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Symmetry, Volume 14, Issue 3 (March 2022) – 202 articles

Cover Story (view full-size image): Symmetry is an intrinsic property of homo-oligomers. In this study, we analyzed the conformational dynamics and flexibility of two amine oxidases, from lentil seedlings (LSAO) and from Euphorbia characias latex (ELAO). Fluorescence spectroscopic data and molecular dynamics demonstrate that slight but significant differences exist at the level of the local tridimensional structure, arising from the presence of large internal cavities, characterized by a different hydration extent. These findings at the light of the topological analysis of the two protein structures demonstrate how the presence of water enhances the degree of connectivity among residues populating the subunits’ interface, which appears mostly asymmetric. View this paper
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Review
Frequency Up-Conversion for Vibration Energy Harvesting: A Review
Symmetry 2022, 14(3), 631; https://doi.org/10.3390/sym14030631 - 21 Mar 2022
Viewed by 761
Abstract
A considerable amount of ambient vibration energy spreads over an ultra-low frequency spectrum. However, conventional resonant-type linear energy harvesters usually operate within high and narrow frequency bands, which cannot match the frequencies of many vibration sources. If the excitation frequency deviates a bit [...] Read more.
A considerable amount of ambient vibration energy spreads over an ultra-low frequency spectrum. However, conventional resonant-type linear energy harvesters usually operate within high and narrow frequency bands, which cannot match the frequencies of many vibration sources. If the excitation frequency deviates a bit from the natural frequency of an energy harvester, the energy harvesting performance will deteriorate drastically. Because of the ultra-low frequency characteristic, it is challenging to reliably harvest energy from the ambient vibrations. To address this mismatching issue, the ultra-low frequency ambient vibrations are converted into high-frequency oscillations using certain mechanical mechanisms, which are termed frequency up-conversion techniques. This paper reviews the existing approaches that can realize frequency up-conversion for enhancing energy harvesting from low-frequency vibration sources. According to their working mechanisms, the existing methods are classified into three categories: impact-based, plucking-based, and snap-through-based approaches. The working principles of the three approaches are explained in detail. Representative designs from all categories are reviewed. This overview on the state-of-the-art frequency up-conversion technology would guide the better design of future kinetic energy harvesting systems. Full article
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Article
Applications of the Atangana–Baleanu Fractional Integral Operator
Symmetry 2022, 14(3), 630; https://doi.org/10.3390/sym14030630 - 21 Mar 2022
Cited by 1 | Viewed by 497
Abstract
Applications of the Atangana–Baleanu fractional integral were considered in recent studies related to geometric function theory to obtain interesting differential subordinations. Additionally, the multiplier transformation was used in many studies, providing elegant results. In this paper, a new operator is defined by combining [...] Read more.
Applications of the Atangana–Baleanu fractional integral were considered in recent studies related to geometric function theory to obtain interesting differential subordinations. Additionally, the multiplier transformation was used in many studies, providing elegant results. In this paper, a new operator is defined by combining those two prolific functions. The newly defined operator is applied for introducing a new subclass of analytic functions, which is investigated concerning certain properties, such as coefficient estimates, distortion theorems, closure theorems, neighborhoods and radii of starlikeness, convexity and close-to-convexity. This class may have symmetric or asymmetric properties. The results could prove interesting due to the new applications of the Atangana–Baleanu fractional integral and of the multiplier transformation. Additionally, the univalence properties of the new subclass of functions could inspire researchers to conduct further investigations related to this newly defined class. Full article
(This article belongs to the Special Issue Symmetry in Pure Mathematics and Real and Complex Analysis)
Article
Stability and Bifurcation Analysis of a Nonlinear Rotating Cantilever Plate System
Symmetry 2022, 14(3), 629; https://doi.org/10.3390/sym14030629 - 21 Mar 2022
Viewed by 614
Abstract
This paper investigates the bifurcation behavior and the stability of the rotating cantilever rectangular plate that is subjected to varying speed and centrifugal force. The local stability of the degenerated equilibrium of nonlinear system with symmetry is observed after analyzing the corresponding characteristic [...] Read more.
This paper investigates the bifurcation behavior and the stability of the rotating cantilever rectangular plate that is subjected to varying speed and centrifugal force. The local stability of the degenerated equilibrium of nonlinear system with symmetry is observed after analyzing the corresponding characteristic equation. In addition to complex phenomena such as static bifurcation and Hopf bifurcation, the 2-D torus bifurcation is investigated in this paper. Thereafter, the steady-state solutions and stability region are obtained using the center manifold theory and normal form method. Finally, numerical simulations are conducted to show the nonlinear dynamical behaviors of the rotating cantilever rectangular plate. Full article
(This article belongs to the Special Issue Symmetry in Nonlinear Structural Dynamics: Topic and Advance)
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Article
Improved Allocation and Reallocation Approaches for Software Trustworthiness Based on Mathematical Programming
Symmetry 2022, 14(3), 628; https://doi.org/10.3390/sym14030628 - 21 Mar 2022
Viewed by 423
Abstract
Software trustworthiness allocation and reallocation are the symmetry of software trustworthiness measure. They can provide the optimization scheme for trustworthiness development and improvement, according to the requirements. The existing allocation and reallocation models do not consider the absolute majority of software trustworthiness classification; [...] Read more.
