离心泵叶轮进口空化形态的试验测量

为研究离心泵叶轮进口部分的空化形态,以一台中等比转数离心泵为对象,在泵进口管路上增加全透明水箱,基于泵产品智能测试系统和图像采集系统,在离心泵闭式试验台上对3种不同流量下叶轮进口的空化形态进行可视化试验研究.试验结果表明:空泡首先在模型泵叶片背面进口边附近初生,空泡的产生位置因运行工况不同而变化;随着装置空化余量NPSHa的下降,多个叶片背面有空泡产生,并随着叶轮的转动,呈现明显的初生、生长和溃灭的动态过程;当泵扬程下降较大时,空泡的分布随叶轮转动变化不大,且靠后盖板一侧的空泡分布小于靠前盖板一侧.     

抽气回热式有机朗肯循环系统热力学分析

为了实现发动机排气余热能的高效回收与利用,设计了抽气回热式有机朗肯循环(ORC)系统.在Matlab环境下,分析了抽气压力、蒸发压力、膨胀机入口温度等因素对系统性能的影响,并利用热力学第一定律及第二定律将抽气回热式ORC和基本ORC进行对比.研究结果表明,在固定蒸发压力下,抽气回热式ORC系统的热效率、炯效率随抽气压力的增大而先增大后减小,工质质量流量随抽气压力的增大而逐渐增大,蒸发器换热量随抽气压力的增大先减小后增大;与基本ORC系统相比,抽气回热式ORC系统的热效率、(火用)效率均有提高,炯损率降低,因此抽气回热式ORC系统余热回收效果更明显.     

Evaluation of the tongue for oscillometric measurement of arterial pressure in anesthetized Beagle dogs

ObjectiveTo evaluate the agreement between oscillometric blood pressure (OBP) measured from the tongue and invasive blood pressure (IBP), and to compare OBPs measured from the tongue with OBPs measured from the pelvic limb and tail.Study designProspective experimental study.AnimalsA total of eight adult Beagle dogs weighing 11.1 ± 1.2 kg.MethodsAnimals were premedicated with intravenous (IV) acepromazine (0.005 mg kg^–1). Anesthesia was induced with alfaxalone (3 mg kg^–1) IV and maintained with isoflurane. The dorsal pedal artery was catheterized for IBP measurements. Systolic (SAP), diastolic (DAP) and mean (MAP) arterial pressure were simultaneously measured from the tongue, pelvic limb and tail. Based on invasive SAP, hypertension (>140 mmHg), normotension (90–140 mmHg) and hypotension (<90 mmHg) were induced by controlling end-tidal isoflurane concentrations and/or dobutamine/dopamine administration. Agreement between paired IBP and OBP measurements was analyzed with reference standards for noninvasive blood pressure devices used in small animals and humans.ResultsRegardless of cuff placement, the mean bias ± standard deviation between IBP and OBP met veterinary (≤10 ± 15 mmHg) and human (<5 ± 8 mmHg) standards for MAP and DAP. SAP measurements provided by the OBP device showed unacceptable agreement with IBP, and the bias between methods increased at higher blood pressures, regardless of cuff site. During hypotension, tongue OBP showed the largest percentage of absolute difference <10 mmHg in relation to IBP for SAP (90%), MAP (97%), and DAP (93%), compared with pelvic limb (60%, 97% and 82%, respectively) and tail OBP (54%, 92% and 77%, respectively).Conclusions and clinical relevanceThe tongue is a clinically useful site for measuring OBP in anesthetized Beagle dogs, providing reliable estimates of MAP and DAP. The tongue could replace other cuff placement sites and may be a relatively suitable site for assessing hypotension.     

