• Tribology and Lubricants
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• 제37권2호
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• pp.77-80
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• 2021

In this study, we investigated the effect of the spring constant on frictional behavior at a nanoscale through molecular dynamics simulation. A small cube-shaped tip was modeled and placed on a flat substrate. We did not apply the normal force to the tip but applied adhesive force between the tip and the substrate. The tip was horizontally pulled by a virtual spring to generate relative motion against the substrate. The controlled spring constant of the virtual spring ranged from 0.3 to 70 N/m to reveal its effect on frictional behavior. During the sliding simulation, we monitored the frictional force and the position of the tip. As the spring constant decreased from 70 to 0.3 N/m, the frictional force increased from 0.1 to 0.25 nN. A logarithmic relationship between the frictional force and spring constant was established. The stick-slip instability and potential energy slope increased with a decreasing spring constant. Based on the results, an increase in the spring constant reduces the probability of trapping in the local minima on the potential energy surface. Thus, the energy loss of escaping the potential well is minimized as the spring constant increases.

• 한국전자통신학회논문지
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• 제14권1호
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• pp.147-154
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• 2019

이 연구에서는 분자들이 노즐과 터빈내부에서 운동하는 거동을 모사하기 위해 분자동력학 시뮬레이션 시스템의 모델을 설계하고 개발하였다. Lennard-Jones Potential 모델을 이용하여 분자들간에 상호 작용을 계산하고, Verlet 알고리듬을 뉴턴의 운동 방정식을 적산하기 위한 수치해석 방법으로 사용하였다. Lennard-Jones Potential 함수를 계산하기 위해, 분자 개수 N에 대해 $O(N^2)$ 계산량을 cutoff $r_c$를 이용하여 O(N)으로 줄여서 계산하여 CPU 시간을 절약할 수 있도록 구현하였다.

• Advances in nano research
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• 제11권6호
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• pp.607-620
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• 2021

In this paper, the vibrations of boron nitride nanotubes (BNNTs) are investigated by considering the electric field. To consider the size effect at nanoscale dimensions, the surface elasticity theory is exploited. The equations of motion of the BNNTs are obtained by applying Hamilton's principle, and the clamped-guided boundary conditions are also considered. The governing equations and boundary conditions are discretized using the differential quadrature method (DQM), and the natural frequency is obtained by using the eigenvalue problem solution. The results are compared with the molecular dynamic simulation in order to validate the accurate values of the surface effects. In the molecular dynamics (MD) simulation, the potential between boron and nitride atoms is considered as the Tersoff type. The Timoshenko beam model is adopted to model BNNT. The vibrations of two types of zigzag and armchair BNNTs are considered. In the result section, the effects of chirality, surface elasticity modulus, surface residual tension, surface density, electric field, length, and thickness of BNNT on natural frequency are investigated. According to the results, it should be noted that, as an efficient non-classical continuum mechanic approach, the surface elasticity theory can be used in scrutinizing the dynamic behavior of BNNTs.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제42회 동계 정기 학술대회 초록집
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• pp.89-89
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• 2012

Arrangement of individual atoms and molecules with atomic precision and understanding the resulting properties at the molecular level are ultimate goals of chemistry, biology, and materials science. For the past three decades, scanning probe microscopy has made strides towards these goals through the direct observation of individual atoms and molecules, enabling the discovery of new and unexpected phenomena. This talk will discuss the origin of forces governing motion of small organic molecules and their extended self-assembly into two-dimensional surface structures by direct observation of individual molecules using scanning tunneling microscopy (STM).

• 한국고분자학회지:고분자과학과기술
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• 제9권2호
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• pp.153-160
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• 1998

• 전기의세계
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• 제27권3호
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• pp.31-35
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• 1978

In this paper, in order to clarify the mature of traps in polymer, the thermally stimulated current (TSC) measurements were mad on high density polyethylene by changing the condition of the high-field treatment such as the strength of the field (Fe), the treatment time (te) and the heating rate (.betha.). In addition, the TSC measured from the HDPE was compared with that from LDPE having different crystallinity. The obtained results can suggest that the trapping proceeds during the high-field treatment and the trap associated with the peak P$_{2}$ may have the closed relation to drystallinity and the release of trapped charge is enhanced by the molecular motion.

