• 생물정신의학
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• 제16권4호
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• pp.238-245
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• 2009

Objectives : Mild Alzheimer's disease(AD) is uncertain to be related to visuospatial working memory subsystem dysfunction. We used the self ordered pointing test(SOPT) to find the characteristics of visuospatial working memory in mild AD. Methods : We compared the visuospatial working memory abilities of 20 patients with mild AD and 20 normal elderly controls(NC) using SOPT, of which stimuli consisted of two stimuli types(A : abstract, C : concrete) and two stimuli numbers(8 and 12). Therefore, working memory was tested using C8, C12, A8, and A12 stimuli conditions in SOPT. Mixed-model ANOVA was conducted with the AD and NC groups as between-subjects factor, with stimuli types and stimuli numbers as the within-subjects factors and with SOPT error rates as the dependent variable. Results : The AD group showed higher error rates in SOPT than the NC group. The NC group showed low error rates in concrete stimuli than in abstract stimuli and in small stimuli numbers than in large stimuli numbers. And the AD group showed no differences between stimuli types or stimuli numbers. Conclusion : AD patients showed a poor performance in visuospatial working memory using concrete stimuli. The result suggests that there is a non-transformation from visual input to phonological working memory in AD. Patients with AD showed a poor performance although in small stimuli number condition of SOPT. It suggests that in AD, visuospatial working memory is not working well although in low central executive loads.

• 대한방사선기술학회지:방사선기술과학
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• 제26권1호
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• pp.31-37
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• 2003

현재 임상에서 사용중인 국산 30 kHz 용량의 PWM방식의 인버터식 X선 장치의 성능을 장치의 출력정확도, 출력파형의 변화 및 영상증배관의 변환계수 등을 평가하여 그 유용성을 알아보았다. 그 결과 촬영용 장치의 관전류, 관전압, 단시간 특성은 KS규정에 대해 매우 양호한 정확도를 유지했고 출력파형도 양호한 특성을 나타내었다. 또한 촬영시 X선 장치의 출력은 단상대비 약 1.7배 정도 많게 나타났다. 투시장치의 성능에서도 관전류, 관전압 및 sopt촬영 관전류, 관전압 모두 최고 5.8% 이하의 양호한 결과를 나타내었으며, 영상증배관의 변환계수는 2년여 사용한 것을 고려할 때 75kV에서 310으로 상당히 높았다. 국내기술로 개발된 고주파식 X선 장치가 성능의 실용적 단계를 넘는 것으로 나타나 앞으로 고주파식 X선 장치가 국내, 외에 많이 보급되고 이용될 것으로 사료된다.

• 한국위성정보통신학회논문지
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• 제8권4호
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• pp.135-141
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• 2013

지하철은 한국에서 가장 많이 이용하는 대중교통으로 수도권에만 하루 유동인구가 일 천만명에 달하는 무선 통신의 HOT SOPT 이라고 볼 수 있다. 여기에는 3개 통신 사업자의 2G/3G/4G/Wi-Fi/T-DMB의 수많은 주파수와 서비스가 공존해 있으며, 지하철 승객과 전철의 통신운용관리를 위한 지하철 자가망도 공존해 있어, 지하철 승객의 안전과 운행을 위하여 이에 대한 상호간의 전파간섭의 영향여부의 검증이 필요하였다. 본 연구와 시험은 서로 다른 주파수/통신 서비스 간의 전파 간섭여부를 확인하는 방법과 시험을 통하여, 지하철 기관과 이동통신사업자는 각 주파수별의 상호영향 간섭이 없음을 확인하고 지하철 승객에게 안전하고 고품질의 통신서비스를 할 수 있는 검증의 자료로써 확인할 수 있었다. 이러한 검증방법은 지하철 공간에서 뿐만이 아닌 어느 지역에서의 상호간섭여부를 확인할 수 있는 일반적인 검증방법으로 적용이 가능하다.

• Advances in materials Research
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• 제13권4호
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• pp.299-319
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• 2024

Due to higher strength-to-weight ratio of composite laminates, they find uses in many weight-sensitive applications like aerospace, automobile and marine structures. From a reliability point of view, accurate prediction of failure of these structures is important. Due to the complexities in the manufacturing processes of composite laminates, there is a variation in the material properties and geometric parameters. Hence stochastic aspects are important while designing the composite laminates. Many existing works of composite laminate failure analysis are based on the deterministic approach but it is important to consider the randomness in the material properties, geometry and loading to predict accurate failure loads. In this paper the statistics of the ultimate failure load of the [0/θ]_s laminated composite plate (LCP) containing the edge crack and voids subjected to the tensile loading are presented in terms of the mean and coefficient of variance (COV). The objective is to better the efficacy of laminate failure by predicting the statistics of the ultimate failure load of LCP with random material, geometric and loading parameters. The stochastic analysis is done by using the extended finite element method (XFEM) combined with the second-order perturbation technique (SOPT). The ultimate failure load of the LCP is obtained by ply-by-ply failure analysis using the ply discount method combined with the Tsai-Wu failure criterion. The aim is to know the effect of the stacking sequence, crack length, crack angle, location of voids and number of voids on the mean and corresponding COV of the ultimate failure load of LCP is investigated. The results of the ultimate failure load obtained by the present method are in good agreement with the existing experimental and numerical results. It is observed that [0/θ]_s LCPs are very sensitive to the randomness in the crack length, applied load, transverse tensile strength of the laminate and modulus of elasticity of the material, so precise control of these parameters is important. The novelty of the present study is, the stochastic implementation in XFEM for the failure prediction of LCPs containing crack and voids.

