• KSII Transactions on Internet and Information Systems (TIIS)
• /
• 제6권8호
• /
• pp.1964-1981
• /
• 2012

In this paper a reversible data hiding scheme based on histogram shifting of host image blocks is presented. This method attempts to use full available capacity for data embedding by dividing the image into non-overlapping blocks. Applying histogram shifting to each block requires that extra information to be saved as overhead data for each block. This extra information (overhead or bookkeeping information) is used in order to extract payload and recover the block to its original state. A method to eliminate the need for this extra information is also introduced. This method uses maximum gap that exists between histogram bins for finding the value of pixels that was used for embedding in sender side. Experimental results show that the proposed method provides higher embedding capacity than the original reversible data hiding based on histogram shifting method and its improved versions in the current literature while it maintains the quality of marked image at an acceptable level.

• Journal of Power Electronics
• /
• 제19권5호
• /
• pp.1303-1314
• /
• 2019

This paper studies the harmonic characteristics of ship electric propulsion systems and their treatment methods. It also adopts effective measures to suppress and prevent ship power systems from affecting ship operation due to the serious damage caused by harmonics. Firstly, the harmonic characteristics of a ship electric propulsion system are reviewed and discussed. Secondly, aiming at problems such as resonant frequency and filter characteristics variations, resonance point migration, and unstable filtering performances in conventional passive filters, a method for fully tuning of a passive dynamic tunable filter (PDTF) is proposed to realize harmonic suppression. Thirdly, to address the problems of the uncontrollable inductance L of traditional air gap iron core reactors and the harmonics of power electronic impedance converters (PEICs), this paper proposes an electromagnetic coupling reactor with impedance transformation and harmonic suppression characteristics (ECRITHS), with the internal filter (IF) designed to suppress the harmonics generated by PEICs. The ECRITHS is characterized by both harmonic suppression and impedance change. Fourthly, the ECRITHS is investigated. This investigation includes the harmonic suppression characteristics and impedance transformation characteristics of the ECRITHS at the fundamental frequency, which shows the good performance of the ECRITHS. Simulation and experimental evaluations of the PDTF are carried out. Multiple PDTFs can be configured to realize multi-order simultaneous dynamic filtering, and can effectively eliminate the current harmonics of ship electric propulsion systems. This is done to reduce the total harmonic distortion (THD) of the supply currents to well below the 5% limit imposed by the IEEE-519 standard. The PDTF also can eliminate harmonic currents in different geographic places by using a low voltage distribution system. Finally, a detailed discussion is presented, with challenges and future implications discussed. The research results are intended to effectively eliminate the harmonics of ship electric power propulsion systems and to improve the power quality of ship power systems. This is of theoretical and practical significance for improving the power quality and power savings of ship power systems.

• Korea-Australia Rheology Journal
• /
• 제15권2호
• /
• pp.55-61
• /
• 2003

The steady shear flow properties of vaseline generally used as a base of the pharmaceutical dosage forms were studied in the consideration of wall slip phenomenon. The purpose of this study was to show that how slip may affect the experimental steady-state flow curves of semisolid ointment bases and to discuss the ways to eliminate (or minimize) wall slip effect in a rotational rheometer. Using both a strain-controlled ARES rheometer and a stress-controlled AR1000 rheometer, the steady shear flow behavior was investigated with various experimental conditions ; the surface roughness, sample preparation, plate diameter, gap size, shearing time, and loading methods were varied. A stress-controlled rheometer was suitable for investigating the flow behavior of semisolid ointment bases which show severe wall slip effects. In the conditions of parallel plates attached with sand paper, treated sample, smaller diameter fixture, larger gap size, shorter shearing time, and normal force control loading method, the wall slip effects could be minimized. A critical shear stress for the onset of slip was extended to above 10,000 dyne/$\textrm{cm}^2$. The wall slip effects could not be perfectly eliminated by any experimental conditions. However, the slip was delayed to higher value of shear stress by selecting proper fixture properties and experimental conditions.

