• Journal of the Korean institute of surface engineering
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• v.49 no.6
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• pp.555-559
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• 2016

A biodegradable nanofiber scaffolds using electrospining provide fibrous guidance cues for controlling cell fate that mimic the native extracellular matrix (ECM). It can create a pattern using conventional electrospining method, but has a difficulty to generate one or more pattern structures. Femtosecond(fs) laser ablation has much interested in patterning on biomaterials in order to distinguish the fundamental or systemic interaction between cell and material surface. The ablated materials with a short pulse duration using femtosecond laser that allows for precise removal of materials without transition of the inherent material properties. In this study, linear grooves and circular craters were fabricated on electrospun nanofiber scaffolds (poly-L-lactide(PLLA)) by femtosecond laser patterning processes. As parametric studies, pulse energy and beam spot size were varied to determine the effects of the laser pulse on groove size. We confirmed controlling pulse energy to $5{\mu}J-20{\mu}J$ and variation of lens maginfication of 2X, 5X, 10X, 20X created grooves of width to approximately $5{\mu}m-50{\mu}m$. Our results demonstrate that femtosecond laser processing is an effective means for flexibly structuring the surface of electrospun PLLA nanofibers.

• Korean Journal of Optics and Photonics
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• v.21 no.6
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• pp.254-258
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• 2010

We investigate an optical technique for beam shaping and optical amplification of a pulsed laser diode without variation of its original properties, such as repetition rate and pulse duration. The horizontal and longitudinal sizes of the pulsed laser diode are 300 and $2{\mu}m$, respectively, and its output power is $1.1mW/cm^2$. The multimodal and elliptical pulse shape of the laser diode is converted to the single-modal and Gaussian pulse shape by using a lensed optical fiber. Since the single-modal lensed fiber coupling from the multimodal pulsed laser diode degrades the output power severely, the output power of the pulsed laser diode is dramatically enhanced by using an optical amplification method based on master oscillated power amplification (MOPA). The pulse qualities of the laser diode are not changed after amplifying the pulse power and the output power was finally measured to be $29mW/cm^2$.

• Korean Journal of Animal Reproduction
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• v.18 no.3
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• pp.217-228
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• 1994

These experiments were carried out to establish the optimal condition of electrostimulatin inducing cell fusion and oocyte activation for nuclear transplantation in mouse embryos. Eggs selected for cell fusion or activation by electrostimulation were equilibrated for 5~10 min. in 0.3M sucrose solution and electrostimulated for 60$\mu$sec using 1 pulse of 60, 70, 80, 90 or 100 volts DC with electrodes 0.2 mm apart. Then they were cultured in 20${mu}ell$ dropsof Tyrode's solution. The results of these experiments are as follows : 1. When one pulse of 60, 70, 80, 90 or 100 volts DC for 60$\mu$sec were applied to 2-cell embryos for fusion of blastomeres, fusion rates were 50.0, 81.7, 91.7, 100 and 100%, respectively ; and developmental rates of fused embryos to blastocyst were 76.7 to 81.5%. Higher fusion rates were observed in 90V and 100V. 2. The average cell number in fused embryos developed to blastocyst was about half of the cell number in diploid controls; and the cell number decreased with increasing of voltages. 3. When pulse numbers were increased, fusion rates improved, but developmental rates were not signficiantly different from the group for which the number of pulse was not increased. And the cell number of blastocyst decreased even more. 4. Oocytes aged for 6hrs after ovulation were electrostimulated for oocyte activation by the same method used for cell fusion. Rates of oocyte activated by electrostimulation were 45.3 to 60.4%, and fragmentation rates were 7.5~15.1%. The lysis rates were 17.0~34.0%. The results of these experiments indicate that the optimal condition for achieving cell fusion and activation is 1 pulse, duration 60$\mu$sec in 90 Volt. The results also show that this condition is suitable for nuclear transplantation using mouse eggs.

