Showing papers by "Kwangwoon University published in 2001"

Effect of pre-treatment on the surface and electrochemical properties of screen-printed carbon paste electrodes.

Abstract: The effect of various electrochemical pre-treatment methods on the surface and electrochemical properties of screen-printed carbon paste electrodes (SPCE) prepared with three different commercial products was examined. It was observed that a positively charged redox couple, e.g., hexaammineruthenium(III), exhibited quasi-reversible behavior at the untreated SPCE. However, the cyclic voltammograms (CVs) of the SPCE prepared with general-purpose carbon inks did not exhibit clear redox peaks to other representative redox couples [e.g., hexacyanoferrate(III), hexachloroiridate(IV), dopamine, and hydroquinone] without activation. Electrochemical pre-treatment methods were sought in four different aqueous solutions, i.e., sulfuric acid, potassium chloride, sodium hydrogencarbonate, and sodium carbonate, applying various activation potentials. It was found that the pre-treatment procedure in saturated Na2CO3 solution at 1.2 V provides a mild and effective condition for activating the SPCE. By measuring the water contact angles at the SPCE surfaces and recording their SEM images, it was confirmed that the electrochemical pre-treatment effectively removes the organic binders from the surface carbon particles. A prolonged period of activation (>5 min) or the use of high potentials (>1.2 V) increased the capacitance of the electrode over 20 μF cm−2. The pre-treated SPCE behaved like a random array microelectrode, exhibiting a sigmoidal-shaped CV at a slow scan rate. The short pre-anodization method in Na2CO3 solution was generally applicable to most SPCE prepared with general-purpose carbon inks.

A mixed-signal sensor interface microinstrument

Abstract: A single-chip implementation of a microinstrumentation system is presented. The chip incorporates voltage, current, and capacitive sensor interfaces; a temperature sensor; a 10-channel, 12-bit analog-to-digital converter; and an 8-bit microcontroller with a 16-bit hardware multiplier and a 40-bit accumulator. Serial and parallel interfaces allow digital communication with a host system. Fabricated in a standard 0.35 μm digital CMOS process, the die occupies 3.8 mm ×4.1 mm, operates from a nominal supply voltage of 3 V, and draws 16 mA when fully powered (850 μA standby current). To facilitate testing of the prototype, extra pads are bonded out to package pins. The chips are packaged in 132-pin ceramic pin-grid-array packages.

Forward-link capacity of a DS/CDMA system with mixed multirate sources

Abstract: Some studies have been done on capacity of a code division multiple access (CDMA) system with mixed multirate sources. However, a vast majority of these studies have concentrated on the reverse-link. This trend comes from the fact that the capacity of a CDMA system is reverse-link limited. However, the forward-link can be a limiting link because emerging data services are likely to require higher data rates in the forward-link than in the reverse-link. In this paper, we analyze and simulate the forward-link capacity of a CDMA system with mixed multirate sources in a multipath fading channel. The outage probability of the forward-link is derived for a CDMA system with mixed multirate sources. By introducing a forward-link power factor, the forward-link Erlang capacity is obtained in a closed form. The forward-link capacity is analyzed in terms of the number of multipaths, the number of RAKE fingers in a mobile station, closed-loop power control, and impact of soft handoff. The results in this paper can be applied to overall system design of a CDMA system with multimedia services in future mobile communication systems.

The effect of culture and self‐construals on predispositions toward verbal communication

Abstract: This study tested the effects of culture and self-construals (i.e., independence and interdependence) on predispositions toward verbal communication. For the purpose of this study, we focused on two main areas of verbal communication predispositions: (a) communication apprehension and (b) argumentativeness. In our path model, we expected that culture-level individualism increases one's construal of self as independent, which, in turn, leads to a higher degree of argumentativeness and a lower level of communication apprehension. We also expected that culture-level individualism decreases one's construal of self as interdependent, which, in turn, leads to a lower degree of argumentativeness and a higher level of communication apprehension. Data to test the model were drawn from undergraduates (N=539) studying in Korea, Hawaii, and mainland U.S. The data were partially consistent with the theoretical predictions made. The implications of the results for theory and practice are discussed.

