教学课程资源库 更多>>

关键词： 分类   包装   危险品   危险货物   国民经济   运输安全   危险物   定级  

摘要： 随着国民经济的飞速发展，危险货物的种类、数量在不断地增多。据统计，全世界海运总量的40％以上是危险物，所以针对危险货物作出正确的分类定级是必不可少的，然后再按照分类定级选择相应的危险货物的专用包装，才能确保运输安全。

关键词： 文件格式要求   格式特征   种类   价值   作用  

摘要： 有观点认为文件格式特征包含在文字布局特征之中。本文以格式为切入点,探讨文件格式与文件格式特征的概念,以书信和书写票据为例,论述其格式要求,结合国家标准、规定及实际案例,研究文件格式特征的种类,其与文字布局特征之间的区别、联系,及其在文件检验中的作用、价值。

关键词： 招标投标   合同   生效时间  

摘要： 由于对相关法律条文的理解不同,在招投标过程中,关于合同成立时间的问题存在着两种不同的观点,并因此在司法实践中产生了两种不同的判决结果,通过对这两种观点进行了整理和分析,对如何解决这一问题进行了一些探讨。

关键词： boar taint   skatole   androstenone   volatile compounds   head space   pig back fat  

摘要： Dynamic Head Space methodology was applied to evaluate the possible contribution of some volatile compounds to the development of boar taint in pig backfat samples with low concentrations of skatole and androstenone, but which had previously been classified as tainted by a trained test panel. Volatile compounds were collected in a trap of graphited charcoal and analysed by GC-MS in Scan mode. Aldehydes and short chain fatty acids, compounds that play a significant role in the development of undesirable aromas in food products, were the main classes of compounds identified in this study, although the possible contribution of other compounds that were detected in a minor proportion - such as alcohols and ketones - was evaluated. Styrene and 1,4-dichlorobenzene, compounds that may have come from an external contamination, showed a high concentration in the samples classified with boar taint, so these compounds could have been responsible for the development of some off-flavours in the fat samples studied in this work. In the same study, skatole and androstenone were also determined by normal phase HPLC and GCMS, respectively. (C) 2005 Published by Elsevier Ltd.

关键词： 光电测距仪   计量检验   乘常数   检定规程   缺陷   全站仪  

摘要： 一、问题之所在自上世纪光电测距仪问世以来,加、乘常数(专指测距仪或全站仪的测距加、乘常数,下同)检验的原理和方法就随即产生.然而直到今天,在我国,加、乘常数这一概念仍然存在模糊,甚至使加、乘常数的计量检验成为虚设.

关键词： 光合作用   氧气   实验改进   初中   生物教学   演示实验  

摘要： 在七年级生物新教材中植物进行光合作用产生氧气并进行检验是一个非常重要的演示实验.教材采用将沉水植物置于玻璃水槽,上罩短管漏斗,再用盛满水的试管套在漏斗上,然后将装置放于阳光充足的环境接受光照,待收集约1/2管气体后,倒转试管再用带火星的木条进行检验该气体是否为氧气.上述方法的缺点是:收集气体缓慢效率低,检验气体步骤较烦琐.笔者经过反复思索和实验,作如下改进:

关键词： flexible endofiberscope   speckle correlation   fluorescence spectroscopy   abnormality detection   cancer diagnosis   colon  

摘要： An integrated and flexible fiber optic endoscope system for diagnostic investigations in medical cavities using specially designed probe distal and proximal ends so as to facilitate simultaneous speckle correlation analysis and fluorescence spectroscopic imaging is presented. (c) 2005 Society of Photo-Optical Instrumentation Engineers.

关键词： crop classification   dimensionality   training sample   time-series   multi-temporal   maximum likelihood  

摘要： The number of training samples per class (n) required for accurate Maximum Likelihood (ML) classification is known to be affected by the number of bands (p) in the input image. However, the general rule which defines that n should be 10p to 30p is often enforced universally in remote sensing without questioning its relevance to the complexity of the specific discrimination problem. Furthermore, identifying this many training samples is often problematic when many classes and/or many bands are used. It is important, then, to test how this generally accepted rule matches common remote sensing discrimination problems because it could be unnecessarily restrictive for many applications. This study was primarily conducted in order to test whether the general rule defining the relationship between n and p was well-suited for ML classification of a relatively simple remote sensing-based discrimination problem. To summarise the mean response of n-to-p for our study site, a Monte Carlo procedure was used to randomly stack various numbers of bands into thousands of separate image combinations that were then classified using an ML algorithm. The bands were randomly selected from a 119-band Enhanced Thematic Mapper-plus (ETM+) dataset comprised of 17 images acquired during the 2001-2002 southern hemisphere summer agricultural growing season over an irrigation area in south-eastern Australia. Results showed that the number of training samples needed for accurate ML classification was much lower than the cur-rent widely accepted rule. Due to the asymptotic nature of the relationship, we found that 95% of the accuracy attained using n = 30p samples could be achieved by using approximately 2p to 4p samples, or <= 1/7th the currently recommended value of n. Our findings show that the number of training samples needed for a simple discrimination problem is much less than that defined by the general rule and therefore the rule should not be universally enforced;the number of training s

关键词： sanctions   nitrogen fixation   cooperation   mutualism   symbiosis   exploitation  

摘要：

Mutualisms can be viewed as biological markets in which partners of different species exchange goods and services to their mutual benefit. Trade between partners with conflicting interests requires mechanisms to prevent exploitation. Partner choice theory proposes that individuals might foil exploiters by preferentially directing benefits to cooperative partners. Here, we test this theory in a wild legume–rhizobium symbiosis.

Rhizobial bacteria inhabit legume root nodules and convert atmospheric dinitrogen (N₂) to a plant available form in exchange for photosynthates. Biological market theory suits this interaction because individual plants exchange resources with multiple rhizobia. Several authors have argued that microbial cooperation could be maintained if plants preferentially allocated resources to nodules harbouring cooperative rhizobial strains. It is well known that crop legumes nodulate non-fixing rhizobia, but allocate few resources to those nodules. However, this hypothesis has not been tested in wild legumes which encounter partners exhibiting natural, continuous variation in symbiotic benefit.

Our greenhouse experiment with a wild legume, Lupinus arboreus, showed that although plants frequently hosted less cooperative strains, the nodules occupied by these strains were smaller. Our survey of wild-grown plants showed that larger nodules house more Bradyrhizobia, indicating that plants may prevent the spread of exploitation by favouring better cooperators.

关键词： misclassification   average coverage criterion   average length criterion   normal approximation  

摘要： We consider the impact of test properties on the required sample size for the Bayesian design problem for comparing two proportions with error-prone data. Specifically, we examine four cases: a single diagnostic test and two independent diagnostic tests, both when the test properties are identical across populations and when they differ. Interval-based and moment-based sample-size determination criteria are contrasted using Monte Carlo simulation methods. We consider an application in which Strongyloides infections are compared in two populations. Copyright (C) 2005 John Wiley & Sons, Ltd.