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非晶合金,即金属玻璃,是一类特殊的由基本化学元素组成的非晶态物质,由于其独特的微观组织结构,展现出了不同于传统晶态合金材料的特殊物性,而成为高性能材料应用领域的重要一员.由于非晶合金的结构无序性,且当前精确表征其微观结构的实验手段缺乏,相应的理论模型也不完善,人们对非晶合金中一些基础物理问题的认识尚且不足,无法形成基本的理论框架来精确地描述其物性产生的微观机理.因而,当前非晶合金研究的核心问题可以概括为:如何建立以微观特征或结构为基础的基本理论框架,准确地概括非晶合金物性的微观机理.在过去几十年里,针对非晶合金的大量研究表明,在非晶合金长程无序的特征中,隐藏着本征的不均匀性和有序,且这些不均匀性的特征与材料物性有着密切的关联,使得建立以不均匀性特征为基础的理论框架成为可能.本文从非晶合金微观特征的不均匀性包括静态不均匀性和动态不均匀性的视角出发,概括性地总结了非晶合金材料与物理研究中取得的丰硕成果,及当前需要关注的重要科学问题,并针对未来可能的研究模式进行了展望. 相似文献
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从永磁体的分子电流观点、退磁场、工艺等出发, 以矩形永磁体为例, 从理论上分析了影响永磁体外部磁场不均匀性的各种因素.研究结果表明, 永磁体外部磁场宏观不均匀性(好场区均匀度和面积相对大小) 和空间距离及永磁体的外形设计密切相关. 退磁场对永磁体外部磁场微观不均匀性有着复杂影响. 永磁体工艺如粉末颗粒、取向度、烧结凝固、机械加工等将影响永磁体外部磁场的不均匀性, 如磁化偏角、对称性、光滑性等.
关键词:
永磁体
外部磁场
不均匀性
退磁场 相似文献
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基于分子动力学模拟技术,采用非高斯参数α_2(t)来描述单元体系Cu的玻璃转变过程中动力学不均匀性的变化.研究表明在β弛豫阶段,非高斯参数α_2(t)随时间的变化满足幂律函数,而非高斯参数峰值α_(max)和β弛豫时间τ_β与温度的关系均符合Arrhenius函数,且温度越接近玻璃转变温度T_g,体系的动力学不均匀性越明显. 相似文献
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通过对传统光伏组件测试设备检验方式的分析,提出了一种一次闪光就能够完成对测试仪工作平面辐照不均匀性测试的方法,在设计中充分使用了国际知名公司新生产的元器件,设计了信号调理电路和数据采集电路,电路设计简单,成本低廉易于实现,采集精度符合设计要求。并编写了上位机的测试程序,对辐照不均匀性测试进行了验证,结果表明测试工艺简单,数据可靠,生产效率高。 相似文献
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基于Zemax软件下的非序列模式(non-sequential mode)光线追迹法,分别模拟复合结构板条介质抽运端面和掺杂介质区工作端面上的光强度分布。由追迹结果可知,经过整形,在抽运面强度分布均匀的抽运光束经过非掺杂介质区传播到掺杂介质工作端面后光束分布均匀性大大降低。研究表明复合结构板条介质中非掺杂介质区影响了抽运光束,即抽运光在非掺杂介质区传播过程中发生全内反射,导致部分光束在实际工作端面的部分区域发生叠加,从而致使实际工作端面抽运光束分布不均匀。最后,依据平面波导匀化理论,从改变非掺杂介质区长度和入射光束发散角大小角度出发,提出改善抽运光束均匀性的思路,并进行了模拟验证。 相似文献
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It has been shown that plasma inhomogeneity reduces the threshold of the parametric instability of two-plasmon decay and, in particular, allows the excitation of plasmons with the same frequency by a spatially uniform pump field. 相似文献
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James Glimm John Grove Yongmin Zhang Srabasti Dutta 《Journal of statistical physics》2002,107(1-2):241-260
In this paper, we present a numerical study of the axisymmetric Richtmyer–Meshkov instability in converging spherical geometry by the front tracking method for the first time. The front tracking method has been successfully used in solving fluid instability problems in both rectangular and curved geometry.(1–6) The central issue for axisymmetric flows is the absence of the rotational symmetry in the (r, z) plane, although the perturbed shape of the initial contact interface appears to have it. The cause of the asymmetry is somewhat obvious. The sinusoidal perturbations appear symmetric only in the cross-sectional view; in actuality they are not symmetric because they represent rings around the z-axis and hence the perturbed mass at the equator, for example, is different from the perturbed mass at the pole. The first purpose of this paper is to quantify the effect of this inherited asymmetry on the growth of the spherical mixing. We find this asymmetry drives the original structure to some degree so that the mixing radius at the north pole is noticeably larger than at the equator during the evolution of chaotic mixing. We also study quantitatively the azimuthal dependence of the mixing statistics, such as the mixing edges, the growth rate and volume fraction. Richtmyer–Meshkov (RM) instabilities in spherical geometry have been a challenge due to the inherent difficulty of their accurate simulation. Our second purpose is to demonstrate that our Front Tracking method can describe the Richtmyer–Meshkov instability growth in a complex flow involving multiple reshocks. We have successfully displayed the converging geometry, reshock process, asymmetry phenomenon through the density and pressure color plots. The quantitative growth rate analysis is also presented. 相似文献
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The trifluoroacetyl distyryl derivative 1-[4-(2-{4-[2-(4-dibutylaminophenyl)-vinyl]-phenyl}-vinyl)-phenyl]-2,2,2-trifluoroethanone was compared with the related monostyryl derivative 1-{4-[2-(4-dibutylaminophenyl)-vinyl]-phenyl}-2,2,2-trifluoroethanone with respect to spectral properties and sensitivity to amines. Both trifluoroacetyl derivatives had their absorbance maximum at around 445 nm. The fluorescence of the distyryl dye, however, was observed at significantly longer wavelengths than that of the monostyryl dye, indicating the effect of structural extension of the chromophore system. Furthermore, the distyryl dye exhibited significantly smaller quantum yields in polar solvents than the