拖拉机安全驾驶室强度非线性有限元分析

为了避免由于拖拉机翻车事故引起的人员伤亡,提高拖拉机工作时的安全性,设计安全可靠的大中马力拖拉机驾驶室,并且使之能通过OECD标准,以某型号拖拉机驾驶室为研究对象,建立了该安全驾驶室的精确三维模型,并采用非线性有限元方法,按照OECD标准规定的要求,对模型进行了加载分析。驾驶室被简化成梁和板单元,采用弹簧单元模拟驾驶室与机身前支架之间的橡胶减震垫。计算结果表明：拖拉机驾驶室在按照试验要求模拟加载完成后,驾驶室变形吸收能量达到OECD标准规定的要求时,驾驶室部分粱和底板的应力已经达到屈服应力,进入了塑性变形,但变形后的驾驶室没有侵入安全容身区。后推、后压、侧推、前压和前推试验中驾驶室的最大变形分别为111、4、168、19和 47 mm,变形最大发生在力的作用位置处。该方法为设计能通过OECD标准试验的拖拉机安全驾驶室提供了一定的参考依据。     

木工圆锯片CAM技术

在木工圆锯片ＣＡＤ的基础上,利用２个模块,将ＣＡＤ产生的数据转换成ＮＣ指令,用通用算法语言实现自动编程,并在数控电火花线切割机上进行了加工,取得了满意结果。     

森林生态制度文化:机构·法律·行为守则

由于个人、政府、企业通过对森林物质文化的生态认知、生态情感、生态响应而产生的生态法律法规、生态行为守则、生态机构组织和管理机制等组成了森林生态制度文化;森林制度文化是森林管理文化的核心,是国家管理森林的主要工具;研究森林制度文化,分析其薄弱环节、落后因素,并加以改进,有助于建设先进、和谐、科学的森林制度文化.     

Structure and temporal shifts in virulence of Pseudoperonospora cubensis populations in the Czech Republic

The structure and temporal dynamics of the virulence of Pseudoperonospora cubensis (causal agent of cucurbit downy mildew) were studied in pathogen populations in the Czech Republic from 2001 to 2010. A total of 398 P. cubensis isolates collected from Cucumis (Cm.) sativus, Cm. melo, Cucurbita (Cr.) maxima, Cr. pepo, Cr. moschata and Citrullus lanatus were analysed for variation in virulence (pathotypes). Virulence was evaluated on a differential set of 12 genotypes of cucurbitaceous plants. All isolates of P. cubensis were characterized by their level of virulence (classified according the number of virulence factors, VF; low VF = 1–4, medium VF = 5–8, high VF = 9–12): high (75%), medium (24%) and low (1%). The structure and dynamics of virulence in the pathogen populations were expressed by pathotypes using tetrad numerical codes and a total of 67 different pathotypes of P. cubensis were determined. The most susceptible group of differentials was Cucumis spp., while the lowest frequency of virulence was recorded on Cr. pepo ssp. pepo, Ci. lanatus and Luffa cylindrica. A high proportion (c. 90%) of isolates was able to infect cucurbit species Benincasa hispida and Lagenaria siceraria, which are not commonly cultivated in the Czech Republic or elsewhere in central Europe. In the recent pathogen populations (2008–2010) there was prevailing frequency (70–100%) of isolates with high numbers (9–12) of virulence factors. ‘Super pathotype’ 15.15.15 was often observed in the study within the pathogen populations and was one of the four most frequently recorded pathotypes. Pseudoperonospora cubensis populations shifted to a higher virulence over time. From 2009 the pathogen population changed dramatically and new pathotypes appeared able to establish natural and serious infection of Cucurbita spp. and Ci. lanatus, which was not observed in 2001–2008. Generally, virulence structure and dynamics of P. cubensis populations are extremely variable in the Czech Republic.     

New,Comprehensive Soil Chemical Methods Book for Australasia

The 1992 Australian Laboratory Handbook of Soil and Water Chemical Methods (the handbook) of Rayment and Higginson defines much of the contemporary soil chemical methodology used in Australia for soil fertility and land-resource survey assessments. In addition, codes from the handbook identify methodological details in Australian soil databases, while the codes summarize most tests used for certification purposes by the Australasian Soil and Plant Analysis Council (ASPAC) in its interlaboratory soil proficiency testing programs. A worthy, comprehensive replacement was required as the handbook is out of date in places and out of print. This article provides information on the handbook's replacement with a new book by Rayment and Lyons, titled Soil Chemical Methods-Australasia. Method codes and other strengths of the handbook have been retained and many new tests have been added. There are new chapters on acid sulfate soils, total miscellaneous elements, and miscellaneous extractable elements, plus inclusions and improvements throughout. Modern analytical techniques, such as flow-injection analysis, inductively coupled plasma–mass spectroscopy (ICP-MS), and potential alternatives to chemical testing offered by near-range and midrange infrared diffuse reflectance spectroscopy, are included. Examples of new additions include the Mehlich 3 “universal” soil test (and derived environmental P tests) and methods for potentially mineralizable nitrogen, labile carbon, particulate organic carbon, and charcoal. Around 200 methods are fully described, while information of measurement performance at different concentrations is provided where credible data were available from multiple, interlaboratory proficiency programs of ASPAC. Procedures for the chemical testing of water are no longer included, except where relevant to saturation extracts of soils. While there are informative and much expanded method preambles and reference lists, the new 2011 book has its focus on methodology. A scheme to agree on recommended methods for different soils and regional locations is outlined.     

