R. Preuss

Anomalous dynamics of cell migration

Cell movement—for example, during embryogenesis or tumor metastasis—is a complex dynamical process resulting from an intricate interplay of multiple components of the cellular migration machinery. At first sight, the paths of migrating cells resemble those of thermally driven Brownian particles. However, cell migration is an active biological process putting a characterization in terms of normal Brownian motion into question. By analyzing the trajectories of wild-type and mutated epithelial (transformed Madin–Darby canine kidney) cells, we show experimentally that anomalous dynamics characterizes cell migration. A superdiffusive increase of the mean squared displacement, non-Gaussian spatial probability distributions, and power-law decays of the velocity autocorrelations is the basis for this interpretation. Almost all results can be explained with a fractional Klein–Kramers equation allowing the quantitative classification of cell migration by a few parameters. Thereby, it discloses the influence and relative importance of individual components of the cellular migration apparatus to the behavior of the cell as a whole.

Quasiparticle Dispersion of the 2D Hubbard Model: From an Insulator to a Metal

On the basis of Quantum-Monte-Carlo results the evolution of the spectral weight

New fit formulae for the sputtering yield

A(\vec k, \omega)

Spectral properties of the one-dimensional Hubbard model.

of the two-dimensional Hubbard model is studied from insulating to metallic behavior. As observed in recent photoemission experiments for cuprates, the electronic excitations display essentially doping-independent features: a quasiparticle-like dispersive narrow band of width of the order of the exchange interaction

Physical model assessment of the energy confinement time scaling in stellarators

J

International Stellarator/Heliotron Database progress on high-beta confinement and operational boundaries

and a broad valence- and conduction-band background. The continuous evolution is traced back to one and the same many-body origin: the doping-dependent antiferromagnetic spin-spin correlation.

A parallel Grad-Shafranov solver for real-time control of tokamak plasmas

New fit formulae for the energy and angular dependencies of the sputtering yield are proposed. Though they are empirical they give a better description of yield data, especially near the threshold for the energy dependence and at low mass ratios for the angular dependence. The new formula for the energy dependence was applied to determine threshold energies for different mass ratios.

Evaluation of chemical erosion data for carbon materials at high ion fluxes using Bayesian probability theory

The spectral properties of the 1-D Hubbard model are obtained from quantum Monte Carlo simulations using the maximum entropy method. The one-particle excitations are characterized by dispersive cosine-like bands. Velocities for spin- and charge excitations are obtained that lead to a conformal charge c=0.98 +/- 0.05 for the largest system simulated (N=84). An exact sum-rule for the spin-excitations is fulfilled accurately with deviations of at most 10% only around 2 kF.

Dimensionally exact form-free energy confinement scaling in W7-AS

The International Stellarator Confinement Database (ISCDB) is a joint effort of the helical device community. It is publicly available at http://www.ipp.mpg.de/ISS and http://iscdb.nifs.ac.jp. The validity of physics models is investigated employing ISCDB data. Bayesian model comparison shows differences in the confinement scaling of data subgroups. Theory-based assessment of pure neoclassical transport regimes, however, indicates scalability which is supported by experimental results in specific W7-AS scenarios. Therefore, neoclassical simulations are employed for predictive purposes in W7-X, accounting for effects due to power deposition, plasma profiles and the ambipolar radial electric field. Neoclassical case studies for W7-X are presented as examples for the neoclassical predictions to be considered as an upper limit of plasma performance.

ASSESSMENT OF GLOBAL STELLARATOR CONFINEMENT: STATUS OF THE INTERNATIONAL STELLARATOR CONFINEMENT DATABASE

The International Stellarator/Heliotron Confinement Database was extended by high-β data compiled from the Large Helical System (LHD) and the W7-AS Stellarator. The main purpose is to enhance the basis for extrapolation of the global confinement properties to the reactor regime. The high-β configurations and experimental achievements in both devices are briefly described. The impact of beta on the configuration parameters and the global confinement is discussed. In particular, the confinement data in the high-β regime are compared with the ISS95 and ISS04 scaling laws which were derived from a database including relatively few high-β cases. In addition, a Bayesian model comparison approach is used to test scaling predictions derived from basic confinement models. Unlike in tokamaks, the operational boundaries in stellarators and helical systems are determined by the available heating power and confinement properties rather than by disruptive stability or density limits. The role of a pressure induced equilibrium limit is discussed in particular. An attempt is made to compare the high-β data with tokamak confinement and with operational boundaries observed in tokamaks. Further extensions of the database by parameters characterizing stability and local transport properties are proposed.