Journal Description
Symmetry
Symmetry
is an international, peer-reviewed, open access journal covering research on symmetry/asymmetry phenomena wherever they occur in all aspects of natural sciences. Symmetry is published monthly online by MDPI.
- Open Access— free for readers, with article processing charges (APC) paid by authors or their institutions.
- High Visibility: indexed within Scopus, SCIE (Web of Science), CAPlus / SciFinder, Inspec, Astrophysics Data System, and other databases.
- Journal Rank: JCR - Q2 (Multidisciplinary Sciences) / CiteScore - Q1 (General Mathematics); Q1 (Physics and Astronomy); Q1 (Computer Science)
- Rapid Publication: manuscripts are peer-reviewed and a first decision is provided to authors approximately 16.2 days after submission; acceptance to publication is undertaken in 3.5 days (median values for papers published in this journal in the second half of 2023).
- Recognition of Reviewers: reviewers who provide timely, thorough peer-review reports receive vouchers entitling them to a discount on the APC of their next publication in any MDPI journal, in appreciation of the work done.
- Testimonials: See what our editors and authors say about Symmetry.
Impact Factor:
2.7 (2022);
5-Year Impact Factor:
2.7 (2022)
Latest Articles
Frequency Analysis of Asymmetric Circular Organic Solar Cells Embedded in an Elastic Medium under Hygrothermal Conditions
Symmetry 2024, 16(5), 577; https://doi.org/10.3390/sym16050577 - 07 May 2024
Abstract
This research represents the first theoretical investigation about the vibration behavior of circular organic solar cells. Therefore, the vibration response of asymmetric circular organic solar cells that represent a perfect renewable energy source is demonstrated. For this purpose, the differential quadrature method (DQM)
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This research represents the first theoretical investigation about the vibration behavior of circular organic solar cells. Therefore, the vibration response of asymmetric circular organic solar cells that represent a perfect renewable energy source is demonstrated. For this purpose, the differential quadrature method (DQM) is employed. The organic solar cell is modeled as a laminated plate consisting of five layers of Al, P3HT:PCBM, PEDOT:PSS, ITO, and Glass. This cell is rested on a Winkler–Pasternak elastic foundation and assumed to be exposed to various types of hygrothermal loadings. There are three different kinds of temperature and moisture variations that are taken into account: uniform, linear, and nonlinear distribution throughout the cell’s thickness. The displacement field is presented based on a new inverse hyperbolic shear deformation theory considering only two unknowns. The motion equations including hygrothermal effect and plate–foundation interaction are established within the framework of Hamilton’s principle. The DQM is utilized to solve these equations. In order to ensure the accuracy of the proposed theory, the present results are compared with those reported by other higher-order theories. A comprehensive parametric illustration is conducted on the impacts of different parameters involving the geometrical configuration, elastic foundation parameters, temperature, and moisture concentration on the deduced eigenfrequency of the circular organic solar cells.
Full article
(This article belongs to the Section Mathematics)
Open AccessEditorial
Editorial for Special Issue “Various Approaches for Generalized Integral Transforms”
by
Hwajoon Kim
Symmetry 2024, 16(5), 576; https://doi.org/10.3390/sym16050576 - 07 May 2024
Abstract
The Laplace transform can be interpreted as a method of converting a function from the time domain to the complex domain [...]
