J. Baek

Pohang University of Science and Technology, Geijitsu, Gyeongsangbuk-do, South Korea

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Publications (47)149.95 Total impact

  • International Journal of Radiation OncologyBiologyPhysics 10/2013; 87(2):S312-S313. · 4.18 Impact Factor
  • International Journal of Radiation OncologyBiologyPhysics 10/2013; 87(2):S279. · 4.18 Impact Factor
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    ABSTRACT: The objective of this study was to determine the incidence of typical and atypical enhancement patterns of hepatocellular carcinomas (HCCs) on multiphasic multidetector row CT (MDCT) and to correlate the enhancement patterns and morphological image findings of HCC with the degree of tumour differentiation. MDCT images of 217 patients with 243 surgically proven HCCs were evaluated through consensus reading by two radiologists. Our MDCT protocol was composed of precontrast, arterial, portal and delayed phases. The reviewers analysed the CT images for degree of attenuation; relative timing of washout; presence of dysmorphic intratumoral vessels, aneurysms and necrosis; tumour size; tumour margin; presence of pseudocapsule; intratumoral heterogeneity; and determined enhancement pattern. The imaging features were correlated with tumour differentiation using Fisher's exact test or the χ(2) test. Among 243 HCCs, 137 (56.4%) showed the typical enhancement pattern of HCC, which is arterial enhancement and washout on portal or equilibrium phase images. In the arterial phase, 190 of 243 (78.2%) HCCs showed hypervascularity, with approximately three quarters of poorly differentiated (PD) (34 of 45, 75.6%) and moderately differentiated (MD) HCCs (92 of 123, 74.8%) showing washout during the portal or delayed phases, vs only 50% of well-differentiated (WD) HCCs (11 of 22; p<0.048). The presence of intratumoral vessels and aneurysms, tumour necrosis, attenuation of precontrast, the relative timing of washout, intratumoral attenuation heterogeneity, tumour margin and tumour size were correlated with the pathological differentiation of HCCs (p<0.05). A typical enhancement of HCCs on MDCT was not unusual (43.6%) and WD and PD HCCs account for most of the atypical enhancement patterns. Early washout favoured MD and PD HCCs rather than WD HCCs, whereas in our study the presence of intratumoral aneurysm was a highly specific finding for PD HCC.
    The British journal of radiology 09/2012; 85(1017):e573-83. · 2.11 Impact Factor
  • Source
    E. Kim, J. Baek
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    ABSTRACT: The droplet ejection behavior from drop-on-demand printhead are investigated numerically in terms of the non-dimensional parameters. The numerical simulation is performed using a volume-of-fluid model. It is important to eject droplet within the printability range, where the droplet is ejected in stable manner without satellite droplets. Generally, the printability range has been determined by Z number, which is the inverse of Oh number. However, it is found that the ejection of droplets with same Z number can exhibit different behavior depending on the value of Ca and We number. Therefore, it is insufficient to determine the printability range only with Z number. Instead, other non-dimensional parameters, such as Ca and We number, should be considered comprehensively.
    Journal of computational fluids engineering. 06/2012; 17(2).
  • S Kim, J Park, J Baek
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    ABSTRACT: The blade angle distribution from the inlet to outlet of an impeller in a centrifugal compressor is known to have significant influence on its flow characteristics. With the aim of understanding the effect of the blade angle distribution, particularly on performance, loss generation, and operating range, four different blade angle distributions were defined with fixed inlet and outlet blade angles, and numerical calculations were conducted over their whole operating ranges, as defined by their stall points and choke conditions. The impeller blade Blade80, which has the smallest variation of blade angle and is relatively radial, was found to exhibit the smallest wall skin friction loss due to its small surface area but the highest blade loading loss. Further, the flow separation near the hub at the suction side and the tip and resulting