双棒串接Nd3+:YAG激光器

根据测量的单根Nd³⁺:YAG棒的热焦距,利用ABCD传输矩阵计算了双棒串接的几种腔型的稳定参量,给出了能够满足高功率、高稳定性激光输出的稳定腔型,实验结果与理论分析基本相符.     

Non-Local Periodic Motions of a Thin Cantilevered Rod

In this work we consider the existence of unforced periodic motionsfor a thin cantilevered elastic rod. In particular, largeamplitude motions that combine bending and twisting of the rodare studied. We use a lumped mass model consisting of a cantilevered planar rod whose base is attached to a torsional spring. The stability of the torsional vibration is studied and then the existence of a oneparameter family of large amplitude periodic motions is demonstrated.     

原位沉析法制备壳聚糖棒材的研究

以壳聚糖凝胶膜为模板,将壳聚糖溶液与NaOH凝固液隔离,利用膜渗透原位沉析法制备了高性能的壳聚糖棒材(d=4.5mm),其弯曲强度、弯曲模量和剪切强度分别为92.4MPa,4.1GPa和36.5MPa.扫描电子显微镜(SEM)分析结果表明,原位沉析法制备的壳聚糖棒材具有同心筒状层叠结构,并对其成型机理进行了探讨.     

Preparation and characterization of superconducting MgB2 rods

Superconducting Cu/Fe/MgB₂ and Steel/Cu/MgB₂ rods were prepared through the ex‐situ modified PIT technique with explosive consolidation method. The phase composition, microstructural features were investigated by X‐ray diffraction and scanning electron microscope. The AC susceptibility for a core samples was measured by the AC susceptometry. Measurements of the magnetization hysteresis loops were also carried out. It is found that no impurity phase was formed in MgB₂ rods. In addition, it was found that grains in both Cu/Fe/MgB₂ and Steel/Cu/MgB₂ rods are densely packed. The magnetic measurements show that the critical temperature of Cu/Fe/MgB₂ and Steel/Cu/MgB₂ rods is 37.7 K and 37.6 K, respectively. The high critical current density of 9.22 × 10⁵ A/cm² (4.1 K, 0.2 T) was obtained for Steel/Cu/MgB₂ rod. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Theory of Intrachain Relaxation Spectra for Polymer Networks Possessing a Short- or Long-Scale Ordering. Effects of the Nematic Ordering on the Relaxation Spectrum of a Polymer Network with Included Rods

We discuss the relaxation properties of polymer networks possessing either short-scale ordering caused by rigidity of network strands or long-scale liquid crystalline order. The main topics of the paper are the equilibrium and local dynamic properties of a polymer network ordered due to nematic-like interactions of the network segments with included rod-like particles. A simplified three chain network model is used. Lagrange multipliers in the equations of motion of hard rods are replaced by their averaged values. This approximation corresponds to modelling the rod-like particles by elastic Gaussian springs, their mean-square lengths independent of the ordering. Nematic-like interactions between network segments and rods are taken into account in terms of the Maier-Saupe mean-field approximation. Nematic ordering of rods induces ordering of the network segments. Relaxation spectrum of the ordered network splits into two main branches for the parallel and perpendicular components of the chain segments with respect to the director. We calculate the relaxation times of a polymer network as functions of the wave number. The relaxation spectrum of an isotropic network and that of the ordered network with included rods are compared.     

杆系结构受横向冲击载荷下弹性波传播的实验研究

利用 Ｓ Ｈ Ｐ Ｂ装置,用空气枪加载就 ３５ Ｃｒ Ｍｎ Ｓｉ钢组成的 Ｌ型杆系结构受横向冲击载荷作用的弹性波传播进行了实验研究,给出了一些力学现象,并与轴向冲击的实验进行了对比,得到了有益的结论。     

Biodegradable ultra high strength poly(L-lactide) rods for bone fixation

The hydrostatic molecular orientation technique was used to explore the highest mechanical improvements achievable for poly-L-lactide (PLLA). The mechanical attributes of these materials designed for bone fracture fixation devices, i.e. bending strength and modulus were measured and compared with those prepared by stretching method. The starting samples were prepared by conventional melt extrusion at 200 °C followed by hydrostatic extrusion at 140 °C using glycerin filled extruder. Uniaxially stretched rods were prepared by drawing in silicon oil at 120 °C. The physical properties of these rods are inadequate as mechanical supports in the dynamic healing process of the bone. Moreover, they underwent a marked strength deterioration when immersed in aqueous buffered solution for 90 days. On the other hand, the hydrostatic extrusion technique produced rods with progressively higher bending strength that showed only a small drop after 90 days hydrolytic degradation. Micrographs suggested a superior molecular orientation and packing, which could be associated with the improved performance. The hydrostatic extrusion technique proved to be a safe and effective approach for strengthening biodegradable polymeric materials for dynamic mechanical support in orthopedic medical devices.