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Waiting time is an important transport quantity that is complementary to average current and its fluctuation. So far all the studies of waiting time distribution (WTD) are limited to steady-state transport (either dc or ac). The existing theory cannot deal with WTD in the transient regime. In this regard, we develop a theoretical formalism based on Keldysh nonequilibrium Green's-function formalism to study WTD. This theory is suitable for dc, ac, and transient transport and can be used for first-principles calculation on realistic systems. We apply this theory to a quantum dot system with an upward bias pulse and calculate cumulants of transferred charge as well as WTD in the transient regime. The oscillatory behavior of WTD is found in the transient regime. We give a general relation between WTD and experimental measured quantity and demonstrate its feasibility for a quantum dot system in the transient regime. [ABSTRACT FROM AUTHOR]

We numerically study the parametric pumped current when magnetic field is applied both in the adiabatic and nonadiabatic regimes. In particular, we investigate the nature of pumped current for systems with resonance as well as antiresonance. It is found that, in the adiabatic regime, the pumped current changes sign across the sharp resonance with long lifetime, while the nonadiabatic pumped current at finite frequency does not. When the lifetime of the resonant level is short, the behaviors of the adiabatic and nonadiabatic pumped currents are similar with sign changes. Our results show that, at the energy where complete transmission occurs, the adiabatic pumped current is zero, while the nonadiabatic pumped current is nonzero. Different from the resonant case, both the adiabatic and nonadiabatic pumped currents are zero at antiresonance with complete reflection. We also investigate the pumped current when the other system parameters such as magnetic field, pumped frequency, and pumping potentials are varied. Interesting behaviors are revealed. Finally, we study the symmetry relation of the pumped current for several systems with different spatial symmetries upon reversal of magnetic field. Different from the previous theoretical prediction, we find that a system with general inversion symmetry can pump out a finite current in both the adiabatic and nonadiabatic regimes with an approximate relation I(B) ≈ I(-B) at small magnetic field. It has been shown theoretically that for systems with reflection symmetry, the pumped current satisfies the relation I(B) = I(-B) in the adiabatic regime. Our results show that even for systems evolving from the inversion to reflection symmetry, the pumped current still obeys the relation I(B) = I(-B) in the adiabatic regime at small magnetic field. [ABSTRACT FROM AUTHOR]

We numerically investigate the statistical properties of Wigner delay time in Anderson disordered 1D, 2D, and quantum dot (QD) systems. The distribution of proper delay time for each conducting channel is found to be universal in ²D and QD systems for all Dyson's symmetry classes and shows a piecewise-power-law behavior in the strongly localized regime. Two power-law behaviors were identified with asymptotical scaling τ-1 .5 and τ-2, respectively, that are independent of the number of conducting channels and Dyson's symmetry class. Two power-law regimes are separated by the relevant time scale τ0 ∼ h/Δ, where Δ is the average level spacing. It is found that the existence of necklace states is responsible for the second power-law behavior τ-2, which has an extremely small distribution probability. [ABSTRACT FROM AUTHOR]

Propellant-plasma interaction has been attracting great interests among most researchers for application to an electrothermal-chemical (ETC) gun. Previous works have shown that propellant-plasma interaction can enhance burning rates due to increased surface erosion of propellants as compared to that of conventional ignition. Plasma radiation and heat convection are the dominant mechanism of energy transfer based on both experimental data and numerical simulation. However, little literatures were reported about a detailed understanding of propellant loading parameters and the plasma flow-field distribution interactions, which is very important in deciding a successful propellant-charge design in ETC guns. The pressure-time curves during interrupted-burning process of different propellants such as triethyeneglycol dinitrate and single-base propellants ignited by plasma were recorded by pressure sensor in interrupted-burning setup. Influence of loading parameters, including loading density, distance between propellants and plasma jet, and propellant holding methods at the same selected location in plasma flow-field on plasma-ignition performance of propellants was discussed based on experimental results. As the loading density of propellants increases, the porosity of the propellant bed becomes small. Moreover, the penetrating depth of plasma into propellant bed shortens. Therefore, the plasma energy attenuates rapidly, and the ignition-delay time of propellants becomes longer. The ignition-delay time is longer when the distance between propellants and plasma jet increases. At the same selected location in plasma flow-held, different holding methods of propellant burning surface to plasma jet have less influence on the ignition, combustion process of propellants, and the ignition-delay time. The matching test results on propellant loading parameters and plasma flow-field distribution interaction play a major role in improving charge configurations at chosen plasma flow-field and understanding plasma-propellant interaction better. [ABSTRACT FROM AUTHOR]

