Comparison between aesthetic and thermal performances of copper oxide and titanium dioxide nano-particulate coatings

Nano-particulate coatings with high reflectance against solar irradiation can control undesirable thermal heating by sunlight absorption. It can reduce the energy consumption for air conditioning of houses and cars. For the objects covered by these coatings and subjected to human sight, e.g. roofing surfaces, high dazzle of reflected visible light can offend the human eyes and spoil the fine view of covered objects. The authors introduced a new optimization method in designing pigmented coatings which considers both thermal and aesthetic effects in previous studies. The optimization is possible by controlling the material, size and concentration of pigment particles. The proposed coatings maximize the reflectance of near infrared (NIR) region to care the thermal effects and minimize the visible (VIS) reflected energy to keep the dark tone because of aesthetic appeal. Two different types of copper oxide pigment particles namely cupric oxide (CuO) and cuprous oxide (Cu₂O) were considered in this study. The optimum characteristics and performances are obtained and compared with titanium dioxide (TiO₂) particle as a typical cool pigment. The results show that cupric oxide has much better performance for our objective.     

Evaluation method for radiative heat transfer in polydisperse water droplets

Simplifications of the model for nongray radiative heat transfer analysis in participating media comprised of polydisperse water droplets are presented. Databases of the radiative properties for a water droplet over a wide range of wavelengths and diameters are constructed using rigorous Mie theory. The accuracy of the radiative properties obtained from the database interpolation is validated by comparing them with those obtained from the Mie calculations. The radiative properties of polydisperse water droplets are compared with those of monodisperse water droplets with equivalent mean diameters. Nongray radiative heat transfer in the anisotropic scattering fog layer, including direct and diffuse solar irradiations and infrared sky flux, is analyzed using REM². The radiative heat fluxes within the fog layer containing polydisperse water droplets are compared with those in the layer containing monodisperse water droplets. Through numerical simulation of the radiative heat transfer, polydisperse water droplets can be approximated by using the Sauter diameter, a technique that can be useful in several research fields, such as engineering and atmospheric science. Although this approximation is valid in the case of pure radiative transfer problems, the Sauter diameter is reconfirmed to be the appropriate diameter for approximating problems in radiative heat transfer, although volume-length mean diameter shows better accordance in some cases. The CPU time for nongray radiative heat transfer analysis with a fog model is evaluated. It is proved that the CPU time is decreased by using the databases and the approximation method for polydisperse particulate media.     

利用新的整体嵌入方法研究高维旋转黑洞的Hawking效应和Unruh效应

首先通过维数约化的方法,在事件视界附近将高维旋转时空线元化为二维度规(仅仅是(t－r)部分),然后利用新的整体嵌入方法研究了(1+1)维时空的Hawking温度(Unruh温度).研究结果验证了Banerjee和Majhi观点的正确性,同时将该观点推广到了高维旋转黑洞的研究,得到了高维旋转黑洞的Hawking 温度(Unruh温度). 关键词： 黑洞 高维旋转 Hawking效应 Unruh效应