排序方式: 共有28条查询结果,搜索用时 62 毫秒
1.
The refined theory of the electroviscous lift forces is presented for the case when the separation distance between the particle and the wall is larger than the double-layer thickness. The theory is based on the lubrication approximation for motion of a long cylinder near a solid wall in creeping flow. The approximate analytical formula for the lift force valid for Pe=1 is derived and compared with the results of numerical calculations performed for an arbitrary Peclet number. The resulting electrokinetic lift force exceeds by several orders of magnitude one predicted by the previously developed theories of the lift force. The results for the electroviscous drag force indicate that when the double layer is thin compared with the particle size, the electroviscous drag is only a small correction (at most 10%) to the hydrodynamic drag force acting on a neutral particle moving near the wall. Copyright 2000 Academic Press. 相似文献
2.
3.
4.
5.
6.
Abstract Great interest has been shown in the kinetics and mechanisms of free radical copolymerizations that produce highly alternating copolymers. In many of these systems the production of alternating copolymers seems to arise naturally, while in others it is necessary to add a metal halide or an organometal halide regulating agent to modify reactivities. Much of the interest in alternating radical copolymerizations centers around the precise mechanism of alternation and in particular whether or not any of the alternation arises from the involvement of monomer-monomer donor-acceptor complexes (sometimes called charge-transfer complexes). 相似文献
7.
The crystal and molecular structure of cis-13,13-dimethyl-13-azoniabicyclo[10.1.0]tridecane iodide has been determined by a three-dimensional, single-crystal, x-ray diffraction study. The compound crystallizes in the orthorhombic space group Pnam with cell dimensions aQ = 21.36 ± .01, bO = 9.07, cO = 8.29 Å. The aziridine ring is fused to the cyclododecane ring with fusion angles of 123.5°. The molecule is bisected by a mirror plane with the cyclododecane portion distorted from its anticipated square conformation. Transannular hydrogen interactions are estimated on the basis of geometric considerations. A final value of R = 0.112 was obtained for the 557 non-equivalent reflections which were observed. 相似文献
8.
Rahman GM Kingston HM Towns TG Vitale RJ Clay KR 《Analytical and bioanalytical chemistry》2005,382(4):1111-1120
Precise and accurate determination of hexavalent chromium in different types of solid environmental sample is regarded as a technical challenge with significant potential error if historically accepted methods are used. Microwave-assisted alkaline extraction (0.5 mol L–1 NaOH+0.28 mol L–1 Na2CO3) followed by anion-exchange chromatographic separation and inductively coupled plasma mass spectrophotometric detection has been shown to provide accurate and precise results. To obtain a better understanding of potential species conversion during and/or after extraction steps, speciated isotope-dilution mass spectrometry (SIDMS) (EPA Method 6800) metrology has been successfully applied as a diagnostic tool with the modified accompanying extraction version of EPA Method 3060A. In our study, aggregate materials distributed over a large area of a major western US state were found to contain a high concentration of total chromium (195±13 to 709±19 g g–1) and significant amounts of Cr6+ (141±6 to 341±29 g g–1) which are at least three orders of magnitude higher than the US EPA threshold limit (0.5 g g–1). Sediment samples from a major western US state, studied independently, were found to contain less (1.77±0.34 g g–1) or no Cr6+ in the presence of significant total chromium. 相似文献
9.
Pedro C. Vasquez Derrick C. Bennett Kishia K. Towns G. Davon Kennedy A. L. Baumstark 《Heteroatom Chemistry》2000,11(4):299-302
A kinetics study of the thermolysis of a series of hexasubstituted‐4,5‐dihydro‐3H‐pyrazoles (pyrazolines 1a: 3,3,4,4‐tetramethyl‐5‐phenyl‐5‐acetoxy; 1b: cis‐3,5‐diphenyl‐3,3,4‐trimethyl‐5‐acetoxy; 1c: cis‐3,5‐diphenyl‐3,4,4‐trimethyl‐5‐methoxy; 1d: 3,3,5‐triphenyl‐4,4‐dimethyl‐5‐acetoxy), which produced the corresponding hexasubstituted cyclopropanes 2a–d in quantitative yields was carried out. The first order rate constants (k1) for thermal decomposition and activation parameters were determined. The relative reactivity series was found to be 1d >> 1b ∼ 1c > 1a. The activation parameters for thermolysis were found to be: for 1a ΔH‡ = 39.8 kcal/mol, ΔS‡ = 14 eu, k150° = 6.8 × 10−5 s−1; for 1b ΔH‡ = 33.5 kcal/mol, ΔS ‡ = 0.2 eu, k150° = 1.7 × 10−4s−1; for 1c ΔH‡ = 32.7 kcal/mol, ΔS‡ = −1.8 eu, k150° = 1.2 × 10−4s−1; for 1d ΔH‡ = 30.1 kcal/mol, ΔS‡ = −1.6 eu, k150° = 8.8 × 10−3s−1. The effect of variation of C3 substituents on the activation parameters for thermolysis paralleled the trend reported for acyclic analogs. The results are consistent with the formation of a (singlet) 1,3‐diradical intermediate with subsequent closure to yield the cyclopropanes. The mechanism of diradical formation appears to involve N2‐C3 bond cleavage as the rate determining step rather than simultaneous two bond scission. © 2000 John Wiley & Sons, Inc. Heteroatom Chem 11:299–302, 2000 相似文献
10.