Kinetic study on the direct nitridation of silicon powders diluted with α-Si3N4 at normal pressure

Silicon nitride (Si₃N₄) powders were prepared by the direct nitridation of silicon powders diluted with α-Si₃N₄ at normal pressure. Silicon powders of 2.2 μm in average diameter were used as the raw materials. The nitriding temperature was from 1623 to 1823 K, and the reaction time ranged from 0 to 20 min. The phase compositions and morphologies of the products were analyzed by X-ray diffraction and scanning electron microscopy, respectively. The effects of nitriding temperature and reaction time on the conversion rate of silicon were determined. Based on the shrinking core model as well as the relationship between the conversion rate of silicon and the reaction time at different temperatures, a simple model was derived to describe the reaction between silicon and nitrogen. The model revealed an asymptotic exponential trend of the silicon conversion rate with time. Three kinetic parameters of silicon nitridation at atmospheric pressure were calculated, including the pre-exponential factor (2.27 cm·s^?1) in the Arrhenius equation, activation energy (114 kJ·mol^?1), and effective diffusion coefficient (6.2×10^?8 cm²·s^?1). A formula was also derived to calculate the reaction rate constant.     

Observation of internal tides and near-inertial motions in the upper 450 m layer of the northern South China Sea

Mooring ADCP current observations from August to November are used to study the barotropic tides, baroclinic tides and near-inertial motions in the upper 450 m layer of the northern South China Sea. The barotropic and baroclinic tides at the mooring station are all dominated by M2, K1, O1, P1, with the barotropic amplitudes being 7.8 cm·s^-1, 7.0 cm·s^-1, 5.4 cm·s^-1 and 3.5 cm·s^-1 respectively. The amplitudes of M2, K1, O1, P1 internal tides vary greatly, which are 12--15 cm·s^-1 in the thermocline, and then decrease with increasing depth. The amplitude of the barootropic near-inertial motions is less than 1 cm·s^-1, contributing little to the barotropic currents. However, that of the baroclinic nearinertial motions can be as large as 5 cm·s^-1. The inclination of tidal ellipse tends to increase with increasing depth, implying upward propagation of energy, while that of the near-inertial ellipse tends to decrease with increasing depth, implying downward propagation of energy.     

Characteristics of Baicalin Synergy with Penicillin or Notopterygium Ethanol Extracts Against Staphylococcus aureus

Introduction Staphylococcus aureus (S. aureus) resistance to most once powerful β-lactame antibiotics is now a severe problem world wide, so agents are urgently needed to reduce or moderate resistance to existing antibiotics. Traditional medicinal herbs …     

Doping effect on thermoelectric properties of nonstoichiometric AgSbTe<Subscript>2</Subscript> compounds

Nonstoichiometric ternary thermoelectric materials Ag_0.84Sb_1.15M_0.01Te_2.16 (M=Ce, Yb, Cu) were prepared by a direct melt-quench and hot press process. The carrier concentration of all the samples increased after doping. Thermoelectric properties, namely electrical conductivity, Seebeck coefficient, and thermal conductivity, were measured from 300 to 673 K. The phase transition occurring at about 418 K representing the phase transition from β-Ag₂Te to α-Ag₂Te influenced the electrical transport properties. The electrical conductivities of Ce and Yb doped samples increased after doping from 1.9×10⁴ to 2.5×10⁴ and 2.3×10⁴ S·m⁻¹, respectively, at 673 K. Also, at room temperature, the Seebeck coefficient of the Ce doped sample relatively increased corresponding to the high carrier concentration due to the changes in the band structure. However, all the thermal conductivities increased after doping at low temperature. Because of the higher thermal conductivity, the dimensionless figure of merit ZT of these doped samples has not been improved.     

Thermodynamic functions and growth constants of web-like ZnO nanostructures

Web-like ZnO nanostructures have been successfully synthesized using the potassium nitrate route at various temperatures to simplify conventional preparation methods. The structures and morphologies of the as-prepared products were characterized by X-ray powder diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM). The results showed that the reaction temperature was an important parameter, and that there was a feedback effect between nano-structure and growth parameters, combined with in situ micro-calorimetry, the reaction rate constants of the three systems were found to have been: 2.43×10-6, 2.70×10-8 and 3.12×10-7s-1 respectively. Furthermore, based on the relationship governing the potential differences between nanoand bulk ZnO, thermodynamic functions of nano-ZnO such as standard molar entropy (Sm,ZnO(nano)), standard molar Gibbs free energy of formation (△rGm,ZnO(nano)), and standard molar enthalpy of formation (△rHm,ZnO(nano)) have been calculated by the electrochemical method.     

