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81.
Photooxygenation of Furylalkylamines: Easy Access to Pyrrolizidine and Indolizidine Scaffolds 下载免费PDF全文
Dr. Dimitris Kalaitzakis Myron Triantafyllakis Manolis Sofiadis Dr. Dimitris Noutsias Prof. Dr. Georgios Vassilikogiannakis 《Angewandte Chemie (International ed. in English)》2016,55(14):4605-4609
A highly adaptable method targeting the ubiquitous and very important pyrrolizidine and indolizidine scaffolds is presented. The general synthetic utility of the method is underscored by its application to the rapid and easy synthesis of five natural products starting from readily accessible alkylfuran precursors. These unprotected primary furylalkylamines are subjected to photooxygenation conditions, which initiate a complex cascade reaction sequence concluding with the production of high value motifs. This sequence can be tailored to need by varying the choice of both photosensitizer and base additive. 相似文献
82.
Dimitris Georgiou Athanasios Megaritis Kyriakos Papadopoulos Vasilios Petropoulos 《Quaestiones Mathematicae》2016,39(3):363-379
Let Y and Z be two fixed topological spaces and C(Y, Z) the set of all continuous maps from Y into Z. We construct and study topologies on C(Y, Z) that we call Fn(τn)-family-open topologies. Furthermore, we find necessary and su?cient conditions such that these topologies to be splitting and jointly continuous. Finally, we present questions concerning a further study on this area. 相似文献
83.
Christopher C. Chang Dimitris N. Politis 《Journal of computational and graphical statistics》2016,25(1):144-166
In this article, we introduce a new class of robust autocorrelation estimators based on interpreting the sample autocorrelation function as a linear regression. We investigate the efficiency and robustness properties of the estimators that result from employing three common robust regression techniques. We discuss the construction of robust autocovariance and positive definite autocorrelation estimates, and their application to AR model fitting. We perform simulation studies with various outlier configurations to compare the different estimators. 相似文献
84.
Bulk Free Radical Polymerization of Methyl Methacrylate and Vinyl Acetate: A Comparative Study 下载免费PDF全文
David Victoria‐Valenzuela Jorge Herrera‐Ordonez Gabriel Luna‐Barcenas George D. Verros Dimitris S. Achilias 《大分子反应工程》2016,10(6):577-587
The model and methodology for estimating diffusion‐controlled rate coefficients for the methyl methacrylate (MMA) polymerization system is extended to the vinyl acetate (VAc) case. Comparison of the kinetic behavior and termination rate coefficients (kt) of both monomers suggests that at low conversions the termination reaction is controlled by the chemical step, whereas at moderate and high conversions it is controlled by the diffusive step which in turn is determined by the segmental diffusion of the long radicals and not by the center of mass diffusion of short radicals. It is found that, for most of the conversion range, diffusion coefficient for VAc is lower than the one for MMA notwithstanding that ktVAc > ktMMA. An explanation of this apparent inconsistency on the base of the model results and in terms of segmental mobility is proposed.
85.
Agrafiotis DK Bandyopadhyay D Farnum M 《Journal of chemical information and modeling》2007,47(1):69-75
A new radial space-filling method for visualizing cluster hierarchies is presented. The method, referred to as a radial clustergram, arranges the clusters into a series of layers, each representing a different level of the tree. It uses adjacency of nodes instead of links to represent parent-child relationships and allocates sufficient screen real estate to each node to allow effective visualization of cluster properties through color-coding. Radial clustergrams combine the most appealing features of other cluster visualization techniques but avoid their pitfalls. Compared to classical dendrograms and hyperbolic trees, they make much more efficient use of space; compared to treemaps, they are more effective in conveying hierarchical structure and displaying properties of nodes higher in the tree. A fisheye lens is used to focus on areas of interest, without losing sight of the global context. The utility of the method is demonstrated using examples from the fields of molecular diversity and conformational analysis. 相似文献
86.
