Simulation of Hydrogenated Amorphous Silicon: Temperature Dependence of Nonequilibrium Distribution Functions for Trap States

The nonequilibrium distribution functions (NDF) for the trap states in the mobility-gap under photo illumination and zero bias voltage are derived by the constructed self-consistent drift-diffusion simulator consisted of the Poisson equation and current continuity equations for hydrogenated amorphous silicon (a-Si:H). As for the temperature dependence of the NDF, we find that the values of the NDF decrease with increasing temperature (the negative temperature dependence) in the energy region near the conduction band for p-type a-Si:H. That is the reverse of the temperature dependence of the equilibrium distribution functions (EDF) for the trap states in the mobility-gap. Furthermore, we show that the new physical characteristic is applicable to the explanation of the temperature characteristic of the photoconductivity caused by the electron hopping in the conduction band tail for a-Si:H. The photoconductivity of a-Si:H decreases with increasing temperature, which is called the thermal quenching (TQ). We show that the TQ observed in a low temperature around 200K for p-type a-Si:H can be explained by the electron hopping model with the p-type NDF having the negative temperature dependence.

Lattice Boltzmann simulation of particle-laden flows using an improved curved boundary condition

In the application of the lattice Boltzmann method (LBM) for the simulation of the interface-resolved particulate flows, the bounce-back (BB) type rules have been widely adopted to handle the complex boundaries of moving particle. However, the original method cannot preserve the integrity of the particle shape, resulting in a low-resolution for the flow description near the solid boundary. Even though the subsequent modified BB scheme, i.e. the curved boundary condition (CBC), improves the overall accuracy, it generally loses the local-computation property of the simple BB. Therefore, a CBC is proposed in this paper, which maintains the two advantages of the second-order accuracy and local computation in the boundary treatment simultaneously. In the present scheme, information of only a single fluid point is needed. Furthermore, the relative distance between the fluid point and the boundary surface is involved, contributing to the second-order accuracy that is validated in the Poiseuille and cylindrical Couette flows. Particularly, it is found that the precision of the present scheme can be greatly improved with the nonequilibrium distribution functions of two directions included. Three more test cases of particle-laden flow, including particle migration in a channel, the sedimentation of a particle under gravity and the drafting-kissing-tumbling (DKT) dynamics of two settling particles, further demonstrate the feasibility and accuracy of the present scheme.

Robust predictions for the large-scale cosmological power deficit from primordial quantum nonequilibrium

The de Broglie–Bohm pilot-wave formulation of quantum theory allows the existence of physical states that violate the Born probability rule. Recent work has shown that in pilot-wave field theory on expanding space relaxation to the Born rule is suppressed for long-wavelength field modes, resulting in a large-scale power deficit [Formula: see text] which for a radiation-dominated expansion is found to have an approximate inverse-tangent dependence on [Formula: see text] (assuming that the width of the initial distribution is smaller than the width of the initial Born-rule distribution and that the initial quantum states are evenly-weighted superpositions of energy states). In this paper, we show that the functional form of [Formula: see text] is robust under changes in the initial nonequilibrium distribution — subject to the limitation of a subquantum width — as well as under the addition of an inflationary era at the end of the radiation-dominated phase. In both cases, the predicted deficit [Formula: see text] remains an inverse-tangent function of [Formula: see text]. Furthermore, with the inflationary phase the dependence of the fitting parameters on the number of superposed pre-inflationary energy states is comparable to that found previously. Our results indicate that, for the assumed broad class of initial conditions, an inverse-tangent power deficit is likely to be a fairly general and robust signature of quantum relaxation in the early universe.