• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.4
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• pp.2777-2783
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• 2015

Peak power reduction is becoming increasingly important not only for grid operators but also for residential users. The scheduling of electric loads tries to reduce the power peak by splitting the power-on period of an electric device into multiple smaller ones and by interleaving the on-periods of every device in a holistic way. This paper analyzes the performance of EDF, LSF, TCBM, and lazy scheduling algorithms and proposes the enhancement schemes. For analysis, we have implemented the scheduling policies in a simulation environment for distributed control systems. Through extensive experiments using real power traces, we discuss their performance characteristics in terms of power deviation, switch count, and temperature violation ratio. To prevent excessive switching, we propose to employ the concept of limited preemptibility and evaluate its effect on performance. It is found that the best performance is achieved when the scheduler capacity is dynamically adjusted to the actual power demand. The experiment results show that, by load scheduling, the probability of having a power deviation greater than 150W is reduced from 21.5% down to 3.2%.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.11
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• pp.5301-5323
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• 2017

Small cell deployment offers a low-cost solution for the boosted traffic demand in heterogeneous cellular networks (HCNs). Besides improved spatial spectrum efficiency and energy efficiency, future HCNs are also featured with the trend of network architecture convergence and feasibility for flexible mobile applications. To achieve these goals, dual connectivity (DC) is playing a more and more important role to support control/user-plane splitting, which enables maintaining fixed control channel connections for reliability. In this paper, we develop a tractable framework for the downlink SINR analysis of DC assisted HCN. Based on stochastic geometry model, the data-control joint coverage probabilities under multi-frequency and single-frequency tiering are derived, which involve quick integrals and admit simple closed-forms in special cases. Monte Carlo simulations confirm the accuracy of the expressions. It is observed that the increase in mobility robustness of DC is at the price of control channel SINR degradation. This degradation severely worsens the joint coverage performance under single-frequency tiering, proving multi-frequency tiering a more feasible networking scheme to utilize the advantage of DC effectively. Moreover, the joint coverage probability can be maximized by adjusting the density ratio of small cell and macro cell eNBs under multi-frequency tiering, though changing cell association bias has little impact on the level of the maximal coverage performance.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.9A
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• pp.685-696
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• 2009

The requirements of the NGA are to provide broader bandwidth, higher splitting ratio, and longer reach than those of the current FTTH. In the TDMA PON accounting for large percentage in the total FTTH, the increase in distance between the OLT and the ONU leads to the increase in propagation delay and in packet delay three times more than the propagation delay. It is because a packet arrived in the ONU is handled through bandwidth request, grant, and transmission. To reduce the increased packet delay, the OLT have to reduce the cycle time. However, it will cause increased overhead and reduced link efficiency. In this paper, we investigate several problems in TDMA PON when the subscriber access network extended to 60 or 100 Km reach as a NGA goal and provide a method that determines an optimal cycle time to satisfy QoS for delay sensitive traffics. In particular, we suggest a variable equalized round trip delay method and a variable cycle time method. It is shown that the former reduces the packet delay and the latter increase the link efficiency.

• Smart Structures and Systems
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• v.17 no.4
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• pp.593-610
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• 2016

In this study, an innovative and smart glass fiber-reinforced polymer (GFRP) hybrid bar was developed for stronger durability of concrete structures. As comparing with the conventional GFRP bar, the smart GFRP Hybrid bar can promise to enhance the modulus of elasticity so that it makes the cracking reduced than the case when the conventional GFRP bar is used. Besides, the GFRP Hybrid bar can effectively resist the corrosion of conventional steel bar by the GFRP outer surface on the steel bar. In order to verify the bond performance of the GFRP hybrid bar for structural reinforcement, uniaxial pull-out test was conducted. The variables were the bar diameter and the number of strands and pitch of the fiber ribs. Tensile tests showed a excellent increase in the modulus of elasticity, 152.1 GPa, as compared to that of the pure GFRP bar (50 GPa). The stress-strain curve was bi-linear, so that the ductile performance could be obtained. For the bond test, the entire GFRP hybrid bar test specimens failed in concrete splitting due to higher shear strength resulting in concrete crushing as a function of bar deformation. Investigation revealed that an increase in the number of strands of fiber ribs enhanced the bond strength, and the pitch guaranteed the bond strength of 19.1 mm diameter hybrid bar with 15.9 mm diameter of core section of deformed steel the ACI 440 1R-15 equation is regarded as more suitable for predicting the bond strength of GFRP hybrid bars, whereas the CSA S806-12 prediction is considered too conservative and is largely influenced by the bar diameter. For further study, various geometrical and material properties such as concrete cover, cross-sectional ratio, and surface treatment should be considered.

• Journal of Communications and Networks
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• v.15 no.3
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• pp.312-320
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• 2013

Home evolved Node-B (HeNB), also called a femtocell or a femto base station, is introduced to provide high data rate to indoor users. However, two main problems arise in femtocell networks: (1) Small coverage area of HeNB, which results in limited cell-splitting gain and ping-pong handover (HO) problems and (2) high inter-femtocell interference because HeNBs may be densely deployed in a small region. In this study, an efficient cooperation mechanism called an HeNB-aided virtual-HO (HaVHO) scheme is proposed to expand the coverage area of femtocells and to reduce inter-femtocell interference. The cooperation among neighbor HeNBs is exploited in HaVHO by enabling an HeNB to relay the data of its neighbor HeNB without an HO. The HaVHO procedure is compatible with the existing long term evolution specification, and the information exchange overhead in HaVHO is relatively low. To estimate the signal to interference plus noise ratio improvement, the area average channel state metric is proposed, and the amount of user throughput enhancement by HaVHO is derived. System-level simulation shows that HaVHO has a better performance than the other four schemes, such as lesser radio link failure, lesser ping-pong handover, lesser short-stay handover, and higher user throughput.