Observation of small-scale processes over shelf break in the East China Sea

The turbulent dissipation along with temperature and salinity was measured on board R/V Dong Fang Hong 2 over the shelf break of the East China Sea from March 7 to 9, 2004. Applying the Turner angle, it is found that the ＇diffusive＇ double diffusion, salt-fingering, and stable stratification coexist in the upper water column of about 50 m. Below that depth, there exists weak salt-fingering. The turbulent dissipation rates are enhanced along the ray paths of M2 internal tides emanating from the shelf break with values ranging from 1.0×10^-9 W·kg^-1 to 1.2×10^-6 W·kg^-1. The corresponding diapycnal mixing rates are from 1×10^-6 m^2· s^-1 to 1×10^-2 m^2· s^-1. The spatially averaged mixing rate over the whole observation section is 2.3×10^-3 m^2· s^-1, which is much larger than 1×10^-5 m^2·s^-1 of the background diapycnal mixing rate in the open ocean.     

Preparation of sol-gel derived microcrystalline corundum abrasives with hexagonal platelets

The effects of different additives on the mechanical properties, microstructures, and wear behavior of corundum abrasives were investigated. When the number of additive phases increases, the sintering temperature and wear rate decrease, while the densification and mechanical properties increase. The additive SiO₂ is responsible for the development of equiaxed grains, whereas both CaO and MgO promote the development of platelike grains. By controlling the molar ratio of additives, it is possible to obtain different microstructures. With SiO₂-MgO-CaO (molar ratio, 2:1:1) as the additives and nano α-Al₂O₃ powders as the seed, microcrystalline corundum abrasives with hexagonal platelets were obtained using sol-gel process by sintering at 1300℃ for 0.5 h. The average diameter and thickness of hexagonal platelets are 1.38 μm and 360 nm respectively, the single-particle compressive strength is 26.44 N, and the wear rate is (3.06±0.21)×10?7 mm3/(N·m).     

SBDR显色剂固相萃取光度法测烟草中的铅

 研究了对磺酸基苯基亚甲基若丹宁(SBDR)与铅的显色反应,在pH为4.0的HAc-NaAc缓冲介质中,吐温-60存在下,该络合物可被WatersSep-Pak-C18固相萃取小柱萃取,小柱上富集的络合物用无水乙醇洗脱后在乙醇介质中,体系λ_max=560nm,ε=1.12×10⁵L·mol^-1·cm^-1.可用分光光度法测定,铅含量在0~6μg/50mL内符合比尔定律,方法用于烟草中铅含量的测定,结果令人满意.     

Supercondcuting properties in MgB2／Fe wires prepared by PIT method

The discovery of superconductivity at 39 K in MgB2has attracted a lot of interest in the world[15]. Recently, many results on the magnetic and transport properties of bulks have been reported. And high critical currentdensities (Jc) in polycrystalline MgB2 materials indicate that Jc is not limited by the weak link of grain boundaries as high temperature superconductor (HTS), suggestingthat MgB2 has a good potential for electrical engineering applications[2,48]. The fabrication of high qua…     

Source rupture process of Lushan M S7.0 earthquake, Sichuan, China and its tectonic implications

The source rupture process of the M _S7.0 Lushan earthquake was here evaluated using 40 long-period P waveforms with even azimuth coverage of stations. Results reveal that the rupture process of the Lushan M _S7.0 event to be simpler than that of the Wenchuan earthquake and also showed significant differences between the two rupture processes. The whole rupture process lasted 36 s and most of the moment was released within the first 13 s. The total released moment is 1.9×10¹⁹N m with M _W=6.8. Rupture propagated upwards and bilaterally to both sides from the initial point, resulting in a large slip region of 40 km×30 km, with the maximum slip of 1.8 m, located above the initial point. No surface displacement was estimated around the epicenter, but displacement was observed about 20 km NE and SW directions of the epicenter. Both showed slips of less than 40 cm. The rupture suddenly stopped at 20 km NE of the initial point. This was consistent with the aftershock activity. This phenomenon indicates the existence of significant variation of the medium or tectonic structure, which may prevent the propagation of the rupture and aftershock activity. The earthquake risk of the left segment of Qianshan fault is worthy of attention.     

