The geodesic flow on nilmanifolds

In this paper we study the geodesic flow on nilmanifolds equipped with a left-invariant metric. We write the underlying definitions and find general formulas for the Poisson involution. As an example we develop the Heisenberg Lie group equipped with its canonical metric. We prove that a family of first integrals giving the complete integrability can be read off at the Lie algebra of the isometry group. We also explain the complete integrability on compact quotients and for any invariant metric.Comment: 24 page

Angular dependent vortex dynamics in superconductors with columnar defects

We explore in detail the angular dependent vortex dynamics in type II superconductors with aligned columnar defects introduced by irradiation with very energetic heavy-ions. We use dc magnetization measurements deep in the vortex solid phase, and ac susceptibility near the solid-liquid transition. We show that aligned columnar defects are an excellent tool to test models for vortex dynamics, particularly if they are tilted with respect to the crystallographic axes, so their effects can be easily distinguished from those arising from mass anisotropy, sample geometry, twin boundaries and intrinsic pinning. This allows us, for instance, to use the uniaxial pinning of the columnar defects as a probe to determine the orientation of the vortices inside a bulk material, which in general is different from the orientation of the applied fields. In some aspects we have found an excellent agreement with the theoretical expectations of the Bose-glass model. The field dependence of the lock-in angle follows remarkably well the 1/H prediction over the whole temperature range of our measurements. In turn, the temperature dependence of the lock-in angle gives strong support to the concept of an effective pinning energy dominated by the entropic smearing effect. On the other hand, both our ac and dc results show that columnar defects produce effective pinning over a wide angular range, and that correlated pinning dominates the scenario for all field orientations. One consequence of this is the existence of a rich variety of vortex staircases.Comment: to be published in International Book series "Studies of High Temperature Superconductors", edited by Anant Narlikar, Nova Science Publishers, New York, Vol 49/50, (2003

Hydrogen peroxide in micropropagation of Lilium: A comparison with a traditional methodology

The micropropagation of Lilium longiflorum requires adequate equipment which may not be afforded by small laboratories or producers. In this work we compared traditional methodology with a protocol that included easily available elements to sterilize materials and culture media, together with addition of hydrogen peroxide (H2O2) into the nutrient media as chemical sterilizer. A series of H2O2 concentrations (0.005, 0.010, 0.015 and 0.020% p/v) was used to control contamination during in vitro establishment and subsequent cultivation; the explant organogenic response was also examined and compared to the traditional micropropagation technique. The level of culture contamination was within acceptable limits in all treatments, though it was higher in the H2O2 treatments (40%) compared to the traditional methodology (20%). There were not significant differences in the number of bulblets per explant, and at the end of the multiplication phase, bulblets from 0.02% H2O2 treatment had greater biomass than from other treatments, indicating a beneficial effect. These bulblets also had a higher relative growth ratio with respect to the traditional method when cultivated for an additional period and showed the highest average bulblet fresh weight. It is expected that this higher bulblet mass would result in better performance during ex vitro cultivation.Fil: Curvetto, Nestor Raul. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Centro de Recursos Naturales Renovables de la Zona Semiárida. Universidad Nacional del Sur. Centro de Recursos Naturales Renovables de la Zona Semiárida; ArgentinaFil: Marinangeli, Pablo Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Centro de Recursos Naturales Renovables de la Zona Semiárida. Universidad Nacional del Sur. Centro de Recursos Naturales Renovables de la Zona Semiárida; ArgentinaFil: Mockel, Gabriela Carolina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Centro de Recursos Naturales Renovables de la Zona Semiárida. Universidad Nacional del Sur. Centro de Recursos Naturales Renovables de la Zona Semiárida; Argentin

A BDNF sensitive mechanism is involved in the fear memory resulting from the interaction between stress and the retrieval of an established trace

The present study investigates the fear memory resulting from the interaction of a stressful experience and the retrieval of an established fear memory trace. Such a combination enhanced both fear expression and fear retention in adult Wistar rats. Likewise, midazolam intra-basolateral amygdala (BLA) infusion prior to stress attenuated the enhancement of fear memory thus suggesting the involvement of a stress-induced reduction of the GABAergic transmission in BLA in the stress-induced enhancing effect. It has been suggested that, unlike the immediate-early gene Zif268 which is related to the reconsolidation process, the expression of hippocampal brain-derived neurotrophic factor (BDNF) is highly correlated with consolidation. We therefore evaluate the relative contribution of these two neurobiological processes to the fear memory resulting from the above-mentioned interaction. Intra-dorsal hippocampus (DH) infusions of either the antisense Zif268 or the inhibitor of the protein degradation (Clasto-Lactacystin β-Lactone), suggested to be involved in the retrieval-dependent destabilization process, did not affect the resulting contextual memory. In contrast, the knockdown of hippocampal BDNF mitigated the stress-induced facilitating influence on fear retention. In addition, the retrieval experience elevated BDNF level in DH at 60 min after recall exclusively in stressed animals. These findings suggest the involvement of a hippocampal BDNF sensitive mechanism in the stress-promoting influence on the fear memory following retrieval.Fil: Giachero, Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Farmacología Experimental de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Farmacología Experimental de Córdoba; ArgentinaFil: Bustos, Silvia Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Farmacología Experimental de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Farmacología Experimental de Córdoba; ArgentinaFil: Calfa, Gaston Diego. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Farmacología Experimental de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Farmacología Experimental de Córdoba; ArgentinaFil: Molina, Víctor Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Farmacología Experimental de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Farmacología Experimental de Córdoba; Argentin

