On the activation energy of diffusion of water in wood

Summary The diffusion equation for water in wood is expanded in terms of temperature and moisture gradient on the assumption that the driving force for the diffusion of water in wood is the partial pressure of water vapour. An analytic expression is then developed for the activation energy of diffusion in terms of enthalpy and entropy changes associated with the sorption process. The expression is compared with another published curve and some similarity was observed.Symbols C water concentration, kg/m³ - D diffusion coefficient for water vapour in wood with vapour pressure as the driving potential, kg/ms Pa - D_c diffusion coefficient for water vapour in wood with water concentration as the driving potential, m²/s - D_c a constant value of D_c, m²/s - E activation energy of diffusion, J/kg - F flow density, kg/m² s - f h/l - h specific enthalpy, J/kg - L l/R T - l latent heat of vapourization of free water, J/kg - l_s latent heat of vapourization of sorbed water, J/kg - p partial pressure of water vapour, Pa - p_s pressure of water vapour at saturation, Pa - R specifc gas constant for water, J/kg K - r relative humidity - s specific entropy, J/kg K - w dry basis moisture content - x length coordinate, m - a constant temperature equal to 6,800 K - -/ln r - _w density of wood (dry mass/moisture volume) at a given moisture content, kg/m³ - s/R - L style as 2 lines above - free water relative to sorbed water The author is grateful to the Editorial Board in relation to the use of (4)     

提高石膏刨花板耐老化性能的进一步研究

本文研究了矿渣硅酸盐水泥对石膏水化性能的影响;水泥加入量与石膏硬化浆体力学强度的关系;石膏中掺入3～12%的矿渣硅酸盐水泥时,对石膏刨花板静曲强度和耐水性能的影响;石膏刨花板表面涂建筑涂料后,对其耐老化性、耐水性以及静曲强度的影响。     

浅谈灌南县如何推进乡村绿化建设

分析了当前灌南县乡村绿化的现状和存在问题,对如何推进灌南县乡村绿化建设进行了探讨,并提出了相应的建议。     

A note on the relationship between electrical properties and thermal conductivity of woods

Summary Wood thermal conductivities (from the literature) are directly related to the electrical properties of the same species (measured by the author) in the density range occurring in nature.The correlation coefficient between permittivity and conductivity was found to be higher than that between conductivity and density for various species of wood. Variation in the chemical components of woods results in variation in the thermal conductivities of woods.The author wishes to thank Dr. M. N. Carroll and Mr. D. G. Miller of this Laboratory for profitable discussions.     

A critical note on a long-running debate in forest economics

Hiley's 1927 paper in the first issue of Forestry argued thateconomics was not just a theoretical discipline, but affectedforestry practice. The long rotations desired by proponentsof forest rental ignored forest capital. Soil rental gave arational basis for choosing silvicultural regime and costingdeviations from the most profitable option. Heavy thinning offeredcompromise between outcomes desired by forest and soil rentalschools. Although Hiley's ideas have influenced British forestry,the forest rental caseis still argued. Development of monetizingtechniques has undermined Hiley's belief that non-market benefitswere ‘imponderable’. It remains importantto separatefour issues: choice of discount rate, treatment of non-marketeffects, construction of performance criteria, and selectionof silvicultural regime.     

A STUDY ON ENERGY OF ARTIFICIAL DAHURIAN LARCH COMMUNITY

By means of calorimetry measurement,the caloric values of various components,the standing crop of energy,not energy production and energy conversing efficiency of an artifi-cial dahurian larch community at Laoshan Plantation Experimental Station of Maoer Shan For-est Farm in the eastern part of northeast China were determined and studied in the present paper.The result of the experiment were as follows:(1)caloric value varied with plant species and plant organs,in general,the order of caloric value was tree,shrub and herb,and for different organs,was leaf, branch,trunk(stem),bark and root.(2)The standing crop of energy of larch community and tree layer were 269.719×10~(10)J/ha.and 264.440×10~10J/ha.respectively.Theree xisted different distributions of energy in various components and different layers.(3)Net ener-gy prduction of larch community and its tree layer were 264.346×10~8J/ha.a and 243.678×10~8J/ha.a respectively.To the photosythetical active radiation on the stand,its energy con-versing eff     

A study on the winter hardiness and the energy resources of overwintering ofScambus sp

In Honghuaerji region,Scambus sp. is an effective natural enemy of the mongolian scotch pine cone weevil (Pissodes validiirostriis Gyll). The percentage of parasitism on larvae of the mongolian scotch pine cone weevil amounts to 20 to 30% commonly, sometimes as high as 45% or more, thus significantly regulating the weevil population. But the high mortality of larvae ofScambus in winter, which according to the surveys (conducted in 1986, 1987, and 1988) were 24.00%, 51.03% and 47.70% respectively, seriously influenced the natural suppression effect. In order to reveal the cause of winter death of this natural enemy, from 1990 authors studied the winter physiological indices, cold hardiness and overwintering protection ofScambus larvae, in the purpose of providing scientific basis of usingScambus in biological control.     

