肉桂双瓣卷蛾种群动态及综合治理研究

通过室内饲养和林间调查相结合的方法,研究了肉桂双瓣卷蛾的种群动态。该虫的发生、消长猖獗成灾与温度、湿度、林分结构和组成、林龄及天敌等环境因子有密切关系。提出了采取预防为主,营林技术措施为基础,生物防治为主导,科学地采取生物、人工、化学防治和保护利用天敌等的综合治理措施,可有效控制其危害。     

Supercritical fluid extraction of sapogenins from tubers of Smilax china

Supercritical CO(2) fluid extraction (SFE-CO(2)) was used to extract the sapogenins after acid hydrolysis from Smilax china tubers. The influence of extraction variables, such as modifier, pressure, temperature and extraction time, were studied. SFE-CO(2) was found to produce higher yield than conventional solvent extraction. The highest yield (0.454%) of sapogenins, mostly containing diosgenin, was obtained using 35 MPa pressure, 65 degrees C and 95% EtOH as a modifier for 180 min, higher than that obtained with conventional extraction methods (0.385%).     

林隙(GAP)干扰研究进展

本文系统地介绍了森林循环的理论、自然干扰的概念、林隙的一般特征和林隙干扰的时空格局。干扰是森林循环的驱动力,干扰形成的林隙是森林循环的起点。林隙的大小、形成年龄、形成方式以及形成木的特征是研究林隙特征的重要参数,虽然不同森林群落中,林隙干扰的频率和程度及其时空变化规律不同,但大多数森林的年平均干扰率是在１％左右。不同的森林类型中,大、小型干扰的比例不同。小型林隙干扰与大型灾难性干扰在不同时空条件下的组合,就形成了不同森林景观的时空变化格局。     

Carbon and nitrogen dynamics under windrowed residues during the establishment phase of a second-rotation hoop pine plantation in subtropical Australia

The dynamics of carbon (C) and nitrogen (N), derived from the decomposition of windrowed harvest residues, was examined in the establishment phase of a second rotation (2R) hoop pine (Araucaria cunninghamii Aiton ex A. Cunn) plantation in subtropical Queensland, Australia. Following harvesting and site preparation, when residues were formed into windrows, in situ N mineralisation was measured in positions along the three tree-planting rows formed between the windrows. The position above the windrow had a higher nitrification rate than the other positions, averaging about 18 kg N ha⁻¹/month compared with 12 and 9 Kg N ha⁻¹ for the positions between and below the windrow positions, respectively. This position also had consistently greater soil moisture.

Macroplots were formed extending 5 m above and 10 m below a windrow. Windrowed residues within the macroplots were replaced by ¹⁵N-labelled material comprising hoop pine foliage, branch and stem. Hoop pine trees were planted within each macroplot with foliar samples taken at 12 and 24 months. Differences in foliar ¹⁵N enrichment between positions within macroplots were <1‰. Soil samples were taken from positions along the macroplots at 6-monthly intervals. Samples revealed an initial release of labile C and N but soil δ¹⁵N showed that residue-derived N was largely immobilised within the windrows for the 30-month sampling period. Whilst the use of windrows may act as a barrier to the down-slope movement of water, the residue N within the windrows may not be available to the trees of the following rotation for a considerable period following planting. Trees closest to the windrows may be able to introduce roots under the windrows thereby gaining access to the available N, but trees in the central tree planting row are unlikely to derive any significant benefit from the decomposition of windrowed residues.     

Comparison of stand dynamics after dieback caused by pine wilt disease among pine forests with different management regimes in western Japan

In pine forests damaged by pine wilt disease, in western Japan, the effect of protection regimes of pine trees on the stand dynamics were examined in the following four stands: (1) lightly damaged stand (age 30–40 years) with no procedure in operation for protecting pine trees; (2) severely damaged stand (age 30–40 years) with no procedure in place for protecting pine trees; (3) severely damaged stand (age 50 years) with a selective cutting of infected trees; (4) severely damaged stand (age 30–40 years) with a selective cutting of infected trees. All the stands had been abandoned before the pine wilt disease damage. The understory structure of the severely damaged stand with no protection procedure was similar to that of the lightly damaged stand. Frequent invasion by tree species and acceleration in the growth of understory trees occurred after the dieback in the selective cutting stand. These results suggest that a deficiency in the canopy layer caused by the dieback resulted in low disturbance intensity in the early stages after the dieback, but the selective cutting increased the intensity by the reduction in the understory as well as the canopy layer. The intensity of the disturbance in the selective cutting stands was larger in the younger stand because it had a higher density of selectively cut pine trees. The different stand structure of pine forests occurred after the dieback because the intensity of the disturbance varied as a result of the selective cutting operation and the stand age.     