Transgenic tobacco plants expressing the Potato virus X open reading frame 3 gene develop specific resistance and necrotic ring symptoms after infection with the homologous virus

Tobacco plants were transformed with the open reading frame 3 gene from Potato virus X (PVX) coding for the p12 protein. Although the transgenic plants exhibited a normal morphological aspect, microscopic examination revealed extensive alterations in leaf tissue structure. After being challenged with PVX, the transgenic plants showed resistance to PVX infection and formation of specific leaf symptoms consisting of concentric rings encircled by necrotic borders. These novel symptoms were accompanied by biochemical changes normally associated with the hypersensitive response (HR) and were absent in noninfected transgenic plants or in PVX-infected nontransgenic plants. No equivalent virus resistance was observed after inoculation with Tobacco mosaic virus or Potato virus Y, suggesting the presence of a specific resistance mechanism. Despite development of HR-like symptoms, systemic acquired resistance was not induced in PVX-infected p12 transgenic plants. No evidence of an RNA-mediated resistance mechanism was found.Fil: Kobayashi, Ken. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres"; ArgentinaFil: Cabral, Silvia. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres"; ArgentinaFil: Calamante, Gabriela. Instituto Nacional de Tecnología Agropecuaria. Centro Nacional de Investigaciones Agropecuarias Castelar. Centro de Investigación en Ciencias Veterinarias y Agronómicas. Instituto de Biotecnología; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; ArgentinaFil: Maldonado, Sara Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; ArgentinaFil: Mentaberry, Alejandro Nestor. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres"; Argentin

The city in dispute: economy and territory in San Carlos de Bariloche

Este artículo problematiza las vinculaciones entre la política urbana y la conformación territorial de la ciudad de San Carlos de Bariloche, a partir del funcionamiento del mercado de tierras y la disputa por la apropiación y uso del espacio urbano. En este sentido, el trabajo aporta una reflexión en torno a la relación entre los modelos de desarrollo económico y urbano de las ciudades contemporáneas, relación que muchas veces se pierde de vista en la literatura, privilegiando uno u otro componente. Para ello, se realiza un estudio de caso del actual Barrio 10 de Diciembre, a través de fuentes documentales y entrevistas en profundidad. Este barrio aparece como un caso paradigmático de disputa de un área de la ciudad a la convergencia entre los intereses económicos del sector privado y un planeamiento urbano completamente funcional a dichos intereses. En este marco, el Barrio 10 de Diciembre ha sido una de las áreas con mayores intentos de relocalización poblacional compulsiva, fundamentados en presiones inmobiliarias y la idea de ciudad que subyace a los diferentes instrumentos de planificación urbana, que reservaban las tierras periféricas para los sectores populares. La historia de este barrio resume muchas de las tensiones, históricas y coyunturales, que estructuraron a la ciudad y que parecen repetirse en otras localidades vinculadas a la explotación turística.This article delves into the linkages between entrepreneurial interests related to real estate and tourism and urban policy in the city of San Carlos de Bariloche, through the dynamics of the land market and the dispute over the appropriation and use of urban space. In this sense, the work provides a reflection on the relationship between the models of economic and urban development of contemporary cities, relationship that is often lost of sight in the literature. To do this, a case study of the Barrio 10 de Diciembre is carried forward, through documentary sources and interviews. This area appears as a paradigmatic case of a disputed area of the city to the convergence between the economic interests of the private sector and a urban planning functional to such interests. In this framework, the Barrio 10 de Diciembre has been one of the areas with more compulsive attempts of eradication, because of real estate pressures and the city image embodied in the different urban planning instruments, which reserve peripheral land for popular sectors. The history of this neighborhood summarizes many of the tensions, historical and contextual, which structured the city and which seem to be replicated in other cities linked to the tourist exploitation.Fil: Guevara, Tomás Alejandro. Universidad Nacional de Rio Negro. Sede Andina; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Nuñez, Paula Gabriela. Universidad Nacional de Rio Negro. Sede Andina; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Thermally assisted interlayer magnetic coupling through Ba0.05Sr0.95TiO3 barriers

We report on the interlayer exchange coupling across insulating barriers observed on Ni80Fe20/Ba0.05Sr0.95TiO3/La0.66Sr0.33MnO3 (Py/BST0.05/LSMO) trilayers. The coupling mechanism has been analyzed in terms of the barrier thickness, samples' substrate, and temperature. We examined the effect of MgO (MGO) and SrTiO3 (STO) (001) single-crystalline substrates on the magnetic coupling and also on the magnetic anisotropies of the samples in order to get a deeper understanding of the magnetism of the structures. We measured a weak coupling mediated by spin-dependent tunneling phenomena whose sign and strength depend on barrier thickness and substrate. An antiferromagnetic (AF) exchange prevails for most of the samples and smoothly increases with the barrier thicknesses as a consequence of the screening effects of the BST0.05. The coupling monotonically increases with temperature in all the samples and this behavior is attributed to thermally assisted mechanisms. The magnetic anisotropy of both magnetic components has a cubic symmetry that in the case of permalloy is added to a small uniaxial component.Fil: Carreira, Santiago José. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Aviles Felix, Luis Steven. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Sirena, Martin. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Alejandro, Gabriela. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Steren, Laura Beatriz. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin