SEASONAL AND DIURNAL VARIATIONS OF PM1.0, PM2.5 AND PM10 IN THE ROADSIDE ENVIRONMENT OF HONG KONG

PM1.0 （fine particles, with diameter 〈 1 pm）, PM2.5 （fine particles, with diameter 〈 2.5μm） and PM10 （coarse particles, with diameter 〈 10 μm） were measured at 24-hour intervals near a high-traffic road in Hong Kong, from October 2004 to September 2005. Mass concentrations were determined for the three particle fractions, averaging for PM1.0, PM2.5 and PM10, respectively, 44.5±18.4, 55.4±25.5 and 81.3±37.7μg·m^-3, PM2.5 was 3.7 times the U.S. EPA＇s annual NAAQS of 15 μg·m^-3,. Overall, PM1.0 accounted for 44 to 69% （average 57%） of PM10, while PM2.5 accounted for 58 to 82% （average 71%） in this study. The particulate masses showed obvious seasonal patterns with high concentrations in cold seasons and low in warm seasons, especially high concentrations of PM2.5-10 during the cold seasons. Diurnal variations of mass concentrations of PM2.5 were determined during July, showing two major peaks in the morning and afternoon rush hours.     

PM2.5 in China： Measurements,sources, visibility and health effects,and mitigation

Concern over the health effects of fine particles in the ambient environment led the U.S. Environmental Protection Agency to develop the first standard for PM2.5 （particulate matter less than 2.5 μm） in 1997. The Particle Technology Laboratory at the University of Minnesota has helped to establish the PM2.5 standard by developing many instruments and samplers to perform atmospheric measurements. In this paper, we review various aspects of PM2.5, including its measurement, source apportionment, visibility and health effects, and mitigation. We focus on PM2.s studies in China and where appropriate, compare them with those obtained in the U.S. Based on accurate PM2.5 sampling, chemical analysis, and source apportionment models, the major PM2.5 sources in China have been identified to be coal combustion, motor vehicle emissions, and industrial sources. Atmospheric visibility has been found to correlate well with PM2.s concentration. Sulfate, ammonium, and nitrate carried by PM2.s, commonly found in coal burning and vehicle emissions, are the dominant contributors to regional haze in China. Short-term exposure to PM2.s is strongly associated with the increased risk of morbidity and mortality from cardiovascular and respiratory diseases in China. The strategy for PMzs mitigation must be based on reducing the pollutants from the two primary sources of coal-fired power plants and vehicle emissions. Although conventional Particulate Emission Control Devices （PECD） such as electrostatic precipitators in Chinese coal-fired power plants are generally effective for large particles, most of them may not have high collection efficiency of PM2.5. Baghouse filtration is gradually incorporated into the PECD to increase the PM2.5 collection efficiency. By adopting stringent vehicle emissions standard such as Euro 5 and 6, the emissions from vehicles can be gradually reduced over the years. An integrative approach, from collaboration among academia, government, and industries, can effectively manage and mitigate the PM2.s p     

The contribution of small leaks in a baghouse filter to dust emission in the PM2.5 range—A system approach

The contribution of leakage in a baghouse filter (defined as a short circuit between the upstream and downstream sides of the filter) to the emission of fine particles is quantified in comparison to other dust emission sources, and the influence of key operating variables on overall system response is analyzed. The study was conducted on a well-maintained pilot-scale filter unit (9 bags of 500 g/m² calendered polyester needle felt; total surface area 4.2 m²) operated in Δp-controlled mode over a range of pulsing intensities, with two types of test dust (one free-flowing and the other cohesive) at inlet concentrations of 10 and 30 g/m³. Leaks included single holes between 0.5 and 4 mm diameter, intentionally placed in either the plenum plate or one of the filter bags, as well as seamlines from bag confectioning. Emissions were separated by source into a transient contribution due to dust penetration through the filter bags after each cleaning pulse, and a continuous contribution from leaks. This separation was based on a novel method of data processing that relies on time-resolved concentration measurements with a specially calibrated optical particle counter. Tiny leaks on the order of 1 mm generated the same emission level as all the bags combined, and dominated continuous emissions. The equivalent leak cross section (leakage = media emission) was about 1 ppm of the total installed filter surface, independent of upstream dust concentration. Leakage through open seamlines amounted to 75% of media emissions in case of free-flowing test dust. Leakage was restricted to aerodynamic diameters less than ∼5 μm (roughly the PM_2.5 mass fraction). For comparison, time-averaged mass penetration through conventional needle-felt media ranged from about 10⁻⁵ to 10⁻⁶, depending on cohesiveness of the particle material and pulse cleaning intensity, giving emission levels between about 0.02 and 0.2 mg/m³ at the reference concentration of 10 g/m².     

