Systematic coarse-graining of the dynamics of entangled polymer melts: the road from chemistry to rheology

For optimal processing and design of entangled polymeric materials it is important to establish a rigorous link between the detailed molecular composition of the polymer and the viscoelastic properties of the macroscopic melt. We review current and past computer simulation techniques and critically assess their ability to provide such a link between chemistry and rheology. We distinguish between two classes of coarse-graining levels, which we term coarse-grained molecular dynamics (CGMD) and coarse-grained stochastic dynamics (CGSD). In CGMD the coarse-grained beads are still relatively hard, thus automatically preventing bond crossing. This also implies an upper limit on the number of atoms that can be lumped together and therefore on the longest chain lengths that can be studied. To reach a higher degree of coarse-graining, in CGSD many more atoms are lumped together, leading to relatively soft beads. In that case friction and stochastic forces dominate the interactions, and actions must be undertaken to prevent bond crossing. We also review alternative methods that make use of the tube model of polymer dynamics, by obtaining the entanglement characteristics through a primitive path analysis and by simulation of a primitive chain network. We finally review super-coarse-grained methods in which an entire polymer is represented by a single particle, and comment on ways to include memory effects and transient forces.Comment: Topical review, 31 pages, 10 figure

Cortical Activation Patterns of Cue-Paced Foot Movement in Subacute Stroke Patients

[EN] Limb movement is associated with well defined cortical activation patterns. Structural and functional changes in the brain affect the characteristics of these patterns (strength and topography). Novel strategies for poststroke motor rehabilitation could monitor cortical activity as an additional index of engagement and/or recovery. In this work we analyze differences in cortical activation related to movements of the affected vs. unaffected foot (dorsiflexion). Our results show stronger cortical activation during movements of the affected foot, and stronger responses at the vertex. Online assessment of cortical activation and the experiment described in this work could be added to traditional motor rehabilitation.This work was supported by the FP7 EU Research Project BETTER (247935). The authors are thankful to Silvia Mena del Horno and Javier Bonilla for assistance during the experiments.Belda Lois, JM. (2013). Cortical Activation Patterns of Cue-Paced Foot Movement in Subacute Stroke Patients. Biomedical Engineering / Biomedizinische Technik. 58(1):1-2. https://doi.org/10.1515/bmt-2013-4446S1258

Variational Perturbation Theory for Markov Processes

We develop a convergent variational perturbation theory for conditional probability densities of Markov processes. The power of the theory is illustrated by applying it to the diffusion of a particle in an anharmonic potential.Comment: Author Information under http://www.physik.fu-berlin.de/~kleinert/institution.html Latest update of paper also at http://www.physik.fu-berlin.de/~kleinert/33

The Energy-Momentum Tensor in Noncommutative Gauge Field Models

We discuss the different possibilities of constructing the various energy-momentum tensors for noncommutative gauge field models. We use Jackiw's method in order to get symmetric and gauge invariant stress tensors--at least for commutative gauge field theories. The noncommutative counterparts are analyzed with the same methods. The issues for the noncommutative cases are worked out.Comment: 11 pages, completed reference

Interaction patterns for auditory user interfaces

Presented at the 11th International Conference on Auditory Display (ICAD2005)This paper proposes the use of interaction patterns in the design process of auditory displays in human-computer interaction. To avoid introducing visual concepts in auditory design, a common ground for developing user interfaces without determining their means of representation is proposed. This meta domain allows for the design of user interfaces which can be equally realised in different interaction modalities or multi-modal settings. Although this work focuses on the auditory domain the concept shown is developed keeping in mind that it should be equally applicable in other modalities. A set of mode independent interaction patterns for design in the meta domain are introduced along with their transformation into the auditory domain. A real world application was chosen to evaluate the approach. MS Explorer was analysed, described through the mode independent interaction patterns and transformed into the auditory domain making extensive use of 3D audio rendering techniques. The result, a virtual audio reality version of a file manager, was evaluated with normally sighted persons as well as visually impaired and blind participants showing the feasibility and usability of the approach

Optical Properties of Vanadium in 4H Silicon Carbide for Quantum Technology

We study the optical properties of tetravalent vanadium impurities in 4H silicon carbide (4H SiC). Emission from two crystalline sites is observed at wavelengths of 1.28 \mum and 1.33 \mum, with optical lifetimes of 163 ns and 43 ns. Group theory and ab initio density functional supercell calculations enable unequivocal site assignment and shed light on the spectral features of the defects. We conclude with a brief outlook on applications in quantum photonics

Theory of Spin Fluctuation-Induced Superconductivity Based on a d-p Model. II. -Superconducting State-

The superconducting state of a two-dimensional d-p model is studied from the spin fluctuation point of view by using a strong coupling theory. The fluctuation exchange (FLEX) approximatoin is employed to calculate the spin fluctuations and the superconducting gap functions self-consistently in the optimal- and over-doped regions of hole concentration. The gap function has a symmetry of d_{x^2 - y^2} type and develops below the transition temperature T_c more rapidly than in the BCS model. Its saturation value at the maximum is about 10 T_c. When the spin fluctuation-induced superconductivity is well stabilized at low temperatures in the optimal regime, the imaginary part of the antiferromagnetic spin susceptibility shows a very sharp resonance peak reminiscent of the 41 meV peak observed in the neutron scattering experiment on YBCO. The one-particle spectral density around k=(pi,0) shows sharp quasi-particle peaks followed by dip and hump structures bearing resemblance to the features observed in the angle-resolved photoemission experiment. With increasing doping concentration these features gradually disappear.Comment: 13 pages(LaTeX), 20 eps figure