San Luis Potosí, Mexico
San Luis Potosí, Mexico
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Baro J.,University of Barcelona | Illa X.,University of Barcelona | Planes A.,University of Barcelona | Salje E.K.H.,University of Cambridge | And 3 more authors.
Physical Review Letters | Year: 2013

It has long been stated that there are profound analogies between fracture experiments and earthquakes; however, few works attempt a complete characterization of the parallels between these so separate phenomena. We study the acoustic emission events produced during the compression of Vycor (SiO 2). The Gutenberg-Richter law, the modified Omori's law, and the law of aftershock productivity hold for a minimum of 5 decades, are independent of the compression rate, and keep stationary for all the duration of the experiments. The waiting-time distribution fulfills a unified scaling law with a power-law exponent close to 2.45 for long times, which is explained in terms of the temporal variations of the activity rate. © 2013 American Physical Society.

Melchor-Aguilar D.,IPICYT | Kharitonov V.,Sankt Petersburg State University
International Journal of Robust and Nonlinear Control | Year: 2010

In this paper we consider a special class of integral delay systems arising in several stability problems of time-delay systems. For these integral systems we derive stability and robust stability conditions in terms of Lyapunov-Krasovskii functionals. More explicitly, after providing the stability conditions we compute quadratic functionals and apply them to derive exponential estimates for solutions, and robust stability conditions for perturbed integral delay systems. Copyright © 2008 John Wiley & Sons, Ltd.

Reyes-Reyes M.,Autonomous University of San Luis Potosi | Cruz-Cruz I.,Autonomous University of San Luis Potosi | Lopez-Sandoval R.,IPICYT
Journal of Physical Chemistry C | Year: 2010

A significant increase of the electrical conductivity of PEDOT:PSS films, brought about by the addition of dimethyl sulfate (DMS, (CH3) 2SO4), while preserving the films excellent flexibility and visible-light transparency, is reported. The electrical and morphological properties of the films were studied as a function of DMS concentration. At an optimal concentration of around 1:25 (DMS to PEDOT:PSS), the conductivity of the films is enhanced by a factor on the order of 1880 times that of pristine PEDOT:PSS films. Extensive spectroscopic measurements using absorbance, Raman, and FTIR techniques, as well as structural characterization by AFM microscopy, were performed. These measurements support the idea that the mechanism responsible for the conductivity enhancement is the partial replacement of the PSS- segments by SO4 -2 anionic sulfates when a small amount of DMS is added to a PEDOT:PSS solution. This mechanism is associated with an increase of doping, and this doping can be understood in the following manner: due to that the SO3 - ions of the PSS segment only carry one negative charge, it is more probable for them to create polaronic states, whereas the SO4 -2 ions are double charged, increasing the possibility of creating bipolaron carriers in the PEDOT backbone. In this way, the partial replacement of the PSS- segments by SO4 -2 ions increases the bipolaron population by an ion exchange process, and, as a consequence, the doping level is increased. © 2010 American Chemical Society.

Segura-Cardenas E.,Autonomous University of San Luis Potosi | Reyes-Reyes M.,Autonomous University of San Luis Potosi | Lopez-Sandoval R.,IPICYT
Journal of Physical Chemistry C | Year: 2012

The effects of the addition of different alcohol content (methanol, ethanol, octanol) to the ferrocene-xylene reaction mixture on the graphitization and the surface functionalization of multiwalled carbon nanotubes (f-MWCNTs) have been studied. The addition of very low alcohol content to the ferrocene-xylene mixture has negative effects on the average length of f-MWCNTs, which is possibly related to the use of ultrasound irradiation for mixing the xylene/alcohol reactants. As the alcohol content in the reaction mixture is increased, the oxygen atoms coming from the alcohol begin to have a positive effect on the average length of the synthesized f-MWCNTs, and at a volume ratio around 1:0.1 (xylene/alcohol), a relatively high alcohol content compared with other reports, the maximal increment on average length of the carbon nanotubes is obtained, and the graphitic quality of the sample, as a whole, is improved. After this optimal volume, the increase in the alcohol content in the ferrocene xylene solution results in more oxygen atoms and in stronger oxidative environment, which hinders the growth of f-MWCNTs. Moreover, the ratio between oxygen and carbon atoms of the alcohol molecule is responsible of the morphological and structural differences of the f-MWCNTs synthesized using the same volume but different type of alcohol. Finally, the use of alcohol introduces functional groups on the walls of MWCNTs increasing their chemical reactivity. © 2012 American Chemical Society.

Campos-Canton E.,Autonomous University of San Luis Potosi | Barajas-Ramirez J.G.,IPICyT | Solis-Perales G.,University of Guadalajara | Femat R.,IPICyT
Chaos | Year: 2010

In this paper, we present a class of three-dimensional dynamical systems having multiscrolls which we call unstable dissipative systems (UDSs). The UDSs are dissipative in one of its components but unstable in the other two. This class of systems is constructed with a switching law to display various multiscroll strange attractors. The multiscroll strange attractors result from the combination of several unstable "one-spiral" trajectories by means of switching. Each of these trajectories lies around a saddle hyperbolic stationary point. Thus, we describe how a piecewise-linear switching system yields multiscroll attractors, symmetric or asymmetric, with chaotic behavior. © 2010 American Institute of Physics.

