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Symmetry, Volume 13, Issue 1 (January 2021) – 154 articles

Cover Story (view full-size image): The blossom of a cyclamen contains different elements of chirality, the sepals and the petals. The molecule Ibuprofen contains different elements of chirality, the configuration at Cα, the conformation of the bond Cα–C’, and the flat tetrahedron of the formerly planar carboxylic group CαC’OOH, which interact selectively. View this paper.
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Open AccessArticle
The Symmetric Nature of the Position Distribution of the Human Body Center of Gravity during Propelling Manual Wheelchairs with Innovative Propulsion Systems
Symmetry 2021, 13(1), 154; https://0-doi-org.brum.beds.ac.uk/10.3390/sym13010154 - 19 Jan 2021
Viewed by 360
Abstract
Objective: The main objective of the tests conducted was to analyze the position variability of the human body’s center of gravity during propelling the wheelchair, and to demonstrate the properties enabling the description of this variability by means of plane figures with a [...] Read more.
Objective: The main objective of the tests conducted was to analyze the position variability of the human body’s center of gravity during propelling the wheelchair, and to demonstrate the properties enabling the description of this variability by means of plane figures with a symmetry axis. A secondary objective was to show the impact of the used manual propulsion type and the wheelchair inclination angle in relation to the plane on the dimensions of the position variability areas of the center of gravity. Method and materials: Three patients participated in the research representing 50 centiles of anthropometric dimensions. Each patient carried out fifteen measurement tests on three wheelchairs for three inclination angles of the wheelchair frame in relation to the level. Each measurement test consisted of five propulsion cycles for which the positions of the center of gravity were determined with the sampling frequency of 100 Hz. The measured positions of the center of gravity were approximated with ellipses containing 95.4% of the measurements conducted, assuming their dimension scaling basis in the form of the double value of standard deviation defined based on the registered results. Results: Based on the measurements conducted, the average values of five ellipses parameters were determined for nine cases in which a variable was the type of wheelchair propulsion and its inclination angle in relation to the level. The area of the highest variability of the position of the center of gravity was measured for the wheelchair with a multispeed transmission. The average dimensions of the ellipse semi-axis amounted to 108.53 mm for the semi-axis a and 29.75 for the semi-axis b, the average position of the ellipse center amounted to x = 114.51 mm and y = −10.53 mm, and the average inclination angle of the ellipse α amounted to −6.92°. The area of the lowest variability of the position of the center of gravity was measured for the wheelchair with a hybrid transmission. In this case, the average dimensions of the ellipse semi-axis amounted to 64.07 mm for the semi-axis a and 33.85 for the semi-axis b; whereas, the average position of the ellipse center amounted to x = 245.13 mm and y = −28.24 mm, and the average inclination angle of the ellipse α amounted to −0.56°. Full article
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Open AccessReview
A Unified Mathematical Formalism for First to Third Order Dielectric Response of Matter: Application to Surface-Specific Two-Colour Vibrational Optical Spectroscopy
Symmetry 2021, 13(1), 153; https://0-doi-org.brum.beds.ac.uk/10.3390/sym13010153 - 19 Jan 2021
Cited by 1 | Viewed by 399
Abstract
To take advantage of the singular properties of matter, as well as to characterize it, we need to interact with it. The role of optical spectroscopies is to enable us to demonstrate the existence of physical objects by observing their response to light [...] Read more.
To take advantage of the singular properties of matter, as well as to characterize it, we need to interact with it. The role of optical spectroscopies is to enable us to demonstrate the existence of physical objects by observing their response to light excitation. The ability of spectroscopy to reveal the structure and properties of matter then relies on mathematical functions called optical (or dielectric) response functions. Technically, these are tensor Green’s functions, and not scalar functions. The complexity of this tensor formalism sometimes leads to confusion within some articles and books. Here, we do clarify this formalism by introducing the physical foundations of linear and non-linear spectroscopies as simple and rigorous as possible. We dwell on both the mathematical and experimental aspects, examining extinction, infrared, Raman and sum-frequency generation spectroscopies. In this review, we thus give a personal presentation with the aim of offering the reader a coherent vision of linear and non-linear optics, and to remove the ambiguities that we have encountered in reference books and articles. Full article
(This article belongs to the Special Issue Recent Advances in Linear and Nonlinear Optics)
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Open AccessArticle
Stability Analysis of an LTI System with Diagonal Norm Bounded Linear Differential Inclusions
Symmetry 2021, 13(1), 152; https://0-doi-org.brum.beds.ac.uk/10.3390/sym13010152 - 19 Jan 2021
Viewed by 260
Abstract
In this article, we present a stability analysis of linear time-invariant systems in control theory. The linear time-invariant systems under consideration involve the diagonal norm bounded linear differential inclusions. We propose a methodology based on low-rank ordinary differential equations. We construct an equivalent [...] Read more.
In this article, we present a stability analysis of linear time-invariant systems in control theory. The linear time-invariant systems under consideration involve the diagonal norm bounded linear differential inclusions. We propose a methodology based on low-rank ordinary differential equations. We construct an equivalent time-invariant system (linear) and use it to acquire an optimization problem whose solutions are given in terms of a system of differential equations. An iterative method is then used to solve the system of differential equations. The stability of linear time-invariant systems with diagonal norm bounded differential inclusion is studied by analyzing the Spectrum of equivalent systems. Full article
Open AccessArticle
Dynamics of Cardiovascular Muscle Using a Non-Linear Symmetric Oscillator
Symmetry 2021, 13(1), 151; https://0-doi-org.brum.beds.ac.uk/10.3390/sym13010151 - 18 Jan 2021
Viewed by 297
Abstract
In this paper, a complete non-linear symmetric oscillator model using the Hamiltonian approach has been developed and used to describe the cardiovascular conduction process’s dynamics, as the signal generated from the cardiovascular muscle is non-deterministic and random. Electrocardiogram (ECG) signal is a significant [...] Read more.
