• Journal of Communications and Networks
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• v.11 no.1
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• pp.26-35
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• 2009

In this paper, we investigate how to do resource allocation to guarantee a minimum user data rate at low signaling overhead in multi-cell orthogonal frequency division multiple access (OFDMA) wireless systems. We devise dynamic resource allocation (DRA) algorithms that can minimize the QoS violation ratio (i.e., the ratio of the number of users who fail to get the requested data rate to the total number of users in the overall network). We assume an OFDMA system that allows dynamic control of frequency reuse factor (FRF) of each sub-carrier. The proposed DRA algorithms determine the FRFs of the sub-carriers and allocate them to the users adaptively based on inter-cell interference and load distribution. In order to reduce the signaling overhead, we adopt a hierarchical resource allocation architecture which divides the resource allocation decision into the inter-cell coordinator (ICC) and the base station (BS) levels. We limit the information available at the ICC only to the load of each cell, that is, the total number of sub-carriers required for supporting the data rate requirement of all the users. We then present the DRA with limited coordination (DRA-LC) algorithm where the ICC performs load-adaptive inter-cell resource allocation with the limited information while the BS performs intra-cell resource allocation with full information about its own cell. For performance comparison, we design a centralized algorithm called DRA with full coordination (DRA-FC). Simulation results reveal that the DRA-LC algorithm can perform close to the DRA-FC algorithm at very low signaling overhead. In addition, it turns out to improve the QoS performance of the cell-boundary users, and achieve a better fairness among neighboring cells under non-uniform load distribution.

• KDI Journal of Economic Policy
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• v.33 no.3
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• pp.163-209
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• 2011

This study empirically analyzes whether political rent-seeking behavior exits in Korea. The empirical analysis shows that there is a cyclical decline in aggregate revenue immediately following the election year. However, when using other aggregate fiscal variables including aggregate revenue, fiscal balance, tax and public burden ratio, no such cyclical deterioration are found. By sector, the expenditures of the economic affairs show a cyclical increase in the year right after the election. In addition, as the ratio of ruling party senators to total senators is high, the expenditures of the economic affairs tend to increase more and this tendency becomes more stronger right after the presidential election year. Such a result turns out to be consistent even when the expenditure was analyzed separately from the mandatory and discretionary expenditures by sector. This is a testimony to the existence of political rent-seeking behavior in Korea.

• Korea journal of population studies
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• v.24 no.2
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• pp.117-147
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• 2001

The main purpose of this paper is to analyze sex and age composition of the 1994 North Korean census data. First this paper describes the background information concerning the first population census ever taken in North Korea since the separation of the North and South. It utilizes the available data to explain the trend and current population status of North Korea. The focus of this research is to point out and analyze the problems in the sex and age composition of the North Korean census data. One of the most striking characteristics of the census data is that an enormous portion of the young male population was excluded from the census counts. Such omissions are strongly suggested by a incredible drop in sex ratios for the age groups of 16 to 25. In addition, the total sum of the population by age groups turns out to be substantially smaller than the total sum of the population by geographical regions. The total discrepancy amounts to 691 thousand. Along with sex ratios and age ratios, Myers indices, UN age-sex accuracy indices, indices of relative difference, and indices of dissimilarity are calculated to analyze the characteristics and accuracy of sex and age composition in the North Korean census data. Finally, this paper readjusts the sex and age composition of the 1994 census data, and attempts to produce a more accurate population of North Korea.

• Journal of the Korean Society for Nondestructive Testing
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• v.33 no.2
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• pp.219-225
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• 2013

Separate and layered transmitting and receiving spiral coil arrays had been used for the optimized individual applications of magnetostrictive type long-range ultrasonic testing. In this study, it was demonstrated that when taking advantages of the spiral coils with the leg width reduced to be half of the previous one and of the empty spaces due to the decrease of leg width, the transmitting and receiving coil array can be arranged to form a single layer structure allowing more easy use and fabrication. Because of the number of turns of the receiving coils that is proportional to their leg width, the sensitivity of the single layer coil array was about half that of the corresponding double layer coil array while it allowed the receiving amplifier to get faster recovery from a saturation due to the main bang echo. It was also found that the two types of coil arrays have almost the same performances in the view points of signal-to-noise ratio and directivity control.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.10
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• pp.1408-1416
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• 2001

Mean flow fields in the near wake of a square cylinder have been studied experimentally using a Particle Image Velocimetry (PIV). Ensemble-averaged velocity fields are successfully measured fur the square cylinder wake including the reverse flow region which arises many difficulties in accurate measurement by using conventional techniques, Experiments are performed at two free stream velocities of U$\_$$\infty$/ = 1.27m/s and 3.03m/s. The corresponding Reynolds numbers based on the free-stream velocity and cylinder diameter are 1600 and 3900, respectively. The intensity of free-stream turbulence is less than 1%, the blockage ratio (D/H) is 6.6% and the aspect ratio (W/D) is 40. The effect of Reynolds number on the near wake of a square cylinder has been investigated by the global mean velocity and instantaneous velocity fields. The most striking feature is that the length of the recirculating region increases with increasing Reynolds number, which turns out totally reverse trend compared with those observed in the circular cylinder wake at the same range of Reynolds number. Fer the case of higher Reynolds number, the mean velocity data agree well with those of relevant existing data obtained at much higher Reynolds numbers, which reflects the general aspect of sharp-edged bluff body wake.