Full article
(This article belongs to the Special Issue Various Approaches for Generalized Integral Transforms)
Open AccessArticle
Domain Transformation of Distortion Costs for Efficient JPEG Steganography with Symmetric Embedding
by
Yuanfeng Pan and Jiangqun Ni
Symmetry 2024, 16(5), 575; https://doi.org/10.3390/sym16050575 - 07 May 2024
Abstract
Nowadays, most image steganographic schemes embed secret messages by minimizing a well-designed distortion cost function for the corresponding domain, i.e., the spatial domain for spatial image steganography or the JPEG (Joint Photographic Experts Group) domain for JPEG image steganography. In this paper, we
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Nowadays, most image steganographic schemes embed secret messages by minimizing a well-designed distortion cost function for the corresponding domain, i.e., the spatial domain for spatial image steganography or the JPEG (Joint Photographic Experts Group) domain for JPEG image steganography. In this paper, we break the boundary between these two types of schemes by establishing a theoretical link between the distortion costs in the spatial domain and those in the JPEG domain and thus propose a scheme for domain transformations of distortion costs for efficient JPEG steganography with symmetric embedding, which can directly convert the spatial distortion cost into its JPEG counterpart. Specifically, by formulating the distortion cost function for JPEG images in the decompressed spatial domain, a closed-form expression for a distortion cost cross-domain transformation is derived theoretically, which precisely characterizes the conversion from the distortion costs obtained by existing spatial steganographic schemes to those applied in JPEG steganography. Experimental results demonstrate that the proposed method outperforms other advanced JPEG steganographic schemes, e.g., JUNIWARD (JPEG steganography with Universal Wavelet Relative Distortion), JMiPOD (JPEG steganography by Minimizing the Power of the Optimal Detector), and DCDT (Distortion Cost Domain Transformation), in resisting the detection of various advanced steganalyzers.
Full article
(This article belongs to the Section Computer)
Open AccessArticle
Novel Distance Measures of q-Rung Orthopair Fuzzy Sets and Their Applications
by
Donglai Wang, Yige Yuan, Zhe Liu, Sijia Zhu and Zhifang Sun
Symmetry 2024, 16(5), 574; https://doi.org/10.3390/sym16050574 - 07 May 2024
Abstract
The q-rung orthopair fuzzy sets (q-ROFSs), a novel concept for processing vague information, offer a more potent and all-encompassing method compared to traditional fuzzy sets, intuitionistic fuzzy sets, and Pythagorean fuzzy sets. The inclusion of the parameter q allows for
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The q-rung orthopair fuzzy sets (q-ROFSs), a novel concept for processing vague information, offer a more potent and all-encompassing method compared to traditional fuzzy sets, intuitionistic fuzzy sets, and Pythagorean fuzzy sets. The inclusion of the parameter q allows for the q-rung orthopair fuzzy sets to capture a broader range of uncertainty of information. In this paper, we present two novel distance measures for q-ROFSs inspired by the Jensen–Shannon divergence, called and , and we analyze some properties they satisfy, such as non-degeneracy, symmetry, boundedness, and triangular inequality. Then, the normalized distance measures, called and , are proposed and we verify their rationality through numerical experiments. Finally, we apply the proposed distance measures to practical scenarios, including pattern recognition and multicriteria decision-making, and the results demonstrate the effectiveness of the proposed distance measures.
Full article
(This article belongs to the Special Issue Recent Developments on Fuzzy Sets Extensions)
Open AccessArticle
A Nonlinear Programming Approach to Solving Interval-Valued Intuitionistic Hesitant Noncooperative Fuzzy Matrix Games
by
Shuvasree Karmakar and Mijanur Rahaman Seikh
Symmetry 2024, 16(5), 573; https://doi.org/10.3390/sym16050573 - 07 May 2024
Abstract
Initially, fuzzy sets and intuitionistic fuzzy sets were used to address real-world problems with imprecise data. Eventually, the notion of the hesitant fuzzy set was formulated to handle decision makers’ reluctance to accept asymmetric information. However, in certain scenarios, asymmetric information is gathered
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Initially, fuzzy sets and intuitionistic fuzzy sets were used to address real-world problems with imprecise data. Eventually, the notion of the hesitant fuzzy set was formulated to handle decision makers’ reluctance to accept asymmetric information. However, in certain scenarios, asymmetric information is gathered in terms of a possible range of acceptance and nonacceptance by players rather than specific values. Furthermore, decision makers exhibit some hesitancy regarding this information. In such a situation, all the aforementioned expansions of fuzzy sets are unable to accurately represent the scenario. The purpose of this article is to present asymmetric information situations in which the range of choices takes into account the hesitancy of players in accepting or not accepting information. To illustrate these problems, we develop matrix games that consider the payoffs of interval-valued intuitionistic hesitant fuzzy elements (IIHFEs). Dealing with these types of fuzzy programming problems requires a significant amount of effort. To solve these matrix games, we formulate two interval-valued intuitionistic hesitant fuzzy programming problems. Preserving the hesitant nature of the payoffs to determine the optimal strategies, these two problems are transformed into two nonlinear programming problems. This transformation involves using mathematical operations for IIHFEs. Here, we construct a novel aggregation operator of IIHFEs, viz., min-max operators of IIHFEs. This operator is suitable for applying the developed methodology. The cogency and applicability of the proposed methodology are verified through a numerical example based on the situation of conflict between hackers and defenders to prevent damage to cybersecurity. To validate the superiority of the proposed model along with the computed results, we provide comparisons with the existing models.
