The elastic properties of ZnO nanofilms with different film thickness, surface orientations and loading directions are investigated by using molecular mechanics (MM) method. The size dependence of ...elastic properties is relevant to both the film surface crystallographic orientation and loading direction. Both atomic structure analysis and energy calculation are employed to identify the mechanisms of the size-dependent elastic properties, under different loading directions and surface orientations. Upon small axial deformation, the relationship between intralayer and interlayer bond length variation and film elastic stiffness is established; it is found that the atomic layers with larger bond length variation have higher elastic stiffness. The strain energies of atomic layers of ZnO nanofilm and bulk are decoupled, from which the stiffness of film surface, intralayers, and interlayers are derived and compared with their bulk counterparts. The surface stiffness is found to be much lower than that of the interior layers and bulk counterpart, and with the decrease of film thickness, the residual tension-stiffened interior atomic layers are the main contributions of the increased elastic modulus of ZnO nanofilms.
Highly sensitive and selective detection against specific target gases, especially at low-ppb （part per bil- lion） level, remain a great number of challenges in gas sensor applications. In this ...paper, we first present an ordered mesoporous NiFe204 for highly sensitive and selective detection against low-ppb toluene. A series of mesoporous NiFe204 materials were synthesized by templating from mesoporous silica KIT-6 and its framework thickness was reduced from 8.5 to 5 nm by varying the pore size of KIT-6 from 9.4 to 5.6 nm, accompanied with the increase of the specific surface area from 134 to 216 m^2 g^-1. The ordered mesoporous NiFe2O4 with both ultrathin framework of 5 nm and large specific surface area of up to 216 m^2 g^-1 exhibits a highest response （Rgas/Ralr-1 = 77.3） toward 1,000 ppb toluene at 230℃ and is nearly 7.3 and 76.7 times higher than those for the NiFe204 replica with thick framework and its bulk counter- part respectively, which also possesses a quite low limit of detection （〈2 ppb）, and good selectivity.
The gating pathways of mechanosensitive channels of large conductance (MscL) in two bacteria (
Mycobacterium tuberculosis and Escherichia coli) are studied using the finite element method. The ...phenomenological model treats transmembrane helices as elastic rods and the lipid membrane as an elastic sheet of finite thickness; the model is inspired by the crystal structure of MscL. The interactions between various continuum components are derived from molecular-mechanics energy calculations using the CHARMM all-atom force field. Both bacterial MscLs open fully upon in-plane tension in the membrane and the variation of pore diameter with membrane tension is found to be essentially linear. The estimated gating tension is close to the experimental value. The structural variations along the gating pathway are consistent with previous analyses based on structural models with experimental constraints and biased atomistic molecular-dynamics simulations. Upon membrane bending, neither MscL opens substantially, although there is notable and nonmonotonic variation in the pore radius. This emphasizes that the gating behavior of MscL depends critically on the form of the mechanical perturbation and reinforces the idea that the crucial gating parameter is lateral tension in the membrane rather than the curvature of the membrane. Compared to popular all-atom-based techniques such as targeted or steered molecular-dynamics simulations, the finite element method-based continuum-mechanics framework offers a unique alternative to bridge detailed intermolecular interactions and biological processes occurring at large spatial scales and long timescales. It is envisioned that such a hierarchical multiscale framework will find great value in the study of a variety of biological processes involving complex mechanical deformations such as muscle contraction and mechanotransduction.
The mechanisms of pressure-driven water infiltration into single walled carbon nanotubes are explored using molecular dynamics simulations. Both quasi-static and dynamic loading conditions are ...investigated, and the influence of tube size is examined. Under quasi-static loading, the water molecules flow into the tube via surface diffusion at a low pressure and when the external pressure reaches a critical value, the infiltrated water flux can sharply increase to a steady state. Upon dynamic loading, the nominal infiltration length per unit external work is employed to measure the comprehensive effect of the loading rate. It is found that such factor is larger (i.e. infiltration is easier) at a lower loading rate and a larger tube size, which is closely related with the interactions between water molecules and nanotube wall atoms.
We introduce a high performance differential dilatometer based on an all-fiber Michelson interferometer at cryogenic temperature with \(10^{-10}\) resolution in \(\delta L/L\). It resolve the linear ...thermal expansion coefficient by measuring the oscillating changes of sample thickness and sample temperature with the interferometer and in-situ thermometer, respectively. By measuring the linear thermal expansion coefficient \(\alpha\) near the antiferromagnetic transition region of BaFe\(_2\)As\(_2\) as a demonstration, we show our dilatometer is able to measure thin samples with sub-pm-level length change resolution and mK-level temperature resolution. Despite there is residual background thermal expansion of a few nm/K in measurement result, our new dilatometer is sitll a powerful tool for study of phase transition in condensed matter physics, especially significant advantages in fragile materials with sub-100\(\mu\)m thickness and being integrated with multiple synchronous measurements and tuning thanks to the extremely high resolution and contactless nature. The prototype design of this setup can be further improved in many aspects for specific applications.
