Fabrication of MgB2 superconducting films by different methods

MgB₂ superconducting films have been successfully fabricated on single crystal MgO(111) and c-AL₂O₃ substrates by different methods. The film deposited by pulsed laser deposition is c-axis oriented with zero resistance transition temperature of 38.4 K, while the other two films fabricated by chemical vapor deposition and electrophoresis are c-axis textured with the zero resistance transition temperature of 38 K and 39 K, respectively. Magnetization hysteresis measurements yield critical current density J_c of 10⁷ A/cm² at 15 K in zero field for the thin film and of 10⁵ A/cm² for the thick film. For the thin film deposited by chemical vapor deposition, the microwave surface resistance at 10 K is found to be as low as 100 μΩ, which is comparable with that of a high-quality high-temperature superconducting thin film of YBCO.     

电解液浓度和沉积时间对Zn涂层表面形貌影响的研究

采用阳极氧化法在纯钛基体表面制备一层TiO₂纳米管（TiO₂ nanotubes,TNs）,随后采用电化学沉积法在ZnCl₂溶液中于TNs上制备了Zn涂层。采用扫描电子显微镜（scanning electron microscopy,SEM）、能量色散X射线光谱仪（energy dispersive X-ray spectrometer,EDS）和X射线衍射仪（X-ray diffraction,XRD）对涂层的表面和截面形貌、元素含量和相组成进行表征。结果表明：TNs长度为1.5 μm,Zn涂层厚度为2 μm;在沉积的过程中,Zn涂层首先沿着TNs的管壁生长,逐渐覆盖TNs,然后形成球状晶体,最后形成白色颗粒堆叠在TNs上;电解液浓度的增加提高了涂层生长速度,沉积时间的延长使晶体有充足的时间长大;涂层中Zn是以单质形式存在,白色颗粒也主要为Zn单质。     

Involvement of NADPH oxidase NtrbohD in the rapid production of H2O2 induced by ABA in cultured tobacco cell line BY-2

The mechanisms for the production of hydrogen peroxide (H₂O₂) induced by abscisic acid (ABA) were investigated in suspension culture cells of tobacco BY-2 cells. The results showed that the immediate generation of H₂O₂, which was mainly derived from superoxide dismutase-catalyzed dismutation of superoxide radical, was significantly induced by ABA. Furthermore, treatment of the cultured tobacco cells with ABA resulted in a time-dependent quick increase in plasma membrane (PM) NADPH oxidase activity, which coincided on time and magnitude with the elevation in ABA-induced accumulation of H₂O₂. Moreover, these enhanced effects were pronouncedly inhibited by two NADPH oxidase inhibitor, diphenylene iodonium and imidazole, suggesting that PM NADPH oxidase is involved in the rapid accumulation of ₂O₂ in cultured tobacco cells. In addition, analysis of the expression level of NtrbohD, a PM NADPH oxidase gene in tobacco, by RT-PCR and protein gel blot revealed that the gene at both mRNA and protein levels was upregulated by ABA, indicating that NtrbohD participates in the ABA-stimulated rapid production of H₂O₂ in tobacco culture cells. Taken together, these findings suggest that ABA induces the rapid accumulation of reactive oxygen species via NADPH oxidase in suspension culture cells of tobacco, and that NADPH oxidase and H₂O₂ appear to be important components in ABA signal transduction pathway in plants.     

Involvement of NADPH oxidase NtrbohD in the rapid production of H2O2 induced by ABA in cultured tobacco cell line BY-2

The mechanisms for the production of hydrogen peroxide (H₂O₂) induced by abscisic acid (ABA) were investigated in suspension culture cells of tobacco BY-2 cells. The results showed that the immediate generation of H₂O₂, which was mainly derived from superoxide dismutase-catalyzed dismutation of superoxide radical, was significantly induced by ABA. Furthermore, treatment of the cultured tobacco cells with ABA resulted in a time-dependent quick increase in plasma membrane (PM) NADPH oxidase activity, which coincided on time and magnitude with the elevation in ABA-induced accumulation of H₂O₂. Moreover, these enhanced effects were pronouncedly inhibited by two NADPH oxidase inhibitor, diphenylene iodonium and imidazole, suggesting that PM NADPH oxidase is involved in the rapid accumulation of ₂O₂ in cultured tobacco cells. In addition, analysis of the expression level of NtrbohD, a PM NADPH oxidase gene in tobacco, by RT-PCR and protein gel blot revealed that the gene at both mRNA and protein levels was upregulated by ABA, indicating that NtrbohD participates in the ABA-stimulated rapid production of H₂O₂ in tobacco culture cells. Taken together, these findings suggest that ABA induces the rapid accumulation of reactive oxygen species via NADPH oxidase in suspension culture cells of tobacco, and that NADPH oxidase and H₂O₂ appear to be important components in ABA signal transduction pathway in plants.     

