Estimation of the PAR irradiance ratio and its variability under clear-sky conditions at ieodo in the east china sea     

Do -Seong Byun  Yang -Ki Cho 《Ocean Science Journal》2006,41(4):235-244

Determining ‘photosynthetically active radiation’ (PAR) is a key part of calculating phytoplankton productivity in a biogeochemical model. We explore the daily and seasonal variability in the ratio of PAR irradiance to total irradiance that occurred at Ieodo Ocean Research Station (IORS) in the East China Sea under clear-sky conditions in 2004 using a simple radiative transfer model (RTM). Meteorological data observed at IORS and aerosol optical properties derived from Aerosol Robotic Network observations at Gosan are used for the RTM. Preliminary results suggest that the use of simple PA R irradianceratio values is appropriate in calculating phytoplankton productivity as follows: an average of 0.44 (±0.01) in January to an average of 0.48 (±0.01) in July, with average daily variabilities over these periods of about 0.016 (±0.008) and 0.025 (±0.008), respectively. The model experiments demonstrate that variations in the major controlling input parameters (i.e. solar zenith angle, precipitable water vapor and aerosol optical thickness) cause PAR irradiance ratio variation at daily and seasonal timescales. Further, increases (>0.012) in the PAR irradiance ratio just below the sea-surface are positively correlated with high solar zenith angles and strong wind stresses relative to those just above the sea-surface.  相似文献   

Effect of saline intrusion on the properties of cohesive soils in the Red River Delta,Vietnam     

Nguyen Ngoc Truc  Lena Mihova  Toshifumi Mukunoki  Duc Minh Do 《Marine Georesources & Geotechnology》2020,38(1):23-39

Abstract

This study conducted a series of laboratory experiments and established numerical models on selected undisturbed soil samples in the Red River Delta (RRD) to determine the effect of change in soils intruded by saline water. The variation in the technical parameters of soils was verified in soils fully saturated by solution of four salt concentrations, that is, 0.0, 9.9, 19.8, and 33.0?g/L. Results show that the content and composition of clay minerals in cohesive soils before and after saline intrusion are unchanged. The same finding is obtained for clay after removing absorbed water layer by using a centrifuge apparatus. The zeta potential and settlement velocity of soils in the RRD increase when salt is added to the saturated solution. Similarly, the deformation of soils increases proportionally with the salt concentrations of that solution. This result is attributed to the linear decrease in deformation modulus. The decrease in modulus versus salinities is nearly consistent for pressure stages from 100 to 400?kPa. The safety factor of bearing capacity also decreases linearly with salinities. The decrease reaches 12.5–16.3% when soils are in the maximum saline solution. All these changes are considered as the degradation of soils in saline media.  相似文献   

Experimental evaluation of dynamic characteristics of seesaw energy dissipation system for vibration control of structures          下载免费PDF全文

Jae‐Do Kang  Hiroshi Tagawa 《地震工程与结构动力学》2014,43(12):1889-1895

Seesaw energy dissipation system (SEDS), a vibration control system used to provide enhanced seismic protection, has been proposed and investigated numerically. Because of its complicated arrangement, verification experiments are necessary to demonstrate the SEDS damping capacity. This paper presents the results of experimental investigation of the SEDS using fluid viscous dampers. Free vibration tests are conducted to demonstrate the SEDS damping capacity. Results of the free vibration test show that the SEDS has sufficient damping capacity for reduction of the seismic response of the frames. Parametric experimental investigations of the SEDS were conducted, the results of which demonstrate the effects of the system parameter on the damping capacity. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Post‐repair effect of column jackets on aftershock fragilities of damaged RC bridges subjected to successive earthquakes          下载免费PDF全文

Jong‐Su Jeon  Reginald DesRoches  Do Hyung Lee 《地震工程与结构动力学》2016,45(7):1149-1168

In light of recent earthquakes, structures damaged during an initial seismic event (mainshock) may be more vulnerable to severe damage and collapse during a subsequent event (aftershock). In this paper, a framework for the development of aftershock fragilities is presented; these aftershock fragilities define the likelihood that a bridge damaged during an initial event will exhibit a given damage state following one or more subsequent events. The framework is capable of (i) quantifying the cumulative damage of unrepaired bridges subjected to mainshock–aftershock sequences (effect of multiple earthquakes) and (ii) evaluating the effectiveness of column repair schemes such as steel and fiber‐reinforced‐polymer jackets (post‐repair effect of jackets). To achieve this aim, the numerical model of repaired columns is validated using existing experimental results. A non‐seismically designed bridge is chosen as a case study and is modeled for three numerical bridge models: a damaged (but unrepaired) bridge model, and two bridge models with columns repaired with steel and fiber‐reinforced polymer jackets. A series of back‐to‐back dynamic analyses under successive earthquakes are performed for each level of existing damage. Using simulated results, failure probabilities of components for multiple limit states are computed for each bridge model and then are used to evaluate the relative vulnerability of components associated with cumulative damage and column repair. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Fate of Phosphorus in a Grass Buffer Zone Under Concentrated Flow Condition          下载免费PDF全文

Young‐Jin Kim  Hae‐Do Kim  Ji‐Hong Jeon 《洁净——土壤、空气、水》2016,44(6):677-685

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Co-inoculation of Capitella sp. I with its synergistic bacteria enhances degradation of organic matter in organically enriched sediment below fish farms     

Wada M  Zhang D  Do HK  Nishimura M  Tsutsumi H  Kogure K 《Marine pollution bulletin》2008,57(1-5):86-93

