Publicacioneshttp://sedici.unlp.edu.ar:80/handle/10915/868032024-02-21T07:29:23Z2024-02-21T07:29:23ZElectrochemical Preparation and Delivery of Melanin–Iron Covered Gold NanoparticlesGrumelli, Doris EldaVericat, CarolinaBenitez, Guillermo AlfredoRamallo López, José MartínGiovanetti, Lisandro JoséRequejo, Félix GregorioMoreno, Mario Sergio JesúsGonzález Orive, AlejandroHernández Creus, AlbertoSalvarezza, Roberto Carloshttp://sedici.unlp.edu.ar:80/handle/10915/1628582024-02-19T20:08:27Z2009-01-01T00:00:00ZArticulo
ChemPhysChem; vol. 10, no. 2
Thiol-capped gold nanoparticles modified with iron-melanin are attractive because they combine magnetic properties and biocompatibility. The biopolymer modified nanoparticles are prepared and delivered following a three step strategy: i) adsorption of thiol-capped metal nanoparticles on graphite, ii) electrochemical deposition of melanin-iron, iii) potential-induced delivery of the modified nanoparticles to the electrolyte.
2009-01-01T00:00:00ZThiol-capped gold nanoparticles modified with iron-melanin are attractive because they combine magnetic properties and biocompatibility. The biopolymer modified nanoparticles are prepared and delivered following a three step strategy: i) adsorption of thiol-capped metal nanoparticles on graphite, ii) electrochemical deposition of melanin-iron, iii) potential-induced delivery of the modified nanoparticles to the electrolyte.Extrinsic origin of ferromagnetism in single crystalline LaAlO₃ substrates and oxide filmsGolmar, FedericoMudarra Navarro, Azucena MarisolRodríguez Torres, Claudia ElenaSánchez, Francisco HomeroSaccone, Fabio DanielDos Santos Claro, Paula CeciliaBenitez, Guillermo AlfredoSchilardi, Patricia Laurahttp://sedici.unlp.edu.ar:80/handle/10915/1628292024-02-19T20:08:30Z2008-01-01T00:00:00ZArticulo
Applied Physics Letters; vol. 92, no. 26
Commercial LaAlO₃ substrates were thermally cycled simulating a procedure similar to those followed during TiO₂ and SnO₂ dilute magnetic semiconductors’ film pulsed laser deposition. Ferromagneticlike behavior was found in some substrates, in which metallic iron impurities were detected by x-ray photoelectron spectroscopy and total reflection x-ray fluorescence measurements. A thorough experimental investigation, using high resolution techniques, showed that these impurities were introduced by the procedure used to fix the substrates to the oven silicon holders. It is suggested that magnetism observed previously in nominally pure SnO₂ films is of extrinsic origin.
2008-01-01T00:00:00ZCommercial LaAlO₃ substrates were thermally cycled simulating a procedure similar to those followed during TiO₂ and SnO₂ dilute magnetic semiconductors’ film pulsed laser deposition. Ferromagneticlike behavior was found in some substrates, in which metallic iron impurities were detected by x-ray photoelectron spectroscopy and total reflection x-ray fluorescence measurements. A thorough experimental investigation, using high resolution techniques, showed that these impurities were introduced by the procedure used to fix the substrates to the oven silicon holders. It is suggested that magnetism observed previously in nominally pure SnO₂ films is of extrinsic origin.Structural and Mössbauer study of (Sb₀.₇₀Te₀.₃₀)₁₀₀-ₓ Snₓ alloys with x = 0, 2.5, 5.0 and 7.5Rocca, Javier AlejandroBilovol, VitaliyErrandonea, DanielGil Rebaza, Arles VíctorMudarra Navarro, Azucena MarisolMedina Chanduví, Hugo HaroldErrico, Leonardo AntonioArcondo, Bibiana GracielaFontana, Marcelo RaúlCuellar Rodríguez, O.Ureña, María Andreahttp://sedici.unlp.edu.ar:80/handle/10915/1622182024-02-02T20:08:07Z2019-01-01T00:00:00ZArticulo
Journal of Alloys and Compounds; vol. 795
(Sb₀.₇₀Te₀.₃₀)₁₀₀-ₓSnₓ alloys (with x = 0, 2.5, 5.0 and 7.5 at. %) have been synthesized and characterized in order to determine the crystalline structure and properties of materials obtained upon solidification and to extract information about the location of the Sn atom in the Sb-Te matrix. Powder X-ray diffraction (XRD) has been used to determine the crystalline structure, whereas Mössbauer spectroscopy has been utilized to determine the localization and the local structure of the Sn atom in the Sb-Te matrix through the hyperfine interactions of the ¹¹⁹Sn probe with its environment.We found that Sb₇₀Te₃₀ crystallizes in a trigonal structure belonging to P-3m1 space group, while the doping with Sn leads to structural distortions of the unit cell that can be described, for all the Sn concentrations, with the C2/m space group. The hyperfine parameters indicate that tin behaves as Sn(II) and has a slightly distorted environment. Finally, in order to extract all the information that the experimental results contain and to determine the preferential site occupied by the Sn impurities in the Sb-Te matrix, we have performed ab-initio calculations within the framework of the Density Functional Theory. The theoretical results enable us to determine the structural and electronic ground state of (Sb₀.₇₀Te₀.₃₀)₁₀₀-ₓSnₓ compounds and to confirm that Sn atoms substitute Sb atoms in the Sb-Te host.
