高原负地闪前云闪K-型击穿过程的观测研究

利用GPS同步的高时间分辨率闪电电场变化仪,对青藏高原东部地区的雷电特征进行了多点同步观测,得到了1μs时间分辨率的多站同步闪电电场变化资料。利用高频辐射脉冲到达不同测站的时间差,对一次负地闪前的云闪K-型击穿过程进行了分析,得到了其放电过程的起始位置和发展路径.K-型击穿过程起始于云中部的负电荷区,并以1.5×10~7m/s的速度向下部正电荷区域传播。雷暴云中正、负电荷离地高度分别为2.5～3.5km和5.0～6.0km。

Temperature and Nitric Oxide Generation in a Pulsed Arc Discharge Plasma

Nitric oxide （NO） is increasingly being used in medical treatments of high blood pressure, acute respiratory distress syndrome and other illnesses related to the lungs. Currently a NO inhalation system consists of a gas cylinder of N2 mixed with a high concentration of NO. This arrangement is potentially risky due to the possibility of an accidental leak of NO from the cylinder. The presence of NO in the air leads to the formation of nitric dioxide （NO2）, which is toxic to the lungs. Therefore, an on-site generator of NO would be highly desirable for medical doctors to use with patients with lung disease. To develop the NO inhalation system without a gas cylinder, which would include a high concentration of NO, NAMIHIRA et al have recently reported on the production of NO from room air using a pulsed arc discharge. In the present work, the temperature of the pulsed arc discharge plasma used to generate NO was measured to optimize the discharge condition. The results of the temperature measurements showed the temperature of the pulsed arc discharge plasma reached about 10,000 K immediately after discharge initiation and gradually decreased over tens of microseconds. In addition, it was found that NO was formed in a discharge plasma having temperatures higher than 9,000 K and a smaller input energy into the discharge plasma generates NO more efficiently than a larger one.

Synthesis of Propyl-Sulfonic Acid-Functionalized Nanoparticles as Catalysts for Cellobiose Hydrolysis

Functionalization of silica surfaces using organo-silanes is highly sensitive to reaction conditions. Silica-coated nanoparticles were functionalized with propyl-sulfonic acid groups (PS) under different synthesis conditions including, various solvents (Ethanol, methanol, acetonitrile, and toluene), water content in the reaction media (0% to 50%), 3-mercaptopropyl-trimethoxysilane concentration (MPTMS) (0.5% to 10%), and reaction time (6 to 16 h). Size of the PS-nanoparticles was determined by TEM and varied from 3.5 to 20.3 nm with sulfur load. Elemental analysis revealed sulfur contents from 0.8% to 22%. FTIR analysis showed increased C-H band intensities with increasing sulfur content of PS-nanoparticles. Although PS-nanoparticles with sulfur loads under 3% did not improve the hydrolysis of cellobiose, PS acid-functionalized nanoparticles with about 6% S achieved 96.0% cellobiose conversion. The control experiment, without catalyst, converted 32.8% of the initial cellobiose. PS-nanoparticles with (6% - 8% S) were obtained using (0.5%) silane concentration and 15 - 16 h reaction time in ethanol.

纳米级分辨率的光纤位移传感器的设计和建模

本文介绍了一种光纤纳米级分辨率的非接触式测量系统。对实验的设置、噪声和时频响应进行了具体介绍和分析。实验设置包括一项减小激光源波动的技术。并用一个分辨率为1.25nm的激光干涉仪(AXIOM2/20)来监控的线性低电压压电陶瓷驱动台进行标定。光纤传感器具有从50到150μm稳定的准线性测量范围。

豌豆品种对种传花叶病毒的敏感性及病毒的种子传播

用 ELISA(酶联免疫吸附法)测定温室内接毒碗豆叶片或卷须组织中传花叶病毒(PSMV)的含量表明,大多数复合品种中病毒浓度较低,而菜碗和藤蔓型品种的含毒量较高,检测了20个品种的种子传毒率,Maro、Princess 和 Progreta 为零,而 Vedette 达74%.通过种子传毒感病的幼苗上表现出与原亲本病株相同的病毒症状。由 ISEM(免疫吸附电镜)和 ELISA 分别在感病幼苗他萌发3天的胚芽中很容易检测到病毒质粒。

