Symmetry

27 pages, 16382 KiB

Open AccessArticle

Identification of Determinants of the Speed-Reducing Effect of Pedestrian Refuges in Villages Located on a Chosen Regional Road

by Alicja Sołowczuk and Dominik Kacprzak

Symmetry 2019, 11(4), 597; https://doi.org/10.3390/sym11040597 - 25 Apr 2019

Cited by 4 | Viewed by 4415

Abstract

Traffic calming, as a traffic engineering discipline, is becoming an increasingly important aspect of the road engineering process. One of the traffic calming treatments are pedestrian refuges—raised islands located on or at the road centreline. This paper presents factors relevant to the performance [...] Read more.

Traffic calming, as a traffic engineering discipline, is becoming an increasingly important aspect of the road engineering process. One of the traffic calming treatments are pedestrian refuges—raised islands located on or at the road centreline. This paper presents factors relevant to the performance of this kind of traffic calming devices retrofitted on the stretches of regional roads in village areas. To this end, speed surveys were carried out before and after the islands in each direction on purposefully chosen test sections. In order to identify the determinants, each test section was characterised by features including the symmetry of the road layout geometry, surrounding features and the existing traffic signs and, last but not least, visibility of the road ahead. The survey data were used by the authors to perform analyses in order to group the speeds at the pedestrian refuges and relate them to specific factors and, finally, identify the determinants of speed reduction. In this way, the authors arrived at a conclusion that the performance of pedestrian refuges depends on a number of factors rather than solely on their geometric parameters. The analyses showed that the pedestrian refuge geometric parameters, features located in its proximity that influence the driver’s perception and placement of appropriate marking, can, in combination, result in achieving the desired speed reduction and ensure safety of non-motorised users. These hypotheses were tested on a stretch of a regional road in village area at three points of the process: before upgrading, after installation of pedestrian refuges, and after retrofitting of enhancements. Full article

(This article belongs to the Special Issue Multi-Criteria Decision-Making Techniques for Improvement Sustainability Engineering Processes)

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15 pages, 3487 KiB

Open AccessArticle

Hydrogen Power Plant Site Selection Under Fuzzy Multicriteria Decision-Making (FMCDM) Environment Conditions

by Chia-Nan Wang, Ming-Hsien Hsueh and Da-Fu Lin

Symmetry 2019, 11(4), 596; https://doi.org/10.3390/sym11040596 - 25 Apr 2019

Cited by 24 | Viewed by 5417

Abstract

Fuel and energy are basic resources necessary to meet a country’s socioeconomic development needs; further, countries rich in these resources have the best premise for meeting the inputs of an economic system; however, this also poses many political challenges and threats to national [...] Read more.

Fuel and energy are basic resources necessary to meet a country’s socioeconomic development needs; further, countries rich in these resources have the best premise for meeting the inputs of an economic system; however, this also poses many political challenges and threats to national security. Vietnam is located in the Southeast Asian monsoon-humid tropical region and has diverse fuel-energy resources such as coal, petroleum, and hydropower, along with renewable energy sources such as solar energy, biomass energy, and geothermal energy. However, the reality of economic development in recent years shows complex fluctuations in fuel and energy usage, i.e., besides the export of coal and crude oil, Vietnam still has imported processed oil products. To overcome this issue, many hydrogen power plants will be built in the future. This is why we propose fuzzy multicriteria decision-making (FMCDM) for hydrogen power plant site selection in this research. All criteria affecting location selection are determined by experts and literature reviews, and the weight of all criteria are defined by a fuzzy analytic hierarchy process (FAHP). The technique for order of preference by similarity to an ideal solution (TOPSIS) is a multicriteria decision analysis method, which is used for ranking potential locations in the final stage. As a result, the decision-making unit, DMU010 (DMU010), has become the optimal solution for building hydrogen power plants in Vietnam. A multicriteria decision-making (MCDM) model for hydrogen power plant site selection in Vietnam under fuzzy environment conditions is a contribution of this study. This research also provides useful tools for other types of renewable energies in Vietnam and other countries. Full article

(This article belongs to the Special Issue Multi-Criteria Decision-Making Techniques for Improvement Sustainability Engineering Processes)

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11 pages, 273 KiB

Open AccessArticle

Extended Degenerate r-Central Factorial Numbers of the Second Kind and Extended Degenerate r-Central Bell Polynomials

by Dae San Kim, Dmitry V. Dolgy, Taekyun Kim and Dojin Kim

Symmetry 2019, 11(4), 595; https://doi.org/10.3390/sym11040595 - 24 Apr 2019

Cited by 8 | Viewed by 2545

Abstract

In this paper, we introduce the extended degenerate r-central factorial numbers of the second kind and the extended degenerate r-central Bell polynomials. They are extended versions of the degenerate central factorial numbers of the second kind and the degenerate central Bell [...] Read more.

In this paper, we introduce the extended degenerate r-central factorial numbers of the second kind and the extended degenerate r-central Bell polynomials. They are extended versions of the degenerate central factorial numbers of the second kind and the degenerate central Bell polynomials, and also degenerate versions of the extended r-central factorial numbers of the second kind and the extended r-central Bell polynomials, all of which have been studied by Kim and Kim. We study various properties and identities concerning those numbers and polynomials and also their connections. Full article

(This article belongs to the Special Issue Current Trends in Symmetric Polynomials with Their Applications Ⅱ)

17 pages, 332 KiB

Open AccessArticle

Extended Rectangular b-Metric Spaces and Some Fixed Point Theorems for Contractive Mappings

by Zead Mustafa, Vahid Parvaneh, Mohammed M.M. Jaradat and Zoran Kadelburg

Symmetry 2019, 11(4), 594; https://doi.org/10.3390/sym11040594 - 24 Apr 2019

Cited by 23 | Viewed by 4123

Abstract

In this paper, we introduce the class of extended rectangular b-metric spaces as a generalization of both rectangular metric and rectangular b-metric spaces. In addition, some fixed point results connected with certain contractions are obtained and examples are given to illustrate [...] Read more.

