Oblique projections and frames Antezana, Jorge Abel; Corach, Gustavo; Ruiz, Mariano Andres; Stojanoff, Demetrio We characterize those frames on a Hilbert space H which can be represented as the image of an orthonormal basis by an oblique projection defined on an extension K of H. We show that all frames with infinite excess, and frame bounds 1 ≤ A ≤ B,are of this type. This gives a generalization of a result of Han and Larson which only holds for normalized tight frames.

Effects of pH and electrolyte concentration on the binding between a humic acid and an oxazine dye Zanini, Graciela Pilar; Avena, Marcelo Javier; Fiol, Sarah; Arce, Florencio The binding between an oxazine dye and a humic acid was studied in aqueous solutions in the pH range 4-10 and in the supporting electrolyte (KCl) range 0.001-0.1 M. A rather simple spectrophotometric method was developed to construct binding isotherms under conditions were traditional centrifugation or filtration methods fail. The use of this method is possible because humic acid molecules have the ability of changing the spectrum of dye molecules, and this ability is used to quantify the isotherms. All binding isotherms have a Langmuirian shape. The amount of bound dye is strongly dependent on the ionic strength and less dependent on the pH of the solution. The binding is rather strong and mainly driven by non-electrostatic forces. Whereas the Langmuir binding constant is independent of the pH and electrolyte concentration, the number of assessable sites in humic acid for binding oxazine increases by increasing pH and decreasing electrolyte concentration. These results can be directly related to the flexibility of humic acid molecules, which can swell at high pH and low ionic strength, increasing consequently the availability of binding sites. The results also indicate that humic substances may strongly affect the mobility and fate of dyes and related pollutants in the environment.

Arbitrary divergence speed of the least-squares method in infinite-dimensional inverse ill-posed problems Spies, Ruben Daniel; Temperini, Karina Guadalupe A standard engineering procedure for approximating the solutions of an infinite-dimensional inverse problem of the form Ax = y, where A is a given compact linear operator on a Hilbert space X and y is the given data, is to find a sequence {XN} of finite-dimensional approximating subspaces of X whose union is dense in X and to construct the sequence {xN} of least-squares solutions of the problem in X N. In 1980, Seidman showed that if the problem is ill-posed, then, without any additional assumptions on the exact solution or on the sequence of approximating subspaces XN, it cannot be guaranteed that the sequence {xN} will converge to the exact solution. In this paper, this result is extended in the following sense: it is shown that if X is separable, then for any y ∈ X, y ≠ 0 and for any arbitrarily given function there exists an injective, compact linear operator A and an increasing sequence of finite-dimensional subspaces XN ⊂ X such that for all, where xN is the least-squares solution of Ax = y in XN. © 2006 IOP Publishing Ltd.

