种植芦荟,发展农村经济

Aloe,a perennial evergreen thick herb of Lily family with over 80 kinds of medical contents and health protection capabilities of increasing immunity,anti radiation,anti cancer,anti inflammation,delay of decrepit,lowering of blood pressure,and others.The use of aloe has extended to dyestuff,metallurgy,textile and agricultural chemicals,and is of bright prospect of development and utilization.Because of its strong drought enduring ability and high economic value,aloe is of great significance to the economy development,poverty alleviation and improvement and harness of loess in the areas which is suitable to aloe plantation and is suffered from severe soil and water loss.Therefore,knowledge of the biological characteristics,varieties and their cultivation,reproduction and processing of aloe are introduced in the paper.     

基于变权信息熵改进TOPSIS法的水资源承载力评价——以陕西省地级城市为例

[目的]对陕西省各地市水资源承载力(WRCC)状况进行评价,为区域水资源的合理利用和分配提供科学依据。[方法]在引入信息熵进行指标权重计算的基础之上,采用变权法对权重指标反常现象进行修正。依据计算所得权重,采用改进TOPSIS法建立模型。并结合2012年陕西省各地市涉及水资源承载力的相关数据,对陕西省各地市的水资源承载力综合状况评价中进行了应用。[结果]得出了陕西省各地级市的水资源承载力情况排序为:安康市宝鸡市商洛市延安市汉中市渭南市榆林市铜川市咸阳市西安市。发现西安市水资源承载力不足情况最为突出。[结论]利用变权信息熵改进TOPSIS模型计算水资源承载力,操作简便、实用性强,在该领域应用前景广泛。     

青海湖芨芨草干草原浅层土壤温度和导温率的基本特征

通过解析芨芨草(Achnatherum splendens)干草原原生植被生长季中期5、10、20、40、60和80cm 6个土层连续监测的土壤温度资料,探讨其生长季土壤温度和土壤导温率的基本特征。结果表明:芨芨草干草原表层(<20cm)土壤温度日变化明显,遵循正弦波动规律;20-40cm为正弦波动和线性振荡的过渡层,40cm以下无显著日变化。土壤温度日变化振幅(A)和相位(φ)随土壤深度(z)增加分别呈现几何级数衰减(A=4.60e-6.74z,R2=0.93)和线性延迟(φ=6.14z+7.67,R2=0.95)模式;表层土壤温度对脉冲式降水表现为渐变式响应并出现同温层;典型晴天下土壤导温率(κ)随土壤深度增加而指数升高(κ=2×10-7e4.21z,R2=0.92),34.7cm土层的土壤温度日变化与5.0cm反相,而土壤温度日变化恒温层为86.0-102.0cm土层。     

基流分割方法研究进展

[目的]针对基流分割理论和方法所存在的争议,对基流分割研究进展进行综述,为今后基流研究提供参考。[方法]采用综述方法较为系统地阐述了基流的定义,对基流分割方法进行了回顾和分析,包括图解法、数值模拟法、水量平衡法以及同位素和水化学法等。[结果]重点研究和评述了基流分割方法的理论基础、优缺点以及适用范围,提出当前基流分割方法研究所存在的问题及其未来研究的趋势。[结论]迄今为止,尚未找到一种得到普遍认同的基流分割方法,还需进一步加强基流分割理论与方法研究,形成统一、完善的理论体系,科学、合理地确定基流,并探讨基流变化特征及其驱动因子,这将是未来基流研究的重要内容。     

王家岭煤矿风井场地边坡稳定性分析与评价

针对王家岭煤矿风井场地边坡稳定性问题,调查分析了该边坡的工程地质条件和影响边坡稳定性的因素.在用赤平投影法对边坡稳定性进行定性评价的基础上,采用极限平衡法(Sarma法)和有限元法对整个场地典型边坡剖面进行了不同工况条件下的稳定性分析,并给出了安全稳定系数.结果表明,二者分析结果基本一致,验证了所用方法的合理性.对类似工程问题的评价、治理有一定的借鉴和指导意义.     

