A closer look at photochemical reactions of transition-metal compounds by time-resolved EPR Martino, Debora Marcela; Kleverlaan, C. J.; Slageren, J. van; Bussandri, A.; Willigen, H. van; Kiarie, C. A review is given of applications of time-resolved Electron Paramagnetic Resonance (TREPR) in the field of photochemistry of transition metal compounds. The two main TREPR techniques used in these studies are described. A brief overview is given of Chemically Induced Dynamic Electron Polarization (CIDEP) mechanisms that can affect TREPR spectra and that can give insights into the mechanism of photochemical reactions. Following these background sections experimental results are presented. The discussion focuses in particular on the Fourier Transform EPR (FT-EPR) studies of photoinduced metal–alkyl bond homolysis reactions of a series of transition metal (Co, Ru, Re, Pt) complexes carried out by the authors.

Packed-Bed Photocatalytic Reactors. A Packing Structure Model and Its Experimental Validation with Computerized Tomography Irazoqui, Horacio Antonio; Isla, Miguel Angel; Brandi, Rodolfo Juan; Cassano, Alberto Enrique A statistical model is proposed for the description of the spatial structure of a packed bed of spherical-like particles in terms of one- and two-bead distribution functions. This is the first step toward the full modeling of the radiation field in an annular photocatalytic reactor, mainly where the interaction between radiation and the packed beads is concerned. The model has been validated against tomography experiments performed on an up-scaled packing prototype. The three-dimensional structure of its loose random packing has been digitized. On the basis of this structural information, the experimental version of the one-bead distribution function, as well as those of the conditional distribution and the solid volume fraction, could be constructed without mediating models. Then the parameters of the proposed statistical model could be determined by nonlinear regression. The agreement between the functions constructed experimentally and their model-predicted counterparts with the set of regressed model parameters is remarkable considering the highly structured shapes of their profiles. Exact relationships have been established to scale those model parameters bearing dimensions to packings with different bead radii.

The relatively young, metal-poor and distant open cluster NGC 2324 Piatti, Andres Eduardo; Claria Olmedo, Juan Jose; Ahumada, Andrea Veronica We have obtained CCD photometry in the Johnson V, Kron-Cousins I and CT1 Washington systems for NGC 2324, a rich open cluster located ∼35◦ from the Galactic anticentre direction. We measured V magnitudes and V − I colours for 2865 stars and T1 magnitudes and C − T1 colours for 1815 stars in an area of 13. 6 × 13. 6. The comparison of the cluster colour–magnitude diagrams with isochrones of the Geneva group yield E(V − I) = 0.33 ± 0.07 and V − MV = 13.70 ± 0.15 for log t = 8.65 (t = 440 Myr) and Z = 0.008 ([Fe/H] = −0.40), and E(C − T1) = 0.40 ± 0.10 and T1 − MT1 = 13.65 ± 0.15 for the same age and metallicity level. The resulting E(V − I) reddening value implies E(B − V) = 0.25 ± 0.05 and a istance from the Sun of (3.8 ± 0.5) kpc. Star counts carried out within and outside the cluster region allowed us to estimate the cluster angular radius as 5. 3 ± 0. 3 (5.9 pc). When using the E(B − V) reddening value here derived and the original Washington photometric data of Geisler et al. (1991) for the stars confirmed as red cluster giants from Coravel radial velocities, we found [Fe/H] = −0.31 ± 0.04, which is in good agreement with the best fits of isochrones. Therefore, NGC 2324 is found to be a relatively young, metal-poor and distant open cluster located beyond the Perseus spiral arm. A comparison of NGC 2324 with 10 well-known open clusters of nearly the same age shows that the cluster metal abundance and its position in the Galaxy are consistent with the existence of a radial abundance gradient of −0.07 dex kpc−1 in the Galactic disc.

Vibrational and 57Fe-Mo¨ssbauer spectra of LaFeGe2O7 and NdFeGe2O7 Baran, Enrique José; Mercader, Roberto Carlos; Cascales, C. The infrared, Raman and 57Fe-Mo¨ssbauer spectra of LaFeGe2O7 and NdFeGe2O7 were recorded and analysed on the basis of their structural characteristics. Some comparisons with the stoichiometrically related materials containing the heavier lanthanides are made, showing that it is possible to differentiate spectroscopically both groups of materials. The Mo¨ssbauer parameters clearly reflect the small structural differences in the FeO5-polyhedra present in these compounds.