Viscoelastic mechanical properties of biological cells are commonly measured using atomic force microscope (AFM) dynamic indentation with spherical tips. A semiempirical analysis based on numerical ...simulation is built to determine the cell mechanical properties. It is shown that the existing analysis cannot reflect the accurate values of cell elastic/dynamic modulus due to the effects of substrate, indenter tip size, and cell size. Among these factors, substrate not only increases the true contact radius but also interferes the indentation stress field, which can cause the overestimation of cell moduli. Typically, the substrate effect is much stronger than the other two influences in cell indentation; and, thus, the cell modulii are usually overestimated. It is estimated that the moduli can be overestimated by as high as over 200% using the existing analysis. In order to obtain the accurate properties of cells, correction factors that account for these effects are required in the existing analysis.
The relationship between the yield strength and microstructure parameters of a fully lamellar TiAl alloy has been studied systematically. The grain size and the lamellar spacing were chosen as ...microstructure parameters. The experimental results showed that the yield strength increases with the decrease of grain size and more obviously with the decrease of the lamellar spacing. The relationship between yield strength and grain size and lamellar spacing can be approximately described by Hall–Petch relation.
In this doctoral dissertation, a multi-length scale computational approach is utilized to address various aspects of processing and postprocessing of carbon nanotubes, their properties as a function ...of nanoscale morphology and defect structure, and their use in several small-size devices. Chemical Vapor Deposition (CVD) of carbon nanotubes from a gas mixture consisting of methane and hydrogen in the presence of cobalt, nickel or iron catalytic particles in a cylindrical reactor is modeled at the reactor length scale and at atomic length scale. The reactor length-scale model is used to determine the gas-phase fields for temperature, velocity, and various species as well the surface-species coverages and the carbon nanotubes deposition rate. The model is further coupled with a Genetic Algorithm optimization code to determine the process parameters. A kinetic Monte Carlo atomic scale model is developed to simulate the carbon nanotubes growth and defect formation and to reveal the effect which the nominal and local processing conditions may have on the nanotubes morphology and growth rates. Solubilization of the single-walled carbon nanotubes (SWCNTs) in toluene and the SWCNTs functionalized with poly (PmPV-DOctOPV) polymer in toluene is modeled using molecular dynamics simulations. The results obtained show that the solvation Gibbs free energy for the non-functionalized nanotubes in toluene is small but positive. The toluene solution which contains the PmPV-DOctOPV functionalized SWCNTs, on the other hand, is found to be stable and the type of functionalization can be used for separation of the SWCNT bundles into individual nanotubes. The lattice contribution to thermal conductivity of SWCNTs is studied using the molecular dynamics based thermal current auto-correlation functions. The results obtained show that quite accurate lattice thermal conductivities can be obtained using computational cells considerably smaller than the phonon mean free path. Furthermore, the chirality is found to affect lattice thermal conductivity by as much as 20% at a comparable nanotube diameter. Ab-initio density functional theory (DFT) and Green's function combined with the tight-binding method are used to determine the character of molecular-oxygen adsorption, and the effect of molecular-oxygen adsorption and the topological defects on the electrical conductance of SWCNTs. The computational results obtained show that oxygen molecules are physisorbed to the defect-free nanotube walls, but chemisorbed onto the walls containing topological defects. (Abstract shortened by UMI.)
The development of environment friendly and practically feasible technologies or adsorbents to treat water pollution due to heavy metals is urgently required. Herein, Sulphate aluminate cement - ...bentonite (SAC-bentonite) composites were synthesized and used as low-cost and high-efficiency adsorbents to remove Cr3+, Pb2+, and Cd2+ from aqueous solution. The characteristics of SAC-bentonite were analyzed via X-ray diffraction (XRD) and scanning electron microscopy (SEM). Effects of the amount of adsorbent, solution pH, and contact time on the adsorption performance of SAC-bentonite were also studied. The adsorption mechanism was analyzed via XRD, X-ray photoelectron spectroscopy (XPS), and SEM. The results demonstrate that the adsorption capacities of SAC-bentonite for Cr3+ were similar to that of pure bentonite or pure SAC, while the adsorption capacities for Pb2+ and Cd2+ were significantly higher than those for bentonite or SAC. When the ratio of bentonite to SAC was 1:1, the removal efficiency of SAC-bentonite for Cr3+, Pb2+, and Cd2+ was 99.956%, 99.838%, and 99.717%, respectively. The adsorption kinetics was well described by Pseudo-second-order equation.
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•SAC-bentonite composites were prepared as an adsorbent for removing heavy metals.•SAC-bentonite composites show an excellent adsorption of Cr3+, Pb2+, and Cd2+.•The adsorption of Cr3+, Pb2+, and Cd2+ was mainly attributed to cation exchange.
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