• Explosives and Blasting
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• v.22 no.4
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• pp.7-15
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• 2004

An explosion modeling technique was developed by using the spherical discrete element code, PFC3D, which can be used to model the dynamic stress wave propagation phenomenon. The modeling technique is simply based on an idea that the explosion pressure should be applied to a PFC3D particle assembly not in the form of an external force (body force), but in the form of a contact force (surface force). According to this concept, the explosion pressure is applied to the wall particles by the scheme of radius expansion/contraction of inner-hole particles. The output wall force is compared to the input hole pressure in every time step, and a correction routine is activated to control the radius multiplier of the inner-hole particles. A comparative blast simulation far a cement mortar block of $80\times90\times80mm$ was conducted by using the conventional explosion modeling method and the new one. The results of the simulation are presented in a qualitative fashion.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.41 no.3
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• pp.120-128
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• 2018

OLED Display fabrication system is one of the most complicated discrete processing systems in the world. As the glass size grows from $550{\times}650mm$ to $1,500{\times}1,850mm$ in recent years, the efficiency of Automated Material Handling System (AMHS) has become very important and OLED glass manufacturers are trying to improve the overall efficiency of AMHS. Aiming to meet the demand for high efficiency of transportation, various kind of approaches have been applied for improving dispatching rules and facility layout, while simultaneously considering the system parameters such as glass cassettes due date, waiting time, and stocker buffer status. However, these works did not suggest the operational policy and conditions of distribution systems, especially for handling unnecessary material flows such as detour. Based on this motivation, in this paper, we proposed an efficient algorithm for improving detour transportation in OLED FAB. Specifically, we considered an OLED FAB simplifying OLED production environment in a Korean company, where four stockers are constructed for the delivery of Lot in a bay and linked to processing equipments. We developed a simulation model using Automod and performed a numerical experiment using real operational data to test the performance of three operation policies under considerations. We showed that a competitive policy for assigning alternative stocker in case of detour was superior to the current dedicated policy using a specified stocker and other considered policies.

• Journal of Digital Contents Society
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• v.19 no.1
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• pp.35-41
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• 2018

The Q-learning algorithm based on reinforcement learning is useful for learning the goal for one behavior at a time, using a combination of discrete states and actions. In order to learn multiple actions, applying a behavior-based architecture and using an appropriate behavior adjustment method can make a robot perform fast and reliable actions. Q-learning is a popular reinforcement learning method, and is used much for robot learning for its characteristics which are simple, convergent and little affected by the training environment (off-policy). In this paper, Q-learning algorithm is applied to a lamp robot to learn multiple behaviors (human recognition, desk object recognition). As the learning rate of Q-learning may affect the performance of the robot at the learning stage of multiple behaviors, we present the optimal multiple behaviors learning model by changing learning rate.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.9A
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• pp.891-899
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• 2008

The cdma2000 1xEV-DO system controls the data rates of mobile terminals based on a binary overload indicator from the base station and a simple probabilistic model. However, this traffic control scheme has difficulty in controlling the reverse-link traffic load effectively and in guaranteeing a stable operation of the reverse link because each mobile terminal determines the next data rate autonomously. This paper proposes a new trafRc control scheme to improve the system stability, and analyzes the proposed scheme by modeling it as a discrete-time Markov process. The numerical results show that the maximum data rate of the proposed scheme is much higher than that of the conventional one. Moreover, the proposed scheme does not modify the standard physical channel structure, so it is compatible to the existing 1xEV-DO system.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.11
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• pp.5338-5359
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• 2017

In-band full-duplex (IBFD) wireless communication supports symmetric dual transmission between two nodes and asymmetric dual transmission among three nodes, which allows improved throughput for distributed IBFD wireless networks. However, inter-node interference (INI) can affect desired packet reception in the downlink of three-node topology. The current Half-duplex (HD) medium access control (MAC) mechanism RTS/CTS is unable to establish an asymmetric dual link and consequently to suppress INI. In this paper, we propose a medium access control mechanism for use in distributed IBFD wireless networks, FD-DMAC (Full-Duplex Distributed MAC). In this approach, communication nodes only require single channel access to establish symmetric or asymmetric dual link, and we fully consider the two transmission modes of asymmetric dual link. Through FD-DMAC medium access, the neighbors of communication nodes can clearly know network transmission status, which will provide other opportunities of asymmetric IBFD dual communication and solve hidden node problem. Additionally, we leverage FD-DMAC to transmit received power information. This approach can assist communication nodes to adjust transmit powers and suppress INI. Finally, we give a theoretical analysis of network performance using a discrete-time Markov model. The numerical results show that FD-DMAC achieves a significant improvement over RTS/CTS in terms of throughput and delay.

• Journal of Astronomy and Space Sciences
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• v.39 no.4
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• pp.145-158
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• 2022

The dynamics of the outer zone radiation belt has received a lot of attention mainly due to the correlation between the occurrence of enhancing relativistic electron flux and spacecraft operation anomalies or even failures (e.g., Baker et al. 1994). Relativistic electron events are often observed during great storms associated with ultra low frequency (ULF) waves. For example, a large buildup of relativistic electrons was observed during the great storm of March 24, 1991 (e.g., Li et al. 1993; Hudson et al. 1995; Mann et al. 2013). However, the dominant processes which accelerate magnetospheric radiation belt electrons to MeV energies are not well understood. In this paper, we present observations of Pc5 ULF waves in the recovery phase of the Bastille day storm of July 16, 2000 and electron and proton flux simultaneously oscillating with the same frequencies as the waves. The mechanism for the observed electron and proton flux modulations is examined using ground-based and satellite observations. During this storm time, multiple packets of discrete frequency Pc5 ULF waves appeared associated with energetic particle flux oscillations. We model the drift paths of electrons and protons to determine if the particles drift through the ULF wave to understand why some particle fluxes are modulated by the ULF waves and others are not. We also analyze the flux oscillations of electrons and protons as a function of energy to determine if the particle modulations are caused by a ULF wave drift resonance or advection of a particle density gradient. We suggest that the energetic electron and proton modulations by Pc5 ULF waves provide further evidence in support of the important role that ULF waves play in outer radiation belt dyanamics during storm times.