Software trustworthiness allocation and reallocation are the symmetry of software trustworthiness measure. They can provide the optimization scheme for trustworthiness development and improvement, according to the requirements. The existing allocation and reallocation models do not consider the absolute majority of software trustworthiness classification; therefore, they cannot be very accurate in the allocation and reallocation of software trustworthiness. In this paper, improved allocation and reallocation models are constructed, which can resolve the above problem, and their polynomial solving algorithms are designed. At the same time, a demonstration application of the improved models and algorithms is given, and the trustworthiness enhancement specification of spacecraft software, based on factory reports, is established, including trustworthiness development specification and trustworthiness improvement specification. This enhancement specification provides a scientific and reasonable theory and method for the delivery acceptance of spacecraft software, from qualitative to quantitative grading acceptance, and furnishes a standard guarantee for the trustworthy development and improvement of such software. Full article
(This article belongs to the Topic Engineering Mathematics)
Article
Studying Massive Suction Impact on Magneto-Flow of a Hybridized Casson Nanofluid on a Porous Continuous Moving or Fixed Surface
Symmetry 2022, 14(3), 627; https://doi.org/10.3390/sym14030627 - 21 Mar 2022
Cited by 3 | Viewed by 376
Abstract
Non-Newtonian nanofluids flow due to the augmented thermal performances of nanoparticles, and their importance in various sectors plays a vital role in medicine, cosmetics, manufacturing, and engineering processes. In this regard, the present theoretical investigation explores the magneto-flow of Casson hybrid nanofluid through [...] Read more.
Non-Newtonian nanofluids flow due to the augmented thermal performances of nanoparticles, and their importance in various sectors plays a vital role in medicine, cosmetics, manufacturing, and engineering processes. In this regard, the present theoretical investigation explores the magneto-flow of Casson hybrid nanofluid through a continuous moving/fixed surface with significant suction. The nature of spherical copper and alumina dispersed in water was assessed as the conventional heat transfer in Casson fluid with impacts of viscous dissipation and Ohmic heating. Two states are addressed regarding symmetry, one corresponding to a surface moving in parallel with a free stream and the other a surface moving in the opposite direction to the free stream. In the momentum equation, the Casson model with magnetic field effect is exploited. The governing equations are transformed into the necessary equations using transformations invoking symmetric property of the independent variables. The numerical outputs of the nonlinear governing equations are collected using an efficient improved shooting method with fast convergence and low computational cost. Graphical demonstrations of the influence of relevant parameters on symmetrical behavior for velocity, skin friction, Nusselt number, and temperature are shown. Full article
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Article
Multistep Model Predictive Control for Electrical Drives—A Fast Quadratic Programming Solution
Symmetry 2022, 14(3), 626; https://doi.org/10.3390/sym14030626 - 21 Mar 2022
Viewed by 449
Abstract
Due to its merits of fast dynamic response, flexible inclusion of constraints and the ability to handle multiple control targets, model predictive control has been widely applied in the symmetry topologies, e.g., electrical drive systems. Predictive current control is penalized by the high [...] Read more.
Due to its merits of fast dynamic response, flexible inclusion of constraints and the ability to handle multiple control targets, model predictive control has been widely applied in the symmetry topologies, e.g., electrical drive systems. Predictive current control is penalized by the high current ripples at steady state because only one switching state is employed in every sampling period. Although the current quality can be improved at a low switching frequency by the extension of the prediction horizon, the number of searched switching states will grow exponentially. To tackle the aforementioned issue, a fast quadratic programming solver is proposed for multistep predictive current control in this article. First, the predictive current control is described as a quadratic programming problem, in which the objective function is rearranged based on the current derivatives. To avoid the exhaustive search, two vectors close to the reference derivative are preselected in every prediction horizon. Therefore, the number of searched switching states is significantly reduced. Experimental results validate that the predictive current control with a prediction horizon of 5 can achieve an excellent control performance at both steady state and transient state while the computational time is low. Full article
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Article
Numerical Investigation of the Two-Dimensional Fredholm Integral Equations of the Second Kind by Bernstein Operators
Symmetry 2022, 14(3), 625; https://doi.org/10.3390/sym14030625 - 21 Mar 2022
Viewed by 355
Abstract
In this study, the numerical solutions of linear two-dimensional Fredholm integral equations of the second kind via Bernstein operators are considered. The method is presented with illustrative examples for regularized-equal and Chebyshev collocation points. The obtained numerical results from illustrative examples show that [...] Read more.
In this study, the numerical solutions of linear two-dimensional Fredholm integral equations of the second kind via Bernstein operators are considered. The method is presented with illustrative examples for regularized-equal and Chebyshev collocation points. The obtained numerical results from illustrative examples show that the proposed numerical algorithm is accurate and efficient for solving linear two-dimensional Fredholm integral equation of the second kind. Full article
(This article belongs to the Special Issue Numerical Analysis and Its Application and Symmetry)
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Article
Quantum Circuits for the Preparation of Spin Eigenfunctions on Quantum Computers
Symmetry 2022, 14(3), 624; https://doi.org/10.3390/sym14030624 - 21 Mar 2022
Cited by 1 | Viewed by 562
Abstract
The application of quantum algorithms to the study of many-particle quantum systems requires the ability to prepare wave functions that are relevant in the behavior of the system under study. Hamiltonian symmetries are important instruments used to classify relevant many-particle wave functions and [...] Read more.
