• Title/Summary/Keyword: reversibility

Search Result 303, Processing Time 0.037 seconds

Sinusoidal Input Power factor Improved for Single-Phase Buck AC-DC Type Converter (정현파 입력 역률개선을 위한 단상 강압형 AC-DC 컨버터)

  • Jung, S.H.;Kwon, K.S.;Lee, H.W.
    • Proceedings of the KIEE Conference
    • /
    • 2001.11c
    • /
    • pp.338-340
    • /
    • 2001
  • Power factor improved for single-phase buck-converter is studied in the paper. To sinusoidal waveform the input current with a near-unity power factor over a wide variety of operating conditions, the output capacitor is operated with voltage reversibility for the supply by arranging the auxiliary diode and power switching device. Then the output voltage is superposed on the input voltage during on time duration of power switching devices in order to minimize the input current distortion caused by the small input voltage when changing the polarity. The tested setup, using two insulated gate bipolar transistors(IGBT) and a microcomputer, is implemented and IGBT are switched with 20[kHz], which is out of the audible band. Moreover, a rigorous state-space analysis is introduced to predict the operation of the rectifier. The simulated results confirm that the input current can be sinusoidal waveform with a near-unity power factor and a satisfactory output voltage regulation can be achieved.

  • PDF

Solid Oxide Fuel Cells for Power Generation and Hydrogen Production

  • Minh, Nguyen Q.
    • Journal of the Korean Ceramic Society
    • /
    • v.47 no.1
    • /
    • pp.1-7
    • /
    • 2010
  • Solid oxide fuel cells (SOFCs) have been under development for a variety of power generation applications. Power system sizes considered range from small watt-size units (e.g., 50-W portable devices) to very large multi-megawatt systems (e.g., 500-MW base load power plants). Because of the reversibility of its operation, the SOFC has also been developed to operate under reverse or electrolysis mode for hydrogen production from steam (In this case, the cell is referred to as solid oxide electrolysis cell or SOEC.). Potential applications for the SOEC include on-site and large-scale hydrogen production. One critical requirement for practical uses of these systems is long-term performance stability under specified operating conditions. Intrinsic material properties and operating environments can have significant effects on cell performance stability, thus performance degradation rate. This paper discusses potential applications of the SOFC/SOEC, technological status and current research and development (R&D) direction, and certain aspects of long-term performance degradation in the operation of SOFCs/SOECs for power generation/hydrogen production.

Redox Reaction on Polarization Curve Variations of Polymer with Enzymes

  • Park, Chil-Nam
    • Environmental Sciences Bulletin of The Korean Environmental Sciences Society
    • /
    • v.4 no.3
    • /
    • pp.165-171
    • /
    • 2000
  • Experiments were carried out to measure variations in the oxidation potential and current density using the polarization curves of polycarbonate. The results were then examined to identify the influences affecting the oxidation potential related to various conditions, such as temperature, pH, and oxydase(citrate and lipase). The lines representing the active anodic and cathodic dissolution shifted only slightly in the potential direction relative to temperature, pH, and the effect of the enzyme. The Tafel slope for the anodic and cathodic dissolution was determined such that the reversibility polarization was indicated as being effected by various conditions. The slope of the polarization curves describing the active-to-passive transition region shifted noticeably in their direction. Also, by varying the conditions, the optimum conditions for the most ready transform were identified, including temperature, pH, oxidation rate, and resistance of oxidation potential. The critical oxidation sensitivity(I(sub)r/I(sub)f) of the anodic current density peak and maximum passive current density was also determined, which is used in measuring the critical corrosion sensitivity of a polycarbonate.

