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991.
Proposed substitution of apolane-87 for squalane as a nonpolar reference phase in gas chromatography
Squalane is the standard, nonpolar reference phase used in schemes to characterize the solvent strength and selectivity of stationary phases in gas-liquid chromatography. A commentary, supported by additional experimental evidence, is provided to indicate a lack of suitability for this purpose. Primary objections to its use as a reference phase are its high volatility, compositional variations due to the presence of impurities, susceptibility to oxidative degradation, poor film forming and stabilizing properties, and retention properties that are strongly influenced by the character and treatment of the support used to prepare column packings. Because similar problems were not observed, or were much less significant, for the synthetic hydrocarbon Apolane-87, its use as a reference phase is to be preferred. Reference values for retention indexes, gas—liquid partition coefficients, and partial molal Gibbs free energies of solution for a series of solvent-selectivity test solutes are provided for both phases. 相似文献
992.
993.
Some results that have been obtained in the study of strongly and weakly ergodic behavior of non-homogeneous stochastic kernels
are generalized to the case of non-negative kernels. The first generalization simply involves extending the definitions of
weakly and strongly ergiodic behavior to the case of non-negative kernels and using the ergodic coefficient which was first
defined for stochastic kernels by Dobrushin and extended to non-negative kernels by Blum and Reichaw. It happens that this
straightforward extension excludes many cases of non-negative kernels which do exhibit a types of ergodic behavior. In order
to study these cases a definition ofL
1 weakly and strongly ergodic behavior is given in which normalizing by constants is allowed. Sufficient conditions for these
types of ergodic behavior are given. 相似文献
994.
995.
996.
If X1 and X2 are independent and identically distributed (i. i. d.) with finite variance, then has the same distribution as X1 if and only if X1 is normal with mean zero (Pólya [9]). The idea of using linear combinations of i. i. d. random variables to characterize the normal has since been extended to the case where σ∞i=1aiXi has the same distribution as X1. In particular if at least two of the ai's are non-zero and X1 has finite variance, then Laha and Lukacs [8] showed that X1 is normal. They also [7] established the same result without the assumption of finite variance. The purpose of this note is to present a different and easier proof of the characterization under the assumption of finite variance. The idea of the proof follows closely the approach used by Pólya in [9]. The same technique is also used to give a characterization of the exponential distribution. 相似文献
997.
Further calculations have been performed for the dissociation of H2 on copper in which the empirical potential surface has been increased in roughness as suggested by our previous studies. This change is effected through an increase in the barriers to adatom surface diffusion, keeping the minimum energy requirements for dissociation about the same. The result is to bring the calculation into satisfactory agreement with molecular beam experiments. We examine the effect of changing the internal energy (vibration and rotation), mass, (D2), the adatom binding site, and evaluate the validity of the correlating parameter E⊥ = Ecos2θ. 相似文献
998.
Bruce Bowerman H.T. David Dean Isaacson 《Stochastic Processes and their Applications》1977,5(3):221-230
If P is a stochastic matrix corresponding to a stationary, irreducible, positive persistent Markov chain of period d>1, the powers Pn will not converge as n → ∞. However, the subsequences Pnd+k for k=0,1,...d-1, and hence Cesaro averages Σnk-1 Pk/n, will converge. In this paper we determine classes of nonstationary Markov chains for which the analogous subsequences and/or Cesaro averages converge and consider the rates of convergence. The results obtained are then applied to the analysis of expected average cost. 相似文献
999.
1000.
We show that if G is a 3-connected graph of order at least seven, then every longest path between distinct vertices in G contains at least two contractible edges. An immediate corollary is that longest cycles in such graphs contain at least three contractible edges. 相似文献