• Journal of Communications and Networks
• /
• v.12 no.5
• /
• pp.433-441
• /
• 2010

Multihop transmission is a promising technique that helps in achieving broader coverage (excellent network connectivity) and preventing the impairment of wireless channels. This paper proposes a cluster-based multihop wireless network that makes use of the advantages of multihop relaying, i.e., path loss gain, and partial relay selection in each hop, i.e., spatial diversity. In this partial relay selection, the node with the maximum instantaneous channel gain will serve as the sender for the next hop. With the proposed protocol, the transmit power and spectral efficiency can be improved over those in the case of direct transmission and conventional multihop transmission. Moreover, at a high signal-to-noise ratio (SNR), the performance of the system with at least two nodes in each cluster is dependent only on the last hop and not on any of the intermediate hops. For a practically feasible decode-and-forward relay strategy, a compact expression for the probability density function of the end-to-end SNR at the destination is derived. This expression is then used to derive closed-form expressions for the outage probability, average symbol error rate, and average bit error rate for M-ary square quadrature amplitude modulation as well as to determine the spectral efficiency of the system. In addition, the probability of SNR gain over direct transmission is investigated for different environments. The mathematical analysis is verified by various simulation results for demonstrating the accuracy of the theoretical approach.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.18 no.2
• /
• pp.115-124
• /
• 2004

This paper suggested the vibration characteristic improvement by variation mode of ring type ultrasonic motor. Design for the piezoelectric ceramic and elastic body of stator were calculated by the finite element method(FEM) that consider the resonance frequency, vibration mode and coupling efficiency etc. Through the result of vibration analysis from 6 order mode to 8 mode, the 7 order mode was gained very an excellent results that it was the coupling efficient, minimum power loss and bending vibration value. Here over 7 order mode, was acquired that an output current for input voltage was very a large increased results. The result of vibration calculation, from thickness 0.5[mm] to 2[mm], know the fact that the vibration displacement at 0.5[mm] is an high value too. From such analysis result, this paper was manufactured the ultrasonic motor of outer diameter 50[mm], inter 22[mm] having the about 43.86[KHz] resonance frequency. We have gated that a simulation result is 42.2[KHz] and an experiment result is 43.86[KHz]. Then, a propriety of this paper was established the result almost similar to though comparison, investigation of simulation and experiment result.

• The Journal of the Korea Contents Association
• /
• v.15 no.9
• /
• pp.184-194
• /
• 2015

The present study set out to investigate influencing factors on family strength. The sample consisted of 249 male and female married adults who were in the class of social welfare in S cyber university. Analysis revealed that married adults' family strength level was 3.86(above the moderate). Among variables, marital status, religion, income, economic problems couple conflict, conflict with mother-in-law, children's problem, family of origin experiences were associated with family strength. Regression analysis revealed that family cooperation and harmony of family were associated with family strength among 8 sub-factors : overall emotional health of family, conflict resolution, acceptance of separation and loss, permission to others, harmony of family, family cooperation, independence in extended family, power balance in family. These findings highlight the collective characteristics of Korean family and traditional values emphasizing the harmony influences the family strength through the generation.

• Nuclear Engineering and Technology
• /
• v.52 no.3
• /
• pp.597-609
• /
• 2020

Accident Tolerant Fuels have been widely studied since the Fukushima-Daiichi accident in 2011 as one of the options on how to further enhance the safety of nuclear power plants. Deposition of protective coatings on nuclear fuel claddings has been considered as a near-term concept that will reduce the high-temperature oxidation rate and enhance accidental tolerance of the cladding while providing additional benefits during normal operation and transients. This study focuses on experimental testing of Zr-based alloys coated with Cr-based coatings using Physical Vapour Deposition. The results of long-term corrosion tests, as well as tests simulating postulated accidents, are presented. Zr-1%Nb alloy used as nuclear fuel cladding serves as a substrate and Cr, CrN, Cr_xN_y layers are deposited by unbalanced magnetron sputtering and reactive magnetron sputtering. The deposition procedures are optimized in order to improve coating properties. Coated as well as reference uncoated samples were experimentally tested. The presented results include standard long-term corrosion tests at 360℃ in WWER water chemistry, burst (creep) tests and mainly single and double-sided high-temperature steam oxidation tests between 1000 and 1400℃ related to postulated Loss-of-coolant accident and Design extension conditions. Coated and reference samples were characterized pre- and post-testing using mechanical testing (microhardness, ring compression test), Thermal Evolved Gas Analysis analysis (hydrogen, oxygen concentration), optical microscopy, scanning electron microscopy (EDS, WDS, EBSD) and X-ray diffraction.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.34 no.8
• /
• pp.1059-1065
• /
• 2010

An analysis was conducted to predict the hydraulic performance of a reactor coolant pump (RCP) of SMART at the off-design as well as design points. In order to reduce the analysis time efficiently, a single passage containing an impeller and a diffuser was considered as the computational domain. A stage scheme was used to perform a circumferential averaging of the flux on the impeller-diffuser interface. The pressure difference between the inlet and outlet of the pump was determined and was used to compute the head, efficiency, and break horse power (BHP) of a scaled-down model under conditions of steady-state incompressible flow. The predicted curves of the hydraulic performance of an RCP were similar to the typical characteristic curves of a conventional mixed-flow pump. The complex internal fluid flow of a pump, including the internal recirculation loss due to reverse flow, was observed at a low flow rate.

