Youngshin Kim

Inhibition of RhoA but not ROCK induces chondrogenesis of chick limb mesenchymal cells.

Cell shape change and cytoskeletal reorganization are known to be involved in the chondrogenesis. Negative role of RhoA, a cytoskeleton-regulating protein, and its downstream target, Rho-associated protein kinase (ROCK) in the chondrogenesis has been studied in many different culture systems including primary chondrocytes, chondrogenic cell lines, dedifferentiated chondrocytes, and micromass culture of mesenchymal cells. To further investigate the role of RhoA and ROCK in the chondrogenesis, we examined the RhoA-ROCK-myosin light chains (MLC) pathway in low density culture of chick limb bud mesenchymal cells. We observed for the first time that inhibition of RhoA by C3 cell-permeable transferase, CT04, induced chondrogenesis of undifferentiated mesenchymal single cells following dissolution of actin stress fibers. Inhibition of RhoA activity by CT04 was confirmed by pull down assay using the Rho-GTP binding domain of Rhotekin. CT04 also inhibited ROCK activity. In contrast, inhibition of ROCK by Y27632 neither altered the actin stress fibers nor induced chondrogenesis. In addition, inhibition of RhoA or ROCK did not affect the phosphorylation of MLC. Inhibition of myosin light chain kinase (MLCK) by ML-7 or inhibition of myosin ATPase with blebbistatin dissolved actin stress fibers and induced chondrogenesis. ML-7 reduced the MLC phosphorylation. Taken together, our current study suggests that RhoA uses other pathway than ROCK/MLC in the modulation of actin stress fibers and chondrogenesis. Our data also imply that, irrespective of mechanisms, dissolution of actin stress fibers is crucial for chondrogenesis.

Finite element analysis on reduction of the cross talk in ultrasonic transducers

In an ultrasonic transducer, the cross talk between array elements is an important performance degrading factor, and there is strong need to identify the sources of the problem and to find the means to reduce its level. This paper considers two most representative ultrasonic transducers, capacitive micromachined ultrasonic transducer (cMUT) and piezoelectric transducer. Both are linear array immersion transducers. Two-dimensional finite element models of the transducers are constructed using the commercial code ANSYS. We analyze the origin and level of the cross talk between array elements, with evidence of coupling through certain waves such as the Stoneley wave propagating at the transducer-water interface and the Lamb wave propagating in the substrate or the impedance matching layer. For reduction of the cross talk level, the effects of various structural schemes are investigated. They are the change of wafer thickness, the installation of etched trenches of various dimension and sound absorbing materials inside, and installation of polymer walls between array elements for a cMUT as well as the change of the dimension and material of kerfs for a piezoelectric transducer. Results for the two transducers are discussed to describe the general method to reduce the cross talk level in ultrasonic transducers.

Analysis and Reduction of the Cross Talk in Micro-Machined Piezoelectric Ultrasonic Transducers

In a micro-machined ultrasonic array transducer, cross talk between array elements is one of the most important factors affecting the performance of the transducer, and there is strong need to identify the sources of the problem and to find the means to reduce the cross talk level. This paper considers a convex type piezoelectric linear array transducer working at 4.5 MHz when immersed. The transducer is composed of 64 piezoelectric plates separated by kerfs, a thick backing layer, two impedance matching front layers, and an acoustic lens. Through various analyses with twodimensional finite element models of the transducer, we analyzed the origin and level of the cross talk between array elements, with evidence of coupling through certain waves such as a Scholte wave and a Lamb wave. For reduction of the cross talk level, the effects of attenuative polymeric acoustic walls were investigated, which were placed between array elements in the transducer. The responses investigated were cross talk pressure in water, cross talk displacement at the acoustic layers, and cross talk voltage at the piezoelectric elements. The performance of the acoustic walls was compared with that of conventional kerfs implemented in the transducer. According to the results, the material property of the kerf filler and the walls did not have much influence on the level of the cross talk. The geometry and dimension of the kerfs and the polymeric walls turned out to have much larger effects instead. Results of time domain transient analysis, frequency domain harmonic analysis, and spatial radiation pattern analysis were discussed to describe the general method to reduce the cross talk level in the transducer. Introduction Mason type equivalent circuit analysis method is a widely accepted technology to analyze the behavior of micro-machined ultrasonic transducers [1]. However, the equivalent circuit model lacks some important features such as the coupling into the substrate and the ability to predict the cross talk between elements of an array of transducers. Many applications such as ultrasonic imaging, however, demand better understanding and improvement of transducers both in terms of individual device performance and array behavior. Considering that cross coupling between elements is one of the most important factors affecting the performance of an array transducer [2], there is a strong need to develop a multi-dimensional analysis technique to identify the sources of the problem and the means to reduce its effect. In this paper, two dimensional finite element models of micro-machined ultrasonic transducers are constructed using the commercial code ANSYS for multi-dimensional analysis of the cross talk mechanism. The transducers under consideration are piezoelectric transducers. The piezoelectric transducer is composed of a piezoelectric layer, two front matching layers, an acoustic lens and a thick backing material. Through various analyses with the models, we investigate the origin and level of the cross talk between array elements, with evidence of coupling through Stoneley waves at the transducer-water interface and coupling through Lamb waves in the acoustic lens. Further, the effects of various structural variations of the transducers are investigated to reduce the cross talk level. The structural variations include change of dimensions and materials of kerfs as well as acoustic walls placed between piezoelectric array elements. Key Engineering Materials Online: 2004-08-15 ISSN: 1662-9795, Vols. 270-273, pp 1071-1076 doi:10.4028/www.scientific.net/KEM.270-273.1071

