Kyung Tae Kim

National Cancer Center Korea, Kōyō, Gyeonggi Province, South Korea

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Publications (87)121.86 Total impact

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    ABSTRACT: Piwi-interacting RNAs (piRNAs) are 26-31 nt small noncoding RNAs that are processed from their longer precursor transcripts by Piwi proteins. Localization of Piwi and piRNA has been reported mostly in nucleus and cytoplasm of higher eukaryotes germ-line cells, where it is believed that known piRNA sequences are located in repeat regions of nuclear genome in germ-line cells. However, localization of PIWI and piRNA in mammalian somatic cell mitochondria yet remains largely unknown. We identified 29 piRNA sequence alignments from various regions of the human mitochondrial genome. Twelve out 29 piRNA sequences matched stem-loop fragment sequences of 7 distinct tRNAs. We observed their actual expression in mitochondria subcellular fractions by inspecting mitochondrial-specific small RNA-Seq datasets. Of interest, the majority of the 29 piRNAs overlapped with multiple longer transcripts (expressed sequence tags) that are unique to the human mitochondrial genome. The presence of mature piRNAs in mitochondria was detected by qRT-PCR of mitochondrial subcellular RNAs. Further validation showed detection of Piwi by colocalization using anti-Piwil1 and mitochondria organelle-specific protein antibodies.
    Biochemical and Biophysical Research Communications 01/2014; · 2.41 Impact Factor
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    ABSTRACT: Reduced graphene oxide/alumina composite powders were prepared by mixing of graphene oxides and aluminum ions at the molecular-level. It was found that the composite consolidated from the powders showed that reduced graphene oxide were homogeneously dispersed and strongly bonded with the alumina matrix by oxygen atoms presenting at reduced graphene oxide/alumina interfaces. Both the hardness and the toughness of the composites were enhanced simultaneously by the addition of reduced graphene oxide, which act as bridges to restrain the propagation of cracks in the alumina matrix. It is clarified that graphenes can be utilized as promising reinforcements for enhancement in mechanical properties of ceramic materials when the molecular-level mixing process is applied.
    Carbon. 01/2014; 78:212–219.
  • Kyung Tae Kim, Jong Won Lee, Won Ho Jo
    Macromolecular Chemistry and Physics 12/2013; 214(23). · 2.39 Impact Factor
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    ABSTRACT: Aging-dependent physiological conditions are attributed to parenchymal structural changes to cellular functions in aged organisms. To understand these aging-dependent processes, we compared the glucose formation capacity of primary hepatocytes from young (4-month-old) and old (24-month-old) Fisher 344 rats. The primary hepatocytes from old rats showed a higher glucose output and a higher expression of the key gluconeogenesis-regulating enzyme, phosphoenol pyruvate carboxykinase (PEPCK), compared with those from the young animals. The in situ hybridization study showed increased PEPCK mRNA expression in the aged liver tissues. The livers from old rats showed loosened hexagonal hepatic lobular structures, increased collagen accumulation, and high expression of the hypoxia marker hypoxia-inducible factor 1α (HIF1α). Hypoxia increased the PEPCK mRNA and protein expression levels in accordance with the HIF1α expression. PEPCK promoter luciferase reporter assay showed that hypoxia increased PEPCK through transcriptional activation. Furthermore, the Hepatocyte nuclear factor α (HNF4α) protein, but not the HNF4α mRNA level, increased in parallel with the PEPCK mRNA expression under hypoxic conditions. The glucose production increased in hypoxic condition, but this increment diminished by HNF4α siRNA in young hepatocytes. Moreover, increased glucose production from old rat hepatocytes was reversed by the down-regulation of HNF4α through a specific siRNA. This study suggests that the mild hypoxic conditions in response to aging-dependent hepatic structural changes may contribute to the induction of the gluconeogenic enzyme PEPCK through HNF4α protein stabilization.
