Bioconcentration factors for volatile organic compounds in vegetation

Samples of air and leaves were taken at the University of Nevada [Formula: see text] Las Vegas campus and analyzed for volatile organic compounds using vacuum distillation coupled with gas chromatography/mass spectrometry. The data were used to estimate the bioconcentration of volatile organic compounds (VOCs) and to characterize the equilibration of VOCs between the leaves and air. The bioconcentration of volatiles in the leaves of some species can be predicted using the partition coefficients between air and octanol (K(oa)) and only considering VOC absorption in the lipid fraction of leaves. For these leaves, the bioconcentration factors agreed with existing models. Leaves of some species displayed a bioconcentration of volatiles that greatly exceeded theory. These hyperbioconcentration leaves also contain appreciable concentrations of monoterpenes, suggesting that a terpenoid compartment should be considered for the bioconcentration of organic compounds in leaves. Adding an additional "terpenoid" compartment should improve the characterization of volatile organic compounds in the environment. The uptake of VOCs from air by leaves is rapid, and the equilibration rates are seen to be quicker for compounds that have higher vapor pressures. The release of VOCs from the leaves of plants is slower for hyperbioconcentration leaves.     

Preparation and properties of lead-free FeS/Cu-Bi composites by flake powder metallurgy via shift-speed ball milling

Lead-free FeS/Cu-Bi (FCB) self-lubricating composites were prepared via shift-speed ball milling (SSBM) and powder metallurgy. The microstructure and evolution of mixed powders were studied, and the mechanical and tribological properties of the FCB composites were tested. SSBM includes long-term low-speed ball milling (LSBM) and short-term high-speed ball milling (HSBM). In the early LSBM, the matrix phase CuSn10 powder was flattened into flakes, and the lubricating phases FeS and Bi were refined and gradually dispersed on the CuSn10 flakes. After short-term HSBM, FeS and Bi were further trapped on the CuSn10 flakes, which not only improved the bonding performance between the lubricating phase and copper alloy but also protected the continuity of the copper alloy matrix from additional damage. 6 + 1 h SSBM (6 h LSBM + 1 h HSBM) improved the mechanical properties, antifriction and wear resistance of FCB composites. Compared with traditional HSBM, SSBM provides a new way to prepare FCB self-lubricating composites with better comprehensive properties.     

Effect of micronization on physicochemical properties of small yellow croaker (Pseudosciaena polyactis) skull

The aim of this study was to investigate the effect of micronization on the physicochemical properties of small yellow croaker (Pseudosciaena polyactis) skull. Three different micronization treatments were carried out, including ball dry milling (DM), ball wet milling (WM) and jet milling (JM). Physicochemical properties of those three micronized powders were analyzed and compared with those of two coarse powders (before micronization). The results showed, powder from ball wet milling (WM) provided higher oil holding and swelling capacity, better fluidity, with a higher of dissolving protein, whereas, that from JM provided higher bulk density, water holding capacity and solubility of protein, and better ratio of Ca–P. Three milling methods (DM, WM and JM) respectively increased soluble protein to 77.33–90.06%, 82.26–89.51% and 79.56–90.95% with soaking time. The results indicated that three micronization technologies would improve some properties of small yellow croaker skull powder in food applications.     

Compatibility of TCP Reno and TCP Vegas in wireless ad hoc networks

Previous work has shown that TCP (transmission control protocol) Vegas outperforms the more widely deployed TCP Reno in both wired and wireless networks. It was also shown that when both TCP variants coexist on the same wired links, Reno dominates because of its more aggressive behaviour. This paper examines for the first time the compatibility between Reno and Vegas in wireless IEEE 802.11 ad hoc networks. It is shown that Vegas generally dominates in the heterogeneous Reno/Vegas network scenario; a startling result that is inconsistent with what is seen in wired networks. It is shown that the wireless ad hoc network environment does not reward the aggressive behaviour of Reno. On the other hand, Vegas, with its more accurate yet more conservative mechanisms, is able to capture most of the bandwidth. This is found to be true when using the on-demand routing protocols of dynamic source routing (DSR) or ad hoc on-demand distance vector (AODV): the failure of a node to reach a next-hop node because of media access control (MAC)-sublayer repeated collisions is reported to the routing protocol, which then declares a route error that impacts Reno in a more serious way than Vegas. When the table-driven routing protocol destination-sequenced distance vector (DSDV) is used, Reno and Vegas share the network bandwidth in a fairer manner. Generally, fairness in this environment can be improved by reducing the TCP maximum window size.     

