• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2004년도 학술대회지
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• pp.186-194
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• 2004

Experiments were conducted to determine the structural static and dynamic characteristics of air foil bearings. The housing of the bearing on the journal was driven by an impact hammer which was used to simulate dynamic forces acting on the bump loll with various leading condition. Two different bump foils (Cu-coated bump and viscoelastic bump) were tested and the static and dynamic coefficients of two bump foils compared, based on the experimental measurements for a wide range of operating conditions. The static and dynamic characteristics of air foil bearings were extracted 0rpm the frequency response function by least square method and IV(Instrumental Variable) method. The experiment was tested at 0rpm and $10,000\~16,000rpm$, and loaded on $50\~150N$. From the test results, the possibility of the application of high load and high speed condition is suggested.

• 한국안전학회지
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• 제32권3호
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• pp.141-150
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• 2017

A rapid increase in traffic accidents involving senior vehicle occupants has been an issue in Korea because of the aging of the population occurring at one of the fastest rates in the world; unfortunately, few studies beyond several looking at the effect of senior occupants on the level of accident injury severity can be found in the literature. A Multinomial logit model was estimated with Newton-Raphson algorithm to perform bias-reducing penalized likelihood optimization. Model covariates integral to developing the model were included, but the main focus was on the interaction of seating position and injury to senior vehicle occupants. It was found that the likelihood of an accident resulting in a fatality increased: 2.2 times for the driver seat, 2.7 times for the front passenger seat, and even 6.7 times for the rear seat. A mandatory seatbelt law to be extended to the rear seat needs to pass the assembly as soon as possible, and government, industry, and safety groups should be encouraged to join forces to strongly carry out targeted campaigns for the wearing of seatbelts in all vehicle seats to enhance the safety of senior occupants as well as other occupants who are vulnerable to road traffic accidents.

• 경영과학
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• 제19권2호
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• pp.25-39
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• 2002

This study suggests a revised TAM (Technology Acceptance Model)-based performance evaluation model in MS (management science) education. Recently, many MS education programs are developed on the basis of computer and Internet communication technology. Previous researchers used TAM as an individual performance evaluation model, and proved that perceived usefulness and perceived ease of use are the substantive successful factors. This study provides a revised TAM-based conceptual framework for understanding what is involved in improving university MS education and what might be implied by conducting research on its improvement. It is argued in this research that three sets of forces and conditions have a direct and indirect impact on MS education ; first, each student has self efficacy and it is a critical determinant of behavior next, the use of Internet-based information system at MS education affects on the renewal of MS education : and finally, perceived usefulness and perceived ease of use have impacts on behavioral intention and actual system usage. This research concludes with suggestions for which direction this framework provides for future research on the premise and limits of efforts to renew MS education in university.

• Smart Structures and Systems
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• 제11권1호
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• pp.87-102
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• 2013

Vibration-based damage detection methods are popular for structural health monitoring. However, they can only detect fairly large damages. Usually impact pulse, ambient vibrations and sine-wave forces are applied as the excitations. In this paper, we propose the method to use the chaotic excitation to vibrate structures. The attractors built from the output responses are used for the minor damage detection. After the damage is detected, it is further quantified using the Kalman Filter. Simulations are conducted. A 5-story building is subjected to chaotic excitation. The structural responses and related attractors are analyzed. The results show that the attractor distances increase monotonously with the increase of the damage degree. Therefore, damages, including minor damages, can be effectively detected using the proposed approach. With the Kalman Filter, damage which has the stiffness decrease of about 5% or lower can be quantified. The proposed approach will be helpful for detecting and evaluating minor damages at the early stage.

• Wind and Structures
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• 제23권6호
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• pp.577-594
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• 2016

In this paper a practical modelling methodology is presented for a series of aero- servo- elastic- coupled numerical analyses of small wind turbine operation, with particular emphasis on variable speed generator modelling in various wind speed conditions. The following characteristics are determined using the available computer tools: the tip speed ratio as a function of the generator constant (under the assumption of constant wind speed), the turbine coefficient of power as a function of the tip speed ratio (the torque curve is modified accordingly and generator speed and power curves are plotted), turbine power curves and coefficient of power curve as functions of the incoming wind speed. The last stage is to determine forces and torques acting on rotor blades and turbine tower for specific incoming wind speeds in order to examine the impact of the stall phenomena on these values (beyond the rated power of the turbine). It is shown that the obtained results demonstrate a valuable guideline for small wind turbines design process.

