6,073 research outputs found
Scaling Analysis and Evolution Equation of the North Atlantic Oscillation Index Fluctuations
The North Atlantic Oscillation (NAO) monthly index is studied from 1825 till
2002 in order to identify the scaling ranges of its fluctuations upon different
delay times and to find out whether or not it can be regarded as a Markov
process. A Hurst rescaled range analysis and a detrended fluctuation analysis
both indicate the existence of weakly persistent long range time correlations
for the whole scaling range and time span hereby studied. Such correlations are
similar to Brownian fluctuations. The Fokker-Planck equation is derived and
Kramers-Moyal coefficients estimated from the data. They are interpreted in
terms of a drift and a diffusion coefficient as in fluid mechanics. All partial
distribution functions of the NAO monthly index fluctuations have a form close
to a Gaussian, for all time lags, in agreement with the findings of the scaling
analyses. This indicates the lack of predictive power of the present NAO
monthly index. Yet there are some deviations for large (and thus rare) events.
Whence suggestions for other measurements are made if some improved
predictability of the weather/climate in the North Atlantic is of interest. The
subsequent Langevin equation of the NAO signal fluctuations is explicitly
written in terms of the diffusion and drift parameters, and a characteristic
time scale for these is given in appendix.Comment: 6 figures, 54 refs., 16 pages; submitted to Int. J. Mod. Phys. C:
Comput. Phy
On human motion prediction using recurrent neural networks
Human motion modelling is a classical problem at the intersection of graphics
and computer vision, with applications spanning human-computer interaction,
motion synthesis, and motion prediction for virtual and augmented reality.
Following the success of deep learning methods in several computer vision
tasks, recent work has focused on using deep recurrent neural networks (RNNs)
to model human motion, with the goal of learning time-dependent representations
that perform tasks such as short-term motion prediction and long-term human
motion synthesis. We examine recent work, with a focus on the evaluation
methodologies commonly used in the literature, and show that, surprisingly,
state-of-the-art performance can be achieved by a simple baseline that does not
attempt to model motion at all. We investigate this result, and analyze recent
RNN methods by looking at the architectures, loss functions, and training
procedures used in state-of-the-art approaches. We propose three changes to the
standard RNN models typically used for human motion, which result in a simple
and scalable RNN architecture that obtains state-of-the-art performance on
human motion prediction.Comment: Accepted at CVPR 1
On the Projective Geometry of Kalman Filter
Convergence of the Kalman filter is best analyzed by studying the contraction
of the Riccati map in the space of positive definite (covariance) matrices. In
this paper, we explore how this contraction property relates to a more
fundamental non-expansiveness property of filtering maps in the space of
probability distributions endowed with the Hilbert metric. This is viewed as a
preliminary step towards improving the convergence analysis of filtering
algorithms over general graphical models.Comment: 6 page
Statistical Derivation of the Evolution Equation of Liquid Water Path Fluctuations in Clouds
How to distinguish and quantify deterministic and random influences on the
statistics of turbulence data in meteorology cases is discussed from first
principles. Liquid water path (LWP) changes in clouds, as retrieved from radio
signals, upon different delay times, can be regarded as a stochastic Markov
process. A detrended fluctuation analysis method indicates the existence of
long range time correlations. The Fokker-Planck equation which models very
precisely the LWP empirical probability distributions, in
particular, their non-Gaussian heavy tails is explicitly derived and written in
terms of a drift and a diffusion coefficient. Furthermore, Kramers-Moyal
coefficients, as estimated from the empirical data, are found to be in good
agreement with their first principle derivation. Finally, the equivalent
Langevin equation is written for the LWP increments themselves. Thus rather
than the existence of hierarchical structures, like an energy cascade process,
{\it strong correlations} on different , from small to large
ones, are considered to be proven as intrinsic ingredients of such cloud
evolutions.Comment: 17 pages, 6 figures; to be published in Journal of Geophysical
Research - Atmosphere
Maximum Likelihood Estimation of ARMA Model with Error Processes for Replicated Observations
In this paper we analyse the repeated time series model where the fundamental component follows a ARMA process. In the model, the error variance as well as the number of repetition are allowed to change over time. It is shown that the model is identified. The maximum likelihood estimator is derived using the Kalman filter technique. The model considered in this paper can be considered as extension of the models considered by Anderson (1978), Azzalini (1981) and Wong and Miller (1990)ARMA model, Kalman filter, maximum likelihood estimation
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