脉动风速功率谱与随机Fourier幅值谱的关系研究

功率谱密度函数是随机过程在频域内的重要特征量,但由于其本质上是平稳过程的频域数值特征,致使其很难全面反映原始随机过程的概率信息,这就需要从更本源的意义上考察随机过程。本文试图从Fourier随机函数的角度反映随机过程,将经典的功率谱密度函数中具有物理意义的可测变量看作随机变量,利用功率谱与Fourier幅值谱的关系,定义了随机Fourier幅值谱;以Davenport谱为例,证实当地面粗糙度服从对数正态分布、10m高度基本风速服从极值Ⅰ型分布时,可通过功率谱构造具有物理意义的随机Fourier幅值谱。通过实测风速Fourier谱与随机Fourier幅值谱的比较,证明随机Fourier幅值谱的概念具有合理性。     

Experimental assessment on the moving capabilities of mobility-impaired disabled

To take into account reasonably the safety requirements of the disabled on emergency evacuation in the design, usage, management and emergency response of public places, the authors of this paper organized on-site experiments for 100 disabled individuals (40 people with no supporting tools, 20 people using a single crutch and 40 people two crutches) and 17 healthy people at a subway station in Beijing. The experiments were designed to measure the unimpeded free walking speed of the participants during horizontal and stair ascending/descending movement, and to assess the possible impact of passage width on movement speed. Based on the results of the tests, the authors systematically analyzed the speed variation patterns with disability grade, gender and passage width. The validity of the value of an important parameter for evacuation safety design in the prescribed fire codes in mainland China, the width of a single stream of people, is assessed. Finally the results of the experiments are compared with that from other researches to identify the similarities and differences between them.     

Thermal hazard accident investigation of hydrogen peroxide mixing with propanone employing calorimetric approaches

Hydrogen peroxide (H₂O₂), historically, due to its broad applications in the chemical industries, has caused many serious fires and explosions around the world. Its thermal hazards may also be incurred by an incompatible reaction with other chemicals, and a runaway reaction may be induced in the last stage. This study applied thermal analytical methods to explore the H₂O₂ leading to these accidents by incompatibility and to discuss what might be formed by the upset situations. Thermal hazard analysis contained a solvent, propanone (CH₃COCH₃, so-called acetone), which was deliberately selected to mix with H₂O₂ for investigating the degree of thermal hazard. Differential scanning calorimetry (DSC) and vent sizing package 2 (VSP2) were employed to evaluate the thermal hazard of H₂O₂. The results indicated that H₂O₂ is highly hazardous while mixed with propanone, as a potential contaminant. The time to maximum rate (TMR) was used as emergency response time in the chemical industries. Therefore, TMR of H₂O₂ was calculated to be 70 min for runaway reaction (after T₀) and TMR of H₂O₂/propanone was discovered to be 27 min only. Fire and explosion hazards could be successfully lessened if the safety-related data are properly imbedded into manufacturing processes.     

Dynamic pressure induced by a methane–air explosion in a coal mine

The hazardous effect of dynamic pressure and strong gas flows induced by a methane–air mixture explosion in underground coal mines is studied. The dynamic pressure effect of a methane–air explosion was analyzed by numerical simulation, in a duct and tunnel. Compared to the overpressure generated by an explosion that can act on a body, the dynamic pressure caused by the high-speed flow of the gaseous combustion products can cause serious damage as well. At the structural opening of a coal mine, the destruction caused by the dynamic pressure induced by a methane–air explosion is more serious than the overpressure. For a tube or tunnel partially filled by a methane–air mixture, the dynamic pressure is lower than the overpressure in the region occupied by the flammable mixture. Beyond the premixed region, the dynamic pressure is of the same order of magnitude as the overpressure.     

E‐commerce trade in invasive plants

Biological invasions are a major concern in conservation, especially because global transport of species is still increasing rapidly. Conservationists hope to anticipate and thus prevent future invasions by identifying and regulating potentially invasive species through species risk assessments and international trade regulations. Among many introduction pathways of non‐native species, horticulture is a particularly important driver of plant invasions. In recent decades, the horticultural industry expanded globally and changed structurally through the emergence of new distribution channels, including internet trade (e‐commerce). Using an automated search algorithm, we surveyed, on a daily basis, e‐commerce trade on 10 major online auction sites (including eBay) of approximately three‐fifths of the world's spermatophyte flora. Many recognized invasive plant species (>500 species) (i.e., species associated with ecological or socio‐economic problems) were traded daily worldwide on the internet. A markedly higher proportion of invasive than non‐invasive species were available online. Typically, for a particular plant family, 30–80% of recognized invasive species were detected on an auction site, but only a few percentages of all species in the plant family were detected on a site. Families that were more traded had a higher proportion of invasive species than families that were less traded. For woody species, there was a significant positive relationship between the number of regions where a species was sold and the number of regions where it was invasive. Our results indicate that biosecurity is not effectively regulating online plant trade. In the future, automated monitoring of e‐commerce may help prevent the spread of invasive species, provide information on emerging trade connectivity across national borders, and be used in horizon scanning exercises for early detection of new species and their geographic source areas in international trade.     