• 한국정밀공학회지
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• 제14권6호
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• pp.37-43
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• 1997

The technology of Laser lamination joining of silicon steel sheets has been studied in this paper. Conventional sheets lamination process does not meet the requirments for the improvement electric parts performance. In response to this, a new Laser spot joining method has been developed. This study performs the Laser spot lamination joining while synchronizing the sillicon steel sheets in the dies with the press movement. Several conclusions have been drawn in this paper. Effects of beam focus, power, atmosphere gas and press oil etc.

• 한국생산제조학회지
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• 제8권6호
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• pp.113-118
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• 1999

In order to evaluate strength of spot welded joint, at first it is importent that we should know strain distribution near nugget zone. During loading, in HAZ, compressive strain increase with Increase of load, but in nugget zone tensile strain increase. During unloading, on the other hand, even through the decreases, the strain variation is not almost appeared in nugget zone and HAZ. In nugget boundary zone, the strain range increases continuously along with load increase on outer surface, but the strain increases continunously and decreases rapidly beyond yield strength on inner surface. In this paper, strain distribution are measured in inner and outer surface with variation of thickness and load under tensile-shear load. Tensile-shear strength increased as with increase of specimen thickness. As for thickness increase rates are 25%, 50%, 100%, and 150%, tensile-shear strength in crease rates are 40%, 81%, 130% and 228%.

• Steel and Composite Structures
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• 제26권1호
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• pp.1-15
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• 2018

This study reported, the effect of random variation in system properties on bending response of single wall carbon nanotube reinforced composite (SWCNTRC) plates subjected to transverse uniform loading is examined. System parameters such as the SWCNT armchair, material properties, plate thickness and volume fraction of SWCNT are modelled as basic random variables. The basic formulation is based on higher order shear deformation theory to model the system behaviour of the SWCNTRC composite plate. A C0 finite element method in conjunction with the first order perturbation technique procedure developed earlier by the authors for the plate subjected to lateral loading is employed to obtain the mean and variance of the transverse deflection of the plate. The performance of the stochastic SWCNTRC composite model is demonstrated through a comparison of mean transverse central deflection with those results available in the literature and standard deviation of the deflection with an independent First Order perturbation Technique (FOPT), Second Order perturbation Technique (SOPT) and Monte Carlo simulation.

• Journal of Welding and Joining
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• 제5권3호
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• pp.11-18
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• 1987

Effects of electrode tips shapes of spot welding on the galvannealed steel have been studied, and the results obtained from this studies are as follows. 1) Expulsion had no effect on the shear strength of the specimen but been observed on the tensile strength of the specimen. 2) Effect of holding time after welding was neglegible when the spot welding supplies enough heat input. 3) Depending on the sopt welding tip shape it has different weldbility. It has better weldability in the order of pointed shape, truncated shape and dome shape. But the effect of coolind was just the opposite of the above order.

• 한국콘텐츠학회논문지
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• 제5권6호
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• pp.129-137
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• 2005

저궤도 위성통신시스템의 성능분석은 다양한 요소로 다양하게 시도되고 있다. 본 논문은 저궤도 위성통신시스템의 이전까지 연구에 없었던 사용자 밀집도를 고려한 셀 내 단말기 분포에 따른 간섭의 변화를 살펴보고, 단말기 분포 평균 거리에 따른 최대 사용자 수를 살펴보았다. 또한 저궤도 이동 통신시스템에 사용하는 안테나 종류(tapered-apertured antenna gaussian antenna)의 스폿 빔 isolation값에 따른 간섭을 살펴보았다. 이러한 간섭을 저궤도 위성 통신 시스템의 채널용량에 대입하여, 중요한 파라미터(대역폭, 캐리어 수)를 가지고 성능분석을 하였다. tapered-apertured antenna와 gaussian antenna를 비교함으로써, 어느 안테나가 간섭에 더 효과적이고 최적인지 알아보고자 한다.

• Advances in aircraft and spacecraft science
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• 제4권5호
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• pp.585-611
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• 2017

This article covenants with the post buckling witticism of carbon nanotube reinforced composite (CNTRC) beam supported with an elastic foundation in thermal atmospheres with arbitrary assumed random system properties. The arbitrary assumed random system properties are be modeled as uncorrelated Gaussian random input variables. Unvaryingly distributed (UD) and functionally graded (FG) distributions of the carbon nanotube are deliberated. The material belongings of CNTRC beam are presumed to be graded in the beam depth way and appraised through a micromechanical exemplary. The basic equations of a CNTRC beam are imitative constructed on a higher order shear deformation beam (HSDT) theory with von-Karman type nonlinearity. The beam is supported by two parameters Pasternak elastic foundation with Winkler cubic nonlinearity. The thermal dominance is involved in the material properties of CNTRC beam is foreseen to be temperature dependent (TD). The first and second order perturbation method (SOPT) and Monte Carlo sampling (MCS) by way of CO nonlinear finite element method (FEM) through direct iterative way are offered to observe the mean, coefficient of variation (COV) and probability distribution function (PDF) of critical post buckling load. Archetypal outcomes are presented for the volume fraction of CNTRC, slenderness ratios, boundary conditions, underpinning parameters, amplitude ratios, temperature reliant and sovereign random material properties with arbitrary system properties. The present defined tactic is corroborated with the results available in the literature and by employing MCS.