Yong Ki Park

Korea Research Institute of Chemical Technology, Daiden, Daejeon, South Korea

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Publications (61)96.94 Total impact

  • Lin Huang · Chul Wee Lee · Yong Ki Park · Sang-Eon Park
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    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
    No preview · Article · Dec 2010 · ChemInform
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    ABSTRACT: Magnetocardiography (MCG) is a device to measure the weak magnetic fields generated from the heart using a superconducting quantum interference device sensor which converts magnetic flux to voltage and is the most sensitive sensor to detect magnetism. In the previous study, authors found that the values of MCG parameters of patients with non-ST-segment myocardial infarction were greater than those of age-matched controls (AMCs). In this study, we selected five different groups of patients considering their severity. We compared 10 MCG parameters recorded from 19 healthy young subjects (26.8plusmn13.4 years), 19 age-matched healthy subjects (55.4plusmn10.7), 23 stable angina patients (56.4plusmn7.6 years) with no stenosis (=0% on coronary angiogram) and normal echocardiogram, 24 unstable angina patients (61.9plusmn9.8 years) with severe stenosis (ges70%), and 20 Q-wave myocardial infarction (QMI) patients (57.3plusmn11.2 years) with severe stenosis (ges70%). To record the magnetic signals from a heart with minimal noise, a magnetically shielded room was used. The number of abnormal parameters was counted and magnetic field map (MFM) patterns were compared. As a result, young healthy subjects showed the smallest values in all 10 MCG parameters and QMI subjects showed the greatest values. Significant difference was found from dynamics parameters such as current angle, map angle, and distance dynamics between young healthy controls and AMC groups (p>0.05). No significant difference was found from AMC and stable angina groups even though parameter values of stable angina were slightly greater than those of AMC. Significant difference was found from five parameters between AMC and QMI subjects. These results are supportive to the previous analysis. In addition, the abnormal MCG parameters increased when the ischemic disease was worsened. Abnormal MFM patterns were easily found from QMI patients than stable angina pectoris. It is clear that abnormal MFM and parameters - - increase when the status of ischemic heart disease patients are getting worse.
    No preview · Article · Jul 2009 · IEEE Transactions on Magnetics
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    ABSTRACT: We present a computational study of reentry wave propagation using electrophysiological models of human cardiac cells and the associated magnetic field map of a human heart. We examined the details of magnetic field variation and related physiological parameters for reentry waves in two-dimensional (2-D) human atrial tissue and a three-dimensional (3-D) human ventricle model. A 3-D mesh system representing the human ventricle was reconstructed from the surface geometry of a human heart. We used existing human cardiac cell models to simulate action potential (AP) propagation in atrial tissue and 3-D ventricular geometry, and a finite element method and the Galerkin approximation to discretize the 3-D domain spatially. The reentry wave was generated using an S1-S2 protocol. The calculations of the magnetic field pattern assumed a horizontally layered conductor for reentry wave propagation in the 3-D ventricle. We also compared the AP and magnetocardiograph (MCG) magnitudes during reentry wave propagation to those during normal wave propagation. The temporal changes in the reentry wave motion and magnetic field map patterns were also analyzed using two well-known MCG parameters: the current dipole direction and strength. The current vector in a reentry wave forms a rotating spiral. We delineated the magnetic field using the changes in the vector angle during a reentry wave, demonstrating that the MCG pattern can be helpful for theoretical analysis of reentry waves.
    Full-text · Article · Apr 2008 · Progress in Biophysics and Molecular Biology
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    ABSTRACT: Combined micro-Raman/UV-visible (vis)/fluorescence spectroscopy system, which can evaluate an integrated array of more than 10,000 microsamples with a minimuma size of 5 microm within a few hours, has been developed for the first time. The array of microsamples is positioned on a computer-controlled XY translation microstage with a spatial resolution of 1 mum so that the spectra can be mapped with micron precision. Micro-Raman spectrometers have a high spectral resolution of about 2 cm(-1) over the wave number range of 150-3900 cm(-1), while UV-vis and fluorescence spectrometers have high spectral resolutions of 0.4 and 0.1 nm over the wavelength range of 190-900 nm, respectively. In particular, the signal-to-noise ratio of the micro-Raman spectroscopy has been improved by using a holographic Raman grating and a liquid-nitrogen-cooled charge-coupled device detector. The performance of the combined spectroscopy system has been demonstrated by the high-throughput screening of a combinatorial ferroelectric (i.e., BaTi(x)Zr(1-x)O(3)) library. This system makes possible the structure analysis of various materials including ferroelectrics, catalysts, phosphors, polymers, alloys, and so on for the development of novel materials and the ultrasensitive detection of trace amounts of pharmaceuticals and diagnostic agents.
