Comparative Study of Conventional and Quasi-Freestanding Epitaxial Graphenes Grown on 4H-SiC Substrate

Semiconductors - The structural and some other characteristics of quasi-freestanding single-layer graphene obtained by annealing of the buffer layer in the flow of hydrogen are studied in...     

Structure–Transport Correlation Reveals Anisotropic Charge Transport in Coupled PbS Nanocrystal Superlattices

The assembly of colloidal semiconductive nanocrystals into highly ordered superlattices predicts novel structure-related properties by design. However, those structure–property relationships, such as charge transport depending on the structure or even directions of the superlattice, have remained unrevealed so far. Here, electric transport measurements and X-ray nanodiffraction are performed on self-assembled lead sulfide nanocrystal superlattices to investigate direction-dependent charge carrier transport in microscopic domains of these materials. By angular X-ray cross-correlation analysis, the structure and orientation of individual superlattices is determined, which are directly correlated with the electronic properties of the same microdomains. By that, strong evidence for the effect of superlattice crystallinity on the electric conductivity is found. Further, anisotropic charge transport in highly ordered monocrystalline domains is revealed, which is attributed to the dominant effect of shortest interparticle distance. This implies that transport anisotropy should be a general feature of weakly coupled nanocrystal superlattices.     

Exactly Solvable Model Problem on a Graphene Nanoribbon with Zigzag Edges

Semiconductors - Exact analytical expressions for the local densities of states and the occupation numbers of atoms at the zigzag edge of a graphene nanoribbon are derived in the context of a...     

A Model of a Surface Dimer in the Problem of Adsorption

Technical Physics Letters - Abstract—The adsorption system has been represented in a form of two regions: a dimer, which includes the ad particle and substrate surface atom, and the rest of...     

Analysis of the aluminum alloy resistance to the penetration of a steel rod at impact velocities of up to 500 m/s

The penetration of a steel rod into aluminum alloy plates of various thicknesses is examined. The resistance to penetration at its initial stages prior to the rod fracture is found to be determined by the dynamic strength of the plate material, its viscous component (proportional to the plastic strain rate) prevailing at impact velocities of up to 500 m/s. The depth of penetration varies with the velocity and is conditioned by wave processes in the plate, their scale being dependent on its thickness. Institute for Problems of Strength, National Academy of Sciences of Ukraine, Kiev, Ukraine. Translated from Problemy Prochnosti, No. 5, pp. 106–110, September–October, 1998.     

The effect of retained austenite on contact fatigue in Cr−Ni−W carburized steel

This article describes an experiment to determine the effect of retained austenite on the chipping of the case-hardened layer of Cr−Ni−W carburized steel by examining the same case-hardened layer with varying amounts of retained austenite after different heat treatments. The existence of a critical load level was established; contact fatigue resistance can be improved when the loads are above critical. This is determined by deformation of the austenite structure and substructure, the austenite-martensite transformation under the influence of the load, and the retention of the deformed austenite structure in the martensite. Authors' Note: Alloyed steel compositions are presented in the Soviet standard. The first two numbers give the approximate carbon content in hundredths of a percent. The number after the element shows the approximate percentage of the alloying elements. The number one or no number at all means the percentage is about one or less. Bertold B. Vinokur earned his Doctor of Technical Science in physics of metals and metal science at the Ukrainian Academy of Science, Ukraine, in 1978. He is currently retired. Dr. Vinokur is a member of TMS. Alexandr L. Geller earned his Doctor of Technical Science in metal science and heat treatment at Donetsk Technical University, Ukraine, in 1997. He is currently an assistant professor in the Department of Materials Science and Engineering at Donetsk Technical University, Donetsk, Ukraine.     

Enhanced stiffness modeling of manipulators with passive joints

The paper presents a methodology to enhance the stiffness analysis of serial and parallel manipulators with passive joints. It directly takes into account the influence of external and internal loadings on the manipulator configuration and, consequently, on its Jacobians and Hessians. The main contributions of this paper are the introduction of a non-linear stiffness model for the manipulators with passive joints, a relevant numerical technique for computing the Cartesian stiffness and stability criteria for configurations of the kinematic chains. Within the developed technique, the manipulator elements are presented as pseudo-rigid bodies separated by multidimensional virtual springs and perfect passive joints. Simulation examples are presented that deal with parallel manipulators of the Ortholide family and demonstrate the ability of the developed methodology to describe non-linear behavior of the manipulator structure such as a sudden change of the elastic instability properties (buckling).