• Annals of Clinical Neurophysiology
• /
• v.9 no.1
• /
• pp.1-4
• /
• 2007

Vertigo is an illusion of rotation, which results from an imbalance within the vestibular system. This review focuses on two common presentations of spontaneous vertigo: acute prolonged spontaneous vertigo and recurrent spontaneous vertigo. Common causes of acute prolonged spontaneous vertigo include vestibular neuritis, labyrinthitis, and brainstem or cerebellar stroke. The history and detailed neurological/neurotological examinations usually provide the key information for distinguishing between peripheral and central causes of vertigo. Brain MRI is indicated in any patient with acute vertigo accompanied by abnormal neurological signs, profound imbalance, severe headache, and central patterns of nystagmus. Recurrent spontaneous vertigo occurs when there is a sudden, temporary, and largely reversible impairment of resting neural activity of one labyrinth or its central connections, with subsequent recovery to normal or near-normal function. Meniere's disease, migrainous vertigo, and vertebrobasilar insufficiency (VBI) are common causes. The duration of the vertigo attack is a key piece of information in recurrent spontaneous vertigo. Vertigo of vascular origin, such as VBI, typically lasts for several minutes, whereas recurrent vertigo due to peripheral inner-ear abnormalities lasts for hours. Screening neurotological evaluations, and blood tests for autoimmune and otosyphilis are useful in assessment of recurrent spontaneous vertigo that are likely to be peripheral in origin.

• Journal of Power Electronics
• /
• v.17 no.6
• /
• pp.1433-1444
• /
• 2017

A family of non-isolated DC-DC three-port converters (TPCs) that allows for a more flexible power flow among a renewable energy source, an energy storage device and a current-reversible DC bus is introduced. Most of the reported non-isolated topologies in this area consider only a power consuming load. However, for applications such as hybrid-electric vehicle braking systems and DC microgrids, the load power generating capability should also be considered. The proposed three-port family consists of one unidirectional port and two bi-directional ports. Hence, they are well-suited for photovoltaic (PV)-battery-DC bus systems from the power flow viewpoint. Three-port converters are derived by combining different commonly known power converters in an integrated manner while considering the voltage polarity, voltage levels among the ports and the overall voltage conversion ratio. The derived converter topologies are able to allow for seven different modes of operation among the sources and load. A three-port converter which integrates a boost converter with a buck converter is used as a design example. Extensions of these topologies by combining the soft-switching technique with the proposed design example are also presented. Experiment results are given to verify the proposed three-port converter family and its analysis.

• Bulletin of the Korean Chemical Society
• /
• v.34 no.1
• /
• pp.167-173
• /
• 2013

A series of highly efficient red phosphorescent heteroleptic iridium(III) complexes 1-6 containing two cyclometalating 2-(2,4-substitued phenyl)quinoxaline ligands and one chromophoric ancillary ligand were synthesized: (pqx)$_2Ir$(mprz) (1), (dmpqx)$_2Ir$(mprz) (2), (dfpqx)$_2Ir$(mprz) (3), (pqx)$_2Ir$(prz) (4), (dmpqx)$_2Ir$(prz) (5), (dfpqx)$_2Ir$(prz) (6), where pqx = 2-phenylquinoxaline, dfpqx = 2-(2,4-diflourophenyl)quinoxaline, dmpqx = 2-(2,4-dimethoxyphenyl)quinoxaline, prz = 2-pyrazinecarboxylate and mprz = 5-methyl-2-pyrazinecarboxylate. The absorption, emission, electrochemical and thermal properties of the complexes were evaluated for potential applications to organic light-emitting diodes (OLEDs). The structure of complex 2 was also determined by single-crystal X-ray diffraction analysis. Complex 2 exhibited distorted octahedral geometry around the iridium metal ion, for which 2-(2,4-dimethoxyphenyl)quinoxaline N atoms and C atoms of orthometalated phenyl groups are located at the mutual trans and cis-positions, respectively. The emission spectra of the complexes are governed largely by the nature of the cyclometalating ligand, and the phosphorescent peak wavelengths can be tuned from 588 to 630 nm with high quantum efficiencies of 0.64 to 0.86. Cyclic voltammetry revealed irreversible metal-centered oxidation with potentials in the range of 1.16 to 1.89 V as well as two quasi-reversible reduction waves with potentials ranging from -0.94 to -1.54 V due to the sequential addition of two electrons to the more electron-accepting heterocyclic portion of two distinctive cyclometalated C^N ligands.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2016.02a
• /
• pp.431-431
• /
• 2016

Typical Cu(In,Ga)Se2 (CIGS)-based solar cells have a buffer layer between CIGS absorber layer and transparent ZnO front electrode, which plays an important role in improving the cell performance. Among various buffer materials, chemical bath deposition (CBD)-ZnS is being steadily studied to alternative to conventional CdS and the efficiency of CBD-ZnS/CIGS solar cell shows the comparable values with that of CdS/CIGS solar cell. The intriguing thing is that reversible changes occur after exposure to illumination due to the metastable defect states in completed ZnS/CIGS solar cell, which induces an improvement of solar cell performance. Thus, it implies that the understanding of metastable defects in CBD-ZnS/CIGS solar cell is important issue. In this study, we fabricate the ITO/i-ZnO/CBD-ZnS/CIGS/Mo/SLG solar cells by controlling the NH4OH mole concentration (from 2 M to 3.5 M) of CBD-ZnS buffer layer and observe their conversion efficiency with and without light soaking for 1 hr. From the results, NH4OH mole concentration and light exposure can significantly affect the CBD-ZnS/CIGS solar cell performance. In order to investigate that which layer can contain metastable defect states to influence on solar cell performance, impedance spectroscopy and capacitance profiling technique with exposure to illumination have been applied to CBD-ZnS/CIGS solar cell. These techniques give a very useful information on the density of states within the bandgap of CIGS, free carriers density, and light-induced metastable effects. Here, we present the rearranged charge distribution after exposure to illumination and suggest the origin of the metastable defect states in CBD-ZnS/CIGS solar cell.

• 한국정보디스플레이학회:학술대회논문집
• /
• 2008.10a
• /
• pp.883-886
• /
• 2008

In optical information technology, an electro-controllable Photonic Band Gap (PBG) in a photonic crystal (PC) material is potentially useful for the manipulation of light. Despite a great deal of research on PBGs, the reliable use of electro-active PBG material systems is restricted to only a few cases because of the complex and limiting nature of the structures involved. Here, we propose a PBG system that uses a liquid crystal (LC) polymer composite. The composite is made of nematic LCs (NLCs) embedded in polymeric helical networks of photo-polymerized cholesteric LCs (CLCs). The composite film shows a large field-induced reversible color shift over 150 nm of the reflection band, due to the reorientational undulation of the helical axis, similar to the Helfrich effect.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2004.07b
• /
• pp.874-877
• /
• 2004

We carried out this subject to observe electrochemical properties of 1,2-dioleoyl-sn- glycero-3-phosphocholine(DOPC) mixed with fatty acid containing azobenzene group by using cyclic voltammetry with a three-electrode system, An Ag/AgCl reference electrode, a platinum wire counter electrode and LB film-coated ITO working electrode in $NaClO_4$ solution. We investigated the photoisomerization and electrochemical property of the organic ultra thin film of fatty acid containing azobenzene was prepared on the hydrophilic ITO(idium tin oxide) glass plate by LB method. As a result, the absorption spectra of BASH and DOPC of mixture LB films was induced to photoisomerization by alternating irradiation of ultraviolet and visible light. A measuring range was reduced from initial potential to -1350mV, continuously oxidized to 1650 mV and measured to the initial point. The scan rate were 50, 100, 150 and 200 mV/s. As a results, LB films of BASH-DMPC appeared reversible process caused by the reduction-oxidation current from the cyclic voltammogram.

• Journal of Electrochemical Science and Technology
• /
• v.8 no.2
• /
• pp.96-100
• /
• 2017

Iridium(III) bis(2-phenylpyridinato-$N,C^{2^{\prime}}$)acetylacetonate ($(ppy)_2Ir(acac)$), a green dopant used in organic light-emitting devices (OLEDs), was subjected to electrochemical characterization to estimate its formal oxidation potential ($E^{o^{\prime}}$), HOMO energy level ($E_{HOMO}$), electron transfer rate constant ($k^{o^{\prime}}$), and diffusion coefficient ($D_o$). The employed combination of voltammetric methods, i.e., cyclic voltammetry (CV), chronocoulometry (CC), and the Nicholson method, provided meaningful insights into the electron transfer kinetics of $(ppy)_2Ir(acac)$, allowing the determination of $k^{o^{\prime}}$ and $D_o$. The quasi-reversible oxidation of $(ppy)_2Ir(acac)$ furnished information on $E^{o^{\prime}}$ and $E_{HOMO}$, allowing the latter parameter to be easily estimated by electrochemical methods without relying on expensive and complex ultraviolet photoemission spectroscopic (UPS) measurements.

• Journal of the Semiconductor & Display Technology
• /
• v.4 no.4 s.13
• /
• pp.1-4
• /
• 2005

The chemical composition and uniaxial compressive stress are varied to observe their effect on the current-voltage characteristics of ZnO based ceramics. The variation of chemical composition produces two kinds of ceramics showing ohmic and nonohmic current-voltage characteristics. The current at a fixed voltage increased with the increase of the compressive stress for both ohmic and nonohmic ceramics. Ceramics showing nonohmic behavior exhibit better reversible return of current-voltage curve when the applied compressive stress is removed from the ceramics than those showing ohmic behavior do. We found an appropriate chemical composition showing linear relation between current and stress at a fixed voltage. The ceramic materials with an appropriate chemical composition can be used as a potential sensing material in pressure sensors.

• Korean Chemical Engineering Research
• /
• v.49 no.4
• /
• pp.393-399
• /
• 2011

The electrochemical or optical sensors for environmental pollutants are developed over the past several years. Nowadays, the development of colorimetric sensing is particularly challenging since it requires no equipment at all as color changes can be detected by the naked eye. Visual detection can give immediate qualitative information and is becoming increasingly appreciated in terms of quantitative analysis. In addition, simple colorimetric-sensor have shown useful in the detection, identification, and quantification of volatile organic compounds(VOC) in gas phase or heavy metal ion in aqueous phase. In this review, we investigated the wide applications and some drawbacks of colorimetric-sensors. And thus, we try to suggest the methodologies of development approach of multi-functional and reversible colorimetric-sensor.

• ETRI Journal
• /
• v.11 no.2
• /
• pp.120-136
• /
• 1989

최근의 데이터 베이스 응용분야에 있어서 시간에 따른 정보의 변화를 유지관리할 필요성이 대두되고 대용량의 기억장치 가격의 급속한 감소와 함께 이의 이용 기술이 향상되면서 시간주기에 따라 실세계의 상태에 대한 변경과정을 표현하는 시간 즉, 데이터의 변경이력을 지원하는 데이터베이스(Terporal Database)에 관심이 집중되고 있으며, 이러한 요구를 만족시키기 위한 여러 방법들이 연구되고 있다. 일반적으로 시간 지원 데이터베이스 모델은 지원되는 시간의 형태에 따라 Static, Static Rollback, Historical, Temporal, Revision 데이터베이스 모델로 나뉘어진다. 본 논문에서는 시간 및 변경이력을 지원하기 위한 데이터베이스 모델과 이를 위한 데이터베이스 시스템의 주요 설계 Issue들에 관하여 조사분석한 다음, Static Rollback 데이터베이스 모델을 기본으로 하는 "$SR^2DBS$: 시간 지원 데이터베이스 시스팀"의 설계 및 구현에 관하여 기술하였다. $SR^2DBS$은 기존의 관계형 데이터 베이스 시스팀"의 모델을 시간 애트리뷰트를 추가시킴으로서 데이터 베이스의 변경이력관리를 가능케 한 Direct Manipulation Database Processing System으로 데이터베이스의 현상태 뿐만 아니라 시간에 따른 변경이력에 대해서 Screenoriented Relation Browsing & Editing 기능을 제공하며, 다음과 같은 특징을 갖는다. - Screen oriented Processing - Directi-Manipulation of Objects - Object & Revision History of Interest Visibility - Rapid Reversible Actions - Transaction Time & Revision Number Supporting - Roll-back Query Supporting - Han-gul Data Supporting - Two level Storage Structure(Current Version & History Versions)