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排序方式: 共有2456条查询结果,搜索用时 15 毫秒
21.
Single-phase polycrystalline samples of La0.67Ca0.33Mn1−xO3 (x=0.00, 0.02, 0.04, 0.06) have been prepared using the sol-gel method. The structure, magnetocaloric properties and the Curie temperature of the samples with different Mn vacancy concentrations have been investigated. The experimental results show that vacancy doping at the Mn-sites has a significant influence on the magnetic properties of La0.67Ca0.33Mn1−xO3. The Curie temperature decreases monotonically with increasing the Mn-site vacancy concentration x. A remarkable enhancement of the magnetic entropy change has been obtained in the La0.67Ca0.33Mn0.98O3 sample. The entropy change reaches |ΔSM|=3.10 J kg−1 K−1 at its Curie temperature (264 K) under an applied magnetic field H=10 kOe, which is almost the same value as that of pure Gd. 相似文献
22.
利用中子飞行时间技术和BC501A液体闪烁探测器的粒子分辨特性,测量了0°方向、20 MeV氘束轰击厚金属铍靶反应产生的中子源能谱,测量的中子能谱范围为0.7~25.0 MeV。在60°方向放置芪晶体闪烁探测器,由刻度好的BC501A液体闪烁探测器归一校正后,用于中子源强度监测。利用Be(d, n) 反应中子源,采用单粒子灵敏度标定方法,实验标定了0.75~15.75 MeV能量范围内的薄膜闪烁探测器中子能量响应曲线,实验结果与蒙特卡罗模拟计算结果在8%的不确定度范围内一致。 相似文献
23.
Hui Yao Peng-Bin Niu Chao Zhang Wei-Ping Xu Zhi-Jian Li Yi-Hang Nie 《The European Physical Journal B - Condensed Matter and Complex Systems》2018,91(3):57
We theoretically study the thermoelectric transport properties in a quantum dot system with two ferromagnetic leads, the spin-flip scattering and the external magnetic field. The results show that the spin polarization of the leads strongly influences thermoelectric coefficients of the device. For the parallel configuration the peak of figure of merit increases with the increase of polarization strength and non-collinear configuration trends to destroy the improvement of figure of merit induced by lead polarization. While the modulation of the spin-flip scattering on the figure of merit is effective only in the absence of external magnetic field or small magnetic field. In terms of improving the thermoelectric efficiency, the external magnetic field plays a more important role than spin-flip scattering. The thermoelectric efficiency can be significantly enhanced by the magnetic field for a given spin-flip scattering strength. 相似文献
24.
Ordered ferromagnetic-nonmagnetic heterogeneous Fe60Pb40 nanowire arrays were successfully fabricated by alternating current (AC) electrodeposition into nanoporous alumina templates. Transmission electron microscopy (TEM) image and selected-area diffraction (SAED) pattern analysis showed that the Fe60Pb40 nanowires are polycrystalline with an average diameter of 22 nm and lengths up to several micrometers. X-ray diffraction (XRD) observations indicated that α-Fe and fcc Pb phase coexist and do not form metastable alloy phase. The as-deposited samples were annealed at 200, 300, 400 and 500 °C, respectively. Magnetic measurements showed that nanowires have high magnetic anisotropy with their easy axis parallel to the nanowire arrays, and the coercivity of the samples increased with the annealing temperature up to 400 °C and reached a maximum (2650 Oe). The change of magnetic properties associated with the microstructure was discussed. 相似文献
25.
Synthesis of RGO/Cu8S5/PPy Composite Nanosheets with Enhanced Peroxidase‐Like Activity for Sensitive Colorimetric Detection of H2O2 and Phenol 下载免费PDF全文
Yanzhou Jiang Yan Gu Guangdi Nie Maoqiang Chi Zezhou Yang Ce Wang Yen Wei Xiaofeng Lu 《Particle & Particle Systems Characterization》2017,34(3)
In this paper, a novel strategy for the fabrication of reduced graphene oxide (rGO)/Cu8S5/polypyrrole (PPy) composite nanosheets with Cu8S5 nanoparticles and PPy layer anchored on the surface of rGO as peroxidase‐like nanocatalyst is reported. During the synthesis, graphene oxide (GO)/CuO composite nanosheets are prepared first and used as templates, then the sulfuration of CuO and polymerization of pyrrole are accompanied with the reduction of GO, resulting in ternary rGO/Cu8S5/PPy composite nanosheets. The synthesized Cu8S5 nanoparticles with a diameter in the range from tens to hundreds of nanometers are dispersed within PPy decorated rGO nanosheets. The resultant ternary rGO/Cu8S5/PPy composite nanosheets exhibit a higher peroxidase‐like catalytic activity toward the oxidation of 3,3′,5,5′‐tetramethylbenzidine in the presence of H2O2 than GO/CuO and rGO/CuS composite nanosheets, revealing a synergistic effect on their activity. The as‐prepared rGO/Cu8S5/PPy platform provides a simple colorimetric approach for the detection of H2O2 and phenol with a high sensitivity. This work offers a new way for the fabrication of rGO‐based nanocomposite with superior enzyme‐like activity, which displays great potential applications in biocatalysis and environmental monitoring. 相似文献
26.
