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This paper presents some new criteria for partial exponential stability of a slow-fast nonlinear system with a fast scalar variable using periodic averaging methods. Unlike classical averaging techniques, we construct an averaged system by averaging over this fast scalar variable instead of the time variable. We then show that partial exponential stability of the averaged system implies partial exponential stability of the original one. As some intermediate results, we also obtain a new converse Lyapunov theorem and some perturbation theorems for partially exponentially stable systems. We then apply our established criteria to study remote synchronization of Kuramoto-Sakaguchi oscillators coupled by a star network with two peripheral nodes. We analytically show that detuning the natural frequency of the central mediating oscillator can increase the robustness of the remote synchronization against phase shifts.

Poisson Voronoi (PV) tessellations as artificial microstructures are widely used in investigations of material deformation behaviors. However, a PV structure usually describes a relative homogeneous field. This work presents a simple numerical method for generating 2D/3D artificial microstructures based on hierarchical PV tessellations. If grains/particles of a phase cover a large size span, the concept of “artificial phases” can be used to create a more realistic size distribution. From case to case, detailed microstructural features cannot be directly achieved by commercial or free softwares, but they are necessary for a deep or thorough study of the material deformation behavior. PV tessellations created in our process can fulfill individual requirements from material designs. Another reason to use PV tessellations is due to the limited experimental data. Concerning the application of PV microstructures, four examples are given. The FE models and results will be presented in consecutive works, i.e. “part II: applications”., Deutsche Forschungsgemeinschaft, Projekt DEAL

This work reports mathematical modeling and analysis of mixed convection flow of nanofluids with stagnation point by a stretching cylinder. Carbon nanotubes are dispersed as nanomaterial in the baseliquid of water. Heat transfer characteristics are explored through Newtonian heating. Transformation method is employed in order to obtain ODEs. Furthermore series solutions are developed. Variations in flow, temperature, skin friction and local Nusselt number under influential variables have been plotted. It is elaborated that fluid velocity intensifies with rise in curvature parameter, conjugate