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681.
682.
The distributions of the partial pressure of carbon dioxide (pCO2) and total alkalinity (TA) were examined for a 6-month period in the Wailuku and Wailoa rivers and coastal waters of Hilo
Bay on the west coast of the Island of Hawaii, USA. Main results for the largest and turbulent Wailuku River show in the watershed
an oversaturation in CO2 with respect to atmospheric equilibrium and a CO2 undersaturation in the estuary. In the Wailoa river-estuary system, extremely high pCO2 values ranging from 1500 to 10500 ppm were measured with significant shifts in pCO2 from drought to flood period. In the two rivers, water residence time, groundwater inputs and occasional flood events are
the predominant drivers of the spatial and temporal patterns in the distribution of pCO2. In Hilo Bay, CO2 oversaturation dominates and the bay was a source of CO2 to the atmosphere during the study period. TA is conservative along the salinity gradient, indicating calcification in the
bay is not a significant source of CO2 to the atmosphere. 相似文献
683.
Sea level measurements along the southeastern Brazilian coast, between 20° S and 30° S, show the effect of the Sumatra Tsunami
of December 26, 2004. Two records from stations, one located inside an estuary and other inside a bay, shows oscillations
of about 0.20 m range; one additional record from a station facing the open sea shows up to 1.2 m range oscillations. These
oscillations have around 45 min period, starting 20–22 h after the Sumatra earthquake in the Indian Ocean (00:59 UTC) and
lasting for 2 days. A computer modelling of the event reproduces the time of arrival of long shallow-water tsunami waves at
the southeastern Brazilian coast but with slight longer period and amplitudes smaller than observed at the coast, probably
due to its coarse resolution (1/4 of a degree). The high amplitudes observed at the coast suggest a mechanism of amplification
of these waves over the southeastern Brazilian shelf. 相似文献
684.
Mahmoud M. El Banna 《Environmental Geology》2007,52(1):41-49
Beach profile data, covering the coast of Ras El Bar, northeast Nile Delta, collected during the years from 1990 to 2002 combined
with landsat images for the area and sedimentological investigation have been used to identify beach and nearshore seafloor
sediment changes. Along the coast of Ras El Bar, two accretion sectors and one of erosion have been recognized. The first
accretion sector is located west of Damietta harbour, where the harbour jetties have halted the littoral transport, while
the second one is behind a system of detached breakwaters protecting Ras El Bar resort. Both the two sectors are characterized
by growing shoreline with maximum rates ∼15 and 10 m/year, respectively. Also, they have maximum nearshore seafloor accretion
rates of ∼18 and 22 cm/year, respectively. The erosion sector is located east of Damietta port and has a maximum rate of shoreline
retreat ∼−10 m/year. Erosion of its nearshore seafloor is indicated recording a maximum rate of ∼−20 cm/year. The rate of
net sediment volume change in the area indicates shifting of the accretion sector (II) westward, responding to installation
of the new breakwaters unit. The two accretion sectors are characterized by dominance of moderately sorted fine sands in their
shore area which change seaward into less sorting very fine sands. Beach sands of the eroded sector are poorly sorted medium
grain size. The dominant constituents of heavy mineral species in beach and sea-bottom sands are the characteristic assemblages
of the Nile deposits. The sands of the eroded zone are relatively enriched in monazite, zircon, tourmaline, garnet, and rutile. 相似文献
685.
Collapse hazard zonation of qanats in greater Tehran area 总被引:2,自引:0,他引:2
Mohammad H. T. Rayhani M. Hesham El Naggar 《Geotechnical and Geological Engineering》2007,25(3):327-338
Abstarct Several cases of subsidence occurred in greater Tehran resulting from collapse of walls of underground water channel system
known locally as qanat. Many mechanisms contribute to the qanat collapse, which add to the complexity of the problem. The
present research focuses on identifying the main factors that influence qanat collapse and the parameters that should be considered
in modeling their behavior. Some of the important factors that influence the stability and performance of qanats and considered
in the analysis presented here include: qanat geometrical characteristics; loading due to surface structures; underground
water level and geotechnical properties of the soil. A suitable model was chosen and deformational behavior of qanat walls
was simulated. The stability of qanats was evaluated considering both elastic and elasto-plastic soil models. It was found
that qanats in north and northeastern parts of Tehran have high strength and qanats in south and southwestern parts have low
strength. A GIS-based qanat collapse hazard zonation map was prepared. It was found that the hazard of collapse increases
for shallow qanats with any structural loads imposed at the ground surface. As expected, this hazard is much higher for qanats
situated in weak soils. Furthermore, the hazard of collapse is much higher for qanats with larger diameter. 相似文献
686.
687.
688.
689.
H. Evangelista J. Maldonado R. H. M. Godoi E. B. Pereira D. Koch K. Tanizaki-Fonseca R. Van Grieken M. Sampaio A. Setzer A. Alencar S. C. Gonçalves 《Journal of Atmospheric Chemistry》2007,56(3):225-238
The total extent of the atmospheric impacts associated to the aerosol black carbon (BC) emissions from South America is not
completed described. This work presents results of BC monitored during three scientific expeditions (2002, 2003 and 2004)
on board of a Brazilian oceanographic vessel Ary Rongel that covered the South–West Atlantic coast between 22–62°S. This latitudinal
band encloses major urban regions of South America and the outflow region of the SACZ (South Atlantic Convergent Zone), which
is an important mechanism of advective transport of heat, moisture, minor gases and aerosols from the South America continental
land to the Southern Atlantic Ocean. Our results showed that aerosol BC enhanced concentrations from urban/industrial origin
can be transported to the South–West Atlantic Ocean due to the migration of sub-polar fronts that frequently reach tropical/subtropical
regions. Despite the decrease of aerosol BC concentrations southwards (from ∼1,200 ng m−3 at latitude 22°S to ∼10 ng m−3 at latitude 62°S), several observed peak events were attributed to regional urban activities. Most of such events could be
explained by the use of air mass back trajectories analysis. In addition, a global model simulation is presented (Goddard
Institute for Space Studies – GISS GCM BC simulation) to explore the origins of aerosol BC in the South–West Atlantic. The
model allowed isolating the biomass emissions from South America and Africa and industrial (non-biomass) pollution from other
regions of the globe. This model suggests that the apportionment of about half of the aerosol BC at the South–West Atlantic
may derive from South American biomass burning. 相似文献
690.
A micro-mechanical investigation of the dynamic response and liquefaction of saturated granular soils 总被引:4,自引:0,他引:4
A coupled continuum-discrete hydromechanical model was utilized to analyze the meso-scale pore fluid flow and micro-scale solid phase deformation of saturated granular soils. The fluid motion was idealized using averaged Navier–Stokes equations and the discrete element method was employed to model the solid particles. Well established semi-empirical relationships were used to quantify the fluid–particle interactions. Numerical simulations were conducted to investigate the mechanisms of granular deposit liquefaction in the presence of a critical upward pore fluid flow as well as when subjected to a dynamic base excitation. The outcome of these simulations was consistent with experimental observations and revealed valuable information on the micro-mechanical characteristics of soil liquefaction and associated loss of stiffness and strength. 相似文献