振动能量流的计算方法研究

振动能量流法是研究柔性结构振动的重要方法,能量流的计算是其中的关键步骤,传统的基于模态叠加的导纳能量流计算法计算精度不高,处理复杂结构时计算过程复杂,该文提出了基于波动理论的导纳能量流计算方法和基于有限元分析的能量流计算方法。通过对一具体模型计算对比,表明波动计算法精度最高,模态叠加法存在模态截断误差,而有限元法在划分网格细时也能保证计算精度。有限元法是一种适合于各种复杂结构的分析方法,值得在工程上推广。     

项目驱动法在高职PHP程序设计课程中的应用研究

PHP程序设计是高职高专计算机相关专业的一门专业核心课程,结合实际的教学经验,围绕高职课程目标和定位,在教学方法、方式和考核方面提出一些自己的做法,将项目驱动教学法引入课程教学中。结果表明,此方法能更好地激发学生的学习兴趣和学习积极性,提高了教学效果。     

园林绿化施工中树林移植与养护问题的研究

移植是园林绿化种植施工中难度较大的栽植工程,费工费时,因此确保树木移植成活率就显得十分重要。而确保移植树木成活率重要的方法即树木移植后的养护工作,如何做好后期的养护工作是主要研究探讨的内容。     

锥形配流副弹流润滑模型与数值计算方法

为求解高压条件下锥形配流副的润滑模型,该文提出了综合应用有限差分法、液阻网络法和约束最优化复合形法的二元二目标复合形法,研究表明了模型解的存在性和唯一性,并通过实例应用二元二目标复合形法对润滑模型进行了求解。实例结果显示,平衡油槽的无量纲压力随工作压力的变化保持恒定,配流间隙随工作压力增大呈线性减小,而偏心率在工作压力范围内均略小于0,最小为-0.036。研究为锥形配流副弹流润滑特性的分析及其设计提供了参考。     

Sodium Hydroxide Direct Distillation: A Method for Estimating Total Nitrogen in Soil

Soil total nitrogen (N) concentration is commonly measured by Kjeldahl and combustion methods. In this study, a method based on determination of ammonium (NH₄)‐N produced by steam distillation of the soil sample with sodium hydroxide solution (NaOH‐DD) is developed and evaluated for estimating soil total N concentration. The method was evaluated using two sample sets: (A) 44 samples collected from contrasting land uses in central Iran and (B) 344 samples collected from contrasting arable soils across Canada and Maine, USA. Based on this experiment, 10‐min distillation of 5.0 g soil with 20 mL 12.5 M NaOH were selected as the optimum conditions. The NH₄‐N released by the NaOH‐DD method was highly correlated with total N concentration in the sample sets A and B (r = 0.79 and 0.94, respectively). The NaOH‐DD method provides a simple, rapid means of analysis with reduced measurement cost and better health and safety precautions than the traditional Kjeldahl method. Current address for Mehdi Sharifi: Nova Scotia Agricultural College, Department of Plant and Animal Science, Truro, Canada.      

Comparison of two methods for assessment of aggregate stability of agricultural soils in southeast Norway

Abstract

Soil aggregate stability is a crucial property regarding soil erodibility. However, results from different stability-assessment methods differ. The objective of this study was to compare two such methods on a set of southeast Norwegian agricultural soils. Traditionally, a raindrop-impact method has been used to determine the soil aggregate stability of Norwegian soils. Here, a more common, less destructive method was also used, a wet-sieve method using one sieve. Two soil fractions were studied, aggregates of 0.6–2 mm and 2–6 mm in diameter. The soil samples were chosen to give a wide range in clay content (5.7–68.0%) and soil organic matter (1.7–8.5% SOM). Using the wet-sieve method two different pre-treatments were performed; either using air-dried aggregates or slowly pre-wetted, air-dried aggregates. The aggregate stability found using the wet-sieve method gave generally higher stability values for soil aggregates 2–6 mm in diameter than using the standard raindrop-impact method (21% higher on average). Soils with high contents of silt and very fine sand (0.002–0.2 mm), however, were found to be more susceptible to destruction due to raindrop impact than to wet-sieving. Hence, using the wet-sieve method, the silty soils were ranked as more stable than by using the standard raindrop-impact method. Aggregate stability was positively correlated with the SOM and Al-oxides content and negatively correlated with the silt and the very fine sand content (0.002–0.02 mm). Using slowly, pre-wetted air-dried aggregates, which induce rebonding and reduce the effect of slaking, resulted in distinctively higher stability values than using air-dried aggregates in the wet-sieving method (34% higher on average). The wet-sieve method is less laborious and more widely used elsewhere, but the lower disruptive effect on silty soils should be kept in mind when using this method.     

