (
/
) with 4% aq. aIc. Na2C03 and (iv) deprotection of resulting 7-ethoxymethoxy homoisoflavanones (
/
) with 10% CH30H-HC1. The explanations for the formation of (
/
) and (
/
) are given. 相似文献
118.
Chun Hung Cheng Chon-Huat Goh Anita Lee 《The Journal of the Operational Research Society》1996,47(6):794-802
Many existing solution methodologies for machine assignment problems in group technology do not consider factors such as part demand, operation sequence and cost of intercellular moves. We formulate a 0-1 quadratic programming model that takes into account these factors in machine assignment. Two approaches are proposed to solve this problem. The first is an A*-based approach that generates optimal solutions. The second is a heuristic approach developed to solve problems with large number of machines and/or parts. The heuristic approach is shown to be efficient in producing good solutions in a computational study. 相似文献
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