• Investigative Magnetic Resonance Imaging
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• 제25권2호
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• pp.81-92
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• 2021

The role of neuroimaging in patients with acute ischemic stroke has been gradually increasing. The ultimate goal of stroke imaging is to make a streamlined imaging workflow for safe and efficient treatment based on optimized patient selection. In the era of multimodal comprehensive imaging in strokes, imaging based on computed tomography (CT) has been preferred for use in acute ischemic stroke, because, despite the unique strengths of magnetic resonance imaging (MRI), MRI has a longer scan duration than does CT-based imaging. However, recent improvements, such as multicoil technology and novel MRI acceleration techniques, including parallel imaging, simultaneous multi-section imaging, and compressed sensing, highlight the potential of comprehensive MR-based imaging for strokes. In this review, we discuss the role of stroke imaging in acute ischemic stroke management, as well as the strengths and limitations of MR-based imaging. Given these concepts, we review the current MR acceleration techniques that could be applied to stroke imaging and provide an overview of the previous research on each essential sequence: diffusion-weighted imaging, gradient-echo, fluid-attenuated inversion recovery, contrast-enhanced MR angiography, and MR perfusion imaging.

• 가족자원경영과 정책
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• 제27권4호
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• pp.19-33
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• 2023

본 연구는 중국 유학생의 가족건강성이 SNS 중독경향성에 미치는 영향에서 자아탄력성의 매개효과를 살펴보고자 하였다. 이를 위해 한국에 재학 중인 중국 유학생 349명을 대상으로 설문조사를 진행하였고 수집된 자료는 SPSS Statistics version 28 프로그램과 SPSS Process Macro 4.3으로 분석하였다. 주요 연구결과는 다음과 같다. 첫째, 중국 유학생의 SNS 중독경향성, 가족건강성, 자아탄력성을 살펴보면 중간보다 높은 수준으로 나타났다. 둘째, 중국 유학생의 SNS 중독경향성은 SNS 하루 평균 이용 시간은 정적 상관관계를, 가족건강성과 자아탄력성과는 부적 상관관계를 나타냈다. 셋째, 위계적 회귀분석 결과, 성별, 가족과의 연락 빈도, SNS 하루 평균 이용 시간, 가족건강성 중 질적 유대감, 자아탄력성 중 통제성이 유학생들의 SNS 중독경향성에 영향을 미치는 것으로 나타났다. 넷째, 가족건강성이 SNS 중독경향성에 미치는 영향에서 자아탄력성이 완전 매개효과가 있었다. 본 연구는 중국 유학생의 SNS 중독경향성을 예방하는 변인으로 가족건강성과 자아탄력성을 밝혔으며, 이를 통해 중국 유학생의 SNS 중독경향성을 예방하기 위해 상담 개입의 방향성을 제시하였다.

• Journal of the Korean Data and Information Science Society
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• 제15권3호
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• pp.655-662
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• 2004

In this paper, we assume that strengths of two components system follow a type II bivariate Pareto model with bivariate type I censored data. And these two components are subjected to a common stress which is independent of the strengths of the components. We obtain estimators for the system reliability based on likelihood function and relative frequency, respectively. Also we construct approximated confidence intervals for the reliability based on maximum likelihood estimator and relative frequency estimator, respectively. Finally we present a numerical study.

• 한국기계가공학회지
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• 제20권8호
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• pp.52-59
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• 2021

In this study, we experimentally evaluated the mechanical properties and geometric form accuracy in FDM 3D printing processes based on the printing direction, building direction, and layer thickness. The specimen test results showed that the tensile strength increased by over 33% in the printing direction compared to the direction perpendicular to printing and the tensile strength becomes larger as the layer thickness decreased. Furthermore, the tensile and impact strengths in the building direction were significantly reduced due to the difference in the interlayer joining and bonding strengths of the fused material. Additionally, shrinkage of the material due to phase change induced curl distortion especially in thin and long 3D-printed products, which increased as the layer thickness increased.

• Geomechanics and Engineering
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• 제29권3호
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• pp.219-228
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• 2022

The most widely used parameter to represent rock abrasiveness is the Cerchar abrasivity index (CAI). The CAI value can be applied to predict wear in TBM cutters. It has been extensively demonstrated that the CAI is affected significantly by cementation degree, strength, and amount of abrasive minerals, i.e., the quartz content or equivalent quartz content in rocks. The relationship between the properties of rocks and the CAI is investigated in this study. A database comprising 223 observations that includes rock types, uniaxial compressive strengths, Brazilian tensile strengths, equivalent quartz contents, quartz contents, brittleness indices, and CAIs is constructed. A linear model is developed by selecting independent variables while considering multicollinearity after performing multiple regression analyses. Machine learning-based regression methods including support vector regression, regression tree regression, k-nearest neighbors regression, random forest regression, and artificial neural network regression are used in addition to multiple linear regression. The results of the random forest regression model show that it yields the best prediction performance.

• 한국지진공학회논문집
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• 제27권1호
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• pp.49-57
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• 2023

This study investigated the rocking behavior of unreinforced masonry walls and wall piers under cyclic loading. Based on the benchmark tests, the characteristics of load-deformation relations in masonry walls with rocking failure were captured, focusing on observed deformation modes. The rocking strengths of masonry walls (i.e., peak and residual strengths) were evaluated, and the effects of opening configurations on the masonry wall strength were examined. The deformation capacity of the rocking behavior and the hysteresis shape of the load-deformation relations were also identified. Based on the results, modeling approaches for the rocking behavior of masonry walls were discussed.

• 한국지반신소재학회논문집
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• 제16권2호
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• pp.55-66
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• 2017

본 연구에서는 지반 특성에 관계없이 일률적으로 적용되는 피에조콘 관입속도 2cm/s 조건 하에서, 저소성 실트 지반의 경우 부분배수 내지는 완전 배수 현상이 발생된다는 관점에서 저소성 실트 지반의 비배수전단강도선과 완전배수 전단강도선 사이에서의 피에조콘계수($N_{kt}$)에 의한 전단강도 분포 경향을 기준으로 부분배수 전단강도를 평가하였다. 그 결과, 인천, 화성 및 군산 저소성 실트 지반의 부분배수 내부마찰각(${\varphi}^{\prime}$)은 $3{\sim}15^{\circ}$에서 분포하는 것으로 분석되었다. 한편, 강제치환 역해석 결과 및 비압밀비배수 삼축시험으로부터 얻어진 내부마찰각(${\varphi}^{\prime}$)은 소성지수 감소에 따라 $2{\sim}14^{\circ}$의 범위에서 분포되어, CPTU 데이터에 의한 부분배수 내부마찰각(${\varphi}^{\prime}$)과 유사한 경향을 나타내어 이에 대한 적용성을 확인할 수 있었다.

• 한국심리학회지 : 코칭
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• 제6권1호
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• pp.1-32
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• 2022

본 연구의 목적은 초등학교에 다니는 느린학습자를 대상으로 심리·사회성숙도 향상을 위한 강점기반 미술치료 코칭 프로그램을 개발 적용하여 효과성을 검증하는 데 있다. 이를 위해 서울지역에 거주하는 초등학생 느린학습자 32명을 선정하여 실험집단 16명, 통제집단 16명을 구성하였다. 실험집단 16명을 대상으로 강점기반 미술치료 코칭프로그램을 주 1회 60분씩 총 10회 실시하였다. 프로그램의 주 내용은 긍정심리기반 강점을 인식하고 일상생활에서 강점을 활용하는 것, 나의 감정과 타인의 감정을 인식하고 공감하는 것, 구체적인 의사표현 방법을 터득하고 표현해보도록 하는 등의 내용으로 구성되어졌다. 프로그램의 효과성 검증을 위해 심리·사회성숙도 검사(정서적안정감, 사회적유능감, 의사소통능력, 학교생활적응력, 대인관계친화력)를 사전, 사후, 추후1(4주 후), 추후2(12주 후)로 실시한 결과, 사전-사후 유의미하게 향상되었고 프로그램 지속성도 검증되었다. 본 연구결과를 통한 연구의 시사점, 연구의 제한점, 향후 연구에 대한 제언 등으로 논의하였다.

• 한국농공학회논문집
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• 제53권5호
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• pp.25-33
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• 2011

In this paper, the effects of aggregate and curing temperature on strength development characteristics of UP (Unsaturated Polyester)-MMA (Methyl Methacrylate) based polymer mortar under sub-zero temperature are experimentally investigated to provide a criterion for repair and production of precast products. The result showed that the setting time of the binder was 4 minutes at $20^{\circ}C$ whereas 35 minutes at $-20^{\circ}C$. The result also revealed that the compressive, flexural, and splitting tensile strengths of UP-MMA based polymer mortar significantly decreased as the aggregate and curing temperatures decreased. However, sufficient strengths which can be implemented in actual practices -36.6 MPa of compressive strength, 6.11 MPa of flexural strength, and 5.81 MPa of splitting tensile strength - were obtained even though both aggregate and curing temperatures were $-20^{\circ}C$. Strength development of polymer mortar is largely affected by curing temperature rather than aggregate temperature. It was found that the effects of aggregate temperature on strength development become smaller as the curing temperature becomes lower. Also, toughness, a ratio of compressive strength to flexural strength, increased from 3.5 to 5.9 as both aggregate and curing temperatures decreased from $20^{\circ}C$ to $-20^{\circ}C$.

• Advances in concrete construction
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• 제8권4호
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• pp.277-283
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• 2019

In evaluating explosion-protection capacity, safety distance is broadly accepted as the distance at which detonation of a given explosive causes acceptable structural damage. Safety distance can be calculated based on structural response under blast loading and damage criteria. For the applicability of the safety distance, the minimum required stand-off distance should be given when the explosive size is assumed. However, because of the nature of structures, structural details and material characteristics differ, which requires sensitivity analysis of the safety distance. This study examines the safety-distance sensitivity from structural and material property variations. For the safety-distance calculation, a blast analysis module based on the Kingery and Bulmash formula, a structural response module based on a Single Degree of Freedom model, and damage criteria based on a support rotation angle were prepared. Sensitivity analysis was conducted for the Reinforced Concrete one-way slab with different thicknesses, reinforcement ratios, reinforcement yield strengths, and concrete compressive strengths. It was shown that slab thickness has the most significant influence on both inertial force and flexure resistance, but the compressive strength of the concrete is not relevant.