厄米-高斯光束在非Kolmogorov大气湍流中的传输性质

基于广义惠更斯-菲涅尔原理和非Kolmogorov(非K)谱,推导出了厄米-高斯光束在非K大气湍流中传输的束宽、角扩展以及M²因子的解析表达式.数值计算表明,在传输距离比较远(如z≥3 km)时,厄米-高斯光束的束宽、角扩展和M²因子随广义指数参量α的增大而增加直到α=3.11时达到最大值后再随α的增大而减小;随湍流的内尺度l₀的减小而增大;随外尺度l₀的增加而增大(3.6<α<4).但是当广义指数参量α在3<α<3.6区间取值时,束宽和M²因子几乎不随外尺度的增加而变化.     

Hulthén势散射态的解析解

在任意l波的离心项1/r²用λ²e^-λr/(1-e^-λr)²近似表达的条件下,对Hulthén势的径向Schrdinger方程作自变量指数变换,使此转化为超几何微分方程,获得了Hulthén势s波散射态的精确解和非s波散射态的近似解析解.给出了相移的解析表达式和按“k/2π标度”归一化的用超几何函数表示的径向波函数.讨论了解析解的意义.     

利用原子芯片上Z形磁阱囚禁中性87Rb原子

利用解析和数值方法计算了Z形磁阱的囚禁势，发现当囚禁中心和芯片表面距离较远时(该距离和Z形线中部导线的一半长度相差不超过一个量级)，势阱的深度不能近似表示成偏置磁场B_y对应的能量，而要减去囚禁中心的势能高度；而增加B_y进行磁阱压缩到一定值时，势阱深度反而会下降.此外介绍了原子芯片的制作方法，以及利用原子芯片上Z形磁阱囚禁中性⁸⁷Rb原子的实验装置和实验过程.最终有2×10⁶个⁸⁷Rb原子被转移到Z形磁阱中.     

红宝石Cr3+:Al2O3的电子云延伸效应及压力对电子云延伸效应影响(英文)

本文以Cr³⁺自由离子的3d电子径向波函数为基础,对Cr³⁺:Al₂O₃中的电子云延伸效应进行了理论研究,引入了电子云延伸效应系数κ,得到了Cr³⁺:Al₂O₃中Cr³⁺离子的最优化3d电子径向波函数.并研究了压力对电子云延伸效应系数κ的影响.     

Nd掺杂对Bi4Ti3O12铁电薄膜的微结构和铁电性能的影响

利用溶胶-凝胶法在Pt/Ti/SiO₂/Si(100)衬底上制备了Nd掺杂Bi₄Ti₃O₁₂(Bi_4-xNd_xTi₃O₁₂, x=0.00,0.30,0.45,0.75,0.85,1.00,1.50)铁电薄膜样品.研究了Nd掺杂对Bi₄Ti₃O₁₂薄膜的微结构和铁电性能的影响.研究结果表明:Nd掺杂未改变Bi₄Ti₃O₁₂薄膜的基本晶体结构.在掺杂量x<0.45时,Nd³⁺只取代类钙钛矿层中的A位Bi³⁺.当x=0.45时,样品剩余极化强度达最大值,在270kV·cm^-1的电场下为32.7μC·cm^-2.掺杂量进一步增加时,结构无序度开始明显增大,Nd³⁺开始进入(Bi₂O₂)²⁺层,削弱其绝缘层和空间电荷库的作用,导致材料剩余极化逐渐下降.当掺杂量x达到1.50时,掺杂离子最终破坏(Bi₂O₂)²⁺层的结构,材料发生铁电-顺电相变.     

Dissipation of a two-mode squeezed vacuum state in the single-mode amplitude damping channel

We explore how a two-mode squeezed vacuum state sechθ e^{a+b+ tanh θ} |00> evolves when it undergoes a singlemode amplitude dissipative channel with rate of decay κ. We find that in this process not only the squeezing parameter decreases, tanh θ → e^-κt tanh θ, but also the second-mode vacuum state evolves into a chaotic state exp{b⁺bln[1 - e^-2κt tanh² θ]}. The outcome state is no more a pure state, but an entangled mixed state.     

第Ⅱ种强度不等的两态叠加多模叠加态光场的等阶N次方H压缩——2腔模总数与压缩阶数两者之积取奇数的情形

构造了由多模复共轭相干态的相反态|{-Z_j^(a)*}〉q和多模虚共轭相干态的相反态|{-Z_j^(b)*}〉q的线性叠加所组成的第Ⅱ种强度不等的非对称两态叠加多模叠加态光场|Ψ(ab)Ⅱ〉q.利用多模压缩态理论,研究了态|Ψ(ab)Ⅱ〉q的等阶N次方H压缩特性.结果发现,在腔模总数与压缩阶数这两者之积取奇数,则当各对应模的初始相位、各对应模的初始相位差,态间的初始相位差、以及光子干涉项的幅度之和等分别满足一定的量子化条件时,态|Ψ(ab)Ⅱ〉q的第一及第二正交分量可分别呈现出周期性变化的等阶N次方H压缩效应.这与现有报道的结果截然不同.     