• 디지털콘텐츠학회 논문지
• /
• 제19권2호
• /
• pp.285-292
• /
• 2018

최신 ICT 기술은 4차 산업혁명의 핵심으로 향후 각종 산업발전의 교두보 역할을 담당할 것으로 예상되고 있으나 여전히 ICT기술의 격차가 빈부의 격차로 직결되며 그 격차는 더 벌어지고 있다. 개도국에서의 여성 ICT 역량 강화교육은 국가발전을 위한 양질의 인력을 양성할 수 있는 기회가 되고 기술격차를 해소할 수 있는 방안이라고 할 수 있다. 본 연구는 개도국의 학생들에게 교육을 통해 ICT 기술을 보급하기 위한 준비단계로서, 인도네시아의 UHP 대학의 인프라 및 ICT교육현황을 조사하고자 한다. 이에 근거하여 여대생들에게 적절한 ICT 교육콘텐츠를 개발하고 지속적인 교육을 위해 필요한 정책을 제언하고자 한다. 또한 기존연구인 Life 대학 설문조사 결과와 비교분석하여 교육의 효율성을 제고하는 교수법을 모색하고자 한다.

• Journal of Magnetics
• /
• 제18권2호
• /
• pp.117-124
• /
• 2013

Single-phase, brushless DC (BLDC) motors have unequal air-gaps to eliminate the dead-point where the developed torque is zero. Unfortunately, these unequal air-gaps can deteriorate the motor characteristics in the cogging torque. This paper proposes a novel design for a single-phase BLDC motor with an asymmetric notch to solve this problem. In the design method, the asymmetric notches were placed on the stator pole face, which affects the change in permanent magnet shape or the residual flux density of the permanent magnet. Parametric analysis was performed to determine the optimal size and position of the asymmetric notch to reduce the cogging torque. Finite element analysis (FEA) was used to calculate the cogging torque. A more than 28% lower cogging torque compared to the initial model with no notch was achieved.

• Journal of Electrical Engineering and Technology
• /
• 제13권5호
• /
• pp.1978-1985
• /
• 2018

In this paper, a novel single-phase hybrid switched reluctance motor (HSRM) is proposed for hammer breaker application. The hammer breaker requires only unidirectional rotation and high-speed operation. To satisfy the requirements and eliminate torque dead-zone, the rotor of the proposed 4/4 poles SRM is designed with wider pole arc and non-uniform air-gap. This motor has a simple structure and produces low torque ripple. Permanent magnets (PMs) are mounted on the inner stator at a certain position which enables it to park the rotor for self-start and create positive cogging torque in the torque dead-zone. Compared with conventional single-phase switched reluctance motor, HSRM has an increased torque density and relatively low torque ripple. To verify effectiveness, finite element method (FEM) is employed to analyze the performance of the proposed structure. Then, the proposed motor is compared with the existing motor drive system for the same application. The proposed HSRM is easy to manufacture along with competitive performance.

• 기술혁신연구
• /
• 제22권1호
• /
• pp.89-117
• /
• 2014

창조경제를 견인하기 위해 다양성과 창의성이 중시되는 환경에서 여성과학기술인력의 활용은 무엇보다 중요해지고 있으며, 경제적 지위를 측정하는 기준으로 노동의 시장가격인 임금에 대한 분석을 통해 성차별을 인식하고 개선하기 위한 노력이 필요하다. 이에 본 연구에서는 Oaxaca-Ransom 임금분해 방법(1994)을 활용하여 과학기술인력을 대상으로 남녀 임금에 미치는 영향 요인 및 성별 임금 분해를 실시하였다. 연구결과는 다음과 같다. 첫째, 과학기술인력의 특성을 살펴보면 여성의 평균 임금 수준은 남성의 65%에 불과하며, 학력 등 개인적 특성에서 남성이 우세한 것으로 나타났다. 둘째, 임금에 영향을 미치는 변수를 살펴보면 여성과 남성 모두 학력 연령이 높을수록, 근무기간 및 주당근로시간이 많을수록, 관리자 직종에 근무할수록 임금 프리미엄이 존재하는 것으로 나타났다. 셋째, 남성과 여성의 임금분해 결과를 살펴보면, 과학기술인력의 경우 개인적 특성에 의한 생산성 차이가 약 58%, 노동시장에서의 특성에 기인한 성별에 의한 차별은 41%로 나타났다. 비과학기술인력에 비교하였을 시 과학기술인력이 생산성으로 인한 임금격차가 크며 성별에 의한 차별은 덜 한 것으로 나타났다. 그러나, 전공별 및 학력별로 분석한 결과 성에 의한 여성차별은 전체 인력 중 여성의 비율이 낮을수록 노동시장에서 임시근로자 비율이 높을수록 심한 것으로 나타났다. 이를 개선하기 위해서는 여성과학기술인력의 노동시장에서의 여성 불균형 현상이 무엇보다 필요하며, 여성스스로는 개인의 역량을 지속적으로 강화하는 노력이 수반되어야 할 것이다.

