Forecasting nonstationary time series based on Hilbert-Huang transform and machine learning

We propose a modification of the adaptive approach to time series forecasting. On the first stage, the original signal is decomposed with respect to a special empirical adaptive orthogonal basis, and the Hilbert’s integral transform is applied. On the second stage, the resulting orthogonal functions and their instantaneous amplitudes are used as input variables for the machine learning unit that employs a hybrid genetic algorithm to train an artificial neural network and a regressive model based on support vector machines. The efficiency of the proposed approach is demonstrated on real data coming from Nord Pool Spot and Australian National Energy Market.     

Defect formation and recrystallization mechanisms in silicon-on-sapphire films under ion irradiation

The effect of the parameters (energy, dose) of the irradiation of silicon-on-sapphire (SOS) structures with ions Si⁺ ions on the quality of the silicon-film crystal structure after solid-phase epitaxial recrystallization and annealing is studied. It is shown that the most efficient mechanism of crystal-structure recovery is recrystallization from the silicon surface layer which is a seed.     

Structure and optical homogeneity of LiNbO3〈Mg〉 crystals grown from different charges

This paper reports a comparative study of the homogeneity of LiNbO₃〈Mg〉 (≥5 mol % Mg) crystals grown from a charge synthesized using Nb₂O₅〈Mg〉 prepared through homogeneous magnesium doping of a reextract in the Nb₂O₅ extraction step, and LiNbO₃〈Mg〉 crystals prepared through direct doping of a growth charge. The LiNbO₃〈Mg〉 crystals were characterized by optical microscopy and Raman spectroscopy. The results demonstrate that the LiNbO₃〈Mg〉 crystals prepared using homogeneous doping are more structurally uniform.     

Plasma density in discharge sustained in inhomogeneous gas flow by high-power radiation in the terahertz frequency range

We have measured the density of plasma (electron concentration) in discharge maintained in inhomogeneous argon flow under the action of high-power pulsed radiation of gyrotron (frequency, 0.67 THz; power 40 kW; pulse duration, 20–30 μs) in a range of background gas pressures in the discharge chamber from 10^–3 to 300 Torr. The electron concentration at low pressures (10^–3 to 7 Torr) was determined using Starkeffect induced broadening of the H_α atomic emission line (656.3 nm) of hydrogen present in discharge as a small impurity in residual gases. The maximum observed Stark broadening of the H_α line corresponded to a plasma density on the order of 2 × 1016 cm^–3, which exceeded the critical value for the given frequency of radiation sustaining the discharge. At background pressures above 7 Torr, the plasma density was estimated from analysis of the spatiotemporal patterns and waveforms of discharge glow in the visible spectral range. These estimations gave electron concentrations on the level of (1–2) × 10¹⁵ cm^–3.     

Mass Spectrometry Study of C60 and C60-NiF2 Fluorination with Molecular Fluorine

Abstract

Fluorination of [60]fullerene and [60]fullerene-NiF₂(s) has been studied in situ by Knudsen cell mass spectrometry with admission of molecular fluorine. The fluorination processes were controlled in the temperature range 500 ? 800 K at molecular fluorine pressure 10^?4 ? 10^?5 atm. Temperature, time of fluorination and fluorine pressure were varied during the investigation. It was found that variation of these parameters did not lead to the selective fluorination. It was shown that NiF₂(s) significantly influences the composition of the product mixture: a large amount of nickel difluoride in the system suppresses the fluorination reaction while the presence of a small amount promotes the selective fluorination. C₆₀Fi₁₈ (50% in the gas phase) was produced in our experiments under the following conditions: 20 h, 720 K, P(F₂) = 2 10^?4 atm in the prefluorinated (inner surface covered with NiF₂(s) layer) Ni-reactor. An important point of the study was verification of the thermodynamic equilibrium in the system. It was concluded that the equilibrium is not established in the system under study, and the fluorination is governed by kinetic factors.     

Combustion of model compositions based on furazanotetrazine dioxide and dinitrodiazapentane. I. Binary systems

The combustion behavior of high-energy systems based on furazano[3,4-e]tetrazine-4,6-dioxide and 2,4-dinitro-2,4-diazapentane with metal and energetic additives (Al, AlH₃ ammonium perchlorate, ammonium dinitramide, and HMX) has been studied. The burning rate, combustion stability, and characteristic combustion temperatures with pressure variation are estimated. It is found that there is a critical burning rate above which a deflagration-to-explosion transition occurs. The critical conditions depend on the formulation of the compositions.