In this paper, a complete non-linear symmetric oscillator model using the Hamiltonian approach has been developed and used to describe the cardiovascular conduction process’s dynamics, as the signal generated from the cardiovascular muscle is non-deterministic and random. Electrocardiogram (ECG) signal is a significant factor in the cardiovascular system as most of the medical diagnoses can be well understood by observing the ECG signal’s amplitude. A non-linear cardiovascular muscle model has been proposed in this study, where a modified vanderPol symmetric oscillator-based equation is used. Gone are the days whena non-linear system had been designed using the describing function technique. It is better to design a non-linear model using the Hamiltonian dynamical equation for its high accuracy and flexibility. Varying a non-linear spring constant using this type of approach is more comfortable than the traditional describing function technique. Not only that but different initial conditions can also be taken for experimental purposes. It never affects the overall modeling. The Hamiltonian approach provides the energy of an asymmetric oscillatory system of that cardiovascular conduction system. A non-linear symmetric oscillator was initially depicted by the non-linear mass-spring (two degrees of freedom) model. The motion of an uncertain non-linear cardiovascular system has been solved considering second-order approximation, which also demonstrates the possibility of introducing spatial dimensions. Finally, the model’s natural frequency expression has also been simulated and is composed of the previously published result. Full article
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Open AccessArticle
Comparison of Body Composition Monitor and InBody 720 Bioimpedance Devices for Body Composition Estimation in Hemodialysis Patients and Healthy Controls
Symmetry 2021, 13(1), 150; https://0-doi-org.brum.beds.ac.uk/10.3390/sym13010150 - 18 Jan 2021
Viewed by 295
Abstract
Bioelectric impedance devices have become a standard of care not only for peritoneal dialysis but also for hemodialysis patients. We compared the most important body composition variables (extracellular water, intracellular water, total body water and fat mass) measured with the multifrequency bioelectric impedance [...] Read more.
Bioelectric impedance devices have become a standard of care not only for peritoneal dialysis but also for hemodialysis patients. We compared the most important body composition variables (extracellular water, intracellular water, total body water and fat mass) measured with the multifrequency bioelectric impedance device InBody 720 (MF-BIA) and bioimpedance spectroscopy body composition monitor Fresenius (BIS BCM) in hemodialysis patients (n = 51, 175.1 + 7.8 cm, 82.2 + 15.2 kg) and healthy controls (n = 51, 175.1 + 7.6 cm, 82.3 + 15.3 kg). The MF-BIA InBody 720 device compared to the BIS BCM device showed significantly larger total body water and intracellular water estimates and significantly smaller extracellular water and body fat estimates in hemodialysis patients (p < 0.001). These differences (p < 0.001) were similar in the cohort of healthy controls; moreover, we observed high correlations in all variables between the hemodialysis patients and the healthy controls (0.80–0.95, p < 0.001). The mean relative differences in the order of 8% were lower for extracellular water and total body fat, but the limits of agreement were still wide enough to be clinically significant. We conclude that the results of the measurements with InBody 720 and BCM Fresenius cannot be used interchangeably. Physicians and nutritionists involved in the care of hemodialysis patients should be aware of this discrepancy between the two devices and should try to use the same device to track the body in their hemodialysis population in a longitudinal direction. Full article
(This article belongs to the Special Issue Molecule Symmetry, Bioaerosol and Human Health)
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Open AccessArticle
On the Recurrence Properties of Narayana’s Cows Sequence
by
Symmetry 2021, 13(1), 149; https://0-doi-org.brum.beds.ac.uk/10.3390/sym13010149 - 17 Jan 2021
Viewed by 382
Abstract
In this paper, we consider the recurrence properties of two generalized forms of Narayana’s cows sequence. On the one hand, we study Narayana’s cows sequence at negative indices and express it as the linear combination of the sequence at positive indices. On the [...] Read more.
In this paper, we consider the recurrence properties of two generalized forms of Narayana’s cows sequence. On the one hand, we study Narayana’s cows sequence at negative indices and express it as the linear combination of the sequence at positive indices. On the other hand, we study the convolved Narayana number and obtain a computation formula for it. Full article
Open AccessFeature PaperArticle
Iterated Darboux Transformation for Isothermic Surfaces in Terms of Clifford Numbers
Symmetry 2021, 13(1), 148; https://0-doi-org.brum.beds.ac.uk/10.3390/sym13010148 - 17 Jan 2021
Viewed by 347
Abstract
Isothermic surfaces are defined as immersions with the curvture lines admitting conformal parameterization. We present and discuss the reconstruction of the iterated Darboux transformation using Clifford numbers instead of matrices. In particulalr, we derive a symmetric formula for the two-fold Darboux transformation, explicitly [...] Read more.
Isothermic surfaces are defined as immersions with the curvture lines admitting conformal parameterization. We present and discuss the reconstruction of the iterated Darboux transformation using Clifford numbers instead of matrices. In particulalr, we derive a symmetric formula for the two-fold Darboux transformation, explicitly showing Bianchi’s permutability theorem. In algebraic calculations an important role is played by the main anti-automorphism (reversion) of the Clifford algebra C(4,1) and the spinorial norm in the corresponding Spin group. Full article
(This article belongs to the Special Issue Geometric Analysis of Nonlinear Partial Differential Equations)
Open AccessArticle
Deep Learning for Spectrum Sensing in Cognitive Radio
Symmetry 2021, 13(1), 147; https://0-doi-org.brum.beds.ac.uk/10.3390/sym13010147 - 17 Jan 2021
Viewed by 297
Abstract
The detection of primary user signals is essential for optimum utilization of a spectrum by secondary users in cognitive radio (CR). The conventional spectrum sensing schemes have the problem of missed detection/false alarm, which hampers the proper utilization of spectrum. Spectrum sensing through [...] Read more.
