Phase diagram of the random field Ising model on the Bethe lattice

The phase diagram of the random field Ising model on the Bethe lattice with a symmetric dichotomous random field is closely investigated with respect to the transition between the ferromagnetic and paramagnetic regime. Refining arguments of Bleher, Ruiz and Zagrebnov [J. Stat. Phys. 93, 33 (1998)] an exact upper bound for the existence of a unique paramagnetic phase is found which considerably improves the earlier results. Several numerical estimates of transition lines between a ferromagnetic and a paramagnetic regime are presented. The obtained results do not coincide with a lower bound for the onset of ferromagnetism proposed by Bruinsma [Phys. Rev. B 30, 289 (1984)]. If the latter one proves correct this would hint to a region of coexistence of stable ferromagnetic phases and a stable paramagnetic phase.Comment: Article has been condensed and reorganized; Figs 3,5,6 merged; Fig 4 omitted; Some discussion added at end of Sec. III; 9 pages, 5 figs, RevTeX4, AMSTe

The randomly driven Ising ferromagnet, Part I: General formalism and mean field theory

We consider the behavior of an Ising ferromagnet obeying the Glauber dynamics under the influence of a fast switching, random external field. After introducing a general formalism for describing such systems, we consider here the mean-field theory. A novel type of first order phase transition related to spontaneous symmetry breaking and dynamic freezing is found. The non-equilibrium stationary state has a complex structure, which changes as a function of parameters from a singular-continuous distribution with Euclidean or fractal support to an absolutely continuous one.Comment: 12 pages REVTeX/LaTeX format, 12 eps/ps figures. Submitted to Journal of Physics

Implications of grain size evolution on the seismic structure of the oceanic upper mantle

Author Posting. © Elsevier B.V., 2009. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Earth and Planetary Science Letters 282 (2009): 178-189, doi:10.1016/j.epsl.2009.03.014.We construct a 1-D steady-state channel flow model for grain size evolution in the oceanic upper mantle using a composite diffusion-dislocation creep rheology. Grain size evolution is calculated assuming that grain size is controlled by a competition between dynamic recrystallization and grain growth. Applying this grain size evolution model to the oceanic upper mantle we calculate grain size as a function of depth, seafloor age, and mantle water content. The resulting grain size structure is used to predict shear wave velocity (VS) and seismic quality factor (Q). For a plate age of 60 Myr and an olivine water content of 1000 H/106Si, we find that grain size reaches a minimum of ~15 mm at ~150 km depth and then increases to ~20–30 mm at a depth of 400 km. This grain size structure produces a good fit to the low seismic shear wave velocity zone (LVZ) in oceanic upper mantle observed by surface wave studies assuming that the influence of hydrogen on anelastic behavior is similar to that observed for steady state creep. Further it predicts a viscosity of ~1019 Pa s at 150 km depth and dislocation creep to be the dominant deformation mechanism throughout the oceanic upper mantle, consistent with geophysical observations. We predict larger grain sizes than proposed in recent studies, in which the LVZ was explained by a dry mantle and a minimum grain size of 1 mm. However, we show that for a 1 mm grain size, diffusion creep is the dominant deformation mechanism above 100– 200 km depth, inconsistent with abundant observations of seismic anisotropy from surface wave studies. We therefore conclude that a combination of grain size evolution and a hydrated upper mantle is the most likely explanation for both the isotropic and anisotropic seismic structure of the oceanic upper mantle. Our results also suggest that melt extraction from the mantle will be significantly more efficient than predicted in previous modeling studies that assumed grain sizes of ~1 mm.Funding for this research was provided by NSF Grants EAR-06-52707 and EAR-07-38880

A vibrissa-inspired highly flexible tactile sensor: scanning 3D object surfaces providing tactile images

Just as the sense of touch complements vision in various species, several robots could benefit from advanced tactile sensors, in particular when operating under poor visibility. A prominent tactile sense organ, frequently serving as a natural paragon for developing tactile sensors, is the vibrissae of, e.g., rats. Within this study, we present a vibrissa-inspired sensor concept for 3D object scanning and reconstruction to be exemplarily used in mobile robots. The setup consists of a highly flexible rod attached to a 3D force-torque transducer (measuring device). The scanning process is realized by translationally shifting the base of the rod relative to the object. Consequently, the rod sweeps over the object’s surface, undergoing large bending deflections. Then, the support reactions at the base of the rod are evaluated for contact localization. Presenting a method of theoretically generating these support reactions, we provide an important basis for future parameter studies. During scanning, lateral slip of the rod is not actively prevented, in contrast to literature. In this way, we demonstrate the suitability of the sensor for passively dragging it on a mobile robot. Experimental scanning sweeps using an artificial vibrissa (steel wire) of length 50 mm and a glass sphere as a test object with a diameter of 60 mm verify the theoretical results and serve as a proof of concept

Rascacielos, en Hamburgo

This project consists of 21 buildings and 1061 flats, and is divided into two units. One of them contains 716 flats, constructed by the «Barets» prefabrication method, and the other 345 flats, for which the «Camus» system has been adopted. Both techniques make use of solid panels of reinforced concrete for partition walls and floorings, and sandwich type panels for the outer walls. The construction of the balconies is noteworthy, which consist of elements hanging from the outer walls by means of overhangs and cables. Another outstanding feature is the variety of plan and elevation designs, which give a dynamic quality to the total aspect of the buildings.<br><br>El conjunto erigido —21 casas con un total de 1.061 viviendas— consta de dos unidades: una de ellas con 716 viviendas, construidas con el sistema de prefabricación «Barets»; y la otra con 345 viviendas, construidas con el sistema «Camus»; ambos sistemas a base de paneles macizos —realizados en hormigón armado— en muros interiores y forjados; y de paneles tipo «Sandwich» en cerramientos exteriores. Digna de mención es la construcción de los balcones, concebidos y realizados como elementos sustentados en el espacio, y colgados de las fachadas, por medio de ménsulas y elementos metálicos. Igualmente cabe destacar la variedad de plantas y alzados y el extraordinario dinamismo y movimiento del conjunto

Rascacielos, en Hamburgo

This project consists of 21 buildings and 1061 flats, and is divided into two units. One of them contains 716 flats, constructed by the «Barets» prefabrication method, and the other 345 flats, for which the «Camus» system has been adopted. Both techniques make use of solid panels of reinforced concrete for partition walls and floorings, and sandwich type panels for the outer walls. The construction of the balconies is noteworthy, which consist of elements hanging from the outer walls by means of overhangs and cables. Another outstanding feature is the variety of plan and elevation designs, which give a dynamic quality to the total aspect of the buildings.El conjunto erigido —21 casas con un total de 1.061 viviendas— consta de dos unidades: una de ellas con 716 viviendas, construidas con el sistema de prefabricación «Barets»; y la otra con 345 viviendas, construidas con el sistema «Camus»; ambos sistemas a base de paneles macizos —realizados en hormigón armado— en muros interiores y forjados; y de paneles tipo «Sandwich» en cerramientos exteriores. Digna de mención es la construcción de los balcones, concebidos y realizados como elementos sustentados en el espacio, y colgados de las fachadas, por medio de ménsulas y elementos metálicos. Igualmente cabe destacar la variedad de plantas y alzados y el extraordinario dinamismo y movimiento del conjunto