Finite size effects near the onset of the oscillatory instability

A system of two complex Ginzburg - Landau equations is considered that applies at the onset of the oscillatory instability in spatial domains whose size is large (but finite) in one direction; the dependent variables are the slowly modulated complex amplitudes of two counterpropagating wavetrains. In order to obtain a well posed problem, four boundary conditions must be imposed at the boundaries. Two of them were already known, and the other two are first derived in this paper. In the generic case when the group velocity is of order unity, the resulting problem has terms that are not of the same order of magnitude. This fact allows us to consider two distinguished limits and to derive two associated (simpler) sub-models, that are briefly discussed. Our results predict quite a rich variety of complex dynamics that is due to both the modulational instability and finite size effects

Meio de cultura para o enraizamento in vitro de Heliconia chartacea var. Sexy Pink.

A Heliconia chartacea var. Sexy Pink é uma planta ornamental tropical de grande interesse na floricultura brasileira, cuja micropropagação permite a obtenção de mudas em larga escala em espaço e tempo reduzidos. Com o objetivo de determinar a composição do meio de cultura para o enraizamento in vitro da H. chartacea var. Sexy Pink, brotações com 3–5 cm de altura foram cultivados em meio de cultura Murashige e Skoog(1962)com metade da concentração salina original (MS/2) suplementado com diferentes concentrações de sacarose (0; 15; 30; 45 e 60 g L-1). A ausência de uma fonte de açúcar não inibiu a formação de raízes, porém estas foram poucas e muito finas(0,6 raízes/planta). Quando a concentração de sacarose utilizada foi de 15 a 60 g L-1, a produção da biomassa da raiz foi maior, aumentando a possibilidade de sobrevivência na fase de aclimatizaçãocommédiasde2,7 raízes/planta(15 g L-1), 3,4 raízes/planta(30g L-1), 4 raízes/planta (45 g L-1), e a 60 g L-1(3,5 raízes/planta), porém as concentrações de 45 e 60 g L-1de sacarose apresentaram redução na massa seca das raízes(0,20 e 0,21 g/planta respectivamente), pois favoreceu a formação de raízes mais grossas e quebradiças, devido ao maior acúmulo de água nos tecidos. Não foram observadas diferenças significativas no número médio de raízes emitidas por explante nas diferentes concentrações de sacarose a exceção do tratamento controle, porém comparando-se o peso seco das raízes, pode-se afirmar que a adição de sacarose na concentração de 30 g L-1no meio MS/2, foi a que apresentou maior incremento de massa seca da raiz (0,23g/planta) comparado ao tratamento controle (0,38 g/planta). A concentração de 30 g L-1também conferiu um melhor desenvolvimento do sistema radicular com uma média de comprimento da maior raiz de 91 mm, a partir desta concentração, no entanto, houve a redução no comprimento, apresentando média de 82 mm a 45 g L-1e 72 mm a 60 g L-1 próxima a obtida a 15 g L-1(67 mm). Conclui-se que a adição de sacarose na concentração de 30 g L-1no meio MS/2foi a que apresentou maior incremento de massa, demonstrando ser esta concentração mais adequada para o enraizamento da Heliconia chartacea var. Sexy Pink nas condições testadas

Global well-posedness of the KP-I initial-value problem in the energy space

We prove that the KP-I initial value problem is globally well-posed in the natural energy space of the equation

Simulating Reionization: Character and Observability

In recent years there has been considerable progress in our understanding of the nature and properties of the reionization process. In particular, the numerical simulations of this epoch have made a qualitative leap forward, reaching sufficiently large scales to derive the characteristic scales of the reionization process and thus allowing for realistic observational predictions. Our group has recently performed the first such large-scale radiative transfer simulations of reionization, run on top of state-of-the-art simulations of early structure formation. This allowed us to make the first realistic observational predictions about the Epoch of Reionization based on detailed radiative transfer and structure formation simulations. We discuss the basic features of reionization derived from our simulations and some recent results on the observational implications for the high-redshift Ly-alpha sources.Comment: 3 pages, to appear in the Proceedings of First Stars III, Santa Fe, July 2007, AIP Conference Serie

Moduli potentials in string compactifications with fluxes: mapping the Discretuum

