Editor’s Choice Articles

Editor’s Choice articles are based on recommendations by the scientific editors of MDPI journals from around the world. Editors select a small number of articles recently published in the journal that they believe will be particularly interesting to readers, or important in the respective research area. The aim is to provide a snapshot of some of the most exciting work published in the various research areas of the journal.

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Review
Impact of Molecular Symmetry/Asymmetry on Insulin-Sensitizing Treatments for Type 2 Diabetes
Symmetry 2022, 14(6), 1240; https://doi.org/10.3390/sym14061240 - 15 Jun 2022
Cited by 3 | Viewed by 2062
Abstract
Although the advantages and disadvantages of asymmetrical thiazolidinediones as insulin-sensitizers have been well-studied, the relevance of symmetry and asymmetry for thiazolidinediones and biguanides has scarcely been explored. Regarding symmetrical molecules, only one thiazolidinedione and no biguanides have been evaluated and proposed as an [...] Read more.
Although the advantages and disadvantages of asymmetrical thiazolidinediones as insulin-sensitizers have been well-studied, the relevance of symmetry and asymmetry for thiazolidinediones and biguanides has scarcely been explored. Regarding symmetrical molecules, only one thiazolidinedione and no biguanides have been evaluated and proposed as an antihyperglycemic agent for treating type 2 diabetes. Since molecular structure defines physicochemical, pharmacological, and toxicological properties, it is important to gain greater insights into poorly investigated patterns. For example, compounds with intrinsic antioxidant properties commonly have low toxicity. Additionally, the molecular symmetry and asymmetry of ligands are each associated with affinity for certain types of receptors. An advantageous response obtained in one therapeutic application may imply a poor or even adverse effect in another. Within the context of general patterns, each compound must be assessed individually. The current review aimed to summarize the available evidence for the advantages and disadvantages of utilizing symmetrical and asymmetrical thiazolidinediones and biguanides as insulin sensitizers in patients with type 2 diabetes. Other applications of these same compounds are also examined as well as the various uses of additional symmetrical molecules. More research is needed to exploit the potential of symmetrical molecules as insulin sensitizers. Full article
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Review
Recent Advances in Surrogate Modeling Methods for Uncertainty Quantification and Propagation
Symmetry 2022, 14(6), 1219; https://doi.org/10.3390/sym14061219 - 13 Jun 2022
Cited by 11 | Viewed by 2113
Abstract
Surrogate-model-assisted uncertainty treatment practices have been the subject of increasing attention and investigations in recent decades for many symmetrical engineering systems. This paper delivers a review of surrogate modeling methods in both uncertainty quantification and propagation scenarios. To this end, the mathematical models [...] Read more.
Surrogate-model-assisted uncertainty treatment practices have been the subject of increasing attention and investigations in recent decades for many symmetrical engineering systems. This paper delivers a review of surrogate modeling methods in both uncertainty quantification and propagation scenarios. To this end, the mathematical models for uncertainty quantification are firstly reviewed, and theories and advances on probabilistic, non-probabilistic and hybrid ones are discussed. Subsequently, numerical methods for uncertainty propagation are broadly reviewed under different computational strategies. Thirdly, several popular single surrogate models and novel hybrid techniques are reviewed, together with some general criteria for accuracy evaluation. In addition, sample generation techniques to improve the accuracy of surrogate models are discussed for both static sampling and its adaptive version. Finally, closing remarks are provided and future prospects are suggested. Full article
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Article
Crystal Structure of Chiral Drug Prenalterol and Its Precursor Prone to Spontaneous Resolution
Symmetry 2022, 14(6), 1150; https://doi.org/10.3390/sym14061150 - 02 Jun 2022
Cited by 1 | Viewed by 1227
Abstract
Due to the chiral uniformity of proteins and carbohydrates, the basic building blocks of living matter, the mirror symmetry characteristics of drugs are of exceptional importance for medicinal chemistry. In this work, we present a new synthesis of the mono-enantiomeric chiral drug prenalterol [...] Read more.
Due to the chiral uniformity of proteins and carbohydrates, the basic building blocks of living matter, the mirror symmetry characteristics of drugs are of exceptional importance for medicinal chemistry. In this work, we present a new synthesis of the mono-enantiomeric chiral drug prenalterol 1 based on the symmetry-breaking phenomenon, namely, the spontaneous resolution of 4-hydroxyphenyl glycerol ether 2. The single crystal X-ray diffraction method was used to investigate both rac- and (S)-1 as well as (R)-2. A feature of the main crystal-forming supramolecular motif (SMM) for diol 2 is the participation of three different molecules representing different types of hydroxyl groups in the formation of its repeating unit. The type of prenalterol SMM, as in the case of the related drugs propranolol 3 and pindolol 4, appears to be a chirality driven property, and is dictated by the enantiomeric composition of the crystals. In single-enantiomeric forms, infinite one-dimensional chains are realized, organized around helical axes, while in racemates, zero-dimensional cycles are realized, organized around inversion symmetry elements. The results obtained again demonstrate the influence of the chiral polarization of a substance not only on the general (selection of a space group), but also on particular characteristics of matter crystal organization, namely selection of a specific SMM. Full article
(This article belongs to the Special Issue Symmetry and Asymmetry in Medicinal Chemistry)
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Article
MCD and Induced CD of a Tetraphenoxyperylene-Based Dye in Chiral Solvents: An Experimental and Computational Study
Symmetry 2022, 14(6), 1108; https://doi.org/10.3390/sym14061108 - 28 May 2022
Cited by 1 | Viewed by 1427
Abstract
The magnetic circular dichroism (MCD) spectrum of N,N′-bis(2,6-diisopropylphenyl)-1,6,7,12-tetraphenoxyperylene-3,4:9,10-tetracarboxydiimide, also known as Lumogen Red 300 or ROT-300, has been recorded both in achiral and chiral solvents. The induced CD spectra in chiral solvents have, similarly, been recorded. A discussion of the spectroscopic response, both [...] Read more.
The magnetic circular dichroism (MCD) spectrum of N,N′-bis(2,6-diisopropylphenyl)-1,6,7,12-tetraphenoxyperylene-3,4:9,10-tetracarboxydiimide, also known as Lumogen Red 300 or ROT-300, has been recorded both in achiral and chiral solvents. The induced CD spectra in chiral solvents have, similarly, been recorded. A discussion of the spectroscopic response, both in CD and in MCD experiments, is presented in this paper. Both types of spectra have been predicted most satisfactorily by DFT calculations; the CD spectra were obtained by assuming the prevalence of one “enantiomeric” conformer and the same set of conformers could also be used for MCD, since “enantiomeric” structures present identically in MCD spectra. Full article
(This article belongs to the Special Issue Asymmetric Molecules and Chirality Recognition)
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Article
Heat Flow Characteristics of Ferrofluid in Magnetic Field Patterns for Electric Vehicle Power Electronics Cooling
Symmetry 2022, 14(5), 1063; https://doi.org/10.3390/sym14051063 - 22 May 2022
Cited by 5 | Viewed by 1437
Abstract
The ferrofluid is a kind of nanofluid that has magnetization properties in addition to excellent thermophysical properties, which has resulted in an effective performance trend in cooling applications. In the present study, experiments are conducted to investigate the heat flow characteristics of ferrofluid [...] Read more.
