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排序方式: 共有274条查询结果,搜索用时 156 毫秒
61.
Aleena Kiran Majid Niaz Akhtar Muhammad Yousaf Khalid Mujassam Batoo Omar M.Aldossary Salman Naeem Khan 《中国稀土学报(英文版)》2021,39(10):1224-1231
Rare earths(REs) play a key role in distorting spinel structure by creating some defects at the lattice sites and make them suitable for magnetodielectric applications.In the present study,the nanoferrites of CuRE_(0.02)Fe_(1.98)O_4,where REs=Y~(3+),Yb~(3+),Gd~(3+),were prepared using one step sol-gel method.The prepared samples are copper ferrite(CFO),yttrium doped copper ferrite(Y-CFO),ytterbium doped copper ferrite(Yb-CFO) and gadolinium doped copper ferrite(Gd-CFO),respectively.The single-phase structure of all the REs doped nanoferrites was determined by X-ray diffraction(XRD) analysis.The porosity,agglomerations and grain size of the REs doped copper ferrite were examined using field emission scanning electron microscopy(FESEM) analysis.Fourier transform infrared spectroscopy(FTIR)elaborates the phase formation and environmental effects on the REs doped nanoparticles(NPs).The recorded room temperature M-H loops from a vibrating sample magnetometer(VSM) elucidate the magnetic properties of the REs doped spinel nanoferrites.The magnetic saturation(M_s) was calculated in the range of 23.08 to 51.78 emu/g.The calculated coercivity values(272.6 to 705.60 Oe) confirm the soft magnetic behavior of REs doped copper ferrites.Furthermore,the electromagnetic and dielectric properties were assessed using a Vector network analyzer(VNA) from 1 to 6 GHz.The permeability,permittivity,dielectric tangent loss and electric modulus of the REs doped spinel ferrites illustrate that the prepared NPs may be suitable for microwave and high frequency applications. 相似文献
62.
63.
本文介绍了一个基于Web挖掘技术的中文专业搜索引擎的实现和所用的关键技术,提出了类别向量的概念以及如何将Web结构挖掘和内容挖掘结合起来,利用改进的VSM技术实 现网页自动分类的方法。 相似文献
64.
随着云存储服务的发展,越来越多的数据拥有者选择将数据外包给云服务商存储。为了保证数据的安全性,云服务器上的数据应该以密文形式存储。现有的多关键词密文检索技术不能兼顾准确性和安全性的问题,提出一种利用改进的向量空间模型和同态加密技术进行多关键词检索的方案。性能分析表明该方案能够有效地解决密文的多关键词检索问题。 相似文献
65.
Dynamic Web services discovery based on similarity computation 总被引:2,自引:0,他引:2
陈江锋 《哈尔滨工业大学学报(英文版)》2010,17(1):119-122
66.
传统的搜索引擎返回的数据太过庞大,很多情况下用户不能快速地找到自己要的答案。在这种情况下,文中引入FAQ系统。FAQ中如何找到最佳匹配答案,是文中的研究重点。改进了传统的VSM模型,使得它能更好地体现问题中词的权重。重点引人了LDA模型,并用计算机故障领域内的文档资料对它进行训练,得到主题-词的概率分布。通过主题-词中词的概率分布,计算词与词的相关度,提出通过词与词间相关度计算句子与句子间相似度的算法。对两个算法进行综合,得到最终的相似度算法。文中对FAQ进行整理,得到了FAQ问答系统的雏形。通过实验分析,说明相似度算法有很好的效果。 相似文献
67.
