Symmetry

14 pages, 297 KiB

Open AccessEditor’s ChoiceArticle

Null Homology Groups and Stable Currents in Warped Product Submanifolds of Euclidean Spaces

by Yanlin Li, Pişcoran Laurian-Ioan, Akram Ali and Ali H. Alkhaldi

Symmetry 2021, 13(9), 1587; https://doi.org/10.3390/sym13091587 - 28 Aug 2021

Cited by 7 | Viewed by 2381

In this paper, we prove that, for compact warped product submanifolds

M^{n}

in an Euclidean space

E^{n + k}

, there are no stable p-currents, homology groups are vanishing, and

M^{3}

is homotopic to the Euclidean sphere

S^{3}

[...] Read more.

In this paper, we prove that, for compact warped product submanifolds

M^{n}

in an Euclidean space

E^{n + k}

, there are no stable p-currents, homology groups are vanishing, and

M^{3}

is homotopic to the Euclidean sphere

S^{3}

under various extrinsic restrictions, involving the eigenvalue of the warped function, integral Ricci curvature, and the Hessian tensor. The results in this paper can be considered an extension of Xin’s work in the framework of a compact warped product submanifold, when the base manifold is minimal in ambient manifolds. Full article

11 pages, 277 KiB

Open AccessEditor’s ChoiceArticle

On Special Differential Subordinations Using Fractional Integral of Sălăgean and Ruscheweyh Operators

by Alina Alb Lupaş and Georgia Irina Oros

Symmetry 2021, 13(9), 1553; https://doi.org/10.3390/sym13091553 - 24 Aug 2021

Cited by 20 | Viewed by 2333

Abstract

In the present paper, a new operator denoted by

D_{z}^{- λ} L_{α}^{n}

is defined by using the fractional integral of Sălăgean and Ruscheweyh operators. By means of the newly obtained operator, the subclass [...] Read more.

In the present paper, a new operator denoted by

D_{z}^{- λ} L_{α}^{n}

is defined by using the fractional integral of Sălăgean and Ruscheweyh operators. By means of the newly obtained operator, the subclass

S_{n} (δ, α, λ)

of analytic functions in the unit disc is introduced, and various properties and characteristics of this class are derived by applying techniques specific to the differential subordination concept. By studying the operator

D_{z}^{- λ} L_{α}^{n}

, some interesting differential subordinations are also given. Full article

(This article belongs to the Section Mathematics)

43 pages, 11181 KiB

Open AccessEditor’s ChoiceArticle

Neurofunctional Symmetries and Asymmetries during Voluntary out-of- and within-Body Vivid Imagery Concurrent with Orienting Attention and Visuospatial Detection

by Amedeo D’Angiulli, Darren Kenney, Dao Anh Thu Pham, Etienne Lefebvre, Justin Bellavance and Derrick Matthew Buchanan

Symmetry 2021, 13(8), 1549; https://doi.org/10.3390/sym13081549 - 23 Aug 2021

Cited by 6 | Viewed by 4624

Abstract

We explored whether two visual mental imagery experiences may be differentiated by electroencephalographic (EEG) and performance interactions with concurrent orienting external attention (OEA) to stimulus location and subsequent visuospatial detection. We measured within-subject (N = 10) event-related potential (ERP) changes during out-of-body imagery [...] Read more.

We explored whether two visual mental imagery experiences may be differentiated by electroencephalographic (EEG) and performance interactions with concurrent orienting external attention (OEA) to stimulus location and subsequent visuospatial detection. We measured within-subject (N = 10) event-related potential (ERP) changes during out-of-body imagery (OBI)—vivid imagery of a vertical line outside of the head/body—and within-body imagery (WBI)—vivid imagery of the line within one’s own head. Furthermore, we measured ERP changes and line offset Vernier acuity (hyperacuity) performance concurrent with those imagery, compared to baseline detection without imagery. Relative to OEA baseline, OBI yielded larger N200 and P300, whereas WBI yielded larger P50, P100, N400, and P800. Additionally, hyperacuity dropped significantly when concurrent with both imagery types. Partial least squares analysis combined behavioural performance, ERPs, and/or event-related EEG band power (ERBP). For both imagery types, hyperacuity reduction correlated with opposite frontal and occipital ERP amplitude and polarity changes. Furthermore, ERP modulation and ERBP synchronizations for all EEG frequencies correlated inversely with hyperacuity. Dipole Source Localization Analysis revealed unique generators in the left middle temporal gyrus (WBI) and in the right frontal middle gyrus (OBI), whereas the common generators were in the left precuneus and middle occipital cortex (cuneus). Imagery experiences, we conclude, can be identified by symmetric and asymmetric combined neurophysiological-behavioural patterns in interactions with the width of attentional focus. Full article

(This article belongs to the Special Issue Symmetry and Asymmetry in Brain Behavior and Perception II)

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9 pages, 4288 KiB

Open AccessEditor’s ChoiceArticle

Individual Laterality in Ghost Crabs (Ocypode saratan) Influences Burrowing Behavior

by Reuven Yosef, Michal Daraby, Alexei Semionovikh and Jakub Z. Kosicki

Symmetry 2021, 13(8), 1512; https://doi.org/10.3390/sym13081512 - 17 Aug 2021

Cited by 9 | Viewed by 3828

Abstract

Behavioral handedness is known to enhance an individual’s handling capabilities. However, the ecological advantages in brachyuran crustaceans remain unclear, despite the Ocypode species having been studied extensively. Thus, in this study, we analyzed the laterality of the endemic Red Sea ghost crab on [...] Read more.

Behavioral handedness is known to enhance an individual’s handling capabilities. However, the ecological advantages in brachyuran crustaceans remain unclear, despite the Ocypode species having been studied extensively. Thus, in this study, we analyzed the laterality of the endemic Red Sea ghost crab on one beach in Eilat, Israel. We successfully documented the laterality of the large cheliped in 125 crabs; in 60 (48.0%), the right cheliped was larger, and in 64 (51.2%), the left. We also observed temporal segregation between the right- and left-clawed crabs. The right-handed crabs start activity just after sunrise, while left-handed crabs appear ca. 40 min after it. Similarly, temporal segregations were also observed in the evening. The right-clawed crab activity peaked ca. 20 min before sunset, while the left-clawed crabs were active uniformly. Additionally, burrow entrances corresponded to the larger cheliped of the resident individual and is probably a self-defense-related behavior. We conclude that cheliped laterality in O. saratan populations should be considered as a bimodal trait, where left- and right-handedness is not under natural selection pressure. Full article

(This article belongs to the Special Issue Symmetry and Biology Section: Feature Papers in Neuroscience and Behavior)

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Graphical abstract

26 pages, 2979 KiB

Open AccessEditor’s ChoiceReview

Nanofluids for the Next Generation Thermal Management of Electronics: A Review

by Ana Moita, António Moreira and José Pereira

Symmetry 2021, 13(8), 1362; https://doi.org/10.3390/sym13081362 - 27 Jul 2021

Cited by 60 | Viewed by 9339

Abstract

Nowadays, the thermal management of electronic components, devices and systems is one of the most important challenges of this technological field. The ever-increasing miniaturization also entails the pressing need for the dissipation of higher power energy under the form of heat per unit [...] Read more.

Nowadays, the thermal management of electronic components, devices and systems is one of the most important challenges of this technological field. The ever-increasing miniaturization also entails the pressing need for the dissipation of higher power energy under the form of heat per unit of surface area by the cooling systems. The current work briefly describes the use on those cooling systems of the novel heat transfer fluids named nanofluids. Although not intensively applied in our daily use of electronic devices and appliances, the nanofluids have merited an in-depth research and investigative focus, with several recently published papers on the subject. The development of this cooling approach should give a sustained foothold to go on to further studies and developments on continuous miniaturization, together with more energy-efficient cooling systems and devices. Indeed, the superior thermophysical properties of the nanofluids, which are highlighted in this review, make those innovative fluids very promising for the aforementioned purpose. Moreover, the present work intends to contribute to the knowledge of the nanofluids and its most prominent results from the typical nanoparticles/base fluid mixtures used and combined in technical and functional solutions, based on fluid-surface interfacial flows. Full article

(This article belongs to the Special Issue Liquid-Solid Interfacial Phenomena on Complex Surfaces)

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18 pages, 550 KiB

Open AccessEditor’s ChoiceArticle

New Conservation Laws and Exact Cosmological Solutions in Brans–Dicke Cosmology with an Extra Scalar Field

by Antonios Mitsopoulos, Michael Tsamparlis, Genly Leon and Andronikos Paliathanasis

Symmetry 2021, 13(8), 1364; https://doi.org/10.3390/sym13081364 - 27 Jul 2021

Cited by 11 | Viewed by 3056

Abstract

The derivation of conservation laws and invariant functions is an essential procedure for the investigation of nonlinear dynamical systems. In this study, we consider a two-field cosmological model with scalar fields defined in the Jordan frame. In particular, we consider a Brans–Dicke scalar [...] Read more.

The derivation of conservation laws and invariant functions is an essential procedure for the investigation of nonlinear dynamical systems. In this study, we consider a two-field cosmological model with scalar fields defined in the Jordan frame. In particular, we consider a Brans–Dicke scalar field theory and for the second scalar field we consider a quintessence scalar field minimally coupled to gravity. For this cosmological model, we apply for the first time a new technique for the derivation of conservation laws without the application of variational symmetries. The results are applied for the derivation of new exact solutions. The stability properties of the scaling solutions are investigated and criteria for the nature of the second field according to the stability of these solutions are determined. Full article

(This article belongs to the Section Physics)

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15 pages, 1791 KiB

Open AccessEditor’s ChoiceArticle

Feature Ranking and Differential Evolution for Feature Selection in Brushless DC Motor Fault Diagnosis

by Chun-Yao Lee and Chen-Hsu Hung

Symmetry 2021, 13(7), 1291; https://doi.org/10.3390/sym13071291 - 18 Jul 2021

Cited by 14 | Viewed by 3424

Abstract

A fault diagnosis system with the ability to recognize many different faults obviously has a certain complexity. Therefore, improving the performance of similar systems has attracted much research interest. This article proposes a system of feature ranking and differential evolution for feature selection [...] Read more.