Anisotropy of the Wear Behavior for Carbon Nanotube-Reinforced 6061Al Composites

Carbon nanotube(CNT)-reinforced 6061Al(CNT/6061Al)composites with directionally aligned CNT were fabricated,and their wear behavior was investigated.The results indicate that the wear properties of CNT/6061Al composites exhibited a significant anisotropy.A certain CNT concentrations(1 wt%and 2 wt%)could effectively improve the wear resistance of CNT/6061Al composites along the CNT circumferential and CNT radial directions for the load transfer,grain refinement and self-lubrication effect of CNT.The Brass{011}<211>and{112}<110>textures inhibited the load transfer effect of CNT along the CNT radial direction,resulting in a better wear resistance along CNT circumferential direction than CNT radial direction.Along the CNT axial direction,the weak deformability of composites caused by the intensifying<111>fiber texture was the main reasons for the poor wear resistance of CNT/6061Al composites with increasing CNT concentration.

Efect of Nanometer WC Coating on Thermal Conductivity of Diamond/6061 Composites

Diamond has poor interface tolerance with Al.To enhance interface bonding,in this study,tungsten carbide(WC)nanocoatings on the surface of diamond particles were prepared using sol–gel and in-situ reaction methods.WO_(3) sol–gel with two concentrations,0.2 mol/L,and 0.5 mol/L,was,respectively,coated on diamond particles,then sintered at 1250℃for 2 h to produce WC nanocoatings.The concentration of 0.2 mol/L WO_(3) sol–gel was not enough to cover the surface of the diamond completely,while 0.5 mol/L WO_(3) sol–gel could fully cover it.Moreover,WO_(3) was preferentially deposited on{100}planes of the diamond.WO_(3) converted to WC in-situ nanocoatings after sintering due to the in-situ reaction of WO_(3) and diamond.The diamond-reinforced Al composites with and without WC coating were fabricated by powder metallurgy.The diamond/Al composite without coating has a thermal conductivity of 584.7 W/mK,while the composite with a coating formed by 0.2 mol/L and 0.5 mol/L WO_(3) sol–gel showed thermal conductivities of 626.1 W/mK and 584.2 W/mK,respectively.The moderate thickness of nanocoatings formed by 0.2 mol/L WO_(3) sol–gel could enhance interface bonding,therefore improving thermal conductivity.The nanocoating produced by 0.5 mol/L WO_(3) sol–gel cracked during the fabrication of the composite,leading to Al12W formation and a decrease in thermal conductivity.

Effects of welding speed on the multiscale residual stresses in frictionstir welded metal matrix composites

The effects of welding speed on the macroscopic and microscopic residual stresses(RSes) in friction stir welded 17 vol.% SiCp/2009 Al-T4 composite plates were studied via neutron diffraction and an improved decoupled hierarchical multiscale modeling methods. Measurements showed that the macroscopic and total RSes had the largest variations in the longitudinal direction(LD). Increasing the welding speed led to higher values of measured LD macroscopic and total RSes in the matrix. The welding speed also significantly influenced the distributions and magnitudes of the microscopic RSes. The RSes were predicted via an improved hierarchical multiscale model, which includes a constant coefficient of friction based thermal model. The RSes in the composite plates before friction stir welding(FSW) were computed and then set as the initial states of the FSW process during modeling. This improved decoupled multiscale model provided improved predictions of the temperature and RSes compared with our previous model.

Effect of heat-input on pitting corrosion behavior of friction stir welded high nitrogen stainless steel

In this study, different welding param eters were selected to investigate the effects of heat-in put on the microstructure and corrosion resistance of the friction stir welded high nitrogen stainless steel joints. The results show ed that, the welding speed had major influence on the duration at elevated tem perature rather than the peak tem perature. The hardness distribution and tensile properties of the nugget zones (NZs) for various joints were very similar while the pitting corrosion behavior of various NZs showed major differences. Large heat-input resulted in the ferrite bands being the pitting location, while tool wear bands were sensitive to pitting corrosion in the low heat-input joints. Cr diffusion and tool wear were the main reasons for pitting. The mechanisms of pitting corrosion in the NZs were analyzed in detail.

