A prerequisite relation describes a basic relation among concepts in cognition, education and other areas. However, as a semantic relation, it has not been well studied in computational linguistics. We investigate the problem of measuring prerequisite relations among concepts and propose a simple link-based metric, namely reference distance (RefD), that effectively models the relation by measuring how differently two concepts refer to each other. Evaluations on two datasets that include seven domains show that our single metric based method outperforms existing supervised learning based methods.
A novel process was developed to prepare electrically conducting maleic anhydride grafted polypropylene (gPP)/expanded graphite (EG) nanocomposites by solution intercalation. The conducting percolation threshold at room temperature (⌽ c ) of the nanocomposites was 0.67 vol %, much lower than that of the conventional conducting composites prepared by melt mixing (⌽ c ϭ 2.96 vol %). When the EG content was 3.90 vol %, the electrical conductivity () of the former reached 2.49 ϫ 10 Ϫ3 S/cm, whereas the of the latter was only 6.85 ϫ 10 Ϫ9 S/cm. The TEM, SEM, and optical microscopy observations confirmed that the significant decrease of ⌽ c and the striking increase of might be attributable to the formation of an EG/gPP conducting multiple network in the nanocomposites, involving the network composed of particles with a large surface-tovolume ratio and several hundred micrometers in size, and the networks composed of the boards or sheets of graphite with high width-to-thickness ratio and particles of fine microscale or nanoscale sizes.
High-performance graphene nanopapers are prepared from an aqueous solution of functional graphenes with benzenesulfonic acid groups via covalent bonds. The formed hydrophobic graphene nanopapers showed the highest tensile strength of 360 MPa and Young's modulus of 102 GPa for samples with 13.7 wt % functional group and annealed at 150 °C. These samples showed a high electrical conductivity of 4.45 × 10(4) S/m after being annealed at 250 °C. The aforementioned properties of graphene nanopapers are much higher than any previously reported data. The properties of nanopapers depend on the degree of functionality on graphenes and the annealing temperatures, which are further evidenced by X-ray photoelectron spectroscopy, FTIR, and X-ray diffraction patterns. Such unique nanopapers can be easily bounded and sandwiched onto any solid surface to give rise to great potentials in many applications such as gas diffusion barriers, EMI shielding, thermal management, and anticorrosion.
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