Micromechanics on Spherical Contact with Roughness

Finite-element methods are used to study non-adhesive, frictionless rough contact of elastic and plastic solids. Roughness on the contact surfaces is realized by self-affine fractal. True contact area between spherical rough surfaces and flat rigid surfaces rises in power law as the external normal load increases. The power exponent is sensitive to surface roughness as well as the curvature of spherical geometry. Surface contact pressures are analyzed and compared for elastic and plastic solids. The distribution of local contact pressure is significantly dependent on the surface roughness and the yield stress of plastic solids.

Development of a model for measuring scientific processing skills based on brain-imaging technology: focused on the experimental design process

The purpose of this study was to develop a model for measuring experimental design ability based on functional magnetic resonance imaging (fMRI) during biological inquiry. More specifically, the researchers developed an experimental design task that measures experimental design ability. Using the developed experimental design task, they measured both the paper experimental design ability and the fMRI experimental design ability of subjects. Subjects’ paper experimental design ability was measured using the quotient equation of experimental design ability, and their fMRI experimental design ability using the brain connectivity coefficient. According to the fMRI results, differences in design ability existed among subjects in terms of brain connectivity coefficient level during the experimental design task. The experimental design ability brain connectivity coefficient level and quotient for each subject were analysed. Statistically significant correlations between subjects’ connectivity strength level among brain activation regions and quotient value guided the establishment of a measuring model. The model measured experimental design ability and could predict an individual’s experimental design ability quotient using his or her brain connectivity coefficient. Hence, the model developed for this study for measuring experimental design ability based on fMRI may serve as a practical measurement of students’ scientific experimental design ability. Furthermore, this study could serve as a founding theory for measuring models of other scientific processing abilities such as observation, question generation, classification, hypothesis generation and hypothesis evaluation.

Observation of Microorganisms in Milk after the Expiration Date Using Dry Rehydratable Film.

ABSTRACT Cultivation of microorganisms such as fungi and bacteria is often not included in scientific inquiries conducted in school because of the difficulty of manufacturing a suitable medium. A method using dry rehydratable film to reduce the need to manufacture a suitable medium and shorten incubation time was developed as an efficient microbial testing method. Using this method, students can easily perform experiments on microorganisms in schools where time and space are limited. For example, we carried out an inquiry on the possibility of drinking refrigerated milk that is already past its expiration date. Through this activity, we could raise issues related to the current shelf-life labeling system implemented in Korea. In addition, the method can measure microorganisms in several ways through air, direct contact, and indirect contact, making the procedure easier to use in scientific activities at school.

Structural Design and Optimization of a 3-Axis Miniaturized Machine Tool with High Precision Positioning Stages

The procedure of structural design on miniaturized machine tool (mMT) is proposed and structural optimization by applying robustness evaluation method is presented in this paper. The design procedure of a kind of mMT which is a 3-axis miniaturized milling machine tool (mMMT) is discussed and three different structures of mMMT are proposed based on previous design procedure. The most suitable structure is selected using robustness evaluation method, which is Taguchi method, due to volumetric error function. The design parameters of selected structure are optimized.