螺纹铣削工艺的选择

总结了在数控加工中心上进行螺纹铣削的一些注意事项,其中包括螺纹铣削刀具的选用及测定、螺纹铣削底径的确定、铣削方式的选择及精度控制等。     

Composition,distribution and sources of polycyclic aromatic hydrocarbons in sediments of the western harbour of alexandria,egypt

Aim and Background  Little data are available on the levels of polycyclic aromatic hydrocarbons (PAHs) in the sediments of the Mediterranean Sea Coast of Egypt in general and the Alexandria coastal zone in particular. It was therefore deemed necessary to set up a monitoring programme to determine the current concentrations of PAHs in bottom sediments, and to identify any area where high concentrations of these potential hazardous contaminants were present in the Western Harbour of Alexandria. Methods  The composition, distribution and the source of PAHs in surficial sediments of the harbour were investigated. To document the spatial PAH input, surficial sediment samples from 23 locations throughout the harbour were analysed. as]Results and Discussion The total PAH load determined in the surficial sediment samples ranged from 8 to 131150 ng g¹ dry wt, generally with most of the samples having total concentrations of PAHs greater than 5000 ng g¹ dry weight. The highest concentration of total PAHs was recorded in sediments of the inner harbour. Ratio values of specific compounds such as phenanthrene to anthracene, fluoranthrene to pyrene, methyl-phen-anthrene to phenanthrene, methyl-dibenzothiophenes to dibenzothiophenes, alkylated to non-alkylated and high molecular weight to low molecular weight PAH, were calculated to evaluate the possible source of PAH contamination in the harbour sediments. Conclusions  Two main sources of PAH in the study area have been found: pyrolytic and petrogenic. Interferences of rather petrogenic and pyrolytic PAH contaminations were noticed for most samples. The dominant sources of PAH appear to be the combustion processes through run-off, industrial and sewage discharges, and atmospheric input. The concentrations of PAHs were generally above levels expected to cause adverse biological effects. Recommendations and outlook  Information from this study and any other relevant studies should be useful in designing future strategies for environmental protection and management of the harbour.     

悬挂犁机组优化方法

采用悬挂犁机组空间力学模型,利用贮备牵引力为目标函数,在性能、边界约束的条件下使用单纯形法和随机方向法对悬挂机构进行了多变量优化设计,获得了满意结果。为适应空间模型需要,在犁体外载表示方面提出并使用了三力三坐标分点表示法。     

原油罐金属底板的腐蚀与防护

针对原油罐区的腐蚀现状，分析了原油罐底板的腐蚀机理，通过对原油一罐的腐蚀调查、底板测厚，以及对罐底脱水中腐蚀介质及沉积物样的化学分析，提出了使用WF－50防腐涂料加阴极保护的方案，该方案可有效地防止原油罐金属底板的腐蚀。     

Assessment and selection of fungal antagonists against Rhizoctonia solani

The soil-borne pathogen Rhizoctonia solani Kühn (teleomorph, Thanatephorus cucumeris [A.B. Frank] Donk) is worldwide responsible for serious damage of many economically important agricultural and horticultural crops. Control of Rhizoctonia diseases is difficult because this pathogen survives for many years as sclerotia in soil or as mycelium in organic matter under numerous environmental conditions. Furthermore, the pathogen has an extremely wide host range. To date, no effective con…     

半干旱区海水灌溉农田土壤盐分运移规律的研究

对在海侵灾害最严重的莱州湾地区,在油葵生育期内利用不同浓度的海水直接灌溉两次,研究0～40cm土层土壤盐分及Na^ 、CI^-、Ca^2 、Mg^2 、K^ 含量的分布、迁移规律,为确定合适的灌溉定额和灌溉次数提供最基础的技术参数。结果表明：①60％以上浓度海水灌溉,5～40cm土层土壤盐分呈积累趋势,次生盐渍化明显;40％海水灌溉后轻微积盐．若无充沛的雨水淋洗,则须结合一定的农业措施以防造成次生盐害;20％海水浓度在灌溉定额为800m^3／hm^2时能保持土壤盐分的盈亏平衡。②Na^ 和CI^-主要分布在5～20cm土层,而Ca^2 和Mg^2 主要在20∽40cm土层,K^ 则极易被淋洗而迁移到40cm以下土层。③0～5cm土层盐分变化剧烈,在油葵整个生育期降雨量为171．7mm的情况下,至收获期时,各处理均能降至灌海水前的水平。     

校园基地土壤理化性质及其改良对策

试验测定了校园基地土壤耕层的一般理化性状,得出如下结论:①花卉基地、菜地土壤结构较好,富含有机质、水解性氮、速效磷,这是多年培肥改土的结果。②蓍草园、桃园土壤有机质含量不高,缺少速效钾。经改良可进一步利用。③学生宿舍院内荒地理化性状均差,目前不宜直接利用。同时提出了相应的土壤改良措施。     

盛花期调节群体底层透光率对棉花产量的影响

在生育稳健、盛花期叶面积指数偏大的棉田 ,以整枝为手段 ,把群体底层透光率调节到 2 2 3%、5 18%和 8 90 % 3个水平。测产表明 ,透光率为 5 18%的处理的成铃率和子棉产量都极显著高于透光率过低和过高的处理 ,其中透光率为 8 90 %的处理子棉产量最低 ,比透光率为 2 2 3%的处理减产达显著水平     

罐底提离时的下节点应力计算

当安装于罐顶上的呼吸阀失灵，或罐内液体的汽化速度增大而又不能及时排放时，罐内的压力增高，部分罐底可能会离开基础而发生罐底提离现象。此时，在下节点处存在着较大的应力，甚至会造成油罐在下节蹼处的破坏。     

Prolonged elevated atmospheric CO2 does not affect decomposition of plant material

Prolonged elevated atmospheric CO₂ might alter decomposition. In a 90-day incubation study, we determined the long-term (9 years) impact of elevated CO₂ on N mineralization of Lolium perenne and Trifolium repens plant material grown at ambient and elevated CO₂ and low- and high-¹⁵N fertilizer additions. No significant differences were observed in recovery rates between any of the treatments, except an N addition effect was observed for L. perenne (0.4 versus 0.5% day⁻¹ in high versus low N). The results suggest that elevated CO₂ did not change plant N mineralization in any of the soils, because of a surplus of available N in the fertilized and leguminous systems, and because of insignificant plant responses to elevated CO₂ in the low soil N availability systems.