摘要:
The synthesis of sulfur heterocycles via the construction of C–S bonds has received considerable attention due to their biological value and extensive pharmaceutical application. While diverse sulfurating agents have been developed over the past few decades, in this regard, elemental sulfur, with advantages of low toxicity, odorless nature and chemical stability, has great potential for the construction of diverse sulfur heterocycles through its direct incorporation into the target molecules in a concise way. Direct functionalization of inert C–H bonds can shorten the number of reaction steps and minimize the amount of waste formed. Hence, heteroannulations via direct C–H sulfuration is considered to be an attractive strategy for the synthesis of sulfur heterocycles. In the last few years, a vast array of concise systems have been reported for the synthesis of some valuable sulfur heterocycles such as thiophenes, thienoindoles, thienothiazoles, thiazoles, benzothiazoles, and thiadiazoles through direct C–H sulfuration/annulations with elemental sulfur. These are discussed in detail in this review.
1 Introduction
2 Thiophenes
3 Thienoindoles
4 Thienothiazoles
5 Other Fused Thiophenes
6 Thiazoles
7 Benzothiazoles
8 Thiadiazoles
9 Others
10 Summary and Outlook
作者:
Xiong, Pei-Ying;Almarashi, Adel;Dhahad, Hayder A.;Alawee, Wissam H.;Abusorrah, Abdullah M.;...
期刊:
Journal of Molecular Liquids,2021年330:115591- ISSN:0167-7322
作者机构:
[Xiong, Pei-Ying] Hunan City Univ, Coll Sci, Yiyang 413000, Peoples R China.;[Almarashi, Adel] Jazan Univ, Coll Sci, Dept Math, Post Box 2097,New Campus, Jazan, Saudi Arabia.;[Dhahad, Hayder A.] Univ Technol Baghdad, Mech Engn Dept, Baghdad, Iraq.;[Alawee, Wissam H.] Univ Technol Baghdad, Control & Syst Engn Dept, Baghdad, Iraq.;[Alawee, Wissam H.] Univ Technol Baghdad, Training & Workshops Ctr, Baghdad, Iraq.
关键词:
Magnetic force;Exergy;Convection;Permeable space;Nanomaterial;Entropy
摘要:
Numerical simulation of hybrid nanomaterial free convection with helps of CVFEM was performed. Dispersing nanomaterial can minimize the exergy loss. The modeling outputs were depicted in terms of 3D plots and contours. Because of reduction of irreversibility with inclusion of nanoparticles, hybrid nanofluid was employed. Increasing Ha results in greater X-d and it is more sensible when convection become stronger. The growth of permeability increases nanomaterial motion and reduces the exergy drop. (C) 2021 Elsevier B.V. All rights reserved.
摘要:
We propose a simple quasi-continuous monolayer graphene structure and achieve a dynamically tunable triple plasmon-induced transparency (PIT) effect in the proposed structure. Additional analyses indicate that the proposed structure contains a self-constructed bright-dark-dark mode system. A uniform theoretical model is introduced to investigate the spectral response characteristics and slow light-effects in the proposed system, and the theoretical and the simulated results exhibit high consistency. In addition, the influences of the Fermi level and the carrier mobility of graphene on transmission spectra are discussed. It is found that each PIT window exhibits an independent dynamical adjustability owing to the quasi-continuity of the proposed structure. Finally, the slow-light effects are investigated based on the calculation of the group refractive index and phase shift. It is found that the structure displays excellent slow-light effects near the PIT windows with high-group indices, and the maximum group index of each PIT window exceeds 1000 when the carrier mobility of graphene increases to 3.5 m2 V−1 s−1. The proposed structure has potential to be used in multichannel filters, optical switches, modulators, and slow light devices. Additionally, the established theoretical model lays a theoretical basis for research on multimode coupling effects.
