种公牛的饲养管理技术

种公牛是提高牛群质量最关健的因素,一头种公牛自然交配,与配母牛一年大约几百头。利用人工授精技术每年比本交能增加几倍。而用牛冷冻精液结合人工授精技术进行冷配每年配种母牛数量少则上万头,多则几万头。本文从饲养种公牛的基本要求出发,对种公牛的特性,营养与日常饲养管理、防疫和疾病防治,以及安全生产多方面做了整理介绍,以供同行参考。     

蝴蝶兰27个品种观赏性状评价

应用主成分分析法对蝴蝶兰27个品种的12个观赏性状进行分析.结果表明:12个性状指标可以分为6个主成分.主成分的方差贡献率达全部性状信息的86.61％；通过计算各品种的重要主成分值.得出10个观赏性状优良的品种.其结果与实际情况相近.     

基于PCA-ARIMA模型的高血压发病率预测

目的高血压发病率是政府和相关医学工作者预防和监测高血压的重要依据之一。方法利用主成分分析(principal component analysis,PCA)对因子进行线性筛选,获得保留因子后利用ARIMA进行建模预测,即为PCA-ARIMA多维时间序列组合预测模型。结果高血压发病率的拟合与独立预测结果表明,PCA-ARIMA优于PCA-MLR、ARIMA等参比模型。结论本文提出的基于主成分分析和ARIMA模型(PCA-ARIMA模型)的建模有助于提高模型的预测精度。     

基于改进蚁群算法的服务组合研究

在服务计算过程中，服务组合问题是其中关键的技术之一。在原子候选服务数目巨大的情况下，经典的算法一般都是寻找问题的最优解，存在运算量大，运行时间长的缺点，蚁群算法并不是寻找服务组合问题的最优解，而是得到用户能够认同的可行解。为了能够更有效的为用户提供各种服务，在静态的服务组合建立过程中，以服务发现的候选原子服务集合中的服务质量为权重，将服务组合问题分解成一个有向无环图，在组合代价为最小的原则下，采用改进的蚁群算法为搜索方法，迭代一定的次数或者达到用户设定的服务质量为算法的终止条件，找到能够组合为用户需要的原子候选服务集合，进而快速、准确的得到用户期望的服务。     

高寒草地西北针茅生长发育特征及与气象因子的关系

利用1999～2009年连续11年的定位观测数据,研究了高寒草地西北针茅的生长发育特征与气象因子的关系。结果表明,在3月中旬,如果气温升高,返青日会推迟,这主要因为高温促使土壤水分蒸发,而土壤干旱阻碍返青;返青后,如果≥0℃的积温不足或累计日照时数不足,针茅的抽穗期会推迟;开花期的当日平均气温在10～20℃,如果抽穗-...     

反刍动物营养学发展现代化进程的回顾及其展望

文章在回顾反刍动物营养学发展的现代化进程的基础上,分析了当前反刍动物营养学的发展趋势,并对其面临的历史任务和优先研究领域进行了论述和展望。     

Performance of rainy season greengram as influenced by land configuration and phosphorus application

A field experiment was carried out for 2 crop years (July‐October) at the Indian Agricultural Research Institute, New Delhi to study the effect of land configuration and phosphorus levels on the growth and yield of rainy season greengram under limited irrigation facility. The crop sown on 2 meter wide broad bed and furrow (BBF) showed higher growth attributes, nodulation, yield attributes and yield compared to flat bed (FB) sowing. Application of 30 and 60 kg P₂O₅ha_‐1 showed significant increase in growth attributes, nodulation, yield attributes and yield as compared to no phosphorus application. The moisture status in the soil determined the optimum dose of phosphorus needed for greengram. The combination of BBF sowing and application of 60 kg P₂O₅ ha^?1 recorded the highest grain yield among all the combinations of land configuration and phosphorus levels.     

主成分综合得分法应用于水质评价的不可靠性

针对在主成分分析基础上,以主成分的贡献率作为权重,对各主成分得分进行加权求和计算"综合得分"的方法进行了数学理论求证和实际数据分析,证实了该方法应用于水质评价时具有不可靠性,并明确提出了导致其不可靠性产生的3个缺陷:以贡献率作为权重忽视了主成分对评价目标的实际影响;相关系数矩阵的特征单位向量可以改变方向,导致"综合得分"表达式不唯一;标准化处理可以导致数据失真。     

Short Root Densities and Surface Phosphatase Activities of Ectomycorrhizal Morphotypes in a Slash Pine Plantation

Abstract

Mineralization is the dominant process controlling soil-solution P in the Spodosols of the southeastern United States. Pine trees growing in these soils are typically colonized by ectomycorrhizal (EM) fungi that are known to produce phosphatases. Little, however, is known of the dynamics of EM short roots or phosphatase activity in tree plantations. To address this question, short root densities, EM morphotypes, and associated surface acid phosphomonoesterase in a 12-year-old Pinus elliottii plantation in northern Florida were evaluated. The density of total (living and dead) short roots changed little from February through June, with a mean of 7.6 cm³ soil. The majority of the short roots, however, were inactive or dead with only 14 to 38% appearing viable upon visual inspection. The majority of the viable short roots were mycorrhizal. The most abundant morphotypes were formed by Cenococcum and Thelephora but these had low phosphatase activity. In contrast, less frequently observed morphotypes had substantially higher rates of enzyme production and these may play an important role in sustainable P nutrition of plantation trees.