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This work considers the parametric identification problem of control objects and signals. The problem feature is the necessity of searching for an approximate solution that provides the improved accuracy of the transition process in the high (or low) values of time. This work suggests a variant that satisfies the requirements of accuracy and robustness to solve the problem. Based on using numerical methods to solve the problem, the variant has its own singularities. Firstly, its instrumental variable allows redistributing the maximum error of the approximate solution by the interval of transient process. Secondly, the variant is applied to the dynamic systems, transfer functions of which have fractional-rational, irrational and transcendental expressions. This work also leads the calculations to illustrate the suggested method that obtains an improved accuracy of the approximation in the initial and final fragments of the transient process.

The mechanisms of high-speed deformation of ultrafine-grained copper produced during severe plastic deformation by equal-channel angular pressing were analyzed using numerical modeling in comparison with those in the case of coarse-crystalline copper. The activity of annihilation processes during nonconservative motion and double cross slip of dislocations was estimated. Their effect on the macroscopic behavior of samples is shown.

The plastic flow of a copper billet calculated using 2D and 3D finite element modeling are compared during a single extrusion of equal-channel angular pressing. Both models predict deformation heterogeneity irrespective of material behavior, die geometry and friction conditions. On the symmetry plane where the numerical approaches can be compared, their strain distributions differ, especially as the processing conditions deviate from the ideal conditions. Overall the three-dimensional finite element model calculates lower plastic strains than the two-dimensional model.

Abstract: A model is proposed for the formation of the substructure in polycrystals during plastic deformation. According to this model, fragmentation of a grain occurs through the formation of a system of diagonal low-angle boundaries, which originate at the edges of a rectangular grain. Misorientation boundaries form through relaxation of a nonsymmetric junction quadrupole disclination configuration accumulated at the grain corners under severe deformation when the disclination strength reaches a certain critical value. The energetics of this process is analyzed. A general case is considered where the disclinations at the junctions of the chosen grain differ in strength. The energetic approach used makes it possible to determine the misorientation angle ωx of the resulting boundaries corresponding to the maximum energy gain and to find the dependence of this angle on the degree of asymmetry of the quadrupole configuration of junction disclinations. According to the proposed model, the splitting of a grain with a short edge greater than 0.5 μm is energetically favorable and decreases the latent energy of the grain for any ratio between the junction disclination strengths if the grain length-to-width ratio is less than 30. It is shown that the minimum possible grain size in the proposed model does not exceed 0.1 μm.

The fatigue behavior of ultrafine-grained copper produced by equal channel angular (ECA) pressing was investigated at temperatures between room temperature and 573 K under a constant stress amplitude of 200 MPa. Cyclic softening was found to be much more evident and the corresponding fatigue life decreases rapidly as temperature increases. This phenomenon was considered as being the result of the grain coarsening and microstructural changes in the coarsened grains associated with the testing temperature. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The cloned alpha-satellite DNA sequences were used to evaluate the specificity and possible variability of repetitive DNA in constitutive heterochromatin of human chromosomes. Five probes with high specificity to individual chromosomes (chromosomes 3, 11, 17, 18, and X) were in situ hybridized to metaphase chromosomes of different individuals. The stable position of alpha-satellite DNA sequences in heterochromatic regions of particular chromosomes was found. Therefore, the chromosome-specific alpha-satellite DNA sequences may be used as molecular markers for heterochromatic regions of certain human chromosomes. The homologous chromosomes of many individuals were characterized by cytologically visible heteromorphisms of hybridization intensity with chromosome-specific alpha-satellite DNA sequences. A special analysis of hybridization between homologues with morphological differences provided the evidence for a high resolution power of the in situ hybridization technique for evaluation of chromosome heteromorphisms. The approaches for detection of heteromorphisms in cases without morphological differences between homologues are discussed. The results obtained indicate that constitutive heterochromatin of human chromosomes has a variable amount of alphasatellite DNA sequences. In situ hybridization of cloned satellite DNA sequences may be used as a new general approach to analysis of chromosome heteromorphisms in man.