发展了声腔的分析和数值模型,对液体火箭发动机不稳定燃烧的抑制作用进行了评定,通过迭代计算研究了二维流动和温度分布变化对声腔调 谐和稳定性能的影响,对不同的声腔几何尺寸和温度梯度的稳定性计算结果表明,燃烧带有较大开口面积的声腔会更大程度地改变振荡的空间分布,这种改变而且影响了驱动和抑制燃烧的机理,讨论了在声腔设计安排中正确选择声腔的几何尺寸,且比较了不同长度和不同直径声腔的阻尼特性,通过考察声吸收系统的方法来最优化系统的阻尼,得到了可供设计参考的结论。 相似文献
27.
Characterisation of precipitate phases in magnesium alloys using electron microdiffraction 总被引:1,自引:0,他引:1
Recent results of the characterisation of the structure, morphology and orientation of fine-scale, strengthening precipitate phases in selected magnesium alloys using transmission electron microscopy and microdiffraction are reviewed. The strengthening precipitate phases in Mg–Y–Nd alloys, aged to maximum hardness at 250°C, have been found to include two metastable precipitate phases β′ and β1, and the equilibrium precipitate β. The β′ phase has a globular form, a base-centred orthorhombic structure (potential point group of mmm), and an orientation relationship such that (100)β′//(1
10)α, [001]β′//[0001]α. The β1 phase has an f.c.c. structure (space group
and an orientation relationship that may be described by
(100)β1//[0001]α, and forms as plates parallel to
The β phase has an f.c.c. structure (space group
) and also forms as plates on
with an orientation relationship with the matrix phase that is identical to that observed for β1 phase. Precipitates in Mg–Al alloys, aged isothermally at 200°C, invariably have the b.c.c. structure of the equilibrium precipitate phase β (Mg17Al12). Three orientation relationships have been observed between β and the matrix phase. Most precipitates have an irrational orientation relationship that approximates to the Burger's relationship, (001)β//(0001)α,
and a faceted lath morphology with habit plane parallel to (0001)α. A minor fraction of precipitates posses an orientation relationship that is of the form
and have a prismatic rod morphology. The long axes of these rods are parallel to [0001]α, and their faceted surfaces are parallel to
A few precipitates are observed to have an orientation relationship such that
and a rod shape, with their long axes apparently inclined with respect to [0001]α. 相似文献
Full-size image
Full-size image
28.
29.
Qiuhua Nie Tiefeng Xu Xiang shen Xudong Zhang 《Journal of Physics and Chemistry of Solids》2006,67(11):2345-2350
The absorption and upconversion fluorescence spectra of a series of Er3+/Yb3+-codoped natrium-germanium-bismuth glasses have been studied. The transition probabilities, excited state lifetimes, and the branching ratios have been predicted for Er3+ based on the Judd-Ofelt theory. At room temperature, an upconversion efficiency of 6.1×10−2 has been obtained for the green emission from the glass with 0.5 wt% Er2O3 and 3.0 wt% Yb2O3 pumped by 980 nm radiation with an intensity of 270 W/cm2. And the “standardized” efficiency for green upconversion light is higher than that reported in lead-germanate, lead-tellurite-germanate, and silicate glasses. The results indicate that the Er3+/Yb3+-codoped natrium-germanium-bismuth oxide glass may be a potential material for developing upconversion optic devices. 相似文献
30.
基于孪生色锁噪声场的互相关效应,从理论上研究了倒V形(RV)四能级飞秒量级差频极化拍与极化拍中五阶非线性极化率,并提出了用一种相位敏感的方法来研究多能级原子相干造成的三光子六波混频过程.在抽泵光束为窄带末端情况下,场关联对信号和极化率的影响都很弱,在非窄带情况下,场关联会使极化强度自相干信号和极化拍信号产生关于零延时的不对称性和时域扫描上的辐射与物质失谐阻尼振荡(RDO),而极化率会产生频域扫描上的RDO振荡.参考光信号是一路传播方向和六波混频信号稍有区别的双光于非简并四波混频信号.五阶非线性响应则由享生
关键词:
外差法
吸收
色散
非线性极化 相似文献