• Title/Summary/Keyword: Field dependence

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Electrode Dependence of Asymmetric Behavior of (La,Sr)CoO₃/Pb(Zr,Ti)O₃/(La,Sr)CoO₃ Thin Film Capacitors ((La,Sr)CoO₃/Pb(Zr,Ti)O₃/(La,Sr)CoO₃박막 캐패시터의 비대칭성의 전극 의존성)

  • 최치홍;이재찬;박배호;노태원
    • Journal of the Korean Ceramic Society
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    • v.35 no.7
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    • pp.647-647
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    • 1998
  • (La,Sr)CoO3/Pb(Zr,Ti)O3/(La,Sr)CoO3 (LSCO) heterostructures have been grown on LaAlO3 substrates by pulsed laser deposition (PLD) to investigate asymmetric polarization of Pb(Zr,Ti)O3 (PZT) thin flims with different electrode configuration. P-V hysteresis loop of LSCO/PZT/LSCO was symmetric. However, LaCoO3 (LCO_/PZT/LSCO showed a largely asymmetric P-V hystersis loop and large relaxation of the remanent polarization at the negatively poled state, which means that the negatively poled state was unstable. On the other hand, LSCO/PZT/LCO exhibited large relaxation of the positively poled state. The asymmetric behavior of the polarized states implies the presence of an interal electric firld inside the PZT layer. It is suggested that internal electric field is caused by built-in voltages at LCO/PZT and LSCO/PZT interfaces. The built-in voltages at LCO/PZT and CSCO/PZT interfaces were 0.6 V and -0.12 V, respectively.

An Experimental Study on Infiltration Characteristics of Facilities for Reducing Runoff Considering Surface Materials According to Housing Lot Developments (택지개발에 따른 표면재료를 고려한 우수유출저감시설의 침투 특성에 관한 실험 연구)

  • Im, Janghyuk;Song, Jaiwoo;Park, Sungsik;Park, Hosang
    • Journal of the Korean GEO-environmental Society
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    • v.8 no.5
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    • pp.47-55
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    • 2007
  • The increment of impermeable land area due to widespread land development caused the adverse impact on urban disaster prevention because it could decrease the peak rate of runoff as well as increase the runoff and peak flow during rainy period. To date, little research has been conducted on the infiltration characteristics and quantitative analysis because of their highly dependence on construction method, paving material, surface permeability, and field condition. Hence, this study was performed to investigate the infiltration characteristics of runoff-reducing facilities according to the type of paving material, which were examined using experimental apparatus with varying paving material and rainfall intensity, and thus to provide fundamental research data for runoff-reducing infiltration facilities. In this study, the infiltration characteristics were examined under the rainfall intensity of 20, 30, 50, 80, 100, 200 mm/hr for a variety type of paving materials such as concrete, asphalt, sand, grassland, and permeable paving material. The infiltration rate for permeable paving material was observed to be more than 93% under the condition of less than 200 mm/hr of rainfall intensity. For the compacted earth and grassland, the ultimate infiltration rate was estimated to be about 13% to 67%. The permeable paving material was concluded to be the most appropriate one for the runoff-reducing infiltration facilities because it has more favorable advantages than others in the light of infiltration volume, disaster prevention, and river training.

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Energy Density Control for the Global Attenuation of Broadband Noise Fields (광대역 잡음의 전역 감쇠를 위한 에너지 밀도 제어)

  • Park, Young-Cheol;Yun, Jeong-Hyeon;Youn, Dae-Hee;Cha, Il-Whan
    • The Journal of the Acoustical Society of Korea
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    • v.15 no.2
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    • pp.21-32
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    • 1996
  • The performance of the energy density control algorithm for controlling a broadband noise is evaluated in a one-dimensional enclosure. To avoid noncausality problem of a control filter, which often happens in a frequency domain optimization, analyses presented in this paper are undertaken in the time domain. This approach provides the form of the causally constrained optimal controller. Numerical results are presented to predict the performance of the active noise control system, and indicate that imp개ved global attenuation of the broadband noise can be achieved by minimizing the energy density, rather than the squared pressure. It is shown that minimizing the energy density at a single location yields global attenuation results that are comparable to minimizing the potential energy. Furthermore, unlike the squared pressure control, the energy density control does not demonstrate any dependence on the error sensor location for this one-dimensional field. A practical implementation of the energy-based control algorithm is presented. Results show that the energy density control can be implemented using the two sensor technique with a tolerable margin of performance degradation.

