基于支持向量机的滴灌灌水器流量预测模型建立与验证

为了直接、准确预测灌水器流量,引入支持向量机预测方法,取灌水器6个工作压力和8个几何参数作为因素,正交设计安排300组灌水器训练样本和30组检测样本,并采用精度较高的SST k-ω模型模拟计算灌水器流量,同时利用遗传算法对支持向量机参数进行优化计算,得到与模拟流量误差最小的流量预测值。结果表明,惩罚参数为100、核函数参数为20时检测样本的流量预测值与模拟值的误差最小,平均相对误差为1.91%,决定系数为0.98,而回归拟合方法计算得到的平均相对误差为6.45%,决定系数为0.93,表明支持向量机预测流量的优越性,且30组试验验证样本的平均相对误差为2.25%,证明支持向量机预测的准确性和可靠性。预测模型建立可有效地提高灌水器研发效率,对水力性能评估和流道结构设计与优化提供依据。     

Effect of High Pressure Processing on the Quality and Endogenous Enzyme Activities of Grass Carp (Ctenopharyngodon idellus) Fillets Stored at 4ºC

ABSTRACT

This study assessed effects of high pressure processing on physicochemical quality and endogenous enzyme activities of grass carp fillets stored at 4 ºC for 21-day storage. Fresh fillets were vacuum-packed and subjected to high pressure processing (0.1, 200, 300, 400, 500, and 600 MPa at room temperature for 15 min). Results showed that high pressure processing significantly delayed microbial growth, and reduced total volatile basic nitrogen (TVB-N) and thiobarbituric acid reactive substances (TBARS) levels of grass carp fillets, especially for the 600 MPa group. On the 21st day, the corresponding increases of 6%, 35%, 45%, 43%, and 53% in hardness were observed for 200 MPa, 300 MPa, 400 MPa, 500 MPa, and 600 MPa samples compared with control samples, respectively. In addition, enzyme activities in different groups decreased during storage. Among them, calpain, and myofibril-bound serine proteinases (MBSP) activities were immediately reduced after high pressure treatments, while the activities of collagenase, cathepsin B, and cathepsin D were significantly (P < 0.05) inhibited when the pressure exceeded 400 MPa. However, the pressure treatments activated cathepsin L initially, and then the activity gradually decreased in treated samples. Generally, high pressure processing reduced activities of most of the endogenous enzymes and improved the quality and extended the shelf life by at least 4 ~ 6 days of refrigerated grass carp fillets.     

Comparison of horse mackerel and tilapia surimi gel based on rheological and <Superscript>1</Superscript>H NMR relaxation properties

ABSTRACT:   Horse mackerel and tilapia surimi were subjected to six different heat and pressure treatments in order to compare gelation characteristics of easy- and difficult-setting gels, that is, temperature dependence, by observing rheological properties and microscopic molecular mobility. The stress–relaxation and proton spin–spin relaxation time (¹H T ₂) of water were measured for all treated gels. Horse mackerel gel demonstrated higher elasticity, large distribution of the stress–relaxation process, and smaller water ¹H T ₂ than tilapia in both heat and pressure treatments. The water ¹H T ₂ was steeply increased in the pressure treatment at around 294 MPa for both fishes. In contrast, the ¹H T ₂ rarely changed in the heat treatment in spite of the considerable change in rheological properties. From the experimental results, it is considered that the gelation of horse mackerel (easy setting) surimi is induced by highly unfolding and re-aggregation of protein, which contributes to the formation of a strong network structure compared with tilapia in both heat and pressure treatments, and that pressure treatments hardly improve the gel strength of tilapia (difficult setting) surimi. The water ¹H T ₂ measurement was used effectively in order to study gelation characteristics of easy- and difficult-setting fish through observing its molecular dynamics.     

