Time filter

Source Type

Mereles M.F.,Chilean Center of Nanosciences and Nanotechnology | Rodas O.,Guyra Paraguay
Climatic Change | Year: 2014

A large portion of the Occidental Region of Paraguay consists of a semi-arid territory with vegetation adapted to the features of this region. For just over a decade, a process of intense deforestation has resulted from the expansion of mechanized farming, carried out without any form of land management or planning; this has led to the fragmentation of the forests in this region. This study has taken satellite imagery from 1975, 1990, 2000 and 2007 with the purpose of determining the average size of the fragments and the rate of forest discontinuity; the results of this multi-temporal imagery analysis show that (a) in some areas of the Central Chaco, the forest matrix was transformed principally into cropped areas; (b) the majority of the fragments are isolated from one other; and (c) the areas mostly covered by forests are in the north-northeastern and northwestern areas and this is mainly as a result of a greater concentration of protected areas. In conclusion, the vulnerability of the vegetation formations increases with the fragmentation process, to which we should add an increased frequency of fires, a reduced resilience and homeostasis of the vegetation formations; thus these are highly exposed to climate change factors. It is imperative that the forest landscapes be restored, through the implementation biological corridors, to ensure the continuity of the remaining forests. © 2014, Springer Science+Business Media Dordrecht.

Troncoso R.E.,Chilean Center of Nanosciences and Nanotechnology | Troncoso R.E.,University of Chile | Nunez T.S.,University of Chile
Annals of Physics | Year: 2014

A phenomenological theory is developed, that accounts for the collective dynamics of a Bose-Einstein condensate of magnons. In terms of such description we discuss the nature of spontaneous macroscopic interference between magnon clouds, highlighting the close relation between such effects and the well known Josephson effects. Using those ideas, we present a detailed calculation of the Josephson oscillations between two magnon clouds, spatially separated in a magnonic Josephson junction. © 2014 Elsevier Inc.

Troncoso R.E.,Chilean Center of Nanosciences and Nanotechnology | Nunez T.S.,University of Chile
Annals of Physics | Year: 2014

We report on the thermal effects on the motion of current-driven massive magnetic skyrmions. The reduced equation for the motion of skyrmion has the form of a stochastic generalized Thiele's equation. We propose an ansatz for the magnetization texture of a non-rigid single skyrmion that depends linearly with the velocity. By using this ansatz it is found that the skyrmion mass tensor is closely related to intrinsic skyrmion parameters, such as Gilbert damping, skyrmion-charge and dissipative force. We have found an exact expression for the average drift velocity as well as the mean-square velocity of the skyrmion. The longitudinal and transverse mobility of skyrmions for small spin-velocity of electrons is also determined and found to be independent of the skyrmion mass. © 2014 Elsevier Inc.

Cardenas C.,University of Chile | Cardenas C.,Chilean Center of Nanosciences and Nanotechnology | Ayers P.W.,McMaster University
Physical Chemistry Chemical Physics | Year: 2013

By computing the electron-transfer energies for two million simulated double acid-base exchange reactions, we assess the reliability of the global hard-soft acid-base (HSAB) principle. We find that the HSAB principle is often thwarted by the tendency of strong acids to prefer strong bases. We define the strong-weak and hard-soft driving forces to characterize the strength of these two competing effects, and assess the reliability of the HSAB principle for different strengths and directions of the hard-soft and strong-weak driving forces. We provide a series of probability tables for making informed predictions about the preferred products of double acid-base exchange reactions. © 2013 The Owner Societies.

