多节点加载预应力锚索格构梁室内模型试验研究

目前,计算格构梁的力学模型中,多采用弹性地基梁法进行计算,而对于边坡上的格构梁,受坡角和锚索倾角的影响,梁底面摩擦力的存在使得格构梁受力变得复杂。因此,在计算中采用合理的计算模型真实地反映格构梁的受力状态显得尤为重要。通过对多节点加载预应力锚索格构梁室内模型试验的研究,认为受边坡坡角和锚索倾角的影响,格构梁底面存在的摩擦力对格构梁的变形和受力状态有较大影响,并对实测结果与理论计算结果进行了对比分析,认为采用考虑摩擦的Winkler弹性地基梁模型能很好地反映格构梁的实际受力状态,更适合于工程应用。     

糖用甜菜物理特性试验分析

摘 要：对收获期"KWS3148"甜菜进行田间状况和物理参数的测定,确定了甜菜种植模式。利用SPSS统计软件,得到了甜菜主要物理几何参数指标的变化区间和频率分布,明确了甜菜在土壤中的相对位置,建立了收获期甜菜的几何物理模型。通过甜菜的起拔力对比测试,得到了土壤自然状态下甜菜所需起拔力为（365±196）N,两侧松土后甜菜所需起拔力为（259±176）N。甜菜的起拔力峰值分别与块根质量、块根截面椭圆的短轴尺寸在0.01水平（双侧）上显著相关,块根质量、块根最大截面尺寸、块根长度在0.01水平（双侧）上双因素显著相关。甜菜起拔力与甜菜品种和土壤的状况相关,与甜菜根系关系不大。试验结果：块根地上高度为（60±24.4）mm,块根横向最大尺寸为（120±28）mm,根块长度为（202±45.3）mm,块根质量为（1198±530）g,甜菜的楔角为（15.3±2.14）度及甜菜的几何模型,可为甜菜的杀秧、收获等机具的设计、研发提供理论基础。     

煤矸石燃烧过程中的动力学特性研究

采用非等温热重分析法研究煤矸石燃烧动力学过程，通过热重（ＴＧ）、差热（ＤＴＡ）、微商热重（ＤＴＧ）实验，提出煤矸石挥发分析出过程的特性参数和反应动力学方程，测算了反映煤矸石燃烧放热特性的差热峰面积指标，并分析探讨了氯化钠等碱金属化合物对煤矸石燃烧动力学过程的影响规律。     

应用平方根肥效方程确定肥料用量应注意的问题

在平方根肥效方程Ｙ＝ａ＋ｂｘ＾０．５＋ｃｘ（Ｃ＜０）基础上建立增产效应方程Ｙ＝ｂｘ＾０．５＋ｃｘ（ｃ＜０）。研究发现增产效应方程中存在Ｒｉ＝２０ω＾０．５－ω等式关系。Ｒｉ＝（Ｙ／Ｙｍａｘ）．１００，称为最增产率。ω＝（ｘ／Ｘｍ）．１００，称最大配肥率，Ｘｍ为Ｙｍａｘ时的Ｘ值。由关等式关系的存在，从而提醒我们：运用平方根方程确定施肥量时，一要注意工作曲线范围内应当包含足够的实测值，二要注意该肥效方     

陕西土壤磷等温吸附特性及其测定条件的研究

以陕西省主要农业土壤为材料，研究选定了土壤磷等温吸附的测定条件：磷添加浓度０－７０ｍｇ／Ｌ，水土比１０：１，平衡时间６天，平衡介质０．０１ｍｏｌ／Ｌ ＫＣｌ。以此条件测定土壤磷等温吸附线，结果表明，Ｌａｎｇｍｕｉｒ方程和Ｆｒｅｕｎｄｌｉｃｈ方程能满意地描述陕西土壤磷的吸附特性；由Ｌａｎｇｍｕｉｒ方程获得的土壤磷最大吸附量（Ｘｍ）、磷吸附反应常数（Ｋ）及磷吸附最大缓冲容量（Ｍｂ）均呈现为黄褐土〉Ｌｏ     

GIS技术在通用土壤流失方程中的应用

通用土壤流失方程（USLE）传入我国后，国内各级研究机构加以深放研究与适用性探索。结合遥感（RS）与地理信息系统（GIS）技术，实现以USLE为构式的区域土壤流失遥感监测，已在我国多处地区进行了尝试应用与实际应用。基于泉州市1996年度水土流失遥感监测所采用的技术路线，阐述了USLE方程因子的GIS生成以及土壤流失量的GIS实现依据。     

