• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2004.05b
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• pp.399-403
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• 2004

In this paper, we have analyzed the TCP throughput of Portable Internet system in 2.3GHz wireless environment with considering user's mobility speed. As the Portable Internet uses large cells compared to wireless LAM and supports user's nobility, we have adapted different wireless channel model to derive the TCP throughput of the system. We have assumed wireless channel is Rayleigh fading channel and the channel is modeled as two-state Markov model with which user's nobility speed can be considered by varying transition matrix of the model. from the simulation results, we have known that higher TCP throughput under the slow fading than under the fast fading. Because the TCP throughput is closely related to the sender's congestion control, the more congestion control is done by the sender, the lower TCP throughput we have. The more congestion control is caused in the sender under the fast fading than the slow fading so the lower TCP throughput is resulted in the fast fading environment.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.180-180
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• 2010

Thin film transistors (TFTs) based on oxide semiconductors have emerged as a promising technology, particularly for active-matrix TFT-based backplanes. Currently, an amorphous oxide semiconductor, such as InGaZnO, has been adopted as the channel layer due to its higher electron mobility. However, accurate and repeatable control of this complex material in mass production is not easy. Therefore, simpler polycrystalline materials, such as ZnO and $SnO_2$, remain possible candidates as the channel layer. Inparticular, ZnO-based TFTs have attracted considerable attention, because of their superior properties that include wide bandgap (3.37eV), transparency, and high field effect mobility when compared with conventional amorphous silicon and polycrystalline silicon TFTs. There are some technical challenges to overcome to achieve manufacturability of ZnO-based TFTs. One of the problems, the stability of ZnO-based TFTs, is as yet unsolved since ZnO-based TFTs usually contain defects in the ZnO channel layer and deep level defects in the channel/dielectric interface that cause problems in device operation. The quality of the interface between the channel and dielectric plays a crucial role in transistor performance, and several insulators have been reported that reduce the number of defects in the channel and the interfacial charge trap defects. Additionally, ZnO TFTs using a high quality interface fabricated by a two step atomic layer deposition (ALD) process showed improvement in device performance In this study, we report the fabrication of high performance ZnO TFTs with a $Si_3N_4$ gate insulator treated using plasma. The interface treatment using electron cyclotron resonance (ECR) $O_2$ plasma improves the interface quality by lowering the interface trap density. This process can be easily adapted for industrial applications because the device structure and fabrication process in this paper are compatible with those of a-Si TFTs.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.37-37
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• 2010

Silicate-silsesquioxane or siloxane-silsesquioxane hybrid thin films are strong candidates as matrix materials for ultra low dielectric constant (low-k) thin films. We synthesized the silicate-silsesquioxane hybrid resins from tetraethoxyorthosilicate (TEOS) and methyltrimethoxysilane (MTMS) through hydrolysis and condensation polymerization by changing their molar ratios ([TEOS]:[MTMS] = 7:3, 5:5, and 3:7), spin-coating on Si(100) wafers. In the case of [TEOS]:[MTMS] 7:3, the dielectric permittivity value of the resultant thin film was measured at 4.30, exceeding that of the thermal oxide (3.9). This high value was thought to be due to Si-OH groups inside the film and more extensive studies were performed in terms of electronic, ionic, and orientational polarizations using Debye equation. The relationship between the mechanical properties and the synthetic conditions of the silicate-silsesquioxane precursors was also investigated. The synthetic conditions of the low-k films have to be chosen to meet both the low orientational polarization and high mechanical properties requirements. In addition, we have investigated a new solution-based approach to the synthesis of semiconducting chalcogenide films for use in thin-film transistor (TFT) devices, in an attempt to develop a simple and robust solution process for the synthesis of inorganic semiconductors. Our material design strategy is to use a sol-gel reaction to carry out the deposition of a spin-coated CdS film, which can then be converted to a xerogel material. These devices were found to exhibit n-channel TFT characteristics with an excellent field-effect mobility (a saturation mobility of ${\sim}\;48\;cm^2V^{-1}s^{-1}$) and low voltage operation (< 5 V). These results show that these semiconducting thin film materials can be used in low-cost and high-performance printable electronics.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• v.35 no.2
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• pp.112-119
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• 2009

