• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.10 no.4
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• pp.297-303
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• 1981

Optimal design of shell and tube heat exchanger system with the working fluids which may condense outside the tubes has been carried out under specified inlet and outlet conditions. Independent variables such as number of parallel series, tube diameter, distribution pitch, tube side pressure loss, baffle cut and shell side pressure loss as well as dependent variables such as shell diameter, number of tubes, number of serial series and number of baffles were all characterized according to the standard. Exhaustive search method was used to construct a computer program together with the calculation of heat transfer rate by LMTD method. stress analysis of maj or parts was made to examine their dimensions satisfying heat transfer and pressure loss requirements. Cost estimation based on the installation, operation and maintenance was also made, A few representative variables, heat transfer area, shell diameter and pressure loss, were used to express cost function, finally giving the optimal selection of all tentative solutions.

• Korean Journal of Optics and Photonics
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• v.26 no.3
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• pp.162-167
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• 2015

In this paper, we developed a MTF (Modulation Transfer Function) measurement system using a knife-edge scanning method for infrared optics. It consists of an objective part to generate the target image, a collimator to make the beam parallel, and a detector to analyze the image. We used a tungsten filament as the light source and MCT (Mercury Cadmium Telluride) to detect the mid-infrared(wavelength $3-5{\mu}m$) image. We measured the MTF of a standard lens (f=5, material ZnSe) to test this instrument and compared the result to the theoretical value calculated using the ZEMAX commercial software. It was found that the difference was within ${\pm}0.035$ at the cut-off frequency (50 1/mm). Also, we calculated the A-type measurement uncertainty to check the reliability of the measurement. The result showed only 0.002 at 20 1/mm in spatial frequency, which means very little variation in the MTF measurement under the same conditions.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.17 no.3
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• pp.678-684
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• 2013

This paper describes a low-power baseband circuit for SAW-less LTE-Advanced transmitters. The proposed transmitter baseband circuit consists of a 2nd-order Tow-Thomas type active RC-LPF and a 1st-order passive RC LPF. It can provide a 7 multi-channel cut-off frequencies and wide gain control range of -41 dB ~ 0 dB with a 1-dB step. The proposed 2nd-order active RC-LPF adopts an op-amp in which three other sub-op amps are in parallel connected to reduce DC current for different cutoff frequency. In addition, each sub-op amp adopts both Miller and feed-forward phase compensation method to achieve an UGBW of more than 1-GHz with a small DC power consumption. The proposed baseband circuit is implemented in 65-nm CMOS technology, consuming DC power from 6.3 mW to 24.1 mW from a 1.2V supply voltage for each different cut-off frequency.

• Restorative Dentistry and Endodontics
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• v.24 no.3
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• pp.465-472
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• 1999

The aim of this study was to determine the shear bond properties of four dentin bonding systems to internal cervical dentin, and to investigate the effect of the pretreatment for removing smear layer and position of dentin on shear bond strength of dentin bonding agents. The materials tested in this study were consisted of four commercially available dentin bonding systems[Allbond 2(AB), Clearfil Linerbond 2(CL), Optibond FL(OP), Scotchbond Multi-purpose(SB)], a restorative light-cured composite resin[Z100]J and a chelating agent[RC-prep(RC)]. Fifty-six freshly extracted human molars were used in this study. Dentin specimens were prepared by first cutting the root of the tooth 1mm below the cementoenamel junction with a diamond bur in a high speed handpiece under air-water coolant, and then removing occlusal part at pulp horn level by means of a second parallel section, The root canal areas were exposed by means of cutting the dent in specimens perpendicular to the root axis. Dentin specimens were randomly assigned to two groups(pretreated group, not-pretreated group) based on the pretreatment method of dentin surface. In pretreated group, RC was applied to dentin surface for 1minute and then rinsed with NaOCl. In not-pretreated group, dentin surface was rinsed with saline Each groups were subdevided into four groups according to dentin bonding systems. Four dentin bonding systems and a restorative resin were applied according to the directions of manufacturer. The dentin-resin specimens were embedded in a cold cure acrylic resin, and were cut with a low speed diamond saw to the dimension of $1{\times}1mm$. The cut specimens were divided into three groups according to the position of internal cervical dentin. The shear bond properties of dentin-resin specimens were measured with Universal testing machine (Zwick, 020, Germany) with the cross head speed of 0.5mm/min. From this experiment. the following results were obtained : 1. In case of shear bond strength, there was no significant difference among dentin bonding systems in not-pretreated groups, whereas in pretreated groups, the shear bond strengths of AB and of SB were statistically significantly higher than those of CL and of OP. 2. The shear bond strengths of AB and of SB in pretreated groups were significantly higher than those in not-pretreated groups. 3. The shear bond strengths of radicular layer of OP were higher than those of occlusal layer of OP in not-pretreated groups, and of AB in pretreated groups. The shear bond strengths of radicular layer of AB and of CL in not-pretreated groups were higher than those in pretreated group.

