Review of Pi2 Models

More than half a century after the discovery of Pi2 pulsations, Pi2 research is still vigorous and evolving. Especially in the last decade, new results have provided supporting evidence for some Pi2 models, challenged earlier interpretations, and led to entirely new models. We have gone beyond the inner magnetosphere and have explored the outer magnetosphere, where Pi2 pulsations have been observed in unexpected places. The new Pi2 models cover virtually all magnetotail regions and their coupling, from the reconnection site via the lobes and plasma sheet to the ionosphere. In addition to understanding the Pi2 phenomenon in itself, it has also been important to study Pi2 pulsations in their role as transient manifestations of the coupling between the magnetosphere and the ionosphere. The transient Pi2 is an integral part of the substorm phenomenon, especially during substorm onset. Key questions about the workings of magnetospheric substorms are still awaiting answers, and research on Pi2 pulsations can help with those answers. Furthermore, the role of Pi2 pulsations in association with other dynamic magnetospheric modes has been explored in the last decade. Thus, the application of Pi2 research has expanded over the years, assuring that Pi2 research will remain active in this decade and beyond. Here we review recent advances, which have given us a new understanding of Pi2 pulsations generated at various places in the magnetosphere during different magnetospheric modes. We review seven Pi2 models found in the literature and show how they are supported by observations from spacecraft and ground observatories as well as numerical simulations. The models have different degrees of maturity; while some enjoy wide acceptance, others are still speculative.     

What was learned from the new VFE-2 experiments

In the present paper the main results of the new experiments from VFE-2 are summarized. These include some force and moment results, surface and off-body measurements, as well as steady and fluctuating quantities. Some critical remarks are added, and an outlook for future investigations is given.     

一种用于热校准风洞的数据采集系统集成及软件设计

简要介绍了研华ＡＤＡＭ４０００系列模块的性能及其特点,并详细阐述了利用该系列模块组成一种用于热校准风洞的数据采集秕 及ＬＡＢＴＥＣＨＣＯＴＲＯＬ组态软件包在整个中的应用。     

Al_2O_3-ZrO_2-SiC_W陶瓷复合材料的显微结构和力学性能

通过XRD、SEM、TEM及EPMA技术研究了Al_2O_3-25vol％ZrO_3(2mol％Y_3O_3)-25vol％SiCw(AZS)三元陶瓷复合材料的显微组织和力学性能。试验结果表明,该材料具有较好的强度和韧性配合,ZrO_2与SiC晶须同时起增韧作用。此外,SiC晶须以及弥散分布在Al_2O_3基体中的ZrO_2粒子也提高了该材料的断裂强度。室温下测得该材料的压痕断裂韧性为10.8MPam~(1/2),抗弯强度为676MPa。     

HIGH SPEED FLOW DESIGN USING THE THEORY OF OSCULATING CONES AND AXISYMMETRIC FLOWS

Ｃｏｎｆｉｇｕｒａｔｉｏｎａｅｒｏｄｙｎａｍｉｃｄｅｓｉｇｎｃｏｎｃｅｐｔｓａｒｅａｉｍｅｄａｔｔｈｅｄｅｆｉｎｉｔｉｏｎｏｆｆｉｎｄｉｎｇａｉｒｆｒａｍｅａｎｄｐｒｏｐｕｌｓｉｏｎｃｏｍｐｏｎｅｎｔｇｅｏｍｅｔｒｉｅｓｗｉｔｈａｃｏｎｔｒｏｌｅｄｆ...     

LTRAN2的一种改进方案

本文提出了LTRAN2的一种改进方案BTRAN2用来分析翼型的各种频率的非定常运动。用E-O调转换格式和ADI方法求解了完全的二维非定常跨音速小扰动位流方程,并用单调转换的AF2格式计算了定常跨音速小扰动方程,以此作为非定常计算的初场。本文给出了带后缘正弦振荡襟翼的NACA 64 A006翼型的绕流和做正弦俯仰振荡的NACA 64 A010翼型的绕流计算结果,它们与Euler方程解或实验数据很吻合。     