The detection of primary user signals is essential for optimum utilization of a spectrum by secondary users in cognitive radio (CR). The conventional spectrum sensing schemes have the problem of missed detection/false alarm, which hampers the proper utilization of spectrum. Spectrum sensing through deep learning minimizes the margin of error in the detection of the free spectrum. This research provides an insight into using a deep neural network for spectrum sensing. A deep learning based model, “DLSenseNet”, is proposed, which exploits structural information of received modulated signals for spectrum sensing. The experiments were performed using RadioML2016.10b dataset and the outcome was studied. It was found that “DLSenseNet” provides better spectrum detection than other sensing models. Full article
(This article belongs to the Section Computer and Engineering Science and Symmetry)
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Open AccessArticle
The Bias toward the Right Side of Others Is Stronger for Hands than for Feet
Symmetry 2021, 13(1), 146; https://0-doi-org.brum.beds.ac.uk/10.3390/sym13010146 - 17 Jan 2021
Viewed by 240
Abstract
As shown by a series of previous studies, ambiguous human bodies performing unimanual or unipedal actions tend to be perceived more frequently as right-handed or right-footed rather than left-handed or left-footed, which indicates a perceptual and attentional bias toward the right side of [...] Read more.
As shown by a series of previous studies, ambiguous human bodies performing unimanual or unipedal actions tend to be perceived more frequently as right-handed or right-footed rather than left-handed or left-footed, which indicates a perceptual and attentional bias toward the right side of others’ body. However, none of such studies assessed whether the relative strength of such a bias differs between the upper and lower limbs. Indeed, given that the prevalence of right-handedness is slightly larger than that of right-footedness, and given that hands provide more information than feet as regards both communicative and aggressive acts, it is plausible that the bias toward the right side of human bodies should be stronger for the hand than for the foot. We performed three experiments in each of which participants had to indicate the rotating direction (revealing the perceived handedness/footedness) of ambiguous human figures with either one limb (arm or leg) or two limbs (one arm and the contralateral leg) extended. The hypothesized advantage of the right hand over the right foot was found in both the second and the third experiment. Full article
(This article belongs to the Special Issue Symmetry and Asymmetry in Brain Behavior and Perception II)
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Open AccessArticle
Finite Pure Plane Strain Bending of Inhomogeneous Anisotropic Sheets
Symmetry 2021, 13(1), 145; https://0-doi-org.brum.beds.ac.uk/10.3390/sym13010145 - 16 Jan 2021
Cited by 1 | Viewed by 276
Abstract
The present paper concerns the general solution for finite plane strain pure bending of incompressible, orthotropic sheets. In contrast to available solutions, the new solution is valid for inhomogeneous distributions of plastic properties. The solution is semi-analytic. A numerical treatment is only necessary [...] Read more.
The present paper concerns the general solution for finite plane strain pure bending of incompressible, orthotropic sheets. In contrast to available solutions, the new solution is valid for inhomogeneous distributions of plastic properties. The solution is semi-analytic. A numerical treatment is only necessary for solving transcendent equations and evaluating ordinary integrals. The solution’s starting point is a transformation between Eulerian and Lagrangian coordinates that is valid for a wide class of constitutive equations. The symmetric distribution relative to the center line of the sheet is separately treated where it is advantageous. It is shown that this type of symmetry simplifies the solution. Hill’s quadratic yield criterion is adopted. Both elastic/plastic and rigid/plastic solutions are derived. Elastic unloading is also considered, and it is shown that reverse plastic yielding occurs at a relatively large inside radius. An illustrative example uses real experimental data. The distribution of plastic properties is symmetric in this example. It is shown that the difference between the elastic/plastic and rigid/plastic solutions is negligible, except at the very beginning of the process. However, the rigid/plastic solution is much simpler and, therefore, can be recommended for practical use at large strains, including calculating the residual stresses. Full article
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Open AccessArticle
Isospin Symmetry Breaking Effects on the Mass-Radius Relation of a Neutron Star
Symmetry 2021, 13(1), 144; https://0-doi-org.brum.beds.ac.uk/10.3390/sym13010144 - 16 Jan 2021
Viewed by 289
Abstract
Isospin symmetry breaking effects on the mass-radius relation of a cold, non-accreting neutron star are studied on the basis of two Skyrme Energy Density Functionals (EDFs). One functional contains isospin symmetry breaking terms other than those typically included in Skyrme EDFs while its [...] Read more.
Isospin symmetry breaking effects on the mass-radius relation of a cold, non-accreting neutron star are studied on the basis of two Skyrme Energy Density Functionals (EDFs). One functional contains isospin symmetry breaking terms other than those typically included in Skyrme EDFs while its counterpart is of standard form. Both functionals are based on the same fitting protocol except for the observables and pseudo-observables sensitive to the isospin symmetry breaking channel. The quality of those functionals is similar in the description of terrestrial observables but choosing either of them has a non-negligible effect on the mass-radius relation and tidal deformability of a neutron star. Further investigations are needed to clarify the effects of isospin symmetry breaking on these and other observables of neutron stars that are, and will become, available. Full article
(This article belongs to the Special Issue Symmetry and Symmetry Breaking in Nuclei)
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Open AccessArticle
Innovative Supplier Selection from Collaboration Perspective with a Hybrid MCDM Model: A Case Study Based on NEVs Manufacturer
Symmetry 2021, 13(1), 143; https://0-doi-org.brum.beds.ac.uk/10.3390/sym13010143 - 16 Jan 2021
Viewed by 271
Abstract
In the context of Chinese innovation-driven strategy, the role of suppliers has been attracting much attention. Since not every supplier can contribute to the buyer’s innovation, scientifically selecting an innovative supplier is highly valued by decision-makers from the new energy vehicle (NEV) manufacturers. [...] Read more.
