CONACyT Research Fellow

Mexico City, Mexico

CONACyT Research Fellow

Mexico City, Mexico
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Aguirre-Ramos H.,University of Guanajuato | Avina-Cervantes J.G.,University of Guanajuato | Cruz-Aceves I.,CONACYT Research Fellow
AIP Conference Proceedings | Year: 2016

This work presents a new method for automatic threshold selection and its application for bone segmentation in CT images. Based on the mean (μ) and standard deviation (σ) values of an automatically selected region from a Gabor filter response, the proposed method prevents the misclassification of medium and high-valued pixels in images with high density of low-valued (background) pixels like those in medical images. The method obtains an average accuracy of 98.9% and a mean local accuracy of 76.7% using a database of 60 CT images. In addition, the proposed method shows a better performance than the comparative threshold (Otsu and Kittler) and clustering (Fuzzy C-means and K-means) methods applied under same conditions. © 2016 Author(s).


Oliveira T.R.,State University of Rio de Janeiro | Estrada A.,CONACYT Research Fellow | Fridman L.M.,National Autonomous University of Mexico
Automatica | Year: 2017

In this paper we introduce a global differentiator based on higher-order sliding modes (HOSM) and dynamic gains to solve the problem of trajectory tracking via output-feedback for a class of uncertain nonlinear plants with arbitrary relative degree and disturbances. Norm observers for the unmeasured state are employed to dominate the disturbances as well as to adapt the gains of the proposed differentiator since the nonlinearities may be state-dependent and time-varying. Uniform global stability and robust exact tracking are guaranteed employing the proposed HOSM based exact differentiator. The obtained results are not restricted to first-order sliding mode control feedback, but applies for second order sliding mode algorithms (twisting, super-twisting and variable gain super-twisting) as well as quasi-continuous HOSM finite-time controllers. Simulations with an aircraft pitch-control application illustrate the claimed properties, even in the presence of measurement noise. © 2017 Elsevier Ltd


PubMed | CONACYT Research Fellow, University of Texas at San Antonio, Research Center Aplicada en Ambiente y Salud and Autonomous University of San Luis Potosi
Type: | Journal: The Science of the total environment | Year: 2016

The aim of this study was to conduct a POP biomonitoring programme for children in high-risk areas. We evaluated 247 serum samples from children between the ages of 6 and 12years old from two zones in Mexico: (1) indigenous zones, which included Cuatlamayan (CUA), Tocoy (TOC), and Santa Maria Picula (SAM); and (2) industrial zones, which included Tercera Chica (TC), Industrial San Luis (IND) and Rincon de San Jose (SJR); Mundo Nuevo (MN); and Alpuyeca (ALP). Our results showed that -endosulfan was similar to CUA, TOC, SAM, TC and MN (178.6-306.9ng/g lipid). -Endosulfan levels were higher in ALP (901.5ng/g lipid), followed by CUA (139.9ng/g lipid) and TOC, SAM, TC and MN, which had similar levels (55.4-64.5ng/g lipid). For endosulfan sulfate, the ALP community had the highest concentration levels (1096.4ng/g lipid), whereas CUA and TOC (212.3 and 289ng/g lipid, respectively) had concentrations similar to those found in SAM and TC (99.5 and 119.1ng/g lipid, respectively). DDE levels were found in malaria-endemic areas of SAM, CUA and TOC (1782.2, 1358.3 and 57.0ng/g lipid), followed by MN (35.1ng/g lipid). HCB concentration levels were found to be higher in MN and SJR (691.8 and 575.4ng/g lipid, respectively), followed by CUA and TC (363.9 and 269.1ng/g lipid, respectively), with levels similar to those found in TOC and SAM (191.8 and 181.9ng/g lipid, respectively). Finally, PCB 101 concentration levels were found to be the highest in ALP (1032.7ng/g lipid), followed by similar levels of SJR and IND (567.5 and 327.3ng/g lipid, respectively) and TC and MN, with 109.1 and 144.5ng/g lipid, respectively. The evidence provided by this exploratory study indicates that the evaluation of the health risks posed to children living in contaminated areas is a high priority health issue.


