• Journal of Communications and Networks
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• v.14 no.5
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• pp.578-587
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• 2012

One of the key elements in the emerging, packet-based long term evolution (LTE) cellular systems is the deployment of multiple femtocells for the improvement of coverage and data rate. However, arbitrary overlaps in the coverage of these femtocells make the handover operation more complex and challenging. As the existing handover strategy of LTE systems considers only carrier to interference plus noise ratio (CINR), it often suffers from resource constraints in the target femtocell, thereby leading to handover failure. In this paper, we propose a new efficient, multi-objective handover solution for LTE cellular systems. The proposed solution considers multiple parameters like signal strength and available bandwidth in the selection of the optimal target cell. This results in a significant increase in the handover success rate, thereby reducing the blocking of handover and new sessions. The overall handover process is modeled and analyzed by a three-dimensional Markov chain. The analytical results for the major performance metrics closely resemble the simulation results. The simulation results show that the proposed multi-objective handover offers considerable improvement in the session blocking rates, session queuing delay, handover latency, and goodput during handover.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.10 no.6
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• pp.55-62
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• 2010

Monitoring systems are able to report certain events at region of interest(ROI) and to take an appropriate action. From industrial product line full of robots to fire detection, intrusion detection, smart grid application, environmental pollution alarm system, monitoring system has widely used in diverse industry sector. Recently, due to advance of wireless communication technology and availability of low cost sensors, intelligent and/or smart monitoring systems such as sensor networks has been developed. Several deployment methods are introduced to meet various monitoring needs and deployment performance criteria are also summarized to be used to identify weak point and be useful at designing monitoring systems. Both efficiency during deployment and usefulness after the deployment should be assessed. Efficiency factors during deployment are elapsed time, energy required, deployment cost, safety, sensor node failure rate, scalability. Usefulness factors after deployment are ROI coverage, connectivity, uniformity, target density similarity, energy consumption rate per unit time and so on.

• Korean Journal of Clinical Pharmacy
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• v.25 no.4
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• pp.223-230
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• 2015

Background: 8,000 children in North Korea died before they reached the 1 year after births in 2013. The high mortality rate of children under five years of age is mainly caused by infectious diseases and malnutrition. The need for national pediatric immunization and supply of vaccines will be vital when the abrupt reunification occurs. Objective: The purpose of this study is to scrutinize the pediatric immunization coverage of North Korea. Additionally it is to estimate the amount and the costs needed to vaccinate. Methods: The target population is the children of North Korea. The method is based on a pre-survey and an interview of North Korea defectors. The target interviewees searched for are as follows; doctors, teachers, and others. The interview includes questions on mortality rates and immunization coverage. The analysis is largely based on the statements of the health care providers within the selected group. Results: The interviewees are 8; 7 female and 1 male. The birth years range from 1956 to 1982. 3 out of 8 are former health care providers; a doctor, a pharmacist, and a nurse. The morbidity rate of infectious diseases exceeds the data from WHO. The immunization coverage is nearly 0% after 1980s. In order to ensure the welfare of North Korean children, at least 8,234,000 vaccine doses, requiring over 105 million U.S. dollars, are needed. Conclusion: The morbidity rate of infectious disease in North Korea is conspicuous. The preparation for supply and expenditure of vaccines is vital.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.7C
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• pp.527-537
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• 2012

In this paper, we propose unmanned vehicle based tracking network (UVTN) architecture and algorithms which employ multiple autonomous unmanned ground vehicles (AUGV) to efficiently follow targets in a group. The goal of UVTN is to maximize the service coverage while tracking target nodes for monitoring or providing the network access. In order to achieve this goal, UVTN performs periodic expansion and contraction which results in optimized redistribution of AUGV's in the network. Also, enhanced algorithms such as fast contraction and longest first are also discussed to improve the performance of UVTN in terms of the average coverage ratio and traveled distance. Simulation results show that the proposed UVTN and enhanced algorithms can effectively track the moving target and provide the consistent coverage.

