• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.3
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• pp.910-932
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• 1996

A problem of determining the effective conductivity of a useful model of sphere-matrix type, disordered three-phase composite media is considered. Specifically, a three-phase media in which two-phase composite spheres, consisting of spheres of conductivity $k_2$((phase 2) and concentric shells of conductivity $k_3$(phase 3), are randomly distributed in a matrix of conductivity $k_1$( (phase 1) is considered. As for the structure models configuring three-phase composite media, three different structure models of PCS, PS-1 and PS-2 models are defined, which are analogous to well-established PCS, PS structure models of two-phase composite media. Futhermore, a generalized PS-PCS structure model is proposed to incorporate thesee three different models in one. Effective condectivity $k^{\ast}$of multiphaes composite media is greatly influenced by the phase connectivity of each disspersed phase material, as well as phase conductivities and phase volume fractions. Phase connectivity of three-phase PCS, PS-1, PS-2 composite media is quantified by the impentrability parameter $\lambda$. Mathematically rigorous first-order cluster bounds on $k^{\ast}$ are derived for these models of three-phase composite media, and as computation examples, first-order cluster bounds on $k^{\ast}$ for three-phase composites consisting of largely different phase conductivities are computed and compared as function of concnectivity parpmeter $\lambda$. Results and discussions are given.

• Journal of KIISE:Databases
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• v.29 no.5
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• pp.367-380
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• 2002

Due to recent increase in applications requiring huge amount of data such as spatial data analysis and image analysis, clustering on large databases has been actively studied. In a hierarchical clustering method, a tree representing hierarchical decomposition of the database is first created, and then, used for efficient clustering. Existing hierarchical clustering methods mainly adopted the bottom-up approach, which creates a tree from the bottom to the topmost level of the hierarchy. These bottom-up methods require at least one scan over the entire database in order to build the tree and need to search most nodes of the tree since the clustering algorithm starts from the leaf level. In this paper, we propose a novel top-down hierarchical clustering method that uses multidimensional indexes that are already maintained in most database applications. Generally, multidimensional indexes have the clustering property storing similar objects in the same (or adjacent) data pares. Using this property we can find adjacent objects without calculating distances among them. We first formally define the cluster based on the density of objects. For the definition, we propose the concept of the region contrast partition based on the density of the region. To speed up the clustering algorithm, we use the branch-and-bound algorithm. We propose the bounds and formally prove their correctness. Experimental results show that the proposed method is at least as effective in quality of clustering as BIRCH, a bottom-up hierarchical clustering method, while reducing the number of page accesses by up to 26～187 times depending on the size of the database. As a result, we believe that the proposed method significantly improves the clustering performance in large databases and is practically usable in various database applications.

• Journal of Korean Society of Environmental Engineers
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• v.35 no.4
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• pp.247-256
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• 2013

In this study, alginate beads containing birnessite (Bir-AB), a highly reactive oxidative catalyst for the transformation of phenolic compounds, was prepared and its 1-naphthol (1-NP) removal efficiency was investigated in a batch test. Based on scanning electron microscopy image, it can be inferred that the alginate gel cluster acts as a bridge which bind the birnessite particles together. Kinetic experiment with Bir-AB of different mixing ratios of birnessite to alginate (Bir : AG=0.25 : 1~1 : 1 w/w) indicate that pseudo-first order kinetic constants, $k(hr^{-1})$ for the 1-NP removals increased about 1.5 times when the birnessite mixing ratio was doubled. The removals of 1-NP was found to be dependent on solution pH and the pesudo-first order rate constants were increased from 0.331 $hr^{-1}$ at pH 10 to 0.661 $hr^{-1}$ at pH 4. The analysis of total organic carbon for the reaction solutions showed that a higher removal of dissolved organic carbon was achieved with Bir-AB as compared to birnessite. HPLC chromatographic analysis of the methanol extract after reaction of 1-NP with Bir-AB suggest that the reaction products could be removed through incorporation into the aliginate beads as a bound residue. Mn ions produced from the oxidative transformation of 1-NP by birnessite were also removed by sorption to Bir-AB. The Bir-AB was recovered quantitatively by simple filtration and was reused twice without significant loss of the initial reactivity.