• Safety and Health at Work
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• 제10권1호
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• pp.87-94
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• 2019

Background: Lead (Pb) exposure in shooting ranges has been reduced by various measures such as jacketed ammunition and lead-free primers. Nevertheless, this may lead to exposure to other metals, potentially resulting in adverse health effects. Methods: In a cross-sectional study, 35 subjects from seven different shooting ranges were studied: four shooting instructors, 10 police officers, 15 Special Forces, and six maintenance staff members. Metals and metalloids were determined in blood and urine by inductively coupled plasma-mass spectrometry. Results: The concentrations of most elements did not differ significantly between groups or compared to reference values, except for Sb and Pt in urine and Pb in blood. Mean values for Sb were considerably higher in urine from the Special Forces ($0.34{\mu}g/L$), the maintenance staff ($0.13{\mu}g/L$), and shooting instructors ($0.32{\mu}g/L$) compared to the police officers before shooting ($0.06{\mu}g/L$) and a Belgian reference value ($0.04{\mu}g/L$). For Pt, the Special Forces showed higher mean urinary concentrations ($0.078{\mu}g/L$) compared to a Belgian reference value (<$0.061{\mu}g/L$). Mean values for blood lead were markedly higher in the Special Forces ($3.9{\mu}g/dL$), maintenance staff ($5.7{\mu}g/dL$), and instructors ($11.7{\mu}g/dL$) compared to police officers ($1.4{\mu}g/dL$). One instructor exceeded the biological exposure index for blood Pb ($38.8{\mu}g/dL$). Conclusion: Since both Pb and Sb were found to be higher in shooting range employees, especially among frequent shooters, it is advisable to provide appropriate protective equipment, education, and medical follow-up for shooting range personnel in addition to careful choice of ammunition.

• 한국콘텐츠학회논문지
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• 제21권1호
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• pp.39-54
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• 2021

본 연구는 2030 청년세대의 모바일 정보 활용수준에 따라 집단을 유형화하고, 유형별 소비자역량과 생활 만족도에 차이가 있는지 실증하고자 하였다. 그리고 세대 내 정보격차에 영향을 미칠 수 있는 요인을 파악하고 자 하였다. 이를 위해 2018년 디지털 정보격차 실태조사 원자료를 활용하여 총 1779부의 유효데이터를 분석하였다. 연구결과, 2030 청년세대의 정보 활용요인은 '개인의 정보활동', '공유활동', '생활서비스', '사회참여', '정보 및 네트워킹', '경제활동'으로 도출되었다. 정보 활용수준에 따라 소비자는 준거집단(46.5%), 고활용집단(27.2), 저활용집단(26.3%) 3가지로 유형화되었으며, 유형별 인구통계학적 특성, 소비자역량, 생활 만족도에서 통계적으로 유의한 차이가 있었다. 그리고 준거집단과 비교하여, 고활용집단과 저활용집단의 정보격차에 영향을 미칠 수 있는 요인을 확인하였다. 본 연구는 2030 청년세대 내 정보 활용수준이 유의한 차이가 있음을 확인하고, 이러한 차이가 정보격차로 이어질 가능성을 피력하였다는 것에 의의가 있다. 청년세대 역시 정보격차의 대상이 될 수 있으며, 향후 정책이나 교육에서도 청년세대 정보격차에 대한 발전된 차원의 논의가 필요할 것이다.

• Advances in aircraft and spacecraft science
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• 제1권3호
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• pp.291-310
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• 2014

An advanced model for the linear flutter analysis is introduced in this paper. Higher-order beam structural models are developed by using the Carrera Unified Formulation, which allows for the straightforward implementation of arbitrarily rich displacement fields without the need of a-priori kinematic assumptions. The strong form of the principle of virtual displacements is used to obtain the equations of motion and the natural boundary conditions for beams in free vibration. An exact dynamic stiffness matrix is then developed by relating the amplitudes of harmonically varying loads to those of the responses. The resulting dynamic stiffness matrix is used with particular reference to the Wittrick-Williams algorithm to carry out free vibration analyses. According to the doublet lattice method, the natural mode shapes are subsequently used as generalized motions for the generation of the unsteady aerodynamic generalized forces. Finally, the g-method is used to conduct flutter analyses of both isotropic and laminated composite lifting surfaces. The obtained results perfectly match those from 1D and 2D finite elements and those from experimental analyses. It can be stated that refined beam models are compulsory to deal with the flutter analysis of wing models whereas classical and lower-order models (up to the second-order) are not able to detect those flutter conditions that are characterized by bending-torsion couplings.