四大家鱼幼鱼响应模拟水轮机流道压力变化研究

研究鱼类对反击式水轮机流道内压力突变的响应,为水电站水轮机的结构优化和生态运行提供技术支撑。实验鱼为四大家鱼1龄幼鱼,体长(100±10)mm、体宽(6±2)mm,鱼体健康、鱼鳞完整;实验装置由变频真空泵、高压舱、压力表、连接气管、高速摄像机组成。对四大家鱼幼鱼分别进行负压承受实验(预设压力值分别为80、60、40、20 kPa)、循环负压承受实验(预设压力值分别为80、60、40、20 kPa)和压力梯度承受实验(预设压力值分别为40、20 kPa),测试鱼的行为状态和损伤状况;实验结束后,实验鱼被分别移入暂养水槽暂养,并观察记录其实验后1、4和12 h的自愈状态;最后解剖实验鱼,观察和记录其脏器损伤状态。结果表明:(1)四大家鱼幼鱼对水体中的压力陡降具有较强的敏感性,出现损伤主要发生在第1次压力陡降过程,损伤程度与最小压力值及压力变化梯度成正相关,负压循环次数的增加不会增加家鱼幼鱼受压力损伤的程度和死亡率;(2)压力最低值和压力梯度是家鱼幼鱼通过水轮机流道下行受到压力损伤的主要原因,随着压力最低值的降低和压力梯度的增大,家鱼幼鱼损伤的程度和死亡率上升;(3)生活在河流中底层的青鱼和草鱼对负压和压力梯度较生活在河流中上层鲢和鳙具有更好的耐受性,在进入水轮机流道前鱼类适应压力状态与鱼体通过水轮机受到压力损伤具有一定的相关性;(4)四大家鱼幼鱼受到压力损伤的阈值为20 kPa,当压力值小于或等于损伤阈值,家鱼幼鱼受到压力损伤。     

半滑舌鳎四倍体鱼苗的诱导与鉴定

采用静水压法处理半滑舌鳎(Cynoglossus semiliaevis)受精卵以抑制其卵裂并进行染色体加倍,筛选出有效的静水压处理起始时间、处理强度及其持续时间。结果表明,孵化水温(23±0.2)℃时,授精后21.5 min,采用40 MPa的静水压压力,休克处理4.5 min,四倍体诱导效果最好,鱼苗四倍体率达到68.3%。采用流式细胞仪分析了四倍体鱼苗细胞DNA含量,表明四倍体鱼苗细胞DNA含量为二倍体对照鱼苗的2倍。通过染色体制作分析表明四倍体鱼苗的染色体数为84条,而二倍体对照鱼苗的染色体数为42条。本研究采用静水压方法,在国内外首次建立了半滑舌鳎四倍体诱导方法。本项技术的建立旨在为大量生产半滑舌鳎三倍体不育群体奠定基础。     

割草机机具参数对抛撒碎草的影响

割草机电机转速和割草线的长短是抛撒碎草的主要影响因素之一.为了研究割草机流道内部机具参数对抛撒碎草的影响,采用直径为39mm的透明有机玻璃保护罩,以直径为1mm的ABS塑料作为实验割草线并变为半长,在电机转速分别为2500 r/min和3500 r/min的情况下,利用粒子图像测速技术(PIV)结合数值模拟,对割草机内部流场的特性进行了研究.     

海水淡化多级泵轴向力试验

针对叶轮轴向力计算方法有多种,且不同经验公式计算的轴向力相差很大的情况,通过对海水淡化多级泵的单级模型泵进行轴向力试验,找出泵腔压力分别与泵流量、扬程以及泵腔径向尺寸的关系,并对传统轴向力理论计算公式进行修正.通过分析可知,轴向力传统理论计算公式的计算结果与轴向力试验数据有一定的差距,这主要是由于传统理论计算是在泵腔内液体以叶轮旋转角速度之半（ω/2）旋转的假设条件下得到的;但两者轴向力的变化趋势相同,均在关死点处达到最大值.用修正的理论公式得到的值与试验值在各流量点、各半径处均能较好的符合.     

基于GT-SUITE的发动机排气压力波仿真分析

为研究排气系统内压力波的形成及其传播过程与发动机工作状况之间的关系,本文利用GT-POWER软件建立一个4缸4行程的汽油发动机模型。结果显示在发动机的一个工作周期内,压力波出现了4个波峰和波谷,分别对应4个气缸的排气行程;修改发动机的转速,会影响排气压力波的幅值、谐波成分、相位等参数;在排气行程末期,排气压力波在排气管内发生干涉、叠加和负压效应。     

供水压力对节点渗灌管出水孔工作压力影响的研究

用土槽模拟试验的方法,对渗灌灌水时供水压力与节点渗灌管出水孔的水压关系进行了试验研究,结果表明:水源供水压力越大,水头损失越大,水头对渗灌管出水均匀效果产生影响,节点式渗灌灌水时供水压力以100cm水柱左右为宜.     

喷雾器恒压防滴技术的试验研究

介绍恒压防滴技术的工作原理和理论计算。并对不同结构参数进行了试验研究。结果表明：恒压防滴装置性能主要由弹簧刚度、阀芯行程和膜片面积决定。且使用恒压防滴技术的喷雾器流量的变异系数小于2％,保证施药精量、准确。