10,154 research outputs found
Exploring Vortex Dynamics in the Presence of Dissipation: Analytical and Numerical Results
In this paper, we systematically examine the stability and dynamics of
vortices under the effect of a phenomenological dissipation used as a
simplified model for the inclusion of the effect of finite temperatures in
atomic Bose-Einstein condensates. An advantage of this simplified model is that
it enables an analytical prediction that can be compared directly (and
favorably) to numerical results. We then extend considerations to a case of
considerable recent experimental interest, namely that of a vortex dipole and
observe good agreement between theory and numerical computations in both the
stability properties (eigenvalues of the vortex dipole stationary states) and
the dynamical evolution of such configurations.Comment: 12 pages, 5 figures, accepted by PR
Phase Transitions and superuniversality in the dynamics of a self-driven particle
We study an active random walker model in which a particle's motion is
determined by a self-generated field. The field encodes information about the
particle's path history. This leads to either self-attractive or self-repelling
behavior. For self-repelling behavior, we find a phase transition in the
dynamics: when the coupling between the field and the walker exceeds a critical
value, the particle's behavior changes from renormalized diffusion to one
characterized by a diverging diffusion coefficient. The dynamical behavior for
all cases is surprisingly independent of dimension and of the noise amplitude.Comment: 14 pages, 4 figure
Surface dissipation in nanoelectromechanical systems: Unified description with the standard tunneling model and effects of metallic electrodes
By modifying and extending recent ideas [C. Seoanez et al., Europhys. Lett.
78, 60002 (2007)], a theoretical framework to describe dissipation processes in
the surfaces of vibrating micro- and nanoelectromechanical devices, thought to
be the main source of friction at low temperatures, is presented. Quality
factors as well as frequency shifts of flexural and torsional modes in doubly
clamped beams and cantilevers are given, showing the scaling with dimensions,
temperature, and other relevant parameters of these systems. Full agreement
with experimental observations is not obtained, leading to a discussion of
limitations and possible modifications of the scheme to reach a quantitative
fitting to experiments. For nanoelectromechanical systems covered with metallic
electrodes, the friction due to electrostatic interaction between the flowing
electrons and static charges in the device and substrate is also studied.Comment: 17 pages, 7 figure
Nonlinear current response of an isolated system of interacting fermions
Nonlinear real-time response of interacting particles is studied on the
example of a one-dimensional tight-binding model of spinless fermions driven by
electric field. Using equations of motion and numerical methods we show that
for a non-integrable case at finite temperatures the major effect of
nonlinearity can be taken into account within the linear response formalism
extended by a renormalization of the kinetic energy due to the Joule heating.
On the other hand, integrable systems show on constant driving a different
universality with a damped oscillating current whereby the frequency is related
but not equal to the Bloch oscillations
The photon to pseudoscalar meson transition form factors
In this talk it is reported on an analysis of the form factors for the
transitions from a photon to one of the pseudoscalar mesons pi0, eta, eta',
etac within the modified perturbative approach in which quark transverse
degrees of freedom are retained. The report is focused on the discussion of the
surprising features the new BaBar data exhibit, namely the sharp rise of the
pi-gamma form factor with the photon virtuality and the strong breaking of
flavor symmetry in the sector of pseudoscalar mesons.Comment: 19 pages, 8 figures, using Latex, talk presented at the conference on
Hadronic Structure, Tatranska Strba (2011
Parton and Hadron Correlations in Jets
Correlation between shower partons is first studied in high jets. Then
in the framework of parton recombination the correlation between pions in
heavy-ion collisions is investigated. Since thermal partons play very different
roles in central and peripheral collisions, it is found that the correlation
functions of the produced hadrons behave very differently at different
centralities, especially at intermediate . The correlation function that
can best exhibit the distinctive features is suggested. There is not a great
deal of overlap between what we can calculate and what has been measured.
Nevertheless, some aspects of our results compare favorably with experimental
data.Comment: 28 pages in Latex + 13 figures. This is a revised version with
extended discussions added without quantitative changes in the result
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