闭式混凝土泵液压系统研究

全面介绍了混凝土泵闭式液压系统及其快速换向、快速推进和柔和推送功能的实现。分析了闭式系统的压力切断和速度敏感控制。通过对闭式系统的分析,用功率键合图方法对泵送系统进行建模,并用Matlab/Simulink进行动态仿真,研究了液压系统的动态特性。     

汽车搭铁线电路故障的诊断与处理

汽车上将蓄电池负极与车身的金属部分相连接的导线通常称为搭铁线。搭铁线虽小,在汽车电路中却起着重要的作用。着重介绍了汽车搭铁线的类型、作用、故障诊断,为正确检修提供参考。     

上市房地产企业零杠杆现象影响因素研究

在利用滑动相关系数描述两市波动溢出强度基础上，实证选择了马尔科夫体制转换ARMA(1,1)刻画我国股市和债市的体制转换特征；接着利用LR检验等验证了MS-ARMA(1,1)整体及各类参数结构变化的显著性；然后利用概率外推法预测了短期内两市的波动溢出强度变动趋势.结果表明，两市体制转换非对称，正相关状态持续期更长，体制转换中存在交替的逃离效应和传染效应特征.     

THE EFFECTS OF WETTING AND REDRYING CYCLE ON PHYSICAL PROPERTIES OF PARTICLEBOARD

INTR0DUCTI0NOvertheyearsmmpresearchershavefoundUFandPFparticleboardstoedsbitsimilarshorttermphysicalpropeniesatlowhumidityandtemperatUre(DeainandOstInan,l983).DifferentbehaviorpatternsbetWeentl1eresinsemefgeasrelativehumidityandtem-peratUrerise,finallycouldresultinthefailureofboards(R0dwell,l99l).AnumberofworkshavequestionedWhetherhydrolysisistheonlyfactorinvolvedinb0ndfailure.Irlereported(l986)thedifferenteffectsofwettingandredryingonthepropertiesofpureUFandPFresinfilms.Soitmaybeim…     

Bond properties of CFRP-high performance concrete subjected to freeze-thaw cycles

通过双面剪切试验,研究了冻融环境下CFRP-高性能混凝土界面粘结性能的发展规律。对比分析了未经冻融和经历25、50、100、150、200及300次冻融循环作用试件的破坏特征、剪应变分布、荷载滑移曲线、粘结承载力以及粘结破坏机理。结果表明,所有试件的界面破坏均发生在混凝土表层内,但随着冻融循环次数的增加,破坏界面有向胶层发展的趋势;经受冻融循环次数较少时(25、50次),界面的粘结强度、刚度及开裂荷载的变化不明显,甚至略微提高;但随着冻融循环次数的进一步增加,界面粘结性能有明显的变化,界面粘结强度、端部滑移量减小,刚度退化,初始开裂荷载水平降低,非线性特征增强。粘结极限承载力与混凝土立方体抗压强度均随冻融循环次数的增长存在先提高后下降的趋势,混凝土强度变化是界面粘结性能变化的最重要因素。     

香蕉秸秆离散元仿真粘结模型参数标定与试验

为提高离散元法对指导香蕉秸秆粉碎还田装备设计与优化的准确性与可靠性,本文利用Hertz-Mindlin with bonding接触模型建立香蕉秸秆离散元粘结模型并进行参数标定。运用高速摄影技术开展碰撞恢复试验、静摩擦及滚动摩擦台架试验,确定了香蕉秸秆碰撞恢复系数、静摩擦因数和滚动摩擦因数等基本离散元模型接触参数。开展香蕉秸秆物理与仿真剪切试验,获得破坏香蕉秸秆外皮的力学特征曲线,确定物理最大剪切力为122.41N;通过中心组合设计（Central composite design, CCD）响应面法确定香蕉秸秆粘结模型的法向接触刚度、切向接触刚度、临界法向应力与临界切向应力的最佳参数组合为5.89×107N/m、2.49×106N/m、1.39×105Pa、1.34×105Pa。以参数标定结果进行仿真验证,结果表明,仿真剪切力结果与物理剪切力相对误差仅为2.34%,验证了该粘结参数标定方法的可行性,可为香蕉秸秆粉碎还田机设计与研究提供理论参考。     

