The role ofAzolla in curbing ammonia volatilization from flooded rice systems

By the year 2020, an additional 300 million tons of rice are needed annually to meet the demands of a growing population. If our natural resource base is to be preserved, intensification strategies should rely on integrated nutrient management, making full use of biological nitrogen fixation. TheAzolla-Anabaena complex is amongst the most effective systems of fixing nitrogen. In this paper we present evidence from greenhouse studies on the potential ofAzolla to curb the volatilization of NH₃ following the application of urea to a mixedAzolla-rice culture, providing a new incentive for developing ways of integratingAzolla in intensive rice cultivation systems.The results of a series of short term greenhouse experiments show that a full cover ofAzolla can significantly reduce losses of applied urea-N from 45 and 50% to 20 and 13% for the 30 and 60 kg N ha^–1 treatments, respectively. About one-quarter of the applied N was tied up in theAzolla biomass. The applied N inhibitedAzolla growth as well as the amount of N fixed. Inoculation with smaller quantities ofAzolla allowing for more vigorousAzolla multiplication was equally effective in reducing NH₃ volatilization and doubled the amount of¹⁵N tied-up byAzolla. The reduction in NH₃ volatilization is largely related to the depression byAzolla of the floodwater pH, which in its absence may reach values between 9 and 10 as a result of algal activity.Early rice growth responded positively to urea as well as the large quantities of appliedAzolla and increased the yield potential of the crop. Smaller quantities ofAzolla alone were not effective in this regard. The conservation of fertilizer N byAzolla, particularly when it fully covered the water, was reflected in a synergistic effect on rice dry matter production, amounting to 9% at the 30 kg N rate and 16% at the 60 kg N rate. In all likelihood this interaction is attributable to the higher efficiency of the applied N. The benefits ofAzolla in conserving basal urea-N even in small quantities (200-500 kg fresh material ha^–1), outweighed competition for the applied N and may be as important as its BNF. The most promising integratedAzolla/rice management systems emerging from our studies should be given further attention under field conditions.     

专家系统在注塑模结构设计中的应用

介绍了知识库与推理机分离专家系统的原理及程序实现方法,并给出了专家系统的应用实例。     

Liquid-Phase Transport During Removal of Organic Binders in Injection-Molded Ceramics

A method has been developed for calculating hydraulic pressures induced by thermal expansion of liquid binders early in the removal cycle, when evaporative losses are negligible and fully saturated conditions prevail. Specific results were obtained for flat compacts containing a common wax binder, mixed with varying amounts of low-density polyethylne. In general, these results show how the risk of hydraulic fracture increases with heating rate and compact thickness. Although pressures are minimal when the binder consists entirely of wax, the continual addition of polyethylene eventually gives rise to unacceptable risk levels, even for relatively thin compacts. Binder removal at elevated temperatures is considered subsequently. In this case, vapor pressures eventually approach a critical level, thereby allowing mass removal by evaporation to overcome the effect of thermal expansion in maintaining full saturation. With the onset of void formation, the developing capillary pressure supersedes hydraulic pressure as the driving force in liquid transport. Besides representing capillary flow, the present formulation also accounts for thermal degradation of the binder during removal. The resulting system of equations was solved numerically for a variety of representative debinding conditions. Predictions for flat compact containing a balanced wax/polyethylene binder indicate that thermal degradation of the polyethylene can give rise to a marked improvement in debinding rates. It turns out, however, that this enhancement is far more effective in thinner compacts.     

Increasing urea-N efficiency for transplanted lowland rice by pneumatic injection: Yield and economics at the farm level

To increase the fertilizer-N efficiency in lowland rice (Oryza sativa L.) cultivation, new management practices are needed. Main cause of the present low efficiency is the low N recovery by plants, as a considerable part of the N applied is lost; deep placement techniques improve the recovery. A pneumatic injector, with which urea prills can be point-placed at a depth of 5–10 cm in paddy soils, was tested in 38 on-farm trials in 1989/90, mostly during the wet season. The experiments, located in Africa and Asia, focussed on differences in grain yield between conventional methods of broadcasting urea and injection by the pneumatic injector, at recommended N-rates. The study shows that the pneumatic injector is effective as a tool to improve the N fertilizer efficiency. The average yield increases per region, resulting from the use of the injector, ranged from about 250 to 1300 kg grain ha^–1. The value of the yield increase would allow most farmers to recover the costs of the injector within one season, even if labour was hired to carry out the injections. The average labour requirement of the injector was 40 hours ha^–1. In Indonesia, injection of prilled urea gave yields similar to those obtained with urea briquettes.     