A fault diagnosis system with the ability to recognize many different faults obviously has a certain complexity. Therefore, improving the performance of similar systems has attracted much research interest. This article proposes a system of feature ranking and differential evolution for feature selection in BLDC fault diagnosis. First, this study used the Hilbert–Huang transform (HHT) to extract the features of four different types of brushless DC motor Hall signal. When there is a fault, the symmetry of the Hall signal will be influenced. Second, we used feature selection based on a distance discriminant (FSDD) to calculate the feature factors which base on the category separability of features to select the features which have a positive correlation with the types. The features were entered sequentially into the two supervised classifiers: backpropagation neural network (BPNN) and linear discriminant analysis (LDA), and the identification results were then evaluated. The feature input for the classifier was derived from the FSDD, and then we optimized the feature rank using differential evolution (DE). Finally, the results were verified from the BLDC motor’s operating environment simulation with the same features by adding appropriate signal-to-noise ratio magnitudes. The identification system obtained an accuracy rate of 96% when there were 14 features. Additionally, the experimental results show that the proposed system has a robust anti-noise ability, and the accuracy rate is 92.04%, even when 20 dB of white Gaussian noise is added to the signal. Moreover, compared with the systems established from the discrete wavelet transform (DWT) and a variety of classifiers, our proposed system has a higher accuracy with fewer features. Full article

(This article belongs to the Special Issue Complex Systems and Its Applications)

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20 pages, 1059 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Building a Fuzzy Classifier Based on Whale Optimization Algorithm to Detect Network Intrusions

by Nikolay Koryshev, Ilya Hodashinsky and Alexander Shelupanov

Symmetry 2021, 13(7), 1211; https://doi.org/10.3390/sym13071211 - 6 Jul 2021

Cited by 14 | Viewed by 3093

Abstract

The quantity of network attacks and the harm from them is constantly increasing, so the detection of these attacks is an urgent task in the information security field. In this paper, we investigate an approach to building intrusion detection systems using a classifier [...] Read more.

The quantity of network attacks and the harm from them is constantly increasing, so the detection of these attacks is an urgent task in the information security field. In this paper, we investigate an approach to building intrusion detection systems using a classifier based on fuzzy rules. The process of creating a fuzzy classifier based on a given set of input and output data can be presented as a solution to the problems of clustering, informative features selection, and the parameters of the rule antecedents optimization. To solve these problems, the whale optimization algorithm is used. The performance of algorithms for constructing a fuzzy classifier based on this metaheuristic is estimated using the KDD Cup 1999 intrusion detection dataset. On average, the resulting classifiers have a type I error of 0.92% and a type II error of 1.07%. The obtained results are also compared with the results of other classifiers. The comparison shows the competitiveness of the proposed method. Full article

(This article belongs to the Special Issue Information Technologies and Electronics Ⅱ)

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12 pages, 1652 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Use of the Molecular Dynamics Method to Investigate the Stability of α-α-Corner Structural Motifs in Proteins

by Vladimir R. Rudnev, Liudmila I. Kulikova, Anna L. Kaysheva, Alexander V. Efimov and Dmitry A. Tikhonov

Symmetry 2021, 13(7), 1193; https://doi.org/10.3390/sym13071193 - 2 Jul 2021

Cited by 6 | Viewed by 3212

Abstract

This study investigated the stability of structural motifs via molecular dynamics, using α-α-corners as an example. A molecular dynamics experiment was performed on a sample of α-α-corners selected by the authors from the PDB database. For the first time during a molecular dynamics [...] Read more.

This study investigated the stability of structural motifs via molecular dynamics, using α-α-corners as an example. A molecular dynamics experiment was performed on a sample of α-α-corners selected by the authors from the PDB database. For the first time during a molecular dynamics experiment, we investigated the characteristics of structural motifs by describing their geometry, including the interplanar distance, area of polygon of the helices projections intersection, and torsion angles between axes of helices in helical pairs. The torsion angles for the constriction amino acids in the equilibrium portion of the molecular dynamics trajectory were analyzed. Using the molecular dynamics method, α-α-corners were found to be autonomous structures that are stable in aquatic environments. Full article

(This article belongs to the Special Issue Medicinal Chemistry: Topics and Advances)

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17 pages, 356 KiB

Open AccessEditor’s ChoiceArticle

Symmetric Ground States for Doubly Nonlocal Equations with Mass Constraint

by Silvia Cingolani, Marco Gallo and Kazunaga Tanaka

Symmetry 2021, 13(7), 1199; https://doi.org/10.3390/sym13071199 - 2 Jul 2021

Cited by 21 | Viewed by 3043

Abstract

We prove the existence of a spherically symmetric solution for a Schrödinger equation with a nonlocal nonlinearity of Choquard type. This term is assumed to be subcritical and satisfy almost optimal assumptions. The mass of of the solution, described by its norm in [...] Read more.

We prove the existence of a spherically symmetric solution for a Schrödinger equation with a nonlocal nonlinearity of Choquard type. This term is assumed to be subcritical and satisfy almost optimal assumptions. The mass of of the solution, described by its norm in the Lebesgue space, is prescribed in advance. The approach to this constrained problem relies on a Lagrange formulation and new deformation arguments. In addition, we prove that the obtained solution is also a ground state, which means that it realizes minimal energy among all the possible solutions to the problem. Full article

(This article belongs to the Special Issue Recent Advance in Mathematical Physics)

11 pages, 2290 KiB

Open AccessEditor’s ChoiceArticle

Monitoring Spin-Crossover Properties by Diffused Reflectivity

by Gelu-Marius Rotaru, Epiphane Codjovi, Pierre-Richard Dahoo, Isabelle Maurin, Jorge Linares and Aurelian Rotaru

Symmetry 2021, 13(7), 1148; https://doi.org/10.3390/sym13071148 - 27 Jun 2021

Cited by 7 | Viewed by 2575

Abstract

In this work we present a detailed study showing the importance of the Kubelka-Munk (KM) correction in the analysis of diffuse reflectivity measurements to characterize spin crossover compounds. Combined reflectance and magnetic susceptibility measurements are carried out as a function of temperature or [...] Read more.

In this work we present a detailed study showing the importance of the Kubelka-Munk (KM) correction in the analysis of diffuse reflectivity measurements to characterize spin crossover compounds. Combined reflectance and magnetic susceptibility measurements are carried out as a function of temperature or time to highlight the conditions under which this correction becomes critical. In particular, we investigate the influence of the color contrast between the two spin states on the reflectance measurements. Interestingly, the samples’ contrast seems to play an important role on the spin-like domain structure as suggested by the symmetry of the FORC diagrams. These latest results are discussed within the framework of Classical Preisach model (CPM). Full article

(This article belongs to the Section Physics)

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19 pages, 2155 KiB

Open AccessEditor’s ChoiceArticle

Get a Grip: Variation in Human Hand Grip Strength and Implications for Human Evolution

by Ameline Bardo, Tracy L. Kivell, Katie Town, Georgina Donati, Haiko Ballieux, Cosmin Stamate, Trudi Edginton and Gillian S. Forrester

Symmetry 2021, 13(7), 1142; https://doi.org/10.3390/sym13071142 - 26 Jun 2021

Cited by 32 | Viewed by 14430

Abstract

Although hand grip strength is critical to the daily lives of humans and our arboreal great ape relatives, the human hand has changed in form and function throughout our evolution due to terrestrial bipedalism, tool use, and directional asymmetry (DA) such as handedness. [...] Read more.

Although hand grip strength is critical to the daily lives of humans and our arboreal great ape relatives, the human hand has changed in form and function throughout our evolution due to terrestrial bipedalism, tool use, and directional asymmetry (DA) such as handedness. Here we investigate how hand form and function interact in modern humans to gain an insight into our evolutionary past. We measured grip strength in a heterogeneous, cross-sectional sample of human participants (n = 662, 17 to 83 years old) to test the potential effects of age, sex, asymmetry (hand dominance and handedness), hand shape, occupation, and practice of sports and musical instruments that involve the hand(s). We found a significant effect of sex and hand dominance on grip strength, but not of handedness, while hand shape and age had a greater influence on female grip strength. Females were significantly weaker with age, but grip strength in females with large hands was less affected than those with long hands. Frequent engagement in hand sports significantly increased grip strength in the non-dominant hand in both sexes, while only males showed a significant effect of occupation, indicating different patterns of hand dominance asymmetries and hand function. These results improve our understanding of the link between form and function in both hands and offer an insight into the evolution of human laterality and dexterity. Full article

(This article belongs to the Special Issue Symmetry in Human Evolution, from Biology to Behaviours)

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21 pages, 11979 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Extreme Poisson’s Ratios of Honeycomb, Re-Entrant, and Zig-Zag Crystals of Binary Hard Discs

by Mikołaj Bilski, Paweł M. Pigłowski and Krzysztof W. Wojciechowski

Symmetry 2021, 13(7), 1127; https://doi.org/10.3390/sym13071127 - 24 Jun 2021

Cited by 21 | Viewed by 3653

Abstract

Two-dimensional (2D) crystalline structures based on a honeycomb geometry are analyzed by computer simulations using the Monte Carlo method in the isobaric-isothermal ensemble. The considered crystals are formed by hard discs (HD) of two different diameters which are very close to each other. [...] Read more.