The effects of fabrication atmosphere condition on the microstructural and mechanical properties of laser direct manufactured stainless steel 17-4 PH

The effects of atmosphere conditions on microstructural and mechanical properties of stainless steel 17-4PH components fabricated by laser direct manufacturing (LDM) were investigated through mea-surements on phase constitution, porosity, tensile strength, fracture morphology, hardness and evolution of substrate temperature. Results showed that the samples produced in air atmosphere condition pos-sessed higher tensile strength and hardness for both as-deposited and heat-treated states than that in Ar chamber condition, due to dispersion strengthening effect of amorphous oxide particles and nitrogen solution strengthening as a result of higher content of oxygen and nitrogen. The temperature of substrate heat accumulation was higher in Ar chamber condition, leading to dramatically lower porosity and more reverse austenite, which also contributed to the lower strength and hardness.

Microstructural Evolution and Mechanical Behavior of Friction-Stir-Welded DP1180 Advanced Ultrahigh Strength Steel

Friction stir lap welding of a DP1180 advanced ultrahigh strength steel was successfully carried out by using three welding tools with different pin lengths. The effects of the welding heat input and material flow on the microstructure evolution of the joints were analyzed in detail. The relationship between pin length and mechanical properties of lap joints was studied. The results showed that the peak temperatures of all joints exceeded A c3, and martensite phases with similar morphologies were formed in the stir zones. These martensite retained good toughness due to the self-tempering effect. The formation of ferrite and tempered martensite was the main reason for the hardness reduction in heat-affected zone. The mechanical properties of the lap joints were determined by loading mode, features of lap interface and the joint defects. When the stir pin was inserted into the lower sheet with a depth of 0.4 mm, the lap joint exhibited the maximum tensile strength of 12.4 kN.

Evolution of the Microstructure and Strength in the Nugget Zone of Friction Stir Welded SiCp/Al-Cu-Mg Composite

A 6 mm-thick SiCp/2009AI composite plate was successfully joined by friction stir welding （FSW） using an ultrahard material tool to investigate the evolution of the microstructure and the strength in the nugget zone （NZ）. While some SiC particles were broken up during FSW, most of them rotated in the matrix. Large compound particles on the interfaces were broken off during FSW, whereas the amorphous layer and small compound particles remained on the interfaces. The dynamically recrystallized AI grains nucleated on the surface of fractured SiC particles during FSW, forming nano-sized grains around the SiC particles. The yield strength of the NZ decreased slightly due to the variation in the size, shape, and distribution of the SiC particles. The clean interfaces were beneficial to the load transfer between SiC particles and AI matrix and then increased the ultimate tensile strength of the NZ.

Achieving ultra-high strength friction stir welded joints of high nitrogen stainless steel by forced water cooling

The microstructure and properties of water-cooled and air-cooled friction stir welded（FSW） ultra-high strength high nitrogen stainless steel joints were comparatively studied. With additional rapid cooling by flowing water, the peak temperature and duration at elevated temperature during FSW were significantly reduced. Compared to those in the air-cooled joint, nugget zone with finer grains（900 nm） and heat affected zone with higher dislocation density were successfully obtained in the water-cooled joint,leading to significantly improved mechanical properties. The wear of the welding tool was significantly reduced with water cooling, resulting in better corrosion resistance during the immersion corrosion test.

Friction Stir Welding of Discontinuously Reinforced Aluminum Matrix Composites:A Review

Friction stir welding （FSW） is considered a promising welding technique for joining the aluminum matrix composites （AMCs） to avoid the drawbacks of the fusion welding. High joint efficiencies of 60%-100% could be obtained in the FSW joints of AMCs. However, due to the existence of hard reinforcing particles in the AMCs, the wearing of welding tool during FSW is an unavoidable problem. Moreover, the low ductility of the AMCs limits the welding process window. As the hard materials such as Ferro-Titanit alloy, cermet, and WC/Co were applied to produce the welding tools, the wearing of the tools was significantly reduced and the sound joints could be achieved at high welding speed for the AMCs with low reinforcement volume fraction. In this article, current state of understanding and development of welding tool wearing and FSW parameters of AMCs are viewed. Furthermore, the factors affecting the microstructure and mechanical properties of the joints are evaluated in detail.

