• 한국재료학회지
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• 제28권6호
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• pp.365-369
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• 2018

We perform density functional theory calculations to study the CO and $O_2$ adsorption chemistry of Pt@X core@shell bimetallic nanoparticles (X = Pd, Rh, Ru, Au, or Ag). To prevent CO-poisoning of Pt nanoparticles, we introduce a Pt@X core-shell nanoparticle model that is composed of exposed surface sites of Pt and facets of X alloying element. We find that Pt@Pd, Pt@Rh, Pt@Ru, and Pt@Ag nanoparticles spatially bind CO and $O_2$, separately, on Pt and X, respectively. Particularly, Pt@Ag nanoparticles show the most well-balanced CO and $O_2$ binding energy values, which are required for facile CO oxidation. On the other hand, the $O_2$ binding energies of Pt@Pd, Pt@Ru, and Pt@Rh nanoparticles are too strong to catalyze further CO oxidation because of the strong oxygen affinity of Pd, Ru, and Rh. The Au shell of Pt@Au nanoparticles preferentially bond CO rather than $O_2$. From a catalysis design perspective, we believe that Pt@Ag is a better-performing Pt-based CO-tolerant CO oxidation catalyst.

• Asian Pacific Journal of Cancer Prevention
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• 제15권17호
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• pp.7187-7193
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• 2014

Background: The aim of this meta-analysis was to compare sensitivities and specificities of fine needle aspiration (FNA) and core needle biopsy (CNB) in the diagnosis of thyroid cancer. Materials and Methods: Articles were screened in Medline, the Cochrane Library, EMBASE and Google Scholar, and subsequently included and excluded based on the patient/problem-intervention-comparison-outcome (PICO) principle. Primary outcome was defined in terms of diagnostic values (sensitivity and specificity) of FNA and CNB for thyroid cancer. Secondary outcome was defined as the accuracy of diagnosis. Compiled FNA and CNB results from the final studies selected as appropriate for meta-analysis were compared with cases for which final pathology diagnoses were available. Statistical analyses were performed for FNA and CNB for all of the selected studies together, and for individual studies using the leave-one-out approach. Results: Article selection and screening yielded five studies for meta-analysis, two of which were prospective and the other three retrospective, for a total of 1,264 patients. Pooled diagnostic sensitivities of FNA and CNB methods were 0.68 and 0.83, respectively, with specificities of 0.93 and 0.94. The areas under the summary ROC curves were 0.905 (${\pm}0.030$) for FNA and 0.745 (${\pm}0.095$) for CNB, with no significant difference between the two. No one study had greater influence than any other on the pooled estimates for diagnostic sensitivity and specificity. Conclusions: FNA and CNB do not differ significantly in sensitivity and specificity for diagnosis of thyroid cancer.

• 한국구조물진단유지관리공학회 논문집
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• 제21권4호
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• pp.110-115
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• 2017

이 연구는 상변화 물질(저온 PCM)을 포함한 경량 콘크리트의 기계적 성능을 검토하기 위해 수행되었다. Micro capsulised PCM은 wax type core와 melamine based wall으로 구성되어있다. 또한, 단일 종류의 PCM의 경우, Vermiculite에 파라핀 왁스를 삽입하고 그 표면을 멜라민 수지로 코팅 하였다. 계면 중합은 1-dodecanol(핵심 물질)과 물(용매) 사이의 표면에서 중합반응이 일어나 벽 물질을 형성한다는 원리에 기반한다. 경량 콘크리트는 10 MPa의 압축 강도, 1.5 MPa의 인장 강도 및 1.0 kg/L의 절건 밀도를 가지며 10 %, 20 % 또는 30 %의 PCM을 포함하고 있다. 이를 위해 예비 배합으로 경량 기포 콘크리트($1.0kg/m^3$)를 제조 한 후 1-dodecanol 및 멜라민의 PCM 마이크로 캡슐과 혼합하여 그 물성을 조사하였다.

