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- Klaus Kroy, Gerd Sauermann, Hans J Herrmann
- Physical review letters
- 2002

We propose a minimal model for aeolian sand dunes. It combines an analytical description of the turbulent wind velocity field above the dune with a continuum saltation model that allows for saturation transients in the sand flux. The model provides a qualitative understanding of important features of real dunes, such as their longitudinal shape and aspect… (More)

We derive a phenomenological continuum saltation model for aeolian sand transport that can serve as an efficient tool for geomorphological applications. The coupled differential equations for the average density and velocity of sand in the saltation layer reproduce both known equilibrium relations for the sand flux and the time evolution of the sand flux as… (More)

- Orencio Durán, Hans J Herrmann
- Physical review letters
- 2006

Vegetation is the most common and most reliable stabilizer of loose soil or sand. This ancient technique is for the first time cast into a set of equations of motion describing the competition between aeolian sand transport and vegetation growth. Our set of equations is then applied to study quantitatively the transition between barchans and parabolic dunes… (More)

- Christian M. Schneider, André A. Moreira, José S. Andrade, Shlomo Havlin, Hans J. Herrmann
- Proceedings of the National Academy of Sciences…
- 2011

Terrorist attacks on transportation networks have traumatized modern societies. With a single blast, it has become possible to paralyze airline traffic, electric power supply, ground transportation or Internet communication. How and at which cost can one restructure the network such that it will become more robust against a malicious attack? We introduce a… (More)

Transverse dunes appear in regions of mainly unidirectional wind and high sand availability. A dune model is extended to two dimensional calculation of the shear stress. It is applied to simulate dynamics and morphology of transverse dunes which seem to reach lateral invariance and do not stop growing. Hence, simulations of two dimensional dune fields have… (More)

- Pedro G Lind, Marta C González, Hans J Herrmann
- Physical review. E, Statistical, nonlinear, and…
- 2005

We investigate the clustering coefficient in bipartite networks where cycles of size three are absent and therefore the standard definition of clustering coefficient cannot be used. Instead, we use another coefficient given by the fraction of cycles with size four, showing that both coefficients yield the same clustering properties. The new coefficient is… (More)

Strongly correlated electrons on an Apollonian network are studied using the Hubbard model. Ground-state and thermodynamic properties, including specific heat, magnetic susceptibility, spin-spin correlation function, double occupancy, and one-electron transfer, are evaluated applying direct diagonalization and quantum Monte Carlo techniques. In the… (More)

- E J R Parteli, O Durán, H J Herrmann
- Physical review. E, Statistical, nonlinear, and…
- 2007

Barchans are dunes of high mobility which have a crescent shape and propagate under conditions of unidirectional wind. However, sand dunes only appear above a critical size, which scales with the saturation distance of the sand flux [P. Hersen, S. Douady, and B. Andreotti, Phys. Rev. Lett. 89, 264301 (2002); B. Andreotti, P. Claudin, and S. Douady, Eur.… (More)

- Noam Levin, Haim Tsoar, Luis P. Maia, Vanda Claudino, Hans Herrmann
- 2006

The changes in color of sand dunes from white to yellow or red is often interpreted to signify their age or their source materials. In this study we demonstrate the effect seasonal inter-dune freshwater ponds have on the bleaching of the color of sand dunes by iron reduction in the anaerobic conditions they create. By combining spectral measurements of… (More)

- Lucilla de Arcangelis, Carla Perrone-Capano, Hans J Herrmann
- Physical review letters
- 2006

Networks of living neurons exhibit an avalanche mode of activity, experimentally found in organotypic cultures. Here we present a model that is based on self-organized criticality and takes into account brain plasticity, which is able to reproduce the spectrum of electroencephalograms (EEG). The model consists of an electrical network with threshold firing… (More)