• Earthquakes and Structures
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• 제19권1호
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• pp.1-16
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• 2020

This study presents an investigation of the dynamic interactions between a surface structure lying on two different soil deposits and a square-shaped buried structure embedded in the soil. To this end, a large number of numerical models are generated by using a well-known Finite Element Method software, i.e., OpenSEES. The interaction phenomenon is assumed to be affected by six different parameters. In the parametric study, these parameters are assumed to have various values in accordance with the engineering practices. A total of 1620 possible combinations of the parameter values are addressed in this study. 30 different numerical models are also generated as the 'free-field cases' to set a reference. The surface structure drift and acceleration amplifications are used as a measure to evaluate the dynamic interactions. The response (i.e., drifts and accelerations) amplifications are calculated as the ratio of the maximum surface structure response in any 'case' to the maximum surface structure response in corresponding free-field case. Variation of the response amplifications with any of the investigated parameters is addressed in this paper. The results obtained from the numerical analyses clearly reveal that the presence of a buried structure in the vicinity of a surface structure can cause both amplification and de-amplification of the surface structure responses, depending on the case parameters.

• 조명전기설비학회논문지
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• 제15권5호
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• pp.14-19
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• 2001

전계해석법을 이용하여 나타내었다. 이때 모의한 GIS 챔버내 금속이물의 위치는 전극부착시, 외함부착시 그리고 자유운동시로 하였다. 그 결과 GIS챔버의 절연파괴전계의 경우, 전극에 파티클 부착시가 가장 작게 나타났고, 파티클 자유운동시가 중간, 외함에 파티클 부착시가 가장 작게 나타남을 알 수 있었다. 또한 파티클 위치에 따른 전계해석의 경우 전극에 파티클 부착시가 가장 크게 나타났고, 파티클 자유운동시가 중간, 외함에 파티클 부착시가 가장 작게 나타났다. 이 결과는 국내 GIS의 절연설계에 설제적인 참고자료가 될 것으로 사료된다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2001년도 추계학술대회 논문집
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• pp.106-110
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• 2001

The ball-end milling process is widely used in the die/mold industries, and it is very suitable for the machining of free-form surfaces. However, this process is inherently inefficient process to compared with the end-milling or face milling process, since it relays upon the machining at the cutter/surface contact point. The machined part is the result of continuous point-to-point machining on the free-form surface. And cusps (or scallops) remain at the machined part along the cutter paths and they give the geometrical roughness of the workpiece. Thus, for the good geometrical roughness of the workpiece, it is required very tightly spaced cutter paths in this ball-endmilling process. However, with the tight cutter paths, the geometrical roughness of the workpiece is not regular on the workpiece since the cusp height is variable in the previously developed ISO-parametric or Cartesian machining methods. This paper suggests a method of tool path generation which makes the geometrical roughness of workpiece be constant through the machined surface. In this method, Ferguson Surface design Model is used and cusp height is derived from the instantaneous curvatures. And, to have constant cusp height, an increment of parameter u or v is estimated along the reference cutter path. In ball-end milling experiments, the cusp pattern was examined, and it was proved that the geometrical roughness could be regular by suggested tool path generation method.