Achieving superior mechanical properties of selective laser melted AlSi10Mg via direct aging treatment

For additive manufactured aluminum alloys,the inferior mechanical properties along the building direction have been a serious weakness.In this study,an optimized heat treatment was developed as a simple and effective solution.The effects of direct aging on microstructure and mechanical properties along the building direction of AlSi10Mg samples produced via selective laser melting(SLM)were investigated.The results showed that,compared with the conventional heat treatment at elevated temperatures,direct aging at temperatures of 130-190℃ could retain the fine grain microstructure of SLM samples and promote further precipitation of Si phase,however,the growth of pores occurred during direct aging.With increasing aging temperature,while finer cell structures were obtained,more and larger pores were developed,resulting in decreased density of the samples.Two types of pore formation mechanisms were identified.Considering the balance between the refinement of cell structure and the growth of pores,aging at 130℃ was determined as the optimized heat treatment for SLM AlSi10Mg samples.The tensile strength along the building direction of the 130℃ aged sample was increased from 403 MPa to 451 MPa,with relatively high elongation of 6.5%.

Low-Cycle Fatigue Properties of Nickel-Based Superalloys Processed by High-Gradient Directional Solidification

The low-cycle fatigue （LCF） properties of DD10 （single-crystal） and DZ53 （columnar-grained） superalloys solidified by liquid-metal cooling （LMC） and high-rate solidification （HRS） processes have been systematically investi- gated. It was found that the LCF life of DZ53 solidified by LMC was obviously better than that solidified by HRS. In contrast, for DD10, LMC showed no remarkable influences on LCF properties at high temperature and only improved LCF properties at intermediate temperature. Microstructure examination showed that the cracks generally initiated at microp- ores in the subsurface at intermediate temperature. However, the cracks occurred on the surface due to oxidation, or persistent slip bands near script-MC at high temperature. Therefore, the benefits of LMC technique can be attributed to both of the reduced casting defects which significantly affect the LCF properties at intermediate temperature and the improved microstructural homogeneity which was strongly correlated to the LCF properties of alloys at high temperature.

Superb Strengthening Effect of Net-Like Distributed Amorphous Al_(2)O_(3)on Creep Resistance of(B_(4)C+Al_(2)O_(3))/Al Neutron-Absorbing Materials

B4C reinforced Al composites are widely used as neutron absorbing materials(NAMs)due to excellent neutron absorbing efficiency,however,such NAMs exhibit poor high-temperature properties.To meet the requirement for structure-function integration,NAMs with enhanced high-temperature mechanical properties are desired.In this work,a novel(B4 C+Al_(2)O_(3))/Al NAM with netlike distribution of Al_(2)O_(3)was fabricated by powder metallurgy method and subjected to high-temperature tensile creep test.It was shown that the creep resistance was enhanced by several orders of magnitude via the addition of only2.1 vol.%netlike-distributed Al_(2)O_(3).(B_(4)C+Al_(2)O_(3))/Al exhibited high apparent stress exponents ranging from 16 to 25 and high apparent activation energy of 364 kJ/mol.The creep behaviour could be rationalized using the substructure-invariant model and its rupture behaviour could be described by the Dobes-Milicka equation.

Dielectric response of BaZrO_(3)/BaTiO_(3) superlattice

We use the first-principles-based molecular dynamic approach to simulate dipolar dynamics of BaZrO_(3)/BaTiO_(3)superlattice,and obtain its dielectric response.The dielectric response is decomposed into its compositional,as well as the in-plane and out-of-plane parts,which are then discussed in the context of chemical ordering of Zr/Ti ions.We reveal that,while the in-plane dielectric response of BaZrO_(3)/BaTiO_(3)superlattice also shows dispersion over probing frequency,it shall not be categorized as relaxor.