11,062 research outputs found
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-GaAlAs) 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
Transport in random quantum dot superlattices
We present a novel model to calculate single-electron states in random
quantum dot superlattices made of wide-gap semiconductors. The source of
disorder comes from the random arrangement of the quantum dots (configurational
disorder) as well as spatial inhomogeneities of their shape (morphological
disorder). Both types of disorder break translational symmetry and prevent the
formation of minibands, as occurs in regimented arrays of quantum dots. The
model correctly describes channel mixing and broadening of allowed energy bands
due to elastic scattering by disorder
Symmetry-Induced Tunnelling in One-Dimensional Disordered Potentials
A new mechanism of tunnelling at macroscopic distances is proposed for a wave
packet localized in one-dimensional disordered potential with mirror symmetry,
V(-x)=V(x). Unlike quantum tunnelling through a regular potential barrier,
which occurs only at the energies lower then the barrier height, the proposed
mechanism of tunnelling exists even for weak white-noise-like scattering
potentials. It also exists in classical circuits of resonant contours with
random resonant frequencies. The latter property may be used as a new method of
secure communication, which does not require coding and decoding of the
transmitting signal.Comment: 10 pages, 4 figure
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
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