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991.
V. Goliáš D. Pittauerová R. Procházka Z. Třískala 《Journal of Radioanalytical and Nuclear Chemistry》2005,266(3):461-470
Summary The activities of218Po,214Po and211Bi were determined in samples obtained of soil/gas. Sampling work was taken in Jáchymov (Czech Republic) at the outcrop of
the Geister-vein,by electrostatic precipitation from filtered soil gas on stainless steel disks.The samples were measured
in a field laboratory using a semi-conductor alpha-spectrometer.The activities of218Po,214Po and211Bi were calculated.Samples taken from active dump material (near-by radon source) exhibited a high211Bi/214Po ratio, while those of the vein outcrop (a relatively deeper source) had a low ratio.A mathematical model was employed to
determine the radon age calculated from the actinon/radon input ratio.This varied in a range of 5.6 to -7.7 seconds.Negative
age values are probably caused by the preference for actinon, which rapidly comes into equilibrium with the source of this
gas. 相似文献
992.
Velázquez MM Ortega F Monroy F Rubio RG Pegiadou S Pérez L Infante MR 《Journal of colloid and interface science》2005,283(1):144-152
We report the formation of Langmuir monolayers of pure zwitterionic hexadecyl 1-N-L-tryptophan glycerol ether (C(16)-TGE) surfactant and mixed monolayers of cationic-zwitterionic surfactant obtained modifying the pH of the subphase. The pressure-area and surface potential-area isotherms and fluorescence microscopy measurements have been used to characterize the surface phase transitions in the monolayers. These transitions appeared at larger areas as the pH decreased from 6.0 to 2.0 and almost disappeared as the pH decreased further. The analysis of the surface potential and the infrared reflection-absorption spectroscopy data suggests that the phase transition is associated with a change of orientation of both the hydrocarbon chain and the aromatic group of the surfactant with respect to the air-water surface. The surface rheology of the monolayers was studied by quasielastic light scattering and by the oscillatory barrier technique. The results indicate that there is at least one relaxation process in the monolayer. 相似文献
993.
Alluisetti GE Almaraz AE Amorebieta VT Doctorovich F Olabe JA 《Journal of the American Chemical Society》2004,126(41):13432-13442
The catalytic disproportionation of NH(2)OH has been studied in anaerobic aqueous solution, pH 6-9.3, at 25.0 degrees C, with Na(3)[Fe(CN)(5)NH(3)].3H(2)O as a precursor of the catalyst, [Fe(II)(CN)(5)H(2)O](3)(-). The oxidation products are N(2), N(2)O, and NO(+) (bound in the nitroprusside ion, NP), and NH(3) is the reduction product. The yields of N(2)/N(2)O increase with pH and with the concentration of NH(2)OH. Fast regime conditions involve a chain process initiated by the NH(2) radical, generated upon coordination of NH(2)OH to [Fe(II)(CN)(5)H(2)O](3)(-). NH(3) and nitroxyl, HNO, are formed in this fast process, and HNO leads to the production of N(2), N(2)O, and NP. An intermediate absorbing at 440 nm is always observed, whose formation and decay depend on the medium conditions. It was identified by UV-vis, RR, and (15)NMR spectroscopies as the diazene-bound [Fe(II)(CN)(5)N(2)H(2)](3)(-) ion and is formed in a competitive process with the radical path, still under the fast regime. At high pH's or NH(2)OH concentrations, an inhibited regime is reached, with slow production of only N(2) and NH(3). The stable red diazene-bridged [(NC)(5)FeHN=NHFe(CN)(5)](6)(-) ion is formed at an advanced degree of NH(2)OH consumption. 相似文献
994.
Román LU Guerra-Ramírez D Morán G Martínez I Hernández JD Cerda-García-Rojas CM Torres-Valencia JM Joseph-Nathan P 《Organic letters》2004,6(2):173-176
[structure: see text] The triterpenes 8,14-seco-oleana-8(26),13-dien-3beta-ol (1) and its acetyl derivative 2 were isolated from Stevia viscida and Stevia eupatoria, respectively. Their structures were elucidated by 2D NMR, including carbon-carbon connectivity experiments, and confirmed by X-ray diffraction analysis of ketone 3. The absolute configuration was determined by NMR analysis of the Mosher esters of 1. The biogenetic implications of the new substances are discussed. 相似文献
995.