    Full-text · Article · Aug 2007 · Review of Scientific Instruments
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    ABSTRACT: Bi-functional nanoparticles (NPs) that consist of silica-coated magnetic cores and luminescent lanthanide (Ln) ions anchored on the silica surface via organic linker molecules are reported. Compared to individual Ln ions, the hybrid NPs show a drastically enhanced photoluminescence due to the efficient ligand-to-metal energy transfer in the Ln-loaded NPs: the new bi-functional NPs could be used in a variety of biological applications involving magnetic separation and optical detection.
    No preview · Article · May 2007 · Chemical Communications
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    ABSTRACT: Magnetocardiography (MCG) has been introduced as an innovative non-invasive diagnostic tool to identify various heart diseases. However, there have been little data on the reliability of MCG parameters. The purpose of this study is to examine the test-retest reliability of different diagnostic parameters derived from MCG. We investigated short-, intermediate-, and long-term reliability of nine parameters from T (max/3)-T (max) interval, and five parameters from each time point such as QRS-wave, the peak of R-, and T-wave were evaluated. Short-term reliability was tested in the youngest 20 subjects (mean age = 26.3 +/- 4.9 years) in three sessions separated by 5 min. Intermediate-term reliability was tested in the 35 subjects with coronary artery disease (CAD) (65.1 +/- 7.1 years) with two recording sessions each in the morning and afternoon, separated by more than four hours. Long-term reliability was tested in seven subjects (37.1 +/- 8.8 years) using seven daily sessions. Interclass correlation coefficients (ICC) showed that test-retest reliability was good to excellent (0.99 > or = ICC > or = 0.80) for six out of nine parameters within T (max/3)-T (max). In addition, all parameters on the peak of R-wave, T-wave, and QRS-wave integrated were good to excellent (0.99 > or = ICC > or = 0.80) except for one parameter of CAD patients showing lower ICC values under 0.7. In conclusion, our study showed that the test-retest characteristics of the studied MCG parameters are generally stable and reliable over periods of minutes to days in subjects with different age spectrums.
    No preview · Article · Feb 2007 · Annals of Biomedical Engineering
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    ABSTRACT: Magnetocardiography (MCG) has been proposed as a noninvasive diagnostic tool to risk-stratify patients with myocardial infarction (MI) and ischemia. The purpose of this study is to find the MCG parameters that are sensitive enough to detect the non-ST-segment elevation myocardial infarction (NSTEMI) patients. MCG data were recorded and analyzed from 165 young controls (mean age = 27.2 +/- 9.0 years), 57 age-matched controls (mean age = 55.9 +/- 10.5 years) and 83 NSTEMI patients (mean age = 59.7 +/- 11.1 years). The MCG recordings were obtained using a 64-channel MCG system in a magnetically shielded room. Statistical analyses were performed for 24 parameters derived from QRS-, R-, T-wave, and ST-T period. Binary boundaries to detect NSTEMI patients out of control subjects were found using the receiver operating characteristic (ROC) curve for each parameter. Fifteen parameters showed a significant difference (P < 0.05 and P < 0.01) between NSTEMI and both of the control groups. For detection of NSTEMI, the angle of the maximum current and the filed map angle on T-wave peak showed the highest diagnostic performance from 75% to 92% including accuracy, sensitivity, specificity, positive predictive value, and negative predictive value (area under ROC curve = 0.87 approximately 0.93). Our study showed that MCG has potential clinical application for detection of NSTEMI and should be further investigated.
    No preview · Article · Jan 2007 · Annals of Medicine
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    ABSTRACT: We have developed biocompatible ferrite (Fe3O4) nanoparticles whose surfaces are functionalized with biotin molecule. The resulting magnetic nanoparticles with an average diameter of 8nm have a biotin-anchored morphology, which gives an exceptionally high affinity for the Cy3-labeled streptavidin. The spectroscopic and magnetic data results confirmed the presence of the interaction between biotin-anchored Fe3O4 particles and Cy3-labeled streptavidins. These biocompatible magnetic nanoparticles can be used as a basic protocol for various biological applications, particularly linking molecules together to create signal generation systems.
