Carlos Fernandes

A method to overcome the limitations of G.O. in axis-symmetric dielectric lens shaping

The design of a cylindrically symmetric dielectric lens antenna is presented for the case of a very squeezed fan-beam. One makes use of geometrical optics (G.O.) to establish the profile of the lens in a first step. A half-integrated solution of Greens formula for bodies with cylindrical symmetry and circularly polarized surface fields is then derived to calculate the radiation pattern. Since the use of G.O. is restricted to some conditions which were observed unsatisfied in our study, a two-steps procedure to reach an acceptable lens shape is then presented. The first step is based on weighting the source beam of the antenna; and the second one is based on simple geometrical interpolation. Prototypes provided experimental results that are consistent with the predicted radiation characteristics and interesting features of such antennas are pointed out.

Tropical specialist vs. climate generalist: Diversification and demographic history of sister species of Carlia skinks from northwestern Australia

Species endemic to the tropical regions are expected to be vulnerable to future climate change due in part to their relatively narrow climatic niches. In addition, these species are more likely to have responded strongly to past climatic change, and this can be explored through phylogeographic analyses. To test the hypothesis that tropical specialists are more sensitive to climate change than climate generalists, we generated and analyse sequence data from mtDNA and ~2500 exons to compare scales of historical persistence and population fluctuation in two sister species of Australian rainbow skinks: the tropical specialist Carlia johnstonei and the climate generalist C. triacantha. We expect the tropical specialist species to have deeper and finer‐scale phylogeographic structure and stronger demographic fluctuations relative to the closely related climate generalist species, which should have had more stable populations through periods of harsh climate in the late Quaternary. Within C. johnstonei, we find that some populations from the northern Kimberley islands are highly divergent from mainland populations. In C. triacantha, one major clade occurs across the deserts and into the mesic Top End, and another occurs primarily in the Kimberley with scattered records eastwards. Where their ranges overlap in the Kimberley, both mitochondrial DNA and nuclear DNA suggest stronger phylogeographic structure and range expansion within the tropical specialist, whereas the climate generalist has minimal structuring and no evidence of recent past range expansion. These results are consistent with the hypothesis that tropical specialists are more sensitive to past climatic change.

Inferring Population Genetic Structure in Widely and Continuously Distributed Carnivores: The Stone Marten (Martes foina) as a Case Study

The stone marten is a widely distributed mustelid in the Palaearctic region that exhibits variable habitat preferences in different parts of its range. The species is a Holocene immigrant from southwest Asia which, according to fossil remains, followed the expansion of the Neolithic farming cultures into Europe and possibly colonized the Iberian Peninsula during the Early Neolithic (ca. 7,000 years BP). However, the population genetic structure and historical biogeography of this generalist carnivore remains essentially unknown. In this study we have combined mitochondrial DNA (mtDNA) sequencing (621 bp) and microsatellite genotyping (23 polymorphic markers) to infer the population genetic structure of the stone marten within the Iberian Peninsula. The mtDNA data revealed low haplotype and nucleotide diversities and a lack of phylogeographic structure, most likely due to a recent colonization of the Iberian Peninsula by a few mtDNA lineages during the Early Neolithic. The microsatellite data set was analysed with a) spatial and non-spatial Bayesian individual-based clustering (IBC) approaches (STRUCTURE, TESS, BAPS and GENELAND), and b) multivariate methods [discriminant analysis of principal components (DAPC) and spatial principal component analysis (sPCA)]. Additionally, because isolation by distance (IBD) is a common spatial genetic pattern in mobile and continuously distributed species and it may represent a challenge to the performance of the above methods, the microsatellite data set was tested for its presence. Overall, the genetic structure of the stone marten in the Iberian Peninsula was characterized by a NE-SW spatial pattern of IBD, and this may explain the observed disagreement between clustering solutions obtained by the different IBC methods. However, there was significant indication for contemporary genetic structuring, albeit weak, into at least three different subpopulations. The detected subdivision could be attributed to the influence of the rivers Ebro, Tagus and Guadiana, suggesting that main watercourses in the Iberian Peninsula may act as semi-permeable barriers to gene flow in stone martens. To our knowledge, this is the first phylogeographic and population genetic study of the species at a broad regional scale. We also wanted to make the case for the importance and benefits of using and comparing multiple different clustering and multivariate methods in spatial genetic analyses of mobile and continuously distributed species.

The genetic legacy of the 19th-century decline of the British polecat: evidence for extensive introgression from feral ferrets

In the 19th century, the British polecat suffered a demographic contraction, as a consequence of direct persecution, reaching its lowest population in the years that preceded the First World War. The polecat is now recovering and expanding throughout Britain, but introgressive hybridization with feral ferrets has been reported, which could be masking the true range of the polecat and introducing domestic genes into the species. We used a fragment of the mitochondrial DNA control region and 11 microsatellite loci to characterize the frequency and extent of hybridization and introgression between the two species and assess whether the 19th‐century decline corresponded to a genetic bottleneck in the polecat. The proportion of admixture detected in the wild was high (31%) and hybrids were more frequently found outside Wales, suggesting that hybridization is more likely to occur along the eastern edge of the polecats range expansion. The patterns observed in the mitochondrial and nuclear DNA data show that introgression was mediated by crosses between male polecats and female ferrets, whose offspring backcrossed with polecats. No first‐generation (F1) hybrids were identified, and the broad range of observed admixture proportions agrees with a scenario of past extensive hybridization between the two species. Using several different methods to investigate demographic history, we did not find consistent evidence for a genetic bottleneck in the British polecat, a result that could be interpreted as a consequence of hybridization with ferrets. Our results highlight the importance of the Welsh polecat population for the conservation and restoration of the genetic identity of the British polecat.

