• Polymer(Korea)
• /
• v.32 no.5
• /
• pp.458-464
• /
• 2008

A successful scaffold should have a highly porous structure and good mechanical stability. High porosity and appropriate pore size provide structural matrix for initial cell attachment and proliferation enabling the exchange of nutrients between the scaffold and environment. In this paper the highly porous scaffold of poly(${\varepsilon}$-caprolactone) electrospun nanofibers could be manufactured with an auxiliary electrode and chemical blowing agent (BA) under several processing conditions, such as the concentration of PCL solution, weight percent of a chemical blowing agent, and decomposition time of a chemical blowing agent. To attain stable electrospinnability and blown nanofiber mats having high microporosity and large pore, a processing condition, 8wt% of PCL solution and 0.5wt% of a chemical blowing agent under $100^{\circ}C$ and decomposition time of $2{\sim}3\;s$, was used. The growth characteristic of human dermal fibroblasts cells cultured in the mats showed the good adhesion and proliferation on the blown mat compared to a normal electrospun mat.

• Geophysics and Geophysical Exploration
• /
• v.22 no.2
• /
• pp.72-79
• /
• 2019

Underwater object detection method adopting electrical resistivity technique was proposed recently, and the need of advanced data processing algorithm development counteracting various marine environmental conditions was required. In this paper, we present an improved water tank experiment system and its operation results, which can provide efficient test and verification. The main features of the system are as follows: 1) All the processes enabling real time process for not only simultaneous gathering of object images but also the electrical field measurement and visualization are carried out at 5 Hz refresh rates. 2) Data acquisition and processing for two detection lines are performed in real time to distinguish the moving direction of a target object. 3) Playback and retest functions for the saved data are equipped. 4) Through the monitoring screen, the movement of the target object and the measurement status of two detection lines can be intuitively identified. We confirmed that the enhanced physical modeling system works properly and facilitates efficient experiments.

• International Journal of Computer Science & Network Security
• /
• v.21 no.5
• /
• pp.160-167
• /
• 2021

The authors of the article investigate the impact of digitalization on the forms change of employment and the labor market in the modern conditions. It is substantiated that digitalization processes directly affect the change of forms of employment and the range of occupations in the labor market, as well as the change of jobs. The positive and negative consequences of changing forms of employment for the economy in the process of digital transformation are analyzed, which include: reduction of personnel costs by employers; dissemination of non-standard, informal employment (electronic freelance, electronic outsourcing, start-employment); enabling employees to manage their working hours; increasing unemployment and imbalance of supply and demand in the labor market; reduction of productivity of enterprises, as a result of reduced productivity of workers with non-standard forms of employment, or with a negative indirect impact on productivity. A model for managing the process of digitalization in the labor market of Ukraine under different scenarios of their implementation, namely evolutionary and forced is devoted. To recognize the possible change in the level of employment in connection with the implementation of the forced scenario of digitalization in Ukraine, a model for estimating probable changes in the labor market is proposed. The directions of development of the state strategy of prevention of risks of reduction of number of workplaces in the course of digitalization are outlined.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.25 no.1
• /
• pp.108-114
• /
• 2021

AVTE(Air Vehicle Test Equipment) is a device to check status of on-board aircraft equipment before and after flight for performing successful UAV(Unmanned Aerial Vehicle) missions. This paper describes software design and test sequence of the AVTE for enabling easy-manual check by the operator and convenient automatic check of on-board electric equipment respectively. The proposed AVTE inspects BIT(Built-In Test) results of on-board LRUs(Line Replacement Units) including avionics and sensor sub-system devices. Also, it monitors all the LRU status and check the normality of aircraft equipment by means of setting specific values of the LRUs and confirming the expected test results. The AVTE prints the test results as a form of report to easily check the normal conditions of the aircraft equipment and operates automatically without operator interaction, thus being thought to effectively reduce workload of the operator.

• Journal of Korean Society of Industrial and Systems Engineering
• /
• v.44 no.4
• /
• pp.12-22
• /
• 2021

This article suggests the machine learning model, i.e., classifier, for predicting the production quality of free-machining 303-series stainless steel(STS303) small rolling wire rods according to the operating condition of the manufacturing process. For the development of the classifier, manufacturing data for 37 operating variables were collected from the manufacturing execution system(MES) of Company S, and the 12 types of derived variables were generated based on literature review and interviews with field experts. This research was performed with data preprocessing, exploratory data analysis, feature selection, machine learning modeling, and the evaluation of alternative models. In the preprocessing stage, missing values and outliers are removed, and oversampling using SMOTE(Synthetic oversampling technique) to resolve data imbalance. Features are selected by variable importance of LASSO(Least absolute shrinkage and selection operator) regression, extreme gradient boosting(XGBoost), and random forest models. Finally, logistic regression, support vector machine(SVM), random forest, and XGBoost are developed as a classifier to predict the adequate or defective products with new operating conditions. The optimal hyper-parameters for each model are investigated by the grid search and random search methods based on k-fold cross-validation. As a result of the experiment, XGBoost showed relatively high predictive performance compared to other models with an accuracy of 0.9929, specificity of 0.9372, F₁-score of 0.9963, and logarithmic loss of 0.0209. The classifier developed in this study is expected to improve productivity by enabling effective management of the manufacturing process for the STS303 small rolling wire rods.