• Computers and Concrete
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• 제26권1호
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• pp.75-94
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• 2020

The aim of this research is to investigate free vibration of a novel five layer Timoshenko microbeam which consists of a transversely flexible porous core made of Al-foam, two graphen platelets (GPL) nanocomposite reinforced layers to enhance the mechanical behavior of the structure as well as two piezo-magneto-electric face sheets layers. This microbeam is subjected to a thermal load and resting on Pasternak's foundation. To accomplish the analysis, constitutive equations of each layer are derived by means of nonlocal strain gradient theory (NSGT) to capture size dependent effects. Then, the Hamilton's principle is employed to obtain the equations of motion for five layer Timoshenko microbeam. They are subsequently solved analytically by applying Navier's method so that discretized governing equations are determined in form of dynamic matrix giving the possibility to gain the natural frequencies of the Timoshenko microbeam. Eventually, after a validation study, the numerical results are presented to study and discuss the influences of various parameters such as nonlocal parameter, strain gradient parameter, aspect ratio, porosity, various volume fraction and distributions of graphene platelets, temperature change and elastic foundation coefficients on natural frequencies of the sandwich microbeam.

• Structural Engineering and Mechanics
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• 제42권5호
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• pp.715-728
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• 2012

This paper deals with determining the fundamental frequency of tall buildings that consist of framed tube, shear core, belt truss and outrigger systems in which the framed tube and shear core vary in size along the height of the structure. The effect of belt truss and outrigger system is modeled as a concentrated rotational linear spring at the belt truss and outrigger system location. Many cantilevered tall structures can be treated as cantilevered beams with variable cross-section in free vibration analysis. In this paper, the continuous approach, in which a tall building is replaced by an idealized cantilever continuum representing the structural characteristics, is employed and by using energy method and Hamilton's variational principle, the governing equation for free vibration of tall building with variable distributed mass and stiffness is obtained. The general solution of governing equation is obtained by making appropriate selection for mass and stiffness distribution functions. By applying the separation of variables method for time and space, the governing partial differential equation of motion is reduced to an ordinary differential equation with variable coefficients with the assumption that the transverse displacement is harmonic. A power-series solution representing the mode shape function of tall building is used. Applying boundary conditions yields the boundary value problem; the frequency equation is established and solved through a numerical process to determine the natural frequencies. Computer program has been developed in Matlab (R2009b, Version 7.9.0.529, Mathworks Inc., California, USA). A numerical example has been solved to demonstrate the reliability of this method. The results of the proposed mathematical model give a good understanding of the structure's dynamic characteristics; it is easy to use, yet reasonably accurate and suitable for quick evaluations during the preliminary design stages.

• Smart Structures and Systems
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• 제26권3호
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• pp.331-343
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• 2020

In this paper, based on the CPT, motion equations for a sandwich plate containing a core and two integrated face-sheets have derived. The structure rests on the Visco-Pasternak foundation, which includes normal and shear modules. The piezo-magnetic core is made of CoFe₂O₄ and also is subjected to 3D magnetic potential. Two face sheets at top and bottom of the core are under electrical fields. Also, in order to obtain more accuracy, the effect of flexoelectricity has took into account at face sheets' relations in this work. Flexoelectricity is a property of all insulators whereby they polarize when subject to an inhomogeneous deformation. This property plays a crucial role in small-scale rather than macro scale. Employing CPT, Hamilton's principle, flexoelectricity considerations, the governing equations are derived and then solved analytically. By present work a detailed numerical study is obtained based on Piezoelectricity, Flexoelectricity and modified couple stress theories to indicate the significant effect of length scale parameter, shear correction factor, aspect and thickness ratios and boundary conditions on natural frequency of sandwich plates. Also, the figures show that there is an excellent agreement between present study and previous researches. These finding can be used for automotive industries, aircrafts, marine vessels and building industries.

• 정보교육학회논문지
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• 제23권6호
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• pp.655-663
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• 2019

소프트웨어 교육에 대한 관심이 늘어감에 따라 컴퓨터과학에 대한 관심도 높아지고 있다. 컴퓨터과학은 컴퓨터와 컴퓨터시스템의 이론과 원리를 학습하는 학문으로서 이러한 컴퓨터과학의 지식과 개념은 소프트웨어 교육의 근본이라고 할 수 있다. 최근에 컴퓨터를 사용하지 않고 컴퓨터 과학의 핵심 내용을 전달하는 방법으로 컴퓨터과학 언플러그드라는 학습 방법이 전 세계적으로 수업에 많이 활용되고 있다. CS 언플러그드는 다양한 놀이 활동을 중심으로 컴퓨터과학의 원리를 배우도록 하는 학습 방법이다. 그러나 문제는 이러한 CS 언플러그드 활동이 실제 컴퓨터과학에서 배우는 핵심교과와 얼마나 연관성이 있는지에 대한 분석 없이 단순한 놀이 수업으로만 이루어지는 것이다. 따라서 본 연구에서는 컴퓨터과학의 핵심 내용과 CS 언플러그드의 다양한 활동에 들어 있는 컴퓨터과학 핵심 내용을 분석하여 비교 연구를 하고자 한다.

