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[en] Highlights: • First report for molecular junction of oligothiophenes contact graphene electrodes. • Obvious difference in transport between molecules with and without amino. • Coexisted negative differential resistance and dual spin-filtering. • Ideal dual spin-filtering effect for molecule with NH2 side group. - Abstract: The influence of chemical side groups is significant in physical or chemical understanding the transport through the single molecular junction. Motivated by the recent successful fabrication and measurement of a single organic molecule sandwiched between graphene electrodes (Prins et al., 2011), here we study the spin-dependent transport properties through a junction of a fused oligothiophenes molecule embedded between two zigzag-edged graphene nanoribbon (ZGNR) electrodes. The molecule with and without an attached amino NH2 side group is considered, respectively, and external magnetic fields or FM stripes are applied onto the ZGNRs to initially orient the magnetic alignment of the electrodes for the spin-dependent consideration. By the ab initio calculations based on the density functional theory combined with nonequilibrium Green’s function formalism, we have demonstrated the remarkable difference in the spin-charge transport property between the junctions of the molecule with and without NH2 side group. In particular, the junction with side group shows more obvious NDR. In addition, it exhibits an interesting dual spin-filtering effect when the magnetic alignment in electrodes is initially antiparallel-oriented. The mechanisms of the results are revealed and discussed in terms of the spin-resolved transmission spectrum associated with the frontier molecular orbitals evolution, the molecular projected self-consistent Hamiltonian eigenvalues, and the local density of states.
[en] We study the attack vulnerability of network with duplication-divergence mechanism. Numerical results have shown that the duplication-divergence network with larger retention probability σ is more robust against target attack relatively. Furthermore, duplication-divergence network is broken down more quickly than its counterpart BA network under target attack. Such result is consistent with the fact of WWW and Internet networks under target attack. So duplication-divergence model is a more realistic one for us to investigate the characteristics of the world wide web in future. We also observe that the exponent γ of degree distribution and average degree are important parameters of networks, reflecting the performance of networks under target attack. Our results are helpful to the research on the security of network.
[en] Fault diagnosis of rolling element bearings is important for improving mechanical system reliability and performance. Vibration signals contain a wealth of complex information useful for state monitoring and fault diagnosis. However, any fault-related impulses in the original signal are often severely tainted by various noises and the interfering vibrations caused by other machine elements. Narrow-band amplitude demodulation has been an effective technique to detect bearing faults by identifying bearing fault characteristic frequencies. To achieve this, the key step is to remove the corrupting noise and interference, and to enhance the weak signatures of the bearing fault. In this paper, a new method based on adaptive wavelet filtering and spectral subtraction is proposed for fault diagnosis in bearings. First, to eliminate the frequency associated with interfering vibrations, the vibration signal is bandpass filtered with a Morlet wavelet filter whose parameters (i.e. center frequency and bandwidth) are selected in separate steps. An alternative and efficient method of determining the center frequency is proposed that utilizes the statistical information contained in the production functions (PFs). The bandwidth parameter is optimized using a local ‘greedy’ scheme along with Shannon wavelet entropy criterion. Then, to further reduce the residual in-band noise in the filtered signal, a spectral subtraction procedure is elaborated after wavelet filtering. Instead of resorting to a reference signal as in the majority of papers in the literature, the new method estimates the power spectral density of the in-band noise from the associated PF. The effectiveness of the proposed method is validated using simulated data, test rig data, and vibration data recorded from the transmission system of a helicopter. The experimental results and comparisons with other methods indicate that the proposed method is an effective approach to detecting the fault-related impulses hidden in vibration signals and performs well for bearing fault diagnosis. (paper)
[en] Highlights: ► We have found the color-tunable long lasting phosphorescent phenomenon of γ-Zn3(PO4)2:Mn2+,Ga3+. ► The distribution of Mn2+ ions in tetrahedral and octahedral lattice changes with the incorporation of Ga3+ ions. ► Both of the red and green afterglow performances from Mn2+ are largely improved by co-doping with Ga3+ ions. ► Ga3+ not only acts the role of adjusting the ratio of the green/red luminescent center but also acts as an electron trap. -- Abstract: Green and red long lasting phosphorescent (LLP) phenomenon in γ-Zn3(PO4)2:Mn2+/Ga3+was systematically investigated. Two emission bands are observed in γ-Zn3(PO4)2:Mn2+/Ga3+, which are respectively centered at 507 nm and 620 nm. The green and the red long afterglow have been observed after removing the ultraviolet light. The spectral overlap between the green emission band and the excitation band monitored at 620 nm, which supports the feasibility of the energy transfer from Mn2+ (CN = 4) to Mn2+ (CN = 6), has been studied. The distribution of Mn2+ ions in tetrahedral and octahedral lattice changes with the incorporation of Ga3+ ions. The ratio of the green to the red enhances because of the increase of Ga3+ concentration. With the introduction of Ga3+, the color of the afterglow has been regulated, and the performance has been improved
[en] Highlights: • Pt-terminated zigzag symmetric nanoribbon of PtS2 show metallic and magnetic properties. • Metallic and magnetic properties are mainly determined by 5d orbits of Pt atoms from two central symmetric edges. • Single PtS2 nanoribbon could have two parallel symmetric metallic channels, while that of MoS2 only have one. - Abstract: Transition metal dichalcogenides (TMD) MoS2 or graphene could be designed to metallic nanoribbons, which always have only one edge show metallic properties due to symmetric protection. In present work, a nanoribbon with two parallel metallic and magnetic edges was designed from a noble TMD PtS2 by employing first-principles calculations based on density functional theory (DFT). Edge energy, bonding charge density, band structure, density of states (DOS) and simulated scanning tunneling microscopy (STM) of four possible edge states of monolayer semiconductive PtS2 were systematically studied. Detailed calculations show that only Pt-terminated edge state among four edge states was relatively stable, metallic and magnetic. Those metallic and magnetic properties mainly contributed from 5d orbits of Pt atoms located at edges. What's more, two of those central symmetric edges coexist in one zigzag nanoribbon, which providing two atomic metallic wires thus may have promising application for the realization of quantum effects, such as Aharanov–Bohm effect and atomic power transmission lines in single nanoribbon.