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Formation mechanism of an aluminium-based chemical conversion coating on AZ91D magnesium alloy

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International Journal of Minerals,Metallurgy and Materials 2010年第5期17卷 641-647页

作者： Wei-ping Li xi-mei Wang Li-qun Zhu Wen Li Key Laboratory of Aerospace Materials and Performance （Ministry of Education of China） School of Materials Science and EngineeringBeihang University Beijing 100083 China

An environmentally clean aluminium-based conversion coating on AZ91D magnesium alloy was studied in aluminium nitrate solutions. The morphology, composition, structure, and formation mechanism of the coating were investigated in detail using scanning electron microscopy/energy dispersion spectrometry, X-ray diffraction, transmission electron microscopy, and electrochemical corrosion tests. The results show that the conversion coating is composed of magnesium, aluminium, and oxygen, and shows an amorphous structure. In the initial stage of coating formation, the grain-like nucleus is composed of Al10O15·xH2O, （Al2O3）5.333, Al2O3, AlO（OH）, MgAl2O4, （Mg0.88Al0.12）（Al0.94Mg0.06）2O4, and （Mg0.68Al0.32）（Al0.84Mg0.16）2O4. The conversion coating formed in the 0.01 mol/L aluminium nitrate solution for 15 min can improve the corrosion resistance of the magnesium alloy greatly. The discussion reveals that the possible formation mechanism for the aluminium-based conversion coating is the reduction reaction on micro-cathodic sites due to the electrochemically heterogeneous magnesium alloy substrate.

关键词： magnesium alloys coatings aluminium nitrate corrosion resistance

Efficient Synthesis of Dicycloalkenopyridines:One-pot Multicomponent Condensation of Aldehydes with Cyclic Ketones

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Chemical Research in Chinese Universities 2009年第5期25卷 657-661页

作者： CAI xi-mei WANG Qi-fang YAN Chao-guo College of Chemistry ＆ Chemical Engineering Yangzhou University Yangzhou 225002 P. R. China

Under microwave irradiation, the one-pot multicomponent condensation reaction of three moles of aromatic aldehydes with two moles of cyclic ketones having free a,a＇-methylene positions such as cyclopentanone or cyclohexanone in the presence of ammonium acetate and acetic acid afforded dicycloalkenopyridines with two a-arylidene groups in high yields. Under the similar reaction condition, the reaction of aromatic aldehydes with 1-tetralone having only one a-methylene position alternatively resulted in 10-aryl-2,3：5,6-dibenzoacridines.

关键词： Pyridine Acridine Microwave irradiation Aromatic aldehyde Cyclic ketone Aldol condensation

Optimal power allocation to minimize SER for multinode amplify-and-forward cooperative communication systems

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The Journal of China Universities of Posts and Telecommunications 2008年第4期15卷 14-18,23页

作者： LIN Fei LIU xi-mei LUO Tao YUE Guang-xin Digital Communications and Networking Laboratory Beijing University of Posts and Telecommunications Beijing 100876 China School of Electronic Information and Control Engineering Shandong Institute of Light Industry Jinan 250353 China

An optimal power allocation （OPA） method with mean channel gains is proposed for a multinode amplify-and-forward cooperative communication system. By making use of M-PSK modulation, a closed-form symbol-error-rate （SER） formulation and corresponding upper bound are first derived. Subsequently the OPA method is utilized to minimize the SER. Comparison of the SER of the proposed OPA method with that of the equal power allocation （EPA） method, shows that the SER of both methods, which is approximately optimal performance, is almost the same when relays are near the source. OPA outperforms the EPA when the relays are near the middle between the source and destination or near the destination. The proposed OPA method depends only on the ratio of mean channel gains of the source-to-relay to those of the relay-to-destination. Extensive simulations are performed to validate the theoretical results.

