1,370 research outputs found
Syntectonic crustal melting and high-grade metamorphism in a transpressional regime, Variscan Massif Central, France
Hot collisional orogens are characterized by abundant syn-kinematic granitic magmatism that profoundly affects their tectono-thermal evolutions. Voluminous granitic magmas, emplaced between 360 and 270 Ma, played a visibly important role in the evolution of the Variscan Orogen. In the Limousin region (western Massif Central, France), syntectonic granite plutons are spatially associated with major strike-slip shear zones that merge to the northwest with the South Armorican Shear Zone. This region allowed us to assess the role of magmatism in a hot transpressional orogen. Microstructural data and U/Pb zircon and monazite ages from a mylonitic leucogranite indicate synkinematic emplacement in a dextral transpressional shear zone at 313 ± 4 Ma. Leucogranites are coeval with cordierite-bearing migmatitic gneisses and vertical lenses of leucosome in strike-slip shear zones. We interpret U/Pb monazite ages of 315 ± 4 Ma for the gneisses and 316 ± 2 Ma for the leucosomes as the minimum age of high-grade metamorphism and migmatization respectively. These data suggest a spatial and temporal relationship between transpression, crustal melting, rapid exhumation and magma ascent, and cooling of high-grade metamorphic rocks. Some granites emplaced in the strike-slip shear zone are bounded at their roof by low dip normal faults that strike N-S, perpendicular to the E-W trend of the belt. The abundant crustal magmatism provided a low-viscosity zone that enhanced Variscan orogenic collapse during continued transpression, inducing the development of normal faults in the transpression zone and thrust faults at the front of the collapsed orogen. © 2009 Elsevier B.V. All rights reserved
Space-time laser instabilities in homogeneously broadened dense media
We investigate the space-time dynamics of a homogeneously broadened single-mode laser when local field correction (LFC) is taken into account. We demonstrate that the Maxwell-Bloch equations modified by LFC admit travelling-wave solutions, as when LFC is not taken into account. Their stability is discussed and compared to the case without LFC
Hot electron cooling by acoustic phonons in graphene
We have investigated the energy loss of hot electrons in metallic graphene by
means of GHz noise thermometry at liquid helium temperature. We observe the
electronic temperature T / V at low bias in agreement with the heat diffusion
to the leads described by the Wiedemann-Franz law. We report on
behavior at high bias, which corresponds to a T4 dependence
of the cooling power. This is the signature of a 2D acoustic phonon cooling
mechanism. From a heat equation analysis of the two regimes we extract accurate
values of the electron-acoustic phonon coupling constant in monolayer
graphene. Our measurements point to an important effect of lattice disorder in
the reduction of , not yet considered by theory. Moreover, our study
provides a strong and firm support to the rising field of graphene bolometric
detectors.Comment: 5 figure
Stabilization of space–time laser instability through the finite transverse extension of pumping
We investigate the space–time dynamics of a homogeneously broadened single-mode laser when diffraction is taken into account. It is well known that such a laser displays instability when pumping reaches the second laser threshold. We show that the laser dynamics can be stabilized by pumping in a domain of finite width. The analysis of stationary solutions to the Maxwell–Bloch equations (evanescent waves, travelling waves, localized solutions) allows the stabilization mechanism to be explained
Evidence of Brillouin scattering in an ytterbium-doped double-clad fiber laser
We have designed and performed an experiment that permitted direct observation of Brillouin backscattering in an Yb-doped double-clad fiber laser. Fifteen Brillouin-shifted frequencies were observed for the first time to our knowledge. We clearly demonstrate that stimulated Brillouin scattering is directly responsible for both fast transient dynamics of the laser and reduction of the laser’s pulse width
Instance Space of the Number Partitioning Problem
Within the replica framework we study analytically the instance space of the
number partitioning problem. This classic integer programming problem consists
of partitioning a sequence of N positive real numbers \{a_1, a_2,..., a_N}
(the instance) into two sets such that the absolute value of the difference of
the sums of over the two sets is minimized. We show that there is an
upper bound to the number of perfect partitions (i.e. partitions
for which that difference is zero) and characterize the statistical properties
of the instances for which those partitions exist. In particular, in the case
that the two sets have the same cardinality (balanced partitions) we find
. Moreover, we show that the disordered model resulting from hte
instance space approach can be viewed as a model of replicators where the
random interactions are given by the Hebb rule.Comment: 7 page
Mutual Information of Population Codes and Distance Measures in Probability Space
We studied the mutual information between a stimulus and a large system
consisting of stochastic, statistically independent elements that respond to a
stimulus. The Mutual Information (MI) of the system saturates exponentially
with system size. A theory of the rate of saturation of the MI is developed. We
show that this rate is controlled by a distance function between the response
probabilities induced by different stimuli. This function, which we term the
{\it Confusion Distance} between two probabilities, is related to the Renyi
-Information.Comment: 11 pages, 3 figures, accepted to PR
Dzyaloshinsky-Moriya Anisotropy in the Spin-1/2 Kagom\'e Compound ZnCu(OH)Cl
We report the determination of the Dzyaloshinsky-Moriya interaction, the
dominant magnetic anisotropy term in the \kagome spin-1/2 compound {\herbert}.
Based on the analysis of the high-temperature electron spin resonance (ESR)
spectra, we find its main component K to be perpendicular to the
\kagome planes. Through the temperature dependent ESR line-width we observe a
building up of nearest-neighbor spin-spin correlations below 150 K.Comment: 4 pages, 3 figures, minor modification
Symmetric sequence processing in a recurrent neural network model with a synchronous dynamics
The synchronous dynamics and the stationary states of a recurrent attractor
neural network model with competing synapses between symmetric sequence
processing and Hebbian pattern reconstruction is studied in this work allowing
for the presence of a self-interaction for each unit. Phase diagrams of
stationary states are obtained exhibiting phases of retrieval, symmetric and
period-two cyclic states as well as correlated and frozen-in states, in the
absence of noise. The frozen-in states are destabilised by synaptic noise and
well separated regions of correlated and cyclic states are obtained. Excitatory
or inhibitory self-interactions yield enlarged phases of fixed-point or cyclic
behaviour.Comment: Accepted for publication in Journal of Physics A: Mathematical and
Theoretica
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