• Title/Summary/Keyword: Sources of variation

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Calibration of $^{192}Ir$ HDR Brachytherapy Source in Air and in a Cylindrical Phantom

  • Djarwani S. Soejoko;I, Arief-Riva'
    • Proceedings of the Korean Society of Medical Physics Conference
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    • 2002.09a
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    • pp.23-27
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    • 2002
  • Two $^{192}$ Ir HDR brachytherapy sources were calibrated with a Farmer ionization chamber in air method and in a PMMA cylindrical phantom. The calibration air method used ionization chamber with buildup cap, and 8 variation distances for center-to-center of the source to chamber. In the optimum distance the measured activity, especially for the high activity source, deviation was 0.3% from the activity provided by manufacturer. Calibration with a PMMA cylindrical phantom was less sensitive, and suitable for quick check method with accuracy less than 10%.

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Micro-Vibration Test on a Two-Axis Gimbal Antenna System with Stepping Motors (스텝핑 모터 특성에 따른 2축 짐발 안테나 시스템의 미소진동 측정 시험)

  • Kim, Dae-Kwan;Choi, Hong-Taek;Park, Gee-Yong
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2012.04a
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    • pp.420-424
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    • 2012
  • A 2-axis gimbal system is one of main disturbance sources affecting on image jitter response of a satellite. The gimbal system can be rotated on its azimuth and elevation axes, resulting in variation of its moment of inertia and structural modes, so that generates non-linear vibration characteristics. In order to estimate the jitter response, it is an indispensable process to characterize micro-vibration disturbance of the 2-axis gimbal system. In the present research, the vibration characteristics of the 2-axis gimbal system was investigated with respect to the types of stepping motors. The micro-vibration tests were performed for 2-phase and 5-phase stepping motors. The test results show that the disturbance can be reduced with vibration attenuation ratio of 60% by replacing the 2-phase stepping motor with the 5-phase one.

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Numerical Simulation of Ammonium Perfluorooctance (PFOA) in Gwangyang Bay (광양만 Ammonium Perfluorooctance (PFOA)의 거동 특성 시뮬레이션)

  • Kim, Dong-Myung
    • Korean Journal of Fisheries and Aquatic Sciences
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    • v.49 no.5
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    • pp.665-670
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    • 2016
  • A three-dimensional ecological model (EMT-3D) was used to simulate the behavior of PFOA in Gwangyang Bay, Korea. The results of sensitivity analysis showed that partition rate, adsorption rate, and settling rate were important factors in the variation in PFOA in particulate organic matter. Bioconcentration was the most significant factor for PFOA in phytoplankton, with the largest effect size. These parameters must therefore be carefully considered when modeling PFOA behavior. In simulations, 30% and 50% reductions in loads from land-based sources of PFOA resulted in concentrations of dissolved PFOA lower than 4 ng/L and 2 ng/L, respectively, in the central part of the bay.

Study on Factors Influencing Cyclic Variations at Idle in Spark Ignition Engine (스파크 점화기관의 공회전 시 싸이클 변동에 영향을 주는 인자 고찰)

  • D.H. Kwon;Park, Y.K.;Kim, J.M.
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 2003.06a
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    • pp.1249-1252
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    • 2003
  • To analyse the cyclic variations in a test engine, the burn parameters are determined on a cycle-to-cycle basis through the analysis of the engine pressure data. Combustion analysis based on cylinder-pressure provides a mechanism through which a combustion researcher can understand the combustion process. The objective of this paper is to identify the most significant sources of cycle-to-cycle combustion variability in a spark ignition engine at idle. The burn rate analysis program was used and the burn parameters were used to determine the variations in the input parameter. In this study, the author investigated the relationship of indicated mean effective pressure, coefficient of variation of indicated mean effective pressure and burn angles, and lowest normalized value in a spark ignition engine for the cyclic variations.

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Factors affecting the properties of recycled concrete by using neural networks

  • Duan, Zhen-Hua;Poon, Chi-Sun
    • Computers and Concrete
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    • v.14 no.5
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    • pp.547-561
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    • 2014
  • Artificial neural networks (ANN) has been proven to be able to predict the compressive strength and elastic modulus of recycled aggregate concrete (RAC) made with recycled aggregates (RAs) from different sources. However, ANN is itself like a black box and the output from the model cannot generate an exact mathematical model that can be used for detailed analysis. So in this study, sensitivity analysis is conducted to further examine the influence of each selected factor on the output value of the models. This is not only conducive to the determination and selection of the more important factors affecting the results, but also can provide guidance for researchers in adjusting mix proportions appropriately when designing RAC based on the variation of these factors.