2019-01-01T00:00:00Z(Sb₀.₇₀Te₀.₃₀)₁₀₀-ₓSnₓ alloys (with x = 0, 2.5, 5.0 and 7.5 at. %) have been synthesized and characterized in order to determine the crystalline structure and properties of materials obtained upon solidification and to extract information about the location of the Sn atom in the Sb-Te matrix. Powder X-ray diffraction (XRD) has been used to determine the crystalline structure, whereas Mössbauer spectroscopy has been utilized to determine the localization and the local structure of the Sn atom in the Sb-Te matrix through the hyperfine interactions of the ¹¹⁹Sn probe with its environment.We found that Sb₇₀Te₃₀ crystallizes in a trigonal structure belonging to P-3m1 space group, while the doping with Sn leads to structural distortions of the unit cell that can be described, for all the Sn concentrations, with the C2/m space group. The hyperfine parameters indicate that tin behaves as Sn(II) and has a slightly distorted environment. Finally, in order to extract all the information that the experimental results contain and to determine the preferential site occupied by the Sn impurities in the Sb-Te matrix, we have performed ab-initio calculations within the framework of the Density Functional Theory. The theoretical results enable us to determine the structural and electronic ground state of (Sb₀.₇₀Te₀.₃₀)₁₀₀-ₓSnₓ compounds and to confirm that Sn atoms substitute Sb atoms in the Sb-Te host.Structural, vibrational and electronic properties in the glass-crystal transition of thin films Sb₇₀Te₃₀ doped with SnBilovol, VitaliyFontana, Marcelo RaúlRocca, Javier AlejandroMedina Chanduví, Hugo HaroldMudarra Navarro, Azucena MarisolGil Rebaza, Arles VíctorErrico, Leonardo AntonioLiang, AkunErrandonea, DanielUreña, María Andreahttp://sedici.unlp.edu.ar:80/handle/10915/1622062024-02-02T20:08:11Z2020-01-01T00:00:00ZArticulo
Journal of Alloys and Compounds; vol. 845
Antimony-telluride based phase-change materials doped with Sn have been proposed to be ideal materials for improving the performance of phase-change memories. It is well known that Sb₇₀Te₃₀ thin films show a sharp fall in the electrical resistance in a narrow temperature range when heating. Therefore, it is interesting to study the effect of adding Sn into this composition. In this work, undoped and Sn-doped SbeTe thin films of composition Snₓ[Sb₀.₇₀Te₀.₃₀]₁₀₀₋ₓ, with x = 0.0, 2.5, 5.0 and 7.5 at. %, have been obtained by pulsed laser deposition. Their electrical resistance has been measured while heating from room temperature to 650 K. A sharp fall in the electrical resistance, associated to the glass-crystal transition, has been detected in all the samples within a narrow temperature range. The onset temperature of this transformation increases with the Sn content. Both as-obtained and thermally-treated films have been structurally characterized by X-ray and by Raman spectroscopy. We have compared the results among these compositions in terms of the identified crystallization products, transformation onset temperatures, transformation temperature ranges and amorphous/crystallized electrical resistance ratio. We have found that the frequency of the Raman modes decreases with Sndoping. Finally, in order to study the electronic structure and to determine the band gap, the frequencies of the allowed Raman modes and the vibration directions of the Sb₇₀Te₃₀ compound, Density Functional Theory based ab initio calculations have been performed as a function of the Sn concentration.
2020-01-01T00:00:00ZAntimony-telluride based phase-change materials doped with Sn have been proposed to be ideal materials for improving the performance of phase-change memories. It is well known that Sb₇₀Te₃₀ thin films show a sharp fall in the electrical resistance in a narrow temperature range when heating. Therefore, it is interesting to study the effect of adding Sn into this composition. In this work, undoped and Sn-doped SbeTe thin films of composition Snₓ[Sb₀.₇₀Te₀.₃₀]₁₀₀₋ₓ, with x = 0.0, 2.5, 5.0 and 7.5 at. %, have been obtained by pulsed laser deposition. Their electrical resistance has been measured while heating from room temperature to 650 K. A sharp fall in the electrical resistance, associated to the glass-crystal transition, has been detected in all the samples within a narrow temperature range. The onset temperature of this transformation increases with the Sn content. Both as-obtained and thermally-treated films have been structurally characterized by X-ray and by Raman spectroscopy. We have compared the results among these compositions in terms of the identified crystallization products, transformation onset temperatures, transformation temperature ranges and amorphous/crystallized electrical resistance ratio. We have found that the frequency of the Raman modes decreases with Sndoping. Finally, in order to study the electronic structure and to determine the band gap, the frequencies of the allowed Raman modes and the vibration directions of the Sb₇₀Te₃₀ compound, Density Functional Theory based ab initio calculations have been performed as a function of the Sn concentration.Electronic Structures and Optical Properties for Nano Particles: Experimental and Theoretical CalculationsAly, Abeer E.Fahmy, Heba M.Medina Chanduví, Hugo HaroldGil Rebaza, Arles VíctorThapa, B.Shankar, A.http://sedici.unlp.edu.ar:80/handle/10915/1621942024-02-02T20:08:12Z2022-01-01T00:00:00ZArticulo
American Journal of Nano Research and Applications; vol. 10, no. 1
The use of copper nanoparticles (Cu NPs) and copper oxide nanoparticles (Cu₂O NPs) has increased dramatically both in the medical and industrial fields. In the present study, we have used various techniques like, dynamic light scattering (DLS) for particle size, zeta potential determination, X-ray diffraction (XRD), transmission electron microscope (TEM) and scanning electron microscope (SEM) for development and characterization of Cu and Cu₂O NPs. We have also performed the ab-initio calculations based on the density functional theory (DFT) where the theoretical results are in well accordance with the experimental reports. The Hubbard correction is included over the generalized gradient approximation (GGA) for a better description of Cu and Cu₂O NPs. The plot of densities of states (DOS) and energy band structures of Cu and Cu₂O nanocrystals predicts the metallic and semiconducting nature of Cu and Cu₂O, respectively. The energy bands and DOS shows strong hybridization of Cu-O and predicts the metallic nature of Cu and semiconducting nature of Cu₂O. The optical absorption results show that both the Cu₂O and Cu samples are absorbing strongly at the minimum energy. The band structure of Cu Nano crystals reveals a metallic nature where the valence band crosses the Fermi energy level at W point. However, an indirect energy band gap can be seen above the EF.
