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利用颗粒离散元方法,研究了由2048个有摩擦的单分散圆盘颗粒组成的体系在各向同性压缩条件下,颗粒摩擦系数μ对颗粒体系结构与振动特性的影响.结果表明:固定压强下,随μ的增大,区分德拜标度与态密度平台的过渡频率ω*与玻色峰频率ωBP均向低频移动,玻色峰高度D(ωBP)/ωBP逐渐增加.主要原因是μ增大导致颗粒体系无序程度增加(平均配位数减小)而在ωω*处出现了大量额外模式.模式分析表明:低频(ω1.0)模式主要是以平动为主的混合模式,中频(1.0ω4.0)模式主要是以平动为主的混合局域化模式,高频(ω4.0)振动模式几乎为纯转动的局域化模式;并且随μ的增大,低频下平动模式更加局域化,同时低频转动模式的贡献也逐渐增加,暗示在高摩擦系数下低频转动模式产生更重要的影响. 相似文献
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利用交叉激光束可以产生一个具有相同势阱且排列整齐的光学点阵.若将冷原子(例如铷原子)注射到光学点阵内,每个原子将会有序地排列在各个势阱内.但原子同时还能利用隧道效应由一个势阱向临近的势阱移动.这类运动是可以利用阱的深度、宽度和阱间距的大小进行控制.如果原子从一个势阱能很容易地向另一个势阱移动,这时光学点阵就会塌陷在一个量子态上,即玻色-爱因斯坦凝聚态(简称为BEC态).在BEC态,原子的集体行为就像是处于无障碍的超流态. 相似文献
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本文提出唯象的玻色型元激发模型,成功地解释低温下(<1K)玻璃的某些反常热力学行为:比热-温度的非线性关系,声速与温度的InT规律,并预测热膨胀系数仍保持为负值.
关键词: 相似文献
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对形如Nt×Nl型准二维无序系统,只考虑格点之间的最近邻跳跃积分,采用特殊的格点编号方案,在单电子近似下,系统的哈密顿量可表示为简明对称矩阵,借助豪斯荷尔德变换将其约化为对称三对角矩阵,再利用负本征值理论及传输矩阵等方法,对系统态密度、局域长度及电导等电子结构特性进行数值计算. 重点研究了准一维四平行链和五平行链无序系统, 将结果与一维单链、准一维双链及三链系统进行对比,发现随维度的增加,系统的能带有所展宽,能态密度分布发生很大的变化,其峰值数量呈偶数规律增加. 并且在能带中心处存在有局域长度大于系统大小的扩展态,处于这些态下的系统具有较大电导. 从单链到多链,相当于扩大了系统的关联范围,使系统出现了类似非对角长程关联的行为.
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准二维无序系统
态密度
局域长度
电导 相似文献
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采用半经典近似方法,研究简谐势阱中二维理想带电玻色气体的磁性质.推导出了该体系的热力学势、相变温度、内能、比热、磁场强度和磁化率随外加磁场的变化关系,进而分析了约束势阱对理想带电玻色气体热力学性质的影响. 相似文献
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n维理想玻色气体性质的普遍描述 总被引:10,自引:4,他引:6
给出了在T>Tc和T<Tc情况下能谱为ε=ap^s的n维简并理想玻色色体的内能、熵、状态程和热容量和普遍表达式。指出存在两种类型的玻以-爱因斯坦凝聚。 相似文献
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The low temperature specific heat of Sm-Al-Co ternary
metallic glasses is investigated and a clear anomaly associated with
the Boson peak is identified. While this anomaly depends slightly on
the chemical composition, it has no dependence on external magnetic
field. To figure out the mechanism of the Boson peak, we interpret
the data within various model frameworks. Unlike earlier
work, our study shows that this Boson peak is mainly ascribed to an
additional T2 term of the specific heat, which may originate
from the quasi-two-dimensional and short-range ordered structure
units possibly existing in the metallic glasses. 相似文献
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Asthalter T. Bauer M. van Bürck U. Sergueev I. Franz H. Chumakov A. I. 《Hyperfine Interactions》2002,144(1-4):77-83
Hyperfine Interactions - We have applied nuclear inelastic absorption (NIA) to the molecular glass former dibutylphthalate/ferrocene, both in bulk and in nanoporous matrices having pore sizes of 50... 相似文献
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在Sm2O3掺杂BaO-B2O3-Al2O3-SiO2-Sm2O3(BBASS)玻璃系统的形成性能的研究基础上,借助MAS NMR以及差热测试技术,研究了玻璃的结构特点以及玻璃组成、热处理条件等因素对玻璃结构的影响。研究表明,在未掺稀土的BBAS玻璃结构中,硼氧多面体主要以[BO3]、[BO4]存在,铝氧多面体主要以[AlO4]、[AlO5]、[AlO6]存在;随着BBAS中BaO含量的增加,硼氧三角体[BO3]逐渐向[BO4]转变,铝氧多面体中的[AlO5]、[AlO6]结构单元逐渐向[AlO4]转变;稀土Sm3+具有较强迫积聚作用,能促使玻璃结构中的硼氧多面体形成巨大的网络结构;热处理对玻璃结构中硼氧多面体和铝氧多面体的配位结构影响不大。 相似文献
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Nicolas F. Richet 《Physica B: Condensed Matter》2009,404(20):3799-3806
