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91.
An enantioselective α-amination of aryl oxindoles catalyzed by a dimeric quinidine has been developed. The reaction is general, broad in substrate scope, and affords the desired products in good yields with good to excellent enantioselectivities. This study provides the first examples of a general organocatalytic method for the creation of nitrogen-containing, tetrasubstituted chiral centers at C(3) of various aryl oxindoles. Furthermore, new catalysts and insights into structural elements of the catalysts that significantly influence enantioselectivities are disclosed. 相似文献
92.
Si Bui Quang Tran Doyoung Byun Vu Dat Nguyen Hadi Teguh Yudistira Myoung Jong Yu Kyun Ho Lee Jaeuk U. Kim 《Journal of Electrostatics》2010,68(2):138-144
In this paper, “end effect”, which represents the deflection of meniscus of boundary nozzles in an array due to asymmetric electric field and repulsive forces between adjacent nozzles, is experimentally investigated and a polymer-based electrospray device is fabricated and tested to minimize the end effect. For the electrically conductive nozzles of electrospray, the end effect could be reduced by dummy nozzles, through which no liquid is supplied, mounted at the boundary of the array. However, the polymer-based electrospray device can eliminate the end effect without using the dummy dry nozzles due to dielectric characteristic. A novel multiple nozzles of Polymethyl Methacrylate (PMMA)-based electrospray device was successfully fabricated and evaluated for reducing the end effect, showing no deflection of menisci through the boundary nozzles. And ten nozzles device was fabricated and observed to eject liquid jet simultaneously. The electrical current of the spray issued from the nozzles of the polymer-based electrospray device is measured with respect to flow rate and shows a good agreement with the scaling law. 相似文献
93.
Kerstin Strupat Viatcheslav Kovtoun Huy Bui Rosa Viner George Stafford Stevan Horning 《Journal of the American Society for Mass Spectrometry》2009,20(8):1451-1463
A MALDI source is interfaced to a modified LTQ Orbitrap XL instrument. This work gives insight into the MALDI source design
and shows results obtained with the MALDI source coupled to an accurate mass, high-resolution hybrid mass spectrometer. MALDI-produced
ions and fragment ions thereof produced in the mass spectrometer may be analyzed and detected by the Orbitrap analyzer at
a maximum mass resolution of 100,000 (FWHM) at m/z 400 with high mass accuracy. An accuracy of ≤2 ppm is achieved by internal mass calibration using lock mass functionality;
using external mass calibration, an accuracy of ≤3 ppm is routinely obtained. External mass calibration of the hybrid mass
spectrometer is performed using a standard calibration mixture of different peptides and matrix components. The instrumental
capabilities are demonstrated for analytical methodologies such as Protein ID using Peptide Mass Fingerprint (PMF) and MS/MS
analyses of small molecule samples. Stability of mass accuracy and signal-to-noise ratio for low samples loads (on plates)
are demonstrated as well as the experimental dynamic range using α-cyano-4-hydroxy cinnamic acid (CHCA) matrix. 相似文献
94.
Wenbin Liu KBS Institute of Mathematics Statistics The University of Kent Canterbury CT NF Engl Wei Gong Ningning Yan LSEC 《计算数学(英文版)》2009,(1):97-114
In this paper, we study numerical methods for an optimal control problem with pointwise state constraints. The traditional approaches often need to deal with the deltasingularity in the dual equation, which causes many difficulties in its theoretical analysis and numerical approximation. In our new approach we reformulate the state-constrained optimal control as a constrained minimization problems only involving the state, whose optimality condition is characterized by a fourth order elliptic variational inequality. Then direct numerical algorithms (nonconforming finite element approximation) are proposed for the inequality, and error estimates of the finite element approximation are derived. Numerical experiments illustrate the effectiveness of the new approach. 相似文献
95.
In this paper, we extend the Perron-Frobenius theorem for positive polynomial operators in Banach lattices. The result obtained
is applied to derive necessary and sufficient conditions for the stability of positive polynomial operators. Then we study
stability radii: complex, real and positive radii of positive polynomial operators and show that in this case the three radii
coincide and can be computed by a simple formula. Finally, a simple example is given to illustrate the obtained results. 相似文献
96.
This paper gives a general formulation of convolutions for arbitrary linear operators from a linear space to a commutative algebra, constructs three convolutions for the Fourier transforms with geometric variables and four generalized convolutions for the Fourier‐cosine, Fourier‐sine transforms. With respect to applications, by using the constructed convolutions normed rings on L1( R n) are constructed, and explicit solutions of integral equations of convolution type are obtained (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
97.
In this paper, we study the stability radii of positive quasipolynomials associated with linear functional difference equations in infinite-dimensional spaces. It is shown that the positive, real and complex stability radii coincide. Moreover, explicit formulas are derived for these stability radii and illustrated by a simple example. 相似文献
98.
Lam T. Bui Hussein A. Abbass Daryl Essam 《Computational Optimization and Applications》2009,42(1):105-139
When solving real-world optimization problems, evolutionary algorithms often require a large number of fitness evaluations
in order to converge to the global optima. Attempts have been made to find techniques to reduce the number of fitness function
evaluations. We propose a novel framework in the context of multi-objective optimization where fitness evaluations are distributed
by creating a limited number of adaptive spheres spanning the search space. These spheres move towards the global Pareto front
as components of a swarm optimization system. We call this process localization. The contribution of the paper is a general
framework for distributed evolutionary multi-objective optimization, in which the individuals in each sphere can be controlled
by any existing evolutionary multi-objective optimization algorithm in the literature. 相似文献
99.
Local pressure is known to be anisotropic across the interfaces separating fluids in equilibrium. Tangential pressure profiles show characteristic negative peaks as a result of surface tension forces parallel to the interface. Nearby attractive forces parallel to the interface are larger than the repulsive forces and, hence, constitute the surface tension. In this work, using molecular dynamics simulations of methane inside nano-scale pores, we show this surface tension behaviour could be significantly influenced by confinement effects. The layering structure, characterised by damped oscillations in local liquid density and tangential pressures, extends deep into the pore and can be a few nanometers thick. The surface tension is measured numerically using local pressures across the interface. Results show that the tension is smaller under confinement and becomes a variable in small pores, mainly controlled by the thickness of the liquid density layering (or liquid saturation) and the pore width. If the liquid saturation inside the pore is high enough, the vapour–liquid interface is not interfered by the pore wall and the surface tension remains the same as the bulk values. The results are important for understanding phase change and multi-phase transport phenomena in nanoporous materials. 相似文献
100.
Nguyen Luu Huu Thu Le Minh Tinh Bui Duc 《The European Physical Journal B - Condensed Matter and Complex Systems》2023,96(8):1-30
The European Physical Journal B - The physical properties of a quantum many-body system can, in principle, be determined by diagonalizing the respective Hamiltonian, but the dimensions of its... 相似文献