Dive depth and plumage air in wettable birds: the extraordinary case of the imperial cormorant Quintana, Flavio Roberto; Wilson, Rory P.; Yorio, Pablo Martin Cormorants are considered to be remarkably efficient divers and hunters. In part, this is due to their wettable plumage with little associated air, which allows them to dive with fewer energetic costs associated with buoyancy from air in the feathers. The literature attributes particularly exceptional diving capabilities to cormorants of the ‘blue-eyed’ taxon. We studied the diving behaviour of 14 male imperial cormorants Phalacrocorax atriceps (included in the blue-eyed taxon) in Patagonia, Argentina, and found that this species did indeed dive deeper, and for longer, than most other non-blue-eyed cormorant species. This species also exhibited longer dive durations for any depth as well as longer recovery periods at the surface for particular dive durations. We propose that this, coupled with atypically long foraging durations at sea in cold water, suggests that cormorants of the blue-eyed complex have a plumage with a substantial layer of insulating air. This is given credence by a simple model. High volumes of plumage air lead to unusually high power requirements during foraging in shallow, warmer waters, which are conditions that tend to favour wettable plumage. However, deep dives and/or cold water should favour the blue-eyed phenotype, which explains their essentially high latitude distribution.

Variability of UVR effects on photosynthesis of summer phytoplankton assemblages from a tropical coastal area of the South China Sea. Kunshan, Gao; Gang Li; Helbling, Eduardo Walter; Villafañe, Virginia Estela From June to September 2005, we carried out experiments todetermine the ultraviolet radiation (UVR) -induced photoinhibitionof summer phytoplankton assemblages from a coastal site ofthe South China Sea. Variability in taxonomic composition wasdetermined throughout the summer, with a peak chlorophyll a(chl a20 lg chl a L)1) dominated by the diatom Skeletonemacostatum that was detected early in the study period; the rest ofthe time samples were characterized by monads and flagellates,with low chl a values (1–5 chl a lg L)1). Surface water sampleswere placed in quartz tubes, inoculated with radiocarbon andexposed to solar radiation for 2–3 h to determine photosyntheticrates under three quality radiation treatments (i.e. PAB, 280–700 nm; PA, 320–700 nm and P, 400–700 nm) using differentfilters and under seven levels of ambient irradiance using neutraldensity screens (P vs E curves). UVR inhibition of samplesexposed to maximum irradiance (i.e. at the surface) varied from)12.2% to 50%, while the daytime-integrated UVR-relatedphotoinhibition in surface seawater varied from )62% to 7%.The effects of UVR on the photosynthetic parameters PBmax andEk were also variable, but UV-B accounted for most of theobserved variability. During sunny days, photosynthesis ofmicroplankton (>20 lm) and piconanoplankton (<20 lm) weresignificantly inhibited by UVR (mostly by UV-B). However,during cloudy days, while piconanoplankton cells were stillinhibited by UVR, microplankton cells used UVR (mostlyUV-A) as the source of energy for photosynthesis, resulting inhigher carbon fixation in samples exposed to UVR than the onesexposed only to photosynthetically active radiation (PAR). Ourresults indicate that size structure and cloudiness clearlycondition the overall impact of UVR on phytoplankton photosynthesisin this tropical site of South China. In addition, modelpredictions for this area considering only PAR for primaryproduction might have underestimated carbon fixation due toUVR contribution.