增加光子奇偶q相干态的高阶压缩效应

通过数值计算研究了增加光子奇q相干态a_q^+m|α>_q^o和增加光子偶q相干态a_q^+m|α>_q^e的高阶压缩效应.结果表明:当q较小时,态a_q^+m|α>_q^o和a_q^+m|α>_q^e都能呈现出强烈的奇次方阶压缩效应,但无偶次方阶压缩效应,而且奇次方阶压缩随m的增大而增强.当m=0时a_q^+m|α>_q^o和a_q^+m|α>_q^e为光场振幅偶次幂的最小测不准态,但当m≠0时它们不是光场振幅偶次幂的最小测不准态.     

2+1维U(1)格点胶球质量的变分计算

本文对具有严格基态解和正确经典连续极限的格点规范哈密顿量,采用变分法,计算了2+1维U(1)规范群0^+－和0⁺⁺胶子态的质量,在深度弱耦合区,得到am(0^+－)随1/g²增大而指数减少,而am(0⁺⁺)=2.78g².     

Dissipation of a two-mode squeezed vacuum state in the single-mode amplitude damping channel

We explore how a two-mode squeezed vacuum state sechθ e^{a+b+ tanh θ} |00> evolves when it undergoes a singlemode amplitude dissipative channel with rate of decay κ. We find that in this process not only the squeezing parameter decreases, tanh θ → e^-κt tanh θ, but also the second-mode vacuum state evolves into a chaotic state exp{b⁺bln[1 - e^-2κt tanh² θ]}. The outcome state is no more a pure state, but an entangled mixed state.     

Phonon transmission and thermal conductance in one-dimensional system with on-site potential disorder

The role of on-site potential disorder on phonon transmission and thermal conductance of one-dimensional system is investigated. We found that the on-site potential disorder can lead to the localization of phonons, and has great effect on the phonon transmission and thermal conductance of the system. As on-site potential disorder W increases, the transmission coefficients decrease, and approach zero at the band edges. Corresponding, the thermal conductance decreases drastically, and the curves for thermal conductance exhibit a series of steps and plateaus. Meanwhile, when the on-site potential disorder W is strong enough, the thermal conductance decreases dramatically with the increase of system size N. We also found that the efficiency of reducing thermal conductance by increasing the on-site potential disorder strength is much better than that by increasing the on-site potential?s amplitude.     

聚对苯撑/LiNi0.5Fe2O4纳米复合热电材料的制备及其性能研究

本文以流变相反应法原位合成了聚对苯撑/LiNi_0.5Fe₂O₄纳米复合热电材料,并对其热电性能进行表征,研究了放电等离子烧结时保温时间对其热电性能的影响.结果发现,复合材料铁氧体颗粒粒径为100---300nm,其外部被一层聚对苯撑膜包覆.电子在Fe²⁺和Fe³⁺之间的跳跃机理在铁氧体电导中占主导作用,因此聚对苯撑/LiNi_0.5Fe₂O₄复合材料具有n型导电特性.随着保温时间增加,复合材料电导率基本不变,但热导率逐渐增大且Seebeck系数逐渐减小,导致热电优值系数降低.由于结合了有机物高电导率和低热导率以及无机材料高赛贝克系数的优点,所制备的复合材料热电性能较单一材料有较大提高.     

Nb掺杂对还原性烧结的TiO2-δ陶瓷的晶体结构及热电性能的影响

利用传统的固相反应法在还原性气氛1200 ℃下分别制备出不同Nb掺杂量的Ti_1-xNb_xO_2-δ陶瓷样品.样品的粉末X射线衍射(XRD)结果显示:Nb掺杂量x较低时样品为多相混合,当Nb掺杂量x>0.02时样品为单一的四方相金红石型结构.在室温到900 K的测试温区,测试了单相样品(x=0.02,0.03,0.04)的电导率、Seebeck系数和热导率.测试 关键词： 氧化钛陶瓷 热电性能 氧空位     

Controlling the energy flow in nonlinear lattices: a model for a thermal rectifier

We address the problem of heat conduction in 1D nonlinear chains; we show that, acting on the parameter which controls the strength of the on-site potential inside a segment of the chain, we induce a transition from conducting to insulating behavior in the whole system. Quite remarkably, the same transition can be observed by increasing the temperatures of the thermal baths at both ends of the chain by the same amount. The control of heat conduction by nonlinearity opens the possibility to propose new devices such as a thermal rectifier.     

Experimental Investigation of Laminar Heat Transfer Inside Trapezoidal Duct Having Different Corner Angles

In this study, steady-state laminar forced flow and heat transfer in a horizontal smooth trapezoidal duct having different corner angles were experimentally investigated in the Reynolds number range from 10² to 10³. Flow is hydrodynamically fully developed and thermally developing under a uniform surface temperature condition. Based on the present experimental data of laminar flow in the thermal entrance region, new engineering correlations were presented for the heat transfer and friction coefficients for each corner angle. The results have shown that as the Reynolds number increases heat transfer coefficient increases but Darcy friction factor decreases. Also, it is observed that average Nusselt number increases while average Darcy friction factor decreases with increasing corner angle of the duct.     

