十字轴径向挤压机的研制

ＨＹＤ－Ｙ６１－４００／６００双动挤压机是十字轴径向挤压的专用设备，本文介绍了该机的主要技术参数、性能及结构特点。它的研制成功为我国精密模锻技术的发展做了巨大贡献。     

错流射流混合过程的基本特性及影响因素

错流射流已被证明是强化流体热质传递最有效的方法之一。介绍了错流射流的结构、基本特性以及在混合过程中的影响因素,并展望了其发展前景。     

Effect of channel length on interdigitated flow-field PEMFC performance: A computational and experimental study

This study examines the effect of increased channel length on the distribution of flow gases and cell performance in an interdigitated flow-field PEMFC. A numerical model was used to simulate the pressure distribution and gas flow in 5 cm and 25 cm channel length interdigitated flow fields that have eight channels with fixed channel and land widths of 1 mm. The results show the distribution of flow under land areas (cross flow) is subject to maldistribution in the longer cell while the shorter cell produces relatively homogenous cross flow along its length. An experimental test cell was designed to run with the same channel lengths, under similar conditions to those modeled. Inlet pressure data was recorded to account for parasitic pump losses, used to calculate net system power curves. Results show that a shorter channel interdigitated flow field may produce both higher maximum power and limiting current densities compared with longer cells.     

A Cross Layer Scheduling Framework for Supporting Bursty Data Applications in WCDMA Networks

In future wireless networks multimedia applications are expected to finally dominate the overall traffic volume. Shared channels are more suitable for the transmission of this type of traffic, as they are able to periodically adjust their transmission rate. In this paper, we introduce a cross-layer framework for WCDMA based networks which aims to make the packet scheduling procedure more efficient. In addition to that, we further propose a traffic scheduling scheme which serves the connections not only according to their delay sensitivity, but also according to the predicted state of their wireless channel. The efficiency of the proposed scheme, in terms of average packet delay and channel utilization is verified via simulations.     

Removing noises caused by motion artefacts in microcirculation maps of human skin in vivo

This paper presents a zero‐padding and cross‐correlation technique‐based correlation mapping optical coherence tomography (ZPCC‐cmOCT) to reconstruct microcirculation maps of human skin in vivo, which can remove the background decorrelation noise caused by motion artefacts. In conventional correlation mapping optical coherence tomography method, the correlation degree of static tissue may be lowered by the motion artefacts due to cardiac and respiratory motion, resulting in background decorrelation noise in microcirculation maps. In zero‐padding and cross‐correlation technique‐based correlation mapping optical coherence tomography method, structural images are first obtained by performing Fourier transform on zero‐padded interference fringes, and then cross‐correlation‐based image registration is utilized to align local areas in two adjacent structural images. Finally, correlation mapping optical coherence tomography method is performed to generate microcirculation maps. Both phantom experiments and in vivo experiments were implemented and the results demonstrate that the proposed method is capable of providing microcirculation maps with the background decorrelation noise removed.     

某型车载雷达天线同步举升系统仿真研究

雷达天线快速、稳定的架设和撤收是举升系统最基本的要求之一,为提高车载雷达机动性,对其举升系统的研究十分重要。通过对天线举升液压系统的分析,建立系统的数学模型,采用交叉耦合控制方式,利用AMESim和Simulink联合仿真技术对系统进行仿真研究,分析比较举升系统在有、无偏载情况下的同步特性。仿真结果表明:交叉耦合控制方式下该举升系统具有工作平稳、可靠性好以及同步精度高等优点。     

高速铁路用热塑性聚酯弹性体发泡材料挤出成型研究

采用挤出成型工艺制备热塑性聚酯弹性体(TPEE)发泡材料。研究了发泡剂的用量,成核剂的种类和用量,交联剂对TPEE挤出发泡材料性能的影响。采用万能力学测试机和扫描电子显微镜分别测试和观察了TPEE发泡材料的力学性能和泡孔结构,并测试了TPEE发泡材料的表观密度。结果表明:TPEE发泡材料的性能与发泡剂用量之间的关系并不是简单的线性关系;恰当的成核剂种类和用量能够为发泡体系提供大量的成核点,进而利于均匀泡孔的生成;加入过氧化二异丙苯(DCP)可提高发泡材料的力学性能,但降低了发泡率和均匀性;合理的加工参数对得到优质的TPEE发泡材料极为重要。综合考虑,当发泡体系中偶氮二甲酰胺(AC)为0.8份,苯甲酸钠为1.6份,采用压缩比为3:1的销钉式单螺杆挤出机,转速为70r/min,挤出温度为205℃,并且不加入DCP的工艺条件下制得的TPEE发泡材料的泡孔结构更为规整,整体性能更为理想。     

