• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.3B
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• pp.408-422
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• 2000

In this paper, we propose a generalized vector channel model for wireless communication systems using antenna arrays. The proposed channel model reflects path loss. spatial-temporal variation of shadowing, multipath fading , Doppler effect, spatial distribution of local scatterers and delay spread due to remote dominant scatterers. In addition, we use a discrete ray model in which respective ray signal experiences independent shadowing, fading and Doppler shift, and impinges on antenna arrays at a distinct angle. Based on the proposed mode. we derive the relations on the spatial and temporal correlations of the received signals and implement a spatial channel simulator. By comparing the theoretical values with the simulated ones, we verify the effectiveness of the implemented simulator. The simulator is then used to generate an arbitrary channel impulse response and to analyze the channel characteristics under various environments.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2003.05a
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• pp.141-146
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• 2003

Time seres of suspended sediment concentration, surface elevation and velocity were measured and analysed to investigate the role of waves and the predominance of infra-gravity wave component for sediment suspension phenomena in the surf zone. For the investigation in detail, we adopted the cross spectral analysis method between sediment concentration and the characteristic values of wave, and ensemble average analysis method about long-period wave component, which is dominant to sediment suspension in the measurement point. The obtained results are summarized as follows: 1) The relationship between sediment concentration and the characteristic values of wave is stronger for the long-period standing wave components(about 60s and 30s) than the long wave components(about 100s), which have the most energetic power, 2) and also, it is cleared that sediment concentration is increased in the case of the phase, the velocity components of the first mode long-period standing wave(60sec) were accelerated toward on-shore direction, that is, the water surface in offshore side is higher than on-shore side.

• Journal of Welding and Joining
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• v.29 no.6
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• pp.65-70
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• 2011

The effect of flip chip bonding parameters on formation of intermetallic compounds (IMCs) between Au stud bumps and Sn-3.5Ag solder was investigated. In this study, flip chip bonding temperature was performed at $260^{\circ}C$ and $300^{\circ}C$ with various bonding times of 5, 10, and 20 sec. AuSn, $AuSn_2$ and $AuSn_4$ IMCs were formed at the interface of joints and (Au, Cu)$_6Sn_5$ IMC was observed near Cu pad side in the joint. At bonding temperature of $260^{\circ}C$, $AuSn_4$ IMC was dominant in the joint compared to other Au-Sn IMCs as bonding time increased. At bonding temperature of $300^{\circ}C$, $AuSn_2$ IMC clusters, which were surrounded by $AuSn_4$ IMC, were observed in the solder joint due to fast diffusivity of Au to molten solder with increased bonding temperature. Bond strength of Au stud bump joined with Sn-3.5Ag solder was about 23 gf/bump and fracture mode of the joint was intergranular fracture between $AuSn_2$ and $AuSn_4$ IMCs regardless bonding conditions.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.10a
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• pp.763-768
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• 2005

Bare-chip packaging becomes more popular along with the miniaturization of IT components. In this paper, we have studied flip-chip process, and developed automated bonding system. Among the several bonding method, NCP bonding is chosen and batch-type equipment is manufactured. The dual optics and vision system aligns the chip with the substrate. The bonding head equipped with temperature and force controllers bonds the chip. The system can be easily modified for other bonding methods such as ACF In bonding process, the bonding forte and temperature are known as the most dominant bonding parameters. A parametric study is performed for these two parameters. For the test sample, we used standard flip-chip test kit which consists of FR4 boards and dummy flip-chips. The bonding test was performed fur two types of flip-chips with different chip size and lead pitch. The bonding temperatures are chosen between $25^{\circ}C\;to\;300^{\circ}C$. The bonding forces are chosen between 5N and 300N. The bonding strength is checked using bonding force tester. After the bonding force test, the samples are examined by microscope to determine the failure mode. The relations between the bonding strength and the bonding parameters are analyzed and compared with bonding models. Finally, the most suitable bonding condition is suggested in terms of temperature and force.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.11
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• pp.4468-4472
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• 2010

SiOC films made by the inductively coupled plasma chemical vapor deposition were researched the relationship between the dielectric constant and the chemical shift. SiOC film obtained by plasma method had the main Si-O-C bond with the molecule vibration mode in the range of $930{\sim}1230\;cm^{-1}$ which consists of C-O and Si-O bonds related to the cross link formation according to the dissociation and recombination. The C-O bond originated from the elongation effect by the neighboring highly electron negative oxygen atoms at terminal C-H bond in Si-$CH_3$ of $1270cm^{-1}$. However, the Si-O bond was formed from the second ionic sites recombined after the dissociation of Si-$CH_3$ of $1270cm^{-1}$. The increase of the Si-O bond induced the redshift as the shift of peak in FTIR spectra because of the increase of right shoulder in main bond. These results mean that SiOC films become more stable and stronger than SiOC film with dominant C-O bond. So it was researched that the roughness was also decreased due to the high degree of amorphous structure at SiOC film with the redshift after annealing.

