Application of polymerizable surfactant in the preparation of polystyrene/nano-Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> composite

Monooctadecyl maleate, as a polymerizable surfactant, was synthesized by the mono-esterification of maleic anhydride and octadecanol, and was utilized to surface-modify nano-Fe₃O₄ particles. A polymerizable magnetic fluid was obtained by directly dispersing modified nano-Fe₃O₄ particles into styrene monomer, and the polystyrene/nano-Fe₃O₄ composite was prepared through free radical polymerization of polymerizable magnetic fluid. The structure and dispersion status in different dispersion phases of modified nano-Fe₃O₄ particles were studied by Fourier transform infrared (FTIR) spectrometry, X-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. The experimental results show that the nano-Fe₃O₄ particles modified by monooctadecyl maleate with the size of about 7–10 nm can be uniformly dispersed into styrene and fixed in the composite during the procedure of polymerization. Thermogravimetric analysis (TGA) and vibrating sample magnetometry (VSM) indicate that the thermal stability of polystyrene/nano-Fe₃O₄ composite is improved compared to that of pure polystyrene, and the composite is a sort of superparamagnetic materials.     

癫痫发作的两种模式

通过分析临床癫痫脑电的最大Lyapunov指数,研究了多种不同诱发背景的癫痫在各个时期(间期、前期、发作期、 发作后期4个时段)的最大Lyapunov指数的时域变化规律,提出癫痫发作具有两种响应模式:(1)睡眠、清醒等状态下的自发癫 痫,大脑受到随机信号的干扰,脑内各子系统之间需经过较复杂的协调作用才能进入高度同步放电状态;(2)闪光刺激等状态 下的诱发癫痫,大脑受到外加高频信号的干扰,脑内各子系统将被快速驱动进入高度同步放电状态。     

The properties of solution precursor plasma spray nanostructured thermal barrier coatings

About 300 μm thickness uniform thermal barrier coatings (TBCs) were deposited on the 1Cr18Ni9Ti samples by solution precursor plasma spray (SPPS).The analysis methods,such as TEM,SEM,and XRD were used to characterize the coatings in the aspects of microstructure and phase compositions.The samples were quenched from 1121 ℃ to room temperature by forced-air to measure the thermal cycling capability.Coatings density were measured by means of water displacement.The experimental results show that grain size of the SPPS TBCs is about 30 nm with desired tetragonal phase ZrO2,and the SPPS TBCs(with 16% porosity) consist of arcuate pores,gelatin and melted particles.The hardness of the coatings is HR45Y38.5 and bond strength between coatings and substrates is 24.2 MPa.The thermal shock test show the coatings have a average life of 500 cycles which is about 2.5 times than that of conventional air plasma spray (APS) TBCs.     

Tissue response of an osteoinductive bioceramic in bone defect rabbit model

HA/TCP and HA rods (?5 mm×10 mm) were made for implantation in New Zealand white rabbit with different condition. Sixty three rabbit were divided into three groups: group 1 (n=18), group 2 (n=27) and group 3 (n=18). In group 1, 10 mm radius was defected, and one HA/TCP rod was implanted in the muscle a distant away from the bone defect area. In group 2, also, 10 mm radius was defected, one HA rod was implanted in the muscle a distant away from the bone defect area. In group 3, two HA/TCP rods were implanted in the dorsal muscle of the rabbit with bone intact. Histological observation showed that in group 1, some new bone was found only two months after implantation (n=2), and obvious immature woven bone could be observed in these bioceramics from the 3^rd month on. However, in group 3, bone began to be found 6 months after implantation (n=2). In group 2, we could not find any bone tissue up to 9 month’s observation. These results suggest that, first, the bone defect model could significantly accelerate bone formation at non-osseous sites in rabbits; second,. HA/TCP bioceramics were confirmed with osteoinductive property while HA bioceramics without osteoinductive property nearly. Thus, bone defect might be a good animal model for further researches for osteoinductive bioceramics.     

Facile synthesis of uniform hollow hematite sub-micro spheres with controllable shell thickness

A simple method was developed to prepare the uniform hematite hollow submicro-spheres with controllable structure and different diameter based on monodisperse poly(styrene-co-acrylic acid) [P(St-co-AA)] particles. The structure and formation mechanism of the hollow spheres were investigated in detail. The control mechanism of shell thickness was also discussed. The results indicated that the shell thickness and coarseness of the synthesized core-shell hematite hollow spheres could be tuned simply by the surface carboxyl content of the P(St-co-AA) particles. This method provided a new approach for the structure control in the preparation of hollow spheres. A Brunauer-Emmett-Teller (BET) test shows that the prepared hollow spheres have large surface areas which were decreased along with the increase of the diameter. The magnetic properties of the as-obtained hematite hollow spheres were investigated. The result showed that the coercivity and saturated magnetization were increased along with the increase of the shell thickness, and the remanent magnetization was increased along with the decrease of the diameter.     

