Evaluation of 2 cement techniques for augmentation of stripped 1.5 mm screw sites in the distal metaphysis of feline radii

OBJECTIVE: To evaluate the effect of 2 cement augmentation techniques on pullout strength of 1.5 mm screws placed in stripped 1.5 mm screw sites in the distal metaphysis of feline radii. STUDY DESIGN: Experimental study. SAMPLE POPULATION: Feline radii (21 pairs). METHODS: Treatment groups (n=4) were allocated according to a Latin square design to 4 sites in each pair of radii. Positive and negative controls were a 1.5 mm screw and a screw of the same diameter in a previously stripped screw hole, respectively. Treatment groups were a 1.5 mm screw implanted in a previously stripped screw hole after injection of polymethylmethacrylate (PMMA) or a bioresorbable calcium phosphate cement (CPC, Norian skeletal repair system (SRS)). The ultimate pullout strength was compared between groups. RESULTS: The mean (+/-SEM) pullout strength of screws augmented with either bone cement was less than that of the positive control group and greater than that of the negative control. Injection of CPC or PMMA before screw implantation increased the pullout strength of the negative control by 86.8+/-22.9% and 104.1+/-32.1%, respectively. Holding power of the positive control screws differed from these 2 groups, and was 274.8+/-39.17% higher than that of the negative control. CONCLUSION: Injection of CPC or PMMA increases but does not restore the holding power of stripped 1.5 mm diameter screws. CLINICAL RELEVANCE: The use of CPC (Norian SRS) augmentation of stripped 1.5 mm diameter screws warrants clinical investigation as it combines biomechanical results similar to PMMA with osteoconduction and resorbability.     

Increased sacral screw purchase minimizes screw loosening in canine triple pelvic osteotomy

OBJECTIVE: To determine if screw loosening in triple pelvic osteotomies (TPO) is minimized when screws cranial to the ilial osteotomy had maximal sacral purchase. STUDY DESIGN: Prospective study. ANIMALS: Forty-six dogs with decreased acetabular coverage of the femoral head and minimal degenerative joint changes. METHODS: TPOs were performed where screws cranial to the ilial osteotomy were inserted to maximally engage sacral bone. Data collected were: use of ilial and ischial cerclage wire, screw length, ventrodorsal radiographic sacral width (most caudal aspect), pelvic canal diameter, and sacral penetration of the 3 cranial screws. On all subsequent radiographs, changes in screw position, pelvic canal diameter, and sacral purchase were noted. RESULTS: For 69 TPOs, 414 screws were used. Mean radiographic cranial screw length was 34.54 mm. Combined sacral depth of all 3 screws was 93.3% of sacral width. All osteotomies healed uneventfully. Twenty-four screws (6%) loosened with 12 being in the most cranial positions. Use of ischial or ilial cerclage wires did not statistically influence screw loosening. Pelvic diameter decreased by a mean of 7.79% from postoperative radiographs to the last radiographic recheck. CONCLUSIONS: By sufficiently engaging the sacrum with screws cranial to the ilial osteotomy, implant failures can be avoided and screw loosening minimized when a 6-hole TPO plate is used. CLINICAL RELEVANCE: To minimize screw-loosening in TPO, screws inserted cranial to the ilial osteotomy should be inserted to maximum sacral depth without penetrating the vertebral canal.     

考虑摩擦和间隙的柔性滚珠丝杠进给系统建模与分析

为了研究高速滚珠丝杠进给伺服系统的动态特性,提出了一种建立进给系统机械子系统振动模型的混合建模方法,采用带有轴向和扭转自由度的欧拉-伯努利梁单元描述丝杠的轴向、扭转和弯曲振动,采用集中参数方法描述交流伺服驱动子系统和进给系统的其余部件,建立了包含摩擦、间隙非线性因素及外切削力干扰的柔性进给系统模型。实验证明了混合模型能够较准确反映机械系统的振动特性。在此基础上,数值仿真分析表明,低速运动中摩擦和间隙非线性会导致进给系统产生较大的速度波动,在高速运动中机械系统的轴向和扭转振动会导致进给系统不稳定。     

Improve regression-based models for prediction of internal-bond strength of particleboard using Buckingham’s pi-theorem

Internal bond (IB) strength is one of the most important me-chanical properties that indicate particleboard quality. The aim of this study was to find a simple regression model that considers the most ...     

