高速列车不锈钢薄板CMT搭接焊工艺研究

为解决高速列车不锈钢薄板搭接MAG密封焊接出现的变形大、过热严重、焊接缺陷多等问题,采用了冷金属过渡CMT焊接代替MAG焊接,并对焊接工艺进行研究。用CMT搭接焊接厚度0.6 mm与1.5 mm的SUS301L奥氏体不锈钢薄板,采用正交试验法确定合适的工艺参数,并对不同组配间隙进行形貌分析。结果表明,装配间隙为0 mm,焊接速度为2000 mm/min,送丝速度为6 m/min时,可得到良好的焊缝成形。     

Investigation of the benefits of plasma deposition for the additive layer manufacture of Ti-6Al-4V

With increasing emphasis on sustainability, additive layer manufacturing (ALM) offers significant advantages in terms of reduced buy-to-fly ratios and improved design flexibility. Plasma wire deposition is a novel ALM technique in which plasma welding and wire feeding are combined. In the present work, a working envelope for the process using Ti-6Al-4V was developed, and regression models were calculated for total wall width, effective wall width and layer height. The plasma wire deposition process is able to produce straight walls of widths up to 17.4 mm giving a maximum effective wall width after machining of 15.9 mm, which is considerably wider than competing processes. In addition, for Ti-6Al-4V the deposition efficiency averages 93% and the maximum deposition rate is 1.8 kg/h. Coarse columnar grains of β phase grew from the base during deposition, which transformed into a Widmanstätten structure of α lamellae on cooling. Bands were identified in the deposits, which had a repetitive basket-weave microstructure that varied in size. The strength measured by micro-indentation hardness of 387 HV on average is as much as 12% higher than the substrate. These preliminary results indicate that plasma wire deposition is likely to be a suitable process for the ALM of large aerospace components.     

芯片级多线程处理器的操作系统调度研究

随着芯片级多线程（CMT）处理器体系结构的迅速发展,操作系统必须采用新型CMT调度,以发挥其体系结构的性能优势。分析CMT调度面临的问题,通过扩展调度域的层次和结构支持CMT处理器内部的负载均衡,利用协同调度避免cache抖动等问题。采用效率、效率瓦特比和公平性等多种指标对操作系统进行性能评价,证明其性能得到优化。     

软件配置管理与ClearCase研究

软件开发管理是使软件开发高效低耗所必需的,而软件配置管理是软件开发管理的关键,因此,软件配置管理成为软件开发过程的必要环节。而自动化的配置管理工具也日渐成为了软件配置的必要条件。此外,该文还初步研究了使用较为广泛的配置管理工具ClearCase。     

基于多宿SCTP的提高整体吞吐量的快速SACK策略

分析了在多宿SCI}P的条件下,链路双方传输数据的几种算法,并基于多宿SCTP提出了一种从最快可抵达的 路径发送SACK报文的策略,它能够消除只有发送端了解链路情况的弊端。仿真实验表明,在两条路径时延不均衡情况 下,快速SACK策略可以极大地提高整体的吞吐量。     

基于SCTP多宿特点的多路径同时传输研究

多宿是SCTP协议的一个重要特点,利用这个特点,发送端可以将数据通过不同的路径发送给接收端。虽然SCTP提供了对多宿的支持,但仅仅是为了提高关联的可靠性,当前SCTP协议只允许同时使用一条路径传输数据;如果能够同时利用多条路径传输数据,必能极大提升关联的吞吐量。分析了基于SCTP多宿特点的多路径同时传输关键技术,这些关键技术包括快重传触发技术、拥塞控制窗口增长技术、延迟应答技术、接收端缓冲区阻塞减轻技术以及重传时的路径选择技术。     

CMT模拟器的设计与实现

片上多线程(CMT)是未来高性能处理器的发展方向，而软件模拟是处理器体系结构研究和设计中不可或缺的技术手段。该文基于SimpleScalar工具集设计并实现了CMT节拍级模拟器——OpenSimCMT，对CMT体系结构的设计和评测提供支持。OpenSimCMT特点如下：(1)支持同时多线程(SMT)和片上多处理器(CMP)的模拟；(2)架构开放，配置灵活，可根据具体研究目标随时进行扩展，添加新的模拟内容及相关统计；(3)功能全面，对线程间资源竞争与共享、各功能单元、流水段、分支预测、多级cache等全方位模拟，模拟结果准确。     

Influence of the Silicon Substrate on Defect Formation in MCT Grown on II-VI Buffered Si Using a Combined Molecular Beam Epitaxy/Metal Organic Vapor Phase Epitaxy Technique

II-VI buffer layers grown by molecular beam epitaxy (MBE) onto silicon exhibit a uniform, slightly faceted surface morphology. However, a number of surface defects are apparent and these are amplified by the subsequent growth of mercury cadmium telluride (MCT) by metal organic vapor phase epitaxy. Some of these defects have been traced to polishing damage present within the silicon substrate. A range of analytical techniques, including x-ray topography, have been used to track the defects from the substrate through to the buffer layer and into the MCT. Defects of this type will cause dead elements in the infrared focal plane arrays and will be a major cause of low operabilities.     

ANN Synthesis Models Trained with Modified GA‐LM Algorithm for ACPWs with Conductor Backing and Substrate Overlaying

Accurate synthesis models based on artificial neural networks (ANNs) are proposed to directly obtain the physical dimensions of an asymmetric coplanar waveguide with conductor backing and substrate overlaying (ACPWCBSO). First, the ACPWCBSO is analyzed with the conformal mapping technique (CMT) to obtain the training data. Then, a modified genetic‐algorithm‐Levenberg‐Marquardt (GA‐LM) algorithm is adopted to train ANNs. In the algorithm, the maximal relative error (MRE) is used as the fitness function of the chromosomes to guarantee that the MRE is small, while the mean square error is used as the error function in LM training to ensure that the average relative error is small. The MRE of ANNs trained with the modified GA‐LM algorithm is less than 8.1%, which is smaller than those trained with the existing GA‐LM algorithm and the LM algorithm (greater than 15%). Lastly, the ANN synthesis models are validated by the CMT analysis, electromagnetic simulation, and measurements.     

流与路径绑定的并行多路径SCTP的设计与实现

随着通信终端上多个网络接口的实现成为可能,并行多路径传输因其具有较高的传输效率而成为研究的热点。本文设计实现了一种SCTP流与路径绑定的并行多路径传输解决方案,将不同的流映射到合适的路径上进行传输,从而解决多路径接收端数据分组乱序的问题,提高网络传输的吞吐量。