Most recent highlights from EPL:
Propagating waves in bounded elastic media: Transition from standing waves to anguilliform kinematics1
by Sophie Ramananarivo et al.
Confined geometries usually involve reflected waves interacting together to form a spatially stationary pattern. A recent study on bio-locomotion, however, has reported that propagating wave kinematics can naturally emerge in a forced elastic rod, even with boundary conditions involving significant reflections. It has been shown that this particular behavior is observed only in the presence of strong damping. Based on those observations, this study aims at giving a quantitative description of the mechanism involved to prevent the build-up of standing waves and generate traveling solutions. The question is discussed here in the framework of handmade artificial swimmers as an example of practical application but we believe that its potential is beyond this scope.
The quantum anomalous Hall effect in a topological insulator thin film — The role of magnetic disorder2
by Shu-guang Cheng.
The quantum anomalous Hall (QAH) effect in a topological insulator thin film is investigated theoretically by using the nonequilibrium Green function method. We use the tight-binding model of a six-terminal topological thin-film Hall bar and focus on the effects of magnetic disorder and electron-hole asymmetry. In the QAH regime, when disorder is considered the electron transmissions contributed by the edge states are suppressed and other transmissions are enhanced. Under proper disorder strength, within an interval around the neutral point, the Hall conductance σxy is quantized (e2/h) and the longitudinal conductance σxy is zero. At the interval edges, σxy decreases quickly and σxy peaks. With the presence of electron-hole asymmetry, the plateau of σxy shifts because the neutral point is shifted. These results are in good agreement with the experimental reports (Chang C. Z. et al., Science 340 (2013) 167). When the distance between longitudinal terminals is longer, σxy peaks are lower and σxy drops sharply at the plateau edge. The effect of a second type of disorder is studied and similar results are obtained.
Detangling flat bands into Fano lattices3
by Sergej Flach et al.
Macroscopically degenerate flat bands (FB) in periodic lattices host compact localized states which appear due to destructive interference and local symmetry. Interference provides a deep connection between the existence of flat band states (FBS) and the appearance of Fano resonances for wave propagation. We introduce generic transformations detangling FBS and dispersive states into lattices of Fano defects. Inverting the transformation, we generate a continuum of FB models. Our procedure allows us to systematically treat perturbations such as disorder and explain the emergence of energy-dependent localization length scaling in terms of Fano resonances.
Overarching framework for data-based modelling4
by Björn Schelter et al.
One of the main modelling paradigms for complex physical systems are networks. When estimating the network structure from measured signals, typically several assumptions such as stationarity are made in the estimation process. Violating these assumptions renders standard analysis techniques fruitless. We here propose a framework to estimate the network structure from measurements of arbitrary non-linear, non-stationary, stochastic processes. To this end, we propose a rigorous mathematical theory that underlies this framework. Based on this theory, we present a highly efficient algorithm and the corresponding statistics that are immediately sensibly applicable to measured signals. We demonstrate its performance in a simulation study. In experiments of transitions between vigilance stages in rodents, we infer small network structures with complex, time-dependent interactions; this suggests biomarkers for such transitions, the key to understand and diagnose numerous diseases such as dementia. We argue that the suggested framework combines features that other approaches followed so far lack.
Fusion yield rate recovery by escaping hot-spot fast ions in the neighboring fuel layer5
by Xian-Zhu Tang et al.
Free-streaming loss by fast ions can deplete the tail population in the hot spot of an inertial confinement fusion (ICF) target. Escaping fast ions in the neighboring fuel layer of a cryogenic target can produce a surplus of fast ions locally. In contrast to the Knudsen layer effect that reduces hot-spot fusion reactivity due to tail ion depletion, the inverse Knudsen layer effect increases fusion reactivity in the neighboring fuel layer. In the case of a burning ICF target in the presence of significant hydrodynamic mix which aggravates the Knudsen layer effect, the yield recovery largely compensates for the yield reduction. For mix-dominated sub-ignition targets, the yield reduction is the dominant process.
- Sophie Ramananarivo et al. 2014. Propagating waves in bounded elastic media: Transition from standing waves to anguilliform kinematics. EPL, 105, 54003. DOI: 10.1209/0295-5075/105/54003 [↩]
- Shu-guang Cheng. 2014. The quantum anomalous Hall effect in a topological insulator thin film —T he role of magnetic disorder. EPL, 105, 57004. DOI: 10.1209/0295-5075/105/57004 [↩]
- Sergej Flach et al. 2014. Detangling flat bands into Fano lattices. EPL, 105, 30001. DOI: 10.1209/0295-5075/105/30001 [↩]
- Björn Schelter et al. 2014. Overarching framework for data-based modelling. EPL, 105, 30004. DOI: 10.1209/0295-5075/105/30004 [↩]
- Xian-Zhu Tang et al. 2014. Fusion yield rate recovery by escaping hot-spot fast ions in the neighboring fuel layer. EPL, 105, 32001. DOI: 10.1209/0295-5075/105/32001 [↩]