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排序方式: 共有852条查询结果,搜索用时 18 毫秒
1.
研究了受外场驱动的两个二能级系统分别与两个单模量子化光场相互作用模型中纠缠演化及转移问题。该工作主要是对外场驱动的Landau-Zener模型进行了研究,采用旋转波近似的方法,通过数值计算详细分析了二能级系统初始状态、能级间的耦合常数以及驱动外场的参数对子系统间纠缠和转移特性的影响。结果表明,适当调节模型中的参数,可以使系统初始纠缠完全转移为光腔场间的纠缠,实现二能级系统与光场间的最大纠缠转移。 相似文献
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当前我国正处于飞速发展的时期,城镇化进程和耕地保护问题逐渐成为每个地方发展过程中突出的矛盾问题.以山东省日照市为例,运用定性和定量研究、文献研究等方法分析日照市城镇化进程与耕地保护的关系,并探讨城镇化进程对耕地保护造成的压力,在此基础上有针对性地提出耕地保护的对策建议. 相似文献
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采用不同的工艺调控技术,实现了一种成分体系可生产具有不同屈强比的经济型冷轧DP780钢,并通过分析力学性能测试结果、TEM和SEM组织形貌特征,得到热轧初始组织、冷轧压下量、连续退火工艺对屈强比的影响。结果表明,当热轧初始组织为F+P(铁素体+珠光体)时,随着平均晶粒尺寸细化至约7.5 μm,屈服强度增加了50 MPa,屈强比由0.48增至0.56;当热轧初始组织变为F+B(铁素体+贝氏体)、以贝氏体为主时,屈服强度达到532 MPa,屈强比增至0.65,同时有利于保证DP780钢的扩孔性和塑性,扩孔率达到86%,特别适用于有扩孔翻边要求的汽车结构件和加强件。此外,适当增加冷轧压下量和降低退火保温温度,均有利于增强基体的强化效应,从而提高屈强比。 相似文献
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《Food Control》2016
Recent outbreaks with fresh produce have raised questions regarding management of quality and safety in the complex supply chains, where cooperatives play a central role. The overall objective of this article was to investigate the role of cooperatives in food quality and safety management in the fresh produce chain, focussing on the food safety management systems implemented on the farms. More specifically, we raise the question how a more market-like or a more hierarchy-like governance of transactions via cooperatives affect the quality and safety management system of the members. The research employed case studies in four cooperatives in Belgium and the Netherlands, each with different size and per cent of contractual sales. Data was collected with a diagnostic tool for assessment of food safety management systems (FSMS) on the farms, and semi-structured interviews with the quality assurance managers of the cooperative firms. Twenty-eight strawberry farms were assessed with the diagnostic tool, seven per each cooperative. Cooperatives play a double role in managing quality and safety in the food supply chain. They are responsible for the supply chain management, including tactical decisions about coordination of quality and safety requirements between customers, cooperative firms and their farmers. At the same time, they are selling the products of their members and make strategic decisions about the governance of transactions in the supply chain, which ultimately may have an impact on the supply chain management and the FSMS on the farms. Farmers in cooperatives with more hierarchical relationships showed better operation of control activities (score 3), and advanced assurance activities at score 4 (advanced level), more science-based, adapted and tested for their effectiveness. This was associated with more effort put in supply chain management by the cooperative to support collaboration and coordination in the chain. However, the largest cooperative had moderate scores for several key control functions, suggesting that large cooperatives with complex business functions may suffer from lower commitment of members, leading to lower FSMS performance at farms. 相似文献
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Electrical resistance tomography (ERT) reconstructs the conductivity distribution from the boundary changes of electrical measurements. The inverse problem of ERT is seriously ill-posed where regularization methods are needed to treat this ill-posedness. A proper choice of regularization parameter which controls the degree of smoothing is very important for these regularization methods. Although have been a variety of methods, such as L-curve method, to choose a reasonable parameter for the problem, these methods usually result in a scalar parameter which cannot distinctly express the spatial characteristic of the conductivity distribution. So a spatially adaptive regularization parameter choice method is proposed for regularizing the inverse problem of ERT based on Tikhonov regularization. Since large regularization parameters can stabilize and smoothen the solution, while small regularization parameters can approximate and sharpen the solution, the proposed method adaptively updates the regularization parameters during the iteration process and provides spatially varying parameter for each pixel of the reconstructed image. When the iteration is stopped, large regularization parameters for the smooth background region and small regularization parameters for the object region can be obtained. The method is discussed using simulated data for some typical conductivity distributions, and further applied to the analysis of real measurement data acquiring from the practical system. The results demonstrate that flexible regularization parameter vectors can be achieved for different distributions and the strength of regularization is adaptively provided for different regions in a specific distribution. The adaptive method achieves an efficient and reliable regularization solution and has outstanding performance in noise immunity especially in smooth background regions. 相似文献
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In this paper, a novel analysis method for iterative learning control (ILC) algorithms is presented. Even though expressed in the lifted system representation and hence in the time-domain, the convergence rate as a function of the frequency content of the error signal can be determined. Subsequently, based on the analysis method, a novel ILC algorithm (F-ILC) is proposed. The convergence rate at specific frequencies can be set directly in the design process, which allows simple tuning and a priori known convergence rates. Using the F-ILC design, it is shown how to predict the required number of iterations until convergence is achieved, depending on the reference trajectory and information on the system repeatability. Numerical examples are given and experimental results obtained on an internal combustion engine test bench are shown for validation. 相似文献
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采用基于密度泛函理论(DFT)的平面波赝势(PW-PP)方法,分别计算纯净以及掺杂Ti的NaAlH4和Na3AlH6的晶格结构参数、能量变化和电子态密度(DOS),分析比较Ti掺杂对NaAlH4和Na3AlH6储氢性能的影响。结果表明:Ti掺杂后的晶格结构比原纯净的NaAlH4和Na3AlH6稳定,且脱氢所需能量减少。Ti替代Na后,Ti吸引周围的H原子,使Al-H键变弱;Ti替代Al,Ti-H键比原Al-H键明显减弱,使掺杂后脱氢所需能量降低。通过对比分析Ti掺杂对NaAlH4和Na3AlH6结构和态密度的影响,得出Ti的催化作用主要发生在脱氢反应的第一步。 相似文献