Thermal conductivity: Recent developments

The detailed spectral energy distribution of the radiation emitted by stars provides information on their composition and physical parameters. Many of the astpophysically important spectral lines of neutral and ionized atoms whose study can lead to a better understanding of the processes occurring in stellar atmosphere and in the interstellar gas lie in the ultraviolet region of the spectrum.

Since ultraviolet radiation from the stars is absorbed by the Earth's atmosphere, observations must be made from space vehicles. In this article some scientific objectives of a programme in ultraviolet astronomy are considered, and a review made of the types of space vehicles and attitude control systems employed. A brief discussion is made of some recent results and their interpretation.     

Two-dimensional gas of disks: Thermal conductivity

The phenomenon of heat conduction in a two-dimensional gas ofN hard disks is studied in the hydrostatic regime by means of nonequilibrium molecular dynamics (N ranging from 100 to 8000). For systems withN1500 the temperature and density profiles observed are in excellent agreement with the continuous theory, but the conductivityk differs from the one derived from Enskog's theory in a systematic way. This difference seems to slowly decrease with increasing density.     

国际地下实验室发展综述*

地下实验室是开展粒子物理学、天体物理学及宇宙学等领域一些重大基础性前沿课题的重要研究场所和良好的低本底环境,建设和发展地下实验室对于一个国家的基础科学研究具有重要科学意义.目前,国际上许多国家都已经建立起地下实验室,而中国一直没有很好的地下实验室,特别是极深地下实验室.2009年,清华大学与二滩水电开发有限责任公司开展战略合作,利用锦屏山隧道建立中国首个世界最深的地下实验室——中国锦屏地下实验室（China Jinping Underground Laboratory, CJPL）,并于2010年12月12日正式启用.中国锦屏地下实验室的建成,标志着中国已经具备开展物理学重大基础前沿科学研究的自主地下实验平台,对于推动我国相关领域的重大基础前沿课题的自主研究意义重大.文章对国际上一些重要地下实验室的情况进行了介绍,并对中国锦屏地下实验室的基本情况进行了介绍.     

国际地下实验室发展综述

地下实验室是开展粒子物理学、天体物理学及宇宙学等领域一些重大基础性前沿课题的重要研究场所和良好的低本底环境,建设和发展地下实验室对于一个国家的基础科学研究具有重要科学意义.目前,国际上许多国家都已经建立起地下实验室,而中国一直没有很好的地下实验室,特别是极深地下实验室.2009年,清华大学与二滩水电开发有限责任公司开展战略合作,利用锦屏山隧道建立中国首个世界最深的地下实验室--中国锦屏地下实验室(China Jinping Underground Laboratory,CJPL),并于2010年12月12日正式启用.中国锦屏地下实验室的建成,标志着中国已经具备开展物理学重大基础前沿科学研究的自主地下实验平台,对于推动我国相关领域的重大基础前沿课题的自主研究意义重大.文章对国际上一些重要地下实验室的情况进行了介绍,并对中国锦屏地下实验室的基本情况进行了介绍.     

Thermal conductivity of nanowires

Thermal conductivity of nanowires(NWs) is a crucial criterion to assess the operating performance of NWs-based device applications, such as in the field of heat dissipation, thermal management, and thermoelectrics. Therefore, numerous research interests have been focused on controlling and manipulating thermal conductivity of one-dimensional materials in the past decade. In this review, we summarize the state-of-the-art research status on thermal conductivity of NWs from both experimental and theoretical studies. Various NWs are included, such as Si, Ge, Bi, Ti, Cu, Ag, Bi_2Te_3, ZnO, AgTe,and their hybrids. First, several important size effects on thermal conductivity of NWs are discussed, such as the length,diameter, orientation, and cross-section. Then, we introduce diverse nanostructuring pathways to control the phonons and thermal transport in NWs, such as alloy, superlattices, core–shell structure, porous structure, resonant structure, and kinked structure. Distinct thermal transport behaviors and the associated underlying physical mechanisms are presented.Finally, we outline the important potential applications of NWs in the fields of thermoelectrics and thermal management,and provide an outlook.     

Thermal conductivity of gaseous refrigerant R 404A

Thermal conductivity of gaseous refrigerant R 404A was studied by the method of coaxial cylinders within the ranges of thermodynamic parameters 309÷422 K and 0.13÷0.184 MPa. The estimated measurement errors for the temperature, pressure, and thermal conductivity are ± 0.05 K, ± 3.75 kPa, and ± 1.5–2.5%, correspondingly. The approximation dependence for thermal conductivity was obtained for the whole studied range of temperatures and pressures. The results obtained were compared with available published data. The work was financially supported by the Russian Foundation for Basic Research (grant No. 04-02-16355).     

Thermal conductivity of liquid refrigerant R404A

Thermal conductivity of liquid ozone-safe refrigerant R404A was studied for the first time in the range of temperatures of 297.9–332.6 K and pressures from the saturation line to 3.7 MPa. The uncertainties of temperature, pressure, and thermal conductivity measurements were estimated to be within ±0.1 K, ±3 kPa, and ±0.15%, correspondingly. Values of thermal conductivity were calculated for liquid R404A at the boiling line. Approximating dependences for thermal conductivity were obtained for the whole range of studied temperatures and pressures, and at the boiling line. The work was financially supported by the Russian Foundation for Basic Research (grant No. 04-02-16355).     

Thermal conductivity of refrigerant 507A in gaseous state

Thermal conductivity of refrigerant 507A in gaseous state has been measured with a stationary method of coaxial cylinders in the temperatures range of 315–425 K and pressures 0.105–1.855 MPa. Estimated values of temperature, pressure, and thermal conductivity measurement errors are, respectively, ± 0.05 K, ± 3.75 kPa and ± 1.5–2.5 %. Approximation dependence for thermal conductivity in the whole studied temperature and pressure range has been obtained. Results have been compared with available literature data.     

