• Transactions of the Korean Society of Automotive Engineers
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• v.20 no.5
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• pp.44-52
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• 2012

Fuel cell electric vehicles have some noise problems due to its air processing unit which is required to feed the ambient air into the fuel cell stack. Discrete-frequency noises are radiated from a centrifugal blower due to rotor-stator interaction. Their fundamental frequency is the blade passing frequency, which is determined by the number of rotor blades and their rotating speed. To reduce such noises, multi-chamber perforated muffler has been designed. In this paper, in order to improve the transmission loss of a perforated muffler, the relationship between the impedance model of a perforated hole and its noise reduction performance is studied, and the applicability of a short-length perforated muffler to air processing unit of fuel cell system is described using acoustic simulation results and experimental data. The acoustic velocity vector across the neck of a perforated hole is very important design factor to optimize the transmission of an intake muffler. The suggested short-length perforated muffler is effective on discrete-frequency noises while keeping the volume of intake muffler minimized.

• Journal of Korean Society for Atmospheric Environment
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• v.29 no.4
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• pp.459-476
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• 2013

Receptor models have been rapidly developed to manage the ambient air quality and to establish effective emission reduction strategies. The models are used to identify various emission sources and apportion quantitatively the ambient pollutant mass based on various measured physico-chemical properties of the air pollutants at the receptor site. Many types of receptor models have been applied to estimate source contributions since those provide fundamental information when establishing reasonable environmental policies in Korea and Foreign countries. In this paper, we will introduce the basic concept and principal of the receptor model, various types of existing models with discussing strong and weak points for each model, and performance procedure of PMF model as the most popular model in the world. Further the trends of receptor modeling studies in Korea and other countries were provided. Finally, the improvement directions of the modeling works for the national and local air quality management were suggested in this paper.

• Journal of Power System Engineering
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• v.5 no.1
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• pp.64-72
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• 2001

According to the regulation of IMO, oil discharge from ships is allowed under 15ppm only and an oil filtering equipment is essential. However, for large ships using heavy fuel oil of over S.G 0.98 and viscosity 380cSt and system oil, it has been in difficulty to process with existing filtering type of oily water separator. A parallel plate type oily water separator which is one of gravity type separators can be used as an assistant equipment for the oil filtering system to meet the present IMO standard of 15 ppm, because it is an efficient method in dealing with a large amount of rich oil with high specific gravity. This work is focused on the fundamental investigation of the performance of the plate type oily water separator by visualization method and PIV(Particle Image Velocimetry) measurement to acquire multi-point velocity data simultaneously. The experimental results showed that the space of the plates acts a significant role in separating process and it was found that an important point to minimize a vortex flow is to flow a large amount of fluid in space of the plates in order to promote the efficiency of separation.

• The Journal of Korean Physical Therapy
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• v.14 no.4
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• pp.423-440
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• 2002

The purpose of this study is to investigate the conception and developmental process of stretching in sports physical therapy. This study is to find conception of stretching, feature and effect, principles and fundamental rule, consideration of enforcement and developmental process in order to use the basic material which is very helpful in the every field and the scene of sports needing stretching. Flexibility is the ability to move muscles and joints through their full ranges of motion. Flexibility is developed by stretching. About player who insufficiency of flexibility, patient and disabled person who restrict of range of motion, older adult who reduce of flexibility, promote of flexibility for upgrading stability and efficiency of body on the based of scientific principles is completed by stretching. The method of stretching has been developed with passive stretching, CR, PNF stretching, PIC stretching, MET stretching in the order. The effects that we can get through stretching are as follows : 1. Enhance physical fitness. 2. Optimize learning, practice and performance of many types of skilled movement. 3. Increase mental and physical relaxation. 4. Promote development of body awareness. 5. Reduce risk of joint sprain or muscle strain. 6. Reduce risk of back problem. 7 Reduce muscular soreness. 8. Reduce the severity of painful menstruation for female athletes. 9. Reduce muscular tension. 10. Advance recognition of body.

• Korean Journal of Remote Sensing
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• v.28 no.6
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• pp.623-632
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• 2012

In this paper, we analyzed the effect of wavelet decomposition levels in feature extraction for anomaly detection from hyperspectral imagery. After wavelet analysis, anomaly detection was experimentally performed using the RX detector algorithm to analyze the detecting capabilities. From the experiment for anomaly detection using CASI imagery, the characteristics of extracted features and the changes of their patterns showed that radiance curves were simplified as wavelet transform progresses and H bands did not show significant differences between target anomaly and background in the previous levels. The results of anomaly detection and their ROC curves showed the best performance when using the appropriate sub-band decided from the visual interpretation of wavelet analysis which was L band at the decomposition level where the overall shape of profile was preserved. The results of this study would be used as fundamental information or guidelines when applying wavelet transform to feature extraction and selection from hyperspectral imagery. However, further researches for various anomaly targets and the quantitative selection of optimal decomposition levels are needed for generalization.