• Radiation Oncology Journal
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• v.38 no.2
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• pp.138-147
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• 2020

Purpose: To evaluate the dosimetric variations in patients of head and neck cancer treated with definitive or adjuvant radiotherapy using optimized non-coplanar (ncVMAT) beams with coplanar (cVMAT) beams using volumetric arc therapy. Materials and Methods: Twenty-two patients of head and neck cancer that had received radiotherapy using VMAT in our department were retrospectively analyzed. Each of the patients was planned using coplanar and non-coplanar orientations using an optimized couch angle and fluences. We analyzed the Conformity Index (C_IRTOG), Dose Homogeneity Index (DHI), Heterogeneity Index (HI_RTOG), low dose volume, target and organs-at-risk coverage in both the plans without changing planning optimization parameters. Results: The prescription dose ranged from 60 Gy to 70 Gy. Using ncVMAT, C_IRTOG, DHI and HI_RTOG, and tumor coverage (ID_95%) had improved, low dose spillage volume in the body V_5Gy was increased and V_10Gy was reduced. Integral dose and intensity-modulated radiation therapy factor had increased in ncVMAT. In the case of non-coplanar beam arrangements, maximum dose (D_max) of right and left humeral head were reduced significantly whereas apex of the right and left lung mean dose were increased. Conclusion: The use of ncVMAT produced better target coverage and sparing of the shoulder and soft tissue of the neck as well as the critical organ compared with the cVMAT in patients of head and neck malignancy.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.18 no.4
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• pp.922-937
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• 2024

Maritime activities are on the rise, there is a growing demand for high-quality communication services that can cover larger areas. However, the transmission of high data rates to maritime users is challenging due to path loss from land base stations, which limits the transmission power. To overcome this challenge, researchers have been exploring the use of buoys in a marine environment as relays for communication technology. This paper proposes a simulation-based approach to investigate the impact of various beamwidths on communication performance when using a buoy as a relay. The objective is to determine the optimal beamwidth that yields the highest data rate for the target location. The approach is based on an offshore wave model where the direction of the buoy changes according to the height of the wave. The study investigates the performance of the relay in the downlink situation using receive beamforming, and the capacity at the user in the three-hop situation is verified using an amplify-and-forward (AF) relay that uses transmit beamforming to the user. The simulation results suggest that the beamwidth of the relay should be adjusted according to the wave conditions to optimize the data rate and relay position that satisfies a data rate superior to the direct path to the target position. Using a buoy as a relay can be a promising solution for enhancing maritime communications, and the simulation-based approach proposed in this paper can provide insights into how to optimize beamwidth for effective communication system design and implementation. In conclusion, the study results suggest that the use of buoys as relays for maritime communication is a feasible solution for expanding coverage and enhancing communication quality. The proposed simulation-based approach provides a useful tool for identifying relay beamwidths for achieving higher data rates in different wave conditions. These findings have significant implications for the design and deployment of communication systems in maritime environments.

• Journal of the Semiconductor & Display Technology
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• v.18 no.1
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• pp.1-4
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• 2019

Reactive sputtering is widely used because of its high deposition rate and high step coverage. The deposition layer is often affected by target poisoning because the target conditions are changed, as well, by reactive gases during the initial stage of sputtering process. The reactive gas affects the deposition rate and process stability (target poisoning), and it also leads unintended oxide interlayer formation. Although the target poisoning mechanism has been well known, little attention has been paid on understanding the interlayer formation during the reactive sputtering. In this research, we studied the interlayer formation during the reactive sputtering. A DC magnetron sputtering process is carried out to deposit an aluminum oxide film on a silicon wafer. From the real-time process monitoring and material analysis, the target poisoning phenomena changes the reactive gas balance at the initial stage, and affects the interlayer formation during the reactive sputtering process.

