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。     

阿维菌素对小鼠雌性生殖细胞的致突变性研究

阿维菌素是我国生产的一种高效广谱抗寄生虫抗生素，对动物的消化道线虫和外寄生虫有很强的驱杀作用。本文选择了第二次减数分裂中期相（ＭＩＩ）卵母细胞和第一次分裂中期相合子染色体畸变分析方法，研究其对哺乳动物雌性生殖细胞的遗传毒性。１．ＭＩＩ卵母细胞染色体畸变分析：根据阿维菌素的小鼠急性毒性试验结果（小鼠经口ＬＤ５０＝１９．１９ｍｇ／ｋｇ），设以下剂量组：１．９２、３．８４和９．６０ｍｇ／ｋｇ（约相当于１     

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。     

生物除草剂研究进展

目前,在世界各地大约分布有3万种杂草,其中约1800种每年会带来约9.7%的总产量损失[1]。而化学除草剂大量使用,造成了一系列的环境问题,如抗药杂草种群的增加、土壤板结、水体污染等,严重影响了和谐可持续的农业发展。随着生物,化学等相关学科的发展,以及环境意识的提高,出现了一种新颖的除草剂——生物除草剂,它是在人们控制下用于杀灭杂草的生物制剂,为一类防除特定杂草的生物制品[2]。它具有显著特点:一是原料来源广(许多农副产品,甚至工业废水都可作为生产原料),制造简便,容易推广;二是微生物类生物除草剂能够通过人工方法,大批量生产并…     

冀东地区干乳期奶牛日粮中微量元素盈缺分析

该试验应用原子吸收光谱法对冀东地区干乳期奶牛基础混合日粮中的铜、铁、锰、锌含量进行测定和盈缺分析,以便为干乳期奶牛日粮配制提供借鉴。试验结果表明,基础混合日粮中铁、铜、锰和锌含量分别为299．87,14．38,37．70和32．67mg／kg。其中,铁含量为NRC（2001）报道干乳期奶牛铁需要量的16倍,是其他文献报道需要量的3倍;铜含量达到干乳期奶牛需要量;锰、锌的含量达到NRC（2001）报道干乳期奶牛铁需要量,而低于文献推荐需要量。     

Effect of early gestational undernutrition on angiogenic factor expression and vascularity in the bovine placentome

The effect of early gestation maternal undernutrition followed by realimentation on placentomal vascular growth and angiogenic factor expression was determined in multiparous beef cows bred to the same bull. Cows gestating only female fetuses (n = 30) were fed in equal numbers to meet the NRC requirements (control) or were fed below the NRC requirements to lose BW (nutrient restricted; NR) from d 30 to 125 of gestation. After slaughter on d 125 of gestation, 10 control and 10 NR cows were necropsied. The remaining NR cows (n = 5) were then fed to achieve a BCS equal to their control group contemporaries (n = 5) by d 220 of gestation. All cows were fed the control diet from d 220 until 250 of gestation, when the remaining control and NR cows were slaughtered and necropsied. At necropsy, placentomes were fixed via perfusion of the caruncular and cotyledonary arteries to determine capillary vascular density. Cotyledonary (fetal placental) and caruncular (maternal placental) tissues also were snap-frozen in liquid nitrogen, and mRNA concentrations of vascular endothelial growth factor and its 2 specific receptors, fms-like tyrosine kinase and kinase insert domain containing receptor, as well as placental growth factor, were determined. There was no effect of diet or day of gestation on the percentage of proliferating caruncular cells. Although diet did not impact cotyledonary cellular proliferation, there was an increase (P < 0.05) in the percentage of proliferating cells on d 250 compared with d 125 of gestation. Nutrient restriction from d 30 to 125 increased (P < or = 0.10) placental mRNA concentrations of placental growth factor and fms-like tyrosine kinase; however, there was no alteration in vascularity. By d 250 of gestation, NR cows had increased (P < 0.05) caruncular capillary surface density and decreased (P < 0.05) cotyledonary capillary area density, capillary number density, and capillary surface density compared with control cows. Although nutrient restriction had little effect on placental vascularity by d 125, upon realimentation, alterations in vascularity became apparent by d 250 of gestation, suggesting a placental programming effect.     

液相色谱-串联质谱法同时检测鸡肉中61种抗菌药物

为建立固相萃取结合液相色谱-串联质谱同时测定鸡肉中磺胺类、喹诺酮类、大环内酯类药物残留的分析方法,通过准确称取2 g鸡肉样品,经PBS缓冲液提取,以Agilent Pleax PCX固相萃取柱净化,最后以液相色谱-串联质谱进行检测.结果显示:在最优试验条件下测得磺胺类、喹诺酮类、大环内酯类抗菌药物线性良好,相关系数(R...     

野马追克喘散治疗猪呼吸道疾病效果试验

目的：应用野马追克喘散新兽药对呼吸道综合征进行临床疗效试验,为推广野马追克喘散提供科学依据。方法：将自然感染、症状典型、猪呼吸道综合征的140头病猪（杜长大三元杂交）,平均体重20～25kg,随机分为7个组,每组20头,其中第Ⅰ、Ⅱ、Ⅲ组用野马追克喘散治疗,分别以高、中、低剂量给药;第Ⅳ、Ⅴ组分别用麻杏石甘散、金花平喘散以常规剂量给药;Ⅵ、Ⅶ组以硫酸卡那霉素注射液（0.2mL/kg体重）和泰乐菌素（0.4mL/kg体重）以常规剂量给药。结果：野马追克喘散的治疗效果较麻杏石甘散和金花平喘散治疗效果好,治愈率也达93.3%。结论：野马追克喘散治疗猪气喘咳嗽疗效较高,收效较快,维持时间较长,是较理想的药物。     

在体外模拟瘤胃发酵条件下N-乙酰-DL-蛋氨酸稳定性的研究

通过两个试验,研究在体外模拟瘤胃发酵条件下N-乙酰-DL-蛋氨酸的降解率。试验1:N-乙酰-DL-蛋氨酸在pH值6.5、温度为39℃的缓冲液中孵育9h,其降解率为3.3%。试验2:运用瘤胃体外发酵技术研究N-乙酰-DL-蛋氨酸不同添加量对pH值、氨态氮、微生物蛋白动态变化的影响。结果表明,添加0.4、0.6gN-乙酰-DL-蛋氨酸发酵3～6h,均能够显著降低体系的pH值;添加0.6gN-乙酰-DL-蛋氨酸发酵12h能够显著提高氨态氮的浓度;N-乙酰-DL-蛋氨酸在发酵过程中不影响微生物蛋白产量。以上结果显示,N-乙酰-DL-蛋氨酸在体外模拟瘤胃发酵的条件下可以稳定存在。     

桑树资源综合利用研究概述

蚕丝业起源于中国,栽桑养蚕是中华民族几千年来的古老传统,形成农、工、商、贸一体化的特色丝绸产业.一直以来,蚕桑生产的主要产品是蚕茧,目的产物是生丝."种好桑、养好蚕、产好丝"是传统蚕业的固有思维模式和生产习惯.