Troncoso R.E.,University of Chile | Troncoso R.E.,Chilean Center of Nanosciences and Nanotechnology | Nunez A.S.,University of Chile
Physical Review B - Condensed Matter and Materials Physics | Year: 2014

We study the behavior of skyrmions in thin films under the action of stochastic torques arising from thermal fluctuations. We find that the Brownian motion of skyrmions is described by a stochastic Thiele's equation and its corresponding Fokker-Planck equation. The resulting Fokker-Planck equation is recognized as the one for a high-friction Brownian particle which has been studied extensively in different physical contexts. It is shown that thermal fluctuations favor the skyrmion motion allowing a finite mobility even in presence of pinning traps. We calculate explicitly the mobility tensor of skyrmions in linear response to an electric current finding that it increases with temperature. © 2014 American Physical Society.

Venegas-Yazigi D.,University of Santiago de Chile | Venegas-Yazigi D.,Chilean Center of Nanosciences and Nanotechnology | Aravena D.,Chilean Center of Nanosciences and Nanotechnology | Aravena D.,University of Chile | And 4 more authors.
Coordination Chemistry Reviews | Year: 2010

Computational methods based on density functional theory have been employed to analyze the magnetic properties of dinuclear bis(phenoxo)-bridged CuII complexes. While the largest part of complexes in that family show antiferromagnetic coupling, we focus our study on those cases with distorted geometries that present ferromagnetic behaviour. The calculations reproduce such a magnetic behaviour, and a structural analysis reveals the main role played by several structural parameters, such as the Cu-O-Cu bridging angle. The out-of-plane shift of the phenoxo ring and the hinge distortion of the Cu2O2 central framework that are also important for similar hydroxo and alkoxo complexes. In this case the conformation of the phenoxo groups and the rotation of the phenyl rings can also play an important role. The last part of this work is dedicated to analyze the influence of the substituents of the phenoxo ring on the magnetic properties, which is especially important for structures with large out-of-plane shifted phenoxo rings. The presence of π electron releasing groups favours a ferromagnetic coupling. © 2010 Elsevier B.V.

Abad-Franch F.,Instituto Leonidas e Maria Deane Fiocruz Amazonia | Vega M.C.,Chilean Center of Nanosciences and Nanotechnology | Rolon M.S.,Chilean Center of Nanosciences and Nanotechnology | Santos W.S.,Instituto Leonidas e Maria Deane Fiocruz Amazonia | And 2 more authors.
PLoS Neglected Tropical Diseases | Year: 2011

Background: Vector control has substantially reduced Chagas disease (ChD) incidence. However, transmission by household-reinfesting triatomines persists, suggesting that entomological surveillance should play a crucial role in the long-term interruption of transmission. Yet, infestation foci become smaller and harder to detect as vector control proceeds, and highly sensitive surveillance methods are needed. Community participation (CP) and vector-detection devices (VDDs) are both thought to enhance surveillance, but this remains to be thoroughly assessed. Methodology/Principal Findings: We searched Medline, Web of Knowledge, Scopus, LILACS, SciELO, the bibliographies of retrieved studies, and our own records. Data from studies describing vector control and/or surveillance interventions were extracted by two reviewers. Outcomes of primary interest included changes in infestation rates and the detection of infestation/reinfestation foci. Most results likely depended on study- and site-specific conditions, precluding meta-analysis, but we re-analysed data from studies comparing vector control and detection methods whenever possible. Results confirm that professional, insecticide-based vector control is highly effective, but also show that reinfestation by native triatomines is common and widespread across Latin America. Bug notification by householders (the simplest CP-based strategy) significantly boosts vector detection probabilities; in comparison, both active searches and VDDs perform poorly, although they might in some cases complement each other. Conclusions/Significance: CP should become a strategic component of ChD surveillance, but only professional insecticide spraying seems consistently effective at eliminating infestation foci. Involvement of stakeholders at all process stages, from planning to evaluation, would probably enhance such CP-based strategies. © 2011 Abad-Franch et al.

