排序方式: 共有237条查询结果,搜索用时 15 毫秒
161.
Yiping Lu Tingju Li Fu Yabo Sun Jianbo Luo Dawei Gencang Yang Yaohe Zhou 《自然科学进展(英文版)》2009,19(11):1619-1624
High undercooling (about 392 K) was achieved in the bulk eutectic Ni70.2Si29.8 alloy melt through glass fluxing combined with cyclic superheating. It is found that the metastable phases Ni3Si2 and NiSi are obtained through slow post-solidification when undercooling exceeds 240 K. The metastable phases are confirmed by using the method of X-ray diffraction and differential scanning calorimetry (DSC). Based on the principle of the free energy minimum and the transient nucleation theory, the phase selection of melt is investigated with regard to the metastable phases formation in the bulk undercooled eutectic Ni70.2Si29.8 melts. The formation of metastable phases from undercooled Ni70.2Si29.8 melts is ascribed to competitive nucleation with the undercooling, i.e. high undercooling facilitates the preferential nucleation of metastable phases. 相似文献
162.
不同介质层的组合 ,有别于单层介质 ,具有特殊的电磁特征 从经典的麦克斯韦电磁场理论出发 ,推导出相对复介电系数ε r 和相对复导磁率 μ r 的表达式 ,引入法向阻抗的概念 在频段 5~ 1 2GHz内 ,利用计算机对n层介质材料进行研究 ,提出寻找介质层匹配的最佳方案 结合实际情况 ,讨论了两种特例 ,并对结果作了分析 图 5 ,参 5 相似文献
163.
双辊铸轧铸嘴型腔的三维流动分析 总被引:2,自引:0,他引:2
建立了双辊铸轧铸嘴型腔的三维流体流动的数学模型 ,应用数值方法计算铸嘴型腔的流场 ,分析了三维流动现象及其特点 ,把计算的铸嘴出口处的流体速度与实验结果相比较 ,两者基本吻合 并得出结论 :铸嘴型腔的结构是影响流体流动的主要因素之一 常规铸轧常用铸嘴出口处熔体速度相对误差达 2 0 %以上 ,不能满足超薄快速铸轧技术的需要 图 6 ,参 5 相似文献
164.
随着测量数据处理特征的变化与要求的发展 ,测量平差模型的影响分析理论获得迅速发展 重点讨论了异常数据诊断统计量的功能特性、数学意义及与传统统计量的关系 用一个简单的数值例子论证了上述方法的实用性 图 1 ,表 1 ,参 4 相似文献
165.
Na Li Dajian Li Weibin Zhang Keke Chang Feng Dang Yong Du Hans J. Seifert 《自然科学进展(英文版)》2019,29(3):265-276
Phase diagrams provide fundamental knowledge about design map of new electrode materials for Li-ion batteries. The CALPHAD (CALculation of PHAse Diagrams) approach is widely applied to the development of phase diagrams and property diagrams in a thermodynamic language. Within the CALPHAD framework, the theoretical modeling can be performed to predict phase equilibria, thermodynamics, electrochemical and physical properties of electrodes. This review provides the successful application of high quality calculated phase diagrams and thermodynamic property diagrams in CALPHAD investigation to both cathodes and anodes of Li-ion batteries, including Li–Co–O, Li–Ni–O, Li–Co–Ni–O, Li–Mn–O, Li–Cu–O, Li–Si, Li–Sb and Li–Sn systems with. The intensive CALPHAD-type research may also predict electrochemical properties, cell performance of the Li-ion batteries to achieve more efficient development of electrode materials. 相似文献
166.
Yuhao Li Fangfei Ma Fangya Yue Qingyuan Ren Hongbo Zhou Guanghong Lu 《自然科学进展(英文版)》2019,29(3):285-294
Here,we review recent computational findings focused on the behavior of transmutation elements (TEs) in Tungsten (W).W is chosen as one of the most promising materials for the divertor armor and plasma facing components in future fusion reactors.However,W in exposure of fusion neutrons can cause the transmutation reaction and produce TEs,such as rhenium and osmium.The presence of TEs can change chemical component of materials,and therefore inevitably influence the microstructure and properties of W materials.Multiscale simulation methods have been employed to investigate the dissolution,diffusion and radiation induced precipitation of TEs,as well as their effects on the behaviors of hydrogen isotopes in W.This systematic review can provide an insightful understanding to estimate the influence of TEs on the properties and performance of Wbased materials. 相似文献
167.
