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Search Results: 1 - 10 of 11986 matches for " Sung Koo Kang "
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Stability for Caputo Fractional Differential Systems
Sung Kyu Choi,Bowon Kang,Namjip Koo
Abstract and Applied Analysis , 2014, DOI: 10.1155/2014/631419
Abstract: We introduce the notion of h-stability for fractional differential systems. Then we investigate the boundedness and h-stability of solutions of Caputo fractional differential systems by using fractional comparison principle and fractional Lyapunov direct method. Furthermore, we give examples to illustrate our results. 1. Introductions and Preliminaries Lakshmikantham et al. [1–5] investigated the basic theory of initial value problems for fractional differential equations involving Riemann-Liouville differential operators of order . They followed the classical approach of the theory of differential equations of integer order in order to compare and contrast the differences as well as the intricacies that might result in development [6, Vol. I]. Li et al. [7] obtained some results about stability of solutions for fractional-order dynamic systems using fractional Lyapunov direct method and fractional comparison principle. Choi and Koo [8] improved on the monotone property of Lemma?? in [5] for the case with a nonnegative real number . Choi et al. [9] also investigated Mittag-Leffler stability of solutions of fractional differential equations by using the fractional comparison principle. In this paper we introduce the notion of -stability for fractional differential equations. Then, we investigate the boundedness and -stability of solutions of Caputo fractional differential systems by using fractional comparison principle and fractional Lyapunov direct method. Furthermore, we give some examples to illustrate our results. For the basic notions and theorems about fractional calculus, we mainly refer to some books [5, 10, 11]. We recall the notions of Mittag-Leffler functions which were originally introduced by Mittag-Leffler in 1903 [12]. Similar to the exponential function frequently used in the solutions of integer-order systems, a function frequently used in the solutions of fractional order systems is the Mittag-Leffler function, defined as where and is the Gamma function [11]. The Mittag-Leffler function with two parameters has the following form: where and . For , we have . Also, . Note that the exponential function possesses the semigroup property (i.e., for all ), but the Mittag-Leffler function does not satisfy the semigroup property unless or [13]. We recall briefly the notions and basic properties about fractional integral operators and fractional derivatives of functions [5, 10]. Let . Definition 1 (see [5]). The Riemann-Liouville fractional integral of order of a function is defined as where (provided that the integral exists in the Lebesgue
The Trust Levels, Trust Determinants, and Spatial Dimensions in Inter-Firm Relationships: A Warehousing Firm’s Perspective in the City of Busan, South Korea  [PDF]
Sinje Sung, Sangmok Kang
iBusiness (IB) , 2012, DOI: 10.4236/ib.2012.44046
Abstract:

This study analyzes the trust level relationships of the warehousing industry firms in the city of Busan, South Korea in regards to their determinants and spatial dimensions. A firm’s environment, such as reputation and renown, forms the relationship between the firm and other firms. The trust levels between firms were determined by the determinants of the trust: Long-term and repeated interaction, information sharing and reciprocity, and interdependence and asset specificity all had an important effect upon the micro or highest level of trust. Proximity and uncertainty influenced the meso or middle level of trust. The culture and norms of the firms & institutional formality affected the macro or lowest level of trust. It was found that the higher the trust levels, the more the respective spatial dimensions generated by the relationship between firms expanded to the national and international dimensions.