• Journal of Korean Academy of Oral and Maxillofacial Radiology
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• v.25 no.2
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• pp.545-553
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• 1995

The subjects of this study consisted of 58 patients with Le Fort fractures, who were admitted to Chonbuk National University Hospital from Jan. 1988 to Oct. 1995. The author classified the maxillofacial fractures by Le Fort classification and examined the. incidence of Le Fort fractures by age, sex and etiology. The purpose of this study was to compare the imagings of conventional radiograms with those of computed tomograms and to aid in the diagnosis of patients with Le Fort fractures. The obtained results were as follows: 1. The Le Fort fractures occured mainly in 3rd and 4th decades, but there was no significant difference between decades. A ratio of men to women was 5.5 : 1. The major etiologic factors were traffic accident(69％), assault(14％) and fall-down(12％). 2. The most common type of Le Fort fracture was type I(49.3％). The numbers of Le Fort II, ill fractures were 41.3％, 9.4％ respectively. And 8.6％ were midsagittal splitting fractures. 3. The discontinuity and haziness of the maxillary sinus were easily detected by Waters' view. In skull PI A view, it was difficult to observe fractures due to overlapping of the other structures, but the haziness of the maxillary sinus was sometimes observed. 4. In Le Fort fracture, the fracture pattern of orbit, the wall of maxillary sinus, nasal bone and pterygoid plate were more easily detected in computed tomograms than in conventional radiograms.

• Journal of the Korean Magnetics Society
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• v.10 no.4
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• pp.183-190
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• 2000

This study aims at making a research into the physical and chemical properties of the neolithic era potterys, which are unearthed from Gosanli, Sagaeli, Bukchonli, Samyangdong and Gonaili districts in Cheju Island, by using X-ray diffraction, X-ray fluorescence spectrometer and Mossbauer spectroscopy. This results are as follows. The principal component of five plain coarse pottery sherds by X-ray fluorescence spectrometer and X-ray diffraction spectrum at the room temperature is silicate mineral which is equal to SiO$_2$, and they also have a little magetite, hematite and goethite. The most existent Fe is Fe$\^$+3/ through Mossbauer spectroscopy analysis of plain coarse pottery sherds and it is presumed that the magnetic hyperfine splitting caused this result. The ratio of Fe$\^$2+//(Fe$\^$2+/+Fe$\^$3+/) is mostly zero by Mossbauer spectrum at the room temperature of plain coarse pottery sherds and it is thought because they were fired in the atmosphere.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.2
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• pp.1032-1037
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• 2011

In this study, simulation and optimization works for a demethanizer column have been performed to obtain ethane and heavier products from a pretreated natural gas stream. Pretreated natural gas feed stream was partially condensed after being precooled by exchanging heat with demethanizer top vapor stream and by using an external refrigeration cycle with a propane refrigerant. Vapor stream was cooled further and partially condensed through a turbo-expander. The power generated from the expansion of turbo-expander was delivered to the compressor for the residue gas compression. Liquid stream was cooled by Joule-Thomson expansion valve and was fed to the middle section of the demethanizer. Recovery percent of ethane for feed natural was set to 80% and methane to ethane molar ratio was fixed as 0.0119. On the other hand, some of the cold heat could be recovered by splitting the feed stream and by exchanging heat with side reboiler in order to reduce the heat duty in the propane refrigeration cycle.

• Advances in concrete construction
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• v.8 no.3
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• pp.239-246
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• 2019

Substitution of natural fine aggregates with industrial by-products like precious slag balls (PS Balls) offers various advantages like technical, economic and environmental which are very important in the present era of sustainability in construction industry. PS balls are manufactured by subjecting steel slag to slag atomizing Technology (SAT) which imparts them the desirable characteristics of fine aggregates. The main objective of this research paper is to assess the feasibility of producing good quality concrete by using PS balls, to identify the potential benefits by their incorporation and to provide solution for increasing their utilization in concrete applications. The study investigates the effect of PS balls as partial replacement of fine aggregates in various percentages (20%, 40%, 60%, 80% and 100%) on mechanical properties of concrete such as compressive strength, splitting tensile strength, and flexural strength. The optimum mix was found to be at 40% replacement of PS balls with maximum strength of 62.89 MPa at 28 days curing. Permeability of concrete was performed and it resulted in a more durable concrete with replacement of PS balls at 40% and 100% as fine aggregates. These two specific values were considered as optimum replacement is 40% and also the maximum possible replacement is 100%. Scanning electron microscope (SEM) analysis was done and it was found that the PS balls in concrete were unaffected and with optimum percentage of PS balls as fine aggregates in concrete resulted in good strength and less cracks. Hence, it is possible to produce good workable concrete with low water to cement ratio and higher strength concrete by incorporating PS balls.

• Journal of Advanced Navigation Technology
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• v.23 no.4
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• pp.309-315
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• 2019

This paper proposes an implementation of unequal power divider with 1:3 and 1:4 splitting ratio in multi-section structure using CPW and offset coupled transmission line. The power divider consists of a multi-section transmission line and a circuit with parallel capacitors and resistors. A multi-section transmission line was implemented by decomposing a ${\lambda}/4$ single transmission line terminated by an arbitrary impedance and converging it with a multi-section transmission line shorter than $90^{\circ}$ electrical length, and RC parallel circuits were connected between transmission lines to obtain reflection coefficient of output port and isolation characteristics between the output port. In this way, it was confirmed that the transmission lines at the unequal power divider designed at 2 GHz were shorter than ${\lambda}/4$ and implemented at least 27% less than the conventional ones, and that the broadband characteristics could be obtained.