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排序方式: 共有137条查询结果,搜索用时 15 毫秒
21.
R. Jaćimović P. Makreski V. Stibilj T. Stafilov 《Journal of Radioanalytical and Nuclear Chemistry》2008,278(3):795-799
Major and trace element contents in iron ore reference materials were investigated using k
0-instrumental neutron activation analysis (k
0-INAA). To avoid iron interferences, radiochemical separation was developed (k
0-RNAA). The determination of the investigated elements in the inorganic phase from hydrochloric acid solution was performed
after radiochemical separation of iron by diisopropyl ether. It was found that after the Fe elimination, the limit of detection
for some elements was much lower that enables their direct determination. The distribution of 39 elements (with intermediate/medium
and long half-life radionuclides) after Fe removal was investigated. 相似文献
22.
We report on the use of EPR spectroscopy and spin trapping technique to detect free radical intermediates formed in the presence of gold nanoparticles. Phosphine- and amine-protected gold nanoparticles were found to initiate air oxidation of organic substrates containing active hydrogen atoms, such as amines and phosphine oxides. Nanoparticles protected by stronger bound ligands (e.g., thiols) were inactive in these reactions. We also found that gold nanoparticles are able to abstract a halogen atom from the halogenated compounds, presumably due to the high affinity of gold metal for halogens. Reaction of Au nanoparticles with chloroform showed an unusual inverse isotope effect. The trichloromethyl spin adduct was observed when Au nanoparticles were mixed with CDCl(3) but not with CHCl(3). This unexpected behaviour suggests that C-H bond breaking is not the rate-determining step in Au-initiated hydrogen abstraction. 相似文献
23.
24.
In the present paper we obtain a sufficient condition for the exponential dichotomy of a strongly continuous, one-parameter
semigroup , in terms of the admissibility of the pair . It is already known the equivalence between the -admissibility condition and and the hyperbolicity of a C
0-semigroup , when we assume a priori that the kernel of the dichotomic projector (denoted here by X
2) is T(t)-invariant and is an invertible operator. We succeed to prove in this paper that the admissibility of the pair still implies the existence of an exponential dichotomy for a C
0-semigroup even in the general case where the kernel of the dichotomic projector, X
2, is not assumed to be T(t)-invariant.
相似文献
25.
Du L Xu L Li J Guo B Stoica P Bahr C Cattafesta LN 《The Journal of the Acoustical Society of America》2010,128(5):2877-2887
In this paper, several covariance-based approaches are proposed for aeroacoustic noise source analysis under the assumptions of a single dominant source and all observers contaminated solely by uncorrelated noise. The Crame?r-Rao Bounds (CRB) of the unbiased source power estimates are also derived. The proposed methods are evaluated using both simulated data as well as data acquired from an airfoil trailing edge noise experiment in an open-jet aeroacoustic facility. The numerical examples show that the covariance-based algorithms significantly outperform an existing least-squares approach and provide accurate power estimates even under low signal-to-noise ratio (SNR) conditions. Furthermore, the mean-squared-errors (MSEs) of the so-obtained estimates are close to the corresponding CRB especially for a large number of data samples. The experimental results show that the power estimates of the proposed approaches are consistent with one another as long as the core analysis assumptions are obeyed. 相似文献
26.
Tanţa Spătaru Petre Osiceanu Cornel Munteanu Nicolae Spătaru Akira Fujishima 《Journal of Solid State Electrochemistry》2012,16(12):3897-3905
In the present work, boron-doped diamond polycrystalline films were used as support for direct anodic deposition of the cobalt oxide, and continuous Co3O4 coatings with reasonably good conductivity were obtained by appropriately adjusting the deposition charge. Further electrochemical deposition of platinum particles on the oxide substrate enabled the formation of a stable composite with a specific capacitance of ca. 431 F?cm?3 that compares well with that available with similar materials obtained by non-electrochemical methods. Additional advantages of electrochemically obtained composites are the lower content of noble metal, the uniform distribution of the charge over an extended potential range, and, importantly, the simplicity of the preparation method. It was also found that when deposited on a Co3O4 substrate, Pt particles show, besides an enhanced active surface area, an improved catalytic activity for methanol anodic oxidation. This behavior was tentatively ascribed to the presence of a high amount of platinum-oxidized species. 相似文献
27.
The stability problem, the existence of periodic solutions and the numerical integration via the Lie-Trotter integrator of the Kirchhoff equations are discussed and some of their properties are pointed out. 相似文献
28.
Gorden Videen Alan Wetmore Melinda Petre Yuriy Shkuratov 《Journal of Quantitative Spectroscopy & Radiative Transfer》2006,100(1-3):406-414
We develop a second-order model of the light scattered by a cloud of randomly positioned dipoles and consider the interference of reciprocal rays that lead to enhanced backscatter and negative polarization. For large pathlength separations, we derive analytic expressions for the individual polarization intensities. 相似文献
29.
Gabriela Ionita Petre Ionita 《Journal of inclusion phenomena and macrocyclic chemistry》2003,45(1-2):79-82
A new crown ether, derived from the 2,2-diphenyl-1-picrylhydrazyl free radical (DPPH) and diaza-18-crown-6 (kryptofix 22) was synthesized.The physico-chemical properties of this new compound were studied using 1H- and 13C-NMR, EPR, UV-Vis, and IR spectroscopy. The compound has acid-base and redox properties, each of these involving a colour change (i.e., fromyellow to red-brown for acid-base processes, and from yellow to violet for redox processes).The transport properties of the compound were studied by means of biphasic (l/l or s/l) systems. Thus, by an acid-base process alkaline cations were transported into an organic phase, as well as arginine; by a redox process, short-lived freeradicals such as .C6H5 and .H were generated and observed by the EPR spin-trapping technique, using t-butyl-phenyl-nitrone (PBN) as spin-trap. 相似文献
30.
P. Budrugeac Alice Luminita Petre E. Segal 《Journal of Thermal Analysis and Calorimetry》1996,47(1):123-134
The validity of isoconversional methods used to evaluate the activation energy is discussed. The authors have shown that the Flynn-Wall-Ozawa and Friedman methods give results that agree with each other only if the activation energy does not change with the degree of conversion. A criterion for the reaction mechanism as expressed by the differential conversion function is suggested too. 相似文献