The ferrofluid is a kind of nanofluid that has magnetization properties in addition to excellent thermophysical properties, which has resulted in an effective performance trend in cooling applications. In the present study, experiments are conducted to investigate the heat flow characteristics of ferrofluid based on thermomagnetic convection under the influence of different magnetic field patterns. The temperature and heat dissipation characteristics are compared for ferrofluid under the influence of no-magnet, I, L, and T magnetic field patterns. The results reveal that the heat gets accumulated within ferrofluid near the heating part in the case of no magnet, whereas the heat flows through ferrofluid under the influence of different magnetic field patterns without any external force. Owing to the thermomagnetic convection characteristic of ferrofluid, the heat dissipates from the heating block and reaches the cooling block by following the path of the I magnetic field pattern. However, in the case of the L and T magnetic field patterns, the thermomagnetic convection characteristic of ferrofluid drives the heat from the heating block to the endpoint location of the pattern instead of the cooling block. The asymmetrical heat dissipation in the case of the L magnetic field pattern and the symmetrical heat dissipation in the case of the T magnetic field pattern are observed following the magnetization path of ferrofluid in the respective cases. The results confirm that the direction of heat flow could be controlled based on the type of magnetic field pattern and its path by utilizing the thermomagnetic behavior of ferrofluid. The proposed lab-scale experimental set-up and results database could be utilized to design an automatic energy transport system for the cooling of power conversion devices in electric vehicles. Full article
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Article
Design of a New Dimension-Changeable Hyperchaotic Model Based on Discrete Memristor
Symmetry 2022, 14(5), 1019; https://doi.org/10.3390/sym14051019 - 17 May 2022
Cited by 7 | Viewed by 1232
Abstract
The application of a memristor in chaotic circuits is increasingly becoming a popular research topic. The influence of a memristor on the dynamics of chaotic systems is worthy of further exploration. In this paper, a multi-dimensional closed-loop coupling model based on a Logistic [...] Read more.
The application of a memristor in chaotic circuits is increasingly becoming a popular research topic. The influence of a memristor on the dynamics of chaotic systems is worthy of further exploration. In this paper, a multi-dimensional closed-loop coupling model based on a Logistic map and Sine map (CLS) is proposed. The new chaotic model is constructed by cascade operation in which the output of the Logistic map is used as the input of the Sine map. Additionally, the one-dimensional map is extended to any dimension through the coupling modulation. In order to further increase the complexity and stability of CLS, the discrete memristor model is introduced to construct a discrete memristor-based coupling model with a Logistic map and a Sine map (MCLS). By analyzing the Lyapunov exponents, bifurcation diagram, complexity, and the 0–1 test result, the comparison result between CLS and MCLS is obtained. The dynamics performance analysis shows that the Lyapunov exponents and bifurcation diagrams present symmetrical distribution with variations of some parameters. The MCLS has parameters whose values can be set in a wider range and can generate more complex and more stable chaotic sequences. It proves that the proposed discrete memristor-based closed-loop coupling model can produce any higher dimension hyperchaotic system and the discrete memristor model can effectively improve the performance of discrete chaotic map and make this hyperchaotic system more stable. Full article
(This article belongs to the Special Issue Discrete and Continuous Memristive Nonlinear Systems and Symmetry)
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Review
Recent Progress of Squaraine-Based Fluorescent Materials and Their Biomedical Applications
Symmetry 2022, 14(5), 966; https://doi.org/10.3390/sym14050966 - 09 May 2022
Cited by 5 | Viewed by 1771
Abstract
Squaraines (SQs) are unusual cyanine dyes with a unique resonance-stabilized zwitterionic structure. These dyes have attracted significant attention in the fields of organic electronics and organic photonics, due to their facile synthesis, intense and narrow visible and near-infrared absorption/emission, high photostability, low biotoxicity, [...] Read more.
Squaraines (SQs) are unusual cyanine dyes with a unique resonance-stabilized zwitterionic structure. These dyes have attracted significant attention in the fields of organic electronics and organic photonics, due to their facile synthesis, intense and narrow visible and near-infrared absorption/emission, high photostability, low biotoxicity, etc. In this review, we summarize the recent progress of SQ-based fluorescent materials and their biomedical applications. After a brief introduction to SQs, general synthetic routes and design principles of SQ-based fluorescent materials, as well as their aggregation-induced luminescence behaviors, are discussed. Subsequently, their biomedical applications for cell imaging and as fluorescent sensors and therapeutic agents are introduced. Finally, a summary and perspective are given for promoting the development of SQs-based fluorescent materials. Full article
(This article belongs to the Special Issue Symmetry in Functional Organic Dyes)
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Review
Structural Brain Asymmetries for Language: A Comparative Approach across Primates
Symmetry 2022, 14(5), 876; https://doi.org/10.3390/sym14050876 - 25 Apr 2022
Cited by 2 | Viewed by 3074
Abstract
Humans are the only species that can speak. Nonhuman primates, however, share some ‘domain-general’ cognitive properties that are essential to language processes. Whether these shared cognitive properties between humans and nonhuman primates are the results of a continuous evolution [homologies] or of a [...] Read more.
Humans are the only species that can speak. Nonhuman primates, however, share some ‘domain-general’ cognitive properties that are essential to language processes. Whether these shared cognitive properties between humans and nonhuman primates are the results of a continuous evolution [homologies] or of a convergent evolution [analogies] remain difficult to demonstrate. However, comparing their respective underlying structure—the brain—to determinate their similarity or their divergence across species is critical to help increase the probability of either of the two hypotheses, respectively. Key areas associated with language processes are the Planum Temporale, Broca’s Area, the Arcuate Fasciculus, Cingulate Sulcus, The Insula, Superior Temporal Sulcus, the Inferior Parietal lobe, and the Central Sulcus. These structures share a fundamental feature: They are functionally and structurally specialised to one hemisphere. Interestingly, several nonhuman primate species, such as chimpanzees and baboons, show human-like structural brain asymmetries for areas homologous to key language regions. The question then arises: for what function did these asymmetries arise in non-linguistic primates, if not for language per se? In an attempt to provide some answers, we review the literature on the lateralisation of the gestural communication system, which may represent the missing behavioural link to brain asymmetries for language area’s homologues in our common ancestor. Full article
(This article belongs to the Special Issue Cognitive and Neurophysiological Models of Brain Asymmetry)
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Review
Cerebral Polymorphisms for Lateralisation: Modelling the Genetic and Phenotypic Architectures of Multiple Functional Modules
Symmetry 2022, 14(4), 814; https://doi.org/10.3390/sym14040814 - 14 Apr 2022
Cited by 7 | Viewed by 3135
Abstract
Recent fMRI and fTCD studies have found that functional modules for aspects of language, praxis, and visuo-spatial functioning, while typically left, left and right hemispheric respectively, frequently show atypical lateralisation. Studies with increasing numbers of modules and participants are finding increasing numbers of [...] Read more.
