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排序方式: 共有3568条查询结果,搜索用时 15 毫秒
1.
K.M. Srinivasamurthy Jagadeesha Angadi V S.P. Kubrin Shiddaling Matteppanavar D.A. Sarychev P. Mohan Kumar Haileeyesus Workineh Azale B. Rudraswamy 《Ceramics International》2018,44(8):9194-9203
Ferrites may contain single domain particles which gets converted into super-paramagnetic state near critical size. To explore the existence of these characteristic feature of ferrites, we have performed magnetization(M-H loop) and Mössbauer spectroscopic studies of Ni2+ substitution effect in Co1-xNixFe2O4 (where x?=?0, 0.25, 0.5, 0.75 and 1) nanoparticles were fabricated by solution combustion route using mixture of carbamide and glucose as fuels for the first time. As prepared samples exhibit spinel cubic structure with lattice parameters which decreases linearly with increase in Ni2+ concentration. The M-H loops reveals that saturation magnetization(Ms), coercive field(Hc) remanence magnetization(Mr) and magnetron number(ηB) decreases significantly with increasing Ni2+ substitution. The variation of saturation magnetization has been explained on the basis of Neel's molecular field theory. The coercive field(Hc) is found strongly dependent on the concentration of Ni2+ and decrease of coercivity suggests that the particles have single domain and exhibits superparamagnetic behavior. The Mössbauer spectroscopy shows two ferrimagnetically relaxed Zeeman sextets distribution at room temperature. The dependence of Mössbauer parameters such as isomer shift, quadru pole splitting, line width and hyperfine magnetic field on Ni2+ concentration have been discussed. Hence our results suggest that synthesized materials are potential candidate for power transformer application. 相似文献
2.
Maria Yousaf Lodhi Muhammad Azhar Khan Majid Niaz Akhtar Muhammad Farooq Warsi Asif Mahmood Shahid M. Ramay 《Ceramics International》2018,44(3):2968-2975
The influence of neodymium and nickel substitution on structural and dielectric parameters was investigated in strontium-barium X-type hexagonal ferrites having composition SrBaCu2?xNixNdyFe28?yO46 (x = 0, 0.2, 0.4, 0.6, 0.8, 1 and y = 0, 0.02, 0.04, 0.06, 0.08, 0.1). Sol-gel method was employed for synthesizing these hexagonal ferrites. The XRD plots of all studied materials which were annealed at 1250 °C show single phase characteristics. Lattice parameter ‘c’ increased as a consequence of larger radius of rare earth ion (Nd3+) as compared to (Fe3+), while lattice parameter ‘a’ showed very small variation. The cell volume was obtained in the range 2508.32–2523.75 (Å3). The inclusion of Nd-Ni also affected X-ray density, bulk density and porosity. The FTIR spectroscopy indicated the particular absorption peaks of hexagonal ferrites and it was performed in the range of 500–700 cm?1. On account of Nd-Ni doping, the dielectric constant, dielectric loss and AC-conductivity showed decreasing trend. The occupancy of Nd3+ ions at octahedral site impedes the valence alternation of Fe3+; therefore there was decrease in dielectric permittivity. Ac conductivity has been decreased from 9.14 to 6.49 (Ω cm)?1 at frequency of 2.7 GHz. The Cole-Cole plots of synthesized materials noticeably revealed grain boundary contribution. The appearance of single semi-circle in impedance Cole-Cole graphs confirms the exceptional role of grain boundaries in the conduction process. The considerably lower dielectric parameters of investigated nano X-type ferrites propose their feasibility for high-frequency applications (phase shifters, dielectric resonators, stealth technology etc). 相似文献
