• Journal of the Korean Chemical Society
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• v.55 no.3
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• pp.495-501
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• 2011

The corrosion inhibitive nature of a flavonoid compound, 3-Hydroxy-7-methoxy-2-phenylchromen-4-one (HMPC), the synergistic effect between HMPC and n-Tetrabutylammonium bromide (TBAB) and their adsorption behavior on mild steel in hydrochloric acid solution were studied by weight loss, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements. The results of weight loss study at different temperatures revealed that the inhibition efficiency increases with inhibitor concentration and decreases with increase in the temperature of the system. The electrochemical studies showed that the inhibitor acts through mixed mode of inhibition and the inhibitor molecules adsorb on the metal - solution interface forming a protective layer. The adsorption of the inhibitor molecules over the metal surface was supported by the obeyed Langmuir's adsorption isotherm, Scanning Electron Microscopic analysis (SEM) and Fourier Transform Infrared (FT-IR) spectroscopic studies.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.20 no.3
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• pp.265-272
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• 2007

The finite element linear buckling analysis of folded plate structures using adaptive h-refinement methods is presented in this paper. The variable-node flat shell element used in this study possesses the drilling D.O.F. which, in addition to improvement of the element behavior, permits an easy connection to other elements with six degrees of freedom per node. The Box-typed structures can be analyzed using these developed flat shell elements. By introducing the variable-node elements some difficulties associated with connecting the different layer patterns, which are common in the adaptive h-refinement on quadrilateral mesh, can be overcome. To obtain better stress field for the error estimation, the super-convergent patch recovery is used. The convergent buckling modes and the critical loads associated with these modes can be obtained.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2008.04a
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• pp.397-401
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• 2008

Knowledge of dynamic characteristics of structural elements often can make difference between success and failure in the design of structure due to resonance effect. In this paper an analytical model of a cantilever beam having midpoint load is considered for structural optimization. This involves creating the geometry which allows parametric study of all design variables. For that purpose optimization of cantilever beam is elaborated in order to find the optimum geometry which minimizes its volume eventually for minimum weight using ANSYS. But such geometry could be obtained by different combinations of width and height, so that it may have the same cross sectional area yet different dynamic behavior. So for optimum safe design, besides minimum volume it should have minimum vibration as well. In order to predict vibration different dynamic analyses are performed simultaneously to solve the eigenvalues problem assuming no damping initially through MATLAB simulations using state space form for modal analysis, which identifies the resonant frequencies and mode shapes belonging to the lowest three modes of vibration. And next by introducing damping effects tip displacement, bending stress and the vertical reaction force at the fixed end is evaluated under some dynamic load of varying frequency, and finally it is discussed how resonance can be avoided for particular design. Investigation of results clearly shows that only structural analysis is not enough to predict the optimum values of dimension for safe design. Potentially this technique will meet maintenance and cost goals of many organizations particularly for the application where dynamic loading is invertible and helps a lot ensuring that the proposed design will be safe for both static and dynamic conditions.

• Structural Engineering and Mechanics
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• v.73 no.6
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• pp.613-620
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• 2020

The research study is focuses on a form of all-bolted joint with the external ring stiffening plate in the prefabricated steel structure. The components are bolted at site after being fabricated in the factory. Six specimens were tested under cyclic loading, and the effects of column axial compression ratio, concrete-filled column, beam flange sub plate, beam web angle cleats, and spliced column on the failure mode, hysteretic behavior and ductility of the joints were analyzed. The results shown that the proposed all-bolted joint with external ring stiffening plate performed high bearing capability, stable inflexibility degradation, high ductility and plump hysteretic curve. The primary failure modes were bucking at beam end, cracking at the variable section of the external ring stiffening plate, and finally welds fracturing between external ring stiffening plate and column wall. The bearing capability of the joints reduced with the axial compression ratio increased. The use of concrete-filled steel tube column can increase the bearing capability of joints. The existence of the beam flange sub plate, and beam web angle cleat improves the energy dissipation, ductility, bearing capacity and original rigidity of the joint, but also increase the stress concentration at the variable section of the external reinforcing ring plate. The proposed joints with spliced column also performed desirable integrity, large bearing capacity, initial stiffness and energy dissipation capacity for engineering application by reasonable design.

