Interplay between classical magnetic moments and superconductivity in quantum one-dimensional conductors: toward a self-sustained topological Majorana phase

We study a one-dimensional (1D) interacting electronic liquid coupled to a 1D array of classical magnetic moments and to a superconductor. We show that at low energy and temperature the magnetic moments and the electrons become strongly entangled and that a magnetic spiral structure emerges without any adjustable parameters. For strong enough coupling between the two, the 1D electronic liquid is driven into a topological superconducting phase supporting Majorana fermions without any fine-tuning of external parameters. Our analysis applies at low enough temperature to a quantum wire in proximity of a superconductor when the hyperfine interaction between electrons and nuclear spins is taken into account or to a chain of magnetic adatoms adsorbed on a superconducting surface.Comment: 7 pages, 2 figures, final versio

Nuclear magnetism and electron order in interacting one-dimensional conductors

The interaction between localized magnetic moments and the electrons of a one-dimensional conductor can lead to an ordered phase in which the magnetic moments and the electrons are tightly bound to each other. We show here that this occurs when a lattice of nuclear spins is embedded in a Luttinger liquid. Experimentally available examples of such a system are single wall carbon nanotubes grown entirely from 13C and GaAs-based quantum wires. In these systems the hyperfine interaction between the nuclear spin and the conduction electron spin is very weak, yet it triggers a strong feedback reaction that results in an ordered phase consisting of a nuclear helimagnet that is inseparably bound to an electronic density wave combining charge and spin degrees of freedom. This effect can be interpreted as a strong renormalization of the nuclear Overhauser field and is a unique signature of Luttinger liquid physics. Through the feedback the order persists up into the millikelvin range. A particular signature is the reduction of the electric conductance by the universal factor 2.Comment: 30 pages, 10 figures; Sec. II contains a 2+ pages summary giving a complete overview to the main conditions and results; v3: updated references, typos correcte

Peter Raschig zum 75. Geburtstag

Peter Raschig wurde am 30. Juli 1934 in Berlin geboren. Seine Kindheit und Jugend verbrachte er bereits in Jessen und hier ist bis heute sein Lebensmittelpunkt. Nach 75 Lebensjahren zählt er nunmehr zu den „Alten Jessnern“. Viele seiner Aktivitäten haben deutliche Spuren hinterlassen, durch die er bei fast jedermann in der Stadt und darüber hinaus bekannt ist. Als Mitglied der Fachgruppe Ornithologie in Jessen erfasst und beringt Peter Raschig schon seit 1971 Weißstörche. Seit 1976 arbeitet er erfolgreich im Arbeitskreis „Weißstorch“ mit, zu dessen Gründungsmitgliedern er zählt. Lange Zeit war er zusätzlich federführend im Biberschutz tätig. So koordinierte er die Bestandserfassungen im Altkreis Jessen und organisierte die Bergung von Totfunden. Im Jahr 1978 wurde Peter Raschig zum Kreisnaturschutzbeauftragten des Altkreises Jessen berufen. Er arbeitet noch heute aktiv als Naturschutzbeauftragter des Landkreises Wittenberg

Designing Learning Information Systems to Customer Needs

The paper presents a marketing-oriented approach to the analysis and design of learning IS. In order to explain the phenomenon of success and failure of learning IS the term “user net value” is introduced. Using this concept, recommendations for a successful design and implementation of learning IS are presented

Influence of Variable Side-Stay Geometry on the Shimmy Dynamics of an Aircraft Dual-Wheel Main Landing Gear

Commercial aircraft are designed to fly but also need to operate safely and efficiently as vehicles on the ground. During taxiing, take-off, and landing the landing gear must operate reliably over a wide range of forward velocities and vertical loads. Specifically, it must maintain straight rolling under a wide variety of operating conditions. It is well known, however, that under certain conditions the wheels of the landing gear may display unwanted oscillations, referred to as shimmy oscillations, during ground maneuvers. Such oscillations are highly unwanted from a safety and a ride-comfort perspective. In this paper we conduct a study into the occurrence of shimmy oscillations in a main landing gear (MLG) of a typical midsize passenger aircraft. Such a gear is characterized by a main strut attached to the wing spar with a side-stay that connects the main strut to an attachment point closer to the fuselage center line. Nonlinear equations of motion are developed for the specific case of a two-wheeled MLG configuration and allow for large angle deflections within the geometrical framework of the system. The dynamics of the MLG are expressed in terms of three degrees of freedom: torsional motion, in-plane motion, and out-of-plane motion (with respect to the side-stay plane). These are modeled by oscillators that are coupled directly through the geometric configuration of the system as well as through the tire/ground interface, which is modeled here by the von Schlippe stretched string approximation of the tire dynamics. The mathematical model is fully parameterized and parameters are chosen to represent a generic (rather than a specific) landing gear. In particular, the positions of the attachment points are fully parameterized so that any orientation of the side-stay plane can be considered. The occurrence of shimmy oscillations is studied by means of a two-parameter bifurcation analysis of the system in terms of the forward velocity of the aircraft and the vertical force acting on the gear. The effect of a changing side-stay plane orientation angle on the bifurcation diagram is investigated. We present a consistent picture that captures the transition of the two-parameter bifurcation diagram as a function of this angle, with a considerable complexity of regions of different types of shimmy oscillations for intermediate and realistic side-stay plane orientations. In particular, we find a region of tristability in which stable torsional, in-plane, and out-of-plane shimmy oscillations coexist