壳聚糖-丁香复合液对牛肉丸的保鲜效果

以样品茵落总数、TVB-N值、pH及感官评分的隶属函数值为主要指标,以壳聚糖液处理和丁香提取液处理为对照组,探讨单一的壳聚糖液和丁香提取液以及壳聚糖-丁香复合液对牛肉丸的保鲜效果.结果表明,壳聚糖-丁香复合液的保鲜效果明显优于单一的壳聚糖液和丁香提取液处理,可使牛肉丸在4℃的贮藏期达到15d左右,相比单一的壳聚糖液和丁香提取液处理组可延长保质期3～6 d.     

高海拔地区百合栽培的花期调控技术初探

该文介绍了百合的生物学特征、对光照、温度及其他环境条件的要求以及这些因素对百合开花的影响,提出在高海拔地区对百合开花期的主要调控技术,为百合的进一步开发利用提供依据。     

螺旋式输送装置参数优化研究

为了提高农业纤维物料螺旋式输送装置的输送性能,降低输送功耗,提高生产率,利用MATLAB软件对比功耗数学模型进行单变量优化分析,并结合试验验证了理论分析的一致性。试验结果表明:螺旋式输送装置输送性能最佳的取值范围是:喂入量30～70 kg/min、螺距300～355 mm、螺旋轴转速97～137 r/min。以比功耗作为输送性能评价指标,采用3因素3水平的Box-Benhnken响应面分析法进行参数优化试验,得到了影响比功耗各因素的主次顺序:喂入量、螺距、螺旋轴转速。以比功耗最小为优化目标,利用Design-expert的优化模块对试验结果进行分析,确定出各因素对指标影响的最佳参数组合:螺距335 mm、螺旋轴转速117 r/min、喂入量30 kg/min,输送性能优化后比优化前提高了8%,上述成果满足预期设计目标,可为螺旋式输送装置的参数优化和结构改进提供一定的参考和指导。     

球磨仪-微波消解石墨炉原子吸收法测定土壤中的铅元素

采用行星式球磨仪制样、微波消解、石墨炉原子吸收法测定了土壤样品中的铅含量,球磨仪制样颗粒超细且均匀,干净卫生,不存在扬尘污染;微波消解仪操作简便快速,消耗试剂少,密闭消解,酸污染少。结果表明:测定土壤标准样品GSS-22的相对误差为1%,GSS-26相对误差为1.2%,测定实际试样相对标准偏差均值为1.6%,均满足试验要求。     

基于DEM仿真与试验验证的双轴螺旋输送机结构优化分析

针对螺旋输送机的输送效率问题,对双轴螺旋输送机输送颗粒物料的过程进行离散元法数值计算,并与单轴螺旋输送机输送物料的试验和模拟结果进行对比。在试验验证了仿真模型和参数正确的基础上,对双轴螺旋输送机的轴距和螺距2个参数与质量流速率(■)间的定量关系进行二元二次多项式拟合,得到拟合优度R~2=0.964 6的回归方程。研究结果表明:1)双轴的相对转动方向对■没有影响;2)螺距和轴距对■均有明显影响。■随着轴距的增大显著增大,大螺距时会在达到极值后趋于稳定或略有下降;■随着螺距的增大先增大至峰值后下降;3)双轴的螺距和轴距对颗粒运动影响显著。两轴中间位置颗粒的最小轴向平动速度与轴距呈现近似线性的递减关系,且螺距越大,其减小趋势越明显。     

基于BP神经网络的甘蔗收获机切割器振动性能研究

针对小型甘蔗收获机切割器不平衡对切割器轴向振动的影响,为实现切割器振动的有效预测以及自动控制信号的获取,通过正交试验并利用BP神经网络技术与回归分析构建出了切割器螺旋以及刀盘振动的BP神经网络模型和回归模型。分析结果表明:基于BP神经网络建立模型的切割器螺旋与刀盘的振动正确拟合率达到了88.89%,且相对误差基本上在5%以内,而回归模型的切割压力正确拟合率只有38.89%。因此,基于BP神经网络建立的模型具有较高的精度,通过此BP神经网络模型,有效地解决了复杂信息特征的提取问题,减少了试验研究的次数与成本,为进一步的切割器刀盘以及螺旋振动的自动控制系统的研发奠定了基础。