Extracellular matrix(ECM) is known to function as a reservoir of endogenous growth factors, can be an effective delivery system of growth factor that easily lost bioactivity in solution. Fibrillar collagens like type I collagen, are the major constituent of the ECM and structural protein of bone. Also, it can be a scaffold for osteoblast migration. The purpose of this study was to compare the effects of absorbable Atelo-collagen Sponge($Teruplug^{(R)}$) insertion in tooth extraction sites on periodontal healing of the mandibular second molar after the extraction of the impacted third molar. The study population comprised 31 cases who had been scheduled for surgical removal of impacted mandibular third molars. All patients were in good general health and were not using any medication that would influence wound healing after surgery. In 15 cases control group, none was inserted into the tooth extraction site. In 16 cases experimental groups, $Teruplug^{(R)}$ was inserted into the tooth extraction site. We evaluated tooth mobility, pocket depth, gingival margin level preoperatively and 1 week, 2 weeks, 4 weeks, and 3 months postoperatively. The change was compared with two groups using Mann-Whitney test. The results were as follows. 1. There was no significant change of tooth mobility on both groups. 2. There was tendency of decreasing of previous pocket depth causing tooth extraction on both groups. 3. On gingival margin level, there was various change according to initial swelling and loss of attachment on both groups. 4. There was tendency of decreasing of gingival margin level on both groups because of removal of inflammation and decreasing of previous pocket depth. 5. There was large change of pocket depth on buccal middle, distal, lingual distal area because of tooth extraction and bone reduction. Compared with the control group and experimental group, we observed significant difference during some periods. The results of this study suggest that absorbable atelo-collagen sponge($Teruplug^{(R)}$) is relatively favorable bone void filler with prevention of tissue collapse, food packing and enhance periodontal healing.

• Journal of Adhesion and Interface
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• v.13 no.3
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• pp.137-144
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• 2012

Chemical functionalization of carbon nanomaterials (CNMs) is generally carried out for increasing interfacial adhesion between filler and polymer matrix for CNM-polymer nanocomposites. The chemically functionalized CNTs can produce strong interfacial bonds with many polymers, allowing CNT based nanocomposites to possess high mechanical and functional properties. Hence, increased surface adhesion can be measured indirectly by observing increased mechanical properties. However, there is a more direct way to observe interfacial bonds between polymer and CNM by measuring piezoresistivity behavior so that we can imagine the behavior of CNM particles in polymer matrix under deflection. Fuctionalization of MWCNT and rGO was carried out by oxidization reaction of MWCNT and rGO with $H_2SO_4/HNO_3$ solution. Electrical resistivities of MWCNT-PMMA and rGO-PMMA composites were decreased after functionalization because of the destructive fuctionalization process. Meanwhile, piezoresistivities of functionalized CNM-PMMA composites showed more sensitive behavior under the same deflection as compared to pristine CNM-PMMA composites. Therefore, mobility of CNM in polymer matrix was found to be improved with chemical functionalization.

• Journal of the Korean Electrochemical Society
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• v.18 no.1
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• pp.1-6
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• 2015

In this study polystyrene derivative, VBCE, having a cyclic carbonate was synthesized by Williamson reaction and polymerized to poly(VBCE) successfully in an usual polymerization conditions. The obtained polymer was blended with PEGMA and the effect of composition on the ionic conductivity was investigated. Interestingly, the ionic conductivity was decreased from $4.2{\times}10^{-5}S\;cm^{-1}$ to $3.93{\times}10^{-6}S\;cm^{-1}$ with the poly(VBCE) contents of 5.8mol%. From the DSC study, it was found that the $T_g$ of the blend was increased from $-50^{\circ}C$ to $-21^{\circ}C$ by the addition of poly(VBCE). Therefore, it is believed that the presence of a polar cyclic carbonate makes polymer matrix harder and it is necessary to design new structures less hindered the mobility of the matrix.

