131,995 research outputs found
Non-equilibrium steady state of sparse systems
A resistor-network picture of transitions is appropriate for the study of
energy absorption by weakly chaotic or weakly interacting driven systems. Such
"sparse" systems reach a novel non-equilibrium steady state (NESS) once coupled
to a bath. In the stochastic case there is an analogy to the physics of
percolating glassy systems, and an extension of the fluctuation-dissipation
phenomenology is proposed. In the mesoscopic case the quantum NESS might differ
enormously from the stochastic NESS, with saturation temperature determined by
the sparsity. A toy model where the sparsity of the system is modeled using a
log-normal random ensemble is analyzed.Comment: 6 pages, 6 figures, EPL accepted versio
Some remarks on stability for a phase-field model with memory
The phase field system with memory can be viewed as a phenomenological extension of the classical phase equations in which memory effects have been taken into account in both fields. Such memory effects could be important for example during phase transition in polymer melts in the proximity of the glass transition temperature where configurational degrees of freedom in the polymer melt constitute slowly relaxing "internal modes" which are di±cult to model explicitly. They should be relevant in particular to glass-liquid-glass transitions where re-entrance effects have been recently reported [27]. We note that in numerical studies based on sharp interface equations obtained from (PFM), grains have been seen to rotate as they shrink [35, 36]. While further modelling and numerical efforts are now being undertaken, the present manuscript is devoted to strengthening the analytical underpinnings of the model
Magnetic field in Cepheus A as deduced from OH maser polarimetric observations
We present the results of MERLIN polarization mapping of OH masers at 1665
and 1667 MHz towards the Cepheus A star-forming region. The maser emission is
spread over a region of 6 arcsec by 10 arcsec, twice the extent previously
detected. In contrast to the 22 GHz water masers, the OH masers associated with
H II regions show neither clear velocity gradients nor regular structures. We
identified ten Zeeman pairs which imply a magnetic field strength along the
line-of-sight from -17.3 to +12.7 mG. The magnetic field is organised on the
arcsecond scale, pointing towards us in the west and away from us in the east
side. The linearly polarized components, detected for the first time, show
regularities in the polarization position angles depending on their position.
The electric vectors of OH masers observed towards the outer parts of H II
regions are consistent with the interstellar magnetic field orientation, while
those seen towards the centres of H II regions are parallel to the radio-jets.
A Zeeman quartet inside a southern H II region has now been monitored for 25
years; we confirm that the magnetic field decays monotonically over that
period.Comment: 10 pages, 6 figures,accepted for publication in MNRA
A Poset Connected to Artin Monoids of Simply Laced Type
Let W be a Weyl group whose type is a simply laced Dynkin diagram. On several
W-orbits of sets of mutually commuting reflections, a poset is described which
plays a role in linear representatons of the corresponding Artin group A. The
poset generalizes many properties of the usual order on positive roots of W
given by height. In this paper, a linear representation of the positive monoid
of A is defined by use of the poset
BMW algebras of simply laced type
It is known that the recently discovered representations of the Artin groups
of type A_n, the braid groups, can be constructed via BMW algebras. We
introduce similar algebras of type D_n and E_n which also lead to the newly
found faithful representations of the Artin groups of the corresponding types.
We establish finite dimensionality of these algebras. Moreover, they have
ideals I_1 and I_2 with I_2 contained in I_1 such that the quotient with
respect to I_1 is the Hecke algebra and I_1/I_2 is a module for the
corresponding Artin group generalizing the Lawrence-Krammer representation.
Finally we give conjectures on the structure, the dimension and parabolic
subalgebras of the BMW algebra, as well as on a generalization of deformations
to Brauer algebras for simply laced spherical type other than A_n.Comment: 39 page
The Quantum Hall Effect: Unified Scaling Theory and Quasi-particles at the Edge
We address two fundamental issues in the physics of the quantum Hall effect:
a unified description of scaling behavior of conductances in the integral and
fractional regimes, and a quasi-particle formulation of the chiral Luttinger
Liquids that describe the dynamics of edge excitations in the fractional
regime.Comment: 11 pages, LateX, 2 figures (not included, available from the
authors), to be published in Proceedings of the International Summer School
on Strongly Correlated Electron Systems, Lajos Kossuth University, Debrecen,
Hungary, Sept 199
Quantum anomalies and linear response theory
The analysis of diffusive energy spreading in quantized chaotic driven
systems, leads to a universal paradigm for the emergence of a quantum anomaly.
In the classical approximation a driven chaotic system exhibits stochastic-like
diffusion in energy space with a coefficient that is proportional to the
intensity of the driving. In the corresponding quantized problem
the coherent transitions are characterized by a generalized Wigner time
, and a self-generated (intrinsic) dephasing process leads to
non-linear dependence of on .Comment: 8 pages, 2 figures, textual improvements (as in published version
Dimension minimization of a quantum automaton
A new model of a Quantum Automaton (QA), working with qubits is proposed. The
quantum states of the automaton can be pure or mixed and are represented by
density operators. This is the appropriated approach to deal with measurements
and dechorence. The linearity of a QA and of the partial trace super-operator,
combined with the properties of invariant subspaces under unitary
transformations, are used to minimize the dimension of the automaton and,
consequently, the number of its working qubits. The results here developed are
valid wether the state set of the QA is finite or not. There are two main
results in this paper: 1) We show that the dimension reduction is possible
whenever the unitary transformations, associated to each letter of the input
alphabet, obey a set of conditions. 2) We develop an algorithm to find out the
equivalent minimal QA and prove that its complexity is polynomial in its
dimension and in the size of the input alphabet.Comment: 26 page
Revivals of Coherence in Chaotic Atom-Optics Billiards
We investigate the coherence properties of thermal atoms confined in optical
dipole traps where the underlying classical dynamics is chaotic. A perturbative
expression derived for the coherence of the echo scheme of [Andersen et. al.,
Phys. Rev. Lett. 90, 023001 (2003)] shows it is a function of the survival
probability or fidelity of eigenstates of the motion of the atoms in the trap.
The echo coherence and the survival probability display "system specific"
features, even when the underlying classical dynamics is chaotic. In
particular, partial revivals in the echo signal and the survival probability
are found for a small shift of the potential. Next, a "semi-classical"
expression for the averaged echo signal is presented and used to calculate the
echo signal for atoms in a light sheet wedge billiard. Revivals in the echo
coherence are found in this system, indicating they may be a generic feature of
dipole traps
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