Ion exchange membranes derived from sulfonated polyaramides
Taeger, A.; Vogel, C.; Lehmann, D.; Jehnichen, D.; Komber, H.; Meier Haack, J.; Ochoa, Nelio Ariel; Nunes, S.P.; Peinemann, K.-V.
Homo- and both random and block copolyaramides of high molecular weights, with sulfonated moieties in the backbone, were obtained by low temperature polycondensation technique in a dipolar aprotic solvent (NMP) using (a) free aromatic diamines in the presence of pyridine as acid acceptor and (b) N,N ′-bis-trimethylsilyl derivatives of the diamines without additional acid acceptor. The addition of low molecular weight electrolytes (LiCl or CaCl2) and in some cases trimesoyl chloride to the reaction mixture was found to be favorable for the synthesis of high molecular weight polyamides. The materials had a theoretical ion exchange capacity of up to 3.14 meq/g. The membranes were characterized in terms of morphology, thermal stability, water-uptake, and ion exchange capacities.
Graptolites from the Upper Llandovery of the Talacasto area, Central Precordillera, San Juan, Argentina
Lenz, Alfred; Cuerda, Alfredo; Peralta, Silvio Heriberto
Graptolites are the most important biostratigraphic tool in the study of the Silurian of the Argentine Precordillera. Since, however, the graptolites are concentrated primarily in the Lower Llandovery and Ludlow of the region, the ages of parts of some stratigraphic units are poorly known. The recovery of a small Upper Llandovery graptolite assemblage in the lower one-third of the La Chilca Formation of the Talacasto area helps in resolving this problem, and that assemblage is the focus of this study. Brachiopods, trilobites, bivalves, and ostracodes are present in the same stratigraphic intervals, but are less common and less studied and, thus, of less biostratigraphic value.
Cuatro nuevas especies del género Liolaemus (Iguania: Liolemidae) perteneciente al grupo boulengeri de la Patagonia, Argentina.; Four new species of Liolaemus are described from the Patagonia region of southern
Argentina.
Abdala, Cristian Simón
Se describen cuatro nuevas especies del género Liolaemus, pertenecientes al grupo boulengeri, caracterizado por la presencia de un parche femoral de escamas agrandadas en la parte posterior del fémur. Una especie fue colectada en el sur de la provincia de Neuquén y las otras tres en el suroeste, centro y este de la provincia de Río Negro, en la Patagónia Argentina. Dentro del grupo las nuevas especies están relacionadas fenéticamente a Liolaemus boulengeri. Se estudiaron 98 caracteres morfológicos externos, referidos principalmente a caracteres de lepidosis, patrón de coloración, y proporciones corporales, corrientemente estudiados en Liolaemus. Las diferencias mas significativas entre estas especies y Liolaemus boulengeri se dan principalmente en el patrón de coloración y en algunos caracteres de escamación. Estas especies ocupan parte de las tres regiones patagónicas que se diferencian con base en la orografía y vegetación asociada. Las nuevas especies del centro y suroeste de la provincia de Río Negro, soportan grandes diferencias de temperatura diarias y estaciónales. Las cuatro especies que se describen aquí se alimentan principalmente de insectos.; our new species of Liolaemus are described from the Patagonia region of southern Argentina. One species was collected in southern Neuquén Province and the other three are from Río Negro Province. Each of the new species has a patch of enlarged scales on the posterior surface of the thighs, indicating their relationship to members of the boulengeri group. Within this group, the four new species are morphologically most similar, and may be most closely related to, Liolaemus boulengeri. A total of 98 external morphological characters, principally squamation, color pattern, and body proportions, were recorded for these new members of the boulengeri group and compared with those for Liolaemus boulengeri. Significant differences between the new species and Liolaemus boulengeri were primarily in color pattern and some aspects of squamation. The new species are distributed over three Patagonian regions with differing geological histories and plant associations. The new species described from central and southwestern Río Negro Province experience substantial differences in daily and seasonal temperature. All four new species eat insects.
