Effects of temporal aggregation in integrated strategic/tactical and strategic forest planning

Integrated approaches to forest planning lead to large models and there is a subsequent need for a reduction of the number of constraints and variables. One way of achieving this is to aggregate data, either spatially or temporally. In this paper an integrated forest planning mixed integer model that takes into account both long-term strategic and shorter-term tactical forest management decisions is utilised. The study analyses the consequences of temporal aggregation in the strategic part of the integrated model, whereas the tactical part is modelled by a fixed set of years divided into seasons. For reference, analyses are also made using a pure strategic linear programming model. Cases using both equal and variable strategic period lengths are presented, and two case study areas are used. Results indicate that integrated plans, as well as strategic plans, are not particularly affected by the number of equal length strategic periods when more than five periods, i.e. less than 20 year period length, are used. When modelling strategic and integrated problems using variable-length periods, care should be taken to ensure that harvest operations late in the planning horizon get enough timing options to be adequately described.     

Visions and realities for a Wik Forestry Industry on Cape York Peninsula,Australia

The large and unutilised native forest timber resource on traditional Wik land on Cape York Peninsula, Australia, could be managed for timber production to contribute to Wik socio-economic objectives. Wik elders have a set of forestry objectives and envisage that these will be best achieved by a timber industry selling unprocessed logs and woodchips. On the other hand, Balkanu Cape York Development Corporation, a government-funded indigenous community development organisation, anticipate that an industry utilising high-technology equipment and producing dried and dressed finished products including strip-flooring will best satisfy Wik forestry objectives. The Wilderness Society envisages small-scale ‘community development’ activities such as protable sawmilling and niche market furniture manufacture as being appropriate types of forestry activities on Wik land. Goal programming analysis of forest use opportunities indicates that Wik forestry objectives are unlikely to be best satisfied by adopting the timber utilisation options espoused by any one of the stakeholder groups.     

Optimal upgrading of forest road networks: Scenario analysis vs. stochastic modelling

A two-stage stochastic model with binary choice in the first stage has been developed to optimise the upgrading of a real-world forest road network, geographically located in the middle of Sweden. We have compared the model with solutions to the same problem from deterministic scenario analysis. Upgrade policies can be achieved swiftly using both approaches, since the road network is of moderate size. However, a deterministic approach is considerably faster when larger problems are involved. The study here, furthermore, indicates that deterministic scenario analysis provides us with quick, near-optimal solutions to the stochastic model, which are of reasonable good quality. We conclude that the model used here is rather insensitive to uncertainty in critical period length, such as the length of spring thaw, at least when applied to the medium-sized problem presented here. Nevertheless, we strongly recommend the use of the stochastic model whenever possible, since the stochastic and deterministic solutions differ, due to the hedging effect in the stochastic solution.     

南方型杨树人工林最适经营密度的研究

针对湖北省南方型杨树人工林的现实特点,根据31块详细样地资料,以密度二次效应模型为基础,利用动态规划方法,对南方型杨树人工林的最适经营密度进行了探讨,同时,在兼顾单株营养面积和群众栽培习惯,以及造林可操作性的前提下,提出了适合于南方型杨树人工林在不同立地条件下的造林株行距,可为造林施工、林分抚育间伐和综合经营提供科学依据。     

林分择伐空间结构优化模型研究

提出了林分择伐空间结构优化的建模方法 ,突破以功能优化为目标的或称功能优化模型的建模思想局限性 ,并建立了林分择伐空间结构优化模型。该模型集成现代森林经理学理论、生物多样性保护与信息技术 ,并成功地与检查法相结合。模型属非线性多目标整数规划 ,目标函数是基于混交、竞争和空间分布格局的空间结构 ,非空间结构作为主要约束条件。MonteCarlo法是模型求解的可行方法。以吉林省汪清林业局金沟岭林场的一个固定样地为例 ,用本模型进行择伐规划 ,得到具有空间位置信息的最优采伐方案。     

用线性规划方法优化景谷县"山区综合开发‘十五''规划"

景谷县“山区综合开发‘十五’规划”提出 10个主要建设项目 ,以此为基础 ,利用线性规划方法 ,对此10个项目进行优化配置。在不增加投资 ,不增加年生产经费的前提下 ,找出年均产值和年均净收益有明显增长的最佳方案 :停建葡萄种植基地、削减咖啡、柴胶寄主树改造两个建设项目规模 ,保持橡胶、蔬菜、小耳猪、沼气、杨梅基地 5个项目的建设规模 ,适当增加茶叶和芒果基地两个项目的建设规模。     

Effects of two different rearing protocols for Holstein bull calves in the first 3 weeks of life on health status,metabolism and subsequent performance

The aim of this study was to investigate the impact of weight gain of calves within the first 3 weeks of life on health status and subsequent performance. Holstein bull calves were reared either intensively (IR; individual hutches and ad libitum milk feeding for the first 3 weeks of life; n = 24), or according to the established protocol [ER; 4 l milk/day in hutches during week 1 and 720 g/day milk replacer (MR) from day 8 to 21 in a group pen; n = 24]. Water, hay and concentrates were freely available to all calves. From week 4, calves of both groups were housed together in a group pen and fed 720 g MR/day; step‐down weaning was performed between week 5 and 10. Key metabolic blood parameters were analysed on day 2, 12, 21 and 70 of life. After weaning, all animals were fed concentrates and corn silage until slaughter at an age of 8 months. Within the first 3 weeks, average daily weight gain was threefold higher in IR calves in relation to ER calves (1.28 vs. 0.38 kg/day, p < 0.001). Neither incidence nor duration of scouring differed significantly between groups. Starter intake (week 4–10) was higher in IR calves in relation to ER calves (49.7 vs. 38.0 kg/calf, p = 0.006). Serum glucose, urea, albumin and insulin were higher at an age of 21 days in IR calves in relation to ER calves; no differences were obvious at an age of 70 days. Plasma GH and IGF‐I concentrations revealed an uncoupling of the somatotropic axis in ER calves within the first 3 weeks of life. At slaughter, body weight of IR calves tended to be higher than that of the ER calves (320 vs. 309 kg, p = 0.07). In conclusion, intensive feeding and individual housing during the first 3 weeks of life had positive long‐term effects on subsequent performance.     

网络广告语言初探

对近期网络上部分知名网站中出现的网络广告进行研究分析,从网络广告这一特定的文体出发,对网络广告语言的特点进行初步的探讨。     

整体语言教学与研究生英语课上的主题讨论

从审视大学英语教学现状人手,阐述整体语言教学思想,探讨在研究生英语课的教学中,开展主题讨论教学活动,培养语言交际能力的问题。     

基于网络流规划的内燃机曲轴与轴瓦选配方法

提出了一种基于网络流规划的选配方法,将解决网络最大流问题的方法运用到曲轴与轴瓦选配问题的求解中,建立选配网络,以获得曲轴与轴瓦的最优装配组合。并通过应用实例验证了该方法的优越性和可行性,提高了选配效率,并使不适配零件数量为最少。