Recent fMRI and fTCD studies have found that functional modules for aspects of language, praxis, and visuo-spatial functioning, while typically left, left and right hemispheric respectively, frequently show atypical lateralisation. Studies with increasing numbers of modules and participants are finding increasing numbers of module combinations, which here are termed cerebral polymorphisms—qualitatively different lateral organisations of cognitive functions. Polymorphisms are more frequent in left-handers than right-handers, but it is far from the case that right-handers all show the lateral organisation of modules described in introductory textbooks. In computational terms, this paper extends the original, monogenic McManus DC (dextral-chance) model of handedness and language dominance to multiple functional modules, and to a polygenic DC model compatible with the molecular genetics of handedness, and with the biology of visceral asymmetries found in primary ciliary dyskinesia. Distributions of cerebral polymorphisms are calculated for families and twins, and consequences and implications of cerebral polymorphisms are explored for explaining aphasia due to cerebral damage, as well as possible talents and deficits arising from atypical inter- and intra-hemispheric modular connections. The model is set in the broader context of the testing of psychological theories, of issues of laterality measurement, of mutation-selection balance, and the evolution of brain and visceral asymmetries. Full article
(This article belongs to the Special Issue Cognitive and Neurophysiological Models of Brain Asymmetry)
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Review
Overview: State-of-the-Art in the Energy Harvesting Based on Piezoelectric Devices for Last Decade
Symmetry 2022, 14(4), 765; https://doi.org/10.3390/sym14040765 - 07 Apr 2022
Cited by 9 | Viewed by 2560
Abstract
Technologies of energy harvesting have been developed intensively since the beginning of the twenty-first century, presenting themselves as alternatives to traditional energy sources (for instance, batteries) for small-dimensional and low-power electronics. Batteries have numerous shortcomings connected, for example, with restricted service life and [...] Read more.
Technologies of energy harvesting have been developed intensively since the beginning of the twenty-first century, presenting themselves as alternatives to traditional energy sources (for instance, batteries) for small-dimensional and low-power electronics. Batteries have numerous shortcomings connected, for example, with restricted service life and the necessity of periodic recharging/replacement that create significant problems for portative and remote devices and for power equipment. Environmental energy covers solar, thermal, and oscillation energy. By this, the vibration energy exists continuously around us due to the operation of numerous artificial structures and mechanisms. Different materials (including piezoelectrics) and conversion mechanisms can transform oscillation energy into electrical energy for use in many devices of energy harvesting. Piezoelectric transducers possessing electric mechanical coupling and demonstrating a high density of power in comparison with electromagnetic and electrostatic sensors are broadly applied for the generation of energy from different oscillation energy sources. For the last decade, novel piezoelectric materials, transformation mechanisms, electrical circuits, and experimental and theoretical approaches with results of computer simulation have been developed for improving different piezoelectric devices of energy harvesting. This overview presents results, obtained in the area of piezoelectric energy harvesting for the last decade, including a wide spectrum of experimental, analytical, and computer simulation investigations. Full article
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Article
Asymmetry in Muscle Strength, Dynamic Balance, and Range of Motion in Adult Symptomatic Hip Dysplasia
Symmetry 2022, 14(4), 748; https://doi.org/10.3390/sym14040748 - 05 Apr 2022
Cited by 4 | Viewed by 1602
Abstract
Hip dysplasia (HD) is a typical developmental abnormality of the hip joint, and discomfort is often found in adulthood. This study compared patients with symptomatic HD in muscle strength, dynamic balance, and range of motion (ROM) with healthy individuals. Patients included those who [...] Read more.
Hip dysplasia (HD) is a typical developmental abnormality of the hip joint, and discomfort is often found in adulthood. This study compared patients with symptomatic HD in muscle strength, dynamic balance, and range of motion (ROM) with healthy individuals. Patients included those who complained of unilateral pain although the lateral center edge angle (LCEA) exhibited bilateral abnormality. Participants (n = 95; men: 46, women: 49) were divided into symptomatic and asymptomatic sides, and a healthy group without a history of hip joint disease (n = 70; men: 30, women: 40) was compared. Hip flexion, extension, abduction, and adduction were performed at an angular velocity of 30°/s using an isokinetic strength test device. The Y-balance test was conducted to measure dynamic balance, and ROM was measured using an electronic goniometer to evaluate flexion, extension, adduction, abduction, and internal and external rotations. In addition, the pain visual analog scale (VAS) and hip and groin outcome scale (HAGOS), a subjective evaluation of the hip joint, were evaluated. ROM (flexion, abduction, internal rotation, and external rotation) was significantly decreased in the HD symptomatic sides of men and women compared to those of the healthy group and the asymptomatic side, and the dynamic balance, flexion, and abduction muscle strength were also lower on the symptomatic sides. Although the LCEA of the HD asymptomatic side was lower than that of the healthy group, there were no significant differences in VAS, flexion, extension, abduction ROM, and extension strength compared to those of healthy individuals. In conclusion, patients with HD were mostly bilateral, and on the symptomatic side, there was a decrease in ROM, dynamic balance, and muscle strength; however, on the asymptomatic side, the function was relatively close to normal. Full article
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Review
Spectrum of Primordial Gravitational Waves in Modified Gravities: A Short Overview
Symmetry 2022, 14(4), 729; https://doi.org/10.3390/sym14040729 - 03 Apr 2022
Cited by 30 | Viewed by 1719
Abstract
In this work, we shall exhaustively study the effects of modified gravity on the energy spectrum of the primordial gravitational waves background. S. Weinberg has also produced significant works related to the primordial gravitational waves, with the most important one being the effects [...] Read more.
In this work, we shall exhaustively study the effects of modified gravity on the energy spectrum of the primordial gravitational waves background. S. Weinberg has also produced significant works related to the primordial gravitational waves, with the most important one being the effects of neutrinos on primordial gravitational waves. With this short review, our main aim is to gather all the necessary information for studying the effects of modified gravity on primordial gravitational waves in a concrete and quantitative way and in a single paper. After reviewing all the necessary techniques for extracting the general relativistic energy spectrum, and how to obtain, in a WKB way, the modified gravity damping or amplifying factor, we concentrate on specific forms of modified gravity of interest. The most important parameter involved for the calculation of the effects of modified gravity on the energy spectrum is the parameter aM, which we calculate for the cases of f(R,ϕ) gravity, Chern–Simons-corrected f(R,ϕ) gravity, Einstein–Gauss–Bonnet-corrected f(R,ϕ) gravity, and higher derivative extended Einstein–Gauss–Bonnet-corrected f(R,ϕ) gravity. The exact form of aM is presented explicitly for the first time in the literature. With regard to Einstein–Gauss–Bonnet-corrected f(R,ϕ) gravity, and higher derivative extended Einstein–Gauss–Bonnet-corrected f(R,ϕ) gravity theories, we focus on the case in which the gravitational wave propagating speed is equal to that of light in a vacuum. We provide expressions for aM expressed in terms of the cosmic time and in terms of the redshift, which can be used directly for the numerical calculation of the effect of modified gravity on the primordial gravitational wave energy spectrum. Full article
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Article
Exploration of Temperature Distribution through a Longitudinal Rectangular Fin with Linear and Exponential Temperature-Dependent Thermal Conductivity Using DTM-Pade Approximant
Symmetry 2022, 14(4), 690; https://doi.org/10.3390/sym14040690 - 26 Mar 2022
Cited by 14 | Viewed by 2224
Abstract
The present study elaborates on the thermal distribution and efficiency of a longitudinal rectangular fin with exponentially varying temperature-dependent thermal conductivity and heat transfer coefficient concerning internal heat generation. Also, the thermal distribution of a fin is comparatively studied for both exponentially varying [...] Read more.
