476 research outputs found
Extended sources of the main events of the Umbria-Marche (1997) seismic sequence inverted from geophysical data
The three largest events of the 1997 Umbria-Marche (Italy) sequence occurred on September 26, 1997 at 00:33
GMT (Event 1, MW=5.7) and 09:40 GMT (Event 2, MW=6.0) in the Colfiorito area and on the October 14, 1997
at 15:23 (Event 3, MW=5.6) in the Sellano area. The availability of different sets of geodetic and seismological
data allowed several studies to characterize the extended sources of events 1-3. In this work, I review some of
the studies that obtain the properties of the seismic sources by inversion of available data. Generally these studies
assume the seismic sources as dislocations or distributions of equivalent point sources in elastic half-spaces.
Following their chronological order, they model increasing complexities of the sources by using an increasing
number of data. Some of the differences between results obtained, such as the top edge depth estimates, are
shown to be due to the different approaches used. Commonly a 1-D crustal model is used in inverting strongmotion
data. Instead homogeneous elastic half-spaces are mainly assumed in inverting geodetic data to obtain
the three main sources of the 1997 Umbria-Marche sequence. Assuming the same crustal structure is important
to make comparable results obtained analyzing seismological data or geodetic data separately, as it has been
done till now for this sequence
Wang-Landau Algorithm: a Theoretical Analysis of the Saturation of the Error
In this work we present a theoretical analysis of the convergence of the
Wang-Landau algorithm [Phys. Rev. Lett. 86, 2050 (2001)] which was introduced
years ago to calculate the density of states in statistical models. We study
the dynamical behavior of the error in the calculation of the density of
states.We conclude that the source of the saturation of the error is due to the
decreasing variations of the refinement parameter. To overcome this limitation,
we present an analytical treatment in which the refinement parameter is scaled
down as a power law instead of exponentially. An extension of the analysis to
the N-fold way variation of the method is also discussed.Comment: 7 pages, 5 figure
The quasi-static approximation of the spring-slider motion
International audienceThe spring-slider is a simple dynamical system consisting in a massive block sliding with friction and pulled through a spring at a given velocity. Understanding the block motion is fundamental for studying more complex phenomena of frictional sliding, such as the seismogenic fault motion. We analyze the dynamical properties of the system, subject to rate- and state-dependent friction laws and forced at a constant load velocity. In particular we study the limits within which the quasi-static model can be used. The latter model approximates the complete model of the system without taking into account the inertia effects. The system parameters are here found to be grouped into three characteristic times of the three dynamics present in the complete model. A necessary condition for the quasi-static approximation to hold is that the characteristic time of the inertial equation is much smaller than the other two characteristic times. We have studied a modification of one of the classical forms of the rate- and state-dependent friction laws. Subsequently we have developed a linear analysis in the neighbourhood of the equilibrium point of the system. For the quasi-static model we rigorously found, by means of a nonlinear analysis, a supercritical Hopf bifurcation, a dynamical property of the complete model. The classical form of the friction laws can be obtained as a particular case of the one we considered, but fails to preserve the Hopf bifurcation in the quasi-static approximation. We conclude that to have a good quasi-static approximation of the system, even in nonlinear conditions, the form of the friction laws considered is a critical factor
Modeling instantaneous dynamic triggering in a 3–D fault system: application to the June 2000 South Iceland seismic sequence