    No preview · Article · Sep 2006 · Chemical Physics Letters
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    Kwang Seok Oh · Yong Ki Park · Seong Ihl Woo
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    ABSTRACT: Highly reliable 64-channel sequential and parallel tubular reactor for high-throughput screening of heterogeneous catalysts is constructed with stainless steel. In order to have a uniform flow rate at each channel, 64 capillaries are placed between the outlet of multiport valve and the inlet of each reactor. Flow rate can be controlled within ±1.5%. Flow distribution can be easily adjusted for sequential and parallel mode of operation. The reactor diameter is too big to have a uniform temperature distribution. Hence, the reactor body is separated into three radial zones and controlled independently with nine thermocouples. Temperature accuracy is ±0.5 °C at 300 °C and ±1 °C at 500 °C in sequential mode, while it is ±2.5 °C in the range of 250–500 °C in parallel mode. The temperature, flow rate, reaction sequence, and product analysis are controlled by LABVIEW™ software and monitored simultaneously with displaying a live graph. The accuracy in the conversion is ±2% at the level of 73% conversion when all reactors are loaded with same amount of catalyst. A quaternary catalyst library of 56 samples composed of Pt, Cu, Fe, and Co supported on AlSBA-15 (SBA-15 substituted with Al) are evaluated in the selective catalytic reduction of NO at various temperatures with our system. The most active compositions are rapidly screened at various temperatures.
    Preview · Article · May 2005 · Review of Scientific Instruments
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    ABSTRACT: Multichannel superconducting quantum interference device (SQUID) systems based on double relaxation oscillation SQUIDs (DROS) were developed for measuring magnetocardiography (MCG) and magnetoencephalography (MEG) signals. Since DROS provides large fluxto-voltage transfer coeffcients, about 10 times larger than the DC SQUIDs, direct readout of the SQUID output was possible using compact roomtemperature electronics. Using DROSs, we fabricated two types of multichannel systems; a 37-channel magnetometer system with circular sensor distribution for measuring radial components of MEG signals, and two planar gradiometer systems of 40-channel and 62-channel measuring tangential components of MCG or MEG signals. The magnetometer system has external feedback to eliminate magnetic coupling with adjacent channels, and reference vector magnetometers were installed to form software gradiometers. The field noise of the magnetometers is around 3 fT&sol;√Hz at 100 Hz inside a magnetically shielded room. The planar gradiometer systems have integrated first-order gradiometer in thin-film form with a baseline of 40 mm. The magnetic field gradient noise of the planar gradiometers is about 1 fT&sol;cm&sol;√Hz at 100 Hz. The planar gradiometers were arranged to measure field components tangential to the body surface, providing efficient measurement of especially MCG signals with smaller sensor coverage than the conventional normal component measurements.
    Full-text · Article · Feb 2005 · IEICE Transactions on Electronics
  • In Seon Kim · Kwon Kyu Yu · Yong Ki Park
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    ABSTRACT: YBCO dc SQUID magnetometers based on bicrystal Josephson junctions on 10 mm × 10 mm STO substrates have been fabricated. We have designed 16-parallel-loop pickup coil SQUID magnetometers with 50 mu m line width for use under a magnetically disturbed environment. The magnetometers exhibit stable flux locked loop operation under magnetically very noisy laboratory environment. We modified the coupling scheme between pickup coil and SQUID washer to replace the conventional narrow and long interconnection lines to reduce the residual inductance of the coupling lines. With the coupling line modification the effective area increased more than 12%. Finally, we could obtain optimized direct coupled YBCO SQUID magnetometer design having field sensitivity B_Phi of 4.5 nT/Phi 0 and magnetic field noise BN of 30 fT/Hz^1/2 measured at 100 Hz.
    No preview · Article · Mar 2004
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    ABSTRACT: We have fabricated single-layer, second-order high T<sub>c</sub> superconducting quantum interference device (SQUID) gradiometers on SrTiO <sub>3</sub> substrates and investigated their noise properties and performance in magnetocardiography. The gradiometer consists of three parallel pickup loops that are directly coupled to a step-edge junction SQUID, in such a way that the coupling polarity of two side loops is opposite to that of the center loop. The overall size of the device is 17.6 mm×6 mm with a baseline of 5.8 mm. The measured gradient noises are 0.45 and 0.84  pT/cm <sup>2</sup>/√ Hz at 1 Hz for the shielded and the unshielded cases, respectively, which correspond to equivalent field noises of 150 and 280  fT /√ Hz , respectively. In spite of the short baseline of 5.8 mm, the high common-mode rejection ratio of the gradiometer, 10<sup>3</sup>, allowed us to record a magnetocardiogram of a human subject, which demonstrates the feasibility of the design in biomagnetic studies. © 2004 American Institute of Physics.