The application of quantum algorithms to the study of many-particle quantum systems requires the ability to prepare wave functions that are relevant in the behavior of the system under study. Hamiltonian symmetries are important instruments used to classify relevant many-particle wave functions and to improve the efficiency of numerical simulations. In this work, quantum circuits for the exact and approximate preparation of total spin eigenfunctions on quantum computers are presented. Two different strategies are discussed and compared: exact recursive construction of total spin eigenfunctions based on the addition theorem of angular momentum, and heuristic approximation of total spin eigenfunctions based on the variational optimization of a suitable cost function. The construction of these quantum circuits is illustrated in detail, and the preparation of total spin eigenfunctions is demonstrated on IBM quantum devices, focusing on three- and five-spin systems on graphs with triangle connectivity. Full article
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Article
A New Meta-Heuristics Data Clustering Algorithm Based on Tabu Search and Adaptive Search Memory
Symmetry 2022, 14(3), 623; https://doi.org/10.3390/sym14030623 - 20 Mar 2022
Cited by 6 | Viewed by 591
Abstract
Clustering is a popular data analysis and data mining problem. Symmetry can be considered as a pre-attentive feature, which can improve shapes and objects, as well as reconstruction and recognition. The symmetry-based clustering methods search for clusters that are symmetric with respect to [...] Read more.
Clustering is a popular data analysis and data mining problem. Symmetry can be considered as a pre-attentive feature, which can improve shapes and objects, as well as reconstruction and recognition. The symmetry-based clustering methods search for clusters that are symmetric with respect to their centers. Furthermore, the K-means (K-M) algorithm can be considered as one of the most common clustering methods. It can be operated more quickly in most conditions, as it is easily implemented. However, it is sensitively initialized and it can be easily trapped in local targets. The Tabu Search (TS) algorithm is a stochastic global optimization technique, while Adaptive Search Memory (ASM) is an important component of TS. ASM is a combination of different memory structures that save statistics about search space and gives TS needed heuristic data to explore search space economically. Thus, a new meta-heuristics algorithm called (MHTSASM) is proposed in this paper for data clustering, which is based on TS and K-M. It uses TS to make economic exploration for data with the help of ASM. It starts with a random initial solution. It obtains neighbors of the current solution called trial solutions and updates memory elements for each iteration. The intensification and diversification strategies are used to enhance the search process. The proposed MHTSASM algorithm performance is compared with multiple clustering techniques based on both optimization and meta-heuristics. The experimental results indicate the superiority of the MHTSASM algorithm compared with other multiple clustering algorithms. Full article
(This article belongs to the Topic Applied Metaheuristic Computing)
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Article
Subclasses of Bi-Univalent Functions Connected with Integral Operator Based upon Lucas Polynomial
Symmetry 2022, 14(3), 622; https://doi.org/10.3390/sym14030622 - 20 Mar 2022
Cited by 3 | Viewed by 385
Abstract
In the contemporary paper, we introduce new subclasses of analytic and bi-univalent functions involving integral operator based upon Lucas polynomial. Furthermore, we find estimates on the first two Taylor-Maclaurin coefficients a2 and a3 for functions in these subclasses and obtain Fekete-Szegö [...] Read more.
In the contemporary paper, we introduce new subclasses of analytic and bi-univalent functions involving integral operator based upon Lucas polynomial. Furthermore, we find estimates on the first two Taylor-Maclaurin coefficients a2 and a3 for functions in these subclasses and obtain Fekete-Szegö problem for these subclasses. Full article
(This article belongs to the Special Issue Symmetry in Functional Equations and Analytic Inequalities III)
Article
2D and 3D Visualization for the Static Bifurcations and Nonlinear Oscillations of a Self-Excited System with Time-Delayed Controller
Symmetry 2022, 14(3), 621; https://doi.org/10.3390/sym14030621 - 20 Mar 2022
Cited by 2 | Viewed by 455
Abstract
This research focuses on the nonlinear vibration control of a self-excited single-degree-of-freedom system. The integral resonant controller (IRC) is introduced to stabilize the unstable motion and suppress nonlinear oscillations of the considered system. The nonlinear dynamical equations that govern the vibratory behaviors of [...] Read more.
This research focuses on the nonlinear vibration control of a self-excited single-degree-of-freedom system. The integral resonant controller (IRC) is introduced to stabilize the unstable motion and suppress nonlinear oscillations of the considered system. The nonlinear dynamical equations that govern the vibratory behaviors of the proposed closed-loop control system are investigated using perturbation analysis, where loop delays have been included in the studied model. The system bifurcation behaviors have been visualized in both the two and three-dimensional spaces, and corresponding dynamical behaviors have been explored numerically using the bifurcation diagrams, Poincaré map, time-response, zero-one chaotic test algorithm, and frequency spectrum. The obtained analytical investigations revealed that the uncontrolled system can oscillate with one of four vibration modes depending on the excitation frequency, which are mono-stable periodic motion, bi-stable periodic motion, periodic and quasi-period motion, and quasi-periodic motion only. In addition, it is found that the existence of time delays in the control loop can either improve or degrade the control performance. Therefore, an objective function has been introduced to design the optimum control parameters. Based on the derived objective function, it is found that the performance of the proposed control strategy is proportional to the product of the control and feedback gains and inversely proportional to the internal loop feedback gain when the loop delays are neglected. Moreover, it is reported that the controller performance is a periodic function of the total sum of the loop delays. Accordingly, the optimal operating conditions of the time-delayed integral resonant controller have been explained. Finally, numerical validations for all obtained analytical results have been performed, where an excellent correspondence between the analytical and numerical investigations has been demonstrated. Full article
(This article belongs to the Special Issue Nonlinear Analysis and Its Applications in Symmetry)
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Article
Moving Forward by Shaking Sideways
Symmetry 2022, 14(3), 620; https://doi.org/10.3390/sym14030620 - 20 Mar 2022
Cited by 1 | Viewed by 406
Abstract
We investigate a simple model for a self-propelled swimmer, which consists of a fluctuating force acting at a point on a rigid body. The rigid body is subject to Newton’s equations with linear friction, corresponding to drag in a viscous fluid. The force [...] Read more.