2022-01-01T00:00:00ZThe use of copper nanoparticles (Cu NPs) and copper oxide nanoparticles (Cu₂O NPs) has increased dramatically both in the medical and industrial fields. In the present study, we have used various techniques like, dynamic light scattering (DLS) for particle size, zeta potential determination, X-ray diffraction (XRD), transmission electron microscope (TEM) and scanning electron microscope (SEM) for development and characterization of Cu and Cu₂O NPs. We have also performed the ab-initio calculations based on the density functional theory (DFT) where the theoretical results are in well accordance with the experimental reports. The Hubbard correction is included over the generalized gradient approximation (GGA) for a better description of Cu and Cu₂O NPs. The plot of densities of states (DOS) and energy band structures of Cu and Cu₂O nanocrystals predicts the metallic and semiconducting nature of Cu and Cu₂O, respectively. The energy bands and DOS shows strong hybridization of Cu-O and predicts the metallic nature of Cu and semiconducting nature of Cu₂O. The optical absorption results show that both the Cu₂O and Cu samples are absorbing strongly at the minimum energy. The band structure of Cu Nano crystals reveals a metallic nature where the valence band crosses the Fermi energy level at W point. However, an indirect energy band gap can be seen above the EF.Structural, Electronic, Magnetic, and Hyperfine Properties of V‑doped SnO₂ (Sn₁₋ₓVₓO₂, x: 0, 0.042, 0.084, and 0.125): A DFT-Based StudyMedina Chanduví, Hugo HaroldMudarra Navarro, Azucena MarisolBilovol, VitaliyErrico, Leonardo AntonioGil Rebaza, Arles Víctorhttp://sedici.unlp.edu.ar:80/handle/10915/1621862024-02-01T20:09:24Z2021-01-01T00:00:00ZArticulo
The Journal of Physical Chemistry C; vol. 125, no. 21
Ab initio electronic structure calculations were performed to study the effect of V-doping on the structural, electronic, and magnetic properties of tin dioxide (Sn₁₋ₓVₓO₂, x: 0.042−0.125). Calculations have been performed using pseudopotentials and plane-wave and full potential linearized augmented plane-wave methods. State-of-the-art Heyd−Scuseria−Ernzerhof (HSE06) exchange−correlation hybrid functional and the Tran−Blaha-modified Becke−Johnson (TB-mBJ) exchange potential were employed. Our calculations showed that V⁴⁺ substitutionally replaces Sn⁴⁺ ions inducing a reduction of the volume cell of SnO₂ and shortening of the metal−oxygen nearest neighbor bond lengths. Spin polarization at the V sites is predicted. Our results indicate that the magnetic ground state of the resulting system is paramagnetic. TB-mBJ and HSE06 accurately describe the experimentally reported dependence of the band gap with x. Our theoretical results for the hyperfine parameters at the Sn sites are in excellent agreement with Mössbauer experiments. Hyperfine parameters at the V sites are also presented.
2021-01-01T00:00:00ZAb initio electronic structure calculations were performed to study the effect of V-doping on the structural, electronic, and magnetic properties of tin dioxide (Sn₁₋ₓVₓO₂, x: 0.042−0.125). Calculations have been performed using pseudopotentials and plane-wave and full potential linearized augmented plane-wave methods. State-of-the-art Heyd−Scuseria−Ernzerhof (HSE06) exchange−correlation hybrid functional and the Tran−Blaha-modified Becke−Johnson (TB-mBJ) exchange potential were employed. Our calculations showed that V⁴⁺ substitutionally replaces Sn⁴⁺ ions inducing a reduction of the volume cell of SnO₂ and shortening of the metal−oxygen nearest neighbor bond lengths. Spin polarization at the V sites is predicted. Our results indicate that the magnetic ground state of the resulting system is paramagnetic. TB-mBJ and HSE06 accurately describe the experimentally reported dependence of the band gap with x. Our theoretical results for the hyperfine parameters at the Sn sites are in excellent agreement with Mössbauer experiments. Hyperfine parameters at the V sites are also presented.Thermodynamic evidence of the ferroelectric Berry phase in europium-based ferrobismuthite Eu₂Bi₂Fe₄O₁₂Gil Rebaza, Arles VíctorDeluque Toro, Críspulo EnriqueMedina Chanduví, Hugo HaroldLandínez Téllez, David ArsenioRoa Rojas, Jairohttp://sedici.unlp.edu.ar:80/handle/10915/1621772024-02-01T20:09:28Z2021-12-01T00:00:00ZArticulo
Journal of Alloys and Compounds; vol. 884
The possible low temperature biferroic feature of Eu₂Bi₂Fe₄O₁₂ complex perovskites was recently reported. The aim of this work is to present a theoretical study of the structural, magnetic, electronic and ferroelectric properties of this material. Several energy minimization processes were performed for three types of cationic distributions, different angles of rotation, octahedral inclination, and some kinds of magnetic ordering. The results reveal that the most stable crystallographic arrangement corresponds to an intercalated distribution of the Eu³⁺ and Bi³⁺ cations between the FeO₆ octahedra. Similarly, energy is minimized for rotations and octahedral inclinations corresponding to angles θₑ = 12.86° and ϕₑ = 13.32°, respectively. With respect to the distribution of magnetic moments, the results reveal that a G-type antiferromagnetic configuration is the most energetically favorable. The electronic structure is studied from ab initio calculations following the formalism of density functional theory and the pseudopotential plane wave method. In this formalism, the exchange and correlation mechanisms are described by means of the generalized gradient approach (GGA + U), considering spin polarization. The ferroelectric characteristic is analysed by determining ferroelectric polarization based on the calculation of the Berry phase. The theoretical results obtained are consistent with the experimental reports, which is why the Eu₂Bi₂Fe₄O₁₂ material is expected to exhibit biferroic behavior at low temperatures, because the Berry phase introduces hybridizations between the 3d-Fe and 2p-O states that favor the occurrence of Dzyaloshinskii-Moriya interactions, which facilitate the occurrence of ferroelectricity coexisting with weak ferromagnetism. An extensive study of the thermodynamic properties in the presence and absence of the Berry phase is undertaken by means of the Debye quasi harmonic model. The specific heat difference with and without the Berry phase reveals the occurrence of a ferroelectric transition at T = 113 K without the application of external pressure. When the applied pressure is incremented, a systematic increase in the transition temperature is observed due to the reduction of overlap between the 3d-Fe orbitals and the 2p-O orbitals in the compressed octahedra of perovskite.
2021-12-01T00:00:00ZThe possible low temperature biferroic feature of Eu₂Bi₂Fe₄O₁₂ complex perovskites was recently reported. The aim of this work is to present a theoretical study of the structural, magnetic, electronic and ferroelectric properties of this material. Several energy minimization processes were performed for three types of cationic distributions, different angles of rotation, octahedral inclination, and some kinds of magnetic ordering. The results reveal that the most stable crystallographic arrangement corresponds to an intercalated distribution of the Eu³⁺ and Bi³⁺ cations between the FeO₆ octahedra. Similarly, energy is minimized for rotations and octahedral inclinations corresponding to angles θₑ = 12.86° and ϕₑ = 13.32°, respectively. With respect to the distribution of magnetic moments, the results reveal that a G-type antiferromagnetic configuration is the most energetically favorable. The electronic structure is studied from ab initio calculations following the formalism of density functional theory and the pseudopotential plane wave method. In this formalism, the exchange and correlation mechanisms are described by means of the generalized gradient approach (GGA + U), considering spin polarization. The ferroelectric characteristic is analysed by determining ferroelectric polarization based on the calculation of the Berry phase. The theoretical results obtained are consistent with the experimental reports, which is why the Eu₂Bi₂Fe₄O₁₂ material is expected to exhibit biferroic behavior at low temperatures, because the Berry phase introduces hybridizations between the 3d-Fe and 2p-O states that favor the occurrence of Dzyaloshinskii-Moriya interactions, which facilitate the occurrence of ferroelectricity coexisting with weak ferromagnetism. An extensive study of the thermodynamic properties in the presence and absence of the Berry phase is undertaken by means of the Debye quasi harmonic model. The specific heat difference with and without the Berry phase reveals the occurrence of a ferroelectric transition at T = 113 K without the application of external pressure. When the applied pressure is incremented, a systematic increase in the transition temperature is observed due to the reduction of overlap between the 3d-Fe orbitals and the 2p-O orbitals in the compressed octahedra of perovskite.Magnetic and optical properties of perovskite-graphene nanocomposites LaFeO₃-rGO: Experimental and DFT calculationsAbdel-Aal, Seham K.Aly, Abeer E.Medina Chanduví, Hugo HaroldGil Rebaza, Arles VíctorAtteia, E.Shankar, A.http://sedici.unlp.edu.ar:80/handle/10915/1620002023-12-27T20:07:50Z2020-10-01T00:00:00ZArticulo
Chemical Physics; vol. 538
We present an experimental and theoretical study of the perovskite-graphene nanocomposites LaFeO3 – rGO, where we demonstrate a easy way to prepare this compound using citrate auto-compulsion method, starting from corresponding metal nitrate and graphene oxide solution. The Hummer’s method was used to prepare graphene oxide by chemical exfoliation of graphite. The structural characterization has been performed using XRD, FT-IR and scanning electron microscope (SEM) to analyze the morphology of the sample, FT-IR, whereas the magnetic properties has been studied using VSM measurements. Furthermore, ab-initio calculations has been performed based on the Density Functional Theory (DFT), where for a better description of the electronic and magnetic properties, the Hubbard correction was considered over the General Gradient Approximation (GGA + U).
2020-10-01T00:00:00ZWe present an experimental and theoretical study of the perovskite-graphene nanocomposites LaFeO3 – rGO, where we demonstrate a easy way to prepare this compound using citrate auto-compulsion method, starting from corresponding metal nitrate and graphene oxide solution. The Hummer’s method was used to prepare graphene oxide by chemical exfoliation of graphite. The structural characterization has been performed using XRD, FT-IR and scanning electron microscope (SEM) to analyze the morphology of the sample, FT-IR, whereas the magnetic properties has been studied using VSM measurements. Furthermore, ab-initio calculations has been performed based on the Density Functional Theory (DFT), where for a better description of the electronic and magnetic properties, the Hubbard correction was considered over the General Gradient Approximation (GGA + U).Applying surface-sensitive techniques to structural and chemical study of uncapped Sn-Sb-Te thin film: A density functional theory - based studyBilovol, V.Medina Chanduví, Hugo HaroldErrico, Leonardo Antoniohttp://sedici.unlp.edu.ar:80/handle/10915/1619932023-12-27T20:07:51Z2021-10-01T00:00:00ZArticulo
Thin Solid Films; vol. 736
We present here a combined experimental and theoretical study of the structural and chemical properties of polycrystalline Sn-Sb-Te film with nominal composition SnSb₂Te₄ grown by pulsed laser deposition technique on mylar substrate. From the experimental side, surface-sensitive techniques as x-ray photoelectron spectroscopy (XPS), grazing incidence x-ray diffractometry (GIXRD) and ¹¹⁹ᵐSn integral conversion electron Möβbauer spectroscopy (ICEMS) have been applied to the study of the film at room-temperature and under normal conditions of pressure. GIXRD showed that the Sn-Sb-Te film adopted a NaCl- type structure (Fm-3m), and in the detection limits, no other crystalline phase was revealed. ICEMS technique unambiguously indicated the coexistence of two different tin fractions: Sn(II), as expected for the SnSb₂Te₄ phase, and Sn(IV), suggesting oxidation of tin. Chemical in-depth profile obtained by means of XPS suggests the oxidation of all the constituent atoms at the topmost layers of the film and the progressive depletion of tin and antimony oxides going depth in the film.
The in-depth atomic concentration profiles also reveals a notorious deficiency of Te in the sample. Theoretically, density functional theory-based calculations (assuming that the Sn-Sb-Te film adopts the Fm-3m structure) support the hypothesis that Te - vacancies sites are occupied by oxygen atoms during the natural oxidation process of Sn-Sb-Te film. Additionally, our calculations demonstrated that only the substitution of Te atoms by oxygen ones induces a semiconducting behavior of the otherwise metallic Sn-Sb-Te host.
2021-10-01T00:00:00ZWe present here a combined experimental and theoretical study of the structural and chemical properties of polycrystalline Sn-Sb-Te film with nominal composition SnSb₂Te₄ grown by pulsed laser deposition technique on mylar substrate. From the experimental side, surface-sensitive techniques as x-ray photoelectron spectroscopy (XPS), grazing incidence x-ray diffractometry (GIXRD) and ¹¹⁹ᵐSn integral conversion electron Möβbauer spectroscopy (ICEMS) have been applied to the study of the film at room-temperature and under normal conditions of pressure. GIXRD showed that the Sn-Sb-Te film adopted a NaCl- type structure (Fm-3m), and in the detection limits, no other crystalline phase was revealed. ICEMS technique unambiguously indicated the coexistence of two different tin fractions: Sn(II), as expected for the SnSb₂Te₄ phase, and Sn(IV), suggesting oxidation of tin. Chemical in-depth profile obtained by means of XPS suggests the oxidation of all the constituent atoms at the topmost layers of the film and the progressive depletion of tin and antimony oxides going depth in the film.
The in-depth atomic concentration profiles also reveals a notorious deficiency of Te in the sample. Theoretically, density functional theory-based calculations (assuming that the Sn-Sb-Te film adopts the Fm-3m structure) support the hypothesis that Te - vacancies sites are occupied by oxygen atoms during the natural oxidation process of Sn-Sb-Te film. Additionally, our calculations demonstrated that only the substitution of Te atoms by oxygen ones induces a semiconducting behavior of the otherwise metallic Sn-Sb-Te host.Reciprocity relations for quantum systems based on Fisher informationPortesi, Mariela AdelinaPujol, Juan ManuelHolik, Federico Hernánhttp://sedici.unlp.edu.ar:80/handle/10915/1608882023-11-29T20:07:26Z2023-01-01T00:00:00ZArticulo
Physical Sciences Forum; vol. 5, no. 1
We study reciprocity relations between fluctuations of the probability distributions corresponding to position and momentum, and other observables, in quantum theory. These kinds of relations have been previously studied in terms of quantifiers based on the Lipschitz constants of the concomitant distributions. However, it turned out that they were not valid for all states. Here, we ask the following question: can those relations be described using other quantifiers? By appealing to the Fisher information, we study reciprocity relations for different families of states. In particular, we look for a connection of this problem with previous works.
2023-01-01T00:00:00ZWe study reciprocity relations between fluctuations of the probability distributions corresponding to position and momentum, and other observables, in quantum theory. These kinds of relations have been previously studied in terms of quantifiers based on the Lipschitz constants of the concomitant distributions. However, it turned out that they were not valid for all states. Here, we ask the following question: can those relations be described using other quantifiers? By appealing to the Fisher information, we study reciprocity relations for different families of states. In particular, we look for a connection of this problem with previous works.Chaotic dynamics of the Hénon map and neuronal input–output: A comparison with
neurophysiological dataGuisande, NatalíPallares Di Nunzio, MonserratMartinez, NatanielRosso, Osvaldo AníbalMontani, Fernando Fabiánhttp://sedici.unlp.edu.ar:80/handle/10915/1608482023-11-29T20:07:29Z2023-04-03T00:00:00ZArticulo
Chaos; vol. 33, no. 4
In this study, the Hénon map was analyzed using quantifiers from information theory in order to compare its dynamics to experimental data from brain regions known to exhibit chaotic behavior. The goal was to investigate the potential of the Hénon map as a model for replicating chaotic brain dynamics in the treatment of Parkinson’s and epilepsy patients. The dynamic properties of the Hénon map were compared with data from the subthalamic nucleus, the medial frontal cortex, and a q-DG model of neuronal input–output with easy numerical implementation to simulate the local behavior of a population. Using information theory tools, Shannon entropy, statistical complexity, and Fisher’s information were analyzed, taking into account the causality of the time series. For this purpose, different windows over the time series were considered. The findings revealed that neither the Hénon map nor the q-DG model could perfectly replicate the dynamics of the brain regions studied. However, with careful consideration of the parameters, scales, and sampling used, they were able to model some characteristics of neural activity. According to these results, normal neural dynamics in the subthalamic nucleus region may present a more complex spectrum within the complexity–entropy causality plane that cannot be represented by chaotic models alone. The dynamic behavior observed in these systems using these tools is highly dependent on the studied temporal scale. As the size of the sample studied increases, the dynamics of the Hénon map become increasingly different from those of biological and artificial neural systems.
2023-04-03T00:00:00ZIn this study, the Hénon map was analyzed using quantifiers from information theory in order to compare its dynamics to experimental data from brain regions known to exhibit chaotic behavior. The goal was to investigate the potential of the Hénon map as a model for replicating chaotic brain dynamics in the treatment of Parkinson’s and epilepsy patients. The dynamic properties of the Hénon map were compared with data from the subthalamic nucleus, the medial frontal cortex, and a q-DG model of neuronal input–output with easy numerical implementation to simulate the local behavior of a population. Using information theory tools, Shannon entropy, statistical complexity, and Fisher’s information were analyzed, taking into account the causality of the time series. For this purpose, different windows over the time series were considered. The findings revealed that neither the Hénon map nor the q-DG model could perfectly replicate the dynamics of the brain regions studied. However, with careful consideration of the parameters, scales, and sampling used, they were able to model some characteristics of neural activity. According to these results, normal neural dynamics in the subthalamic nucleus region may present a more complex spectrum within the complexity–entropy causality plane that cannot be represented by chaotic models alone. The dynamic behavior observed in these systems using these tools is highly dependent on the studied temporal scale. As the size of the sample studied increases, the dynamics of the Hénon map become increasingly different from those of biological and artificial neural systems.Characterizing the information transmission of inverse stochastic resonance and noise-induced activity amplification in neuronal systemsMartinez, NatanielDeza, RobertoMontani, Fernando Fabiánhttp://sedici.unlp.edu.ar:80/handle/10915/1608472023-11-29T20:07:31Z2023-05-02T00:00:00ZArticulo
Physical Review E; vol. 107
Purkinje cells exhibit a reduction of the mean firing rate at intermediate-noise intensities, which is somewhat reminiscent of the response enhancement known as “stochastic resonance” (SR). Although the comparison with the stochastic resonance ends here, the current phenomenon has been given the name “inverse stochastic resonance” (ISR). Recent research has demonstrated that the ISR effect, like its close relative “nonstandard SR” [or, more correctly, noise-induced activity amplification (NIAA)], has been shown to stem from the weak-noise quenching of the initial distribution, in bistable regimes where the metastable state has a larger attraction basin than the global minimum. To understand the underlying mechanism of the ISR and NIAA phenomena, we study the probability distribution function of a one-dimensional system subjected to a bistable potential that has the property of symmetry, i.e., if we change the sign of one of its parameters, we can obtain both phenomena with the same properties in the depth of the wells and the width of their basins of attraction subjected to Gaussian white noise with variable intensity. Previous work has shown that one can theoretically determine the probability distribution function using the convex sum between the behavior at small and high noise intensities. To determine the probability distribution function more precisely, we resort to the “weighted ensemble Brownian dynamics simulation” model, which provides an accurate estimate of the probability distribution function for both low and high noise intensities and, most importantly, for the transition of both behaviors. In this way, on the one hand, we show that both phenomena emerge from a metastable system where, in the case of ISR, the global minimum of the system is in a state of lower activity, while in the case of NIAA, the global minimum is in a state of increased activity, the importance of which does not depend on the width of the basins of attraction. On the other hand, we see that quantifiers such as Fisher information, statistical complexity, and especially Shannon entropy fail to distinguish them, but they show the existence of the mentioned phenomena. Thus, noise management may well be a mechanism by which Purkinje cells find an efficient way to transmit information in the cerebral cortex.
