• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.17 no.1
• /
• pp.151-157
• /
• 2013

In this paper, a comparative analysis of PBTI induced device degradation in nanowire n-channel junctionless and inversion mode Multiple-Gate MOSFET(MuGFETs) has been performed. It has been observed that the threshold voltage is increased after PBTI stress and the threshold voltage variation of junctionless device is less significant than that of inversion mode device. However the degradation rate of junctionless device is less significant than that of inversion mode device. The activation energy of the device degradation is larger in inversion mode device than junctionless device. In order to analyze the more significant PBTI induced device degradation in inversion mode device than junctionless device, 3-dimensional device simulation has been performed. The electron concentration in inversion mode device is equal to the one in junctionless device but the electric field in inversion mode device is larger than junctionless device.

• Solar Energy
• /
• v.16 no.2
• /
• pp.15-37
• /
• 1996

Most of the world's energy demand is met by fossil fuels, mainly petroleum and natural gas. Even though their production is not keeping up with the demand, there are many options before us-solar energy in its direct and indirect forms, nuclear breeders, thermonuclear power, geothermal energy, synthetic fluid fuels, and hydrogen as energy carrier to complement the nonfossil energy sources. But, before these energy alternatives can be utilized, in most cases, it is necessary to conduct extensive research and development work. In order to solve global energy and environmental issues, it is very important to develop and install energy supply systems which utilizes natural energy. The installation of these systems brings the following merits from the viewpoints of energy saving or environmental protection-(a) the positive use of natural energy reduces fossil fuel consumption; and (b) it also prevents environmental degradation. In this paper, the types of natural energy considered is confined to the solar, wind, hydraulic, geothermal and ocean-wave energy. And, the objective of the paper is to describe the state of the art of natural energy and future utilization prospect of them.

• Transactions on Electrical and Electronic Materials
• /
• v.18 no.2
• /
• pp.111-118
• /
• 2017

The increased diversity of different types of energy sources requires moving towards smart distribution networks. This paper proposes a probabilistic DG (distributed generation) units planning model to determine technology type, capacity and location of DG units while simultaneously allocating ESS (energy storage systems) based on pre-determined capacities. This problem is studied in a wind integrated power system considering loads, prices and wind power generation uncertainties. A suitable method for DG unit planning will reduce costs and improve reliability concerns. Objective function is a cost function that minimizes DG investment and operational cost, purchased energy costs from upstream networks, the defined cost to reliability index, energy losses and the investment and degradation costs of ESS. Electrical load is a time variable and the model simulates a typical radial network successfully. The proposed model was solved using the DICOPT solver under GAMS optimization software.

• Journal of Energy Engineering
• /
• v.27 no.3
• /
• pp.63-67
• /
• 2018

The Democratic People's Republic of Korea, or the DPRK, is one of the poorest country in world facing chronic economic, energy and food security issues. Prolonged improper management of economic and natural resources has led to extreme poverty, malnutrition and critically vulnerability to nature's forces. Presistent deforestation and forest degradation in the DPRK has national and global consequences which has attracted attention from international community, whose offering financial and technical assistance for targeted interventions. Through REDD+ programs, the DPRK has the opportunity to establish its credentials as a responsible nation while improving the quality of life of its population. This study offers an enabling context under which suitable climate change action related to forestry can be identified and implemented in the DPRK.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.7 no.8
• /
• pp.1825-1842
• /
• 2013

Rapid growth of the IT industry has led to significant energy consumption in the last decade. Data centers swallow an enormous amount of electrical energy and have high operating costs and carbon dioxide excretions. In response to this, the dynamic consolidation of virtual machines (VMs) allows for efficient resource management and reduces power consumption through the live migration of VMs in the hosts. Moreover, each client typically has a service level agreement (SLA), this leads to stipulations in dealing with energy-performance trade-offs, as aggressive consolidation may lead to performance degradation beyond the negotiation. In this paper we propose a heuristic based resource allocation of VM selection and a VM allocation approach that aims to minimize the total energy consumption and operating costs while meeting the client-level SLA. Our experiment results demonstrate significant enhancements in cloud providers' profit and energy savings while improving the SLA at a certain level.

