• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2004.04b
• /
• pp.157-160
• /
• 2004

Ferroelectric $(Ba_xSr_{1-x})TiO_3$ (BST) thin films have been deposited on (001) MgO single crystals by a pulsed laser deposition (PLD) method. The structure of deposited BST thin films were investigated by an x-ray diffractometer. Calculated c-axis lattice parameters of the BST films exhibit a strong lattice distortion, which was not observed in ceramic BST at room temperature. This lattice distortion of BST has been attributed to strains caused by lattice constant difference between film and substrate, oxygen vacancies in BST film, and thermal expansion difference between film and substrate. Ferroelectric properties at 10 GHz have been measured using a HP 8510C vector network analyzer. Dielectric properties, capacitance tunability and quality factor, of the interdigitaed capacitors fabricated on BST films were calculated from the measured s-parameters. Two distinct behaviors in structural, opitical, and microwave properties of BST films were observed; below and above 200 mTorr of oxygen pressure in the deposition chmber.

• Wind and Structures
• /
• v.34 no.2
• /
• pp.231-257
• /
• 2022

Transmission lines systems are important components of the electrical power infrastructure. However, these systems are vulnerable to damage from high wind events such as hurricanes. This study presents the results from a 1:50 scale aeroelastic model of a multi-span transmission lines system subjected to simulated hurricane winds. The transmission lines system considered in this study consists of three lattice towers, four spans of conductors and two end-frames. The aeroelastic tests were conducted at the NSF NHERI Wall of Wind Experimental Facility (WOW EF) at the Florida International University (FIU). A horizontal distortion scaling technique was used in order to fit the entire model on the WOW turntable. The system was tested at various wind speeds ranging from 35 m/s to 78 m/s (equivalent full-scale speeds) for varying wind directions. A system identification (SID) technique was used to evaluate experimental-based along-wind aerodynamic damping coefficients and compare with their theoretical counterparts. Comparisons were done for two aeroelastic models: (i) a self-supported lattice tower, and (ii) a multi-span transmission lines system. A buffeting analysis was conducted to estimate the response of the conductors and compare it to measured experimental values. The responses of the single lattice tower and the multi-span transmission lines system were compared. The coupling effects seem to drastically change the aerodynamic damping of the system, compared to the single lattice tower case. The estimation of the drag forces on the conductors are in good agreement with their experimental counterparts. The incorporation of the change in turbulence intensity along the height of the towers appears to better estimate the response of the transmission tower, in comparison with previous methods which assumed constant turbulence intensity. Dynamic amplification factors and gust effect factors were computed, and comparisons were made with code specific values. The resonance contribution is shown to reach a maximum of 18% and 30% of the peak response of the stand-alone tower and entire system, respectively.

• The Journal of Engineering Geology
• /
• v.30 no.3
• /
• pp.237-251
• /
• 2020

This study examined structural analysis of supports in tunnel and displacement and underground stress of tunnel by measurement, in order to evaluate the performance of high-strength lattice girders developed as a substitute for H-profiles. According to the three-dimensional nonlinear structural analysis results of the tunnel support, the load and displacement relationship between the H-profiles and the high-strength lattice girders showed almost the same behavior, and the maximum load of the high-strength lattice girders were 1.0 to 1.2 times greater than the H-profiles. By the results of the three-dimensional tunnel cross-section analysis of the supports, the axial force was occurred largely in the lower left and right sides of the tunnel, and showed a similar trend to the field test values. In the results of the measurement of the roof settlement and rod extension, the final displacement of the steel arch rib (H-profile) and high-strength lattice girder section in tunnel was converged to a constant value without significant difference within the first management standard of 23.5 mm. According to the results of underground displacement measurement, the final change amount of the two support sections showed a slight displacement change, but converged to a constant value within the first management standard of 10 mm. By the results of measurement of shotcrete stress and steel arch rib stress, the final change amount of the two support sections showed a slight stress change, but converged to a constant value within the first management standard of 81.1 kg/㎠ and 54.2 tonf.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.6 no.4
• /
• pp.600-608
• /
• 1996

Specific structural properties of Li intercalation reaction into the spinel relatedmanganese dioxide, $Li_{x}Mn_{2}O_{4}(0.2{\leq}x{\leq}2.0)$, are investigated by X-ray diffractional and electrochemical studies of Li/1M $LiClO_{4}$-propylene carbonate solution/$Li_{x}Mn_{2}O_{4}$ cell. The effect of the chemical composition and the reaction temperature on electrochemical parameter of $Li_{x}Mn_{2}O_{4}$ are studied by the phenomena of phase-transition, analysis of crystal lattice, fine structure, and thermal analysis. Treatment of the spinel $Li_{x}Mn_{2}O_{4}$ with aqueous acid was found to result in conversiton of $Li_{x}Mn_{2}O_{4}$ to nearly pure $MnO_{2}$, as evidenced by a reduction in the lattice constant $a_{c}$ from 8.255 to $8.031\;{\AA}$. At a composition range of $0.2{\leq}x{\leq}0.6$ in $Li_{x}Mn_{2}O_{4}$ the reduction proceeded in a homogeneous phase, which was characterized by a constant voltage of 3.9~3.7 V together with a lattice constant of $8.255\;{\AA}$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2001.07a
• /
• pp.894-896
• /
• 2001

The Polypropylene films which are made by refinement of its pellet and formed as crystals are exposed to Radiation. As the results, degradation effects were observed in non-crystalline regions. It is thus considered that the effects occur by destroying of lattice binding force by Radiation. The distribution of degradation was increased with irradiation quantities of Radiation and dielectric constant of Polypropylene sheets irradiated Radiation was rapidly increased from above 10 MHz.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2014.02a
• /
• pp.199.1-199.1
• /
• 2014

In nonlinear optics, the properties of nonlinear optical responses such as polarization and nonlinear analysis of the nonlinear surfaces were investigated using the jellium model by optical second harmonic generation. The nonlinear response of the Al metal surfaces were calculated using TDLDA. Band structure, lattice constant and bulk modulus of the Al metal were investigated. Effective potential and electron density were compared by changing different.

• Proceeding of EDISON Challenge
• /
• 2014.03a
• /
• pp.430-433
• /
• 2014

Perovskite 구조를 가진 코발트 산화물 $SrCoO_3$와 Brownmillerite 구조인 $SrCoO_{2.5}$의 electronic structure를 제1원리 계산을 통해 분석하였다. 이들의 magnetic structure를 계산하여 실험을 통해 알려진 값과 비교하였고, 각 구조에서 코발트 이온이 갖는 spin state를 확인할 수 있었다. 코발트 이온은 $SrCoO_3$에서 intermediate spin state(IS)를, $SrCoO_{2.5}$에서는 high spin state(HS)를 갖는데 이것이 lattice constant의 차이에 의한 것인지, 아니라면 차이의 원인은 무엇인지 density of state를 분석함으로써 알아보았다.

• Proceeding of EDISON Challenge
• /
• 2015.03a
• /
• pp.392-395
• /
• 2015

Metal Mono Chalcogenides(MMC)는 각각의 III족 metal 원자당한개의 chalchogen 원자를 갖고 있는(MX, M=Ga and In, X=S, Se, and Te)층상구조 화합물이다. MMC가 주목받는 가장 큰 이유는 single tetralayer MMC(SL-MMC)라는 2차원 구조를 갖기 때문이다. 2차원 물질은 다양한 물리적 현상을 증명하기 용이하다는 특징을 갖는다. 이 논문에서 우리는 SL-MMC중 Ga-MMC에서 chalchogen 원자가 변화함에 따라 바뀌는 실험 lattice constant를 조사하여 band gap과 formation energy를 Density Function Theory(DFT)로 계산했다.

• Journal of Magnetics
• /
• v.3 no.1
• /
• pp.1-3
• /
• 1998

Valence state of the Sm metal is investigated using the total energy linearized muffin-tin orbital (LMTO) band method for the observed Sm-type crystal structure. We have considered both the relativistic and the semi-relativistic description of 4f-core electrons. We have found that, in the paramagnetic phase of bulk Sm, the trivalent valence state is more stable at the observed lattice constant than the divalent valence state.

• Proceedings of the Optical Society of Korea Conference
• /
• 2008.07a
• /
• pp.329-330
• /
• 2008

We experimentally demonstrate resonant-wavelength control of a series of an Si-based photonic crystal nanocavity. The cavities show a linear dependence on these parameters, a 1 nm increase of lattice constant leading to 4.2 nm increase of the resonant wavelength. The results have a small standard deviation of wavelength 1.1 nm between samples on a single chip.