monostyryl dye.Both dyes were capable of chemically reacting with amines in that their trifluoroacetyl function was converted into a hemiaminal. Consequently, absorbance and fluorescence of both dyes were shifted to shorter wavelengths. The positions of the fluorescence maxima of the spectra when converting from trifluoroacetyl to hemiaminal form were shifted by an almost identical amount for both mono- and distyryl derivative. The hemiaminal form of the distyryl derivative, however, exhibited much larger quantum yields in both polar and nonpolar solvents than the hemiaminal form of the monostyryl dye. The structural extension of the chromophore affected the sensitivity to amines by enhancing the chemical reactivity of the distyryl dye over the monostyryl derivative. 相似文献
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文章首先采用单相浮阻力模型对不同加速度下Rayleigh-Taylor不稳定性诱发的物质渗透边界的演化过程进行了计算, 揭示了该混合在常加速度和变加速度情况下不同的发展规律, 并通过与实验结果的比较分析, 验证了该模型的适用性.在此基础上, 发展了多相浮阻力模型, 采用该模型对常加速度情况下含尘气体中的Rayleigh-Taylor不稳定性诱导混合进行了研究, 发现混合区宽度随着颗粒数密度和颗粒尺寸的增大而减小, 揭示了气体中所含杂质抑制混合发展的规律. 相似文献
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The effect of uniform rotation on the self gravitational instability of an infinite homogeneous magnetised gas particle medium in the presence of suspended particles is investigated. The equations of the problem are linearized and the general dispersion relation for such system is obtained. The rotation is assumed along two different directions and separate dispersion relation for each case is obtained. The dispersion relation for propagation parallel and perpendicular to the uniform magnetic field along with rotation is derived. The effect of suspended particles on the different modes of propagation is investigated. It is found that in presence of suspended particles, magnetic field, rotation and viscosity, Jeans' criterion determines the condition of gravitational instability of gas-particle medium. 相似文献
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实验研究微波对蛋清蛋白粉与葡萄糖干样混合体系的影响,构建微波条件下蛋清蛋白-葡萄糖圆柱体反应模型。通过改变微波的功率,时间和位置,采用红外热像仪、荧光、紫外,高效液相色谱等方法研究微波场中蛋清蛋白糖基化产物不均匀性。将蛋清蛋白粉末与葡萄糖等质量混合,手工震荡和研钵充分研磨后在平皿表面铺一薄层粉末,放置于微波炉中心反应。将反应后的样品按左、中、右分成三个规则区域均匀采样。热像图表明微波功率越高,样品表面温度越高。凝胶电泳图表明240 W微波加热30 min样品边缘已经发生了反应,而且样品中间部分几乎还未反应;自由氨基含量测定表明高功率长时间微波作用才会观测到明显糖基化反应而低功率短时间条件下反应不明显,且边缘部分的样品反应总是比中间部分的样品剧烈;通过荧光光谱可知,蛋清蛋白和葡萄糖发生了反应,而样品边缘部分荧光强度降低得比样品中间部分多说明样品边缘反应更加剧烈;紫外光谱测定表明越剧烈的微波条件样品紫外吸收越多,边缘部分紫外吸收最高。液相结果也证实了这一点,糖基化样品边缘部分5-羟甲基糠醛(HMF)含量明显高于样品中间部分,且随时间和功率逐渐增加。 相似文献
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YANG Yinwei YUAN Baoshan YANG Qingwei ZHANG Yipo SONG Xianying LI Xu ZHENG Yinjia CAO Zeng 《核工业西南物理研究院年报(英文版)》2005,(1):17-19
1 Generation of vertical instability
Tokamak experiments show that the energy confinement time and performance are better, and the larger plasma current can be achieved for non-circular cross-sectional shape of plasma than circular cross-section. However, the external magnetic fields which are used to produce the non-circular cross sectional shape also cause the confined plasma to become unstable to small vertical displacement. In general, the ratio of elongation k is larger, the possibility of instability is more. In practice, this vertical displacement mode stabilized by feedback control system or other provided external radial magnetic field to balance out the plasma motion. Under some of situations the control system may be fail due to rapid growth rate of instability exceeding the ability of controlling. The plasma will then move vertically upwards or downwards depending upon the characteristics of instability and control failure. 相似文献
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Recently several rare earth chelates have been found that induce large and dramatic chemical shifts when complexed with a ligand.1 This is due to paramagnetic shielding, the mechanism of which is observed to be a pseudo-contact shift. In cases such as this involving dynamic equilibria where exchange of protons is rapid compared to observation time, the observed chemical shift represents an average environment determined by the time the proton nuclei spend at each site. The effective site of the complex is a lone pair donor such as the oxygen of a carbonyl group, alcohol, or ether, or the nitrogen of various nitrogen containing groups. The oxygen bearing compounds could theoretically form strong complexes with the added possibility of multiple complexes with chelates. The nitrogen bearing compounds of weak donor strength and containing only a lone pair would presumably form only the 1:1 complex. 相似文献