Refine
Year of publication
- 2001 (460) (remove)
Document Type
- Article (345)
- Monograph/Edited Volume (78)
- Doctoral Thesis (31)
- Working Paper (3)
- Habilitation Thesis (2)
- Review (1)
Language
- English (460) (remove)
Is part of the Bibliography
- yes (460) (remove)
Keywords
- chaos (2)
- synchronization (2)
- Affixabfolge (1)
- Akkretionsscheiben (1)
- Autokorrelation (1)
- Berlin (1)
- Boosting (1)
- Brewsterwinkel-Mikroskopie (1)
- Chaos (1)
- Chaostheorie (1)
- Chaotische Sattel (1)
- Cholesterin (1)
- Dissoziation (1)
- Distributed Morphology (1)
- Dynamische Systeme (1)
- Effekt (1)
- Elektrolyte (1)
- Feld (1)
- Fettsäure (1)
- Fettsäuren (1)
- Flexion (1)
- GIXD (1)
- Hidden Markov Model (HMM) (1)
- Hungarian-German bilinguals (1)
- Hydrodynamik (1)
- Interaktion (1)
- Isothermen (1)
- Klassifikation mit großem Margin (1)
- Kosmopolit (1)
- Langmuir Monoschicht (1)
- Large Margin Classification (1)
- Leistungsspektrum (1)
- Linienspannung (1)
- Mathematical Optimization (1)
- Mathematische Optimierung (1)
- Merapi (1)
- Monoschicht (1)
- Morphologie (1)
- Multistability (1)
- Multistabilität (1)
- Nichtlineare Dynamik (1)
- Nichtlineare Systeme (1)
- Nichtlineares dynamisches System / Harmonische Analyse / Fraktal (1)
- Oberflächenpotential (1)
- Optimality Theory (1)
- Optimalitätstheorie (1)
- P hasensynchronisierung (1)
- Phase (1)
- Power Monitoring (1)
- Rauschen (1)
- Regression (1)
- Regularisierung (1)
- Regularization (1)
- Seismic Array Methods (1)
- Simulation (1)
- Sternwinde (1)
- Stochastische Prozesse (1)
- Strahlungstransport (1)
- Stromverbrauchüberwachung (1)
- Strukturbildung (1)
- Support Vectors (1)
- Support-Vector Lernen (1)
- Synchronisation (1)
- Synchronisierung (1)
- System (1)
- Theorie (1)
- Thermodynamische Eigenschaft (1)
- Time Series Analysis (1)
- Wasseroberfläche (1)
- Weltbürger (1)
- accretion disks (1)
- affix order (1)
- autocorrelation (1)
- chaotic (1)
- chaotic saddle (1)
- chaotisch (1)
- charged systems (1)
- classification (1)
- cognates (1)
- complex (1)
- complex systems (1)
- coupled (1)
- dynamical systems (1)
- electric double layer (1)
- electrolytes (1)
- elektrische Doppelschicht (1)
- field (1)
- foreign language acquisition (1)
- gekoppelt (1)
- geladene Systeme (1)
- hydrodynamics (1)
- inflection (1)
- interaction (1)
- interference (1)
- komplex (1)
- komplexe Systeme (1)
- language transfer (1)
- meanfield (1)
- monitoring (1)
- morphology (1)
- noise (1)
- nonlinear dynamics (1)
- nonlinear systems (1)
- o (1)
- pattern recognition (1)
- phase (1)
- phase synchronization (1)
- power spectrum (1)
- radiative transfer (1)
- simulation (1)
- stellar winds (1)
- stochastic processes (1)
- system (1)
- theory (1)
- transition (1)
- volcanic seismology (1)
- Übergang (1)
Institute
- Institut für Physik und Astronomie (128)
- Institut für Biochemie und Biologie (65)
- Institut für Mathematik (62)
- Institut für Chemie (31)
- Institut für Geowissenschaften (24)
- Institut für Informatik und Computational Science (22)
- Institut für Umweltwissenschaften und Geographie (20)
- Wirtschaftswissenschaften (20)
- Department Psychologie (18)
- Institut für Ernährungswissenschaft (16)
The Problem of front propagation in flowing media is addressed for laminar velocity fields in two dimensions. Three representative cases are discussed: stationary cellular flow, stationary shear flow, and percolating flow. Production terms of Fisher-Kolmogorov-Petrovskii-Piskunov type and of Arrhenius type are considered under the assumption of no feedback of the concentration on the velocity. Numerical simulations of advection-reaction-diffusion equations have been performed by an algorithm based on discrete-time maps. The results show a generic enhancement of the speed of front propagation by the underlying flow. For small molecular diffusivity, the front speed <i>V<sub><i>f</sub> depends on the typical flow velocity <i>U as<sup> </sup>a power law with an exponent depending on the topological properties of the flow, and on the ratio of reactive and advective time scales. For open-streamline flows we find always<sup> </sup><i>V<sub><i>f</sub>~<i>U, whereas for cellular flows we observe <i>V<sub><i>f</ sub>~<i>U<sup>1/4</sup> for fast advection and <i>V<sub><i>f</sub>~<i>U<sup>3/4</sup> for slow advection.