Optical spectroscopy on individual CdSe/ZnMnSe quantum dots

Abstract: Optical single dot studies in wide-band gap diluted magnetic CdSe/ZnMnSe quantum dots have been performed. Due to the sample design, the photoluminescence energy of the quantum dot signal is energetically below the internal Mn2+ transition, resulting in high quantum efficiencies comparable to nonmagnetic CdSe/ZnSe quantum dots. Magnetic-field- and temperature-dependent measurements on individual dots clearly demonstrate the exchange interaction between single excitons and individual Mn2+ ions, resulting in a giant Zeeman effect and a formation of quasi-zero-dimensional magnetic polarons.

A planar amperometric creatinine biosensor employing an insoluble oxidizing agent for removing redox-active interferences.

Abstract: A planar microchip-based creatinine biosensor employing an oxidizing layer (e.g., a PbO2 film), where interfering redox-active substances are broken (i.e., oxidized) to redox-inactive products, was developed to facilitate the microfabrication of the sensor and to provide improved, reliable determination of creatinine in physiological samples. The feasibility of using hydrophilic polyurethanes in permselective barrier membranes for creatinine biosensors and the effect of adding a silanizing agent (adhesion promoter) on the sensor performance (e.g., sensitivity, stability, and lifetime) are described. The proposed creatinine microsensor with a three-layer configuration, i.e., enzyme, protecting, and oxidizing layers, exhibits good electrochemical performance in terms of response time (t95% = 98 s at 100 → 200 μM creatinine change), linearity (1−1000 μM, r = 0.9997), detection limit (0.8 μM), and lifetime (∼35 days). The creatinine biosensor devised in a differential sensing arrangement that compensates the ...

Fibroblast culture on surface-modified poly (glycolide-co-ε-caprolactone) scaffold for soft tissue regeneration

Abstract: Novel porous matrices made of a copolymer of glycolide (G) and e-caprolactone (CL) (51 : 49, Mw 103 000) was prepared for tissue engineering using a solvent-casting particulate leaching method. Poly(glycolide-co-e-caprolactone) (PGCL) copolymer showed a rubber-like elastic characteristic, in addition to an amorphous property and fast biodegradability. In order to investigate the effect on the fibroblast culture, PGCL scaffolds of varying porosity and pore size, in addition to surfacehydrolysis or collagen coating, were studied. The large pore-sized scaffold (pore size >150 μm) demonstrated a much greater cell adhesion and proliferation than the small pore-sized one. In addition, the higher porosity, the better the cell adhesion and proliferation. The surface-hydrolyzed PGCL scaffold showed enhanced cell adhesion and proliferation compared with the unmodified one. Type I collagen coating revealed a more pronounced contribution for increased cell interactions than the surface-hydrolyzed one. These results d...

MRED: a new approach to random early detection

Abstract: In order to reduce the increasing packet loss rates caused by an exponential increase in network traffic, the IETF (Internet Engineering Task Force) is considering the deployment of active queue management techniques such as RED (random early detection). While active queue management in routers and gateways can potentially reduce packet loss rates in the Internet, this paper has demonstrated the inherent weakness of current techniques and shows that they are ineffective in preventing high loss rates. The inherent problem with these queue management algorithms is that they all use queue lengths as the indicator of the severity of congestion. In order to solve this problem, a new active queue management algorithm called MRED is proposed. MRED computes the packet drop probability based on our heuristic method rather than the simple method used in RED. Using simulation, MRED is shown to perform better than existing queue management schemes.