A polychaete, Capitella sp. I has been shown to degrade organics actively in organically enriched sediment below fish farms. Our aim of the present study is to enhance the biological treatment of sediment by co-inoculation of Capitella sp. I with bacterial isolates that possess high degrading potential for organic matter. We isolated a total of 200 bacterial strains from fecal pellets, burrow lining, worm body, and sediment, and selected six of them for the degradation experiments in the sediment microcosms. With two out of the six isolates, tentatively identified as Vibrio sp. and Vibrio cyclitrophicus by 16SrDNA sequence, we found the TOC reduction rate was stimulated in sediment co-inoculated with the worms and each of the bacteria. In contrast, this was not observed in sediments inoculated only with the worms or the bacterium. These results strongly suggest that co-inoculation of Capitella sp. I with bacteria improves biodegradation.  相似文献   

Holocene estuarine sediments as a source of arsenic in Pleistocene groundwater in suburbs of Hanoi,Vietnam     

Keisuke Kuroda  Takeshi Hayashi  Ayako Funabiki  An Thuan Do  Vu Duc Canh  Tran Thi Viet Nga  Satoshi Takizawa 《Hydrogeology Journal》2017,25(4):1137-1152

Groundwater pollution by arsenic is a major health threat in suburban areas of Hanoi, Vietnam. The present study evaluates the effect of the sedimentary environments of the Pleistocene and Holocene deposits, and the recharge systems, on the groundwater arsenic pollution in Hanoi suburbs distant from the Red River. At two study sites (Linh Dam and Tai Mo communes), undisturbed soil cores identified a Pleistocene confined aquifer (PCA) and Holocene unconfined aquifer (HUA) as major aquifers, and Holocene estuarine and deltaic sediments as an aquitard layer between the two aquifers. The Holocene estuarine sediments (approximately 25–40 m depth, 9.6–4.8 cal ka BP) contained notably high concentrations of arsenic and organic matter, both likely to have been accumulated by mangroves during the Holocene sea-level highstand. The pore waters in these particular sediments exhibited elevated levels of arsenic and dissolved organic carbon. Arsenic in groundwater was higher in the PCA (25–94 μg/L) than in the HUA (5.2–42 μg/L), in both the monitoring wells and neighboring household tubewells. Elevated arsenic concentration in the PCA groundwater was likely due to vertical infiltration through the arsenic-rich and organic-matter-rich overlying Holocene estuarine sediments, caused by massive groundwater abstraction from the PCA. Countermeasures to prevent arsenic pollution of the PCA groundwater may include seeking alternative water resources, reducing water consumption, and/or appropriate choice of aquifers for groundwater supply.  相似文献   

Observations of ammonia in galacticHii regions     

J. W. S. Vilas Boas  E. Scalise Jr.  J. L. Monteiro Do Vale 《Astrophysics and Space Science》1988,141(2):339-346

The ammonia emission associated with southern galacticHii regions have been studied. Some physical parameters, computed for each individual sources, were derived and a brief discussion follows.  相似文献   

Rainfall-triggered large landslides on 15 December 2005 in Van Canh District, Binh Dinh Province, Vietnam   总被引：2，自引：2，他引：0  

Do Minh Duc 《Landslides》2013,10(2):219-230

Landslides are one of the most dangerous hazards in Vietnam. Most landslides occur at excavated slopes, and natural slope failures are rare in the country. However, the volume of natural slope failures can be very significant and can badly affect large areas. After a long period of heavy rainfall in the fourth quarter of 2005 in Van Canh district, a series of landslides with volumes of 20,000–195,000 m³ occurred on 15 December 2005. The travel distances for the landslides reached over 300–400 m, and the landslides caused some remarkable loud booming noises. The failures took place on natural slopes with unfavorable geological settings and slope angles of 28–31°. The rainfall in the fourth quarter of 2005 is estimated to have a return period of 100 years and was the main triggering factor. Because of the large affected area and low population density, resettling people from the dangerous landslide-prone residential areas to safer sites was the most appropriate solution. In order to do so, a map of landslide susceptibility was produced that took into account slope angle, distance to faults, and slope aspect. The map includes four levels from low to very high susceptibility to landslides.  相似文献   

Limited Consequences of Seagrass Decline on Benthic Macrofauna and Associated Biotic Indicators     

V. Tu Do  Hugues Blanchet  Xavier de Montaudouin  Nicolas Lavesque 《Estuaries and Coasts》2013,36(4):795-807

Marine phanerogams are ecosystem engineers, as their presence induces major environmental changes that impact on the benthic fauna. Consequently, modifications to the structure of benthic communities would be expected to be associated with seagrass decline. Since 2005, Zostera noltii seagrass beds in Arcachon Bay (France), the largest in Europe, have undergone a severe decline. Twelve stations distributed throughout the lagoon were sampled in 2002, and all were found to be densely planted at that time. Subsequently, the same stations were revisited in 2010 and seagrass cover had drastically decreased by that time. Based on benthic macrofauna, multidimensional scaling (MDS) analysis identified four groups. Years were separated. In 2002, two groups were distinct in relation to the water body, since in 2010 separation between the two other groups was related to seagrass occurrence. When looking at community structure and dominant species there were moderate differences within and between years, independent of seagrass decline. Seagrass loss did not drastically modify the species composition as they were preserved in the remaining seagrass patches. However, there was a drop in macrofauna abundance in unvegetated muddy compared with abundance in the remaining seagrass areas. Epifauna was particularly affected by seagrass decline. Among biotic indicators based on macrofauna, multivariate indicator MISS (Macrobenthic Index in Sheltered Systems) was in agreement with the similarity of macrofauna structure among groups, while other tested indicators performed badly in relation to seagrass occurrence. However, no index detected seagrass loss, highlighting the necessity of maintaining a separate survey on seagrass cover.  相似文献