BER Performance of Finite in Time Optimal FTN Signals for the Viterbi Algorithm

In this article, we consider the faster than Nyquist (FTN) technology in aspects of the application of the Viterbi algorithm (VA). Finite in time optimal FTN signals are used to provide a symbol rate higher than the “Nyquist barrier” without any encoding. These signals are obtained as the solutions of the corresponding optimization problem. Optimal signals are characterized by intersymbol interference (ISI). This fact leads to significant bit error rate (BER) performance degradation for “classical” forms of signals. However, ISI can be controlled by the restriction of the optimization problem. So we can use optimal signals in conditions of increased duration and an increased symbol rate without significant energy losses. The additional symbol rate increase leads to the increase of the reception algorithm complexity. We consider the application of VA for optimal FTN signals reception. The application of VA for receiving optimal FTN signals with increased duration provides close to the potential performance of BER, while the symbol rate is twice above the Nyquist limit.     

Structure,surface topography and electrochemical properties of cast films formed by fullerenes and their compositions with salt matrices

Some properties of films based on fullerene and pyridyl substituted fullerenopyrrolidines were studied. Both direct casting and immobilizing electroactive substances in the tetraoctylammonium bromide (TOAB) or tetraphenylphosphonium bromide matrices were used for modification of the ITO electrode surface. In accordance with X-ray diffraction, pyridyl substituted fullerenopyrrolidines are amorphous, and the lamellar structure of TOAB is retained when fullerene is present in the film. The differences, which are observed in the absorption spectra of the cast coatings of the individual fullerenes or fullerenes in the TOAB matrix as compared with solution spectra testify to the electronic interaction between fullerene molecules in a solid phase. At that, the quaternary ammonium salt participates immediately in the coating self-organization. Atomic force microscopy showed that both the solution composition and addends in the C₆₀ molecules influence the film morphology. Disintegration of fullerenes in the TOAB matrix and their interaction with hydrocarbon chains of TOAB provide the hydrophobic surrounding required for reversible electrochemical reduction of fullerene on an electrode in an aqueous solution. The differences observed for C₆₀ embedded in the tetraphenylphosphonium bromide and TOAB films accentuate the role of a layered structure of the matrix for the reversible electrochemical behavior of fullerene in aqueous solution.     

Double-frequency oscillations of an impulse neuron equation with two delays

The dynamics of the generalized impulse neuron equation with two delays are studied. A local analysis of the loss of the stability of the nonzero equilibrium state is carried out. The phase reorganizations of the equation under study are numerically analyzed using the obtained asymptotic formulas.     

Generalized excitation of a coaxial cylindrical lens

Calculations are made of the cardinal elements of a coaxial lens when annular beams are focused onto its axis. An empirical formula is obtained for the excitation of the lens which takes into account its power, and the transverse and longitudinal dimensions, and can be used to obtain simple expressions for the position of the focus and the initial radius of the axial trajectory of the beam. Pis’ma Zh. Tekh. Fiz. 25, 39–43 (October 26, 1999)     

Double-stage poly-o-phenylenediamine modification with palladium nanoparticles

Accumulation of palladium ions in poly-o-phenylenediamine (PPD) redox polymeric matrix was studied by means of cyclic voltammetry (CVA), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and spectroelectrochemistry. CVA and XPS studies demonstrated nitrogen atoms binding palladium cations upon impregnation of PPD film with palladium chloride solution. Higher residual reduced or partially reduced PPD form of cathodic polymer doping was shown to increase the number of palladium cations in the polymeric matrix. AFM recorded a significant effect produced to the film surface structure by intercalation of both palladium cations and metal formed by reduction of cations.