RELATIONSHIP BETWEEN HORIZONTAL EXTINCTION COEFFICIENT AND PM10 CONCENTRATION IN XI＇AN, CHINA, DURING 1980-2002

Based on daily visibility data obtained from 1980-2002 and air pollution index data from 2001-2004 in Xi＇an, long-term variations and relationships for daily horizontal extinction coefficient and mass concentration of PM10 have been evaluated. A decreasing trend was found in horizontal extinction coefficient during the past 23 years, with higher values observed in 1980s relative to 1990s, and the highest and lowest values in winter and summer, respectively. Significant correlation and similar seasonal variations existed between horizontal extinction coefficient and PM10 concentration, suggesting the high influence of PM10 to the visibility drop at a site in the Guanzhong Plain of central China during the past two decades.     

Characteristics of elemental carbon and organic carbon in PM10 during spring and autumn in Chongqing, China

PM10 （particulate matter with aerodynamic diameter less than 10 μm） samples were collected simultaneously at nine urban sites and one urban background site during two intensive observation campaigns in 2006. Concentrations of elemental carbon （EC） and organic carbon （OC） in PM10 were analyzed using an element analyzer. The characteristics regarding spatial and seasonal distribution patterns of OC and EC concentrations and their contributions to PM10 mass, as well as correlation between OC and EC, were investigated in detail. The average OC and EC concentrations for urban sites were 57.5 ± 20.8 and 8.3 ± 3.9 μg/m^3, respectively, both being around three times higher than those for urban background site. As a whole, EC concentrations did not show distinct seasonal variations, though OC concentrations were generally higher in autumn than in spring. For urban sites, total carbonaceous aerosol （TCA） accounted for 33.2% in spring and 35.0% in autumn of PM10 mass. The OC and EC concentrations were found significantly correlated to each other both in spring and in autumn, implying the existence of similar emission sources such as coal combustion. The OC/EC ratios generally exceeded 2.0, indicating the presence of secondary organic carbon （SOC）, whose estimated concentration for urban Chongqing was 26.7 and 39.4μg/m^3, accounting for 48.9 and 61.9% of the total OC observed in the samples, in spring and in autumn, respectively.     

2.5维自愈合C/SiC复合材料弹性性能预测

试验研究了2.5维自愈合C/SiC复合材料（2.5D-C/SiC）的面内弹性性能。根据复合材料的细观结构特点,建立了2.5D-C/SiC的弹性模量预测模型。计算结果与试验值吻合较好,证明了模型及计算方法的正确性。通过改变经纱编织角、纤维束中纤维数以及经纱穿过纬纱的层数,得到了经纱体积含量、纬纱体积含量、纤维总体积含量以及弹性模量随上述参数的变化规律。保持碳化硅与碳化硼总体积分数不变,改变碳化硼与碳化硅的体积比α,得到了弹性模量随α的变化关系。     

Ti_3SiC_2/PM304摩擦副的高温摩擦学性能

本文考察了Ti3SiC2/PM304摩擦副从室温到630℃范围的摩擦磨损性能,并与Ni-Cr合金/PM304摩擦副的摩擦磨损性能进行了对比.结果表明:Ti3SiC2/PM304摩擦副具有比Ni-Cr合金/PM304摩擦副更好的摩擦磨损性能,特别是在400～630℃的温度范围内,Ti3SiC2/PM304摩擦副具有优异的摩擦磨损性能.从室温到300℃,Ti3SiC2/PM304摩擦副的磨损机制为Ti3SiC2晶粒拔出、脱落后与转移的PM304形成机械混合层,随着环境温度的升高机械混合作用加强.在400～630℃范围内,摩擦界面的机械混合作用受到显著抑制,在Ti3SiC2磨损表面形成富集银的转移润滑膜,而转移润滑膜的连续性对摩擦副的摩擦磨损性能影响较大.     

