1,618 research outputs found
Dielectric breakdown and avalanches at non-equilibrium metal-insulator transitions
Motivated by recent experiments on the finite temperature Mott transition in
VO2 films, we propose a classical coarse-grained dielectric breakdown model
where each degree of freedom represents a nanograin which transitions from
insulator to metal with increasing temperature and voltage at random thresholds
due to quenched disorder. We describe the properties of the resulting
non-equilibrium metal-insulator transition and explain the universal
characteristics of the resistance jump distribution. We predict that by tuning
voltage, another critical point is approached, which separates a phase of
"bolt"-like avalanches from percolation-like ones.Comment: 4 pages, 3 figure
Fault slip-rate variations during crustal-scale strain localisation, central Italy
Rates of plate motion are generally uniform over 10–102 Myrs timescales. Faults between tectonic plates might, therefore, be expected to show temporally-uniform slip-rates if the same number of faults remain active. For an extending region of the Eurasia-Africa plate boundary, Italy, finite throw values (vertical component of the slip) for seismogenic normal faults are less than that predicted when recent throw-rates are extrapolated over the fault lifetimes. The effect correlates with distance from the fault system tips and demonstrates that the slip-rates on centrally-located faults have increased with time. Neighbouring normal faults were active in the Quaternary but show no signs of surface faulting during the latest Pleistocene to Holocene. Death of these faults has provided the extra strain per unit time to drive the increased slip-rates measured on other faults. Thus, fault interaction and death modify slip-rates and seismic hazards associated with plate tectonics
A COMPARATIVE MORPHOLOGICAL STUDY OF THE KOS-NISYROS-TILOS VOLCANOSEDIMENTARY BASINS
A swath bathymetric map of Kos-Nisyros-Tilos Volcanic field was created with 50m grid interval, with 10 m isobaths at a scale 1:100.000 using SEABEAM 1180 (180 kHz) multibeam system for depths 500m. Five basins have been distinguished in the circum-volcanic area of Nisyros: 1)Eastern Kos basin, the larger and deeper one, with an average sea-bottom depth of 630m. Submarine canyons within the basin occur along the southern coastline of Kos cutting the isobaths from 150 up to 400m depth. A shallow crater with relative topography of ±70m has been discovered at the bottom of the basin (600-670m) 2)Western Kos basin with average depth of 520m. The basin is separated from the Eastern Kos Basin by a rise between Yali and Kos at 400m depth. This basin is separated from the Western Nisyros basin by the Kondeliousa rise. 3)The Western Nisyros basin is located between Kondeliousa rise and western Kos platform with depths of 550m. 4)The Southern Nisyros basin constitutes the northern end of the large Karpathos basin which reaches more than 2000m depth towards the south. 5)The Tilos basin with depths of 600m occurs southeast of Nisyros Island, separated from South Nisyros Basin through a rise of less than 400m depth. The Pachia-Pergoussa and Yali-Nisyros basins are shallow structures within the intra-volcanic relief of Nisyros and surrounding islets. The geometrty of each basin is discussed in relation to the volcanic and tectonic structure of the graben between Kos and Tilos.The intensity of the active geodynamic acrtivity is demonstrated by the creation of a volcanic relief of 1400m in the Nisyros volcanic field
Tectonic structure and volcanic centers at the eastern edge of the aegean volcanic arc around Nisyros island
The recent volcanic activity at the eastern edge of the Aegean Volcanic Arc is limited within a neotectonic graben structure which is developed in an E-W general direction between the alpine basement of Kos Island to the north and the alpine basement of Tilos Island to the south. In between the boundary faults of the neotectonic graben there is an extended volcanic area comprising several individual volcanic centers, which penetrate through the thick post-alpine sedimentary deposits of the graben
Bending crystals: Emergence of fractal dislocation structures
We provide a minimal continuum model for mesoscale plasticity, explaining the
cellular dislocation structures observed in deformed crystals. Our dislocation
density tensor evolves from random, smooth initial conditions to form
self-similar structures strikingly similar to those seen experimentally -
reproducing both the fractal morphologies and some features of the scaling of
cell sizes and misorientations analyzed experimentally. Our model provides a
framework for understanding emergent dislocation structures on the mesoscale, a
bridge across a computationally demanding mesoscale gap in the multiscale
modeling program, and a new example of self-similar structure formation in
non-equilibrium systems.Comment: 4 pages, 4 figures, 5 movies (They can be found at
http://www.lassp.cornell.edu/sethna/Plasticity/SelfSimilarity.html .) In
press at Phys. Rev. Let