关键词： amplify-and-forward multinode cooperative communications SER power allocation

Non-Smooth Morphologies of Typical Plant Leaf Surfaces and Their Anti-Adhesion Effects

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Journal of Bionic Engineering 2007年第1期4卷 33-40页

作者： Lu-quan Ren Shu-jie Wang xi-mei Tian Zhi-wu Han Lin-na Yan Zhao-mei Qiu Key Laboratory of Terrain-Machine Bionics Engineering （Ministry of Education China） Jilin University （Nanling Campus） Changchun 130022 P. R. China

The micromorphologies of surfaces of several typical plant leaves were investigated by scanning electron microscopy（SEM）. Different non-smooth surface characteristics were described and classified. The hydrophobicity and anti-adhesion of non-smooth leaf surfaces were quantitatively measured. Results show that the morphology of epidermal cells and the morphology and distribution density of epicuticular wax directly affect the hydrophobicity and anti-adhesion. The surface with uniformly distributed convex units shows the best anti-adhesion, and the surface with regularly arranged trellis units displays better anti-adhesion. In contrast, the surface with randomly distributed hair units performs relatively bad anti-adheslon. The hydrophobic models of papilla-ciliary and fold-setal non-smooth surfaces were set up to determine the impacts of geometric parameters on the hydrophobicity. This study may provide an insight into surface machine molding and apparent morphology design for biomimetics engineering.

关键词： bionics non-smooth leaf surface hydrophobicity anti-adhesion

Effect and mechanism of siderite on reverse flotation of hematite

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International Journal of Minerals,Metallurgy and Materials 2016年第4期23卷 373-379页

作者： Wan-zhong Yin Dong Li xi-mei Luo Jin Yao Qian-yu Sun College of Resources and Civil Engineering Northeastern University College of Zijin Mining Fuzhou University Faculty of Land Resource Engineering Kunming University of Science and Technology

The effects of siderite on reverse flotation of hematite were investigated using micro flotation, adsorption tests, and Fourier transform infrared spectroscopy. The flotation results show that interactions between siderite and quartz are the main reasons that siderite significantly influences the floatability. The interactions are attributed to dissolved siderite species and fine siderite particles. The interaction due to the dissolved species is, however, dominant. Derjaguin-Landau-Verwey-Overbeek（DLVO） theoretical calculations reveal that adhesion on quartz increases when the siderite particle size decreases and that fine particles partly influence quartz floatability. Chemical solution calculations indicate that the dissolved species of siderite might convert the surface of active quartz to CaCO_3 precipitates that can be depressed by starch. The theoretical calculations are in good agreement with the results of adsorption tests and FTIR spectroscopy and explain the reasons why siderite significantly influences reverse flotation of hematite.

关键词： hematite siderite reverse flotation solution chemistry

The Effect of Vineyard Cover Crop on Main Monomeric Phenols of Grape Berry and Wine in Vitis viniferal L. cv. Cabernet Sauvignon

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Agricultural Sciences in China 2010年第3期9卷 440-448页

作者： xi Zhu-mei ZHANG Zhen-wen CHENG Yu-feng LI Hua College of Enology Northwest A＆F University/Shaanxi Engineering Research Center for Viti-Viniculture Yangling 712100 P.R.China

This study was conducted to determine the effect of cover crop inter-row in vineyard on main mono-phenol content of grape berry and wine. Three such cover crops, two perennial legumes （white clover and alfalfa） and a perennial gramineous grass （tall fescue） were sown in vineyard. The main phenolic compounds of mature grape berry and wines vinified under the same conditions were extracted with ethyl acetate and diethyl ether and analyzed by high- performance liquid chromatography （HPLC） by comparing to soil tillage. A total of ten phenolic compounds were identified and quantified in the different grape berry and wines, including nonflavonoids （hydroxybenzoic and hydroxycinnamic acids） and flavonoids （flavanols and flavonols）. The concentration of flavonoid compounds （409.43 to 538.63 mg kg^-1 and 56.16 to 81.30 mg L^-1） was higher than nonflavonoids （76.91 to 98.85 mg kg^-1 and 30.65 to 41.22 mg L^-1） for Cabernet Sauvignon grape and wine under different treatments, respectively. In the flavonoid phenolics, Catechin was the most abundant in the different grapes and wines, accounting for 74.94 to 79.70% and 48.60 to 50.62% of total nonanthocyanin phenolics quantified, respectively. Compared to soil tillage, the sward treatments showed a higher content of main mono-phenol and total nonanthocyanin phenolics in grapes and wines. There were significant differences between two cover crop treatments （tall fescue and white clover） and soil tillage for the content of benzoic acid, salicylic acid, caffeic acid, catechin, and total phenolics in the grape berry （P 〈 0.05 or P〈0.01）. The wine from tall fescue cover crop had the highest gallic acid, caffeic acid and catechin. Cover crop system increased the total nonanthocyanin phenolics of grapes and wines in order of the four treatments： tall fescue, white clover, alfalfa, and soil tillage （control）. Cover crop in vineyard increased total phenols of grape berry and wine, and thus improved the quality of wine evidently.

