林木种子介电分选试验研究

通过对林木种子介电特性的研究,分析了影响林木种子介电特性的因素和种子介电常数与种子活力之间的相关性。通过林木种子介电分选机分级,分别测试出各级种子的介电常数和活力指数,结果表明,活力高的种子介电常数较小,活力低的种子介电常数较大。     

林木种子在介电分选电场中受力分析

文章讨论了林木种子的介电特性及细胞电生理特性。建立了林木种子的电特性物理模型。研究了种子在电场中的受力机理,分析了种子在异性电极电场中的受力,指出了以往仅从种子宏观线性介电常数解释介电分选机理的不足,为林木种子介电分选提供科学的理论依据。     

常用林木种子品质检验方法

林木种子是林业生产中最基本的物质,林木种子质量好坏直接影响林木的成长发育,开展林木种子质量检验,并通过林木种子质量分析,确定种子使用价值,提高种子质量是林木种子经营中的一项重要工作。林木种子品质包括遗传品质和播种     

林木种子精选技术的引进与创新

通过引进吸收芬兰LANNEN PLANT SYSTEMS公司和瑞典BBC公司生产的林木种子精选设备重力分选和净种分级关键技术,对国内已有林木种子精选设备1QLS-50进行了改进.并结合我国林木种子特点开展集成,创新了适合国内多种林木种子重力分选与净种分级的一体机.通过对国内原有林木种子精选设备、新林木种子精选设备、芬兰...     

提高林木种子生命力和安全贮藏

介绍了种子的贮藏意义、目的和国内外贮藏林木种子的研究及概况。重点论述了影响林木种子生命力的因素,介绍了国家有关种子的法律法规及国家标准《林木种子贮藏》,并对贮藏方法给予具体指导。     

国家工商行政管理总局关于加强林木种子广告管理的通知

各省、自治区、直辖市及计划单列市工商行政管理局:为加强林木种子广告监管,规范林木种子广告的发布,维护林木种子生产、经营者和使用者的合法权益,现就有关问题通知如下:一、林木种子生产、经营者,利用各种媒介和形式发布林木种子广告,应当遵守法律和本通知的规定。林木种子是     

介电式林木种子清选机分选原理的研究

研究了林木种子介电式清选机分选的基本原理、林木种子分选时的运动及受力历程，建立了林木种子分选数学模型，综合分析了各因素对分选性能的影响。试验表明，林木种子介电式分选可按种子的介电特性和物理机械特性进行分选，开拓了林木种子分选新领域。     

对我省林木良种生产与管理的探讨

一、林木种子事业的发展情况建国初期,完全是不加选择地采收利用自然种子。到六十年代初期,种子工作有了加强,1964年,省林业厅设置了种苗站,负责造林用种的催收和调剂。但是到了1960年种苗站解体,从此停止了林木种子的计划调拨,直到1976年才得以恢复,此后林木种子事业有较大的发展,林木种子计划采收量大幅度上升。据统计,1950至1986年全省林木     

林木种子产量的预测

林区产业结构调整后,林木种子也成为了人们喜爱的食品,加强对林木种子的预测有着重要的现实意义,从而介绍林木种子产量的预测的几种方法。     

林木种子贮藏方法

林木种子是林业生产中最重要的基本物质,种子贮藏的好坏直接影响着林木种子的质量,以至影响林木的生长发育。因此,全面掌握林木种子贮藏知识,既是提高林木种子的使用价值,又是提高种子经营所面临的一项重要工作。1　干藏法干藏法就是把种子贮藏在干燥的环境中。这种方法简...     

