Non-linear Dynamics of Two-Level Systems in Non-equilibrium

The dielectric loss of amorphous materials along with noise and decoherence are the major limiting factors for many applications at low temperatures like superconducting circuits, Josephson junctions and quantum computing. These effects are nowadays understood as the consequence of an ensemble of quantum mechanical two-level systems (TLSs), which are described as additional broadly distributed low-energy excitations in the sample. In this context, the thesis at hand presents a unique property of an amorphous material when two pump-tones are applied. In this limit the utilized LC-resonator is emitting at the intermediate frequency of the two off-resonant driving fields. The underlying mechanism can be explained by a non-linear interaction of the rf-field with the TLSs and the resonator, which creates additional lines in the frequency spectrum and thereby a self-biasing effect. The corresponding measurements also define a specific set of parameters for the occurrence of this emission limit, which is well described by a phenomenological approach in the context of the Landau-Zener-Stückelberg formalism. The obtained results thus complement the bigger picture of TLSs and open up a new approach for further investigations

Russian Security Policy and Cooperation with the West

The West must find new ways to cooperate with Russia now that Vladimir Putin and Dmitry Medvedev have used its energy revenues to transform the country into a resurgent power and developed an assertive policy towards the West. The Russian Federation has come back to the international arena as a resurgent superpower thanks to its oil and gas revenues and the leadership of Vladimir Putin and Dmitry Medvedev. An assertive Russian superpower has adopted a tough anti-Western stance in its external security policy against both NATO’s expansion towards the East and against the deployment of the US missile shield programme in Europe. The Kremlim has used energy as an instrument of power in the Ukraine and has employed military power in Georgia, and new documents, such as the 2003 Defence White Paper, the 2007 Overview of Foreign Policy, the 2008 Foreign Policy Concept and the 2009 National Security Strategy express a consistent line of thought in Putin and Medvedev’s foreign and security policy. This ARI reviews the developments in Russia’s foreign security policy,the continuity in the ideas and action of both Russian leaders, the challenges and opportunities of Russian-Western cooperation in Afghanistan and the energy security and military-operational issues that can be addressed through a bottom-up approach

Stellar Signatures of AGN Jet Triggered Star Formation

To investigate feedback between relativistic jets emanating from Active Galactic Nuclei (AGN) and the stellar population of the host galaxy, we analyze the long-term evolution of the galaxy-scale simulations by Gaibler et al. (2012) of jets in massive, gas-rich galaxies at z ~ 2 - 3 and of stars formed in the host galaxies. We find strong, jet-induced differences in the resulting stellar populations of galaxies that host relativistic jets and galaxies that do not, including correlations in stellar locations, velocities, and ages. Jets are found to generate distributions of increased radial and vertical velocities that persist long enough to effectively extend the stellar structure of the host. The jets cause the formation of bow shocks that move out through the disk, generating rings of star formation within the disk. The bow shock often accelerates pockets of gas in which stars form, yielding populations of stars with significant radial and vertical velocities, some of which have large enough velocities to escape the galaxy. These stellar population signatures can serve to identify past jet activity as well as jet-induced star formation

Evolution of first-year and second-year snow properties on sea ice in the Weddell Sea during spring-summer transition

Observations of snow properties, superimposed ice, and atmospheric heat fluxes have been performed on first-year and second-year sea ice in the western Weddell Sea, Antarctica. Snow in this region is particular as it does usually survive summer ablation. Measurements were performed during Ice Station Polarstern (ISPOL), a 5-week drift station of the German icebreaker RV Polarstern. Net heat flux to the snowpack was 8 W m−2, causing only 0.1 to 0.2 m of thinning of both snow cover types, thinner first-year and thicker second-year snow. Snow thinning was dominated by compaction and evaporation, whereas melt was of minor importance and occurred only internally at or close to the surface. Characteristic differences between snow on first-year and second-year ice were found in snow thickness, temperature, and stratigraphy. Snow on second-year ice was thicker, colder, denser, and more layered than on first-year ice. Metamorphism and ablation, and thus mass balance, were similar between both regimes, because they depend more on surface heat fluxes and less on underground properties. Ice freeboard was mostly negative, but flooding occurred mainly on first-year ice. Snow and ice interface temperature did not reach the melting point during the observation period. Nevertheless, formation of discontinuous superimposed ice was observed. Color tracer experiments suggest considerable meltwater percolation within the snow, despite below-melting temperatures of lower layers. Strong meridional gradients of snow and sea-ice properties were found in this region. They suggest similar gradients in atmospheric and oceanographic conditions and implicate their importance for melt processes and the location of the summer ice edge

