空间钢框架结构的几何与材料非线性分析

本文采用有限变形理论及内力屈服面塑性流动理论对空间钢框架的极限承载力进行了弹塑性在形全过程分析。理论与算例都表明，本文方法精度较高，而计算又不过于复杂。     

高强度铝钒土型壳的溃散性试验研究

用"P"盐对低密度(<1.28克/厘米~3)水玻璃改性处理,可使精铸型壳残留强度σ弯稳定在(9～15)×10~5Pa范围内,初步解决了推广这一新工艺的难题.     

集成材胶合工艺的研究

以水曲柳、核桃楸和长白鱼鳞云杉为试验用材,采用水性高分子聚合物异氰酸酯作胶黏剂,以单位压力、加压时间和涂胶量为试验因子进行集成材的胶合试验,并对其胶合性能进行检验。通过试验结果分析,得出较优的胶合工艺条件为：单位压力2．0MPa(水曲柳、核桃楸)、1．5MPa(长白鱼鳞云杉),加压时间为60min．涂胶量为250g／m^2。     

Mechanical testing of a steel-reinforced epoxy resin bar and clamp for external skeletal fixation of long-bone fractures in cats

AIMS: To provide veterinarians with confidence when using a commercially available epoxy resin in external skeletal fixators (ESF), testing was conducted to determine exothermia during curing of the epoxy resin compared to polymethylmethacrylate (PMMA), the hardness of the epoxy resin as a bar over 16 weeks, and the strength of the epoxy resin bar compared with metal clamps in similarly constructed Type 1a ESF constructs simulating the repair of feline long bone fractures.

METHODS: Exothermia of the epoxy resin during curing was tested against PMMA with surface temperatures recorded over the first 15 minutes of curing, using four samples of each product. The hardness of 90 identical epoxy resin bars was tested by subjecting them to cyclic loads (1,000 cycles of 20.5?N, every 7 days) over a 16-week period and impact testing 10 bars every 2 weeks. Ten bars that were not subjected to cyclic loads were impact tested at 0 weeks and another 10 at 16 weeks. Strength of the epoxy resin product, as a bar and clamp composite, was tested against metal SK and Kirschner-Ehmer (KE) clamps and bars in Type 1a, tied-in intramedullary pin, ESF constructs with either 90° or 75° pin placement, subjected to compressive and bending loads to 75?N.

RESULTS: The maximum temperature during curing of the epoxy resin (min 39.8, max 43.0)°C was less than the PMMA (min 85.2, max 98.5)°C (p<0.001). There was no change in hardness of the epoxy resin bars over the 16 weeks of cyclic loading (p=0.58). There were no differences between the median strength of the epoxy resin, SK or KE ESF constructs in compression or bending when tested to 75?N (p>0.05). Stiffness of constructs with 75° pin placement was greater for SK than epoxy resin constructs in compression (p=0.046), and was greater for KE than epoxy resin constructs in bending (p=0.033).

CONCLUSIONS: The epoxy resin tested was found to be less exothermic than PMMA; bars made from the epoxy resin showed durability over an expected fracture healing timeframe and had mechanical strength characteristics comparable to metal bar and clamp ESF constructs.

CLINICAL RELEVANCE: The epoxy resin ESF construct tested in this study can be considered a suitable replacement for SK or KE ESF constructs in the treatment of feline long-bone fractures, in terms of mechanical strength.     

Tibiotarsus bone characteristics and tibial dyschondroplasia incidence of broilers fed diets supplemented with leucine and valine

Two experiments were conducted to study the effect of standardized ileal digestible (SID) leucine and valine levels on tibiotarsus bone characteristics and the incidence of tibial dyschondroplasia of broilers from day 1 to 21 (Experiment I) and day 21 to 42 post‐hatch (Experiment II). Each experimental phase was evaluated independently. In both experiments, a total of 1,500 one‐day‐old Cobb 500 male broiler chickens were distributed in a completely randomized design 5 × 5 factorial arrangement for a total of 25 treatments. The SID leucine and valine levels were ranged from 10.0 to 19.6 g/kg, and 6.0 to 12.0 g/kg from day 1 to 21 post‐hatch, respectively, while day 21 to 42 post‐hatch ranged from 10.0 to 18.0 g leucine/kg, and 5.2 to 11.2 g valine/kg. Serum calcium and phosphorus, bone concentrations of calcium, phosphorus and ash, diameter and Seedor index of the tibiotarsus were not affected (p > .05) by the treatments at 21 or 42 days of age. There was an interaction (p ≤.06) between the SID levels of leucine and valine on tibiotarsus breaking strength at 21 days, but not at 42 days of age (p > .05). Tibiotarsus breaking strength was maximized in broilers from day 1 to 21 with the dietary levels of leucine and valine at 14.2 and 9.0 g/kg respectively. Dietary leucine levels reduced linearly (p < .05) the hypertrophic zone of tibiotarsus cartilage at 21 days of age. Therefore, leucine and valine supplementation interact positively on bone strength of broilers from day 1 to 21 post‐hatch. Leucine can be a useful amino acid for reducing the hypertrophic cartilage zone in broilers from day 1 to 21, but not from day 21 to 42 post‐hatch.     

