Nanoscale Magnetic Stirring Bars for Heterogeneous Catalysis in Microscopic Systems

Nanometer‐sized magnetic stirring bars containing Pd nanoparticles (denoted as Fe₃O₄‐NC‐PZS‐Pd) for heterogeneous catalysis in microscopic system were prepared through a facile two‐step process. In the hydrogenation of styrene, Fe₃O₄‐NC‐PZS‐Pd showed an activity similar to that of the commercial Pd/C catalyst, but much better stability. In microscopic catalytic systems, Fe₃O₄‐NC‐PZS‐Pd can effectively stir the reaction solution within microdrops to accelerate mass transfer, and displays far better catalytic activity than the commercial Pd/C for the hydrogenation of methylene blue in an array of microdroplets. These results suggested that the Fe₃O₄‐NC‐PZS‐Pd could be used as nanoscale stirring bars in nanoreactors.     

Bending of Bars under a Follower Load

Exact solutions of the problem of nonlinear bending of a thin bar under a point follower load are given. The problem is studied for an arbitrary follower angle and the particular cases of axial and transverse follower forces are considered. The solutions are written in unified parametric form and expressed in terms of Jacobi elliptic functions.     

Contribution to 3D impact problems: collisions between two slender steel barsUne contribution aux problèmes d'impact en trois dimensions : collisions entre deux barres élancées

This Note deals with the three-dimensional phenomenon of collision between two slender steel bars. The problem posed is whether the restitution concept developed in rigid-body theory is relevant in the case of such slender contactors. Some elements of an answer are provided through the use of two complementary approaches of collision, a theoretical one based on coefficients of restitution and series of experiments. Our main conclusion is that the alleged Newton coefficient of restitution varies according to the impact location on the rods. To cite this article: C. Le Saux et al., C. R. Mecanique 332 (2004).     

基于构件层次的铰接杆系结构几何稳定性讨论

考察构件刚度和构件撤除对杆件系统几何稳定性的影响.从常规结构稳定理论的角度审视铰接杆件系统几何稳定性问题.基于结构稳定的能量准则和刚度矩阵的构成分析,重新考察了Maxwell准则和平衡矩阵准则的充分必要性.解释了构件零刚度和构件撤除对体系几何稳定性影响的一致性.利用自应力矩阵的特性,提出并证明了一种快速识别杆系结构中“必需杆”的方法.一种多根构件撤除后体系几何稳定性的判别准则进而被发展.该判别准则的数值效率体现在仅利用原结构平衡矩阵一次分解后的信息,杆件撤除后体系平衡矩阵的秩可通过两小规模矩阵秩之间的关系来表示.     

双杠三维测力系统的研制及应用

双柑三维测力系统由三维测力传感器、动态电阻应变仪，７Ｔ１７Ｓ数字信号处理机组成，可提供各种实时处理的测量数据及图形。经运动员实际测试，取得了比较满意的结果，可用于双杠运动员的实际训练中。     

On the torsion of functionally graded anisotropic linearly elastic bars

The torsion of homogeneous, isotropic, linearly elastic cylindricalbars has been the subject of numerous investigations from theoretical,computational and applied viewpoints. It is well known thatin this case, the circular shaft is the only one whose cross-sectiondoes not involve a warping displacement in the axial direction.For an inhomogeneous, isotropic, circular bar, there is alsono warping of the cross-section provided that the shear modulusvaries only in the radial direction. For general anisotropicmaterials, torsion induces bending and vice versa. For thoseanisotropic materials with at least one plane of elastic symmetrynormal to the axial direction, pure torsion is possible. Forhomogeneous materials of this type and special inhomogeneousmaterials, it has been shown by various arguments that no warpingoccurs for bars of particular elliptical cross-section. Here,we provide a unified derivation of the foregoing results. Somediscussion of torsional rigidities is also given.     

A FINITE ELEMENT ANALYSIS OF THE LARGE PLASTIC DEFORMATION BEHAVIOR OF AMORPHOUS GLASSY CIRCULAR POLYMERIC BARS

The BPA eight chain molecular network model is introduced into the finite element for-mulation of elastic-plastic large deformation.And then,the tensile deformation localization develop-ment of the amorphous glassy circular polymeric bars(such as polycarbonates)is numerically simulat-ed.The simulated results are compared with experimental ones,and very good consistence betweennumerical simulation and experiment is obtained,which shows the efficiency of the finite elementanalysis.Finally,the influences of the microstructure parameter S_ on tensile neck-propagation andtriaxial stress effect are studied.     

Sensorial analysis evaluation in cereal bars preserved by ionizing radiation processing

Gamma-rays utilized as a food-processing treatment to eliminate insect contamination is well established in food industries. Recent troubles in Brazilian cereal bars commercialization require a special consumer's attention because some products were contaminated by insects. To solve the problem, food-irradiation treatment was utilized as a safe and effective solution. The final product was free of insect contamination. The aim of this study was to determine the best radiation dose processing utilized to disinfestations and detect some change on sensorial characteristic by sensorial analysis in cereal bars. In this study, three different kinds of cereal bars were purchased in São Paulo (Brazil) in supermarkets and irradiated with 1.0, 2.0 and 3.0 kGy at “Instituto de Pesquisas Energéticas e Nucleares” (IPEN-CNEN/SP). The samples were treated with ionizing radiation using a ⁶⁰Co gamma-ray facility (Gammacell 220, A.E.C.L.). That radiation doses were used successfully as an anti-insect treatment in the cereal bars, since in some food industries doses up to 3.0 kGy are used to guarantee at least a dose of 1.0 kGy in internal cereal bars package. Sensorial analysis was necessary since cereal bars contain ingredients very sensitive to ionizing radiation process.     

CFRP阶梯加固钢板端部胶层应力的理论模型研究

CFRP阶梯加固可以有效减小CFRP端部胶层应力,防止胶层过早剥离而导致CFRP加固失效．文中通过理论推导建立CFRP阶梯加固钢板的端部胶层剪应力和正应力的理论模型,并采用有限元模型验证了理论模型,然后利用理论模型研究了加固参数对胶层应力的影响．研究结果表明：理论模型可以有效地计算端部胶层应力,且当阶梯端部长度超过“最小端部长度”时,理论模型可以准确计算端部胶层的最大应力值及其发生位置;利用理论模型便于分析各种参数对端部胶层应力的影响,其中胶层厚度、阶梯数量和CFRP厚度对端部胶层应力影响较大．     

Surface treatment of CFRP composites using femtosecond laser radiation

In the present work, we investigate the surface treatment of carbon fiber-reinforced polymer (CFRP) composites by laser ablation with femtosecond laser radiation. For this purpose, unidirectional carbon fiber-reinforced epoxy matrix composites were treated with femtosecond laser pulses of 1024 nm wavelength and 550 fs duration. Laser tracks were inscribed on the material surface using pulse energies and scanning speeds in the range 0.1–0.5 mJ and 0.1–5 mm/s, respectively. The morphology of the laser treated surfaces was investigated by field emission scanning electron microscopy. We show that, by using the appropriate processing parameters, a selective removal of the epoxy resin can be achieved, leaving the carbon fibers exposed. In addition, sub-micron laser induced periodic surface structures (LIPSS) are created on the carbon fibers surface, which may be potentially beneficial for the improvement of the fiber to matrix adhesion in adhesive bonds between CFRP parts.