Boo-Hyung Ryu

Design and Modeling of Piezoelectric Pump for Microfluid Devices

Recently, there has been increased incessantly an interest in research area on microfluidic pump for electronic and biological applications. The proposed pump takes an unobtrusive operation into the simple displacing mechanism using peristaltic traveling waves without the physical moving valves. However, this piezopump makes up a radical design, based on the operation of the stator on the piezoelectric motor. The ATILA simulation performs to estimate the operating frequency of the vibrating wave mode, and optimize the design conditions of piezopump such as pump structure, elastic materials, piezoelectric ceramics, and z-displacement on the elastic traveling wave of piezopump. The best measured value of the pumping rate is about 118 μ l/min under the following parameters: 4-wave mode, the operating frequency of 50 kHz and the peak voltage of 200 V.

Thermally stimulated current study in γ-ray irradiated low density polyethylene

Abstract Thermally stimulated current and relaxation map analysis (RMA) were used to characterize the low temperature transition of low density polyethylene (LDPE). Four current peaks were observed. The peaks at about −125°C, −25°C, and 90°C are indications of the γ-, β-, α-transition, respectively, and a new, formerly unknown peak at about 50°C will be attributed to the space charge relaxation. The RMA data showed that compensation temperature (Tc) and degree of disorder increased with increasing the γ-ray intensity and decreasing antioxidant content, whereas the compensation time (τc) decreased. It can be concluded that the cooperative molecular motion in LDPE system becomes more active as the γ-ray intensity increases and antioxidant content decreases.

Dielectric properties on the radiation and thermal aged PEEK

The dielectric properties of gamma-ray irradiated and thermally aged polyetheretherketone (PEEK) have been investigated. Results of the temperature dependency of the dielectric properties indicated that the glass transition temperature of the aged PEEK increased with radiation and thermal ageing. The frequency dependency of dielectric properties implied that the magnitude of radiation and thermal induced dipoles and ions increased as radiation and thermal ageing. The values of the relaxation intensity calculated using Cole-Coles circular arc can be useful for the evaluation of the degradation level of PEEK.

Radiation effects on electrical and mechanical properties of LDPE/EVA blends

The radiation effects on electrical and mechanical properties of LDPE/EVA blends with various vinyl acetate contents were investigated. Radiation degradation of LDPE/EVA blends was studied using TGA, volume resistivity, dissipation factor, elongation at break, and E-modulus. As vinyl acetate contents of LDPE/EVA blends increased, the electrical insulation characteristics were deteriorated but the flexibility was improved. As irradiation dose was increased, the electrical insulation characteristics were improved, but the flexibility was deteriorated

Chemiluminescence Properties of Gamma-Ray Irradiated LDPE

Radiation degradation of low density polyethylene (LDPE) was evaluated by using chemiluminescence characteristics. After a irradiation with 60Co ¿-ray up to 500 kGy under nitrogen, oxygen, and air atmospheres at room temperature LDPEs were applied for the measured chemiluminescence. The results showed that the intensity of chemiluminescence was related to the radiation-induced oxidation and the integrated chemiluminescence response increased with an increasing radiation dose. These observations were further proved by FT-IR. Therefore, chemiluminescence emission measurement could be a useful tool for a characterization of the radiation-induced effects of LDPE.

Dielectric Relaxation Behavior of PEEK during the Loss of the Coolant Accident

Dielectric relaxation behavior of poly(etheretherketone) (PEEK) during the loss of coolant accident (LOCA) was investigated. The result of the temperature dependency of the dielectric properties indicated that the glass transition temperature of the aged PEEK increased as increasing radiation doses and thermal ageing time. The relaxation intensity calculated using Cole-Coles circular arc could be useful for the evaluation of the PEEK degradation.

Radiation effects on electrical treeing resistance and mechanical characteristics of low density polyethylene containing barbituric acid derivatives

The treeing resistance of low density polyethylene containing barbituric acid derivatives under radiation environments were investigated. Barbituric acid, 4-aminouracil and 4-amino-6-hydroxy-2-mercapto pyrimidine were selected for treeing inhibitors. LDPE with the additives were irradiated by Co/sup 60/ /spl gamma/-rays. The treeing inception voltage and tree propagation was observed for electrical insulation properties, and the elongation at break was observed for the mechanical properties, to clarify the relation between the molecular structure and the electrical tree characteristics. Also thermoluminescence and gel contents were carried out at various dosages. LDPE containing treeing inhibitors showed better electrical insulation characteristics than pure LDPE. From the measurements, barbituric acid among the treeing inhibitors had the best treeing and radiation resistance.

Radiation effects on treeing resistance of low density polyethylene containing treeing inhibitors

The effectiveness of treeing resistance in low density polyethylene containing azocompounds were investigated under radiation environments. 4-(4-nitrophenylazo)-1-naphthol and 4-(4-nitrophenylazo) resorcinol were selected for treeing inhibitors. LDPE containing the additives were crosslinked with dicumyl peroxide, irradiated by /sup 60/Co /spl gamma/-ray in the presence of air at room temperature. Treeing inception voltage, AC breakdown strength measurements were carried out for electrical insulation characteristics, thermoluminescence and gel contents were analyzed as various irradiation doses also. LDPE with treeing inhibitors showed much better insulation characteristics than pure LDPE. It is interpreted that molecular structures, polar groups and the type of radicals connected on the benzene ring of the additives affected electrical characteristics. From the results, 4-(4-nitrophenylazo) resorcinol was the most effective upon the best treeing and radiation resistance.

Tree initiation characteristics in LDPE with different crystallinities

It is well known that the degree of crystallinity is an important quantitative concept. By itself, or in consort with other key structural variables, it governs a variety of microscopic and macroscopic properties. In this experiment, we changed conditions of crystallization to study characteristics of apparent tree inception stress and electrical tree propagation in different degrees of crystallinity and we made specimens with a needle-plane electrode system of LDPE. We observed inception and propagation of electrical trees by an optical microscope interfaced with a computer and investigated the characteristics of the phase resolved PD pulses accompanying the tree propagation. As the tip radius increased, tree inception stress converged to a constant value. In addition, as the the degree of crystallinity is increased, the tree inception voltage is also increased.

Oxygenation and defect generation processes in YBa2Cu3O7 − δ bulk superconductors prepared by a melt process

Abstract Defect formation processes during oxygenation were investigated in a melt-processed YBa 2 Cu 3 O 7 − δ bulk superconductor. Oxygenation at 550 °C resulted in a formation of tweed-like twin with some microcracks. Non-uniform phase transition occurred for the specimen annealed at 450 °C as well as the microcracking by an oxygen-induced stress. It is suggested that there was a critical stress, σ t − c , where the stress relief mode was changed from twin formation into crack formation. Below σ t − c , the stress was relieved by a formation of twins. Above σ t − c , the stress was relieved by a generation of microcracks.