Study on ceramic photonic bandgap structure with three-dimensional diamond lattice

A novel process, which was based on powder injection molding, was investigated for the fabrication of ceramic photonic bandgap structure with three-dimensional diamond lattice. The SiO2-TiO2 ceramic powder was mixed with a water-soluble agent to produce slurry. The slurry was then injected into an epoxy mold with inverse diamond lattice, fabricated by the stereolitographic rapid prototyping process. To increase the density of the green compact, cold isostatic pressing was applied on the unit. Using thermal debinding, the water-soluble agent and the epoxy were extracted at 360 and 650 K, respectively. Sintering was immediately done at 950 K for 5 h and the desired three-dimensional ceramic structure was obtained. The calculated band diagram for this structure indicated the existence of an absolute photonic bandgap for all wave vectors. At 14.7-18.5 GHz, a complete band gap was located with a maximum attenuation of 30 dB at 17 GHz, when transmission was measured in the 〈100〉 direction between 10 and 20 GHz.     

HCl酸洗伊利石增白改性实验

通过依次改变HCl浓度、反应时间、反应温度以分别确定HCL酸洗对伊利石增白效果的影响,并采用XRD、SEM和XPS等检测手段对伊利石原矿及增白效果较好的伊利石样品进行表征,以寻求伊利石白度增加的原因。实验表明:HCl酸洗在一定程度上可以增加伊利石白度,适当延长反应时间、增加反应温度以及提高HCl浓度有助于提高伊利石的白度。     

基于光流场的图像分割

基于光流场的图像分割通常用到3个光流模型:仿射变换模型、平面光流模型和二次光流模型,其中仿射模型和平面模型是二次模型的特例。当分别用这3个模型拟合同一光流场时,仿射模型的拟合残差平方和最大,二次模型最小,平面模型居中。但是回归分析的理论表明二次模型并不一定总是最优的。应用回归分析有关待估参数的假设检验准则,可以在这3个模型中选择1个相对最优模型并用于拟合光流场,实现图像分割。算例表明,应用回归分析的假设检验准则选择出最优光流模型,用于图像分割可以取得较好的分割结果。     

Effective Thermal Conductivity of Moist Porous Sintered Nickel Material

The effective thermal conductivity of capillary structures is an important parameter in the thermal performance analysis of loop heat pipes (LHP). In this paper, the effective thermal conductivity of porous sintered nickel material filled with water, ethanediol, and glycerin were measured by means of the hot disk thermal constant analyzer. The measured data were compared with similar measured data and calculated values from models in the literature. The results indicate that the thermal conductivity of the porous material depends on the thermal conductivity of the fluid, the filled ratio, and the porosity of the material.Paper presented at the Seventh Asian Thermophysical Properties Conference, August 23–28, 2004, Hefei and Huangshan, Anhui, P. R. China     

Formation of amorphous and nanocrystalline phases in high velocity oxy-fuel thermally sprayed a Fe–Cr–Si–B–Mn alloy

High velocity oxy-fuel (HVOF) thermal spray was used to deposit a Fe–Cr–Si–B alloy coating onto stainless steel (1Cr18Ni9Ti) substrate. Microstructures of the powder and the coating were investigated by X-ray diffraction (XRD), scanning election microscopy (SEM), transmission election microscopy (TEM) and differential scanning calorimeter (DSC). The coating had layered morphologies due to the deposition and solidification of successive molten or half-molten splats. The microstructures of the coating consisted of a Fe–Cr-rich matrix and several kinds of borides. The Fe–Cr-rich matrix contained both amorphous phase and nanocrystalline grains with a size of 10–50 nm. The crystallization temperature of the amorphous phase was about 605 °C. The formation of the amorphous phase was attributed to the high cooling rates of molten droplets and the proper powder compositions by effective addition of Cr, Mn, Si and B. The nanocrystalline grains could result from crystallization in amorphous region or interface of the amorphous phase and borides by homogeneous and heterogeneous nucleation.     

Effects of Y concentration on luminescence properties of PbWO4 single crystals

The effects of Y³⁺ doping at different concentration on the luminescnece properties of PbWO₄ crystals have been investigated by means of Fourier transform infrared (FT-IR) spectrum, optical transmission, thermoluminescence (TL), X-ray excited luminescence (XEL), photoluminescence (PL) under excitation of UV light and light yield measurements. The series PbWO₄:Y crystal samples were grown by modified Bridgman method and the concentration of Y³⁺ in the melt was in the range of 0–1.0 mol%. The slight blue-shift and evident red-shift of the absorption edge in PbWO₄ crystal were observed at low and heavy doping concentration, respectively. TL peaks in the range of from room temperature to 250 °C disappeared after the doping with Y³⁺. With the increase of doping concentration, the luminescence intensity in the XEL and PL spectra was found to decrease accordingly, especially in the case of heavy doping. The measuring results demonstrate that Y³⁺ doping concentration below 100 ppm in the crystal seems to be the best for optimizing the optical and scintillation properties of the material. The mechanism of Y³⁺ doping concentration influence on luminescence was also discussed in this paper.     

Sr and Ba substitution in charge ordered Pr0.5Ca0.5MnO3: Sharp steps in the magnetic and transport properties for a narrow composition range

The magnetic and transport properties of Pr_0.5Ca_0.5−xA_xMnO₃ (A = Sr, Ba) have been investigated in this paper. The substitution of Ca with bigger cations such as Sr and Ba can favour the field-induced ferromagnetism and induce sharp steps in the magnetization versus field and resistivity versus field curves. These properties strongly depend on the thermal history of the samples. All the results have been interpreted by a martensitic-like mechanism based on phase separation induced by A-site size mismatch. The above model can also explain the result that the less efficient ability of Sr substitution than Ba substitution to induce ferromagnetism and sharp steps. Another interesting feature in the system is the existence of an optimum substitution range to induce magnetization steps and reach high field-induced magnetization values for both Sr (x = 0.07–0.10) and Ba (x = 0.01–0.08) substitution. We suggest that the disappearance of the steps beyond the optimum substitution range possibly results from the different nature of phase separation in the optimum substitution range and beyond this range.     

Synthesis of CdS nanoplates by PAA-assisted hydrothermal approach

Triangular and hexagonal CdS nanoplates, with average size about 100 nm and average thickness range from 10 to 30 nm, have been synthesized in the presence of poly (acrylic acid) (PAA) assisted hydrothermal process at 180 °C. The structural characteristics, morphology, and optical properties of the as-prepared CdS products were investigated. UV–vis spectroscopy measurement reveals that the products show a strong quantum size effect. Based on the experiment results, the possible formation mechanism of CdS nanoplates has been proposed.     

α钛合金在室温和低温的冲击韧性

为了考察Al,Sn,Zr,Mo合金元素对α钛合金在室温和77 K低温(液氮)下的缺口冲击韧性(冲击值Ak)的影响,采用示波冲击试验机测试了Ti-2Al,Ti-2Sn,Ti-2Zr和Ti-1Mo 4种α钛合金在室温和77K下的Ak值,并计算了表征其冲击韧性的弹性变形功、塑性变形功和裂纹扩展撕裂功.用扫描电镜观察了4种合金冲击试样断口的形貌.计算数据和显微组织表明,4种合金均显示韧性特征,4种合金元素对冲击韧性贡献的顺序为:Mo＞Zr＞Sn＞Al.