Quasi-fractal Structure Research Articles

Polarization properties of quasi-fractal porous particles

Numerous studies of cometary dust have shown that it has a fairly complex hierarchical structure. At the same time, space missions have provided evidence of solid particles. Computer modeling of light scattering, for which agglomerate debris particles were used, showed that the characteristics of the scattered light strongly depend on the presence of solid particles. We propose a model that makes it possible to fractalize the agglomerate debris particles. A particle constructed in accordance with the proposed model combines large and small fragments. Depending on the model parameters, you can make the particle fluffier or more compact. A comparison of the degree of linear polarization between quasi-fractal porous particles and solid particles, as well as between quasi-fractal porous particles and Maxwell Garnett particles is carried out. It has been established that there is the difference between really porous particles and particles, for which the porosity is taken into account by the Maxwell Garrett theory. We recommend using the Maxwell Garnett theory only for studying uniformly distributed inclusions, and for quasi-fractal structures it is better to use the exact calculations.

Investigation of the capabilities of the method of characteristic patterns for graphical presentation of large amounts of information

The author examines new challenges of ergonomics and occupational health, including unknown risks, issues of prevention, and ethics. The author also presents an overview of modern bioinformatics systems and visualization methods in bioinformatics. The researcher analyzed the health risks of human interaction with large volumes of textual information and advanced computational methods to prevent computer syndrome, including overstrain of the visual analyzer and pain in the back, neck, and hands. The study aims to analyze the representations of hereditary molecular genetic information in the form of graphic patterns available for visual perception, characterizing the initial data, and study the possibility of visualizing large amounts of data using the method of characteristic patterns. The author developed new methods of presenting large volumes of hereditary genetic information in bioinformatic systems. The basis of the method is information processing based on computer algorithms. The methods allow us to visually assess the differences in the genetic structure of various species of living organisms and identify the features of their nucleotide composition. The fixation of the internal ordering of the information signal in an individual graphical quasi-fractal structure is a characteristic feature of the methods considered. It makes it possible to expand the possibilities of visual-analytical thinking of a person when interacting with large amounts of information through bioinformatics tools.

Kink-antikink collisions in the periodic [formula omitted] model

We borrow the form of potential of the well-known kink-bearing φ4 system in the range between its two vacua and paste it repeatedly into the other ranges to introduce the periodic φ4 system. The paper is devoted to providing a comparative numerical study of the properties of the two systems. Although the two systems are quite similar for a kink (antikink) solution, they usually exhibit different behaviors throughout collisions. For instance, they have different critical velocities, different results during collisions, and a different rule in their quasi-fractal structures. Their quasi-fractal structures will be studied in the disturbed kink-antikink collisions as well. Hence, three types of scattering windows will be introduced with respect to the incoming speed, the amplitude, and initial phase of the internal mode, respectively. Moreover, a detailed comparative study of the collisions between two kinks and one antikink will be done at the end.

Fractal dimension of phylogenetically different parts of the human cerebellum (magnetic resonance imaging study)

In recent years, fractal analysis has been increasingly used as a morphometric method, which allows to assess the complexity of the organization of quasi-fractal biological structures, including the cerebellum. The aim of the study was to determine the value of fractal dimension of phylogenetically different parts of the cerebellum by studying magnetic resonance imaging of the brain using the method of pixel dilation and to identify gender and age characteristics of individual variability of fractal dimension of the cerebellum and its external linear contour. The study was performed on the magnetic resonance images of the brain of 120 relatively healthy patients in age 18-86 years (65 women, 55 men). T2 weighted tomographic images were investigated. Fractal analysis was performed using the method of pixel dilation in the author’s modification. Fractal dimension (FD) values were determined for cerebellar tomographic images segmented with brightness values of 100 (FD100), 90 (FD90) and in the range of 100-90 (FD100-90 or fractal dimension of the outer cerebellar contour) in its upper and lower lobes, which include phylogenetically different zones. The obtained data were processed using generally accepted statistical methods. The average value of FD100 of the upper lobe of the cerebellum was 1.816±0.005, the lower lobe – 1.855±0.005. The average value of FD90 of the upper lobe of the cerebellum was 1.734±009, the lower lobe – 1.768±0.009. The average value of FD100-90 of the upper lobe of the cerebellum was 1.370±0.009, the lower lobe – 1.431±0.008. All three values of the fractal dimension of the lower lobe, which lobules have a lower phylogenetic age, are statistically significantly higher than the corresponding values of the fractal dimension of the upper lobe, have a more pronounced correlation with age than in the upper lobe. The developed research algorithm can be used to assess the condition of the cerebellum as an additional morphometric method during magnetic resonance imaging study of the brain.