• Journal of Astronomy and Space Sciences
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• 제23권3호
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• pp.269-288
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• 2006

We revised the OTFTOOL which was developed in Five College Radio Astronomy Observatory (FCRAO) for the On-The-Fly (OTF) observation. Besides the improvement of data resampling function of conventional OTFTOOL, we added a new SELF referencing mode and data pre-reduction function. Since OTF observation data have a large redundancy, we can choose and use only good quality samples excluding bad samples. Sorting out the bad samples is based on the floating level, rms level, antenna trajectory, elevation, $T_{sys}$, and number of samples. And, spikes are also removed. Referencing method can be chosen between CLASSICAL mode in which the references are taken from the OFFs observation and ELLIPSOIDAL mode in which the references are taken from the inner source free region (this is named as SELF reference). Baseline is subtracted with the source free channel windows and the baseline order chosen by the user. Passing through these procedures, the raw OTF data will be an FITS datacube. The revised-OTFTOOL maximizes the advantages of OTF observation by sorting out the bad samples in the earliest stage. And the new self-referencing method, the ELLIPSOIDAL mode, is very powerful to reduce the data. Moreover since it is possible to see the datacube at once without moving them into other data reduction programs, it is very useful and convenient to check whether the data resampling works well or not. We expect that the revised-OTFTOOL can be applied to the facilities of the OTF observation like SRAO, NRAO, and FCRAO.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 춘계학술대회논문집
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• pp.546-551
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• 2001

Space Test Department at KARI(Korea Aerospace Research Institute) plans to carry out the GVT(Ground Vibration Test) for the KSR(Korea Sounding Rocket)-III FM(Flight Model) which is being developed by Space Technology R＆D Division. KSR-III will be an intermediate to the launch vehicle capable of carrying satellites to their orbits. GVT offers very important information to predict the behavior of KSR in its operation, and to develop the flight control and aerodynamic analysis. For development of test facilities, testing and analysis methods which can be used for the future test, Space Test Department has performed the GVT with KSR-II PFM(Proto-Flight Model) at Satellite Integration ＆ Test Center of KARl This paper discusses the procedures, techniques and the results of it. In this test, to simulate free-free condition, test object hung in the air by 4 bungee cords specially devised. The GVT was carried out using pure random excitation technique with MIMO(Multi-Input-Multi-Output) method with three electromagnetic shakers, and poly-reference parameter estimation was used to identify the modal parameters. As the result of the test, 11 mode shapes and modal parameters below 200㎐ were identified and compared with analytical results.

• 한국광학회지
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• 제8권1호
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• pp.68-72
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• 1997

$^{13}$C$_{2}$H$_{2}$ 분자의 빛살 흡수선 중 분산천이 광섬유의 영분산 파장에 가까운 1549.49 nm 파장의 흡수선에 DFB-LD (distributed feedback laser diode)의 주파수를 안정화시켰다. 이 주파수 안정화된 DFB-LD와 광섬유 파브리-페로 필터의 투과 및 반사특성을 이용하여 광섬유 파브리-페로 필터의 중심주파수를 안정화시켰다. 자유분광너비(free spectral range)가 100 GHz인 안정화된 광섬유 파브리-페로 필터의 공진 조건에 파장이 다른 3개의 DFB-LD 빛살을 투과시켜 DFB-LD들을 안정화시킴으로써 주파수분할 다중을 하였다. 또한 레이저를 디더링(dithering) 방법으로 안정화시켰을 때 디더링 전류에 따른 레이저의 선폭변화는 600 MHz/mA였다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제6권4호
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• pp.1024-1040
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• 2014

The theoretical background and a numerical solution procedure for a time domain hydroelastic code are presented in this paper. The code combines a VOF-based free surface flow solver with a flexible body motion solver where the body linear elastic deformation is described by a modal superposition of dry mode shapes expressed in a local floating frame of reference. These mode shapes can be obtained from any finite element code. The floating frame undergoes a pseudo rigid-body motion which allows for a large rigid body translation and rotation and fully preserves the coupling with the local structural deformation. The formulation relies on the ability of the flow solver to provide the total fluid action on the body including e.g. the viscous forces, hydrostatic and hydrodynamic forces, slamming forces and the fluid damping. A numerical simulation of a flexible barge is provided and compared to experiments to show that the VOF-based flow solver has this ability and the code has the potential to predict the global hydroelastic responses accurately.