The effects of visible light post-treatment on the spectrum and frequencies of γ-ray-induced mutations at five specific loci and of macrodeletions of the X chromosome in post-meiotic male germ cells in mutant c(3)G17 of Drosophila melanogaster were studied. It was found that post-treatment by light decreased the yield of chromosome rearrangements to the extent of 1·5 to 2 times, but not that of point mutations.

The chromosomal distribution of sequences homologous to 18 coned alpha satellite fragments was established by in situ hybridization. It appeared that all the cloned sequences were members of small repeated families located on single chromosome pairs. Among the sequences studied specific molecular markers for chromosomes 3, 4, 10,11,17,18 and X were found. Comparison of the hybridization spectra obtained under non-stringent conditions and of restriction site periodicities in different chromosome-specific families allowed the identification of three “suprachromosomal” families, each located on a characteristic set of chromosomes. The three families together cover all the autosomes and the X chromosome. These data plus those reported previously allow part of the phylogenetic tree of chromosome-specific alpha satellite repeats to be drawn. Each suprachromosomal family has presumably originated from a distinct ancestral sequence and consists of certain types of monomers. Ancestral sequences have evolved into a number of chromosome-specific families by cycles of interchromosomal transfers and subsequent amplification events. The high homogeneity of chromosome-specific families may be a result of intrachromosomal homogenization of amplification units in chromosome-specific alpha satellite domains.

Conservation of DNA segments performing sequence-related functions is a landmark of selection and functional significance. Phylogenetic variability of alpha satellite and apparent absence of conserved regions calls its functional significance into question, even though sequence- specific alpha satellite-binding proteins pJα and CENP-B have been discovered. Moreover, the function of pJα is obscure and CENP-B binding satellite DNA, which is thought to participate in centromere formation, is found only in few species and not necessarily in all chromosomes. Analysis of alpha satellite evolution allows us to recognize the order in this variability. Here we report a new alpha satellite suprachromosomal family, which together with the four defined earlier, covers all known alpha satellite sequences. Although each family has its characteristic types of monomers, they all descend from two prototypes, A and B. We show that most differences between prototypes are concentrated in a short region (positions 35 to 51), which exists in two alternative states: it matches a binding site for pJα in type A and the one for CENP-B in type B. Lower primates have only type A monomers whereas great apes have both A and B. The new family is formed by monomeric types almost identical to A and B prototypes, thus representing a living relic of alpha satellite. Analysis of these data shows that selection-driven evolution, rather than random fixation of mutations, formed the distinction between A and B types. To our knowledge, this is the first evidence for selection in any of the known satellite DNAs.

Equations are derived for describing a classical system interacting arbitrarily with a quantum two-level system. The solutions for the case of two converging electron terms are analysed and applied to the problem of electronic excitation resonant transfer or resonant charge exchange. It is supposed that the classical motion of the particles (molecules) possesses a stochastic character and may be represented by the Fokker-Plank equation, when the interaction with the quantum degrees of freedom are absent. The model allows us to trace theoretically the change of excitation transfer kinetics when passing from gas to liquid and from liquid to the solid state. The general formula for one-, two- and three-dimensional relative motions are found and the three-dimensional case is discussed in detail.

X-ray diffraction patterns of nanocrystalline copper have been obtained by computer simulation. The influence of grain size, thickness and structure of grain boundaries and crystal lattice distortions on the X-ray diffraction patterns was studied using the kinematical theory of X-ray scattering. Such specific features of the X-ray patterns of nanocrystalline materials as a decreased maximum peak intensity, a displacement of the position of the centre of gravity of the peaks, a change in the profile and an increase in the background have been analysed. It is shown that these specific features can be explained not only by the effect of such structural factors as crystallite size and grain-boundary thickness but also, and principally, by the presence of elastic atomic displacements in the bulk of the crystallites owing to long-range stress fields of extrinsic grain boundary dislocations. The role of the crystallographic texture in the formation of X-ray diffraction patterns of nanocrystalline copper has also been investigated.