The supercritical mixture ethanol-carbon dioxide (EtOH-CO2) with mole fraction of ethanol X(EtOH) congruent with 0.1 was investigated at 348 K, by employing the molecular dynamics simulation technique in the canonical ensemble. The local intermolecular structure of the fluid was studied in terms of the calculated appropriate pair radial distribution functions. The estimated average local coordination numbers and mole fractions around the species in the mixture reveal the existence of local composition enhancement of ethanol around the ethanol molecules. This finding indicates the nonideal mixing behavior of the mixture due to the existence of aggregation between the ethanol molecules. Furthermore, the local environment redistribution dynamics have been explored by analyzing the time correlation functions (TCFs) of the total local coordination number (solvent, cosolvent) around the cosolvent molecules in appropriate parts. The analysis of these total TCFs in the auto-(solvent-solvent, cosolvent-cosolvent) and cross-(solvent-cosolvent, cosolvent-solvent) TCFs has shown that the time dependent redistribution process of the first solvation shell of ethanol is mainly determined by the redistribution of the CO2 solvent molecules. These results might be explained on the basis of the CO2-CO2 and EtOH-CO2 intermolecular forces, which are sufficiently weaker in comparison to the EtOH-EtOH hydrogen bonding interactions, creating in this way a significantly faster redistribution of the CO2 molecules in comparison with EtOH. Finally, the self-diffusion coefficients and the single reorientational dynamics of both the cosolvent and solvent species in the mixture have been predicted and discussed in relationship with the local environment around the species, which in the case of the EtOH molecules seem to be strongly affected. 相似文献
87.
Afrati T Dendrinou-Samara C Raptopoulou C Terzis A Tangoulis V Kessissoglou DP 《Dalton transactions (Cambridge, England : 2003)》2007,(44):5156-5164
The use of phenyl 2-pyridyl ketoxime (PhPyCNO)/X(-)"blends" (X(-) = OH(-), Cl(-), ClO(4)(-)) in copper chemistry has yielded trinuclear clusters that have been characterized as inverse-9-metallacrown-3 accommodating one or two anions. The magnetic behaviour has shown a large antiferromagnetic interaction. The discrepancy between the Brillouin curve and the experiment has been assigned to the influence of the antisymmetric interaction. By introducing in the magnetization formula the antisymmetric terms derived from the fitting of the susceptibility data the simulated curve become almost superimposable to the experimental one. From the EPR findings it has been shown that the compound [Cu(3)(PhPyCNO)(3)(OCH(3))(Cl)(ClO(4))] () having isosceles magnetic symmetry or lower (delta not equal 0), the antisymmetric exchange is important (G not equal 0) and DeltaE > hv. The structures of the two complexes have been determined by single-crystal X-ray crystallography. 相似文献
88.
Dimitris Karlis Evdokia Xekalaki 《Annals of the Institute of Statistical Mathematics》1999,51(1):149-162
Poisson mixtures are usually used to describe overdispersed data. Finite Poisson mixtures are used in many practical situations where often it is of interest to determine the number of components in the mixture. Identifying how many components comprise a mixture remains a difficult problem. The likelihood ratio test (LRT) is a general statistical procedure to use. Unfortunately, a number of specific problems arise and the classical theory fails to hold. In this paper a new procedure is proposed that is based on testing whether a new component can be added to a finite Poisson mixture which eventually leads to the number of components in the mixture. It is a sequential testing procedure based on the well known LRT that utilises a resampling technique to construct the distribution of the test statistic. The application of the procedure to real data reveals some interesting features of the distribution of the test statistic. 相似文献
89.
We report on a rheooptical investigation of hairy-rod poly(p-phenylene) solutions at different concentrations and temperatures. These polymers have a reasonably high persistence length
(about 28 nm) and behave as worm-like chains in dilute solutions, whereas they form nearly spherical fractal aggregates with
internal anisotropy at higher concentrations. By exposing these systems to time-dependent simple shear and following the evolution
of birefringence in start-up and its subsequent relaxation upon the cessation of shear, we find a substantial broadening of
the cluster size distribution, resulting from flow-induced cluster deformation and break-up. In contrast to the very dilute
solutions, where polymers align in the flow direction, the deformed clusters main axes are aligned in the vorticity direction,
presumably due to their strong steric local pretransitional type of ordering, with the constituent polymers following the
velocity vector. At the highest concentration, which corresponds to a weak gel, shear is shown to break-up the gel and the
steady-state response of a broad-size aggregate suspension is eventually recovered.
Received: 18 February 1999/Accepted: 6 July 1999 相似文献
90.