NUMBER CONCENTRATION, SIZE DISTRIBUTION AND FINE PARTICLE FRACTION OF TROPOSPHERIC AND STRATOSPHERIC AEROSOLS

1. Introduction The number concentration and size distribution of at-mospheric particles are the two major parameters for aerosol radiative forcing calculation, as the aerosol bur-dens affect the radiative transfer of solar and terrestrial emissions, while the size distribution of atmospheric aerosol is critical to all climatic influences (IPCC, 2001). However most measurements on the characteristics of the number-size distribution were carried out near the earth surface, with only a few exte…     

SEASONAL CHARACTERIZATION OF DUST DAYS, MASS CONCENTRATION AND DRY DEPOSITION OF ATMOSPHERIC AEROSOLS OVER QINGDAO, CHINA

1. Introduction Aerosols play an important role in affecting the atmos-pheric quality, cloud formation and precipitation, influenc-ing the energy balance of the earth-atmosphere system (Sokolik et al., 2001; Cao et al., 2003), although their concentration is very low. Recently, studies on atmospheric aerosols and their radiative forcing have been the inter-esting research area in global and/or regional environment and climate changes (Zhang et al., 2001; Menon et al., 2002). Among them, much…     

SPATIAL AND SEASONAL DISTRIBUTIONS OF ATMOSPHERIC CARBONACEOUS AEROSOLS IN PEARL RIVER DELTA REGION, CHINA

Concentrations and spatial distributions of organic carbon (OC) and elemental carbon (EC) in atmospheric particles were measured at 8 sites in four cities (Hong Kong, Guangzhou, Shenzhen and Zhuhai) of Pearl River Delta Region (PRDR), China during 2001 winter period and 2002 summer period. PM2.5 (particie diameter smaller than 2.5 um) and PM10 (particie diameter smaller than 10 um) samples were collected on pre-fired quartz filters with mini-volume samplers and analyzed using thermal optical reflectance (TOR) method. The average PM2.5and PM10 Ievel were 60.1 and 93.1 μg·m-3, respectively, with PM2.5 constituting 65.3% of the PM10 mass. The average OC and EC concentrations in PM2.5 were 12.0 and 5.1 μg·m-3, respectively, while those in PM10 were 16.0 and 6.5 μg·m-3, respectively. The carbo-naceous aerosol accounted for 37.2% of the PM2.5 and 32.8% of the PM10. The highest concentrations of OC and EC were observed at Guangzhou city in both vvinter and summer seasons. The average OC/EC ratios were 2.     

Impacts of biomass-burning on aerosol properties of a severe haze event over Shanghai

Anthropogenic aerosols have significant impacts on the environment and human health in the Yangtze River Delta region, one of the most densely populated regions in the world. A biomass-burning plume swept across this area (Shanghai) in May 2009, leading to changes in the physical and optical properties of aerosols, which were investigated using ground-based remote sensing and in situ measurements via comparisons with dust pollution and background conditions. Experiments show that the biomass-burning plume led to an increase in the average aerosol optical depth (AOD) at 500 nm from 0.73 to 1.00 (37% higher), an absorption Angstrom exponent (AAE) of 1.48, and an increase in the Angstrom exponent (α) up to 1.53. Furthermore, local dust aerosols derived from road dust and/or construction dust also led to higher values of AOD (2.68) and AAE (2.16), and a daily average value of α of 1.05. For the biomass-burning plume, the aerosol particles exhibited significant variations in short-wavelength spectra. The single scattering albedo at 670 nm decreased remarkably under the influence of the biomass-burning plume, indicating the significant absorptive ability of the biomass-burning pollution and higher ratio of absorption aerosols within the plume. Under the effects of the biomass-burning, the volume concentration of fine-mode aerosols increased significantly and the PM-fine/PM-coarse volume concentration ratio reached 12.33. This relatively large change in fine-mode particles indicates that biomass-burning has a greater impact on fine-mode aerosols than on coarse-mode aerosols.     

MODELING OF ORGANIC CARBON AEROSOL DISTRIBUTIONS OVER EAST ASIA IN THE SPRINGTIME

1. Introduction Atmospheric aerosols are a chemical mixture of solid and liquid particles suspended in ambient air. They range in size from the smallest superfine particles, having di-ameters of a few nano-meters (nm), to coarse mode parti-cles, with diameters of several micrometers (mm) or more. From a climatic point of view, probably the most critical subset of atmospheric aerosols are those in the fine or accumulation mode, having diameters ranging from about 0.1 mm to a few micrometers. Th…     

COMPARISON OF SIMULATING MINERAL DUST AEROSOLS IN EAST ASIA BY TWO EMISSION SCHEMES

Two common surface-dust emission schemes using critical wind speed and friction velocity were compared with the regional climate model RegCM3 in East Asia. In the comparison, transport of mineral dust and its distribution were simulated from March to April, 2001. Simulation results were also compared with TOMS aerosol index, showing that obvious differences exist in dust emission quantity and its column burden simulated by the dust emission schemes of friction velocity and wind speed criteria. The results obtained by the wind speed criterion are higher than that by friction velocity, bringing forth the problem whether or not the dust emission scheme matches the model. The obvious difference in the two schemes also explains the uncertainty of simulating mineral dust aerosol by modeling.     

Transport of black carbon aerosols from non-local sources: A case study in Shanghai

Black carbon (BC) aerosol mass carried by winds of varying directions from non-local sources was estimated based on hourly measured data of BC mass concentration (C_BC) and meteorological parameters from January 2008 to December 2012 in Shanghai, and the relationship between annual average C_BC and wind speed was analyzed. The results show that the annual average C_BC decreased with wind speed for speeds exceeding 0.3 m/s. The relationship between the two was determined by a linear fit with correlation coefficient 0.88. Assuming BC aerosol mass of non-local sources transported by a southeast wind was zero, annual average BC concentrations (μg/m³) carried by winds of variable direction were 1.99 (southwest), 1.95 (west), 1.15 (northwest), 0.54 (south), 0.39 (north), 0.01 (northeast), and 0.01 (east). BC aerosol mass of non-local sources transported by wind to Shanghai was about 6404.05 t per year, among which the total contribution of southwest, west, and northwest winds was nearly 84%. The aerosol mass transported to Shanghai in winter accounted for 35% that of the entire year, and was greater than that of the other seasons.     

Magnetic filtration of an iron oxide aerosol by means of magnetizable grates

The cleaning of gases with low concentrations of small ferromagnetic or paramagnetic particles is a difficult task for conventional filtration. A new alternative procedure, magnetic filtration, is used in this work. Iron oxide aerosol was generated by elutriation of iron oxide particles from a fluidized bed consisting of a mixture of Geldart-C iron oxide powder and large spherical Geldart-B sand particles. The aerosol was filtered by means of a magnetic filter which consisted of one, two or three iron grates staggered to each other. The experimental installation contained also an isokinetic sampling system and a Microtrac SRA 150 Particle Analyser. A theoretical expression for filtration efficiency was deduced from a previous model taking into account the different forces acting on the iron oxide particles. Experimental filtration efficiency matches quite well calculated theoretical efficiency. It was found that an increase in particle size, in thee number of grates or in the applied magnetic field produced higher filtration efficiencies up to 100% in some cases. In all filtration experiments pressure drop through the magnetic filter was very small.     

球型密闭容器中铝粉爆炸机理的研究

对中心点火球型密闭容器中的铝粉爆炸进行了实验和理论两方面的研究。实验采用２０立升的球。除测量压力外，还通过系踪平均法测试了流场的湍流强度，并利用电子显微镜和Ｘ光衍射仪分析了铝粉及其燃烧后残渣的形状和组分。文中对２０立升和５０立升球型容器中铝粉燃烧的全过程进行了数值模拟。对于可测量的量如压力和压力上升速率，计算结果与实验结果基本相符。基于反应区外质点的熵几乎不变这一事实，对计算获得的参数剖面还进行了理论分析。     

TENSILE STRENGTH FOR SPLITTING FAILURE OF BRITTLE PARTICLES WITH CONSIDERATION OF POISSON''''S RATIO

1. Introduction The core mechanism of comminution could be reduced to the breakage of individual particles that occurs through contact with other particles or with the grinding media, or with the solid walls of the mill (Potapov & Campbell, 1994). When a particle is subjected to a load, the nature of the stress field around and within the brittle particle, its material properties, and the size and distribution of micro-flaws within the particle govern the size and shape distribution of the fra…     

INTERACTION-MEDIATED GROWTH OF CARBON NANOTUBES ON ACICULAR SILICA-COATED a-Fe CATALYST BY CHEMICAL VAPOR DEPOSITION BY CHEMICAL VAPOR DEPOSITION

1. Introduction Carbon nanotubes (CNTs), a kind of the most advanced nanomaterials with novel properties and promising for many applications, have aroused great interest of the world in a number of research fields (Iijima, 1991; Baughman et al., 2002; Iijima & Ichihashi, 1993; Rao & Govindaraj, 2002; Rueckes et al., 2000; Adrian et al., 2001; Javey et al., 2003). Catalytic chemical vapor deposition (CCVD) is re-garded as the most suitable method for the preparation of microstructured CN…     

INTERACTION-MEDIATED GROWTH OF CARBON NANOTUBES ON ACICULAR SILICA-COATED α-Fe CATALYST BY CHEMICAL VAPOR DEPOSITION

Multi-walled carbon nanotubes (MWNTs) with 20 nm outer diameter were prepared by chemical vapor deposition of ethylene using ultrafine surface-modified acicular α-Fe catalyst particles.The growth mechanism of MWNTs on the larger catalyst particles are attributed to the interaction between the Fe nanoparticles with the surface-modified silica layer.This interaction-mediated growth mechanism is illustrated by studying the electronic,atomic and crystal properties of surface-modified catalysts and MWNTs products by characterization with X-ray diffraction (XRD),transmission electron microscopy (TEM),high resolution transmission electron microscopy (HRTEM),thermal gravimetric analysis (TGA) and Raman spectra.     

Effects of the mass and volume shrinkage of ground chip and pellet particles on drying rates

The effects of varying the mass and volume of ground chip and pellet particles on the particle drying rate were analyzed. Samples of whole pellets and chips were hammer milled using a 3.2 mm screen and the ground chip and pellet particles were found to have similar size distributions, although the pellet particles were denser and more spherical than the chip particles. Prior to drying, water was added to the particles to obtain 0.10, 0.30, 0.50, 0.70, and 0.90 moisture contents (on a dry mass basis). The moistened particles were subsequently dried in a constant temperature thin layer dryer set at 50, 100, 150, or 200 °C under dry pure nitrogen, dry compressed air, or atmospheric air. The chip and pellet particles exhibited similar degrees of shrinkage, but the pellet particles underwent a greater reduction in their bulk volume during drying. It appears that the more spherical pellet particles are prone to shrinkage in more than one direction, whereas the needle-like chip particle shrink only in one direction. A variable radius first order drying model was found to fit the experimental data better than a fixed radius model.     

PREPARATION OF TiO2 PHOTOCATALYST ANCHORED ON ACTIVATED CARBON FIBERS AND ITS PHOTODEGRADATION OF METHYLENE BLUE

TiO2 particulate photocatalyst anchored on activated carbon fibers (ACFs) was prepared by a molecular adsorption-deposition method. The TiO2 particles deposited on the carbon fibers formed a coating of about 100 nm in thickness. The photocatalyst prepared was characterized by means of SEM, EDS, XRD and UV-vis adsorption spectroscopy. Anatase-type TiO2 was uniquely developed, and the micrographic structure of ACFs was not damaged during preparation. The roomy space between adjacent carbon fibers could allow UV-light to penetrate into the felt-form photocatalyst to a certain depth, so that a three dimensional environment was formed for the photocatalytic reaction.Such TiO2/ACFs photocatalyst exhibited its photocatalytic reactivity in photodegradation of concentrated methylene blue(MB) solutions. The MB molecules in the bulk solutions was supposed to be condensed around TiO2 particles by adsorption by ACFs. Therefore, the photocatalyst possesses the combined effect of adsorption by activated carbon fibers and photocatalytic reactivity of anatase-type TiO2 on MB photodegradation.     

Fluidization behavior of graphitized glassy particles in a fluidized carbon bed cooling process for investment casting

Fluidized Carbon Bed Cooling (FCBC) is an innovative investment casting process for directional solidification of superalloy components. It takes advantage of a fluidized bed with a base of small glassy carbon beads for cooling and other low-density particles that form an insulating layer by floating to the bed surface. This so-called “Dynamic Baffle” protects the fluidized bed from the direct heat input from the high-temperature heating zone and provides the basis for an improved bed microstructure. The prerequisites for a stable casting process are stable fluidization conditions where neither collapse of the bed nor particle blow out at excessive bubble formation occur.This work aimed to investigate the fluidization behavior of spherical carbon bed material in argon and air at temperatures between 20 to 350 °C. Systematic studies at reduced pressures using the FCBC prototype device were performed to understand the stable fluidization conditions at all stages of the investment casting process. The particle shape factor and size distribution characterization and the measurement of the powder’s minimum fluidization velocity and bed voidage show that this material can be fully utilized as a cooling and buoyancy medium during the FCBC process.     

