The quasi-free-standing nature of graphene on H-saturated SiC(0001)

We report on an investigation of quasi-free-standing graphene on 6H-SiC(0001) which was prepared by intercalation of hydrogen under the buffer layer. Using infrared absorption spectroscopy we prove that the SiC(0001) surface is saturated with hydrogen. Raman spectra demonstrate the conversion of the buffer layer into graphene which exhibits a slight tensile strain and short range defects. The layers are hole doped (p = 5.0-6.5 x 10^12 cm^(-2)) with a carrier mobility of 3,100 cm^2/Vs at room temperature. Compared to graphene on the buffer layer a strongly reduced temperature dependence of the mobility is observed for graphene on H-terminated SiC(0001)which justifies the term "quasi-free-standing".Comment: 3 pages, 3 figures, accepted for publication in Applied Physics Letter

The movement-image of the movement-machine: Deleuze, cinema and the London Underground.

This thesis addresses the London Underground in the light of Gilles Deleuze's philosophy of cinema. The first chapter gives an overview of the aspects of Deleuze's philosophy, which are of particular interest in the context of architectural theory. The main postulates of transcendental empiricism are explained, followed by the four major concepts: space, time, image and event. The second chapter deals with Deleuze's understanding of the cinematic frame. The relationship between the frame and the content of framing is shown as possibly inherently dynamic. A description of the major points regarding the Underground corridor follows, with the explanation of the condition of the walking body and its relation to the surrounds. Finally, the notion of the cinematic frame and acts of framing are utilised for the conceptualisation of the Underground corridor, showing the notion of movement to be of crucial importance. Chapter three regards the platform event in relation to the cinematic shot, which is explained to be a matter of conversion of movement. The specificity of the Underground platform is related, and the relationship between the body and the moving object of the train explained. The conjunction between the platform and the shot is then proposed, to show that the platform stands at a point of conversion of movement, transforming body's relationship to its environment. Chapter four is the discussion of the Underground carriage, and its understanding in the light of Deleuze's conceptualisation of the cinematic close-up. The close-up is shown to represent a specific, qualitative transformation, which marks the shift of movement in the direction of expression. The concept of any-space-whatever is then related as an example of Deleuze's transformation of the close-up of the face to the object and then to a spatial figure. The specifics of the Underground carriage are related, introducing the notion of the motionless body inside a moving confinement, as well as the presentation of 'facialisation.' The third part of the chapter sees the explanation of the carriage event in the light of the close-up/affection-image, and it pays special attention to the transformation of movement into expression. Finally, Chapter Five sees the discussion of the Underground in general, and its relation to the city. Deleuze's understanding of the concept of montage is explained in particular its relationship to time and construction of continuities and wholes across ruptures. The Underground is discussed as an urban system and its relation to the city that harbours it addressed. Finally, a particular understanding of urban montage is proposed, one wholly dependent on the presence of the Underground system

Deep reinforcement learning in World-Earth system models to discover sustainable management strategies

Increasingly complex, non-linear World-Earth system models are used for describing the dynamics of the biophysical Earth system and the socio-economic and socio-cultural World of human societies and their interactions. Identifying pathways towards a sustainable future in these models for informing policy makers and the wider public, e.g. pathways leading to a robust mitigation of dangerous anthropogenic climate change, is a challenging and widely investigated task in the field of climate research and broader Earth system science. This problem is particularly difficult when constraints on avoiding transgressions of planetary boundaries and social foundations need to be taken into account. In this work, we propose to combine recently developed machine learning techniques, namely deep reinforcement learning (DRL), with classical analysis of trajectories in the World-Earth system. Based on the concept of the agent-environment interface, we develop an agent that is generally able to act and learn in variable manageable environment models of the Earth system. We demonstrate the potential of our framework by applying DRL algorithms to two stylized World-Earth system models. Conceptually, we explore thereby the feasibility of finding novel global governance policies leading into a safe and just operating space constrained by certain planetary and socio-economic boundaries. The artificially intelligent agent learns that the timing of a specific mix of taxing carbon emissions and subsidies on renewables is of crucial relevance for finding World-Earth system trajectories that are sustainable on the long term.Comment: 16 pages, 8 figure

Emergent inequality and business cycles in a simple behavioral macroeconomic model

Standard macroeconomic models assume that households are rational in the sense that they are perfect utility maximizers and explain economic dynamics in terms of shocks that drive the economy away from the steady state. Here we build on a standard macroeconomic model in which a single rational representative household makes a savings decision of how much to consume or invest. In our model, households are myopic boundedly rational heterogeneous agents embedded in a social network. From time to time each household updates its savings rate by copying the savings rate of its neighbor with the highest consumption. If the updating time is short, the economy is stuck in a poverty trap, but for longer updating times economic output approaches its optimal value, and we observe a critical transition to an economy with irregular endogenous oscillations in economic output, resembling a business cycle. In this regime households divide into two groups: poor households with low savings rates and rich households with high savings rates. Thus, inequality and economic dynamics both occur spontaneously as a consequence of imperfect household decision-making. Adding a few “rational” agents with a fixed savings rate equal to the long-term optimum allows us to match business cycle timescales. Our work here supports an alternative program of research that substitutes utility maximization for behaviorally grounded decision-making

Correlation Structures of Correlated Binomial Models and Implied Default Distribution

We show how to analyze and interpret the correlation structures, the conditional expectation values and correlation coefficients of exchangeable Bernoulli random variables. We study implied default distributions for the iTraxx-CJ tranches and some popular probabilistic models, including the Gaussian copula model, Beta binomial distribution model and long-range Ising model. We interpret the differences in their profiles in terms of the correlation structures. The implied default distribution has singular correlation structures, reflecting the credit market implications. We point out two possible origins of the singular behavior.Comment: 16 pages, 7 figure

Comparison of photoacoustic spectroscopy and cavity ring-down spectroscopy for ambient methane monitoring at Hohenpeißenberg

With an atmospheric concentration of approximately 2000 parts per billion (ppbV, 10−9), methane (CH4) is the second most abundant greenhouse gas (GHG) in the atmosphere after carbon dioxide (CO2). The task of long-term and spatially resolved GHG monitoring to verify whether climate policy actions are effective is becoming more crucial as climate change progresses. In this paper we report the CH4 concentration readings of our photoacoustic (PA) sensor over a 5 d period at Hohenpeißenberg, Germany. As a reference device, a calibrated cavity ring-down spectrometer, Picarro G2301, from the meteorological observatory of the German Weather Service (DWD) was employed. Trace gas measurements with photoacoustic instruments promise to provide low detection limits at comparably low costs. However, PA devices are often susceptible to cross-sensitivities related to fluctuating environmental conditions, e.g. ambient humidity. The obtained results show that for PA sensor systems non-radiative relaxation effects induced by varying humidity are a non-negligible factor. Applying algorithm compensation techniques, which are capable of calculating the influence of non-radiative relaxation effects on the photoacoustic signal, increase the accuracy of the photoacoustic sensor significantly. With an average relative deviation of 1.11 % from the G2301, the photoacoustic sensor shows good agreement with the reference instrument.</p