EFFECT OF PRECIPITANT ON THE PROPERTIES OF ULTRAFINE YTTRIA POW DER PRODUCED BY PRE CIPITATION METHOD

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退火处理对SiCw／Al复合材料应力腐蚀开裂行为的影响

采用双悬壁梁试验方法,研究了不同温度的退火处理对纯铝基复合材料及ＬＹ１２铝基复合材料应力腐蚀开裂行为的影响,应力测试及透射电镜观察结果表明,不同温度的退火处理通过松驰复合材料的残余应力改变基体的位错组态改善了复合材料的应力腐蚀性。     

软土物理力学指标的统计关系研究

收集了广东地区150多个原状软土的物理力学指标数据,对指标相互关系进行研究。研究的结果表明:各参数与含水量W、孔隙比e存在一定的关系。研究的结果对在软土工程有着重要意义。     

On the interpretation of the forbidden spots observed in the electron diffraction patterns of flat Au triangular nanoparticles

In many cases nanostructures present forbidden spots in their electron diffraction patterns when they are observed by transmission electron microscopy (TEM). To interpret their TEM and high resolution transmission electron microscopy (HRTEM) images properly, an understanding of the origin of these spots is necessary. In this work we comment on the origin of the forbidden spots observed in the [111] and [112] electron diffraction patterns of flat gold triangular nanoparticles. The forbidden spots were successfully indexed as corresponding to the first laue Zone (FOLZ) and the HRTEM images presented a contrast produced by the interference of the zero-order Laue zone (ZOLZ) and FOLZ spots. We discuss the use of the forbidden spots in the study of the structure of nanoparticles and show that they are related to the shape and incompleteness of layers in the very thin particles.     

再生水回用于景观水体的水质控制系统研究

再生水回用于景观水体中,水华是需要考虑的主要问题之一。本文从再生水水质特点和再生水环境中优势藻类及其生理、生长特点着手,对有效控制水华的水质控制系统进行了试验,得出了系统的关键工艺参数。最后,从系统生态学的角度,提出了再生水回用于景观水体的水质控制的综合系统。     

Leaving home,returning home: Migration as a labor market choice for Alaska Natives

We investigate determinants of the pattern of recent migration of Alaska Natives between rural homelands and urban areas. A review of the literature on moving in the North American North suggests that economic opportunities draw migrants, although such opportunities must be viewed in the context of the mixed subsistence-cash economy prevailing in rural areas of the region. Consequently, we model Native migration as a simultaneous decision with labor market participation in a mixed economy. Estimated equations explaining individual Alaska Native migration choices using the U.S. Census Public Use Microdata Sample (PUMS) are consistent with the model, and also suggest that perceived opportunities differ between women and men.The authors acknowledge financial support from the National Science Foundation, grant OPP-9521459. An earlier version of this paper was presented to the 1998 annual meeting of the Western Regional Science Association     

挤压后硼酸铝晶须增强铝复合材料表面的腐蚀特征

利用原于力显微镜观察了挤压态Al18B4O33 w／pure Al复合材料早期腐蚀过程中表面形貌的变化特征．研究了沿与挤压方向成不同角度截取的Al18B4O33 w／pure Al复合材料在3．5％NaCl溶液中的腐蚀规律．结果表明：晶须与基体的界面是腐蚀易于发生的地方．点蚀首先在晶须的端部产生，随后沿着晶须与基体的界面扩展．挤压后沿与挤压方向成不同角度截取的Al18B4O33 w／pure Al复合材料表面腐蚀坑的深度存在差别．     

Studies of nanocrystalline Pd alloy films coated by electroless deposition

The microstructures of thin coating films of pure palladium and palladium alloys deposited from organic electrolytes onto different metallic substrates by electroless plating method have been investigated. The coatings are dense, pore-free 0.005–1 μm thick films with high adhesive strength to the substrate surface. X-ray spectral analysis, X-ray phase analysis, transmission and scanning electron microscopy were used to determine the composition and structure of alloy coatings of binary systems: Pd–Au, Pd–Ag, Pd–Ni, Pd–Pb, and ternary system Pd–Au–Ni. The coatings of Pd–Au, Pd–Ag, and Pd–Ni have a solid solution structure, whereas Pd–Pb is intermetallic compound. It has been found that the deposited films consist of nanocrystalline grains with sizes in the range of 11–35 nm. Scanning and transmission electron microscopy investigations reveal the existence of clusters formed by nanocrystalline grains. The origin for the formation of nanocrystalline structures of coating films is discussed.     

Design and development of multiple emulsion for enhancement of oral bioavailability of acyclovir

The objective of this investigation was to design and develop water-in-oil-in-water type multiple emulsions (w/o/w emulsions) entrapping acyclovir for improving its oral bioavailability. Multiple emulsions (MEs) were prepared and optimized using Span-80 and Span-83 as lipophilic surfactant and Brij-35 as hydrophilic surfactant. The physio-chemical properties of the w/o/w emulsions - particle size, viscosity, phase separation (centrifugation test) and entrapment efficiency were measured and evaluated along with macroscopic and microscopic observations to confirm multiple nature, homogeneity and globule size. Stability study, in vitro and ex vivo release studies were performed followed by in vivo studies in rats. Stable w/o/w emulsions with a particle size of 33.098 ± 2.985 µm and 85.25 ± 4.865% entrapment efficiency were obtained. Stability studies showed that the concentration of lipophilic surfactant was very important for stability of MEs. Drug release from the prepared formulations showed initial rapid release followed by a much slower release. In vivo studies in rats indicated prolonged release and better oral bioavailability as compared to drug solution. The overall results of this study show the potential of the w/o/w emulsions as promising drug delivery systems for acyclovir.     

Synthesis of CeB6 thin films by physical vapor deposition and their field emission investigations

High quality CeB₆ thin films have been obtained through direct evaporation of raw micron-sized CeB₆ powders at a pressure of 70 Pa. The X-ray diffraction (XRD), Raman spectrum, scanning electron microscope (SEM), transmission electron microscopy (TEM), selected-area electron diffraction (SAED) and the field-emission equipment were used to characterize the morphology, structure, composition and FE properties of the samples. The XRD and Raman spectrum analysis results show the as-prepared product is cubic phase CeB₆. The TEM, SAED and HRTEM analysis reveal that the samples are mixtures of thin films (polycrystalline) and small crystals (single crystallines aligned preferentially in the [1 1 0] direction). Compared to oxide nanostructures, field-emission measurements show that the CeB₆ films have better FE performance with turn-on field and threshold field of 12.93 V/μm and 14.86 V/μm, respectively.