20,118 research outputs found
Time dependent intrinsic correlation analysis of temperature and dissolved oxygen time series using empirical mode decomposition
In the marine environment, many fields have fluctuations over a large range
of different spatial and temporal scales. These quantities can be nonlinear
\red{and} non-stationary, and often interact with each other. A good method to
study the multiple scale dynamics of such time series, and their correlations,
is needed. In this paper an application of an empirical mode decomposition
based time dependent intrinsic correlation, \red{of} two coastal oceanic time
series, temperature and dissolved oxygen (saturation percentage) is presented.
The two time series are recorded every 20 minutes \red{for} 7 years, from 2004
to 2011. The application of the Empirical Mode Decomposition on such time
series is illustrated, and the power spectra of the time series are estimated
using the Hilbert transform (Hilbert spectral analysis). Power-law regimes are
found with slopes of 1.33 for dissolved oxygen and 1.68 for temperature at high
frequencies (between 1.2 and 12 hours) \red{with} both close to 1.9 for lower
frequencies (time scales from 2 to 100 days). Moreover, the time evolution and
scale dependence of cross correlations between both series are considered. The
trends are perfectly anti-correlated. The modes of mean year 3 and 1 year have
also negative correlation, whereas higher frequency modes have a much smaller
correlation. The estimation of time-dependent intrinsic correlations helps to
show patterns of correlations at different scales, for different modes.Comment: 35 pages with 22 figure
Lagrangian Cascade in Three-Dimensional Homogeneous and Isotropic Turbulence
In this work, the scaling statistics of the dissipation along Lagrangian
trajectories are investigated by using fluid tracer particles obtained from a
high resolution direct numerical simulation with . Both the
energy dissipation rate and the local time averaged
agree rather well with the lognormal distribution hypothesis.
Several statistics are then examined. It is found that the autocorrelation
function of and variance of
obey a log-law with scaling exponent
compatible with the intermittency parameter . The
th-order moment of has a clear power-law on the inertial
range . The measured scaling exponent agrees
remarkably with where is the scaling exponent
estimated using the Hilbert methodology. All these results suggest that the
dissipation along Lagrangian trajectories could be modelled by a multiplicative
cascade.Comment: 10 pages with 7 figures accepted for Journal of Fluid Mechanics as
Rapid
PID and PID-like controller design by pole assignment within D-stable regions
This paper presents a new PID and PID-like controller design method that permits the designer to control the desired dynamic performance of a closed-loop system by first specifying a set of desired D-stable regions in the complex plane and then running a numerical optimisation algorithm to find the controller parameters such that all the roots of the closed-loop system are within the specified regions. This method can be used for stable and unstable plants with high order degree, for plants with time delay, for controller with more than three design parameters, and for various controller configurations. It also allows a unified treatment of the controller design for both continuous and discrete systems. Examples and comparative simulation results are pro-vided to illustrate its merit
Arbitrary-order Hilbert spectral analysis for time series possessing scaling statistics: a comparison study with detrended fluctuation analysis and wavelet leaders
In this paper we present an extended version of Hilbert-Huang transform,
namely arbitrary-order Hilbert spectral analysis, to characterize the
scale-invariant properties of a time series directly in an amplitude-frequency
space. We first show numerically that due to a nonlinear distortion,
traditional methods require high-order harmonic components to represent
nonlinear processes, except for the Hilbert-based method. This will lead to an
artificial energy flux from the low-frequency (large scale) to the
high-frequency (small scale) part. Thus the power law, if it exists, is
contaminated. We then compare the Hilbert method with structure functions (SF),
detrended fluctuation analysis (DFA), and wavelet leader (WL) by analyzing
fractional Brownian motion and synthesized multifractal time series. For the
former simulation, we find that all methods provide comparable results. For the
latter simulation, we perform simulations with an intermittent parameter {\mu}
= 0.15. We find that the SF underestimates scaling exponent when q > 3. The
Hilbert method provides a slight underestimation when q > 5. However, both DFA
and WL overestimate the scaling exponents when q > 5. It seems that Hilbert and
DFA methods provide better singularity spectra than SF and WL. We finally apply
all methods to a passive scalar (temperature) data obtained from a jet
experiment with a Taylor's microscale Reynolds number Relambda \simeq 250. Due
to the presence of strong ramp-cliff structures, the SF fails to detect the
power law behavior. For the traditional method, the ramp-cliff structure causes
a serious artificial energy flux from the low-frequency (large scale) to the
high-frequency (small scale) part. Thus DFA and WL underestimate the scaling
exponents. However, the Hilbert method provides scaling exponents
{\xi}{\theta}(q) quite close to the one for longitudinal velocity.Comment: 13 pages, 10 figure
Static and dynamic structure factors in the Haldane phase of the bilinear-biquadratic spin-1
The excitation spectra of the T=0 dynamic structure factors for the spin,
dimer, and trimer fluctuation operators as well as for the newly defined center
fluctuation operator in the one-dimensional S=1 Heisenberg model wi th
isotropic bilinear and biquadratic exchange are
investigated via the recursion method for systems with up to N=18 site s over
the predicted range, , of the topologically ordered
Haldane phase. The four static and dynamic structure factors probe t he
ordering tendencies in the various coupling regimes and the elementary and
composite excitations which dominate the T=0 dynamics. At (VBS point), the dynamically relevant spectra in the invariant
subspaces with total spin are dominated by a branch of magnon
states , by continua of two-magnon scattering states , and by discrete branches of two-magnon bound states with positive
interaction energy . The dimer and trimer spectra at ar e
found to consist of single modes with -independent excitation energies
and , where is
the ground-state energy per site. The basic structure of the dynamically
relevant excitation spectrum remains the same over a substantial parameter
range within the Haldane phase. At the transition to the dimerized phase
(), the two-magnon excitations turn into two-spinon excitations.Comment: 12 pages, 4 Postscript figure
Inelastic X-ray scattering from valence electrons near absorption edges of FeTe and TiSe
We study resonant inelastic x-ray scattering (RIXS) peaks corresponding to
low energy particle-hole excited states of metallic FeTe and semi-metallic
TiSe for photon incident energy tuned near the absorption edge of
Fe and Ti respectively. We show that the cross section amplitudes are well
described within a renormalization group theory where the effect of the core
electrons is captured by effective dielectric functions expressed in terms of
the the atomic scattering parameters of Fe and Ti. This method can be
used to extract the dynamical structure factor from experimental RIXS spectra
in metallic systems.Comment: 6 pages, 4 figure
Multifractal Scaling of Thermally-Activated Rupture Processes
We propose a ``multifractal stress activation'' model combining thermally
activated rupture and long memory stress relaxation, which predicts that
seismic decay rates after mainshocks follow the Omori law with
exponents linearly increasing with the magnitude of the mainshock and
the inverse temperature. We carefully test this prediction on earthquake
sequences in the Southern California Earthquake catalog: we find power law
relaxations of seismic sequences triggered by mainshocks with exponents
increasing with the mainshock magnitude by approximately for each
magnitude unit increase, from to ,
in good agreement with the prediction of the multifractal model.Comment: four pages and 2 figure
Sol-gel niobium pentoxide coatings: Applications to photovoltaic energy conversion and electrochromism
In the last decade the sol-gel process became a promising method to synthesize materials in form of coatings, nanoscale powders and porous systems. Several products or devices made with such a process already exist on the market. This paper briefly reviews the state of the art in the development of electrochromic coatings and devices and nanocrystalline solar cells achieved during the last decade using sol-gel derived pure and doped niobium pentoxide
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