• Korean Journal of Construction Engineering and Management
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• v.19 no.2
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• pp.50-60
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• 2018

Recently, modular construction method has been widely applied to projects with repetitive processes including dormitory, the residential facility, and the hotel construction due to reduced labor input and shortened construction schedule. Generally, about 40% of total on-site construction cost excluding unit installation cost, is put on exterior finishing work, and thus management of finishing work is deemed important in maintaining the targeted schedule and cost. Since limited equipment is shared so that subsequent activities are not affected while carrying out on-site installation and finishing work, lifting plan becomes more important for modular projects with greater portion of finishing work load. In this regard, tower crane operation plan may take the form of a single cycle or multiple cycles in which equipment efficiency can be affected. However, difficulties exist in evaluating alternatives to tower crane operation plans supporting unit installation and finishing work. Therefore, this study aims to evaluate the alternative of tower crane operation method according to the cyclic period setting in modular building site to determine the effect on T/C uptime and process by parameterizing lifting time for unit and exterior finishing material, lift cycle for unit and exterior finishing material and time required for finishing work. Accordingly, this study develops a simulation model that can increase the tower crane efficiency by controlling the work speed. An academic contribution of this study is to suggest a resource leveling method applying the concept of lifting cycle, and further is expected to be managerially used as a basis for an alternative evaluation of equipment plan.

• Geomechanics and Engineering
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• v.14 no.6
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• pp.545-552
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• 2018

Blast-induced ground vibrations by a significant amount of explosives may cause many problems for mining slope stability. Geological discontinuities have a significant influence on the transmission of dynamic pressure of detonation and according to their position relative to the slope face may have damaging or useful impacts on the slope stability. In this study, the effect of geological discontinuities was investigated by modelling a slope with geological discontinuities through applying the dynamic pressure in three-dimensional discrete element code (3DEC). The geological discontinuities in four states that generally apperceived in mine slopes are considered. Given the advantages of the pressure decay function defined by some researcher, this type of function was used to develop the pressure-time profile. The peak particle velocities (PPV) values were monitored along an axis by utilization of Fish programming language and the results were used as an indicator to measure the effects. As shown in the discontinuity-free model, PPV empirical models are reliable in rocks lacking discontinuities or tightly jointed rock masses. According to the other results, the empirical models cannot be used for the case where the rock mass contains discontinuities with any direction or dip. With regard to PPVs, when the direction of discontinuities is opposite to that of the slope face, the dynamic pressure of detonation is significantly damped toward the slope direction at the surface of discontinuities. On the other hand, when the discontinuities are horizontal, the dynamic pressure of detonation affects the rock mass to a large distance.

• Bulletin of the Korean Chemical Society
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• v.32 no.8
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• pp.2765-2770
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• 2011

Organic dye-doped glasses, viz., ruthenium (II) tris(4,7'-diphenyl-1,10'-phenanthroline) $[Ru(dpp)_3]^{2+}$ incorporated into thin silica xerogel films produced by the sol-gel method, were prepared and their $O_2$ quenching properties investigated as a function of the $[Ru(dpp)_3]^{2+}$ concentration (3-400 ${\mu}M$) within the xerogel. The ratio of the luminescence from the $[Ru(dpp)_3]^{2+}$-doped films in the presence of $N_2$ and $O_2$ ($I_{N2}/I_{O2}$) was used to describe the film sensitivity to $O_2$ quenching. ($I_{N2}/I_{O2}$ changed three-fold over the $[Ru(dpp)_3]^{2+}$ concentration range. Time-resolved intensity decay studies showed that there are two discrete $[Ru(dpp)_3]^{2+}$ populations within the xerogels (${\tau}_1$ ~ 300 ns; ${\tau}_2$ ~ 3000 ns) whose relative fraction changes as the $[Ru(dpp)_3]^{2+}$ concentration changes. The increased $O_2$ sensitivity that is observed at the higher $[Ru(dpp)_3]^{2+}$ concentrations is a manifestation of a greater fraction of the 3000 ns $[Ru(dpp)_3]^{2+}$ species (more susceptible to $O_2$ quenching). A model is presented to describe the observed response characteristics resulting from $[Ru(dpp)_3]^{2+}$ distribution within the xerogel.

• Korea journal of population studies
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• v.35 no.2
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• pp.29-53
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• 2012

This research studies how women's hourly wages affect childbearing using data from the National Longitudinal Survey of Youth. The results of discrete time hazard model show that the relationship between women's hourly wage and fertility is dynamic. Overall relationship looks negative, but they are not consistent across education levels. Women who have a high school diploma or less have a tendency to decrease childbearing when their wages increase. But women who have some college experience or a college degree are likely to have children when their wages increase. It means that only for highly educated women who are likely to be in high paying decent jobs, the rise of income can be used as a resource for reconciling the mother's and worker's roles. Or, for less educated women who are likely to be in the low paying jobs, the rise of income is not large enough to lessen role incompatibility.