Temperature‐stable unfilled tungsten bronze dielectric ceramics: Ba3.5Sm1.5Fe0.75Nb9.25O30

Unfilled tungsten bronze ceramic Ba_3.5Sm_1.5Fe_0.75Nb_9.25O₃₀ was prepared by a conventional solid‐state reaction method. Its structure, microstructure, and dielectric properties were investigated. Dielectric behaviors indicate that the ceramics are ferroelectric at room temperature with a remnant polarization ~1.61 μC/cm² and a coercive field ~13.91 kV/cm. Ba_3.5Sm_1.5Fe_0.75Nb_9.25O₃₀ ceramics have temperature stability with a high dielectric constant (ε_r) varying from 172 to 202 at the temperature range ?55 to 200°C (at 1 MHz). Capacitance change rate of the sample is less than 15%. These results indicate that Ba_3.5Sm_1.5Fe_0.75Nb_9.25O₃₀ ceramics might be promising in temperature‐stable multi‐layer ceramic capacitors.     

Synthesis of mesoporous aluminosilicates with low Si/Al ratios using a single-source molecular precursor under acidic conditions

A single molecular precursor, bis(sec-butoxy)-aluminoxy-triethoxysilane, was used as aluminum source for the synthesis of mesoporous aluminosilicates with Si/Al ratios ranging from 1 to 10 under acidic conditions. Aluminum can be stoichiometrically incorporated into the mesoporous materials at pH = 1.5. The mesoporous aluminosilicates synthesized with the single molecular precursor display larger unit cell parameter and pore diameter than that of the materials prepared with aluminum sulfate, aluminum nitrate, aluminum hydroxide, and aluminum isopropoxide as the aluminum sources. IR spectra of adsorbed pyridine and NH₃-TPD showed that both Br?nsted acidic sites and Lewis acid sites with medium strength are present in the materials. However, no direct relationship between the acidic properties and the content of aluminum was observed when the Si/Al ratios of the mesoporous aluminosilicates are lower than 10.     

Periodic mesoporous hybrid monolith with hierarchical macro–mesopores

We describe the synthesis of hybrid monolith with hierarchically macro–mesoporous structure by a sol–gel process from the mixture of 1,4-bis(triethoxysilyl)benzene (BTEB) and tetraethoxysilane (TEOS) using poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (P123) as structure directing agent under acid medium. The ordered mesoporous structure is embedded in the skeleton of the well-defined co-continuous macropore of the hybrid monolith. The influence of aging condition, acidic concentration, P123/Si ratio and TMB/P123 ratio on the macro- and meso-structure of the resultant monolith was investigated in details. The three-successive aging processes are necessary for the mesostructural order of the monolith to survive the surfactant removing process. The well-defined co-continuous macropore could be formed with the aid of TMB, which probably delays the phase separation rate during the sol–gel process through enhancing the interaction between the hydrophobic BTEB with P123 surfactant micelles. The macro–mesoporous hybrid monolith with phenylene bridged in the mesoporous framework may have potential application as a novel kind of stationary phase for high performance liquid chromatography (HPLC).     

K2NbOF5系氟化物玻璃的制备及性质研究

研制了新型的铌氟化物玻璃体系K_2NbOF_5-MF_3(M=Al,Ga),并进行了IR光谱,Vis-UV光谱、热性质、密度和折射率的测定。对K_2NbOF_5-GaF_3系玻璃还进行了电导率的测试,成份为61K_2NbOF_5·39GaF_3的玻璃,在T=272℃时,σ=2.1×10~(-5)Ω~(-1)·cm~(-1)。Vis-UV光谱测定表明,在玻璃中铌仅以Nb~(5+)离子形式存在,无Nb~(3+)离子。一些样品的红外光谱研究表明,铌氟玻璃的红外透过截止波长为8.0μm。     

三维激光扫描数据采集系统的摄像机标定技术研究

在计算机视觉激光扫描测量系统中 ,物体的空间坐标与计算机图像坐标之间存在着复杂的非线性映射关系。通过建立基于一阶径向畸变的摄像机数学模型 ,用线性方程组描述了三维空间坐标点与计算机图像坐标点的关系 ,利用带有 3 0个标准圆孔的金属平面孔型靶标对由两个摄像机构成的摄像机参数标定 ,提出“两步法”对摄像机模型参数逐步求解 ,从而彻底改变了传统的摄像机标定依赖于非线性优化方法。实验证明 ,这种标定新技术较以往算法更为快速、简便、实用 ,精度更高     

浅析拱桥的一般加固技术

文章利用拱桥加固理论,分析说明了拱桥加固的依据,并由此举例说明一些常见拱桥的一般加固技术,提出加固拱桥时可根据现状而采取合适的加固方法。     

Friction and wear behavior of the polyurethane composites reinforced with potassium titanate whiskers under dry sliding and water lubrication

A series of polyurethane (PU)/potassium titanate whiskers (PTW) composites modified by a high molecular weight hydroxyl-terminated polydimethylsiloxane (HTPDMS) were prepared. The PTW is modified by 2,4-diisocyanatotoluene (2,4-TDI). The effect of the PTW content on the mechanical and tribological properties of the PU composites was studied. Tensile strength of the PU composites increased with the addition of PTW. The friction and wear experiments were tested on a MRH-3 model ring-on-block test rig at different sliding speeds and loads under dry sliding and water lubrication. Experimental results revealed that the small content of PTW contributed to largely improve the tribological properties of the PU composites. The coefficient of friction (COF) of the composites increased and the wear rate value decreased with increasing PTW. Scanning electron microscopic (SEM) investigations showed that the worn surfaces of the PTW-reinforced PU composites was smoother than pure polyurethane under given load and sliding speed.     

强化管理和谐发展让健康长江造福人民

2007年，是长江水利委员会各项工作重点突破、整体推进、亮点频现、特色鲜明的一年，是治江事业实现新的发展和跨越的一年。党的十七大描绘的全面建设小康社会蓝图赋予了治江工作新的战略机遇，党和国家把长江治理开发和保护工作放在了更加突出的位置。经济社会的持续快速发展为加快治江事业发展创造了有利条件，     

镇远西峡电站增容改造实践

结合具体的数据和计算方法，详细介绍镇远西峡电站增容改造过程，取得了很好的效果。表15个。