274 research outputs found
A hybrid spectral/spatial method to evaluate the active Green's function of large planar rectangular arrays: a combined asymptotic/numerical algorithm
No full textThe article illustrates a formulation to evaluate the array Green's function (AGF) of large finite planar phased array for observation points on the array plane, possibly close to the array contour. The procedure is based on the AGF representation in terms of a double spectral integral, whose integration paths are properly deformed to have an exponential attenuation of the integrand. The diffraction integral is evaluated numerically for point close to the array edges while an asymptotic treatment is proposed far from the edges. This latter comprises higher order contributions. Thanks to the convergence properties, the final algorithm is numerically accurate, stable and more efficient with respect to the individual element summation for large arrays. It also constitutes the basic step for the efficient evaluation of the AGF of a multilayer environment
Truncated Floquet wave full-wave analysis of large phased arrays of open-ended waveguides with a nonuniform amplitude excitation
No full textRecently, an efficient hybrid asymptotic-method of
moments (MoM) approach has been proposed for the analysis of
large periodic planar arrays of elements excited with equal amplitude
and linear phase. The aforementioned method, which is based
on a Floquet wave diffraction representation of the array Green’s
function (AGF), is here extended to treat arrays with tapered amplitude
excitation. To this end, the asymptotic AGF is refined by
introducing additional “slope” diffraction contributions. An appropriate
“fringe” integral equation, solved via a MoM scheme,
provides the effects of array truncation in addition to the infinite
array solution. The dimension of the corresponding linear algebraic
system is independent of the number of elements of the array.
Numerical results are provided to prove the accuracy and the efficiency
of this method with respect to an ordinary element-by-element
MoM
T(FW)2 analysis of large arrays of open ended waveguides with a global tapered excitation
No full textThe Truncated Floquet Wave Full-Wave (T(FW)2) analysis is generalized to large arrays with a tapered amplitude excitation. Numerical results are given to demonstrate the extreme accuracy and the numerical efficiency of the technique
A glimpse into the past : phylogenesis and protein domain analysis of the group XIV of C-type lectins in vertebrates
No full textBackground The group XIV of C-type lectin domain-containing proteins (CTLDcps) is one of the seventeen groups of CTLDcps discovered in mammals and composed by four members: CD93, Clec14A, CD248 and Thrombomodulin, which have shown to be important players in cancer and vascular biology. Although these proteins belong to the same family, their phylogenetic relationship has never been dissected. To resolve their evolution and characterize their protein domain composition we investigated CTLDcp genes in gnathostomes and cyclostomes and, by means of phylogenetic approaches as well as synteny analyses, we inferred an evolutionary scheme that attempts to unravel their evolution in modern vertebrates. Results Here, we evidenced the paralogy of the group XIV of CTLDcps in gnathostomes and discovered that a gene loss of CD248 and Clec14A occurred in different vertebrate groups, with CD248 being lost due to chromosome disruption in birds, while Clec14A loss in monotremes and marsupials did not involve chromosome rearrangements. Moreover, employing genome annotations of different lampreys as well as one hagfish species, we investigated the origin and evolution of modern group XIV of CTLDcps. Furthermore, we carefully retrieved and annotated gnathostome CTLDcp domains, pointed out important differences in domain composition between gnathostome classes, and assessed codon substitution rate of each domain by analyzing nonsynonymous (Ka) over synonymous (Ks) substitutions using one representative species per gnathostome order. Conclusions CTLDcps appeared with the advent of early vertebrates after a whole genome duplication followed by a sporadic tandem duplication. These duplication events gave rise to three CTLDcps in the ancestral vertebrate that underwent further duplications caused by the independent polyploidizations that characterized the evolution of cyclostomes and gnathostomes. Importantly, our analyses of CTLDcps in gnathostomes revealed critical inter-class differences in both extracellular and intracellular domains, which might help the interpretation of experimental results and the understanding of differences between animal models
Una tecnica ibrida asintotica-metodo dei momenti per l’analisi di antenne a schiera di grandi dimensioni
No full text
NGS applications to understand invertebrate biodiversity of Antarctica and mechanisms of gene expression involved in climatic changes
No full textHuman activities, such as greenhouse emissions and pollution, are leading to global warming, environmental changes and biodiversity reduction. Pristine environments such as those of Antarctica are not immune to these phenomena, as is noticeable from the temperature shifts and ice-melting registered within the continent in recent decades. To date, many scientists focused on how marine species react to these changes but no molecular data are currently available for continental terrestrial invertebrates and in particular for Collembola (=springtails). Therefore, part of my PhD project was to study the transcriptomic response of the endemic Antarctic springtail Cryptopygus terranovus following a mid-term exposure of 20 days at 18°C. Expression data were compared with wild specimens sampled in native environment. Although individual plasticity in transcript modulation was recorded, several pathways appear to be differentially modulated: protein catabolism, fatty acid metabolism and a sexual response characterized by spermatid development were induced, while lipid catabolism was downregulated in treated samples. Moreover, the temperature experienced by these micro-invertebrates is a pivotal parameter to understand these animals' ecology and physiology. However, at present, detailed knowledge of microhabitat physical conditions in Antarctica is limited and biased towards sub-Antarctic and maritime Antarctic regions. To better understand these temperature conditions, it was analysed a year-round temperature data in ponds and soils in an area of the Victoria Land coast, comparing these measurements with air temperatures from the closest automatic weather station. Important difference in temperature dynamics between the air, soil and pond datasets was registered. Ponds were the warmest sites overall, mostly differing with the air temperatures due to their greater thermal capacity, which also influenced their patterns of freeze-thaw cycles and mean daily thermal excursion.
