• Smart Structures and Systems
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• 제19권1호
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• pp.105-113
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• 2017

A microstructure-dependent dynamic model for silicon nanobeams with axial motion is developed by considering the effects of nonlocal elasticity and surface energy. The nanobeam is considered to subject to both transverse and longitudinal loads arising from nanostructural surface effect and all positive directions of physical quantities are defined clearly prior to modeling so as to clarify the confusions of sign in governing equations of previous work. The nonlocal and surface effects are taken into consideration in the dynamic behaviors of silicon nanobeams with axial motion including circular natural frequency, vibration mode, transverse displacement and critical speed. Various supporting conditions are presented to investigate the circular frequencies by a numerical method and the effects of many variables such as nonlocal nanoscale, axial velocity and external loads on non-dimensional circular frequencies are addressed. It is found that both nonlocal and surface effects play remarkable roles on the dynamics of nanobeams with axial motion and cause the frequencies and critical speed to decrease compared with the classical continuum results. The comparisons of the non-dimensional calculation values by present and previous studies validate the correctness of the present work. Additionally, numerical examples for silicon nanobeams with axial motion are addressed to show the nonlocal and surface effects on circular frequencies intuitively. Results obtained in this paper are helpful for the design and optimization of nanobeam-like microstructures based sensors and oscillators at nanoscale with desired dynamic mechanical properties.

• Wind and Structures
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• 제35권5호
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• pp.309-322
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• 2022

Due to the complex terrain around high-speed railways, the windbreaks were established along different landforms, resulting in irregular windbreak transition regions between different subgrade infrastructures (flat ground, cutting, embankment, etc). In this paper, the effect of a windbreak transition on the wind flow around railways subjected to crosswinds was studied. Wind tunnel testing was conducted to study the wind speed change around a windbreak transition on flat ground with a uniform wind speed inflow, and the collected data were used to validate a numerical simulation based on a detached eddy simulation method. The validated numerical method was then used to investigate the effect of the windbreak transition from the flat ground to cutting (the "cutting" is a railway subgrade type formed by digging down from the original ground) for three different wind incidence angles of 90°, 75°, and 105°. The deterioration mechanism of the flow fields and the reasons behind the occurrence of the peak wind velocities were explained in detail. The results showed that for the windbreak transition on flat ground, the impact was small. For the transition from the flat ground to the cutting, the influence was relatively large. The significant increase in the wind speeds was due to the right-angle structure of the windbreak transition, which resulted in sudden changes of the wind velocity as well as the direction. In addition, the height mismatch in the transition region worsened the protective effect of a typical windbreak.

• 한국ITS학회 논문지
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• 제12권6호
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• pp.116-126
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• 2013

강설, 안개발생 등 기상상태의 변화는 운전자의 주행환경에 영향을 미치는 기상요인으로 기상악화 시 차량의 차두간격과 속도에 영향을 미치게 되어 도로용량을 감소시키고, 교통사고 발생으로 인한 차로감소 등의 상황을 유발하여 맑은 날보다 더 큰 혼잡을 발생시키는 것으로 분석되었다. 운전자의 시정을 감소시키는 기상악화는 통행속도가 높은 고속도로가 일반도로 보다 기상상태에 따른 통행속도 변화 민감도와 교통사고 심각도가 높게 나타나는 특성이 있다고 분석됨에 따라 고속도로의 교통류 특성변화에는 시정거리가 중요하게 작용하는 것으로 판단되었다. 따라서 본 연구에서는 통행속도가 높은 고속도로 기본구간의 교통류 특성에 영향을 미치는 주요 요인으로 교통량과 속도를 선정하였으며, 일정수준 이상의 교통량 확보가 가능한 수도권내 고속도로를 분석대상으로 선정하고 기상자료와 교통자료를 수집하여 시정거리 변화에 따른 고속도로 교통류 특성변화에 관한 연구를 수행하였다. 본 연구의 수행을 위하여 기존 문헌 고찰을 통해 자료수집 및 분석방법을 수립하고 고속도로의 시정거리 수준을 선정하며, 통계적 차이 검증을 수행하고 시정거리에 따른 고속도로의 교통류 특성 변화를 분석하여 용량 및 서비스 수준 분석 시 적용할 수 있는 방안을 강구하고자 한다.

