• The Journal of the Korea institute of electronic communication sciences
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• v.9 no.6
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• pp.689-694
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• 2014

DDoS attacks on MANET makes disable any node which support network function, cause critical results as a stopping of entire network service or separation to some parts. Packet aggregation, which gather some pieces of short length into a certain length of data, improves transmission performances on MANETs. In this paper, some effects on transmission performance of packet aggregation transmission be caused by DDoS Attacks are measured and analyzed in point of end-to-end level. MANET simulator, based on NS-2, is used for measurement end-to-end performances. MOS, connection rate, delay and packet loss rate is used as performance parameters. VoIP traffic is used for object service measurement. Finally, it is suggested that number of packet aggregation is more then 4 for keeping the transmission quality over MANETs under DDoS attacks.

• Journal of Korean Academy of Nursing
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• v.47 no.5
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• pp.700-711
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• 2017

Purpose: This study aimed to test a proposed structural equation model in which bullying experience, conflict management styles and psychological empowerment predict psychological well-being among Chinese nursing students in clinical placement. Methods: Three hundred and sixty-six nursing students recruited from five hospitals in J city and Y city were assessed with self-report questionnaires on bullying experience, conflict management styles, psychological empowerment and psychological well-being including depression, self-esteem, and academic major satisfaction. Data were analyzed using SPSS version 20.0 and AMOS version 22.0. Results: The evaluation parameters included the comparative fit index at .90, the goodness of fit index at .93, the root mean square error of approximation at .07, and ${\chi}^2/df$ ratio at 2.66, indicating that the proposed structural equation model provided a good fit to the data. Experience of being bullied during clinical placement, conflict management styles and psychological empowerment explained 93.0% of the variance and had significant effects on psychological well-being, with conflict management styles and psychological empowerment mediating the association between bullying and psychological well-being. Conclusion: The findings indicated that mediation by conflict management styles and psychological empowerment alleviated the negative influence of bullying on psychological well-being. To limit bullying and its negative effects, development of effective guidelines to deal with bullying will be a critical tool for both Chinese nursing students and their instructors. Further research should incorporate conflict management styles and psychological empowerment into the specific intervention strategies for handling bullying behaviors among nursing students and staff nurses and promoting nursing students' psychological well-being.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.30A no.12
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• pp.51-59
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• 1993

A 4${\times}10^{19}cm^{3}$ carbon-doped base AlGaAs/GaAs HBY was grown using carbontetracholoride(CCl$_4$) by atmospheric pressure MOCVD. Abruptness of emitter-base junction was characterized by SIMS(secondary ion mass spectorscopy) and the doping concentration of base layer was confirmed by DXRD(double crystal X-ray diffractometry). Mesa-type HBTs were fabricated using wet etching and lift-off technique. The base sheet resistance of R$_{sheet}$=550${\Omega}$/square was measured using TLM(transmission line model) method. The fabricated transistor achieved a collector-base junction breakdown voltage of BV$_{CBO}$=25V and a critical collector current density of J$_{O}$=40kA/cm$^2$ at V$_{CE}$=2V. The 50$\times$100$\mu$$^2$ emitter transistor showed a common emitter DC current gain of h$_{FE}$=30 at a collector current density of JS1CT=5kA/cm$^2$ and a base current ideality factor of ηS1EBT=1.4. The high frequency characterization of 5$\times$50$\mu$m$^2$ emitter transistor was carried out by on-wafer S-parameter measurement at 0.1~18.1GHz. Current gain cutoff frequency of f$_{T}$=27GHz and maximum oscillation frequency of f$_{max}$=16GHz were obtained from the measured Sparameter and device parameters of small-signal lumped-element equivalent network were extracted using Libra software. The fabricated HBT was proved to be useful to high speed and power spplications.

• Journal of Hydrogen and New Energy
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• v.22 no.5
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• pp.686-698
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• 2011

Mathematical models for char-slag interaction and near-wall particle segregation developed by Montagnaro et. al. were applied to predict various aspects of coal gasification in an up-flow entrained gasifier of commercial scale. For this purpose, some computer simulations were performed using gPROMS as the numerical solver. Typical design parameters and operating conditions of the commercial gasifiers were used as input values for the simulation. Development of a densely dispersed phase of solid carbon was found to have a critical effect on both carbon conversion and ash flow behavior. In general, such a slow-moving phase was turned out to enhance carbon conversion by lengthening the residence time of char or soot particles. Furthermore, it was also found that guiding the transfer of char or soot into the closer part of the wall to coal burner is favorable in terms of gasification efficiency and vitrified ash collection. Finally, to a certain degree densely dispersed phase of carbon showed an yield-enhancing effect of syngas.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.14 no.4
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• pp.935-938
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• 2010

Indium-tin-oxide (ITO) films show a low electrical resistance and high transmittance in the visible range of an optical spectrum. The transparent electrodes have to get resistivity and sheet resistance less than $1{\times}10^{-3}{\Omega}/cm$ and $10^3{\Omega}/sq$ respectively and transmittance over 80% at wavelength of 380nm~780nm. This study establishes DC magnetron sputtering process condition on ITO thin film by measuring electrical and optical properties of the thin film. As results, we obtained $300\;{\mu}{\Omega}cm$ resistivity of ITO films with good transmittance (above 90 %) under 90:10 wt% composition rate of $In_2O_3:SnO_2$. Also, we understood that the ITO thin film by DC magnetron sputtering depends on the deposition condition, especially substrate temperature, and the composition rate of $In_2O_3:SnO_2$ that is one of the most critical parameters was successfully optimized for high qualified transparent electrodes.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.297-297
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• 2008