天然气发动机燃烧过程非线性动力学特性

利用非线性动力学数据分析技术对增压中冷天然气发动机燃烧过程的动力学特性进行了研究,结果表明:混合气浓度从当量比=1.00降低到稀燃极限时由缸压时间序列重构的二维相空间中,系统运动轨线都是有限范围内的非周期运动,轨线具有复杂、扭曲、重叠的几何结构;无论发动机是在当量混合气还是稀燃极限条件下运行,嵌入维m大于某一值以后,吸引子的关联维D均能达到饱和值且为分数,随着混合气变稀,燃烧循环变动增加,D逐渐增加,当=1.00、0.77、0.70和0.63时D分别为1.27、1.33、1.58和1.87,最大Lyapunov指数(LLE)大于零,分别为0.008 6、0.011、0.013和0.015 7,因此天然气发动机燃烧系统是一个低维非线性混沌系统。     

流体播种技术发展及其关键技术分析

干旱缺水是影响旱作农业的重要因素,研究旱作节水技术是保证国民经济正常发展和农业可持续发展的前提和基础.流体播种是一种抗旱、节水、增产的新技术.为此,在调查和试验研究的基础上介绍了流体播种技术及其在节水,提高出苗率、成活率等方面的特点;简述了保水剂的发展和应用情况以及流体播种机具的研究现状;分析了影响流体播种技术应用的排种器伤种、流体播种液的配制、播种精度和均匀度、保水剂的使用经济性等关键技术问题,并探讨了其解决措施,可为流体播种技术和播种机具的研究提供参考.     

Adopters,testers or pseudo-adopters? Dynamics of the use of improved tree fallows by farmers in western Kenya

Although there has been increasing research on the adoption of agroforestry technologies over the last decade, few such studies have assessed uptake over a long period and many are based on a single snapshot in time. Furthermore, most of these studies have mainly looked at non-adopters and adopters: only recently have social scientists considered testers. A further category of users neglected in adoption studies has been re-adopters of technologies. Studying this group provides an interesting and more nuanced understanding of adoption and re-adoption. Methodologically, most adoption studies use quantitative methods and fail to link their findings to wider socio-economic, political and institutional settings. This paper presents a study of the dynamics of improved tree fallow use by farmers in Siaya and Vihiga districts of western Kenya over a period of eight years. It uses both qualitative and quantitative data to critically discuss the motivations of adopters, testers/rejecters and re-adopters. The results show that the process of adoption is highly dynamic and variable with farmers planting improved fallows and discontinuing or re-adopting them due to a whole range of factors, of which soil fertility improvement is just one. These factors included incentives from projects, the tying of adoption to credit programmes, prestige, participation in seminars/tours and the availability of a seed market from projects promoting improved fallows. Farmers planting improved fallows for such reasons may be termed ‘pseudo-adopters’. There were significant differences in adoption between the two districts, with more farmers in Siaya planting improved fallows than in Vihiga. A majority of farmers in Vihiga (53%) who were given seed never planted improved fallows, even though they had been exposed to the technology. Some 40% of farmers in Siaya and 38% in Vihiga planted improved fallows but later rejected them. This has some important implications for research and development. For improved fallow technologies to be attractive to farmers, they must provide other tangible economic benefits besides soil fertility improvement. This presents a challenge to researchers who must better attune themselves to the needs and demands of farmers if they wish to see their research findings widely adopted.     

双蜗壳式双吸泵隔板结构对叶轮径向力的影响

分别对单、双蜗壳式双吸泵10个工况点进行全三维流道的数值模拟和试验测试,发现由于双蜗壳式泵内部隔板设计不合理,导致双蜗壳泵较单蜗壳泵在原设计工况点的扬程、效率分别相对下降了21.8％和41.3％.依据双蜗壳设计基本原理,对隔板结构提出3种改进方案,利用雷诺时均方法( RANS)和SSTk -ω湍流模型对每一方案进行全三维流道的定常数值模拟.模拟和试验结果表明:2号双蜗壳泵既保持了泵原有的水力性能,又能够有效地减小叶轮径向力,因此得到双蜗壳式双吸泵中隔板结构的最优设计模型:起始位置为隔舌绕基圆旋转180°、曲线方程为对数螺旋线、终止位置为隔板起始点旋转180°.     

Suitability of Multi-Agent Simulations to study irrigated system viability: application to case studies in the Senegal River Valley

It is assumed that Agent-Based Modeling is a useful technique for water management issues. In particular, it may provide a suitable framework for representing irrigated systems. The objective of this paper is to demonstrate its potential for a specific use: research on irrigated systems’ viability in the Senegal River Valley. The main assumption to be verified is that Multi-Agent Systems constitute a suitable architecture to study theoretically irrigated systems’ viability using simulations. By using Multi-Agent Systems, virtual irrigated systems can be designed that might then be used as virtual laboratories. These virtual labs constitute an alternative when real labs cannot exist for some reason.

In this paper we report on experiments we have conducted using such virtual labs for exploring an Agent-Based Model through the simulation of scenarios. A scenario is defined as a triplet: an environment, a set of individual rules, a set of collective rules. It is evaluated according to the longevity of the irrigated system. An index is defined, based on the ratio of long-enduring simulations among a set of repetitions of a given scenario. Even if simulation results display significant diversity for a given scenario due to random factors in the processes simulated, the ratio of long-enduring simulations is repeatable. This entails to explore the overall behavior of the virtual irrigated system and to build theories concerning the viability of Senegalese irrigated systems. An example is given showing the need for strong coherence for a given environment among individual rules and collective rules.