Página 1 dos resultados de 1136 itens digitais encontrados em 0.003 segundos

## ‣ Propriedades aritméticas e topológicas de uma classe de fractais de rauzy; Arithmetic and topological properties of a subclass of the so-called Rauzy's fractals

Rodrigues, Tatiana Miguel
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Relevância na Pesquisa
36.992659%
Estudamos as propriedades aritméticas, geométricas e topológicas de uma classe dos chamados Fractais de Rauzy. Estudamos partucularmente o azulejamento periódico do plano complexo C induzido por eles, assim como a dimensão de Hausdorff de suas fronteiras. Tal trabalho exige um estudo detalhado da fronteira destes conjuntos, que está associada às propriedades aritméticas da 'alpha' -representação dos números complexos com respeito a um certo número algébrico 'alfa'; We study the arithmetic, geometric and topological properties of a class of the so-called Rauzy's fractals. In particular we study the periodic tiling of the complex plane C induced by them and the Hausdorff dimension of its boundary. Such work is connected to a detailed study of the boundary of such sets and the arithmetic properties of the 'alpha' representation of complex numbers with respect to a certain algebraic number 'alpha'

## ‣ Tilings induced by a class of cubic Rauzy fractals

Loridant, B.; Messaoudi, A.; Surer, P.; Thuswaldner, J. M.
Tipo: Artigo de Revista Científica Formato: 6-31
Português
Relevância na Pesquisa
37.249778%
We study aperiodic and periodic tilings induced by the Rauzy fractal and its subtiles associated with beta-substitutions related to the polynomial x3-ax2-bx-1 for a≥b≥1. In particular, we compute the corresponding boundary graphs, describing the adjacencies in the tilings. These graphs are a valuable tool for more advanced studies of the topological properties of the Rauzy fractals. As an example, we show that the Rauzy fractals are not homeomorphic to a closed disc as soon as a≤2b-4. The methods presented in this paper may be used to obtain similar results for other classes of substitutions.© 2012 Elsevier B.V. All rights reserved.

## ‣ Geometry, dynamics and fractals

Bevilacqua,Luiz; Barros,Marcelo M.; Galeão,Augusto.C.R.N.
Fonte: Associação Brasileira de Engenharia e Ciências Mecânicas - ABCM Publicador: Associação Brasileira de Engenharia e Ciências Mecânicas - ABCM
Tipo: Artigo de Revista Científica Formato: text/html
Relevância na Pesquisa
36.992659%
Consider a collection of elastic wires folded according to a given pattern induced by a sequence of fractal plane curves. The folded wires can act as elastic springs. Therefore it is easy to build up a corresponding sequence of simple oscillators composed by the elastic springs clamped at one end and carrying a mass at the opposite end. The oscillation periods of the ordered sequence of these oscillators are related following a power law and therefore display a fractal structure. The periods of each oscillator clearly depend on the mechanical properties of the wire, on the mass at the end and on the boundary conditions. Therefore there are infinitely many possibilities to design a dynamical fractal sequence in opposition to the well defined fractal dimension of the underneath geometric sequence. Nevertheless the geometric fractal dimension of the primordial geometric curve is always related somehow to the dynamical fractal dimension characterizing the oscillation period sequence. It is important to emphasize that the dynamical fractal dimension of a given sequence built up after the geometry of a primordial one is not unique. This peculiarity introduces the possibility to have a broader information spectrum about the geometry which is otherwise impossible to achieve. This effect is clearly demonstrated for random fractals. The present paper deals with a particular family of curves...

## ‣ A class of cubic Rauzy fractals

Bastos, J.; Messaoudi, A.; Rodrigues, T.; Smania, D.
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 114-130
Português
Relevância na Pesquisa
36.992659%
Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Processo FAPESP: 2013/24541-0; Processo FAPESP: 2008/02841-4; Processo FAPESP: 2010108654-1; In this paper, we study arithmetical and topological properties for a class of Rauzy fractals R-a given by the polynomial x(3) - ax(2) + x - 1 where a >= 2 is an integer. In particular, we prove the number of neighbors of R-a in the periodic tiling is equal to 8. We also give explicitly an automaton that generates the boundary of R-a. As a consequence, we prove that R-2 is homeomorphic to a topological disk.