作者机构:
[Xiong, Pei-Ying] Hunan City Univ, Sch Sci, Yiyang 413000, Peoples R China.;[Jahanshahi, Hadi] Univ Manitoba, Dept Mech Engn, Winnipeg, MB R3T 5V6, Canada.;[Alcaraz, Raul] Univ Castilla La Mancha UCLM, Res Grp Elect Biomed & Telecommun Engn, Cuenca 16071, Spain.;[Chu, Yu-Ming] Huzhou Univ, Dept Math, Huzhou 313000, Peoples R China.;[Chu, Yu-Ming] Changsha Univ Sci & Technol, Hunan Prov Key Lab Math Modeling & Anal Engn, Changsha 410114, Peoples R China.
关键词:
Chaos;Fractional calculus;Hidden attractors;Self-excited system;Robust control;Intelligent control technique;Disturbance observer
摘要:
An immense body of research has focused on chaotic systems, mainly because of their interesting applications in a wide variety of fields. A comprehensive understanding and synchronization of chaotic systems play pivotal roles in practical applications. To this end, the present study investigates a multi stable fractional-order chaotic system. Firstly, some dynamical features of the system are described, and the chaotic behaviour of the system is verified. Then, both spectral entropy and spectral Min-Entropy are computed, and the phenomenon of multi-stability is shown. Besides, the combination of a new chattering-free robust sliding mode controller with a neural network observer is proposed for the synchronization of the fractional-order system. With the neural network estimator, unknown functions of the system are obtained, and the effects of disturbances are completely taken into account. Also, based on the Lyapunov stability theorem, the asymptotical stability of the closed-loop system is confirmed. Lastly, the proposed control technique is applied to the fractional-order system. Numerical results demonstrate the chattering-free and effective performance of the proposed control method for uncertain systems in the presence of unknown time-varying external disturbances. (c) 2021 Elsevier Ltd. All rights reserved.
关键词:
Mining and manufacturing;Rock weathering;Fertilizer and pesticide use;Principal component analysis;Mixed metal pollution;Surface water pollution
摘要:
This study collected past sampling data on total concentrations of 12 heavy metals (Cd, Pb, Cr, Hg, Zn, Cu, Ni, Al, Fe, Mn, As, and Co) in surface water bodies, i.e., 168 rivers and 71 lakes, from 1972 to 2017. The intent was to investigate the levels and sources of heavy metal pollution across five decades and five continents. Mean heavy metal concentrations in global river and lake water, and the number of heavy metals with concentrations greater than the published threshold limits as per the standards of both the World Health Organization (WHO) and the United States Environmental Protection Agency (USEPA) were generally lower in the 1970s and 1980s than in the 1990s, 2000s, and 2010s. Over time, heavy metal pollution in surface water has changed from single metal pollution to mixed metal pollution. Heavy metal concentrations in water, and the number of heavy metals with concentrations above the threshold limits for both WHO and USEPA standards were lower in the developed countries of Europe and North America, and higher in the developing countries of Africa, Asia, and South America. Over time, the main sources of metal pollution have changed from mining and manufacturing to rock weathering and waste discharge. The main metal sources differed across the five continents, with fertilizer and pesticide use, along with rock weathering, being dominant in Africa. Mining and manufacturing, along with rock weathering, were dominant in Asia and Europe. Mining and manufacturing, along with fertilizer and pesticide use, were dominant sources in North America, while four sources (mining and manufacturing, fertilizer and pesticide use, rock weathering, and waste discharge) were responsible for the majority of heavy metal pollution in the river and lake water bodies of South America. Additionally, implementing rigorous standards on metal emissions and recycling metals from wastewater are effective for controlling heavy metal source pollution. (C) 2020 The Authors. Published by Elsevier B.V.
期刊:
Mathematical Inequalities and Applications,2020年23(1):77-93 ISSN:1331-4343
通讯作者:
Chu, Yu-Ming
作者机构:
[Yang, Zhen-Hang] Huzhou Univ, Dept Math, Huzhou 313000, Peoples R China.;[Qian, Wei-Mao] Huzhou Broadcast & TV Univ, Sch Continuing Educ, Huzhou 313000, Peoples R China.;[Zhang, Wen] Icahn Sch Med Mt Sinai, Friedman Brain Inst, New York, NY 10029 USA.;[Chu, Yu-Ming] Hunan City Univ, Coll Sci, Yiyang 413000, Peoples R China.;[Chu, Yu-Ming] Changsha Univ Sci & Technol, Sch Math & Stat, Changsha 410114, Peoples R China.