Modeling the dielectric properties of wood

A method for calculating the complex dielectric permittivity of an anisotropic wood structure at microwave frequencies is presented. A numerical model for describing the 3D wood structure containing fibers, rays, vessels and cracks with changeable dimensions and material composition is built. This model is introduced into an efficient solver that calculates the effective dielectric constant of any 3D structure of dielectric materials. Using our numerical model we succeeded in theoretically reproducing the results of recent measurements of the dielectric permittivity of wood, in various directions and various moisture contents. The qualitative agreement is realistic, reproducing all the trends of the changes in ɛ as the direction of the electric field and the moisture content are varied. The quantitative agreement is practical and reliable for engineering calculations with an average deviation of ±10% in ɛ′ and ±5% in ɛ′′. As microwave processing of wood involves internal temperatures as high as 150°C and pressures of up to 5 atm, the dielectric properties of wood were also calculated with the same numerical model by simulating high internal temperature and pressure. A comparison between the calculated and measured values shows once again how accurate the model reproduces the empirical study.     

Dielectric properties of Simon poplar wood flour/polypropylene composite at oven-dry state

Interfacial compatibility is a crucial factor to the performance of wood-plastic composites （WPCs）. Yet, so far, the coupling mechanisms of WPC have not been completely understood. In order to further clarify the interfacial coupling mechanism, the dielectric constant and dielectric loss factor of Simon poplar wood flour/polypropylene composites without additives at different wood contents were measured at oven-dry state, and parameters and thermodynamic quantities of the relaxation process were also analyzed and calculated. Consequently, an obvious relaxation process based on the reorientation of methanol groups in amorphous region of wood cell wall was observed exactly that its dielectric loss factor peak decreased with the decreasing wood content within the measured range of 50%-100%. With the trend of dielectric relaxation strength, the two changing trends both revealed that the existence of polypropylene could hinder reorientation of methanol groups. Following the decreasing wood contents, the effect of the hindrance on the dielectric properties turned obvious gradually. It elucidated that introduction of polypropylene caused the quantities of hydrogen bonds formed between each methanol group and the groups around it change. The same conclusion could be drawn from the analysis of thermodynamic quantities during the dielectric relaxation progress.     

Dielectric properties of copper-ethanolamine treated Chinese fir (Cunninghamia lanceolata Hook.)

In order to clarify the interaction between copper and wood substances in wood treated with copper containing water-borne wood preservatives, the dielectric constant ε′ and dielectric loss factor ε″ of untreated wood and wood treated with four concentration levels of copper-ethanolamine (Cu-EA) solutions were determined within a temperature range from –100 to 40°C and a frequency range from 100 to 1 MHz. Three dielectric relaxation processes were observed in the ε″ spectrum; among them R-I is based on the reorientation of methylol groups in the amorphous region of wood cell walls and R-II is related to wood extractives. R-III appeared in Cu-EA treated wood, and its magnitude decreases with the concentration of Cu-EA solutions used in this experiment. This relaxation process was considered to be based on the reorientation of copper-ethanolamine-wood complexes in wood cell walls. At low copper retention, the hydrogen in the complex can form hydrogen bonding with adjacent hydroxyl groups, which results in a strong bonding state between copper and wood; at high copper retention, the numerous copper-ethanolamine complexes not only hinder them from forming hydrogen bonding with adjacent wood molecules due to steric hindrance, but also weaken the interaction between wood molecules themselves, which corresponds to reducing ε″ values of both R-I and R-III processes. The results explain the fact of in-creasing copper leaching in wood treated with high concentration copper-based water-borne preservatives.     

Dielectric anisotropy of oven- and air-dried wood evaluated using a free space millimeter wave

