渔船拖网绞机恒张力控制系统的设计与仿真

针对拖网捕捞作业中较难保持曳纲张力恒值的问题,设计并搭建了基于模糊PID控制的渔船拖网绞机恒张力控制系统。在对渔船拖网绞机传动原理研究的基础上,建立恒张力控制系统的传递函数,构建模糊PID控制器,通过控制拖网绞机转速而调节曳纲张力。介绍了系统硬、软件的构成,并利用MATLAB进行仿真验证。仿真结果表明,模糊PID控制能在0.8 s内实现曳纲张力恒值,并能在收到干扰后0.7 s内恢复到之前的稳定状态,性能优于传统PID控制和模糊控制。研究表明,基于模糊PID控制的渔船拖网绞机恒张力控制系统具有系统响应快、超调量小、鲁棒性强等特点,能够有效地保持曳纲张力恒值,提高捕捞效率,具有较强实践指导意义。     

河淤土区玉米3种肥料配比的应用效果比较

通过田间试验方法,研究并比较3种不同N、P、K配比施肥与当地常规施肥在玉米上的应用效果。试验结果表明,当河淤土区玉米生产的N、P、K适宜配比为N∶P2O5∶K2O=1.0∶0.5∶（0.4～0.5）时,既可增加作物产量,又具有显著的经济效益。     

竹层积材的非均匀性与纵向曲翘

讨论竹材与竹层积材非均匀性和纵向曲翘行为,由于竹篾的几何尺寸和组坯方式决定了竹层积材的非均匀性和随机性,从而决定了其非对称性。参照英国有关标准,测试了竹层压板的纵向曲翘行为。结果表明:材料有可能发生超过结构材要求的纵向曲翘。今后在建立有关标准时应增加相关条目。     

Rotational position of curved saw logs and warp of the sawn timber

With the development of scanning technology in sawmills, it is possible to optimise log rotational position when sawing. However, choosing a different rotational position than horns down might be detrimental for the board shape after drying, especially for curved logs. Thus, there is a need to investigate at what level of log curve it is possible to freely rotate logs without causing board warp. This study was carried out through a test sawing that was conducted at a sawmill situated in the middle of Sweden. The tests were made on 177 Norway spruce logs, with varying amount of curve. Half of the logs were sawn in the horns-down position, half were sawn rotated perpendicular to horns down. Log shape and warp of the dried boards were measured. The results indicated a relationship between board spring, log curve and choice of rotational position. Furthermore, board bow was related to log curve but not rotational position. It can be concluded that for straight logs, with a bow height of less than 15 mm, an unconventional rotational position does not cause excess spring in the boards. Bow and twist are not affected by the rotational position at all.     

利用几何形态测量学方法分析唐鱼群体的形态变异

唐鱼是华南地区小型亚科鱼类的典型代表,国家Ⅱ级保护水生野生动物。本研究利用基于地标点的几何形态测量学方法分析了唐鱼8个野生种群和2个养殖群体的形态变异,旨在从形态学的角度了解唐鱼不同种群间的分化程度,为唐鱼保护策略的制定提供科学依据。新鲜标本冰冻麻醉后随即置于95%酒精中固定,用Nikon D-800单反相机拍照获得固定标本的标准图像。利用tps系列软件提取地标点坐标值,进行相对扭曲主成分分析、网格变形分析和判别分析来解释唐鱼的形态变异。相对扭曲主成分分析结果显示,第1、2、3主成分分别解释了总变异的48.20%、23.12%和14.83%,降维效果较好。其中,Ⅱ型地标点12、13、14和15贡献较大,四者合计贡献率达71.28%,反映出唐鱼群体的形态变异主要表现在眼径大小和头部形态。逐步判别分析和交互验证分析的总体判别正确率分别为97.6%和92.0%,能有效识别唐鱼群体。研究结果还揭示了唐鱼野生种群和养殖群体之间存在显著的形态差异。基于上述结果以及唐鱼呈点状分布的事实,建议将唐鱼的7个野生种群(越南种群除外)各自作为单独的保护单元进行重点保护,同时建议禁止在野外放流养殖群体。     

Rectangularity of planed Scots pine (Pinus sylvestris) planks

Abstract

This study deals with how warp affects the cross-sectional shape of planed planks. A total of 20 planks with dry target cross-sectional dimensions of 50×150 mm were planed to 45×145 mm. The rectangularity of five cross sections of every plank was measured before and after planing. The cutting depths were measured in 10 positions in the cross sections, and the angles between the planks and the cutters were calculated. Also, the warp, that is, twist, bow, crook, and cup, was measured before and after planing. All the studied properties pointed in the same direction. In terms of both rectangularity and angles of cut, the problems were larger in the top and butt ends of the investigated planks than in the intermediate parts, and the main reason for deviations from the desired result after planing was twist.     