2023-05-02T00:00:00ZPurkinje cells exhibit a reduction of the mean firing rate at intermediate-noise intensities, which is somewhat reminiscent of the response enhancement known as “stochastic resonance” (SR). Although the comparison with the stochastic resonance ends here, the current phenomenon has been given the name “inverse stochastic resonance” (ISR). Recent research has demonstrated that the ISR effect, like its close relative “nonstandard SR” [or, more correctly, noise-induced activity amplification (NIAA)], has been shown to stem from the weak-noise quenching of the initial distribution, in bistable regimes where the metastable state has a larger attraction basin than the global minimum. To understand the underlying mechanism of the ISR and NIAA phenomena, we study the probability distribution function of a one-dimensional system subjected to a bistable potential that has the property of symmetry, i.e., if we change the sign of one of its parameters, we can obtain both phenomena with the same properties in the depth of the wells and the width of their basins of attraction subjected to Gaussian white noise with variable intensity. Previous work has shown that one can theoretically determine the probability distribution function using the convex sum between the behavior at small and high noise intensities. To determine the probability distribution function more precisely, we resort to the “weighted ensemble Brownian dynamics simulation” model, which provides an accurate estimate of the probability distribution function for both low and high noise intensities and, most importantly, for the transition of both behaviors. In this way, on the one hand, we show that both phenomena emerge from a metastable system where, in the case of ISR, the global minimum of the system is in a state of lower activity, while in the case of NIAA, the global minimum is in a state of increased activity, the importance of which does not depend on the width of the basins of attraction. On the other hand, we see that quantifiers such as Fisher information, statistical complexity, and especially Shannon entropy fail to distinguish them, but they show the existence of the mentioned phenomena. Thus, noise management may well be a mechanism by which Purkinje cells find an efficient way to transmit information in the cerebral cortex.Quasi-magical fermion numbers and thermal many-body dynamicsPlastino, Ángel LuisMonteoliva, DianaPlastino, Ángel Ricardohttp://sedici.unlp.edu.ar:80/handle/10915/1608192023-11-28T20:07:13Z2023-01-01T00:00:00ZArticulo
Axioms; vol. 12, no. 5
This work scrutinizes, using statistical mechanics indicators, important traits displayed by quantum many-body systems. Our statistical mechanics quantifiers are employed, in the context of Gibbs’ canonical ensemble at temperature T. A new quantifier of this sort is also presented here. The present discussion focuses attention on the role played by the fermion number N in many-fermion dynamics, that is, N is our protagonist. We have discovered discovers particular values of N for which the thermal indicators exhibit unexpected abrupt variations. Such a fact reflects an unanticipated characteristic of fermionic dynamics.
2023-01-01T00:00:00ZThis work scrutinizes, using statistical mechanics indicators, important traits displayed by quantum many-body systems. Our statistical mechanics quantifiers are employed, in the context of Gibbs’ canonical ensemble at temperature T. A new quantifier of this sort is also presented here. The present discussion focuses attention on the role played by the fermion number N in many-fermion dynamics, that is, N is our protagonist. We have discovered discovers particular values of N for which the thermal indicators exhibit unexpected abrupt variations. Such a fact reflects an unanticipated characteristic of fermionic dynamics.Abnormal EEG signal energy in the elderly: a wavelet analysis of event-related potentials during a stroop taskSánchez-Moguel, Sergio MBaravalle, RománGonzález-Salinas, SofíaRosso, Osvaldo AníbalFernández, ThalíaMontani, Fernando Fabiánhttp://sedici.unlp.edu.ar:80/handle/10915/1604432023-11-23T20:43:12Z2022-04-26T00:00:00ZArticulo
Journal of Neuroscience Methods; vol. 376
Background: Previous work showed that elderly with excess in theta activity in their resting state electroencephalogram (EEG) are at higher risk of cognitive decline than those with a normal EEG. By using event-related potentials (ERP) during a counting Stroop task, our prior work showed that elderly with theta excess have a large P300 component compared with normal EEG group. This increased activity could be related to a higher EEG signal energy used during this task.
New method: By wavelet analysis applied to ERP obtained during a counting Stroop task we quantified the energy in the different frequency bands of a group of elderly with altered EEG.
Results: In theta and alpha bands, the total energy was higher in elderly subjects with theta excess, specifically in the stimulus categorization window (258–516 ms). Both groups solved the task with similar efficiency.
Comparison with existing methods: The traditional ERP analysis in elderly compares voltage among conditions and groups for a given time window, while the frequency composition is not usually examined. We complemented our previous ERP analysis using a wavelet methodology. Furthermore, we showed the advantages of wavelet analysis over Short Time Fourier Transform when exploring EEG signal during this task.
Conclusions: The higher EEG signal energy in ERP might reflect undergoing neurobiological mechanisms that allow the elderly with theta excess to cope with the cognitive task with similar behavioral results as the normal EEG group. This increased energy could promote a metabolic and cellular dysregulation causing a greater decline in cognitive function.
2022-04-26T00:00:00ZBackground: Previous work showed that elderly with excess in theta activity in their resting state electroencephalogram (EEG) are at higher risk of cognitive decline than those with a normal EEG. By using event-related potentials (ERP) during a counting Stroop task, our prior work showed that elderly with theta excess have a large P300 component compared with normal EEG group. This increased activity could be related to a higher EEG signal energy used during this task.
