Vortex glass state in superconductors with fractal clusters of normal phase

The influence of fractal clusters of a normal phase on the dynamics of vortices in a percolation superconductor is considered. It is established that a vortex glass state is formed in superconductors with a fractal cluster structure. The vortex glass phase can be identified by the initial part of its current-voltage characteristic. The dependence of the glassy exponent on the fractal dimension of normal phase cluster boundaries is found.     

Boundedness problem for lossy counter machines

The decidability of the boundedness problem for lossy Minsky counter machines is studied. It is proved that, for Minsky machines with three counters, the boundedness problem is undecidable for any lossiness on the set of machine configurations. The notion of counter reset one-register machines is introduced; these machines are capable of simulating two-counter machines with a reset lossiness relation. It is proved that the boundedness problem for reset one-register machines (and, therefore, reset two-counter machines) is decidable.     

A study on shuffle, stopwatches and independently evolving clocks

We show that stopwatch automata are equivalent with timed shuffle expressions, an extension of timed regular expressions with the shuffle operation. Since the emptiness problem is undecidable for stopwatch automata, and hence also for timed shuffle expressions, we introduce a decidable subclass of stopwatch automata called partitioned stopwatch automata. We give for this class an equivalent subclass of timed shuffle expressions and investigate closure properties by showing that partitioned stopwatch automata are closed under union, concatenation, star, shuffle and renaming, but not under intersection. We also show that partitioned stopwatch automata are equivalent with distributed time-asynchronous automata, which are asynchronous compositions of timed automata in which time may evolve independently.     

Electrical strength of thin polyaniline films

The electrical strength of in-situ polymerized polyaniline films converted to non-conducting polyaniline base has been compared with the strength of solution-cast polystyrene and poly(methyl methacrylate) films of sub-micrometre thickness. The electrical lifetime of polyaniline film exponentially decreases with the growing electric-field strength. The electric-field strength at breakdown increases with increasing rate of electric field build-up. The breakdown areas in polyaniline films have been characterized by Raman spectroscopy. The possible physical mechanism of the breakdown in thin polymer films is discussed. The proposed concept is based on the steep increase of current density during the transition from the quadratic law at space-limited charge to the regime of complete saturation of traps. As a result, the Joule heat causes the degradation of polyaniline followed by the evaporation of chain fragments in the breakdown area.     

Wavelet data analysis of EXAFS spectra

The application of wavelet transform to the analysis of the extended X-ray absorption fine structure (EXAFS) from perovskite-type compounds is presented on the example of the Re L₃-edge in ReO₃ and Co K-edge in LaCoO₃. We propose a modified wavelet transform procedure, which allows better discrimination of the overlapped contributions into the EXAFS signal.     

Homomorphic Public-Key Cryptosystems and Encrypting Boolean Circuits

Given an arbitrary finite nontrivial group, we describe a probabilistic public-key cryptosystem in which the decryption function is chosen to be a suitable epimorphism from the free product of finite Abelian groups onto this finite group. It extends the quadratic residue cryptosystem (based on a homomorphism onto the group of two elements) due to Rabin – Goldwasser – Micali. The security of the cryptosystem relies on the intractability of factoring integers. As an immediate corollary of the main construction, we obtain a more direct proof (based on the Barrington technique) of Sander-Young-Yung result on an encrypted simulation of a boolean circuit of the logarithmic depth.     

Hard corrosion-resistant coatings for constructional applications

This is an overview of modern methods used to harden metal products. Capabilities and drawbacks of each method are analyzed with respect to requirements imposed on coatings intended for use in precision engineering. A fundamentally new approach to the creation of nanostructured hardening layers at low temperatures has been proposed. Three classes of tungsten carbide coatings that mutually differ by the combination of their microhardness, viscosity, and thickness have been described. Some physicochemical features of the synthesis of tungsten carbide compounds, their structure, and their mechanical properties have been established. According to tribological tests, the abrasive resistance of tungsten semicarbide is almost twice as high as the abrasive resistance of the VK-6 hard alloy. The absolute abrasive wear resistance of the carbide coating in the presence of a lubricant is ten times higher than that of the hard alloy. Particular applications of the tungsten carbide coatings and their advantages over commercially available materials and coatings have been described.