三维稳态晶体生长的物理本质

考虑在均匀流场的作用下,分析了金属熔液凝固过程中晶体生长的三维稳态数学模型.应用傅里叶级数展开法,在周期性条件下得到了相应的八阶常微分方程的精确解析解,并确定了解中各系数之间的关系.该解揭示了在均匀流场的作用下,晶体生长呈现了一种周期性振荡式的模式,从理论上证实了固液界面前沿浓度呈现指数振荡衰减性是晶体生长的一个本质特性.     

三端口四态变量CNN原理在肿瘤生长方程中应用

提出了一种在抗癌免疫监视下的肿瘤生长细胞神经网络(GISAC CNN)模型.用具有3个端口4个态变量CNN的解析判别法研究了GUSAC CNN的分歧图.数值模拟了癌细胞扩散和清除过程.研究结果似乎表明:效应细胞对癌细胞的清除起着至关重要作用,细胞组织中存在免疫缺陷,可能导致癌细胞的转移与扩散.     

LED城市照明示范工程应注意的问题

该文主要介绍了半导体(LED)在城市照明示范工程应用中应该注意的一些问题。论文包含有LED的性能和特点、科技部十城万盏半导体照明示范工程的要求及内容、示范工程应遵循的设计标准、LED照明器具应满足的技术要求等。     

A Composite Formation Route to Well‐Crystalline Manganese Oxide Nanocrystals: High Catalytic Activity of Manganate–Alumina Nanocomposites

Manganese oxide nanocrystals are combined with aluminum oxide nanocrystals to improve their crystallinity via calcination without a significant increase of crystal size. A nanocomposite, consisting of two metal oxides, can be synthesized by the reaction between permanganate anions and aluminum oxyhydroxide keggin cations. The as‐prepared manganese oxide–aluminum oxide nanocomposite is X‐ray amorphous whereas heat‐treatment gives rise to the crystallization of an α‐MnO₂ phase at 600 °C and Mn₃O₄/Mn₂O₃ and γ‐Al₂O₃ phases at 800 °C. Electron microscopy and N₂ adsorption‐desorption‐isotherm analysis clearly demonstrate that the as‐prepared nanocomposite is composed of a porous assembly of monodisperse primary particles with a size of ～20 nm and a surface area of >410 m² g^?1. Of particular interest is that the small particle size of the as‐prepared nanocomposite is well‐maintained up to 600 °C, a result of the prevention of the growth of manganate grains through nanoscale mixing with alumina grains. The calcined nanocomposite shows very‐high catalytic activity for the oxidation of cyclohexene with an extremely high conversion efficiency of >95% within 15 min. The present results show that the improvement of the crystallinity without significant crystal growth is very crucial for optimizing the catalytic activity of manganese oxide nanocrystals.     

Posttraumatic growth among Norwegian children and adolescents exposed to the 2004 tsunami.

This study examined posttraumatic growth (PTG), positive change experienced as a result of the struggle with trauma, in children and adolescents exposed to a high-impact disaster, after which their experience of secondary adversity was minimal. The study also examined whether reduction in posttraumatic stress symptoms (PTSS) over time related to reports of PTG. There were 105 participants, age 6 to 17 years, who were directly exposed to the 2004 tsunami in Southeast Asia. They were interviewed 10 and 30 months after the disaster—PTSS was assessed at both time points, and PTG was assessed at 30 months. The individual's subjective reactions to the event and concurrent PTSS (30-months post-tsunami) were independently and positively related to PTG, whereas the decrease in PTSS was not related to growth. Children and youth in this study reported lower absolute levels of PTG than those in other studies. Taken in sum, findings suggest that secondary adversities may influence posttraumatic reactions and ongoing distress, which are hypothesized to play a key role in the development of PTG. In the absence of such secondary stressors, continued distress in the form of PTSS may serve to catalyze the growth process. Implications for clinical practice are discussed. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Observation and formation mechanism of individual graphene foils inside multi-walled carbon nanotubes

The formation of individual graphene foils (GF) has been evidenced in the present study inside multi-walled carbon nanotubes. The graphene foils are attached on one side to a catalyst nanoparticle and on the other side to the internal walls of the nanotube. Moreover, results suggest that a necking process occurs in which internal carbon walls are deformed until formation of the graphene foil. A possible mechanism for the GF formation is then proposed.     

Synergistic effect of composite template and La-doping on microdynamic behavior of photogenerated carriers in mesoporous nano-TiO2

The traditional view that the role of the composite template that is adopted in the preparation of nano-TiO₂ is only for forming a pore structure and increasing the material's specific surface area is challenged by this study. The complex impact of the composite template and La-doping on the microdynamic behavior of photo-generation free charge carriers (FCCs) in the mesoporous nano-TiO₂ is investigated using the transient photovoltaic (TPV) technique, supplemented by electric field-induced surface photovoltaic spectroscopy and a computer simulation method. The experimental results reveal that utilizing an appropriate composite template, such as polyethylene glycol and octadecylamine with a molar ratio of 1:1, may result in the rapid separation and prolonged diffusion distance of electron–hole pairs that were excited by a 355 nm and 50 μJ laser pulse. These may be responsible for the stronger and broader TPV response in the microsecond and millisecond regions of the La-doped nano-TiO₂ in TPV spectroscopy, as compared with that for materials that used other composite templates. This response is closely related to the reduced content of the surface state located at 367 nm. A suitable level of La-doping, however, was only responsible for the stronger and broader TPV response in the microsecond region of the spectrum of the nano-TiO₂. The computer simulation results confirm that the photo-generation FCCs microdynamic characteristics in the microsecond region may partially originate from the state density distribution of both the d-electron in the antibonding orbital and the p-electron in the bonding orbital moving up to higher levels, and from a broader band-gap after La-doping in the anatase lattice cell.     

Synthesis of acicular α-Bi2O3 microcrystals by microwave-assisted hydrothermal method

ABSTRACT

Materials based on bismuth(III) oxide are candidate to be used in optical and electronic devices because of their properties such as a variable band gap, photoconductivity, photoluminescence, high refractive index, and dielectric permittivity. These properties are dependent of several factors, e.g., present phases and crystal morphology. The microwave-assisted hydrothermal method (MAH) is a fast and efficient approach of synthesis to obtain semiconductor powders. However, the synthesis of monoclinic bismuth oxide (α-Bi₂O₃) with acicular morphology by MAH was not found in literature. In this paper, microcrystals of acicular α-Bi₂O₃ (monophasic) were successfully obtained by MAH using a synthesis temperature of 80°C for 0.5?h. X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron, and transmission electron microscopies showed the formation of a monoclinic structure (space group P21/c) with acicular morphology that grew along the [001] direction. The temperature and time necessary to synthetize acicular microcrystals were significantly lower than those found for acicular microcrystals obtained by conventional hydrothermal method.     

The effect of roll-processing orientation on stress corrosion cracking of warm-rolled 304L stainless steel in oxygenated and deoxygenated high temperature pure water

Stress corrosion crack growth rates of 304L stainless steel after one-directionally warm-rolled along the longitudinal (L) direction were measured in oxygenated and deoxygenated pure water at 288 °C. The fracture mode is mainly intergranular in the Transverse-longitudinal (T-L) orientation specimen, while it is occasionally intergranular in the Longitudinal-transverse (L-T) orientation specimen. The crack growth rates in the T-L orientation are higher than those in the L-T orientation in both oxygenated and deoxygenated environments, which is related to the effective cracking growth path as the result of microstructural anisotropy and applied loading direction.