• Structural Engineering and Mechanics
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• 제62권6호
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• pp.725-737
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• 2017

An analytical method considering axial equilibrium is proposed for the short- and long-term analyses of shear lag effect in reinforced concrete (RC) box girders. The axial equilibrium of box girders is taken into account by using an additional generalized displacement, referred to as the longitudinal displacement of the web. Three independent shear lag functions are introduced to describe different shear lag intensities of the top, bottom, and cantilever plates. The time-dependent material properties of the concrete are simulated by the age-adjusted effective modulus method (AEMM), while the reinforcement is assumed to behave in a linear-elastic fashion. The differential equations are derived based on the longitudinal displacement of the web, the vertical displacement of the cross section, and the shear lag functions of the flanges. The time-dependent expressions of the generalized displacements are then deduced for box girders subjected to uniformly distributed loads. The accuracy of the proposed method is validated against the finite element results regarding the short- and long-term responses of a simply-supported RC box girder. Furthermore, creep analyses considering and neglecting shrinkage are performed to quantify the time effects on the long-term behavior of a continuous RC box girder. The results show that the proposed method can well evaluate both the short- and long-term behavior of box girders, and that concrete shrinkage has a considerable impact on the concrete stresses and internal forces, while concrete creep can remarkably affect the long-term deflections.

• Geomechanics and Engineering
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• 제13권2호
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• pp.301-318
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• 2017

Based on the existing research results, a three-dimensional failure mechanism of tunnel face was constructed. The dynamic seismic effect was taken into account on the basis of quasi-static method, and the nonlinear Mohr-Coulomb failure criterion was introduced into the limit analysis by using the tangent technique. The collapse pressure along with the failure scope of tunnel face was obtained through nonlinear limit analysis. Results show that nonlinear coefficient and initial cohesion have a significant impact on the collapse pressure and failure zone. However, horizontal seismic coefficient and vertical seismic proportional coefficient merely affect the collapse pressure and the location of failure surface. And their influences on the volume and height of failure mechanism are not obvious. By virtue of reliability theory, the influences of horizontal and vertical seismic forces on supporting pressure were discussed. Meanwhile, safety factors and supporting pressures with respect to 3 different safety levels are also obtained, which may provide references to seismic design of tunnels.

• 지역연구
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• 제6권2호
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• pp.107-121
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• 1990

The structural change of occupational composition with the coming of post-industrial society is most evidently observed in the developed country. Specially representative of social changes is the emergence of new occupational sectors, such as the so-called quaternary and quinary sectors, which are based on the use of information technology and managerial skills. The paper raises the question of how and in what this chage of occupational components in a mtro area affects the existing residential structure over the period. In order to extend the discussion of the question, the related hypothetical statements on urban spatial impact due to transformation of the society have xtnsively considered and identified a possible multicenter structure concentration and deconcentration of new jobs and population over the metro area. For further examination, the renowned high tech city of Minneaplis -St. Paul has been selected and the occupational labour forces data for 1960 and 1980 analyzed. As a whole, this area has experienced a dispersal and reconcentration of population in new patterns which have resulted from changes in the occupational structure. In particular, the residential area of white-coller workers(the quaternary / quinary or information workers) has expanded into the city from a suburban core area. In this process, a large proportion of the manual-worker's residential areas in the central city either disappeared or diminished. Consequently, other isolated centers created by the manualworker residents are emerging in both the central city and suburbs. Thus, the development of mulitple centers or cores based on the distribution of occupational characteristics can be considered as a typical ongoing pattern of metro areas in the Unite States.

• The Journal of Asian Finance, Economics and Business
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• 제5권2호
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• pp.63-72
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• 2018

Researches based on the pattern of planned behavior holds that the three variables of entrepreneurial attitudes, subjective norms, and perceived behavior control influence each other and influence entrepreneurial intentions respectively. However, there are also different, even conflicting research conclusions that continue to emerge. Researches based on the pattern of alertness, believe that profit opportunities and individuals' pursuit to truth are the driving forces. Many scholars have demonstrated the impact of individual entrepreneurial alertness on entrepreneurial intentions. However, as an exogenous causal agent, profit opportunities have a logical problem: if there are no other assumptions, the mere existence of opportunities does not adequately explain entrepreneurial alertness. To address this gap, this study considered samples from mainland China, where entrepreneurial activities are very active currently, to test the role that entrepreneurial alertness is assumed to play in the planned behavior model. The results show that the three dimensions of alertness, individually partly intermediate the influence of entrepreneurial attitude on entrepreneurial intention, the influence of subjective norms on entrepreneurial intention, and that of perceived behavior control on entrepreneurial intention. This article studied the production of entrepreneurial intention by integrating the two patterns of planned behavior and alertness through empirical analysis, and opened up a new field for subsequent research on entrepreneurial intention.

• 항공우주시스템공학회지
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• 제6권1호
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• pp.26-32
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• 2012

A shock absorber with magnetic effects is suggested for a lunar space-ship expected to launch in 2025. The device consists of a copper steel combined tube, two magnets, and a piston. The piston is designed to move a magnet through the tube when it is pushed by an external impact. While the magnet is moving in the tube, it generates the eddy current force with the copper part of the tube and it also makes the large friction force with the steel part of the tube. Beside, it gets resistive forces against its movement such as the magnetic force with a steel-ring at the first time of the movement and the repulsive force with a same pole opposed magnet at the end time of the movement. In this thesis, results of analyses and experiments of each force are represented and the expected performance of the electromagnetic shock absorber is drawn from the results.