Neueste Entwicklungen beim baulichen Brandschutz von Straßentunneln

In der jüngeren Vergangenheit hat sich gezeigt, dass Straßen tunnel durch größere Brände in erheblichem Umfang geschädigt werden können. In der Folge wurden verschiedene internationale Forschungsprojekte durchgeführt, um den baulichen Brandschutz von Straßentunneln weiterzuentwickeln. Aufbauend auf den internationalen Forschungsprojekten wurden vom BMVBS und der BASt drei nationale Forschungsprojekte zum baulichen Brandschutz von Straßentunneln initiiert. In diesen Projekten wurden vorhandene Temperatur‐Zeit‐Verläufe (sog. “Brandkurven”) für Straßentunnel, Brandver suche in Tunneln und reale Brände in Straßentunneln im Hinblick auf eine mögliche Anwendung zur Bemessung des baulichen Brandschutzes von Straßentunneln analysiert. Außerdem wurden die Temperatureindringung in die Tunnelinnenschale und die Tragfähigkeit von üblichen Tunnelquerschnitten infolge Brandeinwirkung numerisch ermittelt. Schließlich wurde anhand von Brandversuchen an großmaßstäblichen Probekörpern die Wirkung von PP‐Faserbeton auf das Abplatzverhalten von Innenschalenbeton untersucht. Über das Vorgehen und die Ergebnisse dieser Forschungsprojekte wird im Folgenden berichtet. Latest developments for structural fire protection of road tunnels. In the recent past it was shown that road tunnels can be damaged severely by large fires. For that reason several international research projects were carried out for further development of structural fire protection of road tunnels. Based on international research projects three national research projects were initiated by the Federal Ministry of Transport, Building and Urban Development (BMVBS) and the Federal Highway Research Institute (BASt). In the course of these projects existing temperature‐time‐progressions (so called ”fire curves”) for road tunnels, fire tests in tunnels and real fires in road tunnels were analyzed with regard to a possible application for the design of structural fire protection of road tunnels. Furthermore the temperature penetration in the tunnel lining and the load bearing capacity of usual tunnel sections were numerically examined under fire influence. Finally the influence of fiber‐modified concrete on the effect of explosive spalling was investigated by means of large scale fire tests on specimens made of concrete for tunnel lining. In the following procedures and results of the national research projects are described.     

Fast computation of wideband RCS using characteristic basis function method and asymptotic waveform evaluation technique

The Asymptotic Waveform Evaluation (AWE) technique is an extrapolation method that provides a reduced-order model of linear system and has already been successfully used to analyze wideband electromagnetic scattering problems. As the number of unknowns increases, the size of Method Of Moments (MOM) impedance matrix grows very rapidly, so it is a prohibitive task for the computation of wideband Radar Cross Section (RCS) from electrically large object or multi-objects using the traditional AWE technique that needs to solve directly matrix inversion. In this paper, an AWE technique based on the Characteristic Basis Function (CBF) method, which can reduce the matrix size to a manageable size for direct matrix inversion, is proposed to analyze electromagnetic scattering from multi-objects over a given frequency band. Numerical examples are presented to illustrate the computational accuracy and efficiency of the proposed method.     

Modeling transfer of Escherichia coli O157:H7 and Staphylococcus aureus during slicing of a cooked meat product

Cross contamination is one of the most important contributing factors in foodborne illnesses originating in household environments. The objective of this research was to determine the transfer coefficients between a contaminated domestic slicing machine and a cooked meat product, during slicing. The microorganisms tested were Staphylococcus aureus (Gram positive) and Escherichia coli O157:H7 (Gram negative). The results showed that both microorganisms were able to transfer to all slices examined (20 successively sliced) and at different inoculum levels on the blade (10⁸, 10⁶ and 10⁴ cfu/blade). The results also showed that the number of log cfu transferred per slice, during slicing, decreased logarithmically for both microorganisms at inoculum levels of 8 and 6 log cfu/blade. The type of microorganism significantly influenced transfer coefficients (p < 0.05) and there was an interaction between inoculum level and transfer coefficient for S. aureus (p < 0.05), but not E. coli O157:H7. Finally, to describe bacterial transfer during slicing, two models (log-linear and Weibull) were fitted to concentration on slice data for both microorganisms (at 6 and 8 log cfu/blade), obtaining a good fit to data (R²  0.73).