Turbo-coded optical direct-detection CDMA system with PPM modulation

Abstract: The performance of an optical code division multiple access (CDMA) system with turbo coding is analyzed and simulated. Turbo codes are parallel concatenated convolutional codes (PCCCs) in which the information bits are first encoded by a recursive systematic convolutional code, and then, after passing through an interleaver, are encoded by a second systematic convolutional encoder. Turbo coding is superimposed on an intensity-modulated optical channel with pulse-position modulation (PPM) and direct detection of the received optical signal, and the performance is evaluated in terms of an upper bound on bit error probability. From the simulation results, it is seen that turbo coding offers considerable coding gain over other methods, with reasonable encoding/decoding complexity. Also, it is demonstrated that, for a fixed code rate, the performance of the optical CDMA system can be substantially improved by increasing the interleaver length and the number of iterations. Serially concatenated convolutional codes (SCCCs) are also considered, and are shown to perform comparably to PCCC in general and better than PCCCs for the case of large signal photocounts. The results in this paper can be applied, for example, to indoor optical wireless LANs.

Conversion of Methane to Higher Hydrocarbons in Pulsed DC Barrier Discharge at Atmospheric Pressure

Abstract: Conversion of methane to C2/C3 or higher hydrocarbons in a pulsed DC barrier discharge at atmospheric pressure was studied. Non-equilibrium plasma was generated in the barrier discharge reactor. In this plasma, electrons which had sufficient energy collided with the molecules of methane, which were then activated and coupled to C2/C3 or higher hydrocarbons. The effect of the change of applied voltage, pulse frequency and methane flow rate on methane conversion, selectivities and yields of products was studied. Methane conversion to higher hydrocarbons was about 25% as the maximum. Ethane, propane and ethylene were produced as primary products, including a small amount of unidentified C4 hydrocarbons. The selectivity and yield of ethane as a main product came to about 80% and 17% as the highest, respectively. The selectivities of ethane and ethylene were influenced not by the change of pulse frequency but by the change of applied voltage and methane flow rate. However, in case of propane, the selectivity was independent of those condition changes. The effect of the packing materials such as glass and A12O3 bead on methane conversion was also considered, showing that A12O3 played a role in enhancing the selectivity of ethane remarkably as a catalyst.

Fabrication of wirelike InAs quantum dots on 2°-off GaAs (100) substrates by changing the thickness of the InAs layer

Abstract: Wirelike InAs quatum dots (QDs) grown on 2°-off (100) GaAs substrates by changing the thickness of the InAs layer were successfully fabricated. The sizes of the InAs QDs along the step lines increased with increasing the thickness of the InAs layer, and their increases were attributed to transform of the InAs QDs into the wirelike InAs QDs. The optimal thicknesses of the InAs layers for the wirelike QDs and the interval of the wirelike QDs were significantly affected by the terrace width resulting from the bunching effect due to the thickness variations of the GaAs buffer layers grown on 2°-off (100) GaAs substrates. These results indicate that these wirelike InAs QDs are useful for applications in nanoelectronic devices, such as wrap gate single electron transistors.

H-BSP: A Hierarchical BSP Computation Model

Abstract: This paper presents a new parallel computing model, called H-BSP, which adds a hierarchical concept to the BSP(Bulk Synchronous Parallel) computing model. An H-BSP program consists of a number of BSP groups which are dynamically created at run time and executed in a hierarchical fashion. H-BSP allows algorithm designers to develop more efficient algorithms by utilizing processor locality in the program. Based on the distributed memory model, H-BSP provides a group-based programming paradigm and supports Divide & Conquer algorithms efficiently. This paper describes the structure of the H-BSP model, complexity analysis and some examples of H-BSP algorithm. Also presented is the performance characteristics of H-BSP algorithms based on the simulation analysis. Simulation results show that H-BSP takes advantages of processor locality and performs well in low bandwidth networks or in a constant-valence architecture such as 2-dimensional mesh. It is also proved that H-BSP can predict algorithm performance better than BSP, due to its locality-preserving nature.