We present a model of seismogenesis on an extended 3–D fault subjected to the external perturbations of coseismic stress changes due to an earthquake occurred on another fault (the causative fault). As an application, we consider the spatio–temporal stress distribution produced by the MS = 6.6 June 17, 2000 mainshock in the South Iceland Seismic Zone (SISZ) on the Hvalhnúkur fault. The latter is located nearly 64 km from the causative fault and failed 26 s after the mainshock with an estimated magnitude Mw  [5, 5.5], providing an example of instantaneous dynamic triggering. The stress perturbations are computed by means of a discrete wavenumber and reflectivity code. The response of the perturbed fault is then analyzed solving the truly 3–D, fully dynamic (or spontaneous) problem, accounting for crustal stratification. In a previous study, the response of the Hvalhnúkur fault was analyzed by using a spring–slider fault model, comparing the estimated perturbed failure time with the observed origin time. In addition to the perturbed failure time, the present model can provide numerical estimates of many other dynamical features of the triggered event that can be compared with available observations: the rupture history of the whole fault plane and its final extension and the seismic moment of the 26 s event. We show the key differences existing between a mass–spring model and the present extended fault model, in particular we show the essential role of the load exerted by the other slipping points of the fault. By considering both rate– and state–dependent laws and non–linear slip–dependent law, we show how the dynamics of the 26 s fault strongly depends on the assumed constitutive law and initial stress conditions. In the case of rate– and state– dependent governing laws, assuming an initial effective normal stress distribution which is suitable for the SISZ and consistent with previously stated conditions of instantaneous dynamic triggering of the Hvalhnúkur fault, we obtain results in general agreement with observations
Climacostol reduces tumour progression in a mouse model of melanoma via the p53-dependent intrinsic apoptotic programme
Climacostol, a compound produced by the ciliated protozoan Climacostomum virens, displayed cytotoxic properties in vitro. This study demonstrates that it has anti-tumour potential. Climacostol caused a reduction of viability/proliferation of B16-F10 mouse melanoma cells, a rapidly occurring DNA damage, and induced the intrinsic apoptotic pathway characterised by the dissipation of the mitochondrial membrane potential, the translocation of Bax to the mitochondria, the release of Cytochrome c from the mitochondria, and the activation of Caspase 9-dependent cleavage of Caspase 3. The apoptotic mechanism of climacostol was found to rely on the up-regulation of p53 and its targets Noxa and Puma. In vivo analysis of B16-F10 allografts revealed a persistent inhibition of tumour growth rate when melanomas were treated with intra-tumoural injections of climacostol. In addition, it significantly improved the survival of transplanted mice, decreased tumour weight, induced a remarkable reduction of viable cells inside the tumour, activated apoptosis and up-regulated the p53 signalling network. Importantly, climacostol toxicity was more selective against tumour than non-tumour cells. The anti-tumour properties of climacostol and the molecular events associated with its action indicate that it is a powerful agent that may be considered for the design of pro-apoptotic drugs for melanoma therapy
Evidences of instantaneous dynamic triggering during the seismic sequence of year 2000 in South Iceland
We analyze the coseismic stress perturbation during the June 17th, 2000 South Iceland seismic sequence; the mainshock (MS 6.6) was followed by three large events within few tens of seconds (8, 26, and 30 s, respectively) located within 80 km. The aim of this paper is to investigate short-term fault interaction and instantaneous triggering. This happens when a fault perturbed by a stress change fails before the end of the transient stress perturbation. We compute the shear, normal, and Coulomb stress changes as functions of time in a stratified elastic half-space by using discrete wavenumber and reflectivity methods. We calculate dynamic stresses caused by the mainshock at the hypocenters of these three subsequent events. Our numerical results show that the onset of the last two events is slightly delayed with respect to the arrival time of the second positive peak of Coulomb stress variation, while the first event occurred after the first positive stress peak. We have also analysed the response of a spring-slider system representing a fault governed by a rate- and state-dependent friction law, perturbed by shear and normal stress variations caused by the mainshock. The fault response to the computed stress perturbations is always clock advanced. We have found suitable constitutive parameters of the modelled fault that allow the instantaneous dynamic triggering of these three earthquakes. If the initial sliding velocity is comparable with the tectonic loading velocity, we obtained failure times close to the observed origin times for low values of the initial effective normal stress
Aseismic deformation associated with an earthquake swarm in the northern Apennines (Italy)
