173 research outputs found
Time-frequency analysis of chaotic systems
We describe a method for analyzing the phase space structures of Hamiltonian
systems. This method is based on a time-frequency decomposition of a trajectory
using wavelets. The ridges of the time-frequency landscape of a trajectory,
also called instantaneous frequencies, enable us to analyze the phase space
structures. In particular, this method detects resonance trappings and
transitions and allows a characterization of the notion of weak and strong
chaos. We illustrate the method with the trajectories of the standard map and
the hydrogen atom in crossed magnetic and elliptically polarized microwave
fields.Comment: 36 pages, 18 figure
Double-ionization mechanisms of magnesium driven by electron impact
We study double ionization of Mg by electron impact through the vantage point of classical mechanics. We consider all electron-electron correlations in a Coulomb four-body problem, where three electrons belong to the atom and the fourth electron causes the impact ionization. From our model we compute the double-ionization probability of Mg for impact energies from 15 to 125 eV. Double ionization occurs through eight double-ionization mechanisms, which we classify into four categories: inner shell capture, direct, delay, and ionized inner shell mechanisms. We show that delay and ionized inner shell mechanisms require electron-electron correlations among the four electrons, and are responsible for the second increase in the double-ionization probability. Furthermore, we show that our theoretical prediction about the relative prominence of certain double-ionization mechanisms is in agreement with experimental results on the relative prominence of non-first- over first-order mechanisms
Guiding-center motion for electrons in strong laser fields
We consider the dynamics of electrons in combined strong laser and Coulomb
fields. Under a timescale separation condition, we reduce this dynamics to a
guiding-center framework. More precisely, we derive a hierarchy of models for
the guiding-center dynamics based on averaging over the fast motion of the
electron using Lie transforms. The reduced models we obtain describe well the
different ionization channels, in particular, the conditions under which an
electron is rescattered by the ionic core or is directly ionized. The
comparison between these models highlights the models which are best suited for
a qualitative and quantitative agreement with the parent dynamics
Production of trans-Neptunian binaries through chaos-assisted capture
The recent discovery of binary objects in the Kuiper-belt opens an invaluable
window into past and present conditions in the trans-Neptunian part of the
Solar System. For example, knowledge of how these objects formed can be used to
impose constraints on planetary formation theories. We have recently proposed a
binary-object formation model based on the notion of chaos-assisted capture.
Here we present a more detailed analysis with calculations performed in the
spatial (three-dimensional) three- and four-body Hill approximations. It is
assumed that the potential binary partners are initially following heliocentric
Keplerian orbits and that their relative motion becomes perturbed as these
objects undergo close encounters. First, the mass, velocity, and orbital
element distribu- tions which favour binary formation are identified in the
circular and elliptical Hill limits. We then consider intruder scattering in
the circular Hill four-body problem and find that the chaos-assisted capture
mechanism is consistent with observed, apparently randomly distributed, binary
mutual orbit inclinations. It also predicts asymmetric distributions of
retrograde versus prograde orbits. The time-delay induced by chaos on particle
transport through the Hill sphere is analogous to the formation of a resonance
in a chemical reaction. Implications for binary formation rates are considered
and the 'fine-tuning' problem recently identified by Noll et al. (2007) is also
addressed.Comment: submitted to MNRA
The Transition State in a Noisy Environment
Transition State Theory overestimates reaction rates in solution because
conventional dividing surfaces between reagents and products are crossed many
times by the same reactive trajectory. We describe a recipe for constructing a
time-dependent dividing surface free of such recrossings in the presence of
noise. The no-recrossing limit of Transition State Theory thus becomes
generally available for the description of reactions in a fluctuating
environment
Mechanism of delayed double ionization in a strong laser field
When intense laser pulses release correlated electrons, the time delay
between the ionizations may last more than one laser cycle. We show that this
"Recollision-Excitation with Subsequent Ionization" pathway originates from the
inner electron being promoted to a sticky region by a recollision where it is
trapped for a long time before ionizing. We identify the mechanism which
regulates this region, and predict oscillations in the double ionization yield
with laser intensity
Renormalization group approach to vibrational energy transfer in protein
Renormalization group method is applied to the study of vibrational energy
transfer in protein molecule. An effective Lagrangian and associated equations
of motion to describe the resonant energy transfer are analyzed in terms of the
first-order perturbative renormalization group theory that has been developed
as a unified tool for global asymptotic analysis. After the elimination of
singular terms associated with the Fermi resonance, amplitude equations to
describe the slow dynamics of vibrational energy transfer are derived, which
recover the result obtained by a technique developed in nonlinear optics [S.J.
Lade, Y.S. Kivshar, Phys. Lett. A 372 (2008) 1077].Comment: 11 page
A Low Profile Wideband Log Periodic Microstrip Antenna Design for C-Band Applications
In this study, a wideband low profile microstrip antenna design for C-band applications is presented. The proposed antenna consists of a monopol log periodic patch in the equilateral triangular dimensions with the microstrip line fed and a rectangular ground plane. The antenna has 9Ă—19.8 mm2 overall size, thickness of 1.6 mm and 4.3 dielectric constant. According to the simulation results, the proposed antenna has a very wide bandwidth while operating in the frequency band of 4.25-7.95 GHz and 5 GHz resonance frequency. The proposed antenna was also prototyped on FR4 substrate with the 0.02 tangent loss and the measurement results were quite similar by the simulated results
Bottlenecks to vibrational energy flow in OCS: Structures and mechanisms
Finding the causes for the nonstatistical vibrational energy relaxation in
the planar carbonyl sulfide (OCS) molecule is a longstanding problem in
chemical physics: Not only is the relaxation incomplete long past the predicted
statistical relaxation time, but it also consists of a sequence of abrupt
transitions between long-lived regions of localized energy modes. We report on
the phase space bottlenecks responsible for this slow and uneven vibrational
energy flow in this Hamiltonian system with three degrees of freedom. They
belong to a particular class of two-dimensional invariant tori which are
organized around elliptic periodic orbits. We relate the trapping and
transition mechanisms with the linear stability of these structures.Comment: 13 pages, 13 figure
- …