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San Luis Potosí, Mexico

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

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. Source

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

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. Source

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

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. Source

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

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. Source

Munoz-Sandoval E.,IPICyT
Journal of Nanoparticle Research

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. Source

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