96 research outputs found
An Optimization Based Empirical Mode Decomposition Scheme for Images
Bidimensional empirical mode decompositions (BEMD) have been developed to decompose any bivariate function or image
additively into multiscale components, so-called intrinsic mode functions (IMFs), which are approximately orthogonal to each other with respect to the inner product. In this paper, a novel optimization problem is designed to achieve this decomposition which takes into account important features desired of the BEMD. Specifically, we propose a data-adapted iterative method which we call Opt-BEMD which minimizes in each iteration a smoothness functional subject to inequality constraints involving the strictly local extrema of the image. In this way, the method constructs a sparse data-adapted basis for the input function as well as an envelope in a mathematically stringent sense. Moreover, we propose an ensemble version of Opt-BEMD to strengthen its performance when applied to noise-contaminated images or images with only few extrema
A unique polar representation of the hyperanalytic signal
The hyperanalytic signal is the straight forward generalization of the
classical analytic signal. It is defined by a complexification of two canonical
complex signals, which can be considered as an inverse operation of the
Cayley-Dickson form of the quaternion. Inspired by the polar form of an
analytic signal where the real instantaneous envelope and phase can be
determined, this paper presents a novel method to generate a polar
representation of the hyperanalytic signal, in which the continuously complex
envelope and phase can be uniquely defined. Comparing to other existing
methods, the proposed polar representation does not have sign ambiguity between
the envelope and the phase, which makes the definition of the instantaneous
complex frequency possible.Comment: 2014 IEEE International Conference on Acoustics, Speech, and Signal
Processing (ICASSP
A different view on the vector-valued empirical mode decomposition (VEMD)
The empirical mode decomposition (EMD) has achieved its reputation by
providing a multi-scale time-frequency representation of nonlinear and/or
nonstationary signals. To extend this method to vector-valued signals (VvS) in
multidimensional (multi-D) space, a multivariate EMD (MEMD) has been designed
recently, which employs an ensemble projection to extract local extremum
locations (LELs) of the given VvS with respect to different projection
directions. This idea successfully overcomes the problems of locally defining
extrema of VvS. Different from the MEMD, where vector-valued envelopes (VvEs)
are interpolated based on LELs extracted from the 1-D projected signal, the
vector-valued EMD (VEMD) proposed in this paper employs a novel back projection
method to interpolate the VvEs from 1-D envelopes in the projected space.
Considering typical 4-D coordinates (3-D location and time), we show by
numerical simulations that the VEMD outperforms state-of-art methods.Comment: 7th International Congress on Image and Signal Processing (CISP
Deep Learning for Feynman's Path Integral in Strong-Field Time-Dependent Dynamics
Feynman's path integral approach is to sum over all possible spatio-temporal
paths to reproduce the quantum wave function and the corresponding time
evolution, which has enormous potential to reveal quantum processes in
classical view. However, the complete characterization of quantum wave function
with infinite paths is a formidable challenge, which greatly limits the
application potential, especially in the strong-field physics and attosecond
science. Instead of brute-force tracking every path one by one, here we propose
deep-learning-performed strong-field Feynman's formulation with
pre-classification scheme which can predict directly the final results only
with data of initial conditions, so as to attack unsurmountable tasks by
existing strong-field methods and explore new physics. Our results build up a
bridge between deep learning and strong-field physics through the Feynman's
path integral, which would boost applications of deep learning to study the
ultrafast time-dependent dynamics in strong-field physics and attosecond
science, and shed a new light on the quantum-classical correspondence
Probing material absorption and optical nonlinearity of integrated photonic materials
Optical microresonators with high quality () factors are essential to a
wide range of integrated photonic devices. Steady efforts have been directed
towards increasing microresonator factors across a variety of platforms.
With success in reducing microfabrication process-related optical loss as a
limitation of , the ultimate attainable , as determined solely by the
constituent microresonator material absorption, has come into focus. Here, we
report measurements of the material-limited factors in several photonic
material platforms. High- microresonators are fabricated from thin films of
SiO, SiN, AlGaAs and TaO. By using
cavity-enhanced photothermal spectroscopy, the material-limited is
determined. The method simultaneously measures the Kerr nonlinearity in each
material and reveals how material nonlinearity and ultimate vary in a
complementary fashion across photonic materials. Besides guiding microresonator
design and material development in four material platforms, the results help
establish performance limits in future photonic integrated systems.Comment: Maodong Gao, Qi-Fan Yang and Qing-Xin Ji contributed equally to this
work. 9 pages, 4 figures, 1 tabl
Two ultraviolet radiation datasets that cover China
Ultraviolet (UV) radiation has significant effects on ecosystems, environments, and human health, as well as atmospheric processes and climate change. Two ultraviolet radiation datasets are described in this paper. One contains hourly observations of UV radiation measured at 40 Chinese Ecosystem Research Network stations from 2005 to 2015. CUV3 broadband radiometers were used to observe the UV radiation, with an accuracy of 5%, which meets the World Meteorology Organization's measurement standards. The extremum method was used to control the quality of the measured datasets. The other dataset contains daily cumulative UV radiation estimates that were calculated using an all-sky estimation model combined with a hybrid model. The reconstructed daily UV radiation data span from 1961 to 2014. The mean absolute bias error and root-mean-square error are smaller than 30% at most stations, and most of the mean bias error values are negative, which indicates underestimation of the UV radiation intensity. These datasets can improve our basic knowledge of the spatial and temporal variations in UV radiation. Additionally, these datasets can be used in studies of potential ozone formation and atmospheric oxidation, as well as simulations of ecological processes
The influence of macrophytes on sediment resuspension and the effect of associated nutrients in a shallow and large lake (Lake Taihu, China)
A yearlong campaign to examine sediment resuspension was conducted in large, shallow and eutrophic Lake Taihu, China, to investigate the influence of vegetation on sediment resuspension and its nutrient effects. The study was conducted at 6 sites located in both phytoplankton-dominated zone and macrophyte-dominated zone of the lake, lasting for a total of 13 months, with collections made at two-week intervals. Sediment resuspension in Taihu, with a two-week high average rate of 1771 g.m(-2).d(-1) and a yearly average rate of 377 g.m(-2).d(-1), is much stronger than in many other lakes worldwide, as Taihu is quite shallow and contains a long fetch. The occurrence of macrophytes, however, provided quite strong abatement of sediment resuspension, which may reduce the sediment resuspension rate up to 29-fold. The contribution of nitrogen and phosphorus to the water column from sediment resuspension was estimated as 0.34 mg.L-1 and 0.051 mg.L-1 in the phytoplankton-dominated zone. Sediment resuspension also largely reduced transparency and then stimulated phytoplankton growth. Therefore, sediment resuspension may be one of the most important factors delaying the recovery of eutrophic Lake Taihu, and the influence of sediment resuspension on water quality must also be taken into account by the lake managers when they determine the restoration target.Peer reviewe
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