КВАЗІФРАКТАЛЬНА ДІЕЛЕКТРИЧНА РЕЗОНАТОРНА АНТЕНА НА ОСНОВІ ПАРАЛЕЛЕПІПЕДА

В роботі наведено пропозиції щодо реалізації діелектричних резонаторних антен на основі квазіфрактальних структур, що характеризуються відсутністю рекурсивного повторення. В якості базового елемента запропоновано використання паралелепіпеда. З метою визначення впливу геометрії на просторовочастотні характеристики антени проведено моделювання за допомогою пакету електродинамічного моделювання Ansoft HFSS. На основі введених допущень досліджувались амплітудна частотна характеристика та коефіцієнт стоячої хвилі. На основі аналізу моделей геометрії антени визначені оптимальні варіанти компоновки центрального та периферійних елементів.

Chessboard AMC Surface Based on Quasi-Fractal Structure for Wideband RCS Reduction

A chessboard artificial magnetic conductor surface based on the quasi-fractal structure is proposed for wideband radar cross-section (RCS) reduction. The chessboard configuration is formed by two different cells with 180° ± 37° phase difference over more than 90% frequency bandwidth. The quasi-fractal structure is utilized to achieve the wideband and compact characteristics. Monostatic and bistatic RCS of the proposed chessboard surface are analyzed, and the results are compared with those of equal-sized perfect electric conductor ground plane. Because the scattered fields of the chessboard surface are redirected toward four quadrants, a remarkable RCS reduction of 10 dB can be realized from 5.4 to 14.2 GHz. Measured results of the fabricated prototype satisfactorily agree with the simulated ones.

Quasi-fractal PBG structures for Multi-Beam Devices

Quasi-fractal PBG structures for Multi-Beam Devices

Quasi-fractal axial-symmetric structure feeded by segment of nongrounded coplanar line

Background. Developments in telecommunication technologies and global implementation of wireless systems calls far new types of antenna systems. Microstrip antennas look the most promising in this field since they possess multiband operation capability with small dimensions and low weight, high degree of integration with other microstrip circuits and can be used as elements of phased antenna arrays. Objectives. The goal of this paper was to simulate electrodynamic characteristics of quasi-fractal radiating structure with complex composition based on a microstrip monopole, to optimize parameters of the excitation element in the form of unshielded coplanar waveguide segment. Matherials and methods. Quasi-fractal radiating structure with complex composition based on a microstrip monopole consists of dielectric substrate, microstrip monopole with quasy-fractal aperture, an unshielded coplanar waveguide segment. The analysis was based on the Finite Elements Method with Integral Equation Method used to account for electromagnetic fields at infinity. Results. Within scope of numerical simulation spectral characteristics of the antenna were analyzed. Comparative analysis of spectral characteristics of canonical disk resonator excited with a microstrip line segment and canonical disk resonator excited with a segment of a coplanar line with eigenmode spectrum of a quasi-fractal excited with a segment of a coplanar waveguide was performed. Influence of dielectric substrate permittivity value on frequency and power characteristics of the radiating structure was studied. It was shown that variations in dielectric permittivity value lead to significant changes of frequency response in the higher frequency band only, wherein increase of dielectric permittivity value leads to a shift of frequency response minima towards lower frequencies of the given frequency band. It was determined that radiating structure is dualband and bandwidth of operating bands was different. Lower frequency bandwidth on dB was , and higher frequency bandwidth was . Numerical simulation of power characteristics was performed with the radiation patterns presented as elevation patterns with fixed azimuthal angle at various frequencies. Possible methods of radiating structure parameters correction with the goal of improving power characteristics and external circuits matching were given. Conclusions. Within scope of numerical simulation was determined that the given quasi-fractal radiating structure with complex composition based on a microstrip monopole can provide effective radiation with acceptable parasitic loss rate. The structure can provide acceptable level of external circuits matching in wide enough frequency band. The ability to form radiated fields with given characteristics in two operating bands.

Wideband RCS reduction of slot‐coupled patch antenna by AMC structure

A novel approach to realise the wideband and polarisation-independent radar cross-section (RCS) reduction of a slot-coupled patch antenna is proposed. The RCS reduction is based on the unique reflection phase properties of artificial magnetic conductor (AMC) and perfect electric conductor (PEC) cell. By using the quasi-fractal structure in AMC design, 180° ± 37° reflection phase difference between AMC and PEC cells is obtained over 109% (6.4–21.7 GHz) frequency range. Then, the two different unit cells are applied properly to a slot-coupled patch antenna for wideband RCS reduction. The simulated and measured results indicate that the proposed antenna realises a remarkable RCS reduction between 6.0 and 30.0 GHz for both phi- and theta-polarised waves. Moreover, the radiation characteristics of the antenna are well kept simultaneously.

Optimization of hierarchical structure and nanoscale-enabled plasmonic refraction for window electrodes in photovoltaics.

