How Does Folding Modulate Thermal Conductivity of Graphene

We study thermal transport in folded graphene nanoribbons using molecular dynamics simulations and the non-equilibrium Green's function method. It is found that the thermal conductivity of flat graphene nanoribbons can be modulated by folding and changing interlayer couplings. The analysis of transmission reveals that the reduction of thermal conductivity is due to scattering of low frequency phonons by the folds. Our results suggest that folding can be utilized in the modulation of thermal transport properties in graphene and other two dimensional materials.Comment: published in Applied Physics Letters 201

Modulation of Thermal Conductivity in Kinked Silicon Nanowires: Phonon Interchanging and Pinching Effects

We perform molecular dynamics simulations to investigate the reduction of the thermal conductivity by kinks in silicon nanowires. The reduction percentage can be as high as 70% at room temperature. The temperature dependence of the reduction is also calculated. By calculating phonon polarization vectors, two mechanisms are found to be responsible for the reduced thermal conductivity: (1) the interchanging effect between the longitudinal and transverse phonon modes and (2) the pinching effect, i.e a new type of localization, for the twisting and transverse phonon modes in the kinked silicon nanowires. Our work demonstrates that the phonon interchanging and pinching effects, induced by kinking, are brand new and effective ways in modulating heat transfer in nanowires, which enables the kinked silicon nanowires to be a promising candidate for thermoelectric materials.Comment: Nano. Lett. accepted (2013

Impacts of Transit-Oriented Development (TOD) on the Travel Behavior of its Residents in Shenzhen, China

Rapid urbanization in cities across the world has generated a number of issues including urban sprawl, segregation of land uses, traffic congestion and negative environmental impacts. Transit-oriented development (TOD) has been considered as the best urban development strategy and planning tool to approach these challenges. It is widely adopted as the urban development guide by planners and decision makers in North America and all over the world. TOD has been practiced by many different cities across the world since the early 1990s, however, its concept and practices in China are still at its experimental stage. The study identifies that implementation of TOD in existing high-density urban spaces is a major challenge in China. A common goal of any successful TOD is to reduce automobile dependency, and encourage the use of public transit (e.g. subway, LRT, bus) and other sustainable travel modes (e.g. walking and cycling). This thesis aims to explore the effectiveness of TOD practices in Shenzhen by assessing the impact to the residents’ travel behavior at the neighbourhood level. Two TOD practices have been selected to be further analyzed in this study – Grand Theatre Station and Houhai Station. Grand Theatre Station is located within the old urban centre, and Houhai station is considered to be a more conventional TOD design which is located in a reclamation area. To conduct the analysis, data is collected from Shenzhen subway authorities, field observations and survey. All the information is visualized using maps and descriptive statistics. The result showed that both sites have experienced a significant growth in subway ridership since the implementation of TOD. Furthermore, TOD practice at Grand Theatre Station is significantly more effective comparing to Houhai Station. With further analysis of the differences between the two cases, three key qualities have been summarized to provide different insights for planners to improve TOD practices in China, they include “rich mix of residential and commercial types”, “walkability/connectivity”, as well as “quality of subway services”. These qualities will be further explored in the study

Optimization of polysaccharides extracted from Verbena officinalis L and their inhibitory effects on invasion and metastasis of colorectal cancer cells

Purpose: To investigate polysaccharides (PEV) extracted from the aerial part of Verbena officinalis L. and their inhibitory effects on the invasion and metastasis of colorectal cancer (CRC) cells.Methods: PEV was extracted by water and the optimization of extraction conditions was performed using a Box-Benhnken design (BBD). The cell viability was evaluated by 4,5-dimethylthiazol-2-yl)2,5-diphenyltetrazolium bromide (MTT) assay. The effects of PEV on cell adhesion and invasion were evaluated by Transwell invasion, wound healing migration and adhesion assays in vitro. The effects of PEV on the expressions of matrix metalloproteinase-9 (MMP-9), mesenchymal-epithelial transition factor (C-met), E-cadherin (E-CAD), cyclooxygenase-2 (COX-2) and E-prostanoid 2 receptor (EP2) were investigated by western blot.Results: The BBD model was established successfully for the optimization of PEV extraction (p <0.0001). The results indicate that PEV (50, 100 and 200 μg/mL) had significant inhibitory effects on cell invasion and migration of SW480 cells (p < 0.05). PEV also significantly decreased cell adhesion of SW480 cells. By treating with PEV, the expressions of C-met, MMP-9, COX-2 and EP2 were decreased, whereas the expression of E-CAD increased in SW480 cells.Conclusion: RSM is effective for optimizing the extraction conditions of PEV. More importantly, PEV significantly inhibits the invasion and metastasis of SW480 cells by regulating the expression of MMP-9, C-met, E-CAD, COX-2 and EP2. Thus, PEV has the potential to be developed into therapeutic drugs for CRC in the future.Keywords: Polysaccharides, Colorectal cancer, Verbena officinalis, SW480 cell lines, Cell invasion, Metastasi

Prospects for probing the interaction between dark energy and dark matter using gravitational-wave dark sirens with neutron star tidal deformation

Gravitational wave (GW) standard siren observations provide a rather useful tool to explore the evolution of the universe. In this work, we wish to investigate whether the dark sirens with neutron star (NS) deformation from third-generation (3G) GW detectors could help probe the interaction between dark energy and dark matter. We simulate the GW dark sirens of four detection strategies based on the three-year observation and consider four phenomenological interacting dark energy models to perform cosmological analysis. We find that GW dark sirens could provide tight constraints on $\Omega_{\rm m}$ and $H_0$ in the four IDE models, but perform not well in constraining the dimensionless coupling parameter $\beta$ with the interaction proportional to the energy density of cold dark matter. Nevertheless, the parameter degeneracy orientations of CMB and GW are almost orthogonal, and thus the combination of them could effectively break cosmological parameter degeneracies, with the constraint errors of $\beta$ being 0.00068-0.018. In addition, we choose three typical equation of states (EoSs) of NS, i.e., SLy, MPA1, and MS1, to investigate the effect of NS's EoS in cosmological analysis. The stiffer EoS could give tighter constraints than the softer EoS. Nonetheless, the combination of CMB and GW dark sirens (using different EoSs of NS) shows basically the same constraint results of cosmological parameters. We conclude that the dark sirens from 3G GW detectors would play a crucial role in helping probe the interaction between dark energy and dark matter, and the CMB+GW results are basically not affected by the EoS of NS.Comment: 12 pages, 9 figure