瑞利型非简并四波混频:一种研究超快过程的新方法

文章提出了用瑞利型非简并四波混频来研究物质的超快过程，与传统的时间领域技术不同，瑞利型非简并四波混频是一种频率领域的光谱学方法，它的时间分辨率与激光的脉冲宽度无关。     

瑞利增强非简并四波混频的时域不对称性研究

基于场关联原理,采用非相干光时延四波混频法研究了瑞利增强非简并四波混频的时域特性.利用二阶场关联函数理论揭示出混频信号在时域的细微变化,发现信号展示出时域不对称性并且在τ<0时会出现振荡结构,而这种时域不对称性反映了该三阶非线性极化过程的特点.     

用时间延迟方法压低喇曼增强非简并四波混频谱的热背底

证明了使用时延方法可再现淹没在热背底中的喇曼信号，并且喇曼增强非简并四波混频光谱恢复为通常煌带有源于分子取向栅非共振背底的非对称线型，实验结果与理论予示一致。     

四波混频光谱术

本文介绍我们用四波混频研究光与物质相互作用方面取得的新进展．其中包括拉曼增强非简并四波混频，用时间延迟方法区分分子取向栅及热栅，多能级吸收带的非相干光时间延迟四波混频，激光感生螺旋结构及用时间分辨简并四波混频研究原子的碰撞线宽变窄效应．     

布里渊增强非简并四波混频

在CS₂介质中观测到由声波引起的布里渊增强非简并四波混频(NFWM)和由分子取向栅产生的瑞利型NFWM.研究发现,分子取向栅与声波之间并不是相互独立的,声波的存在会破坏瑞利型NFWM和布里渊增强NFWM极化之间的相位关系. 关键词： 四波混频 布里渊散射 瑞利散射     

用喇曼增强非简并四波混频测量喇曼模的横向弛豫时间

在频率域研究了用喇曼增强非简并四波混频(RENFWM)测量喇曼模的横向弛豫时间,得到消背底的RENFWM光谱,对实验曲线进行拟合,获得苯和甲苯的振动模的横向弛豫时间分别为1.5ps和2ps。     

缀饰原子系统中双光子共振非简并四波混频

本文研究了缀饰原子系统中的双光子共振非简并四波混频.理论上我们研究了多普勒增宽的四能级系统中耦合光场对双光子共振非简并四波混频的影响,发现加入强耦合场后,非简并四波混频频谱出现Autler-Townes分裂;在不同双光子共振失谐时,由于量子干涉双光子共振非简并四波混频的信号能够被抑制或增强.实验上我们在Ba原子蒸汽中,通过引入基态6s2和自电离里德堡态6pnd之间的原子相干证实了该现象.本方法提供了一种不仅可以测得共振频率和横向弛豫,而且可以测得两个高激发原子态之间的跃迁的偶极矩阵元的新的光谱学工具.     

应用双非简并四波混频理论研究原子的碰撞效应

在己有实验的基础上,提出了由双光子共振非简并四波混频和碰撞再构非简并四波混频组成用于研究原子碰撞效应的双非简并四波混频理论,分析了缓冲气压、温度、共振失谐和碰撞展宽系数对双非简并四波混频谱线的影响.在由基态、中间态和激发态组成的级联三能级系统中,双非简并四波混频可同时研究碰撞引起的激发态谱线展宽和碰撞引起的中间态能级再分布现象.与测量纵向弛豫碰撞展宽的传统实验方法不同,本文方法是一种纯光学的相干测量技术,可以同时测量激发态与基态间的横向弛豫Γ_(20)和中间态与基态间的横向弛豫Γ_(21)的碰撞展宽.     