Buffer layers play an important role in the development of high critical current density coated conductor. $LaMnO_3$, $SrTiO_3$ and $BaZrO_3$ buffer layers were compatible with MgO surfaces and also provide a good template for growing high current density REBCO(RE=Rare earth) films. Systematic studies on the influences of pulsed laser deposition parameters (deposition temperature, deposition pressure, processing gas, laser energy density, etc.) on microstructure and texture properties of $LaMnO_3$, $SrTiO_3$ and $BaZrO_3$ films as buffer layer deposited on ion-beam assisted deposition MgO (IBAD_MgO) template by pulse laser deposition method, were carried out. These results will be presented together with the discussion on the possible use of this material in HTS coated conductor as buffer.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.31 no.5
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• pp.235-241
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• 2018

The internal pressure is a critical parameter for designing a pressure vessel. The static pressure that a pressure vessel must withstand is usually determined according to the various codes and standards with simple formula or numerical simulations considering the geometric parameters such as diameter and thickness of a vessel. However, there is no specific codes or technical standards we can use practically for designing of pressure vessels which have to endure the detonation pressure. Detonation pressure is a kind of dynamic pressure which causes an impulsive pressure on the vessel wall in a extremely short time duration. In addition, it is known that the magnitude of reflected pressure at the vessel wall due to the explosion can be over twice the incident pressure. Therefore, if we only consider the reflected pressure, the design of the pressure vessel can be too conservative from the economical point of view. In this study, we suggest a practical method to evaluate the magnitude of maximum allowable pressure that the pressure vessel can withstand against the detonation inside a vessel. As an example to validate the proposed method, we consider the pressure vessel containing hydrogen gas.

• Smart Structures and Systems
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• v.17 no.6
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• pp.957-980
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• 2016

Structural damage detection (SDD) is a challenging task in the field of structural health monitoring (SHM). As an exploring attempt to the SDD problem, a hybrid self-adaptive Firefly-Nelder-Mead (SA-FNM) algorithm is proposed for the SDD problem in this study. First of all, the basic principle of firefly algorithm (FA) is introduced. The Nelder-Mead (NM) algorithm is incorporated into FA for improving the local searching ability. A new strategy for exchanging the information in the firefly group is introduced into the SA-FNM for reducing the computation cost. A random walk strategy for the best firefly and a self-adaptive control strategy of three key parameters, such as light absorption, randomization parameter and critical distance, are proposed for preferably balancing the exploitation and exploration ability of the SA-FNM. The computing performance of the SA-FNM is evaluated and compared with the basic FA by three benchmark functions. Secondly, the SDD problem is mathematically converted into a constrained optimization problem, which is then hopefully solved by the SA-FNM algorithm. A multi-step method is proposed for finding the minimum fitness with a big probability. In order to assess the accuracy and the feasibility of the proposed method, a two-storey rigid frame structure without considering the finite element model (FEM) error and a steel beam with considering the model error are taken examples for numerical simulations. Finally, a series of experimental studies on damage detection of a steel beam with four damage patterns are performed in laboratory. The illustrated results show that the proposed method can accurately identify the structural damage. Some valuable conclusions are made and related issues are discussed as well.

• Steel and Composite Structures
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• v.20 no.1
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• pp.127-145
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• 2016

Composite column design is strongly influenced by the computation of the critical buckling load, which is very sensitive to the effective flexural stiffness (EI) of the column. Because of this, the behaviour of a composite column under lateral loading and its response to deflection is largely determined by the EI of the member. Thus, prediction models used for composite member design should accurately mirror this behaviour. However, EI varies due to several design parameters, and the implementation of high-strength materials, which are not considered by the current composite design codes of practice. The reliability of the design methods from six codes of practice (i.e., AS 5100, AS/NZS 2327, Eurocode 4, AISC 2010, ACI 318, and AIJ) for composite columns is studied in this paper. Also, the reliability of these codes of practice against a serviceability limit state criterion are estimated based on the combined use of the test-based statistical procedure proposed by Johnson and Huang (1997) and Monte Carlo simulations. The composite columns database includes 100 tests of circular concrete-filled tubes, rectangular concrete-filled tubes, and concrete-encased steel composite columns. A summary of the reliability analysis procedure and the evaluated reliability indices are provided. The reasons for the reliability analysis results are discussed to provide useful insight and supporting information for a possible revision of available codes of practice.

• Computers and Concrete
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• v.22 no.2
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• pp.167-182
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• 2018

The modeling of loss of bond between reinforcing bars (rebars) and concrete due to corrosion is useful in studying the behavior and prediction of residual load bearing capacity of corroded reinforced concrete (RC) members. In the present work, first the possibility of using different methods to simulate the rebars-concrete bonding, which is used in three-dimensional (3D) finite element (FE) modeling of corroded RC beams, was explored. The cohesive surface interaction method was found to be most suitable for simulating the bond between rebars and concrete. Secondly, using the cohesive surface interaction approach, the 3D FE modeling of the behavior of non-corroded and corroded RC beams was carried out in an ABAQUS environment. Experimental data, reported in literature, were used to validate the models. Then using the developed models, a parametric study was conducted to examine the effects of some parameters, such as degree and location of the corrosion, on the behavior and residual capacity of the corroded beams. The results obtained from the parametric analysis using the developed model showed that corrosion in top compression rebars has very small effect on the flexural behaviors of beams with small flexural reinforcement ratio that is less than the maximum ratio specified in ACI-318-14 (singly RC beam). In addition, the reduction of steel yield strength in tension reinforcement due to corrosion is the main source of reducing the load bearing capacity of corroded RC beams. The most critical corrosion-induced damage is the complete loss of bond between rebars and the concrete as it causes sudden failure and the beam acts as un-reinforced beam.