高强铝合金中间相Al2 Cu,Al2 CuMg和MgZn2性能的第一性原理计算

采用第一性原理平面波赝势方法,计算Al-Zn-Mg-Cu系高强铝合金主要中间相Al2 Cu,Al2 CuMg和MgZn2的结合能、形成焓、弹性常数及态密度。计算结果表明：3相结合能按MgZn2>Al2 CuMg>Al2 Cu顺序递减;形成焓按MgZn2>Al2 Cu>Al2 CuMg顺序递减;Al2 Cu具有很高的弹性模量,同时具有一定的塑性,可以作为合金的强化相;Al2 CuMg是典型的脆性相,并表现出明显的各向异性,容易诱导产生裂纹;MgZn2具有良好的塑性,同时熔点较低,是合金的主要强化相;3相中均存在离子键的相互作用,提高了结构稳定性;通过适当降低Cu,Mg含量,提高Zn的含量,有利于生成MgZn2相,进一步提高合金的综合性能。     

ZrB2 粉体制备技术的研究进展

综述了国内外ZrB2粉体制备技术如固相法、液相法和气相法的研究进展,详细分析了各种制备技术的特点,并展望了ZrB2粉体制备技术的发展方向。     

二维爆震波数值模拟

针对爆震发动机的多维效应,利用CFD计算软件对单管脉冲爆震发动机进行了二维的数值模拟。以氢气和氧气混合物为例,仿真了爆震波在管内的传播过程以及传出管外后的流场情况。模拟所得的爆震波参数与文献中的计算结果和实验值基本一致,验证了模拟的正确性。爆震波传出爆震管后退化成一道激波,对该激波的流动情况进行了分析。     

环氧改性有机硅/Al-Sm_2O_3复合涂层的耐温性能

以Al粉、Sm_2O_3为颜料,环氧改性有机硅为黏合剂,采用喷涂法制备了环氧改性有机硅/Al-Sm_2O_3复合涂层。研究了不同耐热温度及耐热时间对涂层外观、微结构、近红外反射率、红外发射率及力学性能的影响。结果表明:所制备涂层在300℃下热处理5 h后,其外观、微结构保持不变;发射率和1.06μm近红外反射率可分别低至0.607和64.7%;涂层的硬度、附着力和耐冲击强度等力学性能可分别保持在4 H、1级和50 kg·cm;所制备涂层在250℃下热处理100 h后,其外观、微结构仍然保持不变;发射率和1.06μm近红外反射率可分别低至0.624和67.1%;涂层的硬度、附着力和耐冲击强度等力学性能可分别保持在4 H、1级和50 kg·cm。     

Track monitoring when tracking with multiple 2D passive sensors

A fast method of track monitoring is presented which determines what tracks are good and what tracks have had data association problems and should be eliminated. The philosophy of tracking in a dense target environment with limited central processing unit (CPU) time is to acquire the targets, track them with as simple a filter as will meet requirements, and monitor the tracks to determine if they are still tracking a target or are tracking incorrect returns and should be terminated. After termination the true targets are reacquired. However, it is difficult to determine from simple track monitoring the correct interpretation of a poor track. Poor tracks can be a result of a sensor failure, target maneuver, or incorrect data association. The author describes track monitoring and provides a solution to this dilemma when tracking with multiple two-dimensional passive sensors. The method is much faster than other monitoring methods.<>     

二维变厚板的J积分分析

本文将J.R.Rice提出的J积分公式扩充应用到二维变厚板。本文把变厚度的影响以修正项形式引入J积分公式,从而推导出二维变厚板的J积分扩充表达式。      

Vibrational relaxation of CO2 (m,nl, p) in a CO2-N2 mixture. Part 1: Survey of available data

The knowledge of the vibrational relaxation reaction rates of diatomic and triatomic molecules is required for the modelling of numerous gaseous mixtures such as the Earth atmosphere (involving radiation transfer phenomena), exhaust plumes, afterbody wakes, Mars atmosphere, shock waves and chemical lasers. It enables a better understanding of the chemical reaction product rates and provides the populations of the radiating levels. In this study, we consider the few lowest vibrational levels of a CO₂-N₂ mixture and the V-T and V-V energy transfer processes between these levels. The reaction rates given by experimental and theoretical studies and by different surveys of data supplied by a bibliographic search are presented. Then, comparisons of the data available for the most important processes are shown. The usual assumptions concerning the vibrational relaxation of CO₂ (m, n^l, p) are recalled and briefly discussed.     

