Young H. Kim

Analysis of an asymmetrical piezoelectric annular bimorph using impedance and admittance matrices

A theoretical model is presented for the analysis of an asymmetrical piezoelectric annular bimorph (APAB) in dynamic harmonic motion. The APAB is assumed to be so thin that the thickness dependent stresses vanish throughout. The conjugate parameters of the admittance and impedance matrices are derived using the variational principle. Both the extensional and flexural motions are considered in deriving the motional equations and the boundary conditions. By using the symmetry characteristic of the admittance matrix, the derivation procedure for the impedance and admittance matrices is thus greatly simplified. The resonance and antiresonance frequencies and the effective electromechanical coupling factors are calculated using the matrices. These present methods are applied to three special cases: a single piezoelectric ring in extensional motion, a triple-layer APAB in series or parallel connection, and a triple-layer APAB with sensor and actuator. The results are compared with previous publication and finit...

Persistent activation of STAT3 by PIM2‐driven positive feedback loop for epithelial‐mesenchymal transition in breast cancer

Metastasis of breast cancer is promoted by epithelial–mesenchymal transition (EMT). Emerging evidence suggests that STAT3 is a critical signaling node in EMT and is constitutively activated in many carcinomas, including breast cancer. However, its signaling mechanisms underlying persistent activation of STAT3 associated with EMT remain obscure. Here, we report that PIM2 promotes activation of STAT3 through induction of cytokines. Activation of STAT3 caused an increase in PIM2 expression, implicating a positive feedback loop between PIM2 and STAT3. In agreement, targeting of either PIM2, STAT3 or PIM2‐dependent cytokines suppressed EMT‐associated migratory and invasive properties through inhibition of ZEB1. Taken together, our findings identify the signaling mechanisms underlying the persistent activation of STAT3 and the oncogenic role of PIM2 in EMT in breast cancer.

Impedance and admittance matrices of symmetric piezoelectric annular bimorphs and their applications

The 5 x 5 impedance and admittance matrices of a symmetric triple-layer piezoelectric annular bimorph (PAB) are presented and the PAB with the piezoelectric layers partially covering the shim layer in harmonic motion is analyzed using the matrices. The electromechanical flow vectors are defined as the mechanical displacements and rotations at the inner and outer boundaries and the electric current of the piezoelectric layer; the conjugate parameters, i.e., the electromechanical effort vectors, are accordingly defined. The impedance matrix which relates the flow vector with the effort vector is divided into three matrices, the mechanical, electrical, and electromechanical coupling impedance matrices; each matrix is represented by a block network with five ports. The resonance and the antiresonance frequencies and the effective electromechanical coupling factors of the PAB excited by the partially covering piezoelectric layers are then calculated for various boundary conditions imposed at the inner and outer surfaces. The numerical results by the impedance matrix are compared with those by the finite element methods; they are in excellent agreement with each other. It is also shown that the matrix representations can be easily applied to the piezoelectric circular bimorph (PCB) with the extended shim layer.

A new 2-pyrone derivative, 5-bromo-3-(3-hydroxyprop-1-ynyl)-2H-pyran-2-one, suppresses stemness in glioma stem-like cells.

Glioma cells with stem cell properties, termed glioma stem-like cells (GSCs), have been linked to tumor formation, maintenance, and progression and are responsible for the failure of chemotherapy and radiotherapy. Because conventional glioma treatments often fail to eliminate GSCs completely, residual surviving GSCs are able to repopulate the tumor. Compounds that target GSCs might be helpful in overcoming resistance to anticancer treatments in human brain tumors. In this study, we showed that 5-bromo-3-(3-hydroxyprop-1-ynyl)-2H-pyran-2-one (BHP), a new 2-pyrone derivative, suppressed the maintenance of the GSC population in both a glioma cell line and patient-derived glioma cells. Treatment of GSCs with BHP effectively inhibited sphere formation and suppressed the CD133+ cell population. Treatment with BHP also suppressed expression of the stemness-regulating transcription factors Sox2, Notch2, and β-catenin in sphere-cultured glioma cells. Treatment of GSCs with BHP significantly suppressed two fundamental characteristics of cancer stem cells: self-renewal and tumorigenicity. BHP treatment dramatically inhibited clone-forming ability at the single-cell level and suppressed in vivo tumor formation. BHP markedly inhibited both phosphoinositide 3-kinase/Akt and Ras/Raf-1/extracellular signal-regulated kinase signaling, which suggests that one or both of these pathways are involved in BHP-induced suppression of GSCs. In addition, treatment with BHP effectively sensitized GSCs to chemotherapy and radiotherapy. Taken together, these results indicate that BHP targets GSCs and enhances their sensitivity to anticancer treatments and suggest that BHP treatment may be useful for treating brain tumors by eliminating GSCs.