Full article
(This article belongs to the Special Issue Recent Developments on Fuzzy Sets Extensions)
Open AccessArticle
Towards Modelling Mechanical Shaking Using Potential Energy Surfaces: A Toy Model Analysis
by
Sergei D. Odintsov and Vasilis K. Oikonomou
Symmetry 2024, 16(5), 572; https://doi.org/10.3390/sym16050572 - 07 May 2024
Abstract
In this work, we formalize the effect of mechanical shaking by using various forms of an externally exerted force, which may be constant or may be position-dependent, and we examine the changes in the potential energy surfaces that quantify the chemical reaction. We
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In this work, we formalize the effect of mechanical shaking by using various forms of an externally exerted force, which may be constant or may be position-dependent, and we examine the changes in the potential energy surfaces that quantify the chemical reaction. We use a simple toy model to model the potential energy surfaces of a chemical reaction, and we study the effect of a constant or position-dependent externally exerted force for various forms of the force. As we demonstrate, the effect of the force can be quite dramatic on the potential energy surfaces, which acquire new stationary points and new Newton trajectories that are distinct from the original ones that were obtained in the absence of mechanochemical effects. We also introduce a new approach to mechanochemical interactions, using a dynamical systems approach for the Newton trajectories. As we show, the dynamical system attractor properties of the trajectories in the phase space are identical to the stationary points of the potential energy surfaces, but the phase space contains much more information regarding the possible evolution of the chemical reaction—information that is quantified by the existence of unstable or saddle fixed points in the phase space. We also discuss how an experimental method for a suitable symmetric liquid solution substance might formalize the effect of shaking via various forms of external force, even in the form of an extended coordinate-dependent force matrix. This approach may experimentally quantify the Epstein effect of shaking in chemical solutions via mechanochemistry methods.
Full article
(This article belongs to the Special Issue Symmetry: Recent Developments in Engineering Science and Applications)
Open AccessArticle
Cross-Water–Air Optical Wireless Communication Using Orthogonal Time–Frequency Space Modulation
by
Dianbin Lian, Yan Gao and Jie Lian
Symmetry 2024, 16(5), 571; https://doi.org/10.3390/sym16050571 - 07 May 2024
Abstract
This paper examines the communication difficulties encountered in cross-media wireless optical transmission through simulated research on the utilization of orthogonal time and frequency space (OTFS) modulation technology. Our analysis and comparison demonstrate that OTFS significantly improves the reliability and throughput of data transmission
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This paper examines the communication difficulties encountered in cross-media wireless optical transmission through simulated research on the utilization of orthogonal time and frequency space (OTFS) modulation technology. Our analysis and comparison demonstrate that OTFS significantly improves the reliability and throughput of data transmission in intricate multipath channel settings. In contrast to conventional orthogonal frequency division multiplexing (OFDM) technology, OTFS displays better resilience and transmission effectiveness. We foresee additional enhancements and progress in OTFS technology to present a sturdier and more efficient resolution for wireless communication, thereby providing valuable perspectives and encouragement for associated research initiatives. Our results underscore the capability of OTFS technology to transform wireless communication systems in demanding multipath channel conditions.
