8,411 research outputs found
Signatures of homoclinic motion in quantum chaos
Homoclinic motion plays a key role in the organization of classical chaos in
Hamiltonian systems. In this Letter, we show that it also imprints a clear
signature in the corresponding quantum spectra. By numerically studying the
fluctuations of the widths of wavefunctions localized along periodic orbits we
reveal the existence of an oscillatory behavior, that is explained solely in
terms of the primary homoclinic motion. Furthermore, our results indicate that
it survives the semiclassical limit.Comment: 5 pages, 4 figure
Localization of Eigenfunctions in the Stadium Billiard
We present a systematic survey of scarring and symmetry effects in the
stadium billiard. The localization of individual eigenfunctions in Husimi phase
space is studied first, and it is demonstrated that on average there is more
localization than can be accounted for on the basis of random-matrix theory,
even after removal of bouncing-ball states and visible scars. A major point of
the paper is that symmetry considerations, including parity and time-reversal
symmetries, enter to influence the total amount of localization. The properties
of the local density of states spectrum are also investigated, as a function of
phase space location. Aside from the bouncing-ball region of phase space,
excess localization of the spectrum is found on short periodic orbits and along
certain symmetry-related lines; the origin of all these sources of localization
is discussed quantitatively and comparison is made with analytical predictions.
Scarring is observed to be present in all the energy ranges considered. In
light of these results the excess localization in individual eigenstates is
interpreted as being primarily due to symmetry effects; another source of
excess localization, scarring by multiple unstable periodic orbits, is smaller
by a factor of .Comment: 31 pages, including 10 figure
Forming double-barred galaxies from dynamically cool inner disks
About one-third of early-type barred galaxies host small-scale secondary bars. The formation and evolution of such double-barred (S2B) galaxies remain far from being well understood. In order to understand the formation of such systems, we explore a large parameter space of isolated pure-disk simulations. We show that a dynamically cool inner disk embedded in a hotter outer disk can naturally generate a steady secondary bar while the outer disk forms a large-scale primary bar. The independent bar instabilities of inner and outer disks result in long-lived double-barred structures whose dynamical properties are comparable to those in observations. This formation scenario indicates that the secondary bar might form from the general bar instability, the same as the primary bar. Under some circumstances, the interaction of the bars and the disk leads to the two bars aligning or single, nuclear, bars only. Simulations that are cool enough of the center to experience clump instabilities may also generate steady S2B galaxies. In this case, the secondary bars are “fast,” i.e., the bar length is close to the co-rotation radius. This is the first time that S2B galaxies containing a fast secondary bar are reported. Previous orbit-based studies had suggested that fast secondary bars were not dynamically possibl
Redox-Active Nanomaterials For Nanomedicine Applications
Nanomedicine utilizes the remarkable properties of nanomaterials for the diagnosis, treatment, and prevention of disease. Many of these nanomaterials have been shown to have robust antioxidative properties, potentially functioning as strong scavengers of reactive oxygen species. Conversely, several nanomaterials have also been shown to promote the generation of reactive oxygen species, which may precipitate the onset of oxidative stress, a state that is thought to contribute to the development of a variety of adverse conditions. As such, the impacts of nanomaterials on biological entities are often associated with and influenced by their specific redox properties. In this review, we overview several classes of nanomaterials that have been or projected to be used across a wide range of biomedical applications, with discussion focusing on their unique redox properties. Nanomaterials examined include iron, cerium, and titanium metal oxide nanoparticles, gold, silver, and selenium nanoparticles, and various nanoscale carbon allotropes such as graphene, carbon nanotubes, fullerenes, and their derivatives/variations. Principal topics of discussion include the chemical mechanisms by which the nanomaterials directly interact with biological entities and the biological cascades that are thus indirectly impacted. Selected case studies highlighting the redox properties of nanomaterials and how they affect biological responses are used to exemplify the biologically-relevant redox mechanisms for each of the described nanomaterials
Spatial Correlation in Quantum Chaotic Systems with Time-reversal Symmetry: Theory and Experiment
The correlation between the values of wavefunctions at two different spatial
points is examined for chaotic systems with time-reversal symmetry. Employing a
supermatrix method, we find that there exist long-range Friedel oscillations of
the wave function density for a given eigenstate, although the background
wavefunction density fluctuates strongly. We show that for large fluctuations,
once the value of the wave function at one point is known, its spatial
dependence becomes highly predictable for increasingly large space around this
point. These results are compared with the experimental wave functions obtained
from billiard-shaped microwave cavities and very good agreement is
demonstrated.Comment: 12 pages, REVTeX3+epsf, two EPS figures. Minor modification
Quantization with Action-Angle Coherent States
For a single degree of freedom confined mechanical system with given energy,
we know that the motion is always periodic and action-angle variables are
convenient choice as conjugate phase-space variables. We construct action-angle
coherent states in view to provide a quantization scheme that yields precisely
a given observed energy spectrum for such a system. This construction
is based on a Bayesian approach: each family corresponds to a choice of
probability distributions such that the classical energy averaged with respect
to this probability distribution is precisely up to a constant shift. The
formalism is viewed as a natural extension of the Bohr-Sommerfeld rule and an
alternative to the canonical quantization. In particular, it also yields a
satisfactory angle operator as a bounded self-adjoint operator
Deformations and dilations of chaotic billiards, dissipation rate, and quasi-orthogonality of the boundary wavefunctions
We consider chaotic billiards in d dimensions, and study the matrix elements
M_{nm} corresponding to general deformations of the boundary. We analyze the
dependence of |M_{nm}|^2 on \omega = (E_n-E_m)/\hbar using semiclassical
considerations. This relates to an estimate of the energy dissipation rate when
the deformation is periodic at frequency \omega. We show that for dilations and
translations of the boundary, |M_{nm}|^2 vanishes like \omega^4 as \omega -> 0,
for rotations like \omega^2, whereas for generic deformations it goes to a
constant. Such special cases lead to quasi-orthogonality of the eigenstates on
the boundary.Comment: 4 pages, 3 figure
The Inhibition of Mixing in Chaotic Quantum Dynamics
We study the quantum chaotic dynamics of an initially well-localized wave
packet in a cosine potential perturbed by an external time-dependent force. For
our choice of initial condition and with small but finite, we find that
the wave packet behaves classically (meaning that the quantum behavior is
indistinguishable from that of the analogous classical system) as long as the
motion is confined to the interior of the remnant separatrix of the cosine
potential. Once the classical motion becomes unbounded, however, we find that
quantum interference effects dominate. This interference leads to a long-lived
accumulation of quantum amplitude on top of the cosine barrier. This pinning of
the amplitude on the barrier is a dynamic mechanism for the quantum inhibition
of classical mixing.Comment: 20 pages, RevTeX format with 6 Postscript figures appended in
uuencoded tar.Z forma
Classical and quantum chaos in a circular billiard with a straight cut
We study classical and quantum dynamics of a particle in a circular billiard
with a straight cut. This system can be integrable, nonintegrable with soft
chaos, or nonintegrable with hard chaos, as we vary the size of the cut. We use
a quantum web to show differences in the quantum manifestations of classical
chaos for these three different regimes.Comment: LaTeX2e, 8 pages including 3 Postscript figures and 4 GIF figures,
submitted to Phys. Rev.
Phase Transitions in SO(3) Lattice Gauge Theory
The phase diagram of SO(3) lattice gauge theory is investigated by Monte
Carlo techniques on both symmetric and asymmetric lattices with a view (i) to
understanding the relationship between the bulk transition and the
deconfinement transition, and (ii) to resolving the current ambiguity about the
nature of the high temperature phase. A number of tests, including an
introduction of a magnetic field and measurement of different correlation
functions in the phases with positive and negative values for the adjoint
Polyakov line, lead to the conclusion that the two phases correspond to the
same physical state. Studies on lattices of different sizes reveal only one
phase transition for this theory on all of them and it appears to have a
deconfining nature.Comment: Latex 19 pages, 9 figures. Minor changes in introduction and summary
sections. The version that appeared in journa
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