Two-dimensional (2D) crystalline structures based on a honeycomb geometry are analyzed by computer simulations using the Monte Carlo method in the isobaric-isothermal ensemble. The considered crystals are formed by hard discs (HD) of two different diameters which are very close to each other. In contrast to equidiameter HD, which crystallize into a homogeneous solid which is elastically isotropic due to its six-fold symmetry axis, the systems studied in this work contain artificial patterns and can be either isotropic or anisotropic. It turns out that the symmetry of the patterns obtained by the appropriate arrangement of two types of discs strongly influences their elastic properties. The Poisson’s ratio (PR) of each of the considered structures was studied in two aspects: (a) its dependence on the external isotropic pressure and (b) in the function of the direction angle, in which the deformation of the system takes place, since some of the structures are anisotropic. In order to accomplish the latter, the general analytic formula for the orientational dependence of PR in 2D systems was used. The PR analysis at extremely high pressures has shown that for the vast majority of the considered structures it is approximately direction independent (isotropic) and tends to the upper limit for isotropic 2D systems, which is equal to

+ 1

. This is in contrast to systems of equidiameter discs for which it tends to

0.13

, i.e., a value almost eight times smaller. Full article

(This article belongs to the Special Issue Metamaterials and Symmetry)

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15 pages, 2837 KiB

Open AccessEditor’s ChoiceArticle

In Silico Investigation on the Interaction of Chiral Phytochemicals from Opuntia ficus-indica with SARS-CoV-2 M^pro

by Caterina Vicidomini, Valentina Roviello and Giovanni N. Roviello

Symmetry 2021, 13(6), 1041; https://doi.org/10.3390/sym13061041 - 9 Jun 2021

Cited by 42 | Viewed by 6724

Abstract

Opuntia ficus-indica is a cactaceous plant native to America but, nowadays, widely found worldwide, having been the most common domesticated species of cactus grown as a crop plant in semiarid and arid parts of the globe, including several Mediterranean basin countries. Opuntia ficus-indica [...] Read more.

Opuntia ficus-indica is a cactaceous plant native to America but, nowadays, widely found worldwide, having been the most common domesticated species of cactus grown as a crop plant in semiarid and arid parts of the globe, including several Mediterranean basin countries. Opuntia ficus-indica can be regarded as a medicinal plant, being source of numerous bioactive phytochemicals such as vitamins, polyphenols, and amino acids. The urgent need for therapeutic treatments for the COronaVIrus Disease 19 (COVID-19), caused by the Severe Acute Respiratory Syndrome (SARS)-Coronavirus (CoV)-2, justifies the great attention currently being paid not only to repurposed antiviral drugs, but also to natural products and herbal medications. In this context, the anti-COVID-19 utility of Opuntia ficus-indica as source of potential antiviral drugs was investigated in this work on the basis of the activity of some of its phytochemical constituents. The antiviral potential was evaluated in silico in docking experiments with M^pro, i.e., the main protease of SARS-CoV-2, that is one of the most investigated protein targets of therapeutic strategies for COVID-19. By using two web-based molecular docking programs (1-Click Mcule and COVID-19 Docking Server), we found, for several flavonols and flavonol glucosides isolated from Opuntia ficus-indica, good binding affinities for M^pro, and in particular, binding energies lower than −7.0 kcal/mol were predicted for astragalin, isorhamnetin, isorhamnetin 3-O-glucoside, 3-O-caffeoyl quinic acid, and quercetin 5,4′-dimethyl ether. Among these compounds, the chiral compound astragalin showed in our in silico studies the highest affinity for M^pro (−8.7 kcal/mol) and also a low toxicity profile, emerging, thus, as an interesting protease inhibitor candidate for anti-COVID-19 strategies. Full article

(This article belongs to the Special Issue Symmetry and Its Application in the Structural and Biochemical Characterization of Enzymes and Protein Complexes)

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15 pages, 1552 KiB

Open AccessEditor’s ChoiceArticle

The Association among Autistic Traits, Interactional Synchrony and Typical Pattern of Motor Planning and Execution in Neurotypical Individuals

by Michal Granner-Shuman, Anat Dahan, Roi Yozevitch and Hila Zahava Gvirts Problovski

Symmetry 2021, 13(6), 1034; https://doi.org/10.3390/sym13061034 - 8 Jun 2021

Cited by 9 | Viewed by 3486

Abstract

Autism spectrum disorder (ASD) is characterized by deficits in interactional synchrony and motor performance, but little is known about the association between them. The current study investigated the association among aberrant interactional synchrony (as measured by interactors’ symmetry in the form of the [...] Read more.

Autism spectrum disorder (ASD) is characterized by deficits in interactional synchrony and motor performance, but little is known about the association between them. The current study investigated the association among aberrant interactional synchrony (as measured by interactors’ symmetry in the form of the hand at each time-point along movement’s execution), motor functioning and the level of Autistic traits. In this study, autistic traits were evaluated by the Autistic Spectrum Quotient (AQ). Two tasks were used: (1) an interactional synchrony task where participants and the research assistant were instructed to move their hands together; and (2) a motor planning task which allows for continuous monitoring of natural hand movements. Pearson correlation analysis indicated a significant association between lower communication skills (i.e., higher AQ communication scores) and lower intentional synchrony rates. In addition, lower communication skills were found associated with typical patterns of motor planning and execution characterized by shorter time to start the movement and higher value of max speed. Mediator analyses supported the notion that aberrant intentional synchrony in individuals with low communication skills is partially mediated through typical patterns of motor planning and execution. These results suggest typical patterns of motor functions may account for intentional synchrony difficulties. Full article

(This article belongs to the Special Issue Symmetry and Asymmetry: From Evolution to Neuroscience)

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29 pages, 1453 KiB

Open AccessEditor’s ChoiceArticle

IDM Benchmarks for the LHC and Future Colliders

by Jan Kalinowski, Tania Robens, Dorota Sokołowska and Aleksander Filip Żarnecki

Symmetry 2021, 13(6), 991; https://doi.org/10.3390/sym13060991 - 2 Jun 2021

Cited by 36 | Viewed by 3638

Abstract

We present cross-section expectations for various processes and collider options, for benchmark scenarios of the Inert Doublet Model, a Two Higgs Doublet Model with a dark matter candidate. The proposed scenarios are consistent with current dark matter constraints, including the most recent bounds [...] Read more.

We present cross-section expectations for various processes and collider options, for benchmark scenarios of the Inert Doublet Model, a Two Higgs Doublet Model with a dark matter candidate. The proposed scenarios are consistent with current dark matter constraints, including the most recent bounds from the XENON1T experiment and relic density, as well as with known collider and low-energy limits. These benchmarks, chosen in earlier work for studies at

e^{+} e^{-}

colliders, exhibit a variety of kinematic features that should be explored at current and future runs of the LHC. We provide cross sections for all relevant production processes at 13 TeV, 27 TeV and 100 TeV proton collider, as well as for a possible 10 TeV and 30 TeV muon collider. Full article

(This article belongs to the Special Issue Higher Order Radiative Corrections in QCD)

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44 pages, 3475 KiB

Open AccessEditor’s ChoiceReview

Handedness Development: A Model for Investigating the Development of Hemispheric Specialization and Interhemispheric Coordination

by George F. Michel

Symmetry 2021, 13(6), 992; https://doi.org/10.3390/sym13060992 - 2 Jun 2021

Cited by 22 | Viewed by 6755

Abstract

The author presents his perspective on the character of science, development, and handedness and relates these to his investigations of the early development of handedness. After presenting some ideas on what hemispheric specialization of function might mean for neural processing and how handedness [...] Read more.

The author presents his perspective on the character of science, development, and handedness and relates these to his investigations of the early development of handedness. After presenting some ideas on what hemispheric specialization of function might mean for neural processing and how handedness should be assessed, the neuroscience of control of the arms/hands and interhemispheric communication and coordination are examined for how developmental processes can affect these mechanisms. The author’s work on the development of early handedness is reviewed and placed within a context of cascading events in which different forms of handedness emerge from earlier forms but not in a deterministic manner. This approach supports a continuous rather than categorical distribution of handedness and accounts for the predominance of right-handedness while maintaining a minority of left-handedness. Finally, the relation of the development of handedness to the development of several language and cognitive skills is examined. Full article

(This article belongs to the Special Issue Symmetry and Asymmetry: From Evolution to Neuroscience)

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9 pages, 237 KiB

Open AccessEditor’s ChoiceArticle

An Application of the Principle of Differential Subordination to Analytic Functions Involving Atangana–Baleanu Fractional Integral of Bessel Functions

by Alina Alb Lupaş and Adriana Cătaş

Symmetry 2021, 13(6), 971; https://doi.org/10.3390/sym13060971 - 31 May 2021

Cited by 12 | Viewed by 2340

Abstract

The aim of this paper is to establish certain subordination results for analytic functions involving Atangana–Baleanu fractional integral of Bessel functions. Studying subordination properties by using various types of operators is a technique that is widely used. Full article

(This article belongs to the Section Mathematics)

14 pages, 1223 KiB

Open AccessEditor’s ChoiceArticle

The Qualitative and Quantitative Study of Radiation Sources with a Model Configuration of the Electrode System

by Victor V. Kuzenov and Sergei V. Ryzhkov

Symmetry 2021, 13(6), 927; https://doi.org/10.3390/sym13060927 - 23 May 2021

Cited by 36 | Viewed by 3367

Abstract

This research is devoted to the calculation and theoretical analysis of physical processes in the powerful electric discharge sources of UV radiation and shock waves with required and controlled technical and physical characteristics. Based on the calculations, the processes of converting the initially [...] Read more.

This research is devoted to the calculation and theoretical analysis of physical processes in the powerful electric discharge sources of UV radiation and shock waves with required and controlled technical and physical characteristics. Based on the calculations, the processes of converting the initially stored electromagnetic energy into internal, kinetic, magnetic and radiation energy formed in the electro-discharge plasma sources of plasma formation were studied, and the interactions of discharged plasma and its radiation with matter in different aggregate states were also studied. All the main magneto-plasma dynamic and radiative parameters of plasma formation in the electric discharge sources of UV radiation and shock waves are obtained. Full article

(This article belongs to the Special Issue Plasma and Thermal Physics)

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21 pages, 325 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Different Faces of Generalized Holographic Dark Energy

by Shin’ichi Nojiri, Sergei D. Odintsov and Tanmoy Paul

Symmetry 2021, 13(6), 928; https://doi.org/10.3390/sym13060928 - 23 May 2021

Cited by 143 | Viewed by 4235

Abstract

In the formalism of generalized holographic dark energy (HDE), the holographic cut-off is generalized to depend upon [...] Read more.