• Advances in concrete construction
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• v.6 no.2
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• pp.199-220
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• 2018

In this study, the effects of sulphuric acid on the mechanical performance and the durability of Engineered Cementitious Composites (ECC) specimens were investigated. The carbon fiber reinforced polymer (CFRP) and basalt fiber reinforced polymer (BFRP) fabrics were used to evaluate the performances of the confined and unconfined ECC specimens under static and cyclic loading in the acidic environment. In addition, the use of CFRP and BFRP fabrics as a rehabilitation technique was also studied for the specimens exposed to the sulphuric acid environment. The polyvinyl alcohol (PVA) fiber with a fraction of 2% was used in the research. Two different PVA-ECC concretes were produced using low lime fly ash (LCFA) and high lime fly ash (HCFA) with the fly ash-to-OPC ratio of 1.2. Unwrapped PVA-ECC specimens were also produced as a reference concrete and all concrete specimens were continuously immersed in 5% sulphuric acid solution ($H_2SO_4$). The mechanical performance and the durability of specimens were evaluated by means of the visual inspection, weight change, static and cyclic loading, and failure mode. In addition, microscopic changes of the PVA-ECC specimens due to sulphuric acid attack were also assessed using scanning electron microscopy (SEM) to understand the macroscale behavior of the specimens. Results indicated that PVA-ECC specimens produced with low lime fly ash (LCFA) showed superior performance than the specimens produced with high lime fly ash (HCFA) in the acidic environment. In addition, confinement of ECC specimens with BFRP and CFRP fabrics significantly improved compressive strength, ductility, and durability of the specimens. PVA-ECC specimens wrapped with carbon FRP fabric showed better mechanical performance and durability properties than the specimens wrapped with basalt FRP fabric. Both FRP materials can be used as a rehabilitation material in the acidic environment.

• Journal of the Korean Applied Science and Technology
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• v.33 no.3
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• pp.540-548
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• 2016

The non-Newtonian flow curves of sodium bis-(2-ethylhexyl)sulfosuccinate-water lamellar liquid crystals were obtained in various concentrations and temperatures by using a cone-plate rheometer. By applying non-Newtonian flow equation to the flow curves for AOT-water lamellar liquid crystal samples, the rheological parameters were obtained. Particular attention is given to the hysteresis loop detected when the liquid crystal samples are shear under increasing-decreasing shear stress modes which result in thixotropic and dilatant behavior. Sodium bis-(2-ethylhexyl)sulfosuccinate-water lamellar liquid crystals behave as weak gels when they are subjected to shear flow, but when the applied stress surpasses the yield stress, they exhibit non-linear viscoelasticity. Upon decreasing shear rate, the dispersion still preserves much of its structure and consequently its shear stress remains higher than the values measured in the increasing shear rate mode.

• Membrane and Water Treatment
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• v.9 no.5
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• pp.373-383
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• 2018

Fouling by solids and microorganisms is the major obstacle limiting the efficient use of membrane wastewater treatment. In our previous study, two stages microalgae/membrane filtration system was proposed to treat anaerobic digested palm oil mill effluent (AnPOME). This two stages microalgae/membrane filtration system had showed great potential for the treatment of AnPOME with high removal of COD, $NH_3-N$, $PO_4{^{3-}}$, TSS, turbidity, and colour. However, fouling behavior of the membrane in this two stages microalgae/membrane filtration system was still unknown. In this study, empirical models that describe permeate flux decline for dead-end filtration (pore blocking - complete, intermediate, and standard; and cake layer formation) presented by Hermia were used to fit the experimental results in identifying the fouling mechanism under different experimental conditions. Both centrifuged and non-centrifuged samples were taken from the medium with 3 days RT intervals, from day 0 to day 12 to study their influence on fouling mechanisms described by Hermia for ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO) filtration mode. Besides, a more detailed study on the use of resistance-in-series model for deadend filtration was done to investigate the fouling mechanisms involved in membrane filtration of AnPOME collected after microalgae treatment. The results showed that fouling of UF and NF membrane was mainly caused by cake layer formation and it was also supported by the analysis for resistance-in-series model. Whereas, fouling of RO membrane was dominated by concentration polarization.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.28 no.3
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• pp.591-603
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• 2018

