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Search Results: 1 - 10 of 418424 matches for " J.-H. Kim "
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Existence of Solutions of Nonlinear Stochastic Volterra Fredholm Integral Equations of Mixed Type
K. Balachandran,J.-H. Kim
International Journal of Mathematics and Mathematical Sciences , 2010, DOI: 10.1155/2010/603819
Abstract: We establish sufficient conditions for the existence anduniqueness of random solutions of nonlinear Volterra-Fredholm stochastic integralequations of mixed type by using admissibility theory and fixed point theorems. Theresults obtained in this paper generalize the results of several papers.
On solutions of general nonlinear stochastic integral equations
K. Balachandran,J.-H. Kim
International Journal of Stochastic Analysis , 2006, DOI: 10.1155/jamsa/2006/45979
Abstract: We study the existence, uniqueness, and stability of random solutions of a general class of nonlinear stochastic integral equations by using the Banach fixed point theorem. The results obtained in this paper generalize the results of Szynal and Wędrychowicz (1993).
Domain Independent Vocabulary Generation and Its Use in Category-based Small Footprint Language Model
KIM, K.-H.,KIM, J.-H.
Advances in Electrical and Computer Engineering , 2011, DOI: 10.4316/aece.2011.01013
Abstract: The work in this paper pertains to domain independent vocabulary generation and its use in category-based small footprint Language Model (LM). Two major constraints of the conventional LMs in the embedded environment are memory capacity limitation and data sparsity for the domain-specific application. This data sparsity adversely affects vocabulary coverage and LM performance. To overcome these constraints, we define a set of domain independent categories using a Part-Of-Speech (POS) tagged corpus. Also, we generate a domain independent vocabulary based on this set using the corpus and knowledge base. Then, we propose a mathematical framework for a category-based LM using this set. In this LM, one word can be assigned assign multiple categories. In order to reduce its memory requirements, we propose a tree-based data structure. In addition, we determine the history length of a category n-gram, and the independent assumption applying to a category history generation. The proposed vocabulary generation method illustrates at least 13.68% relative improvement in coverage for a SMS text corpus, where data are sparse due to the difficulties in data collection. The proposed category-based LM requires only 215KB which is 55% and 13% compared to the conventional category-based LM and the word-based LM, respectively. It successively improves the performance, achieving 54.9% and 60.6% perplexity reduction compared to the conventional category-based LM and the word-based LM in terms of normalized perplexity.
Influence of the Asian monsoon on net ecosystem carbon exchange in two major ecosystems in Korea
H. Kwon, J. Kim, J. Hong,J.-H. Lim
Biogeosciences (BG) & Discussions (BGD) , 2010,
Abstract: Considering the feedback in radiation, temperature, and soil moisture with alterations in rainfall patterns, the influence of the changing monsoon on Net Ecosystem CO2 Exchange (NEE) can be critical to the estimation of carbon balance in Asia. In this paper, we examined CO2 fluxes measured by the eddy covariance method from 2004 to 2008 in two major ecosystems in the KoFlux sites in Korea, i.e., the Gwangneung Deciduous forest (GDK) and the Haenam Farmland (HFK). Our objectives were to identify the repeatability of the mid-season depression of NEE encountered at the two sites based on the single-year observation, and to further scrutinize its cause, effect, and interannual variability by using multi-year observations. In both GDK and HFK sites, the mid-season depression of NEE was reproduced each year but with different timing, magnitude, and mechanism. At the GDK site, a predominant factor causing the mid-season depression was a decreased solar radiation and the consequent reduction in Gross Primary Productivity (GPP) during the summer monsoon period. At the HFK site, however, the monsoonal effect was less pronounced and the apparent mid-season depression was mainly a result of the management practices such as cultivation of spring barley and rice transplantation. Other flux observation sites in East Asia also showed a decline in radiation but with a lesser degree during the monsoon season, resulting in less pronounced depression in NEE. In our study, the observed depressions in NEE caused both GDK and HFK sites to become a weaker carbon sink or even a source in the middle of the growing season. On average, the GDK site (with maximum leaf area index of ~5) was a weak carbon sink with NEE of 84 gC m 2 y 1. Despite about 20% larger GPP (of 1321 gC m 2y 1) in comparison with the GDK site, the HFK site (with maximum leaf area index of 3–4) was a weaker carbon sink with NEE of 58 gC m 2 y 1 because of greater ecosystem respiration (of 1263 gC m 2 y 1). These NEE values were near the low end of the ranges reported in the literature for similar ecosystems in mid-latitudes. With the projected trends of the extended length of monsoon with more intensive rainfalls in East Asia, the observed delicate coupling between carbon and hydrological cycles may turn these key ecosystems into carbon neutral.
Corrigendum to "Thirty thousand years of vegetation development and climate change in Angola (Ocean Drilling Program Site 1078)" published in Clim. Past, 4, 107–124, 2008
L. M. Dupont, H. Behling,J.-H. Kim
Climate of the Past (CP) & Discussions (CPD) , 2011,
Abstract: No abstract available.
