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81.
Ouriadov AV MacGregor RP Balcom BJ 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2004,169(1):174-186
A multiple echo, single point imaging technique, employing a local surface coil probe, is presented for examination of thin film samples. Depth images with a nominal resolution of 5 microm were acquired with acquisition times on the order of 10 min. The method may be used to observe dynamic phenomenon such as polymerization, wetting, and drying in thin film samples. It is readily adapted to spatially resolved diffusion coefficient and T2 relaxation time mapping. 相似文献
82.
Beer L Britten JF Brusso JL Cordes AW Haddon RC Itkis ME MacGregor DS Oakley RT Reed RW Robertson CM 《Journal of the American Chemical Society》2003,125(47):14394-14403
New synthetic routes to 1,2,3-dithiazolo-1,2,3-dithiazolylium salts, based on double Herz condensations of N-alkylated 2,6-diaminopyridinium salts with sulfur monochloride, have been developed. The two prototypal 1,2,3-dithiazolo-1,2,3-dithiazolyl radicals HBPMe and HBPEt have been prepared and characterized in solution by cyclic voltammetry and EPR spectroscopy. Measured electrochemical cell potentials and computed (B3LYP/6-31G) gas-phase disproportionation enthalpies favor a low on-site Coulombic repulsion energy U in the solid state. The crystal structures of HBPR (R = Me, Et) have been determined by X-ray crystallography (at 293 K). Both consist of slipped pi-stacks of undimerized radicals, with many close intermolecular S- - -S contacts. Magnetic, conductivity, and optical measurements have been performed and the results interpreted in light of extended Hückel band calculations. The crystalline materials are paramagnetic above 100 K, with room-temperature conductivities sigma(RT) of 10(-5)-10(-6) S cm(-1); the slightly greater conductivity of the R = Et compound can be associated with a more well developed band structure. We suggest a Mott-Hubbard insulator ground state for these materials, with an on-site Coulomb repulsion energy U of about 1.0 eV. 相似文献
83.
84.
Beer L Brusso JL Cordes AW Haddon RC Itkis ME Kirschbaum K MacGregor DS Oakley RT Pinkerton AA Reed RW 《Journal of the American Chemical Society》2002,124(32):9498-9509
Alkylation of the zwitterionic heterocycle 8-chloro-bis[1,2,3]dithiazolo[4,5-b:5',4'-e]pyridine (ClBP) with alkyl triflates affords 8-chloro-4-alkyl-4H-bis[1,2,3]dithiazolo[4,5-b:5',4'-e]pyridin-2-ium triflates [ClBPR][OTf] (R = Me, Et, Pr). Reduction of these salts with decamethylferrocene affords the corresponding ClBPR radicals as thermally stable crystalline solids. The radicals have been characterized in solution by cyclic voltammetry and EPR spectroscopy. Measured electrochemical cell potentials and computed (B3LYP/6-31G) gas-phase disproportionation enthalpies are consistent with a low on-site Coulombic barrier U to charge transfer in the solid state. The crystal structures of ClBPR (R = Me, Et, Pr) have been determined by X-ray crystallography (at 293 K). All three structures consist of slipped pi-stacks of undimerized radicals, with many close intermolecular S.S contacts. ClBPMe undergoes a phase transition at 93 K to a slightly modified slipped pi-stack arrangement, the structure of which has also been established crystallographically (at 25 K). Variable-temperature magnetic and conductivity measurements have been performed, and the results interpreted in light of extended Hückel band calculations. The room-temperature conductivities of ClBPR systems (sigma(RT) approximately 10(-)(5) to 10(-)(6) S cm(-)(1)), as well as the weak 1D ferromagnetism exhibited by ClBPMe, are interpreted in terms of weak intermolecular overlap along the pi-stacks. The latter is caused by slippage of the molecular plates, a feature necessitated by the steric size of the R and Cl groups on the pyridine ring. 相似文献
85.
Robert R. MacGregor Joanna S. Fowler Alfred P. Wolf 《Journal of chromatography. A》1992,590(2):354-358
A high-performance liquid chromatographic method has been developed for the quantitation of the enantiomers of cocaine. Mixtures of the naturally occurring (−)-cocaine and synthetically produced (+)-cocaine were hydrolysed in water to (+) and (−)-benzoyl ecgonine. Esterification with an optically pure 2-octanol resulted in diastereoisomers that could be separated on bare silica gel using an acetonitrile-aqueous ammonium phosphate mobile phase. 相似文献
86.
Kim Y.-M. Kostanski L. K. MacGregor J. F. Hamielec A. E. 《Journal of Thermal Analysis and Calorimetry》2004,78(1):153-164
Both epoxides and vinyl ethers can be polymerized cationically albeit through different intermediates. However, in the case
of epoxide-vinyl ether mixtures the exact mechanism of cationically initiated polymerization is unclear. Thus, although vinyl
ethers can be used as reactive diluents for epoxides it is uncertain how they would affect their reactivity. Cationic photocuring
of diepoxides has many industrial applications. Better understanding of the photopolymerization of epoxy-vinyl ether mixtures
can lead to new applications of cationically photocured systems. In this work, photo-DSC and real-time Fourier Transform Infrared
Spectroscopy (RT-FTIR) were used to study cationic photopolymerization of diepoxides and vinyl ethers. In the case of mixtures
of aromatic epoxides with tri(ethylene glycol) divinyl ether, TEGDVE, photo-DSC measurements revealed a greatly reduced reactivity
in comparison to the homopolymerizations and suggested the lack of copolymerization between aromatic epoxides and TEGDVE.
