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.
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).
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.