The potential of young,green finger-jointed Eucalyptus grandis lumber for roof truss manufacturing

South Africa is a timber-scarce country that will most probably experience a shortage of structural softwood lumber in the near future. In this study the concept of using young, green finger-jointed Eucalyptus grandis lumber was evaluated for possible application in roof truss structures while the timber is still in the green, unseasoned state. Drying will occur naturally while the lumber is fixed within the roof truss structure. The objectives of this study were (1) to investigate the strength and stiffness variation of the finger-jointed E. grandis product in both the green and dry state for different age and dimension lumber, (2) to investigate the variation in density, warp and checking in the lumber when dried in a simulated roof-space environment and (3) to evaluate the potential of this finger-jointed product as a component in roof truss structures. Green finger-jointed E. grandis lumber of ages 5, 11 and 18 years and dimensions 48×73?mm and 36×111?mm from Limpopo province were evaluated. The study showed that the young finger-jointed E. grandis timber had very good flexural, tensile parallel to grain, and shear properties in both the green and dry state. The mean and characteristic modulus of elasticity and modulus of rupture values of the finger-jointed E. grandis product were higher and the variation lower in comparison to currently used South African pine sources. The tensile perpendicular to grain and compression perpendicular to grain strength did not conform to SANS requirements for the lowest structural grade (S5). Both tree age and product dimension were sources for variation in the physical and strength properties. Based on the results from this study the concept of producing roof trusses from green, finger-jointed young E. grandis timber has potential.     

作物种质资源的非生态性偏差和人类行为下的种质生态伦理

作物的生产是以利用自然生态能量为前提的物质生产,任何作物种质资源都要回归自然生态系统才能进行能量截获和物质合成,因此,作物种质的“运筹”需要接受种质生态伦理的约束。种质生态伦理是指种质资源对其生存的外部生态环境所产生作用的伦理性约束,是种质资源作为非单一属性自然资源秉承自然法则的内在动力和外在要求。本文阐述了作物种质资源的非生态性偏差并对非生态性偏差进行了生态学分析,提出了“种质运筹”的概念,并论述了种质生态伦理约束的理论内核,从种质生态伦理角度诠释了种质运筹的伦理生态学内涵。     

Modelling of adequate pretwist for obtaining straight timber

Abstract

Wood in general and wooden studs in particular are often distorted owing to uneven shrinkage during the drying process in the sawmill. Twist is often the most detrimental of all types of distortion, and it is caused by spiral grain in combination with variations in moisture content. For sawmills, the objective is to produce dried, straight boards, and one method of dealing with boards with excessive spiral grain is to sort them out and then dry them in a pretwisted position to obtain straight boards after drying. A model using the finite element (FE) method for the simulation of drying twist distortions was first calibrated against laboratory experiments in which boards were dried with and without restraints and pretwists. After the calibration, the FE results were compared with industrial test results for boards that were dried without restraints or with restraints with zero pretwist, i.e. straight restraints. The FE model used an elastic–ideally plastic material model to obtain permanent deformations. The calibration was to set the yield stresses so that there was a good match between FE results and results from the laboratory experiments. The comparison between the industrial test results and the FE results showed that the FE model is capable of realistic simulations of drying boards with and without restraints and presumably also pretwists.     

The influence of warp length on trawl dimension and catch of walleye pollock <Emphasis Type="Italic">Theragra chalcogramma</Emphasis> in a bottom trawl survey

ABSTRACT:   Variations in trawl dimension, bottom contact, and catch with differing warp lengths during walleye pollock surveys conducted by the Fisheries Research Agency were examined. The ratio of warp length to fishing depth (scope ratio) was set at 2.5, 3.0 and 3.5 at depths of 110 m. At a 2.5 scope ratio, the net mouth shape and footgear contact fluctuated, as the trawl door did not contact the bottom. Footgear contact was complete when the scope ratio was 3.0 or more. Walleye pollock, sculpins and flatfishes were the main catch in all tows, and the catch increased with scope ratio. There was no difference in the length frequency of walleye pollock ( n  = 300) captured at 2.5 and 3.0 scope ratio. However, the length frequency at 3.5 was significantly different from that of other scope ratios. These results suggest that at a scope ratio of 3.0 or more, the trawl door will not leave the bottom at any depths. To compliment echo surveys for walleye pollock, a 3.0 scope ratio would be optimal, since the catch data for a 3.5 scope ratio was dissimilar from that of scope ratios.