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111.
112.
Billen J Guillarme D Rudaz S Veuthey JL Ritchie H Grady B Desmet G 《Journal of chromatography. A》2007,1161(1-2):224-233
To study the influence of the particle size distribution (PSD), we measured the chromatographic performance of a series of sub-2 microm particle high performance liquid chromatography (HPLC) columns packed with four different particle mixtures having a purposely imposed different size distribution. Using the reduced kinetic plot representation by plotting the separation impedance (E(0)) versus the plate number ratio (N(opt)/N), the different columns could be classified according to their chromatographic performance without the need to specify a mean particle diameter or a molecular diffusion coefficient, as is needed in the classical reduced plate height and flow resistance analysis. The present analysis shows that it is not so much the width or span of the particle size distribution, but rather the presence of fines that greatly determines the chromatographic performance of particulate columns. 相似文献
113.
Srinivasan S Lee MW Grady MC Soroush M Rappe AM 《The journal of physical chemistry. A》2011,115(6):1125-1132
This paper presents computational evidence for the occurrence of diradical mechanism of self-initiation in thermal polymerization of methyl methacrylate. Two self-initiation mechanisms of interest were explored with first-principles density functional theory calculations. Singlet and triplet potential energy surfaces were constructed. The formation of two Diels-Alder adducts, cis- and trans-dimethyl 1,2-dimethylcyclobutane-1,2-dicarboxylate and dimethyl 2-methyl-5-methylidene-hexanedioate, on the singlet surface was identified. Transition states were calculated using B3LYP/6-31G* and assessed using MP2/6-31G*. The calculated energy barriers and rate constants with different levels of theory were found to show good agreement to corresponding data obtained from laboratory experiments. The presence of a diradical intermediate on the triplet surface was identified. When MCSCF/6-31G* was used, the spin-orbit coupling constant for the singlet to triplet crossover was calculated to be 2.5 cm(-1). The mechanism of monoradical generation via a hydrogen abstraction by both triplet and singlet diradicals from a third monomer was identified to be the most likely mechanism of initiation in spontaneous polymerization of methyl methacrylate. 相似文献
114.
Complexity in human transportation networks: a comparative analysis of worldwide air transportation and global cargo-ship movements 总被引:2,自引:0,他引:2
O. Woolley-Meza C. Thiemann D. Grady J. J. Lee H. Seebens B. Blasius D. Brockmann 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,84(4):589-600
We present a comparative network-theoretic analysis of the two largest global
transportation networks: the worldwide air-transportation network (WAN) and the global
cargo-ship network (GCSN). We show that both networks exhibit surprising statistical
similarities despite significant differences in topology and connectivity. Both networks
exhibit a discontinuity in node and link betweenness distributions which implies that
these networks naturally segregate into two different classes of nodes and links. We
introduce a technique based on effective distances, shortest paths and shortest path trees
for strongly weighted symmetric networks and show that in a shortest path tree
representation the most significant features of both networks can be readily seen. We show
that effective shortest path distance, unlike conventional geographic distance measures,
strongly correlates with node centrality measures. Using the new technique we show that
network resilience can be investigated more precisely than with contemporary techniques
that are based on percolation theory. We extract a functional relationship between node
characteristics and resilience to network disruption. Finally we discuss the results,
their implications and conclude that dynamic processes that evolve on both networks are
expected to share universal dynamic characteristics. 相似文献