## ‣ A Cross-age study of students' understanding of fractals

Karakus,Fatih
Tipo: Artigo de Revista Científica Formato: text/html
Relevância na Pesquisa
27.381472%
The purpose of this study is to examine how students understand fractals depending on age. Students' understandings were examined in four dimensions: defining fractals, determining fractals, finding fractal patterns rules and mathematical operations with fractals. The study was conducted with 187 students (grades 8, 9, 10) by using a two-tier test consisting of nine questions prepared based on the literature and Turkish mathematics and geometry curriculums. The findings showed that in all grades, students may have misunderstandings and lack of knowledge about fractals. Moreover, students can identify and determine the fractals, but when the grade level increased, this success decreases. Although students were able to intuitively determine a shape as fractal or not, they had some problems in finding pattern rules and formulizing them.

## ‣ Disconnected Julia sets and gaps in the spectrum of Laplacians on symmetric finitely ramified fractals

Hare, Katheryn; Steinhurst, Benjamin; Teplyaev, Alexander; Zhou, Denglin
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
27.381472%
It is known that Laplacian operators on many fractals have gaps in their spectra. This fact precludes the possibility that a Weyl-type ratio can have a limit and is also a key ingredient in proving that the Fourier series on such fractals can have better convergence results than in the classical setting. In this paper we prove that the existence of gaps is equivalent to the total disconnectedness of the Julia set of the spectral decimation function for the class of fully symmetric p.c.f. fractals, and for self-similar fully symmetric finitely ramified fractals with regular harmonic structure. We also formulate conjectures related to geometry of finitely ramified fractals with spectral gaps, to complex spectral dimensions, and to convergence of Fourier series on such fractals.; Comment: 16 pages

## ‣ The structure factor of fat deterministic Vicsek fractals: a small-angle scattering study

Anitas, E. M.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.32477%
We study here the small-angle scattering structure factor for deterministic fat fractals in the reciprocal space. It is shown that fat fractals are exact self-similar in the range of iterations having the same values of the scaling factor, and therefore in each of these ranges all the properties of regular fractals can be inferred to fat fractals. In order to illustrate the above findings we introduce deterministic fattened versions of Vicsek deterministic fractals. We calculate the mono- and polydisperse structure factor and study its scattering properties.

## ‣ Statistical Mechanics and Quantum Fields on Fractals

Akkermans, Eric
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.32477%
Fractals define a new and interesting realm for a discussion of basic phenomena in quantum field theory and statistical mechanics. This interest results from specific properties of fractals, e.g., their dilatation symmetry and the corresponding absence of Fourier mode decomposition. Moreover, the existence of a set of distinct dimensions characterizing the physical properties (spatial or spectral) of fractals make them a useful testing ground for dimensionality dependent physical problems. This paper addresses specific problems including the behavior of the heat kernel and spectral zeta functions on fractals and their importance in the expression of spectral properties in quantum physics. Finally, we apply these results to specific problems such as thermodynamics of quantum radiation by a fractal blackbody.; Comment: 21 pages, 2 figures, 1 table. Proceedings of the conference : Applications of Fractals and Dynamical Systems in Science and Economics Edited by: David Carfi, Michel L. Lapidus, Erin P. J. Pearse, and Machiel van Frankenhuijsen. Contemporary Mathematics (CONM) book series