The depressor mandible muscle in anurans
Manzano, Adriana Silvina; Moro, Silvina; Abdala, Virginia Sara Luz
It is well known that the diversity in anuran cranial structures is large, observed in the variation of the bone structure and associated muscles. The depresso mandibulae is the jaw muscle that opens the mouth and was considered by many authors useful in delimiting anuran groups. However, there is still much controversy on the value of the m. depressor mandibulae as a relationship-indicating character. The goal of this project is to explore the morphological diversity of the depressor mandibulae muscle among different families of Anura. Specimens including 60 genera of 17 families of Anura were dissected, using traditional techniques of macroanatomy. Fifteen morphological groups can be distinguished within the anuran species analyzed. The insertion point demonstrates little variation. The overall pattern of the origin is also quite stable, with some exceptions. The great diversity in shape of the m. depressor mandibulae correlates with the plethora of patterns already mentioned for cranial morphology in anurans. However, it is difficult to asign a specific morphology to a given higher taxon. We also found no evidence that variations in the m. depressor mandibulae are associated with particular habits.
Two weighted inequalities for maximal functions related to Cesàro convergence
Bernardis, Ana Lucia; Martín Reyes, Francisco Javier
We characterize the pairs of weights (u, v) for which the maximal operator Mα- f (x) = supR>0 R-1-α ∫x-Rx-2R |f (s)|(x - R - s)α ds, -1 <α < 0, is of weak and restricted weak type (p, p) with respect to u(x) dx and v(x) dx. As a consequence we obtain analogous results for Mαf (x) = supR>0 R-1-α ∫R<|x-y|<2R |f(y)|(|x - y| -R)α dy. We apply the results to the study of the Cesàro-α convergence of singular integrals.
The Cesàro maximal operator in dimension greater than one
Bernardis, Ana Lucia; Martín Reyes, Francisco Javier
We consider a maximal operators defined on Rn which is related to the Cesaro continuity of functions. We characterize the weights w for which the maximal operator is of weak type, strong type and restricted weak type (p, p) with respect to the measure w(x) dx.
Metadiscurso y producción escrita en estudiantes universitarios"
Padilla Sabate, Constanza
En este trabajo se exponen las conclusiones de una investigación de campo acerca de los procesos de escritura y de metacognición en estudiantes universitarios. Los datos de los subprocesos de la producción escrita, se obtuvieron a partir de la adaptación de la técnica de protocolo de razonamiento en voz alta de L. Flower y J. Hayes (1996), aplicada en una población de 100 estudiantes universitarios, distribuidos en 20 grupos, a quienes se les solicitó la producción grupal de un artículo de opinión y la realización simultánea del protocolo por parte de un observador no participante. Para la recolección de datos de los aspectos metadiscursivos, se administró una encuesta semiestructurada a los mismos estudiantes, con el objetivo de hacer observables sus representaciones acerca de sus propios procesos, desde la enunciación explícita de sus dificultades discursivas. Del análisis, cuantificación e interpretación de los datos, se destacan problemas en el procesamiento de bajo nivel (gramática, ortografía y léxico), tanto a nivel discursivo como metadiscursivo, y dificultades recurrentes en el procesamiento de alto nivel (organización y jerarquización de las ideas, y monitoreo del proceso). Estas dificultades se infieren, fundamentalmente, a partir de la escasa verbalización sobre estos procesos y de la calidad de los productos escritos obtenidos. Los resultados de esta investigación son de especial relevancia para un replanteo de la didáctica de la lengua en los distintos niveles del sistema educativo.
Literatura testimonial en Argentina. Pájaros sin luz de Noemí Ciollaro (1999)
Nofal, Silvia Rossana
El trabajo postula las una lectura sobre las modulaciones de género en la escritura testimonial. La obra de Ciollaro se ubica en una zona gris, alejada de los relatos producidos en términos de victoria o derrota.
