• Journal of the Institute of Convergence Signal Processing
• /
• v.6 no.1
• /
• pp.33-38
• /
• 2005

Degradation is generated by several causes in the process of digitalization or transmission of data. And its essential cause is noise. Therefore, researches for wavelet-based methods which reconstruct signal degraded by noise have continued. In AWGN(addtive white gaussian noise) environment, the general trend for denoising is to use the thresholding method. Reconstructed signal includes a lot of noise because these methods only consider statistical characteristic regarding noise. In this paper, we present a new method which uses the cumulation of wavelet detail coefficients. As a result, reconstruction of edges and denoising performance are improved. Also we compare existing methods using SNR(signal-to-noise ratio) as the standard of judgement of improvemental effect.

• Journal of KIISE:Computer Systems and Theory
• /
• v.30 no.7_8
• /
• pp.426-433
• /
• 2003

Management policies of Web Proxy Cache, for the QoS of Web users, are mainly focused on the page replacement and the data consistency policy. But the two subjects have been studied independently to each other regardless of its possibility of cooperation. In this paper, we introduce the performance improvement obtained by adapting the characteristic of LMF used in data consistency policy to LRU, thus taking the better performance synergy as a result of complementary cooperation. Various policies for the management of Web Proxy Cache are in progress, this study can be a way of performance guide to increase cache hit ratio and reduce the transmission overhead of Web Server.

• The KIPS Transactions:PartC
• /
• v.15C no.1
• /
• pp.51-60
• /
• 2008

Micro-mobility protocols have been developed to reduce the control message overhead due to movements of mobile nodes. With the spread of mobile devices, services using mobile nodes are increasing and multicast services are becoming more important in providing multimedia services. In this paper we propose a new multicast protocol suitable for micro-mobility environments. The proposed protocol is designed to maintain optimal multicast routing paths and continue to provide multicast services without disruption in spite of frequent handoffs due to movements of mobile nodes. We used simulation to evaluate the proposed protocol, compared its performance with existing multicast protocols for mobile environments including bi-directional tunneling, remote subscription, and MMA, and observed that the proposed protocol exhibited better performance in terms of transmission success ratio and overhead on the network.

• Macromolecular Research
• /
• v.15 no.5
• /
• pp.449-458
• /
• 2007

The aims of this study were to investigate the intercalation of polymer chains with organoclays and improve the thermo-mechanical properties of poly(butylene terephthalate) (PBT) hybrids by comparing PBT hybrids synthesized using two different organoclays. The organoclays; dodecyltriphenylphosphonium-montmorillonite ($C_{12}PPh-MMT$) and dodecyltriphenylphosphonium-mica ($C_{12}PPh-Mica$), were used to fabricate the PBT hybrid fibers. Variations in the properties of the hybrid fibers with the organoclays within the polymer matrix, as well as the draw ratio (DR), are discussed. The thermo-mechanical properties and morphologies of the PBT hybrid fibers were characterized using differential scanning calorimetry, thermogravimetric analysis, wide-angle X-ray diffraction, electron microscopy and mechanical tensile properties analysis. The nanostructures of the hybrid fibers were determined using both scanning and transmission electron microscopies, which showed some of the clay layers to be well dispersed within the matrix polymer, although some clustered or agglomerated particles were also detected. The thermal properties of the hybrid fibers were found to be better than those of the pure PBT fibers at a DR = 1. The tensile mechanical properties of the $C_{12}PPh-MMT$ hybrid fibers were found to worsen with increasing DR. However, the initial moduli of the $C_{12}PPh-Mica$ hybrid fibers were found to slightly increase on increasing the DR from 1 to 18.

• Journal of Welding and Joining
• /
• v.30 no.4
• /
• pp.38-43
• /
• 2012

Using a fiber laser heat source, an oil pressure sensor was fabricated to measure the pressure in commercial vehicles. A stepping motor was used for the rotational and translational motion in the diaphragms and hardware joining. Laser welding process algorism including shielding gas control and vision system was integrated by using LabVIEW software for the high quality welding and in-line monitoring purpose. For the maximum flexibility in pressure transmission to the pressure sensor, thin sheet metal diaphragm, $25{\sim}50{\mu}m$(SUS-316L), was used and the diaphragms were optimally designed with FEM analysis. The welded samples were cross-sectioned the observation showed that the maximum depth ratio was more than seven times of diaphragms. The maximum welding speed was measured to be as high as 50in/mm by the developed automation mechanism. The fabricated prototypes were tested for the proof pressure, spring constant and sealing. The FEM results of spring constant measurement was as accurate as up to 80% of the design value and the sensor was safely operated up to the nominal pressure of 10bars.