Thermal conductivity of isotopically enriched Si: revisited

The thermal conductivity of isotopically enriched ²⁸Si (enrichment better than 99.9%) was redetermined independently in three laboratories by high precision experiments on a total of four samples of different shape and degree of isotope enrichment in the range from 5 to 300 K with particular emphasis on the range near room temperature. The results obtained in the different laboratories are in good agreement with each other. They indicate that at room temperature the thermal conductivity of isotopically enriched ²⁸Si exceeds the thermal conductivity of Si with a natural, unmodified isotope mixture by 10±2%. This finding is in disagreement with an earlier report by Ruf et al. At ∼26 K the thermal conductivity of ²⁸Si reaches a maximum. The maximum value depends on sample shape and the degree of isotope enrichment and exceeds the thermal conductivity of natural Si by a factor of ∼8 for a 99.982% ²⁸Si enriched sample. The thermal conductivity of Si with natural isotope composition is consistently found to be ∼3% lower than the values recommended in the literature.     

Further property of Lennard-Jones fluid: Thermal conductivity

In this paper, we calculate the thermal conductivity of noble gases, methane, and three noble gas mixtures including He+Kr, He+Xe, and Kr+Xe assuming they obey Lennard-Jones (LJ) (12-6) model potential. One of the required quantities to calculate the thermal conductivity of these systems is the pair correlation function. Therefore, we solve numerically the Ornstein-Zernike (OZ) integral equation using the mean spherical approximation (MSA) to obtain the pair correlation functions. We use these functions to obtain the thermal conductivity, then compare our results with the available data. According to the results obtained from the present work for pure and mixtures of LJ fluids reveals that the integral equations method is suitable for predicting the thermal conductivity of this class of fluid.     

New developments in technologically important magnetic materials

In the past decade there has been a number of new developments in magnetic materials that should pave the way for expanded applications. These include: highly oriented high induction silicon steel; new varieties of permalloys, especially near 65% Ni; amorphous soft magnetic materials of the type (Fe, Co, Ni)₈₀ (P, B, Al)₂₀ produced by continuous rapid quenching; rare earth-cobalt permanent magnets with _iH_c to 150 kA/m and (BH)_max to 200 kJ/m³; ductile chromium cobalt iron permanent magnets with properties comparable to the alnicos; new families of ductile semihard magnets particularly for miniature self-latching dry reed contacts; and a new memory technology based on magnetic bubbles. These new developments will be discussed along with prospects for future applications.     

Thermal conductivity of superconducting niobium

The phonon scattering term in the superconducting state of the electronic conduction has been obtained for niobium which is regarded as an intermediate coupling superconductor. The limiting slope for the phonon scattering term of the reduced thermal conductivity against reduced temperature has been found to be 2.8, as compared with 1.5 for weak coupling superconductors.     

Thermal conductivity of liquid Ga

We present accurate values of the thermal conductivity of liquid Ga calculated from measurements of the Lorenz number and the electrical conductivity.     

Thermal conductivity of bismuth tellurite

This paper reports on the results of investigations of the thermal conductivity along the three crystallographic directions in bismuth tellurite crystals. It is found that bismuth tellurite exhibits a low thermal conductivity inherent in glasses and disordered solid solutions. At temperatures below the Debye temperature, the thermal conductivity coefficients depend on the temperature as \(\sqrt T \), which is characteristic of disordered solid solutions. The temperature dependence of the thermal conductivity of bismuth tellurite is calculated in the framework of the Debye model.     

Thermal conductivity of gallium sulfide

The results of investigating of the thermal conducitivity of a GaS single crystal in directions parallel and perpendicular to the c axis in the temperature interval 5–300 K are reported. The investigations show that the degree of anisotropy of the thermal conductivity of GaS decreases with temperature. Fiz. Tverd. Tela (St. Petersburg) 41, 24–25 (January 1999)     

金属纳米颗粒的热导率

本文使用统计模拟方法对金属纳米颗粒的电子平均自由程进行了计算,并考察了纳米颗粒的晶格比热和声子平均群速度,最后应用动力学理论对纳米颗粒的电子热导率和声子热导率分别进行了求解.研究结果表明:具有相同特征尺寸的方形、球形纳米颗粒的无量纲电子(或声子)平均自由程比较接近.金属纳米颗粒的电子热导率远大于声子热导率;电子、声子热导率随着直径减小呈现降低趋势,而电子热导率的颗粒尺度依赖性比声子热导率更为明显;随着颗粒直径进一步减小,声子热导率与电子热导率趋于同一数量级.当纳米颗粒特征尺寸大于4倍块材电子(或声子)平均自由程,其电子(或声子)热导率的颗粒尺度依赖性将减弱.     

Thermal conductivity of e-beam coatings

We present the results of the study on the thermal conductivity of different thin film materials produced by conventional thermal evaporation. The main features of the thermal pulse method employed for the measurement of the thermal conductivity are described. Thermal conductivity can be measured by determining the traveling time of a thermal wave propagating trough the film. A pump laser beam is directed onto a sample consisting of a thin transparent test layer and a totally absorbing substrate for the laser wavelength. As a consequence of the laser pulse, a temperature profile builds up at the substrate-film interface. A thermal pulse starts to diffuse from the substrate-film interface to the surface of the layer. Therefore, the temperature rise at the surface of the test layer starts with a time delay with respect to the laser pulse. The time delay depends on the propagation time of the thermal wave through the layer and is related to the thermal conductivity and the thickness of the layer. Measurements are evaluated by calculations based on the finite difference method. The results show that the analyzed thin films have lower thermal conductivity than the corresponding materials in bulk form.