ABS copolymer-activated carbon mixed matrix membranes for CO 2/CH4 separation Anson, Marcia; Marchese, Jose; Garis, Eduardo; Ochoa, Nelio Ariel; Pagliero, Cecilia Liliana The performance of various novel mixed matrix composite (MMC) membranes for separation of CO2 from CH4 was investigated as a function of carbon loading. Acrylonitrile-butadiene-styrene (ABS) copolymer was used as the polymer matrix and two micro-mesoporous activated carbons (AC) were chosen as inorganic fillers. A thorough analysis of the effect of temperature and pressure on the permeation rates of CO2 and CH4 and selective properties of the ABS-AC composite membranes was done. Measurements were made for each system at four different temperatures in the range 20-50 °C, and in the feed pressure range from 2 to 8 × 105 Pa. The ABS-AC membranes showed a simultaneous increase of CO2 gas permeabilities (40-600%) and CO2/CH4 selectivities (40-100%) over the intrinsic ABS permselectivity by increasing the percentage of carbon loaded in the mixed matrix composite membrane.

Nonlinear uncertainty model of a magnetic suspension system Agamennoni, Osvaldo Enrique; Skrjanc, Igor; Lepetic, Marco; Chiacchiarini, Hector Gerardo; Matko, Drago The nonlinear identification of a nominal model as well as the uncertainty bounds of a magnetic suspension system is developed. This system has a nonsymmetric dynamic behavior; it has an undershoot but not an overshoot. The proposed model structure is a cascade of a global linear fuzzy dynamic block followed by a piecewise linear function. This model structure allows a proper identification of the system dynamic and a tight description of the uncertainties.

Empirical viscous coefficients of dilute solutions of tetraethylene glycol dimethyl ether in 2-propanol and in 2-butanol at different temperatures Aznarez, Silvia; Amid, Adrián; Ferreyra de Ruiz Holgado, Mercedes Marta Elsa; Arancibia, Eleuterio Luis This paper reports experimental viscosities and densities of binary mixtures containing tetraethylene glycol dimethyl ether+(2-propanol, 2-butanol) at four different temperatures (288.15, 298.15, 308.15 and 318.15 K), over the mole fraction (x) range of tetraethylene glycol dimethyl ether between 0 V x V 0.1 and at atmospheric pressure. The empirical coefficients (bG, cG and DG1,2*0) were determined from the viscosity values of the binary mixtures in the dilute zone of tetraethylene glycol dimethyl ether, using the Tamamushi – Isono empirical relationship between the thermodynamic function, DG1,2*0, with the mole fraction of tetraethylene glycol dimethyl ether (x) at a particular temperature. The Jones –Dole coefficient (B) was calculated in a graphical way. Both contributions, the energetic and the volumetric ones, to coefficient (B) were obtained. A comparative study of the Jones –Dole coefficient B and the coefficient bG of the solutions of tetraethylene glycol dimethyl ether in 2-alkanol with tetraethylene glycol dimethyl ether in 1-alkanol data, obtained from literature, was carried out. The results are discussed qualitatively using the rate process Eyring theory, applied to viscous flow.

Mecanismos moleculares involucrados en el proceso de fusión de gametas en mamíferos Cuasnicu, Patricia Sara; Cohen, Debora Juana; Busso, Dolores; Da Ros, Vanina Gabriela; Maldera, Julieta Antonella; Goldweic, Nadia Micaela La fusión de las gametas es un evento crucial en el proceso de fertilización que involucra la interacción de dominios específicos de las membranas plasmáticas del espermatozoide y del ovocito. Durante los últimos años, se ha comenzado a identificar a los componentes moleculares específicos involucrados en dicho evento. En el presente trabajo se describirán las moléculas mejor caracterizadas que han sido propuestas como candidatas a mediar la fusión de las gametas en mamíferos.