鸡生长轴相关基因的研究进展

摘要：神经内分泌生长轴，又称脑垂体生长轴，在动物的生长发育过程中发挥重要的调节作用。下丘脑分泌的生长抑素(somatostatin, SS)和生长激素释放激素(growth hormone releasing hormone, GHRH)、垂体分泌的鸡生长激素(chicken growth hormone, cGH )、靶器官（如肝脏）分泌的鸡生长激素受体(chicken growth hormone receptor, cGHR)和胰岛素样生长因子-Ⅰ(insulin-like growth factor-Ⅰ, IGF-Ⅰ)，以及下丘脑-垂体-靶器官作用通路构成了鸡生长轴的基本内容。介绍了近几年来鸡生长轴的各激素（因子）及其受体的基因研究，以及相互间的作用机制，以进一步探索家禽的生长调控机理。     

低坡变截面架空层对流对粮食平房仓屋面隔热性能的影响

设置架空层能有效减少粮食平房仓屋面的辐射得热。与普通架空层相比,变截面架空层通过气流加速,可有效改善粮仓“闷顶”问题。为了研究变截面架空层几何和运行参数对传热性能的影响,基于粮食平房仓实际尺寸,建立了具有等截面架空层、变截面架空层和未加架空层屋面的3种粮食平房仓缩尺模型（1∶28）,对恒定通风量条件下3种架空层设置模式的屋面隔热性能进行了对比试验研究。结果表明：等截面模式下,最优工况可将粮堆表层温度控制在25℃以内,外界升温后粮堆表层升高1.75℃;变截面模式下（渐缩比0.500）可将粮堆表层温度控制在24℃以内,外界升温后粮堆表层升温仅0.50℃。基于试验数据利用FLUENT软件进行数值建模,进一步研究了体现变截面架空层气流通道收缩性的渐缩比对表征对流的无量纲努谢尔特数Nu和瑞利数Ra的影响,数值计算结果表明在采用变截面架空层时,局部隔热性能在渐缩比为0.500时最佳,研究结果可为粮食平房仓屋面隔热改造提供理论依据和设计参考。     

三道梁流域综合治理的经验

北四家乡三道梁流域位于辽宁省北票市北部,是全国水土保持重点治理区二期工程、大凌河中下游一期工程列入的重点流域。三道梁流域列入重点治理后,乡党委、政府把该项目列入议事日程,并抓住这一契机,发动群众,依靠群众,扎扎实实地开展水土流失综合治理,５年取得明显...     

污灌区土壤对Cr（Ⅵ）的吸附和还原作用研究

通过静态吸附实验和土柱淋溶实验，研究了污灌区土壤对Ｃｒ（Ⅵ）的吸附和还原作用。结果表明，土壤对Ｃｒ（Ⅵ）的吸附符合Ｌａｎｇｍｕｉｒ吸附等温方程。进入土壤后，Ｃｒ（Ⅵ）被土壤固相组分吸附和还原为Ｃｒ（Ⅵ），从而降低了Ｃｒ（Ⅵ）对农作物的危害性。     

A new approach for modelling vertical stress distribution at the soil/tyre interface to predict the compaction of cultivated soils by using the PLAXIS code

Soil compaction by agricultural machines can have adverse effects on crop production and the environment. Different models based on the Finite Element Method have been proposed to calculate soil compaction intensity as a function of vehicle and soil properties. One problem when modelling soil compaction due to traffic is the estimation of vertical stress distribution at the soil surface, as the vertical stress is inhomogeneous (non-uniform) and depends on soil and tyre properties. However, uniform stress distribution at the soil/tyre interface is used to predict the compaction of cultivated soils in most FEM compaction models. We propose a new approach to numerically model vertical stress distribution perpendicular to the driving direction at the soil/tyre interface, employing the FEM models of PLAXIS code. The approach consists of a beam (characterised by its geometric dimensions and flexural rigidity) introduced at the soil surface and loaded with a uniform stress with the aim to simulate the action of a wheel at the soil surface. Different shapes of stress distribution are then obtained numerically at the soil surface by varying the flexural rigidity of the beam and the mechanical parameters of the soil. PLAXIS simulations show that the soil type (soil texture) modifies the shape of the stress distribution at the edges of the contact interface: a parabolic form is obtained for sand, whereas a U-shaped is obtained for clay. The flexural rigidity of the beam changes the shape of distribution which varies from a homogenous (uniform) to an inhomogeneous distribution (parabolic or U-shaped distribution). These results agree with the measurements of stress distributions for different soils in the literature. We compared simulations of bulk density using PLAXIS to measurement data from compaction tests on a loamy soil. The results show that simulations are improved when using a U-shaped vertical stress distribution which replaces a homogenous one. Therefore, the use of a beam (cylinder) with various flexural rigidities at the soil surface can be used to generate the appropriate distribution of vertical stress for soil compaction modelling during traffic.     

