Green function techniques in the treatment of quantum transport at the molecular scale

The theoretical investigation of charge (and spin) transport at nanometer length scales requires the use of advanced and powerful techniques able to deal with the dynamical properties of the relevant physical systems, to explicitly include out-of-equilibrium situations typical for electrical/heat transport as well as to take into account interaction effects in a systematic way. Equilibrium Green function techniques and their extension to non-equilibrium situations via the Keldysh formalism build one of the pillars of current state-of-the-art approaches to quantum transport which have been implemented in both model Hamiltonian formulations and first-principle methodologies. We offer a tutorial overview of the applications of Green functions to deal with some fundamental aspects of charge transport at the nanoscale, mainly focusing on applications to model Hamiltonian formulations.Comment: Tutorial review, LaTeX, 129 pages, 41 figures, 300 references, submitted to Springer series "Lecture Notes in Physics

A Mixture of “Cheats” and “Co-Operators” Can Enable Maximal Group Benefit

It is commonly assumed that the world would be best off if everyone co-operates. Experimental and mathematical analysis of “co-operation” in yeast show why this isn't always the case

Oxygen dependence of metabolic fluxes and energy generation of Saccharomyces cerevisiae CEN.PK113-1A

<p>Abstract</p> <p>Background</p> <p>The yeast <it>Saccharomyces cerevisiae </it>is able to adjust to external oxygen availability by utilizing both respirative and fermentative metabolic modes. Adjusting the metabolic mode involves alteration of the intracellular metabolic fluxes that are determined by the cell's multilevel regulatory network. Oxygen is a major determinant of the physiology of <it>S. cerevisiae </it>but understanding of the oxygen dependence of intracellular flux distributions is still scarce.</p> <p>Results</p> <p>Metabolic flux distributions of <it>S. cerevisiae </it>CEN.PK113-1A growing in glucose-limited chemostat cultures at a dilution rate of 0.1 h^-1with 20.9%, 2.8%, 1.0%, 0.5% or 0.0% O₂in the inlet gas were quantified by ¹³C-MFA. Metabolic flux ratios from fractional [U-¹³C]glucose labelling experiments were used to solve the underdetermined MFA system of central carbon metabolism of <it>S. cerevisiae</it>.</p> <p>While ethanol production was observed already in 2.8% oxygen, only minor differences in the flux distribution were observed, compared to fully aerobic conditions. However, in 1.0% and 0.5% oxygen the respiratory rate was severely restricted, resulting in progressively reduced fluxes through the TCA cycle and the direction of major fluxes to the fermentative pathway. A redistribution of fluxes was observed in all branching points of central carbon metabolism. Yet only when oxygen provision was reduced to 0.5%, was the biomass yield exceeded by the yields of ethanol and CO₂. Respirative ATP generation provided 59% of the ATP demand in fully aerobic conditions and still a substantial 25% in 0.5% oxygenation. An extensive redistribution of fluxes was observed in anaerobic conditions compared to all the aerobic conditions. Positive correlation between the transcriptional levels of metabolic enzymes and the corresponding fluxes in the different oxygenation conditions was found only in the respirative pathway.</p> <p>Conclusion</p> <p>¹³C-constrained MFA enabled quantitative determination of intracellular fluxes in conditions of different redox challenges without including redox cofactors in metabolite mass balances. A redistribution of fluxes was observed not only for respirative, respiro-fermentative and fermentative metabolisms, but also for cells grown with 2.8%, 1.0% and 0.5% oxygen. Although the cellular metabolism was respiro-fermentative in each of these low oxygen conditions, the actual amount of oxygen available resulted in different contributions through respirative and fermentative pathways.</p

Metallic, magnetic and molecular nanocontacts

Scanning tunnelling microscopy and break-junction experiments realize metallic and molecular nanocontacts that act as ideal one-dimensional channels between macroscopic electrodes. Emergent nanoscale phenomena typical of these systems encompass structural, mechanical, electronic, transport, and magnetic properties. This Review focuses on the theoretical explanation of some of these properties obtained with the help of first-principles methods. By tracing parallel theoretical and experimental developments from the discovery of nanowire formation and conductance quantization in gold nanowires to recent observations of emergent magnetism and Kondo correlations, we exemplify the main concepts and ingredients needed to bring together ab initio calculations and physical observations. It can be anticipated that diode, sensor, spin-valve and spin-filter functionalities relevant for spintronics and molecular electronics applications will benefit from the physical understanding thus obtained

