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711.
Percec V Holerca MN Nummelin S Morrison JJ Glodde M Smidrkal J Peterca M Rosen BM Uchida S Balagurusamy VS Sienkowska MJ Heiney PA 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(24):6216-6241
General, efficient and inexpensive methods for the synthesis of dendritic building blocks methyl 3',4'-dihydroxybiphenyl-4-carboxylate, 3',5'-dihydroxybiphenyl-4-carboxylate, and methyl 3',4',5'-trihydroxybiphenyl-4-carboxylate were elaborated. In all syntheses the major step involved an inexpensive Ni(II)-catalyzed Suzuki cross-coupling reaction. These three building blocks were employed together with methyl 4'-hydroxybiphenyl-4-carboxylate in a convergent iterative strategy to synthesize seven libraries containing up to three generations of 3',4'-, 3',5'-, and 3',4',5'-substituted biphenyl-4-methyl ether based amphiphilic dendrons. These dendrons self-assemble into supramolecular dendrimers that self-organize into periodic assemblies. Structural and retrostructural analysis of their assemblies demonstrated that these dendrons self-assemble into hollow and non-hollow supramolecular dendrimers exhibiting dimensions of up to twice those reported for architecturally related dendrons based on benzyl ether repeat units. These new dendrons expand the structural diversity and demonstrate the generality of the concept of self-assembling dendrons based on amphiphilic arylmethyl ethers. 相似文献
712.
The authors of the present paper outline aspects on the optimization of the a TR-type industrial robot structure movements in order to generate the manipulation space to a flexible manufacturing cell with a parallel organization designed for the pallet and container operation of paint-filled recipients. The paper contains the direct and inverted geometrical modelling of the robot structure using the 3*3 rotation matrix method and the algebra method. After knowing the characteristic point movement of the prehension device, graphics for the variation of the TR robot's general coordinates and for the trajectory of the prehension device's characteristic point of its work space were performed by using the Mathematica 6.0 soft. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
713.
We construct an example of a 2-dimensional Stein normal space X with one singular point x
0 such that X\{x
0} is simply connected and it satisfies the disk condition. This answers a question raised by Forn?ss and Narasimhan. We also
prove that any increasing union of Stein open sets contained in a Stein space of dimension 2 satisfies the disk condition.
Starting from the above example we exhibit, without using deformation theory, a new type of 2-dimensional holes which cannot
be filled. 相似文献
714.
The subject matter of this paper concerns the numerical approximation of reduced Vlasov–Maxwell models by semi-Lagrangian
schemes. Such reduced systems have been introduced recently in the literature for studying the laser–plasma interaction. We
recall the main existence and uniqueness results on these topics, we present the semi-Lagrangian scheme and finally we establish
the convergence of this scheme. 相似文献
715.
Strongly motivated by its possible applications in Mechanics, in our previous work (Pitea and Postolache (Optim. Lett. doi:10.1007/s11590-010-0272-0, 2011)), we initiated an optimization theory for the second order jet bundle. We considered the problem of minimization of vectors of curvilinear functionals (well known as mechanical work), thought as multi-time multi-objective variational problems, subject to PDE and/or PDI constraints. Within this framework, we introduced necessary conditions. As natural continuation of our results in Pitea and Postolache (Optim. Lett. doi:10.1007/s11590-010-0272-0, 2011), the present work introduces a study of sufficient efficiency conditions. While the background in Sect. 2 is introductory, the theory in Sect. 3 is new as a whole, containing our results. 相似文献
716.
Caleap M Drinkwater BW Wilcox PD 《The Journal of the Acoustical Society of America》2012,131(3):2036-2047
Propagation of plane compressional waves in a non-viscous fluid with a dense distribution of identical spherical scatterers is investigated. The analysis is based on the multiple scattering approach proposed by Fikioris and Waterman, and is generalized to include arbitrary choice of the pair-correlation functions used to represent the distribution of the scatterers. A closed form solution for the effective wavenumber as a function of the concentration of pair-correlated finite-size spheres is derived up to the second order. In the limit of uncorrelated point-scatterers, this solution is identical to that obtained by Lloyd and Berry. Different pair-correlation functions are exemplified and compared, and the resulting differences discussed. 相似文献
717.
Bogdan M. Diaconu Mihai Cruceru Adina Teodora Gheorghian Luminiţa Georgeta Popescu 《Journal of Quantitative Spectroscopy & Radiative Transfer》2012,113(16):2100-2112
View factor – defined as fraction of total outgoing radiation from surface 1 intercepted by surface 2 – is a key concept in solving the radiative heat transfer in systems of surfaces. Analytical forms of the view factor have been developed by means of integration for many conventional systems of 2D and 3D surfaces in various spatial positions. However, little investigation has been carried out for situations in which there is no complete visibility between the surfaces involved in radiative exchange due to configuration of 3D surfaces or due to presence of interposing object that obstruct partially the mutual visibility.Radiative heat exchange was modeled in a finite length cylindrical annulus consisting of non-isothermal diffusely-emitting surfaces. The canonical definition of the view factor was extended by means of an analytical approach to both 3D and 2D surfaces with shading effects (incomplete mutual visibility) and numerical algorithms were developed in order to calculate view factors values and test view factor algebra rules. The system considered in this paper was an axysymmetric cylindrical annulus – frequently used in many heat transfer applications. View factor values for various surface elements were calculated by means of numerical integration. View factor algebra rules – summation and reciprocity – were verified. 相似文献
718.
Single crystals of tungstenite (WS2) have been grown by direct vapour transport or sublimation method. An etchant capable of revealing the sites of dislocations has been developed. The effects of etching time, etchant concentration and temperature on the selective etch rate have been worked out. It is seen that the etch rate is independent on time, but is influenced by the temperature and concentration of the etchant. The values of activation energy determined from the etch rate against temperature plots established that the process of etching in chromic acid is chemical reaction rate controlled. The effect of addition of HF to the above etchant has led to some further interesting results. 相似文献
719.
720.
Mathematical Programming - We consider solving nonlinear optimization problems with a stochastic objective and deterministic equality constraints. We assume for the objective that its evaluation,... 相似文献