• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.11
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• pp.934-943
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• 2018

In these days, demand for agile spacecraft is gradually increasing, due to the fact that agile spacecraft can improve mission capability. In this paper, an attitude control logic based on reaction wheels that can enhance agility of spacecraft is proposed. Three methods are suggested, and all three or part of them can be integrated to the existing attitude control system. First, a feedforward/feedback controller is introduced, and its pros and cons are provided, compared to the conventional feedback controller. Second, an attitude command generation method that fully utilizes torque/momentum capacities of reaction wheels is proposed. Third, a torque (current) control mode for internal wheel control is introduced. Numerical results verify that the settling time can be significantly reduced by employing the feedforward/feedback control method, especially for large angle maneuver.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.10
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• pp.677-690
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• 2022

By using an actuator disk method based flow solver, aerodynamic analysis is carried out for a dual ducted fan aircraft, which is one of the VTOL compound aircrafts, and its associated ground effect is analyzed. The characteristics and accuracy of the solver for ground effect analysis is evaluated through a comparison with the results obtained from the sliding mesh technique. The aerodynamic performance and flow field characteristics with respect to the distance from the ground are analyzed. As the ground distance decreases, the fan thrust increases, but the deterioration of total normal force and hovering flight efficiency is identified owing to the decrease in the vertical force of the duct, fuselage, and wing. By examining the flow field in the bottom of the fuselage, the ground vortices and fountain flow generated by the interaction of the fan wake and ground are identified, and their influence on the aerodynamic performance is analyzed. The strength and characteristics of outwash with respect to the ground distance and azimuth direction are analyzed through comparison/examination of velocity profile. Influence of the ground effect with respect to collective pitch angle is also identified.

• Journal of Korea Multimedia Society
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• v.11 no.2
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• pp.247-256
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• 2008

Recently, natural disasters like flooding damages have frequently occurred as to typhoons and local downpours affected by the climate changes. Many researches have actively been studied in analysing runoff models, the verification of their parameters, and the inflow on surfaces in order to lessen the damages. However, much time and effort needs in generating input files of the models in most current researches. Therefore, in this paper we develop a system for generating a simulation input data automatically. This system is connected to the EPA-SWMM based on the spatial data in the UIS systems and consists the simulation module for analysing urban flooding and the SWMM simulator module. Also, we construct a prototype using a range of regular inundation to generate a simulation input file. This system gives advantages showing inundation areas based on the map viewer as well as lessening errors of input data and simulation time.

• Journal of The Korean Association of Information Education
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• v.8 no.3
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• pp.365-372
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• 2004

The purpose of this study is to develop FVU, which enables teachers effectively to construct self-page on the screen, to reduce the size of file for teaching, and to correct many different kinds of event which was already made in the previous. The instrument used in the development of this Editor is UML(Unified Modeling Language), which is object-oriented methodology. The Authoring tool developed in this study is named FVU. The first page which is needed in class can be constructed by using VUEditor in FVU. Using VUEditor can get Instructional Syllabus exported into VUAuthor through Vector-transformation. Through this procedure, the size of image file comes to be reduced into forming low band width, which results in solving the problem of network traffic. Also, Instructor can create image, shape and text, and delete and correct errors or mistakes which make in the course of constructing materials for teaching. In conclusion, this VUEditor enables program designer to construct the first page, even without using such applied program as Image Tool and Power Point. This VUEditor makes instructor to make some contents for teaching easily.

• Progress in Medical Physics
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• v.15 no.4
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• pp.179-185
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• 2004

To deal with tumor motion from respiration is one of the important issues for the advanced treatment techniques, such as the intensity modulated radiation therapy (IMRT), the image guided radiation therapy (IGRT), the three dimensional conformal therapy (3D-CRT) and the Cyber Knife. Studies including the active breath control (ABC) and the gated radiation therapy have been reported. Authors have developed the device for reducing the respiration effects and the diaphragm motions with this device were observed to determined the effectiveness of the device. The device consists of four belts to immobilize diaphragm motion and the vacuum cushion. Diaphragm motions without and with device were monitored fluoroscopically. Diaphragm motion ranges were found to be 1.14 ～ 3.14 cm (average 2.14 cm) without the device and 0.72～1.95 cm (average 1.16 cm) with the device. The motion ranges were decreased 20 ～ 68.4% (average 44.9%.) However, the respiration cycle was increased from 4.4 seconds to 3.7 seconds. The CTV-PTV margin could be decreased significantly with the device developed in this study, which may be applied to the treatments of the tumor sited diaphragm region.

