Stochastic multi-site generation of daily rainfall occurrence in south Florida     

Tae-woong Kim  Hosung Ahn  Gunhui Chung  Chulsang Yoo 《Stochastic Environmental Research and Risk Assessment (SERRA)》2008,22(6):705-717

This paper presents a stochastic model to generate daily rainfall occurrences at multiple gauging stations in south Florida. The model developed in this study is a space–time model that takes into account the spatial as well as temporal dependences of daily rainfall occurrence based on a chain-dependent process. In the model, a Markovian method was used to represent the temporal dependence of daily rainfall occurrence and a direct acyclic graph (DAG) method was introduced to encode the spatial dependence of daily rainfall occurrences among gauging stations. The DAG method provides an optimal sequence of generation by maximizing the spatial dependence index of daily rainfall occurrences over the region. The proposed space–time model shows more promising performance in generating rainfall occurrences in time and space than the conventional Markov type model. The space–time model well represents the temporal as well as the spatial dependence of daily rainfall occurrences, which can reduce the complexity in the generation of daily rainfall amounts.  相似文献   

Holding capacity of suction caisson anchors embedded in cohesive soils based on finite element analysis     

Jaehun Ahn  Hanmin Lee  Yun‐Tae Kim 《国际地质力学数值与分析法杂志》2014,38(15):1541-1555

The foundations of offshore structures have been intensively studied to provide design guidelines for oil platforms. Recently, techniques developed for the oil industry have found new applications in the design of foundations for offshore wind turbines. There are simplified analytical solutions for the holding capacity of suction anchors, which are based on postulated failure mechanisms and are often compared with the results of finite element analyses. The merit of the results of a finite element analysis over the simplified solutions is that the finite element analysis satisfies all the basic equations in mechanics and does not require the assumption of reasonable failure mechanisms. The aim of this study is, based on the results of extensive finite element analyses, to provide a set of formulae for the estimation of the holding capacities of optimally loaded suction caisson anchors embedded in cohesive soils with a linear strength distribution. The bearing capacity factor and the depth of the optimal loading point are also estimated and reported. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Impact of urbanization on recent temperature and precipitation trends in the Korean peninsula   总被引：1，自引：0，他引：1  

Jong-Seong Kug  Min-Seop Ahn 《Asia-Pacific Journal of Atmospheric Sciences》2013,49(2):151-159

Urbanization has a significant impact on climate in urban areas. In this study, we investigate urbanization impacts on temperature and precipitation trends in Korean peninsula based on statistical relationship between these trends and local population growth. We found that there is a significant positive correlation between temperature rise and local population growth, indicating that urbanization has a significant contribution to temperature increase in city climate. As for temperature, the population growth in Korean cities is positively correlated with precipitation trend. The positive correlation is higher during summer time when small-scale convective activity is dominant. Furthermore, it is demonstrated that the correlation is significantly increased when stations in rural areas and small cities are excluded. Such nonlinear relation between precipitation and urbanization is also discussed.  相似文献   

Profiles of the resonance doublets formed in bipolar winds in symbiotic stars     

Jerry Jaiyul Yoo  Hee-Won Lee  Sang-Hyeon Ahn 《Monthly notices of the Royal Astronomical Society》2002,334(4):974-982

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Natural frequency and damping ratio of a vertically vibrated surface foundation     

Jaehun Ahn  Giovanna Biscontin  Jose M. Roësset 《Soil Dynamics and Earthquake Engineering》2011

It is possible and common to obtain equivalent natural frequency and damping for a soil-foundation system from results of experimental or numerical analysis assuming the system has a single degree of freedom. Three approaches to extract natural frequency and damping were applied to the vertically vibrated soil-foundation system. The sensitivity of the computed natural frequency and damping to the soil properties was evaluated through parametric studies. About 10–20% of discrepancy in values of natural frequency was observed due to different approaches. The results help to assess the reliability of equivalent soil properties determined from the reported natural frequency of the system. Finally the results obtained using theoretical predictions with linear soil properties measured in situ were compared to those calculated from experimental data. The prediction and experimental results showed good agreements if the embedment of the foundation is neglected with stepped sine test but considered with impulse test.  相似文献   

Doppler Shifts of the Hα Line and the Ca ii 854.2 nm Line in a Quiet Region of the Sun Observed with the FISS/NST     

Jongchul Chae  Hyung-Min Park  Kwangsu Ahn  Heesu Yang  Young-Deuk Park  Kyung-Suk Cho  Wenda Cao 《Solar physics》2013,288(1):89-103

The characteristics of Doppler shifts in a quiet region of the Sun are compared between the Hα line and the Ca?ii infrared line at 854.2 nm. A small area of 16″×40″ was observed for about half an hour with the Fast Imaging Solar Spectrograph (FISS) of the 1.6 meter New Solar Telescope (NST) at Big Bear Solar Observatory. The observed area contains a network region and an internetwork region, and identified in the network region are fibrils and bright points. We infer Doppler velocity v _m from each line profile at each individual point with the lambdameter method as a function of half wavelength separation Δλ. It is confirmed that the bisector of the spatially averaged Ca?ii line profile has an inverse C-shape with a significant peak redshift of +?1.8 km?s^?1. In contrast, the bisector of the spatially averaged Hα line profile has a C-shape with a small peak blueshift of ??0.5 km?s^?1. In both lines, the bisectors of bright network points are significantly redshifted not only at the line centers, but also at the wings. The Ca?ii Doppler shifts are found to be correlated with the Hα ones with the strongest correlation occurring in the internetwork region. Moreover, we find that here the Doppler shifts in the two lines are essentially in phase. We discuss the physical implications of our results in view of the formation of the Hα line and Ca?ii 854.2 nm line in the quiet region chromosphere.  相似文献   