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Characteristics of InGaAs/GaAs/AlGaAs Double Barrier Quantum Well Infrared Photodetectors

  • Park, Min-Su;Kim, Ho-Seong;Yang, Hyeon-Deok;Song, Jin-Dong;Kim, Sang-Hyeok;Yun, Ye-Seul;Choe, Won-Jun
    • Proceedings of the Korean Vacuum Society Conference
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    • 2014.02a
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    • pp.324-325
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    • 2014
  • Quantum wells infrared photodetectors (QWIPs) have been used to detect infrared radiations through the principle based on the localized stated in quantum wells (QWs) [1]. The mature III-V compound semiconductor technology used to fabricate these devices results in much lower costs, larger array sizes, higher pixel operability, and better uniformity than those achievable with competing technologies such as HgCdTe. Especially, GaAs/AlGaAs QWIPs have been extensively used for large focal plane arrays (FPAs) of infrared imaging system. However, the research efforts for increasing sensitivity and operating temperature of the QWIPs still have pursued. The modification of heterostructures [2] and the various fabrications for preventing polarization selection rule [3] were suggested. In order to enhance optical performances of the QWIPs, double barrier quantum well (DBQW) structures will be introduced as the absorption layers for the suggested QWIPs. The DBWQ structure is an adequate solution for photodetectors working in the mid-wavelength infrared (MWIR) region and broadens the responsivity spectrum [4]. In this study, InGaAs/GaAs/AlGaAs double barrier quantum well infrared photodetectors (DB-QWIPs) are successfully fabricated and characterized. The heterostructures of the InGaAs/GaAs/AlGaAs DB-QWIPs are grown by molecular beam epitaxy (MBE) system. Photoluminescence (PL) spectroscopy is used to examine the heterostructures of the InGaAs/GaAs/AlGaAs DB-QWIP. The mesa-type DB-QWIPs (Area : $2mm{\times}2mm$) are fabricated by conventional optical lithography and wet etching process and Ni/Ge/Au ohmic contacts were evaporated onto the top and bottom layers. The dark current are measured at different temperatures and the temperature and applied bias dependence of the intersubband photocurrents are studied by using Fourier transform infrared spectrometer (FTIR) system equipped with cryostat. The photovoltaic behavior of the DB-QWIPs can be observed up to 120 K due to the generated built-in electric field caused from the asymmetric heterostructures of the DB-QWIPs. The fabricated DB-QWIPs exhibit spectral photoresponses at wavelengths range from 3 to $7{\mu}m$. Grating structure formed on the window surface of the DB-QWIP will induce the enhancement of optical responses.

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Mössbauer Studied of Multiferroic Bi2/3La1/3FeO3 Nanoparticles (Multiferroic Bi2/3La1/3FeO3 나노입자의 Mössbauer 연구)

  • Lee, Seung-Wha
    • Journal of the Korean Magnetics Society
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    • v.16 no.1
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    • pp.28-33
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    • 2006
  • La substituted perovskite $BiFeO_3$ have been prepared by a sol-gel method. Magnetic and structural properties of the powders were characterized with Mossbauer spectroscopy, XRD, SEM, and TG-DTA. The crystal structure is found to be a rhombohedrally distorted perovskite structure with the lattice constant $\alpha=3.985{\AA}\;and\;\alpha=89.5^{\circ}.\;Bi_{2/3}La_{1/3}FeO_3$ powders that were annealed at and above $600^{\circ}C$ have a single-phase perovskite structure. However, powders annealed at $900^{\circ}C$ have a typical perovskite structure with small amount of $Bi_2O_3$ phase. The Neel temperature of $Bi_{2/3}La_{1/3}FeO_3$ is found to be $680\pm3K$. The isomer shift value at room temperature is found to be 0.27 mm/s relative to the Fe metal, which is consistent with high-spin $Fe^{3+}$ charge states. Debye temperature far$Bi_{2/3}La_{1/3}FeO_3$ is found to be $305\pm5K$. The average hyperfine field $H_{hf}(T)$ of the $Bi_{2/3}La_{1/3}FeO_3$, shows a temperature dependence of $[H_{hf}(T)-H_{hf}(0)]/H_{hf}(0)=-0.42(T/T_N)^{3/2}-0.13(T/T_N)^{5/2}$ for $T/T_N<0.7$ indicative of spin-wave excitation.

