• Composites Research
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• v.37 no.3
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• pp.219-225
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• 2024

It is essential to develop a light-weight, high-performance structure for the deployable reflector antenna, which is the payload of a reconnaissance satellite, considering launch and orbital operation performance. Among them, the composite main reflector is a key component that constitutes a deployable reflector antenna. In particular, the development of a high-performance main reflector is required to acquire high-quality satellite images after agile attitude control maneuvers during satellite missions. To develop main reflector, the initial design of the main reflector was confirmed considering the structural performance according to the laminate stacking design and material properties of the composite main reflector that constitutes the deployable reflector antenna. Based on the initial design, four types of composite main reflectors were manufactured with the variable for manufacturing process. As variables for manufacturing process, the curing process of the composite structure, the application of adhesive film between the carbon fiber composite sheet and the honeycomb core, and the venting path inside the sandwich composite were selected. After manufacture main reflector, weight measurement, non-destructive testing(NDT), surface error measurement, and modal test were performed on the four types of main reflectors produced. By selecting a manufacturing process that does not apply adhesive film and includes venting path, for a composite main reflector with light weight and structural performance, we developed and verified a main reflector that can be applied to the SAR(Synthetic Aperture Rader) satellite.

• The Journal of the Acoustical Society of Korea
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• v.43 no.2
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• pp.214-224
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• 2024

Sonobuoys are disposable devices that utilize sound waves for information gathering, detecting engine noises, and capturing various acoustic characteristics. They play a crucial role in accurately detecting underwater targets, making them effective detection systems in anti-submarine warfare. Existing sonobuoy deployment methods in multistatic systems often rely on fixed patterns or heuristic-based rules, lacking efficiency in terms of the number of sonobuoys deployed and operational time due to the unpredictable mobility of the underwater targets. Thus, this paper proposes an optimal sonobuoy placement strategy for Unmanned Aerial Vehicles (UAVs) to overcome the limitations of conventional sonobuoy deployment methods. The proposed approach utilizes reinforcement learning in a simulation-based experimental environment that considers the movements of the underwater targets. The Unity ML-Agents framework is employed, and the Proximal Policy Optimization (PPO) algorithm is utilized for UAV learning in a virtual operational environment with real-time interactions. The reward function is designed to consider the number of sonobuoys deployed and the cost associated with sound sources and receivers, enabling effective learning. The proposed reinforcement learning-based deployment strategy compared to the conventional sonobuoy deployment methods in the same experimental environment demonstrates superior performance in terms of detection success rate, deployed sonobuoy count, and operational time.

• The Journal of the Acoustical Society of Korea
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• v.43 no.2
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• pp.225-233
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• 2024

Active sonar transmits sound waves to detect covertly maneuvering underwater objects and detects the signals reflected back from the target. However, in addition to the target's echo, the active sonar's received signal is mixed with seafloor, sea surface reverberation, biological noise, and other noise, making target recognition difficult. Conventional techniques for detecting signals above a threshold not only cause false detections or miss targets depending on the set threshold, but also have the problem of having to set an appropriate threshold for various underwater environments. To overcome this, research has been conducted on automatic calculation of threshold values through techniques such as Constant False Alarm Rate (CFAR) and application of advanced tracking filters and association techniques, but there are limitations in environments where a significant number of detections occur. As deep learning technology has recently developed, efforts have been made to apply it in the field of underwater target detection, but it is very difficult to acquire active sonar data for discriminator learning, so not only is the data rare, but there are only a very small number of targets and a relatively large number of non-targets. There are difficulties due to the imbalance of data. In this paper, the image of the energy distribution of the detection signal is used, and a classifier is learned in a way that takes into account the imbalance of the data to distinguish between targets and non-targets and added to the existing technique. Through the proposed technique, target misclassification was minimized and non-targets were eliminated, making target recognition easier for active sonar operators. And the effectiveness of the proposed technique was verified through sea experiment data obtained in the East Sea.

• The Journal of the Convergence on Culture Technology
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• v.10 no.5
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• pp.23-28
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• 2024

So far, most of the military trainings were carried out in the field, and were influenced by the various parameters of the weather, the climate and the civil complaints regarding the noise. Also, it's the reality that the considerable time and resources are required to maneuver the weapon system used for the military training. Furthermore, the serious damage and casualties during tha military training are important parameters that can't be ignored. Recently, with the development of 5G communication networks and XR technologies, XR technologies are used in various fields that participate with multilateral parts, i.e. in military technology and training. In this paper, to implement the military education, 5G communication network and military education training system were established. The military education training system were composed that over 10 persons were possible to train in the various circumstances such as counter combat, mountains combat, urban combat and beaches combat. Also it is possible to fight with AI combatants, and train the gun disassembly and assembly, and train the various firing exercise. The military training system of using XR technologies were applied to the multilateral military training, and we analyzed the satisfaction results for the experienced persons of this XR system.

