Using the Proximal Gradient and the Accelerated Proximal Gradient as a Canonical Polyadic tensor decomposition Algorithms in difficult situations

Canonical Polyadic (CP) tensor decomposition is useful in many real-world applications due to its uniqueness, and the ease of interpretation of its factor matrices. This work addresses the problem of calculating the CP decomposition of tensors in difficult cases where the factor matrices in one or all modes are almost collinear - i.e. bottleneck or swamp problems arise. This is done by introducing a constraint on the coherences of the factor matrices that ensures the existence of a best low-rank approximation, which makes it possible to estimate these highly correlated factors. Two new algorithms optimizing the CP decomposition based on proximal methods are proposed. Simulation results are provided and demonstrate the good behaviour of these algorithms, as well as a better compromise between accuracy and convergence speed than other algorithms in the literature

Performance Index for Tensor Polyadic Decompositions

International audienceIt is proposed to isolate the computation of the scaling matrix in CP tensor decompositions. This has two implications. First, the conditioning of the problem shows up explicitly, and could be controlled via a constraint on the so-called coherences. Second, a performance measure concerning only the factor matrices can be exactly calculated, and does not present the optimistic bias of the minimal error generally utilized in the literature. In fact, for tensors of order $d$, it suffices to solve a degree-2 polynomial system in $d$ variables. We subsequently give an explicit solution when d=3

Surface Mixing and Biological Activity in The North African Upwelling

International audienceNear-shore water along The North African margin represent one of the world's major upwelling regions. It is characterized by a high productivity of plankton associated with large commercial fisheries. Being characterized by physical structures of oceanic front such as eddies and filaments that influence the biological productivity, the study of these physical oceanic structures in connection with the chlorophyll has a fundamental importance for understanding how the plankton distributions is controlled. The aim of this work is to study the horizontal stirring and mixing in the upwelling area using attracting/repelling Lagrangian coherent structures (LCS) obtained as subset of hyperstreamline of the Cauchy-Green strain tensor, whom the normal repulsion rate is larger than tangential stretch over backward/forward time interval, and their link to the chlorophyll fronts concentrations, based on 10 years satellite data. These LCS move with the flow as material line, thus the horizontal mixing is calculated from the intersection of theses LCS with the finite time lyapunov exponent (FTLE) map. The temporal variability of surface stirring is compared to the fronts chlorophyll concentration, showing similar seasonal variations, nearly coincident maxima and minima, leading to a global positive correlation. This contradicts a recent work on the same region, which found negative correlation. However this work was based on Finite Size Lyapunov Exponent, (FSLE) whose output is a plot of scalar distributions. FSLE can only provide LCS for sharp enough ridges of nearly constant height. In the other hand, the method we use here (variational theory of hyperbolic LCS) yields analytical solutions of LCS as material lines that extremize the normal repulsion/attraction overall nearby material lines

Robust Detection of the North-West African Upwelling From SST Images

International audienceAnalysis and study of coastal upwelling using sea surface temperature (SST) satellite images is a common procedure because of its coast effectiveness (economic, time, frequency, and manpower). Developing on the Ekman theory, we propose a robust method to identify the upwelling regions along the northwest African margin. The proposed method comes to overcome the issues encountered in a recent method devoted for the same purpose and for the same upwelling system. Afterward, we show how our method can serve as a framework to study and monitor the spatio-temporal variability of the upwelling phenomenon in the studied region

A Fourier approach to Lagrangian vortex detection

International audienceWe study the transport properties of coherent vortices over a finite time duration. Here we reveal that such vortices can be identified based on frequency-domain representation of Lagrangian trajectories. We use Fourier analysis to convert particles' trajectories from their time domain to a presentation in the frequency domain. We then identify and extract coherent vortices as material surfaces along which particles' trajectories share similar frequencies. Our method identifies all coherent vortices in an automatic manner, showing high vortices' monitoring capacity. We illustrate our new method by identifying and extracting Lagrangian coherent vortices in different two-and three-dimensional flows

On Detectability of Moroccan Coastal Upwelling in Sea Surface Temperature Satellite Images

International audienceThis work aims at automatically identify the upwelling areas in coastal ocean of Morocco using the Sea Surface Temperature (SST) satellite images. This has been done by using the fuzzy clustering technique. The proposed approach is started with the application of Gustafson-Kessel clustering algorithm in order to detect groups in each SST image with homogenous and non-overlapping temper-ature, resulting in a c-partitioned labeled image. Cluster validity indices are used to select the c-partition that best reproduces the shape of upwelling areas. An area opening technique is developed that is used to filter out the residuals noise and fine structures in offshore waters not belonging to the upwelling regions. The de-veloped algorithm is applied and adjusted over a database of 70 SST images from years 2007 and 2008, covering the southern part of Moroccan atlantic coast. The system was evaluated by an oceanographer and provided acceptable results for a wide variety of oceanographic conditions

