• International Journal of Aeronautical and Space Sciences
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• 제9권1호
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• pp.1-30
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• 2008

When the stagnation temperature of a perfect gas increases, the specific heats and their ratio do not remain constant any more and start to vary with this temperature. The gas remains perfect; its state equation remains always valid, except, it is named in more by calorically imperfect gas. The aim of this work is to trace the profiles of the supersonic axisymmetric Minimum Length Nozzle to have a uniform and parallel flow at the exit section, when the stagnation temperature is taken into account, lower than the dissociation threshold of the molecules, and to have for each exit Mach number and stagnation temperature shape of nozzle. The method of characteristics is used with the algorithm of the second order finite differences method. The form of the nozzle has a point of deflection and an initial angle of expansion. The comparison is made with the calorically perfect gas. The application is for air.

• 천문학회보
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• 제36권2호
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• pp.107.1-107.1
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• 2011

Density Probability Distribution Functions (PDFs) are a classic statistical way to study properties of Interstellar Medium (ISM) turbulence. In our three-dimensional MHD simulations, density PDFs of the position-position velocity (PPV) spaces are close to a log-normal distribution. the PDF widths depend on the plasma parameters such as magnetic strength and sonic Mach number. Futhermore, we compare these simulations results to Galactic molecular clouds observed by Jackson et. al (2006). By fitting of the velocity dispersion in the spectral line observation, volume density PDFs of the defined molecular clouds indicate that the sound speeds of the turbulences seem to have a few times larger than the simulation results. In order to understand the inconsistency with general characteristics of turbulence, we consider other simulations inducing the turbulent flow randomly at small driving scales. We find that the density PDF width decreases at more smaller driving scale. Finally, the simulations suggest that sources of ISM turbulence in Galactic molecular clouds can be important on small scales.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1998년도 하계학술대회 논문집 E
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• pp.1656-1658
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• 1998

This paper deals with a measurement system of a distance between lightning strokes and observatory station and spectrum analysis of electric fields radiated from lightning discharges. The distance measurement system, which consists of a loop type magnetic field sensor, a microphone and one chip microprocessor, is connected to a personal computer through RS232 port to acquire and process the data. This system is to use a difference of propagation velocity between an electromagnetic wave and a sonic wave produced by lightning discharge. Also, an electric field waveform and a frequency spectrum were investigated by an electric field measurement system with a hemisphere antenna and a spectrum analyzer with a biconical antenna and a log-periodic antenna, respectively. The results would be used as a basic reference to protect the power systems and electric circuits from lightning overvoltages.

• 자동차안전학회지
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• 제7권1호
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• pp.20-26
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• 2015

In vehicle development process, durability test should be carried out in field condition. Nowadays there are many customer live there multiple conditions. It makes change of the car's material. Such change causes to lose a bolt. Diversifications of climatic conditions are also a matter of loosening the bolt. To avoid this problem, to identify the cause of the problem, and the solution should be applied. To avoid problems during the durability development test should be measured by the clamping force. Ultrasonic instruments clamping force without affecting the torque can be measured. This instrument is part of the problem by monitoring the clamping force required to obtain objective data.

• 설비공학논문집
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• 제14권11호
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• pp.880-889
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• 2002

The purpose of the present study is to examine the factors affecting the heat transfer limitations of screen mesh heat pipe for electronic cooling by theoretical analysis. Diameter of pipe was 6 mm, and mesh numbers are 50, 100, 150, 200 and 250 and water was selected as a working fluid. According to the change of mesh number, wick layer, inclination and saturation temperature, capillary pressure, pumping pressure, liquid friction coefficient in wick, vapor friction coefficient, capillary limitation, entrainment limitation, sonic limitation and boiling limitation we analyzed by theoretical design method of a heat pipe. As some results, the capillary limitation in small diameter of heat pipe is largely affected by mesh number and wick layer.

