陕西省丹汉江流域土壤侵蚀经济损失分析

【目的】分析陕西省丹汉江流域土壤侵蚀的经济损失,为水土流失状况评价提供参考。【方法】利用环境经济学的原理,采用市场价值法、机会成本法和影子工程法等,结合最新调查数据,对陕西省丹汉江流域土壤侵蚀造成的经济损失进行估算。【结果】陕西省丹汉江流域每年土壤侵蚀经济损失为112.884亿元。土壤养分流失损失、土壤水分流失损失、土地废弃损失和泥沙滞留、淤积损失分别占96.028%,0.589%,1.528%和1.855%。单位水土流失面积的土壤侵蚀经济损失为42.97万元/km2。各市单位水土流失面积的土壤侵蚀经济损失大小依次为安康市>商洛市>汉中市>宝鸡市>西安市。强度损失的县(区)主要集中在2个区域,即汉江源头的宁强县、略阳县和汉江中游的安康市大部及丹江上游的镇安县、山阳县。【结论】单位水土流失面积的土壤侵蚀经济损失与土壤侵蚀模数之间具有显著相关性,可以作为评价水土流失状况的一个直观、重要的指标。     

四川省西充县土壤侵蚀模数数学模型和侵蚀强度分级的研究

本文根据50余座山塘水库的泥沙实测数据,应用逐步回归分析方法,建立了土壤侵蚀模数数学模型。方程表明影响土壤侵蚀模数的主要因子依次为:陡坡开荒面积、坡度、林地面积和坡耕地面积。文中还根据土壤侵蚀模数及其主要影响因素,使用逐步判别分析力法,对土壤侵蚀强度进行了分级,从而提高了分级的可靠性。该研究成果可应用于四川盆地的高丘中谷及中丘中谷地区。     

北方城市利用绿地滞蓄汛雨的分析与研究

以雨水、绿地和硬化面为研究对象，根据不同降水重现期来分析不同比例集水面面积比例和不同下凹深度的绿地对雨水的入渗和产流系数，通过数据计算和分析，得出比较明显的结果，采用下凹式绿地对滞蓄和入渗雨水效果显著，雨水资源利用的潜力巨大。     

路面结构的动荷载效应及对反分析结果的影响

采用有限元方法分析路面结构的动、静荷载作用响应，并与弹性层状体系理论分析结果比较，表明路面结构的动、静荷载反应有明显的差别。路基不同深度处存在刚性下卧层时，考虑静荷载作用的分析结果有显著的差别，而考虑动荷载作用的分析结果差别不大。在利用动态弯沉盆数据进行路面结构模量反分析时，如忽视动荷载的影响，则反算结果误差很大，甚至不可信。如果按照动力学模型进行路面结构反分析，结果可基本不受下卧层的影响。     

3种散生竹的单根抗拉力学特性

植被在改善生态环境、减少水土流失、涵养水源、固土护坡等方面具有其他工程措施所不能替代的作用.现有研究表明,植物根系对土壤的力学作用,能够稳定土层结构、提高土壤的抗剪强度,是植被实现固土护坡的重要手段(Roering et al.,2003;李绍才等,2006;吕春娟等,2011). 林木根系的抗拉力学特性是影响根系固土护坡效果的重要因素(陈丽华等,2008).植物根系由众多单根构成,单根是发生根土力学作用的基本单元,单根的抗拉能力及抵抗形变能力决定了植株受外力时的整体形变状态及对土壤的约束能力,因此,具有较大抗拉强度的单根构成的根系将有助于土壤的稳固和增强.     

Natural durability of wood of ten native species from northeastern Mexico

Thorn scrub vegetation in Mexico is distributed over 50 million ha, where native tree species are the source of forage, timber, firewood and charcoal. Research describing wood durability of species from this vegetation type has not been fully determined, nor classified according to international standards. Thus, the aim of this study was to determine and classify the natural durability of ten woody species. Their natural durability was determined according to the European Pre-Norm 807, the loss of dynamic modulus of elasticity (MOEdyn) (MPa) was determined and wood mass loss (g) after being exposed to Trametes versicolor and Coniophora puteana fungi. Wood durability was classified according to the European Norm 350-1. Highly significant differences (p<0.001) were found between the durability of woody species. The more durable species with lower MOEdyn lost were Condalia hookeri (57.5%±0.6%), Havardia pallens (58.2%±0.4%) and Acacia schaffneri (58.9%±6.3%). Species with lower mass loss after exposed to Coniophora puteana were Ebenopsis ebano (6.3%±1.9%), Condalia hookeri (8.6%±2.3%) and Cordia boissieri (11.8%±2.3%). E. ebano (7.1%±2.4%), Condalia hookeri (8.2%±2.5%) and Cordia boissieri (11.5%±3.1%) showed the lower mass lost after exposed to T. versicolor. According to European Norm 350-1, three woody species were classified as very durable and durable species.     

