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Ductile Phase Toughened Brittle Materials

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Journal of Materials Science & Technology 1996年第2期12卷 124-134页

作者： Sun, xd Yeomans, JA UNIV SURREY DEPT MAT SCI & ENGNGUILDFORD GU2 5XHSURREYENGLAND

Toughening of brittle materials by the inclusion of ductile phases is governed by several important factors which include ceramic-ductile phase interfacial bond strength, physical and chemical compatibility between ceramic and ductile phase, geometry and mechanical properties of ductile phase. The present understanding of the effect of these factors on toughening is reviewed and clarified. Continuous ductile phases (network, fibre or plate) are found to be more efficient for the toughening of brittle materials than discrete ductile particles. However, ductile particle toughened brittle materials have the advantages of material homogeneity, isotropy, and particularly better high temperature properties. It has been demonstrated that the influence of interfacial bond strength is determined by the geometry of the ductile phase in the composites. For the comparatively continuous ductile phase, such as ductile network, fibre or plate, comparatively weak interfacial bond strength can promote partial debonding of the brittle matrix-ductile phase interface during crack propagation and is beneficial for toughening. For discrete particulate ductile phase toughened brittle materials, the small gauge length of the ductile phase often results in the ductile phase pull-out during crack propagation which is the main limitation to toughening. Thus strong bond strength is required to ensure the bridging of the crack by the ductile phase. The coefficient of thermal expansion (CTE) mismatch between matrix and ductile phase has also been correlated with the geometry of the ductile phase. In most of the ceramic/metal systems, the CTE of the ductile metal phase is greater than that of the ceramic matrix. In the case of ductile network, fibre or plate, the residual stress created by the CTE mismatch can contribute to toughening through its influence on the initial crack opening stress while the bridging of the crack by the ductile phase is still ensured. However, for discrete ductile parti

关键词： Brittleness

Shock effects and history of the Yanzhuang meteorite: a case different from L-chondrites

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Chinese Science Bulletin 1997年第22期42卷 1889-1894页

作者： Chen, M Xie, xd Chinese Acad Sci Guangzhou Inst Geochem Guangzhou 510640 Peoples R China

MANY ordinary chondrites contain the networks of black veins with the widths from

关键词： chondrite H-group L-group shock vein shock effect history.

Chemoprevention of tea on colorectal cancer induced by dimethylhydrazine in Wistar rats

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World Journal of Gastroenterology 2000年第5期6卷 699-703页

作者： Jia xd Han C 中国预防医学科学院营养与食品卫生所北京

AIM To investigate the chemopreventiveeffects of green tea and tea pigment on 1,2-dimethylhydrazine(DMH)-induced rat *** Male weaning Wistar rats wererandomly allocated into four *** in thepositive control group were given *** DMH,once a week for ten weeks;rats in tea-treated groups,with the same DMH treatment asin the positive group,received 2% green tea and0.1% tea pigments;rats in the negative controlgroup were given *** of the samevolume of saline as well as DMH in the *** were sacrified and necropsied atthe end of week 16 and week *** Aberrant cryptic foci(ACF)wereformed in animals in DMH-treated groups at theend of week *** to the DMH group,green tea and tea pigments groups had less ACF(148.25 and 204.25,respectively,P<0.01).Atthe end of week 32,all rats in DMH groupdeveloped large intestinal *** resultsalso showed that DMH increased labeling index(LI)of proliferating cell nuclear antigen(PCNA)of intestinal mucosa and the expression of ***,in the tea-treated groups,PCNA-LI was significantly reduced as compared withthe positive control group(36.63 and 40.36 inthe green tea group and tea pigment group,respectively,at the end of the experiment,P<0.01).ras-p21 expression was alsosignificantly reduced(2.07 and 2.36 in the colontumors of rats in the green tea group and teapigments group,respectively at the end of theexperiment,P<0.01).Furthermore,green tea and tea pigment inhibited the expression of Bcl-2protein(2,5,1,0 and 2,4,1,0,respectively,at the end of the experiment P<0.01),andinduced expression of Bax protein(0,1,3,4and 0,1,4,3,respectively,P<0.01).CONCLUSION Chinese green tea drinkinginhibited ACF and colonic tumors formation inrats,which showed that tea had a significantchemopreventive effect on DMH-inducedcolorectal *** effects may bedue to suppression of cell proliferation andinduction of apoptosis in the intestina

关键词： colorectal neoplasms dimethylhydrazine tea apoptosis aberant crypt foci rats proliferating cell nuclear antigen chemoprevention

Study on Electrophotographic Properties for Dual Layered Photoreceptor

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Chinese Chemical Letters 1997年第6期8卷 535-538页

作者： Zhou, SQ Deng, xd CHINESE ACAD SCI INST CHEMBEIJING 100080PEOPLES R CHINA

One kind of dual layer function separated architecture photoreceptors was prepared. As compared with that of single layered photoreceptor made of the same photogenerator material, their absorption spectra and electrophotographic properties were investigated systematically. The experimental results indicate that phthalocyanine compounds are appropriate photogenerators. The existence of CTL in the dual layered photoreceptor efficiently accelerated photodecay process and bring about a lower V-r value, and higher light sensitivity than that of single layered photoreceptor. These are attributed to carrier injection from CGL to CTL. The process might be interpreted as assistance sensitization effect based on carrier injection. It might play an important role in promoting the performance of dual layered photoreceptor.