The present study elaborates on the thermal distribution and efficiency of a longitudinal rectangular fin with exponentially varying temperature-dependent thermal conductivity and heat transfer coefficient concerning internal heat generation. Also, the thermal distribution of a fin is comparatively studied for both exponentially varying temperature-dependent thermal conductivity and linearly varying temperature-dependent thermal conductivity. Further, the thermal distribution of a longitudinal fin is examined by using ANSYS software with different fin materials. Many physical mechanisms can be explained by ordinary differential equations (ODEs) with symmetrical behavior, the significance of which varies based on the perspective. The governing equation of the considered problem is reduced to a non-linear ODE with the assistance of dimensionless terms. The resultant equation is solved analytically using the DTM-Pade approximant and is also solved numerically using Runge-Kutta Fehlberg’s fourth-fifth (RKF-45) order method. The features of dimensionless parameters influencing the fin efficiency and temperature profile are discussed through graphical representation for exponentially and linearly varying temperature-dependent thermal conductivity. This study ensures that the temperature field enhances for the higher magnitude of thermal conductivity parameter, whereas it diminishes for diverse values of the thermo-geometric parameter. Also, greater values of heat generation and heat transfer parameters enhance the temperature profile. Highlight: Thermal distribution through a rectangular profiled straight fin is examined. Linear and non-linear thermal properties are considered. The combined impact of conduction, convection, and internal heat generation is taken for modeling the energy equation of the fin. Thermal simulation is performed for Aluminum Alloy 6061 (AA 6061) and Cast Iron using ANSYS. Full article
(This article belongs to the Special Issue Solid Mechanics and Mechanical Mechanics)
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Review
How Symmetry Influences the Dissociation of Protonated Cyclic Peptides
Symmetry 2022, 14(4), 679; https://doi.org/10.3390/sym14040679 - 25 Mar 2022
Cited by 2 | Viewed by 1587
Abstract
Protonated cyclic dipeptides undergo collision-induced dissociation, and this reaction mechanism strongly depends on the symmetry and the nature of the residues. We review the main dissociation mechanism for a series of cyclic dipeptides, obtained through chemical dynamics simulations. The systems range from the [...] Read more.
Protonated cyclic dipeptides undergo collision-induced dissociation, and this reaction mechanism strongly depends on the symmetry and the nature of the residues. We review the main dissociation mechanism for a series of cyclic dipeptides, obtained through chemical dynamics simulations. The systems range from the symmetrical cyclo-(glycyl-glycyl), with two possible symmetrical protonation sites located on the peptide ring, to cyclo-(tyrosyl-prolyl), where the symmetry of protonation sites on the peptide ring is broken by the dissimilar nature of the different residues. Finally, cyclo-(phenylalanyl-histidyl) shows a completely asymmetric situation, with the proton located on one of the dipeptide side chains, which explains the peculiar fragmentation mechanism induced by shuttling the proton, whose efficiency is strongly dependent on the relative chirality of the residues. Full article
(This article belongs to the Special Issue Asymmetric Molecules and Chirality Recognition)
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Article
From Memristor-Modeled Jerk System to the Nonlinear Systems with Memristor
Symmetry 2022, 14(4), 659; https://doi.org/10.3390/sym14040659 - 24 Mar 2022
Cited by 7 | Viewed by 1576
Abstract
Based on the proposed generalized memristor, a new jerk system is proposed. The complex dynamics of the system are investigated by means of bifurcation diagrams, Lyapunov exponents, and MSampEn, and rich dynamics are observed. Moreover, the circuits of the generalized memristor and the [...] Read more.
Based on the proposed generalized memristor, a new jerk system is proposed. The complex dynamics of the system are investigated by means of bifurcation diagrams, Lyapunov exponents, and MSampEn, and rich dynamics are observed. Moreover, the circuits of the generalized memristor and the jerk system are physically implemented in the hardware level. The experimental results show that the memristor circuit can generate “8”-shaped pinched hysteresis loops, and the observed attractors match well with the numerical simulations results. In this paper, we summarize nonlinear systems with memristors in the references. It indicates that there are two symmetry methods to find a memristor model in nonlinear systems. However, some of them cannot be realized using the memristor devices, although a memristor model can be found. For example, the famous Lorenz system contains a memristor function, but it cannot be realized using the memristor device. The principles regarding whether nonlinear systems with a memristor function can be realized using a memristor device are discussed. Full article
(This article belongs to the Special Issue Discrete and Continuous Memristive Nonlinear Systems and Symmetry)
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Article
Evolution of Microstructure, Texture and Corrosion Properties of Additively Manufactured AlSi10Mg Alloy Subjected to Equal Channel Angular Pressing (ECAP)
Symmetry 2022, 14(4), 674; https://doi.org/10.3390/sym14040674 - 24 Mar 2022
Cited by 6 | Viewed by 1544
Abstract
In the selective laser melting process (SLM), the region irradiated by the laser beam is melted and quickly solidified, forming solidification lines (laser scan tracks) with symmetrical shapes. Because of the unique (rapid) crystallization conditions, the subgrain structures, typically observed inside these solidification [...] Read more.
In the selective laser melting process (SLM), the region irradiated by the laser beam is melted and quickly solidified, forming solidification lines (laser scan tracks) with symmetrical shapes. Because of the unique (rapid) crystallization conditions, the subgrain structures, typically observed inside these solidification lines, could also have variable geometric symmetrical patterns, e.g., cellular, pentagonal, or hexagonal cellular. The existence of such distinctive microstructures in SLM-made alloys has a significant impact on their superior mechanical and corrosion properties. Thus, any modification of this symmetrical microstructure (due to post-processing) can degrade or improve the properties of SLM-fabricated alloys. This study presents the experimental results on the effects of heat treatment and ECAP on microstructure modification and corrosion behavior of SLM-fabricated AlSi10Mg alloy. Light microscopy, scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), and X-ray diffraction (XRD) were used for microstructural analysis. The corrosion properties of the given samples were determined using open-circuit potential (OCP), potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) techniques. EBSD observations showed that the imposed strain resulted in an obvious reduction in grain size to ~1.42 µm and ~0.24 µm after the first and second ECAP passes, respectively. Electrochemical tests revealed that the corrosion resistance of the ECAP-processed AlSi10Mg alloy improved significantly, which was confirmed by a nobler Ecorr and lower Icorr values, and higher polarization resistance. The final results indicated that the strain-induced crystalline defects provided more nucleation sites for the formation of a denser and thicker oxide film, thus enhancing the corrosion resistance of the AlSi10Mg alloy. Full article
(This article belongs to the Special Issue Advances in Materials Science with Symmetry/Asymmetry)
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Article
Symmetry Constraints on Spin Order Transfer in Parahydrogen-Induced Polarization (PHIP)
Symmetry 2022, 14(3), 530; https://doi.org/10.3390/sym14030530 - 04 Mar 2022
Cited by 2 | Viewed by 2025
Abstract
It is well known that the association of parahydrogen (pH2) with an unsaturated molecule or a transient metalorganic complex can enhance the intensity of NMR signals; the effect is known as parahydrogen-induced polarization (PHIP). During recent decades, numerous methods were proposed [...] Read more.