The validity of high frequency technique and time-domain measurement to nanoscale electronic devices provides an imperious demand to explore the ultrafast electron dynamics and nonlinear responses accompanied with material science in theory. In this work, we carried out a first principles calculation to research the dynamic response in both frequency and time domain of a nanoscale Cu/black phosphorus (Cu/BP) transistor. The system shows n-type transport behaviors due to the charge transfer from the Cu/BP contact to the central BP section, which is different from the p-type pristine BP transistor. By adjusting the gate voltage, on-off ratio of conductance can reach up to 103 which is expected to further increase with the length of the central BP section. The Cu/BP transistor always shows capacitive-like behaviors even at high frequency, and cut-off frequency is estimated up to 75 THz. Transient current evolution shows abundant quantum scattering behaviors, and two important time scales were analyzed. The tune-on time is comparable to the Fermi velocity of pristine BP, and is roughly independent of the magnitudes of bias voltages. The relaxation time is roughly hundreds of femtoseconds, which corresponds to the cut-off frequency up to a point and can be further reduced by dephasing effect. The rapid response of hundreds of femtoseconds indicates that the Cu/BP transistor maybe work as high frequency nanoscale electronic device. [ABSTRACT FROM AUTHOR]

We numerically investigate the valley-polarized current in symmetric and asymmetric zigzag graphene nanoribbons (ZGNRs) by the adiabatic pump, and the effect of spatial symmetry is considered by introducing different pumping regions. It is found that pumping potentials with the symmetry Vp(x, y) = Vp(−x, y) can generate the largest valley-polarized current. The valley-polarized currents with the pumping potential symmetry Vp(x, y) = Vp(x, −y) and with Vp(x, y) = Vp(−x, −y) of symmetric ZGNRs are much smaller than those of asymmetric ZGNRs. We also find and of symmetric ZGNRs decrease and increase with the increasing pumping amplitude, respectively. Moreover, the dephasing effect from the electron–phonon coupling within the Buttiker dephasing scheme is introduced. The valley-polarized current of the symmetric ZGNRs with Vp(x, y) = Vp(x, −y) increases with the increase of the dephasing strength while that with Vp(x, y) = Vp(−x, −y) decreases as the dephasing strength increases. [ABSTRACT FROM AUTHOR]

We conducted a 3 × 3 × 2 experiment to verify the moral preference hypothesis and extend the boundary conditions of the moral frame effect. Participants played a trade-off game (TOG), in which they unilaterally choose between an equitable or efficient option. We manipulated the labeling of the options to describe the equitable versus efficient option as morally right, and controlled the amount of the stakes and division schemes in the TOG. We found there was a significant effect of moral frame when stakes were low in the TOG, and participants would choose a morally right option whether it was equitable or efficient. However, the effect of moral frame was nonsignificant when the stakes were high. In addition, the division schemes in the TOG had a great impact on the moral frame effect. Therefore, we found that when participants’ interest in the options remains the same or the changes are small, and other players’ interest changes greatly, the moral frame effect is not significant. [ABSTRACT FROM AUTHOR]

A photoinduced current of a layered MoS2-based transistor is studied from first-principles. Under the illumination of circular polarized light, a valley-polarized current is generated, which can be tuned by the gate voltage. For monolayer MoS2, the valley-polarized spin-up (down) electron current at K () points is induced by the right (left) circular polarized light. The valley polarization is found to reach +1.0 (−1.0) for the valley current that carried such a K () index. For bilayer MoS2, the spin-up (down) current can be induced at both K and valleys by the right (left) circular light. In contrast to monolayer MoS2, the photoinduced valley polarization shows asymmetric behavior upon reversal of the gate voltage. Our results show that the valley polarization of the photoinduced current can be modulated by the circular polarized light and the gate voltage. All the results can be well understood using a simple kp model. [ABSTRACT FROM AUTHOR]

We numerically investigate the statistical properties of electrochemical capacitance in disordered two-dimensional mesoscopic capacitors. Based on the tight-binding Hamiltonian, the Green's function formalism is adopted to study the average electrochemical capacitance, its fluctuation as well as the distribution of capacitance of the disordered mesoscopic capacitors for three different ensembles: orthogonal (symmetry index β = 1), unitary (β = 2), and symplectic (β = 4). It is found that the electrochemical capacitance in the disordered systems exhibits universal behavior. In the case of a single conducting channel, the electrochemical capacitance follows a symmetric Gaussian distribution at weak disorders as expected from the random matrix theory. In the strongly disordered regime, the distribution is found to be a sharply one-sided form with a nearly constant tail in the large capacitance region. This behavior is due to the existence of the necklace states in disordered systems, which is characterized by the multiresonance that gives rise to a large density of states. In addition, it is found that the necklace state also enhances the fluctuation of electrochemical capacitance in the case of a single conducting channel. When the number of conducting channels increases, the influence of necklace states becomes less important. For a large number of conducting channels, the electrochemical capacitance fluctuation develops a plateau region in the strongly disordered regime. The plateau value is identified as universal electrochemical capacitance fluctuation, which is independent of system parameters such as disorder strength, Fermi energy, geometric capacitance, and system size. Importantly, the universal electrochemical capacitance fluctuation is the same for all three ensembles, suggesting a superuniversal behavior. [ABSTRACT FROM AUTHOR]

