Numerical simulation of deformations and forces of a floating fish cage collar in waves

The dynamic behavior of a fish cage collar in waves was investigated using a numerical model based on the finite element method. The floating collar and mooring system were divided into a series of line segments modeled by straight massless model segments with a node at each end. To verify the validity of the numerical model, research data from other authors were cited and compared with the simulated results, the comparison of results showed a good agreement. The numerical model was then applied to a dynamic simulation of a floating cage collar in waves to analyze its elastic deformation and mooring line tension. The simulated results indicated that the greatest deformation of the collar taken place in the position of the mooring line connection point when incident waves were in the same direction. An increase in the length of mooring line would help to decrease the mooring line tension of the collar. Furthermore, the effects of collar dimension, including collar circumference, pipe diameter in cross-section, and pipe thickness, on the dynamic behavior of the floating collar were discussed. The results of this study provided a better understanding of the dynamic behavior of the fish cage collar.     

不同结构尼龙网防风效应的风洞模拟

为对比不同结构尼龙网不同风速下的防风效应,开展对均匀型(A)、上密下疏型(B)、上疏下密型(C)3种不同结构尼龙网在6 m·s~(-1)、9 m·s~(-1)、12 m·s~(-1)指示风速下的风洞模拟试验。通过对不同结构尼龙网各风速下加速率等值线图和防风效能的对比分析,结果表明:1 3种结构尼龙网风场存在相似性但差异明显。B型尼龙网风影区下部存在加速区,A、C型则不存在;C型风影区中心位置较低。2 A、C型尼龙网防风效应随风速增大而降低,B型则相反。3测量范围内C型尼龙网防风效应明显优于A、B型。实际应用中应综合考虑沙障结构、风况等因素,尼龙网栅栏的布设建议选用上疏下密型结构。     

The effect of soil texture and organic amendment on the hydrological behaviour of coarse-textured soils

To gain more insight into the hydrological behaviour of coarse-textured soils, the physical properties of artificially created soil mixtures with different texture were determined. The mixtures were prepared according to the specifications of the United States Golf Association (USGA) for constructing putting greens. In addition, the effect of 10 vol.% organic matter addition was studied. The soil moisture retention and hydraulic conductivity relationships of the different mixtures were determined and their hydrological behaviour was studied using the numerical model SoWaM. Both texture and organic matter addition substantially affected the hydraulic properties. Hydraulic conductivity significantly increased with increasing coarseness while moisture retention decreased. On the other hand, organic matter addition reduced saturated hydraulic conductivity by a factor of 10 to 100 and distinctly increased moisture retention capacity. The amounts of total available water were increased by the addition of organic matter between 144% (slightly coarse texture) and 434% (very coarse texture). Results indicate that the mixtures can contain only 2–16% plant available water and therefore need frequent irrigation to maintain plant growth. Addition of organic matter seems a good solution to reduce the irrigation water requirements but it increases the risk of ponding or runoff because of large reductions in the saturated hydraulic conductivity sometimes to below the rate of 3.6 m/day recommended by the USGA.     

Potential for organic Chilean wine

Abstract

The potential for extending organic wine production in Chile is discussed in relation to its history and present situation. The main objective is to present an overview of the production of organic wine in Chile, its certification, and national and international markets. During the wine harvesting season in March and April 2006, the authors visited and interviewed staff at four Chilean organic wineries. The wineries were all situated in the wine-producing centre of the country and were of variable sizes. One of the certification bodies in Chile was also interviewed. In addition to the field studies and interviews in Chile, various written information has been used. Second to Argentina, Chile is the country that produces most wine in Latin America. Vineyards cover a total of 110 000 hectares of the country's two million hectares of arable land. A study carried out in 2005 showed that 2000 hectares (almost 2%) of vineyards are organically cultivated. The organic production is operated by 32 different companies, which produce organic wine mainly for exportation to the international market. In Chile, the number of certified organic wine producers has increased in recent years in a trend directed by international demand and possible competitive advantages for Chilean wines. In order for a wine to be called ‘organic’ or ‘wine made from organically grown grapes’, the cultivation and final product must be approved by a certification company. In Chile there are three main active certification bodies; one national (Certificadora Chile Orgánico, CCO) and two international (the Swiss company IMO and the German company BCS). The study reveals a country with innovation and energy but facing strong pressures from the international market and its jungle of laws and directives, and the differing prestige of different certifications and labels. Chile as a wine-producing country has many competitors, and the production of organic wine could be a way to find diversity and exploit new market ground where environmental consideration concerns and sustainability are important targets.     

一维Theta-神经元网络中细胞耦合作用时间对细胞放电行为的影响

通过对一维Theta-神经元网络中细胞耦合作用时间的讨论,得到较长时间的耦合作用时间会使网络中单放电行波变为多放电行波,并通过数值模拟对理论加以验证.     