• 대한방사선기술학회지:방사선기술과학
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• 제15권1호
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• pp.65-78
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• 1992

Routine chest radiography is generally imaged by high voltage technique but some radiological technologists use low voltage for imaging. High voltage is usually said between $120\;kV{\sim}140\;kV$. Some RTs like using heavy filtration but others seldom like using it. However which is better for use calcium tungustate film screen system or ortho system and high contrast film or wide latitude c-type film for the exculusive use of chest radiography. We could not make a decision which is ideal method for use. In my opinion any method is not always exellent for chest radiography. In my experiments that I had at Kaken hospital in Japan last year I expect to keep the balance between image quality and diagnostic range and to reduce radiation dose for patients. My experiments are as follows. 1. We have looked into system characteristics(speed and contrast) in accordance with kVp($80{\sim}140$) and added filter($no{\sim}1/16\;VL$) in three screen film systems(BX3+CRONEX4, SRO750+MGH, SRO750+MGL). 2. We have looked into skin dose and film dose with same D=1.8 lung field density in accordance with kVp($80{\sim}140$) and added filter($no{\sim}1/16\;VL$) in three screen film systems. 3. We have compared with the evaluation between correlation of physical image quality(MTF) and optical diagnostic capability. Result are follows. 1. Speed of BX3+CRONEX4 became higher in accodance with kVp and thickness of filter but speed of ortho system was not as like regular system. Thicker filter diminished the speed over 100 kV range in SRO750+MGL. In case of SRO750+MGH speed of 1/16VL filter was looked into lower than speed of 1/4VL filter. Sensitivity of ortho system depends on tube voltage and added filter. 2. Skin dose has been detected $225\;{\mu}Gy{\sim}66\;{\mu}Gy$ in BX3+CRONEX4 from 80 kV, no filter to 140 kV, 1/16VL filter. SRO750+MGH could reduce the patient dose $1/2{\sim}1/3$ level in comparison to that of BX3+CRONEX4. 3. The higher kV was the worse MTF became the thicker filter was the worse MTF became too. MTF of BX3+CRONEX4 was detected better than MTF of SRO750+MGH but SRO750+MGH's optical detectability of small lesion in lung field came out better than that of BX3+CRONEX4. Conclusion Recently routine chest radiography is generally imaged by high voltage but it seems to be there are some questions in using of film screen combination. In high voltage chest radiography the subject contrast will come down that means latitude become wider. In this case if we select the low contrast film screen system(C or L type) the film contrast will fall down extremly and detectability of small lesion will be deteriorated. Wide latitude C, L type film has a merit of high detectability on mediastinum. Furthermore high contrast film screen system has the advantage to keep the high contrast in low density region as like mediastinum and heart shadow. Therefore in low subject contrast high voltage chest radiography we would rather choose the high contrast film screen system(H type) I think. From a view point of patient dose detectability of mediastinum and lung field. The optimum technical facter was found out 120 kV, 1/16VL filter : BX3+CRONEX4, 140 kV, 1/4VL filter : SRO750+MGH, 100 kV, 1/4VL filter : SRO750+MGL.