We investigate a simple model for a self-propelled swimmer, which consists of a fluctuating force acting at a point on a rigid body. The rigid body is subject to Newton’s equations with linear friction, corresponding to drag in a viscous fluid. The force has zero time average, so net motion is challenging. We show that the swimmer can inch forward by shaking from side to side and exploiting friction coupled with nonlinearity. For large enough forcing amplitude it can reverse direction and swim backward. Full article
(This article belongs to the Special Issue Symmetry and Symmetry-Breaking in Fluid Dynamics)
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Article
Protecting the Intellectual Property of Speaker Recognition Model by Black-Box Watermarking in the Frequency Domain
Symmetry 2022, 14(3), 619; https://doi.org/10.3390/sym14030619 - 20 Mar 2022
Cited by 2 | Viewed by 537
Abstract
Benefiting from the rapid development of computer hardware and big data, deep neural networks (DNNs) have been widely applied in commercial speaker recognition systems, achieving a kind of symmetry between “machine-learning-as-a-service” providers and consumers. However, this symmetry is threatened by attackers whose goal [...] Read more.
Benefiting from the rapid development of computer hardware and big data, deep neural networks (DNNs) have been widely applied in commercial speaker recognition systems, achieving a kind of symmetry between “machine-learning-as-a-service” providers and consumers. However, this symmetry is threatened by attackers whose goal is to illegally steal and use the service. It is necessary to protect these DNN models from symmetry breaking, i.e., intellectual property (IP) infringement, which motivated the authors to present a black-box watermarking method for IP protection of the speaker recognition model in this paper. The proposed method enables verification of the ownership of the target marked model by querying the model with a set of carefully crafted trigger audio samples, without knowing the internal details of the model. To achieve this goal, the proposed method marks the host model by training it with normal audio samples and carefully crafted trigger audio samples. The trigger audio samples are constructed by adding a trigger signal in the frequency domain of normal audio samples, which enables the trigger audio samples to not only resist against malicious attack but also avoid introducing noticeable distortion. In order to not impair the performance of the speaker recognition model on its original task, a new label is assigned to all the trigger audio samples. The experimental results show that the proposed black-box DNN watermarking method can not only reliably protect the intellectual property of the speaker recognition model but also maintain the performance of the speaker recognition model on its original task, which verifies the superiority and maintains the symmetry between “machine-learning-as-a-service” providers and consumers. Full article
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Article
Double Controlled Quasi Metric Like Spaces
Symmetry 2022, 14(3), 618; https://doi.org/10.3390/sym14030618 - 19 Mar 2022
Viewed by 578
Abstract
In this article, we present a generalization of the double controlled metric like spaces, called quasi double controlled metric like spaces, by assuming that the symmetric condition is not necessary satisfied. Moreover, the self distance is not necessary zero. Full article
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Article
Swing-By Applications and Estimation of the Van Allen Belts’ Radiation Exposure for a Spacecraft in a Low Thrust Transfer to the Moon
Symmetry 2022, 14(3), 617; https://doi.org/10.3390/sym14030617 - 19 Mar 2022
Viewed by 552
Abstract
This paper presents a handful of the underlying properties of a spacecraft’s transfer from a low Earth orbit (LEO) to the moon’s orbit using an electric propulsion (low-thrust) system. The use of analytical and numerical-analytical modeling in complex natural and technical processes is [...] Read more.
This paper presents a handful of the underlying properties of a spacecraft’s transfer from a low Earth orbit (LEO) to the moon’s orbit using an electric propulsion (low-thrust) system. The use of analytical and numerical-analytical modeling in complex natural and technical processes is a key factor in this issue of Symmetry, which has been thoroughly explored in this paper. First, an optimization problem was considered to find the locations and lengths of the thrust arcs that maximizes the final mass of the spacecraft for a number of transfer orbits, thereby limiting the scope of trajectories to the most fuel-efficient ones. In addition to this, the Van Allen belts were modelled according to the density of electrons and protons in each point of space, in order to measure the total radiation absorbed by the spacecraft through an integration of the density of particles over the corresponding time. The simulations were then able to predict the relationship between the fluence of the particles and several initial parameters, such as the initial orbit’s eccentricity and the propulsion system’s characteristics. Then, a multi-linear regression and an artificial neural network were fitted to the data through a regression that related the fluence of protons and electrons as a function of the following parameters: mission time, specific impulse, thrust, final mass (i.e., propellant consumption) and the initial height of the perigee, eccentricity and inclination. This analysis was proven to be powerful due to the expressive values from statistical tests, showing underlying positive correlations between thrust, mission time and final spacecraft mass with the fluence of particles, and negative correlations between specific impulse, initial orbit eccentricity, inclination and the height of the perigee with the fluence of particles. Finally, an analysis of a swing-by maneuver was also carried out, together with the radiation incidence, revealing hidden dependencies of the increments in energy and velocity with respect to the fuel consumption, radiation absorption, propulsion system and initial orbit parameters. Full article
(This article belongs to the Special Issue Advances in Mechanics and Control)
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Article
Structural Characterization of Mono- and Dimethylphosphatidylethanolamines from Various Organisms Using a Complex Analytical Strategy including Chiral Chromatography
Symmetry 2022, 14(3), 616; https://doi.org/10.3390/sym14030616 - 19 Mar 2022
Viewed by 663
Abstract
Two minor phospholipids, i.e., mono- and/or dimethylphosphatidylethanolamines, are widespread in many organisms, from bacteria to higher plants and animals. A molecular mixture of methyl-PE and dimethyl-PE was obtained from total lipids by liquid chromatography and further identified by mass spectrometry. Total methyl-PE and [...] Read more.
