Isotopic effects on the thermal conductivity of graphene nanoribbons: localization mechanism

Thermal conductivity of graphene nanoribbons (GNR) with length 106~{\AA} and width 4.92~{\AA} after isotopic doping is investigated by molecular dynamics with quantum correction. Two interesting phenomena are found: (1) isotopic doping reduces thermal conductivity effectively in low doping region, and the reduction slows down in high doping region; (2) thermal conductivity increases with increasing temperature in both pure and doped GNR; but the increasing behavior is much more slowly in the doped GNR than that in pure ones. Further studies reveal that the physics of these two phenomena is related to the localized phonon modes, whose number increases quickly (slowly) with increasing isotopic doping in low (high) isotopic doping region.Comment: 6 fig

Multi-color light curves and orbital period research of eclipsing binary V1073 Cyg

New Multi-color $B$ $V$ $R_c$ $I_c$ photometric observation are presented for W UMa type eclipsing binary V1073 Cyg. The multi-color light curves analysis with the Wilson-Devinney(W-D) procedure acquired the absolute parameters of this system, showing that V1073Cyg is a shallow contact binary system with fill-out factor $f=0.124(\pm0.011)$. We collected all available times of light minima spanning 119 years including CCD data to construct the O-C curve and made detailed O-C analysis. The O-C diagram shows that the period change is complex. There exist a long-term continuous decrease and a cyclic variation. The period is decreasing at a rate of $\dot P=-1.04(\pm0.18)\times 10^{-10}$ $days\cdot{cycle}^{-1}$, and with the period decrease, V1073 Cyg will evolve to deep contact stage. The cyclic variation with a period of $P_3=82.7(\pm3.6) years$ and an amplitude of $A=0.028(\pm0.002) day$ may be explained by the magnetic activity of one or both components or the light travel time effect (LTTE) caused by a distant third companion with $M_3({i'}=90^{\circ})=0.511M_\odot$.Comment: 15 pages, 5 figure

Thermal conductance of graphene and dimerite

We investigate the phonon thermal conductance of graphene regarding the graphene sheet as the large-width limit of graphene strips in the ballistic limit. We find that the thermal conductance depends weakly on the direction angle $\theta$ of the thermal flux periodically with period $\pi/3$. It is further shown that the nature of this directional dependence is the directional dependence of group velocities of the phonon modes in the graphene, originating from the $D_{6h}$ symmetry in the honeycomb structure. By breaking the $D_{6h}$ symmetry in graphene, we see more obvious anisotropic effect in the thermal conductance as demonstrated by dimerite.Comment: enlarged version, in PR

Young's modulus of Graphene: a molecular dynamics study

The Young's modulus of graphene is investigated through the intrinsic thermal vibration in graphene which is `observed' by molecular dynamics, and the results agree quite well with the recent experiment [Science \textbf{321}, 385 (2008)]. This method is further applied to show that the Young's modulus of graphene: 1. increases with increasing size and saturation is reached after a threshold value of the size; 2. increases from 0.95 TPa to 1.1 TPa as temperature increases in the region [100, 500]K; 3. is insensitive to the isotopic disorder in the low disorder region ($< 5$), and decreases gradually after further increasing the disorder percentage.Comment: accepted by PRB, brief report, discussion on Poisson ratio adde