Preparation of high molecular weight poly(vinyl alcohol) with high yield using low-temperature solution polymerization of vinyl acetate

Abstract: Vinyl acetate (VAc) was solution-polymerized in tertiary butyl alcohol (TBA) and in dimethyl sulfoxide (DMSO) having low chain transfer constant at 30, 40, and 50°C, using a low temperature initiator, 2,2′-azobis(2,4-dimethylvaleronitrile) (ADMVN). The effects of polymerization temperature and initiator concentration were investigated in terms of polymerization behavior and molecular structures of poly(vinyl acetate) (PVAc) and corresponding poly(vinyl alcohol) (PVA) obtained by saponification with sodium hydroxide. The polymerization rates of VAc in TBA and in DMSO were proportional to the 0.49 and 0.72 powers of ADMVN concentration, respectively. For the same polymerization conditions, TBA was absolutely superior to DMSO in increasing the molecular weight of PVA. In contrast, TBA was inferior to DMSO in causing conversion to polymer, indicating that the initiation rate of VAc in TBA was lower than that in DMSO. These effects could be explained by a kinetic order of ADMVN concentration calculated using initial rate method and by an activation energy difference of polymerization obtained from the Arrhenius plot. Low-temperature solution polymerization of VAc in TBA or DMSO by adopting ADMVN proved successful in obtaining PVA of high molecular weight (number–average degree of polymerization (Pn): 4100–6100) and of high yield (ultimate conversion of VAc into PVAc: 55–80%) with diminishing heat generated during polymerization. In the case of bulk polymerization of VAc at the same conditions, maximum Pn and conversion of 5200–6200 and 20–30% was obtained, respectively. The Pn and lightness were higher, and the degree of branching was lower with PVA prepared from PVAc polymerized at lower temperatures in TBA. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1003–1012, 2001

Differential Thick‐Film Amperometric Glucose Sensor with an Enzyme‐Immobilized Nitrocellulose Membrane

Abstract: A disposable glucose sensor based on a differential amperometric measurement is fabricated on activated carbon paste electrodes with the use of a glucose oxidase (GOx)-immobilized nitrocellulose (NC) membrane. Two identical three-electrode cells are screen-printed symmetrically on both faces of a single polyester (PE) substrate. Both electrodes of the two-sided sensor strip are covered with NC membranes incorporating a mediator (K3[Fe(CN)6]), one membrane with GOx and the other with bovine serum albumin (i.e., no GOx): the former serves as a glucose-sensing cell and the other as a reference cell. In the differential measurements between these two cells, the response signals toward various redox species other than glucose cancel out. Prior to placing the NC membranes, the working carbon paste electrodes are pretreated by anodizing them in saturated sodium carbonate at 1.2 V (vs. SCE): the electrochemical reversibility of the mediator is found to be enhanced significantly on such an activated electrode. The analytical performance of the proposed differential glucose sensor strip is demonstrated by measuring glucose values in normal and abnormal serum samples: 5.08±0.52 (found) vs. 5.10±0.46 (listed), and 16.56±1.71 (found) vs. 16.92±1.72 (listed).

A distributed proxy server system for wireless mobile Web service

Abstract: The transcoding proxy strategy has been widely used as a means to reduce the delay in retrieving Web pages over wireless mobile data networks. However, this strategy has a serious drawback of being a potential point of failure or a bottleneck of the service. We developed a distributed proxy server system in which multiple proxy servers are installed at geographically dispersed locations and share the workloads among themselves by serving mobile hosts within assigned regions. A new handoff (HO) message protocol is proposed to enable handoffs between proxies as the mobile hosts move between regions. With this proxy server handoff protocol a client agent at the mobile host requests a proxy server to initiate handoff processing and two proxy servers synchronize distilled data for a HTTP session disconnected by the handoff.

