• Advances in nano research
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• 제15권3호
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• pp.263-275
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• 2023

The electron transport properties of Y-type zigzag branched carbon nanotubes (CNTs) are of great significance for micro and nano carbon-based electronic devices and their interconnection. Based on the semi-empirical method combining tight-binding density functional theory and non-equilibrium Green's function, the electron transport properties between the branches of Y-type zigzag branched CNT are studied. The results show that the drain-source current of semiconducting Y-type zigzag branched CNT (8, 0)-(4, 0)-(4, 0) is cut-off and not affected by the gate voltage in a bias voltage range [-0.5 V, 0.5 V]. The current presents a nonlinear change in a bias voltage range [-1.5 V, -0.5 V] and [0.5 V, 1.5 V]. The tangent slope of the current-voltage curve can be changed by the gate voltage to realize the regulation of the current. The regulation effect under negative bias voltage is more significant. For the larger diameter semiconducting Y-type zigzag branched CNT (10, 0)-(5, 0)-(5, 0), only the value of drain-source current increases due to the larger diameter. For metallic Y-type zigzag branched CNT (12, 0)-(6, 0)-(6, 0), the drain-source current presents a linear change in a bias voltage range [-1.5 V, 1.5 V] and is symmetrical about (0, 0). The slope of current-voltage line can be changed by the gate voltage to realize the regulation of the current. For three kinds of Y-type zigzag branched CNT with different diameters and different conductivity, the current-voltage curve trend changes from decline to rise when the branch of drain-source is exchanged. The current regulation effect of semiconducting Y-type zigzag branched CNT under negative bias voltage is also more significant.

• Structural Engineering and Mechanics
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• 제10권4호
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• pp.371-392
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• 2000

Application of "advanced analysis" methods suitable for non-linear analysis and design of steel frame structures permits direct and accurate determination of ultimate system strengths, without resort to simplified elastic methods of analysis and semi-empirical specification equations. However, the application of advanced analysis methods has previously been restricted to steel frames comprising only compact sections that are not influenced by the effects of local buckling. A concentrated plasticity method suitable for practical advanced analysis of steel frame structures comprising non-compact sections is presented in this paper. The pseudo plastic zone method implicitly accounts for the effects of gradual cross-sectional yielding, longitudinal spread of plasticity, initial geometric imperfections, residual stresses, and local buckling. The accuracy and precision of the method for the analysis of steel frames comprising non-compact sections is established by comparison with a comprehensive range of analytical benchmark frame solutions. The pseudo plastic zone method is shown to be more accurate and precise than the conventional individual member design methods based on elastic analysis and specification equations.

• The Korean Journal of Ceramics
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• 제6권3호
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• pp.240-244
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• 2000

The three-dimensional orientation distribution function of a conical shaped tungsten liner prepared by the thermo-mechanical forming process was analyzed by 1.525$\AA$ neutrons to carry out the Rietveld refinement. The pole figure data of three reflections, (110)(220) and (211) were measured. The orientation distribution functions for the normal and radial directions were calculated by the WIMV method. The inverse pole figures of the normal and radial directions were obtained from their orientation distribution functions. The Rietveld refinement was performed with the RIETAN program that was slightly modified for the description of preferred orientation effect. We could successfully do the Rietveld refinement of the strongly textured tungsten liner by applying the pole density of each reflection obtained from the inverse pole figure to the calculated diffraction pattern. The correction method of preferred orientation effect based on the inverse pole figures showed a good improvement over the semi-empirical texture correction based on the direct usage of simple empirical functions.

• 대한기계학회논문집B
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• 제29권4호
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• pp.526-536
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• 2005

A heat dissipation modeling method of EEE parts, or semi-empirical heat dissipation method, is developed for thermal design and analysis an electronic equipment of geostationary satellite. The power consumption measurement value of each functional breadboard is used for the heat dissipation modeling method. For the purpose of conduction heat transfer modeling of EEE parts, surface heat model using very thin ignorable thermal plates is developed instead of conventional lumped capacity nodes. The thermal plates are projected to the printed circuit board and can be modeled and modified easily by numerically preprocessing programs according to design changes. These modeling methods are applied to the thermal design and analysis of CTU (Command and Telemetry Unit) and verified by thermal cycling and vacuum tests.

• 한국정밀공학회지
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• 제14권9호
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• pp.90-100
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• 1997

A full three-dimensional thermo-coupled rigid-viscoplastic finite element method and the currently developed microstructural evolution system which includes semi-empirical equations suggested by different research groups were used together to form an integrated system of process and micro- structure simulation of hot rolling. The distribution and time histroy of the momechanical variables such as temperature, strain, strain rate, and time during pass and between passes were obtained from the finite element analysis of multipass hot rolling processes. The distribution of metallurgical variables were calculated on the basis of instantaneous thermomechanical data. For the verification of this method the evolution of microstructure in plate rolling and shape rolling was simulated and their results were compared with the data available in the literature. Consequently, this approach makes it possible to describe the realistic evolution of microstructure by avoiding the use of erroneous average value and can be used in CAE of multipass hot rolling.