通讯机构:
[Chu, Yu-Ming] H;[Chu, Yu-Ming] C;Hunan City Univ, Coll Sci, Yiyang 413000, Peoples R China.;Changsha Univ Sci & Technol, Sch Math & Stat, Changsha 410114, Peoples R China.
关键词:
Gaussian hypergeometric function;complete elliptic integral;arithmetic-geometric mean
摘要:
In the article, we present several monotonicity properties and bounds for the complete elliptic integral of the first kind. As applications. we find sharp hounds for the arithmetic-geometric mean.
摘要:
In the article, we prove that the function x -> (1-x)K-P(root x) is logarithmically concave on (0, 1) if and only if p >= 7/32, the function x -> K(root x)/ log(1 + 4/root 1 - x) is convex on (0, 1) and the function x -> d(2)/dx(2) [K(root x) - log (1+ 4/root 1 - x)] is absolutely monotonic on (0,1), where K(x) = integral(pi/2)(0) (1 - x(2) sin(2) t)(-1/2) dt ( 0 < x < 1) is the complete elliptic integral of the first kind.
摘要:
Road traffic is an important component of the national economy and social life. Promoting intelligent and Informa ionization construction in the field of road traffic is conducive to the construction of smart cities and the formulation of macro strategies and construction plans for urban traffic development. Aiming at the shortcomings of the current road traffic system, this article, on the basis of combining convolution neural network, situational awareness technology, database and other technologies, takes the road traffic situational awareness system as the research object, and analyzes the information collection, processing, and analysis process of road traffic situational awareness system. Convolutional neural networks (CNN), region-CNN (R-CNN), fast R-CNN, and faster R-CNN are used for vehicle class classification and location identification in road image big data. The deep convolutional neural network model based on road traffic image big data was further established, and the system requirements analysis and system framework design and implementation were carried out. Through the analysis and trial of actual cases, the results show the application effect of the realized road traffic situational awareness system, which provides a scientific reference and basis for the establishment of modern intelligent transportation system.
作者机构:
[Wang, Miao-Kun] Huzhou Univ, Dept Math, Huzhou 313000, Peoples R China.;[Chu, Yu-Ming] Hunan City Univ, Coll Sci, Yiyang 413000, Peoples R China.;[Zhang, Wen] Icahn Sch Med Mt Sinai, Friedman Brain Inst, New York, NY 10029 USA.
通讯机构:
[Chu, Yu-Ming] H;Hunan City Univ, Coll Sci, Yiyang 413000, Peoples R China.
摘要:
In the article, we present several monotonicity theorems and inequalities for the modular equation functions ma(r) and mu a(r), and find the infinite-series formulas for m1/3(r) and m1/4(r) which depend only on r. As applications, we find several precise explicit estimates for the solution of Ramanujan's generalized modular equation.
摘要:
The aim of this research is reinforcing of concrete with variety of fiber reinforced polymer (FRP) configurations and investigates the load capacity and ductility of these connections using an experimental investigation. Six scaled-down RC exterior joints were tested under moderately monotonic loads. The results show that, the shape of the FRP had a different effect on the joint capacity and the connection ductility coefficient. The greatest effect on increasing the ductility factor was seen in the sample where two reinforcement plates were used on both sides of the beam web (RCS5 sample). For the sample with the presence of FRP plates at the top and bottom of the beam (RCS3 sample), the ductility factor was reduced even the load capacity of this sample increased. Except for the RCS3 sample, the rest of the samples exhibited an increase in the ductility factor due to the FRP reinforcement.
摘要:
We establish the monotonicity and convexity properties for several special functions involving the generalized elliptic integrals, and present some new analytic inequalities.
摘要:
In the article, we present the best possible bounds for the weighted Holder mean of the complete p-elliptic integrals of the first and second kinds, which are the generalizations of the previously results for the complete elliptic integrals. (C) 2019 Published by Elsevier Inc.