改进的异步电机直接转矩控制系统仿真

直接转矩控制(DTC)技术存在转矩脉动较大、磁链观测会发生畸变等问题,并面临使用无速度传感器技术的要求。为解决上述问题,本文引入了一种基于12扇区划分的异步电机直接转矩控制系统,采用一种限幅积分算法的定子磁链观测模型,并利用模型参考自适应(MRAS)方案来实现电机转速的辨识。最后通过MATLAB/SIMULINK进行了建模仿真,并与传统直接转矩控制系统进行了对比,仿真结果验证了系统的可行性与正确性。     

基于MATLAB的无刷双馈风力发电机的控制策略研究

在传统风力发电的基础上,以作为风力发电机用的无刷双馈电机为主要研究对象,进行了深入的研究,研究了无刷双馈电机的转子侧和网侧PWM变换器的控制策略,建立转子侧和网侧PWM变换器控制策略的结构模型,把功率绕组和控制绕组分别建立在各自的同步坐标系下,分别进行磁场定向和电压定向矢量控制,从而简化了数学模型,获得了适合的控制策略。最后采用Matlab/Simulink仿真软件建立相应的控制系统仿真模型,模拟三种情景,进行仿真实验,分析实验结果。     

异步电动机节能控制方法及抗干扰技术

主要介绍了异步电机的节能技术,对离心连接方式、变频调速起动方式、降压起动方式、固态起动器起动方式进行了深入的研究。对异步电动机的损耗进行了分析,并对节能控制抗干扰的技术进行了初步的描述。     

浅谈航空磁测中飞机干扰磁场的补偿问题和处理

航空磁测技术不仅在军事领域发挥着巨大作用,随着技术的发展和民用领域需求的增加,它在地质调查、矿产普查等民用领域的作用也越来越大。但是在航空磁测应用中,飞机本身的磁场和飞机飞行中产生的感应磁场和涡流磁场会对磁探仪产生干扰,造成测量误差度。所以,如何实现飞机磁干扰补偿,提高航测精度是当下研究的重点。本文对航空磁测中飞机干扰磁场的补偿问题和处理进行了探讨。     

电机静态监测技术的应用

对交流异步电动机采用静态电流分析法能有效的发现绕组存在的故障.采用静态电流分析与直流电阻测试相结合的方法,保证了电机定子绕组故障判断的准确性和有效性,从而对异步电机故障诊断达到比较理想的效果.     

磁场对蚕的作用

选取刚孵化出来的蚁蚕10头(体长各3毫米),5只放在500高斯磁场的纸盒(即纸盒下放一大磁块)内,另5头放在无磁场的纸盒内,每日同时喂给等量桑叶。实验结果:25日后,那饲养在有磁场的蚕,体长6厘米,而生活在没有磁场的另5头蚕,体长5.3厘米,相差0.7厘米。又在磁     

同步发电机失磁运行工况剖析

通过发电机失磁运行工况的介绍,详细剖析了同步发电机失磁运行的现象以及进入异步运行给电力系统和发电机带来哪些重大影响,物理分析了发电机失磁后不同功角下等值电路、向量图及阻抗圆变化轨动作过程。     

自耦变压器直流偏磁特性仿真与分析

为分析电网自耦变压器遭受直流偏磁的影响,本文应用PSCAD电磁暂态仿真软件搭建了自耦变压器仿真模型,分析了直流偏磁对变压器励磁电流、无功功率损耗以及谐波等的影响程度。仿真结果表明了,随着直流偏磁电流的增加,励磁电流波形逐渐变为尖顶波且谐波含量较大,同时,无功功率损耗也与直流偏磁电流呈线性关系增加。本文的研究成果可为今后国家大型电力网络建设提供一定的参考依据。     

趋磁细菌特性及其应用前景

趋磁细菌具有独特的磁场运动特性、生物学特性,其磁小体可作为生物活性物质的固定载体、磁记忆材料等.笔者介绍了趋磁细菌的发现、种类、特点及趋磁细菌在生物导航、重金属废水处理、地质学研究及医学等方面的应用前景.     