Analysis of Conformability for Cadastral Control Network Using GPS Satellite Surveying (GPS에 의한 지적삼각망의 정합성 분석)

  • Kang, Joon-Mook;Yoon, Hee-Cheon;Kim, Hong-Jin
    • Journal of Korean Society for Geospatial Information Science
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    • v.2 no.1 s.3
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    • pp.121-129
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    • 1994
  • A number of existing cadastral control stations have been destroyed and shifted by a long lapse of time and careless management. Also, results of them are partly poor owing to dependence on conventional survey method. Because of these, it is very difficult in use of results. Hereupon, correction of cadastral results is necessary in level of government. But it is very consumable to check and adjust results with existing equipments and related techniques only. It is required that this problem can be resolved efficiently. This study analyzed the conformability for cadastral control network to GPS, GPS, which determine precise 3-D coordinates on a short time, to positioning of cadastral stations. We chose DaeJon city for the test area of this study and analyzed the precision of network composed of sixteen cadastral control stations. We made comparision the old result and the new outcome which obtained from coordinate transformation method and horizontal network adjustment method. As a result of this, we detected the blunder of cadastral stations. Furthermore, we suggested effective network type according to precision analysis of GPS observation network. Therefore, there is no doubt that GPS surveying can be applied to checking and adjustment of cadastral control network. Hereafter, it is expected that the practical use of GPS is advanced in a field of cadastration.

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Ordered Macropores Prepared in p-Type Silicon (P-형 실리콘에 형성된 정렬된 매크로 공극)

  • Kim, Jae-Hyun;Kim, Gang-Phil;Ryu, Hong-Keun;Suh, Hong-Suk;Lee, Jung-Ho
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2008.06a
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    • pp.241-241
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    • 2008
  • Macrofore formation in silicon and other semiconductors using electrochemical etching processes has been, in the last years, a subject of great attention of both theory and practice. Its first reason of concern is new areas of macropore silicone applications arising from microelectromechanical systems processing (MEMS), membrane techniques, solar cells, sensors, photonic crystals, and new technologies like a silicon-on-nothing (SON) technology. Its formation mechanism with a rich variety of controllable microstructures and their many potential applications have been studied extensively recently. Porous silicon is formed by anodic etching of crystalline silicon in hydrofluoric acid. During the etching process holes are required to enable the dissolution of the silicon anode. For p-type silicon, holes are the majority charge carriers, therefore porous silicon can be formed under the action of a positive bias on the silicon anode. For n-type silicon, holes to dissolve silicon is supplied by illuminating n-type silicon with above-band-gap light which allows sufficient generation of holes. To make a desired three-dimensional nano- or micro-structures, pre-structuring the masked surface in KOH solution to form a periodic array of etch pits before electrochemical etching. Due to enhanced electric field, the holes are efficiently collected at the pore tips for etching. The depletion of holes in the space charge region prevents silicon dissolution at the sidewalls, enabling anisotropic etching for the trenches. This is correct theoretical explanation for n-type Si etching. However, there are a few experimental repors in p-type silicon, while a number of theoretical models have been worked out to explain experimental dependence observed. To perform ordered macrofore formaion for p-type silicon, various kinds of mask patterns to make initial KOH etch pits were used. In order to understand the roles played by the kinds of etching solution in the formation of pillar arrays, we have undertaken a systematic study of the solvent effects in mixtures of HF, N-dimethylformamide (DMF), iso-propanol, and mixtures of HF with water on the macrofore structure formation on monocrystalline p-type silicon with a resistivity varying between 10 ~ 0.01 $\Omega$ cm. The etching solution including the iso-propanol produced a best three dimensional pillar structures. The experimental results are discussed on the base of Lehmann's comprehensive model based on SCR width.

