Rotational levels in quantum dots

Low energy spectra of isotropic quantum dots are calculated in the regime of low electron densities where Coulomb interaction causes strong correlations. The earlier developed pocket state method is generalized to allow for continuous rotations. Detailed predictions are made for dots of shallow confinements and small particle numbers, including the occurance of spin blockades in transport.Comment: RevTeX, 10 pages, 2 figure

Theory of momentum resolved tunneling into a short quantum wire

Motivated by recent tunneling experiments in the parallel wire geometry, we calculate results for momentum resolved tunneling into a short one-dimensional wire, containing a small number of electrons. We derive some general theorems about the momentum dependence, and we carry out exact calculations for up to N=4 electrons in the final state, for a system with screened Coulomb interactions that models the situation of the experiments. We also investigate the limit of large $N$ using a Luttinger-liquid type analysis. We consider the low-density regime, where the system is close to the Wigner crystal limit, and where the energy scale for spin excitations can be much lower than for charge excitations, and we consider temperatures intermediate between the relevant spin energies and charge excitations, as well as temperatures below both energy scales.Comment: 19 pages, 13 figures, clarified text in a few points, added 1 figure, updated reference

Completing Queries: Rewriting of IncompleteWeb Queries under Schema Constraints

Reactive Web systems, Web services, and Web-based publish/ subscribe systems communicate events as XML messages, and in many cases require composite event detection: it is not sufficient to react to single event messages, but events have to be considered in relation to other events that are received over time. Emphasizing language design and formal semantics, we describe the rule-based query language XChangeEQ for detecting composite events. XChangeEQ is designed to completely cover and integrate the four complementary querying dimensions: event data, event composition, temporal relationships, and event accumulation. Semantics are provided as model and fixpoint theories; while this is an established approach for rule languages, it has not been applied for event queries before

Spin and Charge Luttinger-Liquid Parameters of the One-Dimensional Electron Gas

Low-energy properties of the homogeneous electron gas in one dimension are completely described by the group velocities of its charge (plasmon) and spin collective excitations. Because of the long range of the electron-electron interaction, the plasmon velocity is dominated by an electrostatic contribution and can be estimated accurately. In this Letter we report on Quantum Monte Carlo simulations which demonstrate that the spin velocity is substantially decreased by interactions in semiconductor quantum wire realizations of the one-dimensional electron liquid.Comment: 13 pages, figures include

Ladder approximation to spin velocities in quantum wires

The spin sector of charge-spin separated single mode quantum wires is studied, accounting for realistic microscopic electron-electron interactions. We utilize the ladder approximation (LA) to the interaction vertex and exploit thermodynamic relations to obtain spin velocities. Down to not too small carrier densities our results compare well with existing quantum Monte-Carlo (QMC) data. Analyzing second order diagrams we identify logarithmically divergent contributions as crucial which the LA includes but which are missed, for example, by the self-consistent Hartree-Fock approximation. Contrary to other approximations the LA yields a non-trivial spin conductance. Its considerably smaller computational effort compared to numerically exact methods, such as the QMC method, enables us to study overall dependences on interaction parameters. We identify the short distance part of the interaction to govern spin sector properties.Comment: 6 pages, 6 figures, to appear in Physical Review

Zur Gegenwart der Fabrik der Zukunft: Forschungsaktivitäten im bundesdeutschen Maschinenbau

Gegenstand der folgenden Untersuchung sind die Forschungs- und Entwicklungs-(FuE-)Aktivitäten der Unternehmen in der bundesdeutschen Maschinenbauindustrie. Im Mittelpunkt der Analyse stehen strategische Orientierungen dieser Aktivitäten, ihre organisatorische Ausgestaltung in den Unternehmen und die Bedeutung der Zusammenarbeit mit anderen Unternehmen bzw. wissenschaftlichen Einrichtungen. Die These wird vertreten, daß gegenwärtig grundlegende technologische Veränderungen die etablierten FuE-Strukturen in Maschinenbauunternehmen einem zunehmenden Anpassungsdruck aussetzen.The following study is concerned with research and development (R & D) activities in the West German machine-building industry. R & D strategies, the organization of R & D within companies and the relevance of cooperation with other companies or scientific institutions are analyzed. It is argued that fundamental technological change puts increasing pressure on machine-building companies to adapt and restructure traditionally established R&D activities.1. Einleitung 2. Interne FuE-Organisation: Inkrementelle Innovationsstrategie 3. Heterogene Branchenstruktur: Vertikale Koordination 4. Ökonomische Konkurrenzposition: Gefährdete Spitze 5. Technologische Herausforderungen: Technologischer Paradigmenwechsel 6. Reorganisation der FuE-Struktur: Autonomisierung, Diversifikation und Integration 7. Intraindustrielle Zusammenarbeit: Neue Kooperationsformen 8. "Fabrik der Zukunft": Staatliche Steuerungsleistungen? Literatu