基于网格的耕地质量分等成果省级汇总方法

耕地质量分等成果由县、省、国家3级成果组成,省级成果由县级成果汇总获取,是农用地分等工作中必不可少的环节。由于传统的汇总方法对汇总底图的过分依赖性,导致汇总效率低下,汇总后的质量完全取决于汇总底图的质量。基于该缺陷,该文提出利用网格取代汇总底图,将县级成果按照“权属-地类-等别”进行分类,根据面积占优原则确定对应网格所属类别,并通过空间最邻近方法寻找距离县级单元最近的网格单元,建立“网格-县级分等单元”的追溯关系。该文提出了以县行政代码、网格所在行列码、等别、地类组成21位省级汇总网格的编码方法。最后利用平均中心和标准差椭圆检验汇总前后耕地空间分布的相似性。以北京市大兴区为研究区进行了实例验证,大兴区根据“地类-自然等-利用等-经济等”组合共分为8类,根据大兴区耕地的分布,最终确定688个有效耕地网格。利用该文方法实现了省级汇总。经过检验表明,汇总前后耕地分布的平均中心和分布方向仅相差405.6 m和0.34°,说明该汇总方法保证了汇总前后耕地空间分布的一致性。与依赖汇总底图的方法相比较,省去了制作底图的工作量,提高了工作效率,并且将省级耕地定位在每个网格中,通过网格编码能够快速查找到对应位置的耕地质量,方便管理和应用。     

A Method to Improve the Decoding Iteration Convergence Performance of Turbo Codes

Turbo codes is an effective method for digital communication systems to get near channel capacity error correcting performance, its iteration convergence performance is the key factor for practicability. Based on the universal decoding method of Turbo codes, a step increment factor was introduced in the paper to improve the iteration convergence performance. The method to generate the step increment factor was also presented as well as its' computer simulations. Simulation results show the method proposed can improve the convergence performance efficiency for Turbo codes with short interleaver.     

设计距离为7的q元BCH码的周期分布

通过对循环陪集的研究及利用分圆多项式的一个性质,得到了设计距离为7的q元BCH码的周期分布计算公式:码的周期分布为q的幂,当码的周期不等于某些特殊值时,幂为码长与周期的最大公因数.当码的周期为特殊值时,幂为n/b-m[6/b],这里n是码的长度,b是由n和码的周期决定的2到6之间的整数,m是q模n的指数.由此计算公式和Mobius反转公式给出了无内周期码字个数的计数结果.     

Quantitative Analysis of Influence Force of Shanghai Expo on GGDP

Quantitative study of the impact of Shanghai World Expo on green GDP （GGDP） is significant for deploying sustainable development policy in China. The formula of GGDP is： GGDP = GDP--the loss of natural resources environment relegation cost ＋ comprehensive utilized value of waste. Based on this, the study employed vector autoregressive （VAR） model to predict the value of GGDP and other economic variables on condition that there was no Shanghai World Expo. Then Influence of Expo is defined as the rate of increase of GGDP. The result demonstrated that Shanghai World Expo had accelerated the growth rate of GGDP vastly with the elimination of effect of Beijing Olympics. Additionally, the quantitative analysis between GGDP and other economic variables suggested GGDP would replace GDP to evaluate the development of economy. Finally, the paper proposed that incidents like World Expo can enhance the level of influence for a country and that post-impact of Shanghai Expo should continue to be used to promote GGDP and that GGDP should serve as one of the indicators in assessment of political achievement.     

稀疏生成矩阵的低编码复杂度非正规LDPC码性能

提出了一种新的基于稀疏生成矩阵的高性能非正规LDPC码的构造方法，并研究了其性能。与传统的由校验矩阵定义的LDPC码相比，在相同的译码复杂度前提下，非正规LDPC码的编码复杂度更低。模拟结果显示，在加性高斯白噪声信道下，非正规LDPC码的性能要显著优于传统LDPC码。