Los desafíos regionales frente a la mundialización de los territorios: La sociedad mendocina en los 90
Montaña, Elma Carmen
En 1987, tras décadas de crisis de la economía provincial, Mendoza se embarcaba en la reestructuración del viejo modelo vitivinícola tradicional hacia uno más diversificado y orientado hacia las exportaciones. Las transformaciones derivadas del cambio del modelo económico nacional profundizaron este proceso. A más de 15 años de aquel momento y tras una década de debate académico en torno a las posibilidades y riesgos de las economías y los territorios de América Latina frente al pasaje de economías cerradas a modelos abiertos y sobre los efectos de las políticas neoliberales en aplicación, nos preguntamos de qué manera ha transitado Mendoza estas transformaciones. Específicamente, este trabajo se interesa por las fracturas y reposicionamentos ocurridos en la sociedad local y en la manera en la que se transformó el mapa de los actores operando en la provincia respecto del existente a fines de la década del 80. Se analiza la evolución de actores públicos y privados, locales y foráneos. Hubo ganadores, perdedores y una gama de actores que pelean su posición o incluso su supervivencia en el nuevo modelo y cuya suerte depende, en parte, de las opciones que se tomen para el futuro inmediato y de más largo plazo, de las estrategias que se adopten, de los recursos puestos en juego. Finalmente, se explica el interés en la cohesión social por su incidencia en la construcción de identidades compartidas y en el valor de éstas como factores endógenos necesarios a la construcción de un proyecto sustentable de desarrollo local.
Las especies invasoras exóticas en los sistemas de Humedales: El caso del Delta Inferior del Río Paraná; Exotic invader species in wetland ecosystems: The case of the low Delta of the Parana River
Kalesnik, Fabio Alberto; Malvarez, Ana Ines
Wetlands are ecosystems whose functioning relies on hydrologic regimes and small variations of flooding pulses or flooding levels that may produce massive changes in the local biota. These systems are particularly vulnerable to invasion processes, where variations of hydrologic regimens may cause changes in community composition and structure, and are considered to be one of the causes of incorporation of alien species. The delta of the Paraná river may be considered as a mosaic of wetlands, where 11 landscape units may be characterized by different flooding regimes and landscape patterns. In particular, the “Lower Delta Islands” Unit, is characterized by a highly fragmented landscape constituted by natural (marsh and relict patches of native forests) and anthropic environments (Salix commercial afforestations). These juxtapositions may increase considerably the probability of dispersion of alien species. Burkart (1957) mentions 29 exotic species for natural environments. In more recent works only 11 exotic species are mentioned. Lowland environments (marsh) present 4 exotic species (iris, Iris pseudacorus; honeysuckle, Lonicera japónica; Chinese privet, Ligustrum sinense and blackberry, Rubus spp.) but these species do not behave as invaders, since they present very low constancy and cover values. On the other hand, relict patches of native forests, present high cover values for privet, (Ligustrum lucidum), honeysuckle, White mulberry (Morus alba), and maple (Acer negundo). What respects anthropic environments, Valli (1990) analyzed succesional trends in lowland forestations, mentioning 5 exotic species (iris, Faux indigo (Amorpha fructicosa), honeysuckle, and privet), all of them with low cover values. Kalesnik (2001) studied commercial forestations on levee that presented 16 exotic species, of which only 7 behaved as invaders: privet, Fraxinus pennsylvanica, black acacia (Gleditsia triacanthos), honeysuckle, blackberry, maple and Ligustrum lucidum. The development of each species varied among different subunits (“A”, “B” or “C”) of the Lower Delta. While unit “A” presented a very low invasion index, low cover development of alien, and none of the species behaving as invaders, the other two units (“B” and “C”) presented mean values of the invasion index and a high cover of the mentioned exotic species. In unit “A”, the fluvial influence of the Paraná river, acting together with extraordinary flooding events and the fire caused intentionally for hunting activities, may be a possible explication for the absence of invader species. Finally, it may be stated that of a total of 102 exotic species introduces in the Lower Delta, 8,82% behave as invaders in the island sector. This value is in concordance with the pattern found for temperate ecosystems, where only a 10% of introduced species behave as invaders, in contrast to tropical ecosystems, where that proportion is close to 100%.