A Study on the thermal behaviors of a machine tool with linear motors (리니어 모터를 적응한 공작기계의 열변형 특성에 관한 연구)

  • 김종진;조동우
    • Proceedings of the Korean Society of Machine Tool Engineers Conference
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    • 2002.10a
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    • pp.36-40
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    • 2002
  • The development of feed drive system with high speed and accuracy has been a major issue in the machine tool industry. Linear motors can be used as the efficient tool to achieve fast feed mechanism and high accuracy. However. a high speed feed drive system with linear motors can generate heat problems such as the variation of temperature distribution and the resultant thermal stress. In this paper, the important heat sources and the resultant thermal errors are presented. The thermal deformation characteristics of the machine tool with linear motors were identified, which are thermal expansion of linear scale, shrinkage, expansion and bending in the machine tool structure.

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Effects of the Irradiated Current Mode PWM Controller of DC/DC Power Converter (DC/DC 전력 컨버터의 전류모드 PWM 제어기의 방사선 영향)

  • Lho, Young-Hwan;Hwang, Eui-Sung;Lho, Kyeoung-Su;Phouphanonh, Phouphanonh;Khamphoungeun, Khamphoungeun;Han, Chang-Won
    • Proceedings of the KSR Conference
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    • 2011.10a
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    • pp.685-692
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    • 2011
  • DC/DC switching power converters produce DC output voltages from different DC input sources. The converters can be used in regenerative braking of DC motors to return energy back in the supply, resulting in energy savings for the systems containing frequent stops. The current mode DC/DC converter is composed of a PWM (pulse width modulation) controller, a MOSFET, and inductor, etc. Pulse width modulation is applied to control and regulate the total output voltage. It is shown that the variation of threshold voltage at MOSFET and the offset voltage increase caused by radiation effects make the PWM pulse unstable. In the PWM operation, the missing pulses, the changes in pulse width, and a change in the period of the output waveform are studied by simulation program with integrated circuit emphasis (SPICE) and experiments.

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Performance Improvement of Usage Parameter Control for MMPP Traffic Sources in A TM Networks (ATM망에서 MMPP 트래픽 신호원에 대한 사용 상황 감시 제어의 성능 개선)

  • 한길성;오창석
    • Journal of the Korean Institute of Telematics and Electronics B
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    • v.33B no.11
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    • pp.106-115
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    • 1996
  • In this paper, the method using virtual scheduling suggested algorithm (VSSA) is suggested by considering cell delay variation and token rate of leaky bucket. This method is compared with virtual scheduling algorithm (VSA) and virtual scheduling algorithm with no tolerance excessive peak cell rate. As a result, the research shows that the usage parameter control using vSSA makes quality of service better than the usage parameter control using vSA or VSANT does because the suggested method reduces the violated cell probability of conformed peak cell rate and intentionally excessive peak cell rate.

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Yearly Variation of the Energy Use of Apartment Building (대구시 도심 공동주택의 에너지 경년 변화에 관한 연구)

  • 홍원화;이준혁
    • Journal of the Korean housing association
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    • v.13 no.2
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    • pp.1-6
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    • 2002
  • As a result of rapid economic and social change, the number of large-scale builing is expected to increase. In response to the growing increase, It will be a greater demand for up-to-date for heating and cooling, illumination, communication and disaster protection system as well as a sharp rise in overall energy consumption. Gradually the living of apartment building is increasing by growing population. In basic data will be offered for the energy conservation programs, and establishing some standards for the energy consumption in future. By understanding how energy sources are actually utilized in existing apartment houses, we can develop more appropriate strategies to maximize both the efficient use of energy and its conservation.

Characteristization of Spray Combustion and Turbulent Flame Structures in a Typical Diesel Engine Condition (디젤 엔진 운전 조건에서 분무 연소 과정과 난류 화염 구조 특성에 대한 해석)

  • Lee, Young-J.;Huh, Kang-Y.
    • Journal of the Korean Society of Combustion
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    • v.14 no.3
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    • pp.29-36
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    • 2009
  • Simulation is performed to analyze the characteristics of turbulent spray combustion in a diesel engine condition. An extended Conditional Moment Closure (CMC) model is employed to resolve coupling between chemistry and turbulence. Relevant time and length scales and dimensionless numbers are estimated at the tip and the mid spray region during spray development and combustion. The liquid volume fractions are small enough to support validity of droplets assumed as point sources in two-phase flow. The mean scalar dissipation rates (SDR) are lower than the extinction limit to show flame stability throughout the combustion period. The Kolmogorov scales remain relatively constant, while the integral scales increase with decay of turbulence. The chemical time scale decreases abruptly to a small value as ignition occurs with subsequent heat release. The Da and Ka show opposite trends due to variation in the chemical time scale. More work is in progress to identify the spray combustion regimes.

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