  • PDF

Two dimensional FFT by Polynomial Transform (Polynomial 변환을 이용한 고속 2 차원 FFT)

  • 최환석;김원하;한승수
    • Proceedings of the IEEK Conference
    • /
    • 2003.11a
    • /
    • pp.473-476
    • /
    • 2003
  • We suggest 2 dimensional Fast Fourier Transform using Polynomial Transform and integer Fast Fourier Transform. Unlike conventional 2D-FFT using the direct quantization of twiddle factor, the suggested 2D-FFT adopts implemented by the lifting so that the suggested 2D-FFT is power adaptable and reversible. Since the suggested FFT performg integer-to-integer mapping, the transform can be implemented by only bit shifts and auditions without multiplications. In addition. polynomial transform severely reduces the multiplications of 2D-FFT. While preserving the reversibility, complexity of this algorithm is shown to be much lower than that of any other algorithms in terms of the numbers of additions and shifts.

  • PDF

Electrochemical Properties of Graphite-based Electrodes for Redox Flow Batteries

  • Kim, Hyung-Sun
    • Bulletin of the Korean Chemical Society
    • /
    • v.32 no.2
    • /
    • pp.571-575
    • /
    • 2011
  • Graphite-based electrodes were prepared using synthetic graphite (MCMB 1028) or natural graphite (NG) powder using a dimensionally stable anode (DSA) as a substrate. Their electrochemical properties were investigated in vanadiumbased electrolytes to determine how to increase the durability and improve the energy efficiency of redox flow batteries. Cyclic voltammetry (CV) was performed in the voltage range of -0.7 V to 1.6 V vs. SCE at various scan rates to analyze the vanadium redox reaction. The graphite-based electrodes showed a fast redox reaction and good reversibility in a highly concentrated acidic electrolyte. The increased electrochemical activity of the NG-based electrode for the $V^{4+}/V^{5+}$ redox reaction can be attributed to the increased surface concentration of functional groups from the addition of conductive material that served as a catalyst. Therefore, it is expected that this electrode can be used to increase the power density and energy density of redox flow batteries.

Nucleic Acid Aptamers: New Methods for Selection, Stabilization, and Application in Biomedical Science

  • Kong, Hoon Young;Byun, Jonghoe
    • Biomolecules & Therapeutics
    • /
    • v.21 no.6
    • /
    • pp.423-434
    • /
    • 2013
  • The adoption of oligonucleotide aptamer is well on the rise, serving an ever increasing demand for versatility in biomedical field. Through the SELEX (Systematic Evolution of Ligands by EXponential enrichment), aptamer that can bind to specific target with high affinity and specificity can be obtained. Aptamers are single-stranded nucleic acid molecules that can fold into complex three-dimensional structures, forming binding pockets and clefts for the specific recognition and tight binding of any given molecular target. Recently, aptamers have attracted much attention because they not only have all of the advantages of antibodies, but also have unique merits such as thermal stability, ease of synthesis, reversibility, and little immunogenicity. The advent of novel technologies is revolutionizing aptamer applications. Aptamers can be easily modified by various chemical reactions to introduce functional groups and/or nucleotide extensions. They can also be conjugated to therapeutic molecules such as drugs, drug containing carriers, toxins, or photosensitizers. Here, we discuss new SELEX strategies and stabilization methods as well as applications in drug delivery and molecular imaging.

Study on the Characteristics of Cell Reactions for Petroleum- and Coal Tar Pitch-based Carbons as a Negative Electrode for Li-iion Batteries (리튬이온전지용 부극재료인 페트롤리엄 및 콜타르 피치 카본의 전지반응 특성에 관한 연구)

  • 박영태;유광수;김정식
    • Journal of the Korean Ceramic Society
    • /
    • v.37 no.2
    • /
    • pp.128-133
    • /
    • 2000
  • In this work, soft carbons produced by pyrolysis of petroleum and coal-tar pitch were used as the negative electrode for Li-ion batteries. We studeid the charge/discharge capacity and the interfacial reaction of these electrodes by constructing a half cell. Charge/discharge property was studied by a constant-current step and the interfacial reaction between the electrolyte and the surface of a carbon electrode was studied by the cyclic voltammetry. The initial charge/discharge capacity for the coal-tar pitch carbon increased exceedingly with the heat treatment temperature. On hte other hand, the capacity of the petroleum pitch carbon increased with temperature up to 1000$^{\circ}C$, thereafter decreased continuously. While the charge capacity decreased with the cycle number, the reversibility increased above 90%. In addition, the thermal stability and crystallization of petroleum and coal-tar pitches were analyzed by TGA and XRD, respectively.