Guarda A.,Chilean Center of Nanosciences and Nanotechnology | Rubilar J.F.,Chilean Center of Nanosciences and Nanotechnology | Miltz J.,Technion - Israel Institute of Technology | Galotto M.J.,Chilean Center of Nanosciences and Nanotechnology
International Journal of Food Microbiology | Year: 2011

The aim of the present study was to determine the antimicrobial (AM) properties of plastic flexible films with a coating of microcapsules containing carvacrol and thymol as natural AM agents. Microencapsulation of these agents enables their controlled release and leads to the destruction (or growth inhibition) of a broad spectrum of microorganisms such as, Escherichia coli O157:H7, Staphylococcus aureus, Listeria innocua, Saccharomyces cerevisiae and Aspergillus niger. It was found that the studied AM agents are strong inhibitors to the growth of mycelium, but they were not effective against spore germination of mold. Thymol (T) and carvacrol (C) showed a significant AM activity against the studied microorganisms, with minimal inhibitory concentrations (MIC) of 125-250. ppm and 75-375. ppm for thymol and carvacrol respectively. The synergistic effect of combinations of thymol and carvacrol was also studied and it was found that the highest synergism was achieved at a concentration of 50% T and 50% C. The release of the AM agents was carried out at 4 °C during 28. days. The concentration of the microencapsulated AM agents showed a range of zones of inhibition of 4.3-11.3. mm for the microorganisms at 10% of thymol and 10% of carvacrol. At these concentrations the release of the AM agents (within 48. h) was greater than required for the most resistant microorganism (E .coli O157:H7), as reflected by the relatively large zone of inhibition. The results of the present study confirm the suitability of using microencapsulated thymol and carvacrol incorporated in polymer films for AM food packaging. © 2011 Elsevier B.V.

Fuentealba P.,Chilean Center of Nanosciences and Nanotechnology | Cardenas C.,Chilean Center of Nanosciences and Nanotechnology
Journal of Molecular Modeling | Year: 2013

Using an exponential model for the variation in energy with respect to the number of electrons it is shown that, within the model, the hardness, softness, electrophilicity and other global parameters connected to higher order derivatives follow an equalization principle after a molecule is formed from two separated species. Two generalizations of the model are also discussed, one of which presents discontinuity of the chemical potential at integer values of N. © 2012 Springer-Verlag Berlin Heidelberg.

Rolon M.,Chilean Center of Nanosciences and Nanotechnology | Vega M.C.,Chilean Center of Nanosciences and Nanotechnology | Roman F.,Chilean Center of Nanosciences and Nanotechnology | Gomez A.,Chilean Center of Nanosciences and Nanotechnology | de Arias A.R.,Chilean Center of Nanosciences and Nanotechnology
PLoS Neglected Tropical Diseases | Year: 2011

In the Gran Chaco region, control of Triatoma infestans has been limited by persistent domestic infestations despite the efforts of the Vector Control Services. In Paraguay, this region is the highest endemic area in the country, showing high levels of indoor and outdoor infestation. Although sylvatic T. infestans have been found in the Bolivian and Argentine Chaco, similar searches for sylvatic populations of this species in Paraguay had been unsuccessful over the last 20 years. Here we present a new approach to detecting sylvatic Triatominae, using a trained dog, which has successfully confirmed sylvatic populations of T. infestans and other triatomine species in Paraguay. A total of 22 specimens corresponding to dark morph forms of T. infestans were collected, and 14 were confirmed as T. infestans by the mitochondrial cytochrome B gene analysis. Through this analysis, one of which were previously reported and a second that was a new haplotype. Triatomines were captured from amongst vegetation such as dry branches and hollows trees of different species such Aspidosperma quebracho-blanco, Bulnesia sarmientoi and Stetsonia coryne. The colonies found have been small and without apparent infection with Trypanosoma cruzi. During the study, Triatoma sordida and Triatoma guasayana have also been found in ecotopes close to those of T. infestans. © 2011 Rolón et al.

Loading Chilean Center of Nanosciences and Nanotechnology collaborators
Loading Chilean Center of Nanosciences and Nanotechnology collaborators