A proposed Global Boundary Stratotype Section and Point for the base of the Middle Ordovician Series: The Niquivil section, Precordillera of San Juan, Argentina Albanesi, Guillermo Luis; Carrera, Marcelo Gabriel; Cañas, Fernando Luis; Saltzman, Matthew The Niquivil section, Argentine Precordillera, fulfills most of the requirements for a Global Stratotype Section and Point (GSSP) for the base of the Middle Ordovician Series. It has excellent conodont biostratigraphy in a continuous succession of uniform lithology, is readily accessible, and the critical interval is not tectonically affected. The position of the Lower/Middle Ordovician Series boundary in the Central Precordillera is placed at the middle part of the San Juan Formation, an open-platform carbonate unit. The Niquivil section is proposed as a GSSP for the base of the Middle Ordovician, which is marked by the FAD of the conodont Cooperignathus aranda (Cooper). It occurs in level NCA, at the upper part of the Oepikodus evae Zone (overlapping uppermost records of O. evae in association with other guide species); i.e., 100.15 m above the base of the reference section. The auxiliary Peña Sombría section from northern Precordillera records graptolites of the lower (but not lowest) Middle Ordovician in the Isograptus victoriae maximus Zone, few meters above the proposed boundary biohorizon. The range of C. aranda can be correlated with the I. victoriae lunatus Zone up to the lower part of the Undulograptus austrodentatus Zone in diverse sections of the world. C. aranda presents cosmopolitan distribution and occurs in virtually all environments. The proposed GSSP preserves a carbon-isotope record that provides an auxiliary marker of potential global application. Radiometric dating of K-bentonite samples, interbedded with carbonate strata yielding lower records of C. aranda, were recovered from the auxiliary Talacasto section in Central Precordillera (469.8 ± 2.3 Ma, U–Pb SHRIMP dating).Cooperignathus aranda (Cooper). It occurs in level NCA, at the upper part of the Oepikodus evae Zone (overlapping uppermost records of O. evae in association with other guide species); i.e., 100.15 m above the base of the reference section. The auxiliary Peña Sombría section from northern Precordillera records graptolites of the lower (but not lowest) Middle Ordovician in the Isograptus victoriae maximus Zone, few meters above the proposed boundary biohorizon. The range of C. aranda can be correlated with the I. victoriae lunatus Zone up to the lower part of the Undulograptus austrodentatus Zone in diverse sections of the world. C. aranda presents cosmopolitan distribution and occurs in virtually all environments. The proposed GSSP preserves a carbon-isotope record that provides an auxiliary marker of potential global application. Radiometric dating of K-bentonite samples, interbedded with carbonate strata yielding lower records of C. aranda, were recovered from the auxiliary Talacasto section in Central Precordillera (469.8 ± 2.3 Ma, U–Pb SHRIMP dating).(Cooper). It occurs in level NCA, at the upper part of the Oepikodus evae Zone (overlapping uppermost records of O. evae in association with other guide species); i.e., 100.15 m above the base of the reference section. The auxiliary Peña Sombría section from northern Precordillera records graptolites of the lower (but not lowest) Middle Ordovician in the Isograptus victoriae maximus Zone, few meters above the proposed boundary biohorizon. The range of C. aranda can be correlated with the I. victoriae lunatus Zone up to the lower part of the Undulograptus austrodentatus Zone in diverse sections of the world. C. aranda presents cosmopolitan distribution and occurs in virtually all environments. The proposed GSSP preserves a carbon-isotope record that provides an auxiliary marker of potential global application. Radiometric dating of K-bentonite samples, interbedded with carbonate strata yielding lower records of C. aranda, were recovered from the auxiliary Talacasto section in Central Precordillera (469.8 ± 2.3 Ma, U–Pb SHRIMP dating).Oepikodus evae Zone (overlapping uppermost records of O. evae in association with other guide species); i.e., 100.15 m above the base of the reference section. The auxiliary Peña Sombría section from northern Precordillera records graptolites of the lower (but not lowest) Middle Ordovician in the Isograptus victoriae maximus Zone, few meters above the proposed boundary biohorizon. The range of C. aranda can be correlated with the I. victoriae lunatus Zone up to the lower part of the Undulograptus austrodentatus Zone in diverse sections of the world. C. aranda presents cosmopolitan distribution and occurs in virtually all environments. The proposed GSSP preserves a carbon-isotope record that provides an auxiliary marker of potential global application. Radiometric dating of K-bentonite samples, interbedded with carbonate strata yielding lower records of C. aranda, were recovered from the auxiliary Talacasto section in Central Precordillera (469.8 ± 2.3 Ma, U–Pb SHRIMP dating).O. evae in association with other guide species); i.e., 100.15 m above the base of the reference section. The auxiliary Peña Sombría section from northern Precordillera records graptolites of the lower (but not lowest) Middle Ordovician in the Isograptus victoriae maximus Zone, few meters above the proposed boundary biohorizon. The range of C. aranda can be correlated with the I. victoriae lunatus Zone up to the lower part of the Undulograptus austrodentatus Zone in diverse sections of the world. C. aranda presents cosmopolitan distribution and occurs in virtually all environments. The proposed GSSP preserves a carbon-isotope record that provides an auxiliary marker of potential global application. Radiometric dating of K-bentonite samples, interbedded with carbonate strata yielding lower records of C. aranda, were recovered from the auxiliary Talacasto section in Central Precordillera (469.8 ± 2.3 Ma, U–Pb SHRIMP dating).Isograptus victoriae maximus Zone, few meters above the proposed boundary biohorizon. The range of C. aranda can be correlated with the I. victoriae lunatus Zone up to the lower part of the Undulograptus austrodentatus Zone in diverse sections of the world. C. aranda presents cosmopolitan distribution and occurs in virtually all environments. The proposed GSSP preserves a carbon-isotope record that provides an auxiliary marker of potential global application. Radiometric dating of K-bentonite samples, interbedded with carbonate strata yielding lower records of C. aranda, were recovered from the auxiliary Talacasto section in Central Precordillera (469.8 ± 2.3 Ma, U–Pb SHRIMP dating).Zone, few meters above the proposed boundary biohorizon. The range of C. aranda can be correlated with the I. victoriae lunatus Zone up to the lower part of the Undulograptus austrodentatus Zone in diverse sections of the world. C. aranda presents cosmopolitan distribution and occurs in virtually all environments. The proposed GSSP preserves a carbon-isotope record that provides an auxiliary marker of potential global application. Radiometric dating of K-bentonite samples, interbedded with carbonate strata yielding lower records of C. aranda, were recovered from the auxiliary Talacasto section in Central Precordillera (469.8 ± 2.3 Ma, U–Pb SHRIMP dating).C. aranda can be correlated with the I. victoriae lunatus Zone up to the lower part of the Undulograptus austrodentatus Zone in diverse sections of the world. C. aranda presents cosmopolitan distribution and occurs in virtually all environments. The proposed GSSP preserves a carbon-isotope record that provides an auxiliary marker of potential global application. Radiometric dating of K-bentonite samples, interbedded with carbonate strata yielding lower records of C. aranda, were recovered from the auxiliary Talacasto section in Central Precordillera (469.8 ± 2.3 Ma, U–Pb SHRIMP dating).I. victoriae lunatus Zone up to the lower part of the Undulograptus austrodentatus Zone in diverse sections of the world. C. aranda presents cosmopolitan distribution and occurs in virtually all environments. The proposed GSSP preserves a carbon-isotope record that provides an auxiliary marker of potential global application. Radiometric dating of K-bentonite samples, interbedded with carbonate strata yielding lower records of C. aranda, were recovered from the auxiliary Talacasto section in Central Precordillera (469.8 ± 2.3 Ma, U–Pb SHRIMP dating).Undulograptus austrodentatus Zone in diverse sections of the world. C. aranda presents cosmopolitan distribution and occurs in virtually all environments. The proposed GSSP preserves a carbon-isotope record that provides an auxiliary marker of potential global application. Radiometric dating of K-bentonite samples, interbedded with carbonate strata yielding lower records of C. aranda, were recovered from the auxiliary Talacasto section in Central Precordillera (469.8 ± 2.3 Ma, U–Pb SHRIMP dating).C. aranda presents cosmopolitan distribution and occurs in virtually all environments. The proposed GSSP preserves a carbon-isotope record that provides an auxiliary marker of potential global application. Radiometric dating of K-bentonite samples, interbedded with carbonate strata yielding lower records of C. aranda, were recovered from the auxiliary Talacasto section in Central Precordillera (469.8 ± 2.3 Ma, U–Pb SHRIMP dating).C. aranda, were recovered from the auxiliary Talacasto section in Central Precordillera (469.8 ± 2.3 Ma, U–Pb SHRIMP dating).