Deep divers in shallow seas: Southern elephant seals on the Patagonian shelf Campagna, Claudio; Piola, Alberto Ricardo; Marin, Maria Rosa; Lewis, Mirtha Noemi; Zajaczkovski, Uriel; Fernandez, Teresita Josefa Elephant seals are wide-ranging, pelagic, deep-diving (average of 400–600 m) predators that typically travel to open waters and continental shelf edges thousands of kilometers from their land breeding colonies. We report a less common pattern of foraging in the shallow waters of a continental shelf. Southern elephant seals, Mirounga leonina, that breed at Penı´nsula Valde´s (Argentina), face an extended (1,000,000km2; 400–700 km-wide, depending on track), shallow (o150 m) and seasonally productive plateau, the Patagonian shelf. Adults of both sexes usually cross it in rapid transit to other potential foraging grounds on the shelf edge or in the Argentine Basin, but 2–4 year-old juveniles spread over the plateau and spent months in shallow waters. This behavior was recorded for 9 seals (5 males and 4 females) of 23 satellitetrackedjuveniles (springs of 2004 and 2005) and for 2 subadult males studied in previous seasons. Trips included travel trajectories and time spent in areas where swim speed decreased, suggesting foraging. Preferred locations of juvenile females were in the proximity of the shelf break, where stratified waters had relatively high phytoplankton concentrations, but young and subadult males used the relatively cold (7–8 1C), low-salinity (33.3) mid-shelf waters, with depths of 105–120m and a poorly stratified water column. Three of the latter seals, instrumented with  ime–depth recorders, showed dives compatible with benthic feeding and no diel pattern of depths distribution. Regions of the mid-shelf were used in different seasons and were associated with low chlorophyll-a concentration at the time of the visit, suggesting that surface productivity does not overlap with putative quality habitat for benthic foragers. Benthic diving on the shallow mid-shelf would be a resource partitioning strategy advantageous for young males prior to greater energetic demands of a high growth rate and a large body size. Later in life, the more predictable, bathymetry-forced, shelf-break front may offer the food resources that explain the uninterrupted increase of this population over several decades.

Comparisons of IRI TEC predictions with GPS and digisonde measurements at Ebro Mosert, Marta Estela; Gende, Mauricio Alfredo; Brunini, Claudio Antonio; Ezquer, Rodolfo Gerardo; Altadill, D. Vertical TEC measurements obtained with GPS satellite signals (GPSTEC) and total electron content derived from ionograms (ITEC) are compared with the latest version of the International Reference Ionosphere, IRI-2000 (IRITEC). Digisonde data from the Ebro station (40.8°N, 0.5°E) recorded during two years of high solar activity 2000 (Rz 12 = 117) and 2001 (Rz 12 = 111) are used in the study. The results obtained with the three techniques are similar, and as expected, the GPS TEC values are greater than those obtained with the digisonde measurements. The IRI predictions generally overestimate the ITEC values. The diurnal and seasonal variations of the plasmaspheric electron content are also analyzed.

Ionospheric variability studies in Argentina Ezquer, Rodolfo Gerardo; Mosert, Marta Estela This paper reviews and extends studies on ionospheric variability performed by the Argentine scientific community. Ground based ionosonde measurements for different seasonal and solar conditions and vertical total electron content (VTEC) obtained with GPS satellite signals during a high solar activity year are used. Median, quartiles and deciles are used to specify the variability. In general, the results show that: (a) the variability is higher in low solar activity than in high solar activity, and (b) it is larger by night than by day. Moreover, is shown that could be possible specify the variability of foF2 for high solar activity and hours around noon.

Leafminer parasitoids and pest management. Literature review. Salvo, Silvia Adriana; Valladares, Graciela Rosa Leafminers are insects whose larvae live and feed within plant leaves, consuming mesophyll tissue without damaging the leaf epidermis. Several species are considered serious pests on intensive, horticultural, and ornamental crops. Natural enemies are the most frequent source of mortality for this herbivore insect guild, with parasitoids being the most effective and best represented source. This article provides an updated summary of the available research on leafminer parasitoids in relation to pest management. Parasitoids of leafminers are predominantly generalists, and can thus rapidly include in their host ranges newly introduced leafminer species, frequently achieving effective regulation a few years after the pest becomes established. Classical and augmentative biological control strategies are broadly used for leafminer pest management. Several studies have dealt with the simultaneous use of parasitoids together with chemical and cultural control. Many conventional insecticides have detrimental effects on parasitoids; however, others could be compatible with biological control. Although integrated pest management programs employing a combination of several control strategies have achieved success against leafminer pests, the effects of cultural practices that could boost parasitoid populations have been scarcely studied

