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481.
The platinum(II) complexes trans-[PtCl(2)(RR'C=NOH)(2)], where R = R' = Me, RR' = (CH(2))(4) and (CH(2))(5), react with m-chloroperoxybenzoic acid in Me(2)CO to give the platinum(IV) complexes [PtCl(2)(OCMe(2)ON=CRR')(2)] in 50-60% yields. The complexes [PtCl(2)(OCMe(2)ON=CRR')(2)] were characterized by elemental analysis, EI-MS, and IR and Raman spectroscopies; X-ray structure analyses were performed for both trans-[PtCl(2)(OCMe(2)ON=CC(4)H(8))(2)] and trans-[PtCl(2)(OCMe(2)ON=CC(5)H(10))(2)]. The former compound crystallizes in the triclinic space group P&onemacr; with a = 8.088(2) ?, b = 8.327(2) ?, c = 8.475(2) ?, alpha = 103.54(3) degrees, beta = 102.15(3) degrees, gamma = 108.37(3) degrees, V = 501.0(2) ?(3), Z = 1, and rho(calcd) = 1.917 g cm(-)(3). The latter complex crystallizes in the monoclinic space group C2/c with a = 12.5260(10) ?, b = 9.3360(10) ?, c = 18.699(2) ?, beta = 98.320(10) degrees, V = 2163.7(4) ?(3), Z = 4, and rho(calcd) = 1.862 g cm(-)(3). The structures of [PtCl(2)(OCMe(2)ON=CC(4)H(8))(2)] and [PtCl(2)(OCMe(2)ON=CC(5)H(10))(2)] show an octahedron of Pt where two Cl atoms and two chelate ligands are mutually trans, respectively. 相似文献
482.
Lewis acidic aluminum in zeolites, particularly acidity that is inherent to the framework, is an indeterminate concept. A fraction of framework aluminum changes geometry to octahedral coordination in the proton form of zeolite mordenite. Such octahedrally coordinated aluminum is the precursor of a Lewis acid site and its formation is accompanied by a loss in Brønsted acidity. Herein, we show that such Lewis acid sites have a preferred location in the pore structure of mordenite. A greater proportion of these Lewis acid sites resides in the side-pockets than in the main channel. By reverting the octahedrally coordinated aluminum back to a tetrahedral geometry, the corresponding Brønsted acid sites are restored with a concomitant loss in the ability to form Lewis acid sites. Thereby, reversible octahedral–tetrahedral aluminum coordination provides a means to indirectly switch between Lewis and Brønsted acidity. This phenomenon is unique to Lewis acidity that is inherent to the framework, thereby distinguishing it from Lewis acidity originating from extra-framework species. Furthermore, the transformation of framework aluminum into octahedral coordination is decoupled from the generation of distorted tetrahedrally coordinated aluminum, where the latter gives rise to the IR band at 3660 cm−1 in the OH stretching region.Framework-associated aluminum is demonstrated to facilitate a reversible switch between Lewis and Brønsted acidity in zeolites with the Lewis acid sites preferentially populating the side-pockets in the case of mordenite. 相似文献
483.
Hans Kellerer Vitaly A. Strusevich 《4OR: A Quarterly Journal of Operations Research》2012,10(2):111-161
This paper reviews two problems of Boolean non-linear programming: the Symmetric Quadratic Knapsack Problem and the Half-Product Problem. The problems are related since they have a similar quadratic non-separable objective function. For these problems, we focus on the development of fully polynomial-time approximation schemes, especially of those with strongly polynomial time, and on their applications to various scheduling problems. 相似文献
484.
Mikhail A. Kubzin Vitaly A. Strusevich 《4OR: A Quarterly Journal of Operations Research》2005,3(4):303-313
We study a two-machine flow shop scheduling problem with no-wait in process, in which one of the machines is subject to mandatory
maintenance. The length of the maintenance period is defined by a non-decreasing function that depends on the starting time
of that maintenance. The objective is to minimize the completion time of all activities. We present a polynomial-time approximation
scheme for this problem.