Characterization of metallocene Epdm terpolymers with high diene and propylene content crosslinked by dicumyl peroxide and β-radiation Nicolás, Javier; Ressia, Jorge Aníbal; Valles, Enrique Marcelo; Merino, Juan Carlos; Pastor, José María Two metallocene EPDMs with the same weight fraction of ethylene but differing in diene content were crosslinked, either by dicumyl peroxide (DCP) or β-radiation. The effect of different diene and propylene content on the molecular structure and the mechanical properties once the materials were crosslinked was studied. The final gel content was very high due to the large level of unsaturations. The crosslinking process was monitored by FTIR spectroscopy by following the decay of unsaturations and the variation of the carbonyl groups that are related to the oxidation grade. It was found that β-radiation crosslinked samples exhibited a lower oxidation grade than those crosslinked by DCP. An oscillant disc rheometer was employed to follow the evolution of the rheological properties, the scorch time, and the time corresponding to full cure during the crosslinking reaction with DCP. In addition, in order to characterize the state of cure we have studied the rheological properties in shear employing a dynamic parallel plate geometry. These results were correlated with those obtained from the molecular characterization of the soluble fraction by size exclusion chromatography. The experiments indicate that, at low irradiation doses, there is a high rate of chain scission reactions that cause an important decrease in storage modulus. Whereas, at high irradiation doses the rate of chain scission reactions diminishes, thus the storage modulus increases but it still remains at lower levels than those corresponding to the original terpolymers. The tensile properties, hardness (Shore A) and compression set tests also suggest the presence of chain scission reactions.

Provenance and Evolution of the Guarguaráz Complex, Cordillera Frontal, Argentina López, Vanina Lucrecia; Gregori, Daniel Alfredo The Guarguaráz Complex, basement of the Cordillera Frontal, included in the proposed Chilenia Terrane, consists of metasedimentary rocks deposited in clastic and carbonatic platforms. Turbiditic sequences point out to slope or external platform environments. According to geochemical data, the sedimentary protoliths derived through erosion of a mature cratonic continental basement. Volcanic and subvolcanic rocks with N and E-MORB signature were interbeded in the metasedimentary rocks during basin development. A compressional stage, starting with progressive deformation and metamorphism, followed this extensional stage. Continuing deformation led to the emplacement of slices of oceanic crust, conforming an accretionary prism during Late Devonian. The Guarguaráz Complex and equivalent units in western Precordillera and also in the Chilean Coastal Cordillera share common evolutional stages, widely represented along the western Gondwana margin. These evidences imply that Chilenia is not an allochthonous terrane to Gondwana, but a portion of its Early Paleozoic margin. Regional configuration indicates that the Guarguaráz Complex and equivalent units represent the accretionary prism of the Famatinian arc (Middle Ordovician-Late Devonian).

A simple method for domestic animal identification in Argentina using PCR-RFLP analysis of cytochrome b gene Bravi, Claudio Marcelo; Liron, Juan Pedro; Mirol, Patricia Monica; Ripoli, María Verónica; Peral Garcia, Pilar; Giovambattista, Guillermo We developed a simple, quick assay in order to discriminate forensic samples among human, and common domestic and livestock species of the Pampean region, Argentina. A mitochondrial cytochrome b fragment amplified with universal primers was separately digested with three restriction enzymes (AluI, HaeIII, and HinfI) and the resulting fragments were resolved through electrophoresis in polyacrylamide gels. This PCR-RFLP method allowed us to identify the target species and worked on degraded samples. The assay was successfully applied in livestock robbery cases in Argentine, and may be useful when attempting a first assessment as to the specific status of a forensic evidence. © 2004 Elsevier Ireland Ltd. All rights reserved.