An ideal network window electrode for photovoltaic applications should provide an optimal surface coverage, a uniform current density into and/or from a substrate, and a minimum of the overall resistance for a given shading ratio. Here we show that metallic networks with quasi-fractal structure provides a near-perfect practical realization of such an ideal electrode. We find that a leaf venation network, which possesses key characteristics of the optimal structure, indeed outperforms other networks. We further show that elements of hierarchal topology, rather than details of the branching geometry, are of primary importance in optimizing the networks, and demonstrate this experimentally on five model artificial hierarchical networks of varied levels of complexity. In addition to these structural effects, networks containing nanowires are shown to acquire transparency exceeding the geometric constraint due to the plasmonic refraction.

Bio-inspired networks for optoelectronic applications.

Modern optoelectronics needs development of new materials characterized not only by high optical transparency and electrical conductivity, but also by mechanical strength, and flexibility. Recent advances employ grids of metallic micro- and nanowires, but the overall performance of the resulting material composites remains unsatisfactory. In this work, we propose a new strategy: application of natural scaffoldings perfected by evolution. In this context, we study two bio-inspired networks for two specific optoelectronic applications. The first network, intended for solar cells, light sources and similar devices, has a quasi-fractal structure and is derived directly from a chemically extracted leaf venation system. The second network is intended for touch screens and flexible displays, and is obtained by metalizing a spider's silk web. We demonstrate that each of these networks attain an exceptional optoelectonic and mechanical performance for its intended purpose, providing a promising direction in the development of more efficient optoelectronic devices.

Research on the L-band circularly polarized antenna with low RCS level

A novel L-band circularly polarized (CP) microstrip antenna for low radar cross-section (RCS) application is proposed in this paper. A corner-cut squarer radiator is used to implement the CP radiation. The antenna RCS is effectively reduced by the special quasi-fractal structure on the ground plane. Its radiation and scattering performances are simulated and experimentally verified by being compared with those of a commonly used CP microstrip antenna which is chosen as a reference antenna. The results show that the proposed antenna has good radiation performances and lower RCS than the reference antenna. The proposed antenna serves as a good candidate in the design of CP antenna with the requirement of low RCS.

Processing of New Solar Absorbers in Steel Design Based on Partially Cold Roll Bonded Hybrid Semi-Finished Parts

The conventional manufacturing of solar absorbers has the disadvantage that only simple pipe branch channel geometries are possible. For this reason, a new approach of manufacturing solar absorbers is presented with which it is possible to design the channel geometry as a quasi-fractal structure (FracTherm®, developed by Fraunhofer Institute for Solar Energy Systems) and which reduces the pressure drop and the required energy for the pump. To manufacture these new absorbers, a fast, nearly continuous production process was developed which consists of partial cold roll bonding and subsequent hydroforming, similar to symmetric hydroforming of sheet metal pairs. Various channel geometries, which are developed by Fraunhofer ISE, within the hybrid sheet metal, can be applied. Therefore, three technologies are combined to manufacture a new type of solar absorber. A special look is taken at cold roll bonding. By this process, the material for the new solar absorbers (copper-steel-copper/copper-steel-copper hybrid sheet material) is produced using a suitable release agent to avoid the bonding process along the subsequent water channels. To establish manufacturing guidelines, the characterization of the material is necessary. A peel test like ISO 11339 is used to determine the strength of the layers of the hybrid material. At least the forming characteristics of the hybrid material are dominated by the basic material, in this case steel. A further look is given to the hydroforming of the material. Different cross-section geometries have been tested by a simplified experiment to find out the best geometry for the absorber channels, and have been compared with simulation results, too. Hence, for a crack-free forming operation the choice of the die radius and corner radius is decisive as they are within the same range. To show the feasibility of the hydroforming process and validate the process chain, a small demonstrator was manufactured. Finally it is possible to manufacture a steel based solar absorber with a quasi-fractal structure by combining partial cold roll bonding and hydroforming. All these results are used as guidelines for the production of a new absorber with quasi-fractal structure (FracTherm®).

