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Loudi, China

Hunan University of Humanities, Science and Technology (simplified Chinese: 湖南人文科技学院; traditional Chinese: 湖南人文科技學院; pinyin: Húnán Rénwén Kējì Xuéyuàn), established in 1978, is a state-owned provincial university of higher education approved by the Chinese Ministry of Education. It is located in Loudi, a newly built city in central Hunan province, China . Wikipedia.


Wu C.,Hunan University of Humanities, Science and Technology
Molecular Simulation | Year: 2010

This work presents the first molecular dynamics simulation of poly(propylene imine) (PPI) dendrimer in explicit water under various pH conditions. The sizes, shapes, surfaces/volumes and density profiles of the PPI dendrimer are analysed. The PPI dendrimer essentially approaches the perfect sphere under all pH conditions, and higher pH leads to more globular structure. The radius of gyration, solvent-accessible surface area (SASA) and solvent-excluded volume (SEV) are all found to increase significantly from high pH to neutral pH and to level thereafter until low pH, which illustrate the dramatic changes in the whole conformation of the dendrimer. These behaviours of the PPI dendrimer quite differ from those of polyamidoamine [Liu, et al. J. Am. Chem. Soc. 2009, 131, 2798-2799], which can be explained by the favourable interactions arising from the additional amide groups. The density profiles have also been calculated to confirm the shifts of density and back-folding of terminals and penetrations of water. © 2011 Taylor & Francis. Source


Wu C.,Hunan University of Humanities, Science and Technology
Journal of Physical Chemistry B | Year: 2011

Stepwise cooling molecular dynamics (MD) simulations have been carried out on the bulk and film models for poly(ethylene oxide) (PEO) to understand glass transition of amorphous polymer films. Three types of properties-density, energy, and dynamics-are computed and plotted against the temperature for the two systems. It has been confirmed that all these properties can reveal glass transition in both PEO bulk and film systems. All the determined glass transition temperatures (Tg's) drop in the same order of magnitude to the experimental data available. Among various methods, the Tg's obtained from the density and energy data are close to each other if the same space regions are defined, which can suggest the same free volume theory, and dynamic Tg's obtained from mean-squared displacements (MSDs) are highest, which can suggest the kinetic theory for structural relaxation. Consistently, all these Tg's obtained using different methods show that the Tg's of PEO film are lower than those of PEO bulk. The free surface layers of polymer films dictate this offset. © 2011 American Chemical Society. Source


Wu C.,Hunan University of Humanities, Science and Technology
Polymer | Year: 2010

An aqueous poly(vinyl alcohol) (PVA) model has been extensively studied by using the molecular dynamics (MD) simulation method. The employed molecular and force field models are validated against the available data in the literature. In particular, the glass transition temperature (T g) is determined from the specific volume versus temperature, which compares well with the experimental observations. The diffusion coefficients of water (H 2O) through the PVA matrix follow the Arrhenius equations at both temperature regions separated by T g, indicating the existence of free and bound water defined by hydrogen bonds (HBs). It has also been confirmed that HBs occur between PVA and H 2O, between PVA and PVA, between H 2O and H 2O, and all of them play the key roles in the glass transition. The local dynamics suggested by the decorrelations of various bond vectors can be well described by the Williams-Landel-Ferry (WLF) equation. This work demonstrates the cooperative behavior of PVA and H 2O which is responsible for the glass transition of the whole binary system. © 2010 Elsevier Ltd. Source


Ding C.,Hunan University of Humanities, Science and Technology
International Journal of Theoretical Physics | Year: 2014

In the frame of Hamilton-Jacobi method, the back-reactions of the radiating particles together with the total entropy change of the whole system are investigated. The emission probability from this process is found to be equivalent to the null geodesic method. However its physical picture is more clear: the negative energy one of a virtual particle pair is absorbed by the black hole, resulting in the temperature, electric potential and angular velocity increase; then the black hole amount of heat, electric charge and angular momentum can spontaneously transfer to the positive energy particle; when obtaining enough energy, it can escape away to infinity, visible to distant observers. And this method can be applied to any sort of horizons and particles without a specific choice of (regular-across-the-horizon) coordinates. © 2013 Springer Science+Business Media New York. Source


Wu C.,Hunan University of Humanities, Science and Technology
Journal of Molecular Modeling | Year: 2014

The chain tacticity of a polymer is a key influence on its structure and dynamics, which ultimately determine its properties. While they have great potential to elucidate the influence of chain tacticity, all-atom molecular simulations are often restricted to short chains and small systems. In thiswork, two typical stereoregular poly(methyl methacrylate) melts were investigated via multiscale simulations. To improve computational efficiency, systematic coarse-graining was first performed. While the coarse-grained molecular dynamics simulations were able to show the effects of tacticity on intramolecular structure and intermolecular interactions, they were not able to reproduce the exact structural distribution or even the effects of tacticity on the dynamics. An alternative reverse-mapping scheme was therefore developed specifically to treat chain configurations in a direct geometric way. The backmapped all-atomistic simulations were found to accurately reproduce the microscopic features of the polymers. Since the effects of tacticity are rather subtle and therefore difficult to discern, this multiscale simulation scheme is a very important method of investigating complex high molecular weight polymer systems. © Springer-Verlag 2014. Source

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