• Journal of Korean Association for Spatial Structures
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• v.6 no.4 s.22
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• pp.81-92
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• 2006

This paper presents exact solutions for the free vibrations and buckling of rectangular plates having two opposite, simply supported edges subjected to linearly varying normal stresses causing pure in-plane moments, the other two edges being free. Assuming displacement functions which are sinusoidal in the direction of loading (x), the simply supported edge conditions are satisfied exactly. With this the differential equation of motion for the plate is reduced to an ordinary one having variable coefficients (in y). This equation is solved exactly by assuming power series in y and obtaining its proper coefficients (the method of Frobenius). Applying the free edge boundary conditions at y=0, b yields a fourth order characteristic determinant for the critical buckling moments and vibration frequencies. Convergence of the series is studied carefully. Numerical results are obtained for the critical buckling moments and some of their associated mode shapes. Comparisons are made with known results from less accurate one-dimensional beam theory. Free vibration frequency and mode shape results are also presented. Because the buckling and frequency parameters depend upon Poisson's ratio ( V ), results are shown for $0{\leq}v{\leq}0.5$, valid for isotropic materials.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.236-236
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• 2008

(Bi,La)$Ti_3O_{12}$(BLT) thin film is one of the most attractive materials for ferroelectric random access memory (FRAM) applications due to its some excellent properties such as high fatigue endurance, low processing temperature, and large remanent polarization [1-2]. The authors firstly investigated and reported the damascene process of chemical mechanical polishing (CMP) for BLT thin film capacitor on behalf of plasma etching process for fabrication of FRAM [3]. CMP process could prepare the BLT capacitors with the superior process efficiency to the plasma etching process without the well-known problems such as plasma damages and sloped sidewall, which was enough to apply to the fabrication of FRAM [2]. BLT-CMP characteristics showed the typical oxide-CMP characteristics which were related in both pressure and velocity according to Preston's equation and Hernandez's power law [2-4]. Good surface roughness was also obtained for the densification of multilevel memory structure by CMP process [3]. The well prepared BLT capacitors fabricated by CMP process should have the sufficient ferroelectric properties for FRAM; therefore, in this study the electrical properties of the BLT capacitor fabricated by CMP process were analyzed with the process parameters. Especially, the effects of CMP pressure, which had mainly affected the removal rate of BLT thin films [2], on the electrical properties were investigated. In order to check the influences of the pressure in eMP process on the ferroelectric properties of BLT thin films, the electrical test of the BLT capacitors was performed. The polarization-voltage (P-V) characteristics show a decreased the remanent polarization (Pr) value when CMP process was performed with the high pressure. The shape of the hysteresis loop is close to typical loop of BLT thin films in case of the specimen after CMP process with the pressures of 4.9 kPa; however, the shape of the hysteresis loop is not saturated due to high leakage current caused by structural and/or chemical damages in case of the specimen after CMP process with the pressures of 29.4 kPa. The leakage current density obtained with positive bias is one order lower than that with negative bias in case of 29.4 kPa, which was one or two order higher than in case of 4.9 kPa. The high pressure condition was not suitable for the damascene process of BLT thin films due to the defects in electrical properties although the better efficiency of process. by higher removal rate of BLT thin films was obtained with the high pressure of 29.4 kPa in the previous study [2].

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.169-169
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• 2008

To keep pace with scaling trends of CMOS technologies, high-k metal oxides are to be introduced. Due to their high permittivity, high-k materials can achieve the required capacitance with stacks of higher physical thickness to reduce the leakage current through the scaled gate oxide, which make it become much more promising materials to instead of $SiO_2$. As further studying on high-k, an understanding of the relation between the etch characteristics of high-k dielectric materials and plasma properties is required for the low damaged removal process to match standard processing procedure. There are some reports on the dry etching of different high-k materials in ICP and ECR plasma with various plasma parameters, such as different gas combinations ($Cl_2$, $Cl_2/BCl_3$, $Cl_2$/Ar, $SF_6$/Ar, and $CH_4/H_2$/Ar etc). Understanding of the complex behavior of particles at surfaces requires detailed knowledge of both macroscopic and microscopic processes that take place; also certain processes depend critically on temperature and gas pressure. The choice of $BCl_3$ as the chemically active gas results from the fact that it is widely used for the etching o the materials covered by the native oxides due to the effective extraction of oxygen in the form of $BCl_xO_y$ compounds. In this study, the surface reactions and the etch rate of $Al_2O_3$ films in $BCl_3/Cl_2$/Ar plasma were investigated in an inductively coupled plasma(ICP) reactor in terms of the gas mixing ratio, RF power, DC bias and chamber pressure. The variations of relative volume densities for the particles were measured with optical emission spectroscopy (OES). The surface imagination was measured by AFM and SEM. The chemical states of film was investigated using X-ray photoelectron spectroscopy (XPS), which confirmed the existence of nonvolatile etch byproducts.

