2D materials such as graphene, MoS
, and hexagonal BN are the most advanced solid lubricating materials with superior friction and anti-wear performance. However, as a typical surface phenomenon, the ...lubricating properties of 2D materials are largely dependent on the surrounding environment, such as temperature, stress, humidity, oxygen, and other environmental substances. Given the technical challenges in experiment for real-time and in situ detection of microscopic environment-material interaction, recent years have witnessed the acceleration of computational research on the lubrication behavior of 2D materials in realistic environments. This study reviews the up-to-date computational studies for the effect of environmental factors on the lubrication performance of 2D materials, summarizes the theoretical methods in lubrication from classical to quantum-mechanics ones, and emphasizes the importance of quantum method in revealing the lubrication mechanism at atomic and electronic level. An effective simulation method based on ab initio molecular dynamics is also proposed to try to provide more ways to accurately reveal the friction mechanisms and reliably guide the lubricating material design. On the basis of current development, future prospects, and challenges for the simulation and modeling in lubrication with realistic environment are outlined.
State estimation represents a cost-effective solution for power distribution networks monitoring. Generally, current methodologies consider only three-phase models disregarding the estimation of the ...Neutral-to-Earth Voltage (NEV) in multi-grounded systems. In order to fulfill this research gap, this paper presents a novel methodology for estimating NEV and system states using PMU measurements gathered from unbalanced distribution grids with radial topology. In the proposed approach, an optimization problem is formulated being the state variables vector formed by multiphase branch currents in rectangular coordinates and also by the neutral current associated to each system bus. With the purpose of using a limited number of PMUs, three-phase active and reactive power pseudomeasurements are treated as inequality constraints for those buses which are not monitored in real time in order to restore the system observability. The objective function is determined based on the weighted least squares considering the phasor measurements obtained from the grid in rectangular coordinates. Computational simulations are carried out using the Kersting’s NEV test feeder and a modified 33-bus system being the estimated values compared with the four-wire three-phase current injection method to validate the presented results. Different loading scenarios, number of PMUs and case studies are presented to show the effectiveness of the proposed method and the impact on the estimation errors.
•A novel state estimation method for four wire three phase systems is proposed.•System states and neutral-to-earth voltages are estimated using phasor measurement units.•A novel optimization model is proposed using a limited number of measurements.•Three phase branch currents and neutral currents are considered as state variables.
Different pre-strain of uniaxial tensile deformation or cold rolling were applied to 0.02C–18Cr–11Ni-0.15 N austenitic stainless steel to investigate the effect of pre-strain stress modes on hydrogen ...embrittlement (HE). The susceptibility to HE was negligibly affected by tensile pre-strain, but it increased with the degree of pre-strain by cold rolling. This resulted from differences in strain distribution, twinning behavior, and changes in H diffusivity arising from the two deformation methods. Homogeneous strain distribution was observed after uniaxial tensile deformation, whereas the deformation was locally concentrated after cold rolling. This led to localized H adsorption to assist crack propagation. While twinning was the main deformation mechanism in the present steel, only the twins formed during cold rolling were vulnerable to stress localization owing to their crystallographic orientation. These twins acted as initiation sites for H-induced cracking and degraded the HE resistance. Finally, H diffusion was less active in tensile-strained samples, and high HE resistance was effectively maintained despite the increase of strength by pre-straining as a consequence.
This article proposes and analyzes a fractional-order susceptible, infectious, susceptible (SIS) epidemic model with saturated treatment and disease transmission by employing four recent analytical ...techniques along with a novel fractional operator. This model is computationally handled by extended simplest equation method, sech–tanh expansion method, modified Khater method, and modified Kudryashov method. The results’ stable characterization is investigated through the Hamiltonian system’s properties. The analytical solutions are demonstrated through several numerical simulations.