• 반도체디스플레이기술학회지
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• 제13권3호
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• pp.51-55
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• 2014

Ni-CNT(Carbon Nanotubes) composite coating is often used for the surface treatment of mechanical/electronic devices to improve the properties of the Ni coating. For the Ni-CNT coating, the dispersion of CNT fibers is a critical process. In this study, ultrasonic treatment instead of the conventional ball milling was attempted as a dispersion method for the electroless Ni-CNT coating. SEM-EDX analysis was performed and contact angle, sheet resistance, and micro-hardness were measured. Results showed that the ultrasonic treatment was comparable to the ball milling, as a dispersion method, but the difference was negligible. However, combined ball milling and ultrasonic treatment(double treatment) showed much improved micro-hardness value, above 350Hv(close to the value obtained by the Ni-CNT electroplating). In addition, electroless Ni-CNT(double-treated) coatings formed on the thin Ni film deposited by the electroless plating(double coating) showed better mechanical properties. Thus, double treatment and double coating are suggested as an improved electroless Ni-CNT coating method.

• 제어로봇시스템학회논문지
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• 제16권3호
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• pp.239-244
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• 2010

This paper is to present map building of mobile robot using RFID (Radio Frequency Identification) technology and ultrasonic sensor. For mobile robot to perform map building, the mobile robot needs its localization and accurate driving in space. In this reason, firstly, kinematic modeling of mobile robot under non-holonomic constrains is introduced. Secondly, based on this modeling, a tracking controller is designed for tracking a given path based on backstepping method using Lyapunov function. The Lyapunov function is also introduced for proving the stability of the designed tracking controller. Thirdly, 2D map building is performed by RFID system, mobile robot system and ultrasonic sensors. The RFID mobile robot system is composed of DC motor, encoder, ultra sonic sensor, digital compass, RFID receiver and RFID antenna. Finally, the path tracking simulation results and map building experimental results are presented to show the effectiveness of the designed controller.

• 한국세라믹학회지
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• 제37권3호
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• pp.280-287
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• 2000

Adsorption behavior and amount of phenolic resin followed silica (SiO2) formation onto silicon nitride(Si3N4) surface were investigated using electrokinetic sonic amplitude (ESA) technique and with UV spectrometer, to fabricate Si3N4/SiC nano-composite based on reaction between SiO2 formed and phenolic resin absorbed onto Si3N4 particle. The amount of SiO2 formed and carbon from phenolic resin absorbed onto Si3N4 surface were calculated quantitatively to adjust the reaction between SiO2 and phenolic resin, resulting in no residual SiO2 and carbon. As a result, pre-heated tempeature for optimized reaction was below 25$0^{\circ}C$, in which there was no residual SiO2 and carbon.

• 한국주거학회논문집
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• 제18권2호
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• pp.11-20
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• 2007

The purpose of this study is to find the apartment Choice and Housing Satisfaction by the Housing Value Segmentation. Survey questionnaires were conducted on 1103 married women from three residential areas in Daegu. Data were analized by SPSS package program. Major findings are the following: Quality oriented type preferred environment oriented and multiple apartment. Safety investment type answered the bases of the information as of sales/model house, real estate office, oral information from relative neighbor. Ostentation negative type is dissatisfied for the present apartment were listed such as inconvenient inner structure and inner space, education environment for children, privacy protection, convenient transportation for the urban area. Convenience educational environment type is dissatisfied for the present apartment were listed such as inconvenient inner structure and inner space, anti sonic materials, education environment for children, privacy protection.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2002년도 추계종합학술대회
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• pp.457-461
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• 2002

위해환경에서 동작되는 화상로봇에 대한 개발에 관하여 서술하였다. 개발된 로봇은 크게 로봇 제어부와 Host PC 에서의 Visual I/F program으로 구성되어 있다 개발된 로봇의 구동부와 Camera의 구동부는 2자유도를 갖고 있으며 유저 친화적으로 개발된 Joystick으로 원격조종된다. 외부 상황은 비젼 시스템과 초음파 센서로 인식되며, 화상 및 센서 데이터, 명령어 등을 각각 900MHz와 447MHz RF로 통신된다. 개발된 시스템의 효율성을 100m범위의 야외 시험장에서 운용되어 검사되었다.