On Ag-doping in amorphous Sb2S3 thin film by HeNe and HeCd laser exposures and its optical characteristics

Abstract: The metal photodoping effect and material characterization in the system of Ag (10 nm)/a-Sb2S3 (300 nm)/Si-substrate have been investigated using a HeCd laser (λ=325.0 nm ) and a HeNe laser (λ=632.8 nm ) . The Ag thin film is optically transparent for the HeCd laser light. Although an optical-bandgap shrinkage (negative ΔEop or darkening) due to the Ag-doping is observed in the all films exposed to each laser, the ΔEop dependency on photon dose and the Ag-doping profiles are distinctly different. While the maximum value of ΔEop in Sb2S3 films exposed to HeCd laser saturates at about −0.08 eV , the ΔEop in Sb2S3 films exposed to HeNe laser is not saturated and the maximum is a relatively large value (about −0.25 eV). The doping front (with a peak Ag concentration) on the Ag depth profiles always exists at an interface between the chalcogenide and semiconducting substrate. In the case of films exposed to HeNe laser, however, the Ag at the chalcogenide surface is completely depleted and the peak shape appears to be broadly distributed with the doping front as a symmetry center. On the other hand, the films exposed to HeCd laser exhibit a relatively uniform Ag distribution without a surface depletion and with a sharp peak shape. Of course, these differences in Ag-doping phenomena can be ascribed to the differences of optical energy for two types of lasers (above-Eop and sub-Eop exposures). However, we believe that it is also important whether the Ag layer absorbs optically an incident laser power or not, i.e., thermally.

Segregation by color/luminance does not necessarily facilitate motion discrimination in the presence of motion distractors.

Abstract: Under what circumstances is the common motion of a group of elements more easily perceived when the elements differ in color and/or luminance polarity from their surround? Croner and Albright (1997), using a conventional global motion paradigm, first showed that motion coherence thresholds fell when target and distractor elements were made different in color. However, in their paradigm, there was a cue in the static view of the stimulus as to which elements belonged to the target. Arguably, in order to determine whether the visual system automatically groups, or prefilters, the image into different color maps for motion processing, such static form cues should be eliminated. Using various arrangements of the global motion stimulus in which we eliminated all static form cues, we found that global motion thresholds were no better when target and distractors differed in color than when they were identical, except under certain circumstances in which subjects had prior knowledge of the specific target color. We conclude that, in the absence of either static form cues or the possibility of selective attention to the target color, features with similar colors/luminance-polarities are not automatically grouped for global motion analysis.

Multiple information hiding technique using random sequence and hadamard matrix

Abstract: We propose a digital information hiding technique in which we use a combination of a random sequence and the Hadamard matrix to hide multiple information in a digital image. Earlier work used only one random sequence multiplied by an information signal to spread the spectrum of the information signal, making it difficult for a third party to detect the information signal or jam it. But in the case of hiding multiple information in the same digital image, the use of only different random sequences that are generally not orthogonal to each other has some problems because of the cross-correlation between the sequences. Thus we present a new information hiding scheme that can be used to hide multiple information using both a random sequence that spreads the energy level of the data to be hidden and a Hadamard matrix, which results in the random sequence being uncorrelated.

A new three-dimensional 30 GHz bandpass filter using the LIGA micromachined process

Abstract: In this letter, a new micromachined 3-D bandpass filter in the Ka-band is proposed using the LIGA process.The characteristic impedance and design parameters for the 3-D filter are determined from the experimental results and the filter design rule.The filter shows a wide-bandpass characteristic of 39%, with an insertion loss of 1.7 dB at 33.2 GHz, and can be applicable in high-power MMICs. 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 30:199 201, 2001. Contract grant sponsor:KOSEF under the ERC Program through the MINT Research Center, Dongguk University

Structuring element decomposition for efficient implementation of morphological filters

Abstract: In order to implement morphological filters on image processing systems. The size of the structuring element must be small due to the architectural constraints of the systems. The decomposition of the structuring element is required for filters with large structuring elements. An algorithm for the decomposition of an arbitrary 4-connected binary structuring element is developed which enables sub-optimal implementation of binary morphological filters on a 3/spl times/3 pipeline machine. The given structuring element is first decomposed into the union of elements using a sequential search procedure, then each element is further decomposed optimally into 3/spl times/3 elements, resulting in final sub-optimal 3/spl times/3 hybrid decomposition. The proposed algorithm is applied to some structuring elements and results close to the optimum are obtained.