Full article
(This article belongs to the Special Issue Symmetry and Its Application in Wireless Communication)
Open AccessArticle
Brauer Analysis of Some Cayley and Nilpotent Graphs and Its Application in Quantum Entanglement Theory
by
Agustín Moreno Cañadas, Ismael Gutierrez and Odette M. Mendez
Symmetry 2024, 16(5), 570; https://doi.org/10.3390/sym16050570 - 06 May 2024
Abstract
Cayley and nilpotent graphs arise from the interaction between graph theory and algebra and are used to visualize the structures of some algebraic objects as groups and commutative rings. On the other hand, Green and Schroll introduced Brauer graph algebras and Brauer configuration
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Cayley and nilpotent graphs arise from the interaction between graph theory and algebra and are used to visualize the structures of some algebraic objects as groups and commutative rings. On the other hand, Green and Schroll introduced Brauer graph algebras and Brauer configuration algebras to investigate the algebras of tame and wild representation types. An appropriated system of multisets (called a Brauer configuration) induces these algebras via a suitable bounded quiver (or bounded directed graph), and the combinatorial properties of such multisets describe corresponding indecomposable projective modules, the dimensions of the algebras and their centers. Undirected graphs are examples of Brauer configuration messages, and the description of the related data for their induced Brauer configuration algebras is said to be the Brauer analysis of the graph. This paper gives closed formulas for the dimensions of Brauer configuration algebras (and their centers) induced by Cayley and nilpotent graphs defined by some finite groups and finite commutative rings. These procedures allow us to give examples of Hamiltonian digraph constructions based on Cayley graphs. As an application, some quantum entangled states (e.g., Greenberger–Horne–Zeilinger and Dicke states) are described and analyzed as suitable Brauer messages.
Full article
(This article belongs to the Special Issue Symmetry in Graph Algorithms and Graph Theory III)
Open AccessArticle
Number of Volatility Regimes in the Muscat Securities Market Index in Oman Using Markov-Switching GARCH Models
by
Brahim Benaid, Iman Al Hasani and Mhamed Eddahbi
Symmetry 2024, 16(5), 569; https://doi.org/10.3390/sym16050569 - 06 May 2024
Abstract
The predominant approach for studying volatility is through various GARCH specifications, which are widely utilized in model-based analyses. This study focuses on assessing the predictive performance of specific GARCH models, particularly the Markov-Switching GARCH (MS-GARCH). The primary objective is to determine the optimal
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The predominant approach for studying volatility is through various GARCH specifications, which are widely utilized in model-based analyses. This study focuses on assessing the predictive performance of specific GARCH models, particularly the Markov-Switching GARCH (MS-GARCH). The primary objective is to determine the optimal number of regimes within the MS-GARCH framework that effectively captures the conditional variance of the Muscat Securities Market Index (MSMI). To achieve this, we employ the Akaike Information Criterion (AIC) to compare different MS-GARCH models, estimated via Maximum Likelihood Estimation (MLE). Our findings indicate that the chosen models consistently exhibit at least two regimes across various GARCH specifications. Furthermore, a validation using the Value at Risk (VaR) confirms the accuracy of volatility forecasts generated by the selected models.
Full article
(This article belongs to the Special Issue Mathematical Theories, Models and Methods in Applied Sciences: Deterministic, Stochastic and Symmetry Perspectives)
Open AccessReview
A Geometric Approach to the Sundman Transformation and Its Applications to Integrability
by
José F. Cariñena
Symmetry 2024, 16(5), 568; https://doi.org/10.3390/sym16050568 - 06 May 2024
Abstract
A geometric approach to the integrability and reduction of dynamical systems, both when dealing with systems of differential equations and in classical physics, is developed from a modern perspective. The main ingredients of this analysis are infinitesimal symmetries and tensor fields that are
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A geometric approach to the integrability and reduction of dynamical systems, both when dealing with systems of differential equations and in classical physics, is developed from a modern perspective. The main ingredients of this analysis are infinitesimal symmetries and tensor fields that are invariant under the given dynamics. A particular emphasis is placed on the existence of alternative invariant volume forms and the associated Jacobi multiplier theory, and then the Hojman symmetry theory is developed as a complement to the Noether theorem and non-Noether constants of motion. We also recall the geometric approach to Sundman infinitesimal time-reparametrisation for autonomous systems of first-order differential equations and some of its applications to integrability, and an analysis of how to define Sundman transformations for autonomous systems of second-order differential equations is proposed, which shows the necessity of considering alternative tangent bundle structures. A short description of alternative tangent structures is provided, and an application to integrability, namely, the linearisability of scalar second-order differential equations under generalised Sundman transformations, is developed.
