• Transactions of Materials Processing
• /
• v.22 no.4
• /
• pp.204-215
• /
• 2013

As a pressure vessel, a small seamless aluminum liner with inner volume of about 6.75L is made from an initial billet material of AA6061-O. To produce the aluminum liner, warm forging including backward extrusion and head nosing was numerically simulated using a billet initially pre-heated to about $480^{\circ}C$. Compression tests on the billet material were performed at various temperatures and strain rates, and the measured mechanical properties were used in the numerical simulations. For the backward extrusion and the head nosing, the tool geometries were designed based on the desired configuration of the aluminum liner. Furthermore, the structural integrity of the tooling was evaluated to ensure adequate tool life. The seamless aluminum liner has an endurance limit of about 1.47MPa ($15Kg_f/cm^2$), estimated based on the required inner pressure. The results confirm that the small seamless aluminum liner of AA6061-O can be successfully made by using the two stage warm forging procedures without any bursting failures.

• The Korean Journal of Emergency Medical Services
• /
• v.18 no.2
• /
• pp.35-43
• /
• 2014

Purpose: The purpose of this study was to establish novice user guidelines for efficient external laryngeal manipulation for intubation in difficult airway management. Methods: This study included 59 pre-qualified junior and senior emergency medical service students. The participants were instructed at random to intubate a manikin equipped with a cervical collar, thus simulating a difficult airway, using three types of external laryngeal manipulation: bimanual laryngoscopy, backward-rightward pressure, and cricoid pressure. The resultant intubation time and glottic view grade scores were estimated. Results: Intubation time was longest using the bimanual manipulation method, followed by cricoid pressure and backward-rightward pressure. A low Cormack-Lehane glottic view score was obtained regardless of the assisted compression method used. Conclusion: Backward-rightward pressure may be the most efficient method of external laryngeal manipulation on the basis of the intubation time and improvement in glottic view.

• Geotechnical Engineering
• /
• v.10 no.3
• /
• pp.119-134
• /
• 1994

In order to assess the possibility of using steel fibers in the fissured ciays, uniaxial compression tests were performed on both unreinforced and reinforced clay samples containing a pre-existing crack. Test results showed that the steel fiber reinforcement increased resistance to cracks initiation and their propagation, and therefore increased both stress at crack growth initiation and peak stress at failure. The increase in resistance to cracks initiation and their propagation was related to the arresting or deflecting the crack propagation in clay samples by steel fibers. A theoretical interpretation of experimental results was made using fracture mechanics theory and pull-out mechanisms in fiber reinforced materials. It was revealed that the steel fibers had bridging effect through their pull-out action that caused an increased resistance to the propagation of the cracks in the samples. The predicted pull-out force based on theoretical analyses agreed reasonably well with the measured values obtained from pull-out tests.

• Structural Engineering and Mechanics
• /
• v.56 no.6
• /
• pp.917-938
• /
• 2015

The nonlinear numerical analysis of the impact response of reinforced concrete/mortar beam incorporated with the updated Lagrangian method, namely the Smoothed Particle Hydrodynamics (SPH) is carried out in this study. The analysis includes the simulation of the effects of high mass low velocity impact load falling on beam structures. Three material models to describe the localized failure of structural elements are: (1) linear pressure-sensitive yield criteria (Drucker-Prager type) in the pre-peak regime for the concrete/mortar meanwhile, the shear strain energy criterion (Von Mises) is applied for the steel reinforcement (2) nonlinear hardening law by means of modified linear Drucker-Prager envelope by employing the plane cap surface to simulate the irreversible plastic behavior of concrete/mortar (3) implementation of linear and nonlinear softening in tension and compression regions, respectively, to express the complex behavior of concrete material during short time loading condition. Validation upon existing experimental test results is conducted, from which the impact behavior of concrete beams are best described using the SPH model adopting an average velocity and erosion algorithm, where instability in terms of numerical fragmentation is reduced considerably.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.27 no.4
• /
• pp.313-320
• /
• 2014

A tensegrity structure consists of a set of continuous cables in tension and a set of discontinuous struts in compression. The tensegrity structure can be classified into self-stressed and pre-stressed pin-jointed structure. A key step in the design of tensegrity structures is the determination of their equilibrium configuration, known as form-finding. In this paper, three effective methods are presented for form-finding of tensegrity structures. After performing form-finding process, a set of force density and corresponding topology results can be obtained. Then the force density method combined with a genetic algorithm is adopted to uniquely define a single integral feasible set of force densities. Numerical examples are presented that demonstrate the excellent performance of the algorithms.