• Progress in Medical Physics
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• v.13 no.4
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• pp.195-201
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• 2002

Several investigators have presented the effects of external magnetic fields on the dose distributions for clinical electron and photon beams. We focus the low energy electron beam with more lateral scatter In this study we calculated the beam profiles for an clinical electron beam of 6 MeV with longitudinal magnetic fields of 0.5 T-3.0 T using a Monte Carlo code. The principle of dose enhancements in the penumbra region is to deflect the laterally scattered electrons from its initial direction by the skewness of the laterally scattered electrons along the direction of magnetic field lines due to Lorentz force under longitudinal magnetic field. To discuss the dose enhancement effect on the penumbra area from the calculated results, we introduced the simple term of penumbra reduction ratio (PRR), which is defined as the percentage difference between the penumbra with and without magnetic field at the same depth. We found that the average PRR are 33%, and 49% over the depths of 1.5 cm, 2.0 cm, and 2.4 cm for the magnetic fields of 2.0 T and 3.0 T respectively. For the case of 0.5 T and 1.0 T the effects of magnetic filed were not observed significantly. In order to obtain the dose enhancement effects by the external magnetic field, we think that its strength should be more than 2 T approximately. We expect that the PRR would be saturated to 50-60% with magnetic fields of 3 T-5 T As a result of these calculations we found that the penumbra widths can be reduced with increased magnetic fields. This Penumbra reduction is explained as a result of electron lateral spread outside the geometrical edges of the beam in a longitudinal magnetic field. This means that the electron therapy benefits from the external magnetic fields.

• Economic and Environmental Geology
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• v.48 no.3
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• pp.241-246
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• 2015

Helicobacter pylori is an important transmissible human pathogen found on the luminal surface of the gastric epithelium. The organism can persist in the stomach indefinitely and causes gastroduodenal inflammation that may proceed to atrophic gastritis, peptic ulcer, gastric MALT lymphoma, and gastric cancer. Standard triple therapy which consists of proton pump inhibitor (PPI) plus two antibiotics (amoxicillin and clarithromycin) is now generally used in Korea, however, eradication rates of H. pylori has been decreasing due to increasing antibiotic resistance. In this review, current second-line treatment regimens, difficult problems on treatment, necessity of local target therapy, applicability of clay minerals as a drug delivery system (DDS), and a new therapeutic strategy and its study plans will be discussed.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.12
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• pp.2173-2180
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• 2006

Linux has peculiarities of safety, flexibility, and open source. and Linux supports various hardware platforms. But because general Linux was designed for high performance H/W, Linux has several points to support for embedded system with limited resource. Specially, a main point is booting time that is spent to tens of second. In this paper, we purpose a fast booting scheme of Linux for Embedded System and estimate a performance of scheme purposed through realized prototype. Specially, to reduce booting time in environment of embedded system, we optimize boot loader, kernel and root file system. As a result, boot time reduce 28 second to 11 second in HBE-EMPOS II.

• Proceedings of the Korea Information Processing Society Conference
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• 2015.10a
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• pp.1027-1030
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• 2015

하드웨어 디자인 설계에서 초기 단계의 설계 오류 발견은 개발 비용 감소 및 설계 시간 단축 측면에서 그 효과가 매우 크다. 이러한 초기 설계 오류 발견을 위한 대표적인 방법으로는 정형 검증(formal verification)이 있으며, Cadence SMV(Symbolic Model Verifier)는 정형 검증을 위해 Verilog HDL(Hardware Description Language)을 SMV로 자동 변환 해주는 장점이 있지만, 사건 기반 구조(event based structures)의 sensitivity list에 대한 지원을 하지 않는 한계가 있다. 이에 본 논문에서는 Cadence SMV에서 디지털회로(digital circuit) 중 하나인 조합 논리회로(combinational logic circuit)를 sensitivity list가 고려된 검증이 가능하도록 하는 방법을 제안한다. 신뢰성 있는 실험을 위해 본 논문에서는 제안하는 방법의 일반적인 규칙을 도출하였고, 도출된 규칙이 적용된 SMV 파일을 생성하는 자동화 프로그램을 구현하여 실험하였다. 실험결과 제안한 방법을 적용한 경우 기존 Cadence SMV가 발견하지 못한 설계상의 오류를 발견할 수 있었다.

• 대한공업교육학회지
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• v.33 no.2
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• pp.287-299
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• 2008

HTTP is one of the most widely used protocols of the WWW. Currently it uses TCP as the transport layer protocol to provide reliability. The HTTP uses separate TCP connection for each file request and adds unnecessary head-of-line blocking overhead for the file retrieval. The web application is short sized and affected by the increased handover latency of TCP in wireless environment. SCTP has attractive features such as multi-streaming and multi-homing. SCTP's multi-streaming and multi-homing avoid head-of-line blocking problem of TCP and reduce handover latency of TCP in wired and wireless environment. Mean response time is the important measure in most web application. In this paper, we present the comparison of mean response time between HTTP over SCTP with that of HTTP over TCP in wired and wireless environments using NS-2 simulator. We measured mean response time for varying packet loss rate, bandwidth, RTT, and the number of web objects in wired environment and mean response time and packet loss rate for varying moving speed and region size in wireless environment. Our experimental result shows that SCTP reduces the mean response time of TCP based web traffic.