Electric Field Effect Analysis of Thin PbTe films on high-epsilon SrTiO3 Substrate

Thin PbTe films (thickness 500 - 600 angstrom), deposited on SrTiO3, have been investigated by electric field effect (EFE). The high resistivity of such thin films warrants a high sensitivity of the EFE method. The SrTiO3 substrate serves as the dielectric layer in the Gate-Dielectric-PbTe structure. Due to the large dielectric constant of SrTiO3, particularly at low temperatures, the electric displacement D in the film reaches the high value of about 10^8 V/cm, and the EFE introduced charge into the PbTe film amounts to ~ 8 microC/cm2. The high D permits to measure the EFE resistance and Hall constant over a wide region of D, revealing the characteristic features of their D-dependence. An appropriate theoretical model has been formulated, showing that, for such films, one can measure the dependence of the Fermi level on D. In fact, we demonstrate that shifting the Fermi level across the gap by varying D, the density-of-states of the in-gape states can be mapped out. Our results show, that the PbTe layers studied, possess a mobility gap exceeding the gap of bulk PbTe.Comment: 27 pages, 12 figure

RandomFront 2.3: a physical parameterisation of fire spotting for operational fire spread models-implementation in WRF-SFIRE and response analysis with LSFire+

Fire spotting is often responsible for dangerous flare-ups in wildfires and causes secondary ignitions isolated from the primary fire zone, which lead to perilous situations. The main aim of the present research is to provide a versatile probabilistic model for fire spotting that is suitable for implementation as a post-processing scheme at each time step in any of the existing operational large-scale wildfire propagation models, without calling for any major changes in the original framework. In particular, a complete physical parameterisation of fire spotting is presented and the corresponding updated model RandomFront 2.3 is implemented in a coupled fire?atmosphere model: WRF-SFIRE. A test case is simulated and discussed. Moreover, the results from different simulations with a simple model based on the level set method, namely LSFire+, highlight the response of the parameterisation to varying fire intensities, wind conditions and different firebrand radii. The contribution of the firebrands to increasing the fire perimeter varies according to different concurrent conditions, and the simulations show results in agreement with the physical processes. Among the many rigorous approaches available in the literature to model firebrand transport and distribution, the approach presented here proves to be simple yet versatile for application to operational large-scale fire spread models.This research was supported by the Basque Government through the BERC 2014–2017 and BERC 2018–2021 programs. It was also funded by the Spanish Ministry of Economy and Competitiveness MINECO via the BCAM Severo Ochoa SEV-2013-0323 and SEV-2017-0718 accreditations, the MTM2013-40824-P “ASGAL” and MTM2016-76016-R “MIP” projects, and the PhD grant “La Caixa 2014”

Spectral Representation for the Effective Macroscopic Response of a Polycrystal: Application to Third-Order Nonlinear Susceptibility

Erratum: In our paper, we show that the spectral representation for isotropic two-component composites also applies to uniaxial polycrystals. We have learned that this result was, in fact, first conjectured by G.W. Milton. While our derivation is more detailed, our result for the spectral function is the same as Milton's. We very much regret not having been aware of this work at the time of writing our paper. Original abstract: We extend the spectral theory used for the calculation of the effective linear response functions of composites to the case of a polycrystalline material with uniaxially anisotropic microscopic symmetry. As an application, we combine these results with a nonlinear decoupling approximation as modified by Ma et al., to calculate the third-order nonlinear optical susceptibility of a uniaxial polycrystal, assuming that the effective dielectric function of the polycrystal can be calculated within the effective-medium approximation.Comment: v2 includes erratum and the original preprin

Thermal Wave Induced Edge Electrical Field of Pyroelectric: Spatial Pattern Mapping and Effect of Ambient Conditions

We have recently analyzed theoretically the main characteristics of the edge depolarizing electric field (EDEF), in the vicinity of a non-polar face of a pyroelectric. In this work we measured and characterized the EDEF, excited by a harmonical thermal wave. We present here experimental results obtained on a pyroelectric crystal LiTaO3, confirming our theoretical predictions. We present the theoretical analysis and description of the thermal wave and the induced harmonically varying EDEF. The calculations assume an equivalent circuit of a pyroelectric capacitive current source. The measured magnitude of the EDEF and its spatial variation agree well with the theoretical model. The effect of the air pressure at the pyroelectric/air interface, on the EDEF, was determined in the interval 10^3 - 10^-6 torr. We found that EDEF increases significantly with decreasing air pressure, presumably due to diminishing of adsorption screening at the polar faces. Teflon plates, covering the polar faces, prevent accumulation of screening charged particles, resulting in a drastic increase of EDEF