课程文献中心 更多>>

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： 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： 医院感染   临床细菌学检验   感染检测   医疗消费   医务工作者   住院病人   人民币   发生率   患者  

摘要： 医院感染日益成为一个严峻的问题摆在广大医务工作者面前。目前我国每年大约有5000万住院病人，其中约有500万患者出现医院感染，每年造成的额外的医疗消费约100亿人民币。据报道：在美国医院感染的发生率在5％-10％，每年造成的额外的医疗消费约为175-350亿美元。除了经济上的损失以外，更严重的是给患者带来巨大的危害。

关键词： 财政政策   经济周期   传导机制  

摘要： 财政政策一直是我国宏观经济调控的主要方式,并在需求管理中发挥了重要作用。本文定量描述和检验了我国财政政策工具与经济周期波动之间的相依性,在结构VAR模型中刻画了财政政策的作用和反馈过程,并发现我国财政政策操作的相机选择性依赖经济周期的阶段性。在目前我国进入新经济周期的态势下,应当及时调整财政政策的期限结构和政策工具,加强财政政策与货币政策的政策组合作用,以保持经济快速稳定增长。

关键词： Advertising   Cognitive Processes   Learning   Memory   Experimental Design and Analysis (ANOVA)  

摘要： Recall of print material benefits from spacing repetitions of that material, an effect often attributed to varied encodings induced by changes in contextual cues. We examined an alternative explanation: retrieving earlier presentations during later presentations strengthens memory traces, the more so the greater the difficulty of such retrieval. In four experiments we found that (a) study-phase retrieval contributes to the benefits of spacing and (b) inducing variation via changes in ad formatting and content can be counterproductive at long spacing intervals, apparently because such changes decrease the likelihood that earlier presentations will be retrieved during later presentations.

关键词： Groups   Anxiety   Surgical aspects   controlled study  

摘要： Pre-operative anxiety is common and often significant. Ambulatory surgery challenges our pre-operative goal of an anxiety-free patient by requiring people to be 'street ready' within a brief period of time after surgery. Recently, it has been demonstrated that music can be used successfully to relieve patient anxiety before operations, and that audio embedded with tones that create binaural beats within the brain of the listener decreases subjective levels of anxiety in patients with chronic anxiety states. We measured anxiety with the State-Trait Anxiety Inventory questionnaire and compared binaural beat audio (Binaural Group) with an identical soundtrack but without these added tones (Audio Group) and with a third group who received no specific intervention (No Intervention Group). Mean [95% confidence intervals] decreases in anxiety scores were 26.3%[19-33%] in the Binaural Group (p = 0.001 vs. Audio Group, p < 0.0001 vs. No Intervention Group), 11.1%[6-16%] in the Audio Group (p = 0.15 vs. No Intervention Group) and 3.8%[0-7%] in the No Intervention Group. Binaural beat audio has the potential to decrease acute pre-operative anxiety significantly.

关键词： drug intelligence   heroin profiling   neural networks   principal component analysis  

摘要： Artificial neural networks (ANNs) were utilised to validate illicit drug classification in the profiling method used at "Institut de Police Scientifique" of the University of Lausanne (IPS). This method established links between samples using a combination of principal component analysis (PCA) and calculation of a correlation value between samples. Heroin seizures sent to the IPS laboratory were analysed using gas chromatography (GC) to separate the major alkaloids present in illicit heroin. Statistical analysis was then performed on 3371 samples. Initially, PCA was performed as a preliminary screen to identify samples of a similar chemical profile. A correlation value was then calculated for each sample previously identified with PCA. This correlation value was used to determine links between drug samples. These links were then recorded in an Ibase (R) database. From this database the notion of "chemical class" arises, where samples with similar chemical profiles are grouped together. Currently, about 20 "chemical classes" have been identified. The normalised peak areas of six target compounds were then used to train an ANN to classify each sample into its appropriate class. Four hundred and sixty-eight samples were used as a training data set. Sixty samples were treated as blinds and 370 as non-linked samples. The results show that in 96 % of cases the neural network attributed the seizure to the right "chemical class". The application of a neural network was found to be a useful tool to validate the classification of new drug seizures in existing chemical classes. This tool should be increasingly used in such situations involving profile comparisons and classifications. (c) 2005 Elsevier B.V. All rights reserved.