It is well known that the association of parahydrogen (pH2) with an unsaturated molecule or a transient metalorganic complex can enhance the intensity of NMR signals; the effect is known as parahydrogen-induced polarization (PHIP). During recent decades, numerous methods were proposed for converting pH2-derived nuclear spin order to the observable magnetization of protons or other nuclei of interest, usually 13C or 15N. Here, we analyze the constraints imposed by the topological symmetry of the spin systems on the amplitude of transferred polarization. We find that in asymmetric systems, heteronuclei can be polarized to 100%. However, the amplitude drops to 75% in A2BX systems and further to 50% in A3B2X systems. The latter case is of primary importance for biological applications of PHIP using sidearm hydrogenation (PHIP-SAH). If the polarization is transferred to the same type of nuclei, i.e., 1H, symmetry constraints impose significant boundaries on the spin-order distribution. For AB, A2B, A3B, A2B2, AA’(AA’) systems, the maximum average polarization for each spin is 100%, 50%, 33.3%, 25%, and 0, respectively, (where A and B (or A’) came from pH2). Remarkably, if the polarization of all spins in a molecule is summed up, the total polarization grows asymptotically with ~1.27N and can exceed 2 in the absence of symmetry constraints (where N is the number of spins). We also discuss the effect of dipole–dipole-induced pH2 spin-order distribution in heterogeneous catalysis or nematic liquid crystals. Practical examples from the literature illustrate our theoretical analysis. Full article
(This article belongs to the Special Issue Symmetry Principles in the Nuclear Magnetic Resonance)
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Article
Position-Aware Guided Hiding Data Scheme with Reversibility and Adaptivity for Dual Images
Symmetry 2022, 14(3), 509; https://doi.org/10.3390/sym14030509 - 02 Mar 2022
Cited by 4 | Viewed by 1019
Abstract
Reversible data hiding (RDH) in dual images is a technique that shares secret messages into two similar shadow images, while the secret messages and the cover image can be restored only when those two shadows are gathered simultaneously. In this paper, a novel [...] Read more.
Reversible data hiding (RDH) in dual images is a technique that shares secret messages into two similar shadow images, while the secret messages and the cover image can be restored only when those two shadows are gathered simultaneously. In this paper, a novel turtle shell-based RDH hiding scheme based on the symmetric property is presented in order to increase the embedding capacity and maintain good visual quality in dual images under the guidance of position-aware. First, we classify each pixel pair into one of four types according to their locations and then determine a sunflower area centered around it in order to construct the combination of positions and the embedding table. Using the embedding table, the secret messages are concealed into a cover image by generating two shadow images. At the decoder’s side, the complete restoration of the secret messages and the cover image can be accomplished by identifying the position relationship between the two stego-pixel pairs. The experimental results confirmed that the proposed position-aware guided RDH scheme is superior to some of the relevant works on the aspects of embedding capacity or image quality. In addition, the proposed scheme provides a secure communication that can effectively resist attacks on the pixel value difference histogram, relative entropy, and regular singular analysis. Full article
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Article
Neutron Stars with Baryon Number Violation, Probing Dark Sectors
Symmetry 2022, 14(3), 518; https://doi.org/10.3390/sym14030518 - 02 Mar 2022
Cited by 14 | Viewed by 3128
Abstract
The neutron lifetime anomaly has been used to motivate the introduction of new physics with hidden-sector particles coupled to baryon number, and on which neutron stars provide powerful constraints. Although the neutron lifetime anomaly may eventually prove to be of mundane origin, we [...] Read more.
The neutron lifetime anomaly has been used to motivate the introduction of new physics with hidden-sector particles coupled to baryon number, and on which neutron stars provide powerful constraints. Although the neutron lifetime anomaly may eventually prove to be of mundane origin, we use it as motivation for a broader review of the ways that baryon number violation, be it real or apparent, and dark sectors can intertwine and how neutron star observables, both present and future, can constrain them. Full article
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Article
Some Results in the Theory of a Cosserat Thermoelastic Body with Microtemperatures and Inner Structure
Symmetry 2022, 14(3), 511; https://doi.org/10.3390/sym14030511 - 02 Mar 2022
Cited by 3 | Viewed by 1624
Abstract
This study is concerned with the theory of Cosserat thermoelastic media, whose micro-particles possess microtemperatures. The mixed initial boundary value problem considered in this context is transformed in a temporally evolutionary equation on a Hilbert space. Using some results from the theory of [...] Read more.
This study is concerned with the theory of Cosserat thermoelastic media, whose micro-particles possess microtemperatures. The mixed initial boundary value problem considered in this context is transformed in a temporally evolutionary equation on a Hilbert space. Using some results from the theory of semigroups, the existence and uniqueness of solution is proved. In the same manner, it approached the continuous dependence of the solution upon initial data and loads. From what we have studied, neither on the internet nor in the databases, we have not found qualitative issues addressed regarding the mixed problem in the context of the theory of thermoelasticity of Cosserat environments, in which the contribution of inner structure and microtemperatures are taken into account. Full article
(This article belongs to the Special Issue Symmetry in Applied Continuous Mechanics 2022)
Article
Improved Search for Neutron to Mirror-Neutron Oscillations in the Presence of Mirror Magnetic Fields with a Dedicated Apparatus at the PSI UCN Source
Symmetry 2022, 14(3), 503; https://doi.org/10.3390/sym14030503 - 01 Mar 2022
Cited by 14 | Viewed by 2055
Abstract
While the international nEDM collaboration at the Paul Scherrer Institut (PSI) took data in 2017 that covered a considerable fraction of the parameter space of claimed potential signals of hypothetical neutron (n) to mirror-neutron (n) transitions, it could [...] Read more.
While the international nEDM collaboration at the Paul Scherrer Institut (PSI) took data in 2017 that covered a considerable fraction of the parameter space of claimed potential signals of hypothetical neutron (n) to mirror-neutron (n) transitions, it could not test all claimed signal regions at various mirror magnetic fields. Therefore, a new study of nn oscillations using stored ultracold neutrons (UCNs) is underway at PSI, considerably expanding the reach in parameter space of mirror magnetic fields (B) and oscillation time constants (τnn). The new apparatus is designed to test for the anomalous loss of stored ultracold neutrons as a function of an applied magnetic field. The experiment is distinguished from its predecessors by its very large storage vessel (1.47 m3), enhancing its statistical sensitivity. In a test experiment in 2020 we have demonstrated the capabilities of our apparatus. However, the full analysis of our recent data is still pending. Based on already demonstrated performance, we will reach sensitivity to oscillation times τnn/cos(β) well above a hundred seconds, with β being the angle between B and the applied magnetic field B. The scan of B will allow the finding or the comprehensive exclusion of potential signals reported in the analysis of previous experiments and suggested to be consistent with neutron to mirror-neutron oscillations. Full article
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Article
A Search for Cosmic Ray Bursts at 0.1 PeV with a Small Air Shower Array
Symmetry 2022, 14(3), 501; https://doi.org/10.3390/sym14030501 - 01 Mar 2022
Cited by 5 | Viewed by 2069
Abstract
The Cosmic Ray Extremely Distributed Observatory (CREDO) pursues a global research strategy dedicated to the search for correlated cosmic rays, so-called Cosmic Ray Ensembles (CRE). Its general approach to CRE detection does not involve any a priori considerations, and its search strategy encompasses [...] Read more.
The Cosmic Ray Extremely Distributed Observatory (CREDO) pursues a global research strategy dedicated to the search for correlated cosmic rays, so-called Cosmic Ray Ensembles (CRE). Its general approach to CRE detection does not involve any a priori considerations, and its search strategy encompasses both spatial and temporal correlations, on different scales. Here we search for time clustering of the cosmic ray events collected with a small sea-level extensive air shower array at the University of Adelaide. The array consists of seven one-square-metre scintillators enclosing an area of 10 m × 19 m. It has a threshold energy ~0.1 PeV, and records cosmic ray showers at a rate of ~6 mHz. We have examined event arrival times over a period of over 2.5 years in two equipment configurations (without and with GPS timing), recording ~300 k events and ~100 k events. We determined the event time spacing distributions between individual events and the distributions of time periods which contained specific numbers of multiple events. We find that the overall time distributions are as expected for random events. The distribution which was chosen a priori for particular study was for time periods covering five events (four spacings). Overall, these distributions fit closely with expectation, but there are two outliers of short burst periods in data for each configuration. One of these outliers contains eight events within 48 s. The physical characteristics of the array will be discussed together with the analysis procedure, including a comparison between the observed time distributions and expectation based on randomly arriving events. Full article
(This article belongs to the Special Issue Symmetry in Cosmic Ray Detections)
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Article
A Search for Neutron to Mirror Neutron Oscillation Using Neutron Electric Dipole Moment Measurements
Symmetry 2022, 14(3), 487; https://doi.org/10.3390/sym14030487 - 28 Feb 2022
Cited by 7 | Viewed by 1758
Abstract
Baryon number violation is a key ingredient of baryogenesis. It has been hypothesized that there could also be a parity-conjugated copy of the standard model particles, called mirror particles. The existence of such a mirror universe has specific testable implications, especially in the [...] Read more.
