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71.
The time evolution of the density operator of an AB spin system during a double-spin-echo pulse sequence is evaluated analytically by a computer-algebra system. The computer-algebra system allows one to generate the extensive formulas describing the density operator and yields an expression for the integral of the spectral signals. The simulation of spectra for arbitrary sequence timings can be easily performed by this new tool without risking errors that might occur in conventional calculations. The computer-algebra method can be extended straightforward to other pulse angles and types of sequences. The double-spin-echo pulse sequence is used in the point-resolved spectroscopy (PRESS) method which is often applied for volume selective examinationsin vivo. For verification of the results generated by the computer-algebra system,1H spectra from a half-liter spherical sample with an aqueous solution that was 0.1 M in sodium citrate and 0.1 M in sodium acetate were recorded after 90°-180°-180° double-spin-echo pulse sequences on a 1.5-T whole-body unit. The measured behavior of the citrate AB spin system corresponds very well with the theoretical predictions. Thus, the theory provides the basis for the optimization of sequence timings for double-spin-echo measurements with high signal gain from AB systems as, for example, citrate. In addition, the theoretically predicted signal modulations could be fitted to the experimental data, providing the transverse relaxation time of the AB-coupled protons. 相似文献
72.
Bernd Trummer Otto Fruhwirth Klaus Reichmann Gerhard Herzog Werner Sitte Michael Holzinger 《Journal of Electroceramics》2000,5(1):53-61
Conductive LaNiO3 thin film electrodes were deposited by chemical solution deposition (CSD) from nitrate solutions onto polycrystalline Al2O3 and (Ba,Ca)TiO3 PTCR ceramic substrates. The electrical properties of the LaNiO3 thin film on Al2O3 and of the interface consisting of LaNiO3 and the semiconductive oxide ceramic were investigated. The deposited LaNiO3 films were about 250 nm thick and consisted of nanosized particles. The resistivity of the LaNiO3 film was about 3 × 10-3cm at 20°C. The PTCR ceramic consisted of m sized particles and exhibited an electronic resistivity of about 10 cm at 20°C and a steep increase of the resistivity of a few orders of magnitude above the Curie point at about 120°C. The electrical properties of the LaNiO3/PTCR interface were dominated by the properties of a barrier layer between the PTCR ceramic and the LaNiO3 electrode. The potential dependence of the impedance indicated that the barrier layer consisted of a depletion layer within the PTCR ceramic, when the flat band potential of LaNiO3 on the PTCR ceramic at about –250 mV was exceeded. Additionally the formation of an insulating layer at the LaNiO3 electrode has to be taken into account. 相似文献
73.
74.
The cortical actin cytoskeleton undergoes dramatic rearrangements during fertilization of sea urchin eggs. To characterize these changes further, we quantified the relative changes in filamentous actin (F-actin) during fertilization and the first cell cycle in both intact eggs and in isolated cortices by quantitative fluorescence microscopy. The level of F-actin in the intact egg decreased after fertilization and continued to decrease throughout the first cell cycle. By 60 min after fertilization, the level of F-actin had decreased to 50% of the unfertilized sea urchin egg. By cytokinesis, the level of F-actin had decreased to 30% of the unfertilized egg. After completion of cell division, individual blastomeres had 10% of the F-actin in the unfertilized egg. In contrast, there was an increase in cortical F-actin to 370% of the level in the unfertilized egg after fertilization. This increase corresponded to the formation of microvilli. There was little change in the level of cortical F-actin during the first cell cycle. We draw parallels to other systems that increase the amount of F-actin in the Triton-insoluble cytoskeleton by recruiting actin from a Triton-soluble pool of F-actin. 相似文献
75.
76.
Kh Otto 《Canadian Metallurgical Quarterly》1996,(3):34-41
To make a diagnosis and a differential diagnosis of mediastinal tumors always encounters many difficulties. Differentially, the diagnostic spectrum includes a great number of histologically different tumor types. Routine light microscopic techniques are frequently insufficient for a tumor to be classified. This mainly applies to thymomas and malignant lymphomas. So tumor morphological diagnostic techniques have been improved year after year. Immunohistological techniques may further serve as a method of precision diagnosis of tumors. The application of these methods largely changes our logic and implies a close cooperation between diagnosis and therapy. 相似文献
77.
A review of the synthesis and characterization of a new type of stacked, bridged macrocyclic metal complexes, the (μ-cyano)phthalocyaninatometal compounds [PcMCN]n (2) is given. By using the routes described in Fig. 3 the polymers were synthesized with M = Co3+, Fe2+, Fe3+, Mn3+ and Cr3+ as the central metal ion. The compounds were characterized by IR, far-IR, UV, thermal and elemental analysis, and partly by 1H NMR and FD (field desorption) mass spectroscopy.[PcCoCN] (2a) and [PcFeCN]n (2b) exhibit d.c. room temperature conductivities around 10?2 S/cm without doping, thereby showing conductivities which are in the same range as the iodine-doped phthalocyaninatosiloxanes [PcSiO]n. 相似文献
78.
MG Otto AD Mayer PA Clavien A Cavallari KA Gunawardena EA Mueller 《Canadian Metallurgical Quarterly》1998,66(12):1632-1640
79.
S Strand WJ Hofmann A Grambihler H Hug M Volkmann G Otto H Wesch SM Mariani V Hack W Stremmel PH Krammer PR Galle 《Canadian Metallurgical Quarterly》1998,4(5):588-593
We gave auditory examples of two semantic categories through headphones to 100 surgical patients anaesthetized with propofol and enflurane. This presentation was made during certain stages of the procedure, potentially associated with arousal, and during steady-state anaesthesia. Postoperative review using category generation tests showed successful priming in a pre-induction group but no evidence of implicit memory in the anaesthetized groups. These results suggest that timing an auditory input to coincide with surgical stimulation does not increase the probability of retrieval of information by this type of testing. 相似文献
80.
Combined GC/HPLC fingerprinting of petroleums and process streams derived therefrom gives detailed information on their constituents. The silica gel-heptane system affords separation into classes of hydrocarbons which, together with dual u.v. and R.I. modes of detection, gives abundant information on the composition of such samples. GC on a medium-efficiency SCOT column is used as a complementary technique only. Interpretations of HPLC chromatograms for samples ranging from gasolines to bitumens are given. 相似文献