Association of serum adipocytokine levels with cardiac autonomic neuropathy in type 2 diabetic patients
Chan-Hee Jung, Bo-Yeon Kim, Chul-Hee Kim, Sung-Koo Kang, Sang-Hee Jung, Ji-Oh Mok
Cardiovascular Diabetology , 2012, DOI: 10.1186/1475-2840-11-24
Abstract: Therefore, in the present study, we examined the relationship between fasting serum leptin, TNF- alpha and adiponectin and CAN in Korean T2DM patients.A total of 142 T2DM patients (94 males, 48 females) were recruited. CAN was assessed by the five tests according to the Ewing's protocol and the time and frequency domain of the heart rate variability (HRV) was evaluated. Serum TNF-alpha and adiponectin levels were measured using enzyme-linked immunosorbent assay and serum leptin levels were measured using radioimmunoassay.Although, the mean levels of leptin, TNF-alpha and adiponectin were not significantly different between the groups with and without CAN, the levels of leptin and adiponectin had a tendency to increase as the score of CAN increased (p = 0.05, p = 0.036). Serum leptin levels demonstrated a negative correlation with low frequency (LF) in the upright position (p = 0.037). Regarding TNF-alpha, a significant negative correlation was observed with SDNN and RMSSD in the upright position (p = 0.023, p = 0.019). Adiponectin levels were not related to any HRV parameters. Multivariate logistic regression analysis demonstrated that the odds of CAN increased with a longer duration of diabetes (1.25, [1.07-1.47]) and higher homeostatic model of assessment-insulin resistance (HOMA-IR) (5.47, [1.8-16.5]). The relative risks for the presence of CAN were 14.1 and 51.6 for the adiponectin 2nd, 3rd tertiles when compared with first tertile (p-value for trend = 0.022).In the present study, the higher serum adiponectin levels and HOMA-IR were associated with an increased risk for the presence of CAN. Also, the CAN score correlated with the serum adiponectin. Serum adipocytokines such as leptin and TNF-alpha were significantly correlated with parameters of HRV, representative markers of CAN. Future prospective studies with larger number of patients are required to establish a direct relationship between plasma adipocytokine concentrations and the development or severity of
Immobilization of pamidronic acids on the nanotube surface of titanium discs and their interaction with bone cells
Tae-Hyung Koo, Jyoti S Borah, Zhi-Cai Xing, Sung-Mo Moon, Yongsoo Jeong and Inn-Kyu Kang
Nanoscale Research Letters , 2013, DOI: 10.1186/1556-276X-8-124
Abstract: Self-assembled layers of vertically aligned titanium nanotubes were fabricated on a Ti disc by anodization. Pamidronic acids (PDAs) were then immobilized on the nanotube surface to improve osseointegration. Wide-angle X-ray diffraction, X-ray photoelectron microscopy, and scanning electron microscopy were employed to characterize the structure and morphology of the PDA-immobilized TiO2 nanotubes. The in vitro behavior of osteoblast and osteoclast cells cultured on an unmodified and surface-modified Ti disc was examined in terms of cell adhesion, proliferation, and differentiation. Osteoblast adhesion, proliferation, and differentiation were improved substantially by the topography of the TiO2 nanotubes, producing an interlocked cell structure. PDA immobilized on the TiO2 nanotube surface suppressed the viability of the osteoclasts and reduced their bone resorption activity.
18F-FDG PET Metabolic Parameters and MRI Perfusion and Diffusion Parameters in Hepatocellular Carcinoma: A Preliminary Study
Sung Jun Ahn, Mi-Suk Park, Kyung Ah Kim, Jun Yong Park, InSeong Kim, Won Joon Kang, Seung-Koo Lee, Myeong-Jin Kim
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0071571
Abstract: Objectives Glucose metabolism, perfusion, and water diffusion may have a relationship or affect each other in the same tumor. The understanding of their relationship could expand the knowledge of tumor characteristics and contribute to the field of oncologic imaging. The purpose of this study was to evaluate the relationships between metabolism, vasculature and cellularity of advanced hepatocellular carcinoma (HCC), using multimodality imaging such as 18F-FDG positron emission tomography (PET), dynamic contrast enhanced (DCE)-MRI, and diffusion weighted imaging(DWI). Materials and Methods Twenty-one patients with advanced HCC underwent 18F-FDG PET, DCE-MRI, and DWI before treatment. Maximum standard uptake values (SUVmax) from 18F-FDG-PET, variables of the volume transfer constant (Ktrans) from DCE-MRI and apparent diffusion coefficient (ADC) from DWI were obtained for the tumor and their relationships were examined by Spearman’s correlation analysis. The influence of portal vein thrombosis on SUVmax and variables of Ktrans and ADC was evaluated by Mann-Whitney test. Results SUVmax showed significant negative correlation with Ktransmax (ρ = ?0.622, p = 0.002). However, variables of ADC showed no relationship with variables of Ktrans or SUVmax (p>0.05). Whether portal vein thrombosis was present or not did not influence the SUV max and variables of ADC and Ktrans (p>0.05). Conclusion In this study, SUV was shown to be correlated with Ktrans in advanced HCCs; the higher the glucose metabolism a tumor had, the lower the perfusion it had, which might help in guiding target therapy.
