原条捆离散值量的分布及其数值的计算

本文主要论述运材汽车列车上的原条捆在运输过程中的振动问题,并把该原条捆视为具有质量和刚度沿原条捆长度方向变化的变截面承载梁,从而建立了动力学模型及计算式,在理论计算中具有足够的精确度。     

松岭林业局原条大捆装车工艺及效果分析

本文结合松岭林业局伐区原条装车工艺的实际,对装车工艺类型进行了初步的研究和总结。认为对于资源零星分散、吸引量小的作业伐区,采用一台或二台拖拉机作业的原条装车工艺,最宜配置有伸缩杆的原条挂车运材,靠J—50拖拉机推木成捆的原条大捆装车工艺。它省去了绞盘机和锁放装置,效果好,安全可靠,可操作性强,目前是较为理想的装车工艺。     

原条运材汽车列车随机振动的模拟

本文从研究原条运材汽车列车的随机振动和行驶平顺性出发,提出一种运材汽车列车随机振动的计算机模拟方法。将原条运材汽车列车简化为十自由度五点输入的数学力学模型。以LT110+GT15c型原条运材汽车列车为研究对象,在IBM计算机上进行了模拟计算。通过实地试验表明,模拟计算结果和试验结果能较好的吻合。因此,该数学模型可用来预测运材汽车列车的行驶平顺性,以及运材车辆结构参数对运材汽车列车行驶平顺性的影响,也可对运材汽车列车结构参数进行优化设计。     

东北林区汽车到材贮木场造材台的适宜宽度

本文根据东北林区手提式电动链锯造材的工艺要求,提出了造材台宽度的计算方法,并根据翠峦、大丰、方正、东京城、白河、湾沟等22个林业局的“原条运材野帐”随机抽样结果进行了计算。作者认为,东北林区解放CA-10B和东风EQ-140两种车型原条到材的贮木场,造材台的适宜宽度为10—11m;搭脱拉T-148、斯康尼亚LT-110(15t拖车)和斯康尼亚T112H(15t拖车)4种车型的原条到材贮木场,造材台的适宜宽度为14—15m。     

对东北、内蒙古林区贮木场原条贮备工艺布局的研究

多年来，东北、内蒙主林区利用“冬季黄金季节”进行伐区作业和运输生产，取得良好的经济效益，那种随到随卸随造的生产方式已形成规律。这种突击性的生产方式造成贮木场生产的不均衡，给贮木场生产与管理带来很多问题，直接制约着贮木场的发展。在木材运输到贮木场作业之间设置原条贮备区，用它来缓和到材不均衡和调节贮木场生产的不均衡性，是实现贮木场均衡生产的根本措施。根据东北、内蒙古林区贮木场的现状，结合贮木场生产与发展，对东北、内蒙古林区贮木场原条贮备工艺布局进行了分析研究，并将原条贮备工艺布局分为横向贮备工艺布局、纵向贮备工艺布局和纵横结合贮备工艺布局三种类型，通过详细分析比较，指出了各种原条贮备工艺布局的优、缺点和适用条件。     

原条运材汽车列车承载装置容积尺寸的确定

在东北和内蒙古林区随着原始森林采伐量的减少,次生林和人工林采伐量不断增加,原条的平均材积减小,因而对原条运材汽车列车承载装置容积尺寸产生很大影响。本文探讨了原条的平均材积与原条运材汽车列车承载装置容积尺寸的关系。     

原条捆重量对汽车列车承载梁车立柱的侧压力

计算原条运材车辆承载装置(主要是承载梁的车立柱、拉索和开闭器等装置)的强度和确定原条捆的稳定性时,都需要考虑原条捆的重量对承载装置的侧压力。在原条运材汽车列车运行时,运材车     

原条木材弹性模量的测定

原条木材弹性模量是进行原条运材机械设备的静力学和动力学理论研究时所必需的主要特性参数之一。本文仅就原条木材弹性模量的测定方法问题,进行初步探讨。一、理论依据在研究原条的木材弹性模量时,我们把原条视为在外力P 作用下的双支座梁(图1)。在断面上,梁的弹性横向位移取决于原条(梁)的几何参数、弹性模量E 和剪切弹性模量G。当梁(原条)的跨度与其横断面高度的比值较大时,其横向力对梁的变形影响可以忽略。     

简单中央断面积公式测算原条材积的精度

按照现代的工艺方法,多数的森林采伐企业以原条的形式采运森林。森林采伐部门往往直接运送原条到需材单位的贮木场。扎列盖列尔指出,目前这种方式已相当普遍,予计将进一步发展。因此,迫切需要对原条材积的各种测算方法的精度作以检验。我们曾就简单中央断面积公式测算云杉、白桦、山杨原条单材积(去皮)及其总材积的     

原条运材公路曲线加宽与汽车尾杆的研究

原条运材汽车列车在曲线道路上运行，将引起较大的曲线加宽，一般辕杆式汽车列车的加宽值比分离式汽车列车小，而带有尾杆转向补偿器汽车列车的加宽值较小，其值为分离式汽车列车加宽值的一半，增设尾杆是减少曲线加宽值的有效措施。原条运材汽车尾杆长度可由原条汽车列车通过平、竖曲线工况和汽车车架尾部结构确定，尾杆可采用多节伸缩式结构。     