In this paper, we introduce the class of extended rectangular b-metric spaces as a generalization of both rectangular metric and rectangular b-metric spaces. In addition, some fixed point results connected with certain contractions are obtained and examples are given to illustrate these results. Full article

(This article belongs to the Special Issue Symmetric and non-symmetric contractions in various abstract spaces)

16 pages, 5265 KiB

Open AccessArticle

A Device Performance and Data Analytics Concept for Smartphones’ IoT Services and Machine-Type Communication in Cellular Networks

by Kingsley A. Ogudo, Dahj Muwawa Jean Nestor, Osamah Ibrahim Khalaf and Hamed Daei Kasmaei

Symmetry 2019, 11(4), 593; https://doi.org/10.3390/sym11040593 - 24 Apr 2019

Cited by 82 | Viewed by 5456

Abstract

With the advancement of new technologies, the number of connected devices, the amount of data generated, and the need to build an intelligently connected network of things to improve and enrich the human ecosystem open new doors to modifications and adaptations of current [...] Read more.

With the advancement of new technologies, the number of connected devices, the amount of data generated, and the need to build an intelligently connected network of things to improve and enrich the human ecosystem open new doors to modifications and adaptations of current cellular network infrastructures. While more focus is given to low power wide area (LPWA) applications and devices, a significant challenge is the definition of Internet of Things (IoT) use cases and the value generation of applications on already existing IoT devices. Smartphones and related devices are currently manufactured with a wide range of smart sensors such as accelerometers, video sensors, compasses, gyros, proximity sensors, fingerprint sensors, temperature sensors, and biometric sensors used for various purposes. Many of these sensors can be automatically expanded to monitor a user’s daily activities (e.g., fitness workouts), locations, movements, and real-time body temperatures. Mobile network operators (MNOs) play a substantial role in providing IoT communications platforms, as they manage traffic flow in the network. In this paper, we discuss the global concept of IoT and machine-type communication (MTC), and we conduct device performance analytics based on data traffic collected from a cellular network. The experiment equips service providers with a model and framework to monitor device performance in a network. Full article

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26 pages, 329 KiB

Open AccessArticle

Hamilton–Jacobi Wave Theory in Manifestly-Covariant Classical and Quantum Gravity

by Claudio Cremaschini and Massimo Tessarotto

Symmetry 2019, 11(4), 592; https://doi.org/10.3390/sym11040592 - 24 Apr 2019

Cited by 2 | Viewed by 3168

Abstract

The axiomatic geometric structure which lays at the basis of Covariant Classical and Quantum Gravity Theory is investigated. This refers specifically to fundamental aspects of the manifestly-covariant Hamiltonian representation of General Relativity which has recently been developed in the framework of a synchronous [...] Read more.

The axiomatic geometric structure which lays at the basis of Covariant Classical and Quantum Gravity Theory is investigated. This refers specifically to fundamental aspects of the manifestly-covariant Hamiltonian representation of General Relativity which has recently been developed in the framework of a synchronous deDonder–Weyl variational formulation (2015–2019). In such a setting, the canonical variables defining the canonical state acquire different tensorial orders, with the momentum conjugate to the field variable

g_{μ ν}

being realized by the third-order 4-tensor

Π_{μ ν}^{α}

. It is shown that this generates a corresponding Hamilton–Jacobi theory in which the Hamilton principal function is a 4-tensor

S^{α}

. However, in order to express the Hamilton equations as evolution equations and apply standard quantization methods, the canonical variables must have the same tensorial dimension. This can be achieved by projection of the canonical momentum field along prescribed tensorial directions associated with geodesic trajectories defined with respect to the background space-time for either classical test particles or raylights. It is proved that this permits to recover a Hamilton principal function in the appropriate form of 4-scalar type. The corresponding Hamilton–Jacobi wave theory is studied and implications for the manifestly-covariant quantum gravity theory are discussed. This concerns in particular the possibility of achieving at quantum level physical solutions describing massive or massless quanta of the gravitational field. Full article

(This article belongs to the Special Issue Space-Time and Symmetry Properties: Classical and Quantum Descriptions)

12 pages, 3899 KiB

Open AccessArticle

Corn Classification System based on Computer Vision

by Xiaoming Li, Baisheng Dai, Hongmin Sun and Weina Li

Symmetry 2019, 11(4), 591; https://doi.org/10.3390/sym11040591 - 24 Apr 2019

Cited by 38 | Viewed by 7590

Abstract

Automated classification of corn is important for corn sorting in intelligent agriculture. This paper presents a reliable corn classification method based on techniques of computer vision and machine learning. To discriminate different damaged types of corns, a line profile segmentation method is firstly [...] Read more.