Full article
(This article belongs to the Special Issue Selected Papers Symmetry 2023—The Fourth Edition of the International Conference on Symmetry)
Open AccessArticle
Assessment of Non-Coplanar Maneuver Parameters and Perturbing Accelerations Using the Minimal Number of Observations
by
Andrey Baranov
Symmetry 2024, 16(5), 567; https://doi.org/10.3390/sym16050567 - 06 May 2024
Abstract
The algorithms for determining the active space object maneuver parameters in the conditions of near-circular orbits are presented in the paper. The right ascension and declination angles are used to determine the parameters of a single maneuver with transversal and lateral components (the
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The algorithms for determining the active space object maneuver parameters in the conditions of near-circular orbits are presented in the paper. The right ascension and declination angles are used to determine the parameters of a single maneuver with transversal and lateral components (the application moment and the velocity impulse magnitude). Two pairs of angles are used to determine the parameters of the maneuver with only a lateral component. Two pairs of angles are needed for the determination of the parameters of the long-duration maneuver performed by a low-thrust engine (moments of the maneuver start and finish, and components of the acceleration delivered by the engine). The essential detail that makes it possible to determine the parameters of long-duration maneuvers is their symmetry relative to the center of the engine operating interval. Considerable perturbing accelerations, which are not accounted for by traditional perturbing models, affect passive objects, especially membranous objects with a big and variable area-to-mass ratio. This decreases dramatically the accuracy of these objects’ motion propagation. In this paper, the magnitude of perturbing acceleration is determined with the assumption that it is constant and is active throughout the whole time interval from the moment of the last orbit determination to the moment of the new measurement used. Examples of the assessment of maneuvers performed by an object in the geostationary orbit are presented.
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(This article belongs to the Special Issue Advances in Mechanics and Control II)
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Open AccessArticle
Preliminary Analysis of Beam Position Monitor Accuracy
by
Jun He, Yanfeng Sui, Chongyang Liang, Yaoyao Du, Ying Zhao, Wan Zhang, Fangqi Huang, Taoguang Xu, Junhui Yue and Jianshe Cao
Symmetry 2024, 16(5), 566; https://doi.org/10.3390/sym16050566 - 06 May 2024
Abstract
The beam position is the most important reference basis for the operation of synchrotron radiation light sources, particularly for commissioning the first-turn injection of fourth-generation light sources. To improve the accuracy of the beam position measurement, we analyzed methods for calculating the beam
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The beam position is the most important reference basis for the operation of synchrotron radiation light sources, particularly for commissioning the first-turn injection of fourth-generation light sources. To improve the accuracy of the beam position measurement, we analyzed methods for calculating the beam position, and a finite element calculation and the stretched wire calibration system were used to demonstrate the procedure. We proved the relationship between the coverage range, fitting order, scanning step size, and accuracy both theoretically and experimentally, which can provide a basis for selecting the appropriate fitting order for different operation stages of the accelerator. It was proved that the accuracy of beam position calculations using simplified polynomial coefficients is comparable to those without a simplified one, which can save resources for reading electronic processing. The testing results of a batch of beam position monitors (BPMs) were in good agreement with the finite element calculation results, and the small difference between the manufactured BPMs also proved that quality control was performed well, and it benefited from button sorting.