Baryon number violation is a key ingredient of baryogenesis. It has been hypothesized that there could also be a parity-conjugated copy of the standard model particles, called mirror particles. The existence of such a mirror universe has specific testable implications, especially in the domain of neutral particle oscillation, viz. the baryon number violating neutron to mirror-neutron (nn) oscillation. Consequently, there were many experiments that have searched for nn oscillation, and imposed constraints upon the parameters that describe it. Recently, further analysis on some of these results have identified anomalies which could point to the detection of nn oscillation. All the previous efforts searched for nn oscillation by comparing the relative number of ultracold neutrons that survive after a period of storage for one or both of the two cases: (i) comparison of zero applied magnetic field to a non-zero applied magnetic field, and (ii) comparison where the orientation of the applied magnetic field was reversed. However, nn oscillations also lead to variations in the precession frequency of polarized neutrons upon flipping the direction of the applied magnetic field. Precession frequencies are measured, very precisely, by experiments searching for the electric dipole moment. For the first time, we used the data from the latest search for the neutron electric dipole moment to constrain nn oscillation. After compensating for the systematic effects that affect the ratio of precession frequencies of ultracold neutrons and cohabiting 199Hg-atoms, chief among which was due to their motion in non-uniform magnetic field, we constrained any further perturbations due to nn oscillation. We thereby provide a lower limit on the nn oscillation time constant of τnn/|cos(β)|>5.7s,0.36T<B<1.01T (95% C.L.), where β is the angle between the applied magnetic field and the ambient mirror magnetic field. This constraint is the best available in the range of 0.36T<B<0.40T. Full article
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Systematic Review
Genetic Factors That Affect Asymmetric Mandibular Growth—A Systematic Review
Symmetry 2022, 14(3), 490; https://doi.org/10.3390/sym14030490 - 28 Feb 2022
Cited by 3 | Viewed by 1705
Abstract
Facial asymmetry is a feature that occurs to a greater or lesser extent in the general population. As its severity is usually slight, facial asymmetry may not be noticeable to the patient. However, there are cases when severe facial asymmetry not only affects [...] Read more.
Facial asymmetry is a feature that occurs to a greater or lesser extent in the general population. As its severity is usually slight, facial asymmetry may not be noticeable to the patient. However, there are cases when severe facial asymmetry not only affects the facial aesthetics by distorting facial proportions, but also contributes to problems related to the function of the stomatognathic system. The nodal signalling pathway appears to be of particular importance in the process of mandibular asymmetry, as it affects not only structures formed from the first pharyngeal arch, but also other organs, such as the heart and lungs. Following the evaluation of the available literature, the inheritance of mandibular asymmetry is a very complex and multifactorial process, and the genes whose altered expression appears to be a more important potential aetiological factor for asymmetry include PITX2, ACTN3, ENPP1 and ESR1. This systematic review attempts to systematise the available literature concerning the impact of signalling pathway disruption, including the disruption of the nodal signalling pathway, on the development of mandibular asymmetry. Full article
(This article belongs to the Special Issue Dentofacial Asymmetry — Challenges and Perspectives)
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Article
Infrasonic, Acoustic and Seismic Waves Produced by the Axion Quark Nuggets
Symmetry 2022, 14(3), 459; https://doi.org/10.3390/sym14030459 - 24 Feb 2022
Cited by 8 | Viewed by 1370
Abstract
We advocate the idea that Axion Quark Nuggets (AQN) hitting the Earth can be detected by analysing the infrasound, acoustic, and seismic waves which always accompany their passage in the atmosphere and underground. Our estimates for the infrasonic frequency ν5 Hz [...] Read more.
We advocate the idea that Axion Quark Nuggets (AQN) hitting the Earth can be detected by analysing the infrasound, acoustic, and seismic waves which always accompany their passage in the atmosphere and underground. Our estimates for the infrasonic frequency ν5 Hz and overpressure δp0.3 Pa for relatively large size dark matter (DM) nuggets suggest that sensitivity of presently available instruments is already sufficient to detect very intense (but very rare) events today with existing technology. A study of much more frequent but less intense events requires a new type of instrument. We propose a detection strategy for a systematic study to search for such relatively weak and frequent events by using distributed acoustic sensing and briefly mention other possible detection methods. Full article
(This article belongs to the Special Issue The Dark Universe: The Harbinger of a Major Discovery)
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Review
Chirality in Organic and Mineral Systems: A Review of Reactivity and Alteration Processes Relevant to Prebiotic Chemistry and Life Detection Missions
Symmetry 2022, 14(3), 460; https://doi.org/10.3390/sym14030460 - 24 Feb 2022
Cited by 5 | Viewed by 5538
Abstract
Chirality is a central feature in the evolution of biological systems, but the reason for biology’s strong preference for specific chiralities of amino acids, sugars, and other molecules remains a controversial and unanswered question in origins of life research. Biological polymers tend toward [...] Read more.
Chirality is a central feature in the evolution of biological systems, but the reason for biology’s strong preference for specific chiralities of amino acids, sugars, and other molecules remains a controversial and unanswered question in origins of life research. Biological polymers tend toward homochiral systems, which favor the incorporation of a single enantiomer (molecules with a specific chiral configuration) over the other. There have been numerous investigations into the processes that preferentially enrich one enantiomer to understand the evolution of an early, racemic, prebiotic organic world. Chirality can also be a property of minerals; their interaction with chiral organics is important for assessing how post-depositional alteration processes could affect the stereochemical configuration of simple and complex organic molecules. In this paper, we review the properties of organic compounds and minerals as well as the physical, chemical, and geological processes that affect organic and mineral chirality during the preservation and detection of organic compounds. We provide perspectives and discussions on the reactions and analytical techniques that can be performed in the laboratory, and comment on the state of knowledge of flight-capable technologies in current and future planetary missions, with a focus on organics analysis and life detection. Full article
(This article belongs to the Special Issue Chirality, Prebiotic Chemistry, and the Origins of Life)
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Review
Lamellar Tetragonal Symmetry of Amphiphilic Thermotropic Ionic Liquid Crystals in the Framework of Other Closely Related Highly Ordered Structures
Symmetry 2022, 14(2), 394; https://doi.org/10.3390/sym14020394 - 16 Feb 2022
Cited by 1 | Viewed by 1789
Abstract
An overview of the chemical compounds forming the rare smectic T phases is presented with references to the historical context. Thermodynamics (transition temperatures, enthalpies) along with the factors (stereochemical constraints, electrostatic interactions, aliphatic chain stacking, intermolecular forces) contributing to the adoption of tetragonal [...] Read more.
An overview of the chemical compounds forming the rare smectic T phases is presented with references to the historical context. Thermodynamics (transition temperatures, enthalpies) along with the factors (stereochemical constraints, electrostatic interactions, aliphatic chain stacking, intermolecular forces) contributing to the adoption of tetragonal scaffolds are also discussed. Characteristic optical microscopy textures and X-ray diffraction patterns are presented. In parallel, a comparison of the geometrical parameters such as distances between atoms, molecular areas, volumes, and lattice parameters with the closest two-dimensional and three-dimensional organizations, is performed. Full article
(This article belongs to the Collection Feature Papers in Chemistry)
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Article
Attaching Onto or Inserting Into an Intramolecular Hydrogen Bond: Exploring and Controlling a Chirality-Dependent Dilemma for Alcohols
Symmetry 2022, 14(2), 357; https://doi.org/10.3390/sym14020357 - 11 Feb 2022
Cited by 2 | Viewed by 1567
Abstract
Prereactive complexes in noncovalent organocatalysis are sensitive to the relative chirality of the binding partners and to hydrogen bond isomerism. Both effects are present when a transiently chiral alcohol docks on a chiral α-hydroxy ester, turning such 1:1 complexes into elementary, non-reactive [...] Read more.
Prereactive complexes in noncovalent organocatalysis are sensitive to the relative chirality of the binding partners and to hydrogen bond isomerism. Both effects are present when a transiently chiral alcohol docks on a chiral α-hydroxy ester, turning such 1:1 complexes into elementary, non-reactive model systems for chirality induction in the gas phase. With the help of linear infrared and Raman spectroscopy in supersonic jet expansions, conformational preferences are investigated for benzyl alcohol in combination with methyl lactate, also exploring p-chlorination of the alcohol and the achiral homolog methyl glycolate to identify potential London dispersion and chirality effects on the energy sequence. Three of the four combinations prefer barrierless complexation via the hydroxy group of the ester (association). In contrast, the lightest complex predominantly shows insertion into the intramolecular hydrogen bond, such as the analogous lactate and glycolate complexes of methanol. The experimental findings are rationalized with computations, and a uniform helicality induction in the alcohol by the lactate is predicted, independent of insertion into or association with the internal lactate hydrogen bond. p-chlorination of benzyl alcohol has a stabilizing effect on association because the insertion motif prevents a close contact between the chlorine and the hydroxy ester. After simple anharmonicity and substitution corrections, the B3LYP-D3 approach offers a fairly systematic description of the known spectroscopic data on alcohol complexes with α-hydroxy esters. Full article
(This article belongs to the Special Issue Asymmetric Molecules and Chirality Recognition)
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Article
Bayesian Interval Estimation for the Two-Parameter Exponential Distribution Based on the Right Type II Censored Sample
Symmetry 2022, 14(2), 352; https://doi.org/10.3390/sym14020352 - 10 Feb 2022
Cited by 3 | Viewed by 1044
Abstract
The Bayesian interval estimation of the scale parameter for two-parameter exponential distribution is proposed based on the right type II censored sample. Under this type of censoring, two methods of Bayesian joint confidence region of the two parameters are also proposed. The simulation [...] Read more.
The Bayesian interval estimation of the scale parameter for two-parameter exponential distribution is proposed based on the right type II censored sample. Under this type of censoring, two methods of Bayesian joint confidence region of the two parameters are also proposed. The simulation results show that the Bayesian method has a higher coverage probability than the existing method, so the Bayesian method is recommended for use. This research is related to the topic of asymmetrical probability distributions and applications across disciplines. The predictive interval of the future observation based on the right type II censored sample is also provided. One biometrical example is given to illustrate the proposed methods for the Bayesian interval estimations and prediction interval. Full article
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Article
Interface Asymmetry Induced and Surface Pressure Controlled Valence Tautomerism in Monolayers of bis-Phthalocyaninates of Lanthanides
Symmetry 2022, 14(2), 340; https://doi.org/10.3390/sym14020340 - 07 Feb 2022
Cited by 2 | Viewed by 1186
Abstract
Supramolecular systems based on transition metal complexes capable of reversible redox isomerization due to intramolecular electron transfer are one of the most interesting objects from the viewpoint of molecular switches’ design. In the present work, a comparative analysis of valence transformation of lanthanide [...] Read more.
Supramolecular systems based on transition metal complexes capable of reversible redox isomerization due to intramolecular electron transfer are one of the most interesting objects from the viewpoint of molecular switches’ design. In the present work, a comparative analysis of valence transformation of lanthanide complexes (Sm, Er, Tm and Yb) with donor-substituted bis-phthalocyaninates occurring during the formation and compression–extension of Langmuir monolayers was carried out using data of UV–Vis–NIR spectroscopy. It is shown that the numerical values of the Q-band positions in the absorption spectra for the extended monolayers of the complexes under study depend linearly on the ionic radius of the metal center, if the metals have an oxidation state of +2. This makes it possible to draw a direct analogy between the behavior of the studied compounds and analogous europium and cerium complexes, for which direct evidence of the valence tautomerism in such planar systems was obtained earlier. This led to the conclusion that the intramolecular electron transfer from the phthalocyanine ligand to the central metal ion [Ln3+(R4Pc2−)(R4Pc•−)]0→[Ln2+(R4Pc•−)2]0 occurs when solutions of donor-substituted bis-phthalocyaninates of samarium, erbium, thulium, and ytterbium are deposited onto the water subphase, and the reverse redox-isomeric transition is observed in most cases when the monolayer is compressed to high surface pressures. The first of these switches is related to the asymmetry of the air/water interface, and the second one is controlled by the lateral compression–expansion of the monolayer. It has been demonstrated that when bis-phthalocyanine monolayers of lanthanides with variable valence are transferred to solid substrates, the valence state of the metal center, and consequently, the redox-isomeric state of the complex, do not change. This means that we are able to form films with a predetermined state of the complex. Note that the redox-isomeric state of complexes should affect the entire range of physicochemical properties of such films. Full article
(This article belongs to the Special Issue Spin Crossover and Valence Tautomerism: Symmetry Aspects)
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Review
Low-Energy Interactions of Mesons with Participation of the First Radially Excited States in U(3) × U(3) NJL Model
Symmetry 2022, 14(2), 308; https://doi.org/10.3390/sym14020308 - 02 Feb 2022
Cited by 7 | Viewed by 1244
Abstract
The U(3)×U(3) chiral symmetric NJL model describing pseudoscalar, vector, and axial-vector mesons in both the ground state and first radially excited states is shortly presented in this review. In this model, it is possible to [...] Read more.
The U(3)×U(3) chiral symmetric NJL model describing pseudoscalar, vector, and axial-vector mesons in both the ground state and first radially excited states is shortly presented in this review. In this model, it is possible to describe a large number of low-energy interactions of mesons, τ lepton decays into mesons, and processes of meson production in electron–positron annihilations in satisfactory agreement with the experiments. In describing a number of processes, it turned out to be necessary to take into account the interactions of mesons in the final state. Full article
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Article
The Cosmological Constant as Event Horizon
Symmetry 2022, 14(2), 300; https://doi.org/10.3390/sym14020300 - 01 Feb 2022
Cited by 11 | Viewed by 1715
Abstract
General Relativity allows for a cosmological constant (Λ) which has inspired models of cosmic Inflation and Dark Energy. We show instead that rΛ=3/Λ corresponds to an event horizon: a causal boundary term in the action. Our [...] Read more.