Two minor phospholipids, i.e., mono- and/or dimethylphosphatidylethanolamines, are widespread in many organisms, from bacteria to higher plants and animals. A molecular mixture of methyl-PE and dimethyl-PE was obtained from total lipids by liquid chromatography and further identified by mass spectrometry. Total methyl-PE and dimethyl-PE were cleaved by phospholipase C, and the resulting diacylglycerols, in the form of acetyl derivatives, were separated into alkyl-acyl, alkenyl-acyl, and diacylglycerols. Reversed-phase LC/MS allowed dozens of molecular species to be identified and further analyzed. This was performed on a chiral column, and identification by tandem positive ESI revealed that diacyl derivatives from all four bacteria were mixtures of both R and S enantiomers. The same applied to alkenyl-acyl derivatives of anaerobic bacteria. Analysis thus confirmed that some bacteria biosynthesize phospholipids having both sn-glycerol-3-phosphate and sn-glycerol-1-phosphate as precursors. These findings were further supported by data already published in GenBank. The use of chiral chromatography made it possible to prove that both enantiomers of glycerol phosphate of some molecular species of mono- and dimethylphosphatidylethanolamines are present. The result of the analysis can be interpreted that the cultured bacteria do not have homochiral membranes but, on the contrary, have an asymmetric, i.e., heterochiral membranes. Full article
(This article belongs to the Special Issue Recent Advance in Biochemistry, Genetics and Molecular Biology)
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Article
Skorokhod Reflection Problem for Delayed Brownian Motion with Applications to Fractional Queues
Symmetry 2022, 14(3), 615; https://doi.org/10.3390/sym14030615 - 19 Mar 2022
Viewed by 420
Abstract
Several queueing systems in heavy traffic regimes are shown to admit a diffusive approximation in terms of the Reflected Brownian Motion. The latter is defined by solving the Skorokhod reflection problem on the trajectories of a standard Brownian motion. In recent years, fractional [...] Read more.
Several queueing systems in heavy traffic regimes are shown to admit a diffusive approximation in terms of the Reflected Brownian Motion. The latter is defined by solving the Skorokhod reflection problem on the trajectories of a standard Brownian motion. In recent years, fractional queueing systems have been introduced to model a class of queueing systems with heavy-tailed interarrival and service times. In this paper, we consider a subdiffusive approximation for such processes in the heavy traffic regime. To do this, we introduce the Delayed Reflected Brownian Motion by either solving the Skorohod reflection problem on the trajectories of the delayed Brownian motion or by composing the Reflected Brownian Motion with an inverse stable subordinator. The heavy traffic limit is achieved via the continuous mapping theorem. As a further interesting consequence, we obtain a simulation algorithm for the Delayed Reflected Brownian Motion via a continuous-time random walk approximation. Full article
(This article belongs to the Special Issue Stochastic Analysis with Applications and Symmetry)
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Article
Semantic SLAM Based on Deep Learning in Endocavity Environment
Symmetry 2022, 14(3), 614; https://doi.org/10.3390/sym14030614 - 19 Mar 2022
Viewed by 829
Abstract
Traditional endoscopic treatment methods restrict the surgeon’s field of view. New approaches to laparoscopic visualization have emerged due to the advent of robot-assisted surgical techniques. Lumen simultaneous localization and mapping (SLAM) technology can use the image sequence taken by the endoscope to estimate [...] Read more.
Traditional endoscopic treatment methods restrict the surgeon’s field of view. New approaches to laparoscopic visualization have emerged due to the advent of robot-assisted surgical techniques. Lumen simultaneous localization and mapping (SLAM) technology can use the image sequence taken by the endoscope to estimate the pose of the endoscope and reconstruct the lumen scene in minimally invasive surgery. This technology gives the surgeon better visual perception and is the basis for the development of surgical navigation systems as well as medical augmented reality. However, the movement of surgical instruments in the internal cavity can interfere with the SLAM algorithm, and the feature points extracted from the surgical instruments may cause errors. Therefore, we propose a modified endocavity SLAM method combined with deep learning semantic segmentation that introduces a convolution neural network based on U-Net architecture with a symmetric encoder–decoder structure in the visual odometry with the goals of solving the binary segmentation problem between surgical instruments and the lumen background and distinguishing dynamic feature points. Its segmentation performance is improved by using pretrained encoders on the network model to obtain more accurate pixel-level instrument segmentation. In this setting, the semantic segmentation is used to reject the feature points on the surgical instruments and reduce the impact caused by dynamic surgical instruments. This can provide more stable and accurate mapping results compared to ordinary SLAM systems. Full article
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Article
A Method for the Design of Bicomplex Orthogonal DSP Algorithms for Applications in Intelligent Radio Access Networks
Symmetry 2022, 14(3), 613; https://doi.org/10.3390/sym14030613 - 18 Mar 2022
Viewed by 553
Abstract
In this paper, a new method for designing orthogonal bicomplex digital signal processing (DSP) algorithms is developed. In contrast to those previously reported on, the method proposed is universal, since it is not affected by the order or the type of the real [...] Read more.