Effect of fungal exposure on the strength of thermally modified Norway spruce and Scots pine

Abstract

Thermal modification at elevated temperatures changes the chemical, biological and physical properties of wood. In this study, the effects of the level of thermal modification and the decay exposure (natural durability against soft-rot microfungi) on the modulus of elasticity (MOE) and modulus of rupture (MOR) of the sapwood and heartwood of Scots pine and Norway spruce were investigated with a static bending test using a central loading method in accordance with EN 408 (1995). The results were compared with four reference wood species: Siberian larch, bangkirai, merbau and western red cedar. In general, both the thermal modification and the decay exposure decreased the strength properties. On average, the higher the thermal modification temperature, the more MOE and MOR decreased with unexposed samples and increased with decayed samples, compared with the unmodified reference samples. The strength of bangkirai was least reduced in the group of the reference wood species. On average, untreated wood material will be stronger than thermally modified wood material until wood is exposed to decaying fungi. Thermal modification at high temperatures over 210°C very effectively prevents wood from decay; however, strength properties are then affected by thermal modification itself.     

Stiffness moduli of various softwood and hardwood species determined with ultrasound

Abstract

Comprehensive data sets of the elastic constants are available for only a few European wood species. The goal of this study was to provide stiffnesses for the principal directions and planes for further selected European softwoods and hardwoods, to extend the currently existing data sets. For this purpose, a dynamic technique was chosen: the moduli were estimated on the basis of sound velocity and density measurements. The collected data may be helpful for specialists in the relevant research and practical fields, particularly when stresses and strains of structural elements have to be calculated using modelling approaches.     

Variation in selected solid wood properties of young Pinus patula from diverse sites in the Mpumalanga escarpment area in South Africa

Regression analyses identified ‘Growth Days’ (an index expressing site moisture availability) as the only site variable contributing significantly to the prediction to wood density (R² = 0.57), whereas the model predicting grain angle included only ‘Altitude’ (R² = 0.60). These results surfaced during an investigative study to quantify various sources of variation in wood properties and to quantify the effect of a number of site factors on wood properties of Pinus patula grown in the Mpumalanga escarpment area of South Africa. For this purpose, 10 trees were sampled from each of 17 diverse sites for wood property analyses. The effects of site, distance from the pith and differences between trees within site on wood density, transverse shrinkage, grain angle and dynamic modulus of elasticity were investigated. The site factors considered included a wide variety of soil and climatic factors. The effect of radial distance from the pith and differences between individual trees within sites were highly significant, accounting for most of the variation in wood properties. Although the effects of a number of site factors were statistically significant, they generally explained relatively small but important variation in wood properties among sites. The study not only quantified the effects of important sources of variation on a few key wood properties, but it also revealed that the extent of differences between sites can be explained in terms of some specific site factors. It is envisaged that the results will contribute significantly towards the refinement of current forest site classification systems for improved decision-making with respect to wood quality in intensively managed plantation systems.     

基于小波变换的木材声发射驻波信号特征研究

为研究木材损伤断裂时的声发射(AE)信号所激发的驻波信号特征与木材固有特性之间的关系,采用薄木条折断的方式产生AE源,在小波变换的基础上分析驻波频率,并计算纵波传播速率,依据弹性波理论计算出木材顺纹弹性模量(MOE)。首先,在2种不同长度的木材试件一端分别加工出8根80 mm×10 mm的薄木条,通过外加冲击力折断木条以产生AE源,通过放置在试件端面的2个传感器采集原始AE信号,采样频率设定为500 kHz。然后,根据驻波特性确定原始信号的驻波阶段,进而对该阶段AE信号进行4层小波分解,依据分解后信号的时频域特征析取驻波信号波形。最后,依据驻波产生原理计算纵波传播速率,并结合弹性波理论计算试件的MOE。结果表明,拉伸试验测得樟子松和榉木试件的MOE分别为9.30 GPa和11.63 GPa, 800 mm樟子松和榉木试件通过驻波计算所得MOE分别为9.37 GPa和12.34 GPa,与实测MOE的误差分别为0.75%和5.24%;600 mm的樟子松和榉木试件通过驻波计算所得MOE分别为9.31 GPa和11.81 GPa,与实测MOE的误差分别为0.10%和1.55%。