Increase Of Coarse Particles Research Articles

Anisotropic Resilient Modulus Model of Granular Materials Based on Particle Characteristics

Granular materials are widely used for bases or subbases in pavement structures. They typically exhibit strong anisotropic properties which relate to stress states and particle characteristics. The conventional design procedure for flexible pavements underestimates the anisotropy of resilient moduli. This study established an anisotropic resilient modulus model for granular materials that considered gradation and particle shape characteristics. Vertical and horizontal resilient moduli of certain granular materials were measured in self-developed triaxial tests to obtain corresponding model parameters and anisotropic coefficients. Gradation and particle shape models were established to quantify the granular material characteristics, and the parameters were regressed. Particle shapes were obtained via image processing, and the ratio ( η) of particle sphericity to roundness was chosen as a shape parameter. Results show that η increases with the decrease in particle size, and the average values of η for graded gravel and natural laterite are 0.54 and 0.63, respectively. The η distribution curves indicate that the proportion of relatively anisotropic particles, rather than extremely anisotropic particles, results in the differences in particle shape characteristics. The regression relationship between the anisotropic calculation parameters and the model parameters of vertical resilient modulus, gradation, and particle shape was established. Thus, the horizontal resilient modulus and the anisotropic coefficient can be predicted via conventional resilient modulus tests and gradation, and particle shape analysis. This study shows that the anisotropy of granular materials decreases with the increase in coarse particles and the uniformization of the particle size distribution, and it increases with the increase in anisotropic particles and the polarization of the η distribution.

Climate Change and Vegetation Evolution during the Transition from Marine Isotope Stage 5 to 4 Based on Two Typical Profiles at the Southern Chinese Loess Plateau

The geological transitional period from the Marine Isotope Stage (MIS) 5 to 4 during the Quaternary period is a multidimensional change involving monsoon and precipitation variation, vegetation dynamics, and environmental evolution. The first loess layer (L1) and the first paleosol layer (S1) in the Chines Loess Plateau provide excellent high-resolution terrestrial sediment record for this transition. In this work, grain size (GS), CaCO3 content, magnetic susceptibility (MS), and pollen composition were measured at intervals of 2-cm in two representative L1/S1 profiles in the southern Chinese Loess Plateau to reconstruct records of climatic and vegetative changes during this transition. Our results showed that, in general, the paleo-vegetation type was forest-steppe, with Pinus being the commonest tree, and Chenopodiaceae and Artemisia being common herbs in the study area. The topography had a significant impact on the distribution of paleo-vegetation. The increase of coarse particles, the decrease of magnetic susceptibility, and the rising percentage of Gramineae, Artemisia and Chenopodiaceae pollen, all indicated that the paleoclimate became cooler and drier over the transitional period. Besides, we identified a cool event at about 76.8 ka B.P. as revealed by grain-size curves, and in response to this event, the vegetation changed significantly but lagged several hundred years behind the grain size record. This study confirmed the cooling and drying tendency during the MIS 5 to 4 transition phase in the southern margin of the Chinese Loess Plateau. These findings shed light on the climatic change on vegetation evolution during the MIS 5 to 4 transition period.

Strength and Deformation Characteristics of Silty Sand improved by Gravel

Silty sand is a poor filler of highway and railway subgrade, and various physical and chemical improving methods have been applied to increase the strength and stability of silty sand. Adding gravel to silty sand is a routine physical improving method. In this paper, large-scale triaxial tests were carried out on silty sand and improved soil which is obtained by adding 4 different proportions of gravel into the silty sand in order to analyze the strength and deformation characteristics of the improved soil. The stress-strain relations obtained from tiaxial tests were analyzed and the effect of coarse particles and fine particles on the strength and deformation of the specimen were also analyzed. The test results show that with more coarse particles and under a higher confining pressure, a greater deviator stress is required to produce the same axial strain. The increase of coarse particles helps to enlarge the angle of internal friction and cohesion, while the increase of fine particles decreases the angle of internal friction and cohesion. Under low confining pressure, the soil specimens with more coarse particles exhibit evident shear dilation. Under high confining pressure, the soil specimens produce a greater volume strain. Adding appropriate amount of gravel into the silt soil can increase its strength and restrain its deformation, but excessive amount of gravel may produce too much volume deformation.