• Journal of the Korean Ceramic Society
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• v.43 no.4 s.287
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• pp.259-263
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• 2006

The applicability of UPT (Ultrasound Pulse Thermography) for real-time defect detection of the ceramic heating plate is described. The ceramic heating plate with superior insulation and high radiation is used to control the water temperature in underwater environment. The underwater temperature control system can be damaged owing to the short circuit, which resulted from the defect of the ceramic heating plate. A high power ultrasonic energy with pulse duration of 280 ms was injected into the ceramic heating plate in the vertical direction. The ultrasound excited vibration energy sent into the component propagate inside the sample until they were converted to the heat in the vicinity of the defect. Therefore, an injection of the ultrasound pulse wave which results in heat generation, turns the defect into a local thermal wave transmitter. Its local emission is monitored and recorded via the thermal infrared camera at the surface which is processed by image recording system. Measurements were Performed on 4 kinds of samples, composed of 3 intact plates and the defect plate. The observed thermal image revealed two area of crack in the defective ceramic heating plate.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.51 no.6
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• pp.229-235
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• 2002

This paper presents the fabrication of polycrystalline thin film transistor(TFT) using sequential lateral solidification(SLS) of amorphous silicon. The fabricated SLS TFT showed high Performance suitable for active matrix liquid crystal display(AMLCD). The SLS process involves (1) a complete melting of selected area via irradiation through a patterned mask, and (2) a precisely controlled pulse translation of the sample with respect to the mask over a distance shorter than the super lateral growth(SLG) distance so that lateral growth extended over a number of iterative steps. The SLS experiment was performed with 550$\AA$ a-Si using 308nm XeCl laser having $2\mu\textrm{m}$ width. Irradiated laser energy density is 310mJ/$\textrm{cm}^2$ and pulse duration time was 25ns. The translation distance was 0.6$\mu$m/pulse, 0.8$\mu$m/pulse respectively. As a result, a directly solidified grain was obtained. Thin film transistors (TFTs) were fabricated on the poly-Si film made by SLS process. The characteristics of fabricated SLS p -type poly-Si TFT device with 2$\mu\textrm{m}$ channel width and 2$\mu\textrm{m}$ channel length showed the mobility of 115.5$\textrm{cm}^2$/V.s, the threshold voltage of -1.78V, subthreshold slope of 0.29V/dec, $I_{off}$ current of 7$\times$10$^{-l4}$A at $V_{DS}$ =-0.1V and $I_{on}$ / $I_{off}$ ratio of 2.4$\times$10$^{7}$ at $V_{DS}$ =-0.1V. As a result, SLS TFT showed superior characteristics to conventional poly-Si TFTs with identical geometry.y.y.y.

• Journal of the Korean Society of Safety
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• v.22 no.1 s.79
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• pp.36-39
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• 2007

It is important to know Minimum Ignition Energy(MIE) of flammable materials for ignition hazard of chemical processes etc.. Currently a capacitor discharge is used mainly to measure the MIE. Then, it is impossible to control actively discharge energies and discharge time because the MIE measurement uses a high voltage capacitor and fixed capacitor. However, the control of discharge energy and discharge time will be convenient if self-sustain discharge is used. In this paper, we measured the MIE by self-sustain discharge of a pulse shape to propose the new measuring method of the MIE. AS a result, ignition energies are increased gradually as discharge duration time gets longer, and discharge current grows larger. Also, an arc discharge and a glow discharge occurred during the experimental period, and the ignition by glow discharges happened when discharge duration time was $90{\mu}s$, discharge current was 8A and 1A Especially, the MIE occurred the 0.05mm and 0.08mm of the gap distance between discharge electrode in the same discharge duration time.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.1
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• pp.43-50
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• 2012

The effects of parameters related to the finite element simulation of the laser shock peening(LSP) process on the residual stresses of Inconel alloy 600 steel are discussed. In particular, we focus on the maximum pressure, pressure pulse duration, laser spot size, and number of shots. It is found that certain ranges of the maximum pressure and pulse duration can produce the maximum compressive residual stresses near the surface, and thus proper choices of these parameters are important. The residual stresses are not affected by the laser spot size, provided it is larger than a certain size. The magnitudes of the compressive residual stresses and the plastically affected depths are found to increase with an increasing number of shots, but this effect is less pronounced for more shots.

• Korean Journal of Food Science and Technology
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• v.31 no.2
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• pp.368-374
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• 1999

This study was designed to investigate effects of pulsed electric field (PEF) treatment on physiological changes of microbial cells, using domestically fabricated pilot scale PEF device. The effect of non-thermal PEF treatment on physiological characteristics of microorganisms was determined by salt resistance, the amount of UV absorbents, cell staining, recovery rate of defected cells, and changes in structure of cell membrane. Salt resistance of Escherichia coli, Bacillus subtilis and Rhodotorula minuta was examined after PEF treatment at 40 kV/cm, 84 pulse, $10{\mu}s$ pulse duration. Approximately $1\;log_{10}$ cell number of viable microorganisms was decreased by addition of salt. PEF treatment significantly increased the amount of UV absorbents at 260 and 280 nm because of leakage from damaged cell membrane by PEF treatment. Although three kinds of microorganisms treated by PEF were difficult to be observed due to their cell membrane damage, untreated cells were clearly observed by a microscope. PEF-treated R. minuta was not stained by methylene blue due to cell membrane defect. When E. coli, B. subtilis and R. minuta were cultured after PEF treatment, they showed 5, 4, and 8 hr longer lag phase, respectively, compared to control, but growth rates were not affected.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.134-134
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• 2009