In the context of Chinese innovation-driven strategy, the role of suppliers has been attracting much attention. Since not every supplier can contribute to the buyer’s innovation, scientifically selecting an innovative supplier is highly valued by decision-makers from the new energy vehicle (NEV) manufacturers. This paper focuses on proposing a novel decision framework in the context of collaborative innovation, which helps NEV manufacturers to select an innovative supplier who can work hand in hand with them to enhance their innovation performance. First, a novel capability-willingness-risk (C-W-R) evaluation indicator system is established, considering supply risk from a multi-proximity perspective which is tightly tied to collaborative innovation performance, only considered from geographical proximity in previous supplier selection research. Then a hybrid fuzzy-symmetrical multicriteria decision-making (MCDM) model is proposed that integrates fuzzy linguistic sets, best–worst method (BWM), prospect theory (PT) and VIKOR. With this approach, a final ranking is obtained for innovative supplier selection by NEV manufacturers in China. Moreover, sensitivity analysis and comparison analysis illustrate the proposed decision framework’s effectiveness and reliability and dig deep into the buyer−supplier collaborative innovation. Finally, some managerial suggestions are given for supplier selection from the standpoint of NEV manufacturers. Full article
(This article belongs to the Special Issue Symmetry in the Creative Act)
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Open AccessFeature PaperArticle
Discrete-Time Pole-Region Robust Controller for Magnetic Levitation Plant
Symmetry 2021, 13(1), 142; https://0-doi-org.brum.beds.ac.uk/10.3390/sym13010142 - 16 Jan 2021
Viewed by 248
Abstract
Robust pole-placement based on convex DR-regions belongs to the efficient control design techniques for real systems, providing computationally tractable pole-placement design algorithms. The problem arises in the discrete-time domain when the relative damping is prescribed since the corresponding discrete-time domain is [...] Read more.
Robust pole-placement based on convex DR-regions belongs to the efficient control design techniques for real systems, providing computationally tractable pole-placement design algorithms. The problem arises in the discrete-time domain when the relative damping is prescribed since the corresponding discrete-time domain is non-convex, having a “cardioid” shape. In this paper, we further develop our recent results on the inner convex approximations of the cardioid, present systematical analysis of its design parameters and their influence on the corresponding closed loop performance (measured by standard integral of absolute error (IAE) and Total Variance criteria). The application of a robust controller designed with the proposed convex approximation of the discrete-time pole region is illustrated and evaluated on a real laboratory magnetic levitation plant. Full article
(This article belongs to the Special Issue PID Control and Symmetry)
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Open AccessArticle
Comparison of Simulations with a Mean-Field Approach vs. Synthetic Correlated Networks
Symmetry 2021, 13(1), 141; https://0-doi-org.brum.beds.ac.uk/10.3390/sym13010141 - 16 Jan 2021
Viewed by 249
Abstract
It is well known that dynamical processes on complex networks are influenced by the degree correlations. A common way to take these into account in a mean-field approach is to consider the function knn(k) (average nearest neighbors degree). [...] Read more.
It is well known that dynamical processes on complex networks are influenced by the degree correlations. A common way to take these into account in a mean-field approach is to consider the function knn(k) (average nearest neighbors degree). We re-examine the standard choices of knn for scale-free networks and a new family of functions which is independent from the simple ansatz knnkα but still displays a remarkable scale invariance. A rewiring procedure is then used to explicitely construct synthetic networks using the full correlation P(hk) from which knn is derived. We consistently find that the knn functions of concrete synthetic networks deviate from ideal assortativity or disassortativity at large k. The consequences of this deviation on a diffusion process (the network Bass diffusion and its peak time) are numerically computed and discussed for some low-dimensional samples. Finally, we check that although the knn functions of the new family have an asymptotic behavior for large networks different from previous estimates, they satisfy the general criterium for the absence of an epidemic threshold. Full article
(This article belongs to the Section Mathematics and Symmetry)
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Open AccessArticle
On Sombor Index
Symmetry 2021, 13(1), 140; https://0-doi-org.brum.beds.ac.uk/10.3390/sym13010140 - 16 Jan 2021
Viewed by 291
Abstract
The concept of Sombor index (SO) was recently introduced by Gutman in the chemical graph theory. It is a vertex-degree-based topological index and is denoted by Sombor index SO: SO=SO(G)= [...] Read more.
The concept of Sombor index (SO) was recently introduced by Gutman in the chemical graph theory. It is a vertex-degree-based topological index and is denoted by Sombor index SO: SO=SO(G)=vivjE(G)dG(vi)2+dG(vj)2, where dG(vi) is the degree of vertex vi in G. Here, we present novel lower and upper bounds on the Sombor index of graphs by using some graph parameters. Moreover, we obtain several relations on Sombor index with the first and second Zagreb indices of graphs. Finally, we give some conclusions and propose future work. Full article
(This article belongs to the Special Issue Analytical and Computational Properties of Topological Indices)
Open AccessArticle
Behavior of the Eigenvalues and Eignfunctions of the Regge-Type Problem
Symmetry 2021, 13(1), 139; https://0-doi-org.brum.beds.ac.uk/10.3390/sym13010139 - 15 Jan 2021
Viewed by 471
Abstract
This article investigates the spectral theory of the problem of the Regge-type with transmission conditions and discontinuous coefficients. We formulate a new linear operator, by which we can deal with simplicity and boundedness of the eigenpairs of the problem. The aim of this [...] Read more.