We have sequenced the full-length copy of the alpha satellite higher-order repeated unit characteristic of human chromosome 3. Its internal structure, the regular alternations of J1 and J2 type monomers, is typical of the alphoid suprachromosomal family 1. This dimeric order is disrupted by the substitution of one J1 unit by an alien dimer which is not clearly related to any of the established monomeric types. We have also observed some other similar cases of segment substitutions in alpha satellite DNA. They probably represent a special type of molecular event which could be generated by gene conversion. Segment substitutions may be one of the important factors responsible for the extreme variability of localization patterns and actual sequences of alpha satellite DNA that should be taken into account in reconstructions of alpha satellite evolution. Copyright 1993, 1999 Academic Press

The microstructures and properties of copper- and aluminum-based nanocomposites processed through severe plastic torsional straining (SPTS) consolidation of metallic micrometer powders and ceramic nanopowders were investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD), microhardness and electrical resistivity measurements, and mechanical tests. It was shown that the SPTS consolidation of powders is an effective technique for fabricating metal-ceramic nanocomposites with a high density, ultrafine grain size, and high strength. Copper samples processed under a high pressure of 6 GPa exhibited high failure strength and strain as well as unusual strain hardening. Superplastic-like behavior was found in Al-Al2O3nanocomposite samples.

For a two-level system corresponding to a particle of spin ½ in a random field in the Z direction, the relaxation function[image omitted]has been estimated, the magnitude Ω(t) being the sum of the isotropic interactions of the particle in question with particles j executing diffusional motion. Specifically Ω(t)=ω0 + Σ ω(Mj, rj), where ω0 = constant, Mj is a random time-independent parameter, ω(M, r) decreases with r faster than r-3 and rj = rj(t) is a diffusional, random function. From the expression for <σ+(t)>, we establish general features of the relaxation phenomenon for diffusional processes, and calculate the relaxation rate 1/T2 and relaxation shift Δω to be 1/T2-iΔω = 4π[image omitted]CAvMλM, where C is the concentration of particles and λM is the scattering length for an equation of the Schrödinger type with an imaginary potential -iω(M, r) instead of U/ℏ, and diffusion coefficient [image omitted] instead of ℏ/2m. We also found that for the case of 'external' relaxation, the Redfield approach proved valid only under the simultaneous restrictions of low concentration and weak interaction.

Non-adiabatic transitions in two-level systems are investigated theoretically for a random time dependence of ħω, the energy difference, between the levels. We assumed that ω = ω(x) and the coordinate x = x(t) is a random function of time. Diffusion and Poisson processes (both homogeneous and with a source) for x(t) were assumed. The cases of linear crossing terms (ω = γx) and non-linear terms (ω = ωe exp (- αx) + ω0) were considered. Values of the non-adiabatic transition probability per unit time were obtained by perturbation theory for ω1τc << 1 where τc is the correlation time and ω1 is the off-diagonal matrix element.

The E.S.R. line shape of the iminoxyl radical in viscous liquids was investigated at several temperatures. The results are interpreted by theoretical calculation of the line shape at an arbitrary value by using a diffusion model for the motion of the molecules.

Corrosion resistance of ultrafine-grained Ti processed by equal channel angular pressing with 3 passes was investigated. Results indicated that corrosion rate of ultrafine-grained Ti significantly reduced in comparison with coarse grain Ti. Furthermore, corrosion resistance of 3 passes ECAP sample had an obvious distinguish for different extraction planes; normal plane has shown a best corrosion resistance than transversal and extrusion plane, which could be attributed to higher fraction of low angle grain boundary.

The specific resistance of the nanostructured Cu-1.8wt.%Cr-0.8wt.%Zr alloy has been analyzed by means of analytical modeling. The contribution of different structural parameters to the specific resistance of the material has been estimated.

The results of investigation of the Cu-Zn system alloys with 10 wt.% and 30 wt.% Zn, the stacking fault energy (SFE) of which differs by a factor of 2.5, are presented. ECAP and subsequent flat rolling resulted in the refinement of the microstructure. Flat rolling with the reduction degree 95% resulted in the decrease of the concentration of nanotwins formed during ECAP. Flat rolling of ultra-fine grained (UFG) alloys leads to the strength increase and ductility decrease explained by the refinement of the microstructure and decrease in the concentration of deformation twins.

