Quantum chemical simulations of titanium dioxide nanotubes used for photocatalytic water splitting

Titanium dioxide nanotubes (NTs) built from various initial 2D models of TiO2 (a promising catalyst for water splitting) are investigated via density functional theory using the B3LYP hybrid exchange-correlation functional in the localized basis set of a linear combination of atomic orbitals. For TiO₂ NTs (eight different types of morphology) created from four initial 2D structures, full geometry optimization is performed and the main energy parameters, such as the band gap width, energy positions of the valence band top and the conduction band bottom, and NT formation and strain energy, are calculated. Analysis of the NT strain and formation energies enables us to choose their most stable configuration, which can further be employed to simulate NTs doped with impurity atoms capable of serving as efficient centers for the photocatalytic dissociation of water molecules.     

Reduction of threshold of acousto-optic effect in a nematic crystal subject to combined actions

The acousto-optic effect in a homeotropically aligned layer of a nematic liquid crystal was investigated subject to combined actions: 1, for coherent excitation of ultrasonic and viscous waves, 2, for ultrasonic action in an electric field near the Freedericksz transition. The acousto-optic effect threshold was reduced by two orders of magnitude. The experimental results are discussed using the facoustic streaming model. The theoretical analysis is supported by our experimental results.     

Extended Variational Message Passing for Automated Approximate Bayesian Inference

Variational Message Passing (VMP) provides an automatable and efficient algorithmic framework for approximating Bayesian inference in factorized probabilistic models that consist of conjugate exponential family distributions. The automation of Bayesian inference tasks is very important since many data processing problems can be formulated as inference tasks on a generative probabilistic model. However, accurate generative models may also contain deterministic and possibly nonlinear variable mappings and non-conjugate factor pairs that complicate the automatic execution of the VMP algorithm. In this paper, we show that executing VMP in complex models relies on the ability to compute the expectations of the statistics of hidden variables. We extend the applicability of VMP by approximating the required expectation quantities in appropriate cases by importance sampling and Laplace approximation. As a result, the proposed Extended VMP (EVMP) approach supports automated efficient inference for a very wide range of probabilistic model specifications. We implemented EVMP in the Julia language in the probabilistic programming package ForneyLab.jl and show by a number of examples that EVMP renders an almost universal inference engine for factorized probabilistic models.     

Vibrational spectrum of perfluoroethane

We have obtained IR absorption spectra of a C₂F₆ gas and a C₂F₆ cryosolution in Xe (T = 163 K) in the fundamental and overtone ranges. We have interpreted 28 bands of ¹²C¹²CF₆ and three bands of ¹³C¹²CF₆. In the spectral ranges that correspond to vibrations that are combinations with ν₁, ν₇, and ν₅, we observe multiplets, which we attribute to interactions of the type of Fermi resonances between the states ν₁(A _1g ) ∼ ν₆(A _1g ), ν₇(E _g ) ∼ ν₆ + ν₁₁(E _g ) ∼ 2ν₈(E _g ), ν₅(A _2u ) ∼ ν₈ + ν ₁₁(A _2u ). We reveal an anomalous intensity distribution in the spectrum of an asymmetric isotopologue. For the basic and isotopic configurations of perfluoroethane, we calculate the coefficients of shapes of vibrations and the intensities of absorption bands. We reveal that the behavior of the groups ¹²CF₃ and ¹³CF₃ is indifferent to the excitation of doubly degenerate stretching vibrations ν₇(E _g ) and ν₁₀(Eu).     

Frequency converter based on a field electron emitter

An electron field emitter based on a carbon nanotube is considered as a frequency converter of the voltage applied to its electrodes. This property of the emitter relates to the nonlinear form of the current-voltage characteristic described by the classical Fowler-Nordheim expression. Calculations show that the number of higher harmonics in the spectrum of the emission current increases upon a decrease in the applied voltage and with increasing relative amplitude of the ac signal.