• 천문학회지
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• 제38권2호
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• pp.237-240
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• 2005

We present images of L1551 IRS5 at angular resolutions as high as ${\~}$30 mas, corresponding to a spatial resolution of ${\~}$5 AU, made at 7 mm with the VLA. Previously known to be a binary protostellar system, we show that L1551 IRS5 is likely a triple protostellar system. The primary and secondary components have a projected separation of ${\~}$46 AU, whereas the tertiary component has a projected separation of ${\~}$11 AU from the primary component. The circumstellar dust disks of the primary and secondary components have dimensions of ${\~}$15 AU, whereas that of the tertiary component has a dimension of ${\~}$10 AU. Their major axes are closely, but not perfectly, aligned with each other, as well as the major axis of the surrounding flattened, rotating, and contracting molecular condensation (pseudodisk). Furthermore, the orbital motion of the primary and secondary components is in the same direction as the rotational motion of this pseudodisk. We suggest that all three protostellar components formed as a result of the fragmentation of the central region of the molecular pseudo disk. The primary and secondary components, but apparently not the tertiary component, each exhibits a bipolar ionized jet that is centered on and which emergers perpendicular to its associated dust disk. Neither jets are resolved along their base, implying that they are driven within a radial distance of ${\~}$2.5 AU from their central protostars. Finally, we show evidence for what may be dusty matter streams feeding the two main protostellar components.

• 한국과학교육학회지
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• 제22권2호
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• pp.240-251
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• 2002

이 연구에서는 초등학교 자연 교과서, 중학교 과학교과서, 고등학교 화학 교과서와 지구과학 교과서, 그리고 대학교 일반화학 및 일반지구과학 교과서 중심으로 기압과 대기압에 대한 설명 방식의 차이점을 3가지 유형으로 분석하였다. 유형 1은 무게로 설명하는 경우이며, 유형 2는 단위 면적에 작용하는 공기의 압력으로 설명하는 경우이고, 유형 3은 기체 분자 운동으로 설명하는 경우이다. 과학 교과서 분석 결과, 초등학교 자연 교과서는 유형 1로, 중 고등학교 화학 영역 교과서에서는 모두 유형 3으로 설명하였으며, 지구과학 영역 교과서에서는 주로 유형 1로 설명하였다. 한편, 대학교 일반화학 교과서는 주로 유형 1과 유형 2로 설명하였으며, 일반지구과학 교과서는 중 고등학교 지구과학 영역 교과서와 마찬가지로 주로 유형 1로 설명하였다. 이러한 과학 교과서에서 기압과 대기압에 대한 설명 방식의 차이는 학생들이 기압과 대기압을 이해하는데 혼란을 가져올 수 있을 것이라고 생각된다.

• 예술인문사회 융합 멀티미디어 논문지
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• 제8권1호
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• pp.887-894
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• 2018

최근 그래핀을 이용한 나노전자소자에 대한 많은 연구들이 다양한 분야에서 활발하게 이루어지고 있다. 본 연구에서는 분자동력학 시뮬레이션 방법을 사용하여 그래핀 나노리본 트렌치 구조를 이용한 풀러렌 분자 셔틀 소자로의 활용 가능성에 대하여 연구하였다. 그래핀 나노리본 트렌치 구조는 그 나노미터 규모의 분자 저장이 가능한 공간을 만들 수 있어, 이 공간을 활용하여 나노전기전자소자를 제작할 수 있는 가능성을 열어준다. 그래핀 나노리본 트렌치로 흡수된 풀러렌 분자는 외부 작용력의 방향에 따라서 그 위치를 그래핀 나노리본 트렌치 내부에서 조정할 수 있게 되기 때문에, 이를 이용하여 그래핀 나노리본 트랜체 내부에서 플러렌의 위치 조정으로 디지털 정보를 저장할 수 있다. 풀러렌 분자가 그래핀 나노리본 트렌치 내부에서 고랑을 따라서 이동과정에서 다양한 운동에너지 역학이 작용되는 것을 살펴보았다. 본 연구에서는 그래핀 나노리본 트렌치에 흡수된 풀러렌 분자는 나노전지전자소자의 오실레이터, 정보저장소자, 센서 등 다양한 첨단 분야에서 활용가능하다는 것을 연구하였다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2005년도 추계 학술대회논문집
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• pp.11-19
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• 2005

First, methods of numerical analysis of gas-particle flows is classified into micro, meso and macro scale approaches based on the concept of multi-scale mechanics. Next, the explanation moves on to discrete particle simulation where motion of individual particles is calculated numerically using the Newtonian equations of motion. The author focuses on the cases where particle-to-particle interaction has significant effects on the phenomena. Concerning the particle-to-particle interaction, two cases are considered: the one is collision-dominated flows and the other is the contact-dominated flows. To treat this interaction mathematically, techniques named DEM(Distinct Element Method) or DSMC (Direct Simulation Monte Carlo) have been developed DEM, which has been developed in the field of soil mechanics, is useful for the contact -dominated flows and DSMC method, developed in molecular gas flows, is for the collision-dominated flows. Combining DEM or DSMC with CFD (computer fluid dynamics), the discrete particle simulation becomes a more practical tool for industrial flows because not only the particle-particle interaction but particle-fluid interaction can be handled. As examples of simulations, various results are shown, such as hopper flows, particle segregation phenomena, particle mixing in a rotating drum, dense phase pneumatic conveying, spouted bed, dense phase fluidized bed, fast circulating fluidized bed and so on.