    Experimental gerontology 10/2013; · 3.34 Impact Factor
  • Sung Jin Choi, Kyung Tae Kim, Hee Yong Youn
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    ABSTRACT: Currently, sensor networks are widely used in various fields. Here secure operations are required for critical applications since the damages are significant if the network is compromised or disrupted. For the security of wireless sensor network, the earlier schemes typically employ asymmetric cryptography. These schemes are, however, often unsuitable for wireless sensor network due to the limited computational power and energy of the sensor nodes. To address this issue, various approaches have been developed, and the random key predistribution approach has been recognized as an effective approach. One shortcoming, however, is that a common key is not guaranteed to be found between any two nodes wanting to communicate. This paper proposes a new robust key predistribution scheme solving this problem, with which the security is not compromised even though the data exchanged between the nodes are tapped by an adversary. This is achieved by using the keys assigned based on the notion of eigenvalue and eigenvector of a square matrix of a pool of keys. Mathematical analysis and computer simulation reveal that the proposed scheme significantly reduces the overhead required for secure connectivity and energy consumption of sensor nodes compared to the existing approaches.
    International Journal of Distributed Sensor Networks 06/2013; 2013. · 0.73 Impact Factor
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    ABSTRACT: OBJECTIVE: To assess the relationship between mycoplasma infection and human infertility, we determined the concordance of Ureaplasma urealyticum (UU) and Mycoplasma hominis (MH) detection in infertile and fertile couples, and assessed semen parameters in both groups. METHODS: Fifty infertile couples without a female factor attending a fertility clinic and 48 fertile couples were randomly screened for UU and MH. The concordance between partners was compared between the fertile and infertile groups. Semen and endocervical specimens were evaluated using the commercially available Mycofast Evolution2 test. RESULTS: UU was detected in 24 semen specimens (48%) from the infertile men, in 12 specimens from fertile men (25%), in 20 endocervical specimens from infertile women (40%), and 11 from fertile women (22.9%). UU was detected higher in infertile men than in fertile men (P = .022). The concordance of UU was higher in infertile couples (32%) than in fertile couples (12.5%, P = .022). The concordance of MH between male and female partners in the 2 groups did not differ significantly. The mean values of total motility, progressive motility, normal morphology, vitality, and total motile sperm count were significantly lower in sperm from infertile men than from fertile men. Progressive motility and vitality were significantly lower in UU-positive men than in men without UU, and low total motility and total motile sperm count were significantly related to the presence of MH. CONCLUSION: Clinicians should consider the roles of UU and MH in infertility and routinely screen infertile couples for the presence of these mycoplasma species.
    Urology 04/2013; · 2.42 Impact Factor
  • Kyung Tae Kim, Won Ho Jo
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    ABSTRACT: Although graphene itself is a zero-bandgap semimetal, graphene nanoribbon (GNR) with a width smaller than 10 nm exhibits semiconducting behavior that renders them suitable for active materials of electronic devices. Several methods have been reported to produce GNRs, such as lithography, unzipping of CNTs, mechanical exfoliation and CVD. However, the uncontrollable character of these methods or in some case the harsh conditions restrict severely the quality of the resulting graphenes and consequently limit their applications. In this study, we synthesized GNRs with various widths from the corresponding polymer precursors and investigated their TFT properties. For synthesis of GNRs, we first synthesized polymers with phenylene, naphthalene and anthracene units by the Suzuki coupling reaction between dibromine monomer and diboronic ester monomer. The polymers were then converted into the corresponding GNRs through intramolecular cyclodehydrogenation reaction. The cyclodehydrogenation were identified quantitatively by NMR analysis. All GNR-based TFTs showed ambipolar transport behavior. The anthracene-based GNR exhibits the best TFT performance among three GNRs due to longer conjugated length, larger width and stronger π-stacking as compared to phenylene- and naphthalene-based GNRs.
    03/2013;
  • Min Soo Kang, Kyung Tae Kim, Jea Uk Lee, Won Ho Jo
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    ABSTRACT: A high-yielding dispersion of graphene at high concentration in solvent is critical for practical applications. Herein, we demonstrate the formation of a stable dispersion of pristine graphene in ethanol by exfoliating graphite flakes into individual graphene layers using a non-ionic polymer surfactant under bath-type sonication. Oligothiophene-terminated poly(ethylene glycol) was synthesized and used as a non-ionic and amphiphilic surfactant for exfoliating graphite into graphene. A high-quality graphene film was fabricated from the exfoliated graphene solution by the vacuum filtration method. TEM and SEM reveal that the size of exfoliated graphene flakes is larger than 1 μm. When the graphene film was treated with nitric acid and thionyl chloride after washing with solvent, the film showed high performance with a sheet resistance of 0.3 kΩ sq−1 and a transparency of 74% at 550 nm.