New method: By wavelet analysis applied to ERP obtained during a counting Stroop task we quantified the energy in the different frequency bands of a group of elderly with altered EEG.
Results: In theta and alpha bands, the total energy was higher in elderly subjects with theta excess, specifically in the stimulus categorization window (258–516 ms). Both groups solved the task with similar efficiency.
Comparison with existing methods: The traditional ERP analysis in elderly compares voltage among conditions and groups for a given time window, while the frequency composition is not usually examined. We complemented our previous ERP analysis using a wavelet methodology. Furthermore, we showed the advantages of wavelet analysis over Short Time Fourier Transform when exploring EEG signal during this task.
Conclusions: The higher EEG signal energy in ERP might reflect undergoing neurobiological mechanisms that allow the elderly with theta excess to cope with the cognitive task with similar behavioral results as the normal EEG group. This increased energy could promote a metabolic and cellular dysregulation causing a greater decline in cognitive function.High-frequency oscillations in the ripple bands and amplitude information coding: Toward a biomarker of maximum entropy in the preictal signalsGranado, MauroCollavini, SantiagoBaravalle, RománMartínez, NatanielMontemurro, Marcelo A.Rosso, Osvaldo AníbalMontani, Fernando Fabiánhttp://sedici.unlp.edu.ar:80/handle/10915/1604402023-11-23T20:43:14Z2022-09-30T00:00:00ZArticulo
Chaos; vol. 32, no. 9
Intracranial electroencephalography (iEEG) can directly record local field potentials (LFPs) from a large set of neurons in the vicinity of the electrode. To search for possible epileptic biomarkers and to determine the epileptogenic zone that gives rise to seizures, we investigated the dynamics of basal and preictal signals. For this purpose, we explored the dynamics of the recorded time series for different frequency bands considering high-frequency oscillations (HFO) up to 240 Hz. We apply a Hilbert transform to study the amplitude and phase of the signals. The dynamics of the different frequency bands in the time causal entropy-complexity plane, H × C, is characterized by comparing the dynamical evolution of the basal and preictal time series. As the preictal states evolve closer to the time in which the epileptic seizure starts, the, H × C, dynamics changes for the higher frequency bands. The complexity evolves to very low values and the entropy becomes nearer to its maximal value. These quasi-stable states converge to equiprobable states when the entropy is maximal, and the complexity is zero. We could, therefore, speculate that in this case, it corresponds to the minimization of Gibbs free energy. In this case, the maximum entropy is equivalent to the principle of minimum consumption of resources in the system. We can interpret this as the nature of the system evolving temporally in the preictal state in such a way that the consumption of resources by the system is minimal for the amplitude in frequencies between 220–230 and 230–240 Hz.
2022-09-30T00:00:00ZIntracranial electroencephalography (iEEG) can directly record local field potentials (LFPs) from a large set of neurons in the vicinity of the electrode. To search for possible epileptic biomarkers and to determine the epileptogenic zone that gives rise to seizures, we investigated the dynamics of basal and preictal signals. For this purpose, we explored the dynamics of the recorded time series for different frequency bands considering high-frequency oscillations (HFO) up to 240 Hz. We apply a Hilbert transform to study the amplitude and phase of the signals. The dynamics of the different frequency bands in the time causal entropy-complexity plane, H × C, is characterized by comparing the dynamical evolution of the basal and preictal time series. As the preictal states evolve closer to the time in which the epileptic seizure starts, the, H × C, dynamics changes for the higher frequency bands. The complexity evolves to very low values and the entropy becomes nearer to its maximal value. These quasi-stable states converge to equiprobable states when the entropy is maximal, and the complexity is zero. We could, therefore, speculate that in this case, it corresponds to the minimization of Gibbs free energy. In this case, the maximum entropy is equivalent to the principle of minimum consumption of resources in the system. We can interpret this as the nature of the system evolving temporally in the preictal state in such a way that the consumption of resources by the system is minimal for the amplitude in frequencies between 220–230 and 230–240 Hz.Heterogeneity across neural populations: its significance for the dynamics and functions of neural circuitsBaravalle, RománMontani, Fernando Fabiánhttp://sedici.unlp.edu.ar:80/handle/10915/1604382023-11-23T20:43:16Z2021-01-01T00:00:00ZArticulo
Physical Review E; vol. 103, no. 4
Neural populations show patterns of synchronous activity, as they share common correlated inputs. Neurons in the cortex that are connected by strong synapses cause rapid firing explosions. In addition, areas that are connected by weaker synapses have a slower dynamics and they can contribute to asymmetries in the input distributions. The aim of this work is to develop a neural model to investigate how the heterogeneities in the synaptic input distributions affect different levels of organizational activity in the brain dynamics.We analytically show how small changes in the correlation inputs can cause large changes in the interactions of the outputs that lead to a phase transition, demonstrating that a simple variation in the direction of a biased skewed distribution in the neuronal inputs can generate a transition of states in the firing rate, passing from spontaneous silence (“down state”) to an absolute spiking activity (“up state”). We present an exact quantification of the dynamics of the output variables, showing that when considering a biased skewed distribution in the inputs of neuronal population, the critical point is not in an asynchronous or synchronous state but rather at an intermediate value.
2021-01-01T00:00:00ZNeural populations show patterns of synchronous activity, as they share common correlated inputs. Neurons in the cortex that are connected by strong synapses cause rapid firing explosions. In addition, areas that are connected by weaker synapses have a slower dynamics and they can contribute to asymmetries in the input distributions. The aim of this work is to develop a neural model to investigate how the heterogeneities in the synaptic input distributions affect different levels of organizational activity in the brain dynamics.We analytically show how small changes in the correlation inputs can cause large changes in the interactions of the outputs that lead to a phase transition, demonstrating that a simple variation in the direction of a biased skewed distribution in the neuronal inputs can generate a transition of states in the firing rate, passing from spontaneous silence (“down state”) to an absolute spiking activity (“up state”). We present an exact quantification of the dynamics of the output variables, showing that when considering a biased skewed distribution in the inputs of neuronal population, the critical point is not in an asynchronous or synchronous state but rather at an intermediate value.Two-sites’ spin chain as a good statistical representative of an infinite onePennini, FlaviaPlastino, Ángel Luishttp://sedici.unlp.edu.ar:80/handle/10915/1602592023-11-16T20:06:32Z2021-01-01T00:00:00ZArticulo
Results in Physics; vol. 27
We apply information-theory based symbolic quantifiers, related to complexity studies, in order to investigate interacting spin chains, in which there is competition between one-body and two-body quantum interactions.