Forming mechanism of refined granular crystalline of Cu70Ni30 alloy by undercooled solidification

Moth glass fluxing and cyclic superheating techniques were adopted to effectively uudercool the Cu₇₀Ni₃₀ alloy in vacuum. Within the undercooling range of 21 K to 270 K, the microstructure evolution ol the alloy was investigated. When the inell was undercooled to △T > △T', (210 K) , the grain refinement took place abruptly, liascd on the observation of the solidified microstructure, the rnierocheinieal-analysis and the calculated results with UCT model, it is found that the secondary grain refinement mechanism consists of two stages. The dendrite is, firstly, broken into hag-ments owing to the stress caused by uneven shrinking during rapid solidilication, then the fragments, under the driving force of surface and strain energies, merge through the migration of l>ouinlaries, i. c. recryslallization, thus leading to the formation of secondary granular-crystalline .     

Effect of La2O3 on microstructure, mechanical and tribological properties of Ni-W coatings

In this paper, a Ni-W-La2O3 composite coating was prepared by the electrodeposition method. Microhardness tester and environmental scanning electron microscope equipped energy dispersive spectroscopy were employed to investigate the microhardness and the surface morphology of the composite coatings respectively, and the high temperature friction behavior and corrosion resistance of the coatings against molten glass were investigated by using a high temperature tribometer. The results show that La2O3 can refine the microstructure effectively, and make the element distribution uniform, which leads to the increase of average microhardness. La2O3 particulates can reduce the friction coefficient between the composite coating and glass during the sliding process at about 973 K largely, and the corrosion resistance of the La2O3 added Ni-W coatings is effectively improved compared with that of the non-added one, furthermore the mechanism of friction-reducing and anti-corrosion is also discussed.     

Influence of nanometric CeO2 coating on high temperature oxidation of Cr

Isothermal and cyclic oxidation behavior of chromium and its superficially applied nanometric CeO₂ samples were studied at 900℃ in air. Scanning electronic microscopy (SEM), transmission electronic microscopy (TEM) and high resolution electronic microscopy (HREM) were used to examine the morphology and micro-structure of oxide films. It was found that ceria addition greatly improved the anti-oxidation ability of Cr both in isothermal and cyclic oxidizing experiments. Acoustic emission (AE) technique was used in situ to monitor the cracking and spalling of oxide films, and AE signals were analyzed in time-domain and number-domain according to the related oxide fracture model. Laser Raman spectrometer was also used to study the stress status of oxide films formed on Cr with and without ceria. The main reason for the improvement in anti-oxidation of chromium was that ceria greatly reduced the growing speed and grain size of Cr₂O₃. This fine-grained Cr₂O₃ oxide film might have better high temperature plasticity and could relieve parts of compressive stress by means of creeping, and maintained the ridge character and relatively low internal stress level. Meanwhile, ceria application reduced the size and the number of interfacial defects, while remarkably enhanced the adhesive property of Cr₂O₃ oxide scale formed on Cr substrate.     

Influence of nanometric CeO2 coating on high temperature oxidation of Cr

Isothermal and cyclic oxidation behavior of chromium and its superficially applied nanometric CeO₂ samples were studied at 900℃ in air. Scanning electronic microscopy (SEM), transmission electronic microscopy (TEM) and high resolution electronic microscopy (HREM) were used to examine the morphology and micro-structure of oxide films. It was found that ceria addition greatly improved the anti-oxidation ability of Cr both in isothermal and cyclic oxidizing experiments. Acoustic emission (AE) technique was used in situ to monitor the cracking and spalling of oxide films, and AE signals were analyzed in time-domain and number-domain according to the related oxide fracture model. Laser Raman spectrometer was also used to study the stress status of oxide films formed on Cr with and without ceria. The main reason for the improvement in anti-oxidation of chromium was that ceria greatly reduced the growing speed and grain size of Cr₂O₃. This fine-grained Cr₂O₃ oxide film might have better high temperature plasticity and could relieve parts of compressive stress by means of creeping, and maintained the ridge character and relatively low internal stress level. Meanwhile, ceria application reduced the size and the number of interfacial defects, while remarkably enhanced the adhesive property of Cr₂O₃ oxide scale formed on Cr substrate.     

Stabilization effects of third element on CaCu5 type derivatives of rare-earth transition-metal intermetallics

Part of the results of the key project " Search for novel rare-earth functional materials" supported by the National Natural Science Foundation of China is reviewed. In combination with reports in literature, the effects of the third element M on the formation and stability of La2(Co.M)17. R(Fe.M)12 and R3(Fe, M)29 intermetallic compounds are discussed by considering mixing enthalpy of M with rare-earth. Fe and Co. and atomic radius, electronegativity and electronic configurations, etc. It is concluded that the mixing enthalpy and atomic radius dominate the preferential sites and the minimum amount of M required to stabilize a structure, which ultimately affect the magnetic properties of a compound prominently. This review should provide some heuristic hints for exploiting novel rare-earth transition metal functional materials and for improving their performance.     

Leaf cuticular characters of Ginkgo and implications for paleoatmospheric CO2 in the Jurassic

A combination of carbon isotope composition and stomatal characters of fossil leaves provides information about paleoatmospheric CO₂ levels and the physiology of fossil plants. Plant anatomy, physiology, and geochemistry have been employed to reconstruct the paleoatmospheric CO2 concentrations throughout Jurassic time and to investigate the physiological response of fossil Ginkgo to an atmosphere of much higher CO₂ than usual. Our results show that fossil Ginkgo in China lived in an atmosphere with a CO₂ concentration 3—5 times higher than that of today. It used a carbon isotopic discrimination similar to that of the living plant, but had much higher water use efficiency (3—5 times that of the extant). The physiological traits of Ginkgo in different atmospheres suggest that CO₂ might have played a contributory role in the rise and fall of maidenhair trees.     

Leaf cuticular characters of Ginkgo and implications for paleoatmospheric CO2 in the Jurassic

A combination of carbon isotope composition and stomatal characters of fossil leaves provides information about paleoatmospheric CO₂ levels and the physiology of fossil plants. Plant anatomy, physiology, and geochemistry have been employed to reconstruct the paleoatmospheric CO2 concentrations throughout Jurassic time and to investigate the physiological response of fossil Ginkgo to an atmosphere of much higher CO₂ than usual. Our results show that fossil Ginkgo in China lived in an atmosphere with a CO₂ concentration 3—5 times higher than that of today. It used a carbon isotopic discrimination similar to that of the living plant, but had much higher water use efficiency (3—5 times that of the extant). The physiological traits of Ginkgo in different atmospheres suggest that CO₂ might have played a contributory role in the rise and fall of maidenhair trees.     

Non-catalytic nucleation coating for undercooled Cu50Ni50 melt

A non-catalytic nucleation coating (B-F3) was prepared by the high temperature curing process of the sol-gel glass film based on the viscous flow mechanism of the coating. X-ray diffraction technology was adopted to study the crystallization behavior of the coating as a function of treating temperature. It was evident that no crystallization phenomenon happened on the coating which kept stable after the heat treatment of 60 min at 1773 K. The purified melt of Cu₅₀Ni₅₀ was selected to evaluate the effectiveness of undercooling heredity of the coating in the undercooling experiments. The maximum undercooling of the melt solidified in the coated mold could reach 236 K. Based on the solidified microstructural evolution at different undercoolings, a single crystal of the alloy Cu₅₀Ni₅₀ was achieved with no aid of the selection process of the crystal in the mold with the B-F3 coating by means of undercooling technology.     

Phase transition , structure and shape memory effect of Ni47Ti43Hf10 alloy

A Ni₄₇Ti₄₃Hf₁₀ high temperature shape memory alloy is fabricated. The martensitic transformation temperature (TT) is obtained by differential scanning calorimetry and four-probe electrical resistivity measurements. The effect of thermal cycling is investigated and it is found that the TT tends to be stable quickly, which is of benefit to practical applications. The martensite structure is determined to be B19' monoclinic by X-ray diffraction and transmission electron microscopy. One-way and two-way (which is seldom reported before) shape memory properties are studied by tensile and bending tests. The cycling number of two-way shape memory effect is tested for more than 20000 times.     

原位合成CNTs/Cu-Al2O3复合材料的性能研究

对Al的质量分数分别为0.20%,0.35%,0.60%的Cu-Al合金粉末进行内氧化,得到Cu-Al₂O₃粉末。采用化学气相沉积法在Cu-Al₂O₃粉末表面原位生长碳纳米管(carbon nano tubes, CNTs),采用放电等离子烧结工艺成功制备了CNTs/Cu-Al₂O₃复合材料。采用扫描电子显微镜和透射电子显微镜观察了CNTs/Cu-Al₂O₃复合粉末、复合材料断口的形貌。采用显微硬度计、微拉伸试验机、摩擦磨损试验机分别对纯Cu及复合材料的维氏硬度、抗拉强度、摩擦因数进行测试。采用电化学工作站测试复合材料在3.5%NaCl (质量分数)水溶液中的耐腐蚀性能。结果表明,随着Al的质量分数的增加,粉末表面合成的CNTs的数量也增多。Al的质量分数为0.35%时,CNTs/Cu-Al₂O₃复合材料的综合性能最佳,与纯Cu相比,复合材料的抗拉强度和腐蚀电势分别提高了86.4%和43.2%,分别为315 MPa和-0.268 V,摩擦因数降低了53.3%,仅为0.28。     