Subject of this work is the investigation of universal scaling laws which are observed in coupled chaotic systems. Progress is made by replacing the chaotic fluctuations in the perturbation dynamics by stochastic processes. First, a continuous-time stochastic model for weakly coupled chaotic systems is introduced to study the scaling of the Lyapunov exponents with the coupling strength (coupling sensitivity of chaos). By means of the the Fokker-Planck equation scaling relations are derived, which are confirmed by results of numerical simulations. Next, the new effect of avoided crossing of Lyapunov exponents of weakly coupled disordered chaotic systems is described, which is qualitatively similar to the energy level repulsion in quantum systems. Using the scaling relations obtained for the coupling sensitivity of chaos, an asymptotic expression for the distribution function of small spacings between Lyapunov exponents is derived and compared with results of numerical simulations. Finally, the synchronization transition in strongly coupled spatially extended chaotic systems is shown to resemble a continuous phase transition, with the coupling strength and the synchronization error as control and order parameter, respectively. Using results of numerical simulations and theoretical considerations in terms of a multiplicative noise partial differential equation, the universality classes of the observed two types of transition are determined (Kardar-Parisi-Zhang equation with saturating term, directed percolation).
The behavior of the Lyapunov exponents (LEs) of a disordered system consisting of mutually coupled chaotic maps with different parameters is studied. The LEs are demonstrated to exhibit avoided crossing and level repulsion, qualitatively similar to the behavior of energy levels in quantum chaos. Recent results for the coupling dependence of the LEs of two coupled chaotic systems are used to explain the phenomenon and to derive an approximate expression for the distribution functions of LE spacings. The depletion of the level spacing distribution is shown to be exponentially strong at small values. The results are interpreted in terms of the random matrix theory.
Thematic cartography
(2001)
We present an analytical formula for the asymptotic relative entropy of entanglement for Werner states of arbitrary dimensionality. We then demonstrate its validity using methods from convex optimization. This is the first case in which the value of a subadditive entanglement measure has been obtained in the asymptotic limit. This formula also gives the sharpest known upper bound on the distillable entanglement of these states.
Enthalpic barriers to the hydrophobic binding of oligosaccharides to phage P22 tailspike protein
(2001)
Over the last decade the modeling and the storage of biological data has been a topic of wide interest for scientists dealing with biological and biomedical research. Currently most data is still stored in text files which leads to data redundancies and file chaos. In this paper we show how to use relational modeling techniques and relational database technology for modeling and storing biological sequence data, i.e. for data maintained in collections like EMBL or SWISS-PROT to better serve the needs for these application domains. For this reason we propose a two step approach. First, we model the structure (and therefore the meaning of the) data using an Entity-Relationship approach. The ER model leads to a clean design of a relational database schema for storing and retrieving the DNA and protein data extracted from various sources. Our approach provides the clean basis for building complex biological applications that are more amenable to changes and software ports than their file-base counterparts.
Die vorliegende Arbeit stellt eine kritische Übersicht über den Forschungsstand zu multiplen Wh-Konstruktionen im Slavischen dar. Das Ziel ist es, die Unklarheit der Datenlage und die Widersprüchlichkeit der auf solchen "unklaren" Daten basierten Theorien aufzuzeigen. Inhalt: Historischer Hintergrund (Wachowicz 1974) Einige ältere Ansätze Höhepunkt: die folgenschwere Arbeit von Rudin (1988) Probleme: - Das Problem der Zuverlässlichkeit von Daten - Das Problem der Relevanz von Daten "Harte" Fakten: - Strikte Superioritätseffekte im Bulgarischen - Obligatorische Wh-Anhebung im Slavischen Neuere Ansätze: - "Qualitative" Ansätze - "Quantitative" Ansätze - Alternative Ansätze
Preface
(2001)
Hydrological modelling of a Pleistocene landslide-dammed lake in the Santa Maria Basin, NW Argentina
(2001)
Aim and Location In Central European lowland certain plant species grow mainly or exclusively in the corridors of large rivers. In German-speaking plant geography, they are known as "Stromtalpflanzen". The aim of this paper is to review the literature about definitions, explanations and species characteristics and to suggest future directions in research concerning this species group. Results A preliminary list contains 129 ecologically heterogeneous plant species. The mechanisms generating the peculiar distribution pattern may include hydrochory along river corridors, high level of disturbance by water, variable water availability including inundation and summer drought, warm summers, and high nutrient supply on alluvial soils. There is evidence from observational studies for all above mechanisms. However, none of them has been tested experimentally. Demographic data of river corridor plants is limited to very few species, including mainly invasive annuals (Artemisia annua, Bidens frondosa, Cuscuta campestris, Xanthium albinum) and annual (hemi)parasites (Cuscuta campestris, Melampyrum cristatum). Metapopulation studies do not exist to date for European species. part from their habitat requirements, river corridor plants were grouped according to their similarities in overall distribution pattern or in their distribution within particular river corridors. Main conclusions River corridor plants include a high proportion of threatened plant species. In order to preserve them, and in order to understand the mechanisms generating the peculiar distribution pattern, much more has to be known about their population biology and metapopulation dynamics.