Los indígenas de la Patagonia en los libros de texto de la Congregación Salesiana: La construcción de otros internos (1900-1930) Nicoletti, Maria Andrea Nos proponemos analizar la formación de los “otros internos” en los indígenas de la Patagonia, como una construcción en tensión entre mecanismos de particularización y de universalización, a través de un corpus de libros de texto de la Congregación salesiana, entre fines del siglo XIX y principios del siglo XX. Este análisis distingue básicamente tres categorizaciones: la construcción del “indio infiel”, la conceptualización del indígena como “salvaje” pero “salvaje redimido”, y el estereotipo del tehuelche como “indio de la Patagonia”. La primera parte de la fundamentación misionera “ad gentes” del fundador de la Congregación, Don Bosco. La segunda surge del contexto de la conquista al “desierto”, y la tercera de un estereotipo que analizamos desde las fotografías. En este último caso, el prototipo del “indio de la Patagonia” es el tehuelche y no el mapuche, en función de la identificación del mapuche con el “araucano invasor” y de la  imagen de la docilidad tehuelche en la tarea evangelizadora. Los textos salesianos repiten los conceptos etnocentristas y los estereotipos  de salvajismo sobre los indígenas patagónicos que aparecen en los textos oficiales, pero introducen, fieles a su pertenencia a la Iglesia, temáticas que resignifican el concepto del “salvaje” como “infiel” y de la necesidad de “civilizar” con la de evangelizar.; We propose to analyze the formation of intern others in the natives of the Patagonia, as a construction in tension between mechanisms of particularization and of universalization, through the books of the Salesians between the late XIXth century and the early XXth century. We basically distinguish three categorizations: the construction of the unfaithful native, the conceptualization of the native as savage but redeemed savage, and the stereotype of the tehuelche as native of the Patagonia. The first is the missionary theory ad gentes by the founder of the Congregation, Don Bosco. The second emerges from the context of the conquest to the desert, and the third is a stereotype that we analyze from photography. Here, the prototype of the native of the Patagonia is the tehuelche and not the mapuche, due to the identification of the mapuche with the Araucanian invader, and to the image of the tehuelche docility towards evangelization. The Salesians manuals repeat the ethnocentric concepts and the stereotypes of savagery on the Patagonian natives who appear in the official books, but they introduce, loyal to the Church, issues which resignify the term savage as unfaithful and the need to civilize with evangelize.

The peer-Review process for Amercan Antiquity and Latin American Antiquity Lanata, Jose Luis; Aldenderfer, Mark; Jochim, Michael Far from being perfect, the peer-review process is nevertheless the most effective way to assure the quality of a publication. Because they have used peer review from their very beginnings, American Antiquity (AAQ) and Latin American Antiquity (LAQ) are journals of high academic impact with strong reputations in the world academic community. The peer-review process seeks not only to identify the highest-quality manuscripts, but also works to improve the clarity of presentation of any author. The process is based on four fundamental principles: the importance of the diffusion of knowledge, the assurance of the preservation of knowledge in different media, the maintenance of control over the quality of knowledge that is disseminated, and the proper crediting to investigators and their discoveries and scientific contributions. Taken together, these principles maintain the excellence of scientific knowledge in any field (Meadows 1974; Ravetz 1973; Ziman 1968).American Antiquity (AAQ) and Latin American Antiquity (LAQ) are journals of high academic impact with strong reputations in the world academic community. The peer-review process seeks not only to identify the highest-quality manuscripts, but also works to improve the clarity of presentation of any author. The process is based on four fundamental principles: the importance of the diffusion of knowledge, the assurance of the preservation of knowledge in different media, the maintenance of control over the quality of knowledge that is disseminated, and the proper crediting to investigators and their discoveries and scientific contributions. Taken together, these principles maintain the excellence of scientific knowledge in any field (Meadows 1974; Ravetz 1973; Ziman 1968).(LAQ) are journals of high academic impact with strong reputations in the world academic community. The peer-review process seeks not only to identify the highest-quality manuscripts, but also works to improve the clarity of presentation of any author. The process is based on four fundamental principles: the importance of the diffusion of knowledge, the assurance of the preservation of knowledge in different media, the maintenance of control over the quality of knowledge that is disseminated, and the proper crediting to investigators and their discoveries and scientific contributions. Taken together, these principles maintain the excellence of scientific knowledge in any field (Meadows 1974; Ravetz 1973; Ziman 1968).