• 한국운동역학회지
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• 제14권2호
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• pp.69-83
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• 2004

The purpose of this study is searching for technical merits and demerits of each weight lifting player through qualitative motion analysis system. Moreover, It is also analysis the repeating the establishment of exercise purpose and studying for the effect of the field adaptation. The subject of this study was five male weight lifting players who have been engaged in Korean Delegation Team. The institution of exercise target was made through two times qualitative analysis and the result of studying for the effect of the field adaptation was produced before offering feedback. Moreover, two time analysis added after offering feedback. All analysis was based on 2-D visual analysis. The results of this study are as follows: 1. Maximal barbell moving speed in starting phase was decreased after offering feedback. This result implies advancement of technical skills after offering feedback. 2. From starting posture to 앉아받기, forward and backward moving distance of hip joint was decreased after offering feedback in all subjects. This result represents advancement of technical skills after offering feedback. 3. In terms of pull phase, forward and backward moving distance of hip and shoulder joint was decreased after offering feedback in all subjects. This result represents advancement of technical skills after offering feedback. 4. In terms of pull phase, the difference of horizontal value of coordinates was decreased after offering feedback in all subjects. This result represents advancement of technical skills after offering feedback. 5. In terms of pull phase, the motion range of hip joint was decreased after offering feedback in three of five subjects and this represents advancement of technical skills after offering feedback. However, the rest of them were not variable or narrow decreasing. This result represents that feedback system could not brought tremendous effects. 6. From apex point of barbell to 앉아받기, the difference of barbell height was decreased after offering feedback in three of five subjects and this represents advancement of technical skills after offering feedback. However, the rest of them weren't variable or narrow increasing. This result represents that feedback system could not brought tremendous effects. 7. In terms of last-pull phase, the angular velocity of knee joint was increased after offering feedback in four of five subjects and this represents advancement of technical skills after offering feedback. However, the rest of them, only one subject, decreased. This result represents that feedback system could not brought tremendous effects. 8. In terms of last-pull, the conversional tendency of maximal extension to flextion came out all but simultaneously without offering feedback in four of five subjects. This is well-performed technique. Only one subject, however, could not use power effectively because the fact that his maximal extension came out in serial, from ankle to knee and waist means dispersion of power. In addition to, after offering feedback, only one subject made increasing the maximal extension of knee in last-pull and this result represents advancement of skills after offering feedback. However, the rest of them could not make meaningful development after offering feedback. 9. It might be assumed that searching for technical merits and demerits of each weight lifting player through qualitative motion analysis system could improve player's skill.

• The Korean Journal of Physiology
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• 제2권2호
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• pp.83-92
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• 1968

A study was planned to evaluate the effects of removal of the cingulate cortex upon the occurrence of any behavior commonly displayed by the rat, and to compare the effects of cingulectomy with those of removal of the parietal, parieto-occipital, or occipital regions. The subjects were 54 male albino rats (Holtzman strain, body weight $200{\sim}330\;gm$) including 14 rats in which the cingulate gyri between splenium and genu of the corpus callosum were bilaterally ablated by suction (cingulate group), 9 animals which had their parietal cortices (chiefly area 7) partially removed (parietal group), 9 rats whose parietal and occipital regions (chiefly areae 7 & 17), 13 animals in which the occipital cortices (chiefly area 17) were removed bilaterally (occipital group), and 9 normal rats (normal control group). Eighteen observation cages, each of which housed a subject and was provided with food and water ad lib., were arranged in 6 rows on a rack and the behavior of each subject was scanned by an observer at a distance of 1.5 m from the rack. The observer scanned the first and second rows 6 times in 1 min, then proceeded to the 3rd and 4th rows, scanning for another 1 min, and finally to the 5th and 6th rows. The speed of scanning was such that behavioral observations of all of the 18 rats were completed in 3 min, each subject receiving 6 observations. The scanning was repeated every 3 min for 18 min, which constituted one observation session and was followed by a 72 minutes' recess. The whole procedure was repeated through 24 hours so that a total of 576 behavioral observations were made on each subject in 16 observation sessions. Behaviors checked were sleeping, lying, lying and sniffing, standing, standing and sniffing, exploring, eating, drinking, grooming (included were washing, licking, and scratching), and others. Results obtained were as follows: 1. The cingulate group ate significantly more often than the normal control, the parietal, and the parieto-occipital groups. 2. Exploration was significantly less frequent in the cingulate group than in the normal control, the parietal, and the occipital groups. There was, in the case of the cingulate group, a significant negative correlation between the occurrence of eating and the exploratory activity. 3. The general activity, as judged from the value obtained by adding the occurrence of exploration, eating, drinking, grooming, and standing and sniffing, was significantly increased in the cingulate group compared with those of any other groups including the normal control. 4. Though statistically insignificant, the cingulate group slept least often among all the animal groups tested. 5. The parieto-occipital group tended to groom less, and the parietal group to eat less often than the normal control group did, but the difference was not significant. There were no significant differences among all the groups except the cingulate group as regards other behaviors analyzed. Based on the above results, it was inferred that the cingulate cortex exerts an inhibitory influence upon the occurrence of eating and general activity, while it tends to facilitate the occurrence of sleep.