Herramientas para la gestión del uso público en espacios naturales: Procesos participativos; Tools for the management of public use4n wetlands: Public participation De Paula, Malena; Huwiler, Cristina; Viñals, María José; Morant González, Maryland; Ferrer, Carlos; Cabrelles, Gemma; Rigoberto, Noelia; Quintana, Ruben Dario La gestion del uso publico en areas naturales y especialmente en Humedales de Importancia Internacional(Sitios Ramsar), representa un importante reto para planificadores y gestores del territorio que tratan deconjugar la conservation de los valores ecologicos y culturales con la utilidad publica, en areas que se caracterizan por una gran fragilidad ecosistemica.El trabajo parte de la premisa de que la participation de las comunidades locales involucradas en laplanificacion y gestion del uso publico en humedales es la via para asegurar que la mayor parte de los beneficiosque se generen permanezcan en la comunidad y para que se garantice la conservation y restauracion de laintegridad ecologica de los humedales.En este documento se expone el diseño e implementation de herramientas metodologicas de una EstrategiaParticipativa. Se analizan a traves de diferentes casos de estudio los resultados de la aplicacion de dicha metodologia, a distintas situaciones de las comunidades locales respecto a los procesos participativos, en relationcon la planificacion de los humedales y el uso publico.; Community involvement and participation in management decision making for public use of natural areas, and particularly in Wetlands of International Importance (Ram sarsites) and other wetlands, have been recognized as the best way compatible with the maintenance of the cultural values and the natural properties of the ecosystem . This paper was conceived with the premise that local people involvement in wetlands management encouraged by a participative strategic can substantially contribute significantly to maintaining or restoring the ecological integrity of wetlands, as well as contributing to community well being and more equitable access to resources. Through the case studies presented here, the methodology is analyzed in different local communities situations from the point of view of participatory processes for the management of wetlands and the public use.

