梯度铁电薄膜性质研究     

张芹  郭言利 《吉林林学院学报》2010,(6):501-503

以二级相变铁电材料为例,利用推广的Ginzburg-Landau-Devonshire（GLD）理论,研究不均匀结构对梯度铁电薄膜性质的影响.结果表明：退极化场对于两层薄膜中间的极化影响较小,而在薄膜的两端处影响最大;梯度铁电薄膜的平均极化随膜厚按线性规律变化;在接近相变温度时,自发极化消失,梯度铁电薄膜的这一现象与铁电材料的性质相同.在外场不等于零的情况下,得到的梯度铁电薄膜的电滞回线中心对称.  相似文献   

Discussion on Transition Strategy from 3G to 4G     

《保鲜与加工》2003,(9):134-137

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非瞬时或突变的马尔可夫链的一种应用方法   总被引：2，自引：1，他引：1  

张朝阳  陈同英 《福建农林大学学报(自然科学版)》2006,35(4):440-444

介绍对于一种非瞬时或突变的状态转移过程.采用Bayes方法修订马尔可夫过程的状态转移概率矩阵;将先验概率分布修订为后验概率分布;对整个过程的信息加以吸收,得出能够反映整个过程的状态转移概率矩阵,从而达到预测目的.由此还得出一个重要结论:吸收信息的无序性.  相似文献   

Land Cover Transition in Northern Tanzania     

Issa Ouedraogo  Jennie Barron  Siza D. Tumbo  Frederic C. Kahimba 《Land Degradation \u0026amp; Development》2016,27(3):682-692

Land conversion in sub‐Saharan Africa has profound biophysical, ecological, political and social consequences for human well‐being and ecosystem services. Understanding the process of land cover changes and transitions is essential for good ecosystem management policy that would lead to improved agricultural production, human well‐being and ecosystems health. This study aimed to assess land cover transitions in a typical semi‐arid degraded agro‐ecosystems environment within the Pangani river basin in northern Tanzania. Three Landsat images spanning over 30 years were used to detect random and systematic patterns of land cover transition in a landscape dominated by crop and livestock farming. Results revealed that current land cover transition is driven by a systematic process of change dominated by the following: (i) transition from degraded land to sparse bushland (10·8%); (ii) conversion from sparse bushland to dense bushland in lowland areas (6·0%); (iii) conversion from bushland to forest (4·8%); and (iv) conversion from dense bushland to cropland in the highlands (4·5%). Agricultural lands under water harvesting technology adoption show a high degree of persistence (60–80%) between time slices. This suggests that there is a trend in land‐use change towards vegetation improvement in the catchment with a continuous increase in the adoption of water harvesting technologies for crop and livestock farming. This can be interpreted as a sign of agricultural intensification and vegetation regrowth in the catchment. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Vegetative phase change among sweet corn (Zea mays L.) hybrids varying for reaction to common rust (Puccinia sorghi Schw.)     

M. A. Chandler    W. F. Tracy 《Plant Breeding》2007,126(6):569-573

In maize, timing of vegetative phase change has been implicated in the response to certain pests and environmental stresses. Common rust is the most serious disease of sweet corn in the north central United States. Sweet corn hybrids differing for resistance to common rust were evaluated for vegetative phase change traits. There were significant differences among hybrids for all vegetative phase change traits measured, as well as resistance to common rust. Certain hybrids displayed rapid transition (within two leaves) from juvenile to adult vegetation, while others displayed prolonged transition (within four leaves). There were no significant correlations between vegetative phase change traits and common rust severity among the commercial sweet corn hybrids evaluated in this experiment.  相似文献   

Small‐scale cattle raising in East Java,Indonesia: A pathway out of poverty?          下载免费PDF全文

Atien Priyanti  Rob Cramb  Vyta W. Hanifah  I. G. A. P. Mahendri 《Asia Pacific viewpoint》2015,56(3):335-350

