How sharply does the Anderson model depict a single-electron transistor?

The single-impurity Anderson model has been the focus of theoretical studies of molecular junctions and the single-electron transistor, a nanostructured device comprising a quantum dot that bridges two otherwise decoupled metallic leads. The low-temperature transport properties of the model are controlled by the ground-state occupation of the quantum dot, a circumstance that recent density-functional approaches have explored. Here we show that the ground-state dot occupation also parametrizes a linear mapping between the thermal dependence of the zero-bias conductance and a universal function of the temperature scaled by the Kondo temperature. Careful measurements by Grobis and co-workers are very accurately fitted by the universal mapping. Nonetheless, the dot occupation and an asymmetry parameter extracted from the same mapping are relatively distant from the expected values. We conclude that mathematical results derived from the model Hamiltonian reproduce accurately the universal physical properties of the device. In contrast, non-universal features cannot be reproduced quantitatively. To circumvent this limitation, \emph{ab initio} studies of the device at high energies seem necessary, to accurately define the model Hamiltonian. Our conclusion reinforces findings by Gross and coworkers, who applied time-dependent density-functional theory to show that, to describe the low-energy properties of molecular junctions, one must be able to describe the high-energy regime

Current and forthcoming issues in the South African electricity sector

One of the contentious issues in electricity reform is whether there are significant gains from restructuring systems that are moderately well run. South Africa's electricity system is a case in point. The sector's state-owned utility, Eskom, has been generating some of the lowest-priced electricity in the world, has largely achieved revenue adequacy, and has financed the bulk of the government's ambitious electrification program. Moreover, the key technical performance indicators of Eskom's generation plants have reached world-class levels. Yet the sector is confronted today with serious challenges. South Africa's electricity system is currently facing a tight demand/supply balance, and the distribution segment of the industry is in serious financial trouble. This paper provides a careful diagnostic assessment of the industry and identifies a range of policy and restructuring options to improve its performance. It suggests removing distribution from municipal control and privatizing it, calls for vertical and horizontal unbundling, and argues that the cost-benefit analysis of different structural options should focus on investment incentives and not just current operating efficiency.Energy Production and Transportation,Electric Power,Environment and Energy Efficiency,Energy and Environment,Infrastructure Economics

Local solutions in Sobolev spaces with negative indices for the "good" Boussinesq equation

We study the local well-posedness of the initial-value problem for the nonlinear "good" Boussinesq equation with data in Sobolev spaces \textit{$H^s$} for negative indices of $s$.Comment: Referee comments incorporate

Características dos agentes de mudança

Há duas linhas básicas ao longo deste trabalho que podem sumariá-lo. Uma é a dependência comum, entre diversos autores, do trabalho de Lippitt e outros (13) para definir o agente de mudança. A outra reflete o esforço deliberado de vários estudiosos no sentido de ir além do simples conhecimento do que é um agente de mudança, mediante o desempenho de seu papel, ou simplesmente sendo um deles. Dos cinco exemplos vistos sobre esforços para definir os agentes de mudança, E. Rogers (24) na área de desenvolvimento intercultural, Tichy (27) na área de transformação social, Beckhard (1) na área de desenvolvimento organizacional, Gross e outros (7) no setor de instituições educacionais, e Pincus e Minahan (19) no campo de serviço social, todos baseiam-se nos conceitos originais de Lippitt e outros