• The Journal of Engineering Geology
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• v.18 no.4
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• pp.459-470
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• 2008

Types of slope failure related to cut slope stability are interpreted through case analyses, and also factors affecting structurally controlled instability investigated, which are developed by geologic structures along a national road No. 25 across the Cheongwon and Boeun-Guns, Chungbuk. Engineering properties such as orientation, persistence, roughness and uniaxial compressive strength of joints are analyzed by square-inventory method in three areas with well-preserved outcrops. The study area is located in Ogcheon folded bet, and are composed of quartz-schist and quartzite in the Midongsan Formation and phyllite in the Ungyori Formation. Flexural beds by folding, schistosity and cleavage besides joints are developed due to slight metamorphism. Various types of joints developed by folding are formed such as strike-parallel, strike-perpendicular, wedge and wrench joint sets by both initially regional and later superposed folding. Factors of slope instability are created by crossing the orientations of joint, cleavage, bedding and slope one another. In the case that the orientation of a slope is coincident with one of beds, factors causing large-scale failure including plane failure are increased greatly. Also in the region that orientations of the slope and bed are crossed each other at high angle, only local and minor failures are shown in the slope.

• Journal of Korean Tunnelling and Underground Space Association
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• v.10 no.2
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• pp.105-118
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• 2008

Shotcrete is one of the main support materials in tunnelling. Its bonding state on excavated rock surfaces controls the safety of the tunnel: De-bonding of shotcrete from an excavated surface decreases the safety of the tunnel. Meanwhile, the bonding state of shotcrete is affected by blasting during excavation at tunnel face as well as bench cut. Generally, the bonding state of shotcrete can be classified as void, de-bonded, or fully bonded. In this study, the state of the back-surface of shotcrete is investigated using impact-echo (IE) techniques. Numerical simulation of IE technique is performed with ABAQUS. Signals obtained from the IE simulations were analyzed at time, frequency, and time-frequency domains, respectively. Using an integrated active signal processing technique coupled with a Short-Time Fourier Transform (STFT) analysis, the bonding state of the shotcrete can be evaluated accurately. As the bonding state worsens, the amplitude of the first peak past the maximum amplitude in the time domain waveform and the maximum energy of the autospectral density are increasing. The resonance frequency becomes detectable and calculable and the contour in time-frequency domain has a long tail parallel to the time axis. Signal characteristics with respect to ground condition were obtained in case of fully bonded condition. As the ground condition worsens, the length of a long tail parallel to the time axis is lengthened and the contour is located in low frequency range under 10 kHz.

• Journal of the Korean Ceramic Society
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• v.36 no.1
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• pp.43-49
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• 1999

Gas pressure sintered silicon nitride based composites with 0~5wt% $\beta$-Si3N4 whiskers were prepared. The whiskers were unidirectionally oriented by a modified tape casting technqiue and green bodies with various microstructure were formed by changing stacking sequences of sheets cut from the tape. Orientations of the large elongated grains of the sample after gas pressure sintering were the same as the those of the whiskers of green body, and the sintering shrinkage and mechanical properties of sintered sample were consistent with the microstructural characteristics. In case of unidirectional samples, the sintering shrinkage normal to whisker alignment direction was larger than that parallel to the direction. The shrinkage difference inceaed as the whiskercontent increaed. As whisker content increaed, the crack length normal to and parallel to tape casting direction became shorter and larger, respectively. Although the grain size increased by th whisker addition, the flexural strength of unidirectional samples was not lower than that of smaple without the whisker. In case of crossplied and 45$^{\circ}$rotated samples, the anisotropy of mechanical preoperties disappeared.

