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排序方式: 共有216条查询结果,搜索用时 15 毫秒
1.
CV Tomy D Pal SS Banerjee S Ramakrishnan AK Grover S Bhattacharya MJ Higgins G Balakrishnan McK Paul 《Pramana》2002,58(5-6):925-935
The weakly pinned single crystals of the hexagonal 2H-NbSe2 compound have emerged as prototypes for determining and characterizing the phase boundaries of the possible order-disorder
transformations in the vortex matter. We present here a status report based on the ac and dc magnetization measurements of
the peak effect phenomenon in three crystals of 2H-NbSe2, in which the critical current densities vary over two orders of magnitude. We sketch the generic vortex phase diagram of
a weakly pinned superconductor, which also utilizes theoretical proposals. We also establish the connection between the metastability
effects and pinning. 相似文献
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Analysis of caffeine and its metabolites is of interest with respect to caffeine exposure, for kinetic and metabolism studies and for opportunistic in vivo estimation of drug metabolizing enzyme activity in humans and animals. For the latter, analysis is usually done by high-performance liquid chromatography (HPLC) with UV detection. However, this method is close to the detection limit for certain of the metabolites and requires very long chromatography, 30-60 min. We have developed a fast method for the quantification of caffeine and its metabolites 1-methylxanthine, 1-methyluric acid, 1,7-dimethyluric acid, 5-acetylamino-6-amino-3-methyluracil (AAMU) and 5-acetylamino-6-formylamino-3-methyluracil (AFMU) by HPLC tandem mass spectrometry (MS/MS) in urine that requires only its dilution with buffer and centrifugation before injection into the HPLC/MS/MS system. The chromatography lasts 7 min and is followed by 4.5 min for re-equilibration of the HPLC column, giving a total analysis time of 11.5 min. The method provides a great sensitivity improvement with detection limits for all analytes 相似文献
4.
V ? R,T deactivation of the ν4 (243 cm?1) level in BCl3 by HCl has been measured over the range 220–340 K, with an infrared double resonance technique. The deactivation probabilities show an inverse temperature dependence below room temperature, indicating that long-range attractive forces are important in the resonant transfer process. The results are compared with the theory of Sharma and Brau. 相似文献
5.
Direct optical detection of singlet oxygen from a single cell 总被引:1,自引:0,他引:1
Zebger I Snyder JW Andersen LK Poulsen L Gao Z Lambert JD Kristiansen U Ogilby PR 《Photochemistry and photobiology》2004,79(4):319-322
Singlet oxygen has been detected in single nerve cells by its weak 1270 nm phosphorescence (a1deltag --> X3sigmag-) upon irradiation of a photosensitizer incorporated in the cell. Thus, one can now consider the application of direct optical imaging techniques to mechanistic studies of singlet oxygen at the single-cell level. 相似文献
6.
Diagnostic PCR has been used to analyse a wide range of biological materials. Conventional PCR consists of several steps such as sample preparation, template purification, and PCR amplification. PCR is often inhibited by contamination of DNA templates. To increase the sensitivity of the PCR, the removal of PCR inhibitors in sample preparation steps is essential and several methods have been published. The methods are either chemical or based on filtering. Conventional ways of filtering include mechanical filters or washing e.g. by centrifugation. Another way of filtering is the use of electric fields. It has been shown that a cell will experience a force when an inhomogeneous electric field is applied. The effect is called dielectrophoresis (DEP). The resulting force depends on the difference between the internal properties of the cell and the surrounding fluid. DEP has been applied to manipulate cells in many microstructures. In this study, we used DEP as a selective filter for holding cells in a microsystem while the PCR inhibitors were flushed out of the system. Haemoglobin and heparin - natural components of blood - were selected as PCR inhibitors, since the inhibitory effects of these components to PCR have been well documented. The usefulness of DEP in a microsystem to withhold baker's yeast (Saccharomyces cerevisiae) cells while the PCR inhibitors haemoglobin and heparin are removed will be presented and factors that influence the effect of DEP in the microsystem will be discussed. This is the first time dielectrophoresis has been used as a selective filter for removing PCR inhibitors in a microsystem. 相似文献
7.
The development and application of a rocket immunoelectrophoretic and an enzyme activity electrophoretic assay for the qualitative analysis of Geotrichum candidum lipase activity is presented. The sensitivities of the four assays were (in arbitrary units): enzyme activity electrophoresis, 1-0.5; rocket immunoelectrophoresis, 0.5-0.2; radial diffusion, 1; titrimetry, 1. The electrophoretic methods made it possible to distinguish between high and low molecular weight forms of the G. candidum lipases. The enzyme activity electrophoretic methods can be combined with other electrophoretic techniques, as demonstrated here with isoelectric focusing, and produce useful information on physico-chemical differences between different molecular forms of the lipase, e.g. forms with different pI. 相似文献
8.
Praic M. Keane Kyra O'Sullivan Fergus E. Poynton Bjrn C. Poulsen Igor V. Sazanovich Michael Towrie Christine J. Cardin Xue-Zhong Sun Michael W. George Thorfinnur Gunnlaugsson Susan J. Quinn John M. Kelly 《Chemical science》2020,11(32):8600
Ruthenium polypyridyl complexes which can sensitise the photo-oxidation of nucleic acids and other biological molecules show potential for photo-therapeutic applications. In this article a combination of transient visible absorption (TrA) and time-resolved infra-red (TRIR) spectroscopy are used to compare the photo-oxidation of guanine by the enantiomers of [Ru(TAP)2(dppz)]2+ in both polymeric {poly(dG-dC), poly(dA-dT) and natural DNA} and small mixed-sequence duplex-forming oligodeoxynucleotides. The products of electron transfer are readily monitored by the appearance of a characteristic TRIR band centred at ca. 1700 cm−1 for the guanine radical cation and a band centered at ca. 515 nm in the TrA for the reduced ruthenium complex. It is found that efficient electron transfer requires that the complex be intercalated at a G-C base-pair containing site. Significantly, changes in the nucleobase vibrations of the TRIR spectra induced by the bound excited state before electron transfer takes place are used to identify preferred intercalation sites in mixed-sequence oligodeoxynucleotides and natural DNA. Interestingly, with natural DNA, while it is found that quenching is inefficient in the picosecond range, a slower electron transfer process occurs, which is not found with the mixed-sequence duplex-forming oligodeoxynucleotides studied.Efficient electron transfer requires the complex to be intercalated at a G-C base-pair. Identification of preferred intercalation sites is achieved by TRIR monitoring of the nucleobase vibrations before electron transfer. 相似文献
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