• The Journal of the Convergence on Culture Technology
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• v.10 no.5
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• pp.189-193
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• 2024

As cyber threats increase in the defense sector, the security of weapon system software is becoming increasingly important. Currently, most of the embedded software installed in domestic weapon systems operates based on foreign real-time operating systems(RTOS) that have no security. As a result, the localization and security enhancement of embedded software for weapon systems have emerged as urgent tasks. This study aims to propose the application and development strategies of secure RTOS for weapon systems. To this end, we examined the technological trends of domestic and foreign RTOS and secure RTOS, and analyzed the problems of current embedded software in weapon systems. The results revealed major issues such as low localization, vulnerability to cyber attacks, difficulty in maintenance, increased costs, and loss of opportunities for accumulating technological capabilities. An investigation of the current status of embedded software applied to existing weapon systems found that embedded SW are in operation across all fields, including maneuver, firepower, protection, command and control, communication, naval vessels, and aircraft. Among them, 99% rely on foreign RTOS such as VxWorks. A review of the core functions and applicability of secure RTOS to weapon systems suggests that it can be applied to key areas requiring real-time performance and security, such as fire control, navigation devices, and flight control in existing and future weapon systems. However, ensuring performance and reliability, securing verification and compatibility, and systematic government support were raised as prerequisites.

• Korean Journal of Environment and Ecology
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• v.27 no.3
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• pp.327-343
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• 2013

The aim of this study is to perform community analysis and biological assessment of water quality using benthic macroinvertebrate from Wangpi-cheon watershed which is defined as conservation areas of ecosystem and landscape by ministry of environment in Korea. Field survey of the study area was carried out 2 times from June to September in 2012. As a result of the field survey, total 155 species of benthic macroinvertebrates in 74 families, 15 orders, 7 classes and 5 phyla were collected. The findings of community analysis using the classified species and individuals showed relatively low DI(Dominant Index) value of 0.22 and very high value of average H'(Diversity index) as 4.24. And the analyzed results of SI(Similarity Index) according to habitat types using functional feeding groups showed higher values of 94.51% and 93.19% respectively to tributary and main stream after the designation of conservation areas of ecosystem and landscape. These results infer that various species and lots of individual are widely distributed at Wangpi-cheon watershed and stream ecosystem of the study area is healthy and well maintained after the designation of conservation areas. And also, the calculated EPT value was 62.9% as high enough to explain the cleanness of Wangpi-cheon watershed. We evaluated environmental condition and biological water quality by using ESB(Ecological Score of Benthic macroinvertebrate community) and KSI(Korean Saprobic Index). The average evaluated ESB shows very high value of 208.2, therefore Wangpi-cheon watershed is designated as 'First priority protection waters' area and the value of KSI is 0.32 which meets the saprobic water quality standard as 'First class'.

• Journal of the Korean Vacuum Society
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• v.14 no.2
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• pp.78-83
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• 2005

Nanometric crystalline silicon (no-Si) embedded in dielectric medium has been paid attention as an efficient light emitting center for more than a decade. In nc-Si, excitonic electron-hole pairs are considered to attribute to radiative recombination. However the surface defects surrounding no-Si is one of non-radiative decay paths competing with the radiative band edge transition, ultimately which makes the emission efficiency of no-Si very poor. In order to passivate those defects - dangling bonds in the $Si:SiO_2$ interface, hydrogen is usually utilized. The luminescence yield from no-Si is dramatically enhanced by defect termination. However due to relatively high mobility of hydrogen in a matrix, hydrogen-terminated no-Si may no longer sustain the enhancement effect on subsequent thermal processes. Therefore instead of easily reversible hydrogen, phosphorus was introduced by ion implantation, expecting to have the same enhancement effect and to be more resistive against succeeding thermal treatments. Samples were Prepared by 400 keV Si implantation with doses of $1\times10^{17}\;Si/cm^2$ and by multi-energy Phosphorus implantation to make relatively uniform phosphorus concentration in the region where implanted Si ions are distributed. Crystalline silicon was precipitated by annealing at $1,100^{\circ}C$ for 2 hours in Ar environment and subsequent annealing were performed for an hour in Ar at a few temperature stages up to $1,000^{\circ}C$ to show improved thermal resistance. Experimental data such as enhancement effect of PL yield, decay time, peak shift for the phosphorus implanted nc-Si are shown, and the possible mechanisms are discussed as well.

• Journal of Korean Society for Atmospheric Environment
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• v.28 no.3
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• pp.233-248
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• 2012

