Discrete-Time Fractional Variational Problems

We introduce a discrete-time fractional calculus of variations on the time scale $h\mathbb{Z}$, $h > 0$. First and second order necessary optimality conditions are established. Examples illustrating the use of the new Euler-Lagrange and Legendre type conditions are given. They show that solutions to the considered fractional problems become the classical discrete-time solutions when the fractional order of the discrete-derivatives are integer values, and that they converge to the fractional continuous-time solutions when $h$ tends to zero. Our Legendre type condition is useful to eliminate false candidates identified via the Euler-Lagrange fractional equation.Comment: Submitted 24/Nov/2009; Revised 16/Mar/2010; Accepted 3/May/2010; for publication in Signal Processing

Low level of virological failure and drug resistance among patients receiving antiretroviral treatment under programme conditions in Maputo, Mozambique

Mexico AIDS Conference 200

Modelling post-fire vegetation recovery in Portugal

Wildfires in Mediterranean Europe have been increasing in number and extension over the last decades and constitute one of the major disturbances of these ecosystems. Portugal is the country with more burnt area in the last decade and the years of 2003 and 2005 were particularly devastating, the total burned areas of 425 000 and 338 000 ha being several times higher than the corresponding average. The year of 2005 further coincided with one of the most severe droughts since early 20th century. Due to different responses of vegetation to diverse fire regimes and to the complexity of landscape structures, fires have complex effects on vegetation recovery. Remote sensing has revealed to be a powerful tool in studying vegetation dynamics and in monitoring post-fire vegetation recovery, which is crucial to land-management and to prevent erosion. <br><br> The main goals of the present work are (i) to assess the accuracy of a vegetation recovery model previously developed by the authors; (ii) to assess the model's performance, namely its sensitivity to initial conditions, to the temporal length of the input dataset and to missing data; (iii) to study vegetation recovery over two selected areas that were affected by two large wildfire events in the fire seasons of 2003 and 2005, respectively. <br><br> The study relies on monthly values of NDVI over 11 years (1998–2009), at 1 km × 1 km spatial resolution, as obtained by the VEGETATION instrument. According to results from sensitivity analysis, the model is robust and able to provide good estimations of recovery times of vegetation when the regeneration process is regular, even when missing data is present. In respect to the two selected burnt scars, results indicate that fire damage is a determinant factor of regeneration, as less damaged vegetation recovers more rapidly, which is mainly justified by the high coverage of <i>Pinus pinaster</i> over the area, and by the fact that coniferous forests tend to recover slower than transitional woodland-shrub, which tend to dominate the areas following the fire event

Resposta diferencial de genótipos de sorgo para tolerância ao alumínio em solução nutritiva.

Neste trabalho utilizou-se de uma tecnica de solucao nutritiva para identificar, dentre 391 linhagens de sorgo (BAG-Sorgo; 181), CNPMS: 71, SEPON/ICRISAT: 17 e Sacarino: 122, os genotipos que apresentam tolerancia ao aluminio. A avaliacao do comportamento diferencial dessas linhagens baseou-se no crescimento da raiz seminal primaria de plantas jovens de sorgo, em solucao nutritiva contendo niveis variados de Al (0,0, 2,25 e 4,5 mg de Al/1 para sorgo granifero e 0,0, 2,25 e 5,0 mg de Al/1 para sorgo sacarino). A caracteristica usada para a comparacao entre genotipos foi o Comprimento Relativo da Raiz Seminal (CRSS = CRS + AL/CRS - Al, onde CRS = comprimento da Raiz Seminal). Baseando-se na distribuicao percentual dos valores de CRRS obtidos para as diferentes linhagens e nos valores de CRRS encontrados para os materiais controles SC 298 (sensivel ao Al) e SC 283 (tolerante ao Al) tres classes de resposta ao aluminio foram definidas: Sensivel (CRRS 0,70). Dentre os materiais avaliados as seguintes linhagens apresentaram tolerancia aos niveis de 4,5 ou 5,0 mg de Al/1: IS 3625, IS 7173 C (SC 283), IS 12666, 5DX61/6/2, 3DX57/1/1910, 156-P-5-Serere-1, 9DX9/11, Brandes, MN 4004 e MN 1204

Drought impacts on vegetation in the pre- and post-fire events over Iberian Peninsula

The present work aims to study the combined effect of drought and large wildfires in the Iberian Peninsula relying on remotely sensed data of vegetation dynamics and leaf moisture content, in particular monthly NDVI, NDWI and NDDI time series from 1999–2009, derived from VEGETATION dataset. The impact of the exceptional 2004/2005 drought on vegetation was assessed for vegetation recovering from the extraordinary fire season of 2003 and on the conditions that contributed to the onsetting of the fire season of 2005. Drought severity was estimated by the cumulative negative effect on photosynthetic activity (NDVI) and vegetation dryness (NDDI), with about 2/3 of Iberian Peninsula presenting vegetative stress and low water availability conditions, in spring and early summer of 2005. Furthermore, NDDI has shown to be very useful to assess drought, since it combines information on vegetation and water conditions. Moreover, we show that besides looking at the inter-annual variability of NDVI and NDDI, it is useful to evaluate intra-annual changes (δNDVI and δNDDI), as indicators of change in vegetation greenness, allowing a detailed picture of the ability of the different land-cover types to resist to short-term dry conditions. In order to assess drought impact on post-fire regeneration, recovery times were evaluated by a mono-parametric model based on NDVI data and values corresponding to drought months were set to no value. Drought has shown to delay recovery times for several months in all the selected scars from 2003. The analysis of vegetation dynamics and fire selectivity in 2005 suggests that fires tended to occur in pixels presenting lower vegetative and water stress conditions during spring and early summer months. Additionally, pre-fire vegetation dynamics, in particular vegetation density and water availability during spring and early summer, has shown to influence significantly the levels of fire damage. These results stress the role of fuel availability in fire occurrence and impact on the Iberian Peninsula

Efeito de substratos e recipientes na aclimatização de goiabeiras Paluma multiplicadas in vitro.

O objetivo desse trabalho foi determinar oefeito de diferentes tipos de substratos e recipientes na aclimatização de goiabeira Paluma multiplicadas in vitro

The exponent of the non-abelian tensor square and related constructions of pp-groups

Let $G$ be a finite $p$-group. In this paper we obtain bounds for the exponent of the non-abelian tensor square $G \otimes G$ and of $\nu(G)$, which is a certain extension of $G \otimes G$ by $G \times G$. In particular, we bound $\exp(\nu(G))$ in terms of $\exp(\nu(G/N))$ and $\exp(N)$ when $G$ admits some specific normal subgroup $N$. We also establish bounds for $\exp(G \otimes G)$ in terms of $\exp(G)$ and either the nilpotency class or the coclass of the group $G$, improving some existing bounds