基于穷举法的雨水管渠设计流量计算方法研究

[目的]找出雨水管渠设计流量常用计算方法——面积叠加法和流量叠加法中存在的问题,对计算方法进行改进,使雨水设计流量计算结果更加合理。[方法]从下游管段暴雨强度的计算入手,对流量叠加法进行改进,同时提出基于穷举法的最大流量法。[结果]实例计算表明,除起始管段外,改进后的流量叠加法的各管段设计流量均小于面积叠加法,最大流量法各管段设计流量较面积叠加法平均增长7.0%,最大增长13.0%。[结论]运用最大流量法对雨水管渠进行设计,计算结果更合理,更安全,对缓解城市内涝具有重要意义。     

砾石覆盖度测量方法研究

地表砾石是各种水文和侵蚀等过程综合作用的产物,是土壤退化和生态系统恶化的一个标志;反过来这些砾石也影响到侵蚀的各个过程。分别利用视点框架法和照相法对不同粒径样本下(2~6mm,6~20mm,20~60mm)的砾石覆盖度进行了测量,对比分析了不同砾石覆盖度测量方法对其精度的影响。结果表明,采用两种测量方法观测砾石覆盖度均能达到一定精度,视点框架法测量的砾石覆盖度相对误差变化范围为-7.84%~80.86%,平均相对误差为15.69%,照相法测量的砾石覆盖度相对误差变化范围为-48.35%~9.89%,平均相对误差为-11.69%。随着砾石覆盖度的增加,视点框架法测量的相对误差绝对值表现为减小。视点框架法测量的最大相对误差均值的绝对值随着抽样次数的增加而减少,当抽样次数达到约30,相对误差减小的趋势减缓。     

农用地定级因素法与修正法比较分析

以广东省惠阳市农用地定级研究为例，对因素法和修正法两种定级方法进行比较分析，论述了因素法和修正法的定级过程、应用特点、适用范围，以及定级成果的合理性。通过空间区分度(分异性)分析、空间重叠度(相同性)分析、级差收益分析和农用地等、级、价衔接分析，从不同方面论证了两种定级方法的可行性，认为修正法定级结果较符合当地实际。     

基于因素法和修正法的农用地综合定级研究

以陕西省神木县农用地定级研究为例,论述了因素法和修正法两种方法的定级过程,通过空间重叠度分析,有效地将两种方法进行综合,确定农用地级别,并对定级结果进行了验证,定级结果符合当地实际,该研究成果以期为加强农用土地资源管理与土地资产管理打下良好基础。     

黄土颗粒分离方法试验研究

以延安新区I期工程的马兰黄土为研究对象,分别采用筛分法、离心机法和静水沉降法对其进行颗粒分离试验,并利用激光粒度仪对3种分离方法的试验结果进行跟踪对比,以研究最适用于黄土颗粒的分离方法。结果表明:筛分法主要适用于粒径大于0.05mm的黄土颗粒的分离,对粒径小于0.05mm的黄土颗粒分离效果较差,筛分结果的可靠性偏低。离心机法由于自身的局限性且受影响因素较多,试验结果的可靠性较低;静水沉降法主要适用于粒径小于0.05mm的黄土颗粒的分离,颗粒分级效果显著,试验结果的可靠性较高,且试验精度满足要求,但对于粒径小于0.002mm的颗粒分离时间较长。通过3种试验方法的对比可知,在对黄土进行颗粒分离试验时,宜采用筛分—沉降相结合的分离方法,对于大于0.05mm的颗粒宜采用筛分,对于小于0.05mm的颗粒宜采用静水沉降法。     

Relationship between Olsen P and Ammonium Lactate–Extractable P in Portuguese Acid Soils