Criterios y actividades para la evaluación del aprendizaje en cursos universitarios de química; Activities and criteria for the chemical learning evaluation in graduate courses Wainmaier C.; Salinas, Julia Josefa; Viera, Lidia Mabel; Ramírez S. Abstract In this paper we intend to make a contribution to the learning evaluation practice that may accompany those educative proposals whose objective is a comprehensive learning. We adopt a “constructivist” psychological perspective, an epistemological orientation of “scientific realism” and a methodological vision that “integrates quantitative and qualitative strategies”. From this perspective, some dimensions and sub-dimensions taken as learning evaluation criteria, as well as some learning evaluation activities, are proposed for chemical contents at an introductory university level in scientific and technological careers. These criteria, originally developed in educative research, are potentially highly transferable to classroom.

Effects of granule-associated protein PhaP on glycerol-dependent growth and polymer production in poly(3-hydroxybutyrate)-producing Escherichia coli de Almeida, Alejandra; Nikel, Pablo Ivan; Giordano, Andrea Mariana; Pettinari, María Julia Polyhydroxyalkanoates (PHAs) are accumulated as intracellular granules by many bacteria under unfavorable conditions, enhancing their fitness and stress resistance. Poly(3-hydroxybutyrate) (PHB) is the most widespread and best-known PHA. Apart from the genes that catalyze polymer biosynthesis, natural PHA producers have several genes for proteins involved in granule formation and/or with regulatory functions, such as phasins, that have been shown to affect polymer synthesis. This study evaluates the effect of PhaP, a phasin, on bacterial growth and PHB accumulation from glycerol in bioreactor cultures of recombinant Escherichia coli carrying phaBAC from Azotobacter sp. strain FA8. Cells expressing phaP grew more, and accumulated more PHB, both using glucose and using glycerol as carbon sources. When cultures were grown in a bioreactor using glycerol, PhaP-bearing cells produced more polymer (2.6 times) and more biomass (1.9 times) than did those without the phasin. The effect of this protein on growth promotion and polymer accumulation is expected to be even greater in high-density cultures, such as those used in the industrial production of the polymer. The recombinant strain presented in this work has been successfully used for the production of PHB from glycerol in bioreactor studies, allowing the production of 7.9 g/liter of the polymer in a semisynthetic medium in 48-h batch cultures. The development of bacterial strains that can efficiently use this substrate can help to make the industrial production of PHAs economically feasible.

La "conquista del desierto": desde perspectivas hegemónicas y subalternas Briones, Claudia Noemi; Delrio, Walter Mario Este artículo discute algunas de las implicancias materiales y simbólicas del avance militar sobre Pampa y Patagonia desde dos amplios campos. Por un lado, ponderamos el lugar que la llamada “conquista del desierto” ha tenido en la territorialización del estado-nación y en la formación nacional de alteridad en Argentina, trabajando desde las memorias hegemónicas, el sentido común y las políticas públicas. Por el otro, introducimos memorias subalternas que exponen aspectos menos conocidos de las prácticas de disposición de los pueblos originarios, no sólo para explorar las reverberaciones de los procesos de construcción de la nación-como-estado en la diversificación de las trayectorias indígenas, sino también para ampliar los campos de visión que los discursos hegemónicos a menudo restringen. Sobre esta base argumentamos que la política indígena del estado argentino no ha estado meramente basada en “respuestas específicas a casos concretos”, ni operó espasmódicamente, como comúnmente se afirma. Sostenemos por el contrario que partió de promover un ejercicio sistemático, material y conceptual, de des-indianización y des-tribalización, buscando concretar a posteriori del período de conquista militar la imagen de un “desierto” necesitado de pioneros europeos.; This paper discusses some material and symbolic implications of the military annexation of Pampa and Patagonia, by setting the process against two broad frames of reference. On the one hand, we depart from hegemonic memories, common sense understandings and public policies, as to ponder the role of the so-called “conquest of the desert” in the territorialization of the nation-state and the configuration of Argentina’s formation of alterity. On the other, we introduce subaltern memories which expose less known aspects of state practices of indigenous disposal, not only to analyze the effects of state-building processes on the diversification of indigenous trajectories, but also to amplify fields of vision often restricted by hegemonic discourses. On this basis, we argue that Argentina’s Indigenous Policy has not been merely based upon “limited responses to concrete cases” nor operated in spasmodic or random terms, as it has been commonly contended. It has rather promoted a systematic exercise of de-indianization and de-tribalizacion, as to make real the image of a “desert” in need of European pioneers once the militarized period was over.