Windows Event Log is a format that records system log in Windows operating system and methodically manages information about system operation. An event can be caused by system itself or by user's specific actions, and some event logs can be used for corporate security audits, malware detection and so on. In this paper, we choose actions related to corporate security audit and malware detection (External storage connection, Application install, Shared folder usage, Printer usage, Remote connection/disconnection, File/Registry manipulation, Process creation, DNS query, Windows service, PC startup/shutdown, Log on/off, Power saving mode, Network connection/disconnection, Event log deletion and System time change), which can be detected through event log analysis and classify event IDs that occur in each situation. Also, the existing event log tools only include functions related to the EVTX file parse and it is difficult to track user's behavior when used in a forensic investigation. So we implemented new analysis tool in this study which parses EVTX files and user behaviors.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.1
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• pp.366-375
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• 1991

In this study, vibrational behavior of uniform pipe carrying a moving medium is studied by using a transfer matrix and the displacement function derived from the conventional beam theory. In various boundary conditions, flow velocity and mechanical property change of the variation of natural frequency are investigated. The Coriolis term in the original differential equation of motion has been ignored in the investigation. This method is used to study the variation of natural frequency with flow velocity for clamped-clamped, cantilevered, clamped-pinned, pinned-pinned, free-free straight pipe element. It is shown that clamped-clamped, free-free pipe have the highest natural frequency and critical velocity values while cantilevered pipe have the smallest natural frequency for the same mechanical properties. From the vibration effects of mechanical property variation, it is shown that bending stiffness and pipe length variation has large influence on natural frequency and critical velocity. Since the order of transfer matrix is not changed with boundary conditions of pipe element, this method proposed can be easily applied to personal-computer for vibration analysis of pipe element. Furthermore, this method can be extended to three-dimensional system by using a coordinate transformation for the analysis of piping systems.

• Journal of Korean Library and Information Science Society
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• v.31 no.1
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• pp.87-114
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• 2000

The purpose of this study is offering appropriate system and training program to helf the system designer and the trainer in addition to analyze information use behavior about the web search tools and evaluate the estimated system by user groups. The results of the study are as follows $\circledS1$ It is desirable to consider age than other demographic variables in the case of web search tool. $\circledS2$ It is desirable to design Directory Search Tool in the case of web search tool which serves the student user group. $\circledS3$ An Intelligent Search Tool is more appropriate for the students who are using keyword search tool than any other tools. $\circledS4$ A discussion about standard classification of the web information should be accomplished soon because users feel confused in using web search tools due t o absence of standard mode of classification about classified item. $\circledS5$ Librarians need the cognition about data on internet s a source of information and need positive service and user training program about these information because student users hardly get help from librarians or library orientation for learning method to use web search tool. $\circledS6$ Internet use experience and years of computer use had effect on their use ability when using web search tool, whereas computer use experience, library use experience and Online Public Access Catalogs (OPAC) use experience had no effect on it. Especially, OPAC use experience had no effect on use ability of web search tool of student user group because student user groups had no information about internet and web search tool and they did not recognized the difference about search method between web search tool and OPAC. $\circledS7$In the case of web search tool, it si important to index the increasing web resource automatically by a searching robot. But in the case of student users, web search tool is much more needed to index by index expert due to the absence of ability about selecting and combining keyword.