Performance Analysis of Synthetic Mobility Models and Mobile Ad Hoc Routing Protocols

Routing protocols heavily influenced by the node motion applied. Many performance analyses are already done with a lot of flaws. But, they do not look to all influenced constraints. Sometimes, they evaluate routing protocols without taken into consideration mobility models. They often analyze them using one routing protocol. Whereas, Simulation time employed is too short. It mainly impacts performance metrics of many mobility models. Or usually, simulation area used is small. It influences the number of packets received. In this study, we aim to summarize all these several parameters into 90 different scenarios with an average of 1350 simulated files. We will combine some well-known mobility models with the most prominent mobile Ad hoc routing protocols in order to analyze their accurate behaviors in one experimental synthesis paper. That shows results of three performance metrics combined with five mobile ad hoc routing protocols under three synthetic mobility models. All these parameters are applied to two dissimilar simulation areas, a small one with (220 m x 220 m) and a large one with (1020 m x 1020 m). Basing on one exhaustive analysis with all these details like this paper; leads to well understand the accurate behaviors of routing protocols and mobility models used. By displaying the ability of every routing protocol to deal with some topology changes, as well as to ensure network performances

Surface mixing and biological activity in the North-West African upwelling

International audienceNear-shore water along the NorthWest African margin is one of the world's major upwelling regions. It is associated with physical structures of oceanic fronts which influence the biological productivity. The study of these coherent structures in connection with chlorophyll concentration data is of fundamental importance for understanding the spatial distributions of the plankton. In this work, we study the horizontal stirring and mixing in different upwelling areas using Lagrangian coherent structures (LCSs). These LCSs are calculated using the recent geodesic theory of LCSs. We use these LCSs to study the link between the chlorophyll fronts concentrations and surface mixing, based on 10 years of satellite data. These LCSs move with the flow as material lines, thus the horizontal mixing is calculated from the intersection of these LCSs with the finite time Lyapunov exponents (FTLEs) maps. We compare our results with those of a recent study conducted over the same area, but based on Finite Size Lyapunov Exponents (FSLEs) whose output is a plot of scalar distributions. We discuss the differences between FSLE and geodesic theory of LCS. The latter yields analytical solutions of LCSs, while FSLEs can only provide LCSs for sharp enough ridges of nearly constant height

Optimization of UHF RFID five-slotted patch tag design using PSO algorithm for biomedical sensing systems

In this paper, a new flexible wearable radio frequency identification (RFID) five-shaped slot patch tag placed on the human arm is designed for ultra-high frequency (UHF) healthcare sensing applications. The compact proposed tag consists of a patch structure provided with five shaped slot radiators and a flexible substrate, which minimize the human body’s impact on the antenna radiation performance. We have optimized our designed tag using the particle swarm optimization (PSO) method with curve fitting within MATLAB to minimize antenna parameters to achieve a good return loss and an attractive radiation performance in the operating band. The PSO-optimized tag’s performance has been examined over the specific placement in some parts of the human body, such as wrist and chest, to evaluate the tag response and enable our tag antenna conception in wearable biomedical sensing applications. Finally, we have tested the robustness of this tag by evaluating its sensitivity as a function of the antenna radiator placement over the ground plane or by shaping the ground plane substrate for the tag’s position from the human body. Our numerical results show an optimal tag size with good matching features and promising read ranges near the human body

An Efficient Tool for Automatic Delimitation of Moroccan Coastal Upwelling Using SST Images

International audienceAn unsupervised classification method is developed for the coarse segmentation of Moroccan coastal upwelling using the Sea Surface Temperature (SST) satellite images. The algorithm is started with the generation of c-partitioned labeled image using Otsu's method for the purpose of finding regions of homogenous temperatures. Then two well-known validity indices are used to select the c-partition which best reproduce the shape of upwelling area. A region-growing algorithm is developed that is used to remove the noisy structures in the offshore waters not belonging to the upwelling area. The algorithm is used to provide a seasonal variability of upwelling activity in the southern Moroccan Atlantic coast using 70 SST images of the years 2007 and 2008. The performance of the proposed methodology has been validated by an oceanographer, showing its effectiveness for automatic delimitation of Moroccan upwelling region