一种脉冲强电流条件下导线电阻测量方法

在超强激光辐照电容线圈靶产生强磁场实验中,在约50 ps时,线圈电流达到20 kA以上。通过该实验结果与磁场产生理论模型对比,可得出该导线电阻值比常温直流电阻高出3个量级。对导线材料电阻率与趋肤效应的分析结果表明,该电阻值在量级上是合理的。获得超快脉冲强电流条件下的导线电阻值,有助于更深入理解线圈靶产生强磁场过程。     

两组份复合材料光学非线性性质的临界行为

对两组份非线性复合材料的光学非线性性质的临界行为进行了研究。考虑第一组份为非线性材料,其电流、电压间服从I=g1V x1V^β关系;而第二组份为线性材料,电流、电压间满足I—g2V,其中g1,x1是第一组份的线性电导和光学非线性极化率,g2是第二组份的线性电导,β是第一组份材料的光学非线性指数。分别采用了有效介质近似和相对电阻涨落的标度理论两种方法计算了系统有效响应的临界指数随光学非线性指数及维数的变化规律。用不同的方法得到系统的有效线性电导g和有效光学非线性极化率xe(β)的临界指数M(β)和N(β)的结论也不同。有效介质近似得到M(β)=1和N(β)=(β 1)/2,即M(β)与β和d都无关,而N(β)只与有β关而与d无关;而相对电阻涨落标度理论方法得到的M(β)和N(β)与β和d都有关。     

气体火花开关电阻特性

利用二极管输出电压约1 MV、脉宽约40 ns的重复频率Tesla型脉冲功率驱动源,对大间隙、高气压的重复频率氮气火花开关进行了实验研究。通过将开关等效为RLC电路,利用测量得到的形成线电压与锥形段电压来计算氮气火花开关电阻。电阻的变化情况是放电开始时刻比较大,随着放电通道的形成,电阻迅速变小,最终达到级的阻值。通过计算值与理论公式推算值比较,检验Barannik,Rompe-Weizel,Demenik,Toeple,Vlastos公式适用性,并尝试对Rompe-Weizel公式常数项进行了修正。     

Entropy resistance analyses of a two-stream parallel flow heat exchanger with viscous heating

Heat exchangers are widely used in industry, and analyses and optimizations of the performance of heat exchangers are important topics. In this paper, we define the concept of entropy resistance based on the entropy generation analyses of a one-dimensional heat transfer process. With this concept, a two-stream parallel flow heat exchanger with viscous heating is analyzed and discussed. It is found that the minimization of entropy resistance always leads to the maximum heat transfer rate for the discussed two-stream parallel flow heat exchanger, while the minimizations of entropy generation rate, entropy generation numbers, and revised entropy generation number do not always.     

TSC defect level in silicon produced by irradiation with muons of GeV-energy

Deep level transient spectroscopy has been used to observe the reduced concentrations of vacancy-related defects in γ-irradiated n-type Si containing hydrogen atoms. Data are presented on the efficiency and depth of this damage reduction as a function of the duration and temperature of the exposure to the plasma used to introduce the atomic hydrogen. A 3-hour exposure in an H plasma at 300°C prior to irradiation reduced the concentrations of the O-V, V-V and P-V centres by half or more to a depth of ～20 μm, compared to the control samples.     

Electrical characterization of Schottky diodes based on boron doped homoepitaxial diamond films by conducting probe atomic force microscopy

A large planar tungsten carbide (WC) Schottky diode on p-type homoepitaxial diamond was mainly investigated on a microscopic level by atomic force microscopy (AFM) and conducting probe atomic force microscopy (CP-AFM), allowing simultaneous topographic and local electrical resistance imaging measurements. These techniques revealed the existence of a specific microstructure on the WC Schottky contact consisting of electrically insulating islands surrounded by conductive paths. The islands are found to be insulating in the whole range of explored bias [−5 V, +5 V], whereas the current flowing between the islands is 1000 times lower at a reverse bias of −5 V than at a forward bias of +5 V, in agreement with the rectifying ratio found from macroscopic current–voltage (I–V) measurements. CP-AFM provides a prospective imaging tool which is well suited for analyzing the local electrical properties and instabilities of Schottky junctions.     

Mechanical and Thermal Properties of Polypropylene/Silica Aerogel Composites

Polypropylene (PP) composites including various amounts of silica aerogel (SA) microparticles were prepared by melt mixing in an internal mixer. The morphology and microstructure of the prepared composites were investigated by scanning electron microscopy (SEM). Mechanical properties of the samples, including elastic modulus, tensile stress, elongation and stress at break, were measured by tensile tests. In addition, the other mechanical features, including Izod impact strength, hardness and wear resistance, were evaluated and then related to the structure of the PP/SA composites. Furthermore, the thermal characteristics of the composites, such as heat deflection temperature and thermal stability, were studied by thermal gravimetric analysis (TGA). The SEM photographs indicated the satisfactory SA particles dispersion for the compositions of 1% and 3% but agglomeration of the aerogels at higher SA contents. Since the composites became stiffer, the impact and tensile strength decreased. The addition of the SA to the PP matrix yielded harder samples with lower weight loss and coefficients of friction in wear tests. The TGA evaluations confirmed that the presence of SA promoted and upgraded the thermal stability and heat deflection temperature of PP. The thermal results proved the superior potential of PP as an insulator when the SA particles were added.     

Laser polishing of additive manufactured Ti alloys

Laser-based additive manufacturing has attracted much attention as a promising 3D printing method for metallic components in recent years. However, surface roughness of additive manufactured components has been considered as a challenge to achieve high performance. In this work, we demonstrate the capability of fiber laser in polishing rough surface of additive manufactured Ti-based alloys as Ti-6Al-4V and TC11. Both as-received surface and laser-polished surfaces as well as cross-section subsurfaces were analyzed carefully by White-Light Interference, Confocal Microscope, Focus Ion Beam, Scanning Electron Microscopy, Energy Dispersive Spectrometer, and X-ray Diffraction. Results revealed that as-received Ti-based alloys with surface roughness more than 5 µm could be reduce to less than 1 µm through laser polishing process. Moreover, microstructure, microhardness and wear resistance of laser-polished zone was investigated in order to examine the thermal effect of laser polishing processing on the substrate of additive manufactured Ti alloys. This proof-of-concept process has the potential to effectively improve the surface roughness of additive manufactured metallic alloy by local polishing method without damage to the substrate.