Beyond power laws: Universality in the average avalanche shape
We report the measurement of multivariable scaling functions for the temporal
average shape of Barkhausen noise avalanches, and show that they are consistent
with the predictions of simple mean-field theories. We bypass the confounding
factors of time-retarded interactions (eddy currents) by measuring thin permal-
loy films, and bypass thresholding effects and amplifier distortions by
applying Wiener deconvolution. We find experimental shapes that are
approximately symmetric, and track the evolution of the scaling function. We
solve a mean- field theory for the magnetization dynamics and calculate the
form of the scaling function in the presence of a demagnetizing field and a
finite field ramp-rate, yielding quantitative agreement with the experiment.Comment: 13 pages, 14 figure
Topological phases and topological entropy of two-dimensional systems with finite correlation length
We elucidate the topological features of the entanglement entropy of a region
in two dimensional quantum systems in a topological phase with a finite
correlation length . Firstly, we suggest that simpler reduced quantities,
related to the von Neumann entropy, could be defined to compute the topological
entropy. We use our methods to compute the entanglement entropy for the ground
state wave function of a quantum eight-vertex model in its topological phase,
and show that a finite correlation length adds corrections of the same order as
the topological entropy which come from sharp features of the boundary of the
region under study. We also calculate the topological entropy for the ground
state of the quantum dimer model on a triangular lattice by using a mapping to
a loop model. The topological entropy of the state is determined by loop
configurations with a non-trivial winding number around the region under study.
Finally, we consider extensions of the Kitaev wave function, which incorporate
the effects of electric and magnetic charge fluctuations, and use it to
investigate the stability of the topological phase by calculating the
topological entropy.Comment: 17 pages, 4 figures, published versio
Ballistic Spin Injection from Fe into ZnSe and GaAs with a (001), (111), and (110) orientation
We present first-principles calculations of ballistic spin injection in
Fe/GaAs and Fe/ZnSe junctions with orientation (001), (111), and (110). We find
that the symmetry mismatch of the Fe minority-spin states with the
semiconductor conduction states can lead to extremely high spin polarization of
the current through the (001) interface for hot and thermal injection
processes. Such a symmetry mismatch does not exist for the (111) and (110)
interfaces, where smaller spin injection efficiencies are found. The presence
of interface states is found to lower the current spin polarization, both with
and without a Schottky barrier. Finally, a higher bias can also affect the spin
injection efficiency.Comment: 12 pages, 18 figure
Fault specific GIS based seismic hazard maps for the Attica Region, Greece
Traditional seismic hazard assessment methods are based on the historical seismic records for the calculation of an annual probability of exceedance for a particular ground motion level. A new fault specific seismic hazard assessment method is presented, in order to address problems related to the incompleteness and the inhomogeneity of the historical records and to obtain higher spatial resolution of hazard. This method is applied to the region of Attica, which is the most densely populated area in Greece, as nearly half of the country’s population lives in Athens and its surrounding suburbs, in Greater Athens Area. The methodology is based on a database of 22 active faults that could cause damage to Attica in case of seismic rupture. This database provides information about the faults slip rates, lengths and expected magnitudes. The final output of this method are four fault specific seismic hazard maps, showing the recurrence of expected intensities that each locality in the map has been shaken at. These maps offer a high spatial resolution, as they consider the surface geology. Despite the fact that almost half of the Attica region lies on the lowest seismic risk zone according to the official seismic hazard zonation of Greece, different localities have repeatedly experienced strong ground motions during the last 15 kyrs. Moreover, the maximum recurrence for each intensity occurs in different localities across Attica. Highest recurrence for intensity VII (151-156 times over 15 kyrs, or up to 96 year return period) is observed in the central part of the Athens basin. The maximum intensity VIII recurrence (114 times over 15 kyrs, or up to 131 year return period) is observed in the western part of Attica, while the maximum intensity IX (73-77/15kyrs, or 195 year return period) and X (25-29/15kyrs, or 517 year return period) recurrences are observed near the South Alkyonides fault system, which dominates the strong ground motions hazard in the western part of the Attica mainland
- …