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We investigate the effect of the mechanical motion of a quantum dot on the transport properties of a quantum dot shuttle. Employing the equation of motion method for the nonequilibrium Green's function, we show that the oscillation of the dot, i.e., the time-dependent coupling between the dot's electron and the reservoirs, can destroy the Kondo effect. With the increase in the oscillation frequency of the dot, the density of states of the quantum dot shuttle changes from the Kondo-like to a Coulomb-blockade pattern. Increasing the coupling between the dot and the electrodes may partly recover the Kondo peak in the spectrum of the density of states. Understanding of the effect of mechanical motion on the transport properties of an electron shuttle is important for the future application of nanoelectromechanical devices. [ABSTRACT FROM AUTHOR]

We investigate the mechanism for the improvement of p-type doping efficiency in Mg-Al0.14Ga0.86N/GaN superlattices (SLs). It is shown that the hole concentration of SLs increases by nearly an order of magnitude, from 1.1✕1017 to 9.3✕1017 cm-3, when an AlN interlayer is inserted to modulate the strains. Schrodinger-Poisson self-consistent calculations suggest that such an increase could be attributed to the reduction of donor-like defects caused by the strain modulation induced by the AlN interlayer. Additionally, the donor-acceptor pair emission exhibits a remarkable decrease in intensity of the cathodoluminescence spectrum for SLs with an AlN interlayer. This supports the theoretical calculations and indicates that the strain modulation of SLs could be beneficial to the donor-like defect suppression as well as the p-type doping efficiency improvement. [ABSTRACT FROM AUTHOR]

We propose a novel scheme of simultaneous polarization separation and switching, based on the orthogonally-polarized four-wave mixing (FWM) effect, for ultra-high-speed polarization multiplexing (Pol-MUX) fiber networks such as 100-Gbps and 400-Gbps backbone networks. We use theoretical and experimental analysis of the vector theory of FWM to successfully achieve polarization separation and all-optical switching by utilizing a 100-Gbps dual polarization-quadrature phase shift keying (DP-QPSK) signal and two orthogonally-polarized pumps. Both of the polarization-separated QPSK signals have clear constellation diagrams, with root mean square (RMS) error vector magnitudes (EVMs) of 14.32% and 14.11% respectively. The wavelengths of idlers can be created at 30 different wavelengths, which are consistent with International Telecommunication Union-Telecommunication (ITU-T) wavelengths, by flexibly changing the wavelength of the pump light. Moreover, the idlers that have distinct wavelengths have power distributed in a range from −10 dBm to −15 dBm, which can support error-free transmission. The power penaltyis 5 dB lower than that of back-to-back (BTB) signal for both the X- and Y-polarization components measured at a bit error ratio (BER) of 3.8×10−3. Our experimental results indicate that this scheme has promising applications in future backbone networks. [ABSTRACT FROM AUTHOR]

This paper calculates the electron impact excitation rate coefficients from the ground term 2s22p2 3P to the excited terms of the 2s22p2, 2s2p3, 2s22p3s, 2s22p3p, and 2s22p3d configurations of N II. In the calculations, multiconfiguration Dirac-Fork wave functions have been applied to describe the target-ion states and relativistic distorted-wave calculation has been performed to generate fine-structure collision strengths. The collision strengths are then averaged over a Maxwellian distribution of electron velocities in order to generate the effective collision strengths. The calculated rate coefficients are compared with available experimental and theoretical data, and some good agreements are found for the outer shell electron excitations. But for the inner shell electron excitations there are still some differences between the present calculations and available experiments. [ABSTRACT FROM AUTHOR]