The national emission from energy sector accounted for 84.7% of all domestic emissions in 2007. Of the energy-use emissions, the emission from mobile source as one of key categories accounted for 19.4% and further the road transport emission occupied the most dominant portion in the category. The road transport emissions can be estimated on the basis of either the fuel consumed (Tier 1) or the distance travelled by the vehicle types and road types (higher Tiers). The latter approach must be suitable for simultaneously estimating $CO_2$, $CH_4$, and $N_2O$ emissions in local administrative districts. The objective of this study was to estimate 31 municipal GHG emissions from road transportation in Gyeonggi Province, Korea. In 2008, the municipalities were consisted of 2,014 towns expressed as Dong and Ri, the smallest administrative district unit. Since mobile sources are moving across other city and province borders, the emission estimated by fuel sold is in fact impossible to ensure consistency between neighbouring cities and provinces. On the other hand, the emission estimated by distance travelled is also impossible to acquire key activity data such as traffic volume, vehicle type and model, and road type in small towns. To solve the problem, we applied a hierarchical cluster analysis to separate town-by-town road patterns (clusters) based on a priori activity information including traffic volume, population, area, and branch road length obtained from small 151 towns. After identifying 10 road patterns, a rule building expert system was developed by visual basic application (VBA) to assort various unknown road patterns into one of 10 known patterns. The expert system was self-verified with original reference information and then objects in each homogeneous pattern were used to regress traffic volume based on the variables of population, area, and branch road length. The program was then applied to assign all the unknown towns into a known pattern and to automatically estimate traffic volumes by regression equations for each town. Further VKT (vehicle kilometer travelled) for each vehicle type in each town was calculated to be mapped by GIS (geological information system) and road transport emission on the corresponding road section was estimated by multiplying emission factors for each vehicle type. Finally all emissions from local branch roads in Gyeonggi Province could be estimated by summing up emissions from 1,902 towns where road information was registered. As a result of the study, the GHG average emission rate by the branch road transport was 6,101 kilotons of $CO_2$ equivalent per year (kt-$CO_2$ Eq/yr) and the total emissions from both main and branch roads was 24,152 kt-$CO_2$ Eq/yr in Gyeonggi Province. The ratio of branch roads emission to the total was 0.28 in 2008.

• The Korean Journal of Nuclear Medicine Technology
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• v.16 no.1
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• pp.86-90
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• 2012

Purpose: Quantification of myocardial blood flow (MBF) using dynamic PET imaging has the potential to assess coronary artery disease. Rb-82 plays a key role in the clinical assessment of myocardial perfusion using PET. However, MBF could be overestimated due to the underestimation of left ventricular input function in the beginning of the acquisition when the scanner has non-linearity between count rate and activity concentration due to the scanner dead-time. Therefore, in this study, we evaluated the count rate linearity as a function of the activity concentration in PET data acquired in list mode. Materials & methods: A cylindrical phantom (diameter, 12 cm length, 10.5 cm) filled with 296 MBq F-18 solution and 800 mL of water was used to estimate the linearity of the Biograph 40 True Point PET/CT scanner. PET data was acquired with 10 min per frame of 1 bed duration in list mode for different activity concentration levels in 7 half-lives. The images were reconstructed by OSEM and FBP algorithms. Prompt, net true and random counts of PET data according to the activity concentration were measured. Total and background counts were measured by drawing ROI on the phantom images and linearity was measured using background correction. Results: The prompt count rates in list mode were linearly increased proportionally to the activity concentration. At a low activity concentration (<30 kBq/mL), the prompt net true and random count rates were increased with the activity concentration. At a high activity concentration (>30 kBq/mL), the increasing rate of the prompt net true rates was slightly decreased while the increasing rate of random counts was increased. There was no difference in the image intensity linearity between OSEM and FBP algorithms. Conclusion: The Biograph 40 True Point PET/CT scanner showed good linearity of count rate even at a high activity concentration (~370 kBq/mL).The result indicates that the scanner is useful for the quantitative analysis of data in heart dynamic studies using Rb-82, N-13, O-15 and F-18.

• Korean Security Journal
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• no.10
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• pp.355-385
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• 2005

As the system of autonomous police that has been debated for long time is fixed to be introduced by the program of participatory government, this treatise intends to analyze main contents and review controversial items in order to present supplementary measures. The program of participatory government to introduce autonomous police in Korea focuses on converting the autonomous police of Korea from centralized police administration in order to provide 'customized security service' that is appropriate to the regional environment. Thus, if relevant city, county or district considers that it is required to introduce the system autonomous police, the assembly may enforce the decision by enacting ordinance. For enforcement, organization in the unit of section will be established in the line of mayor, county headman and district office. The main role will be security service that is closely related to the life of inhabitants such as crime prevention, patrol, traffic crackdown, etc. as well as public health, sanitation and environmental control which are being performed by autonomous organization at present. However some expected controversial items may be summarized in the following 3 points on the premise of accepting the program of government. First, the point at issue related to the basic function of police. The basic function of police is generally understood as order keeping function such as anterior and preventive job and law enforcing function such as posterior and suppressing job. By the way, the program of government does not endow the autonomous police with investigation right for general crime, thereby raising the controversy that our autonomous police is nothing but the assistant of police. Furthermore, the present national police also expresses its dissatisfaction to the transfer of authority. Second, the issue of balance of security service between self-governing bodies may be raised. The security environment is different between self-governing bodies and thus demand of security is different. Therefore, the security service of autonomous police will reveal difference in qualitative aspect for each self-governing body. Moreover, it can be easily anticipated that the quality of security service may be different as per the financial independence degree. Third, the point at issue anticipated with the operation funded by the budget of self-governing body. As autonomous police is operated by the budget of self-governing body, the following problems may be raised; (1) since police administration is subordinated to general administration, the concentration may be weakened (2) the cooperation between policy agencies may be impeded (3) owing to the difficult in possessing spare police, the mobility of police may be somewhat reduced.