首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
Surface morphologies of Zr52.5 Al10 Ni10 Cu15 Be12.5 bulk metallic glass after being rolled at both a temperature around T9 and near （ Tx - 50） K were investigated with a scanning electron microscopy. Macroscopic and microscopic observation results show that squamae, cracks, steps and wedges exist on the surface when the samples were rolled at temperatures around Ty. However, a smooth and fiat surface appears when the samples were rolled at temperatures near （ Tx - 50） K. These results indicate that the mode of deformation in the supercooled liquid region is a partially homogeneous flow at a temperature around T9, and a fully homogeneous one at temperatures near （ Tx - 50） K. According to the results, it is more feasible to roll the amorphous alloys at temperatures near （ Tx - 50） K to obtain parts with smooth and fiat surface.  相似文献   

2.
Using SnxTi1-xO2 as carriers, CuO/Sn0.9Ti0.1O2 and CuO/Sn0.7Ti0.3O2 catalysts with different loading amounts of copper oxide (CuO) were prepared by an impregnation method. The catalytic properties of CuO/Sn0.9Ti0.1O2 and CuO/Sn0.7Ti0.3O2 were examined using a microreactor-gas chromatography (GC) NO CO reaction system and the methods of BET (Brun- auer-Emmett-Teller), TG-DTA (themogravimetric and differential thermal analysis), X-ray diffraction (XRD) and H2-temperature programmed reduction (TPR). The results showed that NO conversions of Sn0.9Ti0.1O2 and Sn0.7Ti0.3O2 were 47.2% and 43.6% respectively, which increased to 95.3% and 90.9% at 6 wt% CuO loading. However, further increase in CuO loading caused a decrease in the catalytic activity. The nitrogen adsorption-desorption isotherm and pore-size distribution curve of Sn0.9Ti0.1O2 and Sn0.7Ti0.3O2 represented type IV of the BDDT (Brunauer, Deming, Deming and Teller) system and a typical mesoporous sample. There were two CuO diffraction peaks (2θ 35.5° and 38.7°), and the diffraction peak areas increased with increasing CuO loading. TPR analysis also detected three peaks (α, β and γ) from the CuO-loaded catalysts, suggesting that the α peak was the reduction of the highly dispersed copper oxide, the β peak was the reduction of the isolated copper oxide, and the γ peak was the reduction of crystal phase copper oxide. In addition, a fourth peak (δ) of the catalysts meant that the SnxTi1-xO2 mixed oxides could be reductive.  相似文献   

3.
A rice pse(t) (premature senescence, tentatively) mutant line, was isolated from 4500 independent T-DNA inserted transgenic lines. The symptoms of premature senescence appeared more severely than those of the control plants (Zhonghua 11,japonica) at the last development stage. To characterize the mutant and provide basic information on the candidate genes by mapping to a physical region of 220-kb, experiments were carried out in two phytotrons under controlled temperature of 24 ℃ and28 ℃, respectively. The content of chlorophyll, soluble protein and MDA (malondialdehyde), net photosynthesis, the antioxidant enzyme activities of SOD (superoxide dismuase) (EC 1.15.1.1) and POD (peroxidase) (EC 1.11.1.7) and the peptidase activities of leaves were measured from top to bottom according to the leaf positions at the flowering stage. Compared with the control plant,the mutant showed the following characteristics: (1) Higher net photosynthesis rate (Pn) appeared in the 1 st and 2nd leaves, contents of chlorophyll and soluble protein were also higher in the 1 st leaf; (2) The activities of SOD, POD and peptidase were higher according to the leaf position from top to bottom; (3) The symptom of premature senescence was accelerated in the mutant at 28℃treatment. The MDA content and the SOD and POD activities between the 24 ℃ and 28 ℃ treatment mutants were not significantly different. Content of chlorophyll and soluble protein of leaves mutant decreased rapidly at 28 ℃ treatment. The results show that pse(t) is sensitive to high temperature. The probable function of PSE(T) is discussed.  相似文献   

4.
This paper proposes a new approach for multi-objective robust control. The approach extends the standard generalizedl 2 (Gl 2) and generalizedH 2 (GH 2) conditions to a set of new linear matrix inequality (LMI) constraints based on a new stability condition. A technique for variable parameterization is introduced to the multi-objective control problem to preserve the linearity of the synthesis variables. Consequently, the multi-channel multi-objective mixed Gl 2/GH 2 control problem can be solved less conservatively using computationally tractable algorithms developed in the paper. Project supported by the National Natural Science Foundation of China (No. 60374028), and the Scientific Research Foundation for Returned Overseas Chinese Scholars, Ministry of Education (No. [2004]176)  相似文献   