• Steel and Composite Structures
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• v.29 no.4
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• pp.557-567
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• 2018

Cylindrical shell structures buckle at service loads which are much lower than their associated theoretical buckling loads. The main source of this discrepancy is the presence of various imperfections which are created on the cylinder body during different processes as manufacturing, handling, assembling and machining. Many cylindrical shell structures are still designed against buckling based on the experimental data introduced by NASA SP-8007 as conservative lower bound curves. This study employed the numerical based Linear Buckling mode shape Imperfection (LBMI) method and modified it using a stochastic method to assess the effect of geometrical imperfections in more details on the buckling of cylindrical shells with and without the cutout. The comparison of results with those obtained from the numerical Simcple Perturbation Load Imperfection (SPLI) method for cylinders with and without cutout revealed a good correlation. The effect of two parameters of size and number of cutouts on the buckling load was investigated using the linear buckling and Modified LBMI methods. Results confirmed that in cylinders with a small cutout inserting geometrical imperfection using either SPLI or modified LBMI methods significantly reduced the value of the predicted buckling load. However, in cylinders with larger cutouts, the effect of the cutout is dominant, thus considering geometrical imperfection had a minor effect on the buckling loads predicted by both SPLI and modified LBMI methods. Furthermore, the modified LBMI method was employed to evaluate the combination effect of cutout numbers and size on the buckling load. It is shown that in small cutouts, an increasing in the cutout size up to a certain value resulted in a remarkable reduction of the buckling load, and beyond that limit, the buckling loads were constant against D/R ratios. In addition, the cutout number shows a more significant effect on decreasing the buckling load at small D/R ratios than large D/R ratios.

• Journal of the Semiconductor & Display Technology
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• v.18 no.1
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• pp.15-20
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• 2019

Inspection and measurement of surface quality is one of the most critical processes for manufacturing products such as semiconductor wafers, sapphire substrates, and display panels. The vibrations of the inspection and measurement devices are supposed to be the most dominant factors for severe measurement errors and longer measuring time. In this study, dynamic characteristics of an inspection and measurement device are analyzed through frequency response experiment and computer simulation to obtain parameters such as frequencies, magnitudes, mode shapes, and periods of vibrations. And then an active damper which consists of sensor, interface board, and actuator is designed based on the parameters to formulate the most effective reaction signal to suppress the vibrations which is generated by an interface board, and provided by an actuator. If the vibrations are measured by the sensor, the active damper immediately generates and provides the corresponding reaction signal to inspection and measurement device. The result shows that the active damper can suppress structural vibrations effectively and reduce measuring time of the device and enhance the productivity.

• Steel and Composite Structures
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• v.42 no.3
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• pp.407-426
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• 2022

Superior to traditional welded studs, high strength friction-grip bolted shear connectors facilitate the assembling and demounting of the composite members, which maximizes the potential for efficiency in the construction and retrofitting of new and old structures respectively. Hence, it is necessary to investigate the structural properties of high strength friction-grip bolts used in steel concrete composite beams. By means of push-out tests, an experimental study was conducted on post-installed high strength friction-grip bolts, considering the effects of different bolt size, concrete strength, bolt tensile strength and bolt pretension. The test results showed that bolt shear fracture was the dominant failure mode of all specimens. Based on the load-slip curves, uplifting curves and bolt tensile force curves between the precast concrete slab and steel beam obtained by push-out tests, the anti-slip performance of steel-concrete interface and shear behavior of bolt shank were studied, including the quantitative analysis of anti-slip load, and anti-slip stiffness, frictional coefficient, shear stiffness of bolt shank and ultimate shear capacity. Meanwhile, the interfacial anti-slip stiffness and shear stiffness of bolt shank were defined reasonably. In addition, a total of 56 push-out finite element models verified by the experimental results were also developed, and used to conduct parametric analyses for investigating the shear behavior of high-strength bolted shear connectors in steel-concrete composite beams. Finally, on ground of the test results and finite element simulation analysis, a new design formula for predicting shear capacity was proposed by nonlinear fitting, considering the bolt diameter, concrete strength and bolt tensile strength. Comparison of the calculated value from proposed formula and test results given in the relevant references indicated that the proposed formulas can give a reasonable prediction.

• Fisheries and Aquatic Sciences
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• v.25 no.3
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• pp.140-150
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• 2022

A method of ultrahigh performance liquid chromatography coupled to high resolution mass spectrometry (UPLC-HRMS) was established for characterization of the lipid profile of Skipjack tuna. Over 300 lipid molecular species were identified through cross-acquisition in both positive and negative ion mode. Phospholipids (PLs) were dominant in Skipjack tuna. Lysophosphatidylethanolamine (LPE), phosphatidylethanolamine (PE), lysophosphatidylcholine (LPC) and phosphatidylcholine (PC) were the main lipid molecular species in PLs, accounting for 89.24% of the total PLs. The ratio of sphingolipids (SLs) and glycerolipids (GLs) were considerable, accounting for 12.30% and 13.60% of the total lipids respectively. Ceramide (Cer) was the main lipid molecular species of SLs, accounting for 64.96% of total SLs, followed by sphingomyelin (SM), accounting for 25.45% of total SLs. Ether diglycerides (ether DG) were the main lipid molecular species of GLs (97.83%). The main fatty acids (FAs) are unsaturated fatty acids (UFAs) in Skipjack tuna. Besides, a new FAs class branched fatty acid esters of hydroxy fatty acids (FAHFA) was detected, together with the FA. The active lipids identified in this study can be used to evaluate the nutritional value of Skipjack tuna.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.29 no.2
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• pp.179-185
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• 1984

These studies were carried out to evaluate the feasibility of using Alkali Digestibility Value (ADV) of soybean seeds as a selection criterion for cooking quality of soybean grain with rice, and to find out an optimal testing condition, varietal differences in ADV and the effect of cultural environment on the ADV, and its mode of inheritance. The ADV test was achieved succesfully by soaking the soybean grain for 24 hours in 25 to 30% KOH solution at 25 to $30^{\circ}C$. Varietal differences in the ADV were conspicuous, but cultural conditions affected the ADV little. All collected lines for cooking with rice showed high ADV and all the small grain cultivars introduced from abroad had low ADV, while recommended cultivars showed great variation in ADV. The characteristic of low ADV in soybean grains was controlled by single dominant gene.