Spatially Resolved Study of Backscattering in the Quantum Spin Hall State

The discovery of the quantum spin Hall (QSH) state, and topological insulators in general, has sparked strong experimental efforts. Transport studies of the quantum spin Hall state have confirmed the presence of edge states, showed ballistic edge transport in micron-sized samples, and demonstrated the spin polarization of the helical edge states. While these experiments have confirmed the broad theoretical model, the properties of the QSH edge states have not yet been investigated on a local scale. Using scanning gate microscopy to perturb the QSH edge states on a submicron scale, we identify well-localized scattering sites which likely limit the expected nondissipative transport in the helical edge channels. In the micron-sized regions between the scattering sites, the edge states appear to propagate unperturbed, as expected for an ideal QSH system, and are found to be robust against weak induced potential fluctuations

Airflow in subway systems

U-Bahnsysteme sind das Rückgrat der städtischen Mobilität. Sie sind auch kritische Infrastrukturen und hinsichtlich von Sicherheitsfragen von großer Bedeutung. Die Rauchausbreitung in Folge eines Brandes kann heutzutage mit numerischen Simulationen recht gut vorhergesagt werden, sofern valide Randbedingungen angenommen wurden. Die thermischen Differenzen zwischen dem Untergrund und der äußeren Witterung führen zu einer ausgleichenden natürlichen Hintergrundströmung. Diese Ausgleichsströmungen sind jedoch schwer zu ermitteln, da der Piston-Effekt der fahrenden Züge diese stark überprägt. Im Katastrophenfall stoppt der U-Bahn Verkehr unverzüglich, die natürliche Hintergrundströmung bestimmt die Ausbreitungswege von Schadstoffen und muss daher in den numerischen Simulationen berücksichtigt werden. Die faseroptische Temperaturerfassung ermöglicht es in Verbindung mit herkömmlichen Klimamessungen an der Oberfläche die natürliche Hintergrundströmung statistisch zu modellieren.Subway systems are the backbone of urban mobility, but because they are also vulnerable critical infrastructures, safety issues are of great importance. The spread of smoke as a result of a fire can nowadays predict with numerical simulations if the assumed boundary conditions are valid. The thermal differences between the subsurface and the external weather lead to a compensating natural background airflow. However, these compensating airflows are challenging to determine because the piston effect of the moving trains strongly overshadows them. During catastrophic circumstances, the underground stops traffic immediately, the natural background flow determines the dispersion paths of pollutants and must be taken into account for the numerical simulations. Fiber-optic temperature measurement, in combination with conventional climate measurements on the surface, enables the natural background flow to be statistically modeled

Meteorological observations from the automatic weather stations Drescher and Filchner, 1991-2002

Automatic weather stations (AWS) are due to the extreme cold conditions an attractive option to get more dens climatic data from Antarctica. These data is needed for weather forecast models or other climatic models. Data sets of the European Centre for Medium-Range Weather Forecasts (ECMWF) analysis model are used for comparison with AWS in the Weddell Sea. This region if of particular interest for the BRIOS2 (Bremerhaven Regional Ice-Ocean Simulations) model which produce results related to sea ice processes, water mass modifications and circulation patterns, all leading to a better understanding of the thermohaline ocean circulation in the Southern Ocean. Therefore, observation at AWS' can be used as a validation of the ECMWF model and can reveal sources for errors for climate models using a ECMWF forcing

The Influence of subway climatology on gas dispersion and the effectiveness of guided evacuations in a complex subway station

This paper discusses a strategy that integrates data from tracer gas experiments with results from pedestrian simulation software in the evaluation of different evacuation procedures for subway stations in response to a fire or a terrorist attack with chemical, biological, radiological, nuclear and enhanced conventional weapons (CBRNE). The study demonstrates that by combining the two data sets a greater understanding of the impact of different evacuations routes on an evacuee's health is gained. It is shown that by controlling the routes pedestrians would use to exit a subway station, the number of fatalities and evacuees with long term health issues can be reduced. It is highlighted that a dynamic evacuation guiding system based on subway climatology would take into account the source of the toxin, the resulting dispersal of gas, smoke, etc. and the subway climatology at the time. In doing so, it would be possible to identify the most endangered areas and guide passengers via an adaptive escape route using audio and visual techniques. Information on the evolution of the emergency situation could also simultaneously be relayed back to the rescue forces to help to plan the rescue and evacuation procedures and optimise the deployment of the search and rescue teams