Giant suppression of the Drude conductivity due to quantum interference in disordered two-dimensional systems

Temperature and magnetic field dependences of the conductivity in heavily doped, strongly disordered two-dimensional quantum well structures GaAs/In$_x$Ga$_{1-x}$As/GaAs are investigated within wide conductivity and temperature ranges. Role of the interference in the electron transport is studied in the regimes when the phase breaking length $L_\phi$ crosses over the localization length $\xi\sim l\exp{(\pi k_Fl/2)}$ with lowering temperature, where $k_F$ and $l$ are the Fermi quasimomentum and mean free path, respectively. It has been shown that all the experimental data can be understood within framework of simple model of the conductivity over delocalized states. This model differs from the conventional model of the weak localization developed for $k_Fl\gg 1$ and $L_\phi\ll\xi$ by one point: the value of the quantum interference contribution to the conductivity is restricted not only by the phase breaking length $L_\phi$ but by the localization length $\xi$ as well. We show that just the quantity $(\tau_\phi^\ast)^{-1}=\tau_\phi^{-1}+\tau_\xi^{-1}$ rather than $\tau_\phi^{-1}$, where $\tau_\phi\propto T^{-1}$ is the dephasing time and $\tau_\xi\sim\tau\exp(\pi k_F l)$, is responsible for the temperature and magnetic field dependences of the conductivity over the wide range of temperature and disorder strength down to the conductivity of order $10^{-2} e^2/h$.Comment: 11 pages, 15 figure

Injuries Due to Wedging of Bicycle Wheels in On-road Tram Tracks

Background: In cities with trams as public transportation, tram tracks are often on public roads, creating a shared road situation with other road participants like cyclists. Beside the risk of direct collisions, this situation can also lead to bicycle wheels getting wedged in tram tracks, causing cyclists to fall. Objectives: The aim of this study was to gain more insight in the injury pattern of this trauma mechanism and to draw attention to the risks of the infrastructural situation with on-road tram tracks. Patients and Methods: A one-year, prospective, observational cohort study was conducted. All patients admitted after presentation to the emergency department of a level 1 trauma center, who got injured because their bicycle wheels got wedged in tram tracks, were included. Data were collected on patient demographics, type of injury and treatment. Results: Ten patients were included. Six were male. The mean age was 38 years. Six patients required surgery, mostly because of extremity injuries. Mean duration of admission was 4 days. Mean injury severity score was 13. One patient died as a result of the injuries sustained in the accident. Conclusions: Tram tracks on public roads are potentially dangerous and can lead to serious injuries and even mortality amongst cyclist. Operative intervention is frequently needed