关键词： CGL

Ab initio Study on the Molecular Geometry, Electronic Structure and Thermodynamic Properties of Benzotrifuroxan(BTF)

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Chinese Journal of Structural Chemistry 1999年第2期18卷 49-55页

作者： Gong, xd Xiao, HM Dong, HS Nanjing Univ Sci & Technol Dept Chem Nanjing 210094 Peoples R China China Acad Engn Phys Inst Chem Mat Mianyang 610003 Peoples R China

The molecular geometries and electronic structures of two isomers of benzotrifuroxan (BTF) have been studied using ab initio molecular orbital method at the HF/6 31G * level. The calculated results show that the hexanitroso isomer has much higher energy than the tetracyclic form and is unstable. Infrared frequencies have been calculated for the stable tetracyclic structure and scaled by 0.89. The scaled frequencies agree well with the available experimental results, and have been used to derive the standard thermodynamic functions, heat capacity( Cp °), entropy( S °) and enthalpy( H° H 298 °).

关键词： benzotrifuroxan(BTF) ab initio MO method molecular geometry electronic structure IR frequency thermodynamic property

A New Triterpenoid Glycoside from Dichotomanthes tristaniaecarpa

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Chinese Chemical Letters 2000年第11期11卷 1013-1014页

作者： Mei, WL Luo, xd Chen, CX Acad Sinica Kunming Inst Bot Lab Phytochem Kunming 650204 Peoples R China

A new triterpenoid glycoside 1, 1 beta, 2 alpha, 3 alpha, 19 alpha -tetrahydroxyurs-12-en-28-oic acid beta -D glucopyranosyl ester was isolated from Dichotomanthes tristaniaecarpa. The structure was elucidated on the ... 详细信息

关键词： triterpenoid glucoside Dichotomanthes tristaniaecarp Rosaceae

Long-range Correlations in Iodide Cluster Aggregates

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Journal of Materials Science & Technology 1997年第4期13卷 271-273页

作者： Zhang, JZ Yang, xd Li, HD Ye, XY TSING HUA UNIV DEPT CHEMBEIJING 100084PEOPLES R CHINA

The morphology of tin iodide deposits grown during gas-solid transformation demonstrated long-range correlations. These iodide deposits include basically two kinds of forms: fractal structure and dendritic-like structure. The fractal structure was a sort of tin iodide cluster aggregation. Each fractal structure was composed of numerous tin iodide clusters that connected or disconnected with each other. The average size of fractal structures is between 10 and 22 mu m. The dendritic-like structure was also composed of many tin iodide clusters. These clusters aggregated and formed a dendritic pattern.

关键词： Iodine compounds

The Mechanism of the Initial Dark Oxidation of Ethers and the Ether-Oxygen Contact Charge Transfer Complex

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Chinese Chemical Letters 1997年第10期8卷 869-872页

作者： Zhu, JM Cao, WX Feng, xd BEIJING UNIV COLL CHEM & MOL ENGNBEIJING 100871PEOPLES R CHINA

The contact charge transfer (CCT) absorption spectra of isopropyl ether, phenyl isopropyl ether and benzyl isopropyl ether with oxygen were measured. The mechanism of the initial dark oxidation of different ethers via... 详细信息

关键词： De The Mechanism of the Initial Dark Oxidation of Ethers and the Ether-Oxygen Contact Charge Transfer Complex

Carbide Behavior during High Temperature Creep in DZ40M Co-base Superalloy

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Journal of Materials Science & Technology 1999年第6期15卷 515-518页

作者： Jiang, WH Yao, xd Guan, HR Hu, ZQ Chinese Acad Sci Inst Met Res Shenyang 110015 Peoples R China

The carbide behavior of a directionally solidified Co-base superalloy DZ40M has been investigated after creep at 700 degrees C and 900 degrees C. During the high temperature creep, a great amount of secondary carbide, M23C6 precipitated in alloy matrix. At 700 degrees C, the M23C6 precipitation occurred in slip bands, indicating that it was stress-induced, while at 900 degrees C, M23C6 formed surrounding the primary carbides, which is a characteristic of thermally aged alloy. The M23C6 particles pinned up dislocations and subgrain boundaries, strengthening the alloy matrix effectively. The creep crack initiation of DZ40M alloy was exclusively related to the primary carbides. The fracture of the primary carbide and the crack at the interface between them and matrix resulted in the crack formation. Furthermore, it was found that at 900 degrees C, the surface of specimens was oxidized severely and the preferentially oxidized primary carbides acted as crack initiation sites.

关键词： Superalloys