In this paper, a new method for designing orthogonal bicomplex digital signal processing (DSP) algorithms is developed. In contrast to those previously reported on, the method proposed is universal, since it is not affected by the order or the type of the real digital processing algorithm employed as a prototype. The method is based on a transformation starting with either real or complex orthogonal DSP algorithms represented in the z-domain, and transforming them into orthogonal bicomplex algorithms. The proposed new method is applied in the design of bilinear orthogonal bicomplex DSP systems with a canonical number of elements, the main advantage of which is that the order of the digital system is reduced by a factor of four. As well as being canonical, the orthogonal bicomplex digital systems are also symmetrical structures, as a result of which they offer parallelism and subsequent unification. It is experimentally shown that bicomplex orthogonal DSP algorithms acquire the properties of the initial algorithm prototype, irrespective of whether it is real or complex. Since the new design method is universally applicable, it can be used to develop bicomplex orthogonal digital algorithms of any order and type. Being simple, canonical, and symmetrical—and, thus, leading to lower equipment cost, reduced complexity, and higher energy efficiency—these structures may well be appropriate for the enhancement of the implementation of intelligent algorithms in next-generation radio access networks. Full article
(This article belongs to the Special Issue Symmetry and Asymmetry in Communications Engineering Ⅱ)
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Article
Behavior of Vortex-Like Inhomogeneities Originating in Magnetic Films with Modulated Uniaxial Anisotropy in a Planar Magnetic Field
Symmetry 2022, 14(3), 612; https://doi.org/10.3390/sym14030612 - 18 Mar 2022
Viewed by 505
Abstract
This paper investigates the processes of magnetization reversal of a uniaxial ferromagnetic disk containing a columnar defect of the potential well type in perpendicular and planar magnetic fields. The characteristic stages of magnetization reversal of the domain structure of the disk and vortex-like [...] Read more.
This paper investigates the processes of magnetization reversal of a uniaxial ferromagnetic disk containing a columnar defect of the potential well type in perpendicular and planar magnetic fields. The characteristic stages of magnetization reversal of the domain structure of the disk and vortex-like inhomogeneities forming on the defect are determined. The critical fields of their existence are found and an explanation is given for the presence of a significant difference in their values for the perpendicular and planar fields of the defect magnetization reversal. The role of chirality in the behavior of a Bloch-type magnetic skyrmion during the magnetization reversal of a defect in a planar field is shown. Full article
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Article
A Novel Classification Framework for Hyperspectral Image Data by Improved Multilayer Perceptron Combined with Residual Network
Symmetry 2022, 14(3), 611; https://doi.org/10.3390/sym14030611 - 18 Mar 2022
Viewed by 543
Abstract
Convolutional neural networks (CNNs) have attracted extensive attention in the field of modern remote sensing image processing and show outstanding performance in hyperspectral image (HSI) classification. Nevertheless, some hyperspectral images have fixed position priors and parameter sharing between different positions, so the common [...] Read more.
Convolutional neural networks (CNNs) have attracted extensive attention in the field of modern remote sensing image processing and show outstanding performance in hyperspectral image (HSI) classification. Nevertheless, some hyperspectral images have fixed position priors and parameter sharing between different positions, so the common convolution layer may ignore some important fine and useful information and cannot guarantee to effectively capture the optimal image features. This paper proposes an improved multilayer perceptron (IMLP) and IMLP combined with ResNet (IMLP-ResNet) two models for HSI classification. Combined with the characteristics of hyperspectral data, we design IMLP based on three improvements. Specifically, a depthwise over-parameterized convolutional layer is introduced to increase learnable parameters of the model in IMLP, which speeds up the convergence of the model without increasing the computational complexity. Secondly, a Focal Loss function is used to suppress the useless ones in the classification task and enhance the critical spectral–spatial features, which allow the IMLP network to learn more useful hyperspectral image information. Furthermore, to enhance the convergence speed of the network, cosine annealing is introduced to further improve the training performance of IMLP. Furthermore, the IMLP module is combined with a residual network (IMLP-ResNet) to construct a symmetric structure, which extracts more advanced semantic information from hyperspectral images. The proposed IMLP and IMLP-ResNet are tested on the two public HSI datasets (i.e., Indian Pines and Pavia University) and a real hyperspectral dataset (Xuzhou). Experimental results demonstrate the superiority of the proposed IMLP-ResNet method over several state-of-the-art methods with the highest OA, which outperforms CNN by 8.19%, 6.28%, 5.59% and outperforms ResNet by 3.52%, 3.54%, 2.67% on Indian Pines, Pavia University and Xuzhou datasets, respectively, and demonstrates that the well-designed MLPs can also obtain remarkable classification performance of HSI. Full article
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Review
Decentralized Multi-Robot Collision Avoidance: A Systematic Review from 2015 to 2021
Symmetry 2022, 14(3), 610; https://doi.org/10.3390/sym14030610 - 18 Mar 2022
Viewed by 673
Abstract
An exploration task can be performed by a team of mobile robots more efficiently than human counterparts. They can access and give live updates for hard-to-reach areas such as a disaster site or a sewer. However, they face some issues hindering them from [...] Read more.
An exploration task can be performed by a team of mobile robots more efficiently than human counterparts. They can access and give live updates for hard-to-reach areas such as a disaster site or a sewer. However, they face some issues hindering them from optimal path planning due to the symmetrical shape of the environments. Multiple robots are expected to explore more areas in less time while solving robot localization and collision-avoidance issues. When deploying a multi-robot system, it is ensured that the hardware parts do not collide with each other or the surroundings, especially in symmetric environments. Two types of methods are used for collision avoidance: centralized and decentralized. The decentralized approach has mainly been used in recent times, as it is computationally less expensive. This article aims to conduct a systematic literature review of different collision-avoidance strategies and analyze the performance of innovative collision-avoidance techniques. Different methods such as Reinforcement Learning (RL), Model Predictive Control (MPC), Altruistic Coordination, and other approaches followed by selected studies are also discussed. A total of 17 studies are included in this review, extracted from seven databases. Two experimental designs are studied: empty/open space and confined indoor space. Our analysis observed that most of the studies focused on empty/open space scenarios and verified the proposed model only through simulation. ORCA is the primary method, against which all the state-of-the-art techniques are evaluated. This article provides a comparison between different methods used for multi-robot collision avoidance. It discusses if the methods used are focused on safety or path planning. It also sheds light on the limitations of the studies included and possible future directions. Full article
(This article belongs to the Section Computer Science and Symmetry/Asymmetry)
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Article
Genetic-Algorithm-Inspired Difficulty Adjustment for Proof-of-Work Blockchains
Symmetry 2022, 14(3), 609; https://doi.org/10.3390/sym14030609 - 18 Mar 2022
Viewed by 491
Abstract
In blockchains, the principle of proof-of-work (PoW) is used to compute a complex mathematical problem. The computation complexity is governed by the difficulty, adjusted periodically to control the rate at which new blocks are created. The network hash rate determines this, a phenomenon [...] Read more.