Photoautotrophic Growth and Net Photosynthetic Rate of Sweet Potato Plantlets In Vitro as Affected by the Number of Air Exchanges of the Vessel and Type of Supporting Material

Introduction Micropropagation, a plant tissue culture technique, has contributed to producing virus-free, genetically supe-rior plantlets. However, its commercial application is still limited due to its relatively high production costs. The high costs are…     

Crystal structure and negative thermal expansion of solid solution Lu<Subscript>2</Subscript>W<Subscript>3−<Emphasis Type="Italic">x</Emphasis></Subscript>Mo<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>12</Subscript>

A new series of solid solutions Lu₂W_3−x Mo _x O₁₂ (0.5≤x≤2.5) were successfully synthesized by the solid-state method. Their crystal structure and negative thermal expansion properties were studied using high-temperature X-ray powder diffraction and the Rietveld method. All samples of rare-earth tungstates and molybdates are found to crystallize in the same orthorhombic structure with space group Pnca and show the negative thermal expansion phenomena related to transverse vibration of bridging oxygen atoms in the structure. Thermal expansion coefficients (TEC) of Lu₂W_3−x Mo _x O₁₂ are determined as −20.0×10⁻⁶ K⁻¹ for x=0.5 and −16.1×10⁻⁶ K⁻¹ for x=2.5 but -18.6×10⁻⁶ and −16.9×10⁻⁶ K⁻¹ for unsubstituted Lu₂W₃O₁₂ and Lu₂Mo₃O₁₂ in the identical temperature range of 200 to 800°C. High-temperature X-ray diffraction (XRD) data and bond length analysis suggest that the difference between W-O and Mo-O bond is responsible for the change of TECs after the element substitution in this series of solid solutions.     

Magnetic records of heavy metal pollution in urban topsoil in Lanzhou, China

This study is a systematic analysis of the magnetic characteristics and heavy metal elements in soil samples collected from Lanzhou City,China.The 117 surface soil samples were measured to study the feasibility and effectiveness of environmental magnetism for evaluating heavy metal pollution in urban soils.Results of the study indicate that low-coercivity magnetite dominates the magnetic properties in the samples.The high values of the soil magnetic mineral concentration parameters and low values of magnetic particle size parameters are distributed throughout the northern area of Xigu District,the industrial zones of the eastern section of Chengguan District and the districts of the narrow sections connecting Chengguan District and the other three districts;these parameters are fundamentally consistent with the distribution of the high values of the Pollution Load Index and Nemerow Pollution Index.Semi-quantitative studies which use the environmental magnetic method to monitor pollution of heavy metals(such as As,Cr,Cu,Ni,Pb,Zn,and Fe) have shown that when xlf≤35×10-8 m 3 kg-1,it is unpolluted;when 35≤xlf <150×10-8 m3 kg-1,it is moderately polluted to unpolluted;when 150≤xlf <365×10-8 m 3 kg-1,it is moderately polluted;when 365≤xlf <750×10-8 m3 kg-1,fd %<2.7 and ARM /SIRM<0.2×10-3m A-1,it is moderately to highly polluted;when xlf ≥750×10-8 m3 kg-1,xfd %<2.7 and xARM/SIRM<0.2×10-3m A-1,it is highly polluted.The region of moderately to highly polluted distribution is caused by industry and vehicles,showing that the change of pollution in Lanzhou City bears the trend of "vehicle emission + industrial".     

Enhanced thermoelectric properties of Co1-x-yNix+ySb3-xSnx materials

Co_1−x−y Ni_x+y Sb_3−x Sn _x polycrystals were fabricated by vacuum melting combined with hot-press sintering. The effect of alloying on the thermoelectric properties of unfilled skutterudite Co_1−x Ni _x Sb_3−x Sn _x was investigated. A leap of electrical conductivity from the Co_0.93Ni_0.07Sb_2.93Sn_0.07 sample to the Co_0.88Ni_0.12Sb_2.88Sn_0.12 sample occurs during the measurement of electrical conductivity, indicating the adjustment of band structure by proper alloying. The results show that alloying enhances the power factor of the materials. On the basis of alloying, the thermoelectric properties of Co_0.88Ni_0.12Sb_2.88Sn_0.12 are improved by Ni-doping. The thermal conductivities of Ni-doping samples have no reduction, but their power factors have obvious enhancement. The power factor of Co_0.81Ni_0.19Sb_2.88Sn_0.12 reaches 3.0 mW·m⁻¹·K⁻² by Ni doping. The dimensionless thermoelectric figure of merit reaches 0.55 at 773 K for the unfilled Co_0.81Ni_0.19 Sb_2.88Sn_0.12.     