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(This article belongs to the Section Physics)
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Open AccessArticle
Rotated Lorenz Curves of Biological Size Distributions Follow Two Performance Equations
by
Peijian Shi, Linli Deng and Karl J. Niklas
Symmetry 2024, 16(5), 565; https://doi.org/10.3390/sym16050565 - 05 May 2024
Abstract
The Lorenz curve is used to describe the relationship between the cumulative proportion of household income and the number of households of an economy. The extent to which the Lorenz curve deviates from the line of equality (i.e., y = x) is
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The Lorenz curve is used to describe the relationship between the cumulative proportion of household income and the number of households of an economy. The extent to which the Lorenz curve deviates from the line of equality (i.e., y = x) is quantified by the Gini coefficient. Prior models are based on the simulated and empirical data of income distributions. In biology, the Lorenz curves of cell or organ size distributions tend to have similar shapes. When the Lorenz curve is rotated by 135 degrees counterclockwise and shifted to the right by a distance of , a three-parameter performance equation (PE), and its generalized version with five parameters (GPE), accurately describe this rotated and right-shifted curve. However, in prior studies, PE and GPE were not compared with the other Lorenz equations, and little is known about whether the skewness of the distribution could influence the validity of these equations. To address these two issues, simulation data from the beta distributions with different skewness values and six empirical datasets of plant (organ) size distributions were used to compare PE and GPE with three other Lorenz equations in describing the rotated and right-shifted plant (organ) size distributions. The root-mean-square error and Akaike information criterion were used to assess the validity of the two performance equations and the three other Lorenz equations. PE and GPE were both validated in describing the rotated and right-shifted simulation and empirical data of plant (organ) distributions. Nevertheless, GPE worked better than PE and the three other Lorenz equations from the perspectives of the goodness of fit, and the trade-off between the goodness of fit and the model structural complexity. Analyses indicate that GPE provides a powerful tool for quantifying size distributions across a broad spectrum of organic entities and can be used in a variety of ecological and evolutionary applications. Even for the simulation data from hypothetical extreme skewed distribution curves, GPE still worked well.
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(This article belongs to the Section Mathematics)
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Open AccessArticle
Anisotropic Generalization of the ΛCDM Universe Model with Application to the Hubble Tension
by
Øyvind G. Grøn
Symmetry 2024, 16(5), 564; https://doi.org/10.3390/sym16050564 - 05 May 2024
Abstract
I deduce an exact and analytic Bianchi type I solution of Einstein’s field equations, which generalizes the isotropic ΛCDM universe model to a corresponding model with anisotropic expansion. The main point of the article is to present the anisotropic generalization of the ΛCDM
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I deduce an exact and analytic Bianchi type I solution of Einstein’s field equations, which generalizes the isotropic ΛCDM universe model to a corresponding model with anisotropic expansion. The main point of the article is to present the anisotropic generalization of the ΛCDM universe model in a way suitable for investigating how anisotropic expansion modifies observable properties of the ΛCDM universe model. Although such generalizations of the isotropic ΛCDM universe model have been considered earlier, they have never been presented in this form before. Several physical properties of the model are pointed out and compared with properties of special cases, such as the isotropic ΛCDM universe model. The solution is then used to investigate the Hubble tension. It has recently been suggested that the cosmic large-scale anisotropy may solve the Hubble tension. I consider those earlier suggestions and find that the formulae of these papers lead to the result that the anisotropy of the cosmic expansion is too small to solve the Hubble tension. Then, I investigate the problem in a new way, using the exact solution of the field equations. This gives the result that the cosmic expansion anisotropy is still too small to solve the Hubble tension in the general Bianchi type I universe with dust and LIVE (Lorentz Invariant Vacuum Energy with a constant energy density, which is represented by the cosmological constant) and anisotropic expansion in all three directions—even if one neglects the constraints coming from the requirement that the anisotropy should be sufficiently small so that it does not have any significant effect upon the results coming from the calculations of the comic nucleosynthesis during the first ten minutes of the universe. If this constraint is taken into account, the cosmic expansion anisotropy is much too small to solve the Hubble tension.
Full article
(This article belongs to the Special Issue Symmetry in Classical and Quantum Gravity and Field Theory)
Open AccessArticle
Fractional Stochastic Partial Differential Equations: Numerical Advances and Practical Applications—A State of the Art Review
by
Behrouz Parsa Moghaddam, Afshin Babaei, Arman Dabiri and Alexandra Galhano
Symmetry 2024, 16(5), 563; https://doi.org/10.3390/sym16050563 - 05 May 2024
Abstract
This article aims to provide a comprehensive review of the latest advancements in numerical methods and practical implementations in the field of fractional stochastic partial differential equations (FSPDEs). This type of equation integrates fractional calculus, stochastic processes, and differential equations to model complex
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This article aims to provide a comprehensive review of the latest advancements in numerical methods and practical implementations in the field of fractional stochastic partial differential equations (FSPDEs). This type of equation integrates fractional calculus, stochastic processes, and differential equations to model complex dynamical systems characterized by memory and randomness. It introduces the foundational concepts and definitions essential for understanding FSPDEs, followed by a comprehensive review of the diverse numerical methods and analytical techniques developed to tackle these equations. Then, this article highlights the significant expansion in numerical methods, such as spectral and finite element methods, aimed at solving FSPDEs, underscoring their potential for innovative applications across various disciplines.