This article investigates the spectral theory of the problem of the Regge-type with transmission conditions and discontinuous coefficients. We formulate a new linear operator, by which we can deal with simplicity and boundedness of the eigenpairs of the problem. The aim of this work is to conduct that the problem has an infinite number of simple positive eigenvalues. Full article
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Open AccessArticle
Automatic Segmentation and Measurement of Infantile Hemangioma
Symmetry 2021, 13(1), 138; https://0-doi-org.brum.beds.ac.uk/10.3390/sym13010138 - 15 Jan 2021
Viewed by 216
Abstract
Infantile hemangiomas (IHs) are a type of vascular tumors that affect around 10% of newborns. The measurement of the lesion size and the assessment of the evolution is done manually by the physician. This paper presents an algorithm for the automatic computation of [...] Read more.
Infantile hemangiomas (IHs) are a type of vascular tumors that affect around 10% of newborns. The measurement of the lesion size and the assessment of the evolution is done manually by the physician. This paper presents an algorithm for the automatic computation of the IH lesion surface. The image scale is computed by using the Hough transform and the total variation. As pre-processing, a geometric correction step is included, which ensures that the lesions are viewed as perpendicular to the camera. The image segmentation is based on K-means clustering applied on a five-plane image; the five planes being selected from seven planes with the use of the Karhunen-Loeve transform. Two of the seven planes are 2D total variation filters, based on symmetrical kernels, designed to highlight the IH specific texture. The segmentation performance was assessed on 30 images, and a mean border error of 9.31% was obtained. Full article
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Open AccessArticle
Novel Joint Object Detection Algorithm Using Cascading Parallel Detectors
Symmetry 2021, 13(1), 137; https://0-doi-org.brum.beds.ac.uk/10.3390/sym13010137 - 15 Jan 2021
Viewed by 254
Abstract
Object detection is an essential computer vision task that aims to detect target objects from an image. The traditional models are insufficient to generate a high-quality anchor box. To solve the problem, we propose a novel joint model called guided anchoring Region proposal [...] Read more.
Object detection is an essential computer vision task that aims to detect target objects from an image. The traditional models are insufficient to generate a high-quality anchor box. To solve the problem, we propose a novel joint model called guided anchoring Region proposal networks and Cascading Grid Region Convolutional Neural Networks (RCGrid R-CNN), enhancing the ability of object detection. Our proposed model design is a joint object detection algorithm containing an anchor-based and an anchor-free branch in parallel and symmetry. In the anchor-based, we use nine-point spatial information fusion to obtain better anchor box location and introduce the shape prediction method of Guided Anchoring Region Proposal Networks (GA-RPN) to enhance the accuracy of the predicted anchor box. In the anchor-free branch, we introduce the Feature Selective Anchor-Free module (FSAF) to reduce the overlapping anchor boxes to obtain a more accurate anchor box. Furthermore, inspired by cascading theory, we cascade the new-designed detectors to improve the ability of object detection by setting a gradually increasing Intersection over Union (IoU) threshold. Compared with typical baseline models, we comprehensively evaluated our model by conducting experiments on two open datasets: Pascal VOC2007 and COCO2017. The experimental results demonstrate the effectiveness of RCGrid R-CNN in producing a high-quality anchor box. Full article
(This article belongs to the Section Computer and Engineering Science and Symmetry)
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Open AccessArticle
Elite Exploitation: A Combination of Mathematical Concept and EMO Approach for Multi-Objective Decision Making
Symmetry 2021, 13(1), 136; https://0-doi-org.brum.beds.ac.uk/10.3390/sym13010136 - 15 Jan 2021
Viewed by 221
Abstract
This paper explores the combination of a classic mathematical function named “hyperbolic tangent” with a metaheuristic algorithm, and proposes a novel hybrid genetic algorithm called NSGA-II-BnF for multi-objective decision making. Recently, many metaheuristic evolutionary algorithms have been proposed for tackling multi-objective optimization problems [...] Read more.
This paper explores the combination of a classic mathematical function named “hyperbolic tangent” with a metaheuristic algorithm, and proposes a novel hybrid genetic algorithm called NSGA-II-BnF for multi-objective decision making. Recently, many metaheuristic evolutionary algorithms have been proposed for tackling multi-objective optimization problems (MOPs). These algorithms demonstrate excellent capabilities and offer available solutions to decision makers. However, their convergence performance may be challenged by some MOPs with elaborate Pareto fronts such as CFs, WFGs, and UFs, primarily due to the neglect of diversity. We solve this problem by proposing an algorithm with elite exploitation strategy, which contains two parts: first, we design a biased elite allocation strategy, which allocates computation resources appropriately to elites of the population by crowding distance-based roulette. Second, we propose a self-guided fast individual exploitation approach, which guides elites to generate neighbors by a symmetry exploitation operator, which is based on mathematical hyperbolic tangent function. Furthermore, we designed a mechanism to emphasize the algorithm’s applicability, which allows decision makers to adjust the exploitation intensity with their preferences. We compare our proposed NSGA-II-BnF with four other improved versions of NSGA-II (NSGA-IIconflict, rNSGA-II, RPDNSGA-II, and NSGA-II-SDR) and four competitive and widely-used algorithms (MOEA/D-DE, dMOPSO, SPEA-II, and SMPSO) on 36 test problems (DTLZ1–DTLZ7, WGF1–WFG9, UF1–UF10, and CF1–CF10), and measured using two widely used indicators—inverted generational distance (IGD) and hypervolume (HV). Experiment results demonstrate that NSGA-II-BnF exhibits superior performance to most of the algorithms on all test problems. Full article
(This article belongs to the Section Computer and Engineering Science and Symmetry)
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Open AccessArticle
Spontaneous and Stimulated Undulator Radiation in Symmetric and Asymmetric Multi-Periodic Magnetic Fields
Symmetry 2021, 13(1), 135; https://0-doi-org.brum.beds.ac.uk/10.3390/sym13010135 - 15 Jan 2021
Viewed by 247
Abstract
In this work, the radiation from electrons in multi-periodic undulator fields with symmetric and asymmetric harmonics was analyzed using generalized Bessel functions formalism. The asymmetric, symmetric, and anti-symmetric periodic magnetic fields with harmonics were studied in order to get the enhanced radiation of [...] Read more.