Analyzing the displacement time series from continuous GPS (cGPS) with an Independent Component Analysis, we detect a transient deformation signal that correlates both in space and time with a seismic swarm activity (maximum M_w=3.69 ± 0.09) occurred in the hanging wall of the Altotiberina normal fault (Northern Apennines, Italy) in 2013–2014. The geodetic transient lasted ∼6 months and produced a NW-SE trending extension of ∼5.3 mm, consistent with the regional tectonic regime. The seismicity and the geodetic signal are consistent with slip on two splay faults in the Altotiberina fault (ATF) hanging wall. Comparing the seismic moment associated with the geodetic transient and the seismic events, we observe that seismicity accounts for only a fraction of the measured geodetic deformation. The combined seismic and aseismic slip decreased the Coulomb stress on the locked shallow portion of the ATF, while the transition region to the creeping section has been loaded
Thermal fluctuations of an interface near a contact line
The effect of thermal fluctuations near a contact line of a liquid interface
partially wetting an impenetrable substrate is studied analytically and
numerically. Promoting both the interface profile and the contact line position
to random variables, we explore the equilibrium properties of the corresponding
fluctuating contact line problem based on an interfacial Hamiltonian involving
a "contact" binding potential. To facilitate an analytical treatment we
consider the case of a one-dimensional interface. The effective boundary
condition at the contact line is determined by a dimensionless parameter that
encodes the relative importance of thermal energy and substrate energy at the
microscopic scale. We find that this parameter controls the transition from a
partially wetting to a pseudo-partial wetting state, the latter being
characterized by a thin prewetting film of fixed thickness. In the partial
wetting regime, instead, the profile typically approaches the substrate via an
exponentially thinning prewetting film. We show that, independently of the
physics at the microscopic scale, Young's angle is recovered sufficiently far
from the substrate. The fluctuations of the interface and of the contact line
give rise to an effective disjoining pressure, exponentially decreasing with
height. Fluctuations therefore provide a regularization of the singular contact
forces occurring in the corresponding deterministic problem.Comment: 40 Pages, 12 Figure
Ricci-flat Metrics with U(1) Action and the Dirichlet Boundary-value Problem in Riemannian Quantum Gravity and Isoperimetric Inequalities
The Dirichlet boundary-value problem and isoperimetric inequalities for
positive definite regular solutions of the vacuum Einstein equations are
studied in arbitrary dimensions for the class of metrics with boundaries
admitting a U(1) action. We show that in the case of non-trivial bundles
Taub-Bolt infillings are double-valued whereas Taub-Nut and Eguchi-Hanson
infillings are unique. In the case of trivial bundles, there are two
Schwarzschild infillings in arbitrary dimensions. The condition of whether a
particular type of filling in is possible can be expressed as a limitation on
squashing through a functional dependence on dimension in each case. The case
of the Eguchi-Hanson metric is solved in arbitrary dimension. The Taub-Nut and
the Taub-Bolt are solved in four dimensions and methods for arbitrary dimension
are delineated. For the case of Schwarzschild, analytic formulae for the two
infilling black hole masses in arbitrary dimension have been obtained. This
should facilitate the study of black hole dynamics/thermodynamics in higher
dimensions. We found that all infilling solutions are convex. Thus convexity of
the boundary does not guarantee uniqueness of the infilling. Isoperimetric
inequalities involving the volume of the boundary and the volume of the
infilling solutions are then investigated. In particular, the analogues of
Minkowski's celebrated inequality in flat space are found and discussed
providing insight into the geometric nature of these Ricci-flat spaces.Comment: 40 pages, 3 figure
Linking data and BPMN processes to achieve executable models
We describe a formally well founded approach to link data and processes conceptually, based on adopting UML class diagrams to represent data, and BPMN to represent the process. The UML class diagram together with a set of additional process variables, called Artifact, form the information model of the process. All activities of the BPMN process refer to such an information model by means of OCL operation contracts. We show that the resulting semantics while abstract is fully executable. We also provide an implementation of the executor.Peer ReviewedPostprint (author's final draft
- …