On the other hand, for mixtures of 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexane carboxylate, ECH, with TEGDVE the results
indicated high reactivity of the blends. The polymerization mechanism might include copolymerization. To examine this mechanism,
mixtures of the ECH with a tri(ethylene glycol) mono-vinyl ether, TEGMVE, were studied by both photo-DSC and RT-FTIR. Principal
component analysis (PCA) proved to be an efficient tool in analyzing a large matrix of the spectral data from the polymerization
system. PCA was able to provide insight into the reasons for the differences among replicated experiments with the same composition
ratio and supported the hypothesis of copolymerization in the ECH/TEGMVE system. Thus, blends of cycloaliphatic epoxides and
vinyl ethers seem to have a great potential for applications in high-productivity industrial photopolymerization processes.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
87.
Trevor J. Dines Louise D. MacGregor Colin H. Rochester 《Journal of Raman spectroscopy : JRS》2007,38(7):832-840
The protonation of Disperse Orange 25 (DO25) in aqueous solution, and upon adsorption on oxide surfaces, was studied by resonance Raman (RR) spectroscopy. The neutral and protonated forms of DO25 were modelled by DFT calculations of the isolated molecules in the gas phase at the B3‐LYP/DZ level, enabling calculation of the vibrational spectra of these species, together with vibrational assignments. RR spectra show that DO25 is physisorbed on the SiO2 surface, but its adsorption on SiO2 Al2O3 or H‐mordenite results in protonation. This observation indicates the presence of Brønsted acidic sites on these oxide surfaces with pKa values ⩽2.5. RR studies of the adsorption of DO25 can therefore provide useful information on the nature of surface acidity on oxides, which is complementary to that obtained from other probe molecules. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
88.
S. Franczuk I. J. D. MacGregor J. Ahrens J. R. M. Annand J. F. Arneil R. Beck D. Branford P. Grabmayr S. J. Hall T. Hehl P. D. Harty D. G. Ireland J. D. Kellie K. Livingston J. C. McGeorge F. A. Natter S. Oberkirsch R. O. Owens C. J. Y. Powrie J. Ryckebusch M. Sauer A. Settele D. P. Watts 《Physics letters. [Part B]》1999,450(4):88
The photon asymmetry (Σ) of the 12C(
,pn) reaction has been measured using linearly polarised tagged photons at the Mainz microtron MAMI for Eγ=180–340 MeV. The data have been analysed in separate missing energy (Em) regions corresponding to the ejection of nucleons from (1p)2 and (1p)(1s) shells. The measured Σ values for both Em regions are smaller in magnitude than corresponding 2H data, but the (1p)2 results have a similar Eγ dependence. Calculations of direct two-nucleon emission overestimate the magnitude of Σ at all photon energies. 相似文献
89.
The problem of constructing Steiner minimal trees in the Euclidean plane is NP-hard. When in addition obstacles are present, difficulties of constructing obstacle-avoiding Steiner minimal trees are compounded. This problem, which has many obvious practical applications when designing complex transportation and distribution systems, has received very little attention in the literature. The construction of Steiner minimal trees for three terminal points in the Euclidean plane (without obstacles) has been completely solved (among others by Fermat, Torricelli, Cavallieri, Simpson, Heinen) during the span of the last three centuries. This construction is a cornerstone for both exact algorithms and heuristics for the Euclidean Steiner tree problem with arbitrarily many terminal points. An algorithm for three terminal points in the presence of one polygonal convex obstacle is given. It is shown that this algorithm has the worst-case time complexityO(n), wheren is the number of extreme points on the obstacle. As an extension to the underlying algorithm, if the obstacle is appropriately preprocessed inO(n) time, we can solve any problem instance with three arbitrary terminal points and the preprocessed convex polygonal obstacle inO(logn) time. We believe that the three terminal points algorithm will play a critical role in the development of heuristics for problem instances with arbitrarily many terminal points and obstacles. 相似文献
90.
D. G. Middleton J. R. M. Annand M. Ases Antelo C. Ayerbe P. Barneo D. Baumann J. Bermuth J. Bernauer H. P. Blok R. Böhm D. Bosnar M. Ding M. O. Distler J. Friedrich J. García Llongo D. I. Glazier P. Grabmayr T. Hehl J. Heim W. H. A. Hesselink E. Jans G. Jover Mañas M. Kohl L. Lapikás I. J. D. MacGregor I. Martin J. C. McGeorge H. Merkel P. Merle K. Monstad F. Moschini U. Müller R. Pérez Benito Th. Pospischil M. Potokar G. Rosner M. Seimitz H. de Vries Th. Walcher D. P. Watts M. Weinriefer M. Weiss B. Zihlmann 《Few-Body Systems》2008,44(1-4):171-174
This paper reports on measurements of the 3He(e,e′pp) reaction measured at AmPS and the 3He(e,e′pn) reaction measured at MAMI. The measurements were performed in similar kinematics to allow a comparison to be made between the cross sections of the two reactions. Results are shown for both reactions together with a comparison for the 3He(e,e′pp) data with continuum Faddeev calculations. 相似文献