• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1999년도 춘계 학술대회논문집
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• pp.213-218
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• 1999

The $LiBr-H_{2}O$ absorption process on a horizontal tube has been analyzed using the numerical method which incorporates the fully elliptic Navier-Stokes equations for the momentum equations, the energy and mass-diffusion equations. On a staggered grid, the SIMPLER algorithm with the QUICK scheme is used to solve these equations along with the MAC method for the free surface tracking. With the assumption that the absorbent is linear, calculations have been made for various inlet temperature and flow-rate conditions. The detailed results of the parametric study, such as the temperature, concentration, absorption mass flux and wall heat flux distributions are presented. The self-sustained feature of the absorption process is clearly elaborated. The analyses have also been carried out for multiple tube arrangement and the results show that the absorption rate converges after a few tube rows.

• 전자공학회논문지B
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• 제28B권12호
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• pp.38-50
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• 1991

A current-controlled scheme of pulse width modulation voltage source inverter (PWM VSI) has attracted considerable attention due to its fast response with current limit and especially suitable for potentially high performance applications such as AC motor drives and UPS systems. These features yield near-sinusoidal currents in the load with reduced current peaks, lower inverter switching frequency and reduce inverter and load stresses. A high performance current-controlled inverter must have a quick response in transient state and low harmonic current in steady state. This paper compares and shows the controlled-characteristics with hysteresis controller(HC), ramp comparison controller(RCC) and predictive controller(PC) of PWM inverter to control actual current of VSI-IM.

• International Journal of Reliability and Applications
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• 제18권2호
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• pp.21-44
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• 2017

Accelerated life tests (ALTs) are frequently used in manufacturing industries to evaluate the reliability of products within a reasonable amount of time and cost. Test units are subjected to elevated stresses which yield quick failures. Most of the previous works on designing ALT plans are focused on tests that involve a single stress. Many times more than one stress factor influence the product's functioning. This paper deals with the design of optimum modified ramp-stress ALT plan for Burr type XII distribution with Type-I censoring under two stress factors, viz., voltage and switching rate each at two levels- low and high. It is assumed that usage time to failure is power law function of switching rate, and voltage increases linearly with time according to modified ramp-stress scheme. The cumulative exposure model is used to incorporate the effect of changing stresses. The optimum plan is devised using D-optimality criterion wherein the ${\log}_{10}$ of the determinant of Fisher information matrix is maximized. The method developed has been explained using a numerical example and sensitivity carried out.

• Journal of the Korean Data and Information Science Society
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• 제18권3호
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• pp.679-688
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• 2007

We select the 'rapid reading and comprehension method' to promote the reading skill, and want to apply it to students to study how their reading speed and comprehension improves. For this purpose, in this paper, we define reading as an accurate and quick ability to process information, and the object of this research is to verify a scheme to improve the reading skill, which is called the 'rapid reading and comprehension method - reading based on this method means fast reading as well as an accurate understanding which increases the amount of information received'. For data collection, we selected four primary school in the Kimje city. We found out validation the effective improvement of the reading ability by the 'rapid reading and comprehension method program'. The students' reading speed was enhanced by the rapid reading training and the comprehension ability increased as well.

• 한국항해항만학회지
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• 제26권5호
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• pp.549-554
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• 2002

국가는 재난에 대비한 범국가적 해양 구난방제체제 수림이 절실히 요구되고 있다. 그러나 우리나라는 구난방제 시설과 기술이 부족한 관계로 대형 해양사고 발생시 그 처리를 외국기술에 의존하는 형편이다. 이로 인해 가장 중요한 사고초기에 적절한 대처를 못하여 사고의 피해를 크게 확산시킬 우려가 상존하고 있다. 이에 이 논문에서는 해양사고가 발생할 경우 신속하고 효과적인 구난방제작업을 할 수 있도록 구난방제체제의 기반조성과 시설투자, 기술개발 및 능력 배양 등 다각적인 방안을 제시하였다.

• Current Optics and Photonics
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• 제4권4호
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• pp.302-309
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• 2020

An image encryption scheme based on the quick response (QR) code as a data container has aroused wide interest due to the lossless recovery of the decrypted image. In this paper, we apply this method to multi-image encryption. However, since the decrypted image is affected by crosstalk noise, the number of multi-image encryptions is severely limited. To solve this problem, we analyzed the performance of QR code as a data container, and processed the decrypted QR code using the proposed method, so that the number of multi-image encryptions is effectively increased. Finally, we implemented a large image (256 × 256) encryption and decryption.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2001년도 Proceedings ICPE 01 2001 International Conference on Power Electronics
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• pp.295-300
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• 2001

