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951.
This study compared two methods, corrected (separation of T(1) and T(2)* effects) and uncorrected, in order to determine the suitability of the perfusion and permeability measures through Delta R(2)* and Delta R(1) analyses. A dynamic susceptibility contrast dual gradient echo (DSC-DGE) was used to image the fixed phantoms and flow phantoms (Sephadex perfusion phantoms and dialyzer phantom for the permeability measurements). The results confirmed that the corrected relaxation rate was linearly proportional to gadolinium-diethyltriamine pentaacetic acid (Gd-DTPA) concentration, whereas the uncorrected relaxation rate did not in the fixed phantom and simulation experiments. For the perfusion measurements, it was found that the correction process was necessary not only for the Delta R(1) time curve but also for the Delta R(2)* time curve analyses. Perfusion could not be measured without correcting the Delta R(2)* time curve. The water volume, which was expressed as the perfusion amount, was found to be closer to the theoretical value when using the corrected Delta R(1) curve in the calculations. However, this may occur in the low concentration of Gd-DTPA in tissue used in this study. For the permeability measurements based on the two-compartment model, the permeability factor (k(ev); e = extravascular, v = vascular) from the outside to the inside of the hollow fibers was greater in the corrected Delta R(1) method than in the uncorrected Delta R(1) method. The differences between the corrected and the uncorrected Delta R(1) values were confirmed by the simulation experiments. In conclusion, this study proposes that the correction for the relaxation rates, Delta R(2)* and Delta R(1), is indispensable in making accurate perfusion and permeability measurements, and that DSC-DGE is a useful method for obtaining information on perfusion and permeability, simultaneously. 相似文献
952.
Li-cheng Song Wen-xiong Zhang Qing-mei Hu Li-qun Zhao 《Transition Metal Chemistry》2004,29(6):603-606
A new bridged bipyridine ligand, 4-pyridinecarboxylic acid diethylene glycol diester (pcadgd) (1), was synthesized in 86% yield via a one pot reaction of 4-pyridinecarboxylic acid with SOCl2 followed by treatment of the intermediate 4-pyridinecarboxylic acid chloride with diethylene glycol in the presence of Et3N in CH2Cl2. Interestingly, the self-assembly reaction of this ligand with copper(I) bromide in a mixed solvent Me2CO/MeCN resulted in formation of a novel bicyclic dimer [CuBr(pcadgd)]2
(2) in 83% yield. While ligand (1) was characterized by elemental analysis, i.r., and 1H-n.m.r. spectroscopy, dimer (2) was characterized by elemental analysis, thermogravimetric analysis, i.r., 1H n.m.r., and e.s.r. spectroscopy. The X-ray diffraction analysis revealed that (2) is indeed a bicyclic dimer, in which two 19-membered rings share a Cu—Cu metal–metal bond and each of the two Cu atoms posesses a planar trigonal geometry. In addition, the two bromide(-I) ligands are terminal and the two pcadgd ligands are coordinated to the two Cu atoms through their N atoms. 相似文献
953.
Whereas the rates of propene polymerisation catalysed by zirconocene ion pairs are strongly anion-dependent, hexene polymerisations are not; the findings demonstrate the existence of very different kinetic regimes for two closely related reactions. 相似文献
954.
Song YQ 《Magnetic resonance imaging》2003,21(3-4):207-211
Diffusion in porous media has been used as a probe of pore geometry in various NMR techniques. We will examine the effect of time-dependent diffusion in CPMG by showing that the diffusion time in CPMG is approximately the echo time, even in grossly inhomogeneous magnetic fields. Extension of the diffusion time in modified CPMG sequences is discussed. Diffusion in the susceptibility-contrast induced internal field is discussed as a means to probe pore size and pore shape. Finally, we present the general concept of two-dimensional relaxation-type experiments for study of molecules, fluids, materials and their dynamics that are characterized by spin relaxation and diffusion. 相似文献
955.
Song YQ Hürlimann MD Flaum C 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2003,161(2):222-233
This paper describes a method to determine molecular displacements as a function of time in just two scans: one reference scan using the Carr-Purcell-Meiboom-Gill (CPMG) sequence, a second scan using a modified CPMG sequence (KCPMG). Measurements on free diffusion in bulk fluids, and on restricted diffusion in porous rock samples are reported. This technique can also be used for rapid measurement of flow and chemical exchange. 相似文献
956.
Song HY Joo JM Kang JW Kim DS Jung CK Kwak HS Park JH Lee E Hong CY Jeong S Jeon K Park JH 《The Journal of organic chemistry》2003,68(21):8080-8087
The proposed structure of lasonolide A was synthesized employing radical cyclization reactions of beta-alkoxyacrylates for preparation of the tetrahydropyranyl units A and B, but the spectroscopic data did not match those of the natural product. Both enantiomers of a revised structure featuring 17E,25Z double bonds were synthesized, and the (-)-isomer was found to be the biologically active enantiomer. 相似文献
957.
A chemometric resolution method is described for the identification of nitrogen compounds in crude oil. Prefractionation of crude oil into discrete chemical classes was performed by adsorption column chromatography using small quantities of neutral aluminum oxide and silicic acid. Subsequent high-resolution separation of individual components was achieved by using capillary column gas chromatography, and compound types were detected by mass spectrometer. In conjunction with a combined chemometric method, each principal chemical class was further resolved and separated, which made it possible to identify some nitrogen compounds in the investigated oils. To a certain extent, this method could relieve classical analysis of difficulty in identifying those species with poorly low contents or partially chromatographic overlaps, particularly in the cases where authentic standards were not available for addition into the unknown analytical systems to reveal what indeed existed in them. 相似文献
958.
Huh S Wiench JW Trewyn BG Song S Pruski M Lin VS 《Chemical communications (Cambridge, England)》2003,(18):2364-2365
A synthetic method has been developed that can control both multifunctionalization and morphology of the mesoporous organic-inorganic hybrid materials by introducing different molar ratios of organoalkoxysilane precursors to a base-catalyzed co-condensation of silicate. 相似文献
959.
Zhou Z Wang S Zhou W Wang G Jiang L Li W Song S Liu J Sun G Xin Q 《Chemical communications (Cambridge, England)》2003,(3):394-395
A 40 wt% Pt/C cathode electrocatalyst with controlled Pt particle size of approximately 2.9 nm showing better performance than commercial catalyst for direct methanol fuel cell was prepared by a polyol process with water but without using stabilizing agent. 相似文献
960.
High-temperature generalized synthesis of stable ordered mesoporous silica-based materials by using fluorocarbon-hydrocarbon surfactant mixtures 总被引:4,自引:0,他引:4