A simple method is used to determine in an absolute way the low-frequency part of the vibrational density of states, g(ω), from inversion of low-temperature heat capacities of glasses. Calculations have been made from adiabatic measurements performed from 10 to 300 K for vitreous SiO2 and a series of Li, Na and K silicate glasses with up to 50 mol% metal oxide. In all cases, the calculated low-frequency feature is made up of two bands whose maxima lie between 100 and 140 cm−1 and near 400 cm−1. Both the frequency and intensity of the first peak of g(ω) increase linearly with metal oxide content from pure SiO2 to the metasilicate stoichiometry, reflecting weaker bonding with nonbridging oxygens in the order Li, Na, K, i.e., in order of increasing cationic radius and mass. As represented by the peaks found below 50 cm−1 in plots of g(ω)/ω2 vs. ω and below 20 K in plots of Cp/T3 vs. T, the boson peak varies in a different way with composition. Its intensity increases with increasing polymerization for Li and Na silicates whereas the converse holds true for K silicates. These variations agree with the enhancement of the contribution of floppy modes and transverse acoustic modes to the low-frequency vibrational density of states that has previously been reported, but they also point to the importance of localized vibrations in which network modifier cations participate. For either the first peak of g(ω) or the boson peak, however, the size of the alkali cation exerts a stronger influence than the degree of polymerization of the anionic framework. Finally, the universal phenomenology of the boson peak is borne out by the collapse of the calorimetric data on a single master curve when one plots the measurements in a reduced form by using the intensity and position of the peaks as scaling parameters. 相似文献
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Chengguo Ming Hanxiong Liu Feng Song Xiaobin Ren Liqun An Yanming Hao Gangzhi Wang 《Current Applied Physics》2013,13(6):1109-1111
Phosphate glasses doped with Mn4+ ion were prepared using high temperature melting method. Under 408 nm excitation, the peak wavelength and lifetime of the fluorescence are related to the Mn4+ ion concentration. With the increasing of Mn4+ ion concentration, the fluorescence wavelength varies from 605 nm to 685 nm and the lifetime increases from several microseconds to one millisecond. The fluorescence wavelength is variable and the lifetime is tunable for our materials. 相似文献
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References: 《理论物理通讯》2007,47(1):41-44
Making use of the transformation relation among usual, normal, and antinormal ordering for the multimode boson exponential quadratic polynomial operators (BEQPO's)I we present the analytic expression of arbitrary matrix elements for BEQPO's. As a preliminary application, we obtain the exact expressions of partition function about the boson quadratic polynomial system, matrix elements in particle-number, coordinate, and momentum representation, and P representation for the BEQPO's. 相似文献
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Low-temperature, thermally-activated internal friction peaks have been observed in three binary metallic glasses containing only metallic components: Cu50Zr50, Co35Y65 and Co35Dy65. The magnitudes of the activation energies and the characteristic relaxation times obtained for these materials as well as the sharpness of the peaks point to process involving either atomic jumps of a specific nature or similar localized reordering. Possible local structural configurations with built-in, non-uniform stress distributions that could lead to such relaxation effects are discussed. 相似文献