General Relativity allows for a cosmological constant (Λ) which has inspired models of cosmic Inflation and Dark Energy. We show instead that rΛ=3/Λ corresponds to an event horizon: a causal boundary term in the action. Our Universe is expanding inside its Schwarzschild radius rS=rΛ=2GM, which could have originated from a uniform free falling cloud of mass M that collapsed as a Black Hole (BH) 25 Gyrs ago. Such a BH Universe allows for large-scale structure formation without the need of Inflation or Dark Energy. Full article
(This article belongs to the Special Issue Fundamental Constants in Cosmology)
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Review
Functional Chirality: From Small Molecules to Supramolecular Assemblies
Symmetry 2022, 14(2), 292; https://doi.org/10.3390/sym14020292 - 01 Feb 2022
Cited by 8 | Viewed by 3838
Abstract
Many structures in nature look symmetric, but this is not completely accurate, because absolute symmetry is close to death. Chirality (handedness) is one form of living asymmetry. Chirality has been extensively investigated at different levels. Many rules were coined in attempts made for [...] Read more.
Many structures in nature look symmetric, but this is not completely accurate, because absolute symmetry is close to death. Chirality (handedness) is one form of living asymmetry. Chirality has been extensively investigated at different levels. Many rules were coined in attempts made for many decades to have control over the selection of handedness that seems to easily occur in nature. It is certain that if good control is realized on chirality, the roads will be ultimately open towards numerous developments in pharmaceutical, technological, and industrial applications. This tutorial review presents a report on chirality from single molecules to supramolecular assemblies. The realized functions are still in their infancy and have been scarcely converted into actual applications. This review provides an overview for starters in the chirality field of research on concepts, common methodologies, and outstanding accomplishments. It starts with an introductory section on the definitions and classifications of chirality at the different levels of molecular complexity, followed by highlighting the importance of chirality in biological systems and the different means of realizing chirality and its inversion in solid and solution-based systems at molecular and supramolecular levels. Chirality-relevant important findings and (bio-)technological applications are also reported accordingly. Full article
(This article belongs to the Special Issue Symmetry in Material Chemistry: Structures and Activities)
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Systematic Review
A Systematic Review of Non-Pharmacological Interventions to Improve Gait Asymmetries in Neurological Populations
Symmetry 2022, 14(2), 281; https://doi.org/10.3390/sym14020281 - 30 Jan 2022
Cited by 4 | Viewed by 1969
Abstract
Gait asymmetries are commonly observed in neurological populations and linked to decreased gait velocity, balance decrements, increased fall risk, and heightened metabolic cost. Interventions designed to improve gait asymmetries have varying methods and results. The purpose of this systematic review was to investigate [...] Read more.
Gait asymmetries are commonly observed in neurological populations and linked to decreased gait velocity, balance decrements, increased fall risk, and heightened metabolic cost. Interventions designed to improve gait asymmetries have varying methods and results. The purpose of this systematic review was to investigate non-pharmacological interventions to improve gait asymmetries in neurological populations. Keyword searches were conducted using PubMed, CINAHL, and Academic Search Complete. The search yielded 14 studies for inclusion. Gait was assessed using 3D motion capture systems (n = 7), pressure-sensitive mats (e.g., GAITRite; n = 5), and positional sensors (n = 2). The gait variables most commonly analyzed for asymmetry were step length (n = 11), stance time (n = 9), and swing time (n = 5). Interventions to improve gait asymmetries predominantly used gait training techniques via a split-belt treadmill (n = 6), followed by insoles/orthoses (n = 3). The literature suggests that a wide range of methods can be used to improve spatiotemporal asymmetries. However, future research should further examine kinematic and kinetic gait asymmetries. Additionally, researchers should explore the necessary frequency and duration of various intervention strategies to achieve the greatest improvement in gait asymmetries, and to determine the best symmetry equation for quantifying gait asymmetries. Full article
(This article belongs to the Special Issue Symmetry in Cognitive and Behavioural Neuroscience)
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Article
Improving the Statistical Qualities of Pseudo Random Number Generators
Symmetry 2022, 14(2), 269; https://doi.org/10.3390/sym14020269 - 29 Jan 2022
Cited by 3 | Viewed by 1628
Abstract
Pseudo random and true random sequence generators are important components in many scientific and technical fields, playing a fundamental role in the application of the Monte Carlo methods and stochastic simulation. Unfortunately, the quality of the sequences produced by these generators are not [...] Read more.
Pseudo random and true random sequence generators are important components in many scientific and technical fields, playing a fundamental role in the application of the Monte Carlo methods and stochastic simulation. Unfortunately, the quality of the sequences produced by these generators are not always ideal in terms of randomness for many applications. We present a new nonlinear filter design that improves the output sequences of common pseudo random generators in terms of statistical randomness. Taking inspiration from techniques employed in symmetric ciphers, it is based on four seed-dependent substitution boxes, an evolving internal state register, and the combination of different types of operations with the aim of diffusing nonrandom patterns in the input sequence. For statistical analysis we employ a custom initial battery of tests and well-regarded comprehensive packages such as TestU01 and PractRand. Analysis results show that our proposal achieves excellent randomness characteristics and can even transform nonrandom sources (such as a simple counter generator) into perfectly usable pseudo random sequences. Furthermore, performance is excellent while storage consumption is moderate, enabling its implementation in embedded or low power computational platforms. Full article
(This article belongs to the Section Computer Science and Symmetry/Asymmetry)
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Article
Transient Propagation of Spherical Waves in Porous Material: Application of Fractional Calculus
Symmetry 2022, 14(2), 233; https://doi.org/10.3390/sym14020233 - 25 Jan 2022
Cited by 5 | Viewed by 1781
Abstract
A fractional-order wave equation is established and solved for a space of three dimensions using spherical coordinates. An equivalent fluid model is used in which the acoustic wave propagates only in the fluid saturating the porous medium; this model is a special case [...] Read more.
A fractional-order wave equation is established and solved for a space of three dimensions using spherical coordinates. An equivalent fluid model is used in which the acoustic wave propagates only in the fluid saturating the porous medium; this model is a special case of Biot’s theory obtained by the symmetry of the Lagrangian (invariance by translation and rotation). The basic solution of the wave equation is obtained in the time domain by analytically calculating Green’s function of the porous medium and using the properties of the Laplace transforms. Fractional derivatives are used to describe, in the time domain, the fluid–structure interactions, which are of the inertial, viscous, and thermal kind. The solution to the fractional-order wave equation represents the radiation field in the porous medium emitted by a point source. An important result obtained in this study is that the solution of the fractional equation is expressed by recurrence relations that are the consequence of the modified Bessel function of the third kind, which represents a physical solution of the wave equation. This theoretical work with analytical results opens up prospects for the resolution of forward and inverse problems allowing the characterization of a porous medium using spherical waves. Full article
Article
Neutron-Mirror Neutron Oscillations in Absorbing Matter
Symmetry 2022, 14(2), 230; https://doi.org/10.3390/sym14020230 - 25 Jan 2022
Cited by 7 | Viewed by 1657
Abstract
The possibility that a neutron can be transformed to a hidden sector particle remains intriguingly open. Proposed theoretical models conjecture that the hidden sector can be represented by a mirror sector, and the neutron n can oscillate into its sterile mirror twin [...] Read more.
The possibility that a neutron can be transformed to a hidden sector particle remains intriguingly open. Proposed theoretical models conjecture that the hidden sector can be represented by a mirror sector, and the neutron n can oscillate into its sterile mirror twin n, exactly or nearly degenerate in mass with n. Oscillations nn can take place in vacuum or in an environment containing regular matter and a magnetic field, in which only the neutron will be subject to interactions with the environment. We describe the propagation of the oscillating nn system in a cold neutron beam passing through dense absorbing materials in connection to the possible regeneration type of experiments, where the effect of nnn transformation can be observed. Full article
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