The Problem of time and gauge invariance in the quantization of cosmological models. 1. Canonical quantization methods. Shestakova, T. P.; Simeone, Claudio Mauricio The paper is the first of two parts of a work reviewing some approaches to the problem of time in quantum cosmology, which were put forward last decade, and which demonstrated their relation to the problems of reparametrization and gauge invariance of quantum gravity. In the present part we remind basic features of quantum geometrodynamics and minisuperspace cosmological models, and discuss fundamental problems of the Wheeler - DeWitt theory. Various attempts to find a solution to the problem of time are considered in the framework of the canonical approach. Possible solutions to the problem are investigated making use of minisuperspace models, that is, systems with a finite number of degrees of freedom. At the same time, in the last section of the paper we expand our consideration beyond the minisuperspace approximation and briefly review promising ideas by Brown and Kuchar, who propose that dust interacting only gravitationally can be used for time measuring, and the unitary approach by Barvinsky and collaborators. The latter approach admits both the canonical and path integral formulations and anticipates the consideration of recent developments in the path integral approach in the second part of our work.

The paper is the first of two parts of a work reviewing some approaches to the problem of time in quantum cosmology, which were put forward last decade, and which demonstrated their relation to the problems of reparametrization and gauge invariance o Shestakova, T. P.; Simeone, Claudio Mauricio The paper is the second part of the work devoted to the problem of time in quantum cosmology. Here we consider in detail two approaches within the scope of Feynman path integration scheme: The first, by Simeone and collaborators, is gauge-invariant and lies within the unitary approach to a consistent quantization of gravity. It is essentially based on the idea of deparametrization (reduction to physical degrees of freedom) as a first step before quantization. The other approach by Savchenko, Shestakova and Vereshkov is rather radical. It is an attempt to take into account peculiarities of the Universe as a system without asymptotic states that leads to the conclusion that quantum geometrodynamics constructed for such a system is, in general, a gauge-noninvariant theory. However, this theory is shown to be mathematically consistent and the problem of time is solved in this theory in a natural way.

Hormigón armado: la corrosión ataca desde adentro Vazquez, Marcela Vivian; Fernandez, Raúl El hormigón armado es un material compuesto sumamente noble; su extendido uso ha contribuido mucho al desarrollo de nuestras construcciones y, sin duda, lo seguirá haciendo. La vida útil de las estructuras construidas con este material está fuertemente condicionada por la corrosión de sus armaduras de acero. Las patologías del hormigón causadas por la corrosión generan inconvenientes económicos y sociales muy importantes, que deben ser atendidos. Debido a ello, se han encarado estudios electroquímicos que permitieron identificar los factores que determinan el inicio de la corrosión y condicionan su propagación. A partir de los conocimientos obtenidos y de las técnicas desarrolladas, es posible identificar acciones que, aplicadas desde la etapa de proyecto, contribuyen a minimizar su incidencia. Incluso, en caso de que el problema ya esté instalado, es posible realizar un diagnóstico exhaustivo que permite recomendar procedimientos de reparación para extender la vida útil de las estructuras, en óptimas condiciones de servicio. La corrosión puede mantenerse bajo control, solo debemos aprender a convivir con ella.

Vulnerabilidad global y pobreza. Consideraciones conceptuales Foschiatti, Ana Maria Hilda El análisis y la evaluación de la vulnerabilidad realizada desde distintas ópticas y a través de la consideración de temas específicos relacionados, permite detectar áreas susceptibles, diagnosticar la calidad de vida de la población en áreas espaciales localizadas y en sectores marginados, comparar el estado del equipamiento de los servicios, analizar factores socioculturales que influyen en las vulnerabilidades regionales, entre otros. De allí la importancia de su estudio conceptual para comprender la percepción de la población sobre los riesgos, analizar pautas de comportamiento, evaluar actitudes y prácticas y formular recomendaciones para implementar políticas públicas ambientales y sociales.; The analysis and evaluation of vulnerability performed from different points of view and through the consideration of specific related issues, allows the detection of susceptible areas and the diagnosis of the population's life quality in localized spatial areas and marginalized sectors, as well as the comparison of the condition of the services equipment and the analysis of social and cultural factors among others which affect regional vulnerabilities. Therefore the importance of this sort of conceptual study in order to understand the population's perception about risks, to analyze pattern of behavior, to assess attitudes and practices and to formulate recommendations to implement social and environmental public policies.