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(This article belongs to the Section Mathematics)
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Open AccessArticle
Ghost Stars in General Relativity
by
Luis Herrera, Alicia Di Prisco and Justo Ospino
Symmetry 2024, 16(5), 562; https://doi.org/10.3390/sym16050562 - 05 May 2024
Abstract
We explore an idea put forward many years ago by Zeldovich and Novikov concerning the existence of compact objects endowed with arbitrarily small mass. The energy density of such objects, which we call “ghost stars”, is negative in some regions of the fluid
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We explore an idea put forward many years ago by Zeldovich and Novikov concerning the existence of compact objects endowed with arbitrarily small mass. The energy density of such objects, which we call “ghost stars”, is negative in some regions of the fluid distribution, producing a vanishing total mass. Thus, the interior is matched on the boundary surface to Minkowski space–time. Some exact analytical solutions are exhibited and their properties are analyzed. Observational data that could confirm or dismiss the existence of this kind of stellar object are discussed.
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(This article belongs to the Special Issue The Nuclear Physics of Neutron Stars)
Open AccessArticle
Exploring the Dynamics of Dark and Singular Solitons in Optical Fibers Using Extended Rational Sinh–Cosh and Sine–Cosine Methods
by
Annamalai Muniyappan, Kannan Manikandan, Akbota Saparbekova and Nurzhan Serikbayev
Symmetry 2024, 16(5), 561; https://doi.org/10.3390/sym16050561 - 04 May 2024
Abstract
This investigation focuses on the construction of novel dark and singular soliton solutions for the Hirota equation, which models the propagation of ultrashort light pulses in optical fibers. Initially, we employ a wave variable transformation to convert the physical model into ordinary differential
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This investigation focuses on the construction of novel dark and singular soliton solutions for the Hirota equation, which models the propagation of ultrashort light pulses in optical fibers. Initially, we employ a wave variable transformation to convert the physical model into ordinary differential equations. Utilizing extended rational sinh–cosh and sine–cosine techniques, we derive an abundant soliton solution for the transformed system. By plugging these explicit solutions back into the wave transformation, we obtain dark and singular soliton solutions for the Hirota equation. The dynamic evolution of dark soliton profiles is then demonstrated, with a focus on varying physically significant parameters such as wave frequency, strength of third-order dispersion, and wave number. Furthermore, a comprehensive analysis is examined to elucidate how the dark and singular soliton profiles undergo deformation in the background influenced by these arbitrary parameters. The findings presented in this study offer valuable insights that could potentially guide experimental manipulation of dark solitons in optical fibers.
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(This article belongs to the Special Issue Symmetry: Feature Papers 2024)
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Open AccessArticle
Adaptive Fuzzy Fixed-Time Control for Uncertain Nonlinear Systems with Mismatched Disturbances
by
Rongzheng Luo, Lu Zhang and You Li
Symmetry 2024, 16(5), 560; https://doi.org/10.3390/sym16050560 - 04 May 2024
Abstract
This paper focuses on addressing the adaptive fuzzy fixed-time issue for a class of nonlinear systems with uncertainty functions and mismatched disturbances. Fuzzy logical systems are utilized for identifying unknown functions. Additionally, to tackle challenges posed by mismatched disturbances, disturbance observers are constructed
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This paper focuses on addressing the adaptive fuzzy fixed-time issue for a class of nonlinear systems with uncertainty functions and mismatched disturbances. Fuzzy logical systems are utilized for identifying unknown functions. Additionally, to tackle challenges posed by mismatched disturbances, disturbance observers are constructed based on the backstepping method. Utilizing the adding one power integrator approach and the fixed-time control method, this paper introduces a fixed-time adaptive fuzzy control algorithm. Notably, this algorithm accommodates the presence of unknown mismatched disturbances and nonlinear functions. The paper establishes, through the application of the Lyapunov stability theory, that the designed adaptive fixed-time fuzzy control algorithm ensures practical fixed-time stability for the resulting closed-loop systems. Finally, the effectiveness of the derived strategy is demonstrated through an illustrative example involving two cases.
