• Composites Research
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• v.24 no.2
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• pp.38-45
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• 2011

In this paper, we present an optimization method for the single Dallenbach-layer type microwave absorbers composed of E-glass fabric/epoxy composite laminates. The composite prepreg containing carbon nanotubes (CNT) was used to control the electrical property of the composites laminates. The design technology using the genetic algorithm was used to get the optimal thicknesses of the laminates and the filler contents at various center frequencies, for which the numerical model of the complex permittivity of the composite laminate was incorporated. In the optimal design results, the content of CNT increased in proportion to the center frequency, but, on the contrary, the thickness of the microwave absorbers decreased. The permittivity and reflection loss are measured using vector network analyzer and 7 mm coaxial airline. The influence of the mismatches in between measurement and prediction of the thickness and the complex permittivity caused the shift of the center frequency, blunting of the peak at the center frequency and the reduction of the absorbing bandwidth.

• Applied Microscopy
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• v.24 no.1
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• pp.86-101
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• 1994

The development of synovial membrane from knee joint was studied by electron microscope in human fetuses ranging from 20mm to 260mm crown rump length (40days to 30weeks of gestational age). At 40mm fetus, developing synovial tissue was observed in homogenous interzone as a vascular mesenchyme around the periphery. The primitive joint space was appeared after the intermediate layer of the interzone in direct contact with chondrogenic layer at 60mm fetus. Differentiation of the synovial membrane coincided with clarification of the joint cauity. When dilatation of the synovial cavity occurred, the two types of synovial cells were well endowed with rough endoplasmic reticulum. At 100mm fetus, type A cells with a markedly attenuated cytoplasm were found as well as those cells which contained pinocytotic vesicles and vacuoles. By 150-200mm fetuses a majority of the intimal cells were type B. These cells were characterized by abundant rough endoplasmic reticulum and well developed Golgi complex. In contrast, A-type cell had numerous filopodia, pinocytotic vesicles lysosomes, and large vacuoles containing amorphous material. At 260mm fetus, the intimal cells were well developed and plentiful. The most marked difference between the synovial membrane of full-term fetus and adult was the large amount of collagen in the latter. During fetal period, the B-cells were most numerous cell type in the intimal cells. The B-cells were clearly distinguishable from the A-cells by their content of extensive rough endoplasmic reticulum and well developed Golgi complex.

• Journal of the Korean Society for Heat Treatment
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• v.22 no.5
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• pp.282-289
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• 2009

The effects of the high temperature gas nitriding (HTGN), tempering and subzero treatment of STD11 steel have been investigated. HTGN treatment was carried out at $1050^{\circ}C$, $1100^{\circ}C$ and $1150^{\circ}C$ for 1 hr. in an atmosphere of $1\;kg/cm^2$ nitrogen gas. Tempering and double-tempering were performed at $550^{\circ}C$ for 1 hr. The surface layer of HTGN-treated steel appeared the precipitates of $M_2N$, $M_7C_3$ and $M_{23}C_6$ in the matrix of austenite. However, the interior region exhibited martensite with the precipitation of carbides. The nitrogen content of the surface layer appeared ~1.35 wt.%, ~0.83 wt.% and ~0.56 wt.% at the HTGN treatment temperature of $1050^{\circ}C$, $1100^{\circ}C$ and $1150^{\circ}C$, respectively. The surface hardness of double-tempered and subzero-treated steel measured the maximum value of 828 Hv, 960 Hv, 750 HV after HTGN treatment at the $1050^{\circ}C$, $1100^{\circ}C$ and $1150^{\circ}C$, respectively. These hardness value increased above 230~420 Hv compared with the HTGN-treated steel due to the decrease in retained austenite and existence of fine precipitates.