Graff M.,CONACYT Research Fellow | Escalante H.J.,National Institute of Astrophysics, Optics and Electronics | Ornelas-Tellez F.,Universidad Michoacana de San Nicolás de Hidalgo | Tellez E.S.,CONACYT Research Fellow
Natural Computing | Year: 2016

Genetic programming (GP) is an evolutionary algorithm that has received a lot of attention lately due to its success in solving hard world problems. There has been a lot of interest in using GP to tackle forecasting problems. Unfortunately, it is not clear whether GP can outperform traditional forecasting techniques such as auto-regressive models. In this contribution, we present a comparison between standard GP systems qand auto-regressive integrated moving average model and exponential smoothing. This comparison points out particular configurations of GP that are competitive against these forecasting techniques. In addition to this, we propose a novel technique to select a forecaster from a collection of predictions made by different GP systems. The result shows that this selection scheme is competitive with traditional forecasting techniques, and, in a number of cases it is statistically better. © 2016 Springer Science+Business Media Dordrecht


Moreno-Galindo E.G.,University of Colima | Alamilla J.,CONACyT Research Fellow | Sanchez-Chapula J.A.,University of Colima | Tristani-Firouzi M.,University of Utah | Navarro-Polanco R.A.,University of Colima
Pflugers Archiv European Journal of Physiology | Year: 2016

Recently, it has been shown that G protein-coupled receptors (GPCRs) display intrinsic voltage sensitivity. We reported that the voltage sensitivity of M2 muscarinic receptor (M2R) is also ligand specific. Here, we provide additional evidence to understand the mechanism underlying the ligand-specific voltage sensitivity of the M2R. Using ACh, pilocarpine (Pilo), and bethanechol (Beth), we evaluated the agonist-specific effects of voltage by measuring the ACh-activated K+ current (IKACh) in feline and rabbit atrial myocytes and in HEK-293 cells expressing M2R-Kir3.1/Kir3.4. The activation of IKACh by the muscarinic agonist Beth was voltage insensitive, suggesting that the voltage-induced conformational changes in M2R do not modify its affinity for this agonist. Moreover, deactivation of the Beth-evoked IKACh was voltage insensitive. By contrast, deactivation of the ACh-induced IKACh was significantly slower at −100 mV than at +50 mV, while an opposite effect was observed when IKACh was activated by Pilo. These findings are consistent with the voltage affinity pattern observed for these three agonists. Our findings suggest that independent of how voltage disturbs the receptor binding site, the voltage dependence of the signaling pathway is ultimately determined by the agonist. These observations emphasize the pharmacological potential to regulate the M2R-parasympathetic associated cardiac function and also other cellular signaling pathways by exploiting the voltage-dependent properties of GPCRs. © 2016 Springer-Verlag Berlin Heidelberg


Ortega R.,Research Center Cientifica Educacion Superior Of Ensenada | Quintanar L.,National Autonomous University of Mexico | Huesca-Perez E.,CONACYT Research Fellow
Pure and Applied Geophysics | Year: 2016

The East Pacific Rise (EPR) and the Gulf of California (GC) have different tectonic histories. While the EPR has been present for 75 Ma, the GC started only 12.5 Myr. The region that links both systems is the Tamayo Fracture Zone, where a diffuse triple junction is located. A key question to be solved is whether the source mechanisms in this region reflect important variations from the GC to the EPR. Therefore, we analyzed the seismic moment tensors of the GC and the EPR using a full moment tensor inversion. This source model is useful in extensional regimes where isotropic components or complex faults are present. The full moment tensor is the best representation of the fault and slip direction in a rifting process because it resolves for six free parameters, including complex sources of pure shear dislocations. The analysis is similar to the deviatoric case, but the interpretation is different, because physical characteristics in the model allow for choosing a realistic style of rupture. Our results show that there are similarities between focal mechanisms determined by full moment tensors computed for the southern part of the GC and the EPR. We suggest that the EPR is tectonically linked to the GC not only at the diffuse triple junction region but also along the entire province. The rupture patterns of the GC and the EPR are slightly different: whereas the GC is partitioned by means of NW–SE faults, the EPR ruptures through a faulting system NE–SW. The geometrical relations of the extensional province of the GC and the EPR were present since the crustal thinning of the rifting process. Strain partitioning of faults explains easily the nature of the oblique divergence of the GC and the EPR. In addition, in our analysis, we observe clockwise rotation in the structures of the southern part of the GC, suggesting that there is a change in the spatial partitioning of this region. © 2015, Springer International Publishing.


Gonzalez-Gallegos J.G.,CONACYT Research Fellow | Castro-Castro A.,University of Guadalajara
Nordic Journal of Botany | Year: 2016

Salvia evadens (Lamiaceae) is described and illustrated as a new species discovered in Sierra del Halo, Jalisco, Mexico. It is similar in vegetative morphology to S. aequidistans. However, it differs from the latter by having less flowers per verticillaster, lanceolate floral bracts, 5- or 7-veined upper calyx lip, ornate connective with an acute tooth at the middle, and larger flowers and mericarps. A table with similarities and differences between both species is provided. Nordic Journal of Botany © 2016 Nordic Society Oikos.


