• Magazine of the Korea Concrete Institute
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• v.6 no.1
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• pp.89-100
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• 1994

The current test procedure for transfer length, which determine transfer length by measuring concrete strain, has an actual bond stress state in the prestressed pretensioned member : however, it is difficult to determine the bond properties of maximum bond stress and bond stiffness with this method. It is also difficult for design engineer to understand and select a correct safety criterion from the widely distributed results of such a ransfer test alone. An alternative testing procedure is provided here to determine the bond properties without measuring the concrete strain. In this test the bond stress is measured directly by creating a similar boundary condition within the transfer length in a real beam during the transfer of prestressing force. The prestressing force was released step by step by step from the unloading side. The release of force induces a swelling of the strand at the unloading side of concrete block, bonding force in the block, and a bond slip of the strand toward the other side of the block. Two center-hole load cells are used to record the end loads until the point of general bond slip(maximum bond stress). It is suggested that this test procedure be performed with the ordinary transfer test when determining the transfer length in a prestressed, pretensioned concrete beam.

• Korean Journal of Optics and Photonics
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• v.24 no.6
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• pp.342-346
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• 2013

We present the thermal analysis result of die bonding for a high power LED package using a metal hybrid silicone adhesive structure. The simulation structure consists of an LED chip, silicone die adhesive, package substrate, silicone-phosphor encapsulation, Al PCB and a heat-sink. As a result, we demonstrate that the heat generated from the chip is easily dissipated through the metal structure. The thermal resistance of the metal hybrid structure was 1.662 K/W. And the thermal resistance of the total package was 5.91 K/W. This result is comparable to the thermal resistance of a eutectic bonded LED package.

• The Journal of the Acoustical Society of Korea
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• v.43 no.1
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• pp.138-144
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• 2024

This paper presents a bistatic to monostatic conversion technique to analyze the bistatic target strength of submarines. The technique involves determining the transmission path length of acoustic waves, which are emitted from a source, scattered off an underwater target, and eventually received by a receiver. By generating a corresponding virtual scattering surface, this method effectively transforms the target strength analysis problem from bistatic to monostatic. The converted monostatic target strength problem can be assessed using a well-established monostatic numerical methods. The bistatic target strength analysis for Benchmark Target Strength Simulation (BeTTSi), a widely used target strength model were performed. The results were compared with those calculated by boundary element methods and Kirchhoff approximation, and confirmed the validity and the practical applicability of the proposed analysis technique for evaluating submarine target strength.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.16 no.6
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• pp.1266-1272
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• 2012

An InGaZnO thin film transistor with different gate lengths and widths have been fabricated and their device degradations with device sizes have been also performed after negative gate bias stress. The threshold voltage and subthreshold swing have been decreased with decrease of gate length. However, the threshold voltages were increased with the decrease of gate lengths. The transfer curves were negatively shifted after negative gate stress and the threshold voltage was decreased. However, the subthreshold swing was not changed after negative gate stress. This is due to the hole trapping in the gate dielectric materials. The decreases of the threshold voltage variation with the decrease of gate length and the increase of gate width were believed due to the less hole injection into gate dielectrics after a negative gate stress.

• Clean Technology
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• v.7 no.2
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• pp.127-132
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• 2001

The effects of activated-carbon (AC) packing length on the Pressure Swing Adsorption (PSA) performance was investigated for the hydrogen separation from the multicomponent mixture gas. Linear driving force model was used to describe mass transfer between two phase and coupled Langmuir isotherm was used for each component as a nonlinear adsorption isotherm. When two adsorbents with a different adsorption capacity were packed consecutively in one bed, it is very important to determine the packing ratio of zeolite to activated carbon affecting the purity and recovery of the product. The activated carbon packing length in adsorption tower of 120 cm was determinated by the ending point of $CO_2$ contration. The optimum length of an activated carbon layer was 65 cm for production of high-purity hydrogen.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.8
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• pp.1765-1772
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• 2015