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在恶劣天气和机械故障等原因造成航班不能按照原计划执行时,航空公司需要采取相应的措施对航班进行恢复。本文基于经典的资源指派模型,综合考虑了调整时间、换机、联程拉直、取消航班和调机5种恢复策略,提出一种以最小化加权成本为优化目标的航班恢复模型,并设计一种迭代局部搜索算法。首先用构造-修复启发式方法构造可行解,然后从该初始解出发,在飞机路线对的邻域中进行局部搜索。当陷入局部最优后,对解进行扰动,然后从扰动后的解重新出发进行局部搜索。为了提高搜索效率,同时降低陷入局部最优解的概率,局部搜索过程采用模拟退火算法。实例结果表明,本文提出的模型及算法能够在短时间内对受到影响的大规模航班计划进行恢复。 相似文献
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Andrea Mariela Araya-Sibaja Valdir Soldi Carlos Eduardo Maduro Campos Simone Gonçalves Cardoso 《Drug development and industrial pharmacy》2015,41(5):851-858
Progesterone is a natural hormone steroid used in humans for several treatments and in livestock for artificial insemination, which exhibits two polymorphic forms at ambient conditions: form 1 and form 2. Form 2 is metastable and more soluble than form 1; however, it is not suitable to use as powder raw material because it transforms into form 1 by the effects of grinding. A polymorphic screening of progesterone based on polymer-induced heteronucleation method was performed as an alternative to prepare the metastable form. Polyvinyl alcohol, hydroxypropyl methylcellulose (HPMC), dextran, gelatin, polyisoprene (PI) and acrylonitrile-butadiene (NBR) copolymer were used. Crystals were prepared from 0.5, 10 and 40?mg/mL solutions in acetone at room temperature by solvent evaporation. The samples were characterized by X-ray powder diffraction, differential scanning calorimetry (DSC), scanning electron microcopy and attenuated total reflectance infrared Fourier transform spectroscopy. Form 1 was nucleated from 40?mg/mL solutions on the six polymers and from 10?mg/mL solutions on PI and NBR. The mixture of form 1 and form 2 was obtained from 10?mg/mL solution on HPMC, dextran and gelatin and from 0.5?mg/mL solution crystallizations. Therefore, the polymeric devices, which crystallized the metastable and more soluble polymorph (2) of progesterone, would be a promissory alternative for the pharmaceutical applications. 相似文献
7.
The rapid increase in energy demand, the extensive use of fossil fuels and the urgent need to reduce the carbon dioxide emissions have raised concerns in the transportation sector. Alternate renewable and sustainable sources have become the ultimate solution to overcome the expected depletion of fossil fuels.The conversion of lignocellulosic biomass to liquid(BtL) transportation fuels seems to be a promising path and presents advantages over first generation biofuels and fossil fuels. Therefore, development of BtL systems is critical to increase the potential of this resource in a sustainable and economic way.Conversion of lignocellulosic BtL transportation fuels, such as, gasoline, diesel and jet fuel can be accomplished through various thermochemical processes and processing routes. The major steps for the production of BtL fuels involve feedstock selection, physical pretreatment, production of bio-oil, upgrading of bio-oil to transportation fuels and recovery of value-added products. The present work is aiming to give a comprehensive review of the current process technologies following these major steps and the current scenarios of biomass to liquid facilities for the production of biofuels. 相似文献
8.
露天矿山路径优化问题是指在满足特定物理和经济约束之下,搜索最佳运输线路的组合优化问题,对于降低矿山运营成本具有重要的现实意义。但目前常规的露天矿山路径优化算法,主要从静态的道路有向图网络优化出发,无法实现大规模时变动态网络的高效分析和优化决策。本文以扎哈淖尔露天矿为例,将欧式空间内经典的有向图网络分析方法扩展至Clifford代数空间,建立了节点、有向边以及路径的统一表达,提出了路径几何拓扑连通性和标量约束指标的计算方法,实现了几何拓扑计算和数值最优化求解问题的分离;针对传统静态网络分析方法无法动态表达系统能耗变化的问题,建立了基于时变运输功最小化的路径优化模型,并结合行驶阻力特征给出了时变阻力的计算方法;研究了因路面频繁碾压破坏和周期性维护而导致的滚动阻力系数周期性时变效应,并提出计算时变滚动阻力系数的方法;最后为进一步提高算法收敛效率,提出了两组推论和一组数值计算优化策略对遗传算法的数值计算进行了改进。经多次仿真实验验证,算法能快速收敛于全局最优解,说明了算法对于解决矿山实际路径优化问题可行且有效。其次,几何代数化方法的引入也为传统路径优化问题求解提供了一种有效实现拓扑关系计算和数值计算解耦的新方法,弥补了静态网络无法实现时变动态网络分析的不足,为提高露天矿运输系统大规模路网模型的快速效率,提供了一种全新的求解思路。 相似文献
9.
