固定轮系的旋轮线及在车削多面体中的应用

根据坐标变换公式推导了一对定轴齿轮旋轮线的公式,由内、外啮合的公式得出一系列旋轮线图,分析了影响旋轮线性质和形状的有关参数及变化规律。根据定轴轮系的传动性质,可推导出多齿轮固定轮系旋轮线的轨迹。在误差允许的范围内,可以利用定轴轮系的旋轮线在其中心部分形成近似的正多边形的性质来车削正多边形。以正四边形为例,进行了误差分析和试验验证。     

大鼠发情周期中主要生殖激素的变化

动物的生殖过程是由生殖激素严格调控的,深入研究生殖激素对畜牧生产具有重要的指导意义。然而发情周期中生殖激素的变化非常复杂,虽然人们在这方面做了许多的研究,但仍有许多问题仍不明了,对许多问题的认识还存在分歧。文章基于最近十几年的研究成果,以大鼠为对象,在综述了促性腺激素释放激素、促卵泡素、促黄体素、雌二醇及孕酮等几种重要的生殖激素的来源、生物学特性的基础上,着重介绍了这几种生殖激素在大鼠发情周期中的变化,并对影响生殖的因素进行了总结。     

植树挖坑机钻头主轴扭转振动数学建模与求解

介绍国内外机械化植树造林机械发展状况,指出国内植树用挖坑机研究重点,利用空间运动学和机械振动理论以及弹性动力学原理着重分析建立钻头主轴扭转振动模型并用数值方法进行求解,同时系统地分析钻头主轴下端部件与土壤的相互作用力、钻头主轴重力及惯性力等因素的影响,给出动态的准随机边界条件和初始条件.为下一步的钻头动力学特性仿真及整机动态特性研究,合理预测和控制钻头的运动规律,改善钻头的动力学特性,提高钻头工作效率及改进设计方法提供新的理论依据.     

麇鹿肾上腺的组织学观察

取麋鹿肾上腺，常规石蜡切片，HE染色组织学观察。结果表明，肾上腺的组织结构分为被膜、皮质和髓质。被膜由不规则致密结缔组织构成，其内分布有类似未分化细胞。皮质最厚，明显分为3个带，即球状带、束状带，网状带。其中，束状带最厚，占皮质的绝大部分。髓质位于肾上腺中央部位，细胞排列成索。髓质中央有一大的静脉，称中央静脉。     

基于PSO有限元优化直接进给轴伺服动态特性

优化直线电机驱动的直接进给轴伺服动态特性,对提高进给轴的抗干扰性能和加工产品的精度具有重要作用。基于有限元仿真建模的直接进给轴伺服动态特性研究,应用动刚度频谱图来作为伺服动态特性的评价指标,判断直接进给轴共振点所在频段。应用脉冲激励测试进给轴动刚度的方法,依据测量方法确定了直接进给轴的动刚度频谱图,分析了进给轴在不同有限元优化的伺服参数下对动刚度频谱图的影响。通过有限元优化方法和实验相结合,构建了基于有限元优化的伺服参数下直接进给轴动刚度仿真模型。     

MAGNETIC RESONANCE IMAGING OF THE PRESUMED NORMAL CANINE ADRENAL GLANDS

Forty-three dogs without evidence of endocrine disease that underwent spinal or abdominal magnetic resonance imaging (MRI) for clinical reasons were studied. Because the procedures were not optimized for inclusion of the adrenal glands, they were not always visible in all planes. Eighty-five of the 86 adrenal glands were seen and only the left gland in a 6-month-old Irish wolfhound could not be found. The right adrenal gland lay cranial to the left in all of the animals in which both glands were seen. The best landmarks for localization of the glands were vascular; both adrenal glands were always cranial to the ipsilateral renal vessels and in the region of the celiac and cranial mesenteric arteries. Various measurements were made on all the available scan planes. In some dogs the whole adrenal gland was difficult to visualize clearly, and this hindered the measuring process, especially when the right adrenal gland was in close contact with the caudal vena cava. The adrenal glands were mainly linear in shape but also had a variable degree of modification of their poles, especially the cranial pole of the right adrenal gland, which tended to be consistently wider and to present different shapes (rounded, arrowhead, inverted P, hook-shaped, triangular, or dome-shaped). Two main patterns of signal intensity were seen on fast spin echo (FSE) sequences (T2-weighted, T1-weighted, and T1-weighted after administration of a paramagnetic contrast medium): homogeneous and hypointense to surroundings or a corticomedullary type pattern with a hyperintense central area surrounded by a hypointense rim of tissue. The outline of the left adrenal gland was always very clear. The clarity of outline of the right adrenal gland was more variable, especially if it was in contact with the liver or the caudal vena cava. It was felt that the amount of retroperitoneal fat was not as important as stated in the human literature for visualization of the adrenal glands and that with an appropriate selection of scan planes and pulse sequences good assessment of the adrenal glands can be performed with MRI in canine patients.     

