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In the present work, we analyze the hot topic of integer and fractional stages of lithium-ion batteries by using Monte Carlo simulations. While fractional stages have been demonstrated through several experimental, simulation and theoretical measurements, in other experimental techniques, such as electrochemical ones, there is no evidence for them. In previous work, we have analyzed the thermodynamics and kinetics of lithium-ion intercalation using a potential based on empirical parameterization, where multiple stages (integer and fractional) were found and analyzed. The present simulations suggest that if we consider repulsive elastic interactions in addition to electrostatic ones, the Hamiltonian symmetry is broken and there is no evidence for fractional stages. The physical origin of these repulsive interactions is assigned to the increasing graphite layer separation during lithium-ion intercalation. In the light of these simulations, selected experimental data are revisited, validating the presented novel parameterization. The parametrization used here can be used for other kinds of intercalation compounds, such as those involving Na or K.
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Herein, a Monte Carlo study within the canonical assembly has been applied to elucidate the lithium-ion phase transition order of a stage II lithium-graphite intercalation compound (LiC12) around the critical point. The results reveal a weakly first-order phase transition at 354.6 ± 0.5 K via measurements that follows the power laws with effective exponents. The graphite-lithium system was emulated within a lattice-gas model, comprising specific insertion sites arranged in four parallel planes with a triangular geometry. Moreover, two different types of energetic interactions were used: a Lennard-Jones potential, for particle interactions in the same plane, and a power law potential that decreased with distance, for particles in different planes. The energy per site and order parameter distribution were used to classify the order of the transition. Furthermore, the order parameters, susceptibility, and heat capacity were computed and analyzed.
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The deposition of particles in nanoholes is analyzed, taking into account the curvature of their inner walls. Different lattice-gas models of the nanoholes are considered. The heterogeneous surface are shaped from a (100)-surface where a nanohollow are incorporated with parallelepiped or polyhedral geometry. Several deposition stages are identified as a function of the degree of curvature of the inner walls of the nanoholes. The Monte Carlo technique in the grand canonical ensemble is used to calculate isotherms, isosteric heats, energies per site and other thermodynamic properties. This study is based on different magnitudes of the interaction energies between the particles being deposited and those surrounding the nanohole.
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In the present work, we study the adsorption of different monomolecular species on nanoparticles with different sizes and geometries using a grand canonical Monte Carlo method. These species are characterized by repulsive lateral interactions between themselves, as takes place in the case of the adsorption of partially charged atoms or molecules. Nanosize effects are analyzed in terms of adsorption on edge and facet sites. The energy minimization in these systems comes out as a complex conjugation of the repulsive lateral interactions between the adsorbates and the attractive interactions of the adsorbates with the nanoparticle. The phenomenon is analyzed as a function of the occurrence of different ordered structures being formed on the surface of the nanoparticle. We find that layers with different structures may coexist on different facets of the nanoparticle. Finally, a discussion of deposition on flat surfaces and in finite systems is given.
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Adsorption thermodynamics of interacting particles adsorbed on icosahedral and truncated octahedral nanoparticles was studied by a detailed mean-field approximation and Monte Carlo simulations. The nanoparticle is tackled as a multivariate surface, where different types of adsorption sites occur according to coordination with nearest neighbors. In addition, lateral couplings between the adsorbed particles are considered. The analysis covers a wide range of interactions, extending from physical to strong chemical bonds, and different sizes and shapes of nanoparticles.
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A lattice-gas model describing adsorption on nanoparticles of different sizes and shapes is proposed and the adsorption thermodynamics is studied. The nanoparticle is modeled assuming different geometries, and Monte Carlo simulations are performed in the grand canonical ensemble. Adsorption isotherms, differential heats of adsorption, and other relevant thermodynamic properties are analyzed as a function of nanoparticle sizes. The simulations cover a wide range of interactions, ranging from physical to strong chemical bonds.
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We report on thermodynamic modeling and computer simulations on the electrochemical generation of metallic and bimetallic nanoparticles (NPs) by means of quenched molecular dynamics (QMD). The present results suggest that the spontaneous formation of core-shell NPs depends on several factors, i.e. size and shape of the core, chemical composition of the system, and under-/oversaturation conditions. Homo- and heteroatomic prototypical systems were considered. The former systems were Au and Pt. The latter were Ag(core)/Au(shell), Pt(core)/Au(shell), Au(core)/Ag(shell) and Au(core)/Pt(shell).
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In the present work a detailed atomic-level analysis of some of the main diffusion mechanisms which take place during cobalt adatom deposition are studied within atom dynamics (AD) and the nudged elastic band (NEB) method. Our computer simulations reveal a very fast exchange between Co and Au atoms when the deposit is a single cobalt adatom. However, when the nucleus size increases, a decrease in the exchange probability is observed. Activation energies for different transitions are obtained using AD in combination with the NEB method.