In the formalism of generalized holographic dark energy (HDE), the holographic cut-off is generalized to depend upon

L_{IR} = L_{IR} (L_{p}, {\dot{L}}_{p}, {\ddot{L}}_{p}, \dots, L_{f}, {\dot{L}}_{f}, \dots, a)

with

L_{p}

and

L_{f}

being the particle horizon and the future horizon, respectively (moreover, a is the scale factor of the Universe). Based on such formalism, in the present paper, we show that a wide class of dark energy (DE) models can be regarded as different candidates for the generalized HDE family, with respective cut-offs. This can be thought as a symmetry between the generalized HDE and different DE models. In this regard, we considered several entropic dark energy models—such as the Tsallis entropic DE, the Rényi entropic DE, and the Sharma–Mittal entropic DE—and found that they are indeed equivalent with the generalized HDE. Such equivalence between the entropic DE and the generalized HDE is extended to the scenario where the respective exponents of the entropy functions are allowed to vary with the expansion of the Universe. Besides the entropic DE models, the correspondence with the generalized HDE was also established for the quintessence and for the Ricci DE model. In all the above cases, the effective equation of state (EoS) parameter corresponding to the holographic energy density was determined, by which the equivalence of various DE models with the respective generalized HDE models was further confirmed. The equivalent holographic cut-offs were determined by two ways: (1) in terms of the particle horizon and its derivatives, (2) in terms of the future horizon horizon and its derivatives. Full article

(This article belongs to the Special Issue Symmetry: Feature Papers 2022)

16 pages, 2937 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Topology Optimization Method Based on Non-Uniform Rational Basis Spline Hyper-Surfaces for Heat Conduction Problems

by Marco Montemurro and Khalil Refai

Symmetry 2021, 13(5), 888; https://doi.org/10.3390/sym13050888 - 17 May 2021

Cited by 20 | Viewed by 4122

Abstract

This work deals with heat conduction problems formulation in the framework of a CAD-compatible topology optimization method based on a pseudo-density field as a topology descriptor. In particular, the proposed strategy relies, on the one hand, on the use of CAD-compatible Non-Uniform Rational [...] Read more.

This work deals with heat conduction problems formulation in the framework of a CAD-compatible topology optimization method based on a pseudo-density field as a topology descriptor. In particular, the proposed strategy relies, on the one hand, on the use of CAD-compatible Non-Uniform Rational Basis Spline (NURBS) hyper-surfaces to represent the pseudo-density field and, on the other hand, on the well-known Solid Isotropic Material with Penalization (SIMP) approach. The resulting method is then referred to as NURBS-based SIMP method. In this background, heat conduction problems have been reformulated by taking advantage of the properties of the NURBS entities. The influence of the integer parameters, involved in the definition of the NURBS hyper-surface, on the optimized topology is investigated. Furthermore, symmetry constraints, as well as a manufacturing requirement related to the minimum allowable size, are also integrated into the problem formulation without introducing explicit constraint functions, thanks to the NURBS blending functions properties. Finally, since the topological variable is represented by means of a NURBS entity, the geometrical representation of the boundary of the topology is available at each iteration of the optimization process and its reconstruction becomes a straightforward task. The effectiveness of the NURBS-based SIMP method is shown on 2D and 3D benchmark problems taken from the literature. Full article

(This article belongs to the Special Issue Mathematical Theory, Methods, and Its Applications for Industry)

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52 pages, 4723 KiB

Open AccessEditor’s ChoiceReview

Phosphorus Compounds of Natural Origin: Prebiotic, Stereochemistry, Application

by Oleg I. Kolodiazhnyi

Symmetry 2021, 13(5), 889; https://doi.org/10.3390/sym13050889 - 17 May 2021

Cited by 57 | Viewed by 15282

Abstract

Organophosphorus compounds play a vital role as nucleic acids, nucleotide coenzymes, metabolic intermediates and are involved in many biochemical processes. They are part of DNA, RNA, ATP and a number of important biological elements of living organisms. Synthetic compounds of this class have [...] Read more.

Organophosphorus compounds play a vital role as nucleic acids, nucleotide coenzymes, metabolic intermediates and are involved in many biochemical processes. They are part of DNA, RNA, ATP and a number of important biological elements of living organisms. Synthetic compounds of this class have found practical application as agrochemicals, pharmaceuticals, bioregulators, and othrs. In recent years, a large number of phosphorus compounds containing P-O, P-N, P-C bonds have been isolated from natural sources. Many of them have shown interesting biological properties and have become the objects of intensive scientific research. Most of these compounds contain asymmetric centers, the absolute configurations of which have a significant effect on the biological properties of the products of their transformations. This area of research on natural phosphorus compounds is still little-studied, that prompted us to analyze and discuss it in our review. Moreover natural organophosphorus compounds represent interesting models for the development of new biologically active compounds, and a number of promising drugs and agrochemicals have already been obtained on their basis. The review also discusses the history of the development of ideas about the role of organophosphorus compounds and stereochemistry in the origin of life on Earth, starting from the prebiotic period, that allows us in a new way to consider this most important problem of fundamental science. Full article

(This article belongs to the Collection Feature Papers in Chemistry)

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17 pages, 5508 KiB

Open AccessEditor’s ChoiceArticle

Protein Helical Structures: Defining Handedness and Localization Features

by Alla E. Sidorova, Ekaterina V. Malyshko, Aleksey O. Lutsenko, Denis K. Shpigun and Olga E. Bagrova

Symmetry 2021, 13(5), 879; https://doi.org/10.3390/sym13050879 - 15 May 2021

Cited by 11 | Viewed by 3638

Abstract

The quantitative evaluation of the chirality of macromolecule structures remains one of the exciting issues in biophysics. In this paper, we propose methods for quantitative analysis of the chirality of protein helical and superhelical structures. The analysis of the chirality sign of the [...] Read more.

The quantitative evaluation of the chirality of macromolecule structures remains one of the exciting issues in biophysics. In this paper, we propose methods for quantitative analysis of the chirality of protein helical and superhelical structures. The analysis of the chirality sign of the protein helical structures (α-helices and 3₁₀-helices) is based on determining the mixed product of every three consecutive vectors between neighboring reference points—α-carbons atoms. The method for evaluating the chirality sign of coiled-coil structures is based on determining the direction and value of the angle between the coiled-coil axis and the α-helices axes. The chirality sign of the coiled coil is calculated by averaging the value of the cosine of the corresponding angle for all helices forming the superhelix. Chirality maps of helical and superhelical protein structures are presented. Furthermore, we propose an analysis of the distributions of helical and superhelical structures in polypeptide chains of several protein classes. The features common to all studied classes and typical for each protein class are revealed. The data obtained, in all likelihood, can reflect considerations about molecular machines as chiral formations. Full article

(This article belongs to the Special Issue Symmetry in Biophysics)

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15 pages, 813 KiB

Open AccessEditor’s ChoiceArticle

Cyclic Control Optimization Algorithm for Stirling Engines

by Raphael Paul and Karl Heinz Hoffmann

Symmetry 2021, 13(5), 873; https://doi.org/10.3390/sym13050873 - 13 May 2021

Cited by 25 | Viewed by 4370

Abstract

The ideal Stirling cycle describes a specific way to operate an equilibrium Stirling engine. This cycle consists of two isothermal and two isochoric strokes. For non-equilibrium Stirling engines, which may feature various irreversibilities and whose dynamics is characterized by a set of coupled [...] Read more.

The ideal Stirling cycle describes a specific way to operate an equilibrium Stirling engine. This cycle consists of two isothermal and two isochoric strokes. For non-equilibrium Stirling engines, which may feature various irreversibilities and whose dynamics is characterized by a set of coupled ordinary differential equations, a control strategy that is based on the ideal cycle will not necessarily yield the best performance—for example, it will not generally lead to maximum power. In this paper, we present a method to optimize the engine’s piston paths for different objectives; in particular, power and efficiency. Here, the focus is on an indirect iterative gradient algorithm that we use to solve the cyclic optimal control problem. The cyclic optimal control problem leads to a Hamiltonian system that features a symmetry between its state and costate subproblems. The symmetry manifests itself in the existence of mutually related attractive and repulsive limit cycles. Our algorithm exploits these limit cycles to solve the state and costate problems with periodic boundary conditions. A description of the algorithm is provided and it is explained how the control can be embedded in the system dynamics. Moreover, the optimization results obtained for an exemplary Stirling engine model are discussed. For this Stirling engine model, a comparison of the optimized piston paths against harmonic piston paths shows significant gains in both power and efficiency. At the maximum power point, the relative power gain due to the power-optimal control is ca. 28%, whereas the relative efficiency gain due to the efficiency-optimal control at the maximum efficiency point is ca. 10%. Full article

(This article belongs to the Special Issue Mathematical Aspects in Non-equilibrium Thermodynamics)

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14 pages, 6389 KiB

Open AccessEditor’s ChoiceArticle

An Auxetic System Based on Interconnected Y-Elements Inspired by Islamic Geometric Patterns

by Teik-Cheng Lim

Symmetry 2021, 13(5), 865; https://doi.org/10.3390/sym13050865 - 12 May 2021

Cited by 18 | Viewed by 3498

Abstract

A 2D mechanical metamaterial exhibiting perfectly auxetic behavior, i.e., Poisson’s ratio of

- 1

, is proposed in this paper drawing upon inspiration from an Islamic star formed by circumferential arrangement of eight squares, such as the one found at the exterior of [...] Read more.

A 2D mechanical metamaterial exhibiting perfectly auxetic behavior, i.e., Poisson’s ratio of

- 1

, is proposed in this paper drawing upon inspiration from an Islamic star formed by circumferential arrangement of eight squares, such as the one found at the exterior of the Ghiyathiyya Madrasa in Khargird, Iran (built 1438–1444 AD). Each unit of the metamaterial consists of eight pairs of pin-jointed Y-shaped rigid elements, whereby every pair of Y-elements is elastically restrained by a spiral spring. Upon intermediate stretching, each metamaterial unit resembles the north dome of Jameh Mosque, Iran (built 1087–1088 AD), until the attainment of the fully opened configuration, which resembles a structure in Agra, India, near the Taj Mahal. Both infinitesimal and finite deformation models of the effective Young’s modulus for the metamaterial structure were established using strain energy approach in terms of the spiral spring stiffness and geometrical parameters, with assumptions to preserve the eight-fold symmetricity of every metamaterial unit. Results indicate that the prescription of strain raises the effective Young’s modulus in an exponential manner until full extension is attained. This metamaterial is useful for applications where the overall shape of the structure must be conserved in spite of uniaxial application of load, and where deformation is permitted under limited range, which is quickly arrested as the deformation progresses. Full article

(This article belongs to the Special Issue Metamaterials and Symmetry)

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22 pages, 1051 KiB

Open AccessEditor’s ChoiceArticle

Higgs and BSM Physics at the Future Muon Collider

by Roberto Franceschini and Mario Greco

Symmetry 2021, 13(5), 851; https://doi.org/10.3390/sym13050851 - 11 May 2021

Cited by 35 | Viewed by 4772

Abstract

We describe recent work on the physics of the Higgs boson and breaking of the electroweak symmetry at future muon colliders. Starting from the low-energy muon collider at the Higgs boson pole we extend our discussion to the multi-TeV muon collider and outline [...] Read more.

