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排序方式: 共有498条查询结果,搜索用时 772 毫秒
441.
Different mixtures containing atomic krypton and fluorinated compounds (Kr-NF3, Kr-SF6) and atomic krypton, argon and fluorinated compounds (Ar-Kr-NF3, Ar-Kr-SF6, Ar-Kr-F2) were excited with intense e-beam pulses. The fluorescence produced by Kr2F1 was studied using time resolved spectroscopic techniques. Rate constants for the production and quenching of Kr2F1 were deduced from the measurements. In all the mixtures used, at krypton partial pressure higher than about 100 mbar, direct production from Kr12 is considered as the most important formation channel of Kr2F1. 相似文献
442.
443.
2 is investigated with a XeCl laser. It is shown that energy conversion to rotational Stokes radiation can be efficiently obtained
by properly choosing the focusing geometry of pump radiation and the pressure of the Raman medium even at moderate pulse energies.
Energy conversion to the first rotational Stokes at 313.8 nm with efficiencies as high as 38% is obtained with a circularly
polarised XeCl pump beam of 10-mJ energy focused in 30 bar of H2. The spectral and optical characteristics of the pump and the rotational Stokes radiation are analysed.
Received: 29 May 1996/Revised version: 7 March 1997 相似文献
444.
Michail W. Zhelamskij Pierluigi Bruzzone 《Physica C: Superconductivity and its Applications》1998,310(1-4):262-266
A special sensor is proposed for magnetization measurement of superconductors with round cross section under pulsed transversal field. The sensor consists of a saddle shaped pick-up coil attached to the cylindrical superconducting sample, with a controlled geometrical distribution of the turns. The pick up coil carries out a two-dimensional flux integration and the software calculates the loop area in Joules. The sensor has been used during a campaign of ITER subsize conductor tests, showing an excellent agreement (better than 1%) with the results of boil-off calorimetric measurements. The detailed design, the algorithm and the test results are discussed in the paper. Other applications of this test method are proposed. 相似文献
445.
446.
447.
Renato Colle Raffaele Montagnani Pierluigi Riani Oriano Salvetti 《Theoretical chemistry accounts》1978,48(3):251-256
A method is described for calculating SCF open shell orbitals. In comparison with the coupling operator method, a greater velocity of convergency of the iterative process is obtained by taking into account not only the correct variational conditions, but also the best variations of orbitals step by step. 相似文献
448.
Overview of infrared methodologies for trans fat determination 总被引:1,自引:0,他引:1
trans Fatty acids are present in a variety of foods like dairy products, but the major sources are products that contain commercially hydrogenated fats. Some studies have shown that trans fatty acids elevate levels of serum low-density lipoprotein (LDL)-cholesterol and lower high-density lipoprotein (HDL)-cholesterol. The quantitation and identification of trans fatty acid isomers is difficult because of the wide range of positional monoene, diene, and triene fatty acid isomers present in hydrogenated oils. This is complicated by the cis positional isomers that are also present, as well as the lack of commercial chromatographic standards for many fatty acid isomers. In this review, infrared methodologies for the determination of total trans fat are presented. Using an attenuated total reflection (ATR) infrared cell, a novel Fourier transform infrared (FTIR) spectroscopic method that was developed for the rapid (5 min) quantitation of the total trans fatty acid levels in neat (without solvent) fats and oils measured as triacylglycerols (TAG) is discussed. TAG required no derivatization, but had to be melted prior to measurement. The lower limit of trans quantitation was 5% of total fat. The precision of this ATR method was found to be superior to that of transmission infrared official methods. Accuracy was enhanced by generating a symmetric absorption trans infrared band at 966 cm(-1) on a horizontal background. This was achieved by "ratioing" the single-beam spectrum of the trans-containing fat or oil against that of a reference oil or standard having only cis double bonds. Attempts to apply this ATR-FTIR method to food matrixes with low trans fat and/or low total fat content were not satisfactory due to interfering infrared absorptions in the trans region. To overcome this interference, the method was modified by applying the standard addition technique to the ATR-FTIR determination. The modified procedure required more time, but eliminated any adverse impact on accuracy arising from interfering minor food components having absorption bands near 966 cm(-1). 相似文献
449.
Reschiglian P Zattoni A Casolari S Krumlova A Budinska M Chmelík J 《Annali di chimica》2002,92(4):457-467
Cereal starch occurs as two types of micrometer-sized granules, large and small. Large starch granules are more susceptible to enzymatic hydrolysis. When cereal starch is used for fermentation processes, as in brewing of barley malt, the barley strains with the highest content of large starch granules should be preferred. Gravitational field-flow fractionation (GFFF) is a separation method able to fractionate starch samples at low cost and short analysis time. In this work, the search for the best GFFF conditions for the analytical separation of barley starch within an inter-laboratory approach is presented. For different barley strains cultivated under monitored conditions the size distributions of starch granules is here quickly monitored and characterized by GFFF. As a consequence, dimensional characterization of barley starch can allow for the selection of the most suitable strains with the lowest content of non-degradable starch. 相似文献
450.
Giancarlo Bettoni Carlo Franchini Roberto Perrone Vincenzo Tortorella 《Tetrahedron》1980,36(3):409-415
We studied methods of stereospecific synthesis that enabled us to obtain variously substituted morpholinic compounds and to determine their absolute configuration. From a study of the chiroptical properties of synthetic N-[2-pyridyl-N-oxide] derivatives of optically active morpholines, it was possible to correlate the sign of the Cotton effect with the absolute configuration. This correlation agrees with that previously established for derivatives of the piperidine type. By evaluating the various contributions to the Cotton effect of substituents in positions 2 and 3, we established the absolute configuration of bicyclic compounds condensed in the two positions mentioned above. 相似文献