The breakthrough of energy storage technology will enable energy distribution and adaptation across space‐time, which is revolutionary for the generation of energy. Optimizing the energy storage ...performance of polymer dielectrics remains challenging via the physical process of electrical breakdown in solid dielectrics is hard to be intuitively obtained. In this review article, the application of computational simulation technologies is summarized in energy‐storage polymer dielectrics and the effect of control variables and design structures on the material properties with an emphasis on dielectric breakdown and energy storage performance are highlighted. The prediction and evaluation of material properties by combining various data analysis methods are reviewed. Finally, the outlook and challenges are discussed based on their current developments. This article covers not only an overview of the state‐of‐the‐art advances of breakdown modeling in energy‐storage polymer dielectrics but also the prospects that provide a new knob to synthesize high energy‐storage polymer dielectrics via computational simulation and a new research paradigm.
Computational simulation can contribute to an added understanding of physical mechanisms of dielectric breakdown, and various models can be used to point out the design direction of materials structure or interpret experimental results. This review is expected to contribute to the development of high‐energy‐storage dielectrics by facilitating a combination of computational methods and experimental studies.
Hydrodynamics of fluid and particles were simulated using a low density ratio-based kinetic theory of granular flow (KTGF) in supercritical methanol (ScM) fluidized beds (FB). Results indicated that ...the fluidization state of the methanol fluid and particle mixtures change progressively from particulate to aggregative fluidization. A transition exists with wavy-like flows near the bottom and churn-like flows at the upper part along bed height, unlike the homogeneous fluidization in atmospheric methanol fluid FB and turbulent fluidization regime with particle strands in ScM FB. The threshold to identify the occurrence of strands was proposed in terms of mean value and standard deviation of solid volume fractions. The frequencies of particle strands increased with increasing methanol fluid temperatures and pressures. The computed fluid volume fractions agreed with experimental data in a supercritical carbon dioxide fluid fluidized bed.
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•A low density ratio-based kinetic theory of granular flow was used.•Fluidization state changes progressively from particulate to aggregative.•Frequencies and existence time fractions of particle strands were predicted.•Effects of fluid pressures, temperatures and inlet velocities were analyzed.
Unspecific peroxygenases (UPOs) are fungal secreted counterparts of the cytochrome P450 monooxygenases present in most living cells. Both enzyme types share the ability to perform selective ...oxygenation reactions. Moreover, the Marasmius rotula UPO (MroUPO) catalyzes reactions of interest compared with the previously described UPOs, including formation of reactive epoxy fatty acids. To investigate substrate epoxidation, the most frequent positions of oleic acid at the MroUPO heme channel were predicted using binding and molecular dynamics simulations. Then, mutations in neighbor residues were designed aiming at modulating the enzyme epoxidation vs hydroxylation ratio. Both the native (wild-type recombinant) MroUPO and the mutated variants were expressed in Escherichia coli as active enzymes, and their action on oleic and other fatty acids was investigated by gas chromatography–mass spectrometry in combination with kinetic analyses. Interestingly, a small modification of the channel shape in the I153T variant increased the ratio between epoxidized oleic acid and its additionally hydroxylated derivatives. A fully opposite effect was attained with the double I153F/S156F variant that completely abolished the ability of the MroUPO to epoxidize oleic acid (while no activity was detected for the I153V variant). The rationale for these results was revealed by the substrate positioning in the above computational simulations, which predict a shorter distance between the oleic acid double bond and the oxygen atom of the peroxide-activated heme (compound I) in the I153T variant than in the native enzyme, promoting epoxidation. In contrast, the I153F/S156F double mutation fully prevents the approach of oleic acid in the bent conformation required for double-bond epoxidation, although its (sub)terminal hydroxylation was predicted and experimentally confirmed. The I153T mutation also increased the UPO selectivity on polyunsaturated fatty acid epoxidation, strongly reducing the ratio between simple epoxides and their hydroxylated derivatives, with respect to the native UPO.