Personalizing user-agent interaction Schiaffino, Silvia Noemi; Amandi, Analia Adriana Interface agents are computer programs that provide personalized assistance to users with their computer-based tasks. The interface agents developed so far have focused their attention on learning a user´s preferences in a given application domain and on assisting him according to them. However, in order to personalize the interaction with users, interface agents should also learn how to best interact with each user and how to provide them assistance of the right sort at the right time. To fulfil this goal, an interface agent has to discover when the user wants a suggestion to solve a problem or deal with a given situation, when he requires only a warning about it and when he does not need any assistance at all. In this work, we propose a learning algorithm, named WoS, to tackle this problem. Our algorithm is based on the observation of a user´s actions and on a user´s reactions to the agent´s assistance actions. The WoS algorithm enables an interface agent to adapt its behavior and its interaction with a user to the user´s assistance requirements in each particular context.

Post-prior discrepancies in CDW-EIS calculations for ion impact ionization fully differential cross sections Ciappina, Marcelo Fabián; Cravero, Walter Ruben In this work we present fully differential cross sections (FDCSs) calculations using post and prior versions of CDW-EIS theory for helium single ionization by 100 MeV C6+ amu-1 and 3.6 MeV amu -1 Au24+ and Au53+ ions. We performed our calculations for different momentum transfer and ejected electron energies. The influence of internuclear potential on the ejected electron spectra is taken into account in all cases. We compare our calculations with absolute experimental measurements. It is shown that prior version calculations give better agreement with experiments in almost all studied cases.

Leukemia inhibitory factor induces DNA synthesis in Swiss mouse 3T3 cells independently of cyclin D1 expression through a mechanism involving MEK/ERK1/2 activation Dekanty, Andres; Sauane, Moira; Cadenas, Belen; Coluccio Leskow, Federico; Barrio, Maria Marcela; Casala, Jorgelina; Paciencia, Mercedes; Rogers, Florencia; Coso, Omar Adrian; Piwien Pilipuk, Graciela; Rudland, Philip S.; Jimenez de Asua, Luis Adan Felipe Leukemia inhibitory factor (LIF) and oncostatin M (OSM) induce DNA synthesis in Swiss 3T3 cells through common signaling mechanism(s), whereas other related cytokines such as interleukin-6 and ciliary neurotrophic factor do not cause this response. Induction of DNA replication by LIF or prostaglandin F 2α (PGF 2α) occurs, in part, through different signaling events. LIF and OSM specifically trigger STAT1 cytoplasmic to nuclear translocation, whereas PGF 2α fails to do so. However, LIF and PGF 2α can trigger increases in ERK1/2 activity, which are required for their mitogenic responses because U0126, a MEK1/2 inhibitor, prevents both ERK1/2 activation and induction of DNA synthesis by LIF or PGF 2α treatment. PGF 2α induces cyclin D expression and full phosphorylation of retinoblastoma protein. In contrast, LIF fails to promote increases in cyclin D mRNA/protein levels; consequently, LIF induces DNA synthesis without promoting full phosphorylation of retinoblastoma protein (Rb). However, both LIF and PGF 2α increase cyclin E expression. Furthermore, LIF mitogenic action does not involve protein kinase C (PKC) activation, because a PKC inhibitor does not block this effect. In contrast, PKC activity is required for PGF 2α mitogenic action. More importantly, the synergistic effect between LIF and PGF 2α to promote S phase entry is independent of PKC activation. These results show fundamental differences between LIF and PGF 2α-dependent mechanism(s) that induce cellular entry into S phase. These findings are critical in understanding how LIF and other related cytokine-regulated events participate in normal cell cycle control and may also provide clues to unravel crucial processes underlying cancerous cell division.