Did policies to abate atmospheric emissions from traffic have a positive effect in London?

A large number of policy initiatives are being taken at the European level, across the United Kingdom and in London to improve air quality and reduce population exposure to harmful pollutants from traffic emissions. Trends in roadside increments of nitrogen oxides (NOX), nitrogen dioxide (NO2), particulate matter (PM), black carbon (CBLK) and carbon dioxide (CO2) were examined at 65 London monitoring sites for two periods of time: 2005–2009 and 2010–2014. Between 2005 and 2009 there was an overall increase in NO2 reflecting the growing evidence of real world emissions from diesel vehicles. Conversely, NO2 decreased by 10%·year−1 from 2010 onwards along with PM2.5 (−28%·year−1) and black carbon (−11%·year−1). Downwards trends in air pollutants were not fully explained by changes in traffic counts therefore traffic exhaust emission abatement policies were proved to be successful in some locations. PM10 concentrations showed no significant overall change suggesting an increase in coarse particles which offset the decrease in tailpipe emissions; this was especially the case on roads in outer London where an increase in the number of Heavy Good Vehicles (HGVs) was seen. The majority of roads with increasing NOX experienced an increase in buses and coaches. Changes in CO2 from 2010 onwards did not match the downward predictions from reduced traffic flows and improved fleet efficiency. CO2 increased along with increasing HGVs and buses. Polices to manage air pollution provided differential benefits across London's road network. To investigate this, k-means clustering technique was applied to group roads which behaved similarly in terms of trends to evaluate the effectiveness of policies to mitigate traffic emissions. This is the first time that London's roadside monitoring sites have been considered as a population rather than summarized as a mean behaviour only, allowing greater insight into the differential changes in air pollution abatement policies.

Multi-Satellite Observation of an Intense Dust Event over Southwestern China

This study presents the results of a large-scale examination into a dust event that took place over southwestern China, an area that has received relatively little attention in the literature. The sources, transport path, and vertical distribution, as well as formation process of an intense dust storm event that took place over the Sichuan Basin from March 9 to March 14, 2013, were investigated using combined multiple satellite observations and meteorological data. Widespread dust plumes appeared over the Taklimakan Desert, Gobi Desert, and Loess Plateau on March 9. Different from the usual dust storms, the dust plumes did not move downstream directly but settled over the Loess Plateau and Sichuan Basin for several days. Persistent southwestern winds prevailed over eastern China during this period, and could prevent the dust storms from moving directly downstream. Our results suggest that the dust plumes over southwestern China mainly originated from the Gobi Desert. Despite extensive dust plumes over all the Sichuan Basin, PM10 increased sharply to more than 1200 μg/m^3 in the western part of the basin, with only a slight increase in the eastern part. When there was a sharp increase in coarse particles in Chengdu on March 11 and 14, northeasterly winds appeared over northern China. The elevated dust can be blown to the eastern slope of the Tibetan Plateau and deposited in the western Sichuan Basin. However, such intense dust events are not common in southwestern China. In addition, floating dust may not be observed near the surface, but can have an important impact on regional aerosol loading and properties.

Column-integrated aerosol optical and physical properties at a regional background atmosphere in North China Plain

The AERONET level 2.0 data at Xinglong station from February 2006 to July 2011 were used to characterize the aerosol optical and physical properties, including temporal variability, aerosol absorption, classification and properties under dust and haze conditions. The annual mean aerosol optical depth (AOD) and extinction Angstrom exponent (EAE) are 0.28 ± 0.30 and 1.07 ± 0.38, respectively. The seasonal variations of AOD440nm are higher in spring (0.40 ± 0.3) and summer (0.40 ± 0.42) than in autumn (0.20 ± 0.22) and winter (0.19 ± 0.21). The EAE is low in spring (0.96 ± 0.43) and high in summer (1.22 ± 0.38). The EAE is ∼1.25 with an absorption Angstrom exponent (AAE) of ∼1.0–1.5 in Xinglong, which indicates that the dominant type is mixed aerosol (accounting for 88.2% at AAE > 1.0). Almost all of the dust observations occurred in spring. The volume concentrations of both fine and coarse mode particles increase with increasing AOD. In spring, the increase of coarse particles is greater than that of fine aerosols; however, the reverse phenomenon is observed for other seasons. The high AOD at Xinglong could be associated with the growth of fine mode aerosols and addition of coarse mode particles. This background station is not only impacted by dust aerosols from northwest China and south Mongolia but also influenced by long-range transportation of anthropogenic aerosols from south urban and industrialized regions. The mean AOD was 1.49 on the dust day, while AOD was 1.10 on the haze day. The mean EAEs were 0.09 and 1.43 on dust and haze days, respectively.