energy loss give rise to the smallest stall margin of the blades. In contrast, Blade110, which has the largest variation of blade angle, exhibits the largest wall skin friction and hub-to-shroud loading losses but the lowest blade loading loss because the flow from the inlet to the outlet is well guided. As the flow coefficient increases, the performance of Blade110 steeply decreases. The poor performance of Blade110 at high mass flowrates can be explained in terms of flow blockage at the narrow throat. An attempt is made to explain the relationships between the blade angle distributions and the flow characteristics, loss generation, and performance of these impellers.
    Proceedings of the Institution of Mechanical Engineers Part A Journal of Power and Energy 03/2012; 226(2):208-217. · 0.60 Impact Factor
  • Journal of Allergy and Clinical Immunology 02/2012; 129(2):AB4. · 11.25 Impact Factor
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    ABSTRACT: From both spectral analysis and least square fitting on the Earth's polar motion, it has been found that 500-day period component exists with average amplitude of 20 milliarcseconds. Its existence is readily recognized in the residual polar motion time series subtracted of the Chandler and annual components. Prediction of polar motion is enhanced with assuming the existence of this component (r.m.s. error reduction by 50 percent).
    AGU Fall Meeting Abstracts. 12/2011;
  • J. Baek, S. Na, P. Park, B. Choi, S. Cho
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    ABSTRACT: We investigated the effects of different ocean tide models on the prediction of the ocean tide loading in Korean peninsula. The western part of Korean peninsula has large tidal range of water level and complicated rias coasts, so that accurate ocean tidal loading models are necessary for high-precise geodetic applications. The information of coastlines and the accuracy of the ocean tide model are key factors for high accurate ocean tide loading models. Recently, the global ocean tide models based on extensive observations and local tide models for the local area have been released. In this study, we analyzed the accuracy of ocean tide loadings with various ocean tide models. We developed a program for the convolutions of the mass of ocean tide and the load Green's functions. Comparing the computations with GOTIC2, the differences of vertical deformations due to M2 constituent were less than 0.4 mm in the case of the same ocean tide model. The five global ocean tide models, NAO99b, FES2004, DTU10, EOT11a and HAMTIDE, one regional tide model, NAO99Jb, and two local tide models were tested. The tests were performed in two ways. One was to use only global ocean tide models and the other one combined each global tide model and local tide model. Finally, we compared the computations with the GPS observations.
    AGU Fall Meeting Abstracts. 12/2011;
  • European Journal of Cancer 09/2011; 47. · 4.82 Impact Factor
  • European Journal of Cancer 09/2011; 47. · 4.82 Impact Factor
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    ABSTRACT: Objectives:Dentin sialophosphoprotein (DSPP), a typical dentin-specific protein, is mainly expressed in the dentin extracellular matrixand plays a role in dentin mineralization. BMP-2 provides a strong signal for differentiation and mineralization of odontoblasts and osteoblasts. The canonical BMP signaling pathway is known to contribute greatly to biomineralization, however, it is not known whether it is involved in Dspp expression. Here, we investigated this question. Methods: 1. Reverse transcription PCR and quantitative real-time PCR. 2. Site-directed mutagenesis of homeodomain binding sites. 3. Knockdown assays with siRNA. 4. Transient Transfection. 5. Luciferase reporter assay. 6. Electrophoretic Mobility Shift Assay (EMSA) 7. In silico Promoter Analysis Results: Activation of the canonical BMP-2 signaling pathway in MDPC-23, preodontoblast cell, by overexpression of constitutively active Smad1/5 or the downstream transcription factors Dlx5 and Runx2 stimulated Dspp expression. Conversely, knockdown of each element with siRNA significantly blocked the BMP-2-induced Dspp expression. To test whether these transcription factors downstream of BMP-2 are directly involved in regulating Dspp, we analyzed the mouse Dspp promoter. There are 5 well-conserved homeodomain binding elements, H1 to H5, in Dspp proximal promoter regions (-791 to +54). A serial deletion of H1 and H2 greatly changed basal promoter activity and responsiveness to Dlx5 or Msx2. However, further deletions did not change the responsiveness to Dlx5 or Msx2. H1 and H2 sites can be suggested as specific response element of Dlx5 and Msx2, respectively, based on their promoter activity modulation. Conclusions: Thus, the canonical BMP-2 signaling pathway plays a crucial part in the regulation of Dspp expression through the action of Smads, Dlx5, Runx2, and Msx2.