盾构机推力过大原因分析与应对措施

泥水加压平衡盾构机作为一种管道施工机械设备,除本身的液压、电气系统故障外,其余影响盾构推进速度的问题在参数特征上均表现为推力过大.以北江盾构穿越工程使用的M1051盾构机为例,分析了引起盾构机推力过大的人为掉物卡拖车、推进模式选择错误、粘土层糊刀、卵石层隔离刀盘、沙层固结盾尾、盾构机V形姿态的管理和工况因素,并从管理和技术两个方面提出解决措施,可为相同或相似的油气管道盾构施工提供借鉴.(图2,参5)     

A study of measurement of noninvasive blood pressure with the oscillometric device,Sentinel, in isoflurane‐anaesthetized horses

ObjectiveTo assess accuracy of noninvasive blood pressure (NIBP) measured by oscillometric device Sentinel compared to invasive blood pressure (IBP) in anaesthetized horses undergoing surgery. To assess if differences between the NIBP measured by the Sentinel and IBP are associated with recumbency, cuff placement, weight of the horse or acepromazine premedication and to describe usefulness of the Sentinel.Study designProspective study examining replicates of simultaneous NIBP and IBP measurements.AnimalsTwenty-nine horses.MethodsInvasive blood pressure was measured via a catheter in the facial artery, transverse facial artery or metatarsal artery. NIBP was measured using appropriate size cuffs placed on one of two metacarpal or metatarsal bones or the tail in random order. With both techniques systolic (SAP), mean (MAP), and diastolic (DAP) arterial blood pressures and heart rates (HR) were recorded. A mixed effects model compared the IBP to the NIBP values and assessed potential effects of catheter placement, localisation of the cuffs in combination with recumbency, weight of the horse or acepromazine premedication.ResultsNoninvasive blood pressure yielded higher measurements than IBP. Agreement varied with recumbency and cuff position. Estimated mean differences between the two methods decreased from SAP (lateral recumbency: range -5.3 to -56.0 mmHg; dorsal recumbency: range 0.8 to -20.7 mmHg), to MAP (lateral recumbency: range -1.8 to -19.0 mmHg; dorsal recumbency: range 13.9 to -16.4 mmHg) to DAP (lateral recumbency: range 0.5 to -6.6 mmHg; dorsal recumbency: range 21.0 to -15.5 mmHg). NIBP measurement was approximately two times more variable than IBP measurement. No significant difference between IBP and NIBP due to horse's weight or acepromazine premedication was found. In 227 of 1047 (21.7%) measurements the Sentinel did not deliver a result.Conclusion and clinical relevanceAccording to the high variability of NIBP compared to IBP, NIBP measurements as measured by the Sentinel in the manner described here are not considered as an appropriate alternative to IBP to measure blood pressure in anaesthetized horses.     

旋转失速条件下离心泵隔舌区动静干涉效应

为研究旋转失速条件下离心泵隔舌区动静干涉效应和流动特性,采用大涡模拟方法对一离心泵进行了数值模拟,得到了水泵内部流场和隔舌区压力脉动特性。对不同旋转时刻的内部流动进行分析,发现当流量小于0.75倍额定流量时,叶轮中发生了旋转失速,并且由于隔舌附近逆压梯度较大,当叶轮流道通过隔舌处时会发生"固定失速"的流动现象。对旋转失速条件下蜗壳上的压力脉动进行分析,发现蜗壳隔舌处的压力脉动幅值最高,沿着流动方向依次减小。当旋转失速发生以后,蜗壳上的压力脉动幅值约为非失速工况下的2~3倍,并随着流量减小,压力脉动主频幅值增大。在旋转失速初始阶段,隔舌区"固定失速"对压力脉动的影响较弱,旋转失速的影响占主导,蜗壳上的压力脉动主频为0.5倍叶频;而当流量进一步减小至0.25倍额定流量时,隔舌区的"固定失速"对压力脉动的影响作用增强,削弱了旋转失速的作用,蜗壳上靠近隔舌区的压力脉动主频为叶频,而远离隔舌区的位置受"固定失速"影响较小,旋转失速的影响占主导,主频仍是0.5倍叶频。该研究结果可为离心泵机组运行稳定性提供参考。     