  • PDF

A length dependance of monolayer films of long-chain fatty acids (장쇄지방산의 길이에 따른 단분자막의 특성 변화)

  • 구창권;김무군;송경호;박태곤
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
    • /
    • 1996.05a
    • /
    • pp.38-42
    • /
    • 1996
  • The pressure-area isotherm of monolayer at the air-water interface were obtained and the LB films were fabricated onto a quartz slides and quartz crystal by conventional Langmuir-Blodggett(LB) method. The UV absorption spectra of Langmuir-Blodggett(LB) film on quartz slides and spectrum of monolayer formed on quartz crystal have been measured. The photoisomerization of the long-chain fatty avid containing azobenzene were obtained by the application of UV and visible light. The reversibility of photoisomerization were more clear difference when the number of C$\_$n/ increased. At the pressure-area isotherms, the value of surface pressure increment were decreased when the number of C$\_$n/ increased, A surface pressure of 20mN/m was obtained as a proper one for a film deposition. The photoisomerization at LB films were also obtained by application of UV and visible light. So the LB film of long-chain fatty acid containing azobenzene has possibility to being applies to functional molecular devices such as photomemory and light switching.

  • PDF

Improving JPEG-LS Performance Using Location Information

  • Woo, Jae Hyeon;Kim, Hyoung Joong
    • KSII Transactions on Internet and Information Systems (TIIS)
    • /
    • v.10 no.11
    • /
    • pp.5547-5562
    • /
    • 2016
  • JPEG-LS is an international standard for lossless or near-lossless image-compression algorithms. In this paper, a simple method is proposed to improve the performance of the lossless JPEG-LS algorithm. With respect to JPEG-LS and its supplementary explanation, Golomb-Rice (GR) coding is mainly used for entropy coding, but it is not used for long codewords. The proposed method replaces a set of long codewords with a set of shorter location map information. This paper shows how efficiently the location map guarantees reversibility and enhances the compression rate in terms of performance. Experiments have also been conducted to verify the efficiency of the proposed method.

Effects of Cyclic-AMP and Tannin on the Amylase Biosynthesis Induced by Gibberellin in Aleurone Layer II. Amylase (Cyclic-AMP와 탄닌이 지베레린으로 유도되는 Amylase 생합성에 미치는 영향 II. Amylase)

  • 권영명
    • Journal of Plant Biology
    • /
    • v.21 no.1_4
    • /
    • pp.21-27
    • /
    • 1978
  • The effect of tannic acid on GAs and cyclic-AMP promoted amylase induction in barley aleurone layers was examined. Of a variety of adenine compounds, only cyclic-AMP and ADP showed significant activity, and these activities were promoted by addition of theophylline to the incubation medium. When aleurone layers of barley endosperm tissues were incubated with GAs in the presence of tannic acid, the amylase activity in the incubation medium was reduced. Cyclic-AMP induced amylase activity was also reduced by additiion of tannic acid. The cyclic-AMP response promoted was more sensitive to tannin inhibition than GAs response. The inhibitory effect of tannic acid shwoed reversibility by addition of higher concentration of GAs or cyclic-AMP. The tannic acid effect on GAs response was also recovered by addition of a higher concentration of cyclic-AMP. Experiment with polyacrylamide disc electrophoresis showed different isozyme patterns according to the additions in the incubation medium. Inhibitory effects of decursinol and coumarin was compared with that of tannic acid. They showed different zymogram patterns.

  • PDF