    J. Mater. Chem. C. 02/2013; 1(9):1870-1875.
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    Kyung Tae Kim, Injoon Son, Gook Hyun Ha
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    ABSTRACT: Carbon nanotube-dispersed bismuth telluride matrix (CNT/) nanopowders were synthesized by chemical routes followed by a ball-milling process. The microstructures of the synthesized CNT/ nanopowders showed the characteristic microstructure of CNTs dispersed among disc-shaped nanopowders with as an average size of 500 nm in-plane and a few tens of nm in thickness. The prepared nanopowders were sintered into composites with a homogeneous dispersion of CNTs in a matrix. The dimensionless figure-of-merit of the composite showed an enhanced value compared to that of pure at the room temperature due to the reduced thermal conductivity and increased electrical conductivity with the addition of CNTs.
    Journal of Korean Powder Metallurgy Institute. 01/2013; 20(5).
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    ABSTRACT: Logistics is a crucial ingredient in the operation of an organization. Here how to efficiently deliver the supplies to the consumers in the field under the given condition is the key issue. The general logistics system is usually too complex to be modeled mathematically, or the models are overly computation intensive to be applied in real-time environment. This paper proposes a new method for logistics based on multi-agent system using modified A* algorithm to find the best route between the agents. In addition, genetic algorithm and K-medoids algorithm are used for selecting and clustering the agents to maximize the throughput of logistics. Computer simulation verifies the efficiency of the proposed scheme for a complicated application domain of military logistics.
    Information Networking (ICOIN), 2013 International Conference on; 01/2013
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    ABSTRACT: Graphene oxide (GO) prepared in bulk quantities by oxidation of graphite with strong oxidants contains many hydrophilic groups, such as hydroxyl, epoxy, and carboxyl acid. We present a method to efficiently convert these hydrophilic groups into alkyl and alkyl ether groups by a one step reaction of bimolecular nucleophilic substitution with alkyl bromide. The functionalized graphene oxide (fGO) can be homogeneously dispersed as exfoliated monolayers in various organic solvents without degradation of size and shape of graphene oxide sheet. The degree of substitution reaction of each hydrophilic group in GO with alkyl bromide is quantitatively determined by comparing the deconvoluted O 1s X-ray photoelectron spectrum of GO with that of fGO. Addition of a small amount of fGO in poly(ethylene terephthalate) (PET) improves remarkably tensile and gas barrier properties of PET/fGO composite due to homogeneous dispersion of fGO sheets in PET matrix.
    ACS Applied Materials & Interfaces 07/2012; 4(8):4184-91. · 5.01 Impact Factor
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    ABSTRACT: Ti alloy matrix composites reinforced with nanosized TiB whiskers (TiBw/Ti–6Al–4V) were synthesized through an in situ reaction between TiB2 and Ti–6Al–4V powders during a spark plasma sintering process. The TiBw/Ti–6Al–4V composites reinforced by whiskers with an aspect ratio of 58 exhibited threefold greater strengthening efficiency compared to those reinforced by whiskers with low aspect ratios. It was determined that the strengthening originates from the high load-bearing capability of TiB whiskers with a diameter of 100 nm formed in situ in a Ti alloy matrix.
    Scripta Materialia. 04/2012; 66(7):487–490.
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    ABSTRACT: Thermal ablation using radiofrequency is a new, minimally invasive modality employed as an alternative to surgery in patients with benign thyroid nodules and recurrent thyroid cancers. The Task Force Committee of the Korean Society of Thyroid Radiology has developed recommendations for the optimal use of radiofrequency ablation for thyroid nodules. These recommendations are based on a comprehensive analysis of the current literature, the results of multicenter studies, and expert consensus.
