1,746 research outputs found
Universality in escape from a modulated potential well
We show that the rate of activated escape from a periodically modulated
potential displays scaling behavior versus modulation amplitude . For
adiabatic modulation of an optically trapped Brownian particle, measurements
yield with . The theory gives
in the adiabatic limit and predicts a crossover to scaling as
approaches the bifurcation point where the metastable state disappears.Comment: 4 pages, 3 figure
Scaling and crossovers in activated escape near a bifurcation point
Near a bifurcation point a system experiences critical slowing down. This
leads to scaling behavior of fluctuations. We find that a periodically driven
system may display three scaling regimes and scaling crossovers near a
saddle-node bifurcation where a metastable state disappears. The rate of
activated escape scales with the driving field amplitude as , where is the bifurcational value of . With
increasing field frequency the critical exponent changes from
for stationary systems to a dynamical value and then again to
. The analytical results are in agreement with the results of
asymptotic calculations in the scaling region. Numerical calculations and
simulations for a model system support the theory.Comment: 18 page
The effect of anion fluorination in ionic liquids : physical properties of a range of bis(methanesulfonyl)amide salts
Dynamics of a tunneling magnetic impurity: Kondo effect induced incoherence
We study how the formation of the Kondo compensation cloud influences the
dynamical properties of a magnetic impurity that tunnels between two positions
in a metal. The Kondo effect dynamically generates a strong tunneling
impurity-conduction electron coupling, changes the temperature dependence of
the tunneling rate, and may ultimately result in the destruction of the
coherent motion of the particle at zero temperature. We find an interesting
two-channel Kondo fixed point as well for a vanishing overlap between the
electronic states that screen the magnetic impurity. We propose a number of
systems where the predicted features could be observed.Comment: 4 pages, 3 figures, ReVTe
Sequence randomness and polymer collapse transitions
Contrary to expectations based on Harris' criterion, chain disorder with
frustration can modify the universality class of scaling at the theta
transition of heteropolymers. This is shown for a model with random two-body
potentials in 2D on the basis of exact enumeration and accurate Monte Carlo
results. When frustration grows beyond a certain finite threshold, the
temperature below which disorder becomes relevant coincides with the theta one
and scaling exponents definitely start deviating from those valid for
homopolymers.Comment: 4 pages, 4 eps figure
Frequency Characteristics of Visually Induced Motion Sickness
This article was published in the journal, Human Factors [Sage Publications / © Human Factors and Ergonomics Society.]. The definitive version is available at: http://dx.doi.org/10.1177/0018720812469046Objective: The aim of this study was to explore
the frequency response of visually induced motion
sickness (VIMS) for oscillating linear motion in the foreand-
aft axis.
Background: Simulators, virtual environments,
and commercially available video games that create an
illusion of self-motion are often reported to induce
the symptoms seen in response to true motion. Often
this human response can be the limiting factor in the
acceptability and usability of such systems. Whereas
motion sickness in physically moving environments
is known to peak at an oscillation frequency around
0.2 Hz, it has recently been suggested that VIMS peaks
at around 0.06 Hz following the proposal that the
summed response of the visual and vestibular selfmotion
systems is maximized at this frequency. Methods: We exposed 24 participants to random
dot optical flow patterns simulating oscillating foreand-
aft motion within the frequency range of 0.025 to
1.6 Hz. Before and after each 20-min exposure, VIMS was
assessed with the Simulator Sickness Questionnaire.
Also, a standard motion sickness scale was used to rate
symptoms at 1-min intervals during each trial.
Results: VIMS peaked between 0.2 and 0.4 Hz with
a reducing effect at lower and higher frequencies.
Conclusion: The numerical prediction of the
âcrossover frequencyâ hypothesis, and the design
guidance curve previously proposed, cannot be accepted
when the symptoms are purely visually induced.
Application: In conditions in which stationary
observers are exposed to optical flow that simulates
oscillating fore-and-aft motion, frequencies around 0.2
to 0.4 Hz should be avoided
Scaling and universality in the anisotropic Kondo model and the dissipative two-state system
Scaling and universality in the Ohmic two-state system is investigated by
exploiting the equivalence of this model to the anisotropic Kondo model. For
the Ohmic two-state system, we find universal scaling functions for the
specific heat, , static susceptibility, , and
spin relaxation function depending on the reduced
temperature (frequency ), with
the renormalized tunneling frequency, and uniquely specified by the dissipation
strength (). The scaling functions can be used to extract
and in experimental realizations.Comment: 5 pages (LaTeX), 4 EPS figures. Minor changes, typos corrected,
journal reference adde
Evidence of Electromagnetic Absorption by Collective Modes in the Heavy Fermion Superconductor UBe13
We present results of a microwave surface impedance study of the heavy
fermion superconductor UBe13. We clearly observe an absorption peak whose
frequency- and temperature-dependence scales with the BCS gap function.
Resonant absorption into a collective mode, with energy approximately
proportional to the superconducting gap, is proposed as a possible
explantation
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