Synergistically optimizing electrical and thermal transport properties of ntype PbSe

In this paper,we report that the thermoelectric performance of n-type Pb Se could be improved through synergistically optimizing electrical and thermal transport properties via Sb doping and Mg alloying.The carrier concentration was firstly optimized through Sb doping,resulting in a maximum power factor of~15.4μW cm~(-1)K~(-2)and maximum ZT of~0.9 at 873 K in Pb_(0.99)Sb_(0.01)Se.Then,Mg was selected for alloying in Pb sites to produce point defects,which can largely intensify the phonon scattering and lower thermal conductivity.After Mg alloying,the thermal conductivity at 300 K(873 K)was significantly suppressed from~4.6 Wm~(-1)K~(-1)(1.5 Wm~(-1)K~(-1))for Pb_(0.99)Sb_(0.01)Se to~2.9 Wm~(-1)K~(-1)(1.1 Wm~(-1)K~(-1))for Pb_(0.99)Sb_(0.01)Se-6%Mg Se.Through combining Sb doping and Mg alloying,a maximum ZT of~1.1 was achieved at 873 K for Pb_(0.99)Sb_(0.01)Se-6%Mg Se,and the average ZT(ZT_(ave))was increased by 28.6%from~0.42 for Pb_(0.99)Sb_(0.01)Se to~0.54 for Pb_(0.99)Sb_(0.01)Se-6%Mg Se.The results indicate that Pb Se is a robust candidate for medium-temperature thermoelectric applications.     

Third-order optical nonlinearities for lanthanum (III) complexes with 1, 10-phenanthroline components

The nonlinear refractive indexesn ₂ for the ethanol solutions of 1, 10-phenanthroline (2.0 × 10⁻³ mol · L⁻¹), [bis(l, 10-phenanthroline) lanthanum (III)] nitrate (1.0 × 10⁻³ mol · L⁻¹), and [nitrato-fluoracil-bis (1, 10_{-phenanthroline}) lanthanum (III) ] nitrate (1.0 × 10⁻³ mol · L⁻¹) are first measured, the third-order nonlinear optical susceptibilities χ(³) and 〈γ〉 are calculated, and the mechanisms of the third-order optical nonlinearities enhanced by lanthanum (III) are discussed preliminarily.     

Methoprene对SpltNPV增殖及其LC50的影响

 通过对斜纹夜蛾核多角体病毒(SpltNPV)在其不同龄期宿主体内增殖情况的研究,探索保幼激素类似物(JHA)methoprene促进SpltNPV在其宿主体内增殖的途径,为今后广泛利用methoprene进行高效率、低成本增殖昆虫杆状病毒杀虫剂提供理论依据和方法.运用正交组合的方法筛选3种主要因子(病毒感染浓度、methoprene用量和methoprene施用时间)对提高病毒增殖产量进行最佳组合实验.实验确立了以1×10⁷PIBs/mL感染6龄刚蜕皮的斜纹夜蛾幼虫,并于感染第1天滴加10μL methoprene的最佳组合方法,病毒总产量和平均病毒产量分别可达1 856.0×10⁸PIBs和62.2×10⁸PIBs.并测定了methoprene处理对SpltNPV病毒LC₅₀的影响.经methoprene处理后,病毒的LC₅₀由1.578×10⁷PIBs/mL增加至9.151×10⁷PIBs/mL.     

不同生长调节剂提高香荚兰抗逆能力的研究

 研究了6种不同生长调节剂脱落酸(abscisic acid,ABA,5μg·L^-1)、膨大剂(CPPU,5μg·L^-1)、那氏试剂(778诱导剂,5×10⁶μg·L^-1)、烯效唑(uniconazole,10μg·L^-1)、长效BR-120(0.2μg·L^-1)、几丁质(chitin,10μg·L^-1)喷施香荚兰植株对其抗逆能力的影响.结果表明:各种处理后叶片内超氧化物歧化酶(SOD)、过氧化物酶(POD)活性提高和丙二醛(MDA)含量降低.其中,烯效唑的效果最佳,其次为BR-120,其它调节剂也有一定的作用效果此外,还对ABA处理后随取样时间不同植株抗逆能力的变化作了初探.     

Fluorescence Determination of Artemisinin Using Hemoglobin as Catalyst and Pyronine B as Substrate

0 IntroductionMaalnadria siusb atr ompajicosr .he aAltrthe pmrisoibnlienmi (n qtihneghtraoopsiucs,QHS,Fig.1) is a sesquiterpene endoperoxide isola-ted fromArtemisia annuaL., an ancient Chineseherbal medicine usedfor treatment of fever and ma-laria.Studies of the structure and activity relation-ship have shownthat endoperoxide groupis essentialfor anti malarial activity of QHS and absence of thismoiety lead to completely loss in activity of thedrug. Many techniques have been developed to de…     

Binding and endocytosis of monoterbium transferrin by K562 cells

Human serum apotransferrin is the major iron-tran- sport protein in blood. The protein binds iron as Fe3+ at two similar, but not identical, high-affinity binding sites. Although iron bound to human serum apotransferrin is less then 0.1% (~3 mg) of the total body iron, dynamically it is the most important iron pool with the highest rate of turnover. The turnover of transferrin iron is in the order of 30 mg per day and, normally, about 80% of this iron are transported to the bone marrow for hem…