Nonlinear dynamics bond graph model for a spur gear pair system

A nonlinear dynamics bond graph model of gear pair system is established including the time-varying gear mesh stiffness, transmission error and tooth surface conditions. A capacitive component c is introduced to represent the loads and tooth elastic deformation, while the capacity parameter Kj is expressed by time-varying mesh stiffness, and flow Sf represents the influences of the gear transmission error on the system dynamic equations. Then the tooth surface friction bond graph model involving the relationship between the relative velocity and the direction of friction are presented. According to the causal relations and the power flow, the state-space equations of the gear bond graph model are obtained. Research results show that bond graph modeling method can solve the modeling problem of the gear nonlinear dynamics, and this paper is a kind of basis work of the complex mechanical system modeling and the development of bond graph modeling theory.     

灾害性气候条件下优质蛋白玉米黔单11号的表现

优质蛋白玉米杂交种黔单11号是在贵州恶劣灾害气候的环境条件下,选育出来的玉米新品种。经1997、2000、2001年3a试验,观察了灾害性气候对该品种的影响。结果表明:该品种抗逆性较强,播种期遇干旱久晴无雨的天气,土壤田间持水量为43.5％(正常土壤田间持水量60％)、雨水不足,出苗率在85％以上,基本达到苗齐、苗壮:拔节后期喇叭口阶段,遇到久雨少晴气候,遭受水涝灾害,土壤田间持水量达85％以上,部分低洼处被水淹,而玉米生长正常,叶色深绿,根系发达,未发现烂根现象;在抽雄、吐丝、授粉阶段,遭遇伏旱及暴风雨灾害,玉米正常抽雄吐丝授粉结实,产量未造成较大影响,基本上达到常年稳产,每公顷达到8400kg以上。     

Improvement on the properties of gypsum particleboard by adding cement

Gypsum particleboard (GPB) has high thickness swelling (TS), high water absorption (WA), and low mechanical properties compared with cement-bonded particleboard. The properties of GPB were improved by adding cement. The experimental results showed that GPB with the added cement had good physical and mechanical properties compared with those of gypsum particleboard with no added cement. The TS and WA of gypsum particleboard with added cement were reduced by 10%. The mechanical properties of GPB, such as internal bond strength (IB), modulus of rupture (MOR), and modulus of elasticity (MOE), increased when the GPB was made with added cement. The properties of GPB improved relative to the quantity of cement added. With an increase of cement content from 5% to 10%, the TS and WA were reduced, and the IB, MOR, and MOE were increased. In contrast, the TS and WA increased and the IB, MOE, and MOR decreased when the cement content was increased from 15% to 30%. Thus the physical and mechanical properties of GPB were successfully improved when the added cement content was 10%.An outline of this paper was presented at the 47th Annual Meeting of the Japan Wood Research Society in Kochi, April 1997     

中国红壤丘陵区基于突变模型的生态恢复措施下土壤恢复评价

Current methods that utilize simple data or models to evaluate soil restoration under ecological restoration are not sufficiently rigorous.Soil restoration under ecological restoration measures was evaluated in the red soil hilly region of China by applying the catastrophe model.Among 89 soil sites selected,26 (29.21％) were in the middle lobe,10 (11.24％) in the upper lobe,and 53 (70.79％) in the lower lobe of the process surface in the Cusp catastrophe model.The catastrophic direction of the 26 unstable soil sites was to the upper lobe of the process surface according to vegetation cover change and fieldwork.There was a significant negative correlation of the variation in bifurcation set (△ value) with vegetation cover increase,and a higher vegetation cover increase was related to higher unstable probability.The four ecological restoration measures were listed in the order:low-quality forest improvement (LQFI) ＞ arbor-bush-herb mixed plantation (ABHMP) ＞ orchard improvement (OI) ＞ closing measures (CM) according to the proportions of unstable soil sites,which were all higher than no restoration measure,while they were in the order:LQFI ＜ ABHMP ＜ OI ＜ CM according to their △ values,which were all lower than those of no restoration measure.Farmers' assessment of soil restoration under the four ecological restoration measures was in accordance with the proportions of unstable soil sites and inversely proportional to the △ value.Therefore,farmers' assessment can prove the evaluation of soil restoration under ecological restoration measures based on catastrophe model.