Thirty thousand years of vegetation development and climate change in Angola (Ocean Drilling Program Site 1078)
L. M. Dupont, H. Behling,J.-H. Kim
Climate of the Past (CP) & Discussions (CPD) , 2008,
Abstract: ODP Site 1078 situated under the coast of Angola provides the first record of the vegetation history for Angola. The upper 11 m of the core covers the past 30 thousand years, which has been analysed palynologically in decadal to centennial resolution. Alkenone sea surface temperature estimates were analysed in centennial resolution. We studied sea surface temperatures and vegetation development during full glacial, deglacial, and interglacial conditions. During the glacial the vegetation in Angola was very open consisting of grass and heath lands, deserts and semi-deserts, which suggests a cool and dry climate. A change to warmer and more humid conditions is indicated by forest expansion starting in step with the earliest temperature rise in Antarctica, 22 thousand years ago. We infer that around the period of Heinrich Event 1, a northward excursion of the Angola Benguela Front and the Congo Air Boundary resulted in cool sea surface temperatures but rain forest remained present in the northern lowlands of Angola. Rain forest and dry forest area increase 15 thousand years ago. During the Holocene, dry forests and Miombo woodlands expanded. Also in Angola globally recognised climate changes at 8 thousand and 4 thousand years ago had an impact on the vegetation. During the past 2 thousand years, savannah vegetation became dominant.
Thirty thousand years of vegetation development and climate change in Angola (Ocean Drilling Program Site 1078)
L. M. Dupont,H. Behling,J.-H. Kim
Climate of the Past Discussions , 2008,
Abstract: ODP Site 1078 situated under the coast of Angola provides the first record of the vegetation history for Angola. The upper 11 m of the core covers the past 30 thousand years, which has been analysed palynologically in decadal to centennial resolution. Alkenone sea surface temperature estimates were analysed in centennial resolution. We studied sea surface temperatures and vegetation development during full glacial, deglacial, and interglacial conditions. During the glacial the vegetation in Angola was very open consisting of grass and heath lands, deserts and semi-deserts, which suggests a cool and dry climate. A change to warmer and more humid conditions is indicated by forest expansion starting in step with the earliest temperature rise in Antarctica, 22 thousand years ago. We infer that around the period of Heinrich Event 1 a northward excursion of the Angola Benguela Front and the Congolian Air Boundary resulted in cool sea surface temperatures and a northward extension of desert vegetation along the coast. Rain forest and dry forest returned 15 thousand years ago. During the Holocene, dry forests and Miombo woodlands expanded. Also in Angola globally recognised climate changes at 8 thousand and 4 thousand years ago had an impact on the vegetation. During the past 2 thousand years, savannah vegetation became dominant.
Existence of mild solutions of second-order neutral functional differential inclusions with nonlocal conditions in Banach spaces
S. Marshal Anthoni,J.-H. Kim,J. P. Dauer
International Journal of Mathematics and Mathematical Sciences , 2004, DOI: 10.1155/s0161171204310410
Abstract: We study the existence of mild solutions of the nonlinear second-order neutral functional differential and integrodifferential inclusions with nonlocal conditions in Banach spaces. The results are obtained by using the theory of strongly continuous cosine families of bounded linear operators and a fixed point theorem for condensing maps due to Martelli.
High-latitude obliquity forcing drives the agulhas leakage
T. Caley,J.-H. Kim,B. Malaizé,J. Giraudeau
Climate of the Past Discussions , 2011, DOI: 10.5194/cpd-7-2193-2011
Abstract: The Agulhas Current (AC) transport of heat and salt from the Indian Ocean into the South Atlantic around South Africa (Agulhas leakage), has a profound role in the decadal variability of the Atlantic meridional overturning circulation (AMOC), which influences global climate. On glacial-interglacial timescales, paleostudies postulate that Agulhas leakage plays a decisive role for AMOC resumption during terminations (glacial-interglacial transitions). However, efforts to elucidate forcing mechanisms connecting Agulhas leakage with glacial-interglacial AMOC variability have been hampered due to a lack of climate records extracted from the area where the AC originates. Here we present 800-kyr sea surface temperature (SST) and salinity (SSS) records from the "precursor" region of the AC. These records contain strong obliquity-driven 41-kyr cycles, nearly in phase with changes in annual mean insolation and air temperature at high southern latitudes. In contrast, precession-driven cycles were negligible in our SST records, which is surprising given the low-latitude location of the Agulhas leakage. Together, this suggests that long-term Agulhas leakage dynamics are associated with a high latitude rather than a tropical climate forcing mechanism, probably by varying the position of the Southern Hemisphere subtropical convergence (STC) and its associated westerlies. We argue that during terminations stronger Agulhas leakage was triggered by increased obliquity exerting a positive feedback on the global climate system through modulating long-term AMOC variations.
Weldability during the laser lap welding of Al 5052 sheets
J.-K. Kim,H.-S. Lim,J.-H. Cho,C.-H. Kim
Archives of Materials Science and Engineering , 2008,
Abstract: Purpose: The paper presents the effect of the laser welding parameters of the laser focal position, the weldingspeed and the laser output power on the weldability of Al the 5052 alloy during laser lap welding.Design/methodology/approach: Lap welding is conducted on an Al 5052 plate with a thickness of 1 mm.After welding, the bead surfaces and cross sections were evaluated with various laser welding parameters. Thedegree of porosity was also examined by X-ray transmission testing.Findings: The influences of the focal point, the laser power and the welding speed on the formation of bead andon the degree of porosity were experimentally investigated. The bead quality was improved when the beam wasdefocused compared to when it was focused on the surface. It was found that the porosity decreased when the heatinput is lowered, except when the lower plate is not melted.Research limitations/implications: Various types of aluminium alloys, such as sheet, extrusion and castingtypes, are used industrially in diverse combinations. Therefore, it is necessary to evaluate the weldabilities ofthese materials. This research is limited to Al 5052 alloys at present plans are underway to expand it to variousaluminium based alloys.Practical implications: Automotive industries are continuously increasing their use of aluminium alloys inmanufacturing. The results of this research can be referred to by the automotive industry as a basic technique.Originality/value: This research shows the influence of different welding parameters on the weldability duringthe lap welding of Al 5052 Al alloy. The results are based on the extensive experiments.
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