To evaluate the dielectric anisotropy caused by wood structure at a millimeter wave frequency of 100 GHz, the dielectric parameters for flat-sawn specimens of nine wood species at 0 and 11 % moisture content (MC) were measured using a free space method devised for reducing the multiple reflections under an electric field of millimeter waves parallel to longitudinal and tangential directions of wood, and those in radial direction were estimated using a conventional approximation theory. The dielectric parameters in the tangential and radial directions were almost identical and constantly smaller than those in the longitudinal direction. All the dielectric parameters increased with wood density and were larger at 11 than 0 % MC. The dielectric parameters in the longitudinal and transverse directions and the dielectric anisotropy between them were well fitted to the regression lines based on a dielectric mixture model composed of pores and dielectric isotropic wood substance, and a parallel capacitor and Lichtenecker’s exponential formulas were employed to represent the dielectric parameters of the mixture in the longitudinal and transverse directions, respectively. It was concluded that the dielectric anisotropy at 100 GHz is caused by the pore alignment and that the dielectric parameters are almost unaffected by anatomical structures, such as the rays. It was also confirmed that the free space method was effective for the measurement of the dielectric parameters for the flat-sawn specimens.     

关于木材介电性质的研究

介绍了国内、外木材介电性质研究进展概况，为进一步探讨木材的介电性质，并对开发和利用木质品工业具有重要的指导意义。     

Applicability of effective medium theory to wood density measurements using terahertz time-domain spectroscopy

The use of an effective medium theory is important when accurately measuring wood density using millimeter and terahertz wave techniques. To confirm the applicability of this theory to the evaluation of wood density, the relative permittivity and dielectric loss of oven-dry flat-sawn specimens of 11 different wood species were measured in a frequency range of 0.15–1.2 THz using a transmission measurement system for terahertz time-domain spectroscopy. A mixture model based on the effective medium theory well explained the density dependence of relative permittivity over the entire frequency range, while it did not fully explain that of dielectric loss, especially for higher frequencies. This indicates that wood scatters the terahertz wave with a wavelength close to the transverse sectional dimensions of the pores in wood in the same way as Mie scattering. It was found from the dielectric loss spectrum of wood substance that the frequency around 0.23 THz was preferable for the nondestructive evaluation of wood.     

Preparation of synthetic wood composites using ionic liquids

Synthetic wood composite films containing cellulose, hemicelluloses, and lignin, the three major components of natural wood, were prepared in a room temperature ionic liquid solvent, 1-ethyl-3-methylimidazolium acetate, [EMIM][Ac]. Various synthetic wood composites were obtained by dissolution of individual wood components together with additives, including polyethylene glycol (PEG), chitosan, and multi-wall carbon nanotubes (MWNTs) in [EMIM][Ac]. The addition of water affords a gel that was dried in either a low humidity environment or under vacuum. Synthetic wood films showed smoother surface textures, higher water resistance, and higher tensile strengths than cellulose films formed by the same methods. Tailor-made synthetic wood composites were also prepared having a variety of desirable properties, including antimicrobial activities, controlled hydro-phobicity/philicity, high relative dielectric constant, and a high degree of cohesiveness.     

种子介电分选机进料滚筒设计计算的理论分析

通过对种子介电分选机分选工艺过程的分析，根据介电分选对种子进料的要求，提出了种子介电分选机进料滚筒设计理论及主要参数的确定方法。通过分析种子的大小和形状特征，提出了进料滚筒系列化产品设计的理论方法。     

Wood dielectric loss factor prediction with artificial neural networks

An artificial neural network that can predict the dielectric properties of wood was developed and tested with experimental data. The network was capable of accurately predicting the loss factor of two wood species not only as a function of ambient electro-thermal conditions but also as a function of basic wood chemistry. This way, an important predictive tool is created that allows optimization of dielectric heating and drying for many wood species without significant experimentation should their chemical composition be known under variable temperatures, moisture contents and electric filed characteristics.     

种子介电分选技术研究新进展

本文讨论了植物种子的电场、磁场效应,肯定了电磁场处理对种子生理生化指标的正效应,它能提高种子活力和发芽率,增大发芽势;对国内外种子介电分选装置与设备的现状和发展作了介绍和分析;对介电分选机理作了进一步的探讨,提出了区别于传统分选技术的关键因素是电极化力。在分析分选电场的构成及计算方法的同时,对作为分选介质的种子在电场中的状态、介电性质以及影响因素作了说明,指出影响种子介电性质的主要因素是种子含水率