In this work, the radiation from electrons in multi-periodic undulator fields with symmetric and asymmetric harmonics was analyzed using generalized Bessel functions formalism. The asymmetric, symmetric, and anti-symmetric periodic magnetic fields with harmonics were studied in order to get the enhanced radiation of the high harmonics of undulator radiation (UR). The effect on the spontaneous and stimulated UR was explored. The exact integral forms for the Bessel coefficients were obtained for undulators with general symmetric and asymmetric field harmonics. Spectral properties of the radiation from several configurations of the undulator fields with harmonics were compared with each other. The resulting spontaneous UR spectrum and harmonic intensities were obtained analytically in the form of integrals and compared with the respective results that were obtained numerically with SPECTRA program. The dimensionless scaling parameter of a free electron laser (FEL)—the Pierce parameter (ρ)—was computed and compared for the different considered undulators. We studied the differences in the behavior of the high-gain single pass FEL harmonics and the spontaneous UR harmonics in the same undulators. The undulators with variable deflection parameter (k) were considered. The effect of the k parameter (deflection parameter for a common planar undulator) on the spontaneous UR and on the high-gain FEL radiation was explored. In this context, an experiment with variable strength undulators at FLASH 2 FEL was analyzed; the shorter saturated length in high harmonic self-seeding (HHSS) regime vs. self-amplified spontaneous emission (SASE) is explained. Full article
(This article belongs to the Special Issue Advances in Synchrotron and Undulator Radiation Studies)
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Open AccessArticle
The Exact Theory of the Stern–Gerlach Experiment and Why it Does Not Imply that a Fermion Can Only Have Its Spin Up or Down
Symmetry 2021, 13(1), 134; https://0-doi-org.brum.beds.ac.uk/10.3390/sym13010134 - 14 Jan 2021
Viewed by 251
Abstract
The Stern–Gerlach experiment is notoriously counter-intuitive. The official theory is that the spin of a fermion remains always aligned with the magnetic field. Its directions are thus quantized: It can only be spin-up or spin-down. However, that theory is based on mathematical errors [...] Read more.
The Stern–Gerlach experiment is notoriously counter-intuitive. The official theory is that the spin of a fermion remains always aligned with the magnetic field. Its directions are thus quantized: It can only be spin-up or spin-down. However, that theory is based on mathematical errors in the way it (mis)treats spinors and group theory. We present here a mathematically rigorous theory for a fermion in a magnetic field, which is no longer counter-intuitive. It is based on an understanding of spinors in SU(2) which is only Euclidean geometry. Contrary to what Pauli has been reading into the Stern–Gerlach experiment, the spin directions are not quantized. The new corrected paradigm, which solves all conceptual problems, is that the fermions precess around the magnetic-field just as Einstein and Ehrenfest had conjectured. Surprisingly, this leads to only two energy states, which should be qualified as precession-up and precession-down rather than spin-up and spin-down. Indeed, despite the presence of the many different possible angles θ between the spin axis s and the magnetic field B, the fermions can only have two possible energies m0c2±μB. The values ±μB thus do not correspond to the continuum of values μ·B Einstein and Ehrenfest had conjectured. The energy term V=μ·B is a macroscopic quantity. It is a statistical average over a large ensemble of fermions distributed over the two microscopic states with energies ±μB, and as such not valid for individual fermions. The two fermion states with energy ±μB are not potential-energy states. We also explain the mathematically rigorous meaning of the up and down spinors. They represent left-handed and right-handed reference frames, such that now everything is intuitively clear and understandable in simple geometrical terms. The paradigm shift does not affect the Pauli principle. Full article
(This article belongs to the Special Issue Symmetry in the Foundations of Physics)
Open AccessArticle
Design and Optimization of a Fuzzy Logic System for Academic Performance Prediction
Symmetry 2021, 13(1), 133; https://0-doi-org.brum.beds.ac.uk/10.3390/sym13010133 - 14 Jan 2021
Viewed by 285
Abstract
Currently, in Colombia, different problems in education exist; one of them is the inconvenience in tracing and controlling the learning trajectories that decide the topics taught in the country’s educational institutions. This work aims to implement a logic-based system that allows teachers and [...] Read more.