Molecular mechanisms of inhibition of nicotinic acetylcholine receptors by tricyclic antidepressants
Gumilar, Fernanda Andrea; Arias, Hugo Rubén; Spitzmaul, Guillermo Federico; Bouzat, Cecilia Beatriz
In addition to their well known actions on monoamine reuptake, tricyclic antidepressants have been shown to modulate ligand-gated ion channels (LGICs). Since the muscle nicotinic acetylcholine receptor (AChR) has been the model for studying structure-function relationships of LGICs, we analyzed the action of tricyclic antidepressants on this type of AChR at both single-channel and macroscopic current levels. We also determined their effects on ACh equilibrium binding and their interactions with the different conformational states of the AChR. Antidepressants produce a significant concentration-dependent decrease in the duration of clusters of single-channels (eight fold at 20 μM). They also decrease the peak amplitude and increase the decay rate of currents elicited by rapid perfusion of ACh to outside-out patches. In equilibrium binding assays, antidepressants promote the typical high-affinity desensitized state and inhibit binding of [piperidyl-3,4-3H (N)]-(N-(1-(2-thienyl) cyclohexyl)-3,4-piperidine ([3H]TCP) to its locus in resting and desensitized AChRs. The results indicate that tricyclic antidepressants: (i) interact with resting (closed), open, and desensitized channels; (ii) do not affect significantly channel opening and closing rates; (iii) do not act as fast open-channel blockers; (iv) inhibit activation of resting channels; and (v) may increase the rate of long-lived desensitization from the open state.
Phase space structure of multi-dimensional systems by means of the mean exponential growth factor of nearby orbits
Cincotta, Pablo Miguel; Giordano, Claudia Marcela; Simó, C.
In this paper we deal with an alternative technique to study global dynamics in Hamiltonian systems, the mean exponential growth factor of nearby orbits (MEGNO), that proves to be efficient to investigate both regular and stochastic components of phase space. It provides a clear picture of resonance structures, location of stable and unstable periodic orbits as well as a measure of hyperbolicity in chaotic domains which coincides with that given by the Lyapunov characteristic number. Here the MEGNO is applied to a rather simple model, the 3D perturbed quartic oscillator, in order to visualize the structure of its phase space and obtain a quite clear picture of its resonance structure. Examples of application to multi-dimensional canonical maps are also included.
Geomorphologic, circulation and dynamic analysis in a meandering tidal channel, Bahía Blanca Estuary
Angeles, Guillermo Raul; Perillo, Gerardo Miguel E.; Piccolo, Maria Cintia
A meander of La Lista tidal channel (Bahia Blanca Estuary, Argentina) was selected in order to study the relationship between the geoforms that control the meandering channel evolution (mainly tidal flats and marshes) arid the dynamic and circulation characteristics of these channels. To achieve this goal a general survey was made in August 1999. The topographic characteristics of the channel and cross- section profiles from different sectors of the meander were compared with typical river profiles. Morphologic similarities between meander tidal channel cross-section (characterized by bidirectional flows) and meander river cross-section (characterized by unidirectional flows) were analysed. The largest velocities were measured during the ebb period (87 and 67 em S·l for U and V, respectively); during the flood period, the highest values registered were 53 and 33 em S·1 for U and V, respectively. Differences among the tidal current profiles along the meander were observed. Comparing the current velocity gradients in the different stations, the higher variations were observed during the flood period.
Gelation of beta-lactoglobulin in the presence of propylene glycol alginate: kinetics and gel properties
Baeza, Rosa Isabel; Gugliotta, Luis Marcelino; Pilosof, Ana Maria Renata
The role of the non-gelling polysaccharide, propyleneglycol alginate (PGA), on the dynamics of gelation and gel properties of β-lactoglobulin (β-lg) under conditions where the protein alone does not gel (6%) was analyzed. To this end, the kinetics of gelation, aggregation and denaturation of β-lg in the mixed systems (pH 7) were studied at different temperatures (64–88 °C). The presence of PGA increased thermal stability of β-lg. The rate of β-lg denaturation was decreased and the onset and peak denaturation temperatures increased by 2.2–2.4 °C. PGA promoted the formation of larger aggregates that continued to grow in time. An average aggregate diameter of approximately 300 nm is reached at the gel point in the mixed β-lg+PGA systems, irrespective of the heating temperature. Comparing the activation energies for the aggregation (193 kJ/mol), denaturation (422 kJ/mol) and formation of the primary gel structure (1/tgel) (256 kJ/mol) processes in the mixed protein–polysaccharide system, it can be concluded that the rate determining step in the formation of the primary gel structure would be the aggregation of protein. Ea values for the processes after the gel point (solid phase gelation) suggest a diffusion limited process because of the high viscosity of the solid gelling matrix. The characteristics of the mixed β-lg+PGA gels in terms of rheological and textural parameters, water loss and microstructure were studied as a function of heating temperature and time. The extent of aggregation and the type of interactions involved, prior to denaturation seem to be very important in determining the gel structure and its properties.