Araujo-Perez D.J.,University of Central Mexico | Gonzalez-Garcia P.,CONACYT Research Fellow | Poisot M.,University of Papaloapan | Garcia-Gonzalez L.,University of Central Mexico
Materials Chemistry and Physics | Year: 2015

Carbon materials have been obtained by the chlorination reaction of Ti(C5H5)Cl2 at 900 °C, varying the reaction time at 30, 60, 90 and 120 min. The average microstructure, studied by X ray powder diffraction, suggest that these materials consist mainly of disordered carbon with low graphitization degree (from 13.5 to 16.5%). These results are in agreement with the Raman data since the D band (at ≠1350 cm-1) indicates that disordered carbon networks have appeared. The calculated in-plane correlation length increases from 4.04 to 4.70 nm as the chlorination time increases from 30 to 120 min. The textural analyses reveal adsorption isotherms type 1 with hysteresis H4, microporous areas as high as 855 m2/g and pore volume of 0.55 cm3/g. Additionally, an important contribution of mesoporosity, around 3.6 nm, was also detected. © 2015 Elsevier B.V.


Tellez E.S.,CONACYT Research Fellow | Ruiz G.,Universidad Michoacana de San Nicolás de Hidalgo | Chavez E.,CICESE
Information Systems | Year: 2016

The nearest neighbor search problem is fundamental in computer science, and in spite of the effort of a vast number of research groups, the instances allowing an efficient solution are reduced to databases of objects of small intrinsic dimensions. For intrinsically high-dimensional data, the only possible solution is to compromise and use approximate or probabilistic approaches. For the rest of the instances in the middle, there is an overwhelmingly large number of indexes of claimed good performance. However, the problem of parameter selection makes them unwieldy for use outside of the research community. Even if the indexes can be tuned correctly, either the number of operations for the index construction and tuning is prohibitively large or there are obscure parameters to tune-up. Those restrictions force users from different fields to use brute force to solve the problem in real world instances. In this paper, we present a family of indexing algorithms designed for end users. They require as input, the database, a query sample and the amount of space available. Our building blocks are standard discarding rules, and the indexes will add routing objects such as pivots, hyperplane references or cluster centroids. Those indexes are built incrementally and will self-tune by greedily searching for a global optimum in performance. We experimentally show that using this oblivious strategy our indexes are able to outperform state of the art, manually fine-tuned indexes. For example, our indexes are twice as fast than the fastest alternative (LC, EPT or VPT) for most of our datasets. In the case of LC, the faster alternative for high dimensional datasets, the difference is smaller than 5%. In the same case, our indexes are at least one order of magnitude faster to build. This superior performance is maintained for large, high dimensional datasets (100 million 12-dimensional objects). In this benchmark, our best index is two times faster than the closest alternative (VPT), six times faster than the majority of indexes, and more than sixty times faster than the sequential scan. © 2016 Elsevier Ltd. All rights reserved.


PubMed | University of Guanajuato, CONACYT Research Fellow and University of Leipzig
Type: Journal Article | Journal: Sensors (Basel, Switzerland) | Year: 2016

In this paper, a method of vascular structure identification in intraoperative 3D Contrast-Enhanced Ultrasound (CEUS) data is presented. Ultrasound imaging is commonly used in brain tumor surgery to investigate in real time the current status of cerebral structures. The use of an ultrasound contrast agent enables to highlight tumor tissue, but also surrounding blood vessels. However, these structures can be used as landmarks to estimate and correct the brain shift. This work proposes an alternative method for extracting small vascular segments close to the tumor as landmark. The patient image dataset involved in brain tumor operations includes preoperative contrast T1MR (cT1MR) data and 3D intraoperative contrast enhanced ultrasound data acquired before (3D-iCEUS(start) and after (3D-iCEUS(end) tumor resection. Based on rigid registration techniques, a preselected vascular segment in cT1MR is searched in 3D-iCEUS(start) and 3D-iCEUS(end) data. The method was validated by using three similarity measures (Normalized Gradient Field, Normalized Mutual Information and Normalized Cross Correlation). Tests were performed on data obtained from ten patients overcoming a brain tumor operation and it succeeded in nine cases. Despite the small size of the vascular structures, the artifacts in the ultrasound images and the brain tissue deformations, blood vessels were successfully identified.

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