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Non-Outbreak Cause of Cochlodinium Bloom in the Western Coast of Jaran Bay in Summer, 2013 : On the Basis of Nutrient Data (2013년 하계 자란만 서부 연안의 Cochlodinium 적조 미발생 원인 : 영양염 자료를 중심으로)

  • Kwon, Hyeong-Kyu;Kim, Hyun-Jung;Yang, Han-Seob;Oh, Seok-Jin
    • Journal of the Korean Society of Marine Environment & Safety
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    • v.20 no.4
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    • pp.372-381
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    • 2014
  • We investigated cause of non-outbreak of Cochlodinium polykrikoides blooms in the western coast of Jaran Bay during Summer, 2013, by combining chemical field data and physiological data of C. polykrikoides, which had been already published. The predominant species were mainly diatoms, and dominant species was Cerataulina pelagica, Chaetoceros spp., Navicula spp. and Nitzschia spp.. In case of dissolved inorganic nutrients in the western coast of Jaran Bay, dissolved inorganic phosphorus (DIP) was similar to that in previous outbreak period of C. polykrikoides blooms, but dissolved inorganic nitrogen (DIN) was lower. C. polykrikoides might be disadvantageous in competition with diatom species because half-saturation constants (Ks) of C. polykrikoides for inorganic nutrients was lower than those of diatoms. Also, the western coast of Jaran Bay, where DIN concentration is relatively low, was an unfavorable environment for growth of C. polykrikoides characterized by nitrogen dependence. Therefore, C. polykrikoides which have the disadvantageous position for competition of inorganic nutrient might have been suppressed by diatom blooms under environment of low nutrient in the western coast of Jaran Bay.

Neutron Diffraction and Mössbauer Studies of Superexchange Interaction on Al Substituted Co-ferrite (Al이 치환된 Co 페라이트에 관한 뫼스바우어 분광법 및 중성자 회절 연구)

  • Kim, Sam-Jin;Myoung, Bo-Ra;Kim, Chul-Sung;Baek, Kyung-Seon
    • Journal of the Korean Magnetics Society
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    • v.16 no.6
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    • pp.287-292
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    • 2006
  • Al substituted $CoAl_{0.5}Fe_{1.5}O_{4}$ has been studied with x-ray and neutron diffraction, $M\"{o}ssbauer$ spectroscopy and magnetization measurements. $CoAl_{0.5}Fe_{1.5}O_{4}$ revealed a cubic spinel structure of ferrinmagnetic long range ordering at room temperature, with magnetic moments of $Fe^{3+}(A)(-2.29{\mu}_{B}),\;Fe^{3+}(B)(3.81\;{\mu}_{B}),\;Co^{2+}(B)(2.66{\mu}_{B})$, respectively. The temperature dependence of the magnetic hyperfine field in $^{57}Fe$ nuclei at the tetrahedral (A) and octahedral (B) sites was analyzed based on the $N\'{e}el$ theory of magnetism. In the sample of $CoAl_{0.5}Fe_{1.5}O_{4}$, the interaction A-B interaction and intrasublattice A-A superexchange interaction were antiferromagnetic with strengths of $J_{A-B}=-19.3{\pm}0.2k_{B}\;and\;J_{A-A}=-21.6{\pm}0.2k_{B}$, respectively, while the intrasublattice B-B superexchange interaction was found to be ferromagnetic with a strength of $J_{B-B}=3.8{\pm}0.2k_{B}$.

Design of a TL Personal Dosimeter Identifiable PA Exposure and Development of Its Dose Evaluation Algorithm (후방피폭선량계측이 가능한 TL 개인선량계의 설계 및 선량평가 알고리즘 개발)

  • Kwon, J.W.;Kim, H.K.;Yang, J.S.;Kim, J.L.;Lee, J.K.
    • Journal of Radiation Protection and Research
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    • v.29 no.3
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    • pp.179-186
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    • 2004
  • A single-dosimeter worn on the anterior surface of body of a worker was found to provide significant underestimation of dose to the worker when radiation comes from behind of the human body. Recently, several researchers suggested that this kind of underestimation can be corrected to a certain extent by using an extra dosimeter on the back. But this multiple dosimetry also has the disadvantages like overestimation lowering work efficiency or cost burden. In this study, a single dosimeter introducing asymmetric filters enabled to identify PA exposure was designed by monte-carlo simulation and experiments and its dose evaluation algorithm for AP-PA mixed radiation field was established. This algorithm was applicable to penetrating radiation which had the effective energy more than 100 keV. Besides, the dosimeter and algorithm in this study were possible to be applied to near PA exposure.