RNA fingerprinting using RAP-PCR identifies an EBAF homologue mRNA differentially expressed in rat oviduct Valdecantos, Pablo Alberto; Argañaraz, Martin Eduardo; Abate, Carlos Mauricio; Miceli, Dora Cristina As a step towards the identification of genes preferentially expressed in the oviduct during early rat embryo development, we isolated a cDNA fragment (Pr14) by using RNA arbitrarily primed PCR (RAP-PCR), being its expression restricted to oviduct and uterus; its mRNA is mainly expressed in oviduct during late luteal phase and early pregnancy. This fragment is 100% identical to a rat DNA sequence (Accession No. NW_047400) downstream the terminal exon of a Rattus norvegicus gene (Locus Link Accession No. LOC289316) similar to ebaf (endometrial bleeding-associated factor), a novel member of the Transforming Growth Factor superfamily. Northern analyses showed that this sequence hybridizes with 2.9 kb and 4.1 kb mRNAs in early pregnant rat oviducts. However, only the 4.1 kb mRNA was detected in the oviduct of non-pregnant rats, showing an increase from proestrus to diestrus. The expression of this oviduct-uterus specific mRNA suggests that the products of this gene may play a role in the oviductal reproductive process.

Axillary bud viability and dry matter production of Poa ligularis in Patagonian grasslands Souto, Cintia Paola; Becker, G. F.; Siffredi, G. L.; Busso, Carlos Alberto; Sterberg, M. Poa ligularis Nees is one of the dominant perennial grass species in Patagonian grasslands. This is the first field study which investigated the effects of defoliation frequency on its number of viable axillary buds, and subsequent dry matter production during one growing season. Experiments were arranged in a randomized complete block design. Treatments included one defoliation height (10 cm), from one to five times a year, and undefoliated controls. Bud respiratory activity was examined usingthe tetrazolium test and the vital stain Evan's blue. At the end of the growing season, plants that have been defoliated more than three times showed significatively (p<0.05) lower number of respiratory active buds than unclipped controls. A high defoliation frequency increased bud death in stem bases. Both defoliated and undefoliated plants produced more (p<0.05) axillary buds at the periphery than at their center. Defoliation treatments increased shoot weight by 13.4% on average compared with undefoliated controls, but reduced in by 10% the average number of metabolically active axillary buds. This indicates that this reduction, however, was not high enough to constrain dry matter production.It appears that Poa ligularis could tolerate moderate grazing frequency and intensity without compromising its potential regrowth capacity. Longer-term studies of the effects of defoliation on dry matter production and bud metabolic activity are needed to understand the cumulative effects of grazing of P. ligularis in natural grasslands.; Poa ligularis Nees es una de las especies de gramíneas perennes dominantes en los pastizales naturales de la Patagonia. Este es el primer estudio que investigó los efectos de la frequencia de defoliación sobre su número de yemas axilares viables, y subsiguiente producción de materia seca durante una estación de crecimiento. Los estudios se efectuaron utilizando un diseño de bloques completamente al azar. Los tratamientos incluyeron una altura de defoliación (10 cm), de una a cinco veces por año, además de controles no defoliados. La actividad respiratoria de las yemas fue examinada usando el método del tetrazolio y el colorante vital azul de Evans.Hacia el final de la estación de crecimiento, las plantas que habían sido defoliadas más de tres veces mostraron un número significativamente menor (p<0.05) de yemas con actividad respiratoria que los controles no defoliados. Una alta frecuencia de defoliación incrementó la muerte de yemas en las bases de tallos. Todas las plantas- defoliadas o no, produjeron más (p<0.05) yemas axilares en su periferia que en su centro. La defoliación incrementó 13.4% el peso de los tallos en promedio, pero redujo en 10% el número promedio de yemas axilares metabólicamente activas. Esto indica que esta reducción , sin embargo, no fue suficiente como para limitar la producción de materia seca. Parece que P. ligularis toleraría una frecuencia e intensidad moderada de pastoreo sin comprometer su capacidad potencial de rebrote. Se necesitan estudios a más largo plazo de los efectos de la defoliación en la producción de materia seca y actividad metabólica de las yemas para entender los efectos acumulativos del pastoreo de Poa ligularis en los pastizales naturales.

