Language recognition by two-way deterministic pushdown automata

It is proved that any bounded context-free language can be recognized by a two-way deterministic automaton with a finite-rotary counter.Translated from Kibernetika i Sistemnyi Analiz, No. 6, pp. 177–181, November–December 2004.This revised version was published online in April 2005 with a corrected cover date.     

Electrochemical corrosion behavior of amorphous carbon nitride thin films

The corrosion behavior along with biocompatibility and mechanical properties plays an important role in determining of biomedical implants feasibility. Diamond-like carbon seems to be the promising material in which all these three requirements can be achieved. In this study nitrogen doped amorphous carbon (a-C:N) films were deposited on silicon and medical CoCrMo alloy substrates by vacuum glow discharge sputtering technique using different deposition conditions from graphite target. Potentiodynamic polarization tests were employed to assess the corrosion performances of the films at room temperature in 0.89 wt. % NaCl solution. The influence of substrate bias on the electrochemical corrosion behavior was investigated. The highest value off E_corr for CoCrMo substrate was measured on the coating deposited with substrate bias around −0.6 kV. The shift of E_corr to more positive values was about 350 mV.     

The effect of a counterion in a protective moisture-sensitive epoxy–polyelectrolyte/epoxy–carbon sandwich system

In this work, the effect of the ionic form of a KU 2-8 synthetic cation-exchange polyelectrolyte, which was used as a filler in the moisture-sensitive layer, on the behavior of two-layer anticorrosion systems with a low-resistivity damp-proof layer has been studied. The behavior of matrices with sodium (KU 2-8-Na⁺), magnesium (KU 2-8-Mg²⁺), nickel (KU 2-8-Ni²⁺), and zinc ions (KU 2-8-Zn²⁺) has been investigated. The remarkable effect of the nature of studied counterions on moisture-sensitive, protective properties, and behavior of coatings upon cathode polarization of surface has been demonstrated.     

Electrical-percolation effects in epoxy resin/ion-exchange resin/polyaniline anticorrosion composite materials

A new type of epoxy–polyelectrolyte anticorrosion protective material based on epoxy resin, ion-exchange resin, and polyaniline has been studied. Electrical-percolation transitions are observed after submerging stainless-steel plates coated with epoxy–polyelectrolyte compositions in a solution of NaCl. Conductivity data processed within a percolation model show that the modification of ion-exchange resin by polyaniline strongly influences the coating model parameters owing to changes in physicochemical and morphological properties of ion-exchange resin. It is established that the electrochemical response to the action of an aqueous salt solution can be controlled by variation of the material composition.     

Structural transformations in nanoglobular carbon under the action of pulsed high-energy-density electron beam

Exposure of globular (T-900 technical grade) carbon black to submillisecond pulsed electron beam with an energy density of ??40 J/cm² leads to clearly manifested structural transformations of carbon with the formation of highly ordered graphite-like structure and original morphology, as evidenced by the data of high-resolution transmission electron microscopy.     

Synthesis and comparative studies of xerogels,aerogels, and powders based on the ZrO<Subscript>2</Subscript>–Y<Subscript>2</Subscript>O<Subscript>3</Subscript>–СeO<Subscript>2</Subscript> system

The technology of liquid-phase synthesis of mesoporous xerogels and aerogels based on ZrO₂–Y₂O₃–CeO₂ is developed. Xerogels are obtained by the coprecipitation of hydroxides, while aerogels are obtained in accordance with the sol–gel technology: the average pore size is 1.5–17.2 nm and the specific surface area is 120–878 m²/g. Aerogels are characterized by a high degree of porosity: the pore volume attains 1–4 cm³/g. Based on precursor xerogels, nanopowders of a tetragonal solid solution of the (ZrО₂)_0.92(Y₂О₃)_0.03(CeО₂)_0.05 composition with a particle size of 5–9 nm and S _spec = 74 m²/g were fabricated. Due to the high values of their specific surface area, the synthesized xerogels and aerogels are promising as sorbents, catalysts, or catalyst supports.     

Emissivity characteristics of boron and boric oxide at high temperatures

The spectral emissivity of boron at wavelengths λ = 0.45–6 μm during ignition and combustion was determined experimentally. The spatial resolution was not lower than 100 μm. Liquid boric oxide, boron filaments 100 μm in diameter, and artificially made agglomerates of amorphous boron particles 2 mm in size and ≈1.22 g/cm³ in density served as radiation objects. It was determined that, as the surface temperature increased from 1 490 to 2 800 K, the emissivity of boron in the examined range of wavelength decreased almost linearly in an interval of 0.35–0.20. At temperatures of 1400–2100 and wavelength of 0.65 μm, the absorption coefficient of liquid boric oxide was 2.2 ± 0.2 cm⁻¹.     

Structural-phase transformations in near-surface layers of alumina-zirconium ceramics induced by low-energy high-current electron beams

The effect of low-energy high-current electron beams (LEHCEBs) at E = 15 keV on mechanical characteristics of near-surface layers of alumina-zirconium ceramics (AZC) of the 20Al₂O₃-80ZrO₂(Y) composition (in mass %) is investigated by the method of dynamic indentation. It is shown that electron-beam treatment reduces Young’s modulus and nanohardness of this ceramic material. The action of LEHCEBs on the structural-phase state of modified subsurface layers of AZC specimens is analyzed. Their elemental and phase compositions are examined using several techniques: electron-probe X-ray spectral microanalysis (EPMA), secondary-ion mass spectrometry (SIMS), and X-ray diffractometry. It is found out that irradiation of the ceramic material by LEHCEBs stimulates the transitions of an m-phase of zirconium dioxide into a tetragonal modification, and results in a considerable decrease in the alumina phase. Based on the analysis of the data obtained, a conclusion is drawn that it is the processes resulting from irradiation and giving rise to formation of a subsurface layer with a phase composition different from that of the bulk material, which are responsible for the effect of modification of the material mechanical property.