• Journal of the Korean Institute of Telematics and Electronics
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• v.23 no.4
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• pp.484-489
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• 1986

A device with variable stepped oxide layer along the edge region of Schottky junction have been designed and fabricated. The effect of this stepped oxide layer in the edge region improves the breakdown voltage as a result of the by increase of the depletion layer width, and decreases the leakage current as compared to the effect of conventional field oxide layer, when the reverse voltage was applied. Experimental results shown that the Schottky diode with the the reverse voltage was applied. Experimenal results show that the Schottky diode with the optimal stepped oxide layer maintains nearly ideal I-V characteristics and excellent breakdown voltage(170V) by reducing the edge effect inherent in metal-semiconductor contacts. The optimal conditions of stepped oxide layer are 1700\ulcornerin thickness and 10\ulcorner in length.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• v.11B no.4
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• pp.156-163
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• 2001

In this paper an optimal switching angle control of a switched reluctance motor (SRM) drive system is investigated for achieving maximum energy conversion ratio. A new magnetizing method is proposed with a low switching frequency. The proposed algorithm maximizes the positive energy conversion region, which is directly related to the mechanical output, and reduces the reactive power region with the same field energy region. As a consequence, a torque ripple is also sufficiently reduced compared with that of the conventional switching angle magnetizing method. Experimental results show that the proposed scheme provides a high efficiency and a low ripple drive.

• The Transactions of the Korean Institute of Power Electronics
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• v.4 no.5
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• pp.474-482
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• 1999

In this paper, a new field weakening algorithm which maximizes the output torque not only in steady state b but also in transient state is proposed. Considering both voltage and current limit of system, analytic solutions f for optimal torque utilization in field weakening region I and region II are obtained. This algorithm finds optimal currents considering dynamic vol떠ge limit based on flux and speed. So the maximum usage of stator v voltage even in transient state results in the maximum torque and fast response time. Simulation and e experimental results show the effectiveness of the proposed field weakening scheme.

• Journal of the Korean Society for Precision Engineering
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• v.26 no.2
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• pp.141-147
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• 2009

We introduce a noble method to find a variation of the optimal path problem. The problem is to find the optimal decomposition of an original planar region such that the number of paths in the region is minimized. The paths are required to uniformly cover each subregion and the directions of the paths in each sub-region are required to be either entirely vertical or entirely horizontal. We show how we can transform the path problem into a graph s-t cut problem. We solve the transformed s-t cut problem using the Ford-Fulkerson method and show its performance. The approach can be used in zig-zag milling and layerd manufacturing.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.10b
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• pp.143-146
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• 2003

In this paper, a new preform design method is proposed to eliminate the excessive flash in metal forging process. After carrying out finite element simulation of the process with an initial billet, backward particle tracing is performed from the outlet of the flash. Then, the region which belongs to the flash is easily found .. The process is analyzed again with the redesigned billet which is removed that region the above mentioned region. The optimal preform shape which minimizes the amount of flash without changing the forgibility can be obtained in several iterations.

• Proceedings of the KIEE Conference
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• 1999.07b
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• pp.761-763
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• 1999

When the controller designed by the $H{\infty}$ control technique is applied to the object system, sometimes the controller does not satisfy the robust stability and robust performance but only satisfy the nominal performance. In this paper, we derive the region on the frequency response curve of the open-loop transfer function which satisfy the robustness and robust performance of the designed controller. We also derive the region for the suitableness of the weighting function on the frequency response curve of the weighting function. We showed that the robust stability and the robust performance of the $H{\infty}$ optimal control)or by applying the designed controller on an electromechanical actuator system could be improved by determining parameter ${\gamma}$ and weighting function gain ${\alpha}$ using the derived region.

• Journal of the Korean Operations Research and Management Science Society
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• v.21 no.2
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• pp.35-47
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• 1996

The tolerance approach to the sensitivity analysis in linear programming considers simultaneous and independent variations in the coefficients of the objective function or of the right-hand side terms and gives a region in which the coefficients and terms can be changed and still keeps the current optimal basis B for the original problem as an optimal basis for the perturbed problem. In this paper we describe a procedure that expands the region S obtained by the tolerance approach into a larger region R, so that more variations in the objective function coefficients or the right-hand side terms are permissible.

• 제어로봇시스템학회:학술대회논문집
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• 2000.10a
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• pp.174-174
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• 2000

Q-learning, based on discrete state and action space, is a most widely used reinforcement Learning. However, this requires a lot of memory and much time for learning all actions of each state when it is applied to a real mobile robot navigation using continuous state and action space Region-based Q-learning is a reinforcement learning method that estimates action values of real state by using triangular-type action distribution model and relationship with its neighboring state which was defined and learned before. This paper proposes a new Region-based Q-learning which uses a reward assigned only when the agent reached the target, and get out of the Local optimal path with adjustment of random action rate. If this is applied to mobile robot navigation, less memory can be used and robot can move smoothly, and optimal solution can be learned fast. To show the validity of our method, computer simulations are illusrated.

• Journal of Powder Materials
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• v.1 no.2
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• pp.198-207
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• 1994

In order to find an optimal friction-welding condition for Ni-base ODS alloy (MA 754) produced by mechanical alloying, joint experiments were performed with various conditions of friction pressures (50~500 MPa), friction times (1~5 sec) and upset pressures (50~600 MPa). The optimal friction pressure and upset pressure must be above 400 MPa and 500 MPa, respectively, which are determined by tensile strengths and fracture features of as-welded joints. A maximum stress설h of 975 MPa could be obtained under these pressure conditions at friction time of 2 sec. Microstructural features of bonded interface by optical microscope and SEM revealed that the interface regions of all specimens are consisted with three distinct regions and defects such as voids, cracks and wavy interfaces exist in the joints produced under not-optimized conditions. EDS results showed that these defects include oxides composed with elements of Al, Y and Ti. The hardness on the bonded interface was higher than in the base metal region. Specimens fractured in bonded interface region had lower strength values compared to those fractured in base metal region. Surfaces of the former showed a typical intergranular fracture.

• Proceedings of the KOSOMBE Conference
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• v.1997 no.05
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• pp.366-369
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• 1997

In this study, we measured upper right, lower right, upper left region to find the optimal region which represent liver function. We found that the upper right region is optimal because of high accuracy and low standard deviation. For normal subjects all the calculated HEFs were greater than 100% and all those of abnormal ones were less than 80%. Thus HEF can be assumed to discriminate abnormal livers from normal ones. It was found that the patients with surgical operation would survive if both the pre-and the post-operative HEFs are greater than 50%. Therefore HEF method can be a good estimator for surgeon to determine the surgical operation and to evaluate remaining hepatic function after surgery as well as it is reliable and simple.