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41.
Applied Biochemistry and Biotechnology - 相似文献
42.
Discrimination of components in atherosclerotic plaques from human carotid endarterectomy specimens by magnetic resonance imaging ex vivo 总被引:3,自引:0,他引:3
Morrisett J Vick W Sharma R Lawrie G Reardon M Ezell E Schwartz J Hunter G Gorenstein D 《Magnetic resonance imaging》2003,21(5):465-474
Specific MRI techniques have been used to determine the dimensional and compositional properties of atherosclerotic lesions in carotid endarterectomy tissues. A quantitative comparison of areas of specific features in typical tissue segments was performed using MR images and histologic images. The mean difference for the measurements by the two methods was 4.5% for the total vessel, 5.3% for the internal carotid artery lumen, and 5.0% for the external carotid lumen. For other less abundant components, the mean difference was 14.2%. For direct characterization, individual tissue components were isolated by microdissection and their T1 and T2 relaxation times measured. Highly calcified areas typically had rather short T1 (452-837 ms) and short T2 (10.4-18.4 ms). In contrast, regions enriched in lipid had much longer T1 (1,380-1,480 ms) and longer T2 (35.3-49.0 ms). Other components such as thrombus had intermediate T1 (1,180 ms) and short T2 (15.4 ms). T2 parametric imaging was used as a complementary approach for segmentation and quantitation of tissue components. In fresh tissue, several different components exhibited different T2 ranges: calcified/solid lipid (13-18 ms). cellular/ECM (9-30 ms), fluid lipid (35-40 ms): fibrous (50-60 ms). These results demonstrate the utility of MRI for identifying and quantifying specific components of atherosclerotic plaque ex vivo, and suggest its value for these measurements in vivo as well. 相似文献
43.
Traumatic brain injury (TBI) is one of the commonest causes of morbidity and mortality in the developed countries with posttraumatic epilepsy and functional disability being its major sequelae. The purpose of this study was to test the hypothesis whether the normal appearing adjacent gray and white matter regions on T2 and T1 weighted magnetization transfer (MT) weighted images show any abnormality on quantitative imaging in patients with TBI. A total of 51 patients with TBI and 10 normal subjects were included in this study. There were significant differences in T2 and MT ratio values of T2 weighted and T1 weighted MT normal appearing gray matter regions adjacent to focal image abnormality compared to normal gray matter regions in the normal individuals as corresponding contralateral regions of the TBI patient's group (p < 0.05). However the adjoining normal appearing white matter quantitative values did not show any significant change compared to the corresponding contralateral normal white matter values. We conclude that quantitative T2 and MT ratio values provide additional abnormality in patients with TBI that is not discernable on conventional T2 weighted and T1 weighted MT imaging especially in gray matter. This additional information may be of value in overall management of these patients with TBI. 相似文献
44.
A study of damping in fiber-reinforced composites 总被引:1,自引:0,他引:1
Damping contributions from the viscoelastic matrix, interphase and the dissipation resulting from damage sites are considered to evaluate composite material damping coefficients in various loading modes. The paper presents the results of the FEM/Strain energy investigations carried out to predict anisotropic-damping matrix comprising of loss factors η11, η22, η12 and η23 considering the dissipation of energy due to fiber and matrix (two phase) and correlate the same with various micromechanical theories. Damping in three phase (i.e., fiber-interphase-matrix) composite is also calculated as an attempt to understand the effect of interphase. The contribution of energy dissipation due to sliding at the fiber-matrix interface is incorporated to evaluate its effect on η11, η22, η12 and η23 in fiber-reinforced composite having damage in the form of hairline debonding. Comparative studies of the various micromechanical theories/models with FEM/Strain energy method for the prediction of damping coefficients have shown consistency when both the effect of variable nature of stress and the fiber interaction is considered. Parametric damping studies for three phase composite have shown that the change in properties of fiber, matrix and interphase leads to a change in the magnitude of effectiveness of interphase, but the manner in which the interphase would affect the various loss factors depends predominately upon whether the hard or soft interphase is chosen. Analysis of the effect of damage on composite damping indicates that it is sensitive to its orientation and type of loading. 相似文献
45.