Converting Australian tropical rainforest to native Araucariaceae plantations alters soil fungal communities

Native rainforest tree plantations are increasingly viewed as potentially important for high value timber production and provision of a range of ecological services in tropical and subtropical areas. In order to determine the extent to which conversion of rainforest to native Araucariaceae plantation influences soil fungi, we compared soil fungal communities under native rainforest and 73-74 year-old Araucaria bidwillii, Araucaria cunninghamii and Agathis robusta plantations at Gadgarra State Forest, Queensland, Australia. Following direct extraction of DNA from soil, terminal restriction fragment length polymorphism (T-RFLP) analysis of rDNA internal transcribed spacer (ITS) regions was conducted. Ordination analysis of the T-RFLP data revealed significant separation of the fungal communities according to forest type along the first canonical axis, with the native rainforest samples separating from the three Araucariaceae plantations along the second axis. Overall, the most abundant ITS sequences in clone assemblages from the four forest types were Ascomycota, followed by Basidiomycota, Zygomycota and Chitridomycota, however their relative importance varied in individual forest types. The results indicate that conversion of tropical rainforest to monoculture plantations of native trees can significantly alter soil fungal diversity.     

玉米根茬收获系统的有限元模态分析与试验

针对研制的集铲挖和脱土于一体的玉米根茬收获系统,为进一步优化该系统的作业性能,采用有限元模态分析与试验模态分析相结合的研究方法,获得了该系统的前20阶的固有频率,以及各主要工作部件的典型振型。研究结果表明：系统的1～4阶（8.5～29.6?Hz）模态主要表现为升运链的整体弯振;5～14（44.1～124?Hz）阶模态表现为各主要功能部件的横梁及主轴的弯曲、扭转振动;15～20阶模态（135～190?Hz）则主要表现为各功能部件的末端振颤,上述系统模态属性,可为系统结构振动特性的描述及整机作业性能的优化提供依据。     

A procedural approach for studying the radiation regime of infinite and truncated foliage spaces. Part II. Experimental results and discussion

A procedural approach for estimating the realisations of the penetration function was presented as a series of executable, (semi)independent and interfaceable abstractions in an earlier paper. In the present paper, the approach is validated against the turbid medium model for case of both parallel and nonparallel beam radiation extinction in an infinite stand. The predictions of the approach are in good agreement within a cumulative relative error of 4% in the case of parallel beam radiation extinction. The predictions regarding the probability of penumbra compared with the more comprehensive theory of Denholm (1981a, b) are satisfactory in foliage spaces at low values of foliage area index. Finally, to illustrate the flexibility of the approach, the statistical characteristics of the beam radiation regime in a truncated foliage space are investigated, where besides mean values of the penetration function higher order moments like the variance, the autocorrelation coefficient and the sample spectrum in space and time continuum are computed.     

Collaborative Analysis of Wheat Endosperm Compressive Material Properties

The objective measurement of cereal endosperm texture, for wheat (Triticum spp. L.) in particular, is relevant to the milling, processing, and utilization of grain. The objective of this study was to evaluate the interlaboratory results of compression failure testing of wheat endosperm specimens of defined geometry. Parallelepipeds (bricks) and cylinders were prepared from individual soft and hard near‐isogenic wheat kernels and compressed in two orientations (parallel and perpendicular to the long brush‐to‐germ axis). Compression curves were used to derive failure stress, failure strain, work density (area under the curve), and Young's modulus. In all five laboratories, the ability to delineate hard from soft wheat endosperm material properties was quite high. Four laboratories compressed endosperm bricks in the same orientation, on edge; texture class (soft vs. hard) was consistently the greatest source of variation in analysis of variance models (F‐values from 417 to 1401, Young's modulus and failure stress, respectively). Failure stress was found to be the best overall means of measuring the difference in what is known in the vernacular as wheat hardness. Across laboratories, the absolute measures of all four material properties ranged on the order of about two‐ to threefold from low to high, although within a laboratory, results were highly consistent. Laboratory by texture class interaction was deemed to be of minor importance. Brick size and moisture content within the ranges tested were not major sources of variation, and cylinders prepared from endosperm produced results similar to those obtained from bricks. The results suggested that wheat endosperm might express some level of anisotropic behavior, as specimens compressed in the kernel orientation parallel to the long axis failed at lower strain and stress values, with lower work density, when compared with kernel orientation perpendicular to the long axis. A key feature of interlaboratory variation was identified as being instrument rigidity, a subject of ongoing research. In conclusion, the preparation of endosperm specimens of defined size and shape, in combination with compression failure testing at low moisture content (<18%), is useful for objectively delineating the phenomenon known as hardness. The study presented here will advance our ability to objectively measure cereal grain texture and the material properties of endosperm.     