Enhancement of filtration efficiency by electrical charges on nebulized particles

There have been few investigations of effects of electrical charge, carried by lab-generated particles, on filtration efficiency testing. Here, we measured the elementary charge on particles and the fraction of particles carrying that charge with a combined electrometer, differential mobility analyzer, and scanning mobility particle sizer. A typical solid NaCl aerosol and liquid diethylhexyl sebacate (DEHS) aerosol were generated with Collison and Laskin nebulizers, respectively. Our experimental results showed that NaCl aerosols carried more charge after aerosol generation. The average net elementary charge per particle was approximately 0.07. The NaCl aerosol was overall positively charged but contained a mixture of neutral and charged particles. Individual particles could carry at most four elementary charges. According to constant theorem, we speculated that original NaCl aerosol contained 17% neutral, 45% positive-, and 38% negative-charged particles in the diameter range from 30 to 300 nm. A Kr-85 neutralizer was used to decrease the charge on the NaCl particles. Our results indicated that the DEHS aerosol was electrically neutral. The effects of electric charge on particle collection by electret and electroneutral high efficiency particulate air (HEPA) filters were analyzed. Theoretical calculations suggested that charges on original NaCl aerosol particles enhanced the filtration efficiency of HEPA filters.     

碳纳米管的力学

在发现碳纳米管后不久,对于这些有趣结构的力学性质--包括高强度、高硬度、低密度和结构的完美性的理论预测,使人们认识到它们可能具有理想的科技应用价值.对这些预测的实验验证或个别验伪以及大量基于不同模型的计算机模拟方法,使得逾10年来对碳纳米管力学的理解日趋深入但远未达到尽头.本文回顾了理论预测,并对这种微小结构的观察和操作中经常用到的富有挑战性的实验技术进行了讨论.略述了采用的计算方法包括从头算法量子力学模拟、经典分子动力学和连续介质模型.多尺度和多物理模型的发展和模拟工具自然而然作为连接基础科学问题和工程应用的结果而出现,而这个主题仍然正在抓紧研究中.这里介绍了研究此主题的一些方法.注意力主要集中于研究力学性质的揭示方面,如杨氏模量、弯曲刚度、屈曲准则、拉伸和压缩强度.最后,讨论了利用这些性质的几个令人兴奋的应用例子,包括纳米绳束、填充的纳米管、纳米机电系统、纳米传感器和纳米管增强复合材料,引用了349篇参考文献. 图41参349     

Bi-Pb-Sn-Cd四元合金纳米微粒的制备及其摩擦磨损性能研究

通过直接对Bi-Pb-Sn-Cd四元块状合金进行超声分散制备了相应的四元合金纳米微粒;采用X射线衍射仪和热分析仪分析所制备的纳米微粒结构;采用透射电子显微镜考察了纳米颗粒的形貌及尺寸分布;采用四球摩擦磨损试验机考察了纳米颗粒的摩擦学性能.结果表明,所制备的纳米颗粒为低熔点共晶合金纳米微粒,颗粒平均尺寸在10～20 nm之间,其作为润滑油添加剂表现出良好的摩擦学性能.     

颗粒增强复合材料压缩行为的位错动力学模拟

颗粒增强铜基复合材料因具有极高的强度和弹性模量, 优异的导电、导热性能和抗磨损能力, 被广泛应用于航天航空、汽车、电子工业等领域. 第二相强化是其主要的强化方式, 其通过合金中弥散的微粒阻碍位错运动, 可有效提高金属材料的力学性能, 提高其服役安全. 针对该问题本文采用三维离散位错动力学(three-dimensional discrete dislocation dynamics, 3D-DDD)方法, 对微尺度颗粒增强铜基复合材料进行了微柱压缩模拟, 分析了位错与第二相颗粒交互作用对材料力学响应的影响, 揭示第二相颗粒强化的微观机理. 本研究将第二相颗粒视为位错不可穿透的球形微粒, 采用位错绕过机制模拟颗粒与位错的交互作用过程. 通过调控滑移面相对于第二相颗粒中心的距离发现: 屈服应力和应变硬化率均随距离的增大而减小. 研究也发现Schmid因子越高的滑移系, 屈服应力越低, 后续应变硬化率越低. 多位错与颗粒交互作用的模拟发现, 同一滑移面中位错间的反应和不同滑移系中位错的交互作用可能是导致屈服应力和应变硬化率降低的关键.      

Aerosol observation in Fengtai area, Beijing

Measurements of aerosol number concentration and particulate matter with diameter less than 10μm (PM10) mass concentrations of urban background aerosols were performed in Fengtai area, Beijing in 2006. Black carbon (BC) was collected simultaneously from the ground and analyzed to determine the particulate matter components. To satisfy the interest in continuous monitoring of temporal and spatial distribution of aerosols, the relationship between extinction coefficient (visibility) measured by lidar remote sensing and the aerosol number concentration measured from the ground was derived by using statistical method. Vertical particle number concentration profile within the planetary boundary layer could be inversed through the lidar data as well as the statistical relation.