对接型销双向斜抽芯注塑模设计

给出了灯罩注塑模实用结构。该模具型芯由主型芯和副型芯组成，采用将副型芯推出方法实现塑件内侧壁凹槽抽芯，在塑件倾斜通孔处采用对接型销双向分型斜抽芯。既满足制品的成型和抽芯要求，又省去了斜抽芯和水平抽芯机构，模具结构紧凑，脱型可靠，成型塑件质量好。     

配位离子液体［3（CH3CH2）4N+Cl-·（NH2）2CO］的合成及表征

采用尿素和氯化四乙基铵为原料，合成了一种新型的配位离子液体，并通过红外和X－射线粉末衍射对其结构进行了表征。结果表明，尿素和氯化四乙基铵发生反应，使得原来尿素羰基峰由1690.72cm－1转移到了1619.10cm－1。由X－射线粉末衍射图可以看出，在2θ = 30.37°处有新的衍射峰。通过差热－热重分析，配位离子液体在室温到250℃可以稳定存在，与其他有机溶剂相比具有良好的稳定性。     

两极控制图在注塑瓶盖壁厚控制中的应用

针对注塑瓶盖壁厚控制的特点,介绍了统计过程控制(SPC)中的均值-极差(x-R)控制图在塑料瓶盖壁厚控制中的局限性,将两极(L-s)控制图与均值-极差控制图进行了比较,阐述了两极控制图在塑料瓶盖壁厚控制中的优越性,论述了两极控制图的构造原理和控制限计算方法,提出了两极控制图在注塑瓶盖壁厚控制中的应用,并在对两极控制图分析的基础上,对注塑成型的过程能力进行分析和改善。     

Effects of urea fertigation of apple trees on soil pH,exchangeable cations and extractable manganese in a sandy loam soil in New Zealand

Changes in soil pH, exchangeable aluminium (Al), calcium (Ca), magnesium (Mg), and potassium (K) and extractable manganese (Mn) were investigated after urea fertigation of a sandy loam soil in an apple orchard in New Zealand. Urea at three rates (0, 25, 50 kg N ha^–1 yr^–1 or 0, 16.9, 33.8 g N emitter^–1 yr^–1) was applied in 4 equal fertigations. Soil cores at 4 profile depths (0–10, 10–20, 20–40 and 40–60 cm) directly below and 20 cm from the emitter were sampled approximately 4 weeks after each fertigation and in the following winter. Results obtained showed that the largest changes in soil pH and cations occurred in soils directly below the emitter in the 50 kg N ha^–1 yr^–1 treatment where the soil pH decreased by 1.6 pH units at all soil depths. The lowest pH of 4.3 was observed at a depth of 27 cm. Exchangeable Al and extractable Mn levels increased to 11 meq kg^–1 and 78µg g^–1 respectively. Estimated losses of Ca, Mg and K from the upper soil profile depth (0–10 cm) represented 23, 63 and 27% of their respective total exchangeable levels. At lower profile depths (>20 cm), accumulation of displaced K was evident. Variable, and generally non-significant, chemical changes recorded in soils 20 cm from the emitter were attributed to restricted lateral water movement, and therefore urea movement, down the profile.The present study showed that one season of urea fertigation by trickle emitters, applied to a sandy loam, at half the rate conventionally applied to apple orchards (50 kg N ha^–1 yr^–1) resulted in pH and mineral element imbalances which were potentially and sufficiently severe to inhibit tree growth.     

橡胶注射过程中压力变化的研究

对橡胶注射过程中的压力变化进行了理论与实验研究。充模流动模型的压力、能量控制方程分别为：选用高斯方法求解总体有限元方程。实验与计算分析对比证明．本文选用的数学模型和计算方法所得结果与实测结果基本吻合、该模型可用以代替大量的实验，对橡胶充模过程进行模拟，并用Ｇｒａｐｈｅｒ软件对数值结果进行处理，以图表直观地表达出各种因素对充模过程的影响。     

苯酚改性脲醛树脂合成工艺及性能的研究

用苯酚作为改性剂,采用高温(90℃)缩聚反应合成改性脲醛树脂胶粘剂,改进了合成工艺,缩短了反应时间。通过引入苯环改善了耐水、耐老化性能。分析了各因素对改性脲醛树脂的影响,得到甲醛、尿素、苯酚摩尔比为10:8:1时树脂性能最佳,胶合强度和木破率均达到GB／T 17656-1999标准规定值。