    IADR General Session 2011; 03/2011
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    ABSTRACT: Background: All-trans-retinoic acid (RA) and all-trans-retinol (ROL) are not widely used as anti-wrinkle agents due to their irritancy and photo-stability, respectively. Therefore, the safety and photo-stability in the development of RA or ROL derivatives have been an important issue. Aim: To identify the efficacy of retinyl retinoate as an anti-aging agent of cosmetics in treating females over 30 years old with periorbital wrinkles. Methods: The clinical study was a prospective, double-blind, randomized, and controlled study with a total of 11 Korean women. At every 4 weeks, the effectiveness was assessed with a global photodamage score, photographs, and image analysis using replicas and visiometers. The dermal distance and intensity was also evaluated using Dermascan C. Results: A statistically significant improvement in facial wrinkles (P<0.05) in eleven volunteers was observed in a clinical trial. The successive application of 0.06% retinyl retinoate cream for 3 months showed decreased depth and area of wrinkles in comparison with 0.075% retinol cream. The visual wrinkle improvement and the maximum roughness improvement rate (R2) for retinyl retinoate cream were 22% higher than that of retinol cream after 12 weeks. A statistically significant increase was observed after 8 and 4 weeks for dermal distance and dermal intensity, respectively (P<0.05). Conclusions: Retinyl retinoate had characteristic features of new anti-aging agents, and effectively improved facial wrinkle conditions.
    Skin Research and Technology 03/2011; · 1.41 Impact Factor
  • J. Baek, Y. Lee, H. Jee, K. Kim, M. Sohn
    Journal of Allergy and Clinical Immunology 02/2011; 127(2). · 11.25 Impact Factor
  • Fuel and Energy Abstracts 11/2010; 78(3).
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    ABSTRACT: Objectives: MEPE (matrix extracellular phosphoglycoprotein) is a bone-specific matrix protein and is a double-edged sword for biomineralization; the central domain is known to be dentonin that stimulates secondary dentin formation, while the C-terminal ASARM motif is known to be minhibin, a mineralization inhibitor. Thus, understanding the regulation of the gene expression will provide us an insight to control biomineralization. As BMP-2 and Wnt3a are strong stimulators of biomineralization, we investigated transcriptional control mechanism of MEPE expression by these ligands. Methods: Both canonical-BMP or -Wnt signaling activations are responsible for biomineralization. Osteogenic MC3T3-E1 cells were treated with osteogenic ligands like BMP-2 and Wnt3a. Results: The transfection of canonical BMP- or Wnt-pathway mediators such as Smad1/5 and β-catenin or the transfection of their downstream transcription factors such as Dlx5, Runx2 and Lef1 strongly enhanced Mepe mRNA expression. On the contrary, knockdown of each component of each pathway by respective siRNA interrupted BMP-2 or Wnt3a-induced Mepe expression. We identified highly conserved Dlx5, Runx2 or Lef-1 response elements in the Mepe proximal promoter, indicating it is a direct target of these osteogenic transcription factors. These are further proved by EMSA, site-directed mutagenesis and reporter assay, ChIP assay. Furthermore, we also found that Wnt3a treatment strongly stimulated Bmp-2 expression in both mRNA and protein level. Treatment with the conditioned medium (CM) to MC3T3-E1 cells increased phospho-Smad1/5 and their downstream Dlx5 expression, which is not blocked completely by a Wnt-3a blocker, Dkk-1, but almost completely suppressed by the addition of a BMP-2 blocker, Noggin. Conclusion: MEPE is a specific regulator of biomineralization. BMP-2 stimulates Mepe transcription directly by canonical BMP signaling pathway. Wnt3a stimulates Mepe transcription directly by canonical Wnt signaling pathway through β-catenin and Lef-1, and indirectly through the activation of BMP-2 autocrine loop. These results will provide a novel approach to regulate Mepe-mediated biomineralization.