Currently, in Colombia, different problems in education exist; one of them is the inconvenience in tracing and controlling the learning trajectories that decide the topics taught in the country’s educational institutions. This work aims to implement a logic-based system that allows teachers and educational institutions to carry out a continuous monitoring process of students’ academic performance, facilitating early corrections of errors or failures in teaching methods, to promote educational support spaces within the educational institution. Full article
(This article belongs to the Section Computer and Engineering Science and Symmetry)
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Open AccessArticle
Application of Game Theory against Nature in Supporting Bid Pricing in Construction
Symmetry 2021, 13(1), 132; https://0-doi-org.brum.beds.ac.uk/10.3390/sym13010132 - 14 Jan 2021
Viewed by 290
Abstract
The problem of setting prices for construction works is significant for both the investor and contractor companies. The periodically occurring instabilities in the economy require investment process participants to perform detailed market analyses and assessments, as well as to monitor price forecasts in [...] Read more.
The problem of setting prices for construction works is significant for both the investor and contractor companies. The periodically occurring instabilities in the economy require investment process participants to perform detailed market analyses and assessments, as well as to monitor price forecasts in construction. It is only after such an assessment that it is possible within the framework of the initial assumptions for cost calculation to select the basis for setting prices and their levels. The identification and analysis of the risks related to uncontrolled price increases allow contractors to secure their businesses by developing bids that ensure maximum profit. In view of the above, this study proposes an approach based on the use of game theory against nature to identify the optimal variant of a bid estimate. The study considers price forecasts for construction products, which may reduce the negative impact in case the prices increase. The obtained results confirmed the effectiveness of the used decision-making support methods, indicating the optimal strategy to reduce financial losses in times of market instability. The proposed approach also allows for a balance (symmetry) between maximum profit and probability of winning the contract. Full article
(This article belongs to the Special Issue Symmetry in Civil Engineering)
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Open AccessFeature PaperArticle
Properties of Quantizer and Dequantizer Operators for Qudit States and Parametric Down-Conversion
Symmetry 2021, 13(1), 131; https://0-doi-org.brum.beds.ac.uk/10.3390/sym13010131 - 14 Jan 2021
Viewed by 447
Abstract
We review the method of quantizers and dequantizers to construct an invertible map of the density operators onto functions including probability distributions and discuss in detail examples of qubit and qutrit states. The biphoton states existing in the process of parametric down-conversion are [...] Read more.
We review the method of quantizers and dequantizers to construct an invertible map of the density operators onto functions including probability distributions and discuss in detail examples of qubit and qutrit states. The biphoton states existing in the process of parametric down-conversion are studied in the probability representation of quantum mechanics. Full article
Open AccessReview
Zebrafish Melanophores Suggest Novel Functions of Cell Chirality in Tissue Formation
Symmetry 2021, 13(1), 130; https://0-doi-org.brum.beds.ac.uk/10.3390/sym13010130 - 13 Jan 2021
Viewed by 225
Abstract
Several types of cells show left–right asymmetric behavior, unidirectional rotation, or spiral movements. For example, neutrophil-like differentiated HL60 (dHL60) cells show leftward bias in response to chemoattractant. Neurons extend neurites, creating a clockwise spiral. Platelet cells shows unidirectional spiral arrangements of actin fibers. [...] Read more.
Several types of cells show left–right asymmetric behavior, unidirectional rotation, or spiral movements. For example, neutrophil-like differentiated HL60 (dHL60) cells show leftward bias in response to chemoattractant. Neurons extend neurites, creating a clockwise spiral. Platelet cells shows unidirectional spiral arrangements of actin fibers. In the microfabricated culture environment, groups of C2C12 cells (mouse myoblast cell line) were autonomously aligned in a counter-clockwise spiral pattern, and isolated C2C12 cells showed unidirectional spiral pattern of the actin skeleton. This biased directionality suggested that these cells have inherent cell chirality. In addition to these cells, we recently found that melanophores of zebrafish also have an intrinsic cellular chirality that was shown by their counter-clockwise self-rotation. Although this cell chirality is obvious, the function of the cell chirality is still unclear. In this review, we compare the cell chirality of melanophores of zebrafish with other cell chirality and consider the function of cell chirality in morphogenesis. Full article
(This article belongs to the Special Issue Left-Right Asymmetry in Cell Biology)
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Open AccessArticle
Implementing a Symmetric Lightweight Cryptosystem in Highly Constrained IoT Devices by Using a Chaotic S-Box
Symmetry 2021, 13(1), 129; https://0-doi-org.brum.beds.ac.uk/10.3390/sym13010129 - 13 Jan 2021
Viewed by 408
Abstract
In the Internet of Things (IoT), a lot of constrained devices are interconnected. The data collected from those devices can be the target of cyberattacks. In this paper, a lightweight cryptosystem that can be efficiently implemented in highly constrained IOT devices is proposed. [...] Read more.
In the Internet of Things (IoT), a lot of constrained devices are interconnected. The data collected from those devices can be the target of cyberattacks. In this paper, a lightweight cryptosystem that can be efficiently implemented in highly constrained IOT devices is proposed. The algorithm is mainly based on Advanced Encryption Standard (AES) and a new chaotic S-box. Since its adoption by the IEEE 802.15.4 protocol, AES in embedded platforms have been increasingly used. The main cryptographic properties of the generated S-box have been validated. The randomness of the generated S-box has been confirmed by the NIST tests. Experimental results and security analysis demonstrated that the cryptosystem can, on the one hand, reach good encryption results and respects the limitation of the sensor’s resources, on the other hand. So the proposed solution could be reliably applied in image encryption and secure communication between networked smart objects. Full article
(This article belongs to the Section Computer and Engineering Science and Symmetry)
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Open AccessReview
Research Review on Parking Space Detection Method
Symmetry 2021, 13(1), 128; https://0-doi-org.brum.beds.ac.uk/10.3390/sym13010128 - 13 Jan 2021
Viewed by 285
Abstract
The parking assist system is an essential application of the car’s active collision avoidance system in low-speed and complex urban environments, which has been a hot research topic in recent years. Parking space detection is an important step of the parking assistance system, [...] Read more.