Tefroestratigrafía (40 000-2000 a. P.) en el sector caribe de los volcanes Barva, Congo y Hule, Cordillera Central, Costa Rica Alvarado, Guillermo; Salani, Flavia Maria El área de estudio se ubica en el flanco norte de la Cordillera Volcánica Central, en las inmediaciones de los volcanes Poás (históricamente activo), Von Frantizius (activo por lo menos hace 40 000 años), Congo (activo hace unos 6000 años) y comprende la caldera explosiva de la Laguna Hule, que explotó hace 2800 años posiblemente con periodos eruptivos menores hace 1700 y 670 años a.P. y el volcán Barva. Las capas de pómez plinianas (caída y flujos) aflorantes en ambas márgenes del río Sarapiquí son antiguas (> 40 000 años). Se encontraron capas piroclásticas (tobas freatomagmáticas y lapilli pliniano) holocenas con fragmentos líticos y juveniles, procedentes de los volcanes Congo y Hule. Entre las facies asociadas con Congo, se identificaron facies de caída de naturaleza andesítica, correspondientes con distintas erupciones (C1 y C2); facies de flujo piroclástico (pumíceos y menos frecuentemente de bloques y ceniza) y una facies lahárica (datada en 6030 años). Dentro del evento explosivo relacionado con el centro volcánico Hule, se encuentran además de la facies de caída pliniana, depósitos de tobas estratificadas y lapillitas vinculados con procesos de oleadas piroclásticas basales y oleadas asociadas con nubes de cenizas.; The area is located in the north side of the Central Volcanic Range, near the Poás (historically active), Von Frantzius (active at least 40 000 years B.P.) and Congo (active about 6000 years B.P.) volcanoes. It comprises the Hule maar that exploded 2800 years ago and possibly showed some minor eruptive periods about 1700 and 670 years B.P., and the Barva volcano. Pumice sheets (airfall and flow) which crop out in both margins of the Sarapiquí river are older than 40 000 years. Field survey showed the existence of thick pyroclastic sheets (phreatomagmatic tuffs and plinian lapilli) from the Congo and Hule volcanoes. Among the facies associated with Congo we identified airfall facies of andesitic composition and corresponding to different eruptions (C1 y C2); pumice and -less frequent- block and ash pyroclastic flow facies and a lahar facies with a radiocarbon age of 6030 years. Within the explosive event related with the Hule volcanic center, besides the plinian airfall facies, there are stratified tuffs and lapilli deposits corresponding to base surges and ash cloud surges.

Dynamics of the tuning process between singers Urteaga, Raul; Bolcatto, Pablo Guillermo We present a dynamical model describing a predictable human behavior like the tuning process between singers. The purpose, inspired in physiological and behavioral grounds of human beings, is sensitive to all Fourier spectrum of each sound emitted and it contemplates an asymmetric coupling between individuals. We have recorded several tuning exercises and we have confronted the experimental evidence with the results of the model finding a very well agreement between calculated and experimental sonograms.

Keeping dry and crossing membranes Fernandez, Ariel Water sustains life but also imposes constraints on what life should be like. Its high dipole moment, proton donor-acceptor dual nature and rotational freedom make it a powerful former of hydrogen bonds. In solu- ble proteins, this property places stringent constraints on the way proteins interact (1-4) and fold (5). I argue here that the manipulation of intramolecularly underdehydrated or underwrapped electrostatic interactions in proteins can be exploited in engineering strategies to create molecules with an enhanced ability to traverse biological membranes, with potential implications for oral delivery of peptide-based drugs.

Multipeaked polarons in soft potentials Fuentes, Miguel Angel; Maniadis, P.; Kalosakas, G.; Rasmussen, K.; Bishop,A. R.; Kenkre, V. M.; Gaidedei, Yu B. We consider a minimal coupled charge/excitation-lattice model capturing a competition between linear polaronic self-trapping and the self-focusing effects of a soft nonlinear on-site potential. The standard singlehumped polaron ceases to exist above a critical value of the coupling strength, closely related to the inflection point in the nonlinear potential. For couplings beyond this critical value, we find that successive multihumped polaronic solutions correspond to the lowest-energy stationary states of the system, which may admit interesting quantum resonance behavior.

Alkaline phosphatase activity sensitive to environmental salinity and dopamine in muscle of the euryhaline crab Cyrtograpsus angulatus Pinoni, Silvina Andrea; Lopez Mañanes, Alejandra Antonia The occurrence, characteristics and response to environmental salinity and dopamine of alkaline phosphatase (AP) activity were studied in chela muscle of the euryhaline crab Cyrtograpsus angulatus from Mar Chiquita coastal lagoon (Buenos Aires Province, Argentina). Chela muscle exhibited a high AP activity with a Michaelis –Menten kinetic (Km=1.21 mM). AP activity was strongly inhibited by EDTA (I50=2.26 mM). AP activity appeared to be sensitive to environmental salinity. In crabs acclimated to low salinity (10x) AP activity was lower than in 35x salinity. Upon an abrupt change to reduced salinity a short-term decrease of AP activity occurred, concomitant with the transition to hyperregulation. Furthermore, AP activity appeared to be under hormonal control since it was inhibited ‘‘in vivo’’ by 10 4 M dopamine. The response to both environmental salinity and dopamine suggests that AP activity could be a component of muscle regulatory mechanisms at the biochemical level secondary to hyperregulation of C. angulatus. The possible functional relationship of AP activity with Na+ /K+ ATPase in muscle is discussed.

