Jorge Macías

New chemometrics in laser-induced breakdown spectroscopy for recognizing explosive residues

Detection of explosives in traces is an important area for preventing terrorist attacks and for anticipating their disastrous consequences. Laser-induced breakdown spectroscopy (LIBS) has been demonstrated to be an effective analytical technique for the detection and characterization of energetic materials. However, the major obstacle in the identification of explosives is their elevated spectral similarity with those compounds that share an analogous elemental composition. Despite that a number of different chemometric methods have been developed in the past for the detection of explosives, this hurdle remains latent today. Our recent efforts have been focused on the use of an alternative chemometric approach for improving the sensitivity and selectivity of LIBS for residue explosives identification. Through the survey of the spectral responses from the analysis of a variety of organic residues (either explosive or potential confusant materials) located on the surface of a support, relationships between the optical emission behaviors of residues and their corresponding hazardous nature have been extracted. By using the original intensities of the most relevant emission signals (C : CN : C2 : H : N : O) properly projected onto 2D subspaces, different machine learning classifiers have been designed and trained. This approach has been demonstrated to be capable for the identification of organic explosive residues against several potential confusant materials when they are placed on the surface of an aluminum support. False positive and false negative rates better than 5% are achieved. These results evidence a great stride in solving this particular problem, enabling the LIBS technology as a practical tool in complex applications related to homeland security.

Advanced recognition of explosives in traces on polymer surfaces using LIBS and supervised learning classifiers

The large similarity existing in the spectral emissions collected from organic compounds by laser-induced breakdown spectroscopy (LIBS) is a limiting factor for the use of this technology in the real world. Specifically, among the most ambitious challenges of todays LIBS involves the recognition of an organic residue when neglected on the surface of an object of identical nature. Under these circumstances, the development of an efficient algorithm to disclose the minute differences within this highly complex spectral information is crucial for a realistic application of LIBS in countering explosive threats. An approach cemented on scatter plots of characteristic emission features has been developed to identify organic explosives when located on polymeric surfaces (teflon, nylon and polyethylene). By using selected spectral variables, the approach allows to design a concise classifier for alerting when one of four explosives (DNT, TNT, RDX and PETN) is present on the surface of the polymer. Ordinary products (butter, fuel oil, hand cream, olive oil and motor oil) cause no confusion in the decisions taken by the classifier. With rates of false negatives and false positives below 5%, results demonstrate that the classification algorithm enables to label residues according to their harmful nature in the most demanding scenario for a LIBS sensor.

Recognition of explosives fingerprints on objects for courier services using machine learning methods and laser-induced breakdown spectroscopy

During recent years laser-induced breakdown spectroscopy (LIBS) has been considered one of the techniques with larger ability for trace detection of explosives. However, despite of the high sensitivity exhibited for this application, LIBS suffers from a limited selectivity due to difficulties in assigning the molecular origin of the spectral emissions observed. This circumstance makes the recognition of fingerprints a latent challenging problem. In the present manuscript the sorting of six explosives (chloratite, ammonal, DNT, TNT, RDX and PETN) against a broad list of potential harmless interferents (butter, fuel oil, hand cream, olive oil, …), all of them in the form of fingerprints deposited on the surfaces of objects for courier services, has been carried out. When LIBS information is processed through a multi-stage architecture algorithm built from a suitable combination of 3 learning classifiers, an unknown fingerprint may be labeled into a particular class. Neural network classifiers trained by the Levenberg-Marquardt rule were decided within 3D scatter plots projected onto the subspace of the most useful features extracted from the LIBS spectra. Experimental results demonstrate that the presented algorithm sorts fingerprints according to their hazardous character, although its spectral information is virtually identical in appearance, with rates of false negatives and false positives not beyond of 10%. These reported achievements mean a step forward in the technology readiness level of LIBS for this complex application related to defense, homeland security and force protection.