We find de Sitter and flat space solutions with all moduli stabilized in four dimensional supergravity theories derived from the heterotic and type II string theories, and explain how all the previously known obstacles to finding such solutions can be removed. Further, we argue that if the compact manifold allows a large enough space of discrete topological choices then it is possible to tune the parameters of the four dimensional supergravity such that a hierarchy is created and the solutions lie in the outer region of moduli space in which the compact volume is large in string units, the string coupling is weak, and string perturbation theory is valid. We show that at least two light chiral superfields are required for this scenario to work, however, one field is sufficient to obtain a minimum with an acceptably small and negative cosmological constant. We discuss cosmological issues of the scenario and the possible role of anthropic considerations in choosing the vacuum of the theory. We conclude that the most likely stable vacuua are in or near the central region of moduli space where string perturbation theory is not strictly valid, and that anthropic considerations cannot help much in choosing a vacuum.Comment: 34 pages, no figure

The Presence and Distribution of HI Absorbing Gas in Sub-galactic Sized Radio Sources

We consider the incidence of HI absorption in intrinsically small sub-galactic sized extragalactic sources selected from sources classified as Gigahertz Peaked Spectrum (GPS) and Compact Steep Spectrum (CSS) sources. We find that the smaller sources (<0.5 kpc) have larger HI column densities than the larger sources (>0.5 kpc). Both a spherical and an axi-symmetric gas distribution, with a radial power law density profile, can be used to explain this anti-correlation between projected linear size and HI column density. Since most detections occur in objects classified as galaxies, we argue that if the unified schemes apply to GPS/CSSs a disk distribution for the HI is more likely. The most favoured explanation for the compact sizes of the GPS/CSSs is that they are young sources evolving in a power law density medium. For the GPSs with measured expansion velocities, our derived densities are within an order of magnitude of those estimated from ram-pressure confinement of the lobes assuming equipartition. Our results therefore support the youth model.Comment: 12 pages, 8 figures, accepted for publication in A&

Coherent Single Charge Transport in Molecular-Scale Silicon Nanowire Transistors

We report low-temperature electrical transport studies of molecule-scale silicon nanowires. Individual nanowires exhibit well-defined Coulomb blockade oscillations characteristic of charge addition to a single nanostructure with length scales up to at least 400 nm. Further studies demonstrate coherent charge transport through discrete single particle quantum levels extending the whole device, and show that the ground state spin configuration follows the Lieb-Mattis theorem. In addition, depletion of the nanowires suggests that phase coherent single-dot characteristics are accessible in a regime where correlations are strong.Comment: 4 pages and 4 figure

Emergence of a new race of leaf rust with combined virulence to Lr14a and Lr72 genes on durum wheat

Leaf rust is a foliar disease caused by the fungus Puccinia triticina that may severely reduce durum wheat yield. Resistance to this pathogen is common in modern durum germplasm but is frequently based on Lr72 and Lr14a. After accounts of races with virulence to Lr14a gene in France in 2000, the present study reports the detection in 2013 for the first time of a new race with virulence to Lr14a and Lr72. The aim of this work was to characterize the virulence pattern of four Spanish isolates with virulence to Lr14a, and to discuss the consequences of this presence. Rusted leaves from cultivars ‘Don Jaime’ (Lr14a) and ‘Gallareta’ (Lr72) were collected in 2013 in the field at two Spanish sites, one in the south (near Cadiz) and another in the north (near Girona). Spores from single pustule for each cultivar and site were multiplied on susceptible cultivar ‘Don Rafael’. Then, the four isolates were inoculated on a set of 19 isogenic lines Thatcher to characterize their virulence spectrum. All isolates presented the same virulence pattern. They were virulent on both Lr14a and Lr72 and the race was named DBB/BS. This race was very similar to those reported in 2009-11, but with added virulence to Lr14a. The resistance based on Lr14a has therefore been overcome in Spain, by a new race that has likely emerged via stepwise mutation from the local predominating races. This information is important to guide breeders in their breeding programmes and gene deployment strategies

Scanned Probe Microscopy of Electronic Transport in Carbon Nanotubes

We use electrostatic force microscopy and scanned gate microscopy to probe the conducting properties of carbon nanotubes at room temperature. Multi-walled carbon nanotubes are shown to be diffusive conductors, while metallic single-walled carbon nanotubes are ballistic conductors over micron lengths. Semiconducting single-walled carbon nanotubes are shown to have a series of large barriers to conduction along their length. These measurements are also used to probe the contact resistance and locate breaks in carbon nanotube circuits.Comment: 4 page