• Smart Structures and Systems
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• 제19권1호
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• pp.21-31
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• 2017

To control the stochastic vibration of a vibration-sensitive instrument supported on a beam, the beam is designed as a sandwich structure with magneto-rheological visco-elastomer (MRVE) core. The MRVE has dynamic properties such as stiffness and damping adjustable by applied magnetic fields. To achieve better vibration control effectiveness, the optimal bounded parametric control for the MRVE sandwich beam with supported mass under stochastic and deterministic support motion excitations is proposed, and the stochastic and shock vibration suppression capability of the optimally controlled beam with multi-mode coupling is studied. The dynamic behavior of MRVE core is described by the visco-elastic Kelvin-Voigt model with a controllable parameter dependent on applied magnetic fields, and the parameter is considered as an active bounded control. The partial differential equations for horizontal and vertical coupling motions of the sandwich beam are obtained and converted into the multi-mode coupling vibration equations with the bounded nonlinear parametric control according to the Galerkin method. The vibration equations and corresponding performance index construct the optimal bounded parametric control problem. Then the dynamical programming equation for the control problem is derived based on the dynamical programming principle. The optimal bounded parametric control law is obtained by solving the programming equation with the bounded control constraint. The controlled vibration responses of the MRVE sandwich beam under stochastic and shock excitations are obtained by substituting the optimal bounded control into the vibration equations and solving them. The further remarkable vibration suppression capability of the optimal bounded control compared with the passive control and the influence of the control parameters on the stochastic vibration suppression effectiveness are illustrated with numerical results. The proposed optimal bounded parametric control strategy is applicable to smart visco-elastic composite structures under deterministic and stochastic excitations for improving vibration control effectiveness.

• 전기전자학회논문지
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• 제25권1호
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• pp.95-100
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• 2021

조선소에서 선체 블록과 용접 피더의 위치를 알면 작업자의 위치 정보를 쉽게 얻을 수 있다. 이 데이터는 작업장 안전 모니터링 시스템 구축에 매우 유용하다. 그러나 선체 구조와 용접 공정의 특수성 때문에 작업장에 고정 통신망을 적용하기 어렵다. 본 연구에서는 전용 통신선을 대신할 수 있는 유도 전력선 통신을 선체블록과 같은 금속매체에 적용하는 기술을 검토하였다. 용접기의 전원 케이블에 설치할 유도 결합기로 페라이트 코어를 사용하였고, 금속 블록의 지지대에 체결할 결합기로 나노 결정질 코어를 적용하였다. 제안된 커플러는 COMSOL AC/DC 모듈로 3차원 모델링 하였고 동작 원리를 시각화하기 위하여 유한 요소 해석을 수행하였다. 알루미늄 프로파일을 사용한 금속블록 통신 성능 테스트에서 용접 전극의 블록 접촉으로 통신 채널이 형성되었을 때 대역폭은 6 Mbps 이상 유지되었다.

• 식품과학과 산업
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• 제49권2호
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• pp.83-97
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• 2016

본 총설은 음식윤리의 개요를 식품과학과 산업 분야의 전문인에게 설명하고자 한 것이다. 음식윤리는 음식과 관련된 윤리 또는 윤리적 고려이고, 음식윤리의 핵심어는 생명, 행복, 지혜이다. 음식윤리의 제1원리이자 궁극적인 목적은 인류의 지속가능한 생존이다. 그 목적을 달성하기 위해서는 자연과의 공생, 인간과의 공생, 그리고 음식의 본질적 요소의 충족이 필요하다. 그 필요로부터 생명존중, 자연보전, 속임수나 가짜가 없는 분배의 정의, 소비자 최우선 고려, 절제와 균형, 그리고 안전성 확보의 여섯 가지 정언명령이 산출된다. 정언명령에 상응하는 핵심원리는 생명존중, 환경보전, 정의, 소비자 최우선, 동적 평형, 안전성 최우선이다. 핵심원리 접근법은 윤리문제의 해결에 간단하고 명료하며 실질적인 방법이다. 음식윤리강령 역시 핵심원리를 기반으로 한다.