In this work, we report that crystallization speed as well as the electrical and optical properties about the N-doped $Ge_2Sb_2Te_5$ thin films. The 200-nm-thick N-doped $Ge_2Sb_2Te_5$ thin film was deposited on p-type (100) Si and glass substrate by RF reactive sputtering at room temperature. The amorphous-to-crystalline phase transformation of N-doped $Ge_2Sb_2Te_5$ thin films investigated by X-ray diffraction (XRD). Changes in the optical transmittance of as-deposited and annealed films were measured using a UV-VIS-IR spectrophotometer and four-point probe was used to measure the sheet resistance of N-doped $Ge_2Sb_2Te_5$ thin films annealed at different temperature. In addition, the surface morphology and roughness of the films were observed by Atomic Force Microscope (AFM). The crystalline speed of amorphous N-doped $Ge_2Sb_2Te_5$ films were measured by using nano-pulse scanner with 658 nm laser diode (power : 1~17 mW, pulse duration: 10~460 ns). It was found that the crystalline speed of thin films are decreased by adding N and the crystalline temperature is higher. This means that N-dopant in $Ge_2Sb_2Te_5$ thin film plays a role to suppress amorphous-to-crystalline phase transformation.

• Journal of Oral Medicine and Pain
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• v.25 no.4
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• pp.415-425
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• 2000

In order to obtain the basic data concerning the optimal lasing conditions in using Nd:YAG laser as an adjunctive modality of periodontal therapy of root planing without irreversible structural deterioration of cervical cementum, the author selected 36 human teeth having no cervical abrasion and caries (; 12 anteriors, 12 premolars. 12 molars) extracted due to periodontal diseases, and divided them into 4 groups as Group I, II, III and IV (; each group of 3 anteriors, 3 premolars, 3 molars), and prepared a cementum specimen with thickness of $1.0mm{\pm}0.2mm$ sectioned longitudinally at the middle of mesio-distal thickness (; Group I) or horizontally at 1mm-2mm below the cemento-enamel junction (; Group II, III, IV) from each tooth of each group by low speed diamond wheel saw, and treated them with 0.5 M ethylene diamine tetraacetic acid (; EDTA, pH=7.4) for 2 minutes for elimination of remnants during tooth-sectioning. And the author applied the laser energy from a fiberoptic delivered, free running, pulsed Nd:YAG laser (; wavelength 1064nm. pulse duration $120{\mu}sec$, fiber diameter $320{{\mu}m}$) to cementum surfaces in triplicates of one experiment under the following lasing conditions: 1. stationary mode of fiber in contact to cementum surfaces without air-spray (; Group I )/with air-spray (; Group II), 2. unidirectional moving mode of fiber in contact to cementum surfaces under speed of 3mm-4mm/sec without air-spray (; Group III)/with air-spray (; Group IV), 3. energy per pulse (mJ/pulse) [; energy density ($J/cm^{2}$)] in order of 1.0W/10Hz (100J/pulse); $124J/cm^{2}$, 0.5W/10Hz (50mJ/pulse); $62J/cm^{2}$, 0.4W/10Hz (40mJ/pulse); $50J/cm^{2}$, 0.3W/10Hz (30mJ/pulse); $37J/cm^{2}$, 4. exposure time of 1 second. And the author applied the platinum coating on surfaces of cementum specimens, and evaluated the characteristics of ultrastructural change on surfaces of cementum using the scanning electron microscopy. In general the ultrastructural loss of cervical cementum irradiated under the same lasing condition of laser energy density occurred least in specimens of Group IV. And especially, the ultrastructural loss of cervical cementum irradiated under the laser energy density of $37J/cm^{2}$ almost did not occur in specimens of Group IV. Therefore, it is considered that the pulsed Nd:YAG laser should be applied with the lasing conditions of unidirectional moving mode of fiber in contact to cementum surfaces under speed of 3mm-4mm/sec with air-spray and of laser energy density within $37J/cm^{2}$ as an adjunctive modality of periodontal therapy of root planing without irreversible structural deterioration of cervical cementum.