• Transactions of the Korean hydrogen and new energy society
• /
• v.21 no.2
• /
• pp.129-135
• /
• 2010

Homogeneous charge compression ignition (HCCI) engines have the potential to provide both diesel-like efficiency and very low emissions of nitrogen oxide (NOx) and particulate matter(PM). However, several technical issues still must be resolved before HCCI can see application. Among these, steep pressure-rise rate which leads to narrow operating range of HCCI engine continues to be a major issue. This work investigates the combination of two methods to mitigate the excessive pressure-rise rates at high power output, namely fuel stratification and Cooled exhaust-gas recirculation (Cooled EGR), after identifying the each effects to pressure-rise rate. When applying the fuel stratification to simulation, total fuelling width of 0.15 at BDC is set as a equivalent ratio difference based on the previous research. In order to simulate the effects of cooled EGR, $CO_2$ mole fraction in pre-mixture is changed ranging from 0 to 30%. DME which has a characteristic of two-stage ignition is used as a fuel.

• The Korean Journal of Emergency Medical Services
• /
• v.23 no.1
• /
• pp.113-123
• /
• 2019

Purpose: The aim of this study was to provide basic data to improve the survival rate of pre-hospital cardiac arrest patients. This study suggests a more effective method of performing effective chest compressions for a cardiac arrest patient in a moving ambulance. Methods: To compare the differences between gender and license (qualification), SPSS 18.0 (Windows) was used. Independent and paired t-tests were used for differences between before and after wearing a rescuer's belt. Results: The success rate of chest compressions according to gender was higher in males ($68{\pm}21.91%$) than in females ($25.04{\pm}16.88%$). There was no difference according to license ($44.70{\pm}26.63$ for paramedic, $45.05{\pm}19.25$ for nurse). However, the depth (mm) and the success rate (%) were improved during the evaluation of chest compressions when wearing the rescuer's belt (depth: $46.95{\pm}6.49$ vs. $49.55{\pm}6.05$, success rate: $44.80{\pm}24.66$ vs. $57.39{\pm}26.823$). Conclusion: Wearing a rescuer's belt in an ambulance during patient transport can result in deeper and more accurate chest compressions; therefore, it is expected to be effective in recovering the circulation of patient with cardiac arrest.

• International Journal of Computer Science & Network Security
• /
• v.22 no.7
• /
• pp.65-74
• /
• 2022

In natural language processing, commonly used words such as prepositions are referred to as stop-words; they have no inherent meaning and are therefore ignored in indexing and retrieval tasks. The removal of stop-words from Arabic text has a significant impact in terms of reducing the size of a cor- pus text, which leads to an improvement in the effectiveness and performance of Arabic-language processing systems. This study investigated the effectiveness of applying a stop-word lists elimination with normalization as a preprocessing step. The idea was to merge statistical method with the linguistic method to attain the best efficacy, and comparing the effects of this two-pronged approach in reducing corpus size for Ara- bic natural language processing systems. Three stop-word lists were considered: an Arabic Text Lookup Stop-list, Frequency- based Stop-list using Zipf's law, and Combined Stop-list. An experiment was conducted using a selected file from the Arabic Newswire data set. In the experiment, the size of the cor- pus was compared after removing the words contained in each list. The results showed that the best reduction in size was achieved by using the Combined Stop-list with normalization, with a word count reduction of 452930 and a compression rate of 30%.

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2021.11a
• /
• pp.144-145
• /
• 2021

This study analyzed the cases of cracks in piles due to the use of followers under construction conditions where water exists inside the piles, and confirmed whether the piles were cracked through a field test simulating the construction conditions in which water pressure inside the piles was generated by a hammer. According to the construction case, under the construction condition where the pile length is 20% to 30% shorter than the drilled length, about 80% cracks occur, so there is a high possibility of cracking due to water inside the pile. A field test was conducted to confirm the type of pile failure due to hammer under the construction condition in which water exists inside the pile. The pile head was not destroyed by the compressive load, and one or more longitudinal cracks occurred along the PC steel wire. The closed end pile generates water pressure by hammer. the follower and cushion(compression plywood) must be drilled at least 0.4D. It is expected that improved quality control will be possible as the water pressure inside the pile is reduced.

• The Bulletin of The Korean Astronomical Society
• /
• v.45 no.1
• /
• pp.52.2-52.2
• /
• 2020

At quasi-perpendicular shocks in the high-�� (��=Pgas/Pmag~100) intracluster medium (ICM), various microinstabilities occur by the temperature anisotropies and/or drift motions of plasma. In the downstream, the Alfvén ion cyclotron instability (AIC) due to the ion temperature anisotropy (Ti⊥>Ti║) is triggered by shock-reflected ions, the whistler instability (WI) is driven by the electron temperature anisotropy (Te⊥>Te║) as a consequence of the shock compression of magnetic fields, and the mirror instability is generated due to the ion and/or electron temperature anisotropy. At the shock foot, the modified two stream instability (MTSI) is possibly excited by the cross-field drift between ions and electrons. In the upstream, electron firehose instability (EFI) is driven by the electron temperature anisotropy or the relative drift between incoming and reflected electrons. These microinstabilities play important roles in the particle acceleration in ICM shocks, so understanding of the microinstabilities and the resultant plasma waves is essential. In this study, based on a linear stability analysis, the basic properties of the microinstabilities in ICM shocks and the ion/electron scale fluctuations are described. We then discuss the implication of our work on the electron pre-acceleration in ICM shocks.