We describe recent work on the physics of the Higgs boson and breaking of the electroweak symmetry at future muon colliders. Starting from the low-energy muon collider at the Higgs boson pole we extend our discussion to the multi-TeV muon collider and outline the physics case for such machines about the properties of the Higgs boson and physics beyond the Standard Model that can be possibly discovered. Full article

(This article belongs to the Special Issue Physics Potential of the Muon Collider)

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25 pages, 347 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Hermite Functions and Fourier Series

by Enrico Celeghini, Manuel Gadella and Mariano A. del Olmo

Symmetry 2021, 13(5), 853; https://doi.org/10.3390/sym13050853 - 11 May 2021

Cited by 21 | Viewed by 5153

Abstract

Using normalized Hermite functions, we construct bases in the space of square integrable functions on the unit circle (

L^{2} (C)

) and in

l_{2} (Z)

, which are related to each other by means of the [...] Read more.

Using normalized Hermite functions, we construct bases in the space of square integrable functions on the unit circle (

L^{2} (C)

) and in

l_{2} (Z)

, which are related to each other by means of the Fourier transform and the discrete Fourier transform. These relations are unitary. The construction of orthonormal bases requires the use of the Gramm–Schmidt method. On both spaces, we have provided ladder operators with the same properties as the ladder operators for the one-dimensional quantum oscillator. These operators are linear combinations of some multiplication- and differentiation-like operators that, when applied to periodic functions, preserve periodicity. Finally, we have constructed riggings for both

L^{2} (C)

and

l_{2} (Z)

, so that all the mentioned operators are continuous. Full article

(This article belongs to the Special Issue Special Functions and Polynomials)

18 pages, 341 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Applications of Banach Limit in Ulam Stability

by Roman Badora, Janusz Brzdęk and Krzysztof Ciepliński

Symmetry 2021, 13(5), 841; https://doi.org/10.3390/sym13050841 - 10 May 2021

Cited by 18 | Viewed by 2509

Abstract

We show how to get new results on Ulam stability of some functional equations using the Banach limit. We do this with the examples of the linear functional equation in single variable and the Cauchy equation. Full article

(This article belongs to the Special Issue Symmetry in Functional Equations and Inequalities)

29 pages, 8366 KiB

Open AccessEditor’s ChoiceArticle

Elastic Origin of the Unsymmetrical Thermal Hysteresis in Spin Crossover Materials: Evidence of Symmetry Breaking

by Mamadou Ndiaye, Nour El Islam Belmouri, Jorge Linares and Kamel Boukheddaden

Symmetry 2021, 13(5), 828; https://doi.org/10.3390/sym13050828 - 9 May 2021

Cited by 14 | Viewed by 2889

Abstract

The jungle of experimental behaviors of spin-crossover materials contains a tremendous number of unexpected behaviors, among which, the unsymmetrical hysteresis loops having different shapes on heating and cooling, that we often encounter in literature. Excluding an extra effect of crystallographic phase transitions, we [...] Read more.

The jungle of experimental behaviors of spin-crossover materials contains a tremendous number of unexpected behaviors, among which, the unsymmetrical hysteresis loops having different shapes on heating and cooling, that we often encounter in literature. Excluding an extra effect of crystallographic phase transitions, we study here these phenomena from the point of view of elastic modeling and we demonstrate that a simple model accounting for the bond lengths misfits between the high-spin and low-spin states is sufficient to describe the situation of unsymmetrical hysteresis showing plateaus at the transition only on cooling or on heating branches. The idea behind this effect relates to the existence of a discriminant elastic frustration in the lattice, which expresses only along the high-spin to low-spin transition or in the opposite side. The obtained two-step transitions showed characteristics of self-organization of the spin states under the form of stripes, which we explain as an emergence process of antagonist directional elastic interactions inside the lattice. The analysis of the spin state transformation inside the plateau on cooling in terms of two sublattices demonstrated that the elastic-driven self-organization of the spin states is accompanied with a symmetry breaking. Full article

(This article belongs to the Special Issue Symmetry and Symmetry Breaking: Phase Transitions and Critical Phenomena)

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13 pages, 4906 KiB

Open AccessEditor’s ChoiceArticle

On the Relationship between Generalization and Robustness to Adversarial Examples

by Anibal Pedraza, Oscar Deniz and Gloria Bueno

Symmetry 2021, 13(5), 817; https://doi.org/10.3390/sym13050817 - 7 May 2021

Cited by 12 | Viewed by 3472

Abstract

One of the most intriguing phenomenons related to deep learning is the so-called adversarial examples. These samples are visually equivalent to normal inputs, undetectable for humans, yet they cause the networks to output wrong results. The phenomenon can be framed as a symmetry/asymmetry [...] Read more.

One of the most intriguing phenomenons related to deep learning is the so-called adversarial examples. These samples are visually equivalent to normal inputs, undetectable for humans, yet they cause the networks to output wrong results. The phenomenon can be framed as a symmetry/asymmetry problem, whereby inputs to a neural network with a similar/symmetric appearance to regular images, produce an opposite/asymmetric output. Some researchers are focused on developing methods for generating adversarial examples, while others propose defense methods. In parallel, there is a growing interest in characterizing the phenomenon, which is also the focus of this paper. From some well known datasets of common images, like CIFAR-10 and STL-10, a neural network architecture is first trained in a normal regime, where training and validation performances increase, reaching generalization. Additionally, the same architectures and datasets are trained in an overfitting regime, where there is a growing disparity in training and validation performances. The behaviour of these two regimes against adversarial examples is then compared. From the results, we observe greater robustness to adversarial examples in the overfitting regime. We explain this simultaneous loss of generalization and gain in robustness to adversarial examples as another manifestation of the well-known fitting-generalization trade-off. Full article

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32 pages, 2412 KiB

Open AccessEditor’s ChoiceArticle

Copulaesque Versions of the Skew-Normal and Skew-Student Distributions

by Christopher Adcock

Symmetry 2021, 13(5), 815; https://doi.org/10.3390/sym13050815 - 6 May 2021

Cited by 4 | Viewed by 2821

Abstract

A recent paper presents an extension of the skew-normal distribution which is a copula. Under this model, the standardized marginal distributions are standard normal. The copula itself depends on the familiar skewing construction based on the normal distribution function. This paper is concerned [...] Read more.

A recent paper presents an extension of the skew-normal distribution which is a copula. Under this model, the standardized marginal distributions are standard normal. The copula itself depends on the familiar skewing construction based on the normal distribution function. This paper is concerned with two topics. First, the paper presents a number of extensions of the skew-normal copula. Notably these include a case in which the standardized marginal distributions are Student’s t, with different degrees of freedom allowed for each margin. In this case the skewing function need not be the distribution function for Student’s t, but can depend on certain of the special functions. Secondly, several multivariate versions of the skew-normal copula model are presented. The paper contains several illustrative examples. Full article

(This article belongs to the Special Issue Symmetry and Asymmetry in Multivariate Statistics and Data Science)

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44 pages, 4717 KiB

Open AccessEditor’s ChoiceArticle

Extending the Model-Based Controller Design to Higher-Order Plant Models and Measurement Noise

by Mikulas Huba and Damir Vrancic

Symmetry 2021, 13(5), 798; https://doi.org/10.3390/sym13050798 - 4 May 2021

Cited by 20 | Viewed by 3796

Abstract

The article extends a model-based controller design to higher-order systems, focusing on the speed and shapes of the closed loop responses, including the noise attenuation. It shows that, to obtain simple but reliable results, it is necessary to pay attention to the initial [...] Read more.

The article extends a model-based controller design to higher-order systems, focusing on the speed and shapes of the closed loop responses, including the noise attenuation. It shows that, to obtain simple but reliable results, it is necessary to pay attention to the initial process identification and modelling and also to modify the target closed-loop transfer functions, which must remain causal. To attenuate high initial control signal peaks, appropriate pre-filters are introduced. In order to work with as few parameters as possible, all higher-order transfer functions (process models, target closed loops, pre-filters and noise-attenuation filters) are selected in the form of binomial filters with multiple time constants. Consequently, the so-called “half-rule”, used to reduce too complex process transfer functions, has been modified accordingly. Because derived controllers can lead to different transient dynamics depending on the context of use, the article recalls the need to introduce dynamic classes of control to clarify the mission of individual types of controllers. Consequently, also the performance evaluation using the total variation (TV) criterion had to be refined. Indeed, in its original version, TV is not suitable to distinguish between reasonable and excessive control effort due to improper tuning and noise. The modified TVs allow evaluating higher order systems with multiple changes in direction of their control signal increase without contributing to the excessive control increments. The advantages of the proposed modifications, compared to the traditional approaches, are made clear through simulation examples. Full article

(This article belongs to the Special Issue PID Control and Symmetry)

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19 pages, 5042 KiB

Open AccessEditor’s ChoiceArticle

Nanofluids Characterization for Spray Cooling Applications

by Miguel Sanches, Guido Marseglia, Ana P. C. Ribeiro, António L. N. Moreira and Ana S. Moita

Symmetry 2021, 13(5), 788; https://doi.org/10.3390/sym13050788 - 2 May 2021

Cited by 19 | Viewed by 3213

Abstract

In this paper the mathematical and physical correlation between fundamental thermophysical properties of materials, with their structure, for nanofluid thermal performance in spray cooling applications is presented. The present work aims at clarifying the nanofluid characteristics, especially the geometry of their nanoparticles, leading [...] Read more.