• Journal of the Society of Naval Architects of Korea
• /
• v.59 no.3
• /
• pp.157-163
• /
• 2022

An automatic mooring system for a ship consists of a vacuum suction pad and a mechanical part, enabling quick and safe mooring of a ship. In the development of a mooring system, the design of a vacuum suction pad is a key to secure enough mooring forces and achieve stable operation of a mooring system. In the vacuum suction pad, properly designing its rubber seal determines the performance of the suction pad. Therefore, it is necessary to appropriately design the rubber seal for maintaining a high-vacuum condition inside the pad as well as achieving its mechanical robustness for long-time use. Finite element analysis for the design of the rubber seal requires the use of an appropriate strain energy function model to accurately simulate mechanical behavior of the rubber seal material. In this study, we conducted simple uniaxial tensile testing of Chloroprene Rubber (CR) to explore the strain energy function model best-fitted to its experimentally measured engineering strain-stress curves depending on various temperature environments. This study elucidates the temperature-dependent mechanical behaviors of CR and will be foundational to design rubber seal for an automatic mooring system under various temperature conditions.

• Journal of The Korean Society of Agricultural Engineers
• /
• v.64 no.5
• /
• pp.67-77
• /
• 2022

Recently, the trend in structural analysis and design is moving towards the development of reliable system. The reliability-based method defines various limit states related to usability and failure, thereby enabling multiple levels of design according to the importance of a structure. Meanwhile, an actual structure is composed of a set of several elements, and particularly, a frame type is composed of a system in which the members are connected each other. At this time, the actual connection between members is in a semi-rigid condition, not in complete rigid or hinged. This semi-rigid is found in several structures, especially in agricultural facilities designed with lightweight materials. In this study, a system reliability analysis technique for frame structure was established, and applied to an analysis of the semi-rigid connection. Various conditions of correlation were applied to reflect the connectivity between members, and through this, the limitations of existing structural analysis method and the behavioral characteristics of structure were analyzed. The failure probability of the frame member component and the overall structure system was significantly different in consideration of the semi-rigid connection. In addition, it was evaluated that the behavior of structure can be more accurately analyzed if the correlation according to the position of members in a system is further investigated.

• Applied Chemistry for Engineering
• /
• v.33 no.5
• /
• pp.538-544
• /
• 2022

One of the most exciting areas for the development of alternative fuels is the production of biodiesel. To reduce the cost of biodiesel production, in situ trans-esterification has been introduced to simplify the production process by enabling extraction and trans-esterification to occur at a single stage in the presence of a catalyst. In this study, we investigated the feasibility of using non-corrosive and environmentally receptive flying jet plasma as an alternative catalytic route for in situ tran-sesterification of castor bean seeds (CBS). Upon optimizing the reaction conditions, it is elucidated that applying a low ratio of methanol to seeds (≤6:1) has resulted in hindering the in situ trans-esterification and leading to insignificant conversion. The yield of esters has increased from 80.5% to 91.7% as the molar ratio rose from 9:1 to 12:1. Excess alcohol beyond the ratio of 15:1 was shown to have a negative impact on the yield of the produced esters, attributed to an increase in the biodiesel portion prone to dissolving in the co-product (glycerol). An increase in the reaction bulk temperature from 40 to 55 ℃ led to a higher ester content by 50%. Further increases in the bulk temperature beyond 55 ℃ did not affect yields. Regarding the reaction period, the results have shown that 3 h of reaction is adequate for a higher biodiesel yield. The quality of the biodiesel obtained has demonstrated that all physicochemical properties meet the ASTM D6751 specifications.

• Composites Research
• /
• v.20 no.4
• /
• pp.9-17
• /
• 2007

Powder metallurgy has been employed for the development of SiC particle reinforced aluminum metal matrix composites by means of hot isotropic pressing and vacuum hot pressing. A material model based on micro-mechanical approach then has been presented for the processes. Densification occurs by the inelastic flow of matrix materials during the consolidation, and consequently it depends on many process conditions such as applied pressure, temperature and volume fraction of reinforcement. The model is implemented into finite element software so that the process simulation can be performed enabling the predicted relative density to be compared with experimental data. In order to determine the performance of finished products, further tensile test has been conducted using the developed specimens. The effect of internal void of the materials on mechanical properties therefore can be investigated.

• International conference on construction engineering and project management
• /
• 2022.06a
• /
• pp.967-974
• /
• 2022

It is no news that Nigeria's infrastructure challenge is enormous. In the global ranking, Nigeria ranked low in quantity and quality of its infrastructural provision which has a great impact on the ease of business transaction. Low investments in transportation have brought about the current infrastructural deficit. Recently, the Nigerian government has made effort to address at least to some extent the infrastructural deficit through Public-Private Partnership, but this has not yielded the desired result. Moreover, the sustainability issues relating to railway projects such as, emissions, noise pollution, ecosystem, and other environmental issues calls for urgent attention. Hence, this necessitated consideration on sustainability appraisal for the Chinese rail project in Nigeria. This study reviews sustainability of railway projects built by the Chinese firm in Nigeria with particular emphasis on the environmental and social impact of these projects. The study further identified issues and challenges in project implementation with a particular focus on civil dialogue and community engagements. A detailed literature search was conducted on railway projects and infrastructure by systematically reviewing selected published articles.The analysis of the selected articles identified sustainability issues and potential for improvement of Chinese railway projects and how they contribute to or inhibit competitiveness in the Nigerian railway market. From the literature searched, some of the projects constructed by Chinese firm revealed that there is economic and social impact of railway projects delivered by the Chinese firm in terms of capacity development and knowledge transfer potentiality. For instance, in the just concluded Lagos-Ibadan railway projects, the study gathered that the project brought about 5000 jobs and local staff were trained by the Chinese company, this will boost man power and local content capability. Also, it will significantly improve Nigeria's infrastructure and boost its economic development. The study suggests that Nigerian government should ensure and provide an enabling environment that is conducive for investment on the continent. Peace, improved security, and decent governance are the best conditions for sustainable transportation growth.