The aim of this study was to explore the effect of cerium ions on the formation and structure of hydroxyapatite (HAP). All particles, prepared by hydrothermal method, were synthesized at varied XCe =Ce/(Ca+Ce) (from 0 to 10%) with the atomic ratio (Ce + Ca)/P fixed at 1.67. Their morphology, composition and crystal structure were characterized by TEM, EPMA, XRD and FTIR. The results showed that in this composition range the apatite structure is maintained, Ce3+ ions could enter the crystal lattice of apatite and substitute Ca2+ ions. The doping of Ce3+ ions resulted in the decrease of the crystallite size with increase in XCe. The HAP particles without doping were short rods having a diameter from 10 to 20nm and a length from 30 to 50nm. They grew into long needles upon increasing XCe.

Hi-Nicalon碳化硅纤维是一种作为高温下应用的陶瓷基复合材料的增强体。研究温度对Hi-Nicalon碳化硅纤维微观结构及力学性能的影响对于Hi-Nicalon碳化硅纤维的改进和应用具有重要意义。在氩气流的保护下，Hi-Nicalon碳化硅纤维分别在1400，1600 ℃和1800 ℃保温10h进行了退火处理。然后利用高分辨透射电子显微镜和X射线衍射分析方法对其经不同温度退火处理后纤维的微观结构进行表征，并用电子单纤维强力机测定其拉伸强度。研究结果表明：随着退火温度的升高，β-SiC晶粒不断长大；堆垛层错不断形成；游离碳堆垛层数和长度都随之增加，排列也趋于规整。拉伸强度也随着退火温度的升高而降低，经1800℃保温10h退火处理后的纤维的平均强度下降到了1.0GPa。

To estimate the accuracy of quantitative computed tomography (QCT) as a method to measure bone mineral density (BMD) in the vicinity of a titanium prosthesis, we investigated the effects of (1) titanium prosthesis, (2) offset of the longitudinal axis of the bone to be examined from that of the gantry of the CT scanner, (3) size of the

The fracture toughness at crack initiation were determined for bovine cortical bone under tension mode Ⅰ., shear mode Ⅱ., and tear mode Ⅲ. A total of 140 compact tension specimens, compact shear specimens and triple pantleg TP.specimens were used to measure fracture toughness under tension, shear, and tear, respectively. Multiple-sample compliance method was utilized to measure the critical strain energy release rate Gc.at the arWs0.55 crack length, a, to specimen width, W, ratio.. The critical stress intensity factor Kc. was also calculates from the critical loading Pc. of the specimens at the arWs 0.55. The effect of the anisotropy of bone on its resistance to crack initiation under shear and tear loading was investigated as well. Fracture toughness of bone with precrack orientations parallel designed as longitudinal fracture.and vertical designed as transverse racture. to the longitudinal axis of bone were compared. In longitudinal fracture, the critical strain energy release rate Gc. of cortical bone under tension, shear, and tear was 644±102, 2430±836, and 1723±486 Nrm, respectively. In transverse fracture, the critical strain energy release rate Gc.of cortical bone under tension, shear, and tear was 1374±183, 4710±1284, and 4016±948 Nrm, respectively. An unpaired t-test analysis demonstrated that the crack initiation fracture toughness of bone under shear and tear loading were significantly greater than that under tensile loading in both longitudinal and transverse fracture P<0.0001 for all. Our results also suggest that cortical bone has been "designed" to prevent crack initiation in transverse fracture under tension, shear, and tear.

The effects of the volume fraction of SiC particulate reinforcements and the concentration of chloride ions in solution on the localized corrosion characteristics of SiCp/2024 Al metal matrix composites (MMC) were investigated. A scanning micro reference electrode (SMRE) technique was employed to study the dynamic process of pitting initiation and development on the surface of the composites at open-circuit potential. Potentiodynamic polarizations were performed to characterize the electrochemical behavior of the MMCs. The morphology of the localized attack on the MMC sample after corrosion tests were examined by scanning electron microscopy (SEM). The results of electrochemical measurement showed that the composites were less resistant to pit initiation than the corresponding unreinforced metrix alloy. Increase in the volume fraction of SiC preinforcement in the SiCp/2024 Al composites resulted in a significant decrease of pitting potential. In situ potential mapping of active centers on the surfaces of the compositesrevealed that local breakdown of passivity and initiation of micro pitting corrosion could take place even at an open-circuit potential which was more negative than the pitting potential, and the number of active centers on the surfaces of the composites increased as the volume fraction of SiC particulates in MMCs increased. Micro-structural analysis indicated that pitting attack on the composites mainly occurred at SiCp-Al interfaces or inclusions-Al interfaces.