    Korean journal of radiology: official journal of the Korean Radiological Society 03/2012; 13(2):117-25. · 1.32 Impact Factor
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    ABSTRACT: We report a patient who developed subarachnoid hemorrhage (SAH) just after coronary angiography (CAG) with non-ionic contrast media (CM) and minimal dose of heparin. The 55-year-old man had a history of acute ST elevation myocardial infarction that had been treated with primary percutaneous coronary intervention and was admitted for a follow-up CAG. The CAG was performed by the transradial approach, using 1000 U of unfractionated heparin for the luminal coating and 70 mL of iodixanol. At the end of CAG, he complained of nausea and rapidly became stuporous. Brain CT showed a diffusely increased Hounsfield unit (HU) in the cisternal space, similar to leakage of CM. The maximal HU was 65 in the cisternal space. No vascular malformations were detected on cerebral angiography. The patient partially recovered his mental status and motor weakness after 2 days. Two weeks later, subacute SAH was evident on magnetic resonance imaging. The patient was discharged after 28 days.
    Korean Circulation Journal 03/2012; 42(3):197-200.
  • Kyung Tae Kim, Gook Hyun Ha
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    ABSTRACT: In this study, bismuth telluride (Bi2Te3)-based nanopowders with particle size ranging from 100 to 300 nm are prepared by high-energy ball milling. Then, the prepared nanopowders are homogeneously mixed with organic binders to form a paste; this paste is used as the raw material to prepare thick-film thermoelectric modules. The thick film prepared by screen printing followed by hot pressing of p-type pastes show reproducible thermoelectric properties, exhibiting an electrical resistivity of 2.0 m Omega cm and a Seebeck coefficient of 298 muVK-1. The prepared p-type Bi2Te3 thick film has a high power factor because its Seebeck coefficient is significantly higher than that of Bi2Te3 based-bulk materials. These results indicate that a thick film prepared from bismuth telluride nanopowders has potential for use as high-performance thermoelectric modules in practical applications such as power generation and cooling system in electronic devices.
    Journal of Nanoscience and Nanotechnology 02/2012; 12(2):1577-80. · 1.15 Impact Factor
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    ABSTRACT: To evaluate clinical aspects and imaging features of complications encountered in the treatment of benign thyroid nodules with radiofrequency (RF) ablation. Institutional review board approval was obtained for this retrospective study, and informed consent was waived. From June 2002 to September 2009, 1459 patients underwent RF ablation of 1543 thyroid nodules with an RF system with internally cooled electrodes at 13 thyroid centers, which were members of Korean Society of Thyroid Radiology. Numbers and types of major and minor complications were assessed. The authors observed 48 complications (3.3%), 20 major and 28 minor. The major complications were voice changes (n = 15), brachial plexus injury (n = 1), tumor rupture (n = 3), and permanent hypothyroidism (n = 1). The minor complications were hematoma (n = 15), skin burn (n = 4), and vomiting (n = 9). All patients recovered spontaneously except for one with permanent hypothyroidism and one who underwent surgery. Although the complication rate of RF ablation is low, various complications may occur; comprehension of complications and suggested technical tips may prevent complications or properly manage those that occur.
    Radiology 01/2012; 262(1):335-42. · 6.34 Impact Factor
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    ABSTRACT: Vascular endothelial growth factor (VEGF) greatly contributes to the progression of hepatocellular carcinoma (HCC). It is reported that a selective cyclooxygenase-2 (COX-2) inhibitor inhibits cellular proliferation and may attenuate VEGF expression in HCC. We propose that different cascades in the VEGF pathway respond to COX-2 inhibition, depending on the cell types. The six human HCC cell lines--Hep3B, SNU387, SNU182, SNU423, SNU449, and PLC/PRF5--were cultured under normoxic and hypoxic conditions. Cells were treated with a selective COX-2 inhibitor (NS-398) and discoidin domain receptor 2 (DDR2) siRNA, and microarray analysis was performed. NS-398 inhibited HCC proliferation and decreased the expression level of VEGF in HCC cells only under normoxia conditions. In hypoxia conditions, VEGF expression level in Hep3B cell was suppressed, while that in SNU387 cell was increased by NS-398 (P < 0.001). The NS-398-induced increase in VEGF expression in SNU387 cell was associated with the up-regulation of the DDR2 gene. NS-398-treated SNU series cells and PLC/PRF5 cells displayed a robust increase in DDR2 mRNA expression. Also, transfection with DDR2 siRNA decreased the VEGF expression level of SNU387, 423, 449 cells under hypoxia conditions (P < 0.05). In vivo chromatin immunoprecipitation assay demonstrated that NS-398 induces the enhancement of HIF-1α binding on VEGF promoter, leading to the increase in VEGF gene expression in hypoxic conditions. There is strong evidence that it is related to the DDR2 gene expression in SNU387 cells. These findings disclose a novel cell-dependent regulatory mechanism of VEGF involving DDR2 gene in HCC cells.