Growth performance,meat quality,and bone-breaking strength in broilers fed dietary rice hull silicon

Bone problems have been a key issue that perilously affects broilers' health and welfare, resulting in severe economic loss. The present study was aimed at investigating the influence of dietary rice hull silicon (RHS) on the performance, meat quality, and bone-breaking strength of broilers. One hundred 10-day-old Arbor Acres chicks were used in the study. The birds were divided into 5 groups: one group was kept as the control, and other groups were provided with 2.5, 5.0, 7.5, and 10.0 mg/kg dietary RHS along with their basal diets. Results showed that diets containing various levels of dietary RHS did not adversely affect (P > 0.05) the body weight, feed intake, and feed conversion ratio. Drip loss of thigh meat showed a reduced value in the group supplemented with 7.5 mg/kg dietary RHS compared with other groups (P < 0.05), and the lowest thawing loss was observed in the same group; however, it showed no significant difference among other groups. Similarly, thawing loss of breast meat tended to decrease in the dietary RHS groups and significantly decreased (P < 0.05) in the 7.5 mg/kg RHS group. The shear force of breast meat was higher in all RHS groups, and the highest was in the 7.5 mg/kg RHS group (P < 0.05). Although tibia breaking strength increased significantly (P < 0.05) in the 7.5 mg/kg RHS group (P < 0.05), but a significant difference in femur breaking strength was not found among groups. In conclusion, dietary RHS can be used as a natural mineral supplement for improving bone-breaking strength and reducing drip and thawing loss of breast and thigh muscles, particularly RHS at a level of 7.5 mg/kg in broiler diets.     

竹木复合材料胶合界面的研究进展

胶合界面性能好坏直接关系到木质或竹质复合材料的整体宏观性能，关系到材料的使用安全和使用寿命。从竹木单元表面润湿性能、竹木单元表面化学成分分析、竹木胶合界面结构表征、竹木胶合界面力学特性表征以及竹木胶合性能改善方法等方面对木质复合材料、竹质复合材料和竹木复合材料的相关研究进行了简要总结与回顾。这些研究方法和经验对于改善结构用竹木复合材料胶合性能有重要的借鉴价值。     

冻融作用对土壤氮转化影响的研究进展

氮素是限制植物生长的重要营养元素之一,其在土壤中转化程度受多种因素影响,作为中、高纬度或高海拔地区土壤氮转化的重要驱动力,冻融作用对于土壤氮转化过程也存在极大影响。本文基于国内外已有研究成果,概述了土壤冻融循环次数、结冻持续时间以及结冻强度对于土壤氮转化过程的影响。总结出冻融格局的改变对土壤氮转化关系的一般规律：随着冻融格局的改变,均有利于土壤氮的矿化;冻融强度的增加可显著提高土壤硝态氮的含量;冻融格局的改变也会提高N₂O的排放。     

新型排胶调节剂对橡胶树无性系热研8-79胶乳生理参数的影响

合适的采胶强度对于橡胶树持续高产稳产至关重要。最近的大田试验表明,阻断乳管伤口堵塞物积累的一种新型排胶调节剂具有明显的增产效应。以橡胶树无性系热研8-79为材料,通过分析胶乳的几个生理参数,评价该增产效应的采胶强度。结果表明,在8月和10月,新型排胶调节剂处理的第一刀具有明显的增产效应。在测定的几个胶乳生理指标中,胶乳产量显著高于对照,硫醇、蔗糖和无机磷含量以及10月的干胶含量与对照无显著差异,但8月的干胶含量显著低于对照,表明其增产效应主要与胶乳产量增加有关。与0.5%乙烯利相比,施用新型排胶调节剂的不同刀次胶乳生理参数的变化更接近对照,表明采胶强度小于乙烯利。     

轻质无胶蔗渣板的研究

以蔗渣为原料,不采用合成树脂,而是加入少量环保型添加剂(有机酸或糖)压制轻质无胶蔗渣板。探讨了板的密度,以及防水剂的有无对轻质无胶蔗渣板的物理力学性能及热学性能的影响。采用X射线衍射仪(XRD)、傅里叶变换红外光谱仪(FTIR)初步分析了加入添加剂、防水剂对板的物理力学性能及胶合机理的影响,结果表明:随着密度增大,板的导热性能,MOR值和TS值上升;加入添加剂后,板的纤维素结晶度增大;加入少量防水剂(石蜡)后,板的纤维素结晶度没有明显变化,—OH吸收峰强度下降,TS下降明显;在研究范围内,板的导热系数达到国家林业行业标准LY/T 1718-2007所要求的保温材料的要求。本研究既扩大了人造板生产的原料来源,又解决了人造板产品的游离甲醛释放问题。