阿秒和频相位共轭极化拍频的不对称色锁二阶相干控制

研究了级联三能级系统中孪生色锁随机光场的相位共轭阿秒和频极化拍频(ASPB)不对称新效应。从理论上分析了自关联单光子简并四波混频(DFWM)和双光子非简并四波混频(NDFWM)信号辐射场与物质间不对等效应、混合型太赫兹失谐振荡特性,及双光子非简并共振四波混频信号的延时不对称性;同时也分析了由干涉计两臂不平衡色散效应引起的阿秒和频极化拍频信号的延时不对称性,即阿秒和频极化拍频信号的最大值相对于零延时有一个小偏移,结果表明该不对称性并这不影响阿秒和频极化拍频零差探测两偶极禁戒跃迁能级分裂的总体精度。阿秒和频极化拍频作为一种消除多普勒增宽的超快调制过程,从理论上说它可以扩展到任何两偶极禁戒跃迁能级系统。     

等离子体四波混频透射放大理论

研究了寻常波在磁化等离子体中四波混频透射放大理论，得到了简并和非简并时的精确解析解，其结果适用于非磁化等离子体中的电磁波四波混频． 关键词：     

Kinetic theory based lattice Boltzmann equation with viscous dissipation and pressure work for axisymmetric thermal flows

A lattice Boltzmann equation (LBE) for axisymmetric thermal flows is proposed. The model is derived from the kinetic theory which exhibits several features that distinguish it from other previous LBE models. First, the present thermal LBE model is derived from the continuous Boltzmann equation, which has a solid foundation and clear physical significance; Second, the model can recover the energy equation with the viscous dissipation term and work of pressure which are usually ignored by traditional methods and the existing thermal LBE models; Finally, unlike the existing thermal LBE models, no velocity and temperature gradients appear in the force terms which are easy to realize in the present model. The model is validated by thermal flow in a pipe, thermal buoyancy-driven flow, and swirling flow in vertical cylinder by rotating the top and bottom walls. It is found that the numerical results agreed excellently with analytical solution or other numerical results.     

Thermal transport in lithium-ion battery: A micro perspective for thermal management

In recent years, lithium ion (Li-ion) batteries have served as significant power sources in portable electronic devices and electric vehicles because of their high energy density and rate capability. There are growing concerns towards the safety of Li-ion batteries, in which thermal conductivities of anodes, cathodes, electrolytes and separator play key roles for determining the thermal energy transport in Li-ion battery. In this review, we summarize the state-of-the-art studies on the thermal conductivities of commonly used anodes, cathodes, electrolytes and separator in Li-ion batteries, including both theoretical and experimental reports. First, the thermal conductivities of anodes and cathodes are discussed, and the effects of delithiation degree and temperature of materials are also discussed. Then, we review the thermal conductivities of commonly used electrolytes, especially on solid electrolytes. Finally, the basic concept of interfacial thermal conductance and simulation methods are presented, as well as the interfacial thermal conductance between separator and cathodes. This perspective review would provide atomic perspective knowledge to understand thermal transport in Li-ion battery, which will be beneficial to the thermal management and temperature control in electrochemical energy storage devices.     

太阳能热利用技术概况

太阳能是理想的可再生能源.太阳能热利用技术目前还处于发展时期.文章对太阳能热利用成熟技术、先进技术以及当前研究的中心问题进行了简要的概述.成熟技术部分主要包括热水器、太阳灶、太阳房等广为人们使用的太阳能热利用技术;先进技术部分主要阐述了尚处于研究试验阶段的高品位太阳能热利用技术,包括太阳能热发电、太阳能空调制冷、太阳能制氢、太阳能海水淡化及太阳能烟囱发电等;在当前研究的中心问题部分,主要论述了解决太阳能热利用的关键技术问题.     

Carbon nanotube ballistic thermal conductance and its limits

Calculations of the quantum-mechanical ballistic thermal conductance of single-walled carbon nanotubes, graphene, and graphite are presented, which explain previous experimental results, and directly disprove earlier theoretical calculations. The ballistic thermal conductances are smaller than had been previously thought, whereas the maximum sample lengths in which phonon transport remains ballistic are orders of magnitude larger than previously suggested. Good agreement with previous experiments is obtained, which shows that measured lower bounds to the thermal conductance of multiwalled carbon nanotubes are very close to the upper theoretical bounds for graphite. The bounds shown here draw a line between what is physical and unphysical in any measurements or calculations of carbon nanotube thermal conductance, and constitute a necessary test to their validity.     

