• Journal of the Korea Convergence Society
• /
• v.10 no.11
• /
• pp.9-14
• /
• 2019

In modern society drones are actively utilized in the fields of security, defense, agriculture, communication and so on. Smart technology and artificial intelligence software have been developed with convergence, and the field of use is expected to expand further. On the point of the excellent performance of drones one of the essential technologies is the wireless communication that make the ground facility receive the video streaming obtained by the drones in the air. In the research the concept of communication region is proposed to cover the both the low altitude region for Wi-Fi communication and the high altitude region for LTE communication for the sake of video transmission. Also the hybrid communication structure is designed along the proposed concept and the proposed system is implemented as a communication system in the small size which can be mounted in a small size of drone. It is confirmed that the proposed system contains the effectiveness by showing the ability to successfully transmit HD video streaming in the range of 500 meters and the transfer time between two different communication systems is measured in 200msec by the experiments.

• Journal of Korea Port Economic Association
• /
• v.34 no.4
• /
• pp.105-124
• /
• 2018

The purpose of this study is to identify human factors that directly or indirectly cause ship accidents and to suggest implications based on the derived human factors. In particular, we conducted a survey on the basis of the human factors derived from the literature survey and interviews, and applied the revised importance-performance analysis (IPA) to develop implications from a comparison of two groups: seafarers and shipping operations managers. Data were collected from 159 practitioners in the Korean shipping industry. The analysis structure consisted of five major factors with 20 components, including unique factors related to ship and shipping management companies, personal competence, in-vessel organization, and personnel's health, as well as social factors. The result of the IPA analysis indicates that in-vessel organization is the most urgent and major factor for improvement. Some differences exist in the components that should be improved between the two groups. For the seafarer group, an increase in unskilled onboard crew affected sustainable safety activities, thus implying an area of preferential improvement regarding the in-vessel organization factor. However, for the shipping operations managers group, the difference in recognizing safety standards among the crew members on board and the ability to communicate with other crew members should be improved first relative to in-vessel organization factors. The personnel's health factor was identified to be of low importance in both groups. Finally, the importance of improving the safety consciousness level according to the safety education and training implementation for seafarers on board was different for the two groups.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2008.11a
• /
• pp.137-142
• /
• 2008

Ignition characteristics of combustion chamber with LOx lead cyclogram for liquid rocket engine were described. The combustion chamber has chamber pressure of 60 bar, propellant mass flow rate of 89 kg/s, and nozzle expansion of 12. Cold flow test to determine the filling time of propellant for cyclogram with LOx lead supply, ignition test to check the ability to ignite starting fuel from the ignitor, low pressure combustion test to check the propagation of flame into main fuel-oxidizer mixture from starting fuel and the main combustion stage, and design point combustion test to check the combustion performance were performed. Ignition and combustion tests with LOx lead supply were successfully performed and the stable cyclogram of start sequence for combustion chamber was developed.

• Physical Therapy Rehabilitation Science
• /
• v.7 no.2
• /
• pp.61-66
• /
• 2018

Objective: Patellofemoral pain syndrome (PFPS) is a condition that is characterized by patellar discomfort or pain that is aggravated during certain activities such as ascending/descending stairs. The Patellofemoral Disability Index (PDI) was developed to assess the effect of pain on functional activities in individuals with PFPS. The objectives of the current study were to determine the internal consistency, test-retest reliability, and validity of this index. Design: Cross-sectional study. Methods: Forty-one subjects who had PFPS with a mean age of $28.8{\pm}5.0years$ and a mean body mass index of $25.6{\pm}4.7kg/m^2$ participated in the study. All subjects were concurrently enrolled in a clinical trial for which they were instructed to complete hamstring-resistance exercises for 4 weeks. Over the course of the intervention, they completed both the PDI and the Oswestry Disability Index (ODI) at baseline after two weeks, and after four weeks. Pearson correlation coefficient was used to assess the criterion validity. Cronbach's ${\alpha}$ was used to examine the internal consistency. Intraclass correlation coefficients with 95% confidence interval were computed to examine test-retest reliability. Results: Subjects' responses within both the PDI and the ODI yielded Pearson correlation coefficient values that were positive and highly significant (range, 0.73-0.97; p<0.001). There was a high level of internal consistency (Cronbach's ${\alpha}{\geq}0.8$), with the exception of stair climbing (Cronbach's ${\alpha}=0.65$). Intraclass correlation ranged from 0.87 to 0.92, indicating high levels of test-retest reliability. Conclusions: The PDI is a valid, reliable, and feasible method of assessing pain and functional ability in patients with PFPS.

