• 한국통신학회논문지
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• 제31권10B호
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• pp.909-918
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• 2006

최근 인터넷 유선망 뿐 아니라 무선 IP 이동 망에서의 통화 품질 및 서비스 품질(QoS)의 지원 및 관리체계는 매우 중요한 문제로 대두되고 있다. 지금까지 연구된 인터넷 망의 QoS 제공 모델들은 통합서비스(IntServ) 모델, 차등서비스(DiffServ)모델 및 MPLS 등이 대표적이다. 한편, 무선 인터넷 망의 이동성 관리를 위해서 IETF에서는 MIPv4(Mobile IPv4)와 MIPv6 권고안들을 제안하고 있다. 그러나, 이들은 TCP 및 UDP/IP 환경을 근간으로 하여 QoS를 관리하고 이동성의 핸드오버(handover)등을 관리하기 위한 체계들로 많은 중요한 문제들을 야기하고 있다. 본 논문에서는 멀티홈잉와 멀티 스트리밍 기능을 제공하는 전송계층 프로토콜로 설계된 SCTP(Stream Control Transport Protocol)을 이용하여 IP 이동 환경에서 끊김없는(seamless) 서비스 품질을 제공할 수 있는 관리구조(mSCTP)를 언급하고, 이 환경에서의 종단간 QoS 관리체계를 제안한다. 이를 위해서 본 논문에서는 종단간 통신은 SCTP의 멀티홈잉 기능을 이용하고, 이를 통합서비스 모델과 결합하여 IP 이동성환경에서 끊김 없는 QoS 관리 서비스 목적을 달성할 수 있도록 설계하고 이를 평가한다.

• 디자인학연구
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• 제19권2호
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• pp.195-206
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• 2006

컴퓨터 게임 산업의 급속한 성장에도 불구하고 대부분의 게임 타이틀들이 현격한 수익을 내지 못하는 실정이다. 기존마케팅 이론에 의하면 제품의 성공과 실패는 고객의 선호도, 필요, 기대에 대한 만족도에 의존한다고 한다. 역시 게임에서도 사용자의 만족을 극대화하기 위해서는 사용자들이 무엇을 원하고, 좋아할지를 파악하여 이를 게임에 반영할 필요가 있다 본 연구의 목표는 컴퓨터 게임의 사용성 평가를 위한 핵심 디자인 요인을 고찰하는데 있다. 본 연구는 기존의 게임 관련 문헌 고찰을 통하여 사용성 평가 핵심 디자인 요인을 도출하고 게임 플레이 과제와 사후 설문결과를 통하여 MMO (Massively Multi-player Online) 게임 사용성 평가를 실시하여 18가지 사용성 문제점과 그 권장사항을 제시하였다. 그 결과 게임 인터페이스, 게임 플레이, 게임 서사, 게임메커니즘으로 구성된 54 개의 사용성 평가 핵심 디자인 요인을 도출하고 MMO 게임을 위한 새로운 사용성 평가 체계를 개발하였다. 본 연구 결과는 MMO게임 디자인 프로세스의 초기 단계에서 효과적인 디자인 의사결정을 지원하고 게이머의 행동을 이해하는데 중요한 시사점을 제공 할 것으로 기대 된다.

• Smart Structures and Systems
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• 제22권1호
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• pp.81-94
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• 2018

Automatic Generation Control (AGC) has functionally controlled the interchange power flow in order to suppress the dynamic oscillations of frequency and tie-line power deviations as a perturbation occurs in the interconnected multi-area power system. Furthermore, Flexible AC Transmission Systems (FACTS) can effectively assist AGC to more enhance the dynamic stability of power system. So, Static Synchronous Series Compensator (SSSC), one of the well-known FACTS devices, is here applied to accurately control and regulate the load frequency of multi-area multi-source interconnected power system. The research and efforts made in this regard have caused to introduce the Fractional Order Proportional Integral Derivative (FOPID) based SSSC, to alleviate both the most significant issues in multi-area interconnected power systems i.e., frequency and tie-line power deviations. Due to multi-objective nature of aforementioned problem, suppression of the frequency and tie-line power deviations is formularized in the form of a multi-object problem. Considering the high performance of Multi Objective Bees Algorithm (MOBA) in solution of the non-linear objectives, it has been utilized to appropriately unravel the optimization problem. To verify and validate the dynamic performance of self-defined FOPID-SSSC, it has been thoroughly evaluated in three different multi-area interconnected power systems. Meanwhile, the dynamic performance of FOPID-SSSC has been accurately compared with a conventional controller based SSSC while the power systems are affected by different Step Load Perturbations (SLPs). Eventually, the simulation results of all three power systems have transparently demonstrated the dynamic performance of FOPID-SSSC to significantly suppress the frequency and tie-line power deviations as compared to conventional controller based SSSC.

• 한국컴퓨터정보학회논문지
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• 제24권12호
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• pp.75-84
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• 2019

함정 전투체계에는 레이더 장비, 수중센서 장비, 함포 및 미사일 제어용 무장통제 장비들과 같이 체계를 운용하기 위해 필요한 여러 장비들과 이를 통제하기 위한 다기능콘솔이 구성되어 있다. 다기능 콘솔에는 장비들의 상태정보 전시 및 장비들을 통제하기 위한 HCI 기반의 소프트웨어가 탑재되어 있고, 운용자는 탑재된 소프트웨어를 활용하여 함정 전투체계를 운용한다. 하지만 함정 전투체계를 장시간 운용함에 있어 다기능콘솔 전시기의 구조로 인한 신체적 불편함, 다양하고 복잡한 HCI 구성으로 인한 운용자의 피로도 증가 등 문제점들이 발생하고 있다. 이러한 문제점들은 함정 전투체계 운용성을 저하시키는 중요한 요인이 된다. 이를 해결하기 위해, 본 논문에서는 함정 전투체계 개발자들을 대상으로 한 설문조사를 바탕으로 신체적 불편함을 줄일 수 있는 다기능콘솔 전시기 구조 설계와 운용자의 피로도를 줄일 수 있는 직관적인 HCI 설계 방안을 제안한다. 이로 인해, 향후 함정 전투체계 운용자들에게 편의성을 제공하여 기존 함정 전투체계보다 운용성을 향상 시킬 수 있는 장점을 가진다.

• Journal of Electrical Engineering and Technology
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• 제13권4호
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• pp.1459-1473
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• 2018

This paper focuses on voltage control schemes for multi-terminal low-voltage direct current (LVDC) distribution systems. In a multi-terminal LVDC distribution system, there can be multiple AC/DC converters that connect the LVDC distribution system to the AC grids. This configuration can provide enhanced reliability, grid-supporting functionality, and higher efficiency. The main applications of multi-terminal LVDC distribution systems include flexible power exchange between multiple power grids and integration of distributed energy resources (DERs) using DC voltages such as photovoltaics (PVs) and battery energy storage systems (BESSs). In multi-terminal LVDC distribution systems, voltage regulation is one of the most important issues for maintaining the electric power balance between demand and supply and providing high power quality to end customers. This paper focuses on a voltage control method for multi-terminal LVDC distribution system that can efficiently coordinate multiple control units, such as AC/DC converters, PVs and BESSs. In this paper, a control hierarchy is defined for undervoltage (UV) and overvoltage (OV) problems in LVDC distribution systems based on the control priority between the control units. This paper also proposes methods to determine accurate control commands for AC/DC converters and DERs. By using the proposed method, we can effectively maintain the line voltages in multi-terminal LVDC distribution systems in the normal range. The performance of the proposed voltage control method is evaluated by case studies.

• 한국IT서비스학회지
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• 제18권3호
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• pp.17-35
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• 2019

Call centers do not simply play a role of responding to customers' calls, but they have developed into a core unit for maintaining competitiveness through services, marketing, or sales. Since the service quality of call centers heavily affects customer satisfaction, organizations have focused on enhancing it by reducing waiting time and increasing service level. One of the techniques, which improve the service quality of call centers, is to employ multi-skilled agents that can handle more than one type of calls. This study deals with three issues relevant to multi-skilled agents. First, we analyze how the way of allocating a specific group of agents to a set of skills affects the performance of call centers. Secondly, we investigate the relationship between the number of multi-skilled agents and the performance of call centers. Finally, we examine the impact of agent selection rules on the performance of call centers. Two selection rules are compared : the first rule is to assign a call to any available agent at random while the other rule is to assign a call preferably to single-skilled agents over multi-skilled agents when applicable. Based on simulation experiments, we suggest three implications. First, as the length of cycles in the agent-skill configuration network becomes longer, call centers achieve higher service level and shorter waiting time. Secondly, simulation results show that as the portion of multi-skilled agents increases, the performance of call centers improves. However, most of the improvement is attained when the portion of multi-skilled agents is relatively low. Finally, the agent selection rules do not significantly affect the call centers' performance, but the rule of preferring single-skilled agents tends to distribute the workload among agents more equally.

• 한국태양에너지학회 논문집
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• 제27권3호
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• pp.161-167
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• 2007

Zero Energy Multi-House(ZeMH) signifies a residential building which can be self sufficient with just new and renewable energy resources without the aid of any existing fossil fuel. For success of ZeMH, various innovative energy technologies Including passive and active systems should be well integrated with a systematic design approach. The first step for ZeMH is definitely to minimize the conventional heating and cooling loads over 50% with major energy conservation measure and passive solar features which are mainly related to building design components such as super-insulation, super window, including infiltration and ventilation issues. The purpose of this study is to analyze the thermal effect of various building design components in the early design of ZeMH. The process of the study is presented in the following. 1) selection reference model for simulation 2) verification of reference model with computer simulation program(ESP-r 9.0). 3) analysis of effect according to insulation-thickness, kinds of windows, rate of infiltration. and The simulation results indicate that almost 50% savings of conventional heating load in multi-house can be achieved with the optimum design of building components such as super insulation, super window, infiltration, ventilation.

• 한국항공운항학회지
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• 제18권3호
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• pp.55-69
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• 2010

The role of airports in the metropolitan area in Korea is very important which is located on the center of Northeast Asia considered as the highest potential growth continent in the world air transport market. This study includes comparison on service quality between Gimpo Airport and Incheon Airport which are indicated as multi-airport system in the metropolitan area appraised by passengers from Korea, Japan and China, and analysis on primary factors of airport service which affect the customer satisfaction and loyalty. The service quality appraised in the order of Chinese, Korean, and Japanese and the analysis result indicated that the service quality factors which influence on customer satisfaction and loyalty were all different among passengers from three countries. Information service was the priority factor for customer satisfaction to Chinese and Korean, but Japanese considered that personal service was the most important factor. This research paper tried to provide many current issues and guides to operational strategy including plan for the specialized routes of multi-airport system in domestic metropolitan area.

• Journal of Pharmaceutical Investigation
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• 제41권5호
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• pp.263-272
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• 2011

Tablet dosage forms have been preferred over other formulations for the oral drug administration due to their low manufacturing costs and ease of administrations, especially controlled-release applications. Controlled-release tablets are oral dosage forms from which the active pharmaceutical ingredient (API) is released over an intended or extended period of time upon ingestion. This may allow a decrease in the dosing frequency and a reduction in peak plasma concentrations and hence improves patient compliance while reducing the risk of undesirable side effects. Conventional singlelayered matrix tablets have been extensively utilized to deliver APIs into the body. However, these conventional single-layered matrix tablets present suboptimal delivery properties, such as non-linear drug delivery profiles which may cause higher side effects. Recently, a multi-layered technology has been developed to overcome or eliminate the limitations of the singlelayered tablet with more flexibility. This technology can give a good opportunity in formulating new products and help pharmaceutical companies enhancing their life cycle management. In this review, a brief overview on the multi-layered tablets is given focusing on the various tablet designs, manufacturing issues and drug release profiles.

• 설비공학논문집
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• 제22권6호
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• pp.337-344
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• 2010

Good plant-growth conditions can be achieved by means of using greenhouses. One of the main issues in greenhouse cultivation is energy savings through the development of high efficient heating and cooling system. GSHPs are one of the recommended systems to cope with this pending need. The aim of this study is to investigate the heating performance of ground source multi-heat pump system installed in a greenhouse under part load conditions. Daily average heating COP of the heat pump unit was very high by at least 7.4, because of relatively large condenser, evaporator, and mass flow rate through ground loop heat exchanger. However, the system COP, overall heating coefficient of the performance of the system with heat pump unit and GLHX, decreased drastically due to relatively large power consumption of circulating pump under part load condition. It is suggested that the technology to enhance the performance of the ground source multi-heat pump system for a greenhouse under part load conditions should be developed.