A variety of high voltage DC power supplies employing the high frequency inverter are difficult to achieve soft switching considering a quick response and no overshoot response under the wide load variation ranges which are used in medical-use x-ray high voltage generator from 20kV to 150kV in the output voltage and from 0.5mA to 1250mA, respectively. The authors develops soft switching high voltage DC power supply designed for x-ray power generator applications, which uses series resonant inverter circuit topology with a multistage voltage multiplier instead of a conventional high voltage diode rectifier connected to the second-side of a high-voltage transformer with a large turn ratio. A constant on-time dual mode frequency control scheme operating under a principle of zero-current soft switching commutation is described. Introducing the multistage voltage multiplier, the secondary transformer turn-numbers and stray capacitance of high-voltage transformer is effective to be greatly reduced. It is proved that the proposed high-voltage converter topology with dual mode frequency modulation mode control scheme is able to be the transient response and steady-state performance in high-voltage x-ray tube load. The effectiveness of this high voltage converter is evaluated and discussed on the basis of simulation analysis and observed data in experiment.

• 한국콘텐츠학회논문지
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• 제7권4호
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• pp.20-29
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• 2007

전자우편은 인터넷을 이용하는 사용자들에게 중요한 커뮤니케이션의 역할을 담당하고 있다. 하지만, 원하지 않는 광고 정보를 포함한 스팸 메일, 악성코드 형태를 포함한 바이러스 메일 등 대부분이 불필요한 자료들로 인해 전자우편이 가지는 본연의 의미와는 무색하게 사용되고 있어 근본적인 측면에서 스팸 메일의 발송을 방지할 수 있는 방안에 대한 연구가 시급하다. 본 연구에서 전자우편 발송자는 SMS(Short Message Service) 방식으로 별도의 비밀 정보를 전달받고 이를 통해 Domainkey 방식에서 사용하는 개인키/공개키 쌍을 생성하도록 하였으며 기존의 PGP 방식과도 접목하여 전자우편 송신자에 대한 인증 및 메시지에 대한 암복호화 기능을 수행하는 기법을 제안한다. 제안한 기법은 메일 발송 과정에서 발신자에 대한 인증 과정을 수행하므로 스팸 메일의 발송을 방지할 수 있는 기법이다.

• 한국멀티미디어학회논문지
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• 제10권5호
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• pp.623-630
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• 2007

IT 기술의 발전으로 사용자 편의성 요구에 따라 빠른 속도로 유비쿼터스(Ubiquitous) 환경이 조성되고 있다. 유비쿼터스 환경에서는 서비스 제공을 위한 개개인 식별이 중요하기 때문에 RFID(Radio Frequency IDentification) 기술을 핵심적으로 사용하고 있다. RFID란 무선 주파수 인식 기술로 리더의 신호에 의하여 태그가 저장하고 있는 정보를 제공하여 사용자를 식별할 수 있는 기술이다. 높은 인식률과 빠른 인식 속도 등 많은 장점을 가지고 있지만 무선 통신으로 인하여 불법적인 사용자로부터의 도청이 가능하며, 리더의 신호에 의하여 태그가 쉽게 동작하기 때문에 사용자 정보 노출에 대한 문제가 발생하고 있다. 이를 해결하기 위하여 많은 연구가 진행되고 있지만 저가의 수동형 태그에 적용할 수 있는 보안에는 한계가 있기 때문에 일반적으로 해쉬 함수 및 난수를 이용하며, 한 세션에 사용된 값들을 갱신하여 다음 세션에 사용함으로써 보안을 제공하고 있다. 따라서 본 방식은 난수를 이용하여 사용자 프라이버시를 보호하고 값을 갱신하지 않고 가변적인 값을 생성함으로써 동기화를 제공할 수 있도록 하였다.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1997년도 한국자동제어학술회의논문집; 한국전력공사 서울연수원; 17-18 Oct. 1997
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• pp.317-320
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• 1997

In the water purification plant, chemicals are injected for quick purification of raw water. It is clear that the amount of chemicals intrinsically depends on the water quality such as turbidity, temperature, pH and alkalinity etc. However, the process of chemical reaction to improve water quality by the chemicals is not yet fully clarified nor quantified. The feedback signal in the process of coagulant dosage, which should be measured (through the sensor of the plant) to compute the appropriate amount of chemicals, is also not available. Most traditional methods focus on judging the conditions of purifying reaction and determine the amounts of chemicals through manual operation of field experts or jar-test results. This paper presents the method of deriving the optimum dosing rate of coagulant, PAC(Polymerized Aluminium Chloride) for coagulant dosing process in water purification system. A neural network model is developed for coagulant dosing and purifying process. The optimum coagulant dosing rate can be derived the neural network model. Conventionally, four input variables (turbidity, temperature, pH, alkalinity of raw water) are known to be related to the process, while considering the relationships to the reaction of coagulation and flocculation. Also, the turbidity in flocculator is regarded as a new input variable. And the genetic algorithm is utilized to identify the neural network structure. The ability of the proposed scheme validated through the field test is proved to be of considerable practical value.