γ-氨基丁酸对夏季热应激鸡下丘脑-垂体-肾上腺轴的调控作用

本试验旨在研究γ-氨基丁酸(GABA)对夏季热应激鸡下丘脑-垂体-肾上腺(HPA)轴的调控作用及其机制。选择120羽28日龄淮南麻黄母鸡,随机分为4个组,每组5个重复,每个重复6羽鸡。Ⅰ组(对照组)饲喂基础饲粮,Ⅱ、Ⅲ、Ⅳ组分别在基础饲粮中添加50、100和150mg/kgGABA。预试期7d,正试期30d。每日记录鸡舍内温度、相对湿度及各组鸡耗料量。第10、20和30天,每组随机抽取5羽鸡,称重后采集血清,检测血清中促肾上腺皮质激素释放激素(CRH)、促肾上腺皮质激素(ACTH)、皮质酮(Cor)、热休克蛋白70(HSP70)和GABA含量;Ⅰ、Ⅲ组鸡断头取脑,检测脑组织中GABA含量。结果表明:1)第10、20、30天时,Ⅲ组的直肠温度显著或极显著高于Ⅰ组(P<0.05或P<0.01)。2)第21~30天,Ⅱ、Ⅲ组的平均日采食量显著高于Ⅰ组(P<0.05)。第1~10天、第11~20天和第21~30天,Ⅲ、Ⅳ组的平均日增重显著或极显著高于Ⅰ组(P<0.05或P<0.01)。3)第10天时,Ⅱ、Ⅲ组血清中CRH含量显著或极显著低于Ⅰ组(P<0.05或P<0.01);第30天时,Ⅲ、Ⅳ组血清中CRH含量显著低于Ⅰ组(P<0.05)。第10、30天时,Ⅱ、Ⅲ组血清中ACTH含量显著或极显著低于Ⅰ组(P<0.05或P<0.01);第20天时,Ⅲ组血清中ACTH含量显著低于Ⅰ组(P<0.05)。第10天时,Ⅲ组血清中Cor含量显著低于Ⅰ组(P<0.05);第30天时,Ⅱ、Ⅲ、Ⅳ组血清中Cor含量均极显著低于Ⅰ组(P<0.01)。4)第10、30天时,Ⅱ、Ⅲ组血清中HSP70含量显著或极显著低于Ⅰ组(P<0.05或P<0.01);第20天时,Ⅲ组血清中HSP70含量极显著低于Ⅰ组(P<0.01)。5)第10天时,Ⅱ、Ⅲ、Ⅳ组血清中GABA含量显著或极显著高于Ⅰ组(P<0.05或P<0.01);第20、30天时,Ⅳ组血清中GABA含量极显著高于Ⅰ组(P<0.01)。6)第10、30天时,Ⅲ组脑组织中GABA含量显著高于Ⅰ组(P<0.05)。由此可见,饲粮中添加GABA降低了夏季热应激鸡的直肠温度及血清中CRH、ACTH、Cor、HSP70含量,其中以Ⅲ组效果最佳。GABA具有抑制夏季热应激鸡HPA轴激素分泌的功能。     

Dairy cattle behavior classifications based on decision tree learning using 3‐axis neck‐mounted accelerometers

Demand has been increasing recently for an automated monitoring system of animal behavior as a tool for the management of livestock animals. This study investigated the association between the behavior of dairy cattle and the acceleration data collected using three‐axis neck‐mounted accelerometers, as well as the feasibility of improving the precision of behavior classifications through machine learning. In total 38 Holstein dairy cows were used, and kept in four different farms. A logger was mounted to each collar to obtain acceleration data for calculating the activity level and variations. At the same time the behavior of the cattle was observed visually. Characteristic acceleration waves were recorded for eating, rumination, and lying, respectively; and the activity level and variations were significantly different among these behaviors (p < 0.01). Decision tree learning was performed on the data set from Farm A and validated its precision; which proved to be 99.2% in cross‐validation, and 100% in test data sets from Farms B to D. This study showed that highly precise classifications for eating, rumination, and lying is possible by using decision tree learning to calculate the activity level and variations of cattle based on the data obtained by three‐axis accelerometers mounted to a collar.     

Adrenal cortex reactivity in dairy cows differs between lactational stages and between different feeding levels

Changes in ACTH challenge test characteristics in dairy cows changing their physiological status at different lactational stages and different feeding levels were not investigated in terms of repeatability yet. In 23 multiparous Holstein cows (10 cows fed a sole fresh herbage diet without concentrate, 13 cows fed with concentrate), three ACTH challenge tests were performed: once during pregnancy shortly prior to drying off ( T1 ), and in week 3 ( T2 ) and 8 ( T3 ) after parturition. Test characteristics were correlated to performance and metabolic parameters: DMI, BW, energy balance (EB), plasma concentrations of free fatty acids (NEFA) and beta‐hydroxybutyrate (BHB). Basal plasma cortisol concentrations were higher at T1 compared with T2 and T3 (p < .05). The adrenal cortex sensitivity (expressed as total AUC (AUC_t) of cortisol response after ACTH application) was lowest at T2 compared with T1 and T3 (p < .05). Ranking of the individual animals’ responses was not repeatable between time points of the ACTH tests. Enhancing the energy deficiency during early lactation by omission of concentrate did not affect baseline cortisol concentrations in plasma, but decreased peak height at T2 (p < .05). Baseline plasma cortisol concentrations were positively correlated with cortisol peak values after ACTH application, previous lactation performance, milk yield and BW (p < .05). The AUC_t was positively correlated with baseline cortisol concentrations, EB and DMI. Cortisol release after ACTH injection was lower in animals with high plasma concentrations of NEFA, BHB and with higher contents of fat and free fatty acids in milk (p < .05). Cortisol peak height after ACTH administration was higher in cows with a more positive EB, higher DMI and lower plasma concentrations of NEFA and BHB. In summary, cortisol responses to ACTH challenges in this study were not repeatable in dairy cows changing their physiological status.