    No preview · Article · Feb 2004 · Applied Physics Letters
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    ABSTRACT: We have studied properties of the superconducting MgB2 thin films made on sapphire substrates by radio frequency (rf) magnetron co-sputtering of Mg and B. The effects of annealing temperature and Mg:B ratio on the superconducting properties of the film were investigated. Films were prepared by room-temperature co-deposition of Mg and B using two guns and annealed in situ to form the superconducting MgB2 phase. Ar sputtering pressure was 20 mtorr with 5% of hydrogen gas to trap remnant oxygen gas in the deposition chamber. Average rf power density of Mg target was varied from 2 to 4 W cm−2 with that of B fixed at 12 W cm−2. An additional Mg layer was deposited on top to make up for Mg loss during in situ annealing. Films were heated up to 500–750 °C at the rate of 60 °C min−1, annealed for 20 min, and naturally cooled down by turning off the heater. The best results were obtained for films deposited with the rf power of Mg target at 50 W and annealed at 700 °C. The mechanism for MgB2 formation in low-pressure annealing is believed to be that during annealing the local Mg vapour pressure inside the film falls within the thermodynamic window.
    No preview · Article · Nov 2003 · Superconductor Science and Technology
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    ABSTRACT: The removal of nitric oxide from the exhaust gas of lean-burn engines is not fully commercialized since the current catalyst technology cannot meet the strict future emission regulations. Although ZSM-5 ion-exchanged with Pt (Pt/ZSM-5) has been considered as a promising catalyst due to its superior low-temperature activity, it has the drawback of a narrow “temperature window” for activity, i.e. an abrupt decrease in the activity above 300 °C. This paper reports on the preparation of novel Pt/ZSM-5 by subliming Pt(CO)2Cl2 into H-ZSM-5 at 220 °C, resulting in excellent activity within a wide temperature window between 230 and 500 °C. Pre-treatment of this Pt/ZSM-5 can change the width of the temperature window. Moreover, H2O plays a role as a promoter and SO2 reversibly reduces the activity by less than 20%.
    No preview · Article · Jan 2003 · Catalysis Letters
  • In-Seon Kim · Jin-Mok Kim · Hae-Ryong Lim · Yong Ki Park
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    ABSTRACT: The high-T<sub>c</sub> superconducting quantum interference device (SQUID) gradiometer system was developed for operation in unshielded environment. The system consists of the first-order gradiometer and the flux-locked loop electronics. YBa<sub>2</sub>Cu<sub>3</sub>O<sub>7</sub> single-layer first-order SQUID gradiometers were fabricated on 15 mm×7.5 mm SrTiO<sub>3</sub> bicrystal substrates with a baseline of 7 mm. The gradient sensitivities at 77 K and 100 Hz were 0.1 pT/(cm√Hz) in magnetic shielding and 1.4 pT/(cm√Hz) when operated unshielded in our laboratory. The high-T<sub>c</sub> SQUID gradiometer system demonstrated successful measurement of small magnetic fields in a laboratory environment without any shields
    No preview · Article · Apr 2001 · IEEE Transactions on Applied Superconductivity
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    ABSTRACT: We have designed a prototype single-layer second-order high-T<sub>c</sub> SQUID gradiometer that detects the transverse field gradient, and balanced the device by adopting a step-down method. The device consists of symmetrically designed 3 parallel-connected square pickup loops that are directly coupled to the SQUID. The dimensions of side loops are 3 mm outside and 1.8 mm inside. The inner dimension of the center loop is 1 mm. Step-down balancing was achieved by varying the outer dimension of the center loop until a null response was detected under uniform fields. The uniform field was generated by a 250 mm×25 mm square coil wound on a grooved garolite tube. Deviation of the coil field along the abscissa was calculated to be less than 1×10<sup>-5</sup> within the sample range. We have investigated response of the device to field gradients along the transverse direction. Details of the design, fabrication, and results will be discussed
    No preview · Article · Apr 2001 · IEEE Transactions on Applied Superconductivity
  • Hae-Ryong Lim · In-Seon Kim · Yong Ki Park · Dong Ho Kim