Effects of fullerene coalescence on the thermal conductivity of carbon nanopeapods

The heat conduction and its dependence on fullerene coalescence in carbon nanopeapods (CNPs) have been investigated by equilibrium molecular dynamics simulations. The effects of fullerene coalescence on the thermal conductivity of CNPs were discussed under different temperatures. It is shown that the thermal conductivity of the CNPs decreases with the coalescence of encapsulated fullerene molecules. The thermal transmission mechanism of the effect of fullerene coalescence was analysed by the mass transfer contribution, the relative contributions of phonon oscillation frequencies to total heat current and the phonon vibrational density of states (VDOS). The mass transfer in CNPs is mainly attributed to the motion of encapsulated fullerene molecule and it gets more restricted with the coalescence of the fullerene. It shows that the low-frequency phonon modes below 20 THz contribute mostly to thermal conductivity in CNPs. The analysis of VDOS demonstrates that the dominating contribution to heat transfer is from the inner fullerene chain. With the coalescence of fullerene, the interfacial heat transfer between the CNT and fullerene chain is strengthened; however, the heat conduction of the fullerene chain decreases more rapidly at the same time.     

Experimental study of heat transfer characteristics in oscillating fluid flow in tube

In the present work, an experimental investigation of heat transfer enhancement parameters of the oscillating flow heat exchanger under different frequencies, tidal displacement, and heat fluxes is carried out. The effect of different parameters on experimental effective thermal conductivity and convective heat transfer coefficient in cooling region is studied using correlations given by different researchers. A correlation for experimental effective thermal conductivity in terms of S²√ω is derived based on experimental data. This correlation is useful for predicting the optimum value of S²√ω before onset of turbulence.     

Phonon relaxation and heat conduction in one-dimensional Fermiben Pastaben Ulam β lattices by molecular dynamics simulations

The phonon relaxation and heat conduction in one-dimensional Fermi-Pasta-Ulam (FPU) β lattices are studied by using molecular dynamics simulations. The phonon relaxation rate, which dominates the length dependence of the FPU β lattice, is first calculated from the energy autocorrelation function for different modes at various temperatures through equilibrium molecular dynamics simulations. We find that the relaxation rate as a function of wave number k is proportional to k^1.688, which leads to a N^0.41 divergence of the thermal conductivity in the framework of Green-Kubo relation. This is also in good agreement with the data obtained by non-equilibrium molecular dynamics simulations which estimate the length dependence exponent of the thermal conductivity as 0.415. Our results confirm the N^2/5 divergence in one-dimensional FPU β lattices. The effects of the heat flux on the thermal conductivity are also studied by imposing different temperature differences on the two ends of the lattices. We find that the thermal conductivity is insensitive to the heat flux under our simulation conditions. It implies that the linear response theory is applicable towards the heat conduction in one-dimensional FPU β lattices.     

Single-Phase Convective Heat Transfer of Water and Aqua Ethylene Glycol Mixture in a Small-Diameter Tube

A tailor-made convective heat transfer test facility is constructed to study the single-phase convective heat transfer of deionized water and 30 vol% and 60 vol% aqua–ethylene glycol in a stainless steel tube of 4 mm in inner diameter and 1 m in length. The heat flux is varied between 1 and 4 kW·m^?2 and for mass flux ranging from 160 to 475 kg·m^?2 s^?1. The experiments were predominantly conducted only for laminar flow regime. Finally, the heat transfer coefficient is recorded and compared with the conventional theories. It is observed that the presence of ethylene glycol in water decreases the heat transfer coefficient by more than 50%, due to the decreased Reynolds number and thermal conductivity of the mixture.     

碳纳米管电缆式复合材料的热导率

通过非平衡分子动力学方法, 对单壁碳管填充金纳米线的碳纳米管电缆式复合材料开展热导率的模拟分析. 采用Tersoff势函数描述碳-碳原子间的相互作用, Lennard-Jones长程作用势描述碳-金原子间的相互作用, 嵌入原子势函数描述金-金原子间相互作用. 研究结果表明: 相同尺寸下, 金纳米线的电子热导率相较于空碳管以及电缆式复合材料的声子热导率小很多, 对复合材料总热导率的贡献可以忽略; 由于管内金纳米线的存在, 其与碳管的相互作用使得碳管碳原子倾向于沿着轴向振动, 声子间U散射随之减少, 声子平均自由程增加, 导致复合材料热导率明显大于空碳管, 在100–500 K温度范围内高出约20%–45%, 但增大幅度随温升呈降低趋势; 复合材料热导率随着管长增加而增大, 变化趋势和空碳管相似, 但其增长幅度更大; 复合材料和空碳管的热导率随管径增大而减小, 且变化幅度基本一致. 关键词： 碳纳米管 纳米线 电缆式复合材料 导热