• The Journal of Korean Society for Radiation Therapy
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• v.29 no.1
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• pp.57-68
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• 2017

Purpose: The purpose of this study was to compare volumetric modulated arc therapy(VMAT) with fixed-field intensity modulated radiation therapy(IMRT) using non-coplanar beam when the shape of target is irregular and the location is adjacent to organ at risk(OAR). Materials and Methods: The subjects of this study were a total of 6 patients who had radiation therapy for whole scalp(2 patients), partial scalp(2 patients), and whole ventricle(2 patients) by True Beam STX(Varian Medical Systems, USA). VMAT plans consisted of coplanar or non-coplanar arcs which can minimize the volume of OAR included in beamlets. All fixed-field IMRT plans consisted of non-coplanar beams using more than 2 angles of Couch. Results: The VMAT and IMRT plans were compared with regard to the maximum dose of both lens, both optic nerves, optic chiasm, and brain stem and the mean dose of both eyeballs and hippocampus. VMAT plans showed higher dose than ncIMRT plans at more than 6 of all OARs in every patient, and the ratio was from 1.1 times to 8.2 times. In case of total scalp and partial scalp, the volume of brain which received more than 20 Gy in the VMAT plans was 2 times larger than the volume in the ncIMRT plans. In case of whole ventricle, there was no significant difference. Target coverage was satisfied in both plans($PTV_{100%}=95%$). The maximum dose in target volume and required monitor unit(MU) of ncIMRT were higher than them of VMAT plans. Conclusion: Even though ncIMRT is less efficient than VMAT with regard to required MU and treatment time, the dose to OARs is much lower than VMAT and PTV Coverage is similar with VMAT. If the shape of target is irregular and location is adjacent to OAR, comparison VMAT plan with ncIMRT plan deserves to be considered.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.3A
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• pp.240-248
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• 2006

In this paper, we consider an OFDM receiver algorithm design for IEEE 802.11a/p system, which targeting large coverage area while keeping the transmission format unchanged. Particularly, taking into account the inter-symbol interference(ISI) and inter-carrier interference(ICI) that can be induced with large RMS delay spread, we employ channel shortening time-domain equalizer(TEQ) and evaluate the receiver performance in terms of SINR and packet error rate(PER). The preamble defined in IEEE802.11a/p is used to estimated the initial equalizer tap coefficients. Primary purpose of the paper is to give an answer to the question, though partially, whether or not 16-QAM constellation can be used in none line of sight environment at the boundary of a large coverage area. To this end, we first analyze the required TEQ parameters for the target channel environment and then perform simulation for PER performance evaluation in a generic frequency selective fading channel with exponential power-delay profile.

• The Journal of Korean Society for Radiation Therapy
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• v.26 no.2
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• pp.177-182
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• 2014

Purpose : The goal of this study was to compare and analysis the dose distribution and treatment time between Tomotherapy planning with fixed jaw(FJ) and dynamic jaw(DJ). Materials and Methods : Seven patients were selected in the study including five common clinical cases(brain, head and neck(HN), lung, prostate, spine). 1) Helical Tomotherapy plans with FJ and DJ were generated with the same planning parameters such as Modulation factor, Pitch and Field width. 2) Tomo_edge plans with a larger field width were generated to compare to conventional HT delivery with fixed jaw. Dosimetric evaluation indices for target coverage are Dmin, Conformity index(CI) and for whole body including target are $V_{10%}$, $V_{25%}$, $V_{50%}$, $V_{75%}$ using Dose-volume histogram(DVH). Also, Treatment time and Cumulative MU were used for clinical review on Tomo_edge. Results : In case of using the same field width of Tomotherapy planning with FJ and DJ, the averaged variations were $V_{10%}$: -11.91%, $V_{25%}$: -7.6%, $V_{50%}$ :-4.75%, $V_{75%}$: -1.04%. Tomo_edge with a larger field width provides the averaged variations for target coverage: Dmin: -0.72%, CI: -1.25% and also shows the tendency of a sharp $V_{x%}$ decline in low dose area. The clinical improvements in the larger field width with DJ were observed in the treatment time, ranging from -51.21% to -15.11, and the Cumulative MU decrease, ranging from -57.74% to -15.31%. Conclusion : Target coverage achieved by FJ and DJ with the same field width has little differences. But integral doses on whole body efficiently decreased. Compared to the conventional HT delivery, Tomo_edge with a larger field width presents a little worse target coverage. However, it provides faster treatment delivery and improved cranial-caudal target dose conformity. Therefore, Tomo_edge mode is efficient in improving the treatment time and integral dose while maintaining comparable plan quality in clinic.