chemical effect
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2022 ◽  
Vol 8 ◽  
Author(s):  
Huanqing Zhang ◽  
Honggang Sun ◽  
Qiutong Li ◽  
Li Wang

The local structures of U-Co melts have been studied by first-principle calculations. Two sub-peaks are observed in the first peaks of U-U pair distribution functions. The Voronoi polyhedral analyses also show two separate core-shell U-U distances. Therefore, the calculated results propose that U atoms will play dual roles, “chemical” and “topological”, in the local structures of U-Co melts. In addition, the chemical effect of U atoms will be strengthened when containing more U atoms. The interaction of Co and U atoms is slightly affected by the compositions. The Co-centered clusters are mostly prism-like or antiprism-like polyhedral, which can be predicted by the solute-solvent model. The distribution of the coordinated numbers of Co atoms is much narrower than that of U atoms, showing relatively stable Co-centered clusters. The chemical and topological roles of U atoms are intuitively observed in the electron density of U-Co melts, which presents both metallic and covalent bonding characteristics for U-U bonds. In the end, we conclude that the partial localization of U 5f-electron is responsible for the dual roles of U atoms. The present results provide a theoretical understanding of the origin of the local structures of U-Co melts.


Symmetry ◽  
2021 ◽  
Vol 13 (12) ◽  
pp. 2388
Author(s):  
Mohammad H. Nadimi-Shahraki ◽  
Shokooh Taghian ◽  
Seyedali Mirjalili ◽  
Ahmed A. Ewees ◽  
Laith Abualigah ◽  
...  

The moth-flame optimization (MFO) algorithm is an effective nature-inspired algorithm based on the chemical effect of light on moths as an animal with bilateral symmetry. Although it is widely used to solve different optimization problems, its movement strategy affects the convergence and the balance between exploration and exploitation when dealing with complex problems. Since movement strategies significantly affect the performance of algorithms, the use of multi-search strategies can enhance their ability and effectiveness to solve different optimization problems. In this paper, we propose a multi-trial vector-based moth-flame optimization (MTV-MFO) algorithm. In the proposed algorithm, the MFO movement strategy is substituted by the multi-trial vector (MTV) approach to use a combination of different movement strategies, each of which is adjusted to accomplish a particular behavior. The proposed MTV-MFO algorithm uses three different search strategies to enhance the global search ability, maintain the balance between exploration and exploitation, and prevent the original MFO’s premature convergence during the optimization process. Furthermore, the MTV-MFO algorithm uses the knowledge of inferior moths preserved in two archives to prevent premature convergence and avoid local optima. The performance of the MTV-MFO algorithm was evaluated using 29 benchmark problems taken from the CEC 2018 competition on real parameter optimization. The gained results were compared with eight metaheuristic algorithms. The comparison of results shows that the MTV-MFO algorithm is able to provide competitive and superior results to the compared algorithms in terms of accuracy and convergence rate. Moreover, a statistical analysis of the MTV-MFO algorithm and other compared algorithms was conducted, and the effectiveness of our proposed algorithm was also demonstrated experimentally.


2021 ◽  
Author(s):  
Shahid Hussain ABRO ◽  
Alidad CHANDIO ◽  
Asif Ahmed SHAIKH ◽  
Norbaizura NORDIN ◽  
Hamza SUHARWARDI

An attempt has been made in the present research work to investigate the role and influence of chemical effect of aluminum addition in the experimental steel towards the formation of k-carbides. Two steel grades were made with and without aluminum addition by induction melting furnace and were cast to ingots. Steel A has no aluminum addition and steel B has some aluminum content. These ingots were then solution heat treated on a temperature of 1200°C for 2-hours’ time and were cooled in the air. After that, they were hot rolled to drawn in plate and sheet. The small samples were cut from bulk and were then heat-treated at 800°C for 1 hour and quenched. Microstructure by OM and SEM was captured. In steel A there was no k-carbide present in the matrix and surprisingly in steel B, small fine k-carbides were present this was then confirmed by XRD later. OM, SEM, and TEM analysis revealed that the presence of k-carbides in steel B makes less dense. It was concluded that aluminum in conjunction with nitrogen forms the small nitride particles having a high melting point does not dissolve during the melting and casting such particles are known as AlN or aluminum nitride particles was observed by TEM along with EDS was the main reason to support the formation of k-carbides, these fine nano level k-carbides are orderly distributed in the steel matrix as was shown by XRD peaks.