•Pumpkin seeds (PS) acts as effective inhibitors for aluminum corrosion.•The adsorption of PS followed the Langmuir isotherm model.•Adsorption on the surface is analyzed by AFM and SEM/EDAX, ...techniques.•Theoretical data provide in-depth understanding of the experimental results.
For the aeronautics industry, constraints of mechanical strength are paramount. Aluminum and its alloys are widely used for various household and industrial applications. Among the various established and identified aluminum alloys, 7075 alloy, which is an aluminum-zinc, acquires the best mechanical strength. However, this is sensitive to certain localized corrosion phenomena such as pitting corrosion. Pumpkin seeds (PS) were evaluated as a corrosion inhibitor for aluminum alloy 7075-T6 in 3.5% NaCl solution using electrochemical, surface and theoretical studies. PS showed highest inhibition efficiency of 95% at its 1 g/L concentration (298 K). Furthermore, the Pumpkin seeds (PS) acted as a cathodic inhibitor. Adsorption of Pumpkin seeds (PS) on Aluminum alloy surface corresponds to the Langmuir adsorption isotherm. Surface studies carried out using scanning electron microscope (SEM), atomic force microscope (AFM) and X-ray Diffraction (XRD) provide good supports to the polarization and EIS studies. Surface studies also validate that PS becomes effective by adsorbing on the metallic surface. Using DFT investigation, it was derived that effectiveness of the major phytochemical followed the sequence: 9,12-Octadecadienoic acid (Z, Z)-> linoleic acid > palmitic acid.
This research paper investigates the numerical solutions of the nonlinear fractional Ostrovsky equation through five recent numerical schemes (Adomian decomposition (AD), El Kalla (EK), Cubic ...B-Spline (CBS), extended Cubic B-Spline (ECBS), exponential Cubic B-Spline (ExCBS) schemes). We investigate the obtained computational solutions via the generalized Jacobi elliptical functional (JEF) and modified Khater (MK) methods. This model is considered as a mathematical modification model of the Korteweg–de Vries (KdV) equation with respect to the effects of background rotation. The solitary solutions of the well-known mathematical model (KdV equation) usually decay and are replaced by radiating inertia gravity waves. The obtained solitary solutions show the localized wave packet as a persistent and dominant feature. The accuracy of the obtained numerical solutions is investigated by calculating the absolute error between the exact and numerical solutions. Many sketches are given to illustrate the matching between the exact and numerical solutions.
The anticorrosive effect of an epoxy resin (DGEDDS-MDA) based on diglycidyl ether 4, 4′-dihydroxydiphenylsulfone (DGEDDS) and 4,4′-Methylene dianiline (MDA) with and without titanium dioxide (TiO2) ...for carbon steel (CS) corrosion in 3% NaCl solution is reported. The composite of DGEDDS-MDA with TiO2 is designated as DGEDDS-MDA-TiO2. Electrochemical and computational techniques were used to demonstrate the anticorrosive effectiveness of the DGEDDS-MDA and its TiO2 composite. The effect of UV irradiation (for 2000 h) on effectiveness of DGEDDS-MDA and its TiO2 composite showed that the presence of the TiO2 appreciably enhanced the corrosion inhibition effect of DGEDDS-MDA. In order to reinforce the experimental findings, reactivity of DGEDDS-MDA with metallic surface was also studied using computational techniques. DFT study revealed that DGEDDS-MDA interacts strongly with metal surface using donor-acceptor mechanism. Polar functional groups (–OH & –N–) and aromatic rings act as adsorption centers. MD simulations study showed that DGEDDS-MDA adsorbs using flat orientation and its orientation is greatly affected by TiO2.
•A composite of epoxy resin and TiO2 is tested as anticorrosion materials for CS in 3% NaCl.•Electrochemical and computational techniques were used to study the anticorrosive effectiveness•The effect of UV irradiation (for 2000 h) on effectiveness of DGEDDS-MDA and its TiO2 composite.•MD simulations study showed that DGEDDS-MDA adsorbs using flat orientation•Orientation of epoxy resin is greatly affected by TiO2.
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