Yin Liu Zhecheng Wang Li Zhao Jun Zhou Yueqin Wang 《Journal of the American Ceramic Society》2019,102(11):6680-6687
xSrFe12O19/(1−x)NiFe2O4 composites (0 ≤ x ≤ 1.0) were synthesized by using a conventional solid-state synthetic route. The results show that magnetic hysteresis loops of the xSrFe12O19/(1−x)NiFe2O4 composites are similar to those of individual component ferrites, except for the 0.1SrFe12O19/0.9NiFe2O4 and 0.3SrFe12O19/0.7NiFe2O4, suggesting that the hard/soft magnetic phases are well exchange-coupled. The saturation magnetization, coercivity, and remanent magnetization of the xSrFe12O19/(1−x)NiFe2O4 composites are increased with increasing content of SrFe12O19, with maximal values of 42.1 Am2 kg−1, 78.7 kA m−1, 17.2 Am2 kg−1, respectively, as the content x is about 0.5. They are higher than those of the individual components, implying that interface coupling is present in the magnetic composites. The coercivity and remanent magnetization of the composites are increased initially with increasing sintering temperature and then show a downward tendency. For the component SrFe12O19 and NiFe2O4, the minimum reflection losses are −12.5 dB and −18.3 dB at match thicknesses of 2.5 mm and 2 mm, respectively. Compared with those of the component SrFe12O19 and NiFe2O4, the microwave absorption performances of the xSrFe12O19/(1−x)NiFe2O4 composites are improved remarkably, especially for the samples of x = 0.3 and x = 0.9. The minimum reflection losses values of the 0.3SrFe12O19/0.7NiFe2O4 composite are −31.6 dB (12.7 GHz) and −20.2 dB (13 GHz), while those of the 0.9SrFe12O19/0.1NiFe2O4 composites are −23.7 dB (16.3 GHz) and −33.5 dB (15.8 GHz), as the matching thicknesses are 2.5 mm and 2 mm, respectively. Therefore, the xSrFe12O19/(1−x)NiFe2O4 composites could be used as potential microwave absorption materials. 相似文献
10.
为探究南水北调中线水源区丹江口水库浮游植物群落结构变化及其生物多样性,于 2014—2015 年对丹江
口水库进行为期 1 年的调查和分析。发现浮游植物共 8 门 76 属 101 种,其中,绿藻门、蓝藻门及硅藻门占总种数
90.10%,绿藻门种类数最多(45 种),其次是蓝藻门(26 种)和硅藻门(20 种)。浮游植物群落结构随季节变化有所
不同:夏秋季节生物量明显高于冬春季节;优势种在冬季以颗粒直链藻、颗粒直链藻极狭变种、铜绿微囊藻和小
环藻为主,春季以球衣藻、薄甲藻属及小环藻为主,夏季以简单颤藻、单胞衣藻原变种和球衣藻为主,秋季以类颤
藻鱼腥藻、简单颤藻、球衣藻和小环藻为主。应用 Shannon-Wiener 多样性指数 H′、Pielou 均匀度指数 J′、Margalef
丰富度指数 Dm评价水质结果表明:丹江口水库夏秋季水体营养化程度更高。典型对应分析表明:水温、透明度、
总氮、总磷等是影响浮游植物群落结构的主要环境因子,夏秋季受温度影响蓝藻、绿藻数量逐渐增多,一定程度
上增加了受水区生态变化风险。本研究可为南水北调中线水源区丹江口水库生态环境变化及生物迁移风险提供
数据支持。 相似文献