Received: November 2004 / Received version: March 2005
AMS classification:
90B35, 90B30, 90C59
The research was partly supported by INTAS (Project 03-51-5501)
All correspondence to: Vitali A. Strusevich 相似文献
485.
Vitaly V. Fedorchuk 《Topology and its Applications》2007,154(16):2976-2982
In this article we give a sufficient condition for a space X to have the fully closed absolute faX with the property fa(faX)=faX. An example of a compact space X such that the canonical mapping fa(α+1)X→fa(α)X (where α is a given ordinal) is not a homeomorphism is constructed. Also we give an example of a compact space X such that the canonical mapping faX→X is not a homeomorphism but for which there exists a homeomorphism faX→X. 相似文献
486.
487.
Roman?R.?Bavin Dmitry?I.?Furtsov Vladimir?A.?Zabrodin Victor?P.?Tarasov Vitaly?I.?VolkovEmail author 《Applied magnetic resonance》2017,48(2):135-142
The swelling processes of rubbers on the basis of ethylene–propylene SKEPT-40, butadiene–nitrile SKN-18, and fluorine SKF-26 caoutchoucs in transformer oil GK were investigated by 1H nuclear magnetic resonance spectroscopy and 1H NMR relaxation techniques. The main rubber-swelling singularities were developed. It was shown that polymeric affinity to oil decreases in the next rubber row—ethylene–propylene, fluorine, and butadiene–nitrile. The oil molecular mobility is on the contrary increased in the same row. The surface NMR probe express test of oil amount in real production was introduced. 相似文献
488.
V’yacheslav Akkerman Mikhail Ivanov Vitaly Bychkov 《Flow, Turbulence and Combustion》2009,82(3):317-337
Turbulence produced by the piston motion in spark-ignition engines is studied by 2D axisymmetric numerical simulations in
the cylindrical geometry as in the theoretical and experimental work by Breuer et al. (Flow Turbul Combust 74:145, 2005). The simulations are based on the Navier–Stokes gas-dynamic equations including viscosity, thermal conduction and non-slip
at the walls. Piston motion is taken into account as a boundary condition. The turbulent flow is investigated for a wide range
of the engine speed, 1,000–4,000 rpm, assuming both zero and non-zero initial turbulence. The turbulent rms-velocity and the
integral length scale are investigated in axial and radial directions. The rms-turbulent velocity is typically an order-of-magnitude
smaller than the piston speed. In the case of zero initial turbulence, the flow at the top-dead-center may be described as
a combination of two large-scale vortex rings of a size determined by the engine geometry. When initial turbulence is strong,
then the integral turbulent length demonstrates self-similar properties in a large range of crank angles. The results obtained
agree with the experimental observations of Breuer et al. (Flow Turbul Combust 74:145, 2005). 相似文献
489.
Physical mechanism of ultrafast flame acceleration 总被引:1,自引:0,他引:1
We explain the physical mechanism of ultrafast flame acceleration in obstructed channels used in modern experiments on detonation triggering. It is demonstrated that delayed burning between the obstacles creates a powerful jetflow, driving the acceleration. This mechanism is much stronger than the classical Shelkin scenario of flame acceleration due to nonslip at the channel walls. The mechanism under study is independent of the Reynolds number, with turbulence playing only a supplementary role. The flame front accelerates exponentially; the analytical formula for the growth rate is obtained. The theory is validated by extensive direct numerical simulations and comparison to previous experiments. 相似文献
490.
Valeriya G. Melekhina Andrey N. Komogortsev Boris V. Lichitsky Vitaly S. Mityanov Artem N. Fakhrutdinov Arkadii A. Dudinov Vasily A. Migulin Yulia V. Nelyubina Elizaveta K. Melnikova Michail M. Krayushkin 《Tetrahedron letters》2019,60(39):151080
An unexpected photochemical transformation of imidazole derivatives containing the 5-hydroxy-2-methyl-4H-pyran-4-one moiety was discovered, which led to the synthesis of previously unknown imidazo[1,5-a]pyridine-5,8-dione derivatives. The structures of imidazole and imidazo[1,5-a]pyridine-5,8-dione derivatives were unambiguously determined by X-ray diffraction analysis. 相似文献