The results of studying the microstructure, mechanical and electrical properties of the UFG alloy Cu-0.5wt.% Cr, obtained by equal-channel angular pressing (ECAP), followed by cold rolling and subjected to aging, are presented. It was found that, as a result, the average size of the fragmented structure is 160 nm. The results showed that the tensile strength increases with increasing degree of deformation. The maximum strength value of 605 MPa was achieved after a combination of 8 ECAP passes followed by rolling by 95%, while ductility was reduced to 13%. The number of ECAP passes and subsequent rolling practically do not affect the electrical conductivity and is 34-39% of IACS.

The results of the analysis of the deformation behavior of nanostructured Cu-Zn alloys, obtained as a result of severe plastic deformation, implemented by the equal-channel angular pressing method, are presented. The role of structural factors responsible for increasing the strength characteristics and uniform elongation of the Cu-Zn alloys has been revealed.

The results of a study of the strength and conductivity of electrotechnical bulk nanostructured copper alloys obtained by methods of severe plastic deformation is presented. The contribution of the microstructure parameters to the formation of high strength while maintaining sufficient electrical conductivity is discussed.

In this paper, we use the scientometric approach based on the Web of Science Core Collection to analyze the data on publication activity in the area of nanostructured materials processed by severe plastic deformation (SPD) techniques on the following three main topics: ultrafine-grained materials, severe plastic deformation and bulk nanostructured materials. The results marked early 1990s as the starting period for first publications in question as well as their fast development. Pioneer works by Prof. Valiev and his laboratory at that time and their role in the growth of nanoSPD-related research were outlined.

Abstract: The microstructures of ultrafine-grained nanostructured materials developed by severe plastic deformation are widely varied in their grain size and grain-size distribution; grain boundaries and their structures; lattice defects, especially dislocations; point defects; and impurities. All of these features can be influenced by the way severe plastic deformation is applied, and thereby have decisive effects on the physical and mechanical properties of the material. Probably, the most important factors determining microstructure are the imposed stress tensor, the degree and rate of strain, the temperature of deformation, the chemical composition of the deformed material, and the type of crystal lattice, showing that in order to develop specific properties, it is crucial to understand and optimize the microstructure.

A patient with an atypical clinical picture of 18p- syndrome is described. By the in situ hybridization technique we localized the chromosome 18-specific cloned repetitive sequence to metaphase chromosomes of the patient. The predominant hybridization of the probe was found in pericentromeric regions of homologous chromosomes 18. The amount of pericentromeric DNA measured by in situ hybridization differed between homologous chromosomes; and the number of radioactive grains was statistically greater in the normal chromosome 18 than in the aberrant chromosome 18p-. The results indicate that this probe may be useful in clinical cytogenetics for identification of aberrant chromosomes, localization of breakpoints, and studies of C-band DNA polymorphism of chromosome 18.

Severe plastic deformation (SPD) processing is widely used to control and refine the grain size of monolithic metals and alloys, with grain sizes of less than 100 nm produced in recent years. One particular SPD technique, severe plastic torsional straining, has been found to effectively consolidate both micrometre and nanometre sized metallic powders and metalceramic powder mixtures, with resultant grains refined to submicrometre or nanometre size.

In this paper, we report on the microstructure characteristics and strength properties of the Cu-10 wt.% Zn alloy subjected to equal-channel angular pressing (ECAP) and subsequent flat rolling (FR), in order to form an ultrafine-grained (UFG) structure and enhance the strength properties. It is shown that the formed subgrain structure increases the strength characteristics. An increase in the degree of reduction at FR resulted in an increase in the dislocation density and also in an increase in strength. The presence of high-angle grain boundaries increases the ductility of the alloy.

This article investigates the effect of various contents of Cr and Zr on the microstructure and properties of the alloy of the Cu-Cr-Zr system. It has been defined that an increase in the content of Zr leads to a decrease in the grain size both in the initial state and after severe plastic deformation. The increase in the content of Zr significantly enhances the strength of the alloy.

This article presents the base-line design and implementation of the ATLAS Trigger and Data Acquisition system, in particular the Data Flow and High Level Trigger components. The status of the installation and commissioning of the system is also presented. [Copyright &y& Elsevier]