Progesterone treatment reduces NADPH-diaphorase/Nitric oxide synthase in Wobbler mouse motoneuron disease Gonzalez Deniselle, Maria Claudia; Garay, Laura Ines; López, Juan José; Gonzalez, Susana Laura; Mougel, Analía; Guennoun, Rachida; Schumacher, Michael; de Nicola, Alejandro Federico Previous work demonstrated that progesterone (PROG) treatment attenuates morphological, molecular and functional abnormalities in the spinal cord of the Wobbler (Wr) mouse, a genetic model of motoneuron degeneration. Wr mice show a marked up-regulation of the nitric oxide synthesizing enzyme (NOS). Since nitric oxide is a highly reactive species, it may play a role in neuropathology of Wr mice. We now studied if PROG neuroprotection involved changes of NOS activity in motoneurons and astrocytes, determined by the nicotinamide adenine dinucleotide phosphate-diaphorase (NADPHD) histochemical reaction. Two and four-month-old Wr mice at the progressive and stabilization stages of the disease, respectively, and their age-matched controls were left untreated or received a single 20-mg PROG pellet for 18 days. PROG reduced the high number of NADPHD-active motoneurons and white matter astrocytes in 2-month-old Wr mice but was unable to change the low number of NADPHD-active motoneurons in 4-month-old Wr mice or astrocytes in this age group. A large number of motoneurons in 2-month-old Wr mice showed a vacuolated phenotype, which was significantly reverted by PROG treatment. In summary, PROG treatment during the early symptomatic stage of the disease caused a significant reduction of NADPHD-active motoneurons and astrocytes and also reduced vacuolated degenerating cells, suggesting that blockade of NO synthesis and oxidative damage may contribute to steroid neuroprotection.

Effect of androgens on sexual differentiation of pituitary Gamma-Aminobutyric Acid receptor subunit GABAB expression Bianchi, Maria Silvia; Catalano, Paolo Nicolás; Bonaventura, Maria Marta; Silveyra, Patricia; Bettler, Bernhard; Libertun, Carlos; Lux, Victoria Adela R. Previous work demonstrated a sexually dimorphic ontogenic expression of gamma-aminobutyric acid receptors (GABA(B)R) in rat pituitary. As sex steroids determine sex-specific expression patterns, we now studied the effect of sex hormones on pituitary GABA(B)R expression. GABA(B)R subunits, measured by Western blot and by semi-quantitative RT-PCR and luteinizing hormone (LH), follicle-stimulating hormone (FSH) and testosterone measured by RIA were determined in two experimental designs: First experimental design: 8- and 15-day-old females (8F, 15F); 8F and 15F treated with 100 mug testosterone propionate (TP) on day 1 of life (8F100TP, 15F100TP), 8- and 15-day-old males (8M, 15M) and 8M and 15M castrated on day 1 (8MC, 15MC). Second experimental design: 8-day-old female and male animals: 8F, 8F100TP, 8F treated with 1 mug/day TP on days 1-4 (8F1TP), 8F treated with the androgen antagonist Flutamide (Flut: 2.5 mg/100 g BW of pregnant mother on days E17-E23) (8F-Flut), 8M, 8MC, 8M treated with Flut as above (8M-Flut) and 8MC-Flut. In these animals, in addition, GABA, glutamate, aspartate and taurine were measured by HPLC in hypothalami and cortex. In the first set of experiments, GABA(B1)R mRNA/protein expression was higher in 8F than in 15F, 8M or 15M. In 8F100TP, GABA(B1)R mRNA/protein decreased to male levels. TP treatment did not alter GABA(B1)R expression in 15F. There was no difference in GABA(B1)R expression between 8M and 15M and neonatal castration did not modify its expression. In the second set of experiments, TP (1 mug) or Flut did not modify GABA(B1)R in 8F, while 100 microg TP continued to decrease GABA(B1)R expression. In 8M, Flut, alone or with castration, increased GABA(B1)R mRNA/protein expression to 8F. Hypothalamic GABA content followed the same pattern as pituitary GABA(B)R expression in 8-day-old animals, suggesting a cross-regulation. With regard to hormonal levels, 100 microg, but not 1 microg TP altered gonadotropins at 8 days, although both treatments effectively androgenized females as evidenced by lack of cycling. We conclude that androgens, acting pre- and postnatally, decrease pituitary GABA(B)R subunit expression.