• Korean Journal of Materials Research
• /
• v.16 no.12
• /
• pp.719-724
• /
• 2006

Ultrafine mullite powder was prepared from aluminium-secbutoxide and tetraethyl orthosilicate(TEOS) in the molar $Al_2O_3/SiO_2$=3/2. Sol-gel method by partial hydrolysis technique, as it were, first, TEOS was partially hydrolysized and then mixed with Al-secbutoxide for complete hydrolysis was used. X-ray diffraction, infrared spectroscopy and transmission electron microscopy, etc. confirmed that the mullite powder prepared by this method is in the stoichiometric $Al_2O_3/SiO_2$ ratio. Al-Si spinel was formed at $980^{\circ}C$ and ultrafine mullite powder with about 20 nm particle size was obtained above $1,200^{\circ}C$. Also mullite powders calcined at $1,600^{\circ}C$ had a stoichiometric composition, $3Al_2O_3{\cdot}2SiO_2$ and the lattice constants of the mullite powders calcined above $1,200^{\circ}C$ were almost coincided with theoretical values.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.29 no.4 s.235
• /
• pp.512-518
• /
• 2005

Polymeric fibers with nanometer-scale diameters are produced by electrospinning. When the electrical forces at the surface of a polymer solution or melt overcome the surface tension then electrospinning occurs. Polycarbonate has been electrospun. Electrospun fibers are observed by scanning electron microscopy and transmission electron microscopy. The surface morphology of e-spun fiber has been studied by many variables that are involved in different polymer concentrations, solvent mixing ratios and ambient parameters. The average diameters of the electrospun fibers range from 200 nm to 4,570 nm when the PC concentration is decreasing from 15.5\;wt{\%}\;to\;25\;wt{\%}.$ The higher concentration of the polymer solution makes the fibers thicker due to preventing the fiber stretching. With respect evaporation effects, the solvent mixing ratios cause significant changes of the fiber size distribution. As a matter of fact the fiber diameter steadily increases with increasing amount of DMF until the solvent mixture is at THF:DMF ratio of 60:40.

• Journal of Surface Science and Engineering
• /
• v.27 no.5
• /
• pp.253-260
• /
• 1994

Ta-N films were reactively sputter deposited by dc magnetron sputtering from a Ta target with a various Ar-N, gas ratio. Electrical resistivity of pure Ta film was 150$\mu$$\Omega$cm and decreased initially with nitrogen addition, and then increased to a value of 220$\mu$$\Omega$-cm~260$\mu$$\Omega$-cm at 9%~23% nitrogen partial flow. Rutherford backscattering spectrometry(RBS) and Auger electron spectroscopy (AES) analysis show that nitrogen content in the film is increased with the nitrogen partial flow. The film contains 58at.% nitrogen at 36% nitrogen partial flow. Both the phase and the microstructure of the as-deposisted films were investigated by x-ray diffractometry(XRD) adn transmission electron microscopy (TEM) at various nitrogen content. The phase of pure Ta film is identified as $\beta$-Ta with a 200$\AA$~300$\AA$ grain size. The phase of Ta film is changed to bcc-Ta as small amount of nitrogen is added. Crystalline Ta2N film was deposited at 24at.% nitrogen content. Amorphous phase is formed over a range of nitrogen content from about 33at.% to 35at.% while crystalline fcc-TaN is observed to form at 39at.%~48at.% nitrogen content.

• Advances in materials Research
• /
• v.6 no.3
• /
• pp.245-255
• /
• 2017

High energy ball milling is employed to produce iron matrix- multiwall carbon nanotube (MWCNT) reinforced composite. The damage caused to MWCNT due to harsh ball milling condition and its influence on interfacial bonding is studied. Different amount of MWCNT is used to find the optimal percentage of MWCNT for avoidance of the formation of chemical reaction product at the matrix - reinforcement interface. Effect of process control agent is assessed by the use of different materials for the purpose. It is observed that ethanol as a process control agent (PCA) causes degradation of MWCNT reinforcements after milling for two hours whereas solid stearic acid used as process control agent, allows satisfactory conservation of MWCNT structure. It is further noted that at a high MWCNT content (~ 2wt.%), high energy ball milling leads to reaction of iron and carbon and forms iron carbide (cementite) at the iron-MWCNT interface. At low percentage of MWCNT, dissolution of carbon in iron takes place and the amount of reinforcement in iron matrix composite becomes negligibly small. However, under the present ball milling condition (ball to metal ratio~ 6:1 and 200 rpm vial speed) iron-1wt.% MWCNT composite of good interfacial bonding can retain the tubular structure of reinforcing MWCNT.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.11 no.1
• /
• pp.150-156
• /
• 2007

Noise is generated by several causes, when signal is processed. Hence, it generates error in the process of data transmission and decreases recognition ratio of image and speech data. Therefore, after eliminating those noises, a variety of methods for reconstructing the signal have been researched. Recently, wavelet transform which has time-frequency localization and is possible for multiresolution analysis is applied to many fields of technology. Then threshold-and correlation-based methods are proposed for removing noise. But, conventional methods accept a lot of noise as an edge and are impossible to remove the additive white Gaussian noise (AWGN) and the impulse noise at the same time. Therefore, in this paper we proposed new wavelet-based algorithm for reconstructing degraded signal by noise and compared it with conventional methods.