• Proceedings of the Korean Society of Near Infrared Spectroscopy Conference
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• 2001.06a
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• pp.1519-1519
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• 2001

The aim of this work was to test the feasibility of NIRS in analysing textural characteristics of “Pasta Filata” cheese during the shelf-life. For this purpose, 128 samples of “Pasta Filata” cheese, subdivided into two sets on the basis of the wax used to avoid mechanical damages (paraffin, biodegradable wax), were analysed by using an InfraAlyzer 500 (Bran+Luebbe). Analyses were performed at room temperature. Samples were cut into small cylinders (D=3.2 cm, height = 1 cm), in agreement with literature information. Data were processed by using Sesame Software (Bran+Luebbe). Samples were analysed, during the shelf-life, at 90 and 120 days. In parallel, textural characteristics were detected carrying out a compression method by using an Universal Testing Machine Instron model 4301 (Instron Corporation, Canton, Massachusetts). As compression probe was used a cylinder (D = 5.8 cm, height = 3.7 cm) and a speed rate of 20mm/min was applied. The load at 20 mm of compression was recorded on sample cylinders of 1.7 cm (D) by 2 cm (height). Qualitative analysis of full spectra showed the possibility to gather samples on the basis of the days of shelf-life. The textural characteristics of cheese during the shelf-life was evaluated by comparing NIRS data with rheological results. The best correlation was obtained applying MLR to the first derivative of normalized absorbance values at seven wavelengths. Load values were plotted against the NIR prediction values based on first derivatives. NIRS proved to be an useful tool in classifying samples on the basis of the shelf-life period as well as in predicting their textural characteristics ($R^2$= 0.916, SEC = 0.192, SEP = 0.248, SEV = 0.345).

• Journal of Advanced Navigation Technology
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• v.21 no.1
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• pp.107-112
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• 2017

In recent years, electric shock accidents due to electric leakage currents of household appliances such as computers, TVs, refrigerators, and LED lights are continuously occurring in homes and industrial buildings. And it is not easy to check the leakage current of each household appliances connected in parallel at the rear end of the module. In addition, the leakage current flowing through the path of the normal current other than the existing current leakage circuit breakers are installed in the distribution box, only the function to cut off the power when the leakage. Therefore, there are various disasters such as electric shock and fire caused by short circuit of household appliances, and the risk of such leakage current is seriously presented. In this paper, we propose a method to implement a leakage monitoring system that can be monitored at all times using Zigbee communication based on IEEE 80215.4, which has advantages in low power and low cost among short range wireless communication systems.

• Maxillofacial Plastic and Reconstructive Surgery
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• v.13 no.2
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• pp.203-216
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• 1991

Nerve allografts as a bridge of regeneration is useful in the repair of peripheral nerve defect resulting from trauma, and leprosy. But immunological rejection and complicated scar formation is an unavoidable problem in the application of allogeneic nerves. This article is intended to study of the regeneration of allogeneic nerve grafts in rats with histopathologically, scanning electron microscopically. 24 adult male Sprague-Dawley rats were used as the experimental animals. A 2cm skin incision was made on the lateral aspects of limb, parallel to femur. Segments of sciatic nerve trunk taken from rats, 10mm was resected at the middle of the thigh, nerve graft was inserted between the ends of gaps with perineural and epineural suture method with 10-0 prolene. Obsrevation was made simultaneously at 3 day, 1, 2, 3, 4, 5, 6, 8 weeks after surgery. The results were as follows. 1. In light and electronic microscopic studies, marked degenerative change of the graft nerves were observed at 2 weeks after surgery. 2. After surgery, blood clot fromation was observed at 3 day, granualtion tissue formation was observed at 2 week, and fibrous tissue proliferation was observed at 3 week. 3. In change of nerve fiber, there were Wallerian degeneration at early stage, decrease in degeneration at 4 week but degeneration of myeline was continuded at 8 week. 4. At 4 week, schwann cells proliferate at its cut ends to join with the distal and proximal stump of the damaged nerve. 5. Fibrous scar tissues are formed at 2 weeks and increased progressively in 8 weeks, which was interrupted the regeneration of grafted nerve.