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(This article belongs to the Special Issue Advances in Dynamics, Planning and Control of Spacecraft and Related Systems)
Open AccessArticle
Effects of Heating Bituminous Mixtures in a Hot-Gas Drum Based on a Finite Volume Method
by
Xuan Li, Haiying Cheng, Xiaohui Liu and Wenfeng Zhu
Symmetry 2024, 16(5), 559; https://doi.org/10.3390/sym16050559 - 04 May 2024
Abstract
Hot-gas drum heating (HDH) of bituminous mixtures is a new approach to heating bituminous mixtures that is influenced by the parameters of the hot gas and drum. A fluid thermal numerical model was developed to evaluate the effects of heating bituminous mixtures with
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Hot-gas drum heating (HDH) of bituminous mixtures is a new approach to heating bituminous mixtures that is influenced by the parameters of the hot gas and drum. A fluid thermal numerical model was developed to evaluate the effects of heating bituminous mixtures with HDH using a finite-volume method (FVM). The FVM was verified through the heating test of a bituminous mixture. The effects of the drum rotating speed and hot-gas speed on the efficiency of heating the bituminous mixture during HDH were analyzed using Fluent. The results indicated that the drum rotating speed directly influenced the formation of a bituminous-mixture curtain, which had a significant effect on the efficiency of heating the bituminous mixture. The efficiency of the heat exchange between the hot gas and the bituminous mixture was high, with full contact between the hot gas and the bituminous mixture. With an increase in the hot-gas speed, the heating time became shorter; however, the rate of hot-gas utilization was reduced. A symmetrical temperature distribution and a superior heating efficiency of the bituminous mixture were achieved when the drum rotating speed was 7 rpm and the hot-gas speed was 1.4 m/s.
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(This article belongs to the Section Engineering and Materials)
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Identifying the Differences in Symmetry of the Anthropometric Parameters of the Upper Limbs in Relation to Manual Laterality between Athletes Who Practice Sports with and without a Ball
by
Adela Badau and Dana Badau
Symmetry 2024, 16(5), 558; https://doi.org/10.3390/sym16050558 - 04 May 2024
Abstract
The purpose of this study was to identify the asymmetries between the dimensions of the upper limbs, in relation to manual laterality, of the athletes who practice team sports with a ball and those who practice other sports without a ball. We consider
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The purpose of this study was to identify the asymmetries between the dimensions of the upper limbs, in relation to manual laterality, of the athletes who practice team sports with a ball and those who practice other sports without a ball. We consider the fact that ball handling influences the development of anthropometric parameters at the level of the upper limbs and especially at the level of the hand in correlation with the execution technique and with the characteristics of the practiced sport. This study included 161 student-athletes, who were male and right-handed, divided into two groups: the group of athletes practicing ball sports (G_BS) with 79 (49%) subjects and the group of athletes practicing non-ball sports (G_NBS) with 82 (51%) subjects. The anthropometric measurements of the upper limbs were performed on both sides (right and left): upper limb length, hand length, palm length, hand breadth, hand span, pinky finger, ring finger, middle finger, index finger and thumb. The most relevant symmetries, between the two groups, were recorded in the following anthropometric parameters on the right side (recording the smallest average differences): ring finger 0.412 cm and thumb 0.526 cm; for the left side, they were the ring finger 0.379 cm and thumb 0.518 cm. The biggest asymmetries between the two groups were recorded, for both the right and left sides, for the following parameters: upper limb length > 6 cm; hand span > 2 cm; and hand length > 1 cm. For all the anthropometric parameters analyzed, the athletes from the ball sports group (G_BS) recorded higher average values than those from the other group (G_NBS) for both upper limbs. The results of this study reflect the fact that handling the ball over a long period of time, starting from the beginning of practicing the sport until the age of seniority, causes changes in the anthropometric dimensions of the upper segments, causing asymmetries between the dominant (right) and the non-dominant (left) side.
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(This article belongs to the Special Issue Symmetry and Asymmetry in Sport Sciences)
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