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251.
The problem of calculating the noise factor of a traveling-wave gyrotron is solved for a model of a thin annular multistart-helical
electron flux taking into account the effect of the quasistatic space-charge field. Plots of the gain and the noise factor
of the traveling-wave gyrotron versus the electrical parameters of the amplifier are obtained.
Zh. Tekh. Fiz. 68, 130–132 (February 1998) 相似文献
252.
H.-J. Scheibe D. Drescher A. Kolitsch A. Mensch 《Fresenius' Journal of Analytical Chemistry》1995,353(5-8):690-694
Morphology and structure of amorphous carbon films deposited with a pulsed arc source (LASER-ARC) have been studied using microscopical methods (SEM, TEM and AFM), electron diffraction and spectroscopical investigation (EELS). The parameters of the arc source and the deposition conditions (substrate temperature) influence morphology and structure of deposited amorphous carbon films. Especially the incorporation and growth of particles, embedded in the film have been investigated. By particle analysis using an optical microscope a majority of particles that is smaller than 500 nm has been determined. The morphology has been also demonstrated similar by AFM and TEM images. Their number and size of particles is strongly influenced by the deposition temperature. The structure of amorphous film is characterized by the EELS-spectra, but the particle structure was not detectable. 相似文献
253.
Summary A new method of evaluating the Tolman cone angle from X-ray structural data available from the Cambridge Crystallographic Data Base has been developed and a statistical analysis of the cone angles of the phosphines PPh3, PMe2Ph, PMePh2, PMe3, PEt3 and PCy3 (Cy = cyclohexyl) in transition metal complexes has been completed. 相似文献
254.
255.
Xerogels obtained from the acid-catalyzed and ultrasound stimulated hydrolysis of TEOS were submitted to heat treatment at temperatures ranging from 60 to 1100 °C and studied by small-angle X-ray scattering (SAXS). The SAXS intensity as a function of the modulus of the scattering vector q was obtained in the range from q0=0.19 to qm=4.4 nm−1. At 60 °C the xerogels exhibit an apparent surface fractal structure with a fractal dimension DS∼2.5 in a length scale ranging from 1/q1∼1 to 1/qm∼0.22 nm. This structure becomes extremely rough at 120 °C (DS∼3) and at 150 °C, it apparently converts to a mass fractal with a fractal dimension D∼2.4. This may mean an emptying of the pores with preservation of a share of the original mass fractal structure of the wet aged gel, for it had presented a mass fractal dimension D∼2.2. A well characterized porous structure formed by 2.0 nm mean size pores with smooth surface of about 380 m2/g is formed at 300 °C and remains stable until approximately 800 °C. At 900 °C the SAXS intensity vanishes indicating the disappearance of the pores in the probed length scale. The elimination of the nanopores occurs by a mechanism in which the number of pores diminishes keeping constant their mean size. The xerogels exhibit a foaming phenomenon above 900 °C and scatter following Porod's law as does a surface formed by a coarse structure. 相似文献
256.
A reversed-phase liquid chromatographic assay was developed to quantitate prednisolone, prednisone and the 20 alpha-dihydro and 20 beta-dihydro reduced metabolites of both parent compounds in tissue culture media from in vitro perfusions of the human placental lobule. Steroids were extracted from perfusate, using reversed-phase cartridges, with average recoveries of 95.2% or greater. The internal standard for the analyses was 6 alpha-methylprednisolone. In this assay cortisol coelutes with prednisolone, however, no other significant interferences were found. Assay of each steroid was linear in the range 0-1 microgram/ml. Intra-assay coefficients of variation were measured at 10 and 750 ng/ml with ranges of 3.4% (20 alpha-dihydroprednisone) to 8.8% (20 beta-dihydroprednisolone) and 4.1% (20 beta-dihydroprednisone) to 8.8% (prednisone). The corresponding inter-assay coefficients of variation were 3.3% (20 alpha-dihydroprednisone) to 9.1% (20 beta-dihydroprednisolone) and 1.9% (prednisolone) to 3.5% (prednisone). The analyses utilized two C18 columns which were linked together and maintained at 40 degrees C. 相似文献
257.
D. Ivanenko 《Annalen der Physik》1991,503(4):304-304
258.
259.
J. Pill J. Aufenanger K. Stegmeier F. H. Schmidt D. Müller 《Fresenius' Journal of Analytical Chemistry》1987,327(5-6):558-560
Summary The investigation methods of the action of xenobiotics on sterol biosynthesis from 14C-acetate in rat hepatocyte cultures can be developed, with regard to extraction using Extrelut and the separation of the sterol pattern by thin-layer chromatography, in such a way that they are suitable for wider application, e.g., screening. Good visualisation and recognition of changes in the sterol pattern are possible using autoradiography of the thin-layer chromatogram.
Dedicated to Dr. E. Roesch on occasion of his 65th birthday 相似文献
Dünnschicht-Chromatographie von radioaktiv markiertem Cholesterin und Vorstufen aus biologischem Material. Eine einfache und empfindliche Methode zur Untersuchung einer Beeinflussung des Sterolbiosynthesewegs
Dedicated to Dr. E. Roesch on occasion of his 65th birthday 相似文献
260.
Eight emission spectra of pure N2O and N2O + N2 + He mixtures excited by a radio frequency discharge were recorded by Fourier Transform Spectroscopy at a resolution of 0.005 and 0.004 cm−1 in the 4.5 μm region. Results (wavenumbers, band centers, and spectroscopic constants) concerning nine new vibrational transitions which have not been observed before, and which occur between highly excited levels of the bending mode are reported. The derived spectroscopic parameters allow us to reproduce the experimental wavenumbers with an RMS error lower than 4.5 × 10−4 cm−1. 相似文献