不规则形状热结构计算中的任意坐标变换和代数网格生成技术

航天器可重复使用防热结构通常需要采用数值模拟,进行外流场和结构热响应的耦合计算。本文针对前缘类热结构的差分计算中,关于不规则（不能用初等函数表示）区域的热响应计算,应用流场计算的思路,探讨了任意坐标变换和代数网格的生成。给出了有关控制方程、边界条件的处理方法,为进一步耦合计算提供了有关基础。     

Heat conduction in extended X-junctions of single-walled carbon nanotubes

Non-equilibrium molecular dynamics (NEMD) simulations are employed to investigate the longitudinal thermal conductivity of non-orthogonal extended X-junction (EX-junction) of single-walled carbon nanotubes (SWCNTs). Different from standard junctions of SWCNTs, two distinct jumps in the temperature profile around the EX-junction are observed, which are responsible for the larger temperature gradient and reduction in thermal conductivity when compared to standard X-junction. Quantum corrected results show that the longitudinal thermal resistance of the X-junction and EX-junction decreases monotonically with increasing temperature which makes the longitudinal thermal conductivity of the tube with junction less sensitive to temperature above 400 K comparing with the individual pristine tube. The origin of the significant decrease of thermal conductivity of EX-junction is discussed through phonon spectra analysis.     

SiNx薄膜热物性参数实验测量与分析研究

采用一种新的实验测量方案，将金属加热单元与温度探测单元合二为一，间接获得了在半导体和微电子学MEMS领域内有重要用途的SiN_x薄膜的导热系数、发射率、比热容和热扩散系数，并对实验结果进行了不确定度分析，为微电子电路设计和掩模成型工艺等提供了可靠的热物性数据. 实验结果表明，薄膜的导热系数、发射率、热扩散系数远比相应体材质低，而且还与温度、厚度有关，尺寸效应显著，而比热容则与体材质相差不大. 关键词： 微尺度传热 热物性参数 x薄膜')" href="#">SiN_x薄膜 测量技术     

矩形肋片热沉(火积)耗散率最小与最大热阻最小构形优化的比较研究

针对矩形肋片热沉, 分别以最大热阻最小化和基于(火积)耗散定义的当量热阻最小化为优化目标, 采用二维传热模型并结合有限元数值仿真对其进行构形优化, 比较了两种目标下的热沉最优构形, 并分析了全局参数(综合了对流换热系数、肋片占据的总面积及其热导率的函数)和材料占比对两种目标(最大热阻、当量热阻)及其对应最优构形的影响. 结果表明: 热沉外形固定时, 两种目标下均不存在最优的肋片厚度; 热沉外形自由变化时, 两种目标下的最优构形存在一定的差异. 此外, 全局参数对两种目标下的最优构形均没有影响, 而材料占比对两种目标下的最优构形均有较大影响. 提高全局参数和材料占比均可以减小最大热阻最小值和当量热阻最小值, 但对两种目标的减小程度不同. 总体上, 调节热沉结构参数使当量热阻最小, 可以同时获得很好的局部极限性能; 而调节热沉结构参数使最大热阻最小, 获得的整体平均散热性能却较差. 因此, 对本文热沉模型进行优化时, 以当量热阻最小化为优化目标更合理.     

一种测量生物组织热导率的新方法

采用脉冲衰减法可以测量生物组织热导率。但是,Chen等人提出的脉冲衰减法采用了“点热源”假设,而实际测量时,探头有一定的几何尺寸,由此造成了测量时的模型误差。本文采用数值实验的方法对这一误差及其影响因素进行了分析。在此基础上,提出了一种考虑了探头尺寸影响的新的脉冲衰减法,推导出了其测量公式。采用已知热导率的工质进行了验证试验,实验测量结果证实了本文对原有测量方法误差的分析;同时也表明,采用本文提出方法可以将测量误差减小到5%以下。     

Universal Biot number determining stress duration and susceptibility of ceramic cylinders to quenching

A universal Biot number, which not only describes the susceptibility of ceramic cylinders to quenching but also determines the duration that ceramic cylinders are subjected to thermal stress during thermal shock, is theoretically obtained. The analysis proves that thermal shock failure of ceramic cylinders with a Biot number greater than the critical value is a rapid process, which only occurs in the initial heat conduction regime. The results provide a guide to the selection of ceramic materials for thermostructural engineering, with particular reference to thermal shock.