3,011 research outputs found
Seismicity along the western part of the Eurasia-Nubian plate boundary
The seismicity along the western part of the Eurasia-Nubian plate boundary is characterized by a very complex
pattern. In average, the motion is transtensional in the Azores, dextral along the Gloria transform zone and convergent
between the SW Portuguese Atlantic margin and the Ibero-Maghrebian zone. To constraint the factors
controlling the seismicity, we provide a new seismotectonic synthesis using several significant seismic events. We
show that the studied area can be divided into six different regions, each one characterized by a coherent seismicity
pattern. The total seismic moment tensor and the average slip velocities are provided for each one of them. To
understand the spatial distribution of the seismicity, we compute for each event from the focal mechanism the slip
vector and compare it to the relative velocity between the Eurasia and Nubia plates, deduced from global kinematics
models. Despite local departures in the Alboran Sea and in the proximity of the Mid Atlantic Ridge, we find
a good correlation between these two independent vectors sets. Quantitatively, the slip velocities display a linear,
non-affine correlation with the norms of the relative kinematics velocities. The norm of the slip velocities seems to
also depend on the tectonic regime and on the morphology of the plates’ boundary
Variational Principle for Mixed Classical-Quantum Systems
An extended variational principle providing the equations of motion for a
system consisting of interacting classical, quasiclassical and quantum
components is presented, and applied to the model of bilinear coupling. The
relevant dynamical variables are expressed in the form of a quantum state
vector which includes the action of the classical subsystem in its phase
factor. It is shown that the statistical ensemble of Brownian state vectors for
a quantum particle in a classical thermal environment can be described by a
density matrix evolving according to a nonlinear quantum Fokker-Planck
equation. Exact solutions of this equation are obtained for a two-level system
in the limit of high temperatures, considering both stationary and
nonstationary initial states. A treatment of the common time shared by the
quantum system and its classical environment, as a collective variable rather
than as a parameter, is presented in the Appendix.Comment: 16 pages, LaTex; added Figure 2 and Figure
Dissipative dynamics of a two - level system resonantly coupled to a harmonic mode
We propose an approximation scheme to describe the dynamics of the spin-boson
model when the spectral density of the environment shows a peak at a
characteristic frequency which can be very close (or even equal) to
the spin Zeeman frequency . Mapping the problem onto a two-state system
(TSS) coupled to a harmonic oscillator (HO) with frequency we show
that the representation of displaced HO states provides an appropriate basis to
truncate the Hilbert space of the TSS-HO system and therefore a better picture
of the system dynamics. We derive an effective Hamiltonian for the TSS-HO
system, and show it furnishes a very good approximation for the system dynamics
even when its two subsystems are moderately coupled. Finally, assuming the
regime of weak HO-bath coupling and low temperatures, we are able to
analytically evaluate the dissipative TSS dynamics.Comment: 12 pages, 2 figures; V2: Published versio
Quantum dynamics in single spin measurement
We study the quantum dynamics of a model for the single-spin measurement in
magnetic-resonance force microscopy. We consider an oscillating driven
cantilever coupled with the magnetic moment of the sample. Then, the cantilever
is damped through an external bath and its readout is provided by a radiation
field. Conditions for reliable measurements will be discussed.Comment: 7 pages, 3 figure
Conservation law for distributed entanglement of formation and quantum discord
We present a direct relation, based upon a monogamic principle, between
entanglement of formation (EOF) and quantum discord (QD), showing how they are
distributed in an arbitrary tripartite pure system. By extending it to a
paradigmatic situation of a bipartite system coupled to an environment, we
demonstrate that the EOF and the QD obey a conservation relation. By means of
this relation we show that in the deterministic quantum computer with one pure
qubit the protocol has the ability to rearrange the EOF and the QD, which
implies that quantum computation can be understood on a different basis as a
coherent dynamics where quantum correlations are distributed between the qubits
of the computer. Furthermore, for a tripartite mixed state we show that the
balance between distributed EOF and QD results in a stronger version of the
strong subadditivity of entropy.Comment: Published versio
Universal Decoherence in Solids
Symmetry implications for the decoherence of quantum oscillations of a
two-state system in a solid are studied. When the oscillation frequency is
small compared to the Debye frequency, the universal lower bound on the
decoherence due to the atomic environment is derived in terms of the
macroscopic parameters of the solid, with no unknown interaction constants.Comment: 4 pages, no figure
Dynamics of topological defects in a spiral: a scenario for the spin-glass phase of cuprates
We propose that the dissipative dynamics of topological defects in a spiral
state is responsible for the transport properties in the spin-glass phase of
cuprates. Using the collective-coordinate method, we show that topological
defects are coupled to a bath of magnetic excitations. By integrating out the
bath degrees of freedom, we find that the dynamical properties of the
topological defects are dissipative. The calculated damping matrix is related
to the in-plane resistivity, which exhibits an anisotropy and linear
temperature dependence in agreement with experimental data.Comment: 4 pages, as publishe
Non-Markovian Dynamics of Quantum Discord
We evaluate the quantum discord dynamics of two qubits in independent and
common non-Markovian environments. We compare the dynamics of entanglement with
that of quantum discord. For independent reservoirs the quantum discord
vanishes only at discrete instants whereas the entanglement can disappear
during a finite time interval. For a common reservoir, quantum discord and
entanglement can behave very differently with sudden birth of the former but
not of the latter. Furthermore, in this case the quantum discord dynamics
presents sudden changes in the derivative of its time evolution which is
evidenced by the presence of kinks in its behavior at discrete instants of
time.Comment: 6 pages, 4 figure
Improving the Knowledge on Seismogenic Sources in the Lower Tagus Valley for Seismic Hazard Purposes
The Lower Tagus Valley, that includes the metropolitan area of Lisbon, has been struck by several earthquakes which produced significant material damage and loss of lives. Their exact location remains unknown. Our goal is to shed some light into the seismogenic sources in the area using seismic reflection and geological data. In areas with no seismic coverage, potential-field data interpretation was carried out. Seismicity was overlaid to the potential seismogenic structures and high-resolution data was acquired in order to confirm which structures have been active into the Quaternary. Three major fault-zones affecting the Neogene were identified: V. F. Xira, Samora-Alcochete and Pinhal Novo. For the first fault, strong evidences suggest it is active. The other two fault-zones and other structures previously unknown can be correlated with several epicentres. Empirical relationships between maximum moment magnitude and fault area indicate that MW > 6.5 earthquakes can be expected for the larger structures
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