石墨烯薄膜热声性能的三维数值计算与测试

对石墨烯薄膜进行电-热-声耦合的三维建模计算,并将计算结果与实验测试值进行对比分析。首先建立了通电石墨烯薄膜焦耳热的三维模型,计算出石墨烯薄膜表面的温度振荡和稳态温度分布;在此基础上,建立了热黏性声学和压力声学耦合的声扩散模型,计算出空间中声压的分布;分析了基底和空气参数对石墨烯薄膜发声的影响;最后对通电石墨烯薄膜进行温度测试和声压测试。结果表明：三维模型数值计算的温度分布与测试结果吻合良好,数值计算的声压值比一维近似解析解更接近实验值,验证了数值计算方法的有效性。三维模型的数值计算方法在复杂边界条件下分析薄膜的声学性能更具优势。     

热声制冷中的工质选择

在分析热声工作机理,探讨混合工质在热声制冷机中的作用机理的基础上,从工作频率及效率的角度出发,指出了低Ｐｒ数的混合工质对热声效应的积极作用,有利于提高热声驱动器及热声制冷的工作效率,低声速则有利于增强热声转换强度,为选用合适的工作介质提供了依据。     

热声热机的理论研究及其进展

热声现象很早就受到了科学家的注意,近年来在理论上和实际中都有了重大的发展。重点回顾了近几十年来,国内外学者在热声热机理论研究方面取得的重大成就以及目前理论存在的不足。     

行波热声热机的理论与实验研究进展

近年来,随着理论的日趋完善及实验研究的深化,以及行波热声热机理论效率可接近于卡诺循环效率这一优点,使其成为这一领域的研究热点和难点。主要阐述热声热机的理论研究进展,重点介绍了实验方面的研究成果以及国内外行波热声热机实用化的研究进展,并初步预测了热声热机的发展方向。     

回热器非线性热声动力学模型的研究

基于基本的守恒方程,研究了回热器在具有大振幅波动情况下的弱非线性热声动力学模型。其中,动量守恒方程采用理论性强的瞬态Darcy模型,能量守恒方程则包括了多孔介质的高阶耗散效应。采用摄动法,并在唯象的基础上获得了能描述包括声流（直流）在内的非线性动力学效应及由此而导致的非线性时均热声动力学效应的局部解析方程组,对加深回热器工作机理的理解具有一定的指导意义。     

热声热机的网络模型与仿真研究

介绍了热声热机的网络模型和其仿真计算方法。所开发的计算程序能预测热声系统的声场、回热器等元件及系统的阻抗、以及包括制冷量、制冷温度、热流、声功和ＣＯＰ等的性能参数。本模型的仿真研究将为热声系统的优化设计提供前提和依据。     

热声理论的研究进展及其应用

回顾了热声理论研究的发展起源.详细介绍了热声理论的研究内容,对各理论的特点进行了比较.给出热声应用实例,指出微型热声制冷机的应用前景.     

铜基底预处理对CVD法生长石墨烯薄膜的影响

化学气相沉积法是制备大尺寸、高质量石墨烯的有效方法, 其中金属催化剂的性能直接关系到所制备的石墨烯材料的品质, 因此需对金属催化剂进行表面预处理。本文研究了不同的预处理工艺对常用的铜基底催化剂表面状态的影响, 提出了钝化膏酸洗和电化学抛光协同处理的有效方法, 并对电化学抛光工艺参数(抛光电压、时间)以及铜基底退火工艺(退火温度、时间)等进行了系统研究。研究表明: 电化学抛光电压过高、抛光时间过长容易导致过度抛光, 合适的抛光电压和抛光时间分别为8 V和8 min。退火温度和时间对铜催化剂表面晶粒形态影响较大, 经1000 ℃退火处理30 min后, 铜箔表面晶粒尺寸更大, 分布更均匀。此外, 对CVD法生长制备的石墨烯样品进行表征, 电镜图片和拉曼光谱显示, 获得的石墨烯薄膜的层数较少, 且结构缺陷较少。     

热声制冷的应用与分析

在环境问题日益突出的今天,热声制冷作为一种对环境无污染的制冷技术,成为一个大有前途的发展方向,本文介绍了热声制冷的原理,分析了热声制冷机的性能影响因素,并提出了性能优化方法。     

热声热机的频率特性研究

热声效应是热声回热器与热声工质在一定的温度梯度作用下相互作用的结果,热声热机的频率是热声系统的一个重要参数,对于热声制冷机其直接决定了消耗声功而泵热的可能性.分别分析了不考虑热粘效应和考虑热粘效应时空谐振管的谐振频率,认为考虑热粘效应时,谐振频率大于不考虑热粘效应时的频率,同时分析了有温度梯度存在时的热声驱动器和热声制冷机的谐振频率,认为热声器件的存在改变了系统的频率特性,使系统的频率高于没有板叠存在时的频率.此结论对于热声制冷机的设计有重要的指导意义.     

On the temperature dependence of the London penetration depth in a superconductor

In the framework of the electron-phonon theory of superconductivity [1], it is shown that the magnetic field penetration depth _L increases like a certain power of temperature atTT _c due to the low-lying excitations in the phonon spectrum. For the acoustic phonons with the density of states ² the penetration depth increases T ⁵. The origin of such a high power ofT is the same as that in the case of resistivity of the normal metal: the phonon corrections to the electromagnetic vertex should be taken into account, and major terms (T ³) cancel, the surviving ones having a higher power ofT. The possibility of linear and quadratic terms in _L(T) is discussed in a model of electrons interacting with two-level centers [2].     

