Extraction and purification of magnetic nanoparticles from strain of Leptospirillum ferriphilum

The magnetic nanoparticles were extracted from Leptospirillum ferriphilum, strain YSK, isolated from acid mine drainages by treatment with sodium dodecyl sulfate(SDS) and centrifugation through a sucrose density gradient. Transmission electron microscopy(TEM) indicates that the nanoparticles are approximately spherical with a mean diameter of 44 nm, and magnetite crystals in this size range are single magnetic domains. Energy-dispersive X-ray analysis shows that the nanoparticles primarily contain two kinds of elements, iron and oxygen. Thus it can be concluded that the magnetic particles are magnetosomes. Generally, it is thought that cellular magnetotaxis is a direct consequence of the cell possessing magnetosomes. The discovery of magnetosomes in strain YSK can provide the theoretical basis for screening efficient bioleaching bacteria which are specific to different magnetic minerals under an outer magnetic field.     

辣椒素对储粮害虫防治效果研究

以2%辣椒素乙醇溶液均匀喷雾添加于糙米,研究辣椒素对储粮害虫玉米象和赤拟谷盗的拒食和增殖作用。结果表明:辣椒素添加量为4,2g/kg.糙米时,玉米象和赤拟谷盗表现出明显的拒食现象,30d内糙米的因虫损失率,玉米象两个浓度处理组仅为空白对照的26.4%和35.4%;赤拟谷盗处理组仅为空白对照的24.8%和30.6%;辣椒素的添加剂量为0.5g/kg.糙米时,玉米象组、赤拟谷盗组增殖数量分别为空白组的9.23%,26.1%;辣椒素的添加剂量为2g/kg.糙米时,玉米象组存活数仅1头,赤拟谷盗存活数为0。辣椒素的添加使玉米象和赤拟谷盗的增殖受到了明显抑制。     

生物药剂乙基多杀菌素对玉米象的毒杀作用

室内测定新型生物杀虫剂乙基多杀菌素(spinetram)对主要储粮害虫玉米象成虫的控制作用。结果表明,乙基多杀菌素对玉米象成虫具有很强的触杀作用和种群抑制作用。当浓度为16μg/cm2,作用时间48 h时,乙基多杀菌素对玉米象成虫的校正死亡率达97.8%;当处理剂量为1 mg/kg时,乙基多杀菌素对玉米象成虫当代和子代种群抑制率均达100%。乙基多杀菌素对玉米象成虫没有驱避作用。     

Analog VLSI implementation of wavelet transform using switched-current circuits

For applications requiring low-voltage low-power and real-time processing, a novel scheme for the VLSI implementation of wavelet transform (WT) using switched-current (SI) circuits is presented. SI circuits are well suited for these applications since the dilation constant across different scales of the transform can be implemented, and controlled by both the aspect-ratio of the transistors and the clock frequency. The quality of such implementation depends on the accuracy of the corresponding wavelet approximation. First, an optimized procedure based on differential evolution algorithm (DE) is applied to approximate the transfer function of a linear steady-state system whose impulse response is the required wavelet. The proposed approach significantly improves the accuracy of approximation wavelets. Next, the approximation of time-domain wavelet function is implemented by the SI analog filters. Finally, the design of the complete SI filter based on first-order and biquad section as main building block is detailed. Simulations demonstrate the performance of the proposed approach to analog WT implementation.     

Numerical investigation on flow process of liquid metals in melt delivery nozzle during gas atomization process for fine metal powder production

Based on volume of fluid (VoF) interface capturing method and shear-stress transport (SST) k-ω turbulence model, numerical simulation was performed to reveal the flow mechanism of metal melts in melt delivery nozzle (MDN) during gas atomization (GA) process. The experimental validation indicated that the numerical models could give a reasonable prediction on the melt flow process in the MDN. With the decrease of the MDN inner-diameter, the melt flow resistance increased for both molten aluminum and iron, especially achieving an order of 10² kPa in the case of the MDN inner-diameter ≤1 mm. Based on the conventional GA process, the positive pressure was imposed on the viscous aluminum alloy melt to overcome its flow resistance in the MDN, thus producing powders under different MDN inner-diameters. When the MDN inner-diameter was reduced from 4 to 2 mm, the yield of fine powder (<150 μm) soared from 54.7% to 94.2%. The surface quality of powders has also been improved when using a smaller inner-diameter MDN.