In blockchains, the principle of proof-of-work (PoW) is used to compute a complex mathematical problem. The computation complexity is governed by the difficulty, adjusted periodically to control the rate at which new blocks are created. The network hash rate determines this, a phenomenon of symmetry, as the difficulty also increases when the hash rate increases. If the hash rate grows or declines exponentially, the block creation interval cannot be maintained. A genetic algorithm (GA) is proposed as an additional mechanism to the existing difficulty adjustment algorithm for optimizing the blockchain parameters. The study was conducted with four scenarios in mind, including a default scenario that simulates a regular blockchain. All the scenarios with the GA were able to achieve a lower standard deviation of the average block time and difficulty compared to the default blockchain network without GA. The scenario of a fixed difficulty adjustment interval with GA was able to reduce the standard deviation of the average block time by 80.1%, from 497.1 to 98.9, and achieved a moderate median block propagation time of 6.81 s and a stale block rate of 6.67%. Full article
(This article belongs to the Special Issue Computational Intelligence and Soft Computing: Recent Applications)
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Article
Geometric Classification of Warped Products Isometrically Immersed into Conformal Sasakian Space Froms
Symmetry 2022, 14(3), 608; https://doi.org/10.3390/sym14030608 - 18 Mar 2022
Viewed by 453
Abstract
Warped products play important roles in differential geometry, general relativity, and symmetry science. In this paper, we study the warped product pointwise semi-slant submanifolds that are isometrically immersed into conformal Sasakian space form. We show that there does not exist any proper warped [...] Read more.
Warped products play important roles in differential geometry, general relativity, and symmetry science. In this paper, we study the warped product pointwise semi-slant submanifolds that are isometrically immersed into conformal Sasakian space form. We show that there does not exist any proper warped product pointwise semi-slant submanifolds in conformal Sasakian manifolds. We derived some geometric inequalities for squared norm of second fundamental form from a warped product pointwise semi-slant submanifold into a conformal Sasakian manifolds. Full article
(This article belongs to the Special Issue Symmetry and Its Application in Differential Geometry and Topology)
Article
Narrowband Active Noise Control Using Decimated Controller for Disturbance with Close Frequencies
Symmetry 2022, 14(3), 607; https://doi.org/10.3390/sym14030607 - 18 Mar 2022
Viewed by 448
Abstract
In this paper, multi-channel active noise control systems subjected to narrowband disturbances with close frequencies are investigated. Instead of controlling each frequency separately, a mixed-reference signal is assumed and thus a transversal controller is utilized. First, the convergent behaviors of a generalized FxLMS-based [...] Read more.
In this paper, multi-channel active noise control systems subjected to narrowband disturbances with close frequencies are investigated. Instead of controlling each frequency separately, a mixed-reference signal is assumed and thus a transversal controller is utilized. First, the convergent behaviors of a generalized FxLMS-based algorithm are theoretically analyzed in the mean sense, from which the influence of the controller structure on the convergence rate is revealed. A novel narrowband algorithm is then proposed, in which a decimated transversal controller is used to alleviate the computational burden. Simulations based on a 4 × 8 active-noise-control system are carried out to verify the proposed method. The results show that a good convergence rate can be obtained, and the computational complexity can also be greatly reduced. Full article
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Article
Multi-Parameter Quantum Integral Identity Involving Raina’s Function and Corresponding q-Integral Inequalities with Applications
Symmetry 2022, 14(3), 606; https://doi.org/10.3390/sym14030606 - 18 Mar 2022
Viewed by 483
Abstract
Convexity performs its due role in the theoretical field of inequalities according to the nature and conduct of the properties it displays. A correlation connectivity, which is visible between the two variables symmetry and convexity, enhances its importance. In this paper, we derive [...] Read more.
Convexity performs its due role in the theoretical field of inequalities according to the nature and conduct of the properties it displays. A correlation connectivity, which is visible between the two variables symmetry and convexity, enhances its importance. In this paper, we derive a new multi-parameter quantum integral identity involving Raina’s function. Applying this generic identity as an auxiliary result, we establish some new generalized quantum estimates of certain integral inequalities pertaining to the class of Rs-convex functions. Moreover, we give quantum integral inequalities for the product of Rs1- and Rs2-convex functions as well as another quantum result for a function that satisfies a special condition. In order to demonstrate the efficiency of our main results, we offer many important special cases for suitable choices of parameters and finally for Rs-convex functions that are absolute-value bounded. Full article
(This article belongs to the Special Issue Symmetry in Quantum Calculus)
Article
Coupled Fixed Points for Hardy–Rogers Type of Maps and Their Applications in the Investigations of Market Equilibrium in Duopoly Markets for Non-Differentiable, Nonlinear Response Functions
Symmetry 2022, 14(3), 605; https://doi.org/10.3390/sym14030605 - 18 Mar 2022
Viewed by 451
Abstract
In this paper we generalize Hardy–Rogers maps in the context of coupled fixed points. We comment on the symmetry of some of the coefficients involved in the Hardy–Rogers condition, and thus, we deduce a simpler formula. We generalize, with the help of the [...] Read more.