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    ABSTRACT: Step-edge YBa<sub>2</sub>Cu<sub>3</sub>O<sub>7-x</sub> (YBCO) dc SQUID magnetometers on sapphire substrates have been fabricated. CeO<sub>2</sub> buffer layers and YBCO films were deposited in situ on the low angle (~35°) steps formed on the sapphire substrates with various thickness ratio of YBCO thin film to step height. Noise properties of the magnetometer exhibit quite different behavior according to the thickness ratio. The field noise of the dc SQUID magnetometer was measured to be 100~300 fT/√Hz at 100 Hz and about 1.5 pT/√Hz at 1 Hz with a dc bias method, and 450 fT/√Hz at 1 Hz with an ac bias method
    No preview · Article · Apr 2001 · IEEE Transactions on Applied Superconductivity
  • Hae-Ryong Lim · In-Seon Kim · Dong Ho Kim · Yong Ki Park
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    ABSTRACT: YBa2Cu3O7 (YBCO) step edge Josephson junctions were fabricated on sapphire substrates. The steps were formed on r-plane sapphire substrates by using Ar-ion milling with PR masks. The step angle was controlled in the wide range from 20° to 70° by adjusting both the Ar-ion incident angle and the PR mask rotation angle relative to the incident Ar-ion beam. CeO2 buffer layer and in situ YBCO thin films were deposited on the stepped r-plane sapphire substrates by pulsed laser deposition. The YBCO film thickness was varied to obtain the ratio of film thickness to the step height in the range from 0.5 to 1. The step-edge junction exhibited RSJ-like behavior with ICRN product of 100∼300 μV, critical current density of 103∼105 A/cm2 at 77 K.
    No preview · Article · Nov 2000 · Physica C Superconductivity
  • In-Seon Kim · Hae-Ryong Lim · Dong Ho Kim · Yong Ki Park
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    ABSTRACT: YBa2Cu3O7 direct coupled dc SQUID magnetometers based on the step-edge junctions on sapphire substrates have been fabricated. 15-nm-thick CeO2 buffer layer and 120-nm-thick YBa2Cu3O7 film were in situ deposited on the 35° steps formed on the sapphire substrates by Ar ion milling. Large ICRN product of 250 μV with junction resistance RN ∼ 5 ω and critical current IC ∼ 50 μA at 77 K could be obatined reproducibly with 5 μm microbridges. The SQUID magnetometers fabricated on the 1×1 cm2 sapphire substrates based on the step-edge junctions exhibit a voltage modulation depth of 16μV and magnetic field noise of 170 fT/√Hz at 100 Hz for the 70 pH-SQUID.
    No preview · Article · Nov 2000 · Physica C Superconductivity
  • Chul Wee Lee · Woo Jin Lee · Yong Ki Park · Park S.-E
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    ABSTRACT: Vanadium-containing molecular sieves with mesopore structures such as MCM-41 and MCM-48, and micropore structures such as BEA and MFI were synthesized by hydrothermal method. XRD, FT-IR, UV–Vis DRS, EPR and XANES were used to characterize their structure, electronic states, and active sites of vanadium species. All the vanadium containing molecular sieves exhibit a pre-edge peak in the V K-edge XANES. The charge transfer transition bands appear at 250 and 340 nm are attributed to the [VVO]3+ species in the tetrahedral framework position and in the surface wall, respectively. Upon calcining the as-synthesized vanadium-containing samples in the air, VIV species are oxidized to VV which is EPR silent. VV is reduced reversibly by dehydration at 723 K. As for catalytic hydroxylation of benzene, V-MCM-41 shows the highest activity where the turnover number is 64 h−1 at 343 K. Under the higher temperature and the higher acidic conditions, respectively, the catalytic activity is enhanced.
    No preview · Article · Aug 2000 · Catalysis Today

Publication Stats

435 Citations
96.94 Total Impact Points

Institutions

  • 2003-2010
    • Korea Research Institute of Chemical Technology
      • Division of Advanced Material
      Daiden, Daejeon, South Korea
  • 1991-2009
    • Korea Research Institute of Standards and Science
      • • Medical Metrology
      • • Brain and Cognition Measurement Center
      • • Division of Metrology for Quality LIfe
      Daiden, Daejeon, South Korea
  • 1999-2000
    • Yeungnam University
      • Department of Physics
      Gyeongsan, Gyeongsangbuk-do, South Korea
  • 1997
    • Korea University
      • Department of Physics
      Seoul, Seoul, South Korea
  • 1992-1997
    • Korea Advanced Institute of Science and Technology
      • Department of Chemical and Biomolecular Engineering
      Sŏul, Seoul, South Korea
  • 1996
    • Kyung Hee University
      • Computer Engineering Division
      Seoul, Seoul, South Korea