Despite its small area and intensively cropped landscape, East Java accounts for 30% of Indonesia's cattle population. About two million households draw on family labour to raise cattle in backyard sheds and small enclosures, largely for cash income. In this paper, we examine the opportunity for such small‐scale producers to benefit from Indonesia's economic transformation, given the rising urban demand for beef. The paper reports on a study in two contrasting sites in East Java – irrigated lowlands and rainfed uplands – to explore the constraints facing small‐scale cattle producers in these environments, the means by which they have adapted to these constraints (especially by going beyond the farm household to access feed supplies) and possible means to enhance their production systems and incomes. The findings suggest that such cattle production systems can provide a viable source of livelihood, even for resource‐poor households; hence, appropriately adapted cattle improvement programmes are a sensible component of a pro‐poor development strategy.  相似文献   

Soil organic matter beyond molecular structure Part I: Macromolecular and supramolecular characteristics     

Gabriele E. Schaumann 《植物养料与土壤学杂志》2006,169(2):145-156

This contribution reviews and discusses structural aspects of soil organic matter (SOM) and humic substances (HS) with special respect to the macromolecular and the supramolecular view. It can be concluded that (1) dissolved humic acids behave as supramolecular associations of relatively small molecules with an enormous flexibility of reaction of environmental conditions, (2) multivalent cations may increase the apparent molecular weight by the formation of coordinative crosslinks in dissolved and undissolved natural organic matter (NOM), (3) sorption nonlinearity in solid humic acids and SOM may be due to polymer properties of NOM, (4) sorbates affect sorbent characteristics of SOM, and (5) hysteresis and conditioning effects in SOM can up to now best be explained with the polymer analogy. A distinct polydispersivity of SOM over a wide range of molecular masses is to be assumed. The supramolecular and the macromolecular models were derived from humic acids with different composition and on the basis of different sample states. Although the supramolecular model has not explicitely been shown for unfractionated DOM, the combination of all discussed studies suggests supramolecular as well as macromolecular characteristics of NOM. Neither macromolecules nor small molecules can be fully excluded in solid and dissolved SOM. Microregions with different properties provide different types of sorption sites. SOM is suggested to be regarded as amorphous material. This point of view is not restricted to high molecular masses and may supplement our understanding of SOM by the model of physical aging.  相似文献   

The tyranny of taste: the case of organic rice in Cambodia     

Thavat M 《Asia Pacific viewpoint》2011,52(3):285-298

Fair-trade and organic products are often sold at price premiums justified by smaller production volumes that are associated with greater social and environmental responsibility. The consumption of these products confers on the consumer a greater sense of morality – and usually a claim to better taste. This paper tells the story of attempts to promote organic/fair-trade rice production by de facto organic Cambodian farmers for export to North American and European markets in order to assist poor farmers to trade their way out of poverty. It demonstrates that instead of promoting sustainable agriculture and fair trade between developed and developing markets, organic/fair-trade projects may impose First World consumer ideals and tastes that are out of step with the larger realities of agrarian transition in Cambodia and the wider region of developing Southeast Asia.  相似文献   

利用Markov过程预测安吉土地利用格局的变化   总被引：2，自引：0，他引：2  

蒋文伟  管宇  刘彤  周国模  沈振明 《浙江林学院学报》2004,21(3):309-312

根据浙江安吉山区2个时期山地资源清查资料获得的土地利用类型数据,成功地确定了土地利用类型的转移矩阵,并用Markov链模型预测了该山区土地利用类型变化趋势.结果表明,当前该区的土地利用格局正处在一种荒山、农田、居民点及水域逐渐减少,林地、果园用地逐渐增加的变化状态,而且这种变化将持续很长时间,最后达到以山区林地78.4%为主体,同时湿地在不断减少的新的土地利用格局.表3参11  相似文献   

试论经济转型时期国企职工的“主人翁”地位及其实现     

辜堪生 《河南科技大学学报(农学版)》2001,21(1):45-47,60

分析了经济转型时期国企职工的主人翁地位失落的原因，提出了国有企业保障企业职工主人翁地位的措施：充分保证和利用职代会来实现企业的民主管理，很好地利用工会这一企业职工的群众性组织。  相似文献