A hybridized structure constructed by zigzag boron nitride nanoribbon and zigzag graphene nanoribbon is proposed, and their band structures and electronic transport properties are calculated by applying first-principles calculations. The results show that the band gap of the hybridized structure can be tuned and transitions from insulator to metal can be realized by changing the unit number of zigzag graphene nanoribbon. The currents with different spin polarization display different behavior.
The electronic transport properties in phenalenyl molecular device are studied by using nonequilibrium Green’s functions in combination with the density-functional theory. The results show that the electronic transport properties are strongly dependent on the contact geometry. The negative differential resistance behavior with large peak to valley ratio is observed when the molecule contacts the Au electrodes through two second-nearest sites or one second-nearest site and one third-nearest site, while the rectifying performance is observed only when the molecule contacts the Au electrodes through one second-nearest site and one third-nearest site. The mechanisms are proposed for these phenomena.
Emission mechanisms of the shell-type supernova remnant (SNR) RX J1713.7-3946 are studied with multi-wavelength observational data from radio, X-ray, GeV γ-ray to TeV γ-ray band. A Markov Chain Monte Carlo method is employed to explore the high-dimensional model parameter space systematically. Three scenarios for the γ-ray emission are investigated: the leptonic, the hadronic and a hybrid one. Thermal emission from the background plasma is also included to constrain the gas density, assuming ionization equilibrium, and a 2σ upper limit of about 0.03 cm −3 is obtained as far as thermal energies account for a significant fraction of the dissipated kinetic energy of the SNR shock. Although systematic errors dominate the χ 2 of the spectral fit of all models, we find that 1) the leptonic model has the best constrained model parameters, whose values can be easily accommodated with a typical supernova, but gives relatively poor fit to the TeV γ-ray data; 2) The hybrid scenario has one more parameter than the leptonic one and improves the overall spectral fit significantly; 3) The hadronic one, which has three more parameters than the leptonic model, gives the best fit to the overall spectrum with relatively not-well-constrained model parameters and very hard spectra of accelerated particles. The uncertainties of the model parameters decrease significantly if the spectral indices of accelerated electrons and protons are the same. The hybrid and hadronic models also require an energy input into high-energy protons, which seems to be too high compared with typical values of a supernova explosion. Further investigations are required to reconcile these observations with SNR theories.
We study the stochastic electron acceleration by fast mode waves in the
turbulent downstream of weakly magnetized collisionless astrophysical shocks.
The acceleration is most efficient in a dissipative layer, and the model
characteristics are determined by the shock speed, density, magnetic field, and
turbulence decay length. The model explains observations of shell-type
supernova remnants RX J1713.7-3946 and J0852.0-4622 and can be tested by
observations in hard X-rays with the HXMT and NuSTAR or gamma-rays with the
GLAST.Comment: 12 pages, 2 figures, Accepted by ApJ
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