The Modified Gamma Size Distribution Applied to Inhomogeneous and Nonspherical Particles: Key Relationships and Conversions

Abstract The four-parameter modified gamma distribution (MGD) is the most general mathematically convenient model for size distributions of particle types ranging from aerosols and cloud droplets or ice particles to liquid and frozen precipitation. The common three-parameter gamma distribution, the exponential distribution (e.g., Marshall–Palmer), and power-law distribution (e.g., Junge) are all special cases. Depending on the context, the particle “size” used in a given formulation may be the actual geometric diameter, the volume- or area-equivalent spherical diameter, the actual or equivalent radius, the projected or surface area, or the mass. For microphysical and radiative transfer calculations, it is often necessary to convert from one size representation to another, especially when comparing or utilizing distribution parameters obtained from a variety of sources. Furthermore, when the mass scales with Db, with b < 3, as is typical for snow and ice and other particles having a quasi-fractal structure, an exponential or gamma distribution expressed in terms of one size parameter becomes an MGD when expressed in terms of another. The MGD model is therefore more fundamentally relevant to size distributions of nonspherical particles than is often appreciated. The central purpose of this paper is to serve as a concise single-source reference for the mathematical properties of, and conversions between, atmospheric particle size distributions that can expressed as MGDs, including exponential and gamma distributions as special cases. For illustrative purposes, snow particle size distributions published by Sekhon and Srivastava, Braham, and Field et al. are converted to a common representation and directly compared for identical snow water content, allowing large differences in their properties to be discerned and quantified in a way that is not as easily achieved without such conversion.

Monopole antenna based on the modified ground plane for wireless local-area network application

A monopole antenna with modified ground plane is presented for 2.4 and 5 GHz wireless local area network applications in this article.A trapezoid patch and a quasifractal slotted patch are printed on two FR-4 dielectric substrates as the radiator and the ground plane of the antenna, respectively. The element of the quasifractal slot structure is a circular ring with four branches. The radiation characteristics are simulated and experimentally verified, and the results show that the proposed antenna has good radiation performance. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26216

A novel dual-mode dual band bandpass filter using a quasi fractal structure

A quasi fractal structure is introduced to build up a nondegenerate dual mode dual band bandpass filter. In the proposed filter a Koch fractal structure is applied to a microstrip patch resonator for miniaturization and dual band operation. The first band is specified by the first iteration of the fractal patch while the second band is determined with the second iteration. The most important feature is that the second band is independent of the first band and is simply tuned which is a challenge in dual band filters. A precise analysis of operation of the filter is presented. The measured results of the filter have good agreement with the full-wave simulated results.

Monopole Antenna With Quasi-Fractal Slotted Ground Plane for Dual-Band Applications

A quasi-fractal slotted ground plane is applied to a monopole antenna for dual-frequency applications in this letter. A trapezoid patch and a quasi-fractal slot structure are printed on two FR-4 dielectric substrates as the radiator and the ground plane, respectively. The dual operating bands of the antenna are determined by the sizes of the radiator and the quasi-fractal structure. Detailed analysis is made to discuss the impact of the parameters on the operating bands for the further design. Lastly, a design example is presented and compared to a similar antenna with solid ground plane to authorize the presented technique. Its radiation characteristics are simulated and experimentally verified, and the results show that it has better dual-band performances.

RCS Reduction of Array Antenna by Using Bandstop FSS Reflector

This paper investigates the application of a novel frequency selective surface (FSS) reflector for 4×2 dipole array antenna to reduce radar cross section (RCS) out of operating band. The proposed FSS adopting a regular hexagon quasi-fractal structure has good bandstop characteristic. By replacing the metal reflector with this bandstop FSS sheet, the in-band radiation performance of the proposed array antenna is preserved, while the out-of-band backward RCS is significantly reduced. Due to the good angle stability of the given FSS, the monostatic RCS peaks at oblique angle ( = 60°, ϕ = 0°) are also controlled. The measured results demonstrate the feasibility of antenna RCS reduction by this method.

Resonance Analysis of Multilayered Filters with Triadic Cantor-Type One-Dimensional Quasi-Fractal Structures

Multilayered filters with a dielectric distribution along their thickness forming a one-dimensional quasi-fractal structure are theoretically analyzed, focusing on exposing their resonant properties in order to understand a dielectric Menger's sponge resonator [4], [5]. Quasi-fractal refers to the triadic Cantor set with finite generation. First, a novel calculation method that has the ability to deal with filters with fine fractal structures is derived. This method takes advantage of Clifford algebra based on the theory of thin-film optics. The method is then applied to classify resonant modes and, especially, to investigate quality factors for them in terms of the following design parameters: a dielectric constant, a loss tangent, and a stage number. The latter determines fractal structure. Finally, behavior of the filters with perfect fractal structure is considered. A crucial finding is that the high quality factor of the modes is not due to the complete self-similarity, but rather to the breaking of such a fractal symmetry.

Photonic Band Gaps in Two-Dimensional Crystals with FractalStructure

We simulate the changes of the photonic band structure of thecrystal in two dimensions with a quasi-fractal structure when it is confinedto a fractal. The result shows that when the dielectric distribution isconfined, the photonic band structure will be compressed on the whole andthe ground photonic band gap (PBG) closed while the next PBGs shrunk,in conjunction with their position declining in the frequency spectrum.Furthermore, the PBGs in the high zone are much more sensitive thanthose in low zones.