Overview of geostationary ocean color imager (GOCI) and GOCI data processing system (GDPS)   总被引：4，自引：0，他引：4  

Joo-Hyung Ryu  Hee-Jeong Han  Seongick Cho  Young-Je Park  Yu-Hwan Ahn 《Ocean Science Journal》2012,47(3):223-233

GOCI, the world??s first geostationary ocean color satellite, provides images with a spatial resolution of 500 m at hourly intervals up to 8 times a day, allowing observations of short-term changes in the Northeast Asian region. The GOCI Data Processing System (GDPS), a specialized data processing software for GOCI, was developed for real-time generation of various products. This paper describes GOCI characteristics and GDPS workflow/products, so as to enable the efficient utilization of GOCI. To provide quality images and data, atmospheric correction and data analysis algorithms must be improved through continuous Cal/Val. GOCI-II will be developed by 2018 to facilitate in-depth studies on geostationary ocean color satellites.  相似文献   

Energy dependence of Ti/Fe ratio in the Galactic cosmic rays measured by the ATIC-2 experiment     

V. I. Zatsepin  A. D. Panov  N. V. Sokolskaya  J. H. Adams Jr.  H. S. Ahn  G. L. Bashindzhagyan  J. Chang  M. Christl  A. R. Fazely  T. G. Guzik  J. B. Isbert  K. C. Kim  E. N. Kouznetsov  M. Panasyuk  E. S. Seo  J. Watts  J. P. Wefel  J. Wu 《Astronomy Letters》2009,35(5):338-342

Titanium is a rare, secondary nucleus among Galactic cosmic rays. Using the Silicon matrix in the ATIC experiment, Titanium has been separated. The energy dependence of the Ti to Fe flux ratio in the energy region from 5 GeV per nucleon to about 500 GeV per nucleon is presented. The article was translated by the authors.  相似文献   

An assessment of future dryness over Korea based on the ECHAM5-RegCM3 model chain under A1B emission scenario   总被引：2，自引：0，他引：2  

Eun-Soon Im  Joong-Bae Ahn  Do-Woo Kim 《Asia-Pacific Journal of Atmospheric Sciences》2012,48(4):325-337

We analyze the future dryness over Korea based on the projected temperature and precipitation. For fine-scale climate information, the ECHAM5/MPI-OM A1B simulation has been dynamically downscaled using the RegCM3 double-nested system. A 130-year long-term climatology (1971?C2100) from the mother domain (East Asia: 60 km) and nested domain (South Korea: 20 km) is discussed. Based on the intercomparison with CMIP3 participant models, the ECHAM5/MPI-OM provides climatic change information over the East Asia that is not markedly different from other projections. However, the reduction of summer precipitation over Korea is rather different with ensemble mean of CMIP3 participant models. The downscaled results generally follow the behavior of ECHAM5/MPIOM, but substantial fine-scale details are found in the spatial pattern and the change signals become more enhanced at the local scale. In the future projection, significant warming is found regardless of the season and region while the change in precipitation shows a mixed feature with both increasing and decreasing patterns. The increase of temperature enhances the evapotranspiration, and hence the actual water stress becomes more pronounced in the warmer climate. This is related to the negative trends of the self-calibrating Palmer Drought Severity Index (PDSI) to measure the drought condition in Korea. Although PDSI is overall associated with the precipitation variation, its long-term trend tends to be modulated by the temperature trend. It is confirmed that the detrended temperature is shown to mask the decreasing tendency of the PDSI. The result indicates that without an increase in precipitation appropriate for atmospheric moisture demand, future dryness is a more likely condition under global warming.  相似文献   

Effect of alkaline solutions on bentonite properties     

Ha Ngoc Anh  Hyangsig Ahn  Ho Young Jo  Geon-Young Kim 《Environmental Earth Sciences》2017,76(10):374

The influence of alkaline aqueous solutions on the properties of bentonite was investigated to evaluate the performance of bentonitic engineered barriers when contacted with alkaline groundwater. Batch and hydraulic conductivity tests were conducted on Na-bentonite using six different alkaline aqueous solutions. For the batch tests, almost no change in the montmorillonite fraction of the bentonite was observed after reacting with alkaline solutions (pH = 8.4–13.1), regardless of the solution type. On the other hand, aluminosilicate minerals (e.g., albite) were dissolved and secondary minerals (e.g., anorthite) were formed in alkaline NaOH solutions (pH > 13). The cation (Ca or Na) concentration primarily affected the swelling properties of bentonite rather than the pH of the solution, which was comparable to the results of the hydraulic conductivity tests. For the Ca solutions, the hydraulic conductivity of the bentonite specimen to the 0.02 mol/L Ca(OH)₂ solution (6.5 × 10^?9 cm/s) was approximately an order of magnitude lower than that of the bentonite specimen to the 0.02 mol/L Ca(OH)₂ + 1 mol/L CaCl₂ solution (5.0 × 10^?8 cm/s), whereas the hydraulic conductivity to the 0.02 mol/L Ca(OH)₂ + 1 mol/L CaCl₂ solution (pH = 11.3) (5.0 × 10^?8 cm/s) was slightly higher than that to the 1 mol/L CaCl₂ solution (pH_i = 8.4) (4.4 × 10^?8 cm/s). For the NaOH solutions with pH > 13, the hydraulic conductivity of the bentonite specimen decreased with increasing Na concentration, suggesting that the effect of Na concentration was more dominant than that of permeant pH.  相似文献