• Transactions of Materials Processing
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• v.31 no.2
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• pp.64-72
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• 2022

Since aluminum alloys experience both tensile and compression deformation modes during forming process, it is important to understand the role of deformation mode on the hot formability of metallic alloys. In the present work, the hot formability of Al7050 alloy was investigated by conducting both tensile and Gleeble tests at various temperatures and strain rates. Processing maps representing low efficiency regions were observed at low temperature and high strain rate in both tensile and compressive deformation modes while the maximum efficiency regions depended on different deformation modes. Moreover, samples tested at stable processing conditions presented a smaller pore fraction than those at instable conditions that resulted in crack initiation during plastic deformation. This result shows that different deformation modes during plastic forming can affect formability changes of metallic alloys. Understanding of tension-compression behaviors will help us solve this problem.

• Educational Technology International
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• v.16 no.2
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• pp.249-272
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• 2015

This study is a theoretical exploration of project-based service-learning and its application in designing pre-dental curricula. As a response to the limitation of community service courses, service-learning has been implemented as pedagogy in higher education practices. Service-learning connects service and learning by engaging students in activities that address community needs with intentionally designed learning opportunities while adding value to and transforming both service and learning. Project-based service-learning is an extended and more active version of service-learning. Whereas service activities are arranged by instructors in the original service-learning, project-based service-learning provides students with opportunities for exploring problems and root causes on site and then devising and implementing solutions of their own using their talents and creativity. This study proposes a theoretical approach to project-based service-learning and suggests six design components, namely, related curriculum, reflection, reciprocity, service and community engagement, evaluation and recognition, and creative problem solving. Based on the components, 20 design strategies are formulated. The exploration is aimed to provide design guides for professionals attempting to implement project-based service-learning in higher education.

• Educational Technology International
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• v.13 no.1
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• pp.79-100
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• 2012

The focus of this research is on identifying the problems that learners experience during online problem-based learning (e-PBL) from a cognitive perspective. The study is concentrated on learners' cognitive load level at each stage of e-PBL. The research questions are specifically as follows: What is the level of cognitive load at each stage of e-PBL and what is the relationship between cognitive load and group performance? What cognitive difficulties are experienced by learners in e-PBL and what causes cognitive difficulties? In this study, we found that cognitive load was the highest in stage 1 and there was negative relationship between cognitive load at stage 1 and group performance. In addition, learners experienced difficulties during e-PBL such as the complexity of task, the difficulty in collaboration, and the lack of appropriate references. For further study, we will investigate some strategies regarding adjusting learners' cognitive load in the early stages of e-PBL.

• Journal of The Korean Association of Information Education
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• v.13 no.3
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• pp.263-271
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• 2009

Problem solving competency has always been a prime issue in education, and it is defined as core skills of a life competency or as 21st century skills that students need to successfully learn. This study aims to discover the scope and impact of digital textbooks on students' competencies. This study also examines meaningful differences brought about using digital textbooks and taking lessons specifically adapted to improve 5th grade students' problem solving competencies. The pretest-posttest control group design was adopted and a performance-based measurement tool for problem solving competency was developed and applied. The results indicate that the classes using digital textbooks achieved higher scores in problem solving competency. Also, a lesson that was specifically adapted with the aim to improve students' problem solving competency had a positive influence on students' achievement. Moreover, there was reciprocal influence between using digital textbooks and adapting instructions to improve problem solving competency. In conclusion, the effect of digital textbooks should be discussed further while also considering the influence of teachers' instructional strategies.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.7
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• pp.857-864
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• 2013

A laser machining process has been applied in many manufacturing fields and it provides an excellent energy control for treating materials. However, a heat effect during laser machining can deteriorate material properties. Specifically, a thermally induced stress can be a problem in laser-machined structures on a metal surface. In this study, temperature and stress on cold-rolled carbon steel sheet machined with laser hole drilling were explored in an experimental approach and a numerical method. Stresses by temperature gradients inside the materials were generated in fast cooling. The stresses were measured by using a hole-drilling method and the material properties of carbon steel (SCP1-S) were obtained in the experiment. It was found that the stress predicted from the numerical analysis was in agreement with the stresses measured by using the hole-drilling method. The analysis can be applied for evaluating structure characteristics machined with a laser.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.1
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• pp.103-111
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• 2016