Preparation of YAG powder by co-precipitation method in a narrow pH-change environment

YAG(Y3Al5O12) powder was prepared by co-precipitation method.To avoid pH values changing intensely during titration process,the 4 3 NH HCO solution with 4 3 NH NO was used as precipitant solution.The pH change of precipitant solution during titration process,compositions of precursor,phase formation process and morphology of the prepared powder were investigated by means of pH meter,FT-IR,XRD and TEM.The results show that the presence of 4 3 NH NO in 4 3 NH HCO solution is crucial to alleviate the pH change,lower the calcination temperature and meliorate the morphology of YAG powder.The mechanisms were studied in detail.The YAG phase can be obtained at a lower temperature of 900 ℃.The obtained powder,composed of elliptical particles,showed a meliorated morphology.     

采用主成分分析与最邻近法的复合材料板损伤检测实验

文章采用主成分分析结合最邻近法对复合材料板进行了损伤检测实验。首先在正弦扫频激励下,通过测试获得复合材料板在各种损伤工况下的频响函数;然后选取若干种损伤工况的频响函数,经过主成分分析法处理后,提取出各个频响函数携带结构健康状态信息最多的前若干阶主成分,组成最邻近法的样本集;最后采用最邻近法来识别被检测结构频响函数所代表的结构健康状态。该方法的优点是直接利用测试得到的频响函数进行损伤检测,避免了识别结构模态参数所带来的误差,检测过程简单。通过对复合材料板结构不同位置和不同程度损伤的检测实验,验证了该方法用于复合材料层合结构损伤检测的可行性和有效性。     

一种降低WiMAX终端认证时延的机制设计与实现*

用户在移动WiMAX 网络间切换时要进行认证和密钥获取,此过程会耗掉很长的切换时间,对切换性能造成很大的影响。为了降低切换时延,提出把上下文传输协议和认证过程结合起来的机制。该机制是在WiMAX网关中设计context模块,利用context模块对密钥进行存储和分发。实测结果表明,该机制降低了用户切换时认证时延。     

The Young's moduli prediction of random distributed short-fiber-reinforced polypropylene foams using finite element method

The elastic moduli of short-fiber-reinforced foams depend critically on the fiber content and fiber length, as well as on the fiber orientation distribution. Based on periodic tetrakaidecahedrons, the finite element models with short-fiber reinforcement were proposed in this paper to examine the effects of the fiber content and fiber length on Young's modulus. The fiber length distribution and fiber orientation distribution were also considered. The proposed models featured in a three-dimensional diorama with random short-fiber distribution within or on the surfaces of the walls and edges of the closed-cells of polypropylene (PP) foams. The fiber length/orientation distributions were modeled by Gaussian prob-ability density functions. Different fiber volume fractions, different lengths, and different distributions were investigated. The predicted Young's moduli of the PP foams with short-glass-fiber or short-carbon-fiber reinforcement were compared with other theoretic and experimental results, and the agreement was found to be satisfactory. The proposed finite element models were proved to be acceptable to predict the Young's moduli of the grafted closed-cell PP foams with short-fiber reinforcement.     

Light metal compound casting

‘Compound casting’simplifies joining processes by directly casting a metallic melt onto a solid metal substrate. A continuously metallurgic transition is very important for industrial applications, such as joint structures of spaceframe constructions in transport industry. In this project, ‘compound casting’ of light metals is investigated, aiming at weight-saving. The substrate used is a wrought aluminium alloy of type AA5xxx, containing magnesium as main alloying element. The melts are aluminium alloys, containing various alloying elements (Cu, Si, Zn), and magnesium. By replacing the natural oxygen layer with a zinc layer, the inherent wetting difficulties were avoided, and compounds with flawless interfaces were successfully produced (no contraction defects, cracks or oxides). Electron microscopy and EDX investigations as well as optical micrographs of the interfacial areas revealed their continu- ously metallic constitution. Diffusion of alloying elements leads to heat-treatable microstructures in the vicinity of the joining interfaces in Al-Al couples. This permits significant variability of mechanical properties. Without significantly cutting down on wettability, the formation of low-melting intermetallic phases (Al3Mg2 and Al12Mg17 IMPs) at the interface of Al-Mg couples was avoided by applying a protective coating to the substrate.