• Journal of Digital Contents Society
• /
• v.9 no.3
• /
• pp.441-448
• /
• 2008

Recently, several algorithms for scheduling aperiodic tasks have been proposed. Among them, Abdelzaher et al proposed an algorithm to determine the schedulability of aperiodic tasks, and proved that the aperiodic tasks are schedulable if the upperbound of synthetic utilization is less than or equal to $\frac 1{1+\sqrt{1/2}}{\approx}0.59$. But this algorithm has a drawback in that if some tasks, even though they are completed and have no more execution times, are included in the current invocation set, their execution times and deadlines are added to the synthetic utilization. This may lead to a problem in which actually schedulable tasks are decided not to be schedulable. In this paper, we recognize the above mentioned problem and propose an improved synthetic utilization method that can be used to schedule aperiodic tasks more efficiently.

• Progress in Superconductivity and Cryogenics
• /
• v.16 no.2
• /
• pp.36-41
• /
• 2014

Temperature dependence of magnetic moment (m-T) and the magnetization (M-H) at 5 K and 20 K of the in situ processed $MgB_2$ bulk pellets with/without carbon (C) doping were examined. The superconducting critical temperature ($T_c$), the superconducting transition width (${\delta}T$) and the critical current density ($J_c$) were estimated for ten test samples taken from the $MgB_2$ bulk pellets. The reliable m-T characteristics associated with the uniform $MgB_2$ formation were obtained for both $MgB_2$ pellets. The $T_cs$ and ${\delta}Ts$ of all test samples of the undoped $MgB_2$ were the same each other as 37.5 K and 1.5 K, respectively. The $T_cs$ and ${\delta}Ts$ of the C-doped $MgB_2$ were 36.5 K and 2.5 K, respectively. Unlike the m-T characteristics, there existed the difference among the M-H curves of the test samples, which might be caused by the microstructure variation. In spite of the slight $T_c$ decrease, the C doping was effective in enhancing the $J_c$ at 5 K.

• KEPCO Journal on Electric Power and Energy
• /
• v.8 no.1
• /
• pp.43-48
• /
• 2022

Although the distribution system has been structured as complicated as a mesh in the past, the connection points for each line are always kept open, so that it is operated as a radial distribution system (RDS). For RDS, the line utilization rate is determined according to the maximum load on the line, and the utilization rate is usually kept low. In addition, when a fault occurs in the RDS, a power outage of about 3 to 5 minutes occurs until the fault section is separated, and the healthy section is transferred to another line. To improve the disadvantages of the RDS, research on the construction of a networked distribution system (NDS) that linking multiple lines is in progress. Compared to the RDS, the NDS has advantages such as increased facility utilization, load leveling, self-healing, increased capacity connected to distributed generator, and resolution of terminal voltage drop. However, when a fault occurs in the network distribution system, fault current can flow in from all connected lines, and the direction of fault current varies depending on the fault point, so a high-precision fault current direction determination method and high-speed communication are required. Therefore, in this paper, we propose an accurate fault current direction determination method by comparing the peak value polarity of the fault current in the event of a fault, and a communication-based protection coordination method using this method.

• Progress in Superconductivity and Cryogenics
• /
• v.14 no.2
• /
• pp.28-31
• /
• 2012

The study on the dielectric characteristics of gaseous insulation medium is important for designing current leads of superconducting machines using a sub-cooled liquid nitrogen ($LN_2$) cooling method. In a sub-cooled $LN_2$ cooling system, the temperature of gaseous insulation medium surrounding current leads varies from the temperature of coolant to 300 K according to the displacement between the electrode system and the surface of sub-cooled $LN_2$. In this paper, AC withstand voltage experiments on gaseous nitrogen according to temperature are conducted. Also, AC withstand voltage experiments on gaseous nitrogen according to pressure, size of electrode, and gap length between two electrodes are performed. It is found that there is a functional relation between the electrical breakdown voltage and the field utilization factor (${\xi}$). As a result, the empirical formula for estimating an electrical breakdown voltage is deduced by adopting the concept of field utilization factors. It is expected that the experimental results presented in this paper are helpful to design current leads for a high voltage superconducting apparatus such as a superconducting fault current limiter (SFCL) using a sub-cooled $LN_2$ cooling system.