• Tribology and Lubricants
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• v.8 no.2
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• pp.64-72
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• 1992

The recent trends of rotating machinery demand high speed and high temperature operation, and the bearing with new material is required to be developed. Ceramic, especially silicon nitride, have been receiving attention as alternative material to conventional bearing steel. Ceramic ball bearing offers major performance advantages over steel bearing, for instance, high speed, maginal lubrication, high temperature, improved corrosion resistance and nonmagnetic capabilities etc.. In this paper, the mechanical characteristics of ceramic ball bearing (hybrid ceramic bearing and all ceramic bearing) were investigated, and the characteristics of ceramic bearing were compared with that of steel bearing. Deep groove ball bearing 6208 was taken the object of analysis. The main results of analysis were followings: the radial stiffness of hybrid and all ceramic bearing were 112% and 130% that of steel bearing, and the axial stiffness of all ceramic bearing was 110% that of steel bearing. According as rotating speed was up, the ball load, the contact angle, the contact stress and the spin-to-roll ratio between ball and raceway of ceramic bearing were far smaller than these of steel bearing. And there was not a significant difference between the minimum film thickness of ceramic bearing and steel bearing. It is expected that this research is contributed to enhanced fundamental technology for the practical applications of ceramic ball bearing.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.10B
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• pp.866-871
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• 2006

This paper presents the design of a reservation-based MAC protocol to support multimedia traffic over mobile ad-hoc networks and evaluates its performance. Our MAC protocol is based on a hierarchical approach consisting of two sub-layers. The lower sub-layer of the MAC protocol with reservation provides a fundamental access method using CSMA/CA in order to support asynchronous data traffic over mobile ad-hoc networks. The upper sub-layer supports real-time periodic data by making a slot reservation before transmitting actual data. The proposed protocol has been validated through simulations using ns-2. The results show that the proposed MAC protocol can offer higher throughput and lower delay than standard implementations of the IEEE 802.11.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.14 no.5
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• pp.41-48
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• 2005

The Rotating transmission is made up of belts, mass disks and gears. This transmission is controlled electro-mechanically by the motor and operation program. The control strategy of the system can be to change belts' stiffness and the masses of mass disk and gear. This system can be modeled as a rigid body, and also finds broad application in such diverse fields as machine tools, the cruise control system In automobiles, and control in the attitude and gimbals of spacecraft. This Transmission proves the necessity and effect of a closed loop control. The study of the Rotating Transmission excited by its base motion is able not only to predict the rotational performance, but to obtain the fundamental data for vibration isolation. In this research, we compared the response characteristics of the two controllers by means of the experiments on PD controller and PID controller added on integral action. Furthermore, we studied the response abilities such as steady state error, overshoot, and ect. and the response velocities such as rising time, settling time, and ect. in the rotating transmission.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.9-9
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• 2011

There has been strong demand for novel nonvolatile memory technology for low-cost, large-area, and low-power flexible electronics applications. Resistive memories based on metal oxide thin films have been extensively studied for application as next-generation nonvolatile memory devices. However, although the metal oxide-based resistive memories have several advantages, such as good scalability, low-power consumption, and fast switching speed, their application to large-area flexible substrates has been limited due to their material characteristics and necessity of a high-temperature fabrication process. As a promising nonvolatile memory technology for large-area flexible applications, we present a graphene oxide-based memory that can be easily fabricated using a room temperature spin-casting method on flexible substrates and has reliable memory performance in terms of retention and endurance. The microscopic origin of the bipolar resistive switching behaviour was elucidated and is attributed to rupture and formation of conducting filaments at the top amorphous interface layer formed between the graphene oxide film and the top Al metal electrode, via high-resolution transmission electron microscopy and in situ x-ray photoemission spectroscopy. This work provides an important step for developing understanding of the fundamental physics of bipolar resistive switching in graphene oxide films, for the application to future flexible electronics.

• Journal of Biosystems Engineering
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• v.28 no.1
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• pp.27-34
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• 2003

Present combustion engines have reached almost at the limit of development due to the fundamental structural problems. This study was carried out to propose a new concept internal combustion engine which has great potential advantages to the conventional engines. Proposed new concept engine is a kind of rotary engine. A rotor is rotating concentrically in a cylinder which is divided into two partitioning valves. and it makes four compartments in the cylinder. The volumes of each of four compartments are changing continuously with the rotor movement, and performs the functions of intake, compression. expansion and exhaust simultaneously. The results of this study can be summarized as follows. 1. Expected theoretical thermal efficiency is 44.9 percent at the condition of 1000rpm and compression ratio of 8.0. which is almost the same as that of the conventional engines. i.e., piston and Wankel rotary engine. 2. The new concept engine has 2. working strokes in every revolution. Therefore. the new concept engine can reduce the specific weight and volume than four-stroke piston engine. 3. The torque variation is very small. therefore minimal noise and vibration are expectable. 4. The new concept engine can reduce mechanical energy loss than piston engine because neither crank mechanism nor eccentrical motion exists.