This paper reports on the historical development of the Runge-Kutta methods beginning with the simple Euler method up to an embedded 13-stage method. Moreover, the design and the use of those methods under error order, stability and computation time conditions is edited for students of numerical analysis at undergraduate level. The second part presents applications in natural sciences, compares different methods and illustrates some of the difficulties of numerical solutions.
We describe automatic procedures for the selection of DA white dwarfs in the Hamburg/ESO objective-prism survey (HES). For this purpose, and the selection of other stellar objects (e.g., metal-poor stars and carbon stars), a flexible, robust algorithm for detection of stellar absorption and emission lines in the digital spectra of the HES was developed. Broad band (U-B, B-V) and intermediate band (Strömgren c_1) colours can be derived directly from HES spectra, with precisions of sigma U-B=0.092 mag; sigma B-V=0.095 mag; sigma c_1=0.15 mag. We describe simulation techniques that allow one to convert model or slit spectra to HES spectra. These simulated objective-prism spectra are used to determine quantitative selection criteria, and for the study of selection functions. We present an atlas of simulated HES spectra of DA and DB white dwarfs. Our current selection algorithm is tuned to yield maximum efficiency of the candidate sample (minimum contamination with non-DAs). DA candidates are selected in the B-V versus U-B and c_1 versus W_lambda (Hbeta +Hgamma +Hdelta ) parameter spaces. The contamination of the resulting sample with hot subdwarfs is expected to be as low as ~ 8%, while there is essentially no contamination with main sequence or horizontal branch stars. We estimate that with the present set of criteria, ~ 80% of DAs present in the HES database are recovered. A yet higher degree of internal completeness could be reached at the expense of higher contamination. However, the external completeness is limited by additional losses caused by proper motion effects and the epoch differences between direct and spectral plates used in the HES. Based on observations collected at the European Southern Observatory, La Silla and Paranal, Chile.
Laser beam melt ablation - a contact-free machining process - offers several advantages compared to conventional processing mechanisms: there exists no tool wear and even extremely hard or brittle materials can be processed. During ablation the workpiece is molten by a CO2-laser beam, this melt is then driven out by the impulse of a process gas. The idea behind laser ablation is rather simple, but it has a major limitation in practical applications: with increasing ablation rates surface quality of the workpiece processed declines rapidly. At high ablation rates, depending on the process parameters different periodic-like structures can be observed on the ablated surface. These structures show a dependence on the line energy, which has been identified as a fundamental control parameter. In dependence on this parameter several regimes with different behaviours of the process have been separated. These regimes are distinguishable as well in the surfaces obtained as in the signals gained by the measurement of the process emissions. Further aim is to identify the different modes of the system and reach a deeper understanding of the dynamics of the molten material in order to understand the formation of these surface structures. With this it should be possible to influence the system in the direction of avoiding structure formation even at high ablation rates. Relying on the results on-line monitoring and control of the process should be studied.
We study the dynamo properties of asymmetric square patterns in Boussinesq Rayleigh-B'enard convection in a plane horizontal layer. Cases without rotation and with weak rotation about a vertical axis are considered. There exist different types of solutions distinguished by their symmetry, among them such with flows possessing a net helicity and being capable of kinematic dynamo action in the presence as well as in the absence of rotation. In the nonrotating case these flows are, however, always only kinematic, not nonlinear dynamos. Nonlinearly the back-reaction of the magnetic field then forces the solution into the basin of attraction of a roll pattern incapable of dynamo action. But with rotation added parameter regions are found where the Coriolis force counteracts the Lorentz force in such a way that the asymmetric squares are also nonlinear dynamos.
