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901.
The general-relativistic effects of an extreme Reissner-Nordström black hole on the flux of radiation emitted by a hot spot orbiting the hole with a thin accretion disk are investigated. The light curves, the redshift factor, and the solid angle against the spot orbit position are given. The results are then compared with those of a spot orbiting a Schwarzschild black hole. 相似文献
902.
Alvarez-Merino MA Joly JP Carrasco-Marín F Moreno-Castilla C 《Journal of colloid and interface science》2003,260(2):449-453
Intermittent temperature-programmed desorption of ammonia was used to study the strength and population of surface acid sites of tungsten oxide supported on activated carbon pretreated at 350 and 700 degrees C. Catalysts pretreated at 350 degrees C showed two types of surface acid sites and desorption occurred with free readsorption until a temperature of around 300 degrees C was reached. Pretreatment at 700 degrees C produced three different states of ammonia adsorbed on the catalysts and desorption occurred with free readsorption. 相似文献
903.
904.
The temperature dependence of elastic constants of Cd1–x
Zn
x
alloys, havingx=0.021, 0·042 and 0·233 at.%, has been measured in the temperature range from 4·2 to 300 K by the pulse-echo-overlap ultrasonic method. The adiabatic compressibilities and the Debye temperatures have been calculated. All elastic constants with the exception ofc
44 increase slightly with the growing concentration of Zn.The summary of this paper was presented on the 7th Conference on Ultrasonic Methods in ilina, September 11th–13th, 1980. 相似文献
905.
Self-diffusion coefficients of vanadium in the FeV -phase and in the corresponding -solid solution (Fe-47 wt.% V) measured in the temperature ranges 1002–1115 °C (-phase) and 1230–1320 °C are reported. The found results differ fundamentally and significantly from the relations in ordered and disordered solid solutions [9]. The diffusivity in -phase at the transition temperature (T
/=1200 °C) is cca 14 times lower than the diffusivity in the b.c.c. solid solution, the chemical composition of which is the same. The lowering is caused by the different values of frequency factors,D
O=0.11 cm2/s andD
O=45 cm2/s. The effect of the corresponding activation enthalpiesH
=252 kJ/mole andH
=293 kJ/mole is small and quite opposite. The occurence of higher activation enthalpyH
in the -solid solution at temperaturesT>T
/ may be attributed to a certain amount of the f.c.c. phase coexisting in the b.c.c. matrix at concentrationsc
v>27 wt.% at sufficiently high temperatures [7]. A comparison of vanadium self-diffusion characteristics measured in the -phase to the extrapolated values obtained on the basis of the previous measurements [1] in the Fe-V primary solid solutions 1 shows that the diffusivity ratioD
1/D
(1473 K)=33 and that the activation enthalpyH
is by about 3% higher than the valuesH
1 (eq. (5)) measured in the uniphase b.c.c. solid solutions. 相似文献
906.
The kinetics of the hydrogen electrode reactions on Pt in the NaHSO4 + KHSO4 melt at ca. 185°C is studied. Under potentiodynamic conditions both the anodic and cathodic processes can be interpreted with the hydrogen electrode reaction mechanism already known. At potentials more negative than 0.1 V (vs. Ag/Ag+ (0.06 M)) the mechanism of the cathodic reaction changes because of a sulphide species formed on the electrode which is produced by a reduction of the melt components. 相似文献
907.
Ondřej Linhart Alžběta Kolorosová-Mrázová Jan Kratzer Jakub Hraníček Václav Červený 《Analytical letters》2019,52(4):613-632
An ultraviolet-photochemical generator (UV-PVG) capable of post-column on-line transformation of both organic and inorganic mercury species to cold vapor (Hg0) with subsequent detection by quartz tube-atomic absorption spectrometry (QT-AAS) was developed. Mercury(II), methylmercury(I), ethylmercury(I), and phenylmercury(I) were successfully detected after separation by reversed-phase high-performance liquid chromatography (RP-HPLC). Two types of AAS detectors were compared. The first was a commonly used line-source instrument while the second was a high-resolution continuum source (HR-CS) AAS. The latter provided better limits of detection: 0.47?µg?L?1 for Hg(II), 0.84?µg?L?1 for methylmercury(I), 0.80?µg?L?1 for ethylmercury(I), and 2.0?µg?L?1 for phenylmercury(I). The repeatability at 30?μg?L?1 was 3.6%, 4.1%, 6.2%, and 4.5% for these species (n?=?10). These figures of merit were comparable with those reported for more sensitive atomic fluorescence spectrometry. Nine sample extraction procedures were investigated. Extraction by tetramethylammonium hydroxide and HCl at 75?°C was selected as the only method compatible with the proposed separation and detection steps providing high extraction efficiency and no changes in mercury speciation. The applicability of the proposed high-performance liquid chromatography–ultraviolet-photochemical vapor generation–quartz tube-atomic absorption spectrometry method was demonstrated using fish samples and certified reference materials (CRM) DOLT-4 (dogfish liver) and ERM-CE464 (tuna fish). The results were comparable to those obtained by a reference method based on L-cysteine extraction and high-performance liquid chromatography–inductively coupled plasma-mass spectrometry (HPLC–ICP-MS) determination. 相似文献
908.
Summary A method for the determination of chromium(VI) in solid materials with a Cr(VI) content at ppm level in the presence of ca. 10% Cr(III) has been devised. Chromium(VI) is extracted with 0.1M NaOH in a double-water bath (97° C) for 90 min. Differential-pulse polarography in 1M NaOH and spectrophotometry with 1,5-diphenylcarbazide have been tested for use in the final determination of Cr(VI). After extraction in the form of dithiocarbamate into methylisobutylketone or ethylacetate, chromium was determined by flame AAS and DPP in an organic extract. 相似文献
909.
Casalderrey M Souto C Concheiro A Gómez-Amoza JL Martínez-Pacheco R 《Chemical & pharmaceutical bulletin》2000,48(4):458-463
Three processed lactose-cellulose blends of similar composition, particle size and true density were compared as direct compression excipients: one was prepared by dry granulation, one by extrusion-spheronization, and the commercial product Cellactose. Differences among their flow properties depended solely on their different sphericities. Unlike those of the other blends, Cellactose particles exhibited numerous macropores. The mean yield pressures of all three blends were similar to those of direct compression lactoses. Cellactose tablets prepared at a punch pressure that largely eliminated macropores (pores >1 microm) had better mechanical properties but much poorer disintegration than tablets of the other blends prepared at the same punch pressure. However, the tensile strength and disintegration time of Cellactose tablets both fell rapidly as macropore volume was increased by reducing punch pressure, while the enthalpy of wetting/dissolution rose. The strength and water-resistance of well-compacted Cellactose tablets is attributed to the spatial distribution of lactose and cellulose in Cellactose particles, rather than to beta-lactose content or extra-particular structural features. 相似文献
910.
Miguel Clemente-León Eugenio Coronado Carlos J. Gómez-García Eugenia Martínez-Ferrero 《Journal of Cluster Science》2002,13(3):381-407
The use of polyoxometalates (pOM's) as inorganic component in the synthesis of new molecular hybrid materials is presented. Here we show that the combination of organic molecules of the tetrathiafulvalene (TTF) type or perylene (per) with POM's yields new radical salts with unprecedented structures that present interesting magnetic and/or electrical properties or coexistence of both. The first true metallic radical salt containing a POM has been prepared and characterized. We also describe the recent results obtained by combining magnetic POM's with the organometallic cation decamethylferrocene. 相似文献