6,858 research outputs found
On the refinement matrix mask of interpolating Hermite splines
No full textWe propose a new computational approach for constructing the refinement matrix mask of interpolating Hermite splines of any order and with general dilation factor. Our strategy exploits the refinability properties of cardinal B-splines with simple knots and simplifies the constructive procedures proposed so far
Dual univariate interpolatory subdivision of every arity: Algebraic characterization and construction
No full textA new class of univariate stationary interpolatory subdivision schemes of dual type is presented. As opposed to classical primal interpolatory schemes, these new schemes have masks with an even number of elements and are not step-wise interpolants. A complete algebraic characterization, which covers every arity, is given in terms of identities of trigonometric polynomials associated to the schemes. This characterization is based on a necessary condition for refinable functions to have prescribed values at the nodes of a uniform lattice, as a consequence of the Poisson summation formula. A strategy for the construction is then showed, alongside meaningful examples for applications that have comparable or even superior properties, in terms of regularity, length of the support and/or polynomial reproduction, with respect to the primal counterparts
Construction and Evaluation of Pythagorean Hodograph Curves in Exponential-Polynomial Spaces
No full textIn the past few decades polynomial curves with Pythagorean hodograph (PH curves) have received considerable attention due to their usefulness in various CAD/CAM areas, manufacturing, numerical control machining, and robotics. This work deals with classes of PH curves built upon exponential-polynomial spaces (EPH curves). In particular, for the two most frequently encountered exponential-polynomial spaces, we first provide necessary and sufficient conditions to be satisfied by the control polygon of the Bézier-like curve in order to fulfill the PH property. Then, for such EPH curves, fundamental characteristics like parametric speed or arc length are discussed to show the interesting analogies with their well-known polynomial counterparts. Differences and advantages with respect to ordinary PH curves become commendable when discussing the solutions to application problems like the interpolation of first-order Hermite data. Finally, a new evaluation algorithm for EPH curves is proposed and shown to compare favorably with the celebrated de Casteljau--like algorithm and two recently proposed methods: Woźny and Chudy's algorithm and the dynamic evaluation procedure by Yang and Hong
Optimized dual interpolating subdivision schemes
No full textThis work investigates the non-stepwise interpolation property of the recently introduced class of dual interpolating subdivision schemes, and the “loss of memory” phenomenon that comes with it. New differences between schemes having an odd and an even dilation factors are highlighted. In particular, dual interpolating schemes having an odd dilation factor are proven to satisfy a 2-step interpolation property, while an even dilation factor corresponds to a completely non-stepwise interpolation process. These facts are exploited to define an optimized non-uniform level dependent implementation of dual interpolating schemes in order to overcome the computational drawback due to the “loss of memory”
Bezout-like polynomial equations associated with dual univariate interpolating subdivision schemes
No full textThe algebraic characterization of dual univariate interpolating subdivision schemes is investigated. Specifically, we provide a constructive approach for finding dual univariate interpolating subdivision schemes based on the solutions of certain associated
polynomial equations. The proposed approach also makes it possible to identify conditions for the existence of the sought schemes
New algebraic and geometric characterizations of planar quintic Pythagorean-hodograph curves
No full textThe aim of this work is to provide new characterizations of planar quintic Pythagorean-hodograph curves. The first two are algebraic and consist of two and three equations, respectively, in terms of the edges of the Bézier control polygon as complex numbers. These equations are symmetric with respect to the edge indices and cover curves with generic as well as degenerate control polygons. The last two characterizations are geometric and rely both on just two auxiliary points outside the control polygon. One requires two (possibly degenerate) quadrilaterals to be similar, and the other highlights two families of three similar triangles. All characterizations are a step forward with respect to the state of the art, and they can be linked to the well-established counterparts for planar cubic Pythagorean-hodograph curves. The key ingredient for proving the aforementioned results is a novel general expression for the hodograph of the curve
[Poesia] Três poemas de Alberto Secama
No full textThree poems by Alberto Secama. About the author: Alberto Secama is an Angolan poet who has poems published on many websites and on facebook:https://www.facebook.com/Xungurra/abouthttp://www.pordentrodaafrica.com/cultura/africa-em-verso-rio-kwanza-por-alberto-secamahttp://www.pordentrodaafrica.com/cultura/africa-em-verso-zong-por-alberto-secamahttp://www.pordentrodaafrica.com/cultura/coluna-africa-em-verso-o-sol-la-fora-por-alberto-secamaTres poemas de Alberto Secama. Sobre el autor: Alberto Secama es un poeta angoleño que tiene poemas publicados en varios sitios y en el facebook:https://www.facebook.com/Xungurra/abouthttp://www.pordentrodaafrica.com/cultura/africa-em-verso-rio-kwanza-por-alberto-secamahttp://www.pordentrodaafrica.com/cultura/africa-em-verso-zong-por-alberto-secamahttp://www.pordentrodaafrica.com/cultura/coluna-africa-em-verso-o-sol-la-fora-por-alberto-secamaTrês poemas de Alberto Secama. Sobre o autor: Alberto Secama é um poeta angolano que possui poemas publicados em vários sites e no facebook:https://www.facebook.com/Xungurra/abouthttp://www.pordentrodaafrica.com/cultura/africa-em-verso-rio-kwanza-por-alberto-secamahttp://www.pordentrodaafrica.com/cultura/africa-em-verso-zong-por-alberto-secamahttp://www.pordentrodaafrica.com/cultura/coluna-africa-em-verso-o-sol-la-fora-por-alberto-secam
Does a marginal contact with a native species living in a complex domain with a fractional dimension boundary represent a sufficient invasive mechanism for the establishment of a migrating population?
No full textAnimal migrations are dynamic phenomena that can change rapidly or even be lost entirely over time. In particular, when a migrant population finds favorable conditions in a region, it can settle there permanently. Since biological invasions represent a serious threat to biodiversity, we are interested in determining if and when a marginal contact of a moving population with a territory occupied by other populations is sufficient to trigger an invasion mechanism. The interaction problem of a migrant population with a residential one is considered, where the contact occurs just on the boundary of the region occupied by the native population. To study whether and how the migrants induce changes in the ecosystem subject to their transit, two models are considered. The former accounts only for damage on the native species, with no gain for the migrant population. In the second one, migrants are assumed to be predators and therefore gaining an advantage for survivability. The comparison of the two models’ behaviors gives insights on the invasion process. The theoretical analysis of the two models is complemented by numerical simulations. The models suggest that, even without a direct benefit for the migratory population, these kinds of interactions can have serious ecological consequences for the native population that can even lead to its extinction. Comparing the results, it is instead found that if the migrating species is a predator, even this very reduced interaction on the boundary is enough to trigger invasion and migrants permanently settle in the territory
Orizzonti mantovani. Spunti e dinamiche paesaggistiche ne L'Illustrissimo di Alberto Cantoni
No full textIn the literary production of Alberto Cantoni, short story writer and novelist between the nineteenth and twentieth centuries, the novel L'Illustrissimo is highly important both because it is the last publication of the author, from Pomponesco, a small town a few kilometers south of Mantua, both because it summarizes in a single text the different nuances and different directions that his writing has taken over the course of his literary career, also due to a writing and processing time that embraces the entire span of years of his career itself. In the foreground, in addition to the numerous and brilliant characters, one of the protagonists is the Mantuan landscape which, not a simple background, becomes a true literary parameter which in different and significant ways affects the purposes and mechanisms of the novel
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