The transfer constants (Cs) of the polystyrene radical with some derivatives of phthalic acid have been determined. Among the agents used, tetrachlorophthalanhydride (TCPA) differs distinctly from other compounds by its value of Cs 3·1 × 10?3 for thermal and 3·4 × 10?3 for initiated polymerization of styrene. The values of Cs for phthalanhydride, dimethyl phthalate, and tetrachlorodimethyl phthalate are lower by two decimal orders. The considerable decrease in the degree of polymerization of styrene prepared in the presence of TCPA is mainly attributed to the increased reactivity of chlorine atoms in TCPA induced by the acceptor effect of anhydride ring. Participation of a TCPA-styrene complex in transfer reaction has been assumed but not proved. 相似文献
996.
A study of changes in the yields of radiolytic products in two-phase systems with tributyl phosphate
With the aim of studying the effects of volume ratios and composition of the organic phase on the total yields of the main degradation products of tributyl phosphate (TBP) radiolysis, the following two-phase systems were used: water-TBP-carbon tetrachloride and water-TBP-n-alkane with various ratio of TBP in the organic phase and various volume ratios of organic-aqueous phases. We examined the influence of the distribution of two-phase systems components-precursors of radiolytic products on the total yields of the main radiolytic products and mechanism involved. 相似文献
997.
Six new polyamides have been prepared either by polymerization in solution or by interfacial polymerization by reacting perchloroterephthaloyl dichloride with aromatic diamines. The polymers were characterized by i.r. spectroscopy, elemental analysis, DSC, and TGA. The glass transition temperature, the melting temperature, and the thermal decomposition temperature have been determined. In order to estimate the molecular weights, intrinsic viscosities were determined. Some of the polymers showed high thermal stability. 相似文献
998.
Summary The enantiomers of chiral carboxylic acids were separated as their diastereomeric amides with (1R,2R)-(−)-1-(4-nitrophenyl)-2-amino-1,3-propanediol
(“levobase”) and with “dextrobase” (the enantiomer of levobase) by high-performance liquid chromatography using a conventional
C-18 column and various solvent systems containing acetonitrile, methanol, water, and phosphoric acid. 相似文献
999.
José Luis Vilchez Gonzalo Sánchez-Palencia Ramiro Avidad Luis Fermín Capitán-Vallvey Alberto Navalón 《Mikrochimica acta》1993,110(1-3):61-69
A method for the simultaneous determination of yohimbine and boldine in mixtures by first-derivative synchronous spectrofluorimetry has been developed. The method is based on their native fluorescence in 0.1N sulphuric acid medium. The constant wavelength difference chosen to optimize the determination was =em -em=82 nm. Yohimbine was measured at ex//em= 285/367 nm, and boldine at ex/em=272/354 nm. The range of application is 10–500 g/l for yohimbine and 1–50 g/l for boldine. The method was applied to the determination of yohimbine and boldine in synthetic mixtures and pharmaceuticals, with errors generally 2%. Relative standard deviations were about 2%.Dedicated to Professor Fermin Capitán on his 72th birthday 相似文献
1000.
N. Vajda J. Larosa T. Pintér G. Keömley D. Bódizs Zs. Molnár 《Journal of Radioanalytical and Nuclear Chemistry》1993,170(2):399-409
A simple and effective method has been developed for the determination of the transuranium isotopes in primary coolant samples of WWER-440 type reactors. Membrane filters containing undissolved particles from about one liter coolant were destroyed by mineral acids, then americium-curium isotopes and neptunium-plutonium isotopes were coprecipitated sequentially with NdF3 based on their different redox behavior. Alpha-spectra were determined by silicon semiconductor detectors connected to multichannel analyzers. Activity ratios measured in a reactor unit with a failed fuel element were compared with calculated values of the same type of reactor under similar conditions. Parameters of the defective fuel (burnup, original enrichment) could be estimated. 相似文献