Successive negative contrast after partial reinforcement in the consummatory behavior of rats Pellegrini, Santiago; Muzio, Ruben Nestor; Mustaca, Alba Elisabeth; Papini, Mauricio Roberto Rats given access to a 32% sucrose solution later reject a 4% solution significantly more than controls that have only received the 4% solution. In Experiment 1, this consummatory successive negative contrast (cSNC) effect was attenuated by previous exposure to 50% partial reinforcement. Furthermore, recovery from cSNC was also facilitated by partial reinforcement. In Experiment 2, the attenuating effects of partial reinforcement on cSNC were eliminated by administration of the benzodiazepine anxiolytic chlordiazepoxide (5 mg/kg) before nonreinforced trials. In Experiment 3, the attenuating effect of partial reinforcement was greater after a shift from 32 to 6% solution, than after a shift from 32 to 2% solution. The parallels between the effects of partial reinforcement on consummatory and instrumental behavior are discussed.

Parasites as possible cause of mass mortalities of the presently critically endangered clam Mesodesma mactroides on the Southwest Atlantic coast Cremonte, Florencia; Figueras, A. Specimens of Trichodina sp. were found on the gills of 58% of clams with moderate intensities without apparent cell damage. Coccidian were present in the nephridal tubules with both high prevalence (93%) and intensity of infection. Macrogamonts and meronts containing merozoites were the more frequently observed stages, obtruding the lumen of the nephridial tubules and associated with hypertrophying epithelial cells. Gregarines were observed inside the digestive epithelial cells and in the adjacent connective tissue in high intensities, with a prevalence of 64%. They were present alone or in groups of several individuals, in which case the epithelial cells were lysed. Turbellaria specimens were found inhabiting the lumen of the digestive tract, parasitising 30% of examined clams. Additionally, histological preparations from 36 dying clams from Monte Hermoso (40°32’S- 62°21’W, Buenos Aires province, Argentina, collected during mass mortality episode of November 1995) were re-examined. Despite the bad-condition of tissues, the same parasites found in Isla del Jabalí were observed, with the exception of gregarines: Trichodina sp. (100%), coccidians (100% from the five histological sections which included nephrida), turbellaria (14%). To support the hypothesis of a diseases-caused epidemic it is necessary to examine samples from other clam populations and to examine for virus infection.

El conocimiento antropológico del Gran Chaco desde el siglo XVIII hasta mediados del siglo XX Maeder, Ernesto Joaquin A. El artículo está centrado en dos momentos fundamentales en el conocimiento de la región chaqueña. En primero está constituido por la síntesis jesuítica, cuyos resultados se elaboraron en su mayoría a fines del siglo XVIII, pero cuya divulgación quedó en parte interrumpida hasta mucho tiempo después. El segundo corresponde a la época de la incorporación del Chaco a la vida nacional, tanto en la Argentina como en el Paraguay, proceso de ocupación del espacio y organización política y colonización, que llevó a renovar estudios sobre la región, especialmente sobre la población aborigen.. Etapa cuya madurez fue alcanzada entre 1930 y 1940. El artículo menciona los principales aportes de una y otra etapa y destaca el período de olvido o postergación que estos estudios experimentaron en buena parte del siglo XIX.

Extraordinary flexible shell sculpture: the structure and formation of calcified periostracal lamellae in Lucina pensylvanica (Bivalvia: Lucinidae) Taylor, John D.; Glover, Emily; Peharda, Melita; Bigatti, Gregorio; Ball, Alex The lucinid bivalve Lucina pensylvanica possesses an unusual flexible commarginal shell sculpture formed from calcified periostracal lamellae. The lamellae comprise thick, recurved, periostracal extensions with distal calcified scales. The periostracum is also densely embedded with calcareous granules around 2.0−2.5 µm in diameter and a thin (10 µm) layer of prismatic aragonite covers the ventral face of each lamella. Other species of Lucina in the western Atlantic possess calcified scales but with different morphologies and the continuous commarginal ridges of the eastern Atlantic Lucina adansoni and other African species are similarly constructed and homologous. The periostracal lamellae are a probable apomorphy of the genus Lucina and morphology of the calcified structures provides a set of systematic characters of importance in the discrimination of species.

