Three‐dimensionally braided carbon fiber–epoxy composites,a new type of material for osteosynthesis devices. I. Mechanical properties and moisture absorption behavior

In recent years, three‐dimensionally (3D) braided composites have attracted a great deal of attention because of their high‐impact damage tolerance and fatigue life, superior fracture toughness, and so forth, and have been used in aeronautics, military, and transportation. These advantages make them strong candidates for osteosynthesis devices. In this study, 3D braided carbon fiber–epoxy (C_3D/EP) composites were produced via a simple vacuum impregnation technique. The load‐deflection curve, mechanical properties, and influence of fiber volume fraction, braiding angle, and axial reinforcing fibers were examined to determine their suitability for internal fixation devices. It is found that the C_3D/EP composites have excellent toughness and do not show brittleness when fractured because of their relatively high void content. The flexural, shear, and impact strengths of the C_3D/EP composites are excellent. It was shown that a C_3D/EP composite with a stiffness similar to load‐bearing bones can be made while maintaining enough strength. It is concluded that a relatively higher void content and braiding angle is more suitable for the C_3D/EP composites from the viewpoint of requirements of fracture fixation materials. The moisture absorption behavior and changes in mechanical properties caused by moisture uptake were evaluated. Results show that absorbed moisture slightly decreases mechanical properties of the C_3D/EP composites. Contrary to the unreinforced epoxy, the moisture absorption behavior of the C_3D/EP composites cannot be described with Fick's law of diffusion, probably because of the presence of voids and/or 3D fiber structure. The exact mechanisms should be proposed in further investigations. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1031–1039, 2002     

灌溉水库水资源优化调度

以榆社云簇水库为例、以水库灌区多种作物所能达到的最大产值为目标函数，本文研究了一套灌溉水库用水优化调度模型。它包括计划调度模型和实时调度模型两部分，适用于干旱半干旱地区灌溉水量不足的水库的用水调度。     

金刚石排锯及其合理使用

本文分析总结了锯切加工大理石、花岗石、毛板的金刚石排锯条的安装,使用原则,研究了金刚石刀头的配方,结构等质量性能。     

皮革真空鞣制新技术与设备的研究

本文对皮革在真空状态下鞣制进行了试验研究，使鞣制过程的物理—化学氛围得到改善，大大缩短了鞣制时间，废液排放量减少一半以上。     

脉冲啁啾对干涉相关测宽的影响及其消除方法

本文深入讨论了脉冲啁啾的非线性起源及其对干涉相关测宽(等值宽度和条纹计数)法的影响。提出根据干涉相关曲线下包络最大值位置适当降低等值宽度位置和用计算机平均处理干涉相关信息的技术以消除啁啾的影响。     

氢/空气火焰在半开口有障碍管道中的传播特性

针对氢／空气混合物，通过实验研究了其预混火焰在半开口管道中的火焰传播加速现象。结果表明，火焰传播状态随着氢气当量比的变化而发生改变。当氢／空气混合物被点燃后，由于障碍物的扰动，火焰在管道中不断加速传播，并最终到达一准稳态传播。在氢气当量比0．34附近时，火焰速度发生跃变。当氢气当量比足够大时，火焰传播由爆燃态转变为爆轰态。在本实验条件下，爆燃转准爆轰的临界条件是d/λ=2.6(d是圆环形障碍物内径，λ是爆轰格胞尺度）。障碍物阻塞比的变化对最大火焰速度和压力提升的影响不明显。     

Application of Galerkin Method to Dynamical Behavior of Viscoelastic Timoshenko Beam with Finite Deformation

The motion equations governing the dynamical behavior of a viscoelasticTimoshenko beam with finite deformation are derived and simplified byGalerkin method. The viscoelastic material is assumed to obey thethree-dimensional fractional derivative constitutive relation. Thedynamical behaviors of the simplified systems with order 1 and order 2are numerically computed and compared by using the computational methodpresented by the authors. The dynamical behaviors of the systems areuniform qualitatively, but there is a little deviation quantitatively.And the truncated system with order 1 is safer than the one of order 2.It is also shown that the lower order system is reasonable. Theinfluences of the load parameter and the fractional derivative parameter(material parameter) on the deflection of the beam are consideredrespectively. The numerical methods in nonlinear dynamics, such as phasediagram, and Poincaré section, are applied to reveal dynamical behaviorsof the nonlinear viscoelastic Timoshenko beam. There are plenty ofdynamical behaviors, such as periodicity, bifurcation, quasi-periodicityand chaos in the dynamical system.     

Hydrothermal Synthesis of Acicular Lead Titanate Fine Powders

A pure, acicular lead titanate (PbTiO₃) fine powder with a white color has been prepared by hydrothermal synthesis. It is a new phase of PbTiO₃ with I 4 symmetry, cell parameters of a = 12.358 Å and b = 14.541 Å, and a density of 6.80 g.cm⁻³. The influences of pH (12.5 to 14.4), Pb/Ti ratio (1.0 to 1.6) in the feedstock, reaction temperature (130° to 230°C), time (0.25 to 4 h), starting materials, and additives on the formation of acicular PbTiO₃ under hydrothermal conditions have been investigated. The acicular PbTiO₃ with I 4 symmetry, referred to as the PX phase, can be converted to the perovskite-type (PE phase) of PbTiO₃ at about 605°C while its acicular morphology is essentially unchanged. The preferable conditions for preparing pure acicular PX-phase PbTiO₃ are that the pH is 13.0 to 14.0, Pb/Ti ratio is >1.3, reaction temperature is 170° to 200°C, time is 0.5 to 1.0 h, titanium butoxide (Ti[O(CH₂)₃CH₃]₄) is the starting material, and poly(vinyl alcohol) is an additive. The acicular grain of the PX phase is usually less than 100 nm in diameter and more than 1000 nm in length.     

曹魏自耕农经济的恢复与发展

自耕农是曹魏时期生产战线上的主要生产者。汉末战乱造成人口流徙和丧亡 ,使社会上劳动人手紧缺。曹魏政权首先不得不与敌队势力、少数民族、豪强大族等方面展开争夺人口的斗争。其次 ,曹魏创立了针对自耕农的田租户调令。同时 ,曹魏在经济上和政治上执行打击豪强的政策 ,并且还令州郡县地方官吏多方面采取奖励自耕农生产的措施     

单相电焊机计量异常分析

针对单相电焊机采用单相感应式电能表进行计量中出现的圆盘反转现象 ,从理论和试验 2个方面分析和验证了 :由于单相电焊机本身的特点 ,无论它在负载还是空载状态 ,总会有 1块电能表出现圆盘反转 ,这是正常的