集约经营综合利用提升效益--进一步推进四川竹产业发展调研报告

我省竹产业发展经过“十五“期间的快速发展,2005年竹林面积比2000年增加了27．7万hm^2竹产业总产值增加了48亿元,竹产业的一、二、三产业发展已初具规模,全省竹产业已跃上了一个具有一定规模的发展平台,在我省建设完备的森林生态体系和发达的林业产业体系中发挥着越来越重要的作用,竹产业已成为我省一些地方农村经济、社会发展的支柱产业。党的十六届五中全会提出了加强建设社会主义新农村、构建社会主义和谐社会,要求统筹城乡经济发展、千方百计增加农民收人,要求建设资源节约型、环境友好型社会,为我省竹产业发展提出了新的要求,指明了新的方向。如何把党中央的要求落实到我省竹产业发展中,促使我省竹产业再上台阶,已成为我省竹产业发展的重要问题。     

钛与不锈钢扩散连接工艺的研究

本文阐述了钛与不锈钢连接的现状以及必须采用中间过渡夹层的原因，并对工业纯钛TA2和不锈钢1Cr18Ni9Ti的真空扩散连接进行了试验研究。定性分析了温度，压力和时间对接头性能的影响。指出了工业纯钛TA2和不锈钢1Cr18Ni9Ti扩散连接的最佳工艺参数。     

能源植物膏桐的生产与研究现状

膏桐（Jatropha curcas L.）又称小桐子、麻疯树,作为一种多用途油料植物,具有耐贫瘠、耐干旱、病虫害少、速生、含油率高等优点,目前已被世界各地广泛种植和研究,但还需要进一步研究生产管理技术来确保膏桐产业的长远发展,尤其是不同气候条件下管理和施肥体系。作者力求全面探述国内外生产和研究状况,并指出了膏桐产业发展中需要关注的问题。     

Soil physical properties degrade further on skid trails in the year following operations

Short-term recovery of soil physical properties on skid trails was investigated upon cessation of skidding operations and 1 year later. Bulk density and porosity were assessed at three levels of traffic intensity and two slope gradients. Compared to undisturbed areas, bulk density increased, total porosity and macroporosity decreased, and microporosity increased in the compacted areas immediately after skidding. In all cases, changes were significantly greater when traffic intensity was higher and when slopes were steeper. Surface soil compaction did not show any recovery over the 1-year period, illustrating the persistent effects of compaction on soil structure. In fact, surficial compaction further increased and macroporosity further decreased after 1 year of recovery, compared to immediately after skidding. While these changes may reflect inherent small-scale site variability or differences in soil moisture content at times of sampling, direct negative physical impacts on newly exposed soil (such as by raindrops), in addition to the loss of organic matter after canopy removal and skidding, likely delayed any physical recovery, particularly on heavily trafficked trails on steeper slopes. These results raise serious concerns about long-term resilience to traffic on forest soils and indicate the necessity to properly retire skid trails to avoid further soil degradation as trails age.     

Research on the effect of microwave pretreatment on moisture diffusion coefficient of wood

Based on the pathway of moisture diffusion in wood below FSP, an improved moisture diffusion model has been proposed. The theoretical solution of the mathematic model shows that the diffusion coefficient for microwave pretreated wood was increased no more than 3% compared with that of wood without being treated even under extreme condition. Experiments indicate that the pit membrane structure can be effectively destroyed during microwave pretreatment, but the moisture diffusion coefficient can not be significantly improved. In practice, the effect of microwave pretreatment on moisture diffusion coefficient can be ignored. The drying rate of wood during the sequent conventional drying can not be significantly improved by microwave pretreatment.     

A note on a possible source of error in maximum effective pore radius determination in conifer wood

Summary With coniferous timbers, if the fluid system selected for use in maximum effective pore radius determinations has too high an interfacial surface tension, the pressure differential required for the determination can be large enough to cause partial or total pit membrane displacement. Under these circumstances, the results of the method must be interpreted with care.The authors wish to acknowledge the encouragement of Professors Roche and Matthews     

加快林业发展 推进社会主义新农村建设

1林业在社会主义新农村建设中具有不可替代的作用森林是陆地生态系统的主体,是自然生态系统中结构最合理、功能最完善的生物库、资源库、能源库和蓄水库,具有调节气候、涵养水源、保持水土、防风固沙和降低污染等多种生态功能。以森林为工作对象的林业承担着建立完备的森林生态     

Nonisothermal diffusion model based on irreversible thermodynamics

Summary A comparison is made between a nonisothermal diffusion model derived from irreversible thermodynamics and three other equations that have been applied to several series of nonisothermal experiments.     

关于进一步加强林业科技推广工作的思考

总结了湖南林业科技推广工作十几年来所取得的成就，分析了存在的问题。为实现省厅提出的科技推广工作目标和克服束缚林业科技推广工作的困难，作者从进一步建立健全林业科技推广服务体系等五个方面探讨了湖南林业科技推广工作今后努力的方向。     

穆棱林业局西洋参业的再发展

通过对西洋参药用价值、保健功能、市场前景和穆棱林业局所具条件的概述。阐明了穆棱林业局西洋参业再发展的必要性、可行性、规模及投资收益程度。     

生物农药发展现状与加大研发力度的探讨

通过对生物农药发展现状及发展的机遇与前景的分析,进而对加大生物农药研发力度问题作出了探讨。     

时间分数阶扩散方程的并行高效Legendre谱方法

研究了两类时间分数阶扩散方程的并行高效Legendre谱方法,分数阶导数分别代替标准的扩散方程的二阶空间导数和一阶时间导数。空间方向采用高效的Legendre谱方法,时间方向使用了基于Fourier级数展开的Laplace数值逆,并对其参数进行了优化。给出了两类时间分数阶扩散程的数值格式和数值例子,与其他方法比,该方法数值结果更优。