2,233 research outputs found
Theory of Lattice and Electronic Fluctuations in Weakly Localized Spin-Peierls Systems
A theoretical approach to the influence of one-dimensional lattice
fluctuations on electronic properties in weakly localized spin-Peierls systems
is proposed using the renormalization group and the functional integral
techniques. The interplay between the renormalization group flow of correlated
electrons and one-dimensional lattice fluctuations is taken into account by the
one-dimensional functional integral method in the adiabatic limit. Calculations
of spin-Peierls precursor effects on response functions are carried out
explicitely and the prediction for the temperature dependent magnetic
susceptibility and nuclear relaxation is compared with available experimental
data for (TMTTF)PF.Comment: 15 pages, 7 Encapsulated Postscript figure
Emergence of nonlinear behavior in the dynamics of ultracold bosons
We study the evolution of a system of interacting ultracold bosons, which
presents nonlinear, chaotic, behaviors in the limit of very large number of
particles. Using the spectral entropy as an indicator of chaos and three
different numerical approaches : Exact diagonalization, truncated Husimi method
and mean-field (Gross-Pitaevskii) approximation, we put into evidence the
destructive impact of quantum noise on the emergence of the nonlinear dynamics
A mathematical model for the Fermi weak interactions
We consider a mathematical model of the Fermi theory of weak interactions as
patterned according to the well-known current-current coupling of quantum
electrodynamics. We focuss on the example of the decay of the muons into
electrons, positrons and neutrinos but other examples are considered in the
same way. We prove that the Hamiltonian describing this model has a ground
state in the fermionic Fock space for a sufficiently small coupling constant.
Furthermore we determine the absolutely continuous spectrum of the Hamiltonian
and by commutator estimates we prove that the spectrum is absolutely continuous
away from a small neighborhood of the thresholds of the free Hamiltonian. For
all these results we do not use any infrared cutoff or infrared regularization
even if fermions with zero mass are involved
Macroscopic limit of a one-dimensional model for aging fluids
We study a one-dimensional equation arising in the multiscale modeling of
some non-Newtonian fluids. At a given shear rate, the equation provides the
instantaneous mesoscopic response of the fluid, allowing to compute the
corresponding stress. In a simple setting, we study the well-posedness of the
equation and next the long-time behavior of its solution. In the limit of a
response of the fluid much faster than the time variations of the ambient shear
rate, we derive some equivalent macroscopic differential equations that relate
the shear rate and the stress. Our analytical conclusions are confronted to
some numerical experiments. The latter quantitatively confirm our derivations
Mathematical analysis of a one-dimensional model for an aging fluid
We study mathematically a system of partial differential equations arising in
the modelling of an aging fluid, a particular class of non Newtonian fluids. We
prove well-posedness of the equations in appropriate functional spaces and
investigate the longtime behaviour of the solutions
Some complexity and approximation results for coupled-tasks scheduling problem according to topology
We consider the makespan minimization coupled-tasks problem in presence of
compatibility constraints with a specified topology. In particular, we focus on
stretched coupled-tasks, i.e. coupled-tasks having the same sub-tasks execution
time and idle time duration. We study several problems in framework of classic
complexity and approximation for which the compatibility graph is bipartite
(star, chain,. . .). In such a context, we design some efficient
polynomial-time approximation algorithms for an intractable scheduling problem
according to some parameters
Kinematics and Mass Modeling of Messier 33: Halpha observations
As part of a long-term project to revisit the kinematics and dynamics of the
large disc galaxies of the Local Group, we present the first deep, wide-field
(42' x 56') 3D-spectroscopic survey of the ionized gas disc of Messier 33.
Fabry-Perot interferometry has been used to map its Ha distribution and
kinematics at unprecedented angular resolution (<3'') and resolving power
(12600), with the 1.6m telescope at the Observatoire du Mont Megantic. The
ionized gas distribution follows a complex, large-scale spiral structure,
unsurprisingly coincident with the already-known spiral structures of the
neutral and molecular gas discs. The kinematical analysis of the velocity field
shows that the rotation center of the Ha disc is distant from the photometric
center by 170 pc (sky projected distance) and that the kinematical major-axis
position angle and disc inclination are in excellent agreement with photometric
values. The Ha rotation curve agrees very well with the HI rotation curves for
0 6.5 kpc.
The reason for this discrepancy is not well understood. The velocity dispersion
profile is relatively flat around 16 km/s, which is at the low end of velocity
dispersions of nearby star-forming galactic discs. A strong relation is also
found between the Ha velocity dispersion and the Ha intensity. Mass models were
obtained using the Ha rotation curve but, as expected, the dark matter halo's
parameters are not very well constrained since the optical rotation curve only
extends out to 8 kpc.Comment: 26 pages, 18 figures, accepted for publication in MNRA
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