Optimal configuration for programmable Mössbauer experiments

Based on channel independency of recently developed Mössbauer instrumentation an approximation to optimal configuration of experiments is presented. The analysis relies on the presumption that all the available channels of the spectrum are not equally efficient for a given experimental application. A quantification of this concept is presented and a method for different channel layout comparison is proposed. The optimization of recorded spectra is important in dynamic experiments where efficiency in data taking imposes feasibility limits as well as in static applications as a way of reducing experimental time.Facultad de Ciencias Exacta

Ascorbic Acid Encapsulation in Hydrophobic Silica Xerogel

Self-assembled hybrid organo-silica sol-gel materials are rapidly expanding for new and novel applications. The microporous solid silica matrix was used as a carrier for the controlled release of ascorbic acid (AA), selected as cargo molecule. One-step synthesis procedure was optimized for the preparation of silica–molecule composites by using tetraethoxysilane and methyltrimethoxysilane as precursors. The hydrophobic silica xerogel matrices were characterized by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction. Specific surface area and porosity parameters were determined by Brunauer-Emmett-Teller (BET) technique and the matrix surface morphology by scanning electron microscopy (SEM). The observed release pattern could be interesting for the development of AA-fortified food and for use in food packaging.Facultad de Ciencias ExactasCentro de Investigación y Desarrollo en Tecnología de Pintura

On the microstructure and thermal stability of rapidly quenched Fe–B alloys in the intermediate composition range between the crystalline and amorphous states

The structure and the thermal stability of the Fe₀.₈₉B₀.₁₁ rapidly quenched alloy have been investigated. Transmission Mossbauer measurements were carried out as a function of temperature in the range from 148 K to 513 K. Room temperature x-ray diffraction and transmission and conversion-electron Mossbauer experiments, as well as 4.2 K spin-echo nuclear magnetic resonance measurements, were also performed after some selected thermal treatments for one hour between 523 K and 1273 K. Based on these experiments it is suggested that the alloy is inhomogeneous at nanoscopic scale and consists of a fine dispersion of a defective boride phase with an o-Fe₃B-like short-range order, embedded in an α-Fe matrix. This result gives support to the models which indicate phase separation in the amorphous phase with o-Fe3B short-range order prevailing in the hypereutectic iron concentration range. This phase was found to be less stable than the undefective one present in the less boron concentrated alloys. The transformation into the equilibrium phases, analyzed with an Arrhenius-type temperature dependence for the increase of the relative fraction of Fe₂B, led to an activation energy Ea = 1.38 ± 0.68 eV/atom.Facultad de Ciencias Exacta

Ascorbic Acid Encapsulation in Hydrophobic Silica Xerogel

Self-assembled hybrid organo-silica sol-gel materials are rapidly expanding for new and novel applications. The microporous solid silica matrix was used as a carrier for the controlled release of ascorbic acid (AA), selected as cargo molecule. One-step synthesis procedure was optimized for the preparation of silica–molecule composites by using tetraethoxysilane and methyltrimethoxysilane as precursors. The hydrophobic silica xerogel matrices were characterized by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction. Specific surface area and porosity parameters were determined by Brunauer-Emmett-Teller (BET) technique and the matrix surface morphology by scanning electron microscopy (SEM). The observed release pattern could be interesting for the development of AA-fortified food and for use in food packaging.Facultad de Ciencias ExactasCentro de Investigación y Desarrollo en Tecnología de Pintura

Dipolar interaction and demagnetizing effects in magnetic nanoparticle dispersions: introducing the mean-field interacting superparamagnet model

Aiming to analyze relevant aspects of interacting magnetic nanoparticle systems (frequently called interacting superparamagnets), a model is built from magnetic dipolar interaction and demagnetizing mean-field concepts. By making reasonable simplifying approximations, a simple and useful expression for effective demagnetizing factors is achieved, which allows the analysis of uniform and nonuniform spatial distributions of nanoparticles, in particular the occurrence of clustering. This expression is a function of demagnetizing factors associated with specimen shape and clusters shape, and of the mean distances between near neighbor nanoparticles and between clusters, relative to the characteristic sizes of each of these two types of objects, respectively. The model explains effects of magnetic dipolar interactions, such as the observation of apparent nanoparticle magnetic moments smaller than real ones and approaching to zero as temperature decreases. It is shown that by performing a minimum set of experimental determinations along principal directions of geometrically well-defined specimens, model application allows retrieval of nanoparticle intrinsic properties, like mean volume, magnetic moment, and susceptibility in the absence of interactions. It also permits the estimation of mean interparticle and intercluster relative distances, as well as mean values of demagnetizing factors associated with clusters shape. An expression for average magnetic dipolar energy per nanoparticle is also derived, which is a function of specimen effective demagnetizing factor and magnetization. Experimental test of the model was performed by analysis of results reported in the literature and of original results reported here. The first case corresponds to oleic-acid-coated 8-nm magnetite particles dispersed in PEGDA-600 polymer, and the second one to polyacrilic-acid-coated 13-nm magnetite particles dispersed in PVA solutions from which ferrogels were later produced by a physical cross-linking route. In both cases, several specimens were studied covering a range of nanoparticle volume fractions between 0.002 and 0.046. Magnetic response is clearly different when prism-shaped specimens are measured along different principal directions. These results remark the importance of reporting complete information on measurement geometry when communicating magnetic measurement results of interacting magnetic nanoparticles. Intrinsic nanoparticle properties as well as structural information on particles spatial distribution were retrieved from our analysis in addition to, and in excellent agreement with, analysis previously performed by other authors and/or information obtained from FESEM images. In the studied samples, nanoparticles were found to be in close contact to each other within almost randomly oriented clusters. Intercluster mean distance, relative to cluster size, was found to vary between 2.2 and 7.5, depending on particles volume fraction.Instituto de Física La Plat

Stress-induced Gene Expression Sensing Intracellular Heating Triggered by Magnetic Hyperthermia

It is known that alternating magnetic field applications on eukaryotic cells loaded with single domain iron oxide nanoparticles result in high hyperthermic citotoxicity leading to cell dead. Although magnetic hyperthermia therapy for cancer tumours is being developed under this idea, some in vitro assays have shown controversial results indicating that alternating magnetic field triggers large apoptotic effect without significant culture-temperature increase. In agreement with these observations a huge lowering in nanoparticle specific heating rates, when going from the colloidal suspension to cell endosomes, together with cell death, has been reported. Here, we propose a new methodology to determine the occurrence of local heating in cells when alternating magnetic fields in the radiofrequency field range are applied to cell cultures holding very low iron oxide concentrations, being these concentrations insufficient to produce a global cell-culture temperature increase up to therapeutic values. To this end, human lung adenocarcinoma cells (A549 cell line) were transduced with a lentiviral vector encoding the expression of the enhanced green fluorescence protein, EGFP, under the action of the inducible human heat shock protein 70B promoter. This modified A549 cell line was incubated with aqueous suspensions of magnetite core nanoparticles (uncoated or covered with coating agents like citric acid or silicon oxide), and exposed to radiofrequency fields. The application of an alternating magnetic field to cell cultures loaded with nanoparticles resulted in no global temperature increase but EGFP expression. Stress-inducible gene expression scales with uptake and nanoparticle properties like saturation magnetization and heat dissipation efficiency. Our analysis demonstrates that EGFP expression is linked to a localized intracellular temperature increase.Fil: de Sousa, María Elisa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; ArgentinaFil: Carrea, Alejandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Biotecnológicas. Instituto de Investigaciones Biotecnológicas "Dr. Raúl Alfonsín" (sede Chascomús). Universidad Nacional de San Martín. Instituto de Investigaciones Biotecnológicas. Instituto de Investigaciones Biotecnológicas "Dr. Raúl Alfonsín" (sede Chascomús); ArgentinaFil: Mendoza Zélis, Pedro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; ArgentinaFil: Muraca, Diego. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidade Estadual de Campinas; BrasilFil: Mykhaylyk, Olga. Technische Universitat Munchen; AlemaniaFil: Sosa, Yolanda Elena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Bioquímicas de La Plata "Prof. Dr. Rodolfo R. Brenner". Universidad Nacional de la Plata. Facultad de Ciencias Médicas. Instituto de Investigaciones Bioquímicas de La Plata ; ArgentinaFil: Goya, Rodolfo Gustavo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Bioquímicas de La Plata "Prof. Dr. Rodolfo R. Brenner". Universidad Nacional de la Plata. Facultad de Ciencias Médicas. Instituto de Investigaciones Bioquímicas de La Plata ; ArgentinaFil: Sánchez, Francisco Homero. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; ArgentinaFil: Dewey, Ricardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Biotecnológicas. Instituto de Investigaciones Biotecnológicas "Dr. Raúl Alfonsín" (sede Chascomús). Universidad Nacional de San Martín. Instituto de Investigaciones Biotecnológicas. Instituto de Investigaciones Biotecnológicas "Dr. Raúl Alfonsín" (sede Chascomús); ArgentinaFil: Fernández van Raap, Marcela Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; Argentin

Optimal configuration for programmable Mössbauer experiments

Based on channel independency of recently developed Mössbauer instrumentation an approximation to optimal configuration of experiments is presented. The analysis relies on the presumption that all the available channels of the spectrum are not equally efficient for a given experimental application. A quantification of this concept is presented and a method for different channel layout comparison is proposed. The optimization of recorded spectra is important in dynamic experiments where efficiency in data taking imposes feasibility limits as well as in static applications as a way of reducing experimental time.Facultad de Ciencias Exacta

Hidrogeno en intermetálicos de estructura Ti₂Ni

El Hf₂Fe y el Hf₂Co pertenecen a una familia de compuestos que presenta la estructura cúbica del tipo Ti₂Ni y tiene la capacidad de absorber hidrógeno. Ambos compuestos pueden ser estudiados simultáneamente mediante efecto Mössbauer (EM) y por correlaciones angulares perturbadas (CAP) empleando como sondas el ⁵⁷Fe y el ¹⁸¹Hf respectivamente. Se efectuaron medidas CAP y EM sobre el Hf₂FeHₓ. El intermetálico Hf₂CoHₓ fue analizado con EM sustituyendo una pequeña cantidad de Co por ⁵⁷Fe. Ambos compuestos fueron estudiados mediante difracción de rayos X de polvos (DRX). Se presenta un orden de llenado con hidrógeno de sitios intersticiales, según el cual se explica el cambio de los corrimientos isoméricos. Los datos de DRX aportan el conocimiento de la expansión de la red a medida que el hidrógeno es absorbido. Esta expansión más una contribución por vecino explican el aumento del corrimiento isomérico al hidrogenar.Facultad de Ciencias Exacta

Aleaciones amorfas metálicas con una amplia región de líquido sobreenfriado preparadas por aleado mecánico

La aleación amorfa Hf₆₅Al₇.₅Cu₁₇.₅Ni₁₀, preparada por aleado mecánico de los polvos elementales, fue estudiada por difracción de rayos X, calorimetría diferencial de barrido y correlaciones angulares perturbadas. Los rayos X han confirmado el estado amorfo de las aleaciones de partida. Mediante calorimetría se ha observado una amplia zona de líquido sobreenfriado determinándose la temperatura de transición vítrea, Tg=500°C. También se ha observado la presencia de dos efectos exotérmicos indicando un proceso de cristalización en dos etapas. Las correlaciones angulares han confirmado una estructura al azar de iones en todas las muestras hasta los 520°C. Se intentará identificar los productos finales de la cristalización tanto por rayos X como por correlaciones angulares teniendo en cuenta los compuestos intermetálicos esperables de acuerdo a la estequiometría de la aleación.Facultad de Ciencias Exacta

Estudio teórico de corrimientos isoméricos en compuestos intermetálicos

En el presente trabajo hemos calculado los corrimientos isoméricos de compuestos intermetálicos formados por Fe y un metal de la serie 3d, tales como: Ti, V, Cr. Mn y Co. Todos los materiales fueron tratados en la estructura B2 (CsCl). Los estudios se realizaron por medio de cálculos teóricos llevados a cabo con el Full Potential Linear Augmented Plañe Wave (FP-LAPW). También se determinaron parámetros propios de los materiales como modulo de bulk y constante de celda de equilibrio. Para el caso del FeV, se han realizado experimentos para comparar con nuestros datos teóricos.In the present work isomer shifts of intermetallic compounds of Fe and transition metal of 3d series, such as: Ti, V, Cr, Mn and Co has been calculated. The materials were treated in the B2(CsCl) structure. Calculation were done by mean of the FP-LAPW . Additionally we have calculated structural parameters, bulk modulus and lattice constant. Experiments on FeV were carried out.Grupo de Estudio de Materiales y Dispositivos ElectrónicosInstituto de Física de Líquidos y Sistemas BiológicosFacultad de Ciencias Exacta