Genetic instability induced by low doses of x-rays in hamster cells Seoane, Analia Isabel; Güerci, A.; Dulout, Fernando Noel Purpose: Genomic instability involves time delayed events and can be manifested as elevated rates of heritable changes in the progeny of irradiated cells. To study the induction of chromosomal instability by very low doses of radiation Chinese Hamster Ovary (CHO) cells were exposed to 10 - 50 milisieverts (mSv) (≈10 - 50 miligrays (mGy)) of x-rays. Materials and methods: Control and irradiated cell populations were assayed for chromosomal aberrations and assessed using a micronucleus test and anaphase-telophase analysis at the first cell division post-irradiation and at every four population doublings thereafter up to 16 population doublings post-irradiation. Results: Frequencies of micronuclei, anaphase-telophase alterations and chromosomal aberrations were increased when the cells were analysed immediately after x-ray exposure. Micronuclei and anaphase-telophase alterations showed significantly increased frequencies when they were analysed at 12 and 16 population doublings after exposure to 50 mSv. Chromosomal aberrations increased significantly at 12 and 16 population doublings after exposure to 10 mSv and 50 mSv. Conclusions: Our results are consistent with the presence of a phenomenon by which the initial DNA damage in the surviving cells is memorized. Micronuclei and achromatic lessions were the main cytogenetic damage observed in cells exposed to very low doses of x-rays, indicating that these low doses are able to induce genetic instability. © 2007 Informa UK Ltd.

El mito de Fedra en el marco de los debates europeos entre modernización e identidad : D'Annunzio y Unamuno / Sandro Abate Abate, Sandro Desde Eurípides y Séneca, sin olvidar a Racine y Garnier, el mito de Fedra ejerció una especial fascinación sobre el arte y renovó periódicamente su vigencia. La poética de grandes sectores artísticos de finales del siglo XIX, articulada por la remisión al código clasicista y por el apartamiento de toda forma de arte vulgar o burgués, produjo las dos últimas versiones de esta tragedia. la Fedra de Gabriele d’Annunzio (1909) y la Fedra de Miguel de Unamuno (1911), estrenadas en Milán y Madrid, respectivamente. En su conjunto podría decirse que ambas producciones responden al renovado impulso clasicista que ha caracterizado a este segmento cultural que se extiende entre fines del siglo XIX y hasta la Primera Guerra Mundial. Pero a pesar de ello, las dos tragedias consideradas en particular divergen profundamente en los planteos preferenciales que formulan y en los intereses culturales y dramáticos que sus respectivos autores colocaron en escena. Sus respectivos marcos ideológicos –nietzscheano en un caso y cristiano en el otro- explican muchas de estas divergencias.

Reflexión acerca de ética e investigación psicológica Richaud, Maria Cristina Relevant ethical principles in research practice involving people include respect, benefits, and justice. When specifically applied to research projects, various essential topics stem from those principles, such as the informed consent of the people involved, risks and benefits, validity, data processing techniques, and verbal and non-verbal communication, among others. All this relates to the personal ethics of the researcher, which, when non-existent, turn most rules and regulations of no use, since they become ignored by someone who lacks an inner and earnest conviction about his or her expected actions. Knowing how to do ethical research leads to increasing our ability to obtain valid results, the needed co-operation of the people involved, and the essential social support that make up the supporting net of science.; Los principios éticos relevantes en la práctica de la investigación con personas son el respeto, el beneficio y la justicia; de los cuales se desprenden distintas temáticas fundamentales a la hora de investigar, como el consentimiento informado de los participantes, los riesgos y beneficios, la validez, el manejo de los datos, la comunicación verbal y no verbal, entre otras. Esto se remite a la ética personal del investigador, sin la cual pueden resultar inútiles muchas regulaciones y normativas al ser desoídas por quien no tiene la convicción íntima y sincera de cómo debería accionar. El saber realizar investigaciones en forma ética conduce a la habilidad para obtener resultados válidos, la cooperación necesaria de los participantes y el apoyo social necesario para sustentar la ciencia.