Investigation of the contact force distribution and dynamic behaviour of an automobile windshield wiper blade system

The structural behaviour of a windshield wiper system and the dynamic behaviour of the wiper rubber blade are investigated using finite element analysis. Non-linear contact analysis was performed to examine the influences of the structural design variables such as the curvature of the primary beam, the thickness of the yoke, the rotational angle of the yoke and the thickness of the steel beam on the distribution of the contact force along the blade length, and the effects of the vertical load and the coefficient of friction on the vibrational behaviour of the blade were investigated using transient dynamic analysis. Experimental validation was conducted by measuring the contact force distribution and the vibrational behaviour of the rubber blade. The experimental data and the simulated results show good agreement. The contact force distribution is sensitive to changes in the primary beam’s curvature, the yoke’s rotational angle and the steel beam’s thickness. The vertical load and the coefficient of friction both have significant influences on the vibrational behaviour of the rubber blade. It is found that the proper combination of the variables investigated allows a more uniform contact force distribution and less vibration and thereby improves the performance of the wiper blade. These analyses demonstrate the variables that influence the wiper blade behaviour and should provide key insight into means for improving the wiper performance.

Effects of higher‐order harmonics on phase determination in an ultrasonic interferometer

The effect of higher-order harmonic components on phase determination were analyzed to improve the accuracy of transient time measurement in an ultrasonic interferometer with a quadrature detector system. Under ideal conditions the locus of output signals of the phase sensitive detector forms a circle on the phase plane as the frequency changes and any nonideal factor would distort the circle, leading to erratic phase determination. This analysis has shown that the nth-order contribution to the phase is mostly determined by the product of the amplitudes of corresponding components of the reference and echo signals fed to the phase detector. The distortion parameters were obtained by least-squares fitting of the data to the distorted circle in the phase plane, and compared with those roughly estimated from the frequency components of the reference and echo signals. The exemplary numerical phase corrections for the third-order harmonics were carried out, so as to illustrate the improvement in the accuracy of the ultrasonic interferometer.

Effects of phase difference on the binaural perceiving intensity

It is well known fact that human localize the direction of sound source in transverse plane according to interaural time difference in low frequency and interaural level difference on high frequency. In this research, we tested possibility for interaural time difference to be interpreted as interaural level difference when it is perceived by brain. To test the hypothesis, we used sinusoidal wave and commercial music to study the effect of interaural time difference on the perception of loudness. Each sound sample was regulated to have interaural time difference and given to 9 subjects. Subjects were asked to answer which side was louder. For sinusoidal waves, more than 60% of subjects answered side with earlier sound arrival was louder. The effect of interaural time difference on interaural level difference was larger when it interaural time difference was given to lower frequencies. Music samples were regulated with 100 and 500 interaural time difference and 100% of subjects answered side with earlier sound arrival was louder. Results from the experiments imply the possibility for interaural time difference interpretation by interaural level difference on localization of sound sources.

Bonding quality evaluation of layered materials by guided wave dispersion

Multi‐layered materials have been widely used for high performance materials with advanced properties required for the critical parts of structures. The characteristics of bonding quality in multi‐layered materials have been hot issue for a long time. The bonding quality was evaluated by using dispersion of guided wave. Broadband guided waves were generated at oblique incidence angle, and waves reflected at the edge of the specimen were detected by using a pulse‐echo setup. The dispersion curves were obtained from edge‐reflected leaky guided wave for various plates: Single layered plates of aluminum, copper and stainless steel, and double layered plates of aluminum‐stainless steel cladding, epoxy‐bonded aluminum‐stainless and epoxy‐bonded aluminum‐copper. The aluminum‐stainless steel cladding specimen showed similar dispersion for both sides, whereas epoxy‐bonded specimens showed different dispersions which are similar to that of upper layer only. These results imply that the cladding specimen used in the...

Inquiring activities on the acoustic phenomena at the classroom using sound card in personal computer

Inquiring activities on acoustic phenomena have been carried out in the classroom of a high school for highly gifted children. Instead of expensive instruments such as function generators and oscilloscopes, sound cards, installed in a personal computer, were employed for the generation and detection of sound. The stereo function of the sound card offered two sound sources, so that phenomena of interference and beats can be realized in the classroom. The record function of the sound card offered detection of sound, permitting frequency spectrum analysis of sounds from two tuning forks or the sound from a moving fork. Using sound card, a lot of acoustic phenomena can be demonstrated in the classroom. In addition, sound from Rijke tube, which is a typical theromacoustic phenomena, was analyzed by using a sound card. Popup sound of a wine bottle and breaking of wine glasses, which are related to resonace and standing waves, were also investigated. Curiosity of students was greatly increased through a series o...