• Journal of Korea Port Economic Association
• /
• v.33 no.1
• /
• pp.89-110
• /
• 2017

The organization of the shipping conference -an international cartel, was approved by countries that recognized it for stabilizing routes as well as preventing excessive competition among liner shipping companies and recognized the characteristic of the liner service that is regularly repeated in the international liner shipping market. However, due to competition in bulk transportation and development of multimodal transport through new entrants, power expansion and vessel enlargement of non-aligned shipping companies; the shipping conference started collapsing, and was eventually abolished. As the shipping conference played an important role in the liner shipping market, there were changes in the competition structure of the liner shipping market, and this accordingly drove research on the effects of the abolition of the shipping conference on the liner shipping market. The effects of abolition of the shipping conference on the liner shipping market was analyzed after surveying the factors related to abolition of the shipping conference, and through the use of correlation and multiple regression analyses. Subsequent to the abolition of the shipping conference, the liner shipping companies increased global containership bottoms. Consequently, this led to fierce competition of freight charges. As a result, profitability of shipping companies diminished. However, shipping companies with a dominating cost structure recorded profits, while shipping companies with an inferior cost structure started recording a loss.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.35 no.12
• /
• pp.1383-1389
• /
• 2011

The current study focuses on the consistent analysis of heat transfer in multichannel volumetric solar receivers used for concentrating solar power. Changes in the properties of the absorbing material and channel dimensions are considered in an optical model based on the Monte Carlo ray-tracing method and in a one-dimensional heat transfer model that includes conduction, convection, and radiation. The optical model results show that most of the solar radiation energy is absorbed within a very small channel length of around 15 mm because of the large length-to-radius ratio. Classification of radiation losses reveals that at low absorptivity, increased reflection losses cause reduction of the receiver efficiency, notwithstanding the decrease in the emission loss. As the average temperature increases because of the large channel radius or small mass flow rate, both emission and reflection losses increase but the effect of emission losses prevails.

• Journal of the Korean Society for Aviation and Aeronautics
• /
• v.21 no.4
• /
• pp.119-125
• /
• 2013

Since year 2001 to the present time, the aircraft accidents and serious incidents in our country have surpassed 150 occurrences. The Boeing has published the statistical summary of commercial jet airplane accidents annually for the past 10 years on the basis of the occurrence categories defined by the CICTT(CAST/ICAO Common Taxonomy Team), and the number of occurrences is in order of loss of control(LOC-I), controlled flight into terrain(CFIT) and runway excursion (RE). Like the NTSB and the EASA, when fatal and non-fatal accidents are aggregated, though fatality rate is low, abnormal runway contact(ARC), system/component failure(SCF-PP/NP), ground handling(RAMP) rank high in the CICTT occurrence categories. With the less occurrence frequency, it is difficult to statistically analyze the aircraft accidents in our country, thus customarily the accidents and the serious incidents on aggregate are consolidated, and the statistical analysis is performed. This study categorizes the accidents and serious incidents to the domestic transportation aircraft in the past 10 years according to the CICTT occurrence categories, that is compared with foreign practices, and the implications have been discussed. From years 2001 through 2010, the accidents to the domestic transportation aircraft occurred in order of system failure(SCF-NP), ARC and power plant failure(SCF-PP), and when the accidents and the serious incidents are consolidated and analyzed, it is verified that a distribution appears similar to the European accident occurrence categories defined from 300 accident occurrence data.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.39C no.9
• /
• pp.757-766
• /
• 2014

To compensate signal loss due to the channel blockage in satellite communication link, we propose a cooperative communication scheme for OTM(On-The-Move) terminal in next generation satellite communication systems. The proposed scheme configures cooperation subnet with adjacent OTM terminal with the help of ground communication equipment. Shared data is spread by orthogonal spreading code, then the spread sequences are transmitted simultaneously. The receiver combines the power of received signals by EGC(Equal gain combining). The OTM terminal blockage channel is modeled by 2-state Markov chain. We evaluate the bit error rate according to the blockage channel of the channel state for the performance analysis of the proposed scheme. As a result, the proposed scheme shows better BER performance than traditional scheme with the help of subset members. In particular, the proposed scheme shows superior performance as the channel block probability is higher. However, as the number of subset members is increasing, there is a constraint because of the higher multiple access interference.

• Industry Promotion Research
• /
• v.1 no.2
• /
• pp.121-128
• /
• 2016

Cultural heritage means a great lot to a nation's social system and its people's behavior consciousness and plays an important role in its self-development and improvement. It is essential for a nation's self-education and renewal. Improper cultural heritage will be disastrous because it may fall a nation into a loss of terrible chaos. Only the proper cultural heritage can make it always self-awaking, self-correcting and remaining vital in life. This paper, from the perspective of Choi Bu's Pyohaerok, makes a thorough analysis of the unbalance heritage of Chinese ancient culture for thousands of years. For example, many fine traditions gradually vanished in our actual life or only take half their life in heritage nowadays, such as our ancient broad and profound Confucian etiquette, ancient exquisite brocade art and architecture, ancient advanced ship-building technology and many other advanced numerous technological inventions; however, too much unwanted cultural rubbish keeps constant prevailing and takes repeated successions in the life, such as the heavy-form-and-light-content management mode, borrowing power to do evil, neglecting technological inventions long time and generally believing in ghost theory,etc.. This paper mainly focuses on the partial successions of the bad cultural heritage and its bad influence on the country, and concludes that it is just that that makes the country more and more backward. Therefore, the paper makes some pondering over these issues and proposes some related ideas of country-building to attract others participation to deal with them.