The role of albumin replacement in the critically ill veterinary patient

Objective: To review the human and veterinary literature on the physiological role and effects of therapeutic albumin supplementation. Data sources: Data from human and veterinary literature was reviewed. Human data synthesis: Hypoalbuminemia often occurs in a variety of critical illnesses, and contributes to the development of life‐threatening complications, including pulmonary edema, delayed wound healing, feeding intolerance, hypercoaguability, and multiple organ dysfunction. Serum albumin concentration has been used as a prognostic indicator in cases of chronic hypoalbuminemia. The use of albumin replacement therapy in humans is sometimes controversial, but may be associated with improved morbidity and decreased mortality. Veterinary data synthesis: Unlike human literature, there is a paucity of controlled clinical studies in the literature regarding albumin supplementation in veterinary patients. Rather, the majority of published studies were performed in experimental animals or via retrospective analyses. One recent study evaluated the use of plasma to improve albumin concentration in dogs with hypoalbuminemia. Other older studies investigated wound healing in dogs with experimentally induced hypoalbuminemia. As in human medicine, serum albumin concentration may be helpful as a prognostic indicator in critically ill dogs. Conclusion: Albumin is one of the most important proteins in the body because of its role in maintenance of colloid oncotic pressure, substrate transport, buffering capacity, as a mediator of coagulation and wound healing, and free‐radical scavenging. Albumin replacement in veterinary medicine is difficult, but until prospective clinical trials determine the efficacy of albumin replacement are conducted, a suggested clinical guideline would be to maintain albumin concentration at or above 2.0 g/dl utilizing fresh frozen plasma.     

Tillage and wind effects on soil CO2 concentrations in muck soils

Rising atmospheric carbon dioxide (CO₂) concentrations from agricultural activities prompted the need to quantify greenhouse gas emissions to better understand carbon (C) cycling and its role in environmental quality. The specific objective of this work was to determine the effect of no-tillage, deep plowing and wind speeds on the soil CO₂ concentration in muck (organic) soils of the Florida Everglades. Miniature infrared gas analyzers were installed at 30 cm and recorded every 15 min in muck soil plowed with the Harrell Switch Plow (HSP) to 41 cm and in soil Not Tilled (NT), i.e., not plowed in last 9 months. The soil CO₂ concentration exhibited temporal dynamics independent of barometric pressure fluctuations. Loosening the soil resulted in a very rapid decline in CO₂ concentration as a result of “wind-induced” gas exchange from the soil surface. Higher wind speeds during mid-day resulted in a more rapid loss of CO₂ from the HSP than from the NT plots. The subtle trend in the NT plots was similar, but lower in magnitude. Tillage-induced change in soil air porosity enabled wind speed to affect the gas exchange and soil CO₂ concentration at 30 cm, literally drawing the CO₂ out of the soil resulting in a rapid decline in the CO₂ concentration, indicating more rapid soil carbon loss with tillage. At the end of the study, CO₂ concentrations in the NT plots averaged about 3.3% while that in the plowed plots was about 1.4%. Wind and associated aerodynamic pressure fluctuations affect gas exchange from soils, especially tilled muck soils with low bulk densities and high soil air porosity following tillage.     

鱼类镁营养生理的研究进展

镁在动物生理中发挥重要的作用,是动物体内众多酶系的辅助因子和激活剂,也是骨骼和牙齿的重要组成部分。该文就鱼类对镁的需要量及镁与鱼类生长、离子代谢、免疫、抗应激以及渗透压调节等方面的研究进行综述。     

蓖麻籽直筒式压榨侧向压力系数的理论研究

为建立蓖麻籽直筒式压榨侧向压力系数的理论公式,以便于合理地确定直筒式压榨机的榨筒参数,通过进行蓖麻籽直筒式单轴压榨试验,获取蓖麻籽压榨坯密度、侧向应力和轴向应力。试验建立的压榨坯密度与轴向应力的关系曲线和金属粉体压制曲线近似,由此利用金属粉体压制公式进行数据拟合,同时利用试验数据建立了侧向压力系数与轴向应力关系曲线。理论公式计算值与试验实测值的最大相对误差为24.74%,平均误差7.56%,证明了基于压榨塑性模型推导过程建立的侧向压力系数理论模型能较好地描述蓖麻籽侧向压力系数变化。