2021 ◽  
Author(s):  
Jianguo Zhang ◽  
Alan Rodgerson ◽  
Stephen Edwards

Abstract Wellbore instability and lost circulation are two major sources of non-productive time (NPT) in drilling operations worldwide. Non-aqueous fluid (NAF) is often chosen to mitigate this and minimize the chemical effect on wellbore instability in reactive shales. However, it may inadvertently increase the risk of losses. A simple method to optimize internal phase salinity (IPS) of NAF is presented to improve wellbore stability and mitigate the increased possibility of losses. Field cases are used to demonstrate the effects of salinity on wellbore instability and losses, and the application of the proposed method. IPS is optimized by managing bidirectional water movement between the NAF and shale formation via semi-permeable membrane. Typically, higher shale dehydration is designed for shallow reactive shale formation with high water content. Whereas, low or no dehydration is desired for deep naturally fractured or faulted formation by balancing osmotic pressure with hydrostatic pressure difference between mud pressure and pore pressure. The simple approach to managing this is as follows: The water activity profile for the shale formation (aw,shale) is developed based on geomechanical and geothermal information The water activity of drilling fluid (aw,mud) is defined through considering IPS and thermal effects The IPS of NAF is manipulated to manage whether shale dehydration is a requirement or should be avoided If the main challenge is wellbore instability in a chemically reactive shale, then the IPS should be higher than the equivalent salinity of shale formation (or aw,shale > aw, mud) If the main challenge is losses into non-reactive, competent but naturally fractured or faulted shale, then IPS should be at near balance with the formation equivalent salinity (or aw, shale ≈ aw, mud) It is important that salt (e.g. calcium chloride – CaCl2) addition during drilling operations is done judiciously. The real time monitoring of salinity variations, CaCl2 addition, water evaporation, electric stability (ES), cuttings/cavings etc. will help determine if extra salt is required. The myth of the negative effects of IPS on wellbore instability and lost circulation is dispelled by analyzing the field data. The traditional Chinese philosophy: "following Nature is the only criteria to judge if something is right" can be applied in this instance of IPS optimization. A simple and intuitive method to manage IPS is proposed to improve drilling performance.


Author(s):  
Yanfeng Zhang ◽  
Haiyang Yu ◽  
Xiaoxue Tang ◽  
Xue Kong ◽  
Xing'ai Li ◽  
...  

Abstract Sapphire substrates with different orientations have wide applications due to their excellent physical, chemical and optical properties. However, the chemical mechanical polishing of sapphire is challenging due to its chemical inertness, extreme hardness and brittleness. Herein, chemical mechanical polishing of A- and C-plane sapphire was systematically studied using α-Al2O3 and silica abrasives and polishing mechanism was analyzed by X-ray photoemission spectroscopy (XPS) and nanoindentation meter. The high MRR selectivity for C-plane sapphire in α-Al2O3 slurry is the synergy of selective hydration of C-plane and stronger crystal structure of A-plane. The low MRR selectivity for C-plane sapphire in silica slurry can be attributed to the formation of Al2SiO5 on both planes which reduced the impact of strong mechanical effect of α-Al2O3 abrasives. To improve the MRR of A-plane sapphire, a new nanocomposite particle with alumina as the core and silica as the soft shell was prepared by an electrostatic self-assembly method. The new composite abrasives combined the mechanical effect of α-Al2O3 abrasives and chemical effect of silica abrasives and demonstrated substantially higher MRR for A-plane sapphire than pure alumina abrasives, pure silica abrasives and physical mixture of alumina+silica abrasives.


2021 ◽  
Author(s):  
◽  
Matthias Meyer

<p>This thesis focusses on a number of topics in surface enhanced Raman scattering (SERS). The aim of the undertaken research was to deepen the general understanding of the SERS effect and, thereby, to clarify some of the disputed issues, among them: What is the origin of the enhancement? What is the physical or chemical effect of 'salt activation' in SERS systems? Can we observe single-molecules using SERS? Can we determine the absorbate's orientation on the surface? In part one (chapters 1-3), as a general introduction, I start with a short overview of the Raman effect and its relation to other molecular spectroscopic effects (such as fluorescence, Rayleigh scattering, etc... ). Following these basic remarks, the surface enhancementmechanisms underlying SERS are explained (as a largely electromagnetic field enhancement) and are investigated theoretically on the canonicalmodel of a nanoscopic dimer of silver spheres. The second part (chapter 4) reports on the experimental investigation (electron microscopy, in-situ Raman measurements) of a typical real SERS system: Lee & Meisel silver colloids. An emphasis is put on the self-limiting aggregation kinetics which is observed in such systems after salt addition. This is also investigated and rationalised by means of Monte-Carlo simulations which are footed on empiric theoretical considerations for the interaction potential. Part three (chapter 5) contains a discussion of the early attempts on singlemolecule SERS and points out the shortcomings of the previously used ultra-lowconcentration approach. In response, an improved andmore rigorous approach is presented: Bi-Analyte SERS. Examplary applications of the technique are discussed. Within these experiments the capability of the technique to prove/disprove (with statistical soundness) single-molecule sensitivity in any SERS system is demonstrated, and single-molecule enhancement factors are derived. The last part (chapter 6) presents computational studies based on densityfunctional theory and its use in the context of Raman spectroscopy and SERS. Of particular interest here were the Raman tensors, their visual representation appropriate in the SERS case, their relation to the relative intensities of Raman peaks, and their modification when the photon energy approaches the electronic resonance of the molecule. Last, but not least, a conclusion chapter is presented, where I highlight what has contributed by the thesis to the general understanding of the SERS effect.</p>