The microwave emissivity variability of snow covered first-year sea ice from late winter to early summer: a model study

Satellite observations of microwave brightness temperatures between 19 GHz and 85 GHz are the main data sources for operational sea-ice monitoring and retrieval of ice concentrations. However, microwave brightness temperatures depend on the emissivity of snow and ice, which is subject to pronounced seasonal variations and shows significant hemispheric contrasts. These mainly arise from differences in the rate and strength of snow metamorphism and melt. We here use the thermodynamic snow model SNTHERM forced by European Re-Analysis (ERA) interim data and the Microwave Emission Model of Layered Snowpacks (MEMLS), to calculate the sea-ice surface emissivity and to identify the contribution of regional patterns in atmospheric conditions to its variability in the Arctic and Antarctic. The computed emissivities reveal a pronounced seasonal cycle with large regional variability. The emissivity variability increases from winter to early summer and is more pronounced in the Antarctic. In the pre-melt period (January–May, July–November) the standard deviations in surface microwave emissivity due to diurnal, regional and inter-annual variability of atmospheric forcing reach up to Δε = 0.034, 0.043, and 0.097 for 19 GHz, 37 GHz and 85 GHz channels, respectively. Between 2000 and 2009, small but significant positive emissivity trends were observed in the Weddell Sea during November and December as well as in Fram Strait during February, potentially related to earlier melt onset in these regions. The obtained results contribute to a better understanding of the uncertainty and variability of sea-ice concentration and snow-depth retrievals in regions of high sea-ice concentrations

Damped Ly{\alpha} Absorption Systems in Semi-Analytic Models with Multiphase Gas

We investigate the properties of damped Ly{\alpha} absorption systems (DLAs) in semi-analytic models of galaxy formation, including partitioning of cold gas in galactic discs into atomic, molecular, and ionized phases with a molecular gas-based star formation recipe. We investigate two approaches for partitioning gas into these constituents: a pressure-based and a metallicity-based recipe. We identify DLAs by passing lines of sight through our simulations to compute HI column densities. We find that models with "standard" gas radial profiles - where the average specific angular momentum of the gas disc is equal to that of the host dark matter halo - fail to reproduce the observed column density distribution of DLAs. These models also fail to reproduce the distribution of velocity widths {\Delta}v, overproducing low {\Delta}v relative to high {\Delta}v systems. Models with "extended" radial gas profiles - corresponding to gas discs with higher specific angular momentum - are able to reproduce quite well the column density distribution of absorbers over the column density range 19 < log NHI < 22.5 in the redshift range 2 < z < 3.5. The model with pressure-based gas partitioning also reproduces the observed line density of DLAs, HI gas density, and {\Delta}v distribution at z < 3 remarkably well. However all of the models investigated here underproduce DLAs and the HI gas density at z > 3. If this is the case, the flatness in the number of DLAs and HI gas density over the redshift interval 0 < z < 5 may be due to a cosmic coincidence where the majority of DLAs at z > 3 arise from intergalactic gas in filaments while those at z < 3 arise predominantly in galactic discs. We further investigate the dependence of DLA metallicity on redshift and {\Delta}v, and find reasonably good agreement with the observations, particularly when including the effects of metallicity gradients (abbrv.).Comment: 27 pages, 15 figures, submitted to MNRA

Medwedews Sicherheitspolitik: Eine vorläufige Einschätzung

Präsident Medwedew ist seit mehr als einem Jahr im Amt, so dass dies ein passender Moment für eine vorläufige Einschätzung seiner externen Sicherheitspolitik anhand einer Analyse seiner wichtigsten sicherheitspolitischen Dokumente und Erklärungen ist. Im Juli 2008, einige Monate nach seiner Amtseinführung, veröffentlichte Medwedew sein erstes großes Sicherheitsdokument, das außenpolitische Konzept. Kurz nach dem russisch-georgischen Konflikt im August 2008 stellte Medwedew eine zweite sicherheitspolitische Initiative vor, diesmal in Form einer Erklärung wichtiger politischer Prinzipien. Im folgenden Monat, im September 2008, verabschiedete Putins Nachfolger eine spezielle Strategie für die Arktisregion. Und im Mai 2009 ratifizierte Präsident Medwedew Russlands erste Nationale Sicherheitsstrategie. Eine überarbeitete Fassung der russischen Militärdoktrin – neben der Strategie und dem außenpolitischen Konzept der dritte Pfeiler der »Troika« der sicherheitspolitischen Hierarchie des Landes – wird im Verlauf des Jahres 2009 erwartet