In this paper we generalize Hardy–Rogers maps in the context of coupled fixed points. We comment on the symmetry of some of the coefficients involved in the Hardy–Rogers condition, and thus, we deduce a simpler formula. We generalize, with the help of the obtained main theorem, some known results about existence and uniqueness of market equilibrium in duopoly markets. As a consequence, we ascertain that the equilibrium production should be equal for both market participants provided that they have symmetric response functions. With the help of the main theorem, we investigate and enrich some recent results regarding market equilibrium in duopoly markets. We define a generalized response function that includes production and surpluses. Finally, we illustrate a possible application of the main result in the investigation of market equilibrium when the payoff functions are non-differentiable. Full article
(This article belongs to the Section Mathematics and Symmetry/Asymmetry)
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Article
An Enhanced Key Schedule Algorithm of PRESENT-128 Block Cipher for Random and Non-Random Secret Keys
Symmetry 2022, 14(3), 604; https://doi.org/10.3390/sym14030604 - 18 Mar 2022
Viewed by 478
Abstract
The key schedule algorithm (KSA) is a crucial element of symmetric block ciphers with a direct security impact. Despite its undeniable significance, the KSA is still a less focused area in the design of an encryption algorithm. PRESENT is a symmetric lightweight block [...] Read more.
The key schedule algorithm (KSA) is a crucial element of symmetric block ciphers with a direct security impact. Despite its undeniable significance, the KSA is still a less focused area in the design of an encryption algorithm. PRESENT is a symmetric lightweight block cipher that provides the optimal balance between security, performance, and minimal cost in IoT. However, the linear functions in KSA lead to a slow and predictable bit transition, indicating the relationship between round keys. A robust KSA should produce random and independent round keys irrespective of the secret key. Therefore, this research aims to improve the KSA PRESENT-128 block cipher with enhanced randomness, round key bit difference, and the avalanche effect. The experiments on round keys and ciphertext with random, low density and high-density secret key datasets endorse the expected improvements. Moreover, the results show that the improved KSA produces random round keys that successfully pass the NIST randomness test. The bit transition from one round key to another is increased from 20% to 40%, where a greater inclination of the avalanche effect has an increased effect with 50% bit change. On the other hand, the improved KSA PRESENT requires an additional 0.001871 s to generate round keys, as a security cost trade-off. Full article
(This article belongs to the Section Computer Science and Symmetry/Asymmetry)
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Article
Symmetric Properties of Routh–Hurwitz and Schur–Cohn Stability Criteria
Symmetry 2022, 14(3), 603; https://doi.org/10.3390/sym14030603 - 18 Mar 2022
Cited by 1 | Viewed by 478
Abstract
It is often noticed in the literature that some key results on the stability of discrete-time systems of difference equations are obtained from their corresponding results on the stability of continuous-time systems of differential equations using suitable conformal mappings or bilinear transformations. Such [...] Read more.
It is often noticed in the literature that some key results on the stability of discrete-time systems of difference equations are obtained from their corresponding results on the stability of continuous-time systems of differential equations using suitable conformal mappings or bilinear transformations. Such observations lead to the search for a unified approach to the study of root distribution for real and complex polynomials, with respect to the left-half plane for continuous-time systems (Routh–Hurwitz stability) and with respect to the unit disc for discrete-time systems (Schur–Cohn stability). This paper is a further contribution toward this objective. We present, in a systematic way, the similarities, and yet, the differences between these two types of stability, and we highlight the symmetry that exists between them. We also illustrate how results on the stability of continuous-time systems are conveyed to the stability of discrete-time systems through the proposed techniques. It should be mentioned that the results on Schur–Cohn stability are known to be harder to obtain than Routh–Hurwitz stability ones, giving more credibility to the proposed approach. Full article
(This article belongs to the Topic Dynamical Systems: Theory and Applications)
Article
The Consistent Couple Stress Theory-Based Vibration and Post-Buckling Analysis of Bi-directional Functionally Graded Microbeam
Symmetry 2022, 14(3), 602; https://doi.org/10.3390/sym14030602 - 17 Mar 2022
Viewed by 559
Abstract
The present work aims to study the free vibration, buckling and post-buckling behaviors of bidirectional functionally graded (BDFG) microbeams. The material properties of a BDFG microbeam were varied continuously in both thickness and axial directions. Furthermore, four different kinds of material distribution function [...] Read more.
The present work aims to study the free vibration, buckling and post-buckling behaviors of bidirectional functionally graded (BDFG) microbeams. The material properties of a BDFG microbeam were varied continuously in both thickness and axial directions. Furthermore, four different kinds of material distribution function were taken into consideration, two of which were symmetrical in the thickness direction, and the remaining two were asymmetrical. Employing the Timoshenko beam theory and the consistent couple stress theory (CCST), the governing equations and associated boundary conditions of BDFG microbeams were formulated by Hamilton’s principle. The differential quadrature method (DQM) and Newton’s method were applied to solve the eigenvalue problems and buckling path, respectively. Finally, several parametric investigations were carried out to probe the influence of material distribution functions, length to thickness ratio, gradient indexes and size effect on the vibration and buckling behaviors of BDFG microbeam under different boundary conditions. Full article
(This article belongs to the Topic Engineering Mathematics)
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