形变热处理对中碳Cr-Ni-W-Mo钢组织及力学性能的影响

为进一步提高中碳Cr-Ni-W-Mo钢的强塑性,采用Gleeble 3500热模拟试验机在700 ℃温度下进行变形量为20%~50%的形变热处理（TMT）。利用扫描电镜、透射电镜、电子背散射衍射对试验钢组织进行表征,利用拉伸试验机对拉伸性能进行测试,研究TMT工艺对其组织演变和力学性能的影响。结果表明：试验钢在TMT后的组织是包含回火马氏体、下贝氏体、残余奥氏体的复相组织,随着形变量增加,下贝氏体组织及残余奥氏体含量、位错密度相应增加,板条宽度减小;在相变强化、细晶强化及位错强化共同作用下,随着形变量增加,试验钢的强度增加,塑性升高;当形变量为50%时屈服强度达到1 733 MPa,抗拉强度达到2 243 MPa,伸长率为12.66％,与传统热处理相比,分别提高28.18%、12.88%和50.35%,获得了良好的强塑性匹配。     

海带豆腐加工工艺研究

以大豆和海带为原料,采用篝合型凝固剂制作碘含量高的海带豆腐。通过正交试验考察豆浆浓度、海带添加量、凝固剂添加量3个因素对海带豆腐品质的影响。研究表明,最佳加工工艺条件为：大豆与水的比例1：4（W：V）,海带泥与豆浆的比例3：7（W：V）,凝固剂添加量0．2％。     

Arterial oxygen saturation in Tibetan and Han infants born in Lhasa, Tibet

BACKGROUND: Reduced oxygen availability at high altitude is associated with increased neonatal and infant mortality. We hypothesized that native Tibetan infants, whose ancestors have inhabited the Himalayan Plateau for approximately 25,000 years, are better able to maintain adequate oxygenation at high altitude than Han infants, whose ancestors moved to Tibet from lowland areas of China after the Chinese military entered Tibet in 1951. METHODS: We compared arterial oxygen saturation, signs of hypoxemia, and other indexes of neonatal wellbeing at birth and during the first four months of life in 15 Tibetan infants and 15 Han infants at 3658 m above sea level in Lhasa, Tibet. The Han mothers had migrated from lowland China about two years previously. A pulse oximeter was placed on each infant's foot to provide measurements of arterial oxygen saturation distal to the ductus arteriosus. RESULTS: The two groups had similar gestational ages (about 38.9 weeks) and Apgar scores. The Han infants had lower birth weights (2773 +/- 92 g) than the Tibetan infants (3067 +/- 107 g), higher concentrations of cord-blood hemoglobin (18.6 +/- 0.8 g per deciliter, vs. 16.7 +/- 0.4 in the Tibetans), and higher hematocrit values (58.5 +/- 2.4 percent, vs. 51.4 +/- 1.2 percent in the Tibetans). In both groups, arterial oxygen saturation was highest in the first two days after birth and was lower when the infants were asleep than when they were awake. Oxygen saturation values were lower in the Han than in the Tibetan infants at all times and under all conditions during all activities. The values declined in the Han infants from 92 +/- 3 percent while they were awake and 90 +/- 5 percent during quiet sleep at birth to 85 +/- 4 percent while awake and 76 +/- 5 percent during quiet sleep at four months of age. In the Tibetan infants, oxygen saturation values averaged 94 +/- 2 percent while they were awake and 94 +/- 3 percent during quiet sleep at birth and 88 +/- 2 percent while awake and 86 +/- 5 percent during quiet sleep at four months. Han infants had clinical signs of hypoxemia--such as cyanosis during sleep and while feeding--more frequently than Tibetans. CONCLUSIONS: In Lhasa, Tibet, we found that Tibetan newborns had higher arterial oxygen saturation at birth and during the first four months of life than Han newborns. Genetic adaptations may permit adequate oxygenation and confer resistance to the syndrome of pulmonary hypertension and right-heart failure (subacute infantile mountain sickness).     