2.5维自愈合C/SiC复合材料的压缩力学行为

试验研究了2.5维自愈合C/SiC复合材料的压缩力学行为,根据材料的细观结构特点,建立了压缩载荷下的损伤力学模型,得到了经纬向压缩的非线性应力应变关系,预测结果与试验值吻合较好。结果表明,经向和纬向的力学行为不同,纬向的压应力逐渐增大时,切线模量逐渐增大,压缩强度为270.05MPa,而经向压应力逐渐增大时,层间损伤逐渐发生,经纱承受的弯矩越来越大,切线模量逐渐降低,破坏强度为128.66MPa。     

Ti_3SiC_2/PM3O4摩擦副的高温摩擦学性能

本文考察了Ti_3SiC_2/PM304摩擦副从室温到630℃范围的摩擦磨损性能,并与Nj-Cr合金/PM304摩擦副的摩擦磨损性能进行了对比.结果表明:Ti_3SiC_2/PM304摩擦副具有比Ni-Cr合金/PM304摩擦副更好的摩擦磨损性能,特别是在400～630℃的温度范围内,Ti_3SiC_2/PM304摩擦副具有优异的摩擦磨损性能.从室温到300℃,Ti3_SiC_2/PM304摩擦副的磨损机制为Ti_3SiC_2晶粒拔出、脱落后与转移的PM304形成机械混合层,随着环境温度的升高机械混合作用加强.在400～630℃范围内,摩擦界面的机械混合作用受到显著抑制,在Ti3SiC_2磨损表面形成富集银的转移润滑膜,而转移润滑膜的连续性对摩擦副的摩擦磨损性能影响较大.     

继承,发展,开拓,创新

<正>今天是郭永怀先生诞辰110周年,我想就怎样传承郭先生的崇高精神和学术思想,并且落实到我们的实际工作中去谈一点感想。首先,因在简短的发言中不能全面回顾郭先生60年的光辉一生,但其中有一个事例特别值得我们深思。郭先生生活年代的中国是"东亚病夫",不能抵御日本人的侵略,所以,当时的热血青年都在思考救国之道。20世纪上半叶是航空工业突飞猛进的时     

饱和土–隧道动力响应的2.5维有限元–边界元耦合模型

针对饱和土中异形隧道的三维动力响应问题,建立了2.5维有限元与边界元耦合模型.将隧道结构视为弹性体,采用2.5维有限元建立隧道模型;将地基土视为饱和多孔介质,采用2.5维边界元建立饱和土体模型.借助组合辅助问题基本解消除了边界积分方程的奇异性.利用饱和土与隧道接触面的位移、面力连续和完全透水或完全不透水边界条件,实现2.5维有限元和边界元模型的耦合求解.模型具有计算效率高、适用范围广的优点.通过与完全透水和完全不透水边界条件下轴对称问题的半解析解以及单相介质的2.5维有限元与边界元耦合模型对比,验证了本文模型的正确性.最后利用该模型计算了饱和土体中类矩形隧道在移动载荷作用下的三维动力响应,分析了不同土体渗透性下位移及孔隙水压力沿隧道轴向、环向和深度的分布规律.结果表明:(1)孔隙水压力随土体渗透性增大而显著减小,位移受土体渗透性影响小;(2)位移及孔隙水压力在隧道环向主要分布在距载荷作用点两侧约2 m的范围内;(3)孔隙水压力沿深度的衰减比土体位移快,且孔隙水压力和轴向位移沿深度的分布受土体渗透性影响大.     

Ar稀释C2H2+2.5O2预混气高频爆轰的端面结构

为了研究预混气爆轰的内部结构,对不同浓度的Ar稀释的C₂H₂+2.5O₂预混气进行爆轰实验和数值计算。首先,在内径63.5 mm的管道内进行爆轰实验,使用烟熏玻璃记录了不同初始压力下C₂H₂+2.5O₂预混气的爆轰端面结构。使用数字化图像处理技术来分析烟熏玻璃记录的三波点轨迹,以减少人为误差。然后,观察实验结果并描绘规则图形,图像识别程序经过验证后,用于分析实验结果。从端面结构中对封闭图形进行圆的拟合,用胞格半径方差来表示胞格大小的均匀程度;用相邻胞格圆心距的方差来表示胞格分布的规则程度。通过对比不同Ar稀释下半径方差和圆心距方差随胞格数量的变化,给出不同浓度Ar稀释下C₂H₂+2.5O₂预混气的端面胞格尺寸及分布规律,随着Ar浓度的升高,预混气端面胞格分布更加规律。     

Strain hardening in 2D discrete dislocation dynamics simulations: A new ‘2.5D’ algorithm

The two-dimensional discrete dislocation dynamics (2D DD) method, consisting of parallel straight edge dislocations gliding on independent slip systems in a plane strain model of a crystal, is often used to study complicated boundary value problems in crystal plasticity. However, the absence of truly three dimensional mechanisms such as junction formation means that forest hardening cannot be modeled, unless additional so-called ‘2.5D’ constitutive rules are prescribed for short-range dislocation interactions. Here, results from three dimensional dislocation dynamics (3D DD) simulations in an FCC material are used to define new constitutive rules for short-range interactions and junction formation between dislocations on intersecting slip systems in 2D. The mutual strengthening effect of junctions on preexisting obstacles, such as precipitates or grain boundaries, is also accounted for in the model. The new ‘2.5D’ DD model, with no arbitrary adjustable parameters beyond those obtained from lower scale simulation methods, is shown to predict athermal hardening rates, differences in flow behavior for single and multiple slip, and latent hardening ratios. All these phenomena are well-established in the plasticity of crystals and quantitative results predicted by the model are in good agreement with experimental observations.     

