Exopolysaccharides Produced by Streptococcus mutans Glucosyltransferases Modulate the Establishment of Microcolonies within Multispecies Biofilms

Koo, H.,Xiao, J.,Klein, M. I.,Jeon, J. G. American Society for Microbiology 2010 Journal of Bacteriology Vol.192 No.12

<B>ABSTRACT</B><P><I>Streptococcus mutans</I> is a key contributor to the formation of the extracellular polysaccharide (EPS) matrix in dental biofilms. The exopolysaccharides, which are mostly glucans synthesized by streptococcal glucosyltransferases (Gtfs), provide binding sites that promote accumulation of microorganisms on the tooth surface and further establishment of pathogenic biofilms. This study explored (i) the role of <I>S. mutans</I> Gtfs in the development of the EPS matrix and microcolonies in biofilms, (ii) the influence of exopolysaccharides on formation of microcolonies, and (iii) establishment of <I>S. mutans</I> in a multispecies biofilm <I>in vitro</I> using a novel fluorescence labeling technique. Our data show that the ability of <I>S. mutans</I> strains defective in the <I>gtfB</I> gene or the <I>gtfB</I> and <I>gtfC</I> genes to form microcolonies on saliva-coated hydroxyapatite surfaces was markedly disrupted. However, deletion of both <I>gtfB</I> (associated with insoluble glucan synthesis) and <I>gtfC</I> (associated with insoluble and soluble glucan synthesis) is required for the maximum reduction in EPS matrix and biofilm formation. <I>S. mutans</I> grown with sucrose in the presence of <I>Streptococcus oralis</I> and <I>Actinomyces naeslundii</I> steadily formed exopolysaccharides, which allowed the initial clustering of bacterial cells and further development into highly structured microcolonies. Concomitantly, <I>S. mutans</I> became the major species in the mature biofilm. Neither the EPS matrix nor microcolonies were formed in the presence of glucose in the multispecies biofilm. Our data show that GtfB and GtfC are essential for establishment of the EPS matrix, but GtfB appears to be responsible for formation of microcolonies by <I>S. mutans</I>; these Gtf-mediated processes may enhance the competitiveness of <I>S. mutans</I> in the multispecies environment in biofilms on tooth surfaces.</P>

Decay Estimate on the KORTEWEG-DE VRIES Equation with Dissipation

Choi, Y,Jang, J,Koo, H 한국외국어대학교 외국학종합연구센터 부설 기초과학연구소 1996 기초과학연구 Vol.4 No.-

Prior to the study of long time stability of small solutions to the IVP for the generalized Korteweg-de Vries equation with disspation we show decay estimates in time by combining the dispersion with the dissipation effect.

VMOA and compact operator

Choi, Y,Jang, J,Koo, H 한국외국어대학교 외국학종합연구센터 부설 기초과학연구소 1996 기초과학연구 Vol.4 No.-

We prove a characterization of vanishing Carleson measure characterization in terms of compactness of Poisson extension on weighted Lρspaces.

Composition operators on holomorphic Sobolev spaces in B_n

Koo, H.,Park, I. Academic Press 2010 Journal of mathematical analysis and applications Vol.369 No.1

We study the composition operator C<SUB>Φ</SUB> on holomorphic Sobolev spaces induced by an analytic self-map Φ of B<SUB>n</SUB> in C<SUP>n</SUP> that extends to be smooth on B<SUB>n</SUB>@?. We characterize the boundedness and the compactness of C<SUB>Φ</SUB> on A<SUB>α,s</SUB><SUP>p</SUP>, and prove the jump phenomenon of C<SUB>Φ</SUB> on A<SUB>α,s</SUB><SUP>p</SUP>. Moreover, we show an interesting result that the boundedness of C<SUB>Φ</SUB> on A<SUB>α,s</SUB><SUP>p</SUP> is equivalent to the compactness of C<SUB>Φ</SUB>:A<SUB>α,s</SUB><SUP>p</SUP>→A<SUB>β,t</SUB><SUP>q</SUP> for appropriate A<SUB>β,t</SUB><SUP>q</SUP>, for example A<SUB>β,t</SUB><SUP>q</SUP>=A<SUB>α+¼,s</SUB><SUP>p</SUP>. We provide examples to show that our results are sharp.

Trinomial Option Pricing Model

Choi, Y.,Jang, J.,Koo, H. 한국외국어대학교 외국학종합연구센터 부설 기초과학연구소 1996 기초과학연구 Vol.5 No.-

In this paper we find an efficient recursive valuation method for the American option in a trinomial model. Partial and local information of the optimal exercise boundary enables us to find the recursive method.

Enhanced drug-loading and therapeutic efficacy of hydrotropic oligomer-conjugated glycol chitosan nanoparticles for tumor-targeted paclitaxel delivery

Koo, H.,Min, K.H.,Lee, S.C.,Park, J.H.,Park, K.,Jeong, S.Y.,Choi, K.,Kwon, I.C.,Kim, K. Elsevier Science Publishers 2013 Journal of controlled release Vol.172 No.3

