We study effect of addition of graphene on mechanical properties (elastic modulus and Poisson's ratio) of hydroxyapatite composites. Firstly, generating algorithm of random distribution geometric model of graphene/hydroxyapatite composites was created and model's automatic generation program was developed. Then, finite element model of graphene/hydroxyapatite composite was established. Finite element analysis of uniaxial tensile tests of composite materials was carried out. Finally, mechanical properties of different mass fraction of graphene of composite were calculated. Validity of the algorithm is verified by experimental data. It shows that elastic modulus of composite increased 12% to 50% with addition of 0.25% to 1.25% (wt.) graphene. Mechanical properties of hydroxyapatite can be effectively improved by addition of graphene.

We performed first-principles calculations of Mn-doped structures in which Mn atoms substitute Ti atoms.Formation energy,density of state and magnetic moment are calculated for Mn ions doped TiO₂(001) and F-TiO₂(001) thin films.In all doping configurations adsorption of F atoms on surface lowers formation energy of TiO₂:Mn system significantly.Magnetic moments of Mn ions are reduced,whereas those of O atoms on surface are increased.Magnetic moment of O atoms is mainly derived from spin polarization p_x and p_y orbitals.F adsorption promotes doping of Mn atoms and improves stability of structure,magnetism,and metallicity to a certain extent.

With first-principles method based on density functional theory, we studied structural, electronic, and magnetic properties of ZnS(111) surfaces monodoped and bidoped with Mn atoms. In monodoped configuration, the most energetically favorable location of Mn incorporated into ZnS(111) surfaces is in the first Zn atomic layer. Total magnetic moment depends on local structure of Mn atom. In bidoped configuration, short-range ferromagnetism can be explained with existence of strong p-d hybridization between Mn atom and its nearest neighboring S atoms. A Curie temperature of 469 K higher than room temperature is evaluated. Interaction between doping Mn atoms and host semiconductors is major reason for generation of spin polarization. It shows a prospecting prediction for further study of diluted magnetic semiconductors which may be useful in technological application.

Structural,electronic,and magnetic properties of Mn-doped ZnS (110) surfaces are investigated with first-principles method.Geometric parameters,formation energies,magnetic moments,density of states,and electron charge densities are studied.It shows that the lowest formation energy is as a Mn atom doped into the second layer,which indicates that this layer is more stable for Mn-doping.For bidoped case,the most stable configuration is an antiferromagnetic state of two Mn atoms.Total magnetic moments is equal to that of a free Mn atom.The local magnetic moment of Mn atom depends on a hybridization of Mn 3d state and its neighboring S 3p state,that is to say,magnetic moment changes as environment of S atoms alters.Furthermore,electron charge density shows that intensity of covalent bond between Mn and S atoms is greater than that between Zn and S atoms.

First principle calculations are made to study formation energies, partial DOS and magnetic moment of three typical surfaces of ZnS(001):Mn. Two interstitial locations are found more stable as comparing formation energies of Mn at three different locations on ZnS(001):Mn surface. Density of states and electron charge density of three reconstructions in ZnS(001):Mn surface are analyzed. It is found that p-d hybridization between spin up Mn-3d and S-3p orbital exists in three ZnS(001):Mn surface models. The p-d mixing is the strongest as Mn is at substituted location. Since spin down Mn-3d states are relatively local, it is shown that mixing between spin down Mn-3d and S-3p is less. Magnetic moments per supercell are calculated for three surfaces.

The dynamic temperature rise of the enclosed asynchronous motor is computed by solving heat conduction equation. Numerical results show the same order of accuracy as in practical calculation for steady temperature rise.