步行轮式气垫车平顺性研究

分析了步行轮式气垫车气垫系统悬架起伏刚度的影响因素和步行轮、半步行轮对步行轮式气垫车振动的激励特性。文章还介绍和分析了步行轮式气垫车平顺性试验研究结果。     

Chiral stability of synthetic pyrethroid insecticides

Synthetic pyrethroids are chiral compounds consisting of multiple stereoisomers. Evaluation of enantioselectivity in environmental fate and ecotoxicity requires analytical methods that preserve stereoisomer integrity during analysis. In this study, we characterized the stability of stereoisomers from four commonly used pyrethroids, cis-bifenthrin (cis-BF), permethrin (PM), cypermethrin (CP), and cyfluthrin (CF), during gas chromatography (GC) analysis and sample preparation. Stereoisomers of cis-BF and PM were found to be stable, but those of CP and CF were unstable, under heat or in water. Isomer conversion occurred only at the alphaC in CP or CF, causing the analyte stereoisomer to convert to an epimer. At a GC inlet temperature of 260 degrees C, about 9% conversion occurred for CP and CF. In organic solvents and sterile water, stereoisomers of cis-BF and PM were stable, but slow isomer conversion was observed for CP and CF in water at ambient temperature. However, isomer conversion for CP and CF was relatively insignificant (2-3%) when the GC inlet temperature was kept at < or = 180 degrees C or when on-column injection was used. Isomer conversion at the alphaC in water suggests that abiotic processes may also contribute to enantioselectivity observed in the environment for pyrethroids with the asymmetric alphaC.     

柔性杆齿滚筒脱粒机理

传统的水稻脱粒是采用刚性脱粒齿,由于打击力大,造成水稻籽粒破碎或内部破损,从而影响水稻种子的发芽率或大米加工的成米率。为进一步探索降低水稻脱粒破碎或破损率的方法,设计了一种脱粒原理类似刚性杆齿脱粒的柔性杆齿脱粒滚筒,对其脱粒力进行了研究。分析表明在滚筒转速一定的情况下,采用柔性杆齿脱粒增加了与稻穗的接触时间,减少了冲击力,柔性杆齿打击力小于刚性杆齿。脱粒对比试验结果表明,直径小于刚性杆齿的柔性杆齿脱粒滚筒能适应水稻脱粒要求,脱粒指标中破碎率显著低于刚性杆齿滚筒,未脱净率、含杂率、脱粒率和断穗率均与刚性杆齿脱粒滚筒相近。     

A simple wet chemical extraction procedure to characterize soil organic matter (Som): 2. Reproducibility and verification

Abstract

In a previous communication in this journal, a fractionation scheme of soil organic matter (SOM) was presented (1). The goal of this paper is to discuss the reproducibility and verification of this procedure with an expanded data set of 150 samples. Litter compound analysis (LCA) is appropriate to detect small differences in the decomposition degree at a quantitative level which are not detectable with SOM morphology. In contrast, humic compound analysis (HCA) is not appropriate to characterize SOM with regard to quantitative data, because the detected carbon (C) (C recovery rate <800 mg/g TOC) reflects only parts of the total SOM. In addition selected, SOM fractions are determined with both extraction procedures. When counting C as polysaccharides in the LCA and as fulvic acid in the HCA, this gives recovery rates of much more than 100% (>1,200 mg/g TOC). These errors induce both an under‐ or an over‐estimation of C within the combination of the litter and humic compound analyses (LCA+HCA) and the conversion to 100% should not be used. Because of the method problems and limited chemical information provided with HCA, we propose using LCA and additional analytical instuments (e.g. NMR, pyrolysis) to further characterize structures in the non‐litter substances of the SOM pool.     

Mechanical properties of paddy stem with reference to lodging bending moment-curvature diagram

The mechanical properties of cereal crops as related to lodging, breaking strength, rigidity, elasticity, buckling load etc. have been studied by various workers (1～8). These properties were analyzed based on the theory of elastic body conforming to Hook's law. In the previous paper (9) the authors pointed out chat in the process of deformation of paddy culm, starting from slightest bending up to the point of break of the culm, two properties were observed, namely, elasticity and viscoelasticity. These properties can be clearly defined and investigated by the analysis of bending moment-curvature diagram (9) of stem. This paper deals with this diagram in relation to differences in varieties and fertilizer treatments.