El teatro de la escritura : "Apariciones" de Margo Glantz Perilli, Carmen Noemi Margo Glantz apuesta a una literatura que, en curiosas ficciones, trabaja continuidades y fracturas con una mirada descentrada que busca poner en diálogo tradiciones desde un espacio de mujer. El imaginario literario y cultural de la nación moderna mexicana destacó, a lo largo del siglo XX, la virilidad como factor determinante. Glantz construye un lugar de mujer donde el cuerpo femenino hace bulto, se niega a ser transparente. La ficción histórica y el gesto genealógico le permiten inscribir narrativas distintas. En su obra se reconoce la presencia magistral de figuras como Alfonso Reyes. Invención y erudición sustentan densos itinerarios que no eluden la historia al armar la arqueología de un imaginario, que explora restos escriturarios y los usa como material creativo, insertándolos en nuevos sistemas significativos. Margo Glantz sostiene una fuerte relación con las instituciones centrales de la cultura mexicana: la Universidad Autónoma de México, la Academia Mexicana de la Lengua y el claustro de Sor Juana Inés de la Cruz. Su actuación dentro del campo intelectual ha recibido un amplio reconocimiento debido a su tarea filológica y crítica, en la que, de modo magistral y a veces discutido, ha definido momentos de la historia literaria. Podemos adscribirla a lo que, en su análisis de la narrativa mexicana, denominó literatura de la “escritura” por oposición a la literatura de la onda en una particular versión de la antigua polémica entre artepurismo y realismo.

El escritor y las sombras de la Patria: "En esta dulce tierra" de Andrés Rivera; The writer, the shadows and the homeland in Andrés Rivera’s “La dulce tierra” Perilli, Carmen Noemi La novela "En esta dulce tierra" arma un simulacro histórico que se desintegra en una narración de finales múltiples. La intención paródica está en el títtulo donde el circunstancial contrasta con la trama que  instala desde el comienzo la relación estrecha entre el poder y la muerte. La novela trabaja con la literatura decimonónica, en especial con lo que Doris Sommer llama ficciones fundacionales, en particular la Amalia de José Mármol. La nación se imagina como  asilo, lmorgue,  cárcel, sótano. Si Sarmiento invoca la sombra de Facundo, Rivera evoca en Cufré otras sombras, dobles en tiempos y lugares otros.La narración de la historia argentina aparece como la narración de una derrota. Facundo es la sombra de la barbarie, cifra de la naturaleza americana, producto de los llanos riojanos. Cufré es la sombra de una clase “culta” que dibuja en su trayectoria una figura paradojal. Los dos  se convierten en  víctimas de una tierra concebida como naturaleza bárbara en un caso y de una tierra construida como patria siniestra  desde el Poder, una segunda naturaleza que, en esta tierra, tiene el sabor de la muerte.; The novel En esta dulce tierra sets up a historical pretense that disintegrates into several endings. The title is an irony, since terrible events take place in this “sweet land.” It refers to the literature of the XIX century, especially to the founding romances such as that of José Mármol’s Amalia. The nation is envisioned as a closed space relegated by despotism to the asylum, the morgue, the jail, the basement. The characters live an illusion moving from north to south. If Sarmiento invokes the shadow of Facundo, Rivera evokes some of his own shadows in Cufré, doubles in different times and spaces. The narration of the Argentine history is a story of defeat: civilizarion’s. The historical image is pessimistic: the world is ill, blood thirsty and violent. Facundo is the shadow of barbarity, the emblem of the American nature, the produce of the Riojan plains. Cufré is the shadow of an “educated” class whose trajectory draws a paradox. Both are victims of a land conceived in one case as a barbarous nature, and in the other as sinister homeland. Power acts in this land as a second nature with the taste of death.

The first record of amphibians as paratenic hosts of Serpinema larvae (Nematoda; Camallanidae) Gonzalez, Cynthya Elizabeth; Hamann, Mónika Inés Lysapsus limellum Cope, 1862  is a member of the frog family Hylidae. It is distributed exclusively in South America, in Uruguay, Paraguay, Bolivia and the north of Argentina. In Argentina, L. limellum is restricted to some areas adjacent to the Paraguay and Paraná rivers. It shows a great preference for aquatic habitats, and occurs in permanent and semipermanent ponds. Studies on the parasite fauna of L. limellum from Corrientes, Argentina showed the presence of thirty three nematode larvae of the family Camallanidae. Specimens were identified as third-stage of Serpinema cf. trispinosum. The present report represents the first record of Serpinema larvae in amphibians, and suggests the importance of amphibians as paratenic host of freshwater turtle parasites. The genus Serpinema is registered by the first time in Argentina

