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51.
The crystal structures of [pipH]2[WS4] ( 1 ) and the new compounds [pipH]3[WS4](HS) ( 2 ) and [pipH]4[WS4][WOS3] ( 3 ) (pip = piperidine) were determined. Hydrogen bonds between the piperidinium cations and the thiotungstate anions play a dominant structural role. Their strength and number correlates with the degree of distortion found for the tetrahedral anions. Unshared hydrogen bonds have a considerably stronger effect than bifurcated ones; the effect of trifurcated hydrogen bonds is extremely weak. HS? and [WOS3]2? are considerably stronger H bond acceptors than the [WS4]2? anion. 相似文献
52.
53.
Results of a detailed crystallographic study of the structural phase transitions in LiKSO4, carried out using single crystal neutron diffraction at ambient and below-ambient temperatures (300–100 K), are presented. The study indicates two clear phase transitions at 205 K (from space group P63 to space group P31c), at 189 K (to space group Cc) and a third transition at about 130 K in the cooling cycle. The corresponding temperatures are 250 K, 200 K and 138 K in the heating cycle. The existence of twins, mixed phases, and extremely sluggish kinetics for the various phase transitions, as well as the structural details of the various phases in this mixed salt, can explain the apparent inconsistencies in the results of several experimental investigations reported in the literature. 相似文献
54.
Zhongzhi Zhang Shuigeng Zhou Yi Qi Jihong Guan 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,63(4):507-513
The uniform recursive tree (URT) is one of the most important models and has been successfully applied to many fields. Here
we study exactly the topological characteristics and spectral properties of the Laplacian matrix of a deterministic uniform
recursive tree, which is a deterministic version of URT. Firstly, from the perspective of complex networks, we determine the
main structural characteristics of the deterministic tree. The obtained vigorous results show that the network has an exponential
degree distribution, small average path length, power-law distribution of node betweenness, and positive degree-degree correlations.
Then we determine the complete Laplacian spectra (eigenvalues) and their corresponding eigenvectors of the considered graph.
Interestingly, all the Laplacian eigenvalues are distinct. 相似文献
55.
F. Semboloni 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,63(3):295-301
We show that a hierarchical cities structure can be generated by a self-organized process which grows with a bottom-up mechanism,
and that the resulting distribution is power law. First we
analytically prove that the power law distribution satisfies the balance between the offer of the city and the demand of its
basin of attraction, and that the exponent in the Zipf's law corresponds to the multiplier linking the population of the central
city to the population of its basin of attraction. Moreover, the corresponding hierarchical structure shows a variable
spanning factor, and the population of the cities linked
to the same city up in the hierarchy is variable as well. Second a stochastic
dynamic spatial model is proposed, whose numerical results confirm the analytical
findings. In this model, inhabitants minimize the transportation cost, so that the greater
the importance of this cost, the more stable is the system in its microscopic aspect.
After a comparison with the existent methods for the generation of a
power law distribution, conclusions are drawn on the connection of hierarchical
structure, and power law distribution, with the functioning of the system of cities. 相似文献
56.
M. Gligor M. Ausloos 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,63(4):533-539
GDP/capita correlations are investigated in various time windows (TW), for the time interval 1990–2005. The target group of
countries is the set of 25 EU members, 15 till 2004 plus the 10 countries which joined EU later on. The TW-means of the statistical
correlation coefficients are taken as the weights (links) of a fully connected network having the countries as nodes. Thereafter
we define and introduce the overlapping index of weighted network nodes. A cluster structure of EU countries is derived from the statistically relevant eigenvalues and
eigenvectors of the adjacency matrix. This may be considered to yield some information about the structure, stability and
evolution of the EU country clusters in a macroeconomic sense. 相似文献
57.
A. Grabowski N. Kruszewska R. A. Kosiński 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,66(1):107-113
We study properties of five different social systems: (i) internet society of friends consisting of over 106 people, (ii) social network consisting of 3 × 104 individuals, who interact in a large virtual world of Massive Multiplayer Online Role Playing Games (MMORPGs), (iii) over
106 users of music community website, (iv) over 5 × 106 users of gamers community server and (v) over 0.25 × 106 users of books admirer website. Individuals included in large social network form an Internet community and organize themselves
in groups of different sizes. The destiny of those systems, as well as the method of creating of new connections, are different,
however we found that the properties of these networks are very similar.
We have found that the network components size distribution follow the power-law scaling form. In all five systems we have
found interesting scaling laws concerning human dynamics. Our research has shown how long people are interested in a single
task, how much time they devote to it and how fast they are making friends. It is surprising that the time evolution of an
individual connectivity is very similar in each system. 相似文献
58.
Zhongzhi Zhang Shuigeng Zhou Zhan Su Tao Zou Jihong Guan 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,65(1):141-147
In this paper, we define a stochastic Sierpinski gasket, on the basis of which we construct a network called random Sierpinski
network (RSN). We investigate analytically or numerically the statistical characteristics of RSN. The obtained results reveal
that the properties of RSN is particularly rich, it is simultaneously scale-free, small-world, uncorrelated, modular, and
maximal planar. All obtained analytical predictions are successfully contrasted with extensive numerical simulations. Our
network representation method could be applied to study the complexity of some real systems in biological and information
fields. 相似文献
59.
An orthonormal crystal of carbon with PMMA space group (o-C8) was found to be a stable superhard carbon allotrope by particle swarm optimization algorithm and density functional calculations. The phonon spectrum calculations demonstrate that the o-C8 carbon phase is dynamically stable. The volume compression calculations show that it is highly incompressible, with bulk modulus of 298.6 GPa. The calculations demonstrate that it is a low-density superhard material with density of 2.993 g/cm3 and Vickers hardness of 82.4 GPa. 相似文献
60.
Louis R. Pignotti Natcharee Kongprakaiwoot William W. Brennessel Jonas Baltrusaitis Rudy L. Luck Eugenijus Urnezius 《Journal of organometallic chemistry》2008,693(20):3263-3272
Reactions of 1,4-difluoro-2,5-dimethoxybenzene with LDA (1:2) at low temperatures generated organodilithio intermediates; quenching the reaction mixtures with chlorophosphines ClPR2 produced 1,4-bis(phosphino)-2,5-difluoro-3,6-dimethoxybenzenes 1a (R = Ph) and 1b (R = iPr). Demethylation of 1a–b was accomplished by BBr3, yielding bis(phosphino)hydroquinones 2a–b. Treating 2a–b with excess hydrogen peroxide produced bis(phosphinyl)hydroquinones 3a–b. The binucleating properties of 2a were established by the formation of a bimetallic nickel complex upon reaction with Ph2Ni(PMe3)2. Electrochemical activity of hydroquinones 2a–b and 3a–b was examined by cyclic voltammetry. In addition, compounds 2a, 3a and 3b were obtained in crystalline form and characterized by single-crystal X-ray diffraction. The influence of the fluorine substituents on the composition of the frontier orbitals of 2a and 3a was examined by computational methods. 相似文献