• KSBB Journal
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• v.16 no.3
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• pp.237-240
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• 2001

Epithelial cell migration plays an important role in many physiological processes such as morphogenesis and wound healing, and cell mobility requires the release of the cell from its adhesion site. This is directed, at least in part, by limited proteolysis of matrix molecules by matrix metalloproteinases (MMPs). MMPs are zinc-dependent proteases produced by a variety of cell types, and have a fundamental role in tissue remodelling, tumour invasion and metastasis. In addition, the ability of cells to mediate fibrinolytic agent, plasmin. The purpose of this study was to test if vascular endothlial growth factor (VEGF) can regulate the production of MMPs and plasmin by keratinocyte cells. Supernatants from a human keratinocyte cell line grown in the presence or absence of VEGF (10ng/mL) produced ?2.5 fold increases in cell proliferation, and ?3.0 fold increses in MMP-2 and plasmin levels. Our results suggest that VEGF may modulate keratinocyte cell proliferating activity by increasing the abundance of MMP-2 and plasmin, and indicates a role for VEGF in the regulation of keratinocyte behaviour in wound healing and tissue remodelling.

• Journal of Adhesion and Interface
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• v.16 no.2
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• pp.55-62
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• 2015

It was investigated that the effect of surface modification and concentration of fumed silica on the adhesion properties and thermal stability of 2-EHA/AA pressure sensitive adhesive (PSAs) prepared by UV irradiation. The influence of repeating units of crosslinking agent on PSAs were also studied. From SEM analysis, PSAs synthesized with surface modified silica had finer dispersion of silica particles in polymer matrix due to the interfacial interaction. Results of the study showed that increase in tack and peel strength when under 0.3 wt% of silane treated silica were added in the reaction mixture. The addition of PEGDMA for crosslinking agent offers positive effect on adhesion properties in comparison with PSAs using EGDMA for crosslinker, which may be attributed to high mobility of ethylene oxide repeating units in PEGDMA. From the thermal degradation residue of PSAs, it was revealed that thermal stability was improved with silica addition due to the strong interfacial bonding between silane modified silica and polymer matrix, which may act as a thermal barriers into 2-EHA/AA PSAs.

• Journal of the Korean Institute of Telematics and Electronics
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• v.21 no.2
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• pp.71-82
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• 1984

A programme, called BIPOLE, for the numerical analysis of twotimensional n-p-n bipolar transistors was developed. It has included the SRH and Auger recolnbination processes, the mobility dependence on the impurity density and the electric field, and the band-gap narrowing effect. The finite difference equations of the fundamental semiconductor equations are formulated using Newton's method for Poisson's equation and the divergence theorem for the hole and electron continuity equations without physical restrictions. The matrix of the linearized equations is sparse, symmetric M-matrix. For the solution of the linearized equations ICCG method and Gummel's algorithm have been employed. The programme BIPOLE has been applied to various kinds of the steady-state problems of n-p-n transistors. For the examples of applications the variations of common emitter current gain, emitter and diffusion capacitances, and input and output characteristics are calculated. Three-dimensional representations of some D.C. physical quantities such as potential and charge carrier distributions were displayed. This programme will be used for the nome,rical analysis of the distortion phenom ana of two-dimensional n-p-n transistors. The BIPOLE programme is available for everyone.

• Journal of Korea Foundry Society
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• v.39 no.2
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• pp.21-25
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• 2019

Microstructural and corresponding hardness changes of TiFe compounds with Zr (0~6 at%) or Ce (0~3 at%) were studied using samples prepared at different solidification rates. In arc-melted (TiFe)-Zr samples, the $Fe_{23}$ $Zr_6$ and $(Ti,\;Zr)_2Fe$ phases formed in the TiFe matrix, while in the (TiFe)-Ce sample, the $CeO_2$ phase formed along the grain boundary of the TiFe matrix. As the Zr content was increased, the volume fractions of the $Fe_{23}$ $Zr_6$ and $(Ti,\;Zr)_2Fe$ phases increased, forming a network structure. Accordingly, the hardness values of the samples also increased. With a small addition of Ce of approximately 0.1 at%, the as-cast microstructure could be effectively refined, reducing the average grain boundary diameter from ${\sim}100{\mu}m$ to ${\sim}14{\mu}m$. In the rapidly solidified sample prepared through a melt-spinning method, the constituent phases were identical to those of the arc-melted samples while the grains were refined. The microstructural changes of TiFe alloys can affect the hydrogen storage ability as well as the mobility of the hydrogen atoms in the alloys.