A model for determination of multicomponent diffusion coefficients in foods
Gerla, Patricia; Rubiolo, Amelia Catalina
The simultaneous diffusion of NaCl, lactic acid and water in cheese during brining, were experimentally and theoretically evaluated using multicomponent and pseudobinary mass transport models. The average concentration data of each solute in the solid at different process times were correlated with theoretical models determining the diffusion coefficients values for each solute. Applying a ternary model, main and cross diffusion coefficient values for NaCl and lactic acid showed a non-reciprocal flux interaction. The NaCl diffusion rate resulted independent of the lactic acid concentration gradient, while the lactic acid diffusion rate was increased 12 times due to NaCl concentration changes in the cheese. The results established the importance of using multicomponent mass transport models to evaluate the flux variation of solute in the global flux value.
Heat transfer in double-sided cooking of meat patties considering two-dimensional geometry and radial shrinkage
Zorrilla, Susana; Singh, R. Paul
A mathematical model considering a two-dimensional (2-D) cylindrical geometry, radial shrinkage, and thermal properties changing with temperature, was developed to predict temperature profiles in meat patties during double-sided cooking. The hamburger patty was assumed to be initially frozen; therefore, the approach of enthalpy formulation was used. A moving interface separating two regions when the water vaporization temperature is reached and a third type boundary condition at the patty surface considering a contact heat transfer coefficient were assumed in the radial direction. Furthermore, a third type boundary condition considering a combined heat transfer coefficient for radiation and convection and the symmetry condition in the center were assumed in the radial direction. The model was solved according to a method based on an explicit finite difference approximation and was compared with the results obtained by a one-dimensional (1-D) model. The results showed no significant difference when a cylindrical geometry or radial shrinkage was considered to predict the temperature at the geometric center of a patty under normal conditions of hamburger cooking. However, the 2-D model provides a description of temperature in regions close to the circumferential edge of the patty, which is not possible with the 1-D model.
Dynamic optimization of double-sided cooking of meat patties
Zorrilla, Susana; Banga, Julio; Singh, R. Paul
Optimal operating procedures for double-sided cooking of frozen hamburger patties were computed using dynamic optimization techniques. The mathematical statement was to find the optimal control (e.g., heating surface temperature) over cooking time to minimize (or maximize) the performance index J, for example minimize cooking loss, and to ensure the required lethality and safe cooking temperature. The control vector parameterization framework was applied, and stochastic algorithm was used to locate the global optimum with reasonable computation effort (Integrated Controlled Random Search for Dynamic Systems). The performance index improved when the heating temperature profile was considered as control variable and when two control elements of variable size were used (compared with the constant-temperature process or nominal case, ΔJ<3%). When the lower bound was relaxed and two control elements were used, the performance index improved significantly (ΔJ<7%). However, when the top and bottom plate temperatures were considered as two different controls, the plate temperature profiles obtained did not significantly improve the results compared with the nominal cases. When the temperature of the top and bottom plates and gap thickness were considered as control variables, and when two control elements of variable size for gap thickness were used, the performance index improved for long periods of cooking time (ΔJ<2.5%).
Effects of Salts on Crystallization Kinetics and Rheological Behavior of Concentrated α,α-Trehalose Solutions
Cerdeira, Mariana; Puppo, Maria Cecilia; Martini, Silvana; Herrera, Maria Lidia
The effect of addition of CaCl2 · 2H2O and MgCl2 · 6H2O on crystallization kinetics and the rheological behavior of a 70% trehalose solution was studied by polarized light microscopy and dynamic oscillatory rheometry. Salts caused a delay on nucleation with induction times for crystallization longer for Mg2+ than for Ca2+. Divalent cations were incorporated into crystals, changing the growth of certain faces preferentially, which resulted in changes in morphology. Addition of CaCl2 · 2H2O in a high salt/trehalose molar ratio dramatically increased complex modulus (G*), indicating a stronger viscoelastic behavior. A gel-like structure was formed when Ca2+ was added to trehalose solution. The behavior of Mg 2+/trehalose solutions cannot be considered viscoelastic in nature but as a fluid-like system.