• Geomechanics and Engineering
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• 제5권5호
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• pp.379-399
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• 2013

In practice, analysis of laterally loaded piles is carried out using beams on non-linear Winkler springs model (often known as p-y method) due to its simplicity, low computational cost and the ability to model layered soils. In this approach, soil-pile interaction along the depth is characterized by a set of discrete non-linear springs represented by p-y curves where p is the pressure on the soil that causes a relative deformation of y. p-y curves are usually constructed based on semi-empirical correlations. In order to construct API/DNV proposed p-y curve for clay, one needs two values from the monotonic stress-strain test results i.e., undrained strength ($s_u$) and the strain at 50% yield stress (${\varepsilon}_{50}$). This approach may ignore various features for a particular soil which may lead to un-conservative or over-conservative design as not all the data points in the stress-strain relation are used. However, with the increasing ability to simulate soil-structure interaction problems using highly developed computers, the trend has shifted towards a more theoretically sound basis. In this paper, principles of Mobilized Strength Design (MSD) concept is used to construct a continuous p-y curves from experimentally obtained stress-strain relationship of the soil. In the method, the stress-strain graph is scaled by two coefficient $N_C$ (for stress) and $M_C$ (for strain) to obtain the p-y curves. $M_C$ and $N_C$ are derived based on Semi-Analytical Finite Element approach exploiting the axial symmetry where a pile is modelled as a series of embedded discs. An example is considered to show the application of the methodology.

• 한국항공우주학회지
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• 제48권11호
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• pp.849-859
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• 2020

반경험식과 상용 전산해석도구를 이용하여 비행 속도 및 챔버 압력에 따른 유도무기의 기저항력을 예측하였으며, 두 해석 결과는 대체적으로 일치함을 보였다. 노즐에 의한 분사 제트의 과대/과소 팽창에 따라 기저부의 유동 특성과 기저항력의 차이가 관찰되었다. 과대팽창 조건에서는 기저부 상단에 팽창파가 발생되면서 기저부의 압력이 감소하였으며, 외부 자유류의 마하수가 증가함에 따라 팽창파의 강도가 강해지면서 기저부 압력 더욱 감소하였다. 과소 팽창 조건에서는 노즐 후류의 영향으로 기저부 주위에 충격파가 발생하고 이로 인해 기저부 압력이 증가하였으며, 챔버의 압력이 증가할수록 그 영향이 크게 나타났다. 동일 챔버 압력 조건에서는 자유류 마하수가 증가함에 따라 기저부에서 생성되는 충격파가 하류로 이동하면서 기저 압력이 감소하는 특성이 관찰되었다.

• 대한화학회지
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• 제31권1호
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• pp.3-13
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• 1987

알킬알코올의 OH 신축진동 영역에서의 적외선 스펙트라를 $CCl_4$용액내에서 농도를 변화시켜가면서 얻었다. OH신축진동 흡수띠는 수소결합의 형성으로 넓게 낮은 파수영역으로 이동된다. 이러한 띠들을 simplex법을 이용한 컴퓨터프로그램으로 분해하여 3개의 띠를 얻었으며, 각 띠들을 여러가지 형태로 수소결합을 하고 있는 OH기로 구분하였다. 또한 dimer혹은 trimer로 수소결합하고 있는 알코올구조들의 전자구조와 상호작용 에너지를 반경험적 분자궤도 함수법(CNDO/2, INDO)으로 계산하였다. 이들 계산결과는 분해된 적외선 스펙트라의 결과와 잘 일치하였다. 수소결합 형성에 대한 알킬기의 전자구조 효과는 부틸>프로필>에틸>메틸기의 순이었으나, 실험결과에서는 프로필>에틸>부틸>메틸기의 순으로 나타났다. 이것은 부탄올의 벌키성때문인 것으로 생각한다. 제외하고는 모두 증가하였다. 제올라이트에 있는 양이온을 떼어내는데 필요한 에너지는 $H^+\;>\;Li^+\;>\;Na^+$의 순이었으며, 이것은 제올라이트의 골격으로부터 양이온으로 이동되는 전하의 양과 관계가 있다.

• 전기화학회지
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• 제16권3호
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• pp.177-183
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• 2013

고전압에서도 사용 가능한 바인더 개발에 대한 요구가 증대됨에 따라 이에 적합한 내산화성이 우수한 바인더를 양자화학적 모델링에 기반하여 제안하고자 하였다. 각 고분자 poly(acryl amide)(PAM), poly(methyl acrylate)(PMA), poly(vinylidene fluoride)(PVDF), poly(hexafluropropylene)(PHFP)에 대하여 반경험적 방법(Semi-empirical method) 및 밀도범함수 이론(Density Functional Theory, DFT) 방법을 이용하여 단량체부터 사량체까지의 고분자 바인더에 대한 최고 점유 분자 궤도함수(Highest occupied molecular orbital, HOMO) 에너지와 이온화 에너지(Ionization Potential, IP) 값을 구하여 실험 값과 비교하였다. 밀도범함수 방법으로 해석한 결과, PHFP, PVDF, PMA, PAM 순으로 고분자의 내산화성이 좋은 것으로 시뮬레이션을 통해 예측되었고, 이러한 결과는 선형 훑음 전압-전류법(Linear Sweep Voltametry, LSV)으로부터 얻은 실험값과 일치하였다. 또한 이 결과는 HOMO 오비탈의 구조를 분석하여 내산화성이 좋은 원인을 규명하였다.

• Bulletin of the Korean Chemical Society
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• 제23권1호
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• pp.48-52
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• 2002

Using several molecular modeling programs we have performed computer simulations to investigate the complexation behaviors of an ester derivative of p-tert-butylcalix[5]arene (1e) toward a variety of butylammonium ions. Semi-empirical AM1 method was used for calculating the binding energies and the formation enthalpies. MM and CVFF forcefields for molecular mechanics calculations were adapted to express the complexation energies of the host. Molecular dynamics were performed to the calculated complex systems to simulate the ionophoric behavior of the host-guest complexes. The absolute Gibbs free energies of the host (1e) complexed with four kinds of butylammonium ions have been calculated using the Finite Difference Thermodynamic Integration (FDTI) method in Discover. Calculation results show that the trend in complex formation is n-$BuNH_3^+$ > iso-$BuNH_3^+$ >> sec-$BuNH_3^+$ > tert-$BuNH_3^+$, which is in good agreement with the experimental results.