Effect of Aquasorb and Organic Compost Amendments on Soil Water Retention and Evaporation with Different Evaporation Potentials and Soil Textures

Abstract

Aquasorb PR3005A, a hydrophilic polymer (a salt copolymer polyacrylamide), and garden waste compost were added to a loamy sand and a loam soil in pots to assess their impact upon soil physical properties at two different evaporation potentials. Compost was mulched and incorporated, the Aquasorb was incorporated, and their effect on temperature and amelioration of soil water content and evaporation was investigated. Mulching with compost reduced evaporation and increased soil temperature. Maize (Zea mays var. single cross 704) was sown in the same pots later, and growth indicator factors (plant height, fresh and dry weight, root weight, and leaf area) were compared. It was concluded that compost mulch application is beneficial to soil water retention whereas compost incorporation did not show these benefits. Compost mulch advances seedling emergence and enhances early growth through hydrologic soil amelioration. High rates of Aquasorb were also beneficial in advancing the emergence and early growth of maize seeded in loamy sand. The hydration capacity of Aquasorb is reduced as the electrolyte concentration and electrical conductivity are increased. Increased electrolyte concentration in soil solution, through drying, may result in gel dehydration and water release at potentials greater than field capacity, which may be lost to drainage. Furthermore, it is concluded that pot experiments with amendments fail to simulate field conditions.     

Effect of tillage and crop on arbuscular mycorrhiza colonization of winter wheat and triticale under Mediterranean conditions

Large‐scale inoculation with arbuscular mycorrhizal fungi (AMF) is generally impractical in most regions and we have little understanding of the factors that determine inoculation success. Nevertheless, the ability to take full advantage of indigenous AMF for sustainable production needs to be developed within cropping systems. We used part of a long‐term field experiment to understand the influence of tillage and the preceding crop on AMF colonization over the growing season. Arbuscular mycorrhiza colonization rate was more affected by treatment (tillage or the combination of crop and preceding crop) than by the total number of AMF spores in the soil. Conventional tillage (CT) had a statistically significant negative effect (P ≤ 0.05) on spore numbers isolated from the soil, but only in the first year of study. However, the AMF colonization rate was significantly reduced by CT, and the roots of wheat, Triticum aestivum, L, cv. Coa after sunflower, Helianthus annuus L., were less well colonized than were those of triticale, X Triticosecale Wittmack, cv. Alter after wheat, but the affect of tillage was more pronounced than was the effect of crop combination. Under no‐till there was a significant increase in AMF colonization rate throughout the sampling period in both wheat and triticale, indicating that the extraradical mycelium previously produced acted as a source of inoculum. In general, triticale showed greater AMF colonization than wheat, despite the preceding crop being less mycotrophic. Under these experimental conditions, typical of Mediterranean agricultural systems, AMF colonization responded more strongly to tillage practices than to the combination of crop and preceding crop.     

基于SALUS与WebGIS整合的作物生长模拟

SALUS是较为著名的土地可持续使用系统模型，实现了一种基于WebGIS整合SALUS的作物生长仿真系统。详细阐述了数据库和相关功能模块的整合方法，改善了SALUS模型在空间数据处理与仿真结果视觉化的能力。可以让使用者清晰的掌握土壤、天气、灌溉量、施肥量等多种因素对农作物产量的影响，为农作物实施相关的增收管理措施提供了一定的科学依据。并提出了相应的整合方案为实际构建基于WebGIS的作物生长仿真系统提供了一定的技术支撑。     

森林消防车动力性仿真技术研究现状与前景分析

介绍了当前国内外对森林消防车动力性能的研究现状,并对其动力性仿真技术的应用(如MATLAB、CRUISE、ADVISOR、PAST等)进行研究。结果表明,动力性仿真技术在森林消防车的性能研究方面具有良好的应用前景。     

Transect relascope sampling for assessing coarse woody debris: The case of a π/2 relascope angle

In transect relascope sampling, a wide‐angle relascope is used along survey lines for selecting a sample of objects that extend linearly in the plane, e.g. downed logs. The method is closely related to line intersect (intercept) sampling. In this article, a special case of the transect relascope technique is studied. Using a π/2 radian relascope angle, the method becomes invariant to the orientation of the line objects in the population. The reason is that the area of inclusion around objects, through which a survey line should pass for an object to be included, turns out to be circular. In analytical studies and Monte Carlo simulations, the cost‐efficiency of transect relascope and line intersect sampling is evaluated. It is found that transect relascope sampling is a competitive alternative to line intersect sampling in inventories of the total volume of coarse woody debris (in the form of downed logs) in forest compartments.