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为了控制森林资源的消耗,达到“永续利用”的目的。首先必须了解系统的状态,为此,就要对系统的数量特征进行量测,这是可观测性问题。当我们知道了系统的状态,那么,对系统状态施行控制,就能使系统按人的意图运行,实现“永续利用”的目标,这是可控性问题。若是系统既是可观测的又是可控的,那么,这个系统能否保持常久“永续利用”状态,这是系统的稳定性问题。 作者运用现代控制理论,来判别系统的可观测性和可控制性。利用李亚普诺夫第二法(直接法)来判断系统是否稳定。 相似文献
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将林分经理决策问题作为约束非线性方案而建立了数式。生产系统的内在约束因子是生产函数的一部分,因此可以结合进目标函数。如果没有来自外部的约束因素,那么此问题是一种无约束非线性方案。在解决一个实际问题中,比较了三种非线性规划和离散动态规划的 相似文献
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木质材料膨胀应力的测定 总被引：1，自引：0，他引：1
本试验介绍了单向受约束的木材或木质复合板，在含水量从一平衡状态增加到另一状态时对膨胀应力的测定。在试验过程中，解除对试件的约束，使其松驰，由此将导致试件产生约束膨胀的弹性比例。约束和膨胀可用公式表示来一定变形模量，并可与受体束膨胀的弹性比例一起推算木材的尧曲。在试验中，实木或层压木的膨胀往往受到约束，这此约束来自于外部约束力的作用，或来自木材内部相邻层有不同的吸湿与膨胀特性而引起相互约束的内力。在 相似文献
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邓晓嘉 《中南林业科技大学学报(自然科学版)》2008,28(3)
椭圆约束法是解决不等式约束平差问题的方法之一，但目前尚无有效方法将不等式约束条件转换为椭圆约束，提出了一种较简单可行的转换方法，实现了不等式约束到椭圆约束的转换，且通过实例验证了该方法的可行性． 相似文献
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流塑状淤泥中大型泵房沉井的设计与施工 总被引：1，自引：0，他引：1
在流塑状淤泥中实施沉井工程，极易产生突沉、偏沉、反涌和超沉不止等问题，施工操作极难把握。通过方案比选，设计采用在沉井刃脚下预先打入水泥深层搅拌桩，形成联排桩式的地下连续墙结构，对于沉井井壁形成具有一定强度的承拖和支撑墙体，使沉井在淤泥中下沉的过程成为一个可控的工艺，成功地解决了这一工程难题。 相似文献
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苏颜丽 《林业机械与木工设备》2001,29(2):20-22
通过程序将采用不同方法的建筑机械市场预测组合在一个计算与输出系统内，为动态评估提供了较为理想的方法。同时，重点介绍几种常用预测方法教学模型的建立过程及编程技巧，并论述了图形输出系统的作用、动态参数自适应过程以及参数集设置问题，达到预测图形输出自动化。 相似文献
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Spices constitute an important sub-sector of the economy of Sri Lanka. Most perennial spices are cultivated in agroforestry types of farming systems. A field survey was conducted covering 127 agroforestry farmers in six divisional secretariats in Matale district during the period of October to December 2002. Technical efficiency of spice based agroforestry systems was estimated in order to identify the potential increase in production without incurring additional costs for farm inputs. The factors affecting technical efficiency and constraints and potential of the agroforestry system were also investigated. According to a stochastic frontier production function using a Cobb–Douglas model, hired labour, organic fertilizer, inorganic fertilizer, land size, and soil conservation measures showed significant positive effects on the agroforestry production. The mean technical efficiency of the spice based agroforestry systems was 84.32%. According to the inefficiency model the efficiency increased significantly as a result of farm visits by extension officers, participation in farmer training, less sloping lands, more experience, and higher diversity of the agroforestry system. Technical efficiency decreased, however, with higher education level of the farmer and with higher off-farm income. Unsustainability of the agroforestry system is seen as a result of a␣range of constraints related to productivity, market, technology and institutions. 相似文献
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In the água de Gato Watershed on the island of Santiago, Cape Verde Islands, 51 farmers were surveyed regarding their attitudes
and knowledge of agroforestry. The farmers identified eight constraints to agroforestry implementation, with virtually all
indicating that a source of loan funds was the major concern. Space or land constraints and availability of tree seedlings
were identified as constraints by 94% and 88%, respectively. Despite these concerns, 92% of the farmers expressed a willingness
to adopt or improve agroforestry practices in the watershed, with 73% expressing a willingness to establish fruit trees, 53%
willing to establish trees or shrubs for fuelwood, and 16% willing to plant trees for shade. 相似文献
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A general classification of agroforestry practice 总被引：1，自引：0，他引：1
Fergus L. Sinclair 《Agroforestry Systems》1999,46(2):161-180
Present classification schemes confuse agroforestry practices, where trees are intimately associated with agricultural components
at a field scale, with the whole farm and forest systems of which they form a part. In fact, it is common for farming systems
to involve the integration of several reasonably discrete agroforestry practices, on different types of land. The purpose
of a general classification is to identify different types of agroforestry and to group those that are similar, thereby facilitating
communication and the organized storage of information. A new scheme is proposed that uses the ‘practice’ rather than the
‘system’ as the unit of classification. This allows an efficient grouping of practices that have a similar underlying ecology
and prospects for management. A two stage definition of agroforestry is proposed that distinguishes an interdisciplinary approach
to land use from a set of integrated land use practices. Four levels of organization are recognized through analysis of the
role of trees in agricultural landscapes: the land use system, categories of land use within systems, discrete groups of components
(trees, crops, animals) managed together, and functionally connected groups of such discrete practices in time and space.
