Effect of MWCNTs Doping on the Morphology,Structure and Properties of Chitosan Beads

A series of chitosan (CS)/multi-walled carbon nanotubes (MWCNTs) composite hydrogel beads with different MWCNTs contents are prepared via a solution blending method. The effects of MWCNTs on the morphology, structure and properties of chitosan beads have been investigated. Digital pictures show that the composite beads obtained are of good morphological characteristics, and the SEM micrographs indicate that the addition of MWCNTs into CS beads made the surface of the CS/MWCNTs hydrogel beads contain much larger wrinkles. Fourier transform infrared spectra (FTIR) show that the main chain of CS bead is not changed, but there are some electrostatic interactions between CS and MWCNTs, which lead to very significant changes in the crystallization behavior of CS and MWCNTs. The thermal stability of CS/MWCNTs composites at high temperatures is increased with the existence of MWCNTs, indicating a possible electrostatic interaction between MWCNTs and CS lattices to limit the motivation of CS. The adsorption capacity of CS beads doped with a lower percentage of MWCNTs (0.02 wt%) for acid fuchsin is 112.76 mg/g, higher than that of pure CS beads (35.62 mg/g).     

Synthesis of propionate motifs: diastereoselective tandem reactions involving anionic and free radical based processes

Reported herein is a strategy employing a Mukaiyama reaction in tandem with a hydrogen transfer reaction for the elaboration of propionate motifs. The nature of the protecting groups on the chiral beta-alkoxy aldehyde and the type of Lewis acid used are varied to modulate the stereochemical outcome of the tandem reactions. The mode of complexation is thus controlled (monodentate or chelate) for the Mukaiyama reaction to give access to either syn or anti aldol products, precursors of the free radical reduction reaction. The endocyclic effect is subsequently capitalized upon to control the hydrogen transfer step so that the syn-reduced product may be achieved. Proceeding with excellent yield and diastereoselectivity, the synthetic sequence proposed gives access to syn-syn and syn-anti propionate motifs. Also considered is a complementary approach using a chelation-controlled Mukaiyama reaction in tandem with a free radical allylation reaction under the control of the endocyclic effect that leads to the anti-anti product.     

Convergence of a difference scheme for the heat equation in a long strip by artificial boundary conditions

The numerical solution of the heat equation on a strip in two dimensions is considered. An artificial boundary is introduced to make the computational domain finite. On the artificial boundary, an exact boundary condition is proposed to reduce the original problem to an initial‐boundary value problem in a finite computational domain. A difference scheme is constructed by the method of reduction of order to solve the problem in the finite computational domain. It is proved that the difference scheme is uniquely solvable, unconditionally stable and convergent with the convergence order 2 in space and order 3/2 in time in an energy norm. A numerical example demonstrates the theoretical results.© 2007 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 2007     

NUMERICAL SOLUTIONS OF AN EIGENVALUE PROBLEM IN UNBOUNDED DOMAINS

A coupling method of finite element and infinite large element is proposed for the numerical solution of an eigenvalue problem in unbounded domains in this paper. With some conditions satisfied, the considered problem is proved to have discrete spectra. Several numerical experiments are presented. The results demonstrate the feasibility of the proposed method.     

Steklov特征值问题的边界元近似

本文将Ｌａｐｌａｃｅ算子的Ｓｔｅｋｌｏｖ特征值问题归化为一个边界变分问题，从而使原问题的空间维数降低了一维，基于此变分问题给出了Ｓｔｅｋｌｏｖ特征值问题的边界元近似解，计算实例表明此方法是十分有效的。     

The boundary integro-differential equations of three-dimensional Neumann problem in linear elasticity

Summary. In this paper, we mainly consider the three dimensional Neumann problem in linear elasticity, which is reduced to a system of integro-differential equations on the boundary based on a new representation of the derivatives of the double-layer potential. Furthermore a new boundary finite element method for this Neumann problem is presented. Received July 13, 1992 / Revised version received June 28, 1993     

Infrared spectra of CdSb

We present new measurements of infrared reflectivity of CdSb crystals. Phonons were detected for the three crystallographic axes and fitted with the factorized oscillator model. Fourteen out of the fifteen predicted phonons were detected.