The parking assist system is an essential application of the car’s active collision avoidance system in low-speed and complex urban environments, which has been a hot research topic in recent years. Parking space detection is an important step of the parking assistance system, and its research object is parking spaces with symmetrical structures in parking lots. By analyzing and investigating parking space information measured by the sensors, reliable detection of sufficient parking spaces can be realized. First, this article discusses the main problems in the process of detecting parking spaces, illustrating the research significance and current research status of parking space detection methods. In addition, it further introduces some parking space detection methods, including free-space-based methods, parking-space-marking-based methods, user-interface-based methods, and infrastructure-based methods, which are all under methods of parking space selection. Lastly, this article summarizes the parking space detection methods, which gives a clear direction for future research. Full article
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Open AccessArticle
Influence of Mach Number of Main Flow on Film Cooling Characteristics under Supersonic Condition
Symmetry 2021, 13(1), 127; https://0-doi-org.brum.beds.ac.uk/10.3390/sym13010127 - 13 Jan 2021
Viewed by 238
Abstract
The flow and heat transfer characteristics of a film jet inclined to different supersonic situations with a varying Mach number of the main flow were numerically investigated. In supersonic situations, complicated waves are generated by the obstacle of the film jet. In this [...] Read more.
The flow and heat transfer characteristics of a film jet inclined to different supersonic situations with a varying Mach number of the main flow were numerically investigated. In supersonic situations, complicated waves are generated by the obstacle of the film jet. In this work, extra pressure is exerted onto the film jet, causing better film attachment to the wall. The strengthening of attachment decreases mixing between the main flow and film jet, causing better film cooling. We observed multi-interfacial layered structures caused by the film jet under the complicated effect of shock waves. At the interfaces of the film jet and shock waves, additional pressure is exerted on the film towards the wall. The pressure increases as the Mach number of the main flow increases and contributes to the increased adhesion of the gas film, which causes the cooling enhancement under a supersonic condition. In the vicinity of the film hole exit, a local low pressure region is formed under the influence of the supersonic main flow. An aerodynamic convergent–divergent state was formed in the film hole, devastating the state of supersonic congestion of the film hole and further enhancing the film cooling effect. Full article
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Open AccessArticle
Unpaired Image Denoising via Wasserstein GAN in Low-Dose CT Image with Multi-Perceptual Loss and Fidelity Loss
Symmetry 2021, 13(1), 126; https://0-doi-org.brum.beds.ac.uk/10.3390/sym13010126 - 13 Jan 2021
Viewed by 293
Abstract
The use of low-dose computed tomography (LDCT) in medical practice can effectively reduce the radiation risk of patients, but it may increase noise and artefacts, which can compromise diagnostic information. The methods based on deep learning can effectively improve image quality, but most [...] Read more.
The use of low-dose computed tomography (LDCT) in medical practice can effectively reduce the radiation risk of patients, but it may increase noise and artefacts, which can compromise diagnostic information. The methods based on deep learning can effectively improve image quality, but most of them use a training set of aligned image pairs, which are difficult to obtain in practice. In order to solve this problem, on the basis of the Wasserstein generative adversarial network (GAN) framework, we propose a generative adversarial network combining multi-perceptual loss and fidelity loss. Multi-perceptual loss uses the high-level semantic features of the image to achieve the purpose of noise suppression by minimizing the difference between the LDCT image and the normal-dose computed tomography (NDCT) image in the feature space. In addition, L2 loss is used to calculate the loss between the generated image and the original image to constrain the difference between the denoised image and the original image, so as to ensure that the image generated by the network using the unpaired images is not distorted. Experiments show that the proposed method performs comparably to the current deep learning methods which utilize paired image for image denoising. Full article
(This article belongs to the Section Computer and Engineering Science and Symmetry)
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Open AccessArticle
An Efficient Login Authentication System against Multiple Attacks in Mobile Devices
Symmetry 2021, 13(1), 125; https://0-doi-org.brum.beds.ac.uk/10.3390/sym13010125 - 13 Jan 2021
Viewed by 292
Abstract
Access management of IoT devices is extremely important, and a secure login authentication scheme can effectively protect users’ privacy. However, traditional authentication schemes are threatened by shoulder-surfing attacks, and biometric-based schemes, such as fingerprint recognition and face recognition, that are commonly used today [...] Read more.
Access management of IoT devices is extremely important, and a secure login authentication scheme can effectively protect users’ privacy. However, traditional authentication schemes are threatened by shoulder-surfing attacks, and biometric-based schemes, such as fingerprint recognition and face recognition, that are commonly used today can also be cracked. Researchers have proposed some schemes for current attacks, but they are limited by usability. For example, the login authentication process requires additional device support. This method solves the problem of attacks, but it is unusable, which limits its application. At present, most authentication schemes for the Internet of Things and mobile platforms either focus on security, thus ignoring availability, or have excellent convenience but insufficient security. This is a symmetry problem worth exploring. Therefore, users need a new type of login authentication scheme that can balance security and usability to protect users’ private data or maintain device security. In this paper, we propose a login authentication scheme named PinWheel, which combines a textual password, a graphical password, and biometrics to prevent both shoulder-surfing attacks and smudge attacks and solves the current schemes’ lack of usability. We implemented PinWheel and evaluated it from the perspective of security and usability. The experiments required 262 days, and 573 subjects participated in our investigation. The evaluation results show that PinWheel can at least effectively resist both mainstream attacks and is superior to most existing schemes in terms of usability. Full article
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