M. A. F. Basha 《应用聚合物科学杂志》2011,122(3):2121-2129
New nanocomposite hybrid films of a well dispersed cerium disulphate Ce(SO4)2 nanoparticles into the polyvinylpyrrolidone (PVP) matrix were prepared by a casting technique. The nanostructural nature and complex formation were investigated using the transmission electron microscopy (TEM), the nuclear magnetic resonance (NMR), and the Infrared (IR) spectroscopy. The magnetic measurements at room temperature, using a vibrating sample magnetometer (VSM), and the obtained magnetic parameters revealed that the investigated nanocomposites belong to a category of magnetically soft materials that find widespread applications in contemporary fine technologies. Optical absorption spectra were measured in the ultraviolet (UV)–visible region and the fundamental absorption edge Ea, the energy gap Eg and width of the tail of localized states Ee were evaluated and discussed in terms of the solid band theory. The monotonic increase of these optical parameters with the dopant concentration may be attributed to probable segregation effects occurring in the amorphous host matrix. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011 相似文献
68.
《Ceramics International》2020,46(6):7842-7849
W-type BaSr Co2 hexaferrites doped with Mn and Ti of the following composition Ba0.5Sr0.5Co2MnxTixFe16-2xO27 (x = 0.00, 0.50, 1.00, 1.50, 2.00, 2.50) were synthesized by sol-gel auto ignition method. The structure, phase, spectral bands, microstructure, and magnetic behaviors of the MnTi doped BaSr Co2 W-type ferrites were determined using XRD, FTIR, FESEM, and VSM respectively. Structural and physical parameters such as lattice parameters ‘a’ and ‘c’, crystallite size, cell volume, micro strain, porosity, bulk and X-ray density of the MnTi doped BaSr Co2 W-type hexaferrites were evaluated. The detailed and refined structural properties were determined using the Rietveld refinement of the MnTi doped BaSr Co2 W-type hexagonal ferrites. MAUD software was used for the refinement of the MnTi doped BaSr Co2 W-type hexagonal ferrites patterns. Rb, Rwp and Rexp values were found in the range of 10–19 for MnTi doped BaSr Co2 W-type hexagonal ferrites. The force constants at respective sites were also investigated through FTIR studies. FESEM images showed the hexagonal shape of the MnTi doped hexaferrites. Magnetic properties were estimated from the hysteresis loops recorded by VSM. The magnetic properties were decreased with the MnTi doping. However, anisotropic field was also found to be decreased with MnTi doping. This might be due to the ionic radii and nonmagnetic substitution of Ti in BaSr Co2 W-type hexagonal ferrites. The low coercivity values of these ferrites suggest the use of MnTi doped BaSr Co2 W-type ferrites for microwave absorption, memory devices and magnetic radar absorbing materials (MRAMs) in high frequency regime. 相似文献
69.
精益6 Sigma方法在SM公司JD生产线的应用 总被引:1,自引:0,他引:1
针对精益生产思想和6 Sigma管理方法的优缺点,提出只有采用集二者所长的精益6 Sigma方法,才能准确地分析生产价值流,找到生产线上存在的浪费和改进的机会.结合包装生产特点,详细阐述了精益6Sigma方法在包装生产线中的具体运用过程. 相似文献
70.
Obaid ur RahmanSubash Chandra Mohapatra Sharif Ahmad 《Materials Chemistry and Physics》2012,132(1):196-202
The present article reports an energy efficient method for the synthesis of superparamagnetic ferrite (Fe3O4) nanoparticles (10-40 nm) and their annealing effect on the morphology, size, curie temperature and magnetic behavior at 50, 300, 400 and 500 °C. The synthesized nanoparticles were characterized by various spectroscopic techniques like FT-IR and UV-visible. The crystalline structure and particle size were estimated through solid phase as well as the liquid phase using XRD, TEM and DLS techniques. Superparamagnetic behavior of nanoparticles was confirmed by VSM. The EPR study reveals that the main feature of X-Band solid state EPR spectrum has strong transition at geff ∼ 3.23 (2100G) and a relatively weak transition at geff ∼ 2.05 (3300G). The later transition further confirms the super paramagnetic nature of these nano ferrites. The activation energy and order of weight losses of nano ferrites were found to be: 39.6 KJ mol−1 and 0.21 orders (600-800 °C), respectively, analyze with the help of TGA while the specific surface area (23.1 m2 g−1) and pore size (9 Å) were determined by Quanta chrome BET instrument. 相似文献