城市主干路基本路段交通流仿真分析

应用Vissim仿真系统,结合实测数据,对城市主干路基本路段的交通流进行了分析.通过对仿真模型输出的数据进行分析,发现城市主干道交通流呈现出不同的相位特征,应用"三相交通流理论,在城市主干路基本路段的流量-密度平面中将交通流划分自由流、同步流和堵塞流3个相位,并具体讨论各个相位的交通流特性,确定了各个相位的关键阈值,标定了每个相位的区域范围.     

Designing heterogeneous sensor networks for estimating and predicting path travel time dynamics: An information-theoretic modeling approach

With a particular emphasis on the end-to-end travel time prediction problem, this paper proposes an information-theoretic sensor location model that aims to minimize total travel time uncertainties from a set of point, point-to-point and probe sensors in a traffic network. Based on a Kalman filtering structure, the proposed measurement and uncertainty quantification models explicitly take into account several important sources of errors in the travel time estimation/prediction process, such as the uncertainty associated with prior travel time estimates, measurement errors and sampling errors. By considering only critical paths and limited time intervals, this paper selects a path travel time uncertainty criterion to construct a joint sensor location and travel time estimation/prediction framework with a unified modeling of both recurring and non-recurring traffic conditions. An analytical determinant maximization model and heuristic beam-search algorithm are used to find an effective lower bound and solve the combinatorial sensor selection problem. A number of illustrative examples and one case study are used to demonstrate the effectiveness of the proposed methodology.     

Effects of antenna position on readability of RFID tags in a refrigerated sea container of frozen bread at 433 and 915 MHz

Perishable foods are frequently exposed to temperature abuse during transportation and distribution. The use of traditional data loggers do not permit the instantaneous data transmission that radio frequency technology offers. Temperature has a major impact on food quality and safety, particularly when long transit times are imposed. Consequently, using radio frequency identification (RFID) to track and monitor temperature in perishable shipments will bring significant benefits to the cold chain. The goal of this study was to determine the optimal RF antenna placement to achieve full RFID tag readability inside a sea container. Testing was made at two different frequencies (915 and 433 MHz) while the refrigeration unit was running at −25 °C and the container was fully loaded with frozen bread. The sea container was instrumented with eight RFID antennas, three of which were tuned for 433 MHz and five for 915 MHz. All antenna wires exited the container via the forward drain holes. The RFID readers were outside the container and connected to their respective antennas, one at a time. Thirty eight RFID tags were evenly distributed onto the pallets of frozen bread. All RFID tags were active tags capable of reading and recording temperature. Results at 915 MHz showed readability levels between 47% and 79%, with an average of 68.4%, whereas 433 MHz demonstrated 100% readability at all antenna positions. In conclusion, the 433 MHz RFID system appears suitable for real time temperature monitoring of frozen bread inside a sea container. This technology could be applied to other food items similar to frozen bread.     

小鼠肌源性干细胞的分离、培养及其分化能力检测

目的探讨小鼠肌源性干细胞(MDSCs)的原代培养方法及其分化潜能,为肌性泌尿组织的细胞修复、治疗奠定基础。方法运用中性蛋白酶(DispaseⅡ)、胰蛋白酶及Ⅰ型胶原酶联合消化法分离小鼠MDSCs,并运用差速贴壁法进行纯化。倒置显微镜下观察细胞形态,RT-PCR法鉴定MyoD及Desmin的表达,同时对分离的细胞进行成骨、成脂等分化诱导并鉴定。结果运用中性蛋白酶可很好地消化组织,差速贴壁法能得到纯度较高的MDSCs;RT-PCR检测发现MDSCs不表达MyoD以及Desmin,提示其为不同于肌卫星细胞的肌源性干细胞;成骨诱导检测碱性磷酸酶(ALP)染色(+),成脂诱导油红O染色(+);其可自体分化诱导为心肌样细胞,免疫荧光法检测心肌肌钙蛋白(cTnI)呈现阳性结果。结论利用此分离方法可获得纯度较高且具有较强分化潜能的肌源性干细胞,有助于进一步进行组织工程研究。     

提高联网高速公路路径射频识别系统可靠性方法探析

利用标识站信息漏读漏写模型分析整个识别系统中可能出现的错误情况,提出硬件和软件解决方案.研究表明,利用数据分析查询和超时表等关键技术,可以有效提高联网高速公路路径射频识别系统的稳定性.     

模块化6 - SPS SteWart机床位置参数识别

描述了模块化Stewart机床的基座关节位姿识别的一种方法，即通过测量动平台的位置，基座 关节位姿的变化及可伸缩连杆长度增量产生一套识别参数的非线性方程。对于Stewart机床的实际应 用具有重要的指导意义。     

初始模型的不确定性对梁式结构静力损伤识别的影响

结合初始模型和结构损伤的概率定义,给出了一个具有统计意义的梁式结构静力损伤识别方法.在此基础上,重点研究了初始模型的不确定性对损伤识别的影响.经数值分析,发现当初始模型的不确定程度低于或基本相当于损伤程度时,本文的方法依然具有较好的损伤识别效果.而当初始模型的不确定程度超过结构损伤程度时,已无法识别出结构损伤.因此,为了获得较好的损伤识别结果,必须保证初始模型具有足够的精度.     

船载AIS设备在应用存在的主要问题

AIS(船舶自动识别系统)在安装使用中存在着不足急需改进。笔者结合船舶检验工作,对一些具有代表性的问题进行了论述并提出了解决办法和建议。     

大型桥梁钻孔灌注桩施工风险识别与应对策略

文章结合大型桥梁钻孔灌注桩的施工特点,阐述了风险识别的重要性,并采用分解分析法对钻孔灌注桩施工过程中的风险因素进行分析识别,提出了相应的风险应对策略及措施。     

钢筋混凝土桥墩破坏模式识别方法

鉴于破坏模式对钢筋混凝土桥墩抗震加固和基于性能的抗震设计中性能目标量化的重要性,根据钢筋混凝土桥墩的破坏特点和破坏模式,统计分析各国钢筋混凝土桥墩抗震试验资料。基于钢筋混凝土桥墩抗剪需求和能力的关系,对混凝土强度f′c、纵筋配筋率ρl、体积配箍率ρv、规则化的纵筋配筋率、规则化的体积配箍率、轴压比、剪跨比a/h0和规则化的箍筋间距进行双参数相关分析和偏相关分析,确定各因素与桥墩塑性铰区抗剪需求与能力比值Vp/Vn的相关程度。研究结果表明:以ρl≤2.173%、a/h0≥3.880、Vp/Vn=0.7作为钢筋混凝土桥墩弯曲破坏模式的判别条件,以Vp/Vn>1.0且a/h0≤1.865作为剪切破坏模式的判别条件,以1.865≤a/h0≤3.880作为弯剪破坏模式的判别条件是合理的。