Browsing Damage on Pine (Pinus sylvestris and P. contorta) by a migrating moose (Alces alces) Population in Winter: Relation to Habitat Composition and Road Barriers

In Scandinavia, moose (Alces alces L.) sometimes cause severe browsing damage to economically-important pine. Moose-vehicle accidents have spurred construction of fences along roads, and these may interfere with moose migration between summer and winter ranges, or the road alone may be a barrier. If this happens and moose build up along roads, landowners may suffer economically. Therefore, this study investigated whether roads, fences or other factors influence the use of young pine stands by moose. Eighty stands along roads in northern Sweden were evaluated in which individually-browsed branches were counted on 9972 pines. Moose browsing was not significantly related to birch (Betula pendula Roth, B. pubescens Ehrh.) density, nor did it differ between pines (Pinus contorta Douglas or P. sylvestris L.). However, increased pine density, site productivity and proximity to a highway were associated with increased browsing. Further large-scale studies are needed to understand moose habitat selection and the effects of roads.     

Effects of Root Freezing on the Physiology and Growth of Picea glauca,Picea mariana and Pinus banksiana Seedlings Under Different Soil Moisture Regimes

The root systems of 2-yr-old Picea glauca, Picea mariana and Pinus banksiana seedlings were submitted to various frost temperatures during an artificial frost to induce different levels of root damage. Frost-damaged and control seedlings were placed in a greenhouse under high and low soil moisture regimes. Seedling growth and physiology were evaluated periodically. Seedling survival was reduced when root damage reached levels of 60-80%. Root systems of all three species showed partial to total recovery by the end of the experiment. In general, root freezing damage caused reductions in seedling growth, with these reductions becoming less significant over time. Root damage had little to no effect on black spruce and jack pine seedling physiology, while white spruce CO 2 uptake decreased with increasing root damage. Shoot nitrogen content of all three species decreased slightly with increasing root damage.     

Decomposition and nutrient loss from prunings of different contour hedgerow species in tea plantations in the sloping highlands of Sri Lanka

Contour hedgerows of multipurpose tree species in the sloping tea lands of Sri Lanka are expected to reduce soil erosion and also add significant amounts of plant nutrients to the soil via periodic prunings. The objective of this experiment was to characterize the biomass decomposition pattern and quantify the amount of nutrients added through prunings of six tree species (Calliandra calothyrsus, Senna spectabilis, Euphatorium innulifolium, Flemingia congesta, Gliricidia sepium and Tithonia diversifolia) currently being used in hedgerows associated with tea. Withered leaf and stem prunings (50 g) were enclosed in 2-mm litter bags, placed at 5-cm depth and retrieved after one, three, six, nine and 12 weeks. Loss of initial dry weight, N, P and K was measured. Single exponential decay function adequately described both dry weight and nutrient loss. Tree species differed significantly in their rate of breakdown with decomposition constants (k) varying from 0.0299 to 0.2006 week⁻¹ for leaves and from 0.0225 to 0.0633 week⁻¹ for stems. Gliricidia showed the highest k for leaves with the rest in the following descending order: Senna > Tithonia ≥ Euphatorium > Calliandra > Flemingia. A similar pattern was observed for loss of all nutrients with Calliandra and Flemingia always having lower k values than the rest. Although N immobilization was not observed, immobilization of P and K was observed during the first week of incubation in some species, particularly in stem prunings. Annual biomass of prunings differed significantly between tree species in the following descending order: Calliandra > Senna > Flemingia > Tithonia > Gliricidia > Euphatorium. Calliandra added the greatest amount of nutrients annually to the soil with Euphatorium adding the least. Calliandra prunings provided the annual total K requirement and 49% of the N requirement of mature tea. However, none of the species provided more than 5% of the P requirement. It is concluded that among the tree species tested, Calliandra and Flemingia are the most suitable for contour hedgerows in tea plantations of this agroclimatic region because of their higher soil nutrient enrichment capacity and slower decomposition rates which would minimize leaching losses. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effects of Seed Weight and Seed Type on Early Seedling Growth of Pinus sylvestris under Harsh and Optimal Conditions

The effects of seed weight and seed type on seedling growth of Pinus sylvestris (L.) were studied by seeding individually weighed orchard and stand seed in different mixtures under harsh (direct seeding in field) and optimal (seeding in nursery) conditions. In the nursery experiment an increase in the seed weight from 3 to 7 mg increased the seedling height by 10-27% and total weight by 27-113%, and decreased the height/diameter ratio by 5-6% after 2 yrs. With elimination of seed weight effects, orchard seedlings were 2% taller than stand seedlings in year 2. Without elimination of seed weight effects, orchard seedlings were 7-13% taller. In the field experiment an increase in the seed weight from 3 to 7 mg increased seedling height by 18-65%, stem volume by 81-274% and the number of top-buds by 23-34% in year 5. After elimination of seed weight effects, orchard seedlings were 7-13% taller than stand seedlings and without elimination of seed weight effects 20-21% taller after 5 yrs. Even after elimination of both seed weight and genetic effects orchard seedlings were 3-9% larger than stand seedlings in the field experiment. In conclusion, the influence of seed weight and seed type on growth traits and slenderness is highly significant and the influence seems to be greater in harsh conditions.     

