Small scale on-grid PV embedded generation methodologies in South Africa

The IRP 2010-30 update [2] states that 9770 MW of solar photovoltaic (PV) capacity is planned to be installed in South Africa by 2030

Hubbard-I approach to the Mott transition

We expose the relevance of double occupancy conservation symmetry in application of the Hubbard-I approach to strongly correlated electron systems. We propose the utility of a composite method, viz. the Hubbard-I method in conjunction with strong coupling perturbation expansion, for studying systems violating the afore--mentioned symmetry. We support this novel approach by presenting a first successful Hubbard-I type calculation for the description of the metal-insulator Mott transition in a strongly correlated electron system with conserved double occupancies, which is a constrained Hubbard Hamiltonian equivalent to the Hubbard bond charge Hamiltonian with $X=t$. In particular, we obtain the phase diagram of this system for arbitrary fillings, including details of the Mott transition at half-filling. We also compare the Hubbard-I band--splitting Mott transition description with results obtained using the standard Gutzwiller Approximation (GA), and show that the two approximate approaches lead to qualitatively different results. In contrast to the GA applied to the system studied here, the Hubbard-I approach compares favourably with known exact results for the $d=1$ dimensional chain.Comment: This is the version submitted to Physica Status Solidi B. The final published version, taking into account Referee comments, is available exclusively from the publisher's websit

Nonlinear hopping transport in ring systems and open channels

We study the nonlinear hopping transport in one-dimensional rings and open channels. Analytical results are derived for the stationary current response to a constant bias without assuming any specific coupling to the external fields. It is shown that anomalous large effective jump lengths, as observed in recent experiments by taking the ratio of the third order nonlinear and the linear conductivity, can occur already in ordered systems. Rectification effects due to site energy disorder in ring systems are expected to become irrelevant for large system sizes. In open channels in contrast, rectification effects occur already for disorder in the jump barriers and do not vanish in the thermodynamic limit. Numerical solutions for a sinusoidal bias show that the ring system provides a good description for the transport behavior in the open channel for intermediate and high frequencies. For low frequencies temporal variations in the mean particle number have to be taken into account in the open channel, which cannot be captured in the more simple ring model.Comment: 25 pages, 7 figure

Thermodynamic magnetization of a strongly correlated two-dimensional electron system

We measure thermodynamic magnetization of a low-disordered, strongly correlated two-dimensional electron system in silicon. Pauli spin susceptibility is observed to grow critically at low electron densities - behavior that is characteristic of the existence of a phase transition. A new, parameter-free method is used to directly determine the spectrum characteristics (Lande g-factor and the cyclotron mass) when the Fermi level lies outside the spectral gaps and the inter-level interactions between quasiparticles are avoided. It turns out that, unlike in the Stoner scenario, the critical growth of the spin susceptibility originates from the dramatic enhancement of the effective mass, while the enhancement of the g-factor is weak and practically independent of the electron density.Comment: As publishe

Earthworks risk assessment on a heritage railway

The UK is home to a substantial number of heritage and tourist railways, which make a significant contribution to their local economies. They are mostly constructed on the routes of closed lines, and include large numbers of earthworks of uncertain construction and unknown strength. Recently, there have been earthwork collapses, most notably on the Gloucester and Warwickshire Railway during 2010 and 2011. The Office of Rail Regulation has also noted a number of safety incidents on heritage railways, all attributable to management failures. This paper describes an analysis of the Victorian earthworks on the Bo'ness and Kinneil Railway, a 8 km-long heritage railway in central Scotland. The analysis and risk prioritisation method used by Network Rail was found to be unsuitable for direct application to heritage railways, owing to the different operating context. A new system was therefore developed, removing some risk factors from the Network Rail approach, adding others, and modifying further ones. The new system was successfully applied, and the Bo'ness and Kinneil Railway earthworks were found to be generally stable and safe

Quantum railroads and directed localization at the juncture of quantum Hall systems

The integer quantum Hall effect (QHE) and one-dimensional Anderson localization (AL) are limiting special cases of a more general phenomenon, directed localization (DL), predicted to occur in disordered one-dimensional wave guides called "quantum railroads" (QRR). Here we explain the surprising results of recent measurements by Kang et al. [Nature 403, 59 (2000)] of electron transfer between edges of two-dimensional electron systems and identify experimental evidence of QRR's in the general, but until now entirely theoretical, DL regime that unifies the QHE and AL. We propose direct experimental tests of our theory.Comment: 11 pages revtex + 3 jpeg figures, to appear in Phys. Rev.

EPW: A program for calculating the electron-phonon coupling using maximally localized Wannier functions

EPW (Electron-Phonon coupling using Wannier functions) is a program written in FORTRAN90 for calculating the electron-phonon coupling in periodic systems using density-functional perturbation theory and maximally-localized Wannier functions. EPW can calculate electron-phonon interaction self-energies, electron-phonon spectral functions, and total as well as mode-resolved electron-phonon coupling strengths. The calculation of the electron-phonon coupling requires a very accurate sampling of electron-phonon scattering processes throughout the Brillouin zone, hence reliable calculations can be prohibitively time-consuming. EPW combines the Kohn-Sham electronic eigenstates and the vibrational eigenmodes provided by the Quantum-ESPRESSO package [1] with the maximally localized Wannier functions provided by the wannier90 package [2] in order to generate electron-phonon matrix elements on arbitrarily dense Brillouin zone grids using a generalized Fourier interpolation. This feature of EPW leads to fast and accurate calculations of the electron-phonon coupling, and enables the study of the electron-phonon coupling in large and complex systems.Comment: 6 figure