Magnetic penetration depth measurements with the microstrip resonator technique

The microstrip resonator technique is a convenient way to sensitively measure the temperature dependence of the magnetic penetration depth (T) in superconducting thin films. Because the method relies on measuring the resonant frequency of a high-Q transmission line resonator at microwave frequencies, one can very precisely measure small changes in (T). This technique is applied to studying the low-temperature dependence of (T), since that is in principle a measure of the low-lying pair-breaking excitations of the superconductor. We find that the penetration depth in niobium films is consistent with the predictions of weak coupled BCS theory. The low-temperature dependence of (T) inc-axis YBa₂Cu₃O_7– films can be interpreted as either a weak exponential or as a power law. In addition, the measured value of (0) is found to be strongly dependent on the form of the temperature dependence for (T) used in fitting the data. Best fits over the entire temperature range are obtained with a BCS temperature dependence having values for 2(0)/k _BT_c strictly less than 3.5, consistent with our measurements of the temperature dependence of (T) at low temperatures in YBa₂Cu₃O_7– .     

The thermal inertia of materials heated with a laser pulse faster than relaxation time

The nonlocal hyperbolic heat conduction equation is used to describe the thermal inertia of thin metal films (TMF) heated with femtosecond laser pulses. It is shown that for TMF the signatures of thermal inertia are (i) the delay of the heating process and (ii) the strong localization of the thermal energy in TMF.Paper presented at the Fourth International Workshop on Subsecond Thermophysics, June 27–29, 1995, Köln, Germany.     

在p-Si(100)上溅射法生长ZnO的结构和光学特性

室温下在ｐ－Ｓｉ（１００）上采用直流反应磁控溅射法外延生长了ＺｎＯ薄膜。ＸＲＤ测量表明了ＺｎＯ是高度ｃ轴单一取向生长的,ＸＲＣ测量则表明了ＺｎＯ的高质量在室温下的ＰＬ测量中见到了带边发射,其强度与晶体质量有关。     

金属渗透梯度层陶瓷基片在LED散热中的应用

在LED散热领域,铝基板居很大市场份额.介绍了金属渗透梯度层陶瓷基片,这种陶瓷基片由陶瓷与金属材料相互扩散形成的,导热性、绝缘性、抗剥离强度及抗震动性好,可解决大功率LED的散热问题.这种基板已用于制作大功率LED灯,并取得了明显的社会经济效益.     

主控因素对异型头弹丸半侵彻金属靶深度的影响特性研究

为研究异型头弹丸半侵彻金属靶的侵深特性,基于量纲方法对影响侵深的主控因素进行了分析,采用弹道枪加载和LS-DYNA软件对异型头弹丸半侵彻金属靶的作用过程进行了试验和数值模拟研究,分析了异型头弹丸结构、弹丸初速、靶板厚度等因素对侵彻深度的影响规律,获得了侵深随弹丸初速以及靶板厚度的变化曲线。研究结果表明,弹丸初速和靶板厚度是影响侵彻深度的关键因素,并拟合得到了弹丸初速和靶板厚度综合影响下的半侵彻侵深经验公式。研究结果可为半侵彻作用的研究及新型侵彻的工程计算方法等提供参考。     

Measurement of the thermal diffusivity of thin films on substrate by the photoacoustic method

Measurements of the thermal diffusivity of thin films on substrate have been performed by the photoacoustic method. In order to examine the method we have built a new apparatus and proposed (1) a system calibration procedure using optically and thermally thick reference samples and (2) a data analysis procedure based on the RG (Rosencwaig and Gersho) theory. As a result of using a transparent photoacoustic cell, the systematic errors which are caused by stray light have been reduced. With this apparatus, measurements have been performed on platinum, titanium, and stainless steel (SUS304) thin foils (thickness form 50 to 100 µm) with three different liquid backing materials (water, glycerol, and ethyl alcohol). The reproducibility was within ±7% regardless of film thickness and substrate materials.     

Estimation of the depth of frost penetration in both uniform and layered soils in frost-affected regions

One of the most important factors affecting pavement performance is climate, including frost action and precipitation. The performance of pavements in frost-affected regions depends to a large degree on the depth of frost penetration. In this paper, a simple predictive tool is developed to calculate a new correction coefficient depending upon the thermal ratio and fusion parameter. The new correction coefficient can be used in follow-up calculations to estimate the depth of frost penetration for both uniform and layered soils in frost-affected regions to evaluate the performance of pavement. The results of the proposed method are found to be in excellent agreement with reported data in the literature with average absolute deviation being less than 0.8%. The predictive tool is simple, straightforward and can be readily implemented in any standard spreadsheet programme leading to accurate, smooth and non-oscillatory data points. The prime application of the method is as a quick-and-easy evaluation tool in conceptual development and scoping studies in which the depth of frost penetration for both uniform and layered soils in frost-affected regions is being considered. The method may also serve as a benchmark in numerical and rigorous simulation studies.     

Surface effects on the wrinkles in a stiff thin film bonded to a compliant substrate

Surface effects are important to predict the mechanical behavior of nanostructures. In this paper, the wrinkling of a stiff thin film bonded to a compliant substrate is studied using an energy method accounting for surface elasticity and residual surface tension. The wavelength, critical buckling strain and amplitude are obtained analytically. These results provide valuable guide to the precise design and control of the wrinkling profile in many applications ranging from stretchable electronics to micro/nano scale surface patterning and precision metrology.