• Proceedings of the Plant Resources Society of Korea Conference
• /
• 2003.10a
• /
• pp.9-18
• /
• 2003

A method for rapid propagation of mature Jack fruit was developed. Four types of explants (mature embryos, apical meristems of young seedlings, apices from mature plants and nodal segments) were used. It has been found 88% of young apical meristems produced shoots in Campbell and Durzan (CD) medium compared to 60% in Murashige and Skoog (MS) medium. Only 1/3 of them produced multiple shoots. Shoot idtiation from nodal segments was very rare. Mature apices produced callus. Although removed of the sheathing cover around mature buds enhanced the shoot initiation but success rate was low in growth regulator free medium. Embryos respond to the CD medium but not to the MS medium. Embryos from seeds soaked in water for 24 hours produced shoots after 8 weeks of incubation and the success rate was 70% while embryos from dry seeds only produced roots. There was no significant effect of cold storage (refrigeration) for 7 days on shoot initiation from mature embryos (65%) but the ability for shoot induction declines with storage time (55% after 21 days of cold storage). Mature axillary buds were established in Modified Campbell and Durzan (CD) medium supplemented with 0.5mg/1 and IBA. There was a significant difference in the growth performance of shoots according to the period of the year in which explants were collected. Highest (60%) was observed in November-January period. It was only 30% when the explants were collected in February-April or May-July and decreased to 20% in August-October. The shoots produced in November-January showed a higher vigor than those produced in other months. Since Jak fruit show seasonal changes in fruit bearing and shedding of leaves, it can be suggested that the difference in growth performances of tissues cultured in artificial culture media would have been affected by endogenous rhythms.

• Journal of Digital Convergence
• /
• v.19 no.10
• /
• pp.15-20
• /
• 2021

The crisis of university must be overcome by emphasizing the acquisition and use of knowledge for students to participate in and solve contemporary and diverse social/regional problems through educational method innovation. University classes should be a way of contributing to solving human problems, the UN's Sustainable Development Goals(SDGs) and various issues in the community. This study focused on project-based learning to cultivate socially engaged and problem-solving talents. In addition, a problem definition toolkit model was produced and tested to improve problem solving ability. Through follow-up research, I plan to develop a performance measurement model corresponding to the field application-improvement-feedback of Living Lab project classes, and suggest a method that universities can easily apply to the existing curriculum.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.15 no.10
• /
• pp.3834-3857
• /
• 2021

The design of cluster-based routing protocols is necessary for Wireless Sensor Networks (WSN). But, due to the lack of features, the traditional methods face issues, especially on unbalanced energy consumption of routing protocol. This work focuses on enhancing the security and energy efficiency of the system by proposing Energy Efficient Based Secure Routing Protocol (EESRP) which integrates trust management, optimization algorithm and key management. Initially, the locations of the deployed nodes are calculated along with their trust values. Here, packet transfer is maintained securely by compiling a Digital Signature Algorithm (DSA) and Elliptic Curve Cryptography (ECC) approach. Finally, trust, key, location and energy parameters are incorporated in Particle Swarm Optimization (PSO) and meta-heuristic based Harmony Search (HS) method to find the secure shortest path. Our results show that the energy consumption of the proposed approach is 1.06mJ during the transmission mode, and 8.69 mJ during the receive mode which is lower than the existing approaches. The average throughput and the average PDR for the attacks are also high with 72 and 62.5 respectively. The significance of the research is its ability to improve the performance metrics of existing work by combining the advantages of different approaches. After simulating the model, the results have been validated with conventional methods with respect to the number of live nodes, energy efficiency, network lifetime, packet loss rate, scalability, and energy consumption of routing protocol.