The soil phosphorus (P) test in Portugal is based on extraction with ammonium lactate (AL) at acidic pH. Because this test is rarely used in other countries, it is desirable to see whether the AL-P values correlate with the more commonly used P tests. In this work, we compared AL-P with bicarbonate-extractable P (Olsen's method) for a group of 48 samples from Portuguese acidic soils differing widely in P status. Despite their contrasting composition, both reagents extracted phosphate from the same sources, albeit in different proportions. Both Olsen P and AL-P were strongly correlated with resin-extractable and dilute electrolyte-desorbable P, which are respectively related to the soil contents in phytoavailable P and P that can be released to runoff or drainage water. Olsen P and AL-P were strongly correlated (R² = 0.870), the correlation became stronger when three overfertilized soils were excluded (Olsen P = 2.35 + 0.45 AL-P; R² = 0.908; P ≤ 0.001, n = 45). No correlation was observed for a group of soils recently fertilized with Gafsa phosphate probably because the acidic AL reagent dissolved residual calcium phosphate, thus overestimating the soil content in desorbable P. On the basis of the present results and the AL-P-based fertility classes used for fertilizer recommendation purposes, Olsen P–based fertility classes were tentatively proposed for Portuguese acidic soils.     

小型拖拉机土壤压实的有限元预测

农业土壤的基本特征是松软和经常处于非饱和状态，土壤体积密度与含水率既是主要参数又是影响压实的重要因素，且在不断地变化。为了进行有效田间土壤压实管理，根据具体土壤特性，采用一个二维的模型，用有限元方法进行土壤压实预测。模型考虑了应力路径、初始土壤体积密度和含水率等，将土壤体积密度视为平均主应力和最大自然剪切应变的非线性函数，可预测小型拖拉机在非饱和土壤上通过时引起土壤体积密度的变化及应力分布情况等。在华北轻壤土的试验证明，模型具有良好的拟合效果。     

Comparison of Conductimetric and Colorimetric Methods with Distillation–Titration Method of Analyzing Ammonium Nitrogen in Total Kjeldahl Digests

The distillation–titration method (DTM) is a standard procedure used by most laboratories to measure ammonium-nitrogen (NH₄-N) in the total Kjeldahl N (TKN) digests of various kinds of agricultural and environmental samples. These samples may have TKN contents ranging from less than 100 ppb to as high as percentage levels. However, the DTM procedure generally leads to a very low throughput because it is labor intensive and time-consuming. At the current practical quantitation limit (PQL) of 300 ppb established at the Feed and Environmental (FEW) Laboratory, University of Georgia, the DTM procedure is less applicable to low TKN surface water samples. In this study, we therefore compared the performance of diffusion conductivity method (DCM) and colorimetric method (CM) with DTM in measuring NH₄-N in the TKN digests of 29 different samples representing surface waters, lagoons, manures, poultry litters, and environmental wastes. Acceptable accuracy and precision were achieved for various QC samples by all three methods. For widely different sample matrices and TKN contents, the NH₄-N in the TKN digests measured by DCM and CM both agreed well with that measured by DTM. However, the linear working range of CM is limited within 0.2 to 5.0 ppm, whereas DCM is linear at a wider range of 0.01 to 2000 ppm. With DCM, the PQL of TKN is at 13 ppb, much less than the 300 ppb in DTM and 520 ppb in CM. Both DCM and CM require increasing the pH of the working TKN digest to a highly alkaline range. To meet such pH requirement, the minimum dilution need for DCM is twofold, where as that CM is fourfold. Because of greater mandatory dilution requirement coupled with a greater PQL, CM may often fail to measure NH₄-N in the working TKN digest of some low TKN surface water samples. On the other hand, with some environmental waste samples containing TKN at percentage level, CM would require multistep dilution of the digests prior to measurement, thus allowing dilution-related error as well as requiring additional labor. In contrast, DCM can measure both low TKN surface waters and high TKN environmental wastes without any major limitations. Moreover, DCM may work well without any adjustment of sample background in the calibration standards. Thus DCM appears to be an attractive alternative to the labor-intensive and time-consuming DTM for measuring NH₄-N in the TKN digests of various kinds of agricultural and environmental samples in the analytical services laboratories.     

山药组织总RNA提取方法的比较与分析

采用异硫氰酸胍一巯基乙醇联合变性法、Trizol法和CTAB—LiCl法等3种方法,分别对山药叶片和块茎进行总RNA提取效果进行了比较。结果表明,Trizol法难以提取RNA,异硫氰酸胍-巯基乙醇联合变性法提取RNA效果不理想,存在DNA污染,这2种方法不适合于富含多糖类物质的山药组织总RNA的提取;CTAB-LiCl法提取叶片和块茎组织总RNA质量高、完整性好、成功率高,可作为山药类植物总RNA提取的首选方法。