Fractional and integer stages of lithium ion-graphite systems: the role of electrostatic and elastic contributions.

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.

Criticality of the phase transition on stage two in a lattice-gas model of a graphite anode in a lithium-ion battery.

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.

Simulation of selective thermodynamic deposition in nanoholes.

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.

Monomolecular adsorption on nanoparticles with repulsive interactions: a Monte Carlo study.

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.

Computer simulation and detailed mean-field approximation applied to adsorption on nanoparticles.

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.

Computer simulation of adsorption on nanoparticles: the case of attractive interactions.

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.

¿Es necesaria la técnica combinada para la detección del ganglio centinela en el cáncer de mama? / No disponible

Objetivos: Determinar si la punción con colorante mejora los resultados de la biopsia del ganglio centinela. Material y métodos: Ciento cincuenta casos de carcinoma invasor de la mama fueron sometidos a biopsia del ganglio centinela mediante técnica combinada, para determinar si la punción con colorante es rentable. Se realizó inyección subareolar indérmica de una dosis de 0,4 mCi de radioisótopico el día previo a la cirugía. Se practicó gammagrafía en todos los casos. La inyección intraparenquimatosa de 4 cc. de colorante se realizó 20 minutos antes de la cirugía, y se siguió de masaje mamario. Resultados: La tasa de migración fue 92,3% para el radioisótopo y 75% para el colorante (p = 0,01). La media de ganglios resecados fue mayor para la técnica con colorante: 2,6 vs. 1,2 (p = 0,02). No se observaron diferencias en la tasa de falsos negativos (0,2 vs. 0,4) ni en el valor predictivo negativo. La precisión diagnóstica fue mayor para el radioisótopo (90,3% vs. 75% (p = 0,001). El mismo resultado se obtuvo para el porcentaje de éxito técnico (92,3 vs. 75% (0,001)). Conclusiones: La punción con colorante no añade información a la realizada con radioisótopo. A pesar de que la técnica se debe adaptar a las necesidades del centro y a las habilidades del cirujano, una vez superada la curva de validación la técnica radioisotópica por sí misma aporta suficiente información, con menor morbilidad y coste(AU)

Objetives: To determine whether blue dye enhances sentinel node biopsy detection. Material and methods: One hundred fifty hundred consecutive cases of breast cancer were submitted to sentinel node biopsy by combined technique in order to analyze if vital blue was cost-efective. Radioisotope dose was 0,4 mCi of Tc, subareolar intradermic inyection, the day before surgery. Gammagraphy was performed in every case. Colorant was methylene blue, 4 cc administered by intraparenchimatous inyection in upper-outer quadrant 20 minutes previous to surgery, followed by breast massagge. Results: Migration rate was 92.3% for radioisotope and 75% for colorant (p = 0.01). Mean number of nodes excised was higher for colorant: 2,6 vs. 1,2 (p = 0.02). False negative rate showed no difference (0.2 vs. 0.4) nor did negative predictive value. Accuracy to staging (True neg+ true pos./total) was higher for technecium (90.3% vs. 75% (p = 0.001) and so happenned with percentage of technical success (total- no migration): 92.3% vs. 75% (0.001). Conclusions: Colorant did no add any information concerning axillary status. More nodes had to be excised, and bigger incisions were made to achieve direct visualization. Accuracy to stage the lesion and percentage of technical success were higher with radioisotope after the learning curve is achieved and blue injection can be spared(AU)

On the occurrence of stable and supersaturated metastable states in metallic core-shell nanoparticles.

Following the framework established by Hill and Chamberlin [T. L. Hill and R. V. Chamberlin, Proc. Natl. Acad. Sci. U. S. A., 1998, 95, 12779] to analyze the extension of thermodynamics of small systems to metastable states, we have adopted the same basic ideas to study the thermodynamic stability of core-shell nanoparticles. For the first time we are able to address the question of whether or not core-shell nanoparticles have a limit of stability when they are under oversaturation conditions. By the latter, we mean the excess of chemical potential of the adsorbate (shell) atoms with respect to its bulk material, which is the driving force for nanoparticle growth. In this situation the probability density exhibits multiple local maxima associated with different core-shell metastable states. The decrease of the free energy barriers for the growth of the bulk phase of the shell material is analyzed for increasing oversaturation. At large positive oversaturations, the barrier disappears and the core-shell NP become unstable with respect to the bulk deposit of the shell material. A brief discussion on the model is made illustrating its application to a specific system by means of computer simulations using realistic interatomic potentials. One of the most striking results of these specific studies is the occurrence or not of a core-shell under undersaturation conditions depending on nanoparticle size.

Thermodynamic considerations and computer simulations on the formation of core-shell nanoparticles under electrochemical conditions.

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).

Diffusion mechanisms taking place at the early stages of cobalt deposition on Au(111).

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.

[166Dy]Dy/166Ho hydroxide macroaggregates: an in vivo generator system for radiation synovectomy.

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.

Experimental validation of Monte Carlo depth-dose calculations using radiochromic dye film dosimetry for a beta-gamma 153Sm radionuclide applied to the treatment of rheumatoid arthritis.

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.

New findings on the purification and characterization of an anti-bothropic factor from Didelphis marsupialis (opossum) serum.

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.

New findings on the purification and characterization of an antibothropic factor from Didelphis marsupialis (opossum) serum

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