• Nuclear Engineering and Technology
• /
• v.53 no.2
• /
• pp.637-646
• /
• 2021

The free-piston Stirling engine (FPSE) has been widely used in aerospace owing to its advantages of high efficiency, high reliability, and self-starting ability. In this paper, a 20-kW FPSE is proposed by analyzing the requirements of space nuclear power reactor. A code was developed based on an improved simple analysis method to evaluate the performance of the proposed FPSE. The code is benchmarked with experimental data, and the maximum relative error of the output power is 17.1%. Numerical results show that the output power is 21 kW, which satisfies the design requirements. The results show that: a) reducing the pressure shell's thickness can improve the output power significantly; b) the system efficiency increases with the wire porosity, while the growth of system efficiency decreases when the porosity is higher than 80%, and system efficiency exhibits a linear relationship with the temperatures of the cold and hot sides; c) the system efficiency increases with the compression ratio; the compression ratio increases by 16.7% while the system efficiency increases by 42%. This study can provide valuable theoretical support for the design and analysis of FPSEs for space nuclear power reactors.

• International Area Studies Review
• /
• v.14 no.3
• /
• pp.62-84
• /
• 2010

Accurate forecasting of volatility is of considerable interest in financial volatility research, particularly in regard to portfolio allocation, option pricing and risk management because volatility is equal to market risk. So, we attempted to delineate a model with good ability to forecast and identified stylized features of volatility, with a focus on volatility persistence or long memory in the Australian futures market. In this context, we assessed the long-memory property in the volatility of index futures contracts using three conditional volatility models, namely the GARCH, IGARCH and FIGARCH models. We found that the FIGARCH model better captures the long-memory property than do the GARCH and IGARCH models. Additionally, we found that the FIGARCH model provides superior performance in one-day-ahead volatility forecasts. As discussed in this paper, the FIGARCH model should prove a useful technique in forecasting the long-memory volatility in the Australian index futures market.

• Neurospine
• /
• v.15 no.4
• /
• pp.329-337
• /
• 2018

Objective: Machine learning algorithms excel at leveraging big data to identify complex patterns that can be used to aid in clinical decision-making. The objective of this study is to demonstrate the performance of machine learning models in predicting postoperative complications following anterior cervical discectomy and fusion (ACDF). Methods: Artificial neural network (ANN), logistic regression (LR), support vector machine (SVM), and random forest decision tree (RF) models were trained on a multicenter data set of patients undergoing ACDF to predict surgical complications based on readily available patient data. Following training, these models were compared to the predictive capability of American Society of Anesthesiologists (ASA) physical status classification. Results: A total of 20,879 patients were identified as having undergone ACDF. Following exclusion criteria, patients were divided into 14,615 patients for training and 6,264 for testing data sets. ANN and LR consistently outperformed ASA physical status classification in predicting every complication (p < 0.05). The ANN outperformed LR in predicting venous thromboembolism, wound complication, and mortality (p < 0.05). The SVM and RF models were no better than random chance at predicting any of the postoperative complications (p < 0.05). Conclusion: ANN and LR algorithms outperform ASA physical status classification for predicting individual postoperative complications. Additionally, neural networks have greater sensitivity than LR when predicting mortality and wound complications. With the growing size of medical data, the training of machine learning on these large datasets promises to improve risk prognostication, with the ability of continuously learning making them excellent tools in complex clinical scenarios.