El poblamiento inicial del sector austral de las Sierras Pampeanas de Argentina desde la ecología del paisaje Laguens, Andres Gustavo Se presenta un modelo sobre el poblamiento inicial y expansión de poblaciones del sector austral de las Sierras Pampeanas (Córdoba y San Luis) desde la ecología del paisaje. Se consideran las estrategias de movimiento poblacional, la estructura del paisaje, la definición de espacios de habitat y la dispersión de poblaciones hasta el Holoceno medio. Se analizan datos de sitios cazadores recolectores del límite Pleistoceno-Holoceno, hallazgos de posibles asociaciones con megafauna y datos bioantropológicos. Se postula un poblamiento por corredores ambientales de menor costo, desde las llanuras del Este, con posterior definición de distintos contornos de habitat y ajustes tecnológicos.; It is presented a model on the early peopling and expansion of human populations at the southern cone of the Sierras Pampeanas (Cordoba and San Luis) from a landscape ecology perspective. They are considered the strategies of population movements, the structure of the landscape, the definition of spaces of habitat and the dispersion of populations until the middle Holocene. Hunter-gatherers sites at the Pleistocene-Holoceno boundary are analyzed, as well as possible associations with megafauna and bioanthropological data It is advanced a peopling through environmental corridors of lower cost from the plains of the East, with subsequent definition of different habitat contours and technological adjustments.

Threshold resummation for high-transverse-momentum Higgs production at the LHC de Florian, Daniel Enrique; Kulesza, Anna; Vogelsang, Werner We study the resummation of large logarithmic QCD corrections for the process pp → H + X when the Higgs boson H is produced at high transverse momentum. The corrections arise near the threshold for partonic reaction and originate from soft gluon emission. We perform the all-order resummation at next-to-leading logarithmic accuracy and match the resummed result with the next-to-leading order perturbative predictions. The effect of resummation on the Higgs transverse momentum distribution at the LHC is discussed. © SISSA 2006.

Excepción y paradigma de la década infame 1930-1943 Videla, Oscar Ruben El desarrollo histórico de la provincia de Santa Fe ha estado marcado profundamente por las vicisitudes de la vida nacional pero, particularmente en la coyuntura de los años treinta, largas cadenas de rupturas y continuidades nos permiten afirmar que la provincia era al mismo tiempo excepción y paradigma de aquellos procesos más generales. En poco más de una década la provincia se ve profundamente sacudida, por una parte los efectos de una crisis que ataca el corazón de su estructura productiva, por otra parte por una lenta pero persistente transformación de su estructura regional que redefinirá sus actividades agrarias y abrirá paso a un desarrollo industrial con destino de expansión, pero también se conmoverá por los vaivenes que lo llevan del liberalismo reformista de la gestión demoprogresista al predominio (fraude mediante) de un liberalismo conservador, representado en el radicalismo concordancista, de tintes tradicionalistas en lo ideológico pero moderadamente innovadores en la gestión del estado provincial.  En este sentido, para lograr una comprensión al mismo tiempo general y particular de este periodo de la historia provincial el artículo pretende analizar y caracterizar la realidad santafesina desde una perspectiva que articule las diversas escalas de análisis (nacional, provincial y local) con los distintos niveles de análisis de la misma.

El grupo Bunge y la política económica del primer peronismo, 1943-1952 Belini, Claudio Fabian Este trabajo analiza la influencia política e ideológica que el grupo de discípulos de Alejandro Bunge tuvo en la definición de la política económica del primer peronismo. Se sostiene que su postura favorable a la industrialización en los debates de la entreguerra y el influjo que el catolicismo social ejerció en sus miembros le permitió al grupo ejercer influencia sobre la dictadura militar de 1943. El artículo estudia el papel del grupo en la Secretaría de Industria, la elaboración del primer régimen de promoción industrial y los debates económicos de la inmediata posguerra. Se argumenta que el grupo Bunge desempeñó un rol decisivo en la orientación de la política industrial peronista, moldeando sus características básicas y brindando al régimen de Perón los argumentos que la justificaban. A propósito de ello, el trabajo discute la interpretación que otorga excesivo énfasis a factores políticos y sociales, como el enfrentamiento de Perón con los Estados Unidos y las demandas del movimiento obrero, en la orientación que tomó la política industrial peronista.; This paper analyzes the political and ideological influence that the group of disciples of Alejandro Bunge exerted over the definition of the economic policies during the first Peronist administration. It argues that the group's support for industrialization during the interwar period as well as the pressure exerted by social Catholicism upon its members allowed the group to manipulate the 1943 military government. Moreover, this article examines the role of the group in the Industry Secretariat, the formation of the first programof industrialpromotion,and the economic discussions held during the postwar period. It argues that the Bunge group played a decisive role in the orientation of Peronist industrial policies, shapingits basic characteristics, and justifying the policies. In this sense, this paper questions the argument that overly emphasizes the importance of political and social factors that oriented Peronist industrial policies, such as Peron's confrontation with the United States and the demands of the labor movement.