5.
A transgenic barley line (LSY-11-1-1) with overexpressed Phalaris coerulescens thioredoxin gene (PTrx) was employed to measure the growth, protein oxidation, cell viability, and antioxidase activity in barley roots during germination on the presence of 2 mmol/L AlCl3 on filter paper. The results show that (1) compared with the non-transgenic barley, LSY-11-1-1 had enhanced root growth, although both were seriously inhibited after AlCl3 treatment; (2) the degree of protein oxidation and loss of cell viability in roots of LSY-11-1-1 were much less than those in roots of non-transgenic barley, as reflected by lower contents of protein carbonyl and Evans blue uptakes in LSY-11-1-1; (3) activities of catalase (CAT), glutathione peroxidase (GPX), ascorbate peroxidase (APX), and glutathione reductase (GR) in LSY-11-1-1 root tips were generally higher than those in non-transgenic barley root tips, although these antioxidase activities gave a rise to different degrees in both LSY-11-1-1 and non-transgenic barley under aluminum stress. These results indicate that overexpressing PTrx could efficiently protect barley roots from oxidative injury by increasing antioxidase activity, thereby quenching ROS caused by AlCl3 during germination. These properties raise the possibility that transgenic barley with overexpressed PTrx may be used to reduce the aluminum toxicity in acid soils.  相似文献   

6.
A skutterudite-related antimonide, CoFe3Sb12, was prepared with vacuum melting. XRD analysis showed the material contained Sb, FeSb2, CoSb2 and CoSb3 phases. The electrochemical properties of the ball-milled CoFe3Sb12−10 wt% graphite composite were studied using pure lithium as the reference electrode. A maximal lithium inserting capacity of about 860 mAh/g was obtained in the first cycle. The reversible capacity of the material was about 560 mAh/g in the first cycle and decreased toca. 320 mAh/g and 250 mAh/g after 10 and 20 cycles respectively.Ex-situ XRD analyses showed that the antimonides in the pristine material were decomposed after the first discharge and that antimony was the active element for lithium to insert into the host material. Project supported by the National Natural Foundation of China (No. 59771032) and the RFDP of the Education Ministry of China (No. 20010335045)  相似文献   

7.
Study of the SISO mixedH 2/l1 problem for discrete time systems showed that there exists a unique optimal solution which can be approximated within any prescribed missing error bound inl 2 norm with solvable suboptimal solutions and solvable superoptimal solutions. Project supported by the National Natural Science Foundation of China (No. 60174026) and the Scientific Research Foundation for Returned Overseas Chinese Scholars of Zhejiang Province (No. J20020546)  相似文献   

8.
The structural characteristics and optical and electrical properties of molecular-beam-epitaxy (MBE) grown ZnS0.8Se0.2 thin films on indium-tin-oxide(ITO) glas substrates were investigated in this work. TheX-ray diffraction (XRD) results indicated that high quality polycrystalline ZnS0.8Se0.2 thin film grown at the optimized temperature had a prefered orientation along the (111) planes. The transmission electron microscopy (TEM) cross-sectional micrograph of the sample showed a well defined columnar structure with lateral crystal dimension in the order of a few hundred angstroms. Ultraviolet (UV) photoresponsivity as high as 0.01 A/W had been demonstrated and for wavelengths longer than 450 nm, the response was down from the peak response by more than 3 orders of magnitude. The thin ZnS0.8Se0.2 photosensor layer, with a wide energy gap and anisotropic electrical property, makes a transmission UV liquid crystal light valve (LCLV) with high resolution feasible. Project supported by the National Natural Science Foundation of China (No. 59910161981) and RGC grant from the Hong Kong Government Grant (No. NSFC/HKUST 35), China  相似文献   

9.
The main objective of this work was to compare the applicability of the single leaf (the uppermost leaf L1 and the third uppermost leaf L3) modified simple ratio (mSR705 index) and the leaf positional difference in the vegetation index between L1 and L3 (mSR705L1-mSR705L3) in detecting nitrogen (N)-overfertilized rice plants. A field experiment consisting of three rice genotypes and five N fertilization levels (0, 75, 180, 285, and 390 kg N/ha) was conducted at Xiaoshan, Hangzhou, Zhejiang Province, China in 2008. The hyperspectral reflectance (350–2500 nm) and the chlorophyll concentration (ChlC) of L1 and L3 were measured at different stages. The mSR705L1 and mSR705L3 indices appeared not to be highly sensitive to the N rates, especially when the N rate was high (above 180 kg N/ha). The mean mSR705L1-mSR705L3 across the genotypes increased significantly (P<0.05) or considerably from 180 to 285 kg N/ha treatment and from 285 to 390 kg N/ha treatment at all the stages. Also, use of the difference (mSR705L1-mSR705L3) greatly reduced the influence of the stages and genotypes in assessing the N status with reflectance data. The results of this study show that the N-overfertilized rice plants can be effectively detected with the leaf positional difference in the mSR705 index.  相似文献   

10.
Ml0.7Mm0.3Ni3.7Co0.7Mn0.4Al0.2 nanocrystalline hydrogen storage materials are prepared by melt-spinning(MS).X-ray diffraction is used for the measurement of the nanocrystalline size.Compared to the electrode of polycrystalline alloys,the property of activation MH9metal hydride)electrode of the alloys with nanometer scale became worse and the inital discharge capacity decreased.It may be ascribed to the decrease of the total amount of rare earth metals and the increase of oxygen on the surface from the analysis of components of the alloys.After heat-treatment,the electrochemical performance of MH electrode of as-spun alloys could be improved,which could be attributed to the alleviation of the lattice strain.  相似文献   

11.
Well-cubic perovskite lanthanum aluminate (LaAlO3) film on (110) silicon substrate was fabricated by sol-gel method with corresponding inorganic salts. Lanthanum acetate and aluminum acetate glacial acetic acid solutions were prepared via ligand exchange starting from lanthanum nitrate hexahydrate and aluminum nitrate hexahydrate after being refluxed. (CH3CO)2O removed nitrates and the crystallized H2O completely, acetylacetone (AcAc) was partially bidentated with metallic ion of the metallic acetates and formed La(OAc)3−x (AcAc) x which were hydrolyzed into La(AcAc)3−x(OH) x by adding 10 ml 0.4% methyl cellulose (MCL) solution. The La(AcAc)3−x (OH) x , polymerizing and combining with MCL, formed the LaAlO3 sol precursor with heteropolymeric structure and formed film easily. The epitaxial LaAlO3 film on Si(110) substrate was crystallized after being annealed in thermal annealing furnace for 650–750 °C/30 min. The morphologies and microstructures were characterized. The refractive index of the LAO film was 1.942 to 2.007; the dielectric constant and the dissipation factors were estimated to be 23–26 and 2.1×10−4−2.4×10−4 respectively. Project (No. 2002CB613305) supported by the National Basic Research Program (973) of China  相似文献   

12.
Supersaturated solid solutions Fe1-xCx （0≤x≤0.9 ） of wide composition range have been prepared by mechanical alloying process. Nanocrystalline phase was formed for 0 ≤ x ≤ 0.67 and a large grain phase for 0.75 ≤ x ≤ 0.9. The large fraction of graphite volume puts off formation of nanocrystalline phase for high carbon content. In the large grain phase, magnetization follows simple magnetic dilution, and eoereivity He is mainly due to dissolution of carbon at grain boundaries. In the nanocrystalline phase the alloying effect of carbon is revealed by a distinct reduction of average magnetic moment. The increasing lattice constant with increasing carbon content is observed for x ≤ 0.5, suggesting that the high carbon concentration may enhance diffusion of carbon into the Fe lattice. It shows a discontinuity in the Hc variation with a grain size D of nanocrystalline phase. For small grain D below the critical value, Hc increases with D. For a large grain D, Hc decreases with increasing D. The solubility limit of carbon in a-Fe extended by nanocry- stalline phase formation is discussed.  相似文献   

13.
Effect of the content of dopants in the manganese-zinc ferrites on the low power loss is studied by measuring magnetic properties and observing the grain boundary structures. The Mn0.738Zn0.206Fe2.066O4 composition powders were prepared by using conventional ceramic powder processing technique. The microstructure of grain boundary was observed by scanning electron microscope （SEM）. It has been found that power loss is greatly dependent upon the content of the additives.  相似文献   

14.
Systematic studies of the transport properties of La0.67Ca0.33Mn1?xFe x O3 (x=0–0.3) systems showed that with increasing Fe-doping contentx the resistance increases and the insulator-metal transition temperature moves to lower temperature. For small doping content, the transport property satisfies metal transport behavior below the transition temperature, and above the transition temperature it satisfies the small polaron model. This behavior can be explained by Fe3+ doping, which easily forms Fe3+?O2??Mn4+ channel, suppressing the double exchange Mn3+?O2??Mn4+ channel and enhancing the spin scattering of Mn ions induced by antiferromagnetic clusters of Fe ions.  相似文献   

15.
A new concept of low-cost direct air capture technology integrated with a fertilization system is proposed, as an alternative to the application of air derived CO2. A moisture swing sorbent can elevate the CO2 concentration from 400 parts per million (ppm) to several thousand ppm, and this can be used to cultivate plants. Desorption isotherms were determined and are described well by a Langmuir model. The adsorption rate constant and the desorption rate constant were gained at 25 °C, 35 °C, and 45 °C under 1000 ppm concentration of CO2. In accelerated cultivation experiments, the effects of CO2 concentration, light intensity, and spectrum on the CO2 uptake rate of the plants were investigated. A multi-bed desorption system which is capable of providing a continuous and stable CO2 supply for a greenhouse is demonstrated based on the desorption characteristic and CO2 uptake feature of plants. An energy and cost assessment for the integrated system was performed and the results indicated that minimum energy requirements and cost estimate of CO2 are 35.67 kJ/mol and 34.68 USD/t, respectively. This makes direct air capture a competitive and sustainable carbon source for agriculture.  相似文献   

16.
Transgenic Brassica compestris L.spp.chinensis plants expressing a choline oxidase(codA) gene from Arthrobacter globiformis were obtained through Agrobacterium tumefaciens-mediated transformation.In the transgenic plants,codA gene expression and its product transportation to chloroplasts were detected by the enzyme-linked immunosorbent assay(ELISA) examination,immunogold localization,and 1 H-nuclear magnetic resonance( 1 H-NMR) . Stress tolerance was evaluated in the T3 plants under extreme temperature and salinity conditions.The plants of transgenic line 1(L1) showed significantly higher net photosynthetic rate(Pn) and Pn recovery rate under high(45°C,4 h) and low temperature(1°C,48 h) treatments,and higher photosynthetic rate under high salinity conditions(100,200,and 300 mmol/L NaCl,respectively) than the wild-type plants.The enhanced tolerance to high temperature and high salinity stresses in transgenic plants is associated with the accumulation of betaine,which is not found in the wild-type plants.Our results indicate that the introduction of codA gene from Arthrobacter globiformis into Brassica compestris L.spp.chinensis could be a potential strategy for improving the plant tolerance to multiple stresses.  相似文献   

17.
α-diketones and β-diketones react with Grignard reagents in the presence of a catalytic amount of Cp2TiCl2 to yield α-ketols and corresponding ketones respectively. Sulfoxides can be deoxygenated by Cp2TiCl2/Al system. The possible mechanisms are also discussed. Project (No. 20072033) supported by the National Natural Science Foundation of China and the Specialized Research Fund for the Doctoral Program of Higher Education Ministry, China  相似文献   

18.
Dried ground leaves ofPsidium guajava L. (guava) were extracted by water and aqueous ethyl alcohol 50% (1∶10) ratio, and the total phenolic content in the extracts was determined spectrophotometrically according to Folin-Ciocalteu's phenol method and calculated as gallic acid equivalent (GAE). Remarkably high total phenolic content 575.3±15.5 and 511.6±6.2 mg of GAE/g of dried weight material (for ethanol guava leaf extracts and water guava leaf extracts, respectively) were obtained. The antioxidant activity of lyophilized extracts was determined at ambient temperature by means of a 2,2-diphenyl-1-picrylhydryzyl (DPPH') colorimetry with detection scheme at 515 nm. The activity was evaluated by the decrease in absorbance as the result of DPPH' color change from purple to yellow. The higher the sample concentration used, the stronger was the free radical-scavenging effect. The results obtained showed that ascorbic acid was a substantially more powerful antioxidant than the extracts from guava leaf. On the other hand, the commercial guava leaf extracts and ethanol guava leaf extracts showed almost the same antioxidant power whereas water guava leaf extracts showed lower antioxidant activity. The parameter EC50 and the time needed to reach the steady state to EC50 concentration (T EC 50) affected the antiradical capacity of the sample. The antioxidant efficiency (AE) has been shown to be a more adequate parameter for selecting antioxidants than the widely used EC50. This study revealed that guava leaf extracts comprise effective potential source of natural antioxidants.  相似文献   

19.
An ecofriendly heterogeneous polyoxometalate (POM)-gold catalyst Au/BW11/Al2O3 was synthesized and used for solvent-free epoxidation of cyclooctene under mild reaction conditions using molecular oxygen as an oxidant and t-butyl hydroperoxide (TBHP) as an initiator. The catalyst was characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD), induced coupled plasma optical emission spectrometry (ICP-OES), and Brunauer-Emmett-Teller (BET). The catalyst showed good conversion and high selectivity without use of solvents or environmentally harmful oxidants. Moreover, the catalyst is recyclable up to three cycles with no significant loss in selectivity towards epoxide.  相似文献   

20.
This paper describes the preparation and properties of TiNx-SiO2 double-layered antireflective(AR) coatings that were applied with print process. The coating material was analyzed and TiNx was used instead of TiO2 as high refractive material. The influence of solution concentration on AR property was studied. The testing result shows that the coatings using print process are featured with excellent mechanical property and the AR property is comparable to American Southwall AR product. It is expected that the study would promote the industrialization progress in AR coatings.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号