Research priorities for conservation and natural resource management in Oceania's small‐island developing states

For conservation science to effectively inform management, research must focus on creating the scientific knowledge required to solve conservation problems. We identified research questions that, if answered, would increase the effectiveness of conservation and natural resource management practice and policy in Oceania's small‐island developing states. We asked conservation professionals from academia, governmental, and nongovernmental organizations across the region to propose such questions and then identify which were of high priority in an online survey. We compared the high‐priority questions with research questions identified globally and for other regions. Of 270 questions proposed by respondents, 38 were considered high priority, including: What are the highest priority areas for conservation in the face of increasing resource demand and climate change? How should marine protected areas be networked to account for connectivity and climate change? What are the most effective fisheries management policies that contribute to sustainable coral reef fisheries? High‐priority questions related to the particular challenges of undertaking conservation on small‐island developing states and the need for a research agenda that is responsive to the sociocultural context of Oceania. Research priorities for Oceania relative to elsewhere were broadly similar but differed in specific issues relevant to particular conservation contexts. These differences emphasize the importance of involving local practitioners in the identification of research priorities. Priorities were reasonably well aligned among sectoral groups. Only a few questions were widely considered answered, which may indicate a smaller‐than‐expected knowledge‐action gap. We believe these questions can be used to strengthen research collaborations between scientists and practitioners working to further conservation and natural resource management in this region.     

以氢气为主要成分的其他可燃气体对低浓度甲烷爆炸特性的影响

为研究矿井火区中一氧化碳(CO)、氢气(H_2)、乙烯(C_2H_4)和乙烷(C_2H_6)等其他可燃气体对甲烷(CH_4)爆炸特性的影响,利用可视球形气体爆炸系统开展了多元可燃气体爆炸压力特性试验,观察并分析了峰值爆炸压力、最大爆炸压力上升速率及其相应时间。通过高速摄影系统拍摄了视窗范围内爆炸火焰传播图像,基于边缘检测方法确定了火焰前锋位置,继而得到最大火焰传播速度。分析了以氢气为主要成分的其他可燃气体对低浓度CH_4-空气混合物压力特性和火焰传播行为的影响。结果表明,多元可燃气体的存在增加了低浓度CH_4-空气混合物的爆炸危险性。随混合气体体积分数增加,低浓度CH_4-空气混合物的峰值爆炸压力、最大爆炸压力上升速率和最大火焰传播速度非线性增加;此外,到达峰值爆炸压力、最大爆炸压力上升速率的时间显著缩短。     

露天矿山隐伏盲空区精确探测及爆破优化设计

隐伏盲空区是严重威胁露天矿山正常采矿作业的安全隐患,应予以探明并处置。针对露天矿隐伏盲空区探测难度大、崩落处置爆破设计精度差等问题,以白马铁矿1号溜井盲空区为例,首先基于矿山历史资料,利用钻探手段,初步圈定盲空区异常分布范围;然后运用钻孔激光扫描设备进行三维精确扫描,获得盲空区塌腔三维形态和真实边界,并以实测数据为基础,利用逆向建模方法,构建盲空区三维可视化模型;最后根据盲空区的三维空间特征和分布条件,进行爆破分区及参数优化设计。结果表明:采用钻探圈定结合三维激光精确扫描建模的综合探测方法,可获得露天矿山盲空区的可靠信息,准确掌握盲空区垮塌现状,进而为制定更为精准的爆破设计方案提供重要依据,最终达到消除盲空区的目的。研究结果对保障矿山安全生产具有重要意义,同时可为类似工程提供有益参考。     

配置SCR的柴油货车道路运行NOx排放分析

为了研究重型柴油货车在不同道路运行工况下的NO_x排放特性,以一辆配置选择催化还原(Selective CatalyticReduction,SCR)净化系统的国V排放标准的重型柴油货车为研究对象,开展实际道路运行车载排放测试,通过车载排放测试系统实时采集车辆行驶速度、NO_x排放体积分数与排气温度等数据,分析车速、排气温度、路况等对NO_x排放的影响。结果表明,车速低于40 km/h,NO_x排放随车速增大稍有增加; 40～70 km/h,随车速增大NO_x排放降低;高于70 km/h,随车速增大NO_x排放显著降低。车速与排气温度呈线性正相关,排气温度高于150℃,SCR才能显示出对NO_x的净化效果。市区工况车速低,排温低于150℃,SCR不能有效工作;市郊、高速工况下排温高于150℃,SCR催化效率提高,车速增大,排温升高,NO_x排放降低,因此NO_x排放市郊工况低于市区工况,高速工况低于市郊工况。配置SCR的重型柴油货车NO_x高排放区主要集中在中低车速、加速区间内。     

汽车燃料和排放物的快速气相色谱分析

1　IntroductionGaschromatographyisthemostfrequentlyusedmethodsforthespeciationandquantificationoforganiccompoundsingasphaseandliquidphase .Thechemicalanalysisoforganiccompoundsintheautomotivefuelsandexhaustspeciesisanextremelyimportantandcomplexprocedure …