Designing a Self-Organized Approach for Scheduling Bag-of-Tasks

This paper proposes a decentralized and self-organized agent system for dynamically load-balancing tasks arriving in the form of Bags-of-Tasks (BoTs) in large-scale decentralized systems. the approach is inspired by the emergent behavior of the sand pile model, a cellular automaton behaving at the edge of chaos. Depending on the state of the cellular automaton, rather different responses may occur when a new task is assigned to a resource. It may change nothing or generate avalanches that reconfigure the state of the system. the proportion between the abundance of avalanches and their sizes shows a power-law relation, a scale-invariant behavior that does not need to be tuned. That means that large - catastrophic - avalanches are very rare but small ones occur very often. Such a smart and emergent behavior fits well with the idea of non-clairvoyant scheduling, where tasks are load balanced into computing resources trying to maximize the performance but without assuming any knowledge on the tasks features. In order to study the viability of the approach, we have conducted an empirical experimentation which shows that the sand pile is able to find near-optimal schedules by reacting differently to different conditions of workloads and architectures.

Taxonomic status and origin of the Egyptian weasel (Mustela subpalmata) inferred from mitochondrial DNA

Abstract The Egyptian weasel (Mustela subpalmata) is a small mustelid with a distribution restricted to the lower Nile Valley and the Nile Delta. Traditionally considered a subspecies of the least weasel (M. nivalis), it is currently recognized as a separate species based on morphology. Here we present the first genetic assessment of the taxonomic status of the Egyptian weasel by comparing mitochondrial DNA (Cytochrome b gene and control region) sequences to those of least weasels from the western Palearctic, with a focus on the Mediterranean region. Our results provide no evidence to support the view that the Egyptian weasel is genetically distinct from the least weasel, as we found that, for both Cytochrome b and control region, haplotypes were shared between the two taxa. Specifically, the Cytochrome b and control region haplotypes detected in the Egyptian weasel were also present in M. nivalis from Turkey and Malta, two populations genetically analysed here for the first time. Our results suggest that the Egyptian weasel is distinct from the least weasel populations currently living in the Maghreb, which were inferred to be the result of an earlier colonization of North Africa, but the genetic data alone do not allow us to determine whether the Egyptian weasel is native or introduced. Nevertheless, the observed genetic patterns, together with the weasel fossil record in Israel and the unique commensal lifestyle of the Egyptian weasel, are consistent with the hypothesis that the Egyptian population is a relict of past range expansion from the Levant into Egypt. We suggest that the large size and characteristic sexual dimorphism of the Egyptian weasel are likely to represent ecotypic variation, but genomic studies are required to clarify the extent of its functional genetic divergence.

Aging of solar PV plants and mitigation of their consequences

Photovoltaic solar fields are planned to operate during many years, so the monitoring of the plant parameters and performances undoubtedly represents an adequate way to ensure a safe and long term operation for the overall system. Values around 10%/year of photovoltaic system degradation in 1991 fall to 12% in 25 years in PV panels using modules manufactured after 2000, mainly due the recent technology advances seen in the field of renewable. Obviously, these results require that system operation should follow an adequate maintenance. In this work, the main failures in the most critical components of conventional PV solar plants are described and ways to mitigate them are recommended, in order to achieve a reduction of unexpected overthrow occurrences. The photos presented were taken in solar PV plants located in Portugal.

Validation of a Simulation Model for Analysis of Shading Effects on Photovoltaic Panels

Numerical simulation results and modeling on the electrical features of concentrating photovoltaic-thermal (PVT) using the free circuit simulation package from linear technology corporation (LTSPIC ...

IEEE Transactions on Antennas and Propagation Announces a Special Issue on “Antennas and Propagation at mm- and sub mm-waves”

Millimeter and sub-millimeter waves have been the focus of intensive research activities over the past several years. Application of these technologies has advanced beyond traditional high-cost niche uses - mostly related to radio astronomy and space applications - to embrace widespread new consumer applications, some of which show significant market potential. Increased opportunity to exploit these bands is in part created by the spectrum availability that enables extremely high data rates and the inherent miniaturizability of the radio front-ends. This naturally drives concomitant advancements in semiconductor technology at mm-waves and sub-millimeter waves that lower technology deployment cost and make it affordable for applications such as home multi-gigabit wireless systems, active and passive high resolution imaging for medical diagnostic or civil security applications, automotive radar, and body-area networks.

Improvements on Corrugation Pitch Modulated Distributed Coupling Coefficient Distributed Feedback laser structures for single longitudinal mode operation

Optical communication systems depend heavily on the performance of the light emitter, usually a Distributed Feedback (DFB) laser. This paper presents optimised Corrugation-Pitch-Modulated (CPM) Distributed-Coupling-Coefficient (DCC) DFB laser structures specially designed for single longitudinal mode operation. The optimisation process is described and divided into two stages: near and above threshold. Near threshold, the purpose is the simultaneous maximisation of the normalised mode selectivity (S) and the minimisation of the electric field flatness (F). Above threshold, the power emission spectrum is assessed, as well as the Side Mode Suppression Ratio (SMSR). For the CPM-3DCC-DFB, S ≈ 2.54 , F ≈ 0.019 and SMSR ≥ 48dB are achieved, which clearly outperforms similar laser structures proposed elsewhere.