    IADR General Session 2010; 07/2010
  • S Kim, J Park, K Ahn, J Baek
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    ABSTRACT: In this article, an effective optimization performed by the authors, at the design mass flowrate, of a vaned centrifugal compressor using the response surface method is presented. The optimization process was carried out consecutively for the impeller and the diffuser. As a result of the optimization process, the efficiency and pressure ratio of the optimized model were found to be better than those of the original model because of some improvements in flow characteristics. Compared with the original model, dramatic changes in the pressure and entropy contours could be obtained in the optimized model. In order to determine the performance in the off-design operating conditions, an off-design analysis was carried out. Also, the numerical calculations in this optimization process are validated by the experimental results and show good agreement with the experimental results except under choking conditions.
    Proceedings of the Institution of Mechanical Engineers Part A Journal of Power and Energy 03/2010; 224(2):251-259. · 0.60 Impact Factor
  • Journal of Allergy and Clinical Immunology 02/2010; 125(2). · 11.25 Impact Factor
  • Journal of Allergy and Clinical Immunology 02/2010; 125(2). · 11.25 Impact Factor
  • Journal of Allergy and Clinical Immunology 02/2010; 125(2). · 11.25 Impact Factor
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    ABSTRACT: With expanding commercial interests from various application areas, the production of carbon nanotubes (CNTs) in large scale is expected to grow rapidly. The inevitable release of CNTs into the environment and identification of the cytotoxicity of dispersed CNTs prompt the necessity of understanding their transport behavior in porous media. In this study, one-dimensional column experiments were conducted to assess the transport and retention of multi-wall nanotubes (MWNTs) in water-saturated 40-50 mesh Ottawa sand as a function of of tube length. In order to avoid damages to nanotube length by ultrasonication or superacids (e.g., HNO3), a chemical modification method involving a mild acid treatment was adopted to prepare suspensions of MWNTs with three different manufacture-reported (MR) lengths (0.5-2, 10-20, and 50 mum). For each experiment, a pulse (e.g., 5 pore volumes) of MWNT suspension was introduced into the column, followed by 3 pore volumes of MWNT-free solution elution. Measured concentrations of MWNTs in effluent and dissected solid samples were used to construct effluent breakthrough curves and retention profiles, respectively. For an input concentration of ca. 90 mg/L, MWNTs breakthrough concentrations decreased with the increasing MR length. Even with an MR length of 50 mum, MWNTs were readily transported through the packed bed, where ca. 80% of total injected nanotubes passed through the column. While the retention of MWNTs increased with MR length, concentrations of retained nanotubes decreased hyper-exponentially with distance from the column inlet. Further analysis of these findings suggests that clean-bed filtration theory alone is not sufficient to describe MWNT transport and retention behavior in a water-saturated quartz sand.
    AGU Fall Meeting Abstracts. 12/2009;

Publication Stats

351 Citations
149.95 Total Impact Points

Institutions

  • 2010–2012
    • Pohang University of Science and Technology
      • Department of Mechanical Engineering
      Geijitsu, Gyeongsangbuk-do, South Korea
    • Yonsei University Hospital
      • Department of Internal Medicine
      Sŏul, Seoul, South Korea
    • Yonsei University
      • Department of Radiation Oncology
      Sŏul, Seoul, South Korea
  • 2010–2011
    • Seoul National University
      • Department of Dentistry
      Sŏul, Seoul, South Korea
  • 2008
    • Ulsan University Hospital
      Urusan, Ulsan, South Korea
  • 2000–2007
    • Kyungpook National University Hospital
      • Department of Hemato-Oncology
      Sŏul, Seoul, South Korea