New methods to identify and rank high pedestrian crash zones: an illustration

Identifying and ranking high pedestrian crash zones plays a key role in developing efficient and effective strategies to enhance pedestrian safety. This paper presents (1) a Geographical Information Systems (GIS) methodology to study the spatial patterns of pedestrian crashes in order to identify high pedestrian crash zones, and (2) an evaluation of methods to rank these high pedestrian crash zones. The GIS based methodology to identify high pedestrian crash zones includes geocoding crash data, creating crash concentration maps, and then identifying high pedestrian crash zones. Two methods generally used to create crash concentration maps based on density values are the Simple Method and the Kernel Method. Ranking methods such as crash frequency, crash density, and crash rate, as well as composite methods such as the sum-of-the-ranks and the crash score methods are used to rank the selected high pedestrian crash zones. The use of this methodology and ranking methods for high pedestrian crash zones are illustrated using the Las Vegas metropolitan area as the study area. Crash data collected for a 5-year period (1998-2002) were address matched using the street name/reference street name intersection location reference system. A crash concentration map was then created using the Kernel Method as it facilitates the creation of a smooth density surface when compared to the Simple Method. Twenty-two linear high crash zones and seven circular high crash zones were then identified. The GIS based methodology reduced the subjectivity in the analysis process. Results obtained from the evaluation of methods to rank high pedestrian crash zones show a significant variation in ranking when individual methods were considered. However, rankings of high pedestrian crash zones were relatively consistent with little to no variation when the sum-of-the-ranks method and the crash score method were used. Thus, these composite methods are recommended for use in ranking high pedestrian crash zones instead of individual methods.     

飞机座舱数字信息界面交互设计与情境意识研究综述

目的 飞机座舱作为飞机安全高效运行的中枢,对座舱数字信息界面进行合理设计能够提升飞行员处理飞行数据信息及决策的情境意识水平,减少人为因素出错,提升飞行安全。方法 对现有民用飞机及战机座舱的主飞行显示器(PFD)、头盔显示器(HMD)、全景座舱显示器(PCD)等数字信息人机界面设计研究进行梳理和归纳,总结飞机座舱人机交互设计的发展规律和未来发展趋势。结论 从国内外研究综述表明,通过“机”的数字界面信息表征设计和“人”的情境感知、认知工效、认知体验研究,可以加强人机沟通与人机协作,改善飞行员获取飞机信息、判断与决策的认知绩效,有利于飞行员高质量完成飞行任务。     

分区分台阶深孔爆破技术在城市土石方开挖中的应用

城市中心爆破具有周边环境复杂,地下管线密集,安全风险系数高的特点,需采取特殊的爆破施工技术控制爆破有害效应。以汉阳人信汇A地块土石方控制爆破工程为背景,采用高效、安全的分区分台阶深孔爆破技术,在爆区距离被保护体20 m范围内的严格控制区域采用4 m的台阶,孔距2.8 m,排距2.5 m;在爆区距离被保护体20 m外的一般控制区域,采用8 m高的台阶,孔距3 m,排距2.8 m;施工过程中通过使用澳瑞卡高精度雷管、开挖减振沟和密目安全网覆盖等安全辅助措施,保证了周边构筑物及地下管网的安全,且大大提高了施工效率。     

The challenge of predicting flash floods from thunderstorm rainfall

A major characteristic of the hydrometeorology of semi-arid regions is the occurrence of intense thunderstorms that develop very rapidly and cause severe flooding. In summer, monsoon air mass is often of subtropical origin and is characterized by convective instability. The existing observational network has major deficiencies for those regions in providing information that is important to run-off generation. Further, because of the complex interactions between the land surface and the atmosphere, mesoscale atmospheric models are currently able to reproduce only general features of the initiation and development of convective systems. In our research, several interrelated components including the use of satellite data to monitor precipitation, data assimilation of a mesoscale regional atmospheric model, modification of the land component of the mesoscale model to better represent the semi-arid region surface processes that control run-off generation, and the use of ensemble forecasting techniques to improve forecasts of precipitation and run-off potential are investigated. This presentation discusses our ongoing research in this area; preliminary results including an investigation related to the unprecedented flash floods that occurred across the Las Vegas valley (Nevada, USA) in July of 1999 are discussed.     