• Journal of the Korean Society for Heat Treatment
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• v.21 no.5
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• pp.244-250
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• 2008

This study has investigated the surface phase change, hardness variation, surface precipitates, nitrogen content and corrosion resistance in STS 431 (17Cr-2Ni-0.2C-0.01Nb) martensitic stainless steel after high temperature gas nitriding (HTGN) treatment at the temperature range between $1050^{\circ}C$ and $1150^{\circ}C$. The HTGN-treated surface layer appeared $Cr_2N$ of rod type, carbo-nitride of round type and fine precipitates in the austenite matrix. On the other hand the interior region where the nitrogen was not permeated, exhibited martensite phase. The surface hardness showed 250~590 HV, depending on the HTGN treatment conditions, while the interior martensitic phase represented 520 HV. The permeation depth of nitrogen increased with increasing the HTGN-treated temperature. The nitrogen concentration of the surface layer appeared approximately ~0.17% at $1100^{\circ}C$. On comparing the corrosion resistance between solution-annealed and HTGN-treated steels, the corrosion resistance of HTGN-treated steel was superior to that of solution-annealed specimens.

• Polymer(Korea)
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• v.30 no.4
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• pp.291-297
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• 2006

In this study, adsorption properties of oxidized NO by plasma using aminated polyolefin-g-GMA hybrid anion exchange fibers were investigated. The maximum conversion of $NO_2$ by plasma was 49% at the conditions of 200 ppm NO, 10% $O_2$ and 30 L/min of flow rate. The adsorption content for N02 of hybrid anion exchange fibers increased with increasing the swelling ratio and the highest value was 1.5 g $H_2O/g$ IEF. The adsorption of $NO_2$ by hybrid anion exchange fibers were very fast until 10 min and reached its maximum value of 80% at 120 min. Ion exchange capacity of hybrid anion exchange fibers increased with increasing the swelling ratio and it showed the highest 0.6 mmol/g IEF values at L/D=5. The adsorption isotherm model for hybrid anion exchange fibers were closer to Freundlich than Langmuir adsorption isotherm model. It was shown that adsorption of the multi-molecular layer was dominant.

• Magazine of the Korean Society of Agricultural Engineers
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• v.31 no.2
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• pp.66-81
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• 1989

The characteristics of resilient modulus(Mr) which dominates the life of pavement and the design of pavement were investigated on the test specimens which were cement treated and non-treated of the three different soil types. The results are summarized as follows : 1. The resilient modulus was decreased by increasing the cyclic deviator stress ($\sigma$d) , especially the resilient modulus was gradually decreased or sometimes increased when the value of ad was greater than 0.75- 1. 0kg/cm$^2$. 2. The resilient modulus was increased by increasing the homogeneous confined stress ($\sigma$do) and such phenomena were distinct on the coarse soils. 3. The resilient modulus was increased by increasing the ratio of confined stress(Kc), and this phenomena were eminent on the coarse soils too, and the higher permanent strain was showed by increasing the value of Kc. 4. In the drained cyclic triaxial compression test, the value of ad, Kc, and (Oho) was introduced by the following interrelated equations which were similar to the Mr model of Cole. Kcn/Mr=K1(J$_2$/ $\tau$oct)K2 ............. (coarse soli) Mcn/Mr=K3($\sigma$dp/ $\tau$f)k4 ...............(fine soils) 5. The stress path was not much affected by the value of Mr, however, moisture content, dry desity, and contant of fines affected the value of Mr. 6. In the soil-cement specimens, the resilient compression strain($\varepsilon$d) was decreased by the increment of the $\sigma$ho, and Mr was decreased by increasing the $\sigma$d 7. In the flexible pavement. the cement treated layer should be designed not to fail by the fatigue before the designed traffic load, and actually the pavement could cover the traffic load to a certain extent under the post-crack phase, therefore farther studies on this phenomena' are required in the design analysis. 8. The finite element computer program (ANALYS) was used for displacement analysis of pavement containing the cement-treated layer, The result showed that the program used for this analysis was proved to be usable.

