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71.
A mathematical method for the calculation of the dead time (tm) in HPLC was evaluated using a computer simulation approach, in which artificial perturbations were introduced to Simulated homolog retention times. The calculation was based on a modified and extended Grobler and Bálisz (GB) method. Investigated wav how the precision of the calculated tM is affected by: statistical fluctuations in retention times and which, and how many homolog retention times are used. Based on these simulations a two-step procedure for the tM calculation is proposed: In the first step the linearity of log tR, n vs carbon number n is checked using as many homolog retention times as possible. The slope value bo of the first linear regression in the GB method is used for the selection of homolog retention times in the final tM calculation. In the second step the optimal selection of homologs is made and the final tM calculation is carried out. Guidelines for homolog selection are given. 相似文献
72.
M. Karppinen Y. Morita I. Grigoraviciute R.S. Liu 《Journal of solid state chemistry》2005,178(11):3464-3470
Superconductivity characteristics have been systematically evaluated for a two-CuO2-plane copper oxide system, (Cu,Mo)-12s2, upon increasing the number of fluorite-structured layers, s, between the two CuO2 planes. Essentially single-phase samples of (Cu0.75Mo0.25)Sr2YCu2O7+δ (s=1), (Cu0.75Mo0.25)Sr2(Ce0.45Y0.55)2Cu2O9+δ (s=2) and (Cu0.75Mo0.25)Sr2(Ce0.67Y0.33)3Cu2O11+δ (s=3) were synthesized through a conventional solid-state route in air. To make the samples superconductive an additional high-pressure oxygenation (HPO) treatment was required. Such treatment (carried out at 5 GPa and 500 °C in the presence of 75 mol% Ag2O2 as an oxygen source to maximize the Tc) compressed the crystal lattice for the three members of the (Cu0.75Mo0.25)-12s2 series equally, i.e., by 0.01 Å for the a parameter and by 0.07 Å for the c parameter per formula unit. From both Cu L-edge and O K-edge XANES spectra the s=1 sample was found to possess the highest overall hole-doping level among the HPO samples. Accordingly it exhibited the best superconductivity characteristics. With increasing s, both the Tc (s=1: 88 K, s=2: 61 K, s=3: 53 K) and Hirr values got depressed, being well explained by the trend of decreasing CuO2-plane hole concentration with increasing s as revealed from O K-edge XANES spectra for the same samples. Hence, the present results do not suggest any significant (negative) impact on the superconductivity characteristics from the gradually thickened fluorite-structured block itself. 相似文献
73.
Renee J. Soukup-Hein Jeff Schneiderheinze Paul Mehelic Daniel W. Armstrong 《Chromatographia》2007,66(7-8):461-468
Previous work on the LC separation of peptides had shown that macrocyclic glycopeptide stationary phases to be selective for
peptides of five to thirteen amino acids in length. In this work, the selectivity of the teicoplanin stationary phase is compared
to that of a C18 stationary phase for seven diastereomeric enkephalin peptides. The teicoplanin stationary phase separated
all seven diastereomeric enkephalin peptides in a single chromatographic run. The insertion of d-amino acids into the primary enkephalin sequence produced areas of hydrophobicity that influenced retention order on the
C18 stationary phase. However, analogous trends are not observed on the teicoplanin stationary phase, which is more polar
and structurally diverse. Optimization of the mobile phase and the use of a step-gradient for the enkephalin separation on
the teicoplanin stationary phase is discussed. Also, the selectivity of macrocyclic glycopeptide stationary phases for peptides
of 14, 28, 30, and 36 amino acids also is investigated and compared to separation on a C18 stationary phase. A method for
eluting peptides with multiple basic amino acids, which tend to be strongly retained on the macrocyclic glycopeptide stationary
phases, is presented. 相似文献
74.
A. A. Chesnyuk S. N. Mikhaylichenko L. D. Konyushkin S. I. Firgang V. N. Zaplishnyi 《Russian Chemical Bulletin》2005,54(8):1900-1906
New 1,2,4-oxadiazolyl-1,3,5-triazines were synthesized from amidoximes derived from sym-triazine mononitriles. The structure of one of the resulting compounds was studied in detail by X-ray diffraction.
__________
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1845–1850, August, 2005. 相似文献
75.
阶梯扫描伏安法与线性扫描伏安法相关性的理论研究——简单可逆体系 总被引:1,自引:0,他引:1
本文采用Reimann-Stielties(黎曼-斯堤杰斯)级数展开法,指导了简单可逆电极体系的线性扫描伏安法和阶梯扫描伏安法的电流方程式,得到了能有机地统一的这两种最大为基本的伏安法的电流函数表达式,表达式简明直观,在无因次电流函数的基础详细讨论了制约阶梯扫描伏安法和线性扫描伏安法之间相关性程度的各因素,获得了一些新的结论。 相似文献
76.
Examples of exact expressions for the moments (mainly of the mean) of functions of sample moments are given. These provide checks on alternative developments such as asymptotic series for n, and simulation processes. Exact expressions are given for the mean of the square of the sample coefficient of variation, particularly in uniform sampling; Frullani integrals studied by G. H. Hardy arise. It should be kept in mind that exact results for (joint) moment generating functions (mgfs) are of interest as they produce a means of obtaining exact results for (cross) moments—including moments with negative indices. Thus an exact expression for the joint mgf of the 1st two noncentral moments can be used to obtain the mean of the (c.v.)2 (but not for the mean of the c..). A general expression is given for the moment generating function of the sample variance. The limitations of Fisher's symbolic formula for the characteristic function of sample moments (or more general statistics) are noted.This research was sponsored by the Applied Mathematical Sciences Research program, Office of Energy Research, U. S. Department of Energy under contract DE-AC0584OR21400 with the Martin Marietta Energy Systems. Inc. 相似文献
77.
With some applications in view, the following problem is solved in some special case which is not too special. LetF(s) =Σ
n
∞
=1an
λ
n
−s
be a generalized Dirichlet series with 1 =λ
1 <λ
2 < …,λ
n≤Dn, andλ
n+1 -λ
n ≥D
− 1
λ
n+1
− a
where α>0 andD(≥ 1) are constants. Then subject to analytic continuation and some growth conditions, a lower bound is obtained for
. These results will be applied in other papers to appear later. 相似文献
78.
Michel Talagrand 《Journal of Theoretical Probability》1992,5(2):327-331
Consider a (complex) Banach spaceX, such thatX CO, and vectors(X
i
)
i
ofX. Consider an independent standard normal sequence(g
i
)
i
. Then if anX-valued random Fourier series |k|
n
e
ikt
g
k
x
k
satisfies
相似文献
79.
The paper shows a computer-assisted procedure for the optimization of selectivity of two columns coupled in series by tuning the working temperature (using the isothermal mode) and columns coupling-point pressure at constant inlet and outlet carrier gas pressures. The optimization procedure validation was tested by the separation of 32 hydrocarbons in a column series with the aim to resolve the maximum number of components in the shortest possible analysis time.Dedicated to Professor J. F. K. Huber on the occasion of his 65th birthday 相似文献
80.
This paper investigates the rotating flow and heat transfer of a viscous fluid induced by a stretching surface. The nonlinear problem subject to a given skin friction at the boundary is solved. Analytic solution is obtained using homotopy analysis method. The velocity, temperature, and stretching velocity is calculated for different values of the rotation parameter (λ). The obtained results are compared with the well known results of rotating flow induced by a stretching surface by using four sets of boundary conditions. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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