Art therapy as the science of art therapeutic action. A discussion paper to determine the position of the German-speaking scientific community with regard to art therapy diagnostics and intervention

This article examines the current status of art therapy in its process of scientification in the German speaking scientific community. Based on Kriz's definition of Science (1981), an understanding of art therapy as a science of art therapeutic action and the systematic and in-depth accumulation of experiences with this action is elaborated. With this normative understanding, the current state of the discipline concerning especially the diagnostic and interventional aspect of art therapeutic action is examined. The sources are, among others, current and relevant textbooks of art therapy and art therapy dissertations from the past 12 years, which are based on data from specifically performed art therapy. The examined publications draw a differentiated picture of various aspects of art therapy with emphasis on the description and mostly psychodynamic explanation of therapy processes, works and experiences of the patients. Art therapy itself is mainly found in a prescriptive manner of presentation. Actual descriptions of art therapy are found as incidental findings, but have not been in the centre of investigation. This confirms the findings of already existing systematic literature analyzes on art therapy. Subsequently, possible second order solutions to this persistent problem are discussed.Dieser Artikel untersucht den aktuellen Stand der Kunsttherapie im Prozess der Verwissenschaftlichung in der deutschsprachigen Wissenschaftsgemeinschaft. Ausgehend von der Definition von Wissenschaft von Kriz (1981) wird ein Verständnis von Kunsttherapie als Wissenschaft vom kunsttherapeutischen Handeln und der systematischen und vertiefenden Kumulation der damit verbundenen Erfahrungen herausgearbeitet. Mit diesem normativen Verständnis wird der aktuelle Stand der Disziplin mit dem Fokus auf kunsttherapeutischem Diagnostizieren und Intervenieren untersucht. Herangezogen werden unter anderem aktuelle, maßgebliche Lehrbüchern der Kunsttherapie und diejenigen kunsttherapeutischen Dissertationen der letzten 12 Jahre, die Daten aus konkret durchgeführter Kunsttherapie zugrunde legen. Die untersuchten Publikationen zeichnen ein differenziertes Bild vielfältiger Aspekte des kunsttherapeutischen Geschehens mit Schwerpunkt auf der Beschreibung und meist psychodynamischen Erklärung von Therapieprozessen, Werken und Erlebensweisen der Patienten. Kunsttherapeutisches Handeln selbst findet sich überwiegend in präskriptiver Darstellungsweise. Tatsächliches kunsttherapeutisches Handeln jedoch wird allenfalls als Nebenbefund beschrieben, selbst jedoch nicht untersucht. Damit bestätigt sich der Befund bereits vorliegender systematischer Literaturanalysen zur Kunsttherapie. Anschließend werden mögliche Lösungen für diese anhaltende Problemlage diskutiert

Regional and sectoral varieties of capitalism

This study seeks to go beneath the generalizations that constitute characterizations of national economies in order to examine local and sectoral diversity - in particular, forms of capitalist organization at the level of localized sectors. It reports on the findings of research based on detailed case histories of local economies in four different types of production: modernized craft manufacturing (furniture), mass production (motor vehicles), high-technology production (biopharmaceuticals) and high-tech services (television film-making). In each case a local economy in Germany (usually seen counter-factually as an example of a particularly national system) was compared with one elsewhere in Europe: respectively, southern Sweden, Hungary (compared with eastern Germany) and the UK (for two studies). In the analysis, companies act rationally in response to sector-specific challenges, being partly bound by the existing institutional framework that they encounter, but partly acting to alter it. Two possibilities are distinguished and found in the cases. In the first (structurally conservative) case, arrangements of governance in the national innovation and production system prove to be beneficial for the companies and their aim to stand up to international competition. Insofar as national institutions help companies to deal with competition on their markets, they will probably try to preserve these arrangements. In the second (innovative) case, companies turn away from the national context and develop their own local governance structure. If the national institutional structure is seen as not adequate or 'non-fitting' to deal with sectorally specific terms of competition, then the internal and external coordination of companies - in reaction to challenges posed by the market - is likely to deviate from the national structure. In some instances evidence of 'creative incoherence', where local deviation from the national model provides a creative impulse, is found

Creative Local Development in Cologne and London Film and TV Production

This chapter analyses two case studies on public broadcasting in Germany and the UK. The case studies demonstrate several examples of actors at local and sectoral level taking initiatives to resolve apparent deficiencies for their purposes in the ‘normal’ national array of institutions. A particular surprise of the finding is that in doing so both German and British film and television makers have occasionally, usually by chance, hit on institutions more typical of the other country