In this paper the mathematical and physical correlation between fundamental thermophysical properties of materials, with their structure, for nanofluid thermal performance in spray cooling applications is presented. The present work aims at clarifying the nanofluid characteristics, especially the geometry of their nanoparticles, leading to heat transfer enhancement at low particle concentration. The base fluid considered is distilled water with the surfactant cetyltrimethylammonium bromide (CTAB). Alumina and silver are used as nanoparticles. A systematic analysis addresses the effect of nanoparticles concentration and shape in spray hydrodynamics and heat transfer. Spray dynamics is mainly characterized using phase Doppler interferometry. Then, an extensive processing procedure is performed to thermal and spacetime symmetry images obtained with a high-speed thermographic camera to analyze the spray impact on a heated, smooth stainless-steel foil. There is some effect on the nanoparticles’ shape, which is nevertheless minor when compared to the effect of the nanoparticles concentration and to the change in the fluid properties caused by the addition of the surfactant. Hence, increasing the nanoparticles concentration results in lower surface temperatures and high removed heat fluxes. In terms of the effect of the resulting thermophysical properties, increasing the nanofluids concentration resulted in the increase in the thermal conductivity and dynamic viscosity of the nanofluids, which in turn led to a decrease in the heat transfer coefficients. On the other hand, nanofluids specific heat capacity is increased which correlates positively with the spray cooling capacity. The analysis of the parameters that determine the structure, evolution, physics and both spatial and temporal symmetry of the spray is interesting and fundamental to shed light to the fact that only knowledge based in experimental data can guarantee a correct setting of the model numbers. Full article

(This article belongs to the Special Issue Materials Science: Synthesis, Structure, Properties)

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15 pages, 3042 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Cooperation/Competition between Halogen Bonds and Hydrogen Bonds in Complexes of 2,6-Diaminopyridines and X-CY₃ (X = Cl, Br; Y = H, F)

by Barbara Bankiewicz and Marcin Palusiak

Symmetry 2021, 13(5), 766; https://doi.org/10.3390/sym13050766 - 28 Apr 2021

Cited by 6 | Viewed by 3260

Abstract

The DFT calculations have been performed on a series of two-element complexes formed by substituted 2,6-diaminopyridine (R−PDA) and pyridine (R−Pyr) with X−CY₃ molecules (where X = Cl, Br and Y = H, F). The primary aim of this study was to examine [...] Read more.

The DFT calculations have been performed on a series of two-element complexes formed by substituted 2,6-diaminopyridine (R−PDA) and pyridine (R−Pyr) with X−CY₃ molecules (where X = Cl, Br and Y = H, F). The primary aim of this study was to examine the intermolecular hydrogen and halogen bonds in the condition of their mutual coexistence. Symmetry/antisymmetry of the interrelation between three individual interactions is addressed. It appears that halogen bonds play the main role in the stabilization of the structures of the selected systems. However, the occurrence of one or two hydrogen bonds was associated with the favourable geometry of the complexes. Moreover, the impact of different substituent groups attached in the para position to the aromatic ring of the 2,6-diaminopyridine and pyridine on the character of the intermolecular hydrogen and halogen bonds was examined. The results indicate that the presence of electron-donating substituents strengthens the bonds. In turn, the presence of electron-withdrawing substituents reduces the strength of halogen bonds. Additionally, when hydrogen and halogen bonds lose their leading role in the complex formation, the nonspecific electrostatic interactions between dipole moments take their place. Analysis was based on geometric, energetic, and topological parameters of the studied systems. Full article

(This article belongs to the Special Issue Exploring Inter- and Intramolecular Interactions as Building Blocks of Larger Systems)

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14 pages, 261 KiB

Open AccessEditor’s ChoiceArticle

General Fractional Integrals and Derivatives of Arbitrary Order

by Yuri Luchko

Symmetry 2021, 13(5), 755; https://doi.org/10.3390/sym13050755 - 27 Apr 2021

Cited by 85 | Viewed by 4644

Abstract

In this paper, we introduce the general fractional integrals and derivatives of arbitrary order and study some of their basic properties and particular cases. First, a suitable generalization of the Sonine condition is presented, and some important classes of the kernels that satisfy [...] Read more.

In this paper, we introduce the general fractional integrals and derivatives of arbitrary order and study some of their basic properties and particular cases. First, a suitable generalization of the Sonine condition is presented, and some important classes of the kernels that satisfy this condition are introduced. Whereas the kernels of the general fractional derivatives of arbitrary order possess integrable singularities at the point zero, the kernels of the general fractional integrals can—depending on their order—be both singular and continuous at the origin. For the general fractional integrals and derivatives of arbitrary order with the kernels introduced in this paper, two fundamental theorems of fractional calculus are formulated and proved. Full article

(This article belongs to the Special Issue Applied Mathematics and Fractional Calculus)

21 pages, 3817 KiB

Open AccessEditor’s ChoiceArticle

Fingerprint Classification Based on Deep Learning Approaches: Experimental Findings and Comparisons

by Carmelo Militello, Leonardo Rundo, Salvatore Vitabile and Vincenzo Conti

Symmetry 2021, 13(5), 750; https://doi.org/10.3390/sym13050750 - 26 Apr 2021

Cited by 50 | Viewed by 11129

Abstract

Biometric classification plays a key role in fingerprint characterization, especially in the identification process. In fact, reducing the number of comparisons in biometric recognition systems is essential when dealing with large-scale databases. The classification of fingerprints aims to achieve this target by splitting [...] Read more.

Biometric classification plays a key role in fingerprint characterization, especially in the identification process. In fact, reducing the number of comparisons in biometric recognition systems is essential when dealing with large-scale databases. The classification of fingerprints aims to achieve this target by splitting fingerprints into different categories. The general approach of fingerprint classification requires pre-processing techniques that are usually computationally expensive. Deep Learning is emerging as the leading field that has been successfully applied to many areas, such as image processing. This work shows the performance of pre-trained Convolutional Neural Networks (CNNs), tested on two fingerprint databases—namely, PolyU and NIST—and comparisons to other results presented in the literature in order to establish the type of classification that allows us to obtain the best performance in terms of precision and model efficiency, among approaches under examination, namely: AlexNet, GoogLeNet, and ResNet. We present the first study that extensively compares the most used CNN architectures by classifying the fingerprints into four, five, and eight classes. From the experimental results, the best performance was obtained in the classification of the PolyU database by all the tested CNN architectures due to the higher quality of its samples. To confirm the reliability of our study and the results obtained, a statistical analysis based on the McNemar test was performed. Full article

(This article belongs to the Section Computer)

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11 pages, 317 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Radiative and Meson Decays of Y(4230) in Flavor SU(3)

by Luciano Maiani, Antonio Davide Polosa and Verónica Riquer

Symmetry 2021, 13(5), 751; https://doi.org/10.3390/sym13050751 - 26 Apr 2021

Cited by 4 | Viewed by 2491

Abstract

The charmonium-like exotic states

Y (4230)

and the less known

Y (4320)

, produced in

e^{+} e^{-}

collisions, are sources of positive parity exotic hadrons in association with photons or pseudoscalar mesons. We analyze the radiative and [...] Read more.

The charmonium-like exotic states

Y (4230)

and the less known

Y (4320)

, produced in

e^{+} e^{-}

collisions, are sources of positive parity exotic hadrons in association with photons or pseudoscalar mesons. We analyze the radiative and pion decay channels in the compact tetraquark scheme, with a method that proves to work equally well in the most studied

D^{*} \to γ / π + D

decays. The decay of the vector Y into a pion and a

Z_{c}

state requires a flip of charge conjugation and isospin that is described appropriately in the formalism used. Rates are found to depend on the fifth power of pion momentum, which would make the final states

π Z_{c} (4020)

strongly suppressed with respect to

π Z_{c} (3900)

. The agreement with BES III data would be improved considering the

π Z_{c} (4020)

events to be fed by the tail of the

Y (4320)

resonance under the

Y (4230)

. These results should renovate the interest in further clarifying the emerging experimental picture in this mass region. Full article

(This article belongs to the Special Issue Search for New Phenomena in Heavy-Quark Physics)

15 pages, 772 KiB

Open AccessEditor’s ChoiceArticle

Algebra of Symmetry Operators for Klein-Gordon-Fock Equation

by Valeriy V. Obukhov

Symmetry 2021, 13(4), 727; https://doi.org/10.3390/sym13040727 - 20 Apr 2021

Cited by 26 | Viewed by 2762

Abstract

All external electromagnetic fields in which the Klein-Gordon-Fock equation admits the first-order symmetry operators are found, provided that in the space-time

V_{4}

a group of motion

G_{3}

acts simply transitively on a non-null subspace of transitivity

V_{3}

. It is [...] Read more.

All external electromagnetic fields in which the Klein-Gordon-Fock equation admits the first-order symmetry operators are found, provided that in the space-time

V_{4}

a group of motion

G_{3}

acts simply transitively on a non-null subspace of transitivity

V_{3}

. It is shown that in the case of a Riemannian space

V_{n}

, in which the group

G_{r}

acts simply transitively, the algebra of symmetry operators of the n-dimensional Klein-Gordon-Fock equation in an external admissible electromagnetic field coincides with the algebra of operators of the group

G_{r}

. Full article

(This article belongs to the Special Issue Symmetry: Feature Papers 2022)

10 pages, 269 KiB

Open AccessEditor’s ChoiceArticle

Improved Bounds on Lorentz Symmetry Violation from High-Energy Astrophysical Sources

by Brett Altschul

Symmetry 2021, 13(4), 688; https://doi.org/10.3390/sym13040688 - 15 Apr 2021

Cited by 5 | Viewed by 2359

Abstract

Observations of the synchrotron and inverse Compton emissions from ultrarelativistic electrons in astrophysical sources can reveal a great deal about the energy–momentum relations of those electrons. They can thus be used to place bounds on the possibility of Lorentz violation in the electron [...] Read more.