Duality methods with an automatic choice of parameters Application to shallow water equations in conservative form

Summary. In [3] a duality numerical algorithm for solving variational inequalities based on certain properties of the Yosida approximation of maximal monotone operators has been introduced. The performance of this algorithm strongly depends on the choice of two constant parameters. In this paper, we consider a new class of algorithms where these constant parameters are replaced by functions. We show that convergence properties are preserved and look for optimal values of these two functions. In general these optimal values cannot be computed, as they depend on the exact solution. Therefore, we propose some strategies in order to approximate them. The resulting algorithms are applied to three variational inequalities in order to compare their performance with that of the original algorithm.

Improvement and generalization of a finite element shallow-water solver to multi-layer systems

This paper improves and generalizes to multi-layer systems the shallow-water solver presented in [Bermudez et al., IMA J. Numer. Anal., 11, 79–97 (1991)]. The model equations are discretized in time using the method of characteristics and the Euler implicit method. The space discretization is performed using the first-order Raviart–Thomas mixed finite element. A formulation of the non-linear equations to solve at each time step that takes into account regions without water is given, and numerical results are presented in which this situation takes place for the one-dimensional case. These non-linear problems are solved by a duality technique with an automatic choice of parameters that greatly improves the convergence of the algorithm. A preconditioner has been designed for solving the linear problems that appear at each iteration of the duality method, which significantly reduces the computational cost. This is illustrated with some numerical examples. Finally, an application of the multi-layer model to a realistic geometry of the Alboran Sea is presented, giving good results from a qualitative point of view. Copyright

Improved FVM for two-layer shallow-water models: Application to the Strait of Gibraltar

This paper deals with the numerical simulation of flows of stratified fluids through channels with irregular geometry. Channel cross-sections are supposed to be symmetric but not necessarily rectangular. The fluid is supposed to be composed of two shallow layers of immiscible fluids of constant densities, and the flow is assumed to be one-dimensional. Therefore, the equations to be solved are a coupled system composed of two Shallow Water models with source terms involving depth and breadth functions. Extensions of Roes Q-scheme are proposed where a suitable treatment of the coupling and source terms is performed by adapting the techniques developed in [Vazquez-Cendon ME. Improved treatment of source terms in upwind schemes for the shallow water equations in channels with irregular geometry. J Comp Phys 1999;148:497-526; Garcia-Navarro P, Vazquez-Cendon ME. On numerical treatment of the source terms in the shallow water equations. Comput Fluids 2000;29(8):17-45; Castro MJ, Macias J, Pares C. A Q-Scheme for a class of systems of coupled conservation laws with source term. Application to a two-layer 1-D shallow water system. Math Model Numer An 2001;35(1):107-27]. Finally we apply the numerical scheme to the simulation of the flow through the Strait of Gibraltar. Real bathymetric and coast-line data are considered to include in the model the main features of the abrupt geometry of this natural strait connecting the Atlantic Ocean and the Mediterranean Sea. A steady state solution is obtained from lock-exchange initial conditions. This solution is then used as initial condition to simulate the main semidiurnal and diurnal tidal waves in the Strait of Gibraltar through the imposition of suitable boundary conditions obtained from observed tidal data. Comparisons between numerical results and observed data and some tests on friction sensitivity are also presented.

A two-layer finite volume model for flows through channels with irregular geometry: Computation of maximal exchange solutions: Application to the Strait of Gibraltar

Abstract The aim of this paper is to present a numerical model for solving the two layer exchange problem through channels with irregular geometry both in breadth and depth and the obtaining of maximal exchange solutions as defined by Armi and Farmer [J. Fluid Mech. 164 (1986) 27]. First, the equations are presented for each of the two layers of fluid. For numerically approximate the solution of the two layer system, we have considered the first-order upwind scheme presented by M.J. Castro, J. Macias, C. Pares, M.A. Vazquez-Cendon (in preparation). Then, the model is used to compute a maximal exchange solution for a channel with rectangular cross-sections and a single bump. This solution is compared against the approximate analytical solutions provided by Armi and Farmer [J. Fluid Mech. 164 (1986) 53]. Finally, the model is used to obtain a maximal two-layer exchange flow through the Strait of Gibraltar for which a realistic geometry has been considered.