• Journal of the Korean Physical Society
• /
• v.73 no.11
• /
• pp.1675-1678
• /
• 2018

Methylammonium lead halide ($MAPbI_3$) perovskites are considered as promising materials owing to their excellent optical and electrical properties. However, perovskite materials suffer from degradation in air, which limits their practical applications. Here, we demonstrate successful passivation of the $MAPbI_3$ photodetectors through monochloro-para-xylylene (Parylene-C) deposition. The time-dependent photocurrent characteristics were systematically investigated, and we achieved significantly improved device performance and stability with Parylene-C passivation. Based on the excitation-power-dependent photoluminescence (PL) data, we confirmed that Parylene-C can reduce the carrier losses in $MAPbI_3$, leading to the enhancement of photocurrent and PL in $MAPbI_3$ photodetectors.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.62 no.7
• /
• pp.994-1002
• /
• 2013

This study suggests a generalized availability and safety evaluation model to evaluate the influences to the system's fault tolerant capabilities depending on automatic fault detection function such as the automatic periodic testings. The conventional evaluation model of automatic fault detection function deals only with the self diagnostics, and supposes that the fault detection coverage of self diagnostics is always constant. But all of the fault detection methods could be degraded. For example, the periodic surveillance test has the potential human errors or test equipment errors, the self diagnostics has the potential degradation of built-in logics, and the automatic periodic testing has the potential degradation of automatic test facilities. The suggested evaluation models have incorporated the loss or erroneous behaviors of the automatic fault detection methods. The availability and the safety of each module of the safety grade platform have been evaluated as they were applied the automatic periodic test methodology and the fault tolerant evaluation models. The availability and safety of the safety grade platform were improved when applied the automatic periodic testing. Especially the fault tolerant capability of the processor module with a weak self-diagnostics and the process parameter input modules were dramatically improved compared to the conventional cases. In addition, as a result of the safety evaluation of the digital reactor protection system, the system safety of the digital parts was improved about 4 times compared to the conventional cases.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.65 no.4
• /
• pp.555-560
• /
• 2016

Recently, many countries have placed great attention on energy security and climate changes. Governments are promoting the construction of renewable energy projects with regulatory support in Korea. Despite an increasing penetration of renewable resources, however, the photovoltaic and wind power are underutilized due to the endemic problems such as difficulties of output control and intermittent output. The Energy Storage System (ESS) is proposed as a good solution for solving the problems and has been studied in both the private business and the government. However, because of inefficient aspects, the research has been carried out for improving high costs and a small capacity. In addition, the ESS is currently installed for using only one purpose which is frequency regulation or transmission congestion relief such that has an economic limitation. Therefore, methods which are becoming economically justifiable to increase the penetration of the ESS is required. Thus, this paper presents in terms of operation efficiency to improve economic feasibility of the ESS currently used. mainly, there are two aspects for the operation efficiency. Firstly, it is intended to improve the utilization rate through a process that can utilize the ESS for various purposes. It is necessary to be able to use for other purposes by classifying and clustering for increasing the efficiency of availability. The clustering method is proposed to conduct the grouping the ESS. Especially, it is proposed to utilize ESS for frequency regulation service which is the one of ancillary services in the power system. Through case studies, it is confirmed to secure the necessary resources by clustering small size ESS.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.19 no.6
• /
• pp.10-17
• /
• 2015

In this study, to examine seismic reinforcement effect of a school building constructed prior to application of seismic design, a Double I-type damper supported by wall was installed to perform comparative analysis on existing non-seismic designed RC frame. As a result of experiment, while non-seismic designed specimen showed rapid reduction in strength and brittle shear destruction as damages were focused on top and bottom of left and right columns, reinforced specimen showed hysteretic characteristics of a large ellipse with great energy absorption ability, exhibiting perfectly behavior with increased strength and stiffness from damper reinforcement. In addition, as a result of comparing stiffness reduction between the two specimens, specimen reinforced by shear wall type damper was effective in preventing stiffness reduction. Energy dissipation ability of specimen reinforced by Double I-type damper was about 3.5 times as high as energy dissipation ability of non-reinforced specimen. Such enhancement in energy dissipation ability is considered to be the result of improved strength and deformation.

• Journal of Hydrogen and New Energy
• /
• v.24 no.1
• /
• pp.50-60
• /
• 2013

High temperature proton exchange membrane fuel cells (PEMFCs) using phosphoric acid (PA) doped polybenzimidazole (PBI) membranes have been concentrated as one of solutions to the limits with traditional low temperature PEMFCs. However, the amount of reported experimental data is not enough to catch the operational characteristics correlated with cell performance and durability. In this study, design of experiments (DOE) based operational optimization method for high temperature PEMFCs has been proposed. Response surface method (RSM) is very useful to effectively analyze target system's characteristics and to optimize operating conditions for a short time. Thus RSM using central composite design (CCD) as one of methodologies for design of experiments (DOE) was adopted. For this work, the statistic models which predict the performance and degradation rate with respect to the operating conditions have been developed. The developed performance and degradation models exhibit a good agreement with experimental data. Compared to the existing arbitrary operation, the expected cell lifetime and average cell performance during whole operation could be improved by optimizing operating conditions. Furthermore, the proposed optimization method could find different new optimal solutions for operating conditions if the target lifetime of the fuel cell system is changed. It is expected that the proposed method is very useful to find optimal operating conditions and enhance performance and durability for many other types of fuel cell systems.