• Journal of the Korea Society of Computer and Information
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• v.12 no.2 s.46
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• pp.63-70
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• 2007

The Data Encryption Standard (DES) is a block cipher that encrypts a 64 bit block of plaintext into a 64 bit block of ciphertext. The DES has been a worldwide standard for 20 years since it was adopted in 1976. strong. But, due to the rapid development of hardware techniques and cryptanalysis, the DES with 64-bit key is considered to be not secure at the present time. Therefore it became necessary to increase the security of DES. The NG-DES(New Generation DES)[1] is an encryption system which upgrades the encryption security of DES by the key extension and the usage of non-linear f function. It extends not only the size of plaintext and ciphertext to 128 bit but also the Fiestel structure used in each round. This structure has a weak point that the change of each bit of plaintext does not affect all bits of ciphertext simultaneously. In this paper, we propose a modified Fiestel structure of DES and thus increased confusion and diffusion by effectively cross-connecting between outputs in a round and inputs in next round.

• Journal of the Korean Society of Safety
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• v.9 no.4
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• pp.29-41
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• 1994

High temperature tensiles tests, steady state creep tests, internal stress tests and creep rupture tests using Al 7075 alloy were performed over the temperature range of 9$0^{\circ}C$~50$0^{\circ}C$ and stress range of 0.64~17.2(kgf/$\textrm{mm}^2$) in order to investigate the creep behavior and predict creep rupture life From the apparent activation energy Qc and the applied stress exponent n measured, at the temperature range of 9$0^{\circ}C$~l2$0^{\circ}C$, the creep deformation seemed to be controlled by cross slip. On the other hand at the temperature of 20$0^{\circ}C$~23$0^{\circ}C$ the creep deformation seemed to be controlled by dislocation climb but at 47$0^{\circ}C$~50$0^{\circ}C$, by diffusion creep. And the rupture life(t$_{f}$) might be represented by anthermal process attributed to the difference of the applied stress dependence of Internal stress and the ratio of the Internal stress to the applied stress, the thermal activated process attributied to the temperature dependence of the internal stress. Also the ratio between stress dependence of primary creep rate and that of minimum creep rate was measured 0.46, the minimum creep rate is expected to be appromately obtained from master creep curve including the relationship primary creep rate and minumum creep rate. Finally the relationship new rupture parameter and logarithmic stress was represented with including the ratio between the dependence of primary creep rate and that of minimum creep rate, using the new rupture parameter the rupture life predition is exactly expected.d.

• Journal of the Microelectronics and Packaging Society
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• v.13 no.4
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• pp.45-50
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• 2006

Copper via filling is the important factor in 3-D stacking interconnection of SiP (system in package). As the packaging density is getting higher, the size of via is getting smaller. When DC electroplating is applied, a defect-free hole cannot be obtained in a small size via hole. To prevent the defects in holes, pulse and pulse reverse current was applied in copper via filling. The holes, $20\and\;50{\mu}m$ in diameter and $100{\sim}190\;{\mu}m$ in height. The holes were prepared by DRIE method. Ta was sputtered for copper diffusion barrier followed by copper seed layer IMP sputtering. Via specimen were filled by DC, pulse and pulse-reverse current electroplating methods. The effects of additives and current types on copper deposits were investigated. Vertical and horizontal cross section of via were observed by SEM to find the defects in via. When pulse-reverse electroplating method was used, defect free via were successfully obtained.

• Bulletin of the Korean Chemical Society
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• v.29 no.2
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• pp.422-426
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• 2008

Hemodialysis graft coated with paclitaxel prevents stenosis; however, large initial burst release of paclitaxel causes many negative effects such as drug toxicity and inefficient drug loss. Therefore we developed and tested a novel coating method, double dipping, to provide controlled and sustained release of paclitaxel locally. Expanded polytetrafluoroethylene (ePTFE) grafts were dipped twice into a solution of several different paclitaxel concentrations. In vitro release tests of the double dipping method showed that early burst release could be somewhat retarded and followed by sustained release for a long time. We observed the effect of paclitaxel coating by double dipping in porcine model of arterio-venous (AV) grafts between the common carotid artery and the external jugular vein. 12 weeks after constructing AV grafts, cross sections of the graft venous anastomosis were obtained and analyzed. Paclitaxel coated ePTFE grafts by double dipping were observed to prevent neointimal hyperplasia and therefore reduced stenosis of the arteriovenous hemodialysis grafts, especially at the graft venous anastomosis sites. Our results demonstrate that second dipping of ePTFE graft, which was already coated once with paclitaxel, washes off the drug on a surface of the graft and affects the ratio of paclitaxel on the surface to that of the inner space, possibly by diffusion: thus the early burst of drug can be somewhat reduced.

• Korean Journal of Microbiology
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• v.41 no.1
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• pp.47-52
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• 2005

This study was carried out to identify bacterial strains adhered to human scalp hair and to investigate the antibiotic susceptibility of them. A total of 39 isolates were obtained from patients in intensive care units and healthy persons. The most common species isolated was Staphylococcus epidermidis (19 isolates), followed by S. aureus (14 isolates), S. waneri (5 isolates), and S. pasteuri (1 isolate). The susceptibility of isolates to amikacin, ampicillin, bacitracin, carbenicillin, cefazolin, cefoperazone, chloramphenicol, erythromycin, gentamicin, methicillin, nalidixic acid, neomycin, oxacillin, penicillin, streptomycin, tetracycline and vancomycin was determined by the disk diffusion method. All of the antibiotic resistant isolates were obtained from patient scalp hair. To examine the effect of conventional shampoo and detergent SDS on removing of bacteria from hair, we treated hair with culture solution of S. aureus. The bacteria attached to hair were not removed even by repeated washing with detergents. These results suggested that hair could be a source of bacterial contamination in hospital.

