Nonlinear dynamics in superlattices driven by high frequency ac-fields

We investigate the dynamical processes taking place in nanodevices driven by high-frequency electromagnetic fields. We want to elucidate the role of different mechanisms that could lead to loss of quantum coherence. Our results show how the dephasing effects of disorder that destroy after some periods coherent oscillations, such as Rabi oscillations, can be overestimated if we do not consider the electron-electron interactions that can reduce dramatically the decoherence effects of the structural imperfections. Experimental conditions for the observation of the predicted effects are discussed.Comment: REVTEX (8 pages) and 4 figures (Postscript

Intentionally disordered superlattices with high dc conductance

We study disordered quantum-well-based semiconductor superlattices where the disorder is intentional and short-range correlated. Such systems consist of quantum-wells of two different thicknesses randomly distributed along the growth direction, with the additional constraint that wells of one kind always appears in pairs. Imperfections due to interface roughness are considered by allowing the quantum-well thicknesses to fluctuate around their {\em ideal} values. As particular examples, we consider wide-gap (GaAs-Ga$_{1-x}$Al$_{x}$As) and narrow-gap (InAs-GaSb) superlattices. We show the existence of a band of extended states in perfect correlated disordered superlattices, giving rise to a strong enhancement of their finite-temperature dc conductance as compared to usual random ones whenever the Fermi level matches this band. This feature is seen to survive even if interface roughness is taken into account. Our predictions can be used to demonstrate experimentally that structural correlations inhibit the localization effects of disorder, even in the presence of imperfections. This effect might be the basis of new, filter-like or other specific-purpose electronic devices.Comment: REVTeX 3.0, 20 pages, 7 uuencoded compressed PostScript figures as a separate file. Submitted to IEEE J Quantum Elec

Population dynamics of phyllocnistis citrella (Lepidoptera: Gracillariidae) and its parasitoids in Tafí Viejo, Tucumán, Argentina

Seasonal abundance of the citrus leafminer, Phyllocnistis citrella Stainton (Lepidoptera: Gracillariidae), was investigated between Nov 1999 and Apr 2003 in Tafí Viejo (Tucuman province). Phyllocnistis citrella populations increased during spring and summer, declined during fall, and disappeared in the winter. Five species of parasitoids, one exotic and four indigenous, attacked citrus leafminer immature stages in commercial and experimental lemon orchards. Ageniaspis citricola Logvinovskaya (Hymenoptera: Encyrtidae) was the most abundant parasitoid. Cirrospilus neotropicus Diez & Fidalgo (Hymenoptera: Eulophidae) was the most abundant indigenous species, followed by Galeopsomyia fausta LaSalle (Hymenoptera: Eulophidae). The other indigenous species were not common and were only occasionally collected from citrus leafminer larvae. Parasitoids and P. citrella exhibited similar population fluctuations throughout the entire sampling period. A certain degree of synchrony exists between the most abundant parasitoids (A. citricola, C. neotropicus, and G. fausta) and the pest. The highest rates of parasitism were observed in the fall. Ageniaspis citricola exhibited approximately 29.5% parasitism, whereas all the native species together were only 8.2%. Data showed that a clear dependence existed between percentages of parasitism and citrus leafminer population density for the most frequent parasitoid populations. The results of this study show that C. neotropicus has an important role among the native species present in Argentina.Fil: Diez, Patricia Alejandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Universidad Nacional de La Rioja. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Universidad Nacional de Catamarca. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Secretaría de Industria y Minería. Servicio Geológico Minero Argentino. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Provincia de La Rioja. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja; ArgentinaFil: Peña, Jorge E.. University of Florida; Estados UnidosFil: Fidalgo, Patricio. University of Florida; Estados Unido

Using green vaccination to brighten the agronomic future

Crop plants host a variety of pests and diseases that can ultimately reduce agricultural productivity. Current methods of pest and disease control depend largely on pesticides. However, the use of chemicals alone is increasingly regarded as unsustainable due to the development of resistance and the introduction of stricter European regulation. There is a need, therefore, to reduce their use and to pursue the development of new Integrated Pest (and disease) Management (IPM) strategies. Research that focuses on the role that the plant’s immune system can play against these biological threats provides another potential source for future IPM strategies. Plants have sophisticated ways to defend themselves effectively and some stimuli can augment their innate immune capacity to resist future diseases. This phenomenon is known as priming of defence. Studies, mainly in the model plant Arabidopsis thaliana, have unravelled the molecular and physiological mechanisms of this apparent plant ‘vaccination’. This article describes recent findings and provides the ingredients for the “right formulation” in order to integrate green vaccination as a tool for the second green revolution

Critical point for the CAF-F phase transition at charge neutrality in bilayer graphene

We report on magneto-transport measurements up to 30 T performed on a bilayer graphene Hall bar, enclosed by two thin hexagonal boron nitride flakes. Our high mobility sample exhibits an insulating state at neutrality point which evolves into a metallic phase when a strong in-plane field is applied, as expected for a transition from a canted antiferromagnetic to a ferromagnetic spin ordered phase. For the first time we individuate a temperature-independent crossing in the four-terminal resistance as a function of the total magnetic field, corresponding to the critical point of the transition. We show that the critical field scales linearly with the perpendicular component of the field, as expected from the underlying competition between the Zeeman energy and interaction-induced anisotropies. A clear scaling of the resistance is also found and an universal behavior is proposed in the vicinity of the transition

La escritura cinematográfica y el leitmotiv

El artículo defiende la hipótesis de que los símbolos no se han apagado, pues el relato en su forma más actual y más consumida, las películas, contiene imágenes supeditas a un contenido simbólico. Un ejemplo de ello es lo que, desde la teoría del guión, se conoce como “leitmotiv”: un elemento visual y/ o sonoro escogido por el autor(es) para expresa de forma figurada el tema y, por lo tanto, el sentido autorial del filme. El artículo define este elemento retórico, a menudo conectado con ciertos arquetipos, y lo ejemplifica en películas como El séptimo sello (Det sjunde inseglet, 1956), El milagro de Ana Sullivan (The miracle worker, 1962), El último tango en París (Ultimo tango a Parigi, 1972) y Blade Runner (1982 y 1993). The symbols continue in their more current and more consumed form, the movies. The cinema contains images you subordinate to a symbolic content. An example is it that, from the theory of the script, we call the “leitmotiv”. It is a visual and sound element chosen by the author for expressed in a figured way the topic and, therefore, the sense autorial of the film. The article defines this rhetorical element, often connected with certain archetypes, and it exemplifies it in movies like Det sjunde inseglet (1956), The miracle worker (1962), Ultimo tango a Parigi (1972) and Blade Runner (1982 y 1993)