This paper presents an adaptive variable weights tuning system for an integrated chassis control with electronic stability control (ESC) and active front steering (AFS) for lateral stability enhancement. After calculating the control yaw moment needed to stabilize a vehicle with a controller design method, it is distributed into the tire forces generated by ESC and AFS using weighted pseudo-inverse-based control allocation (WPCA). On a low friction road, lateral stability can deteriorate due to high vehicle speed. To cope with the problem, adaptive tuning rules on variable weights of the WPCA are proposed. To check the effectiveness of the proposed method, a simulation was performed on the vehicle simulation package, CarSim.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.386-391
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• 2001

A finite element code based on P2P1 tetra element has been developed for the large eddy simulation (LES) of turbulent flows around a complex geometry. Fractional 4-step algorithm is employed to obtain time accurate solution since it is less expensive than the integrated formulation, in which the velocity and pressure fields are solved at the same time. Crank-Nicolson method is used for second order temporal discretization and Galerkin method is adopted for spatial discretization. For very high Reynolds number flows, which would require a formidable number of nodes to resolve the flow field, SUPG (Streamline Upwind Petrov-Galerkin) method is applied to the quadratic interpolation function for velocity variables, Noting that the calculation of intrinsic time scale is very complicated when using SUPG for quadratic tetra element of velocity variables, the present study uses a unique intrinsic time scale proposed by Codina et al. since it makes the present three-dimensional unstructured code much simpler in terms of implementing SUPG. In order to see the effect of numerical diffusion caused by using an upwind scheme (SUPG), those obtained from P2P1 Galerkin method and P2P1 Petrov-Galerkin approach are compared for the flow around a sphere at some Reynolds number. Smagorinsky model is adopted as subgrid scale models in the context of P2P1 finite element method. As a benchmark problem for code validation, turbulent flows around a sphere and a MIRA model have been studied at various Reynolds numbers.

• Journal of Engineering Education Research
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• v.9 no.3
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• pp.37-48
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• 2006

The purpose of this study is to investigate the response and the recognition of students of blended learning. Set up the following study problem in order to achieve a study purpose. How are a response and a recognition of learner about blended learning? To study, Designed blended learning environment, and analyzed a bulletin board and a log file, and made up a question for 15 weeks after proceeding a class in order to recognition and response about the results operating blended learning. The results as follows: First, A lot of students prefer education in blended learning environment, and participate positively in activity in on-line activity. Second, When study in blended learning environment about media be prudent must select. Third, Confirmed the fact that various role of Instructor needed. Therefore, the design and operation of blended learning, which mixes traditional teaching methods and a modern on-line method, is meaningful.

• The Transactions of the Korean Institute of Power Electronics
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• v.17 no.4
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• pp.306-314
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• 2012

In case of the conventional DC-AC inverter using two DC-DC converters with unipolar output capacitor voltages, for generating the AC output voltage, the output capacitor voltages of its each DC-DC converter must be higher than the DC input voltage. To solve this problem, this paper proposes a single-phase DC-AC inverter using two embedded Z-source converters with bipolar output capacitor voltages. The proposed inverter is composed of two embedded Z-source converters with common DC source and output AC load. The AC output voltage is obtained by the difference of the output capacitor voltages of each converter. Though the output capacitor voltage of converter is relatively low compared to the conventional method, it can be obtained the same AC output voltage. Moreover, by controlling asymmetrically the output capacitor voltage, the AC output voltage of the proposed system is higher than the DC input voltage. To verify the validity of the proposed system, a DSP(TMS320F28335) based single-phase embedded Z-source DC-AC inverter was made and the PSIM simulation was performed under the condition of the DC source 38V. As controlled symmetrically and asymmetrically the output capacitor voltages of each converter, the proposed inverter could produce the AC output voltage with sinusoidal waveform. Particularly, in case of asymmetric control, a higher AC output voltage was obtained. Finally, the efficiency of the proposed system was measured as 95% and 97% respectively in case of symmetric and asymmetric control.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37B no.11
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• pp.965-974
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• 2012

As the use of smart devices has become popular, the number of smart devices connected to network has increased and the amount of traffic from them has grown rapidly. The management of mobile traffic and IP address for smart devices in an enterprise network is crucial problem for efficient operation of network. The information about connection type of a terminal host to the network will be very useful for stable and efficient management of an enterprise network. Also, this information might be used to identify NAT device. In this paper, we propose a methodology to identify the connection type of a terminal host using RTT (Round-Trip-Time) value extracted from captured packets. We prove the feasibility of our proposed method in a target campus network.