KINEMATIC ANALYSIS AND CALCULATION OF SLEWING MECHANISM ON HYDRAULIC EXCAVATOR DRIVEN BY VARIABLE DISPLACEMENT PUMPS WITH TOTAL CONSTANT-hp CONTROL

There are two main problems in the kinematic analysisof slewing mechanism on hydraulic excavator driven by variable displace-ment pumps with total hp-control when the excavator works and it'spumps get into variable displacement state as well.The first is how todetermine the oil flow in the hydraulic system according to the sum ofthe instantaneous pressure existing both in the slewing motor and in theworking cylinder.The second is how to calculate the driving torqueacting on the mechanism according to the instantaneous pressure existingin the motor.At pressent,the methods used for the kinematic analysisof the mechanism are based upon the assumption of the mechanism to bedriven by the fixed displacement pumps or by the variable displacementpumps with individual constant hp-control.But in these ways,theproblems mentioned above cannot be solved.This paper,on the basisof the variable displacement characteristic of the pumps with totalconstant hp-control,analyses the general kinematic pattern of the slewingmechanism in detail,presents the mathematical model and the numericalmethod used for it's kinematic analysis and establishes the the basis forevaluating it's design.     

温度对Olsen法测定潮土速效磷的影响和校正方法的探讨

探讨了温度对Ｏｌｓｅｎ法测定潮土速效磷的影响，结果表明，撮温度和速效磷浸出量之间呈极显著正相关，这种影响又与土壤速效磷贮量有关。根据统计分析得出比率（Ｐ２５／Ｐ１）与温度之间的有关参数，确定了包含土壤磷素水平影响在内的１０￣３０℃温度范围的经验校正式：Ｐ２５＝Ｐｔ（Ａ＋Ｂｔ）经检验，不同土样任意温度下测定值的校正值与２５℃时测定值无显著差异，符合试验要求。     

转基因食品安全性问题的研究现状

近年来转基因食品在世界范围内发展迅速,人们对转基因食品的安全性也日益关注。文章介绍了转基因食品的发展现状、转基因食品安全性研究的内容、评价原则。     

稻麦“双套”轻型简化栽培技术的研究及应用(Ⅰ) ——淮北地区稻棵套播麦的生育特点及栽培对策

系统论述了淮北地区稻棵套播麦播期提前，利于早发壮苗；群体大，高峰苗提前，利于足穗形成；幼苗发育进程提前，利于大穗形成的生育特点，及限制穗、粒、重三因素协调发展相关影响机理，提出了选用抗病品种、适期适量播种、“少食多餐”的平衡施肥方式、冬前保持地表土壤良好环境等配套轻型简化栽培技术，在生产实践中应用，取得了较好的经济效益和社会效益。     

甜（辣）椒耐低温弱光品种筛选方法初探

通过在不同的低温弱光条件下，对８个代表性品种的冷害发生发展规律的研究，初步确定：１５℃／５℃（昼／夜）、光照强度４０００ｌｘ、光照时间８ｈ、处理１５天，是耐低温弱光品种的适宜选择压力。在此条件下，耐低温品种不出现伤害症状和落叶现象，叶片生长速度快；不耐低温品种生长缓慢，落叶严重，且生长点呈黑褐色，以至干枯。品种间差异显著。同时，耐低温品种叶片叶绿素含量增加，而不耐低温品种叶绿素含量下降。这一结果为进一步完善耐低温弱光品种的鉴定方法提供可靠的依据     

草莓的保鲜现状研究

草莓味道鲜美,受到人们的喜爱,但是却难以保藏。目前,草莓的保藏方法主要是控制温度,并使用保鲜剂进行贮藏。控制温度一般通过冷藏库实现。草莓控温在冰点以上进行冰温贮藏比普通的冷藏效果要好。而使用气调库、气调包装则能更好地保持草莓的新鲜度。     