• Korean Chemical Engineering Research
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• v.51 no.4
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• pp.506-512
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• 2013

Biomass and low-grade coals are known to be better potential sources of energy compared to crude oil and natural gas since these materials are readily available and found to have large reserves, respectively. Gasification of these carbonaceous materials produced syngas for chemical synthesis and power generation. Woodchip, sawdust and lignite were gasified with steam in a thermobalance reactor under atmospheric pressure in order to evaluate their kinetic rate information. The effects of gasification temperature ($600{\sim}900^{\circ}C$) and partial pressure of steam (20~90 kPa) on the gasification rate were investigated. The three different types of gas-solid reaction models were applied to the experimental data to predict the behavior of the gasification reactions. The modified volumetric model predicted the conversion data well, thus the model was used to evaluate kinetic parameters in this study. The observed activation energy of biomass, sawdust and lignite gasification reactions were found to be in reasonable range and their rank was found to be sawdust > woodchip > lignite. The expression of apparent reaction rates for steam gasification of the three solids was proposed to provide basic information on the design of coal gasification processes.

• Korean Chemical Engineering Research
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• v.43 no.2
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• pp.286-293
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• 2005

An interpretation on the solid circulation characteristics in a fluidized-bed process has been carried out as a first step to simulate the dry entrained-bed absorption and bubbling-bed regeneration system for $CO_2$ removal from flue gas. A particle population balance has been developed to determine the solid flow rates and particle size distributions in the process. Effects of principal process parameters have been discussed in a laboratory scale process (absorption column: 25 mm i.d., 6 m in height; regeneration column: 0.1 m i.d., 1.2 m in height). The particle size distributions in absorption and regeneration columns were nearly the same. As gas velocity or static bed height in the absorption column increased, soild circulation rate and feed rate of fresh sorbent increased, however, mean particle diameter decreased in the absorption column. As cut diameter of the cyclone of the absorption column increased, solid circulation rate decreased, whereas feed rate of fresh sorbent and mean particle diameter in the absorption column increased. As attrition coefficient of sorbent particle increased, solid circulation rate and feed rate of fresh sorbent increased but mean particle diameter in the absorption column decreased.

• Geophysics and Geophysical Exploration
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• v.11 no.2
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• pp.137-147
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• 2008

Fault rupture directivity of the Odaesan earthquake, which was inferred to be the main cause of the high PGAvalue (> 0.1 g) unusually observed at the near-source region, was analyzed by using the data from the nearby (R < 100 km) dense seismic stations. The Boatwright's method (2007) was adopted for this purpose in which the azimuth and takeoff angle of the unilateral rupture directivity function could be estimated based on the relative peak ground-motions of seismic stations resulting from the nature of the rupture directivity. In this study, the approximate values of the relative peak ground-motions was derived from the difference between the log residuals of the point-source spectral model (Boore, 2003) for the main and secondary events based on the Random Vibration Theory. In this derivation, the spectral difference for a frequency range between the source corner frequencies of main and secondary events was considered to reflect only the effect of the fault directivity. The inversion result of the model parameters for the fault directivity function showed that the fault-plane of NWW-SEE direction dipping steeply to the North with high rupture velocity near upward in SE direction is responsible for the observed high level of ground-motion at the near-source region.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.38 no.6
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• pp.106-112
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• 2001

Unfortunately, the area without economical efficiency, especially the far distance sea, is much lower than that of a urban area-built-up area. It should be promoted the equivalent level to a urban area in the light of future-oriented universal service. Actually, Because propagation environment of mobile communication in the sea is greatly different from that for inland focused on built-up area, a propagation prediction model in the sea should be distinguished from inland-based one. Accordingly, the purpose of this study is to suggest the propagation prediction model for the sea service as a method to minimize unnecessary facilities investment and maintenance caused by additional or new building of a base station. If mobile phone service for far distance sea is provided by expanding limited communication zone of narrow band CDMA mobile communication whose spread band FA is 1.2288MHz. Suggested propagation prediction model includes five parameters to minimize facilities investment of a base station and maximize channel capacity: equivalent line of sight, chip delay by PN code, antenna altitude, power of base station and gain of antennas. Finally, suggested propagation prediction model is simulated and, the results are examined for its utility by comparing with loss of free space.