Structure, Surface, Interaction and Time

Recent years have witnessed the rapid growth and sale of new products in the field of functional materials, together with a relative decline in new products and new processes in the field of commodity chemicals. Different from the commodity chemicals which arecommonly produced by continuous processes in megaquantities, the functional materials are usually produced bybatch processes in small quantities. The utility of the functional materials depends not only on their chemical composition and purity but also on their structures and surfaces,which are governed by what occurs at a molecular/nano scale rather than at the process scale. What knowledge     

COMPOSITION OF INDOOR AEROSOLS AT EMPEROR QIN''''S TERRA-COTTA MUSEUM, XI''''AN, CHINA, DURING SUMMER, 2004

Particle samples were collected in August 2004 both inside and outside Emperor Qin's Terra-Cotta Museum in Xi'an, China. Mass and chemical composition of total suspended particles (JSP, particles with aerodynamic diameter less than-30μm), PM2.5(particles with aerodynamic diameter <2.5μm) were determined. The average levels of indoor PM2.5 and TSP were 108.4 and 172.4 μg·m-3, respectively, with PM2.5 constituting 62.9% of the TSP mass. Sulfate ((32.4±6.2)%), organics ((27.7±8.0)%), and geological material ((12.5±3.4)%) dominated indoor PM2.5, followed by ammonium ((8.9±2.8)%), nitrate ((7.0±2.9)%), and elemental carbon (EC, (3.9±1.5)%). Particle size distribution varied with the number of tourists in the museum. The size of sulfate, organics, EC, nitrate, and ammonium was found to vary in the range of 0.43 to 3.3 μm in fraction. Ion balance indicated that the aerosol was acidic, with insufficient ammonium ions to neutralize the sulfuric and nitric acids. High concentrations of acidic aerosols will erode the Terra-cotta warriors and horses especially in the summer season with high temperature (30℃) and relative humidity (70%) and undesirable solar radiation inside the museum. More attention should be paid to protecting these precious antiques made 2000 years ago.     

等温淬火热处理工艺对Fe-0.5C-2.0Si-2.5Mn钢冲击磨损性能的影响

采用MLD10动载磨粒磨损试验机对成分为Fe-0.5C-2.0Si-2.5Mn的贝氏体/马氏体复相钢进行冲击磨损试验,通过观察磨损率,表层组织演变以及表面磨损形貌的变化过程,重点研究了等温淬火热处理工艺对Fe-0.5C-2.0Si-2.5Mn钢冲击磨损性能的影响,结果表明:经不同热处理后的贝氏体/马氏体复相钢的耐磨性较铸态有明显提高(1.4~2.3倍),随着下贝氏体含量的增加,耐磨性先降低再趋于平稳.当冲击功由1 J增至4 J时,材料磨损性能下降,表面磨损形貌表征塑形破坏加剧;当冲击功为5 J时,组织中出现大量形变马氏体,加工硬化明显,表面磨损形貌较低能冲击下的表面更为平整均匀,磨损性能增强,但出现强烈的脆性断裂倾向.     

A 2.5-D dynamic model for a saturated porous medium: Part I. Green’s function

Based on Biot’s theory, the dynamic 2.5-D Green’s function for a saturated porous medium is obtained using the Fourier transform and the potential decomposition methods. The 2.5-D Green’s function corresponds to the solutions for the following two problems: the point force applied to the solid skeleton, and the dilatation source applied within the pore fluid. By performing the Fourier transform on the governing equations for the 3-D Green’s function, the governing differential equations for the two parts of the 2.5-D Green’s function are established and then solved to obtain the dynamic 2.5-D Green’s function. The derived 2.5-D Green’s function for saturated porous media is verified through comparison with the existing solution for 2.5-D Green’s function for the elastodynamic case and the closed-form 3-D Green’s function for saturated porous media. It is further demonstrated that a simple form 2-D Green’s function for saturated porous media can be been obtained using the potential decomposition method.