## ‣ Micro and Macro Fractals generated by multi-valued dynamical systems

Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.425847%
Given a multi-valued function $\Phi$ on a topological space $X$ we study the properties of its fixed fractal, which is defined as the closure of the orbit $\Phi^\omega(Fix(\Phi))=\bigcup_{n\in\omega}\Phi^n(Fix(\Phi))$ of the set $Fix(\Phi)=\{x\in X:x\in\Phi(x)\}$ of fixed points of $\Phi$. A special attention is paid to the duality between micro-fractals and macro-fractals, which are fixed fractals for a contracting compact-valued function $\Phi$ on a complete metric space $X$ and its inverse multi-function $\Phi^{-1}$. With help of algorithms (described in this paper) we generate various images of macro-fractals which are dual to some well-known micro-fractals like the fractal cross, the Sierpinski triangle, Sierpinski carpet, the Koch curve, or the fractal snowflakes. The obtained images show that macro-fractals have a large-scale fractal structure, which becomes clearly visible after a suitable zooming.; Comment: 16 pages + 32 pages of Appendix with Gallery of Macro-Fractals

## ‣ Using blinking fractals for mathematical modeling of processes of growth in biological systems

Sergeyev, Yaroslav D.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.32477%
Many biological processes and objects can be described by fractals. The paper uses a new type of objects - blinking fractals - that are not covered by traditional theories considering dynamics of self-similarity processes. It is shown that both traditional and blinking fractals can be successfully studied by a recent approach allowing one to work numerically with infinite and infinitesimal numbers. It is shown that blinking fractals can be applied for modeling complex processes of growth of biological systems including their season changes. The new approach allows one to give various quantitative characteristics of the obtained blinking fractals models of biological systems.; Comment: 19 pages, 12 figures

## ‣ Smooth bumps, a Borel theorem and partitions of smooth functions on p.c.f. fractals

Rogers, Luke G; Strichartz, Robert S.; Teplyaev, Alexander
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.32477%
We provide two methods for constructing smooth bump functions and for smoothly cutting off smooth functions on fractals, one using a probabilistic approach and sub-Gaussian estimates for the heat operator, and the other using the analytic theory for p.c.f. fractals and a fixed point argument. The heat semigroup (probabilistic) method is applicable to a more general class of metric measure spaces with Laplacian, including certain infinitely ramified fractals, however the cut off technique involves some loss in smoothness. From the analytic approach we establish a Borel theorem for p.c.f. fractals, showing that to any prescribed jet at a junction point there is a smooth function with that jet. As a consequence we prove that on p.c.f. fractals smooth functions may be cut off with no loss of smoothness, and thus can be smoothly decomposed subordinate to an open cover. The latter result provides a replacement for classical partition of unity arguments in the p.c.f. fractal setting.; Comment: 26 pages. May differ slightly from published (refereed) version

## ‣ Scaling Range and Cutoffs in Empirical Fractals

Malcai, Ofer; Lidar, Daniel A.; Biham, Ofer; Avnir, David
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.381472%
Fractal structures appear in a vast range of physical systems. A literature survey including all experimental papers on fractals which appeared in the six Physical Review journals (A-E and Letters) during the 1990's shows that experimental reports of fractal behavior are typically based on a scaling range $\Delta$ which spans only 0.5 - 2 decades. This range is limited by upper and lower cutoffs either because further data is not accessible or due to crossover bends. Focusing on spatial fractals, a classification is proposed into (a) aggregation; (b) porous media; (c) surfaces and fronts; (d) fracture and (e) critical phenomena. Most of these systems, [except for class (e)] involve processes far from thermal equilibrium. The fact that for self similar fractals [in contrast to the self affine fractals of class (c)] there are hardly any exceptions to the finding of $\Delta \le 2$ decades, raises the possibility that the cutoffs are due to intrinsic properties of the measured systems rather than the specific experimental conditions and apparatus. To examine the origin of the limited range we focus on a class of aggregation systems. In these systems a molecular beam is deposited on a surface, giving rise to nucleation and growth of diffusion-limited-aggregation-like clusters. Scaling arguments are used to show that the required duration of the deposition experiment increases exponentially with $\Delta$. Furthermore...

