6,392 research outputs found
The motion, stability and breakup of a stretching liquid bridge with a receding contact line
The complex behavior of drop deposition on a hydrophobic surface is
considered by looking at a model problem in which the evolution of a
constant-volume liquid bridge is studied as the bridge is stretched. The bridge
is pinned with a fixed diameter at the upper contact point, but the contact
line at the lower attachment point is free to move on a smooth substrate.
Experiments indicate that initially, as the bridge is stretched, the lower
contact line slowly retreats inwards. However at a critical radius, the bridge
becomes unstable, and the contact line accelerates dramatically, moving inwards
very quickly. The bridge subsequently pinches off, and a small droplet is left
on the substrate. A quasi-static analysis, using the Young-Laplace equation, is
used to accurately predict the shape of the bridge during the initial bridge
evolution, including the initial onset of the slow contact line retraction. A
stability analysis is used to predict the onset of pinch-off, and a
one-dimensional dynamical equation, coupled with a Tanner-law for the dynamic
contact angle, is used to model the rapid pinch-off behavior. Excellent
agreement between numerical predictions and experiments is found throughout the
bridge evolution, and the importance of the dynamic contact line model is
demonstrated.Comment: 37 pages, 12 figure
Control of the Bose-Einstein condensate by dissipation. Nonlinear Zeno effect
We show that controlled dissipation can be used as a tool for exploring
fundamental phenomena and managing mesoscopic systems of cold atoms and
Bose-Einstein condensates. Even the simplest boson-Josephson junction, that is,
a Bose-Einstein condensate in a double-well trap, subjected to removal of atoms
from one of the two potential minima allows one to observe such phenomena as
the suppression of losses and the nonlinear Zeno effect. In such a system the
controlled dissipation can be used to create desired macroscopic states and
implement controlled switching among different quantum regimes.Comment: To appear in PRA, 5 pages, 4 figures (one in color) [Typos are
corrected
Sudden transition between classical and quantum decoherence
We study the dynamics of quantum and classical correlations in the presence
of nondissipative decoherence. We discover a class of initial states for which
the quantum correlations, quantified by the quantum discord, are not destroyed
by decoherence for times t < \bar{t}. In this initial time interval classical
correlations decay. For t > \bar{t}, on the other hand, classical correlations
do not change in time and only quantum correlations are lost due to the
interaction with the environment. Therefore, at the transition time \bar{t} the
open system dynamics exhibits a sudden transition from classical to quantum
decoherence regime.Comment: version accepted for publication by Physical Review Letter
Changes in the flagellar bundling time account for variations in swimming behavior of flagellated bacteria in viscous media
Although the motility of the flagellated bacteria, Escherichia coli, has been
widely studied, the effect of viscosity on swimming speed remains
controversial. The swimming mode of wild-type E.coli is often idealized as a
"run-and- tumble" sequence in which periods of swimming at a constant speed are
randomly interrupted by a sudden change of direction at a very low speed. Using
a tracking microscope, we follow cells for extended periods of time in
Newtonian liquids of varying viscosity, and find that the swimming behavior of
a single cell can exhibit a variety of behaviors including run-and-tumble and
"slow-random-walk" in which the cells move at relatively low speed. Although
the characteristic swimming speed varies between individuals and in different
polymer solutions, we find that the skewness of the speed distribution is
solely a function of viscosity and can be used, in concert with the measured
average swimming speed, to determine the effective running speed of each cell.
We hypothesize that differences in the swimming behavior observed in solutions
of different viscosity are due to changes in the flagellar bundling time, which
increases as the viscosity rises, due to the lower rotation rate of the
flagellar motor. A numerical simulation and the use of Resistive Force theory
provide support for this hypothesis
Non-Markovian reservoir-dependent squeezing
The squeezing dynamics of a damped harmonic oscillator are studied for
different types of environment without making the Markovian approximation. The
squeezing dynamics of a coherent state depend on the reservoir spectrum in a
unique way that can, in the weak coupling approximation, be analyzed
analytically. Comparison of squeezing dynamics for Ohmic, sub-Ohmic and
super-Ohmic environments is done showing a clear connection between the
squeezing--non-squeezing oscillations and reservoir structure. Understanding
the effects occurring due to structured reservoirs is important both from a
purely theoretical point of view and in connection with evolving experimental
techniques and future quantum computing applications.Comment: 8 pages, 2 figures, submitted to Proceedings of CEWQO200
Non-Markovian master equation for a damped driven two-state system
We present a detailed microscopic derivation for a non-Markovian master
equation for a driven two-state system interacting with a general structured
reservoir. The master equation is derived using the time-convolutionless
projection operator technique in the limit of weak coupling between the
two-state quantum system and its environment. We briefly discuss the Markov
approximation, the secular approximation and their validity.Comment: 6 pages, submitted to proceedings of CEWQO200
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