2,897 research outputs found
PRIORITIES IN COST SHARING FOR SOIL AND WATER CONSERVATION: A REVEALED PREFERENCE STUDY
Resource /Energy Economics and Policy,
Finite times to equipartition in the thermodynamic limit
We study the time scale T to equipartition in a 1D lattice of N masses
coupled by quartic nonlinear (hard) springs (the Fermi-Pasta-Ulam beta model).
We take the initial energy to be either in a single mode gamma or in a package
of low frequency modes centered at gamma and of width delta-gamma, with both
gamma and delta-gamma proportional to N. These initial conditions both give,
for finite energy densities E/N, a scaling in the thermodynamic limit (large
N), of a finite time to equipartition which is inversely proportional to the
central mode frequency times a power of the energy density E/N. A theory of the
scaling with E/N is presented and compared to the numerical results in the
range 0.03 <= E/N <= 0.8.Comment: Plain TeX, 5 `eps' figures, submitted to Phys. Rev.
Method and apparatus for measuring distance
The invention employs a continuous wave radar technique and apparatus which can be used as a distance measuring system in the presence of background clutter by utilizing small passive transponders. A first continuous electromagnetic wave signal S sub 1 at a first frequency f sub 1 is transmitted from a first location. A transponder carried by a target object positioned at a second (remote) location receives the transmitted signal, phase-coherently divides the f sub 1 frequency and its phase, and re-transmits the transmitted signal as a second continuous electromagnetic wave signal S sub 2 at a lower frequency f sub 2 which is a subharmonic of f sub 1. The re-transmitted signal is received at the first location where a measurement of the phase difference is made between the signals S sub 1 and S sub 2, such measuremnt being indicative of the distance between the first and second locations
Bloch oscillations of cold atoms in optical lattices
This work is devoted to Bloch oscillations (BO) of cold neutral atoms in
optical lattices. After a general introduction to the phenomenon of BO and its
realization in optical lattices, we study different extentions of this problem,
which account for recent developments in this field. These are two-dimensional
BO, decoherence of BO, and BO in correlated systems. Although these problems
are discussed in relation to the system of cold atoms in optical lattices, many
of the results are of general validity and can be well applied to other systems
showing the phenomenon of BO.Comment: submitted to the review section of IJMPB, few misprints are correcte
Analysis of interface conversion processes of ballistic and diffusive motion in driven superlattices
We explore the non-equilibrium dynamics of non-interacting classical
particles in a one-dimensional driven superlattice which is composed of domains
exposed to different time-dependent forces. It is shown how the combination of
directed transport and conversion processes from diffusive to ballistic motion
causes strong correlations between velocity and phase for particles passing
through a superlattice. A detailed understanding of the underlying mechanism
allows us to tune the resulting velocity distributions at distinguished points
in the superlattice by means of local variations of the applied driving force.
As an intriguing application we present a scheme how initially diffusive
particles can be transformed into a monoenergetic pulsed particle beam whose
parameters such as its energy can be varied
Extremely Small Energy Gap in the Quasi-One-Dimensional Conducting Chain Compound SrNbO
Resistivity, optical, and angle-resolved photoemission experiments reveal
unusual one-dimensional electronic properties of highly anisotropic
SrNbO. Along the conducting chain direction we find an extremely small
energy gap of only a few meV at the Fermi level. A discussion in terms of
typical 1D instabilities (Peierls, Mott-Hubbard) shows that neither seems to
provide a satisfactory explanation for the unique properties of SrNbO.Comment: 4 pages, 3 figure
Regular-to-chaotic tunneling rates using a fictitious integrable system
We derive a formula predicting dynamical tunneling rates from regular states
to the chaotic sea in systems with a mixed phase space. Our approach is based
on the introduction of a fictitious integrable system that resembles the
regular dynamics within the island. For the standard map and other kicked
systems we find agreement with numerical results for all regular states in a
regime where resonance-assisted tunneling is not relevant.Comment: 4 pages, 4 figure
Classical diffusion in double-delta-kicked particles
We investigate the classical chaotic diffusion of atoms subjected to {\em
pairs} of closely spaced pulses (`kicks) from standing waves of light (the
-KP). Recent experimental studies with cold atoms implied an
underlying classical diffusion of type very different from the well-known
paradigm of Hamiltonian chaos, the Standard Map.
The kicks in each pair are separated by a small time interval , which together with the kick strength , characterizes the transport.
Phase space for the -KP is partitioned into momentum `cells' partially
separated by momentum-trapping regions where diffusion is slow. We present here
an analytical derivation of the classical diffusion for a -KP
including all important correlations which were used to analyze the
experimental data.
We find a new asymptotic () regime of `hindered' diffusion:
while for the Standard Map the diffusion rate, for , oscillates about the uncorrelated, rate , we find
analytically, that the -KP can equal, but never diffuses faster than,
a random walk rate.
We argue this is due to the destruction of the important classical
`accelerator modes' of the Standard Map.
We analyze the experimental regime , where
quantum localisation lengths are affected by fractal
cell boundaries. We find an approximate asymptotic diffusion rate , in correspondence to a regime in the Standard Map
associated with 'golden-ratio' cantori.Comment: 14 pages, 10 figures, error in equation in appendix correcte
Anderson localization or nonlinear waves? A matter of probability
In linear disordered systems Anderson localization makes any wave packet stay
localized for all times. Its fate in nonlinear disordered systems is under
intense theoretical debate and experimental study. We resolve this dispute
showing that at any small but finite nonlinearity (energy) value there is a
finite probability for Anderson localization to break up and propagating
nonlinear waves to take over. It increases with nonlinearity (energy) and
reaches unity at a certain threshold, determined by the initial wave packet
size. Moreover, the spreading probability stays finite also in the limit of
infinite packet size at fixed total energy. These results are generalized to
higher dimensions as well.Comment: 4 pages, 3 figure
Harmonic Generation from Laser-Irradiated Clusters
The harmonic emission from cluster nanoplasmas subject to short, intense
infrared laser pulses is analyzed by means of particle-in-cell simulations. A
pronounced resonant enhancement of the low-order harmonic yields is found when
the Mie plasma frequency of the ionizing and expanding cluster resonates with
the respective harmonic frequency. We show that a strong, nonlinear resonant
coupling of the cluster electrons with the laser field inhibits coherent
electron motion, suppressing the emitted radiation and restricting the spectrum
to only low-order harmonics. A pump-probe scheme is suggested to monitor the
ionization dynamics of the expanding clusters.Comment: 4 pages, ReVTeX
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