• Journal of Astronomy and Space Sciences
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• v.34 no.4
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• pp.343-352
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• 2017

A space plasma facility has been operated with a back-diffusion-type plasma source installed in a mid-sized vacuum chamber with a diameter of ~1.5 m located in Satellite Technology Research Center (SaTReC), Korea Advanced Institute of Science and Technology (KAIST). To generate plasma with a temperature and density similar to the ionospheric plasma, nickel wires coated with carbonate solution were used as filaments that emit thermal electrons, and the accelerated thermal electrons emitted from the heated wires collide with the neutral gas to form plasma inside the chamber. By using a disk-type Langmuir probe installed inside the vacuum chamber, the generation of plasma similar to the space environment was validated. The characteristics of the plasma according to the grid and plate anode voltages were investigated. The grid voltage of the plasma source is realized as a suitable parameter for manipulating the electron density, while the plate voltage is suitable for adjusting the electron temperature. A simple physical model based on the collision cross-section of electron impact on nitrogen molecule was established to explain the plasma generation mechanism.

• Journal of the Microelectronics and Packaging Society
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• v.12 no.2 s.35
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• pp.149-154
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• 2005

We fabricated Ni/Co(or Co/Ni) composite silicide layers on the non-patterned wafers from Ni(20 nm)/Co(20 nm)/poly-Si(70 nm) structure by rapid thermal annealing of $700{\~}1100^{\circ}C$ for 40 seconds. The sheet resistance, cross-sectional microstructure, and surface roughness were investigated by a four point probe, a field emission scanning electron microscope, and a scanning probe microscope, respectively. The sheet resistance increased abruptly while thickness decreased as silicidation temperature increased. We propose that the poly silicon inversion due to fast metal diffusion lead to decrease silicide thickness. Our results imply that we should consider the serious inversion and fast transformation in designing and process f3r the nano-height fully cobalt nickel composite silicide gates.

• Journal of the Korean Vacuum Society
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• v.5 no.4
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• pp.348-353
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• 1996

Rapid thermal annealing (RTA) was applied to polycrystalline CdTe thin films evaporated on CdS/ITO/glass substrate and the effect of the annealing temperatures and the atmosphere on physical properties of polycrystalline CdTe thin films and CdTe/CdS solar cell characteristics were studied. Results obtained by EDX showed that the bulk composition of CdTe remained stoichiometric after annealing at $550^{\circ}C$ in the air but the surface composition became Cd-rich. Cross-sectional TEM and micro EDX showed that columnar grains and micro-twins remained even after RTA, however, and the sulfur content in the annealed CdTe (added by sulfur diffusion from CdS during the annealing) was much smaller than that by furnace annealing. Among the investigated RTA temperatures and gas environments, the cell made with CdTe annealed at $550^{\circ}C$ in air showed the best solar energy conversion efficiency.

• Magazine of the Korea Concrete Institute
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• v.9 no.2
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• pp.153-161
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• 1997

In the concrete st~uctures exposed to the environmental condition, the water movement is occurred by thc moisture difilsion, and the rnoisturrt distribution in concwt.c is nonunifhrm. Such a non-unif'orm moisture distribution causes tht. diflbrent.ia1 drying shrinkage in concrete structures. From this typc. of' dif'fercntial drying shrinkagr' tensiit-1 stress is occurred in exposure surface of concrete structures. and may result in crack formation. This residual stress is significantly affected by the creep of concrete, and the differential creep is also occurred at the cross section of concrete structures due to moisture difference at each locations. In this study, based on the moisture diffusion theory, a finite element program which is capable of simulating the moisture distribution in concrete was developed. And the analysis method for the differential drying shrinkage was suggested, in which the differential creep was considered. The differential drying shrinkage strain was also measured at various positions of concrete. Finally the validity of analysis method was proved by comparing test results with analytical results.

• Journal of the Korean Society of Safety
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• v.25 no.6
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• pp.86-91
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• 2010

The purpose of this study is to analyze the damage patterns and metal structure of 3 phase mold transformers collected from places where accidents have occurred. Compared to an oil-immersed transformer, a mold transformer has the advantage of requiring a smaller installation area and can be kept clean, while its disadvantages include the fact that abnormal symptoms of an accident are difficult to discover and its repair is impossible. The capacity of the mold transformers collected from places where accidents have occurred was 200kVA with primary voltages being F23,900V, R22,900V, 21,900V, 20,900V, 19,900V, etc., as well as secondary voltages being 380V, 220V, etc. It was found from the analysis on the diffusion of combustion in the damaged mold transformers that fire occurred first inside the U-phase primary winding and that carbonization and heat were diffused to V-phase and W-phase in V-pattern. In addition, from the analysis on the cross-sectional structure of the metal of the melted high voltage winding using a metallurgical microscope, it was found that the boundary surface, voids, and columnar structure were formed when an interlayer short-circuit had occurred Therefore, even though it is not possible to find the cause for the occurrence of an interlayer short-circuit at the inner side of the primary winding, it is thought that, due to the thermal energy generated when the short-circuit occurred, the heat source was diffused to the upper side and outside, causing a secondary accident.