Explanation for the Resistivity Law in Quantum Hall System

We consider a 2D electron system in a strong magnetic field, where the local Hall resistivity $\rho_{xy}(\vec r)$ is a function of position and $\rho_{xx}(\vec r)$ is small compared to $\rho_{xy}$. Particularly if the correlations fall off slowly with distance, or if fluctuations exist on several length scales, one finds that the macroscopic longitudinal resistivity $R_{xx}$ is only weakly dependent on $\rho_{xx}$ and is approximately proportional to the magnitude of fluctuations in $\rho_{xy}$. This may provide an explanation of the empirical law $R_{xx} \propto B \frac{dR_{xy}}{dB}$ where $R_{xy}$ is the Hall resistance, and $B$ is the magnetic field.Comment: 11 pages (REVTeX 3.0). Revised Version. Complete postscript file for this paper is available on the World Wide Web at http://cmtw.harvard.edu/~simon/ ; Preprint number HU-CMT-94S0

MAGNETOLUMINESCENCE OF n-TYPE ONE-SIDE-MODULATION-DOPED QUANTUM WELLS

Nous rendons compte d'expériences de photoluminescence à basse température (2 K) sur des puits quantiques, GaAs-Ga(Al)As à modulation de dopage, dans des champs magnétiques allant jusqu'à 20 T. La comparaison entre la théorie et l'expérience révèle le fort couplage entre les bandes de valence, des oscillations surprenantes sont observées sur l'énergie des transitions de basse énergie.We report magnetoluminescence experiments in a one-side-modulation-doped quantum well performed at 2 K in field up to 20 T. A comparison between calculations and experiments, points out the strong coupling between the valence subbands. Surprising oscillations are observed on lower lying transitions

Reduction of the environmental impact of aviation via optimisation of aircraft size/range and flight network

REIVON is a Clean Sky 2 Technology Evaluator project that investigates to what extent CO2 emissions of global aviation can be reduced via optimisation of aircraft size/range and flight network. Three alternative global flight networks are created, considering (1) splitting long-haul flights into shorter legs (intermediate stop operations, ISO), (2) reducing frequency to the necessary minimum on busy routes using larger aircraft, and (3) a combination of 1 and 2. In all cases, the use of aircraft optimised for specific combinations of range and seating capacity not existing today will be considered. For the first time, REIVON will carry out a holistic analysis of the impact of an optimised flight network on global air transport system stakeholders, such as passengers, aircraft manufacturers, airlines and airports, and of potential measures to support the implementation of such an alternative network