Precedents for this form of analysis are found in the literature and it conforms with generally accepted methods of systems
analysis. Classification of major types of agroforestry practice proceeds primarily according to the components involved and
the predominant usage of land. A secondary scheme further classifies these in terms of the arrangement, density and diversity
of the tree components involved.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
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随着无线通信技术的高速发展,人们对GPRS技术研究也越来越深入,从而激发人们对于远程无线控制技术的热情.研究TMS320F2812在抽油油井的电机控制以及油井系统远程控制,解决远程抄表以及远程控制的多个问题,充分利用DSP的方便快捷、高效的特点.给出该系统的设计思想：通过传感器对油井数据进行采集,经过DSP进行数据处理,然后将数据传输给DTU,再由DTU发送给数据库,通过界面将数据显示出来,针对得到数据进行监测并反馈给油井以实现远程控制.该系统能够提供良好的实时监测与控制,有很好的发展前景. 相似文献
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Adoption of rubber-integrated farm-livelihood systems: contrasting empirical evidence from the Indian context 总被引：2，自引：0，他引：2
This paper examines the influence of important socio-economic, institutional/policy level factors in determining the adoption/non-adoption
of rubber-integrated farming systems in traditional and non-traditional rubber-growing regions in India. The empirical analysis
is based on a survey of rubber growers in the traditional rubber regions of Kerala (south India) and the non-traditional rubber
regions of Assam, Meghalaya, and Tripura (north east India). In sharp contrast to Kerala, where smallholder responses toward
adoption of rubber-integrated farming systems have been lukewarm, the emerging rubber economies (most of which are tribal
communities) of north east (NE) India have shown interest in adopting rubber as an integrated farming system along with pre-existing
land-use livelihood activities. The study clearly demonstrates contrasting empirical evidence of adoption of rubber-integrated
farm-livelihood systems in the rubber-growing regions in Kerala and the NE states in India. The contrasting scenarios of adoption
of rubber-integrated farming systems are mostly explained by region-specific factors dominated by socio-economic, institutional
variables, and policy-level constraints, as also revealed by multivariate analysis. By and large, the findings of the study
have significant bearing on the socio-economic outcomes and the existing institutional development paradigm underlying the
rubber-development programmes introduced in India since independence. The study shows that the existing institutional arrangements
and policies, which evolved historically to facilitate rubber area expansion in the traditional regions (including Kerala),
have been highly instrumental in perpetuating rubber farming as a monoculture system. However, such an institutional mechanism
proves to be highly redundant in the context of the NE states which are otherwise diverse in terms of integrated farm-livelihood
systems and shifting cultivation. 相似文献
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当前,我国人造板产业落后、产能过剩,资源浪费和环境污染严重,人造板供应链上下游发展不匹配,缺乏有效的沟通与协调。文中结合人造板产业实际,界定了由人造板制造商和人造板加工商组成的人造板绿色供应链系统,进而在增值税即征即退和环境税政策背景下,分别构建考虑产能与工艺约束以及突破工艺约束的人造板绿色供应链收益分享契约协调模型,运用经验数据进行对比数值分析并提出了相应的管理启示。 相似文献
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Coconut is a major commercial crop of Sri Lanka. Growing a number of other crops in association with coconuts is a widespread practice in all coconut-growing areas of the country. The rationale for the practice is that other crops can profitably be grown between or under the coconuts during the different growth stages of the palms and thus the overall productivity of the land under this long-duration crop can substantially be increased. The paper gives a concise account of the practice in Sri Lanka indicating the crops most commonly grown as intercrops, arrangement of different crops and early research results on the productivity of the intercrops and their effect on coconuts. Adequate supplies of water and labour are the two major inputs needed for the success of the system. Drought, lack of funds, price instability, lack of technical know-how on intercrop management and problems of timely availability of inputs are the major constraints experienced by farmers in expanding intercropping. Research on both biological and socio-economic aspects is needed to overcome these constraints and extend this potentially attractive system. 相似文献
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Improving shifting cultivation in Southeast Asia by building on indigenous fallow management strategies 总被引：4，自引：0，他引：4
Shifting cultivation continues as the economic mainstay of upland communities in many countries in Southeast Asia. However, the conditions that historically underpinned the sustainability of rotations with long fallows have largely vanished. The imperative to evolve more permanent forms of land use has been exacerbated by rapid population growth, gazettement of remnant wildlands into protected areas, and state policies to sedentarize agriculture and discourage the use of fallows and fire. There are many compelling examples where shifting cultivators have successfully managed local resources to solve local problems. Technical approaches to stabilizing and improving productivity of shifting cultivation systems have not been notably successful. Farmer rejection of researcher-driven solutions has led to greater recognition of farmer constraints. This experience underlined the need for participatory, on-farm research approaches to identify solutions. The challenge is to document and evaluate indigenous strategies for intensification of shifting cultivation through a process of research and development. This process involves identification of promising indigenous practices, characterization of the practices, validation of the utility of the practice for other communities, extrapolation to other locations, verification with key farmers, and wide-scale extension.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献