Automated classification of corn is important for corn sorting in intelligent agriculture. This paper presents a reliable corn classification method based on techniques of computer vision and machine learning. To discriminate different damaged types of corns, a line profile segmentation method is firstly used to segment and separate a group of touching corns. Then, twelve color features and five shape features are extracted for each individual corn object. Finally, a maximum likelihood estimator is trained to classify normal and damaged corns. To evaluate the performance of the proposed method, a private dataset consisting of images of normal corn and six kinds of damage corns, including heat-damaged, germ-damaged, cob-rot-damaged, blue eye mold-damaged, insect-damaged, and surface mold-damaged, were collected in this work. The proposed method achieved an accuracy of 96.67% for the classification between normal corns and the first four common damaged corns, and an accuracy of 74.76% was achieved for the classification between normal corns and six kinds of damaged corns. The experimental results demonstrated the effectiveness of the proposed corn classification system. Full article

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11 pages, 2134 KiB

Open AccessArticle

Supervised Reinforcement Learning via Value Function

by Yaozong Pan, Jian Zhang, Chunhui Yuan and Haitao Yang

Symmetry 2019, 11(4), 590; https://doi.org/10.3390/sym11040590 - 24 Apr 2019

Cited by 2 | Viewed by 4141

Abstract

Using expert samples to improve the performance of reinforcement learning (RL) algorithms has become one of the focuses of research nowadays. However, in different application scenarios, it is hard to guarantee both the quantity and quality of expert samples, which prohibits the practical [...] Read more.

Using expert samples to improve the performance of reinforcement learning (RL) algorithms has become one of the focuses of research nowadays. However, in different application scenarios, it is hard to guarantee both the quantity and quality of expert samples, which prohibits the practical application and performance of such algorithms. In this paper, a novel RL decision optimization method is proposed. The proposed method is capable of reducing the dependence on expert samples via incorporating the decision-making evaluation mechanism. By introducing supervised learning (SL), our method optimizes the decision making of the RL algorithm by using demonstrations or expert samples. Experiments are conducted in Pendulum and Puckworld scenarios to test the proposed method, and we use representative algorithms such as deep Q-network (DQN) and Double DQN (DDQN) as benchmarks. The results demonstrate that the method adopted in this paper can effectively improve the decision-making performance of agents even when the expert samples are not available. Full article

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16 pages, 4383 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

The Hay Inclined Plane in Coalbrookdale (Shropshire, England): Geometric Modeling and Virtual Reconstruction

by José Ignacio Rojas-Sola and Eduardo De la Morena-De la Fuente

Symmetry 2019, 11(4), 589; https://doi.org/10.3390/sym11040589 - 24 Apr 2019

Cited by 17 | Viewed by 3886

Abstract

This article shows the geometric modeling and virtual reconstruction of the inclined plane of Coalbrookdale (Shropshire, England) that was in operation from 1792 to 1894. This historical invention, work of the Englishman William Reynolds, allowed the transportation of boats through channels located at [...] Read more.

This article shows the geometric modeling and virtual reconstruction of the inclined plane of Coalbrookdale (Shropshire, England) that was in operation from 1792 to 1894. This historical invention, work of the Englishman William Reynolds, allowed the transportation of boats through channels located at different levels. Autodesk Inventor Professional software has been used to obtain the 3D CAD model of this historical invention and its geometric documentation. The material for the research is available on the website of the Betancourt Project of the Canary Orotava Foundation for the History of Science. Also, because the single sheet does not have a scale, it has been necessary to adopt a graphic scale so that the dimensions of the different elements are coherent. Furthermore, it has been necessary to establish some dimensional, geometric, and movement restrictions (degrees of freedom) so that the set will work properly. One of the main conclusions is that William Reynolds designed a mechanism seeking a longitudinal symmetry so that, from a single continuous movement, the mechanism allows two vessels to ascend and descend simultaneously. This engineering solution facilitated a doubling of the working capacity of the device, as well as a reduction of the energy needs of the system. Full article

(This article belongs to the Special Issue Symmetry in Engineering Sciences)

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23 pages, 950 KiB

Open AccessArticle

Product Operations on q-Rung Orthopair Fuzzy Graphs

by Songyi Yin, Hongxu Li and Yang Yang

Symmetry 2019, 11(4), 588; https://doi.org/10.3390/sym11040588 - 23 Apr 2019

Cited by 16 | Viewed by 2735

Abstract

The q-rung orthopair fuzzy graph is an extension of intuitionistic fuzzy graph and Pythagorean fuzzy graph. In this paper, the degree and total degree of a vertex in q-rung orthopair fuzzy graphs are firstly defined. Then, some product operations on q [...] Read more.

The q-rung orthopair fuzzy graph is an extension of intuitionistic fuzzy graph and Pythagorean fuzzy graph. In this paper, the degree and total degree of a vertex in q-rung orthopair fuzzy graphs are firstly defined. Then, some product operations on q-rung orthopair fuzzy graphs, including direct product, Cartesian product, semi-strong product, strong product, and lexicographic product, are defined. Furthermore, some theorems about the degree and total degree under these product operations are put forward and elaborated with several examples. In particular, these theorems improve the similar results in single-valued neutrosophic graphs and Pythagorean fuzzy graphs. Full article

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46 pages, 594 KiB

Open AccessEditor’s ChoiceArticle

Hadronic and Hadron-Like Physics of Dark Matter

by Vitaly Beylin, Maxim Yu. Khlopov, Vladimir Kuksa and Nikolay Volchanskiy

Symmetry 2019, 11(4), 587; https://doi.org/10.3390/sym11040587 - 23 Apr 2019

Cited by 32 | Viewed by 4132

Abstract

The problems of simple elementary weakly interacting massive particles (WIMPs) appeal to extend the physical basis for nonbaryonic dark matter. Such extension involves more sophisticated dark matter candidates from physics beyond the Standard Model (BSM) of elementary particles. We discuss several models of [...] Read more.