Observations of the synchrotron and inverse Compton emissions from ultrarelativistic electrons in astrophysical sources can reveal a great deal about the energy–momentum relations of those electrons. They can thus be used to place bounds on the possibility of Lorentz violation in the electron sector. Recent

γ

-ray telescope data allow the Lorentz-violating electron

c^{ν μ}

parameters to be constrained extremely well, so that all bounds are at the level of

7 \times 10^{- 16}

or better. Full article

(This article belongs to the Special Issue Space-Time Symmetries and Violations of Lorentz Invariance)

18 pages, 340 KiB

Open AccessEditor’s ChoiceArticle

Gravity with Explicit Diffeomorphism Breaking

by Robert Bluhm and Yumu Yang

Symmetry 2021, 13(4), 660; https://doi.org/10.3390/sym13040660 - 12 Apr 2021

Cited by 15 | Viewed by 2668

Abstract

Modified theories of gravity that explicitly break diffeomorphism invariance have been used for over a decade to explore open issues related to quantum gravity, dark energy, and dark matter. At the same time, the Standard-Model Extension (SME) has been widely used as a [...] Read more.

Modified theories of gravity that explicitly break diffeomorphism invariance have been used for over a decade to explore open issues related to quantum gravity, dark energy, and dark matter. At the same time, the Standard-Model Extension (SME) has been widely used as a phenomenological framework in investigations of spacetime symmetry breaking. Until recently, it was thought that the SME was suitable only for theories with spontaneous spacetime symmetry breaking due to consistency conditions stemming from the Bianchi identities. However, it has recently been shown that, particularly with matter couplings included, the consistency conditions can also be satisfied in theories with explicit breaking. An overview of how this is achieved is presented, and two examples are examined. The first is massive gravity, which includes a nondynamical background tensor. The second is a model based on a low-energy limit of Hořava gravity, where spacetime has a physically preferred foliation. In both cases, bounds on matter–gravity interactions that explicitly break diffeomorphisms are obtained using the SME. Full article

(This article belongs to the Special Issue Space-Time Symmetries and Violations of Lorentz Invariance)

13 pages, 2140 KiB

Open AccessEditor’s ChoiceArticle

The Fluctuating Asymmetry of the Butterfly Wing Pattern Does Not Change along an Industrial Pollution Gradient

by Vitali Zverev and Mikhail V. Kozlov

Symmetry 2021, 13(4), 626; https://doi.org/10.3390/sym13040626 - 9 Apr 2021

Cited by 9 | Viewed by 3631

Abstract

The rapid and selective responses to changes in habitat structure and climate have made butterflies valuable environmental indicators. In this study, we asked whether the decline in butterfly populations near the copper-nickel smelter in Monchegorsk in northwestern Russia is accompanied by phenotypic stress [...] Read more.

The rapid and selective responses to changes in habitat structure and climate have made butterflies valuable environmental indicators. In this study, we asked whether the decline in butterfly populations near the copper-nickel smelter in Monchegorsk in northwestern Russia is accompanied by phenotypic stress responses to toxic pollutants, expressed as a decrease in body size and an increase in fluctuating asymmetry. We measured the concentrations of nickel and copper, forewing length, and fluctuating asymmetry in two elements of wing patterns in Boloria euphrosyne, Plebejus idas, and Agriades optilete collected 1–65 km from Monchegorsk. Body metal concentrations increased toward the smelter, confirming the local origin of the collected butterflies. The wings of butterflies from the most polluted sites were 5–8% shorter than those in unpolluted localities, suggesting adverse effects of pollution on butterfly fitness due to larval feeding on contaminated plants. However, fluctuating asymmetry averaged across two hindwing spots did not change systematically with pollution, thereby questioning the use of fluctuating asymmetry as an indicator of habitat quality in butterfly conservation projects. Full article

(This article belongs to the Special Issue Fluctuating Asymmetry and Environmental Stress)

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13 pages, 516 KiB

Open AccessEditor’s ChoiceArticle

Scalable Codes for Precision Calculations of Properties of Complex Atomic Systems

by Charles Cheung, Marianna Safronova and Sergey Porsev

Symmetry 2021, 13(4), 621; https://doi.org/10.3390/sym13040621 - 8 Apr 2021

Cited by 21 | Viewed by 3406

Abstract

High precision atomic data are indispensable for studies of fundamental symmetries, tests of fundamental physics postulates, developments of atomic clocks, ultracold atom experiments, astrophysics, plasma science, and many other fields of research. We have developed a new parallel atomic structure code package that [...] Read more.

High precision atomic data are indispensable for studies of fundamental symmetries, tests of fundamental physics postulates, developments of atomic clocks, ultracold atom experiments, astrophysics, plasma science, and many other fields of research. We have developed a new parallel atomic structure code package that enables computations that were not previously possible due to system complexity. This code package also allows much quicker computations to be run with higher accuracy for simple systems. We explored different methods of load-balancing matrix element calculations for many-electron systems, which are very difficult due to the intrinsic nature of the computational methods used to calculate them. Furthermore, dynamic memory allocation and MPI parallelization have been implemented to optimize and accelerate the computations. We have achieved near-perfect linear scalability and efficiency with the number of processors used for calculation, paving the way towards the future where most open-shell systems will finally be able to be treated with good accuracy. We present several examples illustrating new capabilities of the newly developed codes, specifically correlating up to all 60 electrons in the highly charged Ir

^{17 +}

ion and predicting certain properties of Fe

^{16 +}

. Full article

(This article belongs to the Special Issue Development of New Methods in Atomic and Molecular Theory)

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10 pages, 290 KiB

Open AccessEditor’s ChoiceArticle

Regularity Criteria for the 3D Magneto-Hydrodynamics Equations in Anisotropic Lorentz Spaces

by Maria Alessandra Ragusa and Fan Wu

Symmetry 2021, 13(4), 625; https://doi.org/10.3390/sym13040625 - 8 Apr 2021

Cited by 5 | Viewed by 2376

Abstract

In this paper, we investigate the regularity of weak solutions to the 3D incompressible MHD equations. We provide a regularity criterion for weak solutions involving any two groups functions

(\partial_{1} u_{1}, \partial_{1} b_{1})

, [...] Read more.

In this paper, we investigate the regularity of weak solutions to the 3D incompressible MHD equations. We provide a regularity criterion for weak solutions involving any two groups functions

(\partial_{1} u_{1}, \partial_{1} b_{1})

,

(\partial_{2} u_{2}, \partial_{2} b_{2})

and

(\partial_{3} u_{3}, \partial_{3} b_{3})

in anisotropic Lorentz space. Full article

(This article belongs to the Special Issue Applied Mathematics and Fractional Calculus)

32 pages, 1571 KiB

Open AccessEditor’s ChoiceArticle

Two-Stage Hybrid Data Classifiers Based on SVM and kNN Algorithms

by Liliya A. Demidova

Symmetry 2021, 13(4), 615; https://doi.org/10.3390/sym13040615 - 7 Apr 2021

Cited by 34 | Viewed by 5922

Abstract

The paper considers a solution to the problem of developing two-stage hybrid SVM-kNN classifiers with the aim to increase the data classification quality by refining the classification decisions near the class boundary defined by the SVM classifier. In the first stage, the SVM [...] Read more.

The paper considers a solution to the problem of developing two-stage hybrid SVM-kNN classifiers with the aim to increase the data classification quality by refining the classification decisions near the class boundary defined by the SVM classifier. In the first stage, the SVM classifier with default parameters values is developed. Here, the training dataset is designed on the basis of the initial dataset. When developing the SVM classifier, a binary SVM algorithm or one-class SVM algorithm is used. Based on the results of the training of the SVM classifier, two variants of the training dataset are formed for the development of the kNN classifier: a variant that uses all objects from the original training dataset located inside the strip dividing the classes, and a variant that uses only those objects from the initial training dataset that are located inside the area containing all misclassified objects from the class dividing strip. In the second stage, the kNN classifier is developed using the new training dataset above-mentioned. The values of the parameters of the kNN classifier are determined during training to maximize the data classification quality. The data classification quality using the two-stage hybrid SVM-kNN classifier was assessed using various indicators on the test dataset. In the case of the improvement of the quality of classification near the class boundary defined by the SVM classifier using the kNN classifier, the two-stage hybrid SVM-kNN classifier is recommended for further use. The experimental results approve the feasibility of using two-stage hybrid SVM-kNN classifiers in the data classification problem. The experimental results obtained with the application of various datasets confirm the feasibility of using two-stage hybrid SVM-kNN classifiers in the data classification problem. Full article

(This article belongs to the Special Issue 2020 Big Data and Artificial Intelligence Conference)

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14 pages, 1076 KiB

Open AccessEditor’s ChoiceArticle

Kinematic Analysis of Lower Limb Joint Asymmetry During Gait in People with Multiple Sclerosis

by Massimiliano Pau, Bruno Leban, Michela Deidda, Federica Putzolu, Micaela Porta, Giancarlo Coghe and Eleonora Cocco

Symmetry 2021, 13(4), 598; https://doi.org/10.3390/sym13040598 - 3 Apr 2021

Cited by 16 | Viewed by 5094

Abstract

The majority of people with Multiple Sclerosis (pwMS), report lower limb motor dysfunctions, which may relevantly affect postural control, gait and a wide range of activities of daily living. While it is quite common to observe a different impact of the disease on [...] Read more.