Tris(pyrazolyl)methane ligands: Syntheses and structures of monometallic and metallodendritic complexes Sánchez Méndez, Alberto Horacio; Silbestri, Gustavo Fabián; de Jesús, Ernesto; de La Mata, F. Javier; Flores, Juan C.; Gómez, Rafael; Gómez-Sal, Pilar The substituted ligands Me3SiC(pz)3 and Me 3SiOCH2C(pz)3 (2) have been prepared starting from HC(pz)3 and HOCH2C(pz)3. The molecular structure of compound 1 has been determined by X-ray diffraction studies, which show a propeller-like conformation of the pyrazolyl rings. Compound 2 has been found to be useful for the synthesis of [Mo(CO)3{Me 3SiOCH2C(pz)3}] (3), [TiCl2(NtBu) {Me3SiOCH2C(pz)3}] (4), and [PdCl 2{Me3SiOCH2C(pz)3}] (5), through ligand exchange reactions. The characterization of the new complexes is compatible with a tridentate coordination of the ligands in complexes 3 and 4, and a bidentate coordination in 5 as confirmed by an X-ray analysis carried out with the palladium complex. The procedure has been extended for the synthesis of the carbosilane G1-[OCH2C(pz)3]4 (6) and the tetrametallic compound G1-[OCH2C(pz)3Mo(CO) 3]4 (7) (G1 = Si(CH2CH2CH 2Me2Si)4-).

Determinacion de las funciones dielectricas del semiconductor PbI2 Naudi, Andrés Alberto; Albanesi, Eduardo Aldo Presentamos un estudio de las funciones dielectricas del ioduro de plomo, basado en calculos realizados  con un metodo Full Potential Linearized Augmented Plane Wave (FP-LAPW), dentro de la teoria de la funcional densidad (DFT). Los resultados de la estructura electronica indican un band gap directo en el borde de la zona de Brillouin correspondiente al eje mayor de este cristal hexagonal. En el entorno de este punto, tanto la banda de valencia superior como la banda de conduccion inferior tienen un comportamiento parabolico, resultando que el tope de la banda de valencia es principalmente s-Pb, con cierta hibridizacion p-I. Las bandas obtenidas muestran el  comportamiento de un material estructurado en capas, a partir de las cuales hemos obtenido funciones dielectricas anisotropicas, propias de un cristal uniaxial. Nuestros calculos resultan satisfactorios en comparacion con los datos experimentales.

Flavonoids from shoots and roots of Trifolium repens (white clover) grown in presence or absence of the arbuscular mycorrhizal fungus Glomus intraradices Ponce, María Alejandra; Scervino, Jose Martin; Erra Balsells, Rosa; Ocampo, Juan A.; Godeas, Alicia Margarita White clover (Trifolium repens) plants were grown in the presence or absence of the arbuscular mycorrhizal fungus Glomus intraradices. Flavones, 4?,5,6,7,8-pentahydroxy-3-methoxyflavone and 5,6,7,8-tetrahydroxy-3-methoxyflavone, as well as two flavones 3,7-dihydroxy-4´-methoxyflavone and 5,6,7,8-tetrahydroxy-4?-methoxyflavone never previously reported in plants, were isolated. The known 3,5,6,7,8-pentahydroxy-4´-methoxyflavone, 2´,3´,4´,5?,6?-pentahydroxy-chalcone, 6-hydroxykaempferol, 4?,5,6,7,8-pentahydroxyflavone and 3,4?-dimethoxykaempferol were also obtained. Analysis of extracts obtained from roots and shoots revealed that the compositions of the flavonoid mixtures varied with growing conditions. Quercetin, acacetin and rhamnetin accumulated in roots of inoculated plants, whereas they were not detected in non-inoculated plants.

On the universal bahavior of sorption isotherms in disordered mesoporous solids Cordero Sánchez, Salomon; Domínguez, Armando; Kornhauser, Isaac; López, Raúl Horacio; Rojas González, Fernando; Vidales, Ana Maria; Zgrablich, Jorge Andres Adsorption–desorption isotherms in disordered mesoporous solids, described by the Dual Site-Bond Model, are obtained through Monte Carlo simulations and their behavior is correlated to the topological properties of the porous networks and to their percolation properties, extending previous results to the general case of variable connectivity networks. A quasi-universal curve is found which may be useful in the problem of obtaining pore size distributions from the analysis of experimental Adsorption–desorption isotherms.