The problems of simple elementary weakly interacting massive particles (WIMPs) appeal to extend the physical basis for nonbaryonic dark matter. Such extension involves more sophisticated dark matter candidates from physics beyond the Standard Model (BSM) of elementary particles. We discuss several models of dark matter, predicting new colored, hyper-colored or techni-colored particles and their accelerator and non-accelerator probes. The nontrivial properties of the proposed dark matter candidates can shed new light on the dark matter physics. They provide interesting solutions for the puzzles of direct and indirect dark matter search. Full article

(This article belongs to the Special Issue Cosmological Inflation, Dark Matter and Dark Energy)

9 pages, 265 KiB

Open AccessArticle

Derivative Free Fourth Order Solvers of Equations with Applications in Applied Disciplines

by Ramandeep Behl, Ioannis K. Argyros, Fouad Othman Mallawi and J. A. Tenreiro Machado

Symmetry 2019, 11(4), 586; https://doi.org/10.3390/sym11040586 - 23 Apr 2019

Cited by 1 | Viewed by 2317

Abstract

This paper develops efficient equation solvers for real- and complex-valued functions. An earlier study by Lee and Kim, used the Taylor-type expansions and hypotheses on higher than first order derivatives, but no derivatives appeared in the suggested method. However, we have many cases [...] Read more.

This paper develops efficient equation solvers for real- and complex-valued functions. An earlier study by Lee and Kim, used the Taylor-type expansions and hypotheses on higher than first order derivatives, but no derivatives appeared in the suggested method. However, we have many cases where the calculations of the fourth derivative are expensive, or the result is unbounded, or even does not exist. We only use the first order derivative of function

Ω

in the proposed convergence analysis. Hence, we expand the utilization of the earlier scheme, and we study the computable radii of convergence and error bounds based on the Lipschitz constants. Furthermore, the range of starting points is also explored to know how close the initial guess should be considered for assuring convergence. Several numerical examples where earlier studies cannot be applied illustrate the new technique. Full article

(This article belongs to the Special Issue Symmetry in Complex Systems)

13 pages, 3284 KiB

Open AccessArticle

Lightweight Architecture for Real-Time Hand Pose Estimation with Deep Supervision

by Yufei Wu, Xiaofei Ruan, Yu Zhang, Huang Zhou, Shengyu Du and Gang Wu

Symmetry 2019, 11(4), 585; https://doi.org/10.3390/sym11040585 - 23 Apr 2019

Cited by 3 | Viewed by 3538

Abstract

The high demand for computational resources severely hinders the deployment of deep learning applications in resource-limited devices. In this work, we investigate the under-studied but practically important network efficiency problem and present a new, lightweight architecture for hand pose estimation. Our architecture is [...] Read more.

The high demand for computational resources severely hinders the deployment of deep learning applications in resource-limited devices. In this work, we investigate the under-studied but practically important network efficiency problem and present a new, lightweight architecture for hand pose estimation. Our architecture is essentially a deeply-supervised pruned network in which less important layers and branches are removed to achieve a higher real-time inference target on resource-constrained devices without much accuracy compromise. We further make deployment optimization to facilitate the parallel execution capability of central processing units (CPUs). We conduct experiments on NYU and ICVL datasets and develop a demo¹ using the RealSense camera. Experimental results show our lightweight network achieves an average running time of 32 ms (31.3 FPS, the original is 22.7 FPS) before deployment optimization. Meanwhile, the model is only about half parameters size of the original one with 11.9 mm mean joint error. After the further optimization with OpenVINO, the optimized model can run at 56 FPS on CPUs in contrast to 44 FPS running on a graphics processing unit (GPU) (Tensorflow) and it can achieve the real-time goal. Full article

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30 pages, 7472 KiB

Open AccessArticle

Edge Even Graceful Labeling of Cylinder Grid Graph

by Ahmed A. Elsonbaty and Salama Nagy Daoud

Symmetry 2019, 11(4), 584; https://doi.org/10.3390/sym11040584 - 22 Apr 2019

Cited by 6 | Viewed by 3628

Abstract

Edge even graceful labeling (e.e.g., l.) of graphs is a modular technique of edge labeling of graphs, introduced in 2017. An e.e.g., l. of simple finite undirected graph

G = (V (G), E (G))

of order [...] Read more.

Edge even graceful labeling (e.e.g., l.) of graphs is a modular technique of edge labeling of graphs, introduced in 2017. An e.e.g., l. of simple finite undirected graph

G = (V (G), E (G))

of order

P = | (V (G) |

and size

q = | E (G) |

is a bijection

f : E (G) \to {2, 4, \dots, 2 q}

, such that when each vertex

v \in V (G)

is assigned the modular sum of the labels (images of

f

) of the edges incident to

v

, the resulting vertex labels are distinct

\mod 2 r

, where

r = \max (p, q)

. In this work, the family of cylinder grid graphs are studied. Explicit formulas of e.e.g., l. for all of the cases of each member of this family have been proven. Full article

(This article belongs to the Special Issue Discrete Mathematics and Symmetry)

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14 pages, 659 KiB

Open AccessEditor’s ChoiceArticle

A Scalable and Hybrid Intrusion Detection System Based on the Convolutional-LSTM Network

by Muhammad Ashfaq Khan, Md. Rezaul Karim and Yangwoo Kim

Symmetry 2019, 11(4), 583; https://doi.org/10.3390/sym11040583 - 22 Apr 2019

Cited by 131 | Viewed by 13422

Abstract

With the rapid advancements of ubiquitous information and communication technologies, a large number of trustworthy online systems and services have been deployed. However, cybersecurity threats are still mounting. An intrusion detection (ID) system can play a significant role in detecting such security threats. [...] Read more.

With the rapid advancements of ubiquitous information and communication technologies, a large number of trustworthy online systems and services have been deployed. However, cybersecurity threats are still mounting. An intrusion detection (ID) system can play a significant role in detecting such security threats. Thus, developing an intelligent and accurate ID system is a non-trivial research problem. Existing ID systems that are typically used in traditional network intrusion detection system often fail and cannot detect many known and new security threats, largely because those approaches are based on classical machine learning methods that provide less focus on accurate feature selection and classification. Consequently, many known signatures from the attack traffic remain unidentifiable and become latent. Furthermore, since a massive network infrastructure can produce large-scale data, these approaches often fail to handle them flexibly, hence are not scalable. To address these issues and improve the accuracy and scalability, we propose a scalable and hybrid IDS, which is based on Spark ML and the convolutional-LSTM (Conv-LSTM) network. This IDS is a two-stage ID system: the first stage employs the anomaly detection module, which is based on Spark ML. The second stage acts as a misuse detection module, which is based on the Conv-LSTM network, such that both global and local latent threat signatures can be addressed. Evaluations of several baseline models in the ISCX-UNB dataset show that our hybrid IDS can identify network misuses accurately in 97.29% of cases and outperforms state-of-the-art approaches during 10-fold cross-validation tests. Full article

(This article belongs to the Special Issue Symmetry-Adapted Machine Learning for Information Security)

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15 pages, 2306 KiB

Open AccessFeature PaperArticle

Analysis of Periodic Structures Made of Pins Inside a Parallel Plate Waveguide

by Nafsika Memeletzoglou, Carlos Sanchez-Cabello, Francisco Pizarro-Torres and Eva Rajo-Iglesias

Symmetry 2019, 11(4), 582; https://doi.org/10.3390/sym11040582 - 22 Apr 2019

Cited by 13 | Viewed by 4777

Abstract

In this work, we have analyzed different versions of periodic structures made with metallic pins located inside a parallel plate waveguide (PPWG), varying the symmetry and disposition of the pins. The analysis focuses on two main parameters related to wave propagation. On one [...] Read more.

In this work, we have analyzed different versions of periodic structures made with metallic pins located inside a parallel plate waveguide (PPWG), varying the symmetry and disposition of the pins. The analysis focuses on two main parameters related to wave propagation. On one hand, we have studied how the different proposed structures can create a stopband so that the parallel plate modes can be used in gap waveguide technology or filtering structures. On the other hand, we have analyzed the dispersion and equivalent refractive index of the first propagating transverse electromagnetic mode (TEM). The results show how the use of complex structures made with pins in the top and bottom plates of a PPWG have no advantages in terms of the achieved stopband size. However, for the case of the propagating mode, it is possible to find less dispersive modes and a higher range of equivalent refractive indices when using double-pin structures compared to a reference case with single pins. Full article

(This article belongs to the Special Issue Higher Symmetries and Its Application in Microwave Technology, Antennas and Metamaterials)

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8 pages, 4083 KiB

Open AccessEditor’s ChoiceArticle

Fully Metallic Flat Lens Based on Locally Twist-Symmetric Array of Complementary Split-Ring Resonators

by Oskar Dahlberg, Guido Valerio and Oscar Quevedo-Teruel

Symmetry 2019, 11(4), 581; https://doi.org/10.3390/sym11040581 - 22 Apr 2019

Cited by 16 | Viewed by 4350

Abstract

In this article, we demonstrate how twist symmetries can be employed in the design of flat lenses. A lens design is proposed, consisting of 13 perforated metallic sheets separated by an air gap. The perforation in the metal is a two-dimensional array of [...] Read more.

In this article, we demonstrate how twist symmetries can be employed in the design of flat lenses. A lens design is proposed, consisting of 13 perforated metallic sheets separated by an air gap. The perforation in the metal is a two-dimensional array of complementary split-ring resonators. In this specific design, the twist symmetry is local, as it is only applied to the unit cell of the array. Moreover, the twist symmetry is an approximation, as it is only applied to part of the unit cell. First, we demonstrate that, by varying the order of twist symmetry, the phase delay experienced by a wave propagating through the array can be accurately controlled. Secondly, a lens is designed by tailoring the unit cells throughout the aperture of the lens in order to obtain the desired phase delay. Simulation and measurement results demonstrate that the lens successfully transforms a spherical wave emanating from the focal point into a plane wave at the opposite side of the lens. The demonstrated concepts find application in future wireless communication networks where fully-metallic directive antennas are desired. Full article

(This article belongs to the Special Issue Higher Symmetries and Its Application in Microwave Technology, Antennas and Metamaterials)

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19 pages, 478 KiB

Open AccessArticle

Green Simulation of Pandemic Disease Propagation

by Spencer Wilson, Abdullah Alabdulkarim and David Goldsman

Symmetry 2019, 11(4), 580; https://doi.org/10.3390/sym11040580 - 22 Apr 2019

Viewed by 3104

Abstract

This paper is concerned with the efficient stochastic simulation of multiple scenarios of an infectious disease as it propagates through a population. In particular, we propose a simple “green” method to speed up the simulation of disease transmission as we vary the probability [...] Read more.

