18,257 research outputs found
Resonances, Unstable Systems and Irreversibility: Matter Meets Mind
The fundamental time-reversal invariance of dynamical systems can be broken
in various ways. One way is based on the presence of resonances and their
interactions giving rise to unstable dynamical systems, leading to well-defined
time arrows. Associated with these time arrows are semigroups bearing time
orientations. Usually, when time symmetry is broken, two time-oriented
semigroups result, one directed toward the future and one directed toward the
past. If time-reversed states and evolutions are excluded due to resonances,
then the status of these states and their associated backwards-in-time oriented
semigroups is open to question. One possible role for these latter states and
semigroups is as an abstract representation of mental systems as opposed to
material systems. The beginnings of this interpretation will be sketched.Comment: 9 pages. Presented at the CFIF Workshop on TimeAsymmetric Quantum
Theory: The Theory of Resonances, 23-26 July 2003, Instituto Superior
Tecnico, Lisbon, Portugal; and at the Quantum Structures Association Meeting,
7-22 July 2004, University of Denver. Accepted for publication in the
Internation Journal of Theoretical Physic
Spectral signatures of the Luttinger liquid to charge-density-wave transition
Electron- and phonon spectral functions of the one-dimensional,
spinless-fermion Holstein model at half filling are calculated in the four
distinct regimes of the phase diagram, corresponding to an attractive or
repulsive Luttinger liquid at weak electron-phonon coupling, and a band- or
polaronic insulator at strong coupling. The results obtained by means of kernel
polynomial and systematic cluster approaches reveal substantially different
physics in these regimes and further indicate that the size of the phonon
frequency significantly affects the nature of the quantum Peierls phase
transition.Comment: 5 pages, 4 figures; final version, accepted for publication in
Physical Review
Non-linear excitations in 1D correlated insulators
In this work we investigate charge transport in one-dimensional (1D)
insulators via semi-classical and perturbative renormalization group (RG)
methods. We consider the problem of electron-electron, electron-phonon and
electron-two-level system interactions. We show that non-linear collective
modes such as polarons and solitons are reponsible for transport. We find a new
excitation in the Mott insulator: the polaronic soliton. We discuss the
differences between band and Mott insulators in terms of their spin spectrum
and obtain the charge and spin gaps in each one of these systems. We show that
electron-electron interactions provide strong renormalizations of the energy
scales in the problem.Comment: 29 page
Atomic scale lattice distortions and domain wall profiles
We present an atomic scale theory of lattice distortions using strain related
variables and their constraint equations. Our approach connects constrained
{\it atomic length} scale variations to {\it continuum} elasticity and
describes elasticity at several length scales. We apply the approach to a
two-dimensional square lattice with a monatomic basis, and find the elastic
deformations and hierarchical atomic relaxations in the vicinity of a domain
wall between two different homogeneous strain states. We clarify the
microscopic origin of gradient terms, some of which are included
phenomenologically in Ginzburg-Landau theory, by showing that they are
anisotropic.Comment: 6 figure
Polaron Coherence as Origin of the Pseudogap Phase in High Temperature Superconducting Cuprates
Within a two component approach to high Tc copper oxides including polaronic
couplings, we identify the pseudogap phase as the onset of polaron ordering.
This ordering persists in the superconducting phase. A huge isotope effect on
the pseudogap onset temperature is predicted and in agreement with experimental
data. The anomalous temperature dependence of the mean square copper oxygen ion
displacement observed above, at and below Tc stems from an s-wave
superconducting component of the order parameter, whereas a pure d-wave order
parameter alone can be excluded.Comment: 7 pages, 2 figure
Experimental apparatus for investigation of fan aeroelastic instabilities in turbomachinery
The application, installation, and monitoring of dynamic strain gage instrumentation on the rotating fan blades for subsonic stalled flutter mode of the first fan rotor are described. The engine installation, the modifications to the engine controls to obtain off schedule operation of the fan, engine aerodynamic instrumentation, and general data acquisition systems are discussed
- …