Pathak Madhvesh Bohra Rakesh Mehrotra Ram C. Lorenz Ingo-Peter Piotrowski Holger 《Transition Metal Chemistry》2003,28(2):187-192
Reactions of cis-dialkoxy-bis(acetylacetonato)titanium(IV), [(acac)2Ti(OR)2] (R = Et, Pr
i
) with alkoxyalkanols (ROCH2CH2OH) (R = Me, Et, n-Bu) in 1:1 and 1:2 molar ratios in refluxing benzene under anhydrous conditions yield [(acac)2Ti(OR)2–n
(OCH2CH2OR)
n
] (n = 1 or 2) complexes, which were purified by distillation under reduced pressure. On the basis of i.r. and n.m.r. (1H- and 13C-) spectral studies, a cis-octahedral environment around TiIV is proposed. On keeping the distilled dark brown-red viscous liquid [(acac)2Ti(OEt)(OCH2CH2OBu)] for 2 weeks, orange yellow crystals of [(acac)2TiO]2 were obtained. A single crystal X-ray diffraction study suggests the product is a new modification of [(acac)2TiO]2. 相似文献
46.
47.
Low‐temperature sol–gel transformation of methyl silicon precursors to silica‐based hybrid materials
Veena Dhayal Rakesh Bohra Meena Nagar Ajay Kaushik Sanjay Mathur Sven Barth 《应用有机金属化学》2008,22(11):629-636
Six new methyl silicon (IV) precursors of the type [MeSi{ON?C(R)Ar}3] [when R = Me, Ar = 2‐C5H4N ( 1 ), 2‐C4H3O ( 2 ) or 2‐C4H3S ( 3 ); and when R = H, Ar = 2‐C5H4N ( 4 ), 2‐C4H3O ( 5 ) or 2‐C4H3S ( 6 )] were prepared and structurally characterized by various spectroscopic techniques. Molecular weight measurements and FAB (Fast Atomic Bombardment) mass spectral studies indicated their monomeric nature. 1H and 13C{1H} NMR spectral studies suggested the oximate ligands to be monodentate in solution, which was confirmed by 29Si{1H} NMR signals in the region expected for tetra‐coordinated methylsilicon (IV) derivatives. Thermogravimetric analysis of 1 revealed the complex to be thermally labile, decomposing to a hybrid material of definite composition. Two representative compounds ( 2 and 4 ) were studied as single source molecular precursor for low‐temperature transformation to silica‐based hybrid materials using sol–gel technique. Formation of homogenous methyl‐bonded silica materials (MeSiO3/2) at low sintering temperature was observed. The thermogravimetric analysis of the methylsilica material indicated that silicon‐methyl bond is thermally stable up to a temperature of 400 °C. Reaction of 2 and Al(OPri)3 in equimolar ratio in anhydrous toluene yielded a brown‐colored viscous liquid of the composition [MeSi{ON?C(CH3)C4H3O}3.Al(OPri)3]. Spectroscopic techniques 1H, 13C{1H}, 27Al{1H} and 29Si{1H} NMR spectra of the viscous product indicated the presence of tetracoordination around both silicon and aluminum atoms. On hydrolysis it yielded methylated aluminosilicate material with high specific surface area (464 m2/g). Scanning electron micrography confirmed a regular porous structure with porosity in the nanometric range. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
48.
Force-length relations at ambient temperature have been determined for a set of polyethylenes which represent a wide range in molecular weight and molecular constitution. Taking advantage of previous work from this laboratory, samples have been prepared in such a manner that the important independent structural variables can be identified and isolated and their influence on the different aspects of the deformation process assessed. Partial melting-recrystallization processes appear to play an important role. For the linear polymers there is a direct influence of molecular weight. The influence of molecular weight manifests itself in the structure of the interlamellar zone which has a major influence on the initial modulus as well as the ultimate properties. Copolymers and branched copolymers display quite different behavior. The most striking difference is the invariance of the ultimate properties with molecular weight, branching, and level of crystallinity. From the set of experimental results that are presented the molecular factors involved in the deformation process can be sorted out. It becomes quite evident that all of the basic structural regions, characteristic of semicrystalline polymers, contribute to the observations. Focus solely on the changes in the crystallite, in analogy to the deformation of small-molecule crystalline systems, is inadequate in the case of crystalline polymers. 相似文献
49.
Rakesh Kumar Singh P. Senthilkumaran Kehar Singh 《Optics and Lasers in Engineering》2009,47(7-8):831-841
Tight focusing of linearly and circularly polarized vortex beams is studied in the presence of third-order spherical aberration, using vectorial Debye–Wolf integral. Results for total intensity distribution are presented for both polarizations. In addition, results for x-, y-, and z-polarization components are presented for the circularly polarized beam. Generation of longitudinal optical vortex in the tightly focused left circularly polarized beam has also been demonstrated by plotting its phase distribution. Compensation for the effect of spherical aberration has been studied in the presence of defocusing. Effect of aberration on the dark core of a tightly focused azimuthally polarized beam is also investigated. 相似文献
50.