• Journal of IKEEE
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• v.19 no.4
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• pp.491-499
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• 2015

Silicon Carbide(SiC) has large advantage in high temperature and high voltage applications because of its high thermal conductivity and large band gap energy. When using SiC to design power semiconductor devices, edge termination techniques have to be adjusted for its maximum breakdown voltage characteristics. Many edge termination techniques have been proposed, and the most appropriate technique for SiC device is Junction Termination Extension(JTE). In this paper, the change of breakdown voltage efficiency ratio according to the change of doping concentration and passivation oxide charge of each JTE techniques is demonstrated. As a result, the maximum breakdown voltage ratio of Single Zone JTE(SZ-JTE), Double Zone JTE(DZ-JTE), Multiple Floating Zone JTE(MFZ-JTE), and Space Modulated JTE(SM-JTE) is 98.24%, 99.02%, 98.98%, 99.22% each. MFZ-JTE has the smallest and SZ-JTE has the largest sensitivity of breakdown voltage ratios according to the change of JTE doping concentration. Additionally the degradation of breakdown voltage due to the passivation oxide charge is analyzed, and the sensitivity is largest in SZ-JTE and smallest in MFZ-JTE, too. In this paper, DZ-JTE and SM-JTE is the best efficiency JTE techniques than MFZ-JTE which needs large doping concentration in short JTE width.

• International Journal of Advanced Culture Technology
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• v.5 no.1
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• pp.58-63
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• 2017

Emergencies and disasters can happen any time without any warning, and things can change and escalate very quickly, and often it is swift and decisive actions that make all the difference. It is a responsibility of the building facility management to ensure that a proven evacuation plan in place to cover various worst scenario to handled automatically inside the facility. To mapping out optimal safe escape routes is a straightforward undertaking, but does not necessarily guarantee residents the highest level of protection. The emergency evacuation navigation approach is a state-of-the-art that designed to evacuate human livings during an emergencies based on real-time decisions using live sensory data with pre-defined optimum path finding algorithm. The poor decision on causalities and guidance may apparently end the evacuation process and cannot then be remedied. This paper propose a cloud connected emergency evacuation system model to react dynamically to changes in the environment in emergency for safest emergency evacuation using IoT based emergency exit sign system. In the previous researches shows that the performance of optimal routing algorithms for evacuation purposes are more sensitive to the initial distribution of evacuees, the occupancy levels, and the type and level of emergency situations. The heuristic-based evacuees routing algorithms have a problem with the choice of certain parameters which causes evacuation process in real-time. Therefore, this paper proposes an evacuee routing algorithm that optimizes evacuation by making using high computational power of cloud servers. The proposed algorithm is evaluated via a cloud-based simulator with different "simulated casualties" are then re-routed using a Dijkstra's algorithm to obtain new safe emergency evacuation paths against guiding evacuees with a predetermined routing algorithm for them to emergency exits. The performance of proposed approach can be iterated as long as corrective action is still possible and give safe evacuation paths and dynamically configure the emergency exit signs to react for real-time instantaneous safe evacuation guidance.

• Journal of the Korean Magnetics Society
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• v.14 no.4
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• pp.131-137
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• 2004

For the aim of thin electromagnetic wave absorbers used in mobile telecommunication frequency band (0.8-2.0㎓), we investigate high-frequency magnetic, dielectric and microwave absorbing properties of iron particles dispersed in rubber matrix in this study. The major experimental variables are particle shape (sphere and flake) and initial particle size (in the range 5-70 $\mu\textrm{m}$) of iron powders. High value of magnetic permeability and dielectric permittivity can be obtained in the composites containing thin plate-shape (flake) iron particles (of which thickness is less than skin depth in ㎓frequency), which can be produced by mechanical forging of spherical iron powders using an attrition mill. This result is attributed to the reduction of eddy current loss (increase of permeability) and the increase of space charge polarization (increase of permeability). The optimum initial particle size is found to be about 10 $\mu\textrm{m}$ for the attainment of the material parameters (particularly, real part of complex permeability) satisfying the wave impedance matching. With the iron powders controlled in size and shape as absorbent fillers in rubber matrix, the thickness can be reduced to about 0.7mm with respect to -5㏈ reflection loss (70% power absorption) in mobile telecommunication frequency band.