二维受扰超声速喷管流的动态分析

介绍了STAR -CD软件包所采用的控制方程、湍流模型和数值模拟技术。模拟了有出口旋转挡板的拉瓦尔喷管的超声速流场 ,分析了出口旋转挡板转动对超声速喷管流场速度、压力和Ma等参数的动态影响     

Effects of in-situ TiB2 particles on machinability and surface integrity in milling of TiB2/2024 and TiB2/7075 Al composites

In-situ ceramics particle reinforced aluminum matrix composites are favored in the aerospace industry due to excellent properties. However, the hard ceramic particles as the reinforcement phase bring challenges to machining. To study the effect of in-situ TiB₂ particles on machinability and surface integrity of TiB₂/2024 composite and TiB₂/7075 composite, milling experiments were performed, and compared with conventional 2024 and 7075 aluminum alloys. In-situ TiB₂ particles clustered at the grain boundaries and dispersed inside the matrix alloy grains hinder the dislocation movement of the matrix alloy. Therefore, the milling force and temperature of the composites are higher than those of the aluminum alloys due to the increase of the strength and the decrease of the plasticity. In the milling of composites, abrasive wear is the main wear form of carbide tools, due to the scratching of hard nano-TiB₂ particles. The composites containing in-situ TiB₂ particles have machining defects such as smearing, micro-scratches, micro-pits and tail on the machined surface. However, in-situ TiB₂ particles impede the plastic deformation of the composites, which greatly reduces cutting edge marks on the machined surface. Therefore, under the same milling parameters, the surface roughness of TiB₂/2024 composite and TiB₂/7075 composite is much less than that of 2024 and 7075 aluminum alloy respectively. Under the milling conditions of this experiment, the machined subsurface has no metamorphic layer, and the microhardness of the machined surface is almost the same as that of the material. Besides, compared with 2024 and 7075 aluminum alloy, machined surfaces of TiB₂/2024 composite and TiB₂/7075 composite both show tensile residual stress or low magnitude of compressive residual stress.     

C^2光滑的三角形混合曲面片的构造

对任意三角形，本文给出了在边界上已给定顶点型值向量、一阶切矢和二阶导矢的插值型的三角曲面片。这些曲面片可以组合成任意的复杂形状，且组合曲面是Ｃ２ 的。     

Modified Generalized Sign Test Processor for 2-D Radar

The modified generalized sign test processor is a nonparametric, adaptive detector for 2-D search radars. The detector ranks a sample under test with its neighboring samples and integrates (on a pulse-to-pulse basis) the ranks with a two-pole filter. A target is declared when the integrated output exceeds two thresholds. The first threshold is fixed and yields a 10-6 probability of false alarm when the neighboring samples are independent and identically distributed. The second threshold is adaptive and maintains a low false-alarm rate when the integrated neighboring samples are correlated and when there are nonhomogeneities, such as extraneous targets, in the neighboring cells. Using Monte Carlo techniques, probability of false-alarm results, probability of detection curves, and angular accuracy curves have been generated for this detector. The detector was built and PPI photographs are used to indicate the detector's performance when the radar is operated over land clutter.     

微波烧结制备MoSi2 及SiC/ MoSi2 纳米复合陶瓷

采用微波烧结法制备了MoSi2和10vol%SiC/MoSi2纳米复合陶瓷。通过SiC预加热体的混合式加热法和合理的保温结构设计,实现了MoSi2低温阶段的快速升温,提高了温度均匀性。密度和力学性能测试结果表明,1 450℃保温60 min烧结工艺下,MoSi2试样的相对密度达到93.4%,断裂韧度4.5 MPa.m1/2,维氏硬度为10.53 GPa,弯曲强度为186 MPa。10vol%SiC/MoSi2试样尽管相对密度下降为90.3%,但各项力学性能均优于MoSi2试样。相比1 650℃热压烧结,微波烧结温度降低了200℃,MoSi2和SiC/MoSi2试样致密性有所下降,但力学性能有较大提高,尤其是MoSi2试样。断口扫描分析表明,微波烧结试样相对热压烧结试样基体晶粒更细,孔隙细小且分布均匀;SiC/MoSi2试样微波烧结的晶粒细化效果不如MoSi2明显。     

2.5D石英纤维织物增强二氧化硅基复合材料弯曲性能测试研究

简要介绍了2．5D石英纤维织物增强二氧化硅基复合材料弯曲性能测试装置，通过对比试验研究了试样跨厚比、变形测量等对材料弯曲性能的影响，用数理统计的方法对总体均值进行了显著性检验，合理确定了材料弯曲性能测试的试验参数。     

基于VHDL的I^2C总线IP核的设计

简述了I~2C总线的特点；并详细描述了一种在FPGA中实现I~2C总线IP核的设计方法；最后给出I~2C总线IP核在主模式下的收发数据仿真时序图以及实现结果。