Furthermore, to better understand the biodiversity of Collembola two new mitochondrial genomes of Antarctic springtails were sequenced and analysed. They were employed to revise the entire systematic of the class, its nucleotide composition and genome arrangement by comparing them to all the available sequences deposited in Genbank. In the phylogenetic analysis, with minor exceptions, it was confirmed the monophyly of Poduromorpha and Symphypleona sensu stricto (the latter recovered as the most basal group in the springtail phylogenetic tree), whereas monophyly of Neelipleona and Entomobryomorpha was only supported when some critical taxa in these two lineages were excluded. The genome arrangement review allowed to identify four new gene orders (one from the newly sequenced Tullbergia mixta), for a total of 16 models. Finally, nucleotide composition analyses confirmed the low AT bias in Collembola mitochondrial DNA respect to other Hexapoda, and that third codon position is inclined to mutation accumulation, especially in 4-fold amino-amino acids. To ease the process of mitochondrial genome analyses, it was created a web resource named EZmito, a free web server useful to analyse mitochondrial genomes. It is composed of five main tools: (i) EZsplit, useful to download and format sequences directly from the NCBI database; (ii) EZpipe, a pipeline designed to format mitochondrial sequences before the phylogenetic analysis; (iii) EZskew, which helps users to calculate nucleotide biases; (iv) EZcodon, a fast tool which calculates the Relative Synonym Codon Usage of different mtDNA species and (v) EZmix, which recognizes areas of inter molecular similarity indicative of the assembly of chimeric mitochondrial genomes. Interestingly, to date, the most used tool within the hub is EZcodon, followed by EZsplit and EZpipe
A Pole-zero matching method for EBG surfaces composed of a dipole FSS printed on a grounded dielectric slab
No full textA method is presented, for the efficient derivation of the dispersion equation associated with electromagnetic bandgap (EBG) structures composed by loss-less frequency selective surfaces (FSS) printed on stratified dielectric media. The method, valid for the range of frequency where a single propagating Floquet mode occurs, is based on Foster's reactance theorem applied to an equivalent transmission line network. This theorem implies that the admittance functions of frequency which represent the FSS satisfy the pole-zero analytical properties of the driving point LC admittance functions. By these basic properties and by the full-wave identification of the FSS resonances, an analytical form of the dispersion equation is obtained. This equation is next solved for both surface wave and leaky wave modes by a conventional numerical technique. The results are successfully compared with those from a full-wave analysis
A compact formula for the array factor of planar phased arrays with polygonal shape and skewed grid
No full textIn this paper, we present a compact formula for the computation of the array factor (AF) of uniformly excited planar periodic arrays with an arbitrary polygonal contour and a skewed grid. The formulation is based on a simple decomposition of the array as a superposition of infinite angular-sector arrays, whose far field is evaluated in exact closed form. The final result is an exact representation of the AF in terms of contributions from the vertices of the polygonal rim of the array
A pole matching method for the analysis of frequency selective surfaces
No full textIn this work, a pole matching method is presented for the analytical reconstruction, from full-wave data, of the scattering properties of frequency selective surfaces (FSS). This method allows one to synthesize the scattering response of an FSS from the identification of a few parameters, which exhibits a weak dependence with respect to the angle of incidence. This property implies that the full-wave analysis of the FSS can be performed for a limited set of incidence directions, from which the overall response can be obtained by a simple and numerically efficient algorithm. The final outcome is an analytical form for the scattering matrix which may be conveniently used in ray-tracing algorithms, based on local flat-surface approximations of curved FSS
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