分形多孔介质孔道网络模型的构

采用压汞试验获得实际多孔介质的微观结构参数.以冻干马铃薯为例计算了孔隙分形维数,结果表明冻干马铃薯结构具有显著的分形特性.运用位似变换理论、分形理论、Voronoi图以及马铃薯的特征参数等,构建出与马铃薯结构参数相对应的二维分形孔道网络模型.构建的网络模型考虑了影响多孔介质干燥的孔道微细结构特征,模型参数能够很好地反映多孔物料的微观结构.且获得了合理的分形维数.     

多孔介质粗糙表面分形-蒙特卡罗传热研究

为了探究多孔介质在微观粗糙表面结构下的传热,建立了关于粗糙表面的二维、三维模型。基于分形理论,通过与蒙特卡罗法和傅里叶定律的结合,推导出了有效传热系数的表达式。该理论模型通过相关数据的代入计算,讨论分析了粗糙表面面积分形维数和孔隙率对有效传热系数的影响。研究发现孔隙率与有效传热系数呈负相关关系,面积分形维数与有效传热系数也呈负相关关系。该理论研究多孔介质粗糙表面的细微结构的传热,对于具有微观结构的粗糙表面物质传热具有一定的研究参考价值。     

孔喉结构薄膜热质传递的分形模型

运用分形理论,建立了气体在膜介质中的流速模型,基于流速模型推导出气体通过膜介质的扩散系数模型和换热系数模型。分析了膜介质的孔喉比、迂曲分形维数、面积分形维数、孔隙率和固体颗粒直径等微观结构参数对膜介质传热传质的影响。结果表明,孔喉微观结构参数对膜介质的传热传质过程具有重要影响。扩散系数和换热系数与孔隙率、固体颗粒直径和面积分形维数呈正比。喉道直径一定时,固体颗粒直径增大,膜介质内部孔隙直径增加,流动阻力变小,膜介质的传热传质能力增强;扩散系数和换热系数与孔喉比、迂曲分形维数呈反比;固体颗粒直径一定时,孔喉比增大,喉道直径变小,迂曲分形维数增大,面积分形维数减小,流动阻力变大,膜介质的传热传质能力减弱。     

多孔介质物料热风干燥孔道网络模型研究进展

多孔介质物料热风干燥广泛应用于工业干燥各个领域。孔道网络模型干燥理论是一种完全离散化的方法,能建立多孔介质微观结构特征与宏观传递现象之间的联系。常用的孔道网络模型包括二维规则孔道网络模型、二维分形孔道网络模型和非固结双尺度孔道网络模型等。但是对于孔道网络模型的研究,目前还存在人工构造多孔介质网络的困难,模型参数还不能准确描述实际多孔介质物料以及研究结果不能完全反映自然多孔介质干燥过程等问题。今后应进一步探索网络构建新方法,在模型构建中考虑更多的多孔介质物料特性,以期更准确地描述自然多孔介质实际的干燥过程。     

多孔介质物料热风干燥研究进展

多孔介质物料的热风干燥是许多工农业生产部门的重要生产工序,其干燥效能直接影响产品质量.多年来,国内外研究人员在多孔介质物料热风干燥领域进行了大量的研究工作,发展了多孔介质孔道网络模型,分析了分形多孔介质传热传质规律,建立了众多针对具体干燥对象的干燥模型,研制了多种多孔介质湿含量在线检测装置等.为此,从理论分析、数值模拟和实验研究3个层面综述了以上多孔介质物料热风干燥的研究进展,并对其发展趋势进行了展望.     

杨凌包气带深层黄土颗粒分形特性的实验研究

通过对包气带深层黄土土壤样品颗粒组成的分析,研究了土壤颗粒体积分形维数与土壤各粒级含量的关系.同时利用实测的土壤水分特征曲线,拟合得到其分形模型中的孔隙大小分形维数,最后对颗粒体积分形维数与拟合的孔隙大小分形维数的关系进行了对比研究.结果表明:体积分形维数介于2.577～2.748之间,且随包气带层深度的增加分形维数呈减小趋势;体积分形维数与0.5～0.25 mIn、0.02～0.002 mm颗粒含量呈显著负相关,与0.25～0.05 mm、＜0.002 mm颗粒含量呈显著正相关,所建立的多元回归方程拟合的体积分形维数相对误差限为0～0.42%,具有较高的精度;同一质地的颗粒体积分形维数与土壤水分特征曲线分形模型中的孔隙大小分形维数呈良好的线性关系.     

基于分形理论的马铃薯干燥过程水分输运特征分析

基于马铃薯内部结构的异质性和分布随机性,利用分形特性模拟了在干燥过程中的水分输运过程。结果发现结合收缩和分形现象的模型呈无收缩现象连续介质模型更接近实验值,且分形模型的内部压力分布没有出现像连续模型呈比例逐层下降的现象。包括收缩的分形模型与孔的连通性、孔隙率、面积分形维数和孔最小最大直径比值成正比,与迂曲分形维数和迂曲度成反比。     

基于分形理论的结合面法向接触阻尼与损耗因子模型

基于结合面法向阻尼耗能机理及MB接触分形修正模型,提出了一种结合面法向接触阻尼模型及结合面间阻尼损耗因子模型.仿真结果表明,分形维数在较小范围内,法向阻尼与法向总载荷呈微凹弧非线性关系,且随着法向总载荷和分形维数的增大而减小,随着分形尺度参数的增大而增大;分形维数在较大范围内,法向阻尼与法向总载荷呈微凸弧非线性关系,且随着法向总载荷和分形维数的增大而增大,随着分形尺度参数的增大而减小.而结合面损耗因子与法向总载荷呈微凹弧非线性关系且随着法向总载荷的增大而减小,随着分形尺度参数的增大而增大,分形维数在较大值范围内,结合面损耗因子随其增大而增大.     

路表不平的分形特征

介绍了分形及分形维数的基本概念,用分形方法对道路表面进行了分析,并提出了表观分形维数的概念。分析表明,道路表面具有不规则性和统计自相似性,即每一部分都可视为整体缩小尺度之后的相似形。以现有的道路表现功率谱数据为例,根据频谱方法对其分形进行计算,表明测度（功率谱）与尺度（频率）在双对数坐标上呈线性关系,即具有标度不变性,呈现明显的分形特征。道路表现越平坦,其分形维数值越高。表观分形维数结合分形维数的     

基于分形理论的枸杞干燥过程水分输运的特征分析

为了探讨枸杞在热风干燥过程中不同层数、不同温度变化对水分扩散规律和干燥速率快慢的影响,文章采用了分形理论研究了枸杞堆积形成团聚体的内部孔隙的分形特征,并且通过实验测得枸杞在温度为40℃、50℃、60℃、70℃时的含水率和干燥速率,得出不同分形维数、不同温度的含水率和干燥速率随时间的变化关系图。实验中发现,温度一定的情况下,枸杞摆放的层数越多,内部孔隙连通性就越差,迂曲分形维数就越大,干燥所需的时间越长,有效扩散系数越小;层数一定的情况下,即分形维数一定时,干燥速率随温度的升高而升高,含水率的变化与时间成指数关系。该研究为进一步改良枸杞干燥的设备与工艺提供了参考。     

Overland water and salt flows in a set of rice paddies

Cultivation of paddy rice in semiarid areas of the world faces problems related to water scarcity. This paper aims at characterizing water use in a set of paddies located in the central Ebro basin of Spain using experimentation and computer simulation. A commercial field with six interconnected paddies, with a total area of 5.31 ha, was instrumented to measure discharge and water quality at the inflow and at the runoff outlet. The soil was classified as a Typic Calcixerept, and was characterized by a mild salinity (2.5 dS m⁻¹) and an infiltration rate of 5.8 mm day⁻¹. The evolution of flow depth at all paddies was recorded. Data from the 2002 rice-growing season was elaborated using a mass balance approach to estimate the infiltration rate and the evolution of discharge between paddies. Seasonal crop evapotranspiration, estimated with the surface renewal method, was 731 mm (5.1 mm day⁻¹), very similar to that of other summer cereals grown in the area, like corn. The irrigation input was 1874 mm, deep percolation was 830 mm and surface runoff was 372 mm. Irrigation efficiency was estimated as 41%. The quality of surface runoff water was slightly degraded due to evapoconcentration and to the contact with the soil. During the period 2001–2003, the electrical conductivity of surface runoff water was 54% higher than that of irrigation water. However, the runoff water was suitable for irrigation. A mechanistic mass balance model of inter-paddy water flow permitted to conclude that improvements in irrigation efficiency cannot be easily obtained in the experimental conditions. Since deep percolation losses more than double surface runoff losses, a reduction in irrigation discharge would not have much room for efficiency improvement. Simulations also showed that rice irrigation performance was not negatively affected by the fluctuating inflow hydrograph. These hydrographs are typical of turnouts located at the tail end of tertiary irrigation ditches. In fact, these are the sites where rice has been historically cultivated in the study area, since local soils are often saline-sodic and can only grow paddy rice taking advantage of the low salinity of the irrigation water. The low infiltration rate characteristic of these saline-sodic soils (an experimental value of 3.2 mm day⁻¹ was obtained) combined with a reduced irrigation discharge resulted in a simulated irrigation efficiency of 60%. Paddy rice irrigation efficiency can attain reasonable values in the local saline-sodic soils, where the infiltration rate is clearly smaller than the average daily rice evapotranspiration.     

瓦房店市水果生产标准化发展研究

瓦房店市是我国重要的水果生产基地,在国内水果生产领域占有重要地位。随着水果市场化的不断深入,如何满足和适应国内外市场需求成为瓦房店市水果生产的关键问题。从瓦房店市水果生产实际出发,阐述了实施水果生产标准化的必要性,提出了发展水果生产标准化的具体措施。     

金谷子耐旱TG118引种试种及推广应用

对引进的谷子新品种金谷子耐旱TG118进行品种比较试验和多点试种。结果表明：该品种抗旱、耐瘠、适应性强,稳产、高产、抗病抗风抗倒伏强,品质优良,粮草兼用,种植简单,省工易管;一般产量在6000kg/hm2以上,比当地主栽品种增产20%以上。最高产量达9450kg/hm2,适于在辽西北地区推广应用。     

对《种子法》存在问题的探讨

《种子法》是我国种植业第一部法律。自实施以来,为依法加强种子管理提供了有力的法律支撑,促进我国种子产业发生翻天覆地的变化。但随着依法管理工作的深入和种子产业的快速发展,《种子法》及配套规章的一些问题逐步显现出来。对《种子法》及配套规章存在的问题进行深入分析,对需要进一步补充的章节以及需要调整的内容进行深入探讨,以求更加完善和明确。     

Review of the Egyptian experience in implementing land drainage projects

About 30 years have passed since the Government of Egypt embarked on implementing a series of large scale drainage projects. At present, about 3.8 million acres have been provided with drainage systems on the basis of systematic pre-drainage investigations and designs. The target is to provide drains in approximately 6.4 million acres in the Nile Valley and Delta.The implementation of the subsurface drainage system is carried out by the public sector and private contractors under direct supervision of governmental regional departments. The implementation process depends on many factors related to the drainage material, machinery, manpower, site requirements, farmers and organizations involved. Problems and constraints are sometimes challenging, however, the annual rate of implementation has gradually increased to 170,000 acre/year.This paper discusses the different aspects involved in the implementation process of drainage systems. The development in materials, machinery and construction technologies will be reviewed. Institutional and management factors are going to be also considered.     

和谐社会理论建设的几点哲学思考

在新世纪,面对机遇和挑战,党的十六大把“社会更加和谐”作为全面建设更高水平的小康社会的一个重要目标。中国人素有社会和谐的理想;西方人自古也向往社会和谐;借鉴东西方两种和谐社会思想的经验、教训,构建社会主义和谐社会理论。     

A European irrigation map for spatially distributed agricultural modelling

We present a pan-European irrigation map based on regional European statistics, a European land use map and a global irrigation map. The map provides spatial information on the distribution of irrigated areas per crop type which allows determining irrigated areas at the level of spatial modelling units. The map is a requirement for a European scale assessment of the impacts of irrigated agriculture on water resources based on spatially distributed modelling of crop growth and water balance. The irrigation map was compiled in a two step procedure. First, irrigated areas were distributed to potentially irrigated crops at a regional level (European statistical regions NUTS3), combining Farm Structure Survey (FSS) data on irrigated area, crop-specific irrigated area for crops whenever available, and total crop area. Second, crop-specific irrigated area was distributed within each statistical region based on the crop distribution given in our land use map. A global map of irrigated areas with a 5′ resolution was used to further constrain the distribution within each NUTS3 based on the density of irrigated areas. The constrained distribution of irrigated areas as taken from statistics to a high resolution dataset enables us to estimate irrigated areas for various spatial entities, including administrative, natural and artificial units, providing a reasonable input scenario for large-scale distributed modelling applications. The dataset bridges a gap between global datasets and detailed regional data on the distribution of irrigated areas and provides information for various assessments and modelling applications.     

粉质仪和拉伸仪在面粉生产中的应用

在介绍粉质仪和拉伸仪结构和原理的基础上,探讨了粉质曲线中吸水率、形成时间、稳定时间、弱化度和评价值等指标与面粉品质的关系,以及如何根据拉伸曲线中面团最大拉伸阻力、延伸度和拉伸曲线面积等指标来评价面团品质,并结合生产实际,概述了粉质仪和拉伸仪在面粉生产中的作用。     

农村信息化服务的现状及建设措施

分析当前我国农村信息化服务的现状,提出加强农村信息化服务的新举措。     

车辆ABS控制算法的研究及探讨

对现代汽车的ABS控制算法作了一些简单的介绍,同时指出了它们的一些缺陷,相应地提出了几种对ABS的其它控制方法并加以探讨,其中着重论述了ABS门限值控制算法中参考车速的确定方法和基于附着系数的控制算法。