Analysis of travel activity determinants using robust statistics

This study investigates travel behavior determinants based on a multiday travel survey conducted in the region of Ghent, Belgium. Due to the limited data reliability of the data sample and the influence of outliers exerted on classical principal component analysis, robust principal component analysis (ROBPCA) is employed in order to reveal the explanatory variables responsible for most of the variability. Interpretation of the results is eased by utilizing ROSPCA. The application of ROSPCA reveals six distinct principal components where each is determined by a few variables. Among others, our results suggest a key role of variable categories such as journey purpose-related impedance and journey inherent constraints. Surprisingly, the variables associated with journey timing turn out to be less important. Finally, our findings reveal the critical role of outliers in travel behavior analysis. This suggests that a systematic understanding of how outliers contribute to observed mobility behavior patterns, as derived from travel surveys, is needed. In this regard, the proposed methods serve for processing raw data typically used in activity-based modelling.     

Grain refinement in bearing steels using a double-quenching heat-treatment process

A double-quenching (D/Q) process is proposed for heat-treating high carbon-chromium bearing steels to improve the fatigue properties through refinement of the microstructure. The new heat treatment method has two steps: The first step is a nitrocarburizing process that results in high surface hardness and lowers the transformation temperature. The second step is the same as in the conventional quenching process but can be conducted at a considerably lower temperature than in conventional quenching. The microstructure in the material that is caused by the D/Q heat treatment is much finer than in the conventional Q/T (quenching and tempering) process. In order to quantify the performance of the proposed heat-treatment process, various mechanical property tests are carried out. The rolling contact fatigue life of double-quenched bearing steels was eight times higher than in bearing steels that were treated by conventional Q/T.     

Satellite remote sensing of the Polar Oceans

The advent of satellite remote sensing has opened doors for detailed monitoring of the polar regions at a relatively high temporal resolution. Several sensors have been developed over the years, the most noteworthy of which are the visible, the infrared and the microwave systems. The visible and infrared systems are most intelligible to the human eye and provide images that have good spatial resolution. However, because of persistent cloudiness and several months of darkness in the polar regions the most promising sensors appear to be the microwave systems, both passive and active. The passive microwave sensors have been the source of consistently derived ice cover and ice extent data and have provided about fifteen years of global data sets. The Synthetic Aperture Radar (SAR), on the other hand, is noted for very high resolution and a wide range of applications including ice dynamics and ice/wave interaction studies. Nevertheless, there are applications which require the use of the visible and infrared channels, such as the mapping of chlorophyll pigment concentrations in the marginal ice zones which require an ocean color scanner. Also, the infrared sensors are most effective for detecting physical temperatures over cloud-free ice and open water surfaces. Furthermore, altimeters could play an important role in mapping ice surface topography and in evaluating ridge and lead statistics. A review of past, present and future satellite systems, methods and techniques of interpretation and potential applications to the study of the polar oceans is presented.     

Deep foundation pit excavation procedure optimization considering creep deformation on nearby metro tunnelEI北大核心

Research purposes: The existing researches about excavating procedures of deep foundation pit on nearby metro tunnel in soft formation are lack of systematicness, and creep characteristics of soft clay are not usually taken into consideration. This paper takes Qianhaiwan station of Metro Line 11 in Shengzhen as engineering background and considers creep characteristics in sludge formation. The influence of step excavation in the transversal, longitudinal and vertical directions on the deformation of foundation pit and nearby subway tunnel are simulated, which may be expected to provide theoretical basis for choosing foundation pit excavation procedure of Qianhaiwan station. Research conclusions: (1) The segment far away from tunnel should be excavated firstly when only transversal step excavation was undertaken along the horizontal direction of foundation pit. (2) The maximum horizontal displacement of the piles show exponential relations with the number of segments when step excavation of foundation pit was undertaken in vertical and transversal or longitudinal. If thickness of every step excavation was limited in 1.5~2 m, the horizontal displacement of the pile near tunnel can be reduced about 9 percent when there is no horizontal step excavation. (3) Transversal step excavation with segments far from tunnel excavated firstly was found to be the best step excavation method under the same condition of step number and support, and longitudinal and transversal step excavation followed while longitudinal step excavation was the last. (4) The research results have guiding significance for foundation pit of Qianhaiwan station and similar projects.     

激光堆焊工艺在修造领域的应用现状及发展趋势

本文详细阐述了激光堆焊工艺在工业修造领域的应用现状及发展趋势,介绍了激光束的能源、输送和聚焦系统、堆焊材料及激光设备。重点说明了其在修造领域的应用工艺。     

Turbo-Coded Modulation of EVRC Speech Encoder with Unequal Error Protection for Fading Channels

The Enhanced Variable Rate Codec (EVRC) is a standard for the Speech Service Opti6n 3 for Wideband Spread Spectrum Digital System, which has been employed in both IS-95 cellular systems and ANSI J-STC-008 PCS (Personal Communications Systems). This paper investigated the combination of turbo codes with Unequal Error Protection (UEP) and 16-QAM modulation for EVRC codec of Rate 1 to get power and bandwidth efficient coding scheme. The results show that the UEP system outperforms the Equal Error Protection (EEP) one by 1.45dB at BER of 10^-5.     

带功率因数补偿的单相半控桥整流器(一)

介绍了绘制正弦线电流的开关模式单相半控桥整流器,用它来获得功率因数补偿并保持直流环节电压的恒定.在该整流器中使用4个有源开关,以便在交流端电压上产生单极脉宽调制(PWM)电压波形.与中性点箝位变流器(NPC)相比,该整流器没有箝位二极管也能实现三点式PWM控制.控制电路采用两个控制回路:外部控制回路用比例积分电压控制器调整直流环节电压,采用相位闭环电路产生与电源电压同相的正弦波形来实现功率因数补偿.在内部控制回路中,用基于载波的电流控制器跟踪线电流信号.为补偿由于负载变化所引起的中点电压,控制电路采用中点电压补偿器.该整流器的交流侧可产生3个电压电平,并用计算机仿真与试验结果验证了控制算法的有效性.     

新一代车辆标准化的综合性和前瞻性

俄罗斯正在研制新一代车辆并进行车辆检修制度的改革。本文提出标准化工作的前瞻性和综合性,要求车辆与其部件具有等寿命、装卸和调车机械应适应车辆的性能等,这样在铁路行业就会产生巨大的经济效益。     

Windows CE操作系统在机车显示器上的应用研究

介绍Windows CE操作系统的特点,阐述了将嵌入式操作系统Windows CE应用在机车显示器上的整个开发过程,并对其应川结果进行了总结。