Amir Zada Nauman Ali Fazle Subhan Natasha Anwar Muhammad Ishaq Ali Shah Muhammad Ateeq Zahid Hussain Khair Zaman Momin Khan 《自然科学进展(英文版)》2019,29(2):138-144
The photocatalytic activities of g-C_3N_4 can be significantly improved by increasing life time of the photogenerated charges. Here, in this work we introduced TiO_2 as proper energy platform to accept the photogenerated electrons from g-C_3N_4 during photocatalysis. The nanophotocatalysts formed from the combination of a suitable amount of TiO_2 nanoparticles and g-C_3N_4 nanosheets showed 8.75 and 4.22% enhancement in photocatalytic activities for CO_2 reduction and 2-chlorophenol(2-CP) degradation under visible light illumination as compared to bare g-C_3N_4. Based on the surface photovoltage spectra, photoluminescence spectra and examination of formed hydroxyl radicals, it was confirmed that these enhanced photoactivities were attributed to the much-improved charge separation via the electron transfer from g-C_3N_4 to TiO_2. From trapping experiments,it was found that hydroxyl radicals were the major species involved in the photocatalytic degradation of 2-CP.This study is helpful to synthesize efficient photocatalysts to cope with energy and environmental issues. 相似文献
168.
A novel method for the analysis of composition distribution of titanium alloys over a large area(64 mm × 72 mm) was investigated by exploring the original position statistic distribution based on spark spectrum(OPA-SS) in Ti-6.5 Al-1.0 Cr-0.5 Fe-6.0 Mo-3.0-Sn-4.0 Zr titanium alloy. The results showed that OPA-SS could characterize the distribution of elements in different positions on the titanium alloy. The macrosegregation of Sn was the most pronounced, with a statistic segregation degree higher than 18%; the macrosegregation of Mo followed with a statistic segregation degree of 10%; the macrosegregation of Al and Fe was relatively milder,lower than 8%. The main reason for the macrosegregation state of the as-cast Ti-6.5 Al-1.0 Cr-0.5 Fe-6.0 Mo-3.0 Sn-4.0 Zr alloy can be the solute redistribution during liquid solidification and the diffusion rate of each element in the solid phase. 相似文献
169.
Zhiqiang Wang Dianlong Zhao Shidong Yu Zikai Nie Yuwei Li Lijun Zhang 《自然科学进展(英文版)》2019,29(3):316-321
Two-dimensional (2D) phosphorene has been extensively studied for potential electronic and optoelectronic applications.It is easily oxidized by adsorbing oxygen in the air,exhibiting changed materials stability and properties.Yet the impact of oxygen concentrations on stability and electronic properties of oxygen adsorbing phosphorene has never been systematically investigated.In this article,the oxygen adsorbing phosphorene at different oxygen concentrations are studied via first-principles crystal structure searches.We considered stoichiometries of P_8O,P_(16)O_(3)) P_4O and P_8O_(3,)with both single-side and dual-side adsorption for selected case P_4O.The energetically stable structure of each stoichiometry is identified.It has been found that the band gaps show rather wide range change,strongly depending on the oxygen concentration.Interestingly,at the higher oxygen concentration the relatively low band gaps and small carrier effective masses emerge,comparable with the pristine black phosphorus.This may be associated with the appearance of bridged P-O-P bonds as oxygen concentration increasing.The electronic properties are discussed in relation to structural features and chemical bonding. 相似文献
170.
Chunyan Zhu Zhao Chen Shuai Gao Ban Leng Goh Ismail Bin Samsudin Kai Wen Lwe Yunlong Wu Caisheng Wu Xiaodi Su 《自然科学进展(英文版)》2019,29(6):628-640
Quantum dots (QDs) with unique quantum confinement effect and electro-optical properties are attractive for biomedical applications. Toxic effects of traditional semiconductor QDs made of heavy metal ions have serious safety concerns for their undesired environmental or healthy impact. Recent reports on core-shell structure modification of QDs by using biocompatible ligands or polymers is one way to be effectively minimizing toxicity effects of traditional QDs. Furthermore, designs of heave metal-free and metal-free QDs formulations are more promising alternatives, due to the non-toxic and eco-friendly nature of the starting materials. In article, we will review the recent designs of non-toxic or less toxic QDs, including carbon-based, biomolecules-based, silicon-based, and ternary I-III-VI QDs, and their biological applications (bio-imaging, drug delivery, gene therapy and immunoassay). 相似文献