Castle A.B.,U.S. Air force | Gracia-Espino E.,IPICYT | Nieto-Delgado C.,IPICYT | Terrones H.,Catholic University of Louvain | And 3 more authors.
ACS Nano | Year: 2011

The present study aims to investigate biocompatibility of silver nanoparticles (Ag-NPs) anchored to different types of multiwalled carbon nanotubes (MWNTs). The MWNTs were decorated with Ag-NPs via a novel chemical route without using any sulfur containing reagent. Three different MWNTs were used as substrate materials for anchoring Ag-NPs: MWNTs-Ag (pure carbon), COx-MWNTs-Ag (carboxyl functionalized), and CNx-MWNTs-Ag (nitrogen-doped). The Ag-NPs, synthesized without thiol capping groups, and which were strongly anchored to the nanotubes surfaces, exhibit an average size of 7 ± 1, 10 ± 1, and 12 ± 1 nm in MWNTs, COx-MWNTs, and CNx-MWNTs, respectively. To determine biocompatibility of these three types of novel hybrid Ag-nanotube materials, cellular function and immune response were evaluated in the human keratinocyte cell line (HaCaT). Cellular assays revealed marginal toxicity after 24 h, and full cellular recovery was observed at 48 h based on an MTS assay for cellular viability. Therefore, Ag-nanotube systems appear to be very different from isolated dispersed Ag-NPs, and due to the strong interactions between the Ag-NPs and the doped nanotube surfaces, they make the Ag particles less toxic because they are not released easily to the cells. Pure carbon MWNTs appear to start releasing Ag-NPs at periods longer than 1 week by an observed decrease in cell proliferation. However, the use of N- and COx-doped MWNTs do not appear to release Ag-NPs to the cells due to the strong binding to the tube surfaces caused by the doped sites. We envisage the use of COx-MWNTs, and CNx-MWNTs anchored with Ag-NP as efficient drug delivery carriers and biosensors. © 2011 American Chemical Society.

Munoz-Sandoval E.,IPICYT
Journal of Nanoparticle Research | Year: 2014

Carbon nanotubes are currently one of the most important materials due to their strong mechanical resistance, light weight, and transport properties. Since the publication of Ijima's paper on tubular carbon structures (Iijima, Nature 354:56-58, 1991), approximately 80,000 research articles have been published according to the ISI web of science (WOS) database, using "carbon nanotube" as the search criterion in the search by topic option. In this work, the development and impact of nanoscience and nanotechnology (N&N) and carbon nanotubes on several research areas, journals, specific papers, and emerging research areas are analyzed and discussed. Considering the production of papers in these areas from 1997 to 2012, quantitatively speaking, the People's Republic of China is emerging as the leading country in N&N and carbon nanotube research, passing the United States of America. WOS data analysis of nanoscience, nanotechnology, and carbon nanotube research in developed and developing countries is discussed, and some ideas for accelerating the progress in these important research areas are proposed. © 2013 Springer Science+Business Media Dordrecht.

Melchor-Aguilar D.,IPICYT
International Journal of Systems Science | Year: 2014

The robust exponential stability of integral delay systems with exponential kernels is investigated. Sufficient delay-dependent robust conditions expressed in terms of linear matrix inequalities and matrix norms are derived by using the Lyapunov–Krasovskii functional approach. The results are combined with a new result on quadratic stabilisability of the state-feedback synthesis problem in order to derive a new linear matrix inequality methodology of designing a robust non-fragile controller for the finite spectrum assignment of input delay systems that guarantees simultaneously a numerically safe implementation and also the robustness to uncertainty in the system matrices and to perturbation in the feedback gain. © 2014 Taylor & Francis

Melchor-Aguilar D.,IPICYT
Proceedings of the IEEE Conference on Decision and Control | Year: 2011

In this paper, we consider some classes of continuous time difference systems with dicrete and distributed delay terms. For these infinite-dimensional systems we derive sufficient delay-dependent conditions for the exponential stability by using Lyapunov-Krasovskii functionals. © 2011 IEEE.

Campos-Canton E.,IPICyT | Femat R.,IPICyT | Chen G.,City University of Hong Kong
Chaos | Year: 2012

In this paper, we present a class of 3-D unstable dissipative systems, which are stable in two components but unstable in the other one. This class of systems is motivated by whirls, comprised of switching subsystems, which yield strange attractors from the combination of two unstable "one-spiral" trajectories by means of a switching rule. Each one of these trajectories moves around two hyperbolic saddle equilibrium points. Both theoretical and numerical results are provided for verification and demonstration. © 2012 American Institute of Physics.

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