Durum wheat landraces from Syria

Syrian durum wheat landraces from diverse collection sites were evaluated for agronomic performance under arid conditions over two seasons at four locations, at two levels of nutrient availability.Grain yield differed considerably among locations. Within locations, significant population and fertilizer effects were demonstrated. In most cases, maximum yield was achieved by landraces, which demonstrates the breeding value of local germplasm. In a particular environment, the population effect was nonsignificant for total dry matter production, but significant for straw and grain yield. Nitrogen application was ineffective if moisture availability was the dominant growth limiting factor.Correlations between plant characteristics at evaluation and collection site characteristics were limited, and therefore, their utilization in germplasm evaluation appear limited. The negative relation between grain yield and soil nitrogen content at the collection site may be caused by the comparative disadvantage that germplasm from regions with favourable growing conditions has under low-yielding conditions.Particular environmental conditions at the collection site were no indicator for the response to changed growing conditions. Relatively high grain yields under good and adverse growing conditions excluded each other in all but two cases. Also, it was difficult to relate grain yield to regions of collection, as the response of individual landraces from a certain region to changing growing conditions differed strongly. Differentiation on the basis of landrace groups appears more promising. The Hauran landrace group provided the largest number of populations with relatively high grain yields over diverse environments.     

Reciprocal recurrent selection for multitrait indices in maize

Summary Reciprocal recurrent selection was carried out with two populations of maize (Zea mays L.) having good combining ability. We selected for higher grain yield, early maturity, shorter plant height and lodging resistance. Two cycles were completed in two years (four seasons), by resorting to late planting of S1 lines for recombination in the main season in which top-cross families were assessed. Top-crosses and selfings were made in the off-season. The original and improved versions of the populations and their crosses were evaluated in multilocation trials. The superiority of the population hybrid was 10.3% for grain yield, 5.5% for plant height and 1.8 days to silk. The improved hybrid had delayed leaf senescence and better resistance to lodging and post-flowering stalk rots. Among the yield components, only ear girth showed improvement. Syn 2 of the improved population cross showed a yield reduction of 6.2% in comparison to Syn 1. Intrapopulation gains were not significant except for lodging resistance in one population.     

Comparison of pedigree selection and single seed descent for oil yield in linseed (Linum usitatissimum L.)

Summary Four populations of linseed derived from five parents were advanced from the F₂ to the F₆ generation by SSD and to the F₅ by pedigree selection. These populations were used to compare the efficiency of the two methods in order to provide superior genotypes with respect to grain yield and oil content, i.e. oil yield. The results showed minimum differences between pedigree and SSD lines for grain yield, where in only one cross the SSD lines were significantly superior to the pedigree lines. Since pedigree selection was carried out for both, seed yield and oil content, a positive response to selection was expected. However, early selection for yield, a character with low heritability, was not successful. On the contrary, significant differences for oil content were detected between the two groups of lines in three of the four crosses studied. In these cases the pedigree lines were superior to the SSD lines. These results demonstrate that strict selection in early generations for oil content, a character with comparatively high heritability, is feasible and successful in linseed. However, selection for seed yield should be postponed to later inbred generations. Consequently, in breeding for maximum oil yield of linseed a two-step selection procedure is recommended.Abbreviations PS pedigree selection - SSD single seed descent - TGW thousand grain weight     

Introduction: That most remarkable of outside men – Harold Brookfield's intellectual legacy

Abstract: Harold Brookfield's academic career spans more than half a century, traversing small tropical and subtropical islands and mountainous uplands, focusing on people–environment relations and linking to a diversity of institutions and disciplines. His unwavering commitment to fieldwork at the local level and to comparative study is paralleled by a healthy scepticism with respect to academic trends and orthodoxy of any kind, whether intellectual or physical. It is the farmers of the developing world who are the source of much of his inspiration. His theoretical contributions are based essentially on his observations of their practices and his learning from their experiences. His academic insights into the processes of change in rural areas of Melanesia, East and South‐East Asia, Africa and South America, where small‐scale ecological studies are linked to global forces, are of lasting significance.