• Journal of Fisheries and Marine Sciences Education
• /
• v.28 no.4
• /
• pp.947-956
• /
• 2016

This study analysed the documents of Sea Area Utilization Consultation of JongChun and ApHae located in West Coast of Korea and NaJeong located in East Coast of Korea in order to find out problems of site surveys and numerical simulations for coastal erosion projects of ocean physics, and suggested the improvement way to go. Current especially like wave-induced current is the one of the important external forces to handle coastal erosion but underestimated in the west coast. In case of east coast the various tests including wave-induced current were conducted but less efficient to find out the reasons of coastal erosion. The stiffness structure to protect coastal line like beach made the secondary erosion by using them without sufficient analysis for the erosion. In order to consult a Sea Area Utilization Consultation those are needed to review the scenarios for external forces such as wave and tidal currents, the site surveys for external forces, the net sediment analysis for years, the long periods of monitoring, and the guide line and revision of the rule for coastal erosion.

• Korean Journal of Materials Research
• /
• v.24 no.9
• /
• pp.465-468
• /
• 2014

The crystallization effects of boron (B) powder on the phase, full width at half maximum (FWHM) values, and critical properties were investigated for in-situ reacted $MgB_2$ bulk superconductors. The semi-crystalline B powder was heat-treated at different temperatures of 1000, 1300 and $1500^{\circ}C$ for 5 hours in an Ar atmosphere. Then, using as-received and heat-treated B powders, the $MgB_2$ samples were prepared at $600^{\circ}C$ for 40 hours in an Ar atmosphere. As the heat-treatment temperature of the B powder increased, both the particle size of the B powder and crystalline phase increased. In the case of $MgB_2$ samples using B powders heat-treated at above $1300^{\circ}C$, unreacted magnesium (Mg) and B remained due to the improved crystallinity of the B powder. As the heat-treatment temperature of B powder increased, the critical current density of $MgB_2$ decreased continuously due to the reduction of grain boundary density and superconducting volume caused by unreacted Mg and B.

• Journal of the Korea Society of Computer and Information
• /
• v.29 no.5
• /
• pp.143-153
• /
• 2024

This study aims to analyze both the current utilization of e-learning in the scuba diving education sector and the possible improvements by using Delphi analysis. The study administered three rounds of Delphi surveys with 25 specialists, including business executives and educational leaders from scuba diving centers and resorts affiliated with organizations that conduct scuba diving education through e-learning. The comparative analysis of the state of e-learning utilization and factors for improvement revealed significant insights. In terms of expected benefits, the analysis highlighted an increase in user convenience, temporal flexibility in learning activities, and easy access to products. However, it identified major issues such as the simplistic mandatory exams, inadequate professional depth in the feedback provided, and a lack of bidirectional communication between learners and instructors. Recommendations for improvements included enhancing communication through various online communities, conducting mandatory exams offline, and developing a variety of content. Conducting regular program quality evaluations, integrating with various diving communities, and assigning dedicated tutors were deemed crucial factors for future development.

• International conference on construction engineering and project management
• /
• 2015.10a
• /
• pp.299-303
• /
• 2015

Flexible space is an adaptable space that has been increasingly used in many office and academic buildings as it increases the use of the space available and reduces the unnecessary building area. However, the architectural, engineering and construction (AEC) industry lacks a formalized method that helps architects predict and update the space utilization of flexible space during the project development, as such prediction aims to maximize the use of the building space available without exceeding the target utilization policy. Consequently, current manual utilization prediction results in lower accuracy level and limits the maximized use of the flexible space, which has multiple space-use types that affect the prediction of utilization. To address this problem, we identified eight space-use type differentiators (SUTDs) based on the literature review and observations and discussed the use of them in automated space-use analysis (SUA), which can predict the utilization of flexible space via a computer program. This research builds on SUA and contributes to flexible space planning by providing a means of a more comprehensive and accurate SUA.

• Explosives and Blasting
• /
• v.17 no.3
• /
• pp.72-73
• /
• 1999

• Food preservation and processing industry
• /
• v.9 no.2
• /
• pp.21-31
• /
• 2010