Calidad editorial y visibilidad de las revistas: La experiencia de Latindex Aguirre, Marcela; Cetto, Ana María; Córdoba, Saray; Flores, Ana Maria; Román, Adelaida Durante el Primer Taller sobre Publicaciones Científicas en América Latina, celebrado en Guadalajara, México, en 1994, se puso de manifiesto la falta de un sistema de información propio para las revistas científicas que se producen en América Latina y el Caribe. No fue aquella la primera vez que se expresaba la necesidad de contar con un sistema de tal naturaleza. En dicha ocasión, sin embargo, la preocupación tuvo eco en el seno de la UNAM, México, y condujo a la formulación de un proyecto para un sistema regional de información que habría de recoger el universo completo de publicaciones científicas seriadas, en todas las áreas del conocimiento y sin discriminación por idioma o lugar de publicación. Hacia fines de 1995 se tenía una primera versión del proyecto, al cual se dio el nombre de Latindex, Índice Latinoamericano de Publicaciones Científicas Seriadas. Se planteó desde un principio que, al no estar centralizado en una determinada institución o país, el proyecto basaría su fortaleza en el trabajo compartido y en la cercanía a las fuentes que generan o distribuyen datos sobre dichas publicaciones...

Antes y después: Marco de referencia del viaje de James Weddell 1822-1824 Piana, Ernesto Luis La historia de la marca más austral de Weddell está ampliamente divulgada. Su imagen de capitán lobero subsiste muy difundida. Pero la implicancia que el viaje de Weddell tuvo en relación con las exploraciones en las islas del Atlántico Sur, el archipiélago fueguino y la Isla de Tierra del Fuego, más las referencias a sus habitantes, los nómades canoeros, merecen ser conocidas y valoradas. Sin embargo, por tratarse de un libro de viaje, se requiere un marco para el lector que ubique a Weddell en sus circunstancias temporales y espaciales y explicite el valor de este texto Este trabajo presenta una biografía sucinta de él y los datos pertinentes de su contramaestre Brisbane, la importancia y desarrollo de las industrias peletera y de utilización de grasas de los lobos marinos, en esa época, la significación de haber alcanzado la latitud más austral y la duración de esta marca, cómo cambió la apreciación de Tierra del Fuego entre los navegantes a partir de sus descubrimientos y otros temas que valorizan el escrito y clarifican al lector. En particular se hace hincapié en la relación de J Weddell con los Yámana y la importancia que tiene su registro.

Algunos datos históricos de Albardón a través de su patrimonio Ruiz, Viviana; Frau, Silvana Alejandra El departamento de Albardón se encuentra conformado por una cantidad importante de localidades y pueblos cargados de significado, "Las Tapias" es uno de ellos, vinculado con la fundación misma de la provincia de San Juan -1562-. Un pueblo histórico que formó parte de la historia activa de la provincia siendo un nudo en las rutas desde la fundación hasta 1930. Otros lugares históricos se han podido rescatar como la Estación Las Lomitas y la biblioteca San Martín, sitios donde el habitante albardonero se incorporó a la cultura, actividad económica y política provincial, regional y nacional. Como imaginario histórico se analiza el cruce del Río San Juan, barrera natural que separa a Albardón de la Ciudad de San Juan, un cruce cargado de significatividad para los habitantes de la región.

Géneros, significados sociales y prácticas discursivas del guaraní de Corrientes Cerno, Leonardo Aurelio Este trabajo expone algunas de las representaciones y símbolos que componen el imaginario sociocultural relativo al guaraní en comunidades rurales y pueblos del interior de la provincia de Corrientes, y vincula tales componentes con el sistema de usos observados y con prácticas de socialización lingüística específicas. A su vez describe y analiza un conjunto de categorías etnográficas referentes a tipos de hablantes y formas de conducta social relacionadas con el uso del guaraní, y ofrece una interpretación de tales nociones y prácticas teniendo en cuenta el horizonte sociocultural de los actores.

