带双负载运行的VIENNA整流器中点电压平衡控制

针对VIENNA整流器结构固有的中点电压波动问题,可以通过双负载结构中调整负载的大小来观察。文章分析了三相VIENNA整流器的工作原理,采用一种电压电流双环结构,空间矢量调制(SVPWM)方式控制运行。针对三电平结构固有中点电压波动问题,通过调节正负小矢量的作用时间,能够达到双负载在大小不同的情况下,直流电压稳定,中点电压平衡的效果,最后使用MATLAB/Simulink仿真证明了此方案的可行性。     

吡啶羧酸铬对肉鸭后期作用效果初探

选用21日龄樱桃谷鸭36只,采用有重复对照试验,比较饲粮中添加0．2×10－6吡啶羧酸铬对肉鸭生产性能、屠体品质和血液生化指标的影响。结果表明,吡啶羧酸铬对增重、饲料转化率无显著影响,对屠宰率、胸肌率和皮脂率亦无显著影响;但使心重、血清总甘油三酯显著降低,血清总胆固醇、高密度脂蛋白胆固醇显著增加。     

洞庭湖湿地虉草替代大白菜对肉兔生产性能的影响

试验采用48只青年期(40～45日龄、体重约800 g)发育良好、健康无病的新西兰肉兔,随机分为4组:1组饲喂基础日粮,2～4组分别用占日粮5%,15%和25%的虉草Phalaris arundinacea代替日粮中等量的大白菜,试验期35 d.试验结果表明:各组间兔的日增重、屠宰率、料肉比等指标差异均不显著(P＞0.05),可见虉草代替大白菜不影响兔的生长,以15%的替代量的3组增重效果最佳,经济效益最好.     

神犬护主擒犯立奇功

安娜是一个单身的年轻女子,独自居住在美国拉斯维加斯的一栋房子里,和她日夜相伴的是一头心爱的杜伯文犬。     

高温对产蛋鸡的影响与缓解对策分析

1 热应激对产蛋鸡的影响 　　1.1 对产蛋性能的影响 　　高温环境下,家禽首先表现出采食量下降而饮水量增加.试验表明:当舍温在21～25 ℃区间内,温度每升高1℃,鸡采食量相应降低1.5%,产蛋率下降0.5%;在25～32 ℃区间内,温度每升高1℃,鸡采食量相应降低2.5%,产蛋率下降1.5%;而在32～38 ℃区间,每升高1℃,采食量相应降低4.6%,产蛋率下降3%～5%.采食量的下降,引起营养物质摄入不足,导致蛋重减轻,蛋品质下降.……     

天然气抗氧化刘的研究概况

按照美国食品药物管理局(FDA)定义,所谓抗氧化剂是指作为延滞因氧化所引起的劣变、酸败或变色的物质[1].     

QFM合剂麻醉剂量对犬肝、肾功能的影响

QFM合剂是一种新型的犬用复合麻醉制剂。本试验旨在研究其对犬肝、肾功能的影响。试验用7条犬肌肉注射QFM合剂0．15～0．2mL(每千克体质量)，观察比较了注药前、后犬血清GOT、GPT、AKP活性和尿素氮、肌酐含量的变化。结果证明：注药前、后犬血清GOT、GPT、AKP活性和尿素氮、肌酐含量的变化差异不显著，在正常生理范围内。说明QFM合剂应用于犬的麻醉，时犬的肝、肾功能无明显不良影响，进一步证明了QFM合剂应用于犬的临床安全性。     

Effect of different hand-milking techniques on milk production and teat treatment in Zebu dairy cattle

The aim of the study was to test three different hand-milking techniques (“pull down”, “thumb in”, and “full hand grip”) and their effects on milk production and teat treatment. This is important since milk production in many tropical areas still rely on hand-milking. The study was carried out at a peri-urban farm in the Bobo-Dioulasso area in Burkina Faso. Twelve indigenous Zebu cows in early lactation were used in the study. The sequences of the treatments (hand-milking techniques) and the milkers were balanced for carry-over effects between successive periods and days, respectively. The sequences were constructed by using special Latin squares. Yield and composition of saleable milk was not affected by milking technique but there were differences between the milkers in milk yield. There was also a significant interaction for saleable milk yield between milker and milking technique. Hemoglobin in milk was measured as an indicator of teat damage. The hemoglobin content was numerically higher in post-milking strip milk samples than in saleable milk. It was concluded that the amount of milk removed depends mainly on the milker and how well the milking technique works for the individual milker. No effect of milking technique was observed on teat treatment.     

Environmentally sustainable production of food,feed and fuel from natural resources in the tropics

Responding to the challenges posed by global warming, peak oil and biofuels will require a paradigm shift in the practice of agriculture and in the role of live stock within the farming system. Farming systems should aim at maximizing plant biomass production from locally available diversified resources, processing of the biomass on farm to provide food, feed and energy and recycling of all waste materials. The approach that is the subject of this paper is that the generation of electricity can be a by-product of food/feed production. The concept is the fractionation of biomass into inedible cell wall material that can be converted to an inflammable gas by gasification, the gas in turn being the source of fuel for internal combustion engines driving electrical generators. The cell contents and related structures such as tree leaves are used as human food or animal feed. As well as providing food and feed the model is highly appropriate for decentralized small scale production of electricity in rural areas. It also offers opportunities for sequestration of carbon in the form of biochar the solid residue remaining after gasification of the biomass.