We numerically investigate nonlinear asymmetric square patterns in a horizontal convection layer with up-down reflection symmetry. As a novel feature we find the patterns to appear via the skewed varicose instability of rolls. The time-independent nonlinear state is generated by two unstable checkerboard (symmetric square) patterns and their nonlinear interaction. As the bouyancy forces increase the interacting modes give rise to bifurcations leading to a periodic alternation between a nonequilateral hexagonal pattern and the square pattern or to different kinds of standing oscillations.
Metal ion mediated mesomorphism and thin film behaviour of amphitropic tetraazaporphyrin complexes
(2001)
We present a measure of quantum entanglement which is capable of quantifying the degree of entanglement of a multi-partite quantum system. This measure, which is based on a generalization of the Schmidt rank of a pure state, is defined on the full state space and is shown to be an entanglement monotone, that is, it cannot increase under local quantum operations with classical communication and under mixing. For a large class of mixed states this measure of entanglement can be calculated exactly, and it provides a detailed classification of mixed states.
Coating of porous polytetrafluoroethylene films with other polymers for electret applications
(2001)
The scientist as Weltbürger
(2001)
Line driven winds are accelerated by the momentum transfer from photons to a plasma, by absorption and scattering in numerous spectral lines. Line driving is most efficient for ultraviolet radiation, and at plasma temperatures from 10^4 K to 10^5 K. Astronomical objects which show line driven winds include stars of spectral type O, B, and A, Wolf-Rayet stars, and accretion disks over a wide range of scales, from disks in young stellar objects and cataclysmic variables to quasar disks. It is not yet possible to solve the full wind problem numerically, and treat the combined hydrodynamics, radiative transfer, and statistical equilibrium of these flows. The emphasis in the present writing is on wind hydrodynamics, with severe simplifications in the other two areas. I consider three topics in some detail, for reasons of personal involvement. 1. Wind instability, as caused by Doppler de-shadowing of gas parcels. The instability causes the wind gas to be compressed into dense shells enclosed by strong shocks. Fast clouds occur in the space between shells, and collide with the latter. This leads to X-ray flashes which may explain the observed X-ray emission from hot stars. 2. Wind runaway, as caused by a new type of radiative waves. The runaway may explain why observed line driven winds adopt fast, critical solutions instead of shallow (or breeze) solutions. Under certain conditions the wind settles on overloaded solutions, which show a broad deceleration region and kinks in their velocity law. 3. Magnetized winds, as launched from accretion disks around stars or in active galactic nuclei. Line driving is assisted by centrifugal forces along co-rotating poloidal magnetic field lines, and by Lorentz forces due to toroidal field gradients. A vortex sheet starting at the inner disk rim can lead to highly enhanced mass loss rates.
Electrically conducting fluids in motion can act as self-excited dynamos. The magnetic fields of celestial bodies like the Earth and the Sun are generated by such dynamos. Their theory aims at modeling and understanding both the kinematic and dynamic aspects of the underlying processes. Kinematic dynamo models, in which for a prescribed flow the linear induction equation is solved and growth rates of the magnetic field are calculated, have been studied for many decades. But in order to get consistent models and to take into account the back-reaction of the magnetic field on the fluid motion, the full nonlinear system of the magnetohydrodynamic (MHD) equations has to be studied. It is generally accepted that these equations, i.e. the Navier-Stokes equation (NSE) and the induction equation, provide a theoretical basis for the explanation of the dynamo effect. The general idea is that mechanical energy pumped into the fluid by heating or other mechanisms is transferred to the magnetic field by nonlinear interactions. For two special helical flows which are known to be effective kinematic dynamos and which can be produced by appropriate external mechanical forcing, we review the nonlinear dynamo properties found in the framework of the full MHD equations. Specifically, we deal with the ABC flow (named after Arnold, Beltrami and Childress) and the Roberts flow (after G.~O. Roberts). The appearance of generic dynamo effects is demonstrated. Applying special numerical bifurcation-analysis techniques to high-dimensional approximations in Fourier space and varying the Reynolds number (or the strength of the forcing) as the relevant control parameter, qualitative changes in the dynamics are investigated. We follow the bifurcation sequences until chaotic states are reached. The transitions from the primary flows with vanishing magnetic field to dynamo-active states are described in particular detail. In these processes the stagnation points of the flows and their heteroclinic connections play a promoting role for the magnetic field generation. By the example of the Roberts flow we demonstrate how the break up of the heteroclinic lines after the primary bifurcation leads to a complicated intersection of stable and unstable manifolds forming a chaotic web which is in turn correlated with the spatial appearance of the dynamo.