Search results for "Matematica"
showing 10 items of 1637 documents
A note on modified Gabor frames
2001
In this paper we generalize a procedure, originally proposed by Kaiser, which produces a family of (A, B)-frames in ℒ2(R), starting from a given Gabor (A, B)-frame. The procedure is applied to several examples. © Società Italiana di Fisica.
Conjunction of Conditional Events and t-Norms
2019
We study the relationship between a notion of conjunction among conditional events, introduced in recent papers, and the notion of Frank t-norm. By examining different cases, in the setting of coherence, we show each time that the conjunction coincides with a suitable Frank t-norm. In particular, the conjunction may coincide with the Product t-norm, the Minimum t-norm, and Lukasiewicz t-norm. We show by a counterexample, that the prevision assessments obtained by Lukasiewicz t-norm may be not coherent. Then, we give some conditions of coherence when using Lukasiewicz t-norm
Triangular norms and conjunction of conditional events
2019
We study the relationship between a notion of conjunction among conditional events, introduced in recent papers, and the notion of Frank t-norm. By examining different cases, in the setting of coherence, we show each time that the conjunction coincides with a suitable Frank t-norm. In particular, the conjunction may coincide with the Product t-norm, the Minimum t- norm, and Lukasiewicz t-norm. We show by a counterexample, that the prevision assessments obtained by Lukasiewicz t-norm may be not coherent. Then, we give some conditions of coherence when using Lukasiewicz t-norm.
Analysis of Fresnel Zone Plates Focusing Dependence on Operating Frequency
2017
[EN] The focusing properties of Fresnel Zone Plates (FZPs) against frequency are analyzed in this work. It is shown that the FZP focal length depends almost linearly on the operating frequency. Focal depth and focal distortion are also considered, establishing a limit on the frequency span at which the operating frequency can be shifted. An underwater FZP ultrasound focusing system is demonstrated, and experimental results agree with the theoretical analysis and simulations.
Pinhole Zone Plate Lens for Ultrasound Focusing
2017
[EN] The focusing capabilities of a pinhole zone plate lens are presented and compared with those of a conventional Fresnel zone plate lens. The focusing properties are examined both experimentally and numerically. The results confirm that a pinhole zone plate lens can be an alternative to a Fresnel lens. A smooth filtering effect is created in pinhole zone plate lenses, giving rise to a reduction of the side lobes around the principal focus associated with the conventional Fresnel zone plate lens. The manufacturing technique of the pinhole zone plate lens allows the designing and constructing of lenses for different focal lengths quickly and economically and without the need to drill new p…
Locally convex quasi *-algebras with sufficiently many *-representations
2012
AbstractThe main aim of this paper is the investigation of conditions under which a locally convex quasi ⁎-algebra (A[τ],A0) attains sufficiently many (τ,tw)-continuous ⁎-representations in L†(D,H), to separate its points. Having achieved this, a usual notion of bounded elements on A[τ] rises. On the other hand, a natural order exists on (A[τ],A0) related to the topology τ, that also leads to a kind of bounded elements, which we call “order bounded”. What is important is that under certain conditions the latter notion of boundedness coincides with the usual one. Several nice properties of order bounded elements are extracted that enrich the structure of locally convex quasi ⁎-algebras.
Fuzziness in Italy – Traces of a scattered history
2017
The history of Fuzziness in Italy is varied and scattered among a num- ber of research groups. As a matter of fact, “fuzziness” spread in Italy through a sort of spontaneous diffusion, and, also subsequently, no one felt the need to cre- ate some “national” common structure like an Association or similar things. Since a cohesive retelling would be next to impossible, a few members of the Italian fuzzy community have been asked to recount their experience and express their hopes for the future.
Fuzzy fixed points of generalized F2-geraghty type fuzzy mappings and complementary results
2016
The aim of this paper is to introduce generalized F2-Geraghty type fuzzy mappings on a metric space for establishing the existence of fuzzy fixed points of such mappings. As an application of our result, we obtain the existence of common fuzzy fixed point for a generalized F2-Geraghty type fuzzy hybrid pair. These results unify, generalize and complement various known comparable results in the literature. An example and an application to theoretical computer science are presented to support the theory proved herein. Also, to suggest further research on fuzzy mappings, a Feng–Liu type theorem is proved.
Some new fixed point theorems in fuzzy metric spaces
2014
Motivated by Samet et al. [Nonlinear Anal., 75(4) (2012), 2154-2165], we introduce the notions of alpha-phi -fuzzy contractive mapping and beta-psi-fuzzy contractive mapping and prove two theorems which ensure the existence and uniqueness of a fixed point for these two types of mappings. The presented theorems extend, generalize and improve the corresponding results given in the literature.
Common fixed point theorems in fuzzy metric spaces employing CLR_{S} and JCLR_{ST} properties
2014
In this paper, we utilize the $CLR_{S}$ and $JCLR_{ST}$ properties to prove some existence theorems of common fixed point for contractive mappings in fuzzy metric spaces. Our results generalize and extend many known results from the literature. An example and some applications are given to show the usability of the presented results.