蜜蜂定向机制的研究进展

蜜蜂是高度社会化昆虫,其行为非常复杂,而其在飞行、觅食、迁飞等过程中对位置的确定,更是一种极为复杂的行为方式。其定向定位机制包括有太阳罗盘定向、磁场定向、地面标志物定向、偏振光定向等。本文对蜜蜂定向机制研究进展进行综述。     

商会自治的基石——商会自治规范研究

在现代法律秩序中,商会自治规范是制定法的基础和必要的补充,甚至在某些方面替代了制定法;商会自治规范主要包括商会组织规范、行为规范、惩罚规范以及争端解决规范等;其效力仅及于其内部成员;商会自治规范和制定法之间存在冲突,但也存在整合的基础。     

癸氧喹酯干混悬剂含量测定的改进

采用高效液相色谱法测定癸氧喹酯干混悬剂的含量,在2-250μg/mL范围内,峰面积的常用对数与进样量浓度的常用对数呈良好的线性关系,R^2=1(n=5),平均回收率为99.24%~99.51%,RSD在0.05%~0.28%。此方法分析时间短,样品前处理简便、定量结果准确,重现性好,结果满意,为其质量控制提供了依据。     

猪毛色遗传的研究进展

本文概述了猪的毛色类型、猪的毛色遗传模式,着重综述了猪毛色基因分子基础的研究进展,指出存在问题并就未来发展方向做了思考。     

Comparison of 2 methods of centesis of the bursa of the biceps brachii tendon of horses

REASONS FOR PERFORMING STUDY: Centesis of the bicipital bursa using an 8.9 cm long spinal needle has been reported but the alternative of employing a 3.8 cm long hypodermic needle requires validation. OBJECTIVE: To compare the efficacy of 2 different methods of centesis of the bicipital bursa and to evaluate the usefulness of ultrasonographic imaging to determine the location of solution administered when centesis of the bursa is attempted. METHODS: For Trial 1, 6 clinicians, who had no previous experience of centesis of the bicipital bursa, attempted to inject a solution composed of an aqueous radiopaque contrast medium and physiological saline solution (PSS) into the bicipital bursae of 2/12 horses using the previously described distal approach to inject one bursa and a proximal approach to inject the contralateral bursa. The bicipital tendon and bursa were examined ultrasonographically before and after injection; and both shoulders were examined radiographically to identify the location of the medium. In Trial 2, another 6 clinicians, also with no previous experience of centesis, repeated Trial 1, using 6 horses, but the radiopaque contrast medium was mixed with air instead of PSS. RESULTS: Accuracy of centesis using the proximal approach was 39% and that of the distal approach 28%. Ultrasonographic examination of the shoulder allowed the location of solution and air to be accurately predicted in all 12 shoulders examined. CONCLUSIONS: Clinicians who have had no previous experience performing centesis of the bicipital bursa are unlikely to be successful in centesis using either approach. Radiographic examination after injecting a radiopaque contrast medium may be necessary to assess the success of centesis especially if bursal fluid is not obtained during centesis. Injecting air along with the radiopaque contrast medium provides more accurate ultrasonographic confirmation of centesis and better radiographic definition than does injection without air.     

不同样本商品蜂蜜中硒含量的测定

用硝酸和高氯酸消化蜂蜜,使硒游离出来,在微酸性环境下,硒和2,3-二氨基萘(DAN)生成有较强荧光的物质,用环己烷萃取,在激发波长378nm,荧光波长518nm处测定其荧光强度。蜂蜜中硒含量范围:0.10～0.82μg/g。表明:蜂蜜应视为天然富硒营养品。     

乳酸杆菌益生作用机制的研究进展

乳酸杆菌作为益生菌广泛用于人和动物。本文综述了乳酸杆菌改善宿主健康的机制。乳酸杆菌可通过产生抗菌物质如乳酸、过氧化氢、细菌素,或者通过竞争营养或肠道黏附位点来抑制致病菌;通过诱导黏附素的分泌或阻止细胞凋亡而增强肠道的屏障功能,从而保护肠道。文章重点讨论了乳酸杆菌表面成分（表面蛋白、脂磷壁酸和肽聚糖）与肠道受体（Ｃ型凝集素受体、Ｔｏｌｌ样受体和 Ｎｏｄ样受体）,阐述了他们结合后启动免疫调节信号,调控肠道免疫功能以发挥改善健康作用的机制。     

中华人民共和国农业部公告 第267号

为贯彻落实《兽药生产质量管理规范》(简称《兽药GMP》),进一步推动兽药GMP实施进程,我部制定了《兽药生产质量管理规范检查验收办法》,现予公告。本公告自2003年6月1日起施行。附件:兽药生产质量管理规范检查验收办法二○○三年四月十日第一章 总则 第一条 为推动《兽药生产质量管理规范》(以下简称兽药GMP)的实施,规范兽药GMP检查验收工作,制定本办法。 第二条 农业部负责全国兽药GMP管理和检查验收工作;负责制修订兽药GMP检查验收管理规定;负责兽药GMP检查员队伍建设和监督管理工作,负责国际兽药贸易中GMP互认工作。 …     

鸡败血支原体垂直传播模式及其阻断方法

以国际标准强毒Ｒ株人工感染非免疫产蛋鸡,定时扑杀,分别从鼻窦、眶下孔、气管、肺、气囊、卵巢和输卵管分离ＭＧ,并收集感染鸡所产蛋分离ＭＧ。结果表明,人工感染４８小时后上、下呼吸道及肺已被全面感染,９６小时气囊已被感染,１２０小时输卵管已能分离到ＭＧ,卵巢始终分离不到ＭＧ。人工感染鸡自１４４小时便能在其所产蛋中分离出ＭＧ。药物治疗能在７２小时内消除感染,油乳剂苗则需２４天后逐渐降低蛋内ＭＧ分离率,药物卵内注射、种蛋药浴、高温处理均能杀死卵内ＭＧ,但以研制的种蛋浸泡剂药浴效果为最好。     

Effects of size of ingestively masticated fragments of plant tissues on kinetics of digestion of NDF

Ingestively masticated fragments were collected and sized via sieving. Different sizes of esophageal masticate and ruminal digesta fragments, and ground fragments of larger masticated pieces were incubated in vitro, and undigested NDF remaining at intervals of up to 168 h of incubation was determined. The ruminal age-dependent time delay (tau) for onset of digestion of NDF was positively correlated (P < 0.004) with the mean sieve aperture estimated to retain 50% of the fragments between successive sieve apertures (MRA). Degradation rate of potentially degradable NDF (PDF) and level of indigestible NDF were not related (P > 0.10) to MRA of masticated and ground fragments. Estimates of tau were positively related to MRA, with slopes of bermudagrass < corn silage < ruminal fragments of corn silage. It was concluded that fragment size-, and consequently, ruminal age-dependent onset of PDF degradation of a mixture of different fragment sizes results in an age-dependent rate of degradation of the more rapidly degrading of two subentities of PDF. Models are proposed that assume a tau before onset of simultaneous degradation of PDF from two pools characterized as having gamma-modeled age-dependency and age-constant rates. The ruminal age-dependent pool seems to be associated with the faster-degrading pool, and its rate parameter increases with range in MRA in the population of fragments. Conceptually, the ruminal age-dependent rate parameter for PDF degradation seems to represent a composite of several effects: 1) effects of the size-dependent tau; 2) range in MRA of the population of ingestively masticated fragments; and 3) subentities of PDF that degrade via more rapid age-dependent rates compared with subentities of PDF that degrade via age-constant rates. The estimated fractional rates of ruminative comminution of ingestively masticated fragments (0.060 to 0.075/h) were of a magnitude similar to the mean fractional rates of PDF digestion (0.030 to 0.085/h), which implies that ruminative comminution may be first-limiting to fractional rate of PDF digestion. The in vivo roles of ingestive and ruminative mastication of fragments on PDF degradation must be considered in any kinetic system for estimating PDF digestion in the rumen. These results and others in the literature suggest that the rate of surface area exposure rather than intrinsic chemical attributes of PDF may be first-limiting to degradation rate of PDF in vivo.