This paper is concerned with the efficient stochastic simulation of multiple scenarios of an infectious disease as it propagates through a population. In particular, we propose a simple “green” method to speed up the simulation of disease transmission as we vary the probability of infection of the disease from scenario to scenario. After running a baseline scenario, we incrementally increase the probability of infection, and use the common random numbers variance reduction technique to avoid re-simulating certain events in the new scenario that would not otherwise have changed from the previous scenario. A set of Monte Carlo experiments illustrates the effectiveness of the procedure. We also propose various extensions of the method, including its use to estimate the sensitivity of propagation characteristics in response to small changes in the infection probability. Full article

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13 pages, 3709 KiB

Open AccessArticle

Experimental Investigation on the Cooling and Inerting Effects of Liquid Nitrogen Injected into a Confined Space

by Huaijun Ji, Yunzhuo Li, Hetao Su, Wuyi Cheng and Xiang Wu

Symmetry 2019, 11(4), 579; https://doi.org/10.3390/sym11040579 - 22 Apr 2019

Cited by 18 | Viewed by 3053

Abstract

As a highly effective and environmentally benign suppression agent, liquid nitrogen (LN₂) has been widely used for fire extinguishing in plants, dwellings, enclosed underground tunnels, and other confined spaces through cooling and inerting. It is of great significance to understand the [...] Read more.

As a highly effective and environmentally benign suppression agent, liquid nitrogen (LN₂) has been widely used for fire extinguishing in plants, dwellings, enclosed underground tunnels, and other confined spaces through cooling and inerting. It is of great significance to understand the cooling and inerting effects of LN₂ injected into a confined space. A confined-space experimental platform was developed to study the injecting LN₂ into the platform with different injection parameters, such as mass flux, pipe diameter, and inclination angle. In addition, a mathematical model of quantitatively assessing cooling and inerting effects was proposed by using heat transfer capacity, inerting coefficient, and cooling rate. Results showed that the inerting effect was gradually enhanced with a mass flux increasing from 0.014 to 0.026 kg/s and then tended to level off; an appropriate pipe diameter of 12 mm was optimal for the cooling and inerting effects in this experiment. In addition, a positively increasing inclination angle could contribute to the cooling and inerting effects. However, there was little effect on the cooling and inerting with an inclination angle less than 0°. This study can provide technical guidances for environmentally friendly fire extinguishing with LN₂ in a confined space. Full article

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10 pages, 1495 KiB

Open AccessArticle

Convenient Asymmetric Synthesis of Fmoc-(S)-6,6,6-Trifluoro-Norleucine

by Haibo Mei, Zizhen Yin, Toshio Miwa, Hiroki Moriwaki, Hidenori Abe, Jianlin Han and Vadim A. Soloshonok

Symmetry 2019, 11(4), 578; https://doi.org/10.3390/sym11040578 - 21 Apr 2019

Cited by 25 | Viewed by 7395

Abstract

In this work we report a convenient asymmetric synthesis of Fmoc-(S)-6,6,6-trifluoro-norleucine via alkylation reaction of chiral glycine equivalent. The target amino acid of 99% enantiomeric purity was prepared with 82.4% total yield (three steps). Full article

(This article belongs to the Special Issue Amino Acid Chirality)

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10 pages, 4078 KiB

Open AccessArticle

The Symmetry in the Noise-Perturbed Mandelbrot Set

by Tianwen Sun and Da Wang

Symmetry 2019, 11(4), 577; https://doi.org/10.3390/sym11040577 - 21 Apr 2019

Cited by 3 | Viewed by 4450

Abstract

This paper investigates the destruction of the symmetrical structure of the noise-perturbed Mandelbrot set (M-set). By applying the “symmetry criterion” method, we quantitatively compare the damages to the symmetry of the noise-perturbed Mandelbrot set resulting from additive and multiplicative noises. Because of the [...] Read more.

This paper investigates the destruction of the symmetrical structure of the noise-perturbed Mandelbrot set (M-set). By applying the “symmetry criterion” method, we quantitatively compare the damages to the symmetry of the noise-perturbed Mandelbrot set resulting from additive and multiplicative noises. Because of the uneven distribution between the core positions and the edge positions of the noise-perturbed Mandelbrot set, the comparison results reveal a paradox between the visual sense and quantified result. Thus, we propose a new “visual symmetry criterion” method that is more suitable for the measurement of visual asymmetry. Full article

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17 pages, 5117 KiB

Open AccessArticle

A Method to Determine Core Design Problems and a Corresponding Solution Strategy

by Yuanming Xie, Wenqiang Li, Yin Luo, Yan Li and Song Li

Symmetry 2019, 11(4), 576; https://doi.org/10.3390/sym11040576 - 19 Apr 2019

Cited by 2 | Viewed by 3058

Abstract

The lack of information on the correlation between root causes and corresponding control criteria in the importance calculation of root causes of design problems results in less accurate determinations of core problems. Based on the interaction between customer needs, bad product parameters, and [...] Read more.

The lack of information on the correlation between root causes and corresponding control criteria in the importance calculation of root causes of design problems results in less accurate determinations of core problems. Based on the interaction between customer needs, bad product parameters, and root causes, a hierarchical representation model of the design problem is established in this paper. A network layer of bad parameters, including various types of correlations, and a control layer, including technical feasibility and cost, are constructed. Then, a method based on the network analytic hierarchy process is proposed to rank the importance of root causes of the design problem and determine the core problems. Finally, a product design process based on the core problem solving is established to assist designers with improving design quality and efficiency. The design for the coolant flow distribution device in the lower chamber of a third-generation pressurized water reactor is employed as an example to demonstrate the effectiveness of the proposed method. Full article

(This article belongs to the Special Issue Symmetry in Mechanical Engineering)

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26 pages, 2852 KiB

Open AccessArticle

When Considering More Elements: Attribute Correlation in Unsupervised Data Cleaning under Blocking

by Pei Li, Chaofan Dai and Wenqian Wang

Symmetry 2019, 11(4), 575; https://doi.org/10.3390/sym11040575 - 19 Apr 2019

Cited by 2 | Viewed by 2525

Abstract

In banks, governments, and internet companies, due to the increasing demand for data in various information systems and continuously shortening of the cycle for data collection and update, there may be a variety of data quality issues in a database. As the expansion [...] Read more.

