Xiao Z.-J.,Nanjing Normal University |
Liu X.,Xuzhou Normal University
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2011
In this work, we calculate the CP-averaged branching ratios and the polarization fractions of the charmless hadronic Bc→A 2A3 decays within the framework of perturbative QCD (pQCD) approach, where A is either a light P13 or P11 axial-vector meson. These 32 decay modes can occur through the annihilation topology only. Based on the perturbative calculations and phenomenological analysis, we find the following results: (a) the branching ratios of the considered 32 Bc→A 2A3 decays are in the range of 10-5 to 10 -8; (b) Bc→a1b1, K̄10K1+ and some other decays have sizable branching ratios and can be measured at the LHC experiments; (c)the branching ratios of Bc→A 2(P11)A3(P11) decays are generally much larger than those of Bc→A2(P13)A3(P13) decays with a factor around (10∼100); (d)the branching ratios of Bc→K̄10K1+ decays are sensitive to the value of θK, which will be tested by the running LHC and forthcoming SuperB experiments; (e)the large longitudinal polarization contributions govern most considered decays and play the dominant role. © 2011 American Physical Society.
Yu J.,Hefei University of Technology |
Shi F.,Xuzhou Normal University |
Gong L.-Z.,Hefei University of Technology
Accounts of Chemical Research | Year: 2011
Optically pure nitrogenous compounds, and especially nitrogen-containing heterocycles, have drawn intense research attention because of their frequent isolation as natural products. These compounds have wide-ranging biological and pharmaceutical activities, offering potential as new drug candidates. Among the various synthetic approaches to nitrogenous heterocycles, the use of asymmetric multicomponent reactions (MCRs) catalyzed by chiral phosphoric acids has recently emerged as a particularly robust tool. This method combines the prominent merits of MCRs with organocatalysis, thus affording enantio-enriched nitrogenous heterocyclic compounds with excellent enantioselectivity, atom economy, bond-forming efficiency, structural diversity, and complexity. In this Account, we discuss a variety of asymmetric MCRs catalyzed by chiral phosphoric acids that lead to the production of structurally diverse nitrogenous heterocycles.In MCRs, three or more reagents are combined simultaneously to produce a single product containing structural contributions from all the components. These one-pot processes are especially useful in the construction of heterocyclic cores: they can provide a high degree of both complexity and diversity for a targeted set of scaffolds while minimizing the number of synthetic operations. Unfortunately, enantioselective MCRs have thus far been relatively underdeveloped. Particularly lacking are reactions that proceed through imine intermediates, which are formed from the condensation of carbonyls and amines. The concomitant generation of water in the condensation reaction can deactivate some Lewis acid catalysts, resulting in premature termination of the reaction. Thus, chiral catalysts typically must be compatible with water for MCRs to generate nitrogenous compounds. Recently, organocatalytic MCRs have proven valuable in this respect. Brønsted acids, an important class of organocatalysts, are highly compatible with water and thereby offer great potential as chiral catalysts for multicomponent protocols that unavoidably release water molecules during the course of the reaction.We present a detailed investigation of several MCRs catalyzed by chiral phosphoric acids, including Biginelli and Biginelli-like reactions; 1,3-dipolar cycloadditions; aza Diels-Alder reactions; and some other cyclization reactions. These approaches have enabled the facile preparation of 3,4-dihydropyrimidinones, pyrrolidines, piperidines, and dihydropyridines with high optical purity. The synthetic applications of these new protocols are also discussed, together with theoretical studies of the reaction transition states that address the regio- and stereochemistry. In addition, we briefly illustrate the application of a recently developed strategy that involves relay catalysis by a binary system consisting of a chiral phosphoric acid and a metal complex. This technique has provided access to new reactions that generate structurally diverse and complex heterocycles.Enantioselective organocatalytic MCRs remain a challenge, but we illustrate success on several fronts with chiral phosphoric acids as the primary catalysts. Further progress will undoubtedly provide even better access to the chiral nitrogen-containing heterocycles that are not only prevalent as natural products but also serve as key chiral building blocks in organic synthesis. © 2011 American Chemical Society.
Yang L.,Xuzhou Normal University |
Xu L.,Yangzhou University
Information Sciences | Year: 2011
Rough set theory is a powerful mathematical tool for dealing with inexact, uncertain or vague information. The core concepts of rough set theory are information systems and approximation operators of approximation spaces. Approximation operators draw close links between rough set theory and topology. This paper concerns generalized approximation spaces via topological methods and studies topological properties of rough sets. Classical separation axioms, compactness and connectedness for topological spaces are extended to generalized approximation spaces. Relationships among separation axioms for generalized approximation spaces and relationships between topological spaces and their induced generalized approximation spaces are investigated. An example is given to illustrate a new approach to recover missing values for incomplete information systems by regularity of generalized approximation spaces. © 2011 Elsevier Inc. All rights reserved.
Wang F.,Xuzhou Normal University
Advanced Materials Research | Year: 2012
In order to obtain accurate results from computer simulation of the dynamic behavior of conveyor belts an accuracy description of the resistance forces, especially the indentation rolling resistance, is necessary. Since the indentation rolling resistance can account for the major part of the total rolling resistance, it is important to calculate it using a proper method. A new full two-dimensional semi-analytical method based on Maxwell model is developed to rigorously and efficiently simulate and solve the indentation rolling resistance of conveyor belts. In this method, the solution is expanded into a set of Fourier series, a so-called Maxwell model characterizing the viscoelastic properties for the belt cover material is used to relate Fourier coefficients, and a special boundary element is developed to handle the rolling contact boundary condition. A verification example is given to validate the methodology. © (2012) Trans Tech Publications.
Xie X.-J.,Qufu Normal University |
Duan N.,Xuzhou Normal University
IEEE Transactions on Automatic Control | Year: 2010
This note considers output tracking of high-order stochastic nonlinear systems without imposing any restriction on the high-order and the drift and diffusion terms. By using the backstepping design technique, a smooth state-feedback controller is given to guarantee that the solution process is bounded in probability and the error signal between the output and the reference signal can be regulated into a small neighborhood of the origin in probability. A practical example of stochastic benchmark mechanical system and simulation are provided to demonstrate the effectiveness of the control scheme. © 2010 IEEE.