基于平面光极技术研究颤蚓生物扰动对水中Cd2+向沉积物迁移的影响

制备了一种能够选择性识别Cd~(2+)的平面传感膜;该膜具有响应速度快(20 s)、准确性高及稳定性好等特点。利用该传感膜制备的Cd~(2+)平面光极系统,应用于生物扰动存在的水/沉积物体系中,根据体系垂直剖面Cd~(2+)的分布及迁移情况,研究颤蚓生物扰动对上覆水中Cd~(2+)向沉积物迁移的影响。研究发现:制备的Cd~(2+)平面光极系统可以反映出上覆水中Cd~(2+)向沉积物迁移的过程。无生物扰动时,沉积物仅表层及水/沉积物界面下2 cm深度范围内第1~3 d的Cd~(2+)浓度略有升高,随后趋于稳定;深度超过2 cm的沉积物Cd~(2+)浓度几乎不变(同背景浓度)。有生物扰动时,深度约5 cm范围内的沉积物中Cd~(2+)浓度显著增加,深度越浅的沉积物中的Cd~(2+)浓度增加越快,深度超过5 cm的沉积物中Cd~(2+)浓度基本不变。与无生物相比,颤蚓扰动可以显著促进Cd~(2+)由上覆水中向沉积物的迁移。     

δ13C difference between plants and soil organic matter along the eastern slope of Mount Gongga

Carbon isotope ratios (δ¹³C) of plants, litter and soil organic matter (0–5 cm, 5–10 cm and 10–20 cm) on the eastern slope of Mount Gongga were measured. The results show that δ¹³C values of plants, litter and soil organic matter all decrease first and then increase with altitude, i.e δ¹³C values gradually decrease from 1200 to 2100 m a.s.l., and increase from 2100 to 4500 m a.s.l. The δ¹³C altitudinal variations are related to the distribution of C₃ and C₄ plants on the eastern slope of Mount Gongga, because C₄ plants are observed to grow only below 2100 m, while C3 plants occur at all altitudes. There are significantly positive correla-tions among δ¹³C of vegetation, δ¹³C of litter and δ¹³C of soil organic matter, and litter, 0–5 cm, 5–10 cm and 10–20 cm soil or-ganic matter are 0.56‰, 2.87‰, 3.04‰ and 3.49‰ greater in δ¹³C than vegetation, respectively. Considering the influences of rising concentration of atmospheric CO₂ and decreasing δ¹³C of atmospheric CO₂ since the industry revolution on δ¹³C of plants, 1.57‰ is proposed to be the smallest correction value for reconstruction of paleovegetation using δ¹³C of soil organic matter.     

I-V andC-V properties of TiO2 thin film by pulsed-laser reactive deposition

TiO-2 thin films have bee deposited on p-Si(111) substrates by pulsed-laser ablation of metallic Ti target in the O-3 ambient. The current-voltage and capacitance-voltage of the Al/TiO-2/Si capacitors are measured. The results show that the dielectric constant of thin film after being annealed at 700℃ is found to be 46, and the border trap density and the interface state density at the TiO-2/p-Si interface are 1.8×10 12 cm -2 and 2×10 12 eV -1·cm -2, respectively. The conduction mechanisms of as-deposited films are also discussed.     

Density functional theory study of the reaction paths of reactions of CH3C(O)O2 radicals with HO2 in the gas phase

A DFT study on the reactions between CH₃C(O)O₂ and HO₂ radicals has been carried out. It is suggested that both the triplet and singlet potential surfaces involve a complex mechanism with the formation of loosely bound intermediate complexes of reactants and products. The reaction prefers to occur on the triplet surface to produce peracetic acid (CH₃C(O)O₂H) and triplet O₂ molecule. The CH₃C(O)O₂H can further convert into CH₃C(O)O and HO radicals.     

福州盆地南北港冲淤规律与洪涝灾害对策

本文探讨了福州盆地南北港冲淤规律，近年来北港洪水分流量呈上升趋势，洪峰对北港的压力加大，文中还对福州城防洪涝灾害的措施等方面作了研究。     

Density functional theory study of the reaction paths of reactions of CH3C(O)O2 radicals with HO2 in the gas phase

A DFT study on the reactions between CH₃C(O)O₂ and HO₂ radicals has been carried out. It is suggested that both the triplet and singlet potential surfaces involve a complex mechanism with the formation of loosely bound intermediate complexes of reactants and products. The reaction prefers to occur on the triplet surface to produce peracetic acid (CH₃C(O)O₂H) and triplet O₂ molecule. The CH₃C(O)O₂H can further convert into CH₃C(O)O and HO radicals.