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排序方式: 共有327条查询结果,搜索用时 31 毫秒
1.
G. M. Ter-Akopian A. V. Daniel A. S. Fomichev G. S. Popeko A. M. Rodin Yu. Ts. Oganessian J. H. Hamilton A. V. Ramayya J. Kormicki J. K. Hwang D. Fong P. Gore J. D. Cole M. Jandel J. Kliman L. Krupa J. O. Rasmussen I. Y. Lee A. O. Macchiavelli P. Fallon M. A. Stoyer R. Donangelo S. -C. Wu W. Greiner 《Physics of Atomic Nuclei》2004,67(10):1860-1865
Ternary fission of 252Cf was studied at Gammasphere using eight ΔE×E particle telescopes. Helium, beryllium, boron, and carbon light charged particles (LCPs) emitted with kinetic energy more than 9, 21, 26, and 32 MeV, respectively, were identified. The 3368-keV γ transition from the first 2+ excited state in 10Be was found and the population probability ratio N(2+)/N(0+) = 0.160 ± 0.025 was estimated. No evidence was found for 3368-keV γ rays emitted from a triple molecular state. For the first time, charge distributions are obtained for ternary fission fragments emitted with helium, beryllium, and carbon LCPs. 相似文献
2.
Jeffrey C. Johnson Dawn L. Parks 《Computational & Mathematical Organization Theory》1998,4(3):223-239
Earlier research has shown a relationship between various forms of structural centrality and perceived leadership and role
satisfaction in small experimental groups. The limited amount of research on this topic in naturally occurring social networks
has yielded results that often conflict with one another. Different results have generally been attributed to possible differences
in task environments. This paper examines the relationship between two types of structural centrality and perceived influence,
role satisfaction, and perceived effectiveness in an environmental resource management program. Findings in this paper suggest
that the observed differences in relationships between the network and other variables is partly a function of global network
properties (e.g., marginality of subgroups) and related task environments.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
3.
4.
Although hyperconjugation involving alkyl groups to a carbocation is a well-established concept, the analogous charge delocalization generated in anions by electronegative substitution has long been a subject of controversy. We have investigated this phenomenon for the β-hydroxyethyl and β-trifluoroethyl anions using ab initio electronic structure calculations. Split valence basis sets augmented by diffuse functions were used with fully optimized geometries. Three dimensional molecular orbital plots clearly show an in-plane HOMO-LUMO mixing of a C-X σ antibonding orbital with the carbon lone pair which yields hyperconjugative π bonding in the anti conformation. Deformation density maps further demonstrate that this delocalization leads to the development of a π component as well as a previously unrecognized sigma enhancement. These results support and extend the work of Apeloig and that of Schleyer and Kos, but are in opposition to the induction hypothesis of Streitwieser and Holtz. The recent experimental determination of the acidity of (CF3)3CH by Tatlow and their interpretation in terms of fluorine hyperconjugation are also in accord with this work. 相似文献
5.
Kmak Kelly N. Despotopulos John D. Shaughnessy Dawn A. 《Journal of Radioanalytical and Nuclear Chemistry》2019,319(1):257-261
As a continuation of previous work (Kmak et al. in J Radioanal Nucl Chem 314:985–989, 2017), an isotope generator column based on the 210Pb decay chain has been made to produce highly radiopure 210Po. Two replicate studies were performed on AG 50Wx8 columns with an average yield of 90.4 ± 1.9%. 210Pb breakthrough was seen at the 6 month elution for both generators.
相似文献6.
A template-directed strategy to forming a bis(diimide) macrocycle through an intermediate asymmetric [2]catenane is reported. Saponification of the ester linkages within the crown ether component is much slower in the mechanically interlocked structure when compared to the free crown. The predominance of a single translational isomer leads to a dimeric structure, resulting in the generation of infinite channels within the crystal lattice. [structure: see text] 相似文献
7.
Masuda J Maynard DM Nishimura M Ueda T Kowalak JA Markey SP 《Journal of chromatography. A》2005,1063(1-2):57-69
A one- or two-dimensional high performance liquid chromatography system for electrospray ionization mass spectrometers has been developed that is optimized for ion exchange and reversed phase separations. A unique and simple valve configuration permits the use of a variety of non-volatile salts; ammonium sulfate was used in an example of strong cation exchange separations. The system was designed and evaluated for both micro- and nanoflow chromatography. The peptide detection limit was approximately 100 fmol for micro- and 20 fmol for nanoflow, demonstrating the concentration and mass sensitivity improvements expected with nanoelectrospray ionization. The 1D/2D-HPLC MS system is fully automated for routine peptide analyses, compatible with direct injection of proteolytic digests, and exhibits chromatographic reproducibility and sensitivity. Software permits operator selection of either a 1D or 2D configuration with corresponding system parameters as required for individual samples. The hardware elements and resulting performance are described in this paper. 相似文献
8.
Li S Marthandan N Bowerman D Garner HR Kodadek T 《Chemical communications (Cambridge, England)》2005,(5):581-583
We report here a strategy for the photolithographic synthesis of diverse, spatially addressable arrays of cyclic peptides which employs a differential deprotection strategy for the combinatorial addition of side chains to a pre-fabricated cyclic core. 相似文献
9.
Eric A. Gregory Mark R. Buckingham Dawn Z. Clayton Freda J. Wolfenden C.J.S.M. Simpson 《Chemical physics letters》1984,104(4):393-397
Rate constants for the vibrational deactivation of CD4 by the collision partners CD4, He, Ne, Ar, Kr, D2 and O2 have been measured using a laser-fluorescence technique. The results are compared with those for the deactivation of CH4 by the same collision partners and with a modified SSH type theoretical treatment. 相似文献
10.