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301.
Fedor I. Zubkov Julya D. Ershova Vladimir P. Zaytsev Alexandr S. Peregudov Roman S. Borisov Abel M. Maharramov 《Tetrahedron》2009,65(18):3789-9163
The interaction between 1-furyl-1,2,3,4-tetrahydroisoquinolines and unsaturated acids derivatives (acryloyl, methacryloyl, and crotonoyl chloride, maleic and citraconic anhydride) was studied. It was shown that the reaction proceeds via amide formation and subsequent intramolecular Diels-Alder reaction of the furan (IMDAF). The [4+2] cycloaddition proceeded under mild reaction conditions (25-80 °C) and afforded only the exo-adduct in a high yield. With this method, a new approach to the isoindolo[1,2-a]isoquinoline system, the basic structural element of alkaloids Jamtine, Hirsutine, and Nuevamine, is proposed. 相似文献
302.
For every graph G, let . The main result of the paper says that every n-vertex graph G with contains each spanning subgraph H all whose components are isomorphic to graphs in . This generalizes the earlier results of Justesen, Enomoto, and Wang, and is a step towards an Ore-type analogue of the Bollobás-Eldridge-Catlin Conjecture. 相似文献
303.
Henry A. Kierstead Alexandr V. Kostochka Marcelo Mydlarz Endre Szemerédi 《Combinatorica》2010,30(2):217-224
A proper vertex coloring of a graph is equitable if the sizes of color classes differ by at most one. The celebrated Hajnal-Szemerédi Theorem states: For every positive integer
r, every graph with maximum degree at most r has an equitable coloring with r+1 colors. We show that this coloring can be obtained in O(rn
2) time, where n is the number of vertices. 相似文献
304.
The dynamic behavior of thermodynamic system, described by one order parameter and one control parameter, in a small neighborhood of ordinary and bifurcation equilibrium values of the system parameters is studied. Using the general methods of investigating the branching (bifurcations) of solutions for nonlinear equations, we performed an exhaustive analysis of the order parameter dependences on the control parameter in a small vicinity of the equilibrium values of parameters, including the stability analysis of the equilibrium states, and the asymptotic behavior of the order parameter dependences on the control parameter (bifurcation diagrams). The peculiarities of the transition to an unstable state of the system are discussed, and the estimates of the transition time to the unstable state in the neighborhood of ordinary and bifurcation equilibrium values of parameters are given. The influence of an external field on the dynamic behavior of thermodynamic system is analyzed, and the peculiarities of the system dynamic behavior are discussed near the ordinary and bifurcation equilibrium values of parameters in the presence of external field. The dynamic process of magnetization of a ferromagnet is discussed by using the general methods of bifurcation and stability analysis presented in the paper. 相似文献
305.
Thermal transport in semiconductor nanostructures,graphene,and related two-dimensional materials 下载免费PDF全文
We review experimental and theoretical results on thermal transport in semiconductor nanostructures(multilayer thin films, core/shell and segmented nanowires), single-and few-layer graphene, hexagonal boron nitride, molybdenum disulfide, and black phosphorus. Different possibilities of phonon engineering for optimization of electrical and heat conductions are discussed. The role of the phonon energy spectra modification on the thermal conductivity in semiconductor nanostructures is revealed. The dependence of thermal conductivity in graphene and related two-dimensional(2 D) materials on temperature, flake size, defect concentration, edge roughness, and strain is analyzed. 相似文献
306.
Alexandr V. Kuzminykh 《Journal of Geometry》2004,79(1-2):134-145
A family of convex bodies in Ed is called neighborly if the
intersection of every two of them is (d-1)-dimensional. In the present paper we
prove that there is an infinite neighborly family of centrally symmetric convex bodies
in Ed, d 3, such that every two of them are affinely equivalent
(i.e., there is an affine transformation mapping one of them onto another), the
bodies have large groups of affine automorphisms, and the volumes of the bodies are
prescribed. We also prove that there is an infinite neighborly family of centrally
symmetric convex bodies in Ed such that the bodies have large groups of
symmetries. These two results are answers to a problem of B. Grünbaum (1963). We
prove also that there exist arbitrarily large neighborly families of similar convex
d-polytopes in Ed with prescribed diameters and with arbitrarily large
groups of symmetries of the polytopes. 相似文献
307.
The interaction of sound with hydrodynamic turbulence has been studied in detail. The sound absorption decrement, the correlation time and length and the frequency diffusion coefficient for the acoustic wave packet are calculated. The spectral composition of the sound radiated by a unit, turbulent volume and the spectral energy density of sound in equilibrium with the turbulence are studied. The region of applicability of the kinetic equation for sound with a linear dispersion low is found. 相似文献
308.
309.
Alexandr V. Yatsenko Victor A. Tafeenko Sergei G. Zhukov Sergei V. Medvedev Sergei I. Popov 《Structural chemistry》1997,8(3):197-204
Substituted 1-hydroxy-9,10-anthraquinone-9-imines have been found to exhibit tautomeric interconversions between the 9,10- and 1,10-quinonoid forms in the solid state as well as in solution. Single-crystal X-ray crystallography was used to study the structures of 4-(N-acetyl-p-tolylamino)-9-amino-1,10-anthracenedione and 4-hydroxy-1-phenylamino-10-mesitylimino-9(10H)-anthracenone at ambient and low temperatures. The former compound gave crystals belonging to the monoclinic space group P2l/c and, at 295 K,a=9.684(2),b=16.371(3),c=12.097(2) å,=110.41(1), V=1797 å3,Z=4, R(F)=0.042, and GOF=0.863. The latter compound gave crystals belonging to the monoclinic space group C2/c and, at 295 K,a=38.158(8),b=6.322(2),c=19.325(4) å,=101.78(2),V=4564 å3,Z=8, R(F)=0.052, and GOF=0.981, while at 150 K,a=37.852(6),b=6.245(1),c=19.235(4) å,=102.81(1),V=4434 å3,R(F)=0.047, and GOF=1.006. Comparison of the geometric parameters of the two compounds illustrates the considerable zwitterionic nature of the first, a distinctive feature of which is a very short bond N(9)-C(9) whose length is essentially equal to that of a double bond. Molecular modeling studies using AMI semiempirical calculations were shown to be capable of satisfactorily reproducing the energetics of the tautomeric equilibrium once the medium effect was taken into account. 相似文献
310.
Alexandr Kazda 《Algebra Universalis》2016,75(1):75-84
We prove that whenever \({\mathbb {A}}\) is a 3-conservative relational structure with only binary and unary relations, then the algebra of polymorphisms of \({\mathbb {A}}\) either has no Taylor operation (i.e., CSP(\({\mathbb {A}}\)) is NP-complete), or it generates an SD(\({\wedge}\)) variety (i.e., CSP(\({\mathbb {A}}\)) has bounded width). 相似文献