Lake Mead Intake No. 3

As a result of a sustained drought in the Southwestern United States, and in order to maintain existing water capacity in the Las Vegas Valley, the Southern Nevada Water Authority constructed a new deep-water intake (Intake No. 3) located in Lake Mead. The project included a 185 m deep shaft, 4.7 km tunnel under very difficult geological conditions, and marine works for a submerged intake. This paper presents the experience that was gained during the design and construction and the innovative solutions that were developed to handle the difficult conditions that were encountered during tunneling with a dual-mode slurry tunnel-boring machine (TBM) in up to 15 bar (1 bar = 10⁵ Pa) pressure. Specific attention is given to the main challenges that were overcome during the TBM excavation, which included the mode of operation, face support pressures, pre-excavation grouting, and maintenance; to the construction of the intake, which involved deep underwater shaft excavation with blasting using shaped charges; to the construction of the innovative over 1200 t concrete-and-steel intake structure; to the placement of the intake structure in the underwater shaft; and to the docking and connection to an intake tunnel excavated by hybrid TBM.     

大坪隧道掘进中爆破震动的控制

重庆轻轨大坪车站隧道最小埋深仅4m,地面人口密集,建筑物林立。采用了浅孔、多循环和楔形掏槽的分步开挖方式;根据被保护建筑物的安全振速确定最大一段药量;采用了增设减振孔的光面爆破技术;同时严格控制单孔药量。在开挖施工过程中还进行了爆破震动监测。上述技术措施有效地控制了爆破的地震强度,保证了开挖施工的安全,地表建筑物没有损坏。     

Experimental and simulation study of the effect of gravity on the solid-liquid two-phase flow and erosion of ball valve

The ball valve is an important control component in the pipeline hydraulic transmission system. Its internal solid-liquid two-phase flow and erosion characteristics have an important effect on the safety and stability of the entire pipeline system. Therefore, the erosion characteristics and positions of the ball valve body, the spool flow channel, and the pipeline surface behind the valve should be accurately predicted to ensure the safety of the pipeline. In this study, the experimental setup of the ball valve was designed. The experimental study on the erosion caused by the solid-liquid two-phase flow on the inner surface of the ball valve was conducted. And the numerical calculation research based on the CFD-DEM simulation method was performed. Results show that the placement of the ball valve has a great effect on the two-phase flow and erosion distribution inside the valve; the surface of the erosion plate will form a corrugated texture under the impact of particles at small openings; the placement method changes from vertical to horizontal due to the change in the direction of gravity. As a result, the particle distribution easily gathers near some wall surfaces to form a protective layer, which reduces the erosion rate.     

动态随机球的标定误差与测量次数的关系

本文介绍了随机球标定技术的原理。针对随机球标定方法的两种方法(静态法和动态法),本文分别分析了两种方法的标定误差与测量次数之间的关系。依据数理统计原理和合理的假设,理论分析表明静态法是一种特殊的动态法。两种方法的标定误差随测量次数增加呈N-1/2递减。针对动态法,本文进行了动态法随机球标定实验。实验结果表明,动态法的标定误差与测量次数之间近似符合N-1/2规律。     

新型滚珠式多向动力吸振器的理论研究

提出了一种用于控制特殊多方向强迫振动的滚珠式动力吸振器。通过理论分析和数值计算,研究了该吸振器的振动控制机理和主要参数对吸振效果的影响。利用定点理论,优化设计了控制系统的最优频率和最优阻尼。研究表明,利用该结构简单的吸振器可以有效地控制机械或结构在共振频率点附近所发生的特殊的强迫振动响应。     

惯性载荷对高速角接触球轴承最优预紧力的影响分析

高速角接触球轴承拟静力学模型是轴承内部载荷分布的有效分析手段,是动力学分析的基础.对受轴向载荷的高速角接触球轴承的具体算例进行了求解计算,得出了不同转速下钢球与沟道接触力随预紧力的变化规律.计算结果表明:在低转速范围内,钢球与外沟道接触力随着轴向预紧力的增大而线性增大;随着转速的升高,该接触力会呈现非线性变化,表现出先减小后增大的变化趋势.对这一变化规律进行了详细的分析,并从接触疲劳寿命和陀螺转动摩擦生热的角度,提出了确定高速角接触球轴承最佳预紧力的双重约束条件,为高速角接触球轴承的设计与使用提供参考依据.     

Safety effects of traffic signing for left turn flashing yellow arrow signals

In 2010, the left turn flashing yellow arrow (FYA) signal displays were installed at signalized intersections on state routes in the Peoria, Illinois, area. Supplemental traffic signs with text “Left Turn Yield on Flashing Yellow Arrow” were mounted on the mast arm adjacent to the left turn signal at over half of the FYA installations. The purpose of this paper is to present the results of the effectiveness evaluation of the FYA supplemental sign on safety. Analyses are presented on the effects of the FYA supplemental sign for all drivers and a subset of drivers age 65 and older. A crash-based comparison of 164 FYA approaches including 90 approaches with the sign and 74 approaches without the sign showed greater crash reductions when the supplemental FYA sign was present. The results also showed that crashes involving drivers age 65 and older did not experience the same magnitudes of crash reductions as compared to all drivers. The findings of this research indicate that supplemental FYA signs may help in improving safety for left-turning vehicles during the permissive interval. Thus, it is recommended that supplemental signs be used when initially implementing the FYA, and that effort to educate the driving public on new traffic control be made to further improve safety at signalized intersections.     

