我国城市交通问题成因及解决对策初探——基于经济学角度的思考

在理清交通问题的概念的基础上,借助经济学上总供给与总需求理论,分析交通问题产生的原因,最后给出可能的解决方案。     

城市化进程的思考

<正>土耳其著名诗人纳齐姆·希克梅特说"人的一生有两样东西不会忘记,那就是母亲的面孔和城市的面孔"。所谓城市面孔,如果说文化就是表情的话那么建筑就是它的轮廓,成千上万的城市面孔中,大多数只是城域文化差别的体现。     

掺高模量树脂类改性剂的沥青混合料路用性能研究

对在北京施工的掺加了高模量树脂类改性剂(以下简称"路强剂")沥青混合料与普通混合料进行了马歇尔参数特性、高温抗车辙能力、水稳定性对比试验,分析了路强剂对沥青混合料路用性能的影响,阐述了掺加路强剂混合料生产过程质量控制要点及手段。     

浅埋暗挖隧道下穿北京既有城铁车站的过程控制

北京奥运村—八家220 kV送电工程电力隧道下穿城铁13号线五道口车站,介绍了其监控量测方法,并对其监控结果进行了分析。从监控结果来看,新建隧道的施工对既有地铁的影响较小,施工风险得到了较好的控制。     

深部软岩巷道锚网不对称支护技术分析

针对某矿“孤岛”综采工作面的支护变形问题,通过现场试验与MIDAS软件数值模拟计算,提出了锚网复合不对称支护方法,成功地解决了问题。计算和试验结果表明：在不对称支护作用下,巷道两帮变形更为协调,同一断面各锚杆间的受力分布更均匀,从而对巷道整个收敛量起到了较好的控制作用。     

小湾水电站工程的挑战与思考

小湾水电站位于我国西南高山峡谷地区,地形地质条件复杂,坝高、库大,泄洪流量及功率大,技术难度高,在许多方面均超越了现行规程规范及以往的认知,极具挑战性。该工程复杂高边坡、拱坝及拱座、坝基岩体开挖卸荷松弛、混凝土骨料料源、拱坝混凝土温控及裂缝、物探检测与安全监测、引水发电系统及临时设施、"数值小湾"等方面积累的经验和教训,必将使我国的高拱坝建设迈上一个新台阶。     

Arsenic removal by iron-modified activated carbon

Iron-impregnated activated carbons have been found to be very effective in arsenic removal. Oxyanionic arsenic species such as arsenate and arsenite adsorb at the iron oxyhydroxide surface by forming complexes with the surface sites. Our goal has been to load as much iron within the carbon pores as possible while also rendering as much of the iron to be available for sorbing arsenic. Surface oxidation of carbon by HNO3/H2SO4 or by HNO3/KMnO4 increased the amount of iron that could be loaded to 7.6-8.0%; arsenic stayed below 10 ppb until 12,000 bed volumes during rapid small-scale tests (RSSCTs) using Rutland, MA groundwater (40-60 ppb arsenic, and pH of 7.6-8.0). Boehm titrations showed that surface oxidation greatly increased the concentration of carboxylic and phenolic surface groups. Iron impregnation by precipitation or iron salt evaporation was also evaluated. Iron content was increased to 9-17% with internal iron-loading, and to 33.6% with both internal and external iron loading. These iron-tailored carbons reached 25,000-34,000 bed volumes to 10 ppb arsenic breakthrough during RSSCTs. With the 33.6% iron loading, some iron peeled off.     

同轴地埋管换热器岩土热响应试验研究

岩土热物理性质是影响地源热泵系统设计和运营的关键因素,对位于武汉市洪山区的2口不同深度的同轴地埋管换热孔分别进行48 h的热响应试验,并对同轴地埋管换热器内外管之间环形空间中的平均流体温度进行测试.根据同轴地埋管换热器的几何特性,以简便实用的方式测量同轴地埋管换热器环状空间传热流体的平均温度,结合同轴地埋管换热器钻孔热...     

Properties of polyamide 6/multiwalled carbon nanotubes composites: The influence of processing methods

The objective of this work was to elucidate the influence of shear rates on the properties of polyamide 6/multiwalled carbon nanotube (PA6/CNT) composites which was realized by adopting different types of processing methods that feature different orders of magnitude in shear rates, such as compression molding (CM, ~0 s⁻¹), conventional injection molding (CIM, ~10² s⁻¹) and microinjection molding (μIM, ~10⁵ s⁻¹). Electrical conductivity (σ) results indicated that the prevailing high shearing conditions in injection molding was unfavorable for the formation of intact filler network, thereby resulting in a much lower σ than CM counterparts. Moreover, the σ of PA6/CNT microparts was higher than that of CIM macroparts when the filler content was less than 5 wt%, otherwise the σ of CIM macroparts prevailed over that of μIM counterparts. A better filler distribution was observed when PA6/CNT composites were processed under higher shearing conditions, as corroborated by SEM. In addition, CNTs were preferentially aligned along flow direction and a higher degree of CNT orientation was expected with increasing shear rates, as confirmed by Raman spectral analysis. The tensile strength of injection molded PA6/CNT samples increased with increasing filler concentrations, and the more preferential orientation and better distribution of CNT were considered to be the contributing factors. The comparative study of the properties of PA6/CNT composites that processed using different methods was important for their practical applications in industrial sectors.     

Improving the transient thermal response and ablation properties of epoxy-modified silicone rubber composites by adding fluxing agent

In this work, transient thermal response and ablation behavior of liquid silicone rubber composites containing fluxing/ceramic forming fillers were investigated under different heat flows using an oxyacetylene flame. The results indicated that the introduction of zinc borate (ZB) and aluminum oxide (Al₂O₃) effectively reduced the temperature at various depths of the samples, and they improved the thermal insulation properties and lowered pyrolysis rates. The above finding was attributed to the heat absorption arising from water release and melt filling as well as the vitrified reaction of solid melt due to the decomposition of ZB. Besides, the melting and exfoliation of Al₂O₃ and the formation of aluminum silicate (Al₂SiO₅) caused heat absorption effect. Additionally, the mass ablation rates and line ablation rates increased with rising heat flows coupling with a decrease of compressive strength of the char layers. In a nutshell, the effect of adding ZB/Al₂O₃ on the thermal insulation behavior of epoxy-modified vinyl silicone rubber (EMVSR) composites under different heat flows was elucidtaed. This work served as a reference for the design and preparation of flexible ablative materials for thermal protection applications.