排序方式: 共有34条查询结果,搜索用时 15 毫秒
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Queiroz Ana Luiza P. Kerins Brian M. Yadav Jayprakash Farag Fatma Faisal Waleed Crowley Mary Ellen Lawrence Simon E. Moynihan Humphrey A. Healy Anne-Marie Vucen Sonja Crean Abina M. 《Cellulose (London, England)》2021,28(14):8971-8985
Cellulose - Microcrystalline cellulose (MCC) is a semi-crystalline material with inherent variable crystallinity due to raw material source and variable manufacturing conditions. MCC crystallinity... 相似文献
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Ion-selective membrane electrodes doped with the urea- or thiourea-functionalised calix[4]arenes, 5,11,17,23-tetra-tert-butyl-25,27-bis[[4-N′-(phenylureido)butyl]oxy]-26,28-dipropoxy calix[4]arene (I) and 5,11,17,23-tetra-tert-butyl-25,27-bis[[4-(N′-phenylthioureido)-butyl]oxy]-26,28-dipropoxy calix[4]arene (II), were evaluated for anion sensing. Potentiometric results show that these calixarene ionophore-based membrane electrodes exhibit a good sensitivity to aqueous solutions of the monohydrogen orthophosphate species HPO42− in the concentration range 5.0 × 10−5 to 1.0 × 10−1 M, with near-Nernstian response slopes of −33.0 and −28.0 mV dec−1 for ionophores I and II, respectively. Selectivity coefficient values for monohydrogen orthophosphate over a range of common anions were determined by the fixed interference and matched potential methods and indicated that these membrane electrodes exhibit a good selectivity for HPO42− with respect to the other anions, including sulfate and nitrate. 相似文献
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Marie Kissane Orla A. McNamara David Mitchell David M. Coppert Humphrey A. Moynihan Kurt T. Lorenz Anita R. Maguire 《Tetrahedron letters》2012,53(4):403-405
The palladium-catalysed decarboxylative cross-coupling of heterocyclic aromatic carboxylates and aryl halides is described. The cross-coupling proceeds under relatively mild conditions using catalytic Pd(0) and tetrabutylammonium bromide (TBAB). Utilizing a mixed solvent system consisting of N,N-dimethylformamide (DMF) and N-methyl-2-pyrrolidone (NMP), the cross-coupling system operated at temperatures ranging from 80 to 140 °C. 相似文献
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The order parameter model assumes that the state of a glass or liquid depends on T, P and a number of order parameters Zi. Structural relaxation is due to the kinetically impeded evolution of the order parameters following a rapid change in T or P. The linear relaxation function for the evolution of property Q (V or H) in response to a change in X (T or P) is of the form φQX = ΣigiQX exp(?tτi). Expressions are derived for the qeighting coefficients giQX in terms of the dependences of V and H on the various order parameters. It is shown that giVT = giHP and that giVTgiHP/giVPgiHT = II, where II is the Prigogine-Defay ratio. The corresponding relations among the relaxation functions are φVT = φHP and φVTφHP/φVPφHT ? II. The predictions of the order parameter model for structural relaxation are compared with and found generally to agree with existing literature data. A number of suggestions for future investigations to test this model are made. 相似文献
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Electrical conductivity σ0 and electric field relaxation measurements have been carried out as a function of thermal history for two alkali silicate glasses, Na2O3SiO2 and K2O3SiO2. Specimens of each glass with three different thermal histories, two of the anneal-and-quench type and one of the rate-cool type, were studied. The average structural or fictive temperature Tf of each of the specimens was characterized by measuring their indices of refraction. Effects of thermal history on σ0 and its activation enthalpy were in accord with results of previous investigators. That is, for a given type of thermal history σ0 was lower and higher the lower Tf. In addition it was found that for two specimens with the same Tf or index of refraction but different thermal histories the rate-cooled specimen exhibited a lower conductivity than the annealed-and-quenched specimen, in accord with the results of Ritland. The distribution of relaxation times τσ for decay of the electric field due to ionic migration was found to be due primarily to a distribution in the pre-exponential term ln in the equation ; the distribution in was extremely narrow. Differences in thermal history caused small differences in the distribution of τσ, but no difference in the average activation enthalpy for τσ. From this result it appeared that the dependence of the conductivity activation enthalpy on thermal history was due to the effect of thermal history on the temperature dependence of the distribution in τσ. 相似文献
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A study of infrared absorption in the 250–4000 cm?1 region has been carried out for 0.5 As2Se30.5 GeSe2 glasses quantitatively doped with oxide impurity. The frequencies of the intrinsic 2- and 3-phonon absorption bands at 490 and 690 cm?1 correspond well to those predicted from combinations of the high frequency bands in the first order IR and Raman spectra of As2Se3 and GeSe2 glasses.Glasses doped with As2O3 exhibit the same oxide impurity absorptionbands as those doped with GeO2. Unlike As2Se3 glass, at impurity concentrations up to 1000 ppm As2O3, 0.5 As2Se30.5 GeSe2 glass exhibits only one major oxide impurity species, characterized by absorption bands at 780 and 1260 cm?1 and due to oxygen bonded to network Ge. The observation of a much weaker network AsO vibration band at 670 cm?1 confirms that oxygen bonds preferentially to Ge in this glass. The same minor oxide species appears to determine excess IR absorption at the CO2 laser wavelength of 10.6 μm in both As2Se3 and 0.5 As2Se3 0.5 GeSe2 glasses. The frequencies and intensities of absorption bands due to hydrogen impurities are also quite comparable for these two materials. 相似文献
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Complex impedance plots for a 25 Na2O?75 SiO2 glass exposed to the ambient atmosphere indicate the presence of a relaxation at frequencies well below those for the electrical relaxation of the bulk material, but above the frequencies where electrode polarization takes place. This low frequency relaxation is shown to occur in a high resistivity surface layer having a thickness a few times 0.1 μm and formed by the action of atmospheric water vapor. The rate of growth of the surface layer could be monitored by means of the impedance measurements and was found to decrease with the duration of exposure of the glass to the laboratory atmosphere. Complex impedance plots for a chemically durable lithium aluminosilicate glass indicate that the hydrated surface layer thickness is much smaller than in the 25 Na2O?75 SiO2 glass. 相似文献