高精度气动比例压力阀设计与特性分析

设计了一种两级阀芯活塞式结构的以比例电磁铁为控制元件,采用电反馈闭环控制的高精度气动比例压力阀。该阀输出压力在0.6MPa内连续可调,且稳态精度可达0.25 kPa。建立了比例阀完整的非线性动态模型,分析了主要物理和几何参数对系统动态特性和控制性能的影响;构建了输出因子调整的模糊自适应比例加积分控制器,并利用ATmega16单片机实现了压力在设定范围内的快速高精度控制。实验结果表明,该阀在设计压力范围内具有良好的压力和流量特性;和传统PI算法相比,输出因子调整的模糊自适应算法在改善系统响应和控制稳定性的同时,显著提高了稳态控制精度,具有较高的效率和鲁棒性。     

大型竖井式贯流泵装置的数值模拟与性能预测

基于三维不可压流体的雷诺时均方程和Spalart-Allmaras方程湍流模型,采用SIMPLEC算法,对大型竖井贯流式泵站的全流道进行数值模拟,分析流道的流态和叶轮的静压分布规律,揭示竖井式贯流泵流道流体的流动机理;对泵装置的流量和效率进行预测,并与模型试验结果比较分析.结果表明：出水流道内的流动为轴向流动与环向旋转的螺旋形合运动;叶片的静压分布呈现较为明显的规律,升力面的静压整体上较吸力面要高,且叶片吸力面的静压等值线分布较升力面密.性能预测结果和模型试验结果吻合较好.     

半室外环境两相流低压雾化降温数值分析

为了改善夏季半室外空间的环境舒适度,研究了一种节能环保的两相流低压雾化降温技术.利用CFD软件FLUENT对其降温进行了分析,结合半室外环境的气象条件,获得了20μm和40μm两种粒径液滴对降温效果的影响规律.根据半室外环境中的人群活动特征,对其降温效果进行了初步分析.结果表明：在半室外环境中,采用两相流低压雾化降温可以达到较好的降温效果,在1.7 m及1.2 m等两种人体感知区域范围内,采用20μm和40μm两种粒径的细水雾最高温度降幅可达3.5℃,有明显的降温感觉;采用两相流低压雾化降温,不会引起局部环境中相对湿度的明显增加,人体不会感觉到闷热潮湿.两种粒径的细水雾均能完全蒸发,降温增湿的幅度和范围基本相同,没有明显区别.     

不同大气压下直喷式柴油机的性能研究

在大气模拟试验台架上对运行在不同大气压下的直喷式柴油机的经济性、动力性、烟度及噪声特性进行对比试验研究与分析。试验结果表明:随着大气压力的减少,柴油机有效燃油消耗率、小时燃油消耗量、排气温度、烟度及噪声声功率增加,动力性下降。     

PLC及变频调速恒压喷灌系统的设计

针对喷灌系统受作业区域需水量的影响造成系统喷头不能稳定可靠工作的问题,结合工程实例,提出了利用PLC及变频器来实现温室喷灌系统恒压供水.给出了变频调速恒压供水系统原理图,并进行了系统的主电路设计和软件设计.阐述了利用上位机、PIC、变频器、压力变送器、电机-水泵系统等组成的恒压供水系统,能按照设定的工作压力,实时切换泵组投入工频或变频状态运行,达到恒压供水的目的.系统能通过上位机实现下位机的控制参数的设定、系统的实时监测、数据管理等任务,自动化程度高.应用表明,系统实现简单,操作方便,运行稳定,可靠,且具有较好的节能效果.     

液压技术在油菜生产机械中的应用

液压技术在农机中的应用日益广泛,油菜生产机械化装备近几年在国家大力支持下有了较快发展,由于液压技术的优势,在油菜机械装备中也应用越来越多,文章就目前我国油菜生产机械中所应用的液压技术进行了综述和研究。     

常压灌水器在低压条件下水力性能试验研究

鉴于目前国内低压滴灌系统中的滴灌带(管)基本沿用常压滴灌下使用的滴灌带(管),对常压滴灌系统中使用较多的国内6种单翼迷宫和内镶片式滴灌带在低压下的水力性能进行了试验研究,试验结果表明,在2~8 m和6~14 m水头压力范围拟合的流量与压力关系式不相同,在2~8 m水头压力范围的流态指数明显高于在6~14 m水头压力范围的流态指数。在较低压力下测定灌水器的制造偏差时,相比额定压力下所测定的结果表现出增大的趋势,即由于灌水器制造工艺和材料配方引起的制造偏差,在工作压力较低时表现的更为明显。     