## ‣ Controlling the efficiency of trapping in treelike fractals

Wu, Bin; Zhang, Zhongzhi
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.32477%
Efficiently controlling the trapping process, especially the trapping efficiency, is central in the study of trap problem in complex systems, since it is a fundamental mechanism for diverse other dynamic processes. Thus, it is of theoretical and practical significance to study the control technique for trapping problem. In this paper, we study the trapping problem in a family of proposed directed fractals with a deep trap at a central node. The directed fractals are a generalization of previous undirected fractals by introducing the directed edge weights dominated by a parameter. We characterize all the eigenvalues and their degeneracies for an associated matrix governing the trapping process. The eigenvalues are provided through an exact recursive relation deduced from the self-similar structure of the fractals. We also obtain the expressions for the smallest eigenvalue and the mean first-passage time (MFPT) as a measure of trapping efficiency, which is the expected time for the walker to first visit the trap. The MFPT is evaluated according to the proved fact that it is approximately equal to reciprocal of the smallest eigenvalue. We show that the MFPT is controlled by the weight parameter, by modifying which, the MFPT can scale superlinealy...

## ‣ Linear and branched polymers on fractals

Dhar, Deepak; Singh, Yashwant
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.32477%
This is a pedagogical review of the subject of linear polymers on deterministic finitely ramified fractals. For these, one can determine the critical properties exactly by real-space renormalization group technique. We show how this is used to determine the critical exponents of self-avoiding walks on different fractals. The behavior of critical exponents for the $n$-simplex lattice in the limit of large $n$ is determined. We study self-avoiding walks when the fractal dimension of the underlying lattice is just below 2. We then consider the case of linear polymers with attractive interactions, which on some fractals leads to a collapse transition. The fractals also provide a setting where the adsorption of a linear chain near on attractive substrate surface and the zipping-unzipping transition of two mutually interacting chains can be studied analytically. We also discuss briefly the critical properties of branched polymers on fractals.; Comment: 46 pages, 23 figures

## ‣ Determining global mean-first-passage time of random walks on Vicsek fractals using eigenvalues of Laplacian matrices

Zhang, Zhongzhi; Wu, Bin; Zhang, Hongjuan; Zhou, Shuigeng; Guan, Jihong; Wang, Zhigang
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
27.32477%
The family of Vicsek fractals is one of the most important and frequently-studied regular fractal classes, and it is of considerable interest to understand the dynamical processes on this treelike fractal family. In this paper, we investigate discrete random walks on the Vicsek fractals, with the aim to obtain the exact solutions to the global mean first-passage time (GMFPT), defined as the average of first-passage time (FPT) between two nodes over the whole family of fractals. Based on the known connections between FPTs, effective resistance, and the eigenvalues of graph Laplacian, we determine implicitly the GMFPT of the Vicsek fractals, which is corroborated by numerical results. The obtained closed-form solution shows that the GMFPT approximately grows as a power-law function with system size (number of all nodes), with the exponent lies between 1 and 2. We then provide both the upper bound and lower bound for GMFPT of general trees, and show that leading behavior of the upper bound is the square of system size and the dominating scaling of the lower bound varies linearly with system size. We also show that the upper bound can be achieved in linear chains and the lower bound can be reached in star graphs. This study provides a comprehensive understanding of random walks on the Vicsek fractals and general treelike networks.; Comment: Definitive version accepted for publication in Physical Review E

## ‣ V-variable fractals and superfractals

Barnsley, Michael; Hutchinson, John E.; Stenflo, Örjan
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.32477%
Deterministic and random fractals, within the framework of Iterated Function Systems, have been used to model and study a wide range of phenomena across many areas of science and technology. However, for many applications deterministic fractals are locally too similar near distinct points while standard random fractals have too little local correlation. Random fractals are also slow and difficult to compute. These two major problems restricting further applications are solved here by the introduction of V-variable fractals and superfractals.; Comment: 17 pages, 10 figures