• The Transactions of the Korea Information Processing Society
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• v.6 no.7
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• pp.1777-1788
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• 1999

The portability of Java language makes it possible to use heterogeneous computers without re-compiling of application programs. Java applet can also be transported to other computers via Web browser. In this research, a Cooperative Web Computing Environment(CWCE) that uses idle computers on the Intranet for cooperative parallel computing work is suggested. The CWCE allows to use more than a manager computer that sends applets and manages communication between other computers. The number of manager computers can be determined according to the characteristics of computing environment and any chosen application program. It can reduce the amount of communication overhead for the application programs especially with synchronized communication. For the CWCE, a decision function to determine the managing level is provided. The CWCE turns out to be useful computing environment for the applications with less computation request ratio and multi-managing can help to reduce the communication overhead especially for the applications with a high ratio of synchronization purpose communications.

• The Korea Journal of Herbology
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• v.24 no.4
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• pp.101-106
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• 2009

Objectives : We investigated the anti-aging effects on skin with 9 Repetitive steaming and fermenting herbal composition extract (FHE). Methods : Herbal composition is comprised of Panax Ginseng, Rehmannia glutinosa, Polygonum multiflorum and Polygonatum Sibiricum. They steamed and fermented with Saccharomyces cerevisiae and Lactobacillus brevis by turns at 9 times. We measured various effects related to skin aging such as scavenging activity against free radical, cell proliferation, collagen synthesis and toxicity of 9 repetitive steaming and fermenting herbal composition extract were evaluated and compared with herbal composition extract (HE). Results : As the number of steaming and fermenting cycle increased free-radical scavenging activity were increased. But cell proliferating ratio was not increased when the number of steaming and fermenting cycle. The FHE could significantly increase the collagen synthetic ratio compared with HE treated group. And, FHE was showed no toxicity at all tested concentrations. Conclusions : The results of our study propose that FHE has good anti-aging effects on skin.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.17 no.1
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• pp.239-260
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• 2023

The underwater acoustic wireless communication networks are generally formed by the different autonomous underwater acoustic vehicles, and transceivers interconnected to the bottom of the ocean with battery deployed modems. Orthogonal frequency division multiplexing (OFDM) has become the most popular modulation technique in underwater acoustic communication due to its high data transmission and robustness over other symmetrical modulation techniques. To maintain the operability of underwater acoustic communication networks, the power consumption of battery-operated transceivers becomes a vital necessity to be minimized. The OFDM technology has a major lack of peak to average power ratio (PAPR) which results in the consumption of more power, creating non-linear distortion and increasing the bit error rate (BER). To overcome this situation, we have contributed our symmetry research into three dimensions. Firstly, we propose a machine learning-based underwater acoustic communication system through long short-term memory neural network (LSTM-NN). Secondly, the proposed LSTM-NN reduces the PAPR and makes the system reliable and efficient, which turns into a better performance of BER. Finally, the simulation and water tank experimental data results are executed which proves that the LSTM-NN is the best solution for mitigating the PAPR with non-linear distortion and complexity in the overall communication system.

• Journal of the Korean Wood Science and Technology
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• v.37 no.1
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• pp.87-93
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• 2009

Properties and chemical bonding of wood charcoal were investigated to understand the chemistry occurring in wood carbonization. From the pH changes of wood charcoal, it is revealed that it becomes acidic to weakly basic for charcoal carbonized at about $300^{\circ}C$, whereas it turns to basic at higher carbonization temperature higher than $600^{\circ}C$. Also, the ratio of carbon atoms in the charcoal was increased with increasing the carbonization temperature, while those of oxygen and hydrogen atoms. This tendency was significant when the carbonization temperature was increased up to $600^{\circ}C$ and the ratio changes of the atoms became stable at above $600^{\circ}C$. In the changes of chemical bonding, the ratio of C-C bonding was increased and those of C-O-H and C-O-R bonding was decreased significantly. It is considered that bondings connected to oxygen atoms tends to be broken, and the ratio of C-C bonding increased. Consequently, it is expected that this change may causes occurrence of new functional groups. In addition to that, it seems to be that the chemical bondings undergo the partial decomposition, formation, and recombination steps, Because ratio of C=O bonding tended to be increased or decreased by increasing the carbonization temperature. This understanding of chemical bond changes in charcoal can be a compensative consideration on the knowledges made only by physical parameters in the properties of micro-pore which has limited to explain the phenomenon. Also, it is considered that this can be treated as a basic knowledge for upgrading and development of use of wood charcoal.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.42 no.1
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• pp.14-21
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• 1997

This experiment was conducted to identify the growth and yield differences in rice cultural types: Broadcasting on flooded paddy surface(BF), drilling on flooded paddy surface(DF), puddled-soil drill seeding(PD), drill seeding on dried paddy flat(DD), and machine transplanting of lO-day old seedling(MT) at National Honam Agricultural Experiment Station in 1995. Among the cultural types of direct seeding, the number of seedling stand showed high in order of DD>BF>DF>PD. Tillering at early growth stage was faster in MT and effective tiller showed higher in MT than in direct seeding. Growth duration from seeding to heading was longer in direct seeding than in MT for 2-13 days of Dongjinbyeo and 10-18 days of Nonganbyeo. Root distribution ratio at the surface soil revealed high in order of BF>DF>PD>DD and MT. Culm wall thickness of 4th internode was thicker in machine transplanting of 10-day old seedling than in direct seeding, and the depth of buried culm showed deep by turns of MT> DD>PD>DF and BF. The height of center gravity and moment related to lodging revealed higher in direct seeding than machine transplanting that resulted high lodging index by turns of BF>DF>DD> PD among the direct seeding cultural type. Lodging was occured seriously in the order of BF>DF>PD>DD =MT in Dongjinbyeo but wasn't significantly different in Nonganbyeo among the cultural type. The yield components and grain yield showed varietal differences but was not significantly different between in MT and in direct seeding, and among cultural types of direct seeding.