Enhanced drug-loading and therapeutic efficacies are highly essential properties for nanoparticles as tumor-targeting drug carriers. Herein, we developed the glycol chitosan nanoparticles with hydrotropic oligomers (HO-CNPs) as a new tumor targeting drug delivery system. For enhancing drug-loading efficiency of paclitaxel in drug carriers, hydrotropic 2-(4-(vinylbenzyloxy)-N,N-diethylnicotinamide) (VBODENA-COOH) oligomers, that were used for enhancing the aqueous solubility of paclitaxel, were directly conjugated to glycol chitosan polymers. The amphiphilic conjugates readily formed nanoparticle structure (average size=302+/-22nm) in aqueous condition. Water-insoluble paclitaxel (PTX) was readily encapsulated into HO-CNPs with a high drug-loading amount up to 24.2wt.% (2.4 fold higher than other polymeric nanoparticles) by a simple dialysis method. The PTX encapsulated HO-CNPs (PTX-HO-CNPs; average size=343+/-12nm) were very stable in aqueous media up to 50days. Also, PTX-HO-CNPs presented rapid cellular uptake and lower cytotoxicity in cell culture system, compared to Cremophor EL/ethanol formulation of PTX. In tumor-bearing mice, the extravasation and accumulation of PTX-HO-CNPs in tumor tissue were precisely observed by intravital fluorescence imaging techniques. Furthermore, PTX-HO-CNPs showed the higher therapeutic efficacy, compared to Abraxane®, a commercialized PTX-formulation. These overall results demonstrate its potential as a new nano-sized PTX carrier for cancer treatment.

Cancellation properties of composition operators on Bergman spaces

Koo, H.,Wang, M. Academic Press 2015 Journal of mathematical analysis and applications Vol.432 No.2

The compact difference of two composition operators on the Bergman spaces over the unit disc is characterized in [11] in terms of certain cancellation property of the inducing maps at every ''bad'' boundary points, which make each single composition operator not to be compact. In this paper, we completely characterize the compactness of a linear combination of three composition operators on the Bergman space. As one consequence of this characterization, we show that there is no cancellation property for the compactness of double difference of composition operators. More precisely, we show that if φ<SUB>i</SUB> are distinct and none of C<SUB>φ'i</SUB> is compact, then (C<SUB>φ'1</SUB>-C<SUB>φ'2</SUB>)-(C<SUB>φ'3</SUB>-C<SUB>φ'1</SUB>) is compact if and only if both (C<SUB>φ'1</SUB>-C<SUB>φ'2</SUB>) and (C<SUB>φ'3</SUB>-C<SUB>φ'1</SUB>) are compact.

The Effect of CeO2 Antireflection Layer on the Optical Properties of Thermochromic VO2 Film for Smart Window System

Koo, H.,Shin, D.,Bae, S. H.,Ko, K. E.,Chang, S. H.,Park, C. SPRINGER INTRNATIONAL 2014 Journal of materials engineering and performance Vol.23 No.2

CeO2-VO2 bilayer structure was fabricated to investigate the effect of depositing CeO2 film on the optical properties of VO2 film for smart window application. CeO2 was employed as an antireflection (AR) layer material of VO2 film because of its advantages which include high transparency in the visible-near infrared range and high refractive index. All the films were deposited on soda-lime glass substrate by pulsed laser deposition method. Optical calculations were carried out using transfer-matrix method for the purpose of designing CeO2-VO2 bilayer structure with enhanced integrated luminous transmittance (T (lum)) and switching efficiency (Delta T (sol)). The optical constants of VO2 and CeO2 films needed for the optical calculation were measured by spectroscopic ellipsometer. The curve of T (lum) the shape of which depends on the thickness of CeO2 layer, was calculated in each VO2 sample, which showed two maxima. The samples were divided into two groups; one for the highest enhancement of T (lum) and the other for balanced enhancement between T (lum) and Delta T (sol). The sample with the structure of similar to 60 nm CeO2 AR layer on 39-nm thick VO2 film showed large increase of T (lum) (similar to 27%) with Delta T (sol) of similar to 5%, which is the largest increase in T (lum) reported so far. Two samples in the other group showed the balanced enhancement in T (lum) (similar to 57, similar to 50%) and Delta T (sol) (similar to 9, similar to 10.5%). The effect of CeO2 AR layer on the optical properties of VO2 film was confirmed with the optical calculation and the experimental results. CeO2-VO2 bilayer structure showed notable improvement of optical properties compared to the single VO2 film, indicating that CeO2 layer can be effectively used as the antireflection layer while working as a protective layer that can prevent the oxidation of VO2 layer as well.

Joint Carleson measure and the difference of composition operators on A_α^p(B_n)

Koo, H.,Wang, M. Academic Press 2014 Journal of mathematical analysis and applications Vol.419 No.2

We introduce a concept of joint Carleson measure and characterize when the difference of two composition operators on A<SUB>α</SUB><SUP>p</SUP>(B<SUB>n</SUB>), the weighted Bergman space over the unit ball B<SUB>n</SUB> in C<SUP>n</SUP>, is bounded or compact. We apply this joint Carleson measure characterization to composition operators with smooth symbols and construct an interesting example which shows that the boundedness or the compactness depends on p when n≥2. This is in sharp contrast with the single composition operator case where the boundedness or the compactness is independent of p>0. Moreover, the compact difference on the weighted Bergman spaces over the unit disc is known to be independent of p>0, and the compact difference on A<SUB>α</SUB><SUP>p</SUP>(B<SUB>n</SUB>) is known to be independent of p>0 if each composition operator is bounded on A<SUB>β</SUB><SUP>p</SUP>(B<SUB>n</SUB>) for some -1<β<α[2].

韓國女流小說의 文體

丘仁煥(Kooh In-hwan) 숙명여자대학교 아시아여성연구원 1972 아시아여성연구 Vol.11 No.-