In banks, governments, and internet companies, due to the increasing demand for data in various information systems and continuously shortening of the cycle for data collection and update, there may be a variety of data quality issues in a database. As the expansion of data scales, methods such as pre-specifying business rules or introducing expert experience into a repair process are no longer applicable to some information systems requiring rapid responses. In this case, we divided data cleaning into supervised and unsupervised forms according to whether there were interventions in the repair processes and put forward a new dimension suitable for unsupervised cleaning in this paper. For weak logic errors in unsupervised data cleaning, we proposed an attribute correlation-based (ACB)-Framework under blocking, and designed three different data blocking methods to reduce the time complexity and test the impact of clustering accuracy on data cleaning. The experiments showed that the blocking methods could effectively reduce the repair time by maintaining the repair validity. Moreover, we concluded that the blocking methods with a too high clustering accuracy tended to put tuples with the same elements into a data block, which reduced the cleaning ability. In summary, the ACB-Framework with blocking can reduce the corresponding time cost and does not need the guidance of domain knowledge or interventions in repair, which can be applied in information systems requiring rapid responses, such as internet web pages, network servers, and sensor information acquisition. Full article

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17 pages, 7822 KiB

Open AccessArticle

Fractional-Order Fusion Model for Low-Light Image Enhancement

by Qiang Dai, Yi-Fei Pu, Ziaur Rahman and Muhammad Aamir

Symmetry 2019, 11(4), 574; https://doi.org/10.3390/sym11040574 - 19 Apr 2019

Cited by 67 | Viewed by 5178

Abstract

In this paper, a novel fractional-order fusion model (FFM) is presented for low-light image enhancement. Existing image enhancement methods don’t adequately extract contents from low-light areas, suppress noise, and preserve naturalness. To solve these problems, the main contributions of this paper are using [...] Read more.

In this paper, a novel fractional-order fusion model (FFM) is presented for low-light image enhancement. Existing image enhancement methods don’t adequately extract contents from low-light areas, suppress noise, and preserve naturalness. To solve these problems, the main contributions of this paper are using fractional-order mask and the fusion framework to enhance the low-light image. Firstly, the fractional mask is utilized to extract illumination from the input image. Secondly, image exposure adjusts to visible the dark regions. Finally, the fusion approach adopts the extracting of more hidden contents from dim areas. Depending on the experimental results, the fractional-order differential is much better for preserving the visual appearance as compared to traditional integer-order methods. The FFM works well for images having complex or normal low-light conditions. It also shows a trade-off among contrast improvement, detail enhancement, and preservation of the natural feel of the image. Experimental results reveal that the proposed model achieves promising results, and extracts more invisible contents in dark areas. The qualitative and quantitative comparison of several recent and advance state-of-the-art algorithms shows that the proposed model is robust and efficient. Full article

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12 pages, 253 KiB

Open AccessArticle

Thermoelasticity of Initially Stressed Bodies with Voids: A Domain of Influence

by Marin Marin, Mohamed I. A. Othman, Sorin Vlase and Lavinia Codarcea-Munteanu

Symmetry 2019, 11(4), 573; https://doi.org/10.3390/sym11040573 - 19 Apr 2019

Cited by 13 | Viewed by 2296

Abstract

In our study, we will extend the domain of influence in order to cover the thermoelasticity of initially stressed bodies with voids. In what follows, we prove that, for a finite time

t > 0

, the displacement field

u_{i}

, the [...] Read more.

In our study, we will extend the domain of influence in order to cover the thermoelasticity of initially stressed bodies with voids. In what follows, we prove that, for a finite time

t > 0

, the displacement field

u_{i}

, the dipolar displacement field

φ_{j k}

, the temperature

θ

and the change in volume fraction

ϕ

generate no disturbance outside a bounded domain B. Full article

(This article belongs to the Special Issue Symmetry in Applied Continuous Mechanics)

14 pages, 1577 KiB

Open AccessArticle

A Dynamic Simulation of the Immune System Response to Inhibit and Eliminate Abnormal Cells

by S. A. Alharbi and A. S. Rambely

Symmetry 2019, 11(4), 572; https://doi.org/10.3390/sym11040572 - 19 Apr 2019

Cited by 14 | Viewed by 4071

Abstract

Diet has long been considered a risk factor related to an increased risk of cancer. This challenges us to understand the relationship between the immune system and diet when abnormal cells appear in a tissue. In this paper, we propose and analyze a [...] Read more.