Theoretical study of N2O2 interaction with BaO(100) surface Ferullo, Ricardo; Fuente, Silvia Andrea; Branda, Maria Marta; Castellani, Norberto Jorge In this work, the adsorption of the NO dimer on BaO(1 0 0) was studied using the density functional theory (DFT). N2O2 interacts with the surface mainly in three different ways. In the more favoured orientation it adsorbs N-down forming a partially covalent bond with the surface with a charge electron delocalization over the adsorbate. In Tilted and O-down orientations, the dimer interacts in an electrostatic way with the surface Ba cations. The latter bonding modes are possible because an almost full electronic transfer from BaO to N2O2 takes place, producing the N2 species. In all these cases, the N–N distance of dimer decreases substantially due to the occupation of its 2b1 orbital, which has a very strong N–N bonding character. The results suggest that the formation of NO dimer should take place only at relatively high NO coverages.

Characterization and catalytic behavior in the n-butane dehydrogenation of trimetallic InPtSn/MgAl2O4 catalysts Bocanegra, Sonia Alejandra; Castro, Alberto Antonio; Scelza, Osvaldo Antonio; de Miguel, Sergio Ruben This paper deals with the characterization and catalytic dehydrogenation behavior of trimetallic InPtSn catalysts with different Sn content (from 0.12 wt% up to 1.08 wt%) supported on MgAl2O4. The support was initially impregnated with In, followed by a co-impregnation with Pt and Sn. The Pt and In contents in all catalysts were 0.30 wt% and 0.28 wt%, respectively. Besides, two catalysts with a Sn content of 0.37 wt% were prepared by two different methods: (a) successive impregnation (first Pt, second Sn) and (b) impregnation with PtSn complex, [(CH3)4N]2[PtCl2(SnCl3)2]. Experiments of n-butane dehydrogenation reaction were carried out both in continuous flow equipment and in pulse equipment. The catalysts were characterized by TPR, XPS and test reactions of the metallic phase. Trimetallic catalysts display high activity and selectivity to butenes and low deactivation during the n-butane dehydrogenation reaction. In order to analyze the influence of the preparation method on the catalytic performance, the better trimetallic catalyst was selected. It was observed that the different impregnation methods of Pt and Sn lead to trimetallic catalysts with similar catalytic behaviors between them. The characterization studies indicate the existence of geometric effects of In and Sn on Pt sites that produce a dilution of the Pt surface, and also a strong interaction between the three metals, which could lead to alloy formation. These facts positively influence the catalytic performance, thus increasing the activity, the selectivity to butenes and the stability of the metallic phase.

Factors influencing the isobutane yield during the conversion of vacuum gas oil (VGO) under fluidized catalytic cracking (FCC) conditions Passamonti, Francisco Javier; de la Puente, Gabriela; Sedran, Ulises Anselmo Five equilibrium fluidized catalytic cracking (FCC) catalysts of different types, with unit-cell sizes in the range of 24.23-24.29 Å, were evaluated in the conversion of three commercial vacuum gas oil (VGO) feedstocks in a CREC Riser Simulator laboratory reactor at temperatures of 500 and 550°C, a catalyst-to-oil ratio of 6.1, and reaction times in the range of 3-30 s. The results have allowed us to define the main characteristics of the catalysts, in terms of various indexes, such as activity, gasoline yield and quality, and individual yields (using isobutane as a case example). In all cases, isobutane was essentially a primary product. It was observed that the yield of isobutane was linked to the hydrogen transfer properties and the activity of the catalysts. For a given catalyst, the higher the temperature, the less isobutane is formed at the same conversion, because of the lower incidence of hydrogen transfer reactions. The type of feedstock influences the isobutane yields, particularly on low-activity, low-hydrogen-transfer catalysts. The approach is shown to be a proper tool to evaluate commercial FCC catalysts (in this case, in the search for the optimum isobutane yield) and demonstrate that knowledge of the integral evaluations (feedstock, catalyst, and process conditions) is necessary.