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1.
Resistivity-temperature characteristics of sol gel YBa2Cu3Oy samples synthesized in flowing oxygen atmosphere 下载免费PDF全文
The relationship of resistivity versus synthesizing temperature of sol gel YBa_2Cu_3O_y samples was studied when prepared under flowing oxygen conditions. A set of high-temperature ρ-T curves was obtained for the whole process. After the sample finished the test measuring, its resistivity was ρ_{300}=9.83×10^{-3 }Ω·cm at room temperature. The ρ-T curve also showed that the orthorhombic-tetragonal phase transformation of sol-gel YBa_2Cu_3O_y sample occurred at 581℃ for the sample in the rising temperature process, but at 613℃ in the cooling process, lower than that of the samples made by using the conventional powder metallurgy methods. 相似文献
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研究了水-乙腈混合溶液中SO4●-自由基氧化酪氨酸的反应.实验结果表明,SO4●-自由基氧化酪氨酸的反应机制不因乙腈的加入而改变,但所产生的瞬态粒子的动力学行为受到较大影响.随介质中乙腈体积分数的增加,SO4●-的衰变速率减慢而酪氨酸中性自由基(TyrO●)的衰变速率加快.我们认为这两种自由基所呈现出来的相反的溶剂效应是由于其所带电荷的不同.随介质中乙腈体积分数的增加,SO4●-氧化酪氨酸的反应速率减慢.这一实验结果意味着,在有机溶剂存在的情况下TyrO●/ TyrOH的氧化还原电势可能发生了变化,从而旁证了关于TyrO●/ TyrOH的氧化还原电势因酪氨酸从游离状态变到肽或蛋白质中而发生变化的推测. 相似文献
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利用X-射线衍射,扫描电镜,拉曼光谱,等离子发射光谱和比表面测定等方法研究了不同状态下失活及新鲜催化剂的结构,杂种类及含量。结果表明,超温使催化剂晶化明显,制备方法对催化剂结构有直接影响,再生使其强度降低,条形催化剂比较容易粉化,无机杂质是次要的失活原因。 相似文献
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Sandra S. Pröckl 《Tetrahedron》2005,61(41):9855-9859
In situ generation of highly active palladium species by intermediate dissolution of Pd from solid supported catalysts has been demonstrated to be a very successful approach for the activation of aryl chlorides in Heck reactions. The new ‘heterogeneous’ Pd catalysts act as reservoir for molecular Pd species with unsaturated coordination sphere in solution. Crucial Pd leaching and re-deposition onto the support can be controlled by optimization of reaction conditions and by the properties of the catalysts. Pd is re-deposited onto the support at the end of the reaction. The catalysts, palladium supported on activated carbon, on various metal oxides or fluorides and Pd complexes in zeolites, are easy to prepare, though the preparation conditions are crucial. The catalysts convert all aryl bromides completely within minutes (TON 100,000). Aryl chlorides (even deactivated ones) are converted with high yields, within 2-6 h. The catalysts belong to the most active ones in Heck reactions at all (including best homogeneous systems) and fulfill all relevant requirements for practical applications in laboratory and industry. 相似文献
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随着中国经济与社会的快速发展,环境监测引起人们的广泛关注。为了解决目前监控系统的不足,设计一种基于ZigBee和因特网的智能远程监控系统。该系统采用TI公司的CC2530芯片及相应传感器构建ZigBee局域网,将采集到的温湿度信息,经过上位机存储并处理,利用因特网或无线移动网络,在安卓智能手机终端上实现数据的远程传输。通过上位机与手机终端,可以查看当前环境状态,保存历史数据,并进行自动报警。给出系统硬件及软件实现方法,包括节点设计、组网流程、数据传输功能、上位机软件设计、安卓智能手机终端软件设计等。实验测试结果说明该系统工作稳定、容易扩展、上位机及手机操作简便。 相似文献
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Ziyad R. Alashhab Mohammed Anbar Manmeet Mahinderjit Singh Yu-Beng Leau Zaher Ali Al-Sai Sami Abu Alhayja’a 《电子科技学刊:英文版》2021,19(1):25-40
In light of the coronavirus disease 2019 (COVID-19) outbreak caused by the novel coronavirus, companies and institutions have instructed their employees to work from home as a precautionary measure to reduce the risk of contagion. Employees, however, have been exposed to different security risks because of working from home. Moreover, the rapid global spread of COVID-19 has increased the volume of data generated from various sources. Working from home depends mainly on cloud computing (CC) applications that help employees to efficiently accomplish their tasks. The cloud computing environment (CCE) is an unsung hero in the COVID-19 pandemic crisis. It consists of the fast-paced practices for services that reflect the trend of rapidly deployable applications for maintaining data. Despite the increase in the use of CC applications, there is an ongoing research challenge in the domains of CCE concerning data, guaranteeing security, and the availability of CC applications. This paper, to the best of our knowledge, is the first paper that thoroughly explains the impact of the COVID-19 pandemic on CCE. Additionally, this paper also highlights the security risks of working from home during the COVID-19 pandemic. 相似文献