Diet has long been considered a risk factor related to an increased risk of cancer. This challenges us to understand the relationship between the immune system and diet when abnormal cells appear in a tissue. In this paper, we propose and analyze a model from the point of view of a person who follows a healthy diet, i.e., one correlated to the food pyramid, and a person who follows an unhealthy diet. Normal cells and immune cells are used in the design of the model, which aims to describe how the immune system functions when abnormal cells appear in a tissue. The results show that the immune system is able to inhibit and eliminate abnormal cells through the three following stages: the response stage, the interaction stage, and the recovery stage. Specifically, the failure of the immune system to accomplish the interaction stage occurs when a person follows an unhealthy diet. According to the analysis and simulation of our model, we can deduce that dietary pattern has a significant impact on the functioning of the immune system. Full article

(This article belongs to the Special Issue Symmetry in Mathematical Analysis and Applications)

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20 pages, 10751 KiB

Open AccessArticle

Anomaly Detection Based on Mining Six Local Data Features and BP Neural Network

by Yu Zhang, Yuanpeng Zhu, Xuqiao Li, Xiaole Wang and Xutong Guo

Symmetry 2019, 11(4), 571; https://doi.org/10.3390/sym11040571 - 19 Apr 2019

Cited by 9 | Viewed by 4148

Abstract

Key performance indicators (KPIs) are time series with the format of (timestamp, value). The accuracy of KPIs anomaly detection is far beyond our initial expectations sometimes. The reasons include the unbalanced distribution between the normal data and the anomalies as well as the [...] Read more.

Key performance indicators (KPIs) are time series with the format of (timestamp, value). The accuracy of KPIs anomaly detection is far beyond our initial expectations sometimes. The reasons include the unbalanced distribution between the normal data and the anomalies as well as the existence of many different types of the KPIs data curves. In this paper, we propose a new anomaly detection model based on mining six local data features as the input of back-propagation (BP) neural network. By means of vectorization description on a normalized dataset innovatively, the local geometric characteristics of one time series curve could be well described in a precise mathematical way. Differing from some traditional statistics data characteristics describing the entire variation situation of one sequence, the six mined local data features give a subtle insight of local dynamics by describing the local monotonicity, the local convexity/concavity, the local inflection property and peaks distribution of one KPI time series. In order to demonstrate the validity of the proposed model, we applied our method on 14 classical KPIs time series datasets. Numerical results show that the new given scheme achieves an average F₁-score over 90%. Comparison results show that the proposed model detects the anomaly more precisely. Full article

(This article belongs to the Special Issue Symmetry in Engineering Sciences)

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21 pages, 2641 KiB

Open AccessArticle

Stereo Matching Methods for Imperfectly Rectified Stereo Images

by Phuc Hong Nguyen and Chang Wook Ahn

Symmetry 2019, 11(4), 570; https://doi.org/10.3390/sym11040570 - 19 Apr 2019

Cited by 14 | Viewed by 5203

Abstract

Stereo matching has been under development for decades and is an important process for many applications. Difficulties in stereo matching include textureless regions, occlusion, illumination variation, the fattening effect, and discontinuity. These challenges are effectively solved in recently developed stereo matching algorithms. A [...] Read more.

Stereo matching has been under development for decades and is an important process for many applications. Difficulties in stereo matching include textureless regions, occlusion, illumination variation, the fattening effect, and discontinuity. These challenges are effectively solved in recently developed stereo matching algorithms. A new imperfect rectification problem has recently been encountered in stereo matching, and the problem results from the high resolution of stereo images. State-of-the-art stereo matching algorithms fail to exactly reconstruct the depth information using stereo images with imperfect rectification, as the imperfectly rectified image problems are not explicitly taken into account. In this paper, we solve the imperfect rectification problems, and propose matching stereo matching methods that based on absolute differences, square differences, normalized cross correlation, zero-mean normalized cross correlation, and rank and census transforms. Finally, we conduct experiments to evaluate these stereo matching methods using the Middlebury datasets. The experimental results show the proposed stereo matching methods can reduce error rate significantly for stereo images with imperfect rectification. Full article

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10 pages, 378 KiB

Open AccessArticle

Eigenvalue Based Approach for Assessment of Global Robustness of Nonlinear Dynamical Systems

by Robert Vrabel

Symmetry 2019, 11(4), 569; https://doi.org/10.3390/sym11040569 - 19 Apr 2019

Cited by 1 | Viewed by 2363

Abstract

In this paper we have established the sufficient conditions for asymptotic convergence of all solutions of nonlinear dynamical system (with potentially unknown and unbounded external disturbances) to zero with time

t \to \infty .

We showed here that the symmetric part of linear [...] Read more.

In this paper we have established the sufficient conditions for asymptotic convergence of all solutions of nonlinear dynamical system (with potentially unknown and unbounded external disturbances) to zero with time

t \to \infty .

We showed here that the symmetric part of linear part of nonlinear nominal system, or, to be more precise, its time-dependent eigenvalues, play important role in assessment of the robustness of systems. Full article

(This article belongs to the Special Issue Nonlinear Circuits and Systems in Symmetry)

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12 pages, 273 KiB

Open AccessArticle

Tracking Control of a Class of Chaotic Systems

by Anqing Yang, Linshan Li, Zuoxun Wang and Rongwei Guo

Symmetry 2019, 11(4), 568; https://doi.org/10.3390/sym11040568 - 19 Apr 2019

Cited by 15 | Viewed by 2106

Abstract

This paper investigates the asymptotic tracking control problem of the chaotic system. Firstly, a reference system is presented, the output of which can asymptotically track a given command. Then, a both physically implementable and simple controller is designed, by which the given chaotic [...] Read more.

This paper investigates the asymptotic tracking control problem of the chaotic system. Firstly, a reference system is presented, the output of which can asymptotically track a given command. Then, a both physically implementable and simple controller is designed, by which the given chaotic system synchronizes the reference system, and thus the output of such chaotic systems can asymptotically track the given command. It should be pointed out that the output of the given chaotic system can asymptotically track arbitrary desired periodic orbits. Finally, several illustrative examples are taken as example to show the validity and effectiveness of the obtained results. Full article

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Symmetry, Volume 11, Issue 4 (April 2019) – 156 articles

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