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Radiation synovectomy is an effective treatment in patients suffering from inflammatory-rheumatoid and degenerative joint diseases. The aim of this work was to examine the feasibility of preparing dysprosium-166 (166Dy)/holmium-166(166Ho) hydroxide macroaggregates ([166Dy]Dy/166Ho-HM) as an in vivo generator for radiation synovectomy evaluating whether the stability of 166Dy-HM and 166Ho-HM complexes is maintained when the daughter 166Ho is formed. The Monte Carlo (MCNP4B) theoretical depth dose profile for the in vivo [166Dy]Dy/166Ho generator system in a joint model was calculated and compared with that produced by 90Y, 153Sm and 166Ho. 166Dy was obtained by neutron irradiation of enriched 164Dy2O3 in a Triga Mark III reactor. Macroaggregates were prepared by reaction of [166Dy]DyCl3 with 0.5 M NaOH in an ultrasonic bath. [166Dy]Dy/166Ho-HM was obtained with radiochemical purity >99.5% and with the majority of particles in the 2-5 microm range. In vitro studies demonstrated that the radio-macroaggregates are stable in saline solution and human serum without a significant change in the particle size over 14 d, suggesting that no translocation of the daughter nucleus occurs subsequent to beta- decay of 166Dy. Biological studies in normal rats demonstrated high retention in the knee joint even 7 d after [166Dy]Dy/166Ho-HM administration. The Monte Carlo (MCNP4B) theoretical depth dose profiles in a joint model, showed that the in vivo [166Dy]Dy/166Ho generator system would produce 25% and 50% less radiation dose to the articular cartilage and bone surface, respectively, than that produced by 90Y or pure 166Ho in a treatment with the same therapeutic dose to the synovium surface. Despite that 153Sm showed the best depth dose profile sparing doses to healthy tissues, the use of 166Dy could provide the advantage of being applied in patients that cannot be reached within a few hours from a nuclear reactor and to produce less radiation exposure to the medical personnel during the radiopharmaceutical administration.
Assuntos
Disprósio/farmacocinética , Hólmio/farmacocinética , Marcação por Isótopo/métodos , Articulações/metabolismo , Radioisótopos/farmacocinética , Compostos Radiofarmacêuticos/farmacocinética , Animais , Artrite Reumatoide/radioterapia , Disprósio/química , Disprósio/isolamento & purificação , Disprósio/uso terapêutico , Estudos de Viabilidade , Hólmio/química , Hólmio/isolamento & purificação , Hólmio/uso terapêutico , Humanos , Artropatias/radioterapia , Substâncias Macromoleculares/síntese química , Substâncias Macromoleculares/isolamento & purificação , Substâncias Macromoleculares/uso terapêutico , Masculino , Taxa de Depuração Metabólica , Especificidade de Órgãos , Radioisótopos/química , Radioisótopos/isolamento & purificação , Radioisótopos/uso terapêutico , Compostos Radiofarmacêuticos/síntese química , Compostos Radiofarmacêuticos/isolamento & purificação , Compostos Radiofarmacêuticos/uso terapêutico , Ratos , Distribuição TecidualRESUMO
In this work we compare the Monte Carlo (MCNP4B) calculated beta-gamma depth-dose profile for a liquid 153Sm beta-gamma source used in radiation synovectomy with the experimental depth-dose distribution obtained using radiochromic dye film dosimetry. The calculated and experimental depth-dose distribution shows a very good agreement (within 5%) in the region where the dose deposition is dominated by the beta particle component (first 800 microm depth on tissue-equivalent material). The agreement worsens, reaching a maximum deviation of 15%, at depths close to the maximum range of the beta particles. Finally the agreement improves for the region where the gamma component accounts for one-third of the total absorbed dose (depths >1 mm). The possible contributions to these differences are discussed, as well as their relevance for the application of 153Sm in the treatment of rheumatoid arthritis.
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Artrite Reumatoide/radioterapia , Partículas beta , Raios gama , Radioisótopos/uso terapêutico , Samário/uso terapêutico , Corantes , Humanos , Método de Monte Carlo , Radiometria/métodos , Dosagem Radioterapêutica , Reprodutibilidade dos TestesRESUMO
We have used DEAE-Sephacel and Sephacryl S-200 to separate protein fractions from Didelphis marsupialis serum capable of protecting mice from the lethal effect of Bothrops jararaca venom. The fractions separated were homogeneous by conventional electrophoresis using cellulose acetate and polyacrylamide; however, they were heterogeneous on PAGE-SDS, showing similar electrophoretic patterns with or without mercaptoethanol. The protein bands obtained were glycoproteins with a molecular weight of 42,000 to 58,000 Daltons.
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Antivenenos/isolamento & purificação , Venenos de Crotalídeos/imunologia , Gambás/sangue , Animais , Antivenenos/imunologia , Venenos de Crotalídeos/intoxicação , Eletroforese em Acetato de Celulose , Eletroforese em Gel de Poliacrilamida , CamundongosRESUMO
We have used DEAE-Sephacel and Sephacryl S-200 to separate protein fractions from Didelphis marsupialis serum capable of protecting mice from the lethal effect of Bothrops jararaca venom. the fractions separated were homogeneous by conventional electrophoresis using cellulose acetate and polyacrylamide; however, they were heterogeneous on PAGE-SDS, showing similar electrophoretic patterns with or without mercaptoethanol. The protein bands obtained were glycoproteins with a molecular weight of 42,000 to 58,000 Daltons