Potential to harness superior nutritional qualities of exotic baobabs if local adaptation can be conferred through grafting

Baobab leaves form an important part of the local diet in Sahel countries and elsewhere in Africa. Existing leaf nutritional data and agroforestry performance information are based solely on Adansonia digitata L., the baobab of continental Africa. The introduction potential of Adansonia species from the center of diversity in Madagascar and from Australia remains untapped. To assess this potential, the mineral contents and B₁ and B₂ vitamin levels of dried baobab leaves were determined for five-year old trees of A. digitata, A. gibbosa (A. Cunn.) Guymer ex D. Baum, A. rubrostipa Jum. & H. Perrier (syn. A. fony Baill.), A. perrieri Capuron and A. za Baill. grown in an introduction trial in Mali. Nutritional data were evaluated against survival and vigor to identify promising germplasm. Leaf vitamin and crude protein contents were highest in the Madagascar species, especially A. rubrostipa (B₁ 88 mg 100 g⁻¹, B₂ 187 mg 100 g⁻¹, protein 20.7% dry weight). However, the local species far outperformed the introductions in survival, tree height, basal diameter and resistance to termites. We suggest grafting as a way of harnessing the vigor of well-adapted local baobab varieties to the superior nutritional profiles of A. rubrostipa and others. Cross-species grafting tests in Adansonia were successful, thus creating new agroforestry possibilities with different scion/rootstock combinations.     

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.     

Growth of Phlebiopsis gigantea in wood of seven conifer species

Heterobasidion parviporum and Heterobasidion annosum are widely distributed root‐rot fungi that infect conifers throughout Europe. Infection of conifer stumps by spores of these pathogens can be controlled by treating fresh stumps with a competing non‐pathogenic fungus, Phlebiopsis gigantea. In this study, growth of three Latvian strains of P. gigantea and the biological control agent ‘Rotstop’ strain was evaluated in stem pieces of Norway spruce, Scots pine, lodgepole pine, Douglas‐fir, Weymouth pine, Siberian larch and Sitka spruce. The growth rates of one H. parviporum and one H. annosum isolate were also measured in the same stem pieces. The growth rate of P. gigantea varied greatly in wood of different conifer species. It was higher in the three pine species, lower in Norway spruce and lowest in Sitka spruce and Siberian larch, and in Douglas‐fir, this fungus did not grow. The largest area of wood occupied by P. gigantea was in lodgepole pine. Growth of Latvian isolates of P. gigantea in the wood of Pinus and Picea species was comparable to that of the Rotstop isolate. Consequently, stump treatment with local P. gigantea isolates should be recommended. However, our results suggest that Douglas‐fir stump treatment against Heterobasidion by P. gigantea may be ineffective and other stump treatment methods should be considered.     

Stand Structure in Pine,Spruce and Deciduous Forests: A Comparison Between Finnish and Russian Karelia

This study investigated the stand structure in pine, spruce and deciduous forests in the border district of Finland and Russia. A total of 46 mature forest stands was selected as pairs, the members of each pair being as similar as possible with respect to their forest site type, age, moisture and topography. The stands were then compared between the two countries by means of basal areas and number of stems. The proportions of dominating tree species were 2-12% lower, and correspondingly the proportions of secondary tree species higher, in Russian forests. The density of the forest stock was also higher in each forest type in Russia. The forests in the two countries differed most radically in terms of the abundance of dead trees. The amount was two to four times higher in Russian deciduous and spruce forests, and in pine forests the difference was 10-fold. The stand structures indicated that Russian coniferous stands, in particular, were more heterogeneous than intensively managed pine and spruce stands in Finland.     

Growth and Terminal Bud Formation in Picea abies Seedlings Grown with Alternating Diurnal Temperature and Different Light Qualities

The root collar diameter and the height:diameter ratio are of particular importance in container-grown seedlings where a high density in the containers may produce spindly seedlings. Temperature regimes and light quality are known to affect plant growth. The aim of this study was to identify responses in Picea abies (L.) Karst. seedlings grown with light providing different red:far-red ratios and under temperature regimes with alternating day (DT) and night temperature (NT) from negative (DT < NT) to positive (DT > NT) difference (DIF) between DT and NT. Experiments were conducted in controlled environment chambers and in a daylight phytotron. Only limited thermoperiodic responses appeared in P . abies seedlings with respect to seedling height and dry weight accumulation. The formation of terminal buds, however, was clearly delayed in seedlings grown at negative DIF. The results indicate a requirement for day extension light that is high in far-red, to prevent terminal bud formation under natural short-day conditions. An extended study should be conducted to clarify the minimum level of light intensity and the optimal light quality needed to prevent terminal bud formation under natural short-day conditions.     

CAD与建筑设计的关系

本文分析了CAD在设计中引起的正面和负面影响,并进行了系统的阐述,从而使设计者在应用中能够保持客观的态度。