Our system of reference is a well-known XY model with N-spins. We show that most of its thermal features can already be detected with N = 2.
2021-01-01T00:00:00ZWe apply information-theory based symbolic quantifiers, related to complexity studies, in order to investigate interacting spin chains, in which there is competition between one-body and two-body quantum interactions.
Our system of reference is a well-known XY model with N-spins. We show that most of its thermal features can already be detected with N = 2.Information-theoretic methods for studying population codesInce, Robin A.A.Senatore, RiccardoArabzadeh, EhsanMontani, Fernando FabiánDiamond, Mathew E.Panzeri, Stefanohttp://sedici.unlp.edu.ar:80/handle/10915/1602532023-11-16T20:06:34Z2010-01-01T00:00:00ZArticulo
Neural Networks; vol. 23, no. 6
Population coding is the quantitative study of which algorithms or representations are used by the brain to combine together and evaluate the messages carried by different neurons. Here, we review an information-theoretic approach to population coding. We first discuss how to compute the information carried by simultaneously recorded neural populations, and in particular how to reduce the limited sampling bias which affects the calculation of information from a limited amount of experimental data.
We then discuss how to quantify the contribution of individual members of the population, or the interaction between them, to the overall information encoded by the considered group of neurons. We focus in particular on evaluating what is the contribution of interactions up to any given order to the total information. We illustrate this formalism with applications to simulated data with realistic neuronal statistics and to real simultaneous recordings of multiple spike trains.
2010-01-01T00:00:00ZPopulation coding is the quantitative study of which algorithms or representations are used by the brain to combine together and evaluate the messages carried by different neurons. Here, we review an information-theoretic approach to population coding. We first discuss how to compute the information carried by simultaneously recorded neural populations, and in particular how to reduce the limited sampling bias which affects the calculation of information from a limited amount of experimental data.
We then discuss how to quantify the contribution of individual members of the population, or the interaction between them, to the overall information encoded by the considered group of neurons. We focus in particular on evaluating what is the contribution of interactions up to any given order to the total information. We illustrate this formalism with applications to simulated data with realistic neuronal statistics and to real simultaneous recordings of multiple spike trains.Ground state structural, lattice dynamic, thermodynamic and optical properties of the Ba₂CaMoO₆ ordered perovskiteDeluque Toro, Críspulo EnriqueVergara, V. E.Gil Rebaza, Arles VíctorLandínez Téllez, David ArsenioRoa-Rojas, Jairohttp://sedici.unlp.edu.ar:80/handle/10915/1601072023-11-14T20:06:50Z2023-01-01T00:00:00ZArticulo
Physica B: Condensed Matter; vol. 666
Ab-initio calculations based on density functional theory have been performed to establish the ground state properties for the double perovskite type material Ba₂CaMoO₆. The calculations were carried out through the Projector Augmented Wave Method and the exchange and correlation was described using the Perdew-Burke- Ernzerhof parameterization of the Generalized Gradient Approximation. The study included structural analysis of the material, as well as thermodynamic, cell dynamics and optical properties at its transition between the tetragonal I4/m and cubic Fm 3 m phases. The results on the structural stability reveal that the phase with space group of I4/m is more stable. Likewise, the structural phase transition was obtained for a pressure of 0.067 GPa.
On the other hand, the analysis of the electronic properties shows that the material presents a semiconducting behaviour, with a direct band gap of 2.40 eV and 2.26 eV for the tetragonal and cubic structures, respectively. In addition to agreeing with the experimental values reported in the literature, the results suggest possibilities for the application of this material in photodetectors, light emitters and devices for power electronics.
2023-01-01T00:00:00ZAb-initio calculations based on density functional theory have been performed to establish the ground state properties for the double perovskite type material Ba₂CaMoO₆. The calculations were carried out through the Projector Augmented Wave Method and the exchange and correlation was described using the Perdew-Burke- Ernzerhof parameterization of the Generalized Gradient Approximation. The study included structural analysis of the material, as well as thermodynamic, cell dynamics and optical properties at its transition between the tetragonal I4/m and cubic Fm 3 m phases. The results on the structural stability reveal that the phase with space group of I4/m is more stable. Likewise, the structural phase transition was obtained for a pressure of 0.067 GPa.
On the other hand, the analysis of the electronic properties shows that the material presents a semiconducting behaviour, with a direct band gap of 2.40 eV and 2.26 eV for the tetragonal and cubic structures, respectively. In addition to agreeing with the experimental values reported in the literature, the results suggest possibilities for the application of this material in photodetectors, light emitters and devices for power electronics.Dualities and models in various dimensionsMoreno, Enrique FranciscoSchaposnik, Fidel Arturohttp://sedici.unlp.edu.ar:80/handle/10915/1601042023-11-14T20:06:51Z2021-01-01T00:00:00ZArticulo
Physics Letters B; vol. 821
Working within the path-integral framework we first establish a duality between the partition functions of two U(1)gauge theories with a theta term in d =4space-time dimensions. Then, after a dimensional reduction to d =3 dimensions we arrive to the partition function of a U(1) gauge theory coupled to a scalar field with an action that exhibits a Dirac monopole solution. A subsequent reduction to d =2 dimensions leads to the partition function of a theory in which the gauge field decouples from two scalars which have non-trivial vortex-like solutions. Finally this d =2 partition function can be related to the bosonized version of the two-dimensional QED2(Schwinger) model.
2021-01-01T00:00:00ZWorking within the path-integral framework we first establish a duality between the partition functions of two U(1)gauge theories with a theta term in d =4space-time dimensions. Then, after a dimensional reduction to d =3 dimensions we arrive to the partition function of a U(1) gauge theory coupled to a scalar field with an action that exhibits a Dirac monopole solution. A subsequent reduction to d =2 dimensions leads to the partition function of a theory in which the gauge field decouples from two scalars which have non-trivial vortex-like solutions. Finally this d =2 partition function can be related to the bosonized version of the two-dimensional QED2(Schwinger) model.