• Corrosion Science and Technology
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• v.9 no.3
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• pp.122-128
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• 2010

The corrosion of the flexible tube in the automobile exhaust system is caused by the ambient water and chloride ions. Since welding is one of the key processes for the flexible tube manufacturing, it is required to select a proper welding method to prevent the flexible tube corrosion and to increase its lifetime. There are many studies about the efficiency of the welding method, but no systematic study is performed for the effect of welding method on the corrosion property of the austenitic stainless weldment. The aim of the present study is to provide information on the effect of two different welding methods of TIGW (tungsten inert gas welding) and PAW (plasma arc welding) on the corrosion property of austenitic stainless steel weldment. Materials used in this study were two types of the commercial austenitic stainless steel, STS321 and XM15J1, which were used for flexible tube material for the automotive exhaust system. Microstructure was observed by using optical microscopy (OM) and scanning electron microscopy (SEM). To evaluate the corrosion behavior, potentiodynamic and potentiostatic tests were performed. The chemical state of the passive film was analyzed in terms of XPS depth profile. Metallurgical analysis show that the ferrite content in fusion zone of both STS321 and XM15J1 is higher when welded by PAW than by TIGW. The potentiodynamic and potentiostatic test results show that both STS321 and XM15J1 have higher transpassive potential and lower passive current density when welded by PAW than by TIGW. XPS analysis indicates that the stable $Cr_2O_3$ layer at the outermost layer of the passive film is formed when welded by PAW. The result recommends that PAW is more desirable than TIGW to secure corrosion resistance of the flex tube which is usually made of austenitic stainless steel.

• Journal of Korea Multimedia Society
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• v.13 no.4
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• pp.575-581
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• 2010

With widespread use of the Internet and improvements in streaming media and compression technology, digital music, video, and image can be distributed instantaneously across the Internet to end-users. However, most conventional Digital Right Management are often not secure and not fast enough to process the vast amount of data generated by the multimedia applications to meet the real-time constraints. The SVC offers temporal, spatial, and SNR scalability to varying network bandwidth and different application needs. Meanwhile, for many multimedia services, security is an important component to restrict unauthorized content access and distribution. This suggests the need for new cryptography system implementations that can operate at SVC. In this paper, we propose a new scrambling encryption for reserving the characteristic of scalability in MPEG4-SVC. In the base layer, the proposed algorithm is applied and performed the selective scambling. And it encrypts various MVS and intra-mode scrambling in the enhancement layer. In the decryption, it decrypts each encrypted layers by using another encrypted keys. Throughout the experimental results, the proposed algorithms have low complexity in encryption and the robustness of communication errors.

• Journal of KIISE
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• v.43 no.11
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• pp.1281-1297
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• 2016

In recent years, personal videos have seen a tremendous growth due to the substantial increase in the use of smart devices and networking services in which users create and share video content easily without many restrictions. However, taking both into account would significantly improve event detection performance because videos generally have multiple modalities and the frame data in video varies at different time points. This paper proposes an event detection method. In this method, high-level features are first extracted from multiple modalities in the videos, and the features are rearranged according to time sequence. Then the association of the modalities is learned by means of DNN to produce a personal video event detector. In our proposed method, audio and image data are first synchronized and then extracted. Then, the result is input into GoogLeNet as well as Multi-Layer Perceptron (MLP) to extract high-level features. The results are then re-arranged in time sequence, and every video is processed to extract one feature each for training by means of DNN.

• Magazine of the Korean Society of Agricultural Engineers
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• v.32 no.3
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• pp.39-46
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• 1990

This paper was analized the thermal conductivity of polystylene (TENSAR- GEOGRID) embeding into the subbase through frost penetration depth, frost heave, change of bearing capacity, and soil moisture movement due to freezing, thawing and icing actions, and their results were as follows : 1.The change of temperature into the sub-base was much increased by the Tensar-Geogrid insertion, and the frost penetration and frost heave were decreased as the thinner of the insulation thickness but the thawing velocity of melting period was appeared to be faster in case of non-insulated. 2.The frost heave had a close relationship with the thickness of insulations which was reasonably included anti-frost effects. 3.The moisture content during the freezing period of upper layer of the insulation insertion was increased by 15 per cent but it was returned to initial state of the thawing period, and at the down layer temporarily increased by 10 per cent and returned to the original state at once. 4.The insulation was acted as a function of distribution of surcharge, and the settlement of the sub-base was about 1.5 mm under 15 tonnage of load and which was included within the allowable limits. 5.The sliding resistance due to the icing which was induced by the insulation insertion into the sub-base was appeared as more 40 per cent than noninsulation area, so that the insulations should be restricted on the place such as mountains, curved and cross area which were required the braking power under the traffics.