Expression of Aquaporin 5 (AQP5) Promotes Tumor Invasion in Human Non Small Cell Lung Cancer
Young Kwang Chae, Janghee Woo, Mi-Jung Kim, Sung Koo Kang, Myoung Sook Kim, Juna Lee, Seung Koo Lee, Gyungyub Gong, Yong Hee Kim, Jean Charles Soria, Se Jin Jang, David Sidransky, Chulso Moon
PLOS ONE , 2008, DOI: 10.1371/journal.pone.0002162
Abstract: The aquaporins (AQP) are water channel proteins playing a major role in transcellular and transepithelial water movement. Recently, the role of AQPs in human carcinogenesis has become an area of great interest. Here, by immunohistochemistry (IHC), we have found an expression of AQP5 protein in 35.3% (IHC-score: ≥1, 144/408) of the resected NSCLC tissue samples. Cases with AQP5-positive status (IHC-score: ≥2) displayed a higher rate of tumor recurrence than negative ones in NSCLC (54.7% vs. 35.1%, p = 0.005) and worse disease-free survival (p = 0.033; OR = 1.52; 95%CI:1.04?2.23). Further in vitro invasion assay using BEAS-2B and NIH3T3 cells stably transfected with overexpression constructs for full length wild-type AQP5 (AQP5) and its two mutants, N185D which blocks membrane trafficking and S156A which blocks phosphorylation on Ser156, showed that AQP5 induced cell invasions while both mutants did not. In BEAS-2B cells, the expression of AQP5 caused a spindle-like and fibroblastic morphologic change and losses of cell-cell contacts and cell polarity. Only cells with AQP5, not either of two mutants, exhibited a loss of epithelial cell markers and a gain of mesenchymal cell markers. In a human SH3-domains protein array, cellular extracts from BEAS-2B with AQP5 showed a robust binding activity to SH3-domains of the c-Src, Lyn, and Grap2 C-terminal. Furthermore, in immunoprecipitation assay, activated c-Src, phosphorylated on Tyr416, showed a stronger binding activity to cellular extracts from BEAS-2B with AQP5 compared with N185D or S156A mutant. Fluorescence in situ hybridization (FISH) analysis failed to show evidence of genomic amplification, suggesting AQP5 expression as a secondary event. Based on these clinical and molecular observations, we conclude that AQP5, through its phosphorylation on Ser156 and subsequent interaction with c-Src, plays an important role in NSCLC invasion and, therefore, may provide a unique opportunity for developing a novel therapeutic target as well as a prognostic marker in NSCLC.
Systemic chemotherapy for treatment of advanced small bowel adenocarcinoma with prognostic factor analysis: retrospective study
Dong Koo, Sung-Cheol Yun, Yong Hong, Min-Hee Ryu, Jae-Lyun Lee, Heung-Moon Chang, Baek-Yeol Ryoo, Yoon-Koo Kang, Tae Kim
BMC Cancer , 2011, DOI: 10.1186/1471-2407-11-205
Abstract: Data from a total of 91 patients diagnosed with advanced SBA at the Asan Medical Center between January 1989 and December 2009 were retrospectively analyzed. Patients were split into two groups, those who did and did not receive palliative chemotherapy.Overall, 81 patients (89.0%) died, at a median survival time of 6.6 months (95% confidence interval [CI], 5.5 - 7.5 months). The 40 patients receiving chemotherapy showed overall response and disease control rates of 11.1% and 37.0%, respectively, with OS and progression-free survival (PFS) of 11.8 months (95% CI, 4.6 - 19.0 months) and 5.7 months (95% CI, 3.5 - 8.0 months), respectively. The 41 patients who did not receive chemotherapy had an OS of 4.1 months (95% CI, 3.1 - 5.1 months) and a PFS of 1.3 months (95% CI, 0.8 - 1.7 months). Multivariate analysis showed that lack of tumor resection, non-prescription of chemotherapy, liver metastasis, and intra-abdominal lymph node metastasis, were all independently associated with poor survival outcomes. After inverse probability of treatment weighting (IPTW) adjustment, the group that did not receive chemotherapy was at a significantly higher risk of mortality (HR 3.44, 95% CI 2.03 - 5.83, p < 0.001) than were patients receiving chemotherapy.Palliative chemotherapy may improve survival outcomes in patients with advanced SBA.Small bowel cancer is very rare, accounting for 0.46% of all malignancies in the United States and 0.35% in South Korea [1,2]. Adenocarcinoma of the small bowel (SBA) is the most common histological type of such cancer, constituting 35.8% of small bowel malignancies [3]. Although patients with SBA have poor prognosis, few reliable data are available because of the rarity of such tumors. The treatment of choice for SBA is curative surgical resection. However, no standard protocol has been defined for use when SBA relapses or is unresectable because of locally advanced or metastatic status. Although several retrospective analyses have found that chemoth