• Wind and Structures
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• 제10권6호
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• pp.543-554
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• 2007

The suspension bridge is situated in an area of complex topography with both open sea and overland turbulence characteristics, and it is subject to frequent typhoon occurrences. This paper investigates experimentally the possible vortex shedding events of the structure under high wind and typhoon conditions. A single-degree-of-freedom model for the vibration of a unit bridge deck section is adopted to determine the amplitude of vibration and to estimate the parameters related to the lifting force in a vortex shedding event. The results of the studies are presented in a companion paper (Law, et al. 2007). In this paper, statistical analysis on the measured responses of the bridge deck shows that the vibration response at the first torsional mode of the structure has a significant increase at and beyond the critical wind speed for vortex shedding as noted in the wind tunnel tests on a section model of the structure.

• 한국정밀공학회지
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• 제22권4호
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• pp.27-36
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• 2005

Some studies have shown that unstable factors are inherent in WEDM process, causing the instability of the discharging pulse to reach about 40∼60％ in normal machining. Transient stability is an important subject in WEDM process since there is a close relationship between stability and machining performance, such as the characteristics of a machined surface, machining speed and problem of instability like wire rupture phenomenon. Among the many machining parameters affecting WEDM machining state, three specific parameters (Vr, Ip, off time ) are major controllable variables that can be applied in transient stability control. And, this research investigates the implementation and analysis of real-time micro control of the discharging stability of WEDM (Wire Electric Discharge Machining) process.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2003년도 춘계전력전자학술대회 논문집(1)
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• pp.5-9
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• 2003

Conventional variable-speed Induction motor drives with inverters are subject to detrimental effect of zero-sequence voltages, such a shaft voltage and bearing current. This paper presents a way of the suppression of the zero-sequence components in multilevel H-bridge inverters. First examined Is the inherent zero-sequence characteristic of the conventional subharmonic PW method. Then it is shown that the zero-sequence voltage can be eliminated with proper -selection of switching states with space vector modulation. Although this method alone restricts the linear modulation range of control, a combination of the proposed method and the minimum switching method appears to be effective in suppressing the zero-sequence voltage to minimum level while maintaining the linear control range.

• 한국지능시스템학회:학술대회논문집
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• 한국퍼지및지능시스템학회 2003년도 ISIS 2003
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• pp.16-19
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• 2003

This paper describes research on mental commit robot that seeks a different direction from industrial robot, and that is not so rigidly dependent on objective measures such as accuracy and speed. The main goal of this research is to explore a new area in robotics, with an emphasis on human-robot interaction. In the previous research, we categories robots into four categories in terms of appearance. Then, we introduced a cat robot and a seal robot, and evaluated them by interviewing many people. The results showed that physical interaction improved subjective evaluation. Moreover, a priori knowledge of a subject has much influence into subjective interpretation and evaluation of mental commit robot. In this paper, 133 subjects evaluated the seal robot, Paro by questionnaires in an exhibition at the National Museum of Science and Technology in Stockholm, Sweden. This paper reports the results of statistical analysis of evaluation data.