    Journal of Cancer Research and Clinical Oncology 01/2012; 138(1):73-84. · 2.91 Impact Factor
  • Kyung Tae Kim, Hee Yong Youn
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    ABSTRACT: Energy efficiency is a critical issue for sensor network since the network lifetime depends on efficient management of the energy resource of sensor nodes. Particularly, designing energy efficient MAC protocol has a significant influence on the performance of wireless sensor network with regards to the energy. The existing MAC protocols developed for sensor network try to avoid energy waste during idle listening time by controlling the duty cycle of the transmission period. Since the traffic conditions are diverse, they may not always display improvements in energy consumption. In this paper we propose a new energy efficient MAC protocol called dynamic threshold MAC (DT-MAC), which employs a dynamic threshold for the buffer of each sensor node to maximize the energy efficiency regardless of specific network traffic condition. Here the packets are stored in the buffer, and then transmitted when the number of packets in the buffer exceeds the threshold dynamically decided according to the number of hops of the node from the source in the path of packet forwarding. The simulation results using OMNnet++ show that DT-MAC enables significant improvement in energy consumption compared to the existing MAC protocols. The proposed DT-MAC protocol also reduces the number of transmissions of control packets.
    International Journal of Distributed Sensor Networks 01/2012; 2012. · 0.73 Impact Factor
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    ABSTRACT: A novel solution-stamping process for the preparation of a highly conductive aluminum thin film on both rigid and flexible substrates is proposed. The superior electrical properties of Al thin films fabricated by the solution-stamping process compared to silver and gold films fabricated from colloidal nanoparticles are experimentally demonstrated, and their applications in electronic circuits on rigid and flexible substrates and to organic light-emitting diodes (OLEDs) are investigated.
    Advanced Materials 11/2011; 23(46):5524-8. · 14.83 Impact Factor
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    ABSTRACT: The microstructure of carbon nanotube reinforced copper matrix (CNT/Cu) nanocomposites, processed by molecular-level mixing, exhibits CNTs homogeneously dispersed in the Cu matrix. Measured thermal conductivity of the fabricated CNT/Cu nanocomposites decreased as the CNT volume fraction increased from 5% to 10%. A low coefficient of thermal expansion (CTE) was obtained from the 10 vol.% CNT/Cu nanocomposite. These results indicate that embedded CNTs provide CNT/metal interfaces as thermal barriers but also stiffen the metal matrix composites.
    Scripta Materialia 01/2011; · 2.82 Impact Factor

Publication Stats

420 Citations
121.86 Total Impact Points

Institutions

  • 2013–2014
    • National Cancer Center Korea
      • Molecular Epidemiology Branch
      Kōyō, Gyeonggi Province, South Korea
  • 2010–2014
    • Korea Institute of Materials Science
      Sŏngnam, Gyeonggi Province, South Korea
  • 2005–2013
    • Sungkyunkwan University
      • College of Information and Communication Engineering (SoICE)
      Sŏul, Seoul, South Korea
  • 2004–2013
    • Gachon University
      • Department of Electrical Engineering
      Sŏngnam, Gyeonggi Province, South Korea
  • 1998–2013
    • Seoul National University
      • • Department of Materials Science and Engineering
      • • Department of Food and Nutrition
      Sŏul, Seoul, South Korea
  • 2008–2010
    • Konkuk University
      Sŏul, Seoul, South Korea
    • Hanyang University
      • Major in Obstetrics and Gynecology
      Sŏul, Seoul, South Korea
  • 2003–2008
    • Seoul National University Hospital
      Sŏul, Seoul, South Korea
  • 2007
    • Myongji University
      • Department of Mathematics
      Seoul, Seoul, South Korea
  • 2006
    • Korea Institute of Machinery and Materials
      Sŏul, Seoul, South Korea
    • Korea Advanced Institute of Science and Technology
      • Department of Materials Science and Engineering
      Sŏul, Seoul, South Korea