一种超宽带线性调频信号源的设计

超宽带雷达因其距离分辨率高、抗干扰能力强、目标检测和识别能力高等优点,受到世界各国的重视。通常采用倍频器来产生超宽带信号,然而,倍频环节中存在一些影响信号质量的非理想特性。针对该问题,提出利用频谱拼接技术来产生超宽带雷达信号。采样频率越大则输出信号幅度包络失真越小。频谱拼接时间误差小于100 ns时,其主瓣比理想情况增大5%。通过频谱拼接技术能够有效解决幅度失真、高采样频率需要和拼接时间误差等问题。设计了两个直接数字频率合成器同步电路,确保两路正交基带信号同步。频谱拼接技术还能灵活控制信号带宽大小,产生较理想的超宽带线性调频信号。     

分数阶PID扭矩控制在边驱耦合轻轨车辆的应用研究

边驱耦合独立轮对(Independently rotating wheelset,IRW)技术是100%低地板轻轨车(Low floor tram,LFT)的关键技术之一,边驱电机的扭矩控制策略直接影响轻轨车的动力学性能.本文基于5自由度独立轮对的轨行机理,搭建了考虑边驱传动系统的单节轻轨车动力学模型.应用了一种分数阶PID(Fractional order PID,FOPID)扭矩控制策略,优化了车辆的曲线通过性能.采用Riemann-Liouville(RL)分数阶微积分理论及Oustaloup滤波器数值逼近法构成FOPID控制器,通过寻优运算对FOPID参数进行整定,在Simulink平台下建立了整车的集成控制系统.通过扭矩控制器与整车动力学模型s函数联合仿真的方式,开展了100%低地板轻轨车辆的直线与曲线运行特性研究,并将计算结果与无控制的独立轮对模型、传统轮对模型进行了对比分析.研究结果表明,在直线运行下,FOPID控制下的轻轨车能够提高车辆的稳定性,受控轮对的抗轨道不平顺激扰能力较强.在大半径曲线下,无控制的独立轮对曲线通过性较差,而受分数阶PID控制的独立轮对能够表现出与传统轮对一样优异的曲线通过性能;在小半径曲线下,分数阶PID扭矩控制策略能够使轻轨车获得足够的导向力,曲线通过性能明显优于其他模型.     

Simultaneous synthesis of sub and above-ambient heat exchanger networks including expansion process based on an enhanced superstructure model

Synthesis of heat exchanger networks including expansion process is a complex task due to the involvement of both heat and work. A stream that expands through expanders can produce work and cold load, while expansion through valves barely affects heat integration. In addition, expansion through expanders at higher temperature produces more work, but consumes more hot utility. Therefore, there is a need to weigh work production and heat consumption. To this end, an enhanced stage-wise superstructure is proposed that involves synchronous optimization of expander/valve placement and heat integration for each pressure-change sub-stream in stages. A mixed-integer nonlinear programming (MINLP) model is established for synthesizing sub and aboveambient heat exchanger networks with multi-stream expansion, which explicitly considers the optimized selection of end-heaters and end-coolers to adjust temperature requirement. Our proposed method can commendably achieve the optimal selection of expanders and valves in a bid for minimizing exergy consumption and total annual cost. Four example studies are conducted with two distinct objective function (minimization of exergy consumption and total annual cost, respectively) to illustrate the feasibility and efficacy of the proposed method.     

定子双绕组异步电机变频交流发电系统辅助励磁电容和滤波电感的优化设计

提出了定子双绕组异步电机(DWIG)变频交流发电系统中的两个关键参数——辅助励磁电容和滤波电感的优化设计方法.利用DWIG控制绕组无功电流解析表达式对不同转速和负载条件下的控制绕组无功电流进行了分析,获得了它的变化规律,进而确立了辅助励磁电容的优化原则.待辅助励磁电容优化后,根据控制绕组最大无功电流及电流快速响应要求来确定滤波电感的上限;按照抑制电流谐波能力要求来确定滤波电感的下限.样机实验结果表明,按所提优化设计方法选取的辅助励磁电容和滤波电感是合理、有效的,能保证系统稳定运行,且实现了控制变换器容量的最小化.     

网络转型下接入层建设探讨

从介绍综合AC的建设模式及对设备要求入手,阐述了面向网络转型的NGN＋综合AC解决方案.     

基于广义联结度的群法及其在多元胞布局中的应用

本文以广义联结度为基础,提出了一种新的结群方法。它采用有一阈值控制的并行结群方式,并应用与结群过程相反的判断过程来检查群的收敛性,较好地解决了群构造的问题。这一结群法已经在Micro VAX上用C语言实现。用结群结果去指导多元胞的初始布局得到了非常满意的结果。     

IJF－OQPSK数字调制器

无符号间干扰和抖动－交错正交相移键控（ＩＦＪ－ＯＱＰＳＫ）是现代数字调制技术中的一种新的调制方式。在介绍一种新型集成调制芯片的基础上，给出实现ＩＪＦ－ＯＱＰＳＫ调制器的具体电路。