AN EXPERIMENTAL STUDY ON VERTICAL HYDRODYNAMIC FORCE ON A CIRCULAR SLAB NEAR FREE SURFACE BY WATER WAVES

An experimental study has been carried out to investigate the vertical force on a slab of sea-crossing bridge piers in the cases of different hydrodynamic conditions. The experimental study is divided into two parts in terms of regular waves and irregular waves. The hydrodynamic loads acting on the slab are measured by a six component balance and pressures on the bottom of the slab are measured by pressure transducers. It turns out that the vertical lbrce patterns can be considered as impact type and bouyant uplili type. For these two different patterns, time series of the vertical hydrodynamic forcc are measured and analyzed. The influences of wave height, wave period, clearance height of slab on the vertical force arc discussed in detail.

Historical records of polycyclic aromatic hydrocarbon deposition in a shallow eutrophic lake:Impacts of sources and sedimentological conditions

Sediment core samples collected from Lake Chaohu were analyzed for 15 priority polycyclic aromatic hydrocarbons（PAHs）to assess the spatial and temporal distributions of the PAHs during lacustrine sedimentary processes and regional economic development.Assessing the PAH sedimentary records over an approximately 100-year time span,we identified two stages in the PAH inputs and sources（before the 1970 s and after the 1970s）in the eastern lake region near a village,whereas three stages（before the 1950 s,1950s–1990s and after the1990s）were identified in the western lake region near urban and industrial areas.Rapid increases in the PAH depositional fluxes occurred during the second stage due to increased human activities in the Lake Chaohu basin.The composition and isomeric ratios of the PAHs revealed that pyrolysis is the main source of PAHs in this lake.Strong positive relationships between PAH concentration and the total organic carbon concentration,sediment grain size（〈 4 μm）,as well as the local population and Gross Domestic Product indicated that the sedimentary conditions impact the depositional characteristics of the PAHs;simultaneously,socioeconomic activities,such as energy consumption and the levels of urban industrialization and civilization,affect both the composition and abundance of the PAHs.

Two-year measurements of surface ozone at Dangxiong,a remote highland site in the Tibetan Plateau

Measurements of surface O3 and carbon monoxide（CO） were made from September 2009 to August 2011 at Dangxiong（30.48°N, 91.10°E, 4187 m a.s.l.）, a remote highland site in a southern valley of the Nyainqêntanglha Mountains in the Tibetan Plateau, China. The monthly mean O3 mixing ratio ranged from 29.1 to 51.4 ppb, with an average of 38.5 ppb, and the maximum value was observed in May. The average diurnal cycle of O3 concentration showed a minimum in early morning and a maximum in the afternoon, with a broader ＂high platform＂ from the late morning to the late afternoon, and resembled that of surface wind speed. The concentration of surface O3 was highly significantly correlated with tropospheric column O3 over the regions surrounding Dangxiong and with that of surface O3 observed at a site north of the Nyainqêntanglha Mountains, suggesting a good regional representativeness of surface O3 at Dangxiong. In the afternoon when stronger winds blew, surface air showed distinct features of free-atmospheric air, with higher O3, lower CO, and lower relative humidity（RH）. The negative O3-CO and O3-RH correlations in most months indicate a significant influence of air masses from the free troposphere. Trajectory analysis suggests that air masses originating from the south of the site make a negative net contribution to surface O3 and a positive contribution to CO and humidity, and those from the northwest sector contribute conversely to the respective quantities.