关键词： vineyard cover crops inter-row Cabernet Sauvignon grape berry wine monomeric phenols

Spheroidizing Behavior and Spheroidizing Kinetics of W-phase During Solid-Solution Treatment in Mg–Zn–Y–Mn–(B)Alloys

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Acta Metallurgica Sinica(English Letters) 2017年第5期30卷 464-469页

作者： Kai Yang Jin-Shan Zhang xi-mei Zong Wei Liu Chun-xiang Xu College of Materials Science and Engineering TaiyuanUniversity of Technology Taiyuan 030024 China Shanxi Key Laboratory of Advanced Magnesium-based Materials Taiyuan 030024China

The spheroidizing mechanism of W-phase in the Mg–Zn–Y–Mn–（B） alloys during solid-solution treatment was investigated by using kinetic methodologies. The microstructure and mechanical properties of heat-treated Mg_（94）Zn_（2.5）-Y_（2.5）Mn_1 alloy containing 0.003 wt% B were compared with heat-treated Mg_（94）Zn_（2.5）-Y_（2.5）Mn_1 alloy. The heat-treated Mg_（94）Zn_（2.5）-Y_（2.5）Mn_1 alloy with 0.003 wt% B contained fine and uniform W-phase particles, which exhibited optimal mechanical performance. The ultimate tensile strength, yield strength and elongation were 287.7, 125.5 MPa and 21.1%,respectively.

关键词： Magnesium alloys W-phase Spheroidizing Kinetics Microstructure Mechanical properties

Microwave Irradiated Reactions of N-Phenacylpyridinium Chloride with Aromatic Aldehydes and Ketones

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Chinese Chemical Letters 2006年第7期17卷 867-870页

作者： Ping WU xi mei CAI Rong YAO Chao Guo YAN Yangzhou Polytechnic College Yangzhou 225009 College of Chemistry ＆ Chemical Engineering Yangzhou University Yangzhou 225002

In the system of ammonium acetate and acetic acid and under microwave irradiation, N-phenacylpyridinium chloride 1 reacted with chalcone 2 to give 2,4,6-triarylpyrididnes 3a-g in high yields. 3a-g can also be prepared from one-pot reaction of 1 with aromatic aldehydes 4 and substituted acetophenones 5. Under the same conditions 1 can also react with pyridinecar boxaldehyde 6a-e and acetophenone to yield bipyridine derivatives 7a-e. 1 reacted with aromatic aldehyde and cyclohexanone 6 to yield 2,4-diaryltetrahydroquinolines 8a-d. At last 1 reacted with aromatic aldehydes to give 2,4,6-triarylpyrimidine 9a-1. The structure of the products was characterized with 1^H NMR and IR and mass spectroscopy.

关键词： Microwave irradiation chalcone condensation pyridine pyrimidine.

Oscillating Propagation of Kink in Nondissipative Frenkel-Kontorova Chain Due to External DC Force

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Communications in Theoretical Physics 2009年第4期51卷 765-767页

作者： ZENG Shang-You TANG Yi REN xi-mei ZHAO De-Jiang Department of Physics Xiangtan University Xiangtan 411105 China

We report the oscillating propagation of kink in a nondissipative Frenkel-Kontorova （FK） chain driven by external DC force, which is different from the usual propagation of localized modes with equal speed. When the kink moves in the opposite direction of the external DC force, the kink will be accelerated and the potential of the FK chain in the external force field is transformed to be the kinetic energy of the kink. If the kink reaches the boundary of the FK chain, the kink will be bounced back and moves in the opposite direction, then the kink will be decelerated gradually and the kinetic energy of the kink ＆ transformed to be the potential of the FK chain in the external force field. If the speed of the kink reaches zero, the kink will move in the opposite direction again driven by the external DC force, and a new oscillating cycle begins. Simulation result demonstrates exactly the transformation between the kinetic energy of the kink and the potential of the FK chain in the external force field. The interesting energy exchange is induced by the special topology of kinks, and other localized modes, such as breathers and envelope solitons, have no the interesting phenomenon.

关键词： kink nondissipative Frenkel Kontorova chain oscillating propagation external DC force