1,388 research outputs found
Localized mode interactions in 0-pi Josephson junctions
A long Josephson junction containing regions with a phase shift of pi is
considered. By exploiting the defect modes due to the discontinuities present
in the system, it is shown that Josephson junctions with phase-shift can be an
ideal setting for studying localized mode interactions. A phase-shift
configuration acting as a double-well potential is considered and shown to
admit mode tunnelings between the wells. When the phase-shift configuration is
periodic, it is shown that localized excitations forming bright and dark
solitons can be created. Multi-mode approximations are derived confirming the
numerical results.Comment: 4 pages, to appear in Phys. Rev.
Kinetic pathways of the Nematic-Isotropic phase transition as studied by confocal microscopy on rod-like viruses
We investigate the kinetics of phase separation for a mixture of rodlike
viruses (fd) and polymer (dextran), which effectively constitutes a system of
attractive rods. This dispersion is quenched from a flow-induced fully nematic
state into the region where the nematic and the isotropic phase coexist. We
show experimental evidence that the kinetic pathway depends on the overall
concentration. When the quench is made at high concentrations, the system is
meta-stable and we observe typical nucleation-and-growth. For quenches at low
concentration the system is unstable and the system undergoes a spinodal
decomposition. At intermediate concentrations we see the transition between
both demixing processes, where we locate the spinodal point.Comment: 11 pages, 6 figures, accepted in J. Phys.: Condens. Matter as
symposium paper for the 6th Liquid Matter Conference in Utrech
Incongruity, incongruity resolution, and mental states: The measure and modification of situational awareness and control
The research reported here describes the process of induction of various mental states. Our goals were to measure and to manipulate both the behavioral and the neurological correlates of particular mental states that have previously been demonstrated to be either beneficial or deleterious to in-flight performance situations. The experimental paradigm involved developing a context of which the participants were aware, followed by the introduction of an incongruity into that context. The empirical questions involved how the incongruity was resolved and the consequent effects on mental state. The dependent variables were measures of both the short-term ERP changes and the longer-term brain mapping indications of predominant mental states. The mission of NASA Flight Management Division and Human/Automation Integration Branch centers on the understanding and improvement of interaction between a complex system and a human operator. Specifically, the goal is improved efficiency through better operative procedures and control strategies. More efficient performance in demanding flight environments depends on improved situational awareness and replanning for fault management
Cavitation-induced force transition in confined viscous liquids under traction
We perform traction experiments on simple liquids highly confined between
parallel plates. At small separation rates, we observe a simple response
corresponding to a convergent Poiseuille flow. Dramatic changes in the force
response occur at high separation rates, with the appearance of a force plateau
followed by an abrupt drop. By direct observation in the course of the
experiment, we show that cavitation accounts for these features which are
reminiscent of the utmost complex behavior of adhesive films under traction.
Surprisingly enough, this is observed here in purely viscous fluids.Comment: Submitted to Physical Review Letters on May 31, 2002. Related
informations on http://www.crpp.u-bordeaux.fr/tack.htm
Synchronization of organ pipes: experimental observations and modeling
We report measurements on the synchronization properties of organ pipes.
First, we investigate influence of an external acoustical signal from a
loudspeaker on the sound of an organ pipe. Second, the mutual influence of two
pipes with different pitch is analyzed. In analogy to the externally driven, or
mutually coupled self-sustained oscillators, one observes a frequency locking,
which can be explained by synchronization theory. Further, we measure the
dependence of the frequency of the signals emitted by two mutually detuned
pipes with varying distance between the pipes. The spectrum shows a broad
``hump'' structure, not found for coupled oscillators. This indicates a complex
coupling of the two organ pipes leading to nonlinear beat phenomena.Comment: 24 pages, 10 Figures, fully revised, 4 big figures separate in jpeg
format. accepted for Journal of the Acoustical Society of Americ
Attracting curves on families of stationary solutions in two-dimensional Navier-Stokes and reduced magnetohydrodynamics
Correcting non-independent and non-identically distributed errors with surface codes
A common approach to studying the performance of quantum error correcting codes is to assume independent and identically distributed single-qubit errors. However, the available experimental data shows that realistic errors in modern multi-qubit devices are typically neither independent nor identical across qubits. In this work, we develop and investigate the properties of topological surface codes adapted to a known noise structure by Clifford conjugations. We show that the surface code locally tailored to non-uniform single-qubit noise in conjunction with a scalable matching decoder yields an increase in error thresholds and exponential suppression of sub-threshold failure rates when compared to the standard surface code. Furthermore, we study the behaviour of the tailored surface code under local two-qubit noise and show the role that code degeneracy plays in correcting such noise. The proposed methods do not require additional overhead in terms of the number of qubits or gates and use a standard matching decoder, hence come at no extra cost compared to the standard surface-code error correction
Correcting non-independent and non-identically distributed errors with surface codes
A common approach to studying the performance of quantum error correcting
codes is to assume independent and identically distributed single-qubit errors.
However, the available experimental data shows that realistic errors in modern
multi-qubit devices are typically neither independent nor identical across
qubits. In this work, we develop and investigate the properties of topological
surface codes adapted to a known noise structure by Clifford conjugations. We
show that the surface code locally tailored to non-uniform single-qubit noise
in conjunction with a scalable matching decoder yields an increase in error
thresholds and exponential suppression of sub-threshold failure rates when
compared to the standard surface code. Furthermore, we study the behaviour of
the tailored surface code under local two-qubit noise and show the role that
code degeneracy plays in correcting such noise. The proposed methods do not
require additional overhead in terms of the number of qubits or gates and use a
standard matching decoder, hence come at no extra cost compared to the standard
surface-code error correction
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