## ‣ Determining mean first-passage time on a class of treelike regular fractals

Lin, Yuan; Wu, Bin; Zhang, Zhongzhi
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
27.425847%
Relatively general techniques for computing mean first-passage time (MFPT) of random walks on networks with a specific property are very useful, since a universal method for calculating MFPT on general graphs is not available because of their complexity and diversity. In this paper, we present techniques for explicitly determining the partial mean first-passage time (PMFPT), i.e., the average of MFPTs to a given target averaged over all possible starting positions, and the entire mean first-passage time (EMFPT), which is the average of MFPTs over all pairs of nodes on regular treelike fractals. We describe the processes with a family of regular fractals with treelike structure. The proposed fractals include the $T$ fractal and the Peano basin fractal as their special cases. We provide a formula for MFPT between two directly connected nodes in general trees on the basis of which we derive an exact expression for PMFPT to the central node in the fractals. Moreover, we give a technique for calculating EMFPT, which is based on the relationship between characteristic polynomials of the fractals at different generations and avoids the computation of eigenvalues of the characteristic polynomials. Making use of the proposed methods, we obtain analytically the closed-form solutions to PMFPT and EMFPT on the fractals and show how they scale with the number of nodes. In addition...

## ‣ Description of diffusive and propagative behavior on fractals

Campos Moreno, Daniel; Méndez López, Vicenç; Fort Viader, Joaquim
Tipo: Artigo de Revista Científica Formato: application/pdf
Relevância na Pesquisa
27.32477%
The known properties of diffusion on fractals are reviewed in order to give a general outlook of these dynamic processes. After that, we propose a description developed in the context of the intrinsic metric of fractals, which leads us to a differential equation able to describe diffusion in real fractals in the asymptotic regime. We show that our approach has a stronger physical justification than previous works on this field. The most important result we present is the introduction of a dependence on time and space for the conductivity in fractals, which is deduced by scaling arguments and supported by computer simulations. Finally, the diffusion equation is used to introduce the possibility of reaction-diffusion processes on fractals and analyze their properties. Specifically, an analytic expression for the speed of the corresponding travelling fronts, which can be of great interest for application purposes, is derived.

## ‣ A Recursive Fractal Design Generator for Dimensions Zero to Two Implemented within a Two Dimensional Core Graphics Package

Lehmann, Elizabeth
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Português
Relevância na Pesquisa
27.32477%
This thesis incorporates the technique developed by Benoit Mandelbrot to describe recursive fractals into an interactive graphics package based on the Core Graphics System (Core) produced by an ACM SIGGRAPH Committee (1977, 1979). The graphics package encompasses simple standard geometric shapes as well as the recursive fractals. To draw those fractals requires knowing both the basic shape or generator, and the points of recursion. These two pieces are acquired through the using of two windows which allow the generator and the points of recursion to be built. Once built, the fractal recursion level is chosen interactively on the main drawing. The conclusion I reached as a result of this project is that it is possible to integrate fractals in a systematic way into a standard graphics package, much as rectangles and circles are today in most graphics systems.

## ‣ A fractal valued random iteration algorithm and fractal hierachy

Barnsley, Michael; Hutchinson, John; Stenflo, Orjan
Fonte: World Scientific Publishing Company Publicador: World Scientific Publishing Company
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
27.381472%
We describe new families of random fractals, referred to as "V-variable", which are intermediate between the notions of deterministic and of standard random fractals. The parameter V describes the degree of "variability": at each magnification level any V-variable fractals has at most V key "forms" or "shapes". V-variable random fractals have the surprising property that they can be computed using a forward process. More precisely, a version of the usual Random Iteration Algorithm, operating on sets (or measures) rather than points, can be used to sample each family. To present this theory, we review relevant results on fractals (and fractal measures), both deterministic and random. Then our new results are obtained by constructing an iterated function system (a super IPS) from a collection of standard IFSs together with a corresponding set of probabilities. The attractor of the super IFS is called a superfractal; it is a collection of V-variable random fractals (sets or measures) together with an associated probability distribution on this collection. When the underlying space is for example ℝ2, and the transformations are computationally straightforward (such as affine transformations), the superfractal can be sampled by means of the algorithm...