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Biomedical subjects

Yoon Young Kim

Publications and source records attributed to Yoon Young Kim.

8 recordsLinked to original sources
PubMed2006

Proteome analysis of gametophores identified a metallothionein involved in various abiotic stress responses in Physcomitrella patens.

Physcomitrella patens is a model plant for studying gene function using a knockout strategy. To establish a proteome database for P. patens, we resolved over 1,500 soluble proteins from gametophore and protonema tissues by two-dimensional electrophoresis (2-DE) and obtained peptide mass fingerprints (PMFs) by matrix-assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS). Using expressed sequence tags (ESTs), we were able to predict the identities of 90 protein spots. Most of these were related to energy or primary metabolism. Comparative proteome analysis was used to identify proteins specific for each of the tissue types. One of these was a metallothionein type-2 (PpMT2) protein that was highly upregulated in gametophore tissue. PpMT2 was induced in both the gametophore and protonema following culture on solid media and in response to various abiotic stresses such as copper, cadmium, cold, indole-3-acetic acid, and ethylene. We suggest that PpMT2 is not only involved in metal binding and detoxification, but also in many biological aspects as a metal messenger or a protein with additional functions.

Amino Acid Sequence↗
PubMed2006

Waveguide damage detection by the matching pursuit approach employing the dispersion-based chirp functions.

If the wave mode used in guided wave non-destructive inspection is dispersive, reflected pulses from damaged parts may be significantly distorted due to wave dispersion. The main concern, in this case, is how to detect the reflected pulses in noisy signals, and to extract meaningful damage information from the detected pulses. However, current signal processing techniques used for guided wave inspection do not account for pulse dispersion, so the extracted information is often not so accurate. The objective of this study is to develop an efficient technique to deal with dispersed pulses for guided-wave nondestructive evaluation. Our idea is to model dispersed pulses by chirp functions of special form that can simulate up to quadratically varying group delay. To determine the parameters of the chirp functions approximating dispersed, reflected pulses, an adaptive matching pursuit algorithm is employed. Once the characterizing parameters are found, the damage location and extent can be estimated. The proposed method is tested with experimentally measured signals of longitudinal waves in a circular cylinder.

Journal Article↗
PubMed2005

Dispersion-based short-time Fourier transform applied to dispersive wave analysis.

Although time-frequency analysis is effective for characterizing dispersive wave signals, the time-frequency tilings of most conventional analysis methods do not take into account dispersion phenomena. An adaptive time-frequency analysis method is introduced whose time-frequency tiling is determined with respect to the wave dispersion characteristics. In the dispersion-based time-frequency tiling, each time-frequency atom is adaptively rotated in the time-frequency plane, depending on the local wave dispersion. Although this idea can be useful in various problems, its application to the analysis of dispersive wave signals has not been made. In this work, the adaptive time-frequency method was applied to the analysis of dispersive elastic waves measured in waveguide experiments and a theoretical investigation on its time-frequency resolution was presented. The time-frequency resolution of the proposed transform was then compared with that of the standard short-time Fourier transform to show its effectiveness in dealing with dispersive wave signals. In addition, to facilitate the adaptive time-frequency analysis of experimentally measured signals whose dispersion relations are not known, an iterative scheme for determining the relationships was developed. The validity of the present approach in dealing with dispersive waves was verified experimentally.

Journal Article↗
PubMed2005

Torsional wave experiments with a new magnetostrictive transducer configuration.

For the efficient long-range nondestructive structural health inspection of pipes, guided waves have become widely used. Among the various guided wave modes, the torsional wave is most preferred since its first branch is nondispersive. Our objective in this work is to develop a new magnetostrictive transducer configuration to transmit and receive torsional waves in cylindrical waveguides. The conventional magnetostrictive transducer for the generation and measurement of torsional waves consists of solenoid coils and a nickel strip bonded circumferentially to test pipes. The strip must be premagnetized by a permanent magnet before actual measurements. Because of the premagnetization, the transducer is not suitable for the long-term on-line monitoring of pipes buried underground. To avoid the cumbersome premagnetization and to improve the transduction efficiency, we propose a new transducer configuration using several pieces of nickel strips installed at 45 degrees with respect to the pipe axis. If a static bias magnetic field is also applied, the transducer output can be substantially increased. Several experiments were conducted to study the performance of the proposed transducer configuration. The proposed transducer configuration was also applied for damage detection in an aluminum pipe.

Journal Article↗
PubMed2005

Derivation and characterization of new human embryonic stem cell lines: SNUhES1, SNUhES2, and SNUhES3.

Here we report the derivation and characterization of new human embryonic stem cell (hESC) lines, SNUhES1, SNUhES2, and SNUhES3. These cells, established from the inner cell mass using an STO feeder layer, satisfy the criteria that characterize pluripotent hESCs: The cell lines express high levels of alkaline phosphatase, cell surface markers (such as SSEA-3, SSEA-4, TRA-1-60, and TRA-1-81), transcription factor Oct-4, and telomerase. When grafted into severe combined immunodeficient mice after prolonged proliferation, these cells maintained the developmental potentials to form derivatives of all three embryonic germ layers. The cell lines have normal karyotypes and distinct identities, revealed from DNA fingerprinting. Interestingly, analysis by electron microscopy clearly shows the morphological difference between undifferentiated and differentiated hESCs. Undifferentiated hESCs have a high ratio of nucleus to cytoplasm, prominent nucleoli, indistinct cell membranes, free ribosomes, and small mitochondria with a few crista, whereas differentiated cells retain irregular nuclear morphology, desmosomes, extensive cytoplasmic membranes, tonofilaments, and highly developed cellular organelles such as Golgi complex with secretory vesicles, endoplasmic reticulum studded with ribosomes, and large mitochondria. Existence of desmosomes and tonofilaments indicates that these cells differentiated into epithelial cells. When in vitro differentiation potentials of these cell lines into cardiomyocytes were examined, SNUhES3 was found to differentiate into cardiomyocytes most effectively.

Cell Differentiation↗
PubMed2005

Methods for expansion of human embryonic stem cells.

The manipulation of human embryonic stem cells (hESCs) requires refined skills. Here we introduce both mechanical and enzymatic transfer methods for hESCs depending on experimental purpose. We use the mechanical transfer method for maintenance of hESC lines. Although the method is laborious and time-consuming, the technique permits efficient transfer of undifferentiated hESCs and results in similar clump sizes. We implement the enzymatic transfer method when we need the bulk production of cells for various experiments. The enzyme-treated expansion rapidly produces greater amounts of hESCs within a limited time frame. However, the cell clumps vary in size, and there is a probability that both the differentiated and undifferentiated cells will be transferred. In cases in which there are differentiated colonies, the combination of two methods allows mass production of hESCs by excluding differentiated colonies from passage by manual selection before enzyme treatment.

Cell Culture Techniques↗
PubMed2002

Wave selection using a magnetomechanical sensor in a solid cylinder.

Magnetomechanical sensors have received much attention in recent years. However, investigations on the rejection of unwanted wave modes and thus the selection of a desired mode have not been reported. The purpose of this investigation is to present a technique to select only a desired wave mode in a solid ferromagnetic cylinder using a magnetomechanical sensor. To achieve this goal, we propose some bias magnet configurations for each of which either longitudinal or flexural waves alone can be extracted. A simplified theory relating bias magnet arrangement and measured wave modes is developed. Several experimental results confirm the validity of the present investigation.

Journal Article↗