• Journal of Electrical Engineering and Technology
• /
• 제11권4호
• /
• pp.878-888
• /
• 2016

Cogging torque has a negative impact on the operation of permanent magnet machines by increasing torque ripple, speed ripple, acoustic noise and vibration. In this paper Magnet Shifting Method has been used as a tool to reduce the cogging torque in inset Line Start Permanent Magnet Synchronous Motor (LSPMSM). It has been shown that Magnet Shifting Method can effectively eliminate several lower-order harmonics of cogging torque. In order to implement the method, first the expression of cogging torque is studied based on the Fourier analysis. An analytical expression is then introduced based on Permanent Magnet Shifting to reduce cogging torque of LSPMS motors. The method is applied to some existing machine designs and their performances are obtained using Finite Element Analysis (FEA). The effect of magnet shifting on pole mmf (magneto motive force) distribution in air gap is discussed. The side effects of magnet shifting on back-EMF, core losses and torque profile distortion are taken into account in this investigation. Finally the experimental results on two prototypes 24 slot 4 pole inset LSPMS motors have been used to validate the theoretical analysis.

• 대한산업공학회지
• /
• 제38권3호
• /
• pp.220-226
• /
• 2012

The Electric discharge machining (EDM) process is used to minimize the difference between designed feature and machined feature while the most workpiece is removed through the cutting processes. The tiny-deep hole machining and perpendicular wall machining in mold and die are good applications of EDM. Among EDM equipment, the super drill uses the hollowed electrode to eliminate the debris which causes the second discharge with the electrode and degrades the machining quality. Through the hollow, the high pressured discharge oil is supplied to remove the debris together with the spindle rotation. The thin-hollow electrode tends to easily wear out compared to the sold die-sinking electrode and its wear rate is might not allowed to monitor in real time during discharging. Up to now, the wear amount is measured by off line method, which leads machining time to increase because the hole pass-through moment can be check by visual (manually) with the extra tool path. Therefore, this study suggests the attractive method to evaluate the hole pass-through moment in which the gap voltage and z-axis encoder pulse are monitored to predict the moment. The commercial super drill is used to validate the proposed method and the experiment is carried out.

• 소성∙가공
• /
• 제19권6호
• /
• pp.329-336
• /
• 2010

Ring forging process is more appropriate for high-length and thin walled ring, because it utilizes the forging press and hence does not require heavy-duty ring rolling mill. Although ring forging process is very simple and economic for facilities, the process is not efficient because of multi-forging-step and low material utilization. An effective ring forging process is developed using a hollow ingot. When a hollow ingot is used with a workpiece, the ingot can be forged into a final ring without multi-stage pre-forging process, such as, cogging, upsetting, and piercing, etc.. Finally it has advantages of the material utilization and process improvement because a few reheating and forging process are not necessary to make workpiece for ring forging. The important design variables are the applied plastic deformation energy to eliminate cast structure and make uniform properties. In this study, the mechanical properties after forging of hollow cast ingot were investigated from the experiment using circumferential sectional model. Also, the effects of process variables were studied by FEM simulation on the basis of thermo-visco-plastic constitutive equation. Applied strain is different at each position in length direction because diameter of hollow ingot is different in length direction. The different strain distribution become into a narrow gap by additional plastic deformation during diameter extension process.