Size at first maturity, oocyte envelopes and external morphology of the sperm in three species of Lucinidae (Mollusca: Bivalvia) from Florida Keys, USA Bigatti, Gregorio; Peharda, Melita; Taylor, John Gonads in the tropical lunicid bivalves Ctena orbiculata, Codakia orbicularis, and Lucina pensylvanica are located in the cephalopodial mass above the foot and behind the gills. Age estimates for Lucina pensylvanica suggest that individuals less than one year old are immature, as also is C. orbicularis, and that both males and females mature at two years. For Ctena orbiculata, we have no age data, but we consider that this species may also have early development. In July 2002 when water temperatures were high, mature individuals of all three species were spawning or in resorption, and oocyte envelopes were present. Parasites were found in the digestive diverticula of C. orbiculata and L. pensylvanica. External ultrastructure of the spermatozoon shows differences between the three species. Codakia orbicularis and L. pensylvanica have a long-headed spermatozoa, whereas Ctena orbiculata has a middle-size head. Codakia orbicularis possesses a flagellum with a lateral undulating membrane, absent from the two other species.

Reflexiones sobre la dialéctica de escalas en el examen de los procesos de desarrollo geográfico desigual; Reflections on the scale dialectics in the regional geographical development processes analysis Valenzuela, Cristina Ofelia La determinación de las escalas espaciales más adecuadas para el estudio de un problema geográfico concreto es compleja. Significa básicamente la selección inicial de una escala por sobre las demás.Esto a su vez, sugiere la consideración de dos cuestiones: cómo se define una escala y cuál es la adecuada para el estudio de la realidad, ya que lo que parece significativo o tiene sentido en una escala no tiene por qué registrarse en otra con la misma intensidad o importancia. El objetivo del presente trabajo es contribuir a la discusión sobre el tema, subrayando la importancia de las conceptualizaciones sobre las escalas espaciales y su aplicación en el análisis de los procesos de desarrollo geográfico desigual.

Estructura conformacional de pequeños péptidos conteniendo prolina usando cálculos cuánticos y de dinámica molecular Herrera, Fernando Enrique; Sferco, Silvano Juan La prolina es un aminoácido con características particulares, debidas principalmente a la restricción conformacional otorgada por el anillo prirrolidínico. En este trabajo, analizamos la estabilidad del aminoácido y su zwitterión en vacío y en medio acuoso. Se analizaron también distintos dipéptidos con y sin prolina en las conformaciones cis y trans (en vacío y en medio acuoso). Finalmente se analizaron tri y tetrapétidos relacionados con las estructuras PII de colágeno y poliglicina, también en vacío y en medio acuoso. Se utilizaron, para los sistemas en vacío, cálculos UHF utilizando la base gaussiana 3-21G. Para los sistemas en medio acuoso se realizaron simulaciones de dinámica molecular clásica. Para todos los sistemas, se realizaron además, optimizaciones de geometría a través del método de gradientes conjugados. El zwitterión resultó inestable para todas las geometrías estudiadas que incluyeron hasta cuatro moléculas de agua. Se encontró que las repulsiones entre nubes electrónicas de átomos no enlazados son las responsables de que, en dipéptidos sin prolina, la conformación trans sea prácticamente la única que se encuentra experimentalmente, mientras que para dipéptidos con prolina dichas repulsiones están presentes tanto en cis como en trans, explicando por qué se observan ambas experimentalmente. Se encontró también que la poliglicina es estable en vacío, pero se desestabiliza en medio acuoso, mientras que una hebra de colágeno se revela estable tanto en vacío como en medio acuoso.; Proline is a particular aminoacid because of the conformational restriction of the pyrroldinic ring. In this work, we analyzed normal proline and zwitterion stability, in vacuum and in aqueous solution. Several dipeptides with and without proline in trans and cis conformation were analyzed (also in vacuum and in aqueous solution). Finally, tri and tetrapeptides related to PII and collagen structures were analyzed, always in vacuum and in solution. We have used UHF calculations using the 3-21G gaussian basis set for the systems in vacuum. For the systems in aqueous solution, classic molecular dynamics simulations were performed. For all systems, geometric optimizations using conjugate gradient method were also performed. Proline’s zwitterion becomes unstable for all studied geometries and systems that included up four water molecules. Repulsion among electronic clouds of neighboring, nonbonded atoms were found responsible for the experimentally observed cis and trans conformation: dipeptides without proline appear only with the trans conformation whereas dipeptides with proline may exist in both conformations. It was also found that the polyglycine is stable in vacuum but unstable in aqueous solution, while one collagen’s strand reveals to be stable in vacuum as well as in aqueous solution.

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.