Mountain Pass Solutions for a Double-Well Energy

We establish the existence of a mountain pass solution for a variational integral involving a quasiconvex function with a double-well structure in the geometrically linear elasticity setting. We show that under small dead-load perturbations, the Neumann boundary value problem has at least three solutions, a global minimizer, a local minimizer and a mountain pass solution. We show that our variational integral satisfies a Weak Palais-Smale condition (WPS) hence the mountain pass lemma applies.     

光在两单轴晶体间界面的反射和透射

根据位相匹配条件和应该满足的边界方程,在光轴取向任意的条件下,得到了光在两单轴晶体界面的反射和折射的理论表达式,给出了更普遍的公式计算光能量损失以及两束折射光的能量比。数值模拟表明所得结果满足能量守恒,光轴的取向和入射角大小对晶体中折射的o光、e光的能量比有重大影响,但是对反射率影响很小。只要知道了晶体的有关参数及入射条件,利用所给表达式可以计算各光束光能量比,为晶体器件特性研究提供了有力的工具。由于对光轴取向和入射角度没有任何限制,公式具有普遍性。     

Enhancement of ferromagnetic resonance in Al203-doped CozFeAI Heusler alloy film prepared by oblique sputtering

Large and variable in-plane uniaxial magnetic anisotropy in a nanocrystalline （Co2FeA1）97.8（Al2O3）2.2 soft magnetic thin film is obtained by an oblique sputtering method without being induced by magnetic field or post anneaiing. The in-plane uniaxiai magnetic anisotropy varies from 50 Oe to 180 Oe （1 Oe=79.5775 A·m-1） by adjusting the sample＇s position. As a result, the ferromagnetic resonance frequency of the film increases from 1.9 GHz to 3.75 GHz.     

Large-scale pyrosequencing of synthetic DNA: a comparison with results from Sanger dideoxy sequencing

Pyrosequencing is a relatively recent method for sequencing short stretches of DNA. Because both Pyrosequencing and Sanger dideoxy sequencing were recently used to characterize and validate DNA molecular barcodes in a large yeast gene-deletion project, a meta-analysis of those data allow an excellent and timely opportunity for evaluating Pyrosequencing against the current gold standard, Sanger dideoxy sequencing. Starting with yeast genomic DNA, parallel PCR amplification methods were used to prepared 4747 short barcode-containing constructs from 6000 Saccharomyces cerevisiae gene-deletion strains. Pyrosequencing was optimized for average read lengths of 25-30 bases, which included in each case a 20-mer barcode sequence. Results were compared with sequence data obtained by the standard Sanger dideoxy chain termination method. In most cases, sequences obtained by Pyrosequencing and Sanger dideoxy sequencing were of comparable accuracy, and the overall rate of failure was similar. The DNA in the barcodes is derived from synthetic oligonucleotide sequences that were inserted into yeast-deletion-strain genomic DNA by homologous recombination and represents the most significant amount of DNA from a synthetic source that has been sequenced to date. Although more automation and quality control measures are needed, Pyrosequencing was shown to be a fast and convenient method for determining short stretches of DNA sequence.     

Simultaneous measurement of transient stress and flow birefringence in one-sided compression (biaxial extension) of a polymer melt

Summary Investigation of time dependent behaviour of a polystyrene melt is carried out with the aid of a new apparatus for biaxial extension. Use is made of the method of two impinging fluid streams guided by lubricated trumpet shaped metal walls. The flow birefringence is measured in the plane of symmetry and, at the same time, the force is measured which tends to separate the trumpets. The linear stress-optical relation turns out to be valid in this new flow geometry. An accurate value for the stress-optical coefficient can be determined from the relaxation experiments. The stress build-up as calculated from the optical measurements, is compared with the pertinent result of the theory of linear viscoelasticity. For the desired interconversion of dynamic moduli use is made of the approximation by Schwarzl and Struik. The steady state measurements are checked by the results of the non-linear model of Acierno et al.With 16 figures and 2 tables     

Statistical aspects of the identification of material parameters for elasto-plastic models

Summary The presented method to identify material parameters for inelastic deformation laws is based on the numerical analysis of inhomogeneous stress and strain fields received from suitable experiments. Tensile and bending tests were carried out to obtain elastic and hardening parameters. The deformation law for small elasto-plastic strains is presented as a system of nonlinear differential and algebraic equations (DAE) consisting of the stress–strain relation, evolution equations for the internal variables and the yield condition. Different rules for the evolution equations of isotropic, kinematic and distorsional hardening are proposed. The DAE are discretized using an implicit Euler method, and the resulting system of nonlinear algebraic equations is solved using the Newton method. Deterministic optimization procedures are preferred to identify material parameters from a least-squares functional of numerical and measured comparative quantities. The gradient of the objective function was calculated using a semianalytical sensitivity analysis. Due to measurement errors, the optimal sets of material parameters are non unique. The approximate estimation of confidence regions and the calculation of correlation coefficients is presented. The results of several optimization processes for material parameters of elasto-plastic deformation laws show a good agreement between measured and calculated values, but they show also problems which may occur if systematic errors will not be recognized and deleted. Received 30 September 1999; accepted for publication 8 March 2000     

Three-dimensional stability of a rectangular plate under uniaxial tension

The paper studies the three-dimensional stability of an isotropic, linear elastic, rectangular plate under a uniform tensile load applied to its sides. The concept of free strains is used to reduce the three-dimensional problem to a two-dimensional one. It is solved using the three-dimensional linearized theory of stability. An approximate solution of the buckling problem is obtained by the finite-difference method. Numerical results are presented __________ Translated from Prikladnaya Mekhanika, Vol. 42, No. 7, pp. 116–123, July 2006.     

Macroscopic theory of orientation transitions in the extensional flow of side-chain nematic polymers

A macroscopic continuum mechanical model for incompressible side-chain nematic polymers, under isothermal conditions is given. The model is a synthesis of a transient network model and the standard nematorheological model. Simplifications in the model yield constitutive equations that are identical to well known Theological models for polymer melts and for low molar mass nematics. A detailed analysis of four possible composite orientation modes of polymer backbone and mesogenic side groups in uniaxial extensional flow is given. It is shown that the thermal sensitivity of the viscoelastic parameters leads to thermally-induced orientation transitions. The extension rate sensitivity of the competition between elastic and flow orienting effects leads to flow-induced orientation transition. The role of smectic A fluctuations in thermally-induced transitions during uniaxial extensional nematic flow is elucidated. The model is able to predict and explain the experimentally observed orientation modes and thermally-induced orientation transitions of a side-chain nematic polymer subjected to uniaxial extensional flow.