Response to imatinib rechallenge in a patient with a recurrent gastrointestinal stromal tumor after adjuvant therapy: a case report
Yoon-Koo Kang
Journal of Medical Case Reports , 2011, DOI: 10.1186/1752-1947-5-504
Abstract: A 51-year-old Asian woman with a wedge-resected primary gastric gastrointestinal stromal tumor at high risk of relapse underwent two years of adjuvant treatment with imatinib. Only 10 months after the completion of adjuvant imatinib treatment, a computed tomography scan revealed gastrointestinal stromal tumor recurrence in this patient, with multiple peritoneal nodules in the upper abdomen being detected. Our patient was rechallenged with imatinib 400 mg/day and had a partial response after one month of treatment. Imatinib rechallenge was well tolerated by our patient; the only adverse events she experienced were grade 1 edema, anemia and fatigue. Our patient maintained a partial response two years and six months after the imatinib rechallenge. However, computed tomography scans three months later showed that our patient had disease progression.This case report demonstrates that a patient with a gastrointestinal stromal tumor who had previously received adjuvant imatinib therapy responded to imatinib rechallenge as treatment for her recurrent disease. These results indicate that imatinib sensitivity can be maintained in a patient with previous exposure to adjuvant imatinib therapy.Gastrointestinal stromal tumors (GIST) are the most common mesenchymal tumors of the gastrointestinal tract. These tumors are characterized by activating mutations of either receptor tyrosine kinase KIT or, less commonly, platelet-derived growth factor receptor α (PDGFRα) [1]. Imatinib mesylate, an oral selective inhibitor of KIT and PDGFRα, is approved for the treatment of adult patients with unresectable and/or metastatic KIT-positive (KIT+) GIST. It is also indicated for the adjuvant treatment of adult patients following resection of GIST [2]. Current guidelines [3,4] recommend adjuvant treatment with imatinib for at least one year and the use of risk assessment systems based on the main variables of mitotic rate, tumor size, tumor site and tumor rupture to guide patient selection for a
Olfactory receptors in non-chemosensory tissues
NaNa Kang & JaeHyung Koo*
BMB Reports , 2012,
Abstract: Olfactory receptors (ORs) detect volatile chemicals that lead tothe initial perception of smell in the brain. The olfactory receptor(OR) is the first protein that recognizes odorants in theolfactory signal pathway and it is present in over 1,000 genesin mice. It is also the largest member of the G protein-coupledreceptors (GPCRs). Most ORs are extensively expressed in thenasal olfactory epithelium where they perform the appropriatephysiological functions that fit their location. However, recentwhole-genome sequencing shows that ORs have been foundoutside of the olfactory system, suggesting that ORs may playan important role in the ectopic expression of non-chemosensorytissues. The ectopic expressions of ORs and their physiologicalfunctions have attracted more attention recently sinceMOR23 and testicular hOR17-4 have been found to be involvedin skeletal muscle development, regeneration, and humansperm chemotaxis, respectively. When identifying additionalexpression profiles and functions of ORs in non-olfactorytissues, there are limitations posed by the small number ofantibodies available for similar OR genes. This review presentsthe results of a research series that identifies ectopic expressionsand functions of ORs in non-chemosensory tissues toprovide insight into future research directions.
Almost Periodic Solutions of Nonlinear Discrete Volterra Equations with Unbounded Delay
Sung Kyu Choi,Namjip Koo
Advances in Difference Equations , 2008, DOI: 10.1155/2008/692713
Abstract: We study the existence of almost periodic solutions for nonlinear discrete Volterra equations with unbounded delay, as a discrete analogue of the results for integro-differential equations by Y. Hamaya (1993).
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