The majority of people with Multiple Sclerosis (pwMS), report lower limb motor dysfunctions, which may relevantly affect postural control, gait and a wide range of activities of daily living. While it is quite common to observe a different impact of the disease on the two limbs (i.e., one of them is more affected), less clear are the effects of such asymmetry on gait performance. The present retrospective cross-sectional study aimed to characterize the magnitude of interlimb asymmetry in pwMS, particularly as regards the joint kinematics, using parameters derived from angle-angle diagrams. To this end, we analyzed gait patterns of 101 pwMS (55 women, 46 men, mean age 46.3, average Expanded Disability Status Scale (EDSS) score 3.5, range 1–6.5) and 81 unaffected individuals age- and sex-matched who underwent 3D computerized gait analysis carried out using an eight-camera motion capture system. Spatio-temporal parameters and kinematics in the sagittal plane at hip, knee and ankle joints were considered for the analysis. The angular trends of left and right sides were processed to build synchronized angle–angle diagrams (cyclograms) for each joint, and symmetry was assessed by computing several geometrical features such as area, orientation and Trend Symmetry. Based on cyclogram orientation and Trend Symmetry, the results show that pwMS exhibit significantly greater asymmetry in all three joints with respect to unaffected individuals. In particular, orientation values were as follows: 5.1 of pwMS vs. 1.6 of unaffected individuals at hip joint, 7.0 vs. 1.5 at knee and 6.4 vs. 3.0 at ankle (p < 0.001 in all cases), while for Trend Symmetry we obtained at hip 1.7 of pwMS vs. 0.3 of unaffected individuals, 4.2 vs. 0.5 at knee and 8.5 vs. 1.5 at ankle (p < 0.001 in all cases). Moreover, the same parameters were sensitive enough to discriminate individuals of different disability levels. With few exceptions, all the calculated symmetry parameters were found significantly correlated with the main spatio-temporal parameters of gait and the EDSS score. In particular, large correlations were detected between Trend Symmetry and gait speed (with rho values in the range of −0.58 to −0.63 depending on the considered joint, p < 0.001) and between Trend Symmetry and EDSS score (rho = 0.62 to 0.69, p < 0.001). Such results suggest not only that MS is associated with significantly marked interlimb asymmetry during gait but also that such asymmetry worsens as the disease progresses and that it has a relevant impact on gait performances. Full article

(This article belongs to the Special Issue Neuroscience, Neurophysiology and Symmetry)

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12 pages, 2949 KiB

Open AccessEditor’s ChoiceArticle

Electrochemical Comparison on New (Z)-5-(Azulen-1-Ylmethylene)-2-Thioxo-Thiazolidin-4-Ones

by Eleonora-Mihaela Ungureanu, Mariana Popescu (Apostoiu), Georgiana-Luiza Tatu (Arnold), Liviu Birzan, Raluca Isopescu, Gabriela Stanciu and George-Octavian Buica

Symmetry 2021, 13(4), 588; https://doi.org/10.3390/sym13040588 - 2 Apr 2021

Cited by 9 | Viewed by 4296

Abstract

Three (Z)-5-(azulen-1-ylmethylene)-2-thioxo-thiazolidin-4-ones are electrochemically characterized by cyclic voltammetry, differential pulse voltammetry, and rotating disk electrode voltammetry. The electrochemical investigations revealed that the redox potential is influenced by the number and position of the alkyl groups, and the possible oxidation mechanism is proposed. These [...] Read more.

Three (Z)-5-(azulen-1-ylmethylene)-2-thioxo-thiazolidin-4-ones are electrochemically characterized by cyclic voltammetry, differential pulse voltammetry, and rotating disk electrode voltammetry. The electrochemical investigations revealed that the redox potential is influenced by the number and position of the alkyl groups, and the possible oxidation mechanism is proposed. These compounds, after their immobilization on glassy carbon electrodes during oxidative electropolymerization, were examined as complexing ligands for heavy metal ions from aqueous solutions through adsorptive stripping voltammetry. Full article

(This article belongs to the Special Issue Electrochemical Behavior of the Nonbenzenoid Aromatic Hydrocarbon Azulene and Its Derivatives)

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18 pages, 3666 KiB

Open AccessEditor’s ChoiceArticle

High-Capacity Embedding Method Based on Double-Layer Octagon-Shaped Shell Matrix

by Chin-Feng Lee, Jau-Ji Shen, Somya Agrawal and Yen-Hsi Li

Symmetry 2021, 13(4), 583; https://doi.org/10.3390/sym13040583 - 1 Apr 2021

Cited by 9 | Viewed by 2836

Abstract

Data hiding is a technique that embeds a secret message into a cover medium and transfers the hidden information in the secret message to the recipient. In the past, several data hiding methods based on magic matrix have used various geometrical shapes to [...] Read more.

Data hiding is a technique that embeds a secret message into a cover medium and transfers the hidden information in the secret message to the recipient. In the past, several data hiding methods based on magic matrix have used various geometrical shapes to transmit secret data. The embedding capacity achieved in these methods was often limited due to simple geometrical layouts. This paper proposes a data hiding scheme based on a double-layer octagon-shaped shell matrix. Compared to previous octagon-shaped data hiding methods, the proposed method embeds a total of 7 bits in each pixel pair, reaching an embedding capacity of 3.5 bits per pixel (bpp). Experimental results show that the proposed scheme has a higher embedding capacity compared to other irreversible data hiding schemes. Using the proposed method, it is possible to maintain the Peak Signal to Noise Ratio (PSNR) within an acceptable range with the embedding time less than 2 s. Full article

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15 pages, 1262 KiB

Open AccessEditor’s ChoiceArticle

Thermodynamics of Barrow Holographic Dark Energy with Specific Cut-Off

by Gargee Chakraborty, Surajit Chattopadhyay, Ertan Güdekli and Irina Radinschi

Symmetry 2021, 13(4), 562; https://doi.org/10.3390/sym13040562 - 29 Mar 2021

Cited by 46 | Viewed by 5125

Abstract

Motivated by the work of Saridakis (Phys. Rev. D102, 123525 (2020)), the present study reports the cosmological consequences of Barrow holographic dark energy (HDE) and its thermodynamics. The literature demonstrates that dark energy (DE) may result from electroweak symmetry breaking [...] Read more.

Motivated by the work of Saridakis (Phys. Rev. D102, 123525 (2020)), the present study reports the cosmological consequences of Barrow holographic dark energy (HDE) and its thermodynamics. The literature demonstrates that dark energy (DE) may result from electroweak symmetry breaking that triggers a phase transition from early inflation to late-time acceleration. In the present study, we incorporated viscosity in the Barrow HDE. A reconstruction scheme is presented for the parameters associated with Barrow holographic dark energy under the purview of viscous cosmology. The equation of state (EoS) parameter is reconstructed in this scenario and quintessence behaviour is observed. Considering Barrow HDE as a specific case of Nojiri–Odintsov (NO) HDE, we have observed quintom behaviour of the EoS parameter and for some values of n the EoS has been observed to be very close to

- 1

for the current universe. The generalised second law of thermodynamics has come out to be valid in all the scenarios under consideration. Physical viability of considering Barrow HDE as a specific case of NO HDE is demonstrated in this study. Finally, it has been observed that the model under consideration is very close to

Λ

CDM and cannot go beyond it. Full article

(This article belongs to the Special Issue Symmetry: Feature Papers 2022)

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18 pages, 5063 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Structure-Property Relationship in Selected Naphtho- and Anthra-Quinone Derivatives on the Basis of Density Functional Theory and Car–Parrinello Molecular Dynamics

by Beata Kizior, Jarosław J. Panek, Bartłomiej M. Szyja and Aneta Jezierska

Symmetry 2021, 13(4), 564; https://doi.org/10.3390/sym13040564 - 29 Mar 2021

Cited by 5 | Viewed by 3232

Abstract

Intra- and inter-molecular interactions were studied in 2,3-dichloro-5,8-dihydroxy-1,4-naphthoquinone and 1,4-dihydroxy-anthraquinone to shed more light on the molecular assembly phenomena. The electronic ground and excited states features of the compounds were investigated to find structure-property dependencies. The theoretical study was carried out on the [...] Read more.

Intra- and inter-molecular interactions were studied in 2,3-dichloro-5,8-dihydroxy-1,4-naphthoquinone and 1,4-dihydroxy-anthraquinone to shed more light on the molecular assembly phenomena. The electronic ground and excited states features of the compounds were investigated to find structure-property dependencies. The theoretical study was carried out on the basis of Density Functional Theory (DFT), its Time-Dependent (TD-DFT) extension, and using Car–Parrinello Molecular Dynamics (CPMD). In order to show how the environmental effects modulate the physico-chemical properties, the simulations were performed in vacuo, with the solvent reaction field (Polarizable Continuum Model (PCM) and water as a solvent) and crystalline phase. The intramolecular hydrogen bonds and the bridged proton dynamics were analyzed in detail. The aromatic rings and electronic structure changes were estimated using the Harmonic Oscillator Model of Aromaticity (HOMA) and Atoms in Molecules (AIM) theory. The Symmetry-Adapted Perturbation Theory (SAPT) was employed for interaction energy decomposition in the studied dimers and trimers. It was found that the presence of a polar solvent decreased the energy barrier for the bridged proton transfer. However, it did not significantly affect the aromaticity and electronic structure. The SAPT results showed that the mutual polarization of the monomers in the dimer was weak and that the dispersion was responsible for most of the intermolecular attraction. The intermolecular hydrogen bonds seem to be much weaker than the intramolecular bridges. The TD-DFT results confirmed that the electronic excitations do not play any significant role in the intramolecular proton transfer. The CPMD results indicated that the protons are very labile in the hydrogen bridges. Short proton transfer and proton-sharing events were observed, and a correlation between them in the twin bridges was noticed, especially for the first investigated compound. Full article

(This article belongs to the Special Issue Exploring Inter- and Intramolecular Interactions as Building Blocks of Larger Systems)

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21 pages, 4208 KiB

Open AccessEditor’s ChoiceReview

Azulene Moiety as Electron Reservoir in Positively Charged Systems; A Short Survey

by Alexandru C. Razus

Symmetry 2021, 13(4), 526; https://doi.org/10.3390/sym13040526 - 24 Mar 2021

Cited by 17 | Viewed by 4994

Abstract

The non-alternant aromatic azulene, an isomer of alternant naphthalene, differs from the latter in peculiar properties. The large polarization of the π-electron system over the seven and five rings gives to azulene electrophile property a pronounced tendency to donate electrons to an acceptor, [...] Read more.

The non-alternant aromatic azulene, an isomer of alternant naphthalene, differs from the latter in peculiar properties. The large polarization of the π-electron system over the seven and five rings gives to azulene electrophile property a pronounced tendency to donate electrons to an acceptor, substituted at azulene 1 position. This paper presents cases in which azulene transfers electrons to a suitable acceptor as methylium ions, positive charged heteroaromatics and examples of neutral molecules that can accept electrons. The proposed product synthesis was outlined and the expected electron transfer was highlighted by analyzing the NMR, UV-Vis spectra and the pK_R⁺ values. Full article

(This article belongs to the Special Issue Electrochemical Behavior of the Nonbenzenoid Aromatic Hydrocarbon Azulene and Its Derivatives)

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