Conformal representations of the general scalar-tensor theory and cosmological models

The article is a review of cosmological models describing the accelerated expansion of the Universe built by using various conformal representations of the modified Jordan-Brans-Dicke (JBD) theory.     

Robust uniform triangulation algorithm for computer aided design

This paper presents a new robust uniform triangulation algorithm that can be used in CAD/CAM systems to generate and visualize geometry of 3D models. Typically, in CAD/CAM systems 3D geometry consists of 3D surfaces presented by the parametric equations (e.g. surface of revolution, NURBS surfaces) which are defined on a two dimensional domain. Conventional triangulation algorithms (e.g. ear clipping, Voronoi-Delaunay triangulation) do not provide desired quality and high level of accuracy (challenging tasks) for 3D geometry. The approach developed in this paper combines lattice tessellation and conventional triangulation techniques and allows CAD/CAM systems to obtain the required surface quality and accuracy. The algorithm uses a Cartesian lattice to divide the parametric domain into adjacent rectangular cells. These cells are used to generate polygons that are further triangulated to obtain accurate surface representation. The algorithm allows users to control the triangle distribution intensity by adjusting the lattice density. Once triangulated, the 3D model can be used not only for rendering but also in various manufacturing and design applications. The approach presented in this paper can be used to triangulate any parametric surface given in S(u,v) form, e.g. NURBS surfaces, surfaces of revolution, and produces good quality triangulation which can be used in CAD/CAM and computer graphics applications.     

Using Pseudoorthogonal Signals to Reduce Noise Level in Ultrasound Testing of Highly Absorptive Materials

Russian Journal of Nondestructive Testing - To increase the signal-to-noise ratio when testing materials with a high level of absorption, it has been proposed to use complex signals, formed on the...     

New medical materials with an integral lasting effect based on fibre-forming polymers

Textile materials for medical use with immobilized biologically active substances of different classes have been developed. Modified cellulose with drugs incorporated in the macromolecule: enzymes, enzyme complexes, antioxidants, hormones, vitamins, antimicrobial components, was used as substrate. Wound coverings containing drugs of different classes and having a broad spectrum of therapeutic activity were obtained by co-immobilization. __________ Translated from Khimicheskie Volokna, No. 4, pp. 7–9, July–August, 2007.     

Direct Imprinting of Porous Silicon via Metal‐Assisted Chemical Etching

Conventional lithographical techniques used for bulk semiconductors produce dramatically poor results when used for micro and mesoporous materials such as porous silicon (PS). In this work, for the first time, a high‐throughput, single‐step, direct imprinting process for PS not involving plastic deformation or high‐temperature processing is reported. Based on the underlying mechanism of metal‐assisted chemical etching (MACE), this process uses a pre‐patterned polymer stamp coated with a noble metal catalyst to etch PS immersed in an HF‐oxidizer mixture. The process not only overcomes the difficulties in patterning PS but it does so with a stamp that may be reused multiple times depending on its chemical and mechanical degradation. The process is shown to be capable of centimeter‐scale parallel 3D patterning with sub‐20 nm resolution. It is found that PS facilitates mass transport of reactants and products, and the overall etch rate is limited by local depletion of reactants. The versatility of this direct imprinting technique is demonstrated by its ability to produce curvilinear and planar 3D features (e.g., paraboloids, parabolic cylinders, sinusoidal waves, and straight sidewall channels). Miniaturized optical elements such as diffraction gratings and microconcentrators are built and characterized highlighting potential use of PS in silicon photonics.     

TECTONIC EVOLUTION OF THE NORTHERN MARGIN OF THE CENOZOIC ARARAT BASIN,LESSER CAUCASUS,ARMENIA

This paper investigates the structure of the northern margin of the Ararat depression in a study area in SE Armenia. The depression is a Cenozoic intermontane basin located to the south of the Lesser Caucasus. The purpose is to improve understanding of the basin's structure and origin within a regional tectonic framework which has been dominated since the Late Cretaceous by the closure of Neotethys and the Arabia‐Eurasia collision. We suggest that the depression is not a graben controlled by normal faults; rather, based on detailed observations, structures in the study area are interpreted as oblique‐slip reverse and thrust faults activated in post Oligocene‐Miocene times. These compressional faults resulted in the formation of asymmetric fold structures including the Lanjanist and Urts anticlines which are well expressed in the surface relief to the north of the Ararat depression. In general the structural pattern is complicated by secondary normal faults which resulted in superimposed gravitational slope processes and erosion. Major structures in the study area originated in a compressional setting associated with the closure of Neotethys since the latest Cretaceous. Post‐collisional strike‐slip faulting was linked to convergence of the Arabian and Eurasian plate margins. Pliocene and Quaternary structures, some still active, show evidence of structural inheritance. The Armenian portion of the Ararat depression contains obduction‐related nappes, anticlines and thrust faults which have potential as structural traps for hydrocarbons. These should be investigated in detail using advanced geophysical methods including 2D and 3D seismic analyses.     

Modeling the nonlinear dynamic temperature and power oscillations in VVER

The nonlinear dynamic auto-oscillatory regimes of the temperature at the exit from the core and of the power of nuclear reactors are investigated and the quantitative features of the regimes are determined. A physical-mathematical model of the dynamics of a VVER-type nuclear reactor is examined, taking account of the inertial (temperature) and instantaneous (power) feedbacks in the reactor but neglecting the delayed neutrons. Analytical solutions characterizing the auto-oscillatory real-time behavior of the temperature at the exit from the core and of the reactor power are obtained. The period of these oscillations is determined. The model constructed for the dynamics of a reactor is used as a basis to simulate, using the RELAP5/Mod3.2 computer code, certain nonlinear auto-oscillatory processes occurring in the first and second loops of a nuclear power plant with a VVER-440 reactor. It is found that the oscillations of the temperature at the exit from the core and power of the nuclear reactor generate the same period for processes which were calculated.     

Experimental study of embedded and non-embedded ordered granular chains under impulsive excitation

Experimental pulse transmission in impulsively loaded, homogeneous, and dimer granular chains, optionally embedded in a viscoelastic matrix, is studied. All tested chains are composed of spherical elastic beads of common radius. Homogeneous chains were composed of granules with equal mass, whereas dimer chains had alternating ‘heavy’ and ‘light’ granules with different masses. These media are strongly nonlinear due to Hertzian interactions between adjacent beads under compressive loads, and separations and collisions between them in the absence of compression. A series of experimental tests was performed to study primary pulse transmission in the non-embedded chains, and assess the effect of the surrounding viscoelastic matrix on pulse transmission in the embedded ones. For the case of dimer chains, the effect of mass inhomogeneity on pulse attenuation caused by scattering at the interfaces between adjacent beads is studied. In total, two embedded dimer chains, as well as an embedded homogeneous one, were manufactured and tested, and a previous theoretical model is used to compare theoretical predictions to experimental measurements. Whereas one of the non-embedded dimer chains differs from the others in that its light beads are hollow and so its experimental responses are not captured well by our theoretical model, for the other embedded and non-embedded chains, the theoretical predictions match remarkably well with the experimental measurements, despite the complexity in the acoustics induced by the surrounding matrix, and the conceptual simplicity of the theoretical model. The results of this work contribute to the development of practical acoustic metamaterials incorporating embedded granular media.     

Increasing the Rate of Recording Echo Signals with an Ultrasonic Antenna Array Using Code Division Multiple Access Technology

Russian Journal of Nondestructive Testing - The disadvantage of using the digital focusing with an antenna (DFA) method to produce an image of reflectors is a large volume of echo signals and an...