滚珠丝杠副导程误差仿动态测量的研究

本文从滚珠丝杠副导程的定义出发．通过对数显万能工具显微镜的改造，仿照丝杠动态测试仪的结构，利用数学回归分析，实现了对滚珠丝杠副导程误差的测试和分析．为了解决中小企业在无丝杠动态测试设备下测试滚珠丝副导程误差的难题，提供了一种简便．实用的方法．     

Failure mode analysis of lead-free solder joints under high speed impact testing

Using an Instron micro-impact system, this study investigates the failure characteristics of 96.5Sn–3Ag–0.5Cu lead-free solder joints aged at either room temperature or 125 °C, respectively, and then impacted at shear rates of up to 1 m/s. Four types of failure mode are identified, namely M1: interfacial fracture with no residual solder left on the pad; M2: interfacial fracture with residual solder left on the pad; M3: solder ball fracture; and M4: substrate fracture. The experimental results reveal that the solder specimens fail in different failure modes at the same impact speed. The transition from ductile to brittle failure occurs at an impact speed of around 0.5 m/s. At an impact speed of 0.7 (±0.05) m/s or more, over 70% of the specimens fail in the M1 or M2 modes under all of the testing conditions. The isothermal aging process is found to reduce the interfacial strength, and hence the percentage of M3 and M4 mode failures reduces significantly. Overall, the experimental results suggest that the failure mode distribution obtained in high speed impact tests performed at 0.5 m/s provides a feasible component-level quality assurance index.     

Critical stresses and strains at the spall edge of a case hardened bearing due to ball impact

Short spall propagation times of failing main shaft ball bearings of aircraft engines are a serious safety concern for single engine aircraft. Bearing designers would like to understand the impact of four variables namely (i) ball material density, (ii) subsurface residual stress, (iii) gradient in yield strength with depth (case hardening), and (iv) raceway surface hardness/yield strength that are thought to affect spall propagation. Extensive spall propagation experiments have been conducted at AFRL, Ohio in the past few years to address this issue. However, a detailed mechanistic analysis of these experiments has not been performed. This work presents an elastic–plastic finite element (FE) model that simulates a ball impacting a spall edge to determine the relative contributions of the four material variables on spall propagation. The magnitude and extent of damage of the spall edge material is determined based on critical stresses and plastic strains induced by the ball impact. The results indicate that the influence of ball density is greatest on inducing damage at the impacted spall edge when compared to the other three properties, which also agrees with the hybrid bearing spall propagation tests conducted at AFRL.     

三峡深水高土石围堰工程科技创新

三峡二期深水高土石围堰是一项具有挑战性的高难度工程项目，其面临的技术难题远远超过国内外同类工程的水平。在1998—2002年4年多的运行中，围堰保护了左岸大坝和厂房的施工基坑，并经受了1998年长江大洪水的考验，使二期工程得以顺利建成。二期围堰工程质量优良,圆满地完成了历史任务。文章从试验研究、设计施工、组织管理、安全监测及运用后拆除等各个方面进行了全过程、全方位的系统介绍。     

Second harmonic generation of shear waves in crystals

Nonlinear self-interaction of shear waves in electro-elastic crystals is investigated based on the rotationally invariant state function. Theoretical analyses are conducted for cubic, hexagonal, and trigonal crystals. The calculations show that nonlinear self-interaction of shear waves has some characteristics distinctly different from that of longitudinal waves. First, the process of self-interaction to generate its own second harmonic wave is permitted only in some special wave propagation directions for a shear wave. Second, the geometrical nonlinearity originated from finite strain does not contribute to the second harmonic generation (SHG) of shear waves. Therefore, unlike the case of longitudinal wave, the second-order elastic constants do not involve in the nonlinear parameter of the second harmonic generation of shear waves. Third, unlike the nonlinearity parameter of the longitudinal waves, the nonlinear parameter of the shear wave exhibits strong anisotropy, which is directly related to the symmetry of the crystal. In the calculations, the electromechanical coupling nonlinearity is considered for the 6 mm and 3 m symmetry crystals. Complement to the SHG of longitudinal waves already in use, the SHG of shear waves provides more measurements for the determination of third-order elastic constants of solids. The method is applied to a Z-cut lithium niobate (LiNbO/sub 3/) crystal, and its third-order elastic constant c/sub 444/ is determined.