2021 ◽  
Author(s):  
◽  
Matthias Meyer

<p>This thesis focusses on a number of topics in surface enhanced Raman scattering (SERS). The aim of the undertaken research was to deepen the general understanding of the SERS effect and, thereby, to clarify some of the disputed issues, among them: What is the origin of the enhancement? What is the physical or chemical effect of 'salt activation' in SERS systems? Can we observe single-molecules using SERS? Can we determine the absorbate's orientation on the surface? In part one (chapters 1-3), as a general introduction, I start with a short overview of the Raman effect and its relation to other molecular spectroscopic effects (such as fluorescence, Rayleigh scattering, etc... ). Following these basic remarks, the surface enhancementmechanisms underlying SERS are explained (as a largely electromagnetic field enhancement) and are investigated theoretically on the canonicalmodel of a nanoscopic dimer of silver spheres. The second part (chapter 4) reports on the experimental investigation (electron microscopy, in-situ Raman measurements) of a typical real SERS system: Lee & Meisel silver colloids. An emphasis is put on the self-limiting aggregation kinetics which is observed in such systems after salt addition. This is also investigated and rationalised by means of Monte-Carlo simulations which are footed on empiric theoretical considerations for the interaction potential. Part three (chapter 5) contains a discussion of the early attempts on singlemolecule SERS and points out the shortcomings of the previously used ultra-lowconcentration approach. In response, an improved andmore rigorous approach is presented: Bi-Analyte SERS. Examplary applications of the technique are discussed. Within these experiments the capability of the technique to prove/disprove (with statistical soundness) single-molecule sensitivity in any SERS system is demonstrated, and single-molecule enhancement factors are derived. The last part (chapter 6) presents computational studies based on densityfunctional theory and its use in the context of Raman spectroscopy and SERS. Of particular interest here were the Raman tensors, their visual representation appropriate in the SERS case, their relation to the relative intensities of Raman peaks, and their modification when the photon energy approaches the electronic resonance of the molecule. Last, but not least, a conclusion chapter is presented, where I highlight what has contributed by the thesis to the general understanding of the SERS effect.</p>


2021 ◽  
Vol 2021 ◽  
pp. 1-14
Author(s):  
Weijian Zhou ◽  
Song Zhou ◽  
Hongyuan Xi ◽  
Majed Shreka ◽  
Zhao Zhang

The effect of in-cylinder fuel reforming on an n-heptane homogenous charge compression ignition engine has been studied. A dedicated cylinder without a complex control system is proposed for fuel enrichment reforming, which can provide part of the power for the engine. The effects of different reforming species on engine performance and chemical reaction have been simulated by a numerical study. By comparing the combustion characteristics of n-heptane with different equivalence ratios in the reformer cylinder, the optimal n-heptane equivalence ratio has been determined. The enrichment of n-heptane produces sufficient hydrogen (H2) and carbon monoxide (CO), while the hydrocarbon content of the reforming species was low. It was found that the addition of reforming species retards the combustion phase of n-heptane, thereby providing a means of controlling engine performance. In addition, the laminar flame speed and the adiabatic flame temperature of n-heptane increased by adding H2 and CO. Fuel reforming reduced the emission of ethylene, propyne, allene, propylene, butadiene, and nitrogen oxide, but it increased the emissions of acetylene and CO. Moreover, chemical, dilution, and thermodynamic effects of the reforming gas have been studied. The results showed that the chemical effect of the reforming species was less significant than the dilution and thermodynamic effects. These simulation results showed that in-cylinder fuel reforming can effectively improve engine performance and thereby reduce emissions.


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