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991.
W. Vervisch C. Mottet J. Goniakowski 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):311-314
Morphology and atomic structure of supported Pd clusters
on MgO(100) substrate are investigated theoretically using a
mixed approach: a semi-empirical potential for the metal bonding
within the cluster and a potential fitted to
ab initio calculations for
the metal-oxide interaction. We find that the clusters adopt a
truncated pyramidal morphology in agreement with experimental
results. The detailed study of the epitaxial relation as a
function of cluster size shows the existence of a critical size
around 3 nm where elastic strain due to the misfit between the
substrate and the deposit is released by the introduction of
interfacial dislocations. 相似文献
992.
Collisionless star clusters in dynamical equilibrium are of current interest in general relativity and astrophysics. A step-function
distribution is chosen for star clusters. The corresponding equation of state is analogous to a Fermi-gas equation. These
clusters are found to be pulsationally unstable for a central redshift ofZ
c
⩾ 0·54. Further, a model of clusters is developed in which the core has an extremely relativistic equation of state. These
structures are unstable forZ
c
⩾ 2·55 when we use Chandrasekhar’s technique to study their pulsational stability. 相似文献
993.
D S Narayan 《Pramana》1979,12(4):391-395
The production of prompt neutrinos in the beam dump experiment is explained in a cluster model, by postulating the emission
of strange clusters in hadron collisions, besides the usual non-strange clusters. The low mass strange clusters can decay
only by the weak interaction. The leptonic and semi-leptonic decay modes of these clusters give rise to prompt neutrinos.
A prediction of the model is that the ratios <v
e>/π
+ at PS energies would be the same as SPS energies. 相似文献
994.
We consider a finite chain of particles in one dimension, interacting through the Lennard-Jones potential. We prove the ground state is unique, and approaches uniform spacing in the infinite-particle limit.Research supported in part by NSF grant MCS 78-01520. 相似文献
995.
Possible structures for Si10 cluster are considered using a tight-binding model and drawing on significant work done in the past. It is shown that the tight-binding parametrization, fitted to the bulk, is also valid for smaller systems. This model is found to essentially reproduce other published results, but requires much less effort thanab initio techniques—thus, allowing the study of a wide variety of structures and their ions. However, unlike classical force-field calculations, it yields information about the electronic structure of clusters. A new geometric structure for Si10 is found, which is not only of lowest energy, but which also matches the experimental photoelectron band gap and explains the experimental reactivity data. Because of the Jahn-Teller effect, the photoelectron spectrum is very sensitive to geometry. Also, ionization of the cluster alters the geometry slightly. 相似文献
996.
Edward Rosenberg Fabrizio Spada Brooke Martin Luciano Milone 《Journal of organometallic chemistry》2004,689(25):4729-4738
The water-soluble triosmium cluster [Os3(CO)9(μ-η2-(4-CHO)C9H5N)(μ-H)(P(OCH2CH2N(CH3)3I)3)] (4) was tested for its reactivity with plasmid DNA. In contrast to the band retardation previously observed with a related series of positively charged clusters, an intensification and retardation of three discrete bands was observed with increasing cluster concentration. In order to further investigate the apparent modification of DNA by 4, its interaction with a 22-oligomer (sequence 5′-AGT TGT GGT GAC TTT CCC AGG C-3′) was examined. Incubation with this oligonucleotide (pH 7.4 in Tris-HCl buffer and 100 mM NaCl) followed by HPLC analysis revealed the formation of three dose dependent products assigned as covalent modifications at three sites of the oligonucleotide. Incubation of 4 with 32P-ATP labeled oligonucleotide at the 5′-end followed by treatment with piperidine and comparison with the standard Maxam-Gilbert sequencing protocol products revealed only general background cleavage, indicating that the modification products are piperidine labile and suggesting that the modification involved formation of a Schiff base. An alternative approach was then pursued which involved annealing the 4-oligonucleotide products with their complementary strand and treatment of the resulting duplex DNAwith the exonuclease, Exo III. This assay indicated three exonuclease stops, consistent with the three products observed by HPLC whose electrophoretic mobility approximately matched guanine containing fragments when compared with the Maxam-Gilbert sequencing lanes. Reduction of the 4-oligonucleotide products with borohydride reducing agents, followed by treatment with piperidine, resulted in the formation of one product (by HPLC) with the same electrophoretic mobility as the AGTT fragment based on comparison with the Maxam-Gilbert sequencing lanes. This product most likely results from reduction of an initially formed Schiff base adduct (to the corresponding amine) with the guanine of the TGT fragment of the oligonucleotide, and corresponds to the most stable of the three Schiff base adducts detected by HPLC and by incubation with the exonuclease. The other two products are less stable and competitive reduction of the free aldehyde functionality on the cluster in equilibrium with these adducts precludes their detection after treatment with the reducing agents. The formation of the Schiff base adduct is further corroborated by the model reaction of [Os3(CO)10(μ-η2-(4-CHO)C9H5N)(μ-H)] (4′) with acetylated guanine in nonaqueous solvents where disappearance of the aldehyde resonance and the appearance of several new resonances in the 6-9 ppm region of the 1H NMR of the reaction mixture is noted. 相似文献
997.
Izarova N. V. Sokolov M. N. Cadot E. Marrot J. Secheresse F. Fedin V. P. 《Russian Chemical Bulletin》2004,53(7):1503-1506
The polyoxothiometalate complex [{Mo3S4(H2O)5}4(-SiW10O36)4]16– was prepared by the reaction of the cationic triangular molybdenum aqua complex [Mo3S4(H2O)9]4+ (electrophile) with the lacunary polyoxotungstate complex [-SiW10O36]8– (nucleophile). According to the results of single-crystal X-ray diffraction analysis of the dimethylammonium salt, the anionic nanocluster contains 52 molybdenum and tungsten atoms and has a cyclic porphyrin-like structure. 相似文献
998.
999.
Brylev K. A. Virovets A. V. Naumov N. G. Mironov Yu. V. Fenske D. Fedorov V. E. 《Russian Chemical Bulletin》2001,50(7):1140-1143
The new octahedral molybdenum thiocyanide cluster complex K7[Mo6S8(CN)6]·8H2O was synthesized by excision of the cluster core (the reaction of ZnMo6S8 with a melt of KCN). The structure of the complex was established by X-ray diffraction analysis. The reaction of Mo6Se8 with a KCN—KSCN mixture afforded the mixed-ligand cluster anions [Mo6(Se,S)8(CN)6]7–. The salt of composition K1.5Cs5.5[Mo6Se6.8S1.2(CN)6]·8H2O was obtained. The complexes are isostructural to each other and to the selenium analog described previously. The magnetic properties and the electronic and IR spectra were measured and discussed. 相似文献
1000.
M. Kaisermayr B. Sepiol H. Thiess G. Vogl E.E. Alp W. Sturhahn 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,22(3):335-341
Time-domain interferometry of synchrotron radiation (TDI) has recently been used as a tool for investigating diffusion in
glasses. This work deals with an extension of this technique to ordered structures. In a TDI experiment performed on the B2 alloy CoGa at the APS the intensity scattered into Bragg directions showed no detectable quasielastic signal. Experimental
lower limits of the elastic contribution are given. They are in accordance with the coherent scattering function derived in
this paper. This result indicates that TDI can be applied to diffusion in crystalline solids, e.g. intermetallic alloys, by using diffuse scattering. Requirements and limitations of diffuse scattering experiments are discussed.
Received 21 September 2000 and Received in final form 13 December 2000 相似文献