Papers by Author: Cheng Chi Wang

Abstract: Carbon nanotubes (CNTs) have been proposed as one of the most promising materials for nanoelectro-mechanical system due to high elastic modulus, high failure strength and excellent resilience [1,. Recent development of many-body interaction [3, made possible realistic molecular dynamics (MD) simulations of carbon-made systems. We carried out such studies for carbon nanotubes under generic modes of mechanical load: axial compression, bending, and torsion. A singular behavior of the nanotube energy at certain levels of strain corresponds to abrupt change in morphology. In this letter, we report the torsional instability analysis of single wall carbon nanotube filled with hydrogen via molecular dynamics simulations. The simulations are carried out at a temperature 77K which previous study obtained the hydrogen storage inside CNT at this condition [A. C. Dillo. Here we use atomistic simulations to study a flexible surface narrow carbon nanotube with tube diameters 10.8 Å. According to conventional physisorption principles, the gas-adsorption performance of a porous solid is maximized when the pores are no larger than a few molecular diameters [8]. Under these conditions, the potential fields produced at the wall overlap to produce a stronger interaction force than that observed in adsorption on a simple plane. However, the mechanisms responsible for the adsorption and transportation of hydrogen in nanoporous solids or nanopores are not easily observed using experimental methods. As a result, the use of computational methods such as molecular dynamics (MD) or Monte Carlo (MC) simulations have emerged as the method of choice for examining the nanofluidic properties of liquids and gases within nanoporous materials [9,1. Several groups have performed numerical simulations to study the adsorption of water in CNTs [11-1, while others have investigated the diffusion of pure hydrocarbon gases and their mixtures through various SWNTs with diameters ranging from 2 ~ 8 nm [17-19] or the self-and transport diffusion coefficients of inert gases, hydrogen, and methane in infinitely-long SWNTs [20-21]. In general, the results showed that the transport rates in nanotubes are orders of magnitude higher than those measured experimentally in zeolites or other microporous crystalline solids. In addition, it has been shown that the dynamic flow of helium and argon atoms through SWNTs is highly dependent on the temperature of the nanotube wall surface [22]. Specifically, it was shown that the flow rate of the helium and argon atoms, as quantified in terms of their self-diffusion coefficients, increased with an increasing temperature due to the greater thermal activation effect. Previous MD simulations of the nanofluidic properties of liquids and gases generally assumed the nanoporous material to have a rigid structure. However, if the nanoporous material is not in fact rigid, the simulation results may deviate from the true values by several orders of magnitude. Several researchers have investigated the conditions under which the assumption of a rigid lattice is, or is not, reasonable [23, 24]. In general, the results showed that while the use of a rigid lattice was permissible in modeling the nanofluidic properties of a gas or liquid in an unconfined condition, a flexible lattice assumption was required when simulating the properties of a fluid within a constrained channel. Moreover, in real-world conditions, the thermal fluctuations of the CNT wall atoms impact the diffusive behavior of the adsorbed molecules, and must therefore be taken into account. This study performs a series of MD simulations to investigate the transport properties of hydrogen molecules confined within a narrow CNT with a diameter of 10.8 Å (~ 1 nm) at temperatures ranging from 100 ~ 800 K and particle loadings of 0.01~1 No/Å. To ensure the validity of the simulation results, the MD model assumes the tube to have a flexible wall. Hydrogen molecules are treated as spherical particles. In performing the simulations, the hydrogen molecules are assumed to have a perfectly spherical shape. In addition, the interactions between the molecule and the CNT wall atoms and the interactions between the carbon atoms within the CNT wall are modeled using the Lennard-Jones potential [25,2. The simulations focus on the hydrogen adsorption within the SWNT not adsorption in the interstices or the external surface of nanotube bundles.

Abstract: This study employs finite element simulations to investigate the relationship between the equivalent mass and the real mass of end masses adhered to the tip of the cantilever beam of an atomic force microscope. The equivalent mass was determined by analyzing the variation in the resonant frequency of the cantilever beam caused by the addition of the end mass. The analysis considered five different adhesive mass materials, namely copper, aluminum, S45C steel, titanium alloy and magnesium alloy. Furthermore, the analysis also considerd the effect of the position of the adhesive mass on its equivalent mass value. The numerical results indicate that the equivalent adhesive mass is less than the real adhesive mass. The ratio of the equivalent adhesive mass to the real adhesive mass is approximately constant for a given adhesive position and adhesive material and has a value of approximately 0.6361 for a high-density material. Finally, the results show that an offset of the adhesive mass from the tip position causes a slight change in the value of the equivalent mass to real mass ratio.

Abstract: This paper presents a high-precision, non-destructive measurement system for determining the thickness and refractive indices of birefringent optical wave plates. Significantly, the proposed method enables the two refractive indices of the optical sample to be measured simultaneously. The performance of the proposed system is verified using a commercial quartz optical wave plate with known refractive indices of 1.5518 e n = and 1.5427 o n = , respectively, and a thickness of 452.1428 μm. The experimentally determined values of the refractive indices are found to be 1.55190 e n = and 1.54281 o n = , respectively, while the thickness is found to be 452.189 μm, corresponding to an experimental error of approximately 0.046 μm. The measurement resolution of the proposed system exceeds that of the interferometer hardware itself and provides a simple yet highly accurate means of measuring the principal optical parameters of birefringent glass wave plates.

Abstract: This study presents an enhanced common path interference system designed to measure the refractive index of crystal optical components. The proposed system is based on the classic Michelson interferometer and comprises a frequency stabilized helium-neon (He-Ne) laser, a beam splitter, a fixed mirror, an adjustable mirror, and a light detection system. The waveplate of interest was clamped to a rotatory motor and positioned between the beam splitter and the fixed mirror. The refractive index of the waveplate was then derived from the change in rotational angle of the waveplate as it moved from one position of minimum interference to the next. The measurement system proposed in this study is simple in construction, straightforward in operation, and robust to the effects of experimental noise. Furthermore, the system is a non-contact measurement system, and hence does not damage the optical component of interest. The experimental results are found to be in good agreement with the theoretical results. Therefore, the proposed system provides a viable means for the rapid experimental evaluation of the optical characteristics of quartz components.