Personal assistants: Direct manipulation vs. mixed initiative interfaces Armentano, Marcelo Gabriel; Godoy, Daniela Lis; Amandi, Analia Adriana Interface agents are computer programmes that provide assistance to users dealing with computer-based applications. The introduction of agents to user interfaces caused the exploration of new metaphors to enhance user ability to directly manipulate interfaces. In this regard, mixed-initiative interaction refers to a flexible interaction strategy in which agents contribute with users by providing suitable information at the most appropriate time. Mixed-initiative approaches promise to dramatically enhance human-computer interaction by allowing agents to resemble human assistants. In this paper, we report a study on how the interaction metaphor can affect the user perception of agent capabilities and, in turn, the final success of agents.

Exploring RNA Virus Replication in Xenopus Oocytes Gamarnik, Andrea Vanesa; Andino, Raul Microinjection of poliovirus RNA in Xenopus oocytes initiates a complete and authentic viral replication cycle that yields newly synthesized infectious virus. This system can be used to study the molecular mechanism of the different steps involved in virus replication. Interestingly, viral replication only occurs if poliovirus RNA is coinjected with factors present in HeLa extracts. We have determined that two HeLa cell factors are required for viral replication in oocytes, one involved in initiation of translation (polio translation factor) and the other in RNA synthesis. Thus, microinjection in oocytes provides a strategy to identify and further analyze the function of these host cell factors and to biochemically dissect the mechanism of initiation of poliovirus translation and RNA synthesis. Here, we review protocols, approaches, and potential issues that can be addressed using the oocyte system.

Interactions Dans Les Dispersions. Stabilisation Quemada, Daniel; Berli, Claudio Luis Alberto Dans les dispersions et plus généralement dans les fluides complexes, les forces subies par les "particules" interviennent à trois niveaux: aux échelles microscopique, mésoscopique ou macroscopique. Nous les examinerons successivement aux § 2.1, 2.2 et 2.3. Remarquons que les forces à l?échelle microscopique peuvent être séparées en deux groupes: (i) les forces dites externes parce qu´elles résultent de l´action d´un agent extérieur à la suspension. Parmi ces agents, figure, en premier lieu, la pesanteur, qui entraîne une séparation de phase dès que les densités des deux composants de la dispersion sont suffisamment différentes. En second lieu, on trouve les champs électriques, si les particules sont chargées électriquement, ainsi que les champs magnétiques, si les particules sont magnétiques ou simplement chargées (i.e. équivalentes à un courant lorsqu?elles sont en mouvement). Ce sont les possibilités de contrôle des propriétés rhéologiques par l?action de ces champs qui ont donné naissance aux nouvelles classes de matériaux, fluides électro-rhéologiques et ferrofluides signalés dans l?introduction. (ii) les forces dites internes, qui sont des interactions agissant au niveau des particules et qui sont de deux types suivant que l?on se place en milieu très dilué (interaction ?fluide-particule?) ou en milieu semi-dilué ou en milieu concentré (interaction ?particule-particule?).

Relations Viscosite-Fraction Volumique Quemada, Daniel; Berli, Claudio Luis Alberto Nous commencerons donc par discuter dans ce chapitre les résultats des théories exactes, dans le cas des suspensions diluées, en nous appuyant sur les calculs de Batchelor (§4.1), puis nous donnerons un aperçu des possibilités de développement de théories exactes pour les milieux très concentrés, mais néanmoins en essayant d?en montrer les limites lorsqu?on tente de les appliquer à de tels milieux (§4.2). Ensuite, les modèles phénoménologiques, certains directement déduits de plusieurs extensions de la loi d?Einstein, seront présentés et discutés (§4.3), le concept de structure mésoscopique dont la taille dépend de l?écoulement se dégageant progressivement. Enfin, le modèle directement déduit du modèle de SD et prenant en compte les effets de la compacité des structures sera développé (§4.4). On ne discutera pas du très grand nombre de relations purement empiriques (pour lesquelles il existe une revue assez exhaustive [Rutgers, 1962]), dans lesquelles interviennent des paramètres dont l?interprétation n?est pas toujours claire. Il en sera de même de certaines "lois" sous lesquelles sont regroupées un très grand nombre de données expérimentales (cf. par ex. [Thomas, 1961]).