9,777 research outputs found
Effects of additive noise on the stability of glacial cycles
It is well acknowledged that the sequence of glacial-interglacial cycles is
paced by the astronomical forcing. However, how much is the sequence robust
against natural fluctuations associated, for example, with the chaotic motions
of atmosphere and oceans? In this article, the stability of the
glacial-interglacial cycles is investigated on the basis of simple conceptual
models. Specifically, we study the influence of additive white Gaussian noise
on the sequence of the glacial cycles generated by stochastic versions of
several low-order dynamical system models proposed in the literature. In the
original deterministic case, the models exhibit different types of attractors:
a quasiperiodic attractor, a piecewise continuous attractor, strange nonchaotic
attractors, and a chaotic attractor. We show that the combination of the
quasiperiodic astronomical forcing and additive fluctuations induce a form of
temporarily quantised instability. More precisely, climate trajectories
corresponding to different noise realizations generally cluster around a small
number of stable or transiently stable trajectories present in the
deterministic system. Furthermore, these stochastic trajectories may show
sensitive dependence on very small amounts of perturbations at key times.
Consistently with the complexity of each attractor, the number of trajectories
leaking from the clusters may range from almost zero (the model with a
quasiperiodic attractor) to a significant fraction of the total (the model with
a chaotic attractor), the models with strange nonchaotic attractors being
intermediate. Finally, we discuss the implications of this investigation for
research programmes based on numerical simulators. }Comment: Parlty based on a lecture given by M. Crucifix at workshop held in
Rome in 2013 as a part of Mathematics of Planet Earth 201
Thermodynamic aspects of rock friction
Rate- and state-dependent friction law for velocity-step tests is analyzed
from a thermodynamic point of view. A simple macroscopic non-equilibrium
thermodynamic model with a single internal variable reproduces instantaneous
jump and relaxation. Velocity weakening appears as a consequence of a
plasticity related nonlinear coefficient. Permanent part of displacement
corresponds to plastic strain, and relaxation effects are analogous to creep in
thermodynamic rheology.Comment: 13 pages 3 figures. Revision: thermodynamic compatibility of velocity
weakenin
Noise reduction and hyperfine level coherence in spontaneous noise spectroscopy of atomic vapor
We develop a system for measurements of power spectra of transmitted light
intensity fluctuations, in which the extraneous noise, including shot noise, is
reduced. In essence, we just apply light, measure the power of the transmitted
light and derive its power spectrum. We use this to observe the spontaneous
noise spectra of photon atom interactions. Applying light with frequency
modulation, we can also observe the spontaneous noise reflecting the coherence
between the hyperfine levels in the excited state. There are two in novel
components in the measurement system, the noise reduction scheme and the
stabilization of the laser system. The noise reduction mechanism can be used to
reduce the shot noise contribution to arbitrarily low levels through averaging,
in principle. This is combined with differential detection to keep unwanted
noise at low levels. The laser system is stabilized to obtain spectral width
below 1\,kHz without high frequency (MHz) noise. These methods are
described systematically and the performance of the asurement system is
examined through experimental results.Comment: 6pages. 4 figure
Range fluctuations of high energy muons passing through matter
The information about energy spectrum of sea level muons at high energies beyond magnetic spectrographs can be obtained from the underground intensity measurements if the fluctuations problems are solved. The correction factor R for the range fluctuations of high energy muons were calculated by analytical method of Zatsepin, where most probable energy loss parameter are used. It is shown that by using the R at great depth together with the slope, lambda, of the vertical depth-intensity (D-I) curve in the form of exp(-t/lambda), the spectral index, gamma, in the power law energy spectrum of muons at sea level can be obtained
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