In the underwater acoustic communication channels, multipath reflection become the cause of obstacle. Generally, equalizer has been applied to overcome these problems. In this paper, the method was proposed to optimize tap-length of decision feedback equalizer using genetic algorithm. After inputting feed-forward filter length and feed-back filter length as genetic information of the genetic algorithm, it optimize tap-length using BER(bit error rate) calculation in accordance with object function. The object function consist of decision feedback equalizer and BER calculation. For the purpose of BER calculation in the object function, the method was proposed to optimize the tap-length of decision feedback equalizer with genetic algorithm using preamble signals. As a result of experiments, the optimized BER is 0.0355 for signals which were received through a 25m receiver and which were applied to calculate BER merely using preamble signals in object function. When all data were used to calculate BER in object function, the optimized BER is 0.0215.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.4 no.1
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• pp.17-25
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• 2000

ATM PON system is regarded as a solution of the next generation access network because it can cover various types of subscribers in a single platform. In this paper, we describe the merit of the ATM PON and the key protocols for its operation. Above all, the ranging is the most important protocol providing a mean of the time-division multiple access in the system. A problem in the protocol is that the window size, the time interval that ranging cell arrives, is too long. During the interval, user traffics cannot be send to the upstream, which makes the quality of service degraded. In this paper, we suggest a method to minimize the window size when the length of the optic fiber is known with some deviation. The window size can be reduced as 7 % of the conventional method when the deviation of the length is 1 Km.

• Journal of the Korea Convergence Society
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• v.10 no.3
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• pp.73-79
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• 2019

This study simulated external ear canal modeling with different external ear canal lengths, vertical flexion angles, and inner/outer diameter ratios using digital imaging and communications in medicine(DICOM) of the head temporal region and measured the acoustic sensitivity. The experiment was performed by increasing the audible frequency for humans by 200 Hz and expressing the frequency constantly transmitted at 1 Pa as the eardrum acoustic volume and presented the measurements by linear and quadratic curve regression analysis. The results showed that the longer the external ear canal length and the higher the ratio of the outer/inner diameter, the faster the acoustic response at lower frequencies. The acoustic sensitivity correlation of the meta-model using regression analysis showed a 77% influence by the external ear canal length and 5% by the external/internal diameter ratio, while the vertical flexion angle did not show a significant relationship. This showed that auditory acoustic sensitivity of humans is a factor that reacts faster at a low frequency when the external ear canal length is longer and when the difference between the outer and inner diameter is higher.

• Journal of Korean Society of Transportation
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• v.22 no.3 s.74
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• pp.145-157
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• 2004

The cycle length design model of the Korean traffic responsive signal control systems is devised to vary a cycle length as a response to changes in traffic demand in real time by utilizing parameters specified by a system operator and such field information as degrees of saturation of through phases. Since no explicit guideline is provided to a system operator, the system tends to include ambiguity in terms of the system optimization. In addition, the cycle lengths produced by the existing model have yet been verified if they are comparable to the ones minimizing delay. This paper presents the studies conducted (1) to find shortcomings embedded in the existing model by comparing the cycle lengths produced by the model against the ones minimizing delay and (2) to propose a new direction to design a cycle length minimizing delay and excluding such operator oriented parameters. It was found from the study that the cycle lengths from the existing model fail to minimize delay and promote intersection operational conditions to be unsatisfied when traffic volume is low, due to the feature of the changed target operational volume-to-capacity ratio embedded in the model. The 64 different neural network based cycle length design models were developed based on simulation data surrogating field data. The CORSIM optimal cycle lengths minimizing delay were found through the COST software developed for the study. COST searches for the CORSIM optimal cycle length minimizing delay with a heuristic searching method, a hybrid genetic algorithm. Among 64 models, the best one producing cycle lengths close enough to the optimal was selected through statistical tests. It was found from the verification test that the best model designs a cycle length as similar pattern to the ones minimizing delay. The cycle lengths from the proposed model are comparable to the ones from TRANSYT-7F.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.3
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• pp.317-324
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• 2015

The design of anchorage zone in a post-tensioned member has been started from the evaluation of the ultimate resisting capacity as well as the maximum bursting stress developed, and a lot of design codes including AASHTO and PTI describe their design equations to determine the bearing strength of concrete at the anchorage zone. However, these equations usually give conservative results because their derivation is based on the simple anchorage with a wide bearing plate in the surface without any additional consideration for the load transfer mechanism through transverse ribs on the anchorage. To assess the influence of geometric parameters related to the transverse ribs on the resisting capacity of anchorage block, experiments and analysis are conducted. After verifying the validity of numerical model conducted through correlation studies between experimental and analytical results, parametric studies with changes in the transverse ribs are followed and design recommendations for the anchorage block are suggested from the numerical results obtained.