Aerosol characterization in Northern Africa, Northeastern Atlantic, Mediterranean Basin and Middle East from direct-sun AERONET observations

Abstract. We provide an atmospheric aerosol characterization for North Africa, Northeastern Atlantic, Mediterranean and Middle East based on the analysis of quality-assured direct-sun observations of 39 stations of the AErosol RObotic NETwork (AERONET) which include at least an annual cycle within the 1994–2007 period. We extensively test and apply the recently introduced graphical method of Gobbi and co-authors to track and discriminate different aerosol types and quantify the contribution of mineral dust. The method relies on the combined analysis of the Ångström exponent (α) and its spectral curvature δα. Plotting data in these coordinates allows to infer aerosol fine mode radius (Rf) and fractional contribution (η) to total Aerosol Optical Depth (AOD) and separate AOD growth due to fine-mode aerosol humidification and/or coagulation from AOD growth due to the increase in coarse particles or cloud contamination. Our results confirm the robustness of this graphical method. Large mineral dust is found to be the most important constituent in Northern Africa and Middle East. Under specific meteorological conditions, its transport to Southern Europe is observed from spring to autumn and decreasing with latitude. We observe "pure Saharan dust" conditions to show AOD>0.7 (ranging up to 5), α<0.3 and δα<0 corresponding to η<40% and (Rf)~0.13 μm. Small pollution particles are abundant in sites close to urban and industrial areas of Continental and Eastern Europe and Middle East, as well as, important contributions of biomass burning are observed in the sub-Sahel region in winter. These small aerosols are associated to AOD<1, α>1.5 and δα~−0.2 corresponding to η>70% and Rf~0.13 μm. Here, dust mixed with fine pollution aerosols shifts the observations to the region α<0.75, in which the fine mode contribution is less than 40%.

噴霧条件による二次液滴の発生量・気中濃度・付着量変化

To improve the working environment of farmers, the spray test of liquid pesticide was made in a testing greenhouse. TPN (75% wettable powder) diluted 800-fold was sprayed under the various spray conditions, and the change of aerial concentration and sticking amount to a filter paper were measured.And the generation amount of secondary droplets which generate from the target was also measured.The experimental results are summarized as follows.1. The aerial concentration increased with the rise of spray pressure, and this increase greatly depended on the increase of coarse particles more than7μm.2. The humidity in the greenhouse greatly influenced the aerial concentration. When the pesticide was sprayed in a high humidity atmosphere, the aerial concentration become smaller because of the evident decrease of respirable particles less than 7μm.3. The sticking amount increased with the spray pressure rise.4. The generation amount of secondary droplets increased linearly with the spray pressure rise. However, with the increase of nozzle number and low pressure spray, the generation amount could be obviously decreased without reduction of the flow rate. The generation rates of secondary droplets were 13-20%. On the basis of this result, it was proved that about 20% of pesticide sprayed in a cultivating field scatters in the air.

Characteristics of Eolian Influenced Soils in Connecticut: I. Physical Properties

AbstractField and laboratory studies were made on soils strongly influenced by loess in the Central Lowland of Connecticut. Laboratory samples were obtained from 10 profiles located on a grid sampling system in an area east of the Connecticut River. Depth of the loess mantle had an important influence on the particle size composition of the profiles. The greater amounts of coarse particles in the shallower profiles are believed to be due to mixing with the underlying unconformable materials, probably through frost action and tree throw. An increase in coarse particles from the underlying material in the profile results in reductions in water‐holding capacity, capillary pore volume and penetrability, and increases in bulk density and non‐capillary pore volume, but with only a small change in permeability.