Experimental Study of Pressure Influence on Tunnel Transport into 2DEG

We present the concept and the results of pilot measurements of tunneling in a system {Al/$\delta_{Si}$-GaAs} under pressure up to 2 GPa at 4.2 K. The obtained results may indicate the following: the barrier height for {Al/$\delta$-GaAs} equals to 0.86 eV at P=0 and its pressure coefficient is $3 meV/kbar$; charged impurity density in the delta-layer starts to drop from $4.5\times 10^{12} cm^{-2}$ down to $3.8\times 10^{12} cm^{-2}$ at about 1.5 GPa; metal-insulator transition may occur in 2DEG at about 2 GPa

Self-consistent solution of Kohn-Sham equations for infinitely extended systems with inhomogeneous electron gas

The density functional approach in the Kohn-Sham approximation is widely used to study properties of many-electron systems. Due to the nonlinearity of the Kohn-Sham equations, the general self-consistence searching method involves iterations with alternate solving of the Poisson and Schr\"{o}dinger equations. One of problems of such an approach is that the charge distribution renewed by means of the Schr\"{o}dinger equation solution does not conform to boundary conditions of Poisson equation for Coulomb potential. The resulting instability or even divergence of iterations manifests itself most appreciably in the case of infinitely extended systems. The published attempts to deal with this problem are reduced in fact to abandoning the original iterative method and replacing it with some approximate calculation scheme, which is usually semi-empirical and does not permit to evaluate the extent of deviation from the exact solution. In this work, we realize the iterative scheme of solving the Kohn-Sham equations for extended systems with inhomogeneous electron gas, which is based on eliminating the long-range character of Coulomb interaction as the cause of tight coupling between charge distribution and boundary conditions. The suggested algorithm is employed to calculate energy spectrum, self-consistent potential, and electrostatic capacitance of the semi-infinite degenerate electron gas bounded by infinitely high barrier, as well as the work function and surface energy of simple metals in the jellium model. The difference between self-consistent Hartree solutions and those taking into account the exchange-correlation interaction is analyzed. The case study of the metal-semiconductor tunnel contact shows this method being applied to an infinitely extended system where the steady-state current can flow.Comment: 38 pages, 9 figures, to be published in ZhETF (J. Exp. Theor. Phys.

Experimental testing and design model for bent FRP anchors exhibiting fiber rupture failure mode

The implementation of Fiber Reinforced Polymer (FRP) anchors in Externally Bonded Fiber Reinforced Polymer (EBR-FRP) systems is an effective method to increase the bond strength and/or ensure the continuity of the load path between FRP materials and the concrete substrate when EBR-FRP systems are used to strengthen and/or repair existing structures. Multiple design examples of EBR-FRP systems exist in the literature, and design guidelines have been compiled in several countries. However, currently these design guidelines do not specifically include guidance on the design of FRP anchors. This lack of design guidance is one of the main impediments to widespread implementation of FRP anchors in the civil engineering industry. The present study reports an experimental program consisting of 32 bent FRP anchor specimens of different sizes and widths that was undertaken to characterize the behavior of bent FRP anchors when the fiber rupture failure mode is exhibited. A design methodology for the mean value and for the lower bound characteristic values (95 and 99.87 percentile equations) is proposed and the reliability of the methodology is assessed.Enrique del Rey Castillo, Dmytro Dizhur, Michael Griffith, Jason Ingha