Search results for "Fractal"
showing 10 items of 329 documents
VAMPIRE: Vessel assessment and measurement platform for images of the REtina
2011
We present VAMPIRE, a software application for efficient, semi-automatic quantification of retinal vessel properties with large collections of fundus camera images. VAMPIRE is also an international collaborative project of four image processing groups and five clinical centres. The system provides automatic detection of retinal landmarks (optic disc, vasculature), and quantifies key parameters used frequently in investigative studies: vessel width, vessel branching coefficients, and tortuosity. The ultimate vision is to make VAMPIRE available as a public tool, to support quantification and analysis of large collections of fundus camera images.
The Combined Ultra-Small- and Small-Angle Neutron Scattering (USANS/SANS) Technique for Earth Sciences
2009
The extension of the well-known Small-Angle Neutron Scattering (SANS) technique to Ultra-Small Angles (USANS) provides a unique tool for studying hierarchical structures ranging in size from nanometers to micrometers. Hierarchical structures are common for many natural and man-made materials, which show multi-level morphology (atoms–molecules–aggregates–agglomerates), in other words, are made up of structural units encompassing the atomic, molecular, micro- and macroscopic length scales. Combining USANS and SANS data can provide complete structural information for complicated polydisperse systems, allowing the determination of their complex morphology and hence has been successfully applied…
On the Fractal Structure of Evolutionary Trees
2002
We analyse in terms of a fractal tree the time sequences of major evolutionary leaps at various scales: from the scale of the “global” tree of life (appearance of life to homeothermy), to the distinct scales of organization of clades, such as sauropod and theropod dinosaurs, North American equids, rodents, primates including hominids, and echinoderms. We also apply this type of model to the acceleration observed in the economic crisis/no-crisis pattern in Western and pre-Columbian civilizations. In each case we find that these data are consistent with a log-periodic law of acceleration or deceleration, to a high level of statistical significance. Such a law is characterized by a critical ep…
Pattern
2020
The word “pattern” is a very complex term. Generally, it refers to “an arrange- ment that reveals an order, or design, which is meaningful” (cf. Thaker 1999: 427). But a quick look at many of its different domains of application (e.g. theoretical biology, mathematics, aesthetics, linguistics, etc., etc.) proves that “pattern” has a semantic potential richer than one usually expressed by such a definition. For instance, in the framework of the so-called combinatorics on words (cf. at least Lothaire 2012), a pattern is “a word over an alphabet of variables and is meant to describe some kind of repetitive structures” (cf. Rampersard 2017: 98). Therefore, in this first theoretical approach, “th…
Molecular Classification of Pesticides Including Persistent Organic Pollutants, Phenylurea and Sulphonylurea Herbicides
2014
Pesticide residues in wine were analyzed by liquid chromatography–tandem mass spectrometry. Retentions are modelled by structure–property relationships. Bioplastic evolution is an evolutionary perspective conjugating effect of acquired characters and evolutionary indeterminacy–morphological determination–natural selection principles; its application to design co-ordination index barely improves correlations. Fractal dimensions and partition coefficient differentiate pesticides. Classification algorithms are based on information entropy and its production. Pesticides allow a structural classification by nonplanarity, and number of O, S, N and Cl atoms and cycles; different behaviours depend …
Topological effects in ring polymers. II. Influence of persistence length
1999
The interplay of topological constraints and persistence length of ring polymers in their own melt is investigated by means of dynamical Monte Carlo simulations of a three dimensional lattice model. We ask if the results are consistent with an asymptotically regime where the rings behave like (compact) {\em lattice animals} in a self-consistent network of topological constraints imposed by neighbouring rings. Tuning the persistence length provides an efficient route to increase the ring overlap required for this mean-field picture to hold: The {\em effective} Flory exponent for the ring size decreases down to $\nu \stackrel{<}{\sim} 1/3$ with increasing persistence length. Evidence is provi…
Lacunar fractal photon sieves
2007
We present a new family of diffractive lenses whose structure is based on the combination of two concepts: photon sieve and fractal zone plates with variable lacunarity. The focusing properties of different members of this family are examined. It is shown that the sieves provide a smoothing effect on the higher order foci of a conventional lacunar fractal zone plate. However, the characteristic self-similar axial response of the fractal zone plates is always preserved.
Photonic controlled metasurface for intelligent antenna beam steering applications including 6G mobile communication systems
2023
This paper presents a novel metasurface antenna whose radiation characteristics can be remotely controlled by optical means using PIN photodiodes. The proposed reconfigurable antenna is implemented using a single radiating element to minimize the size and complexity. The antenna is shown to exhibit a large impedance bandwidth and is capable of radiating energy in a specified direction. The proposed antenna consists of a standard rectangular patch on which is embedded an H-tree shaped fractal slot of order 3. The fractal slot is used to effectively reduce the physical size of the patch by 75 % and to enhance its impedance bandwidth. A metasurface layer is strategically placed above the patch…
An Ultrasonic Lens Design Based on Prefractal Structures
2016
The improvement in focusing capabilities of a set of annular scatterers arranged in a fractal geometry is theoretically quantified in this work by means of the finite element method (FEM). Two different arrangements of rigid rings in water are used in the analysis. Thus, both a Fresnel ultrasonic lens and an arrangement of rigid rings based on Cantor prefractals are analyzed. Results show that the focusing capacity of the modified fractal lens is better than the Fresnel lens. This new lens is believed to have potential applications for ultrasonic imaging and medical ultrasound fields.
Spatial multifractal properties of wave packets in the Anderson model of localization.
1993
The multifractal properties of electronic wave functions in disordered samples are investigated. In a given energy range all eigenstates are determined for the same disorder configuration in the Anderson model of localization. It is shown that the singularity spectrum and the generalized dimensions change only slowly with energy, aside from statistical fluctuations. More important, the wave packet constructed by linear combination of the eigenstates shows quantitatively the same multifractal properties. Consequences for the transport properties of electronic states in disordered systems are discussed.