Inducible nitric oxide synthase and arterial pressure regulation

AIM and METHODS:To clarify the role of inducible nitric oxide synthase (iNOS) in the regulation of blood pressure,in the present study, we examined the effect of aminoguanidine (AG), a selective inhibitor of iNOS on the hemodinamical response of Dahl salt-sensitive (DS) and Dahl salt-resistant (DR) rats to low (0.3%) or high (8%) sodium chloride (NaCl) infusion by chronical in vivo hemodynamic experiment, and the effect of NaCl or NaCl plus AG infusion on urinary nitrate (NO₃)/nitrite (NO₂), the end product of nitric oxide (NO), excretion by Greiss Reaction. Furthermore, NOS activity assay was also carried out to probe the effect of NaCl and AG on calcium-dependent or independent NOS activity in renal tissue. RESULTS:1. High or low NaCl-infused DR rats and low NaCl-infused DS rats have no hemodinamical response to AG, however, the hypertensive effect of high NaCl (8%) infusion on DS rats were greatly amplified by co-infusion of AG. 2. Administration of high NaCl significantly elevated the iNOS activity of renal tissue, and greatly increased urinary NO₃/NO₂ excretion. CONCLUSION:Inducible NOS is an important modulator of arterial pressure, especially in case of higher blood pressure.     

火龙果茎多糖的超高压提取及抗氧化活性研究

为研究火龙果茎多糖的超高压提取工艺及抗氧化活性。在单因素试验基础上,采用Box-Behnken设计和响应面分析方法,确定超高压提取的最优工艺,并从清除ABTS自由基和DPPH自由基能力方面来评价火龙果茎多糖的体外抗氧化能力。结果表明,火龙果茎多糖的超高压提取的最佳工艺条件为:液固比10∶1(m L∶g)、超高压压力300 MPa、超高压时间4 min。在此工艺条件下多糖得率为(2.83±0.02)%。火龙果茎对ABTS自由基和DPPH自由基具有清除作用,对ABTS自由基和DPPH自由基的清除率IC_(50)分别为浓度为4.3 mg/m L和5.5 mg/m L时。     

Effects of noninvasive delayed limb ischemic preconditioning on prognosis of myocardial infarction

AIM: To study the effects of noninvasive delayed limb ischemia preconditioning (NDLIP) on animal cardiac function, myocardial morphology and myocardial apoptosis after myocardial infarction (MI). METHODS: Healthy SD male rats[n=45, weighing (250±10) g] were randomly divided into 3 groups:MI group:the animal model of MI was established by surgical ligation of left anterior descending artery (LAD) after 2 weeks; NDLIP group:after the success of the MI animal model, NDLIP was carried out every other day until the 4th, 6th and 8th weeks; sham group:as the negative control group, the animals were taken heart LAD threading but no ligation. All rats were fed conventionally. At the end of the 4th, 6th and 8th weeks, all rats were made ventricular intubation, and then the hemodynamic parameters were recorded. The blood samples were withdrawn from the abdominal aorta and the serum was separated via centrifugation. The serum contents of Bcl-2 and Bax were measured by ELISA. Left ventricular anterior wall was homogenized. The mitochondrial respiratory chain complexes Ⅰ, Ⅱ, Ⅲ and Ⅳ in the myocardial tissues were detected by ELISA. RESULTS: At the end of the 4th, 6th and 8th weeks, compared with MI group, left ventricular systolic pressure in NDLIP group was significantly increased, while left ventricular end-diastolic pressure in NDLIP group was significantly decreased (both P<0.05). Mitochondrial respiratory chain complexesⅠ, Ⅱ, Ⅲ and Ⅳ in NDLIP group were significantly increased (P<0.05). The serum level of Bcl-2 in NDLIP group was significantly increased and Bax level was reduced remarkably (both P<0.01). CONCLUSION: NDLIP improves the hemodynamic indexes, promotes the mitochondrial respiratory function and inhibits cell apoptosis, thus improving the prognosis of MI.