We investigated whether or not self-efficacy mediated the enhancing effect of perceived control on purchase intention in online shopping. We randomly assigned 263 participants to experimental conditions in which they encountered different customer services. We assessed their perceived control, self-efficacy, and purchase intention via a self-evaluation survey. Results indicated that participants with the availability of live customer service had a higher level of perceived control and stronger purchase intention. There were significantly positive correlations among perceived control, self-efficacy, and purchase intention. Structural equation modeling showed that self-efficacy was a significant partial mediator of the effect of perceived control on purchase intention, accounting for 17.4% of the total effect. This finding implies that the provision of customer service in online shopping that leads consumers to have a perception of greater control can enhance their self-efficacy, and induce stronger purchase intention. [ABSTRACT FROM AUTHOR]

We report an investigation of the dynamic conductance fluctuation of disordered mesoscopic conductors including one-dimensional, two-dimensional, and quantum dot systems. Our numerical results show that in the quasi-ballistic regime the average emittance is negative, indicating the expected inductive-like behavior. However, in the diffusive and localized regime, the average emittance is still negative. This disagrees qualitatively with the result obtained from random matrix theory. Our analysis suggests that this counterintuitive result is due to the appearance of non-diffusive elements in the system, the necklace states (or the precursor of necklace states in the diffusive regime) whose existence has been confirmed experimentally in an optical system. [ABSTRACT FROM AUTHOR]

For a resonant tunneling structure, it was found experimentally that the shot noise is super-Poissonian in the negative differential region (NDR). From a semiclassical analysis, it is believed that the super-Poissonian behavior is due to fluctuation of the Coulomb interaction. Although there are many studies on shot noise in mesocopic or nanoscale systems, an accounting by first-principles quantum transport theory for super-Poissonian behavior in the NDR is still lacking. In this paper, we develop a theoretical formalism to investigate the contribution of fluctuations of the Coulomb interaction to the shot noise, based on the Keldysh nonequilibrium Green's function method. We applied our theory to study the behavior of dc shot noise of atomic junctions, using the method of nonequilibrium Green's functions combined with density functional theory (NEGF-DFT). In particular, for an atomic carbon wire consisting of four carbon atoms in contact with two Al(100) electrodes, a first-principles calculation within the NEGF-DFT formalism shows a NDR region in the I-V curve at finite bias due to the effective band bottom of the Al lead. We calculated the shot noise spectrum using our theory. Our numerical result shows super-Poissonian behavior with a Fano factor larger than 1 in the NDR region, in agreement with the experimental result. [ABSTRACT FROM AUTHOR]

We report a first-principles investigation of spin-dependent transport properties in two different graphene-based molecular junctions. By applying different temperatures between two leads without bias voltage, spin-dependent currents are driven which depend on reference temperature T, temperature gradient ΔT, and gate voltage Vg. Moreover, pure spin currents without charge currents can be obtained by adjusting T,ΔT, and Vg for both molecular junctions. The directions of pure spin currents in these two molecular junctions are opposite, which can be understood by analyzing the transmission coefficients under equilibrium states. Spin thermopower, thermal conductance, and the figure of merit as functions of T,Vg, and chemical potential μ were also investigated in the linear response regime. Large spin thermopower and spin figure of merit can be obtained by adjusting Vg and μ for each junction, which indicates proper application of spin caloritronic devices of our graphene-based molecular junctions. [ABSTRACT FROM AUTHOR]

A growing body of empirical evidence has shown that although social support (SS) can predict subjective well-being (SWB), the relationship between SS and SWB is still unclear. In this study we investigated the role that positive psychological capital (PPC) plays in the relationship between SS and SWB. The results showed that PPC, SS, and SWB were positively related. The more important result, however, was that PPC mediated the relationship between SS and SWB. The findings are discussed in the context of the importance of PPC for SWB. Limitations in this study and implications for future research are identified. [ABSTRACT FROM AUTHOR]

At the interface between two-dimensional materials with different topologies, topologically protected one-dimensional states (also named zero-line modes) arise. Here, we focus on the quantum anomalous Hall-effect-based zero-line modes formed at the interface between regimes with different Chern numbers. We find that these zero-line modes are chiral and unilaterally conductive due to the breaking of time-reversal invariance. For a beam splitter consisting of two intersecting zero lines, the chirality ensures that a current can only be injected from two of the four terminals. Our numerical results further show that, in the absence of contact resistance, the (anti-)clockwise partitions of the currents from these two terminals are the same owing to the current conservation, which effectively simplifies the partition laws. We find that the partition is robust against the relative shift of Fermi energy but can be adjusted effectively by tuning the relative magnetization strengths at different regimes or relative angles between zero lines. [ABSTRACT FROM AUTHOR]