Non-ideal MHD Properties of Magnetic Flux Tubes in the Solar Photosphere

Magnetic flux tubes reaching from the solar convective zone into the chromosphere have to pass through the relatively cool, and therefore non-ideal (i.e. resistive) photospheric region enclosed between the highly ideal sub-photospheric and chromospheric plasma. It is shown that stationary MHD equilibria of magnetic flux tubes which pass through this region require an inflow of photospheric material into the flux tube and a deviation from iso-rotation along the tube axis. This means that there is a difference in angular velocity of the plasma flow inside the tube below and above the non-ideal region. Both effects increase with decreasing cross section of the tube. Although for characteristic parameters of thick flux tubes the effect is negligible, a scaling law indicates its importance for small-scale structures. The relevance of this "inflow effect" for the expansion of flux tubes above the photosphere is discussed.Comment: 17 pages, 9 figures. Comments welcom

Virtuell über den „Studierendenberg“? Zu Kapazitätswirkungen mediengestützter Lehre

Für Teile der mit technologiebasiertem Lehren und Lernen befassten Scientific Community ist Ressourcenbetrachtung per se eine Provokation. Vertreterinnen und Vertretern des Hochschulmanagements kommen sie dagegen oft gelegen – aus Gründen, die nicht immer der Sache dienen. Gegenüber beiden Positionen ist der vorliegende Beitrag als Versuch zu sehen, in Zeiten ubiquitärer Effizienzforderung im Hochschulsektor der Frage nach möglichen Ressourcenwirkungen von E-Learning nachzugehen, ohne die Qualitätsfrage aus dem Auge zu verlieren. So lautet die mit Blick auf den in Deutschland bis 2012 erwarteten Anstieg der Studierendenzahlen formulierte Leitfrage: Kann durch mediengestütztes Selbststudium die Ausbildungskapazität einer Hochschule gesteigert werden, ohne zusätzliche Lehrende einzustellen und ohne die Qualität der Lehre drastisch abzusenken? Wer hier ein simples „Ja“ oder „Nein“ erwartet, übersieht, dass die Antwort angesichts der Komplexität der Sache einer differenzierten Betrachtung bedarf, für die erhebliche methodische Vorkehrungen und – in Ermangelung empirischer Beispiele – plausible Setzungen erforderlich sind. Im Folgenden wird daher nur eine mögliche Antwort in Form von Modellrechnungen versucht, mit denen sich Kapazitätseffekte verschiedener E-Learning-Szenarien ermitteln lassen. Dazu wird methodisch auf die Kapazitätsberechnung zurückgegriffen, die hier allerdings nur als Planungsinstrument und nicht als Teil einer Rechtsnorm (…) Verwendung findet. (DIPF/ Orig.

Toward more realistic analytic models of the heliotail: Incorporating magnetic flattening via distortion flows

Both physical arguments and simulations of the global heliosphere indicate that the tailward heliopause is flattened considerably in the direction perpendicular to both the incoming flow and the large-scale interstellar magnetic field. Despite this fact, all of the existing global analytical models of the outer heliosheath's magnetic field assume a circular cross section of the heliotail. To eliminate this inconsistency, we introduce a mathematical procedure by which any analytically or numerically given magnetic field can be deformed in such a way that the cross sections along the heliotail axis attain freely prescribed, spatially dependent values for their total area and aspect ratio. The distorting transformation of this method honors both the solenoidality condition and the stationary induction equation with respect to an accompanying flow field, provided that both constraints were already satisfied for the original magnetic and flow fields prior to the transformation. In order to obtain realistic values for the above parameters, we present the first quantitative analysis of the heliotail's overall distortion as seen in state-of-the-art three-dimensional hybrid MHD-kinetic simulations.Comment: 15 pages, 8 figures. Published in The Astrophysical Journa

Theory of measuring the "Luttinger-g" of a one-dimensional quantum dot

We study electron transport through a quantum dot in a Tomonaga-Luttinger liquid with an inhomogeneity induced either by a non-uniform electron interaction or by the presence of tunnel resistances of contacts. The non-analytic temperature behavior of the conductance peaks show crossovers determined by the different energy scales associated with the dot and the inhomogeneity despite the Coulomb blockade remains intact. This suggests an explanation of recent findings in semiconductor quantum wires and carbon nanotubes.Comment: 4 pages, 3 colour figures, to be published with Phys. Rev.

Reading opinion 2/15 : standards of analysis, the Court's discretion, and the legal view of the Advocate General

In Opinion 2/15, the Commission, the European Parliament, the Council, and the Member States litigate whether the Union is exclusively competent to conclude the EU-Singapore Free Trade Agreement (EUSFTA) alone, or whether the EU ought to involve the Member States as independent parties to a ‘mixed’ agreement. The delineation of the scope of EU Common Commercial Policy following the Lisbon Treaty reform of 2009 is central to this proceeding. The Court’s opinion, which stands in the tradition of seminal EU external competence cases such as Opinion 1/78 and Opinion 1/94, will further clarify the Union’s constitutional identity in the area of EU external economic relations and is likely to have vast implications for EU external economic governance. This note, first, reviews the evolution of the Union’s Common Commercial Policy in context of the Court’s past jurisprudence and, secondly, scrutinizes the relevant methodological approaches and standards of analysis, which the Court employs in its competence enquiry. It is argued that the Court retains ample space for discretionary judicial decision-making, which surfaces, most obviously, at the intersection of the competence enquiry and the necessary determination of the appropriate legal bases. The clarification and further refinement of the Court’s analytical standards in its judgment as well as their transparent and consistent application have the potential to substantially reduce incentives for future litigation and inter-institutional political combat. The recent quarrels over the signing, provisional application, and conclusion of CETA provide sufficient emphasis to this point. Using the legal view of Advocate General as a benchmark, this paper, third, discusses the practical implications of the Court’s judgment for EU international trade and investment treaty-making. The article, fourth, proposes a number of institutional alternatives that may serve to ‘save’ EU external economic treaty-making from ‘mixity’ and the pitfalls of the associated treaty-making procedures in the EU and the member states

Transport through a one-dimensional quantum dot

We examine the effects of long-range interactions in a quantum wire with two impurities. We employ the bosonization technique and derive an effective action for the system. The effect of the long-range interaction on the charging energy and spectral properties of the island formed by the impurities and the linear transport is discussed.Comment: 7 pages, 2 figure

Charge and spin addition energies of one dimensional quantumn dot

We derive the effective action for a one dimensional electron island formed between a double barrier in a single channel quantum wire including the electron spin. Current and energy addition terms corresponding to charge and spin are identified. The influence of the range and the strength of the electron interaction and other system parameters on the charge and spin addition energies, and on the excitation spectra of the modes confined within the island is studied. We find by comparison with experiment that spin excitations in addition to non-zero range of the interaction and inhomogeneity effects are important for understanding the electron transport through one dimensional quantum islands in cleaved-edge-overgrowth systems.Comment: 11 pages, 3 figures, to be published in Physical Review