On the convergence of the Bermúdez-Moreno algorithm with constant parameters

Bermúdez-Moreno [5] presents a duality numerical algorithm for solving variational inequalities of the second kind. The performance of this algorithm strongly depends on the choice of two constant parameters. Assuming a further hypothesis of the inf-suptype, we present here a convergence theorem that improves on the one presented in [5]: we prove that the convergence is linear, and we give the expression of the asymptotic error constant and the explicit form of the optimal parameters, as a function of some constants related to the variational inequality. Finally, we present some numerical examples that confirm the theoretical results.

Spatial variability of prodeltaic undulations on the Guadalfeo River prodelta: support to the genetic interpretation as hyperpycnal flow deposits

Abstract Two fields of prodeltaic undulations located off the Guadalfeo River were studied by integrating surficial (multibeam bathymetry, backscatter, sediment samples) and sub-surface (seismic profiles, sediment cores) data. Our main motivation was to analyze the along- and across-shelf variability of the seafloor undulations, in order to obtain useful insights into genetic mechanisms. A geostatistical analysis was performed, based on the determination of characteristic parameters and derived relationships. The undulations occur over a concave-upward surface which shows a seaward-decreasing slope. Most of the undulations are symmetrical to asymmetrically-oriented toward the coast. Two main fields are correlated with the present and previous river mouths. The western field, associated with the modern river mouth, is highly symmetrical, with the higher undulations in an axial position and diminishing the width/height relationship both laterally and downslope. In contrast, the eastern field, associated with an historic river mouth, shows lower-amplitude undulations, the width/height changes are less pronounced, and the undulations are more elongated. The two undulation fields exhibit subseafloor reflections that are subparallel to the seafloor, with peaks that migrate upslope upward in the stratigraphic column and which appear to correlate with coarse-grained layers. We support the contention that prodeltaic undulations off the Guadalfeo River should be regarded as sediment waves. Assuming a sediment-wave process, a strong normal-to-contour sediment flows with a riverine origin (e.g., hyperpycnal flows) may have been active during undulation generation. Both morphometric parameters of the river basin and estimations of sediment concentration during exceptional flood events are in agreement with an episodic activity of high freshwater discharges. Most of the geomorphic parameters and stratigraphic observations indicate a change of sediment supply conditions related to the shift in river mouth position, attributed to a temporal change in the activity of hyperpycnal flows.

A multivariate intercomparison between three oceanic GCMs using observed current and thermocline depth anomalies in the tropical Pacific during 1985-1992

Abstract The thermocline depth anomalies during 1985–1992 and the 15-m current anomalies during 1988–1992 simulated by three oceanic general circulation models (OGCMs) of the tropical Pacific forced by different surface wind stress fields are compared to observations using a multivariate model testing procedure. The Hadley Centre model, OPA from LODYC, Paris, and HOPE from MPI, Hamburg, were forced by wind stress fields derived from the pseudo-wind stress produced from surface marine reports at the Florida State University (FSU) or from the response of atmospheric general circulation models (AGCMs) (ARPEGE, ECHAM3 and the Hadley Centre model) to the observed sea surface temperature (SST). It is found that the three oceanic models simulate the thermocline depth anomalies rather well, although large discrepancies with the observations remain, in particular, in the eastern part of the Pacific, and that they simulate them better than the surface current anomalies, without clear correspondence in model skill between the two variables. The simulated thermocline depth anomalies are also less sensitive to the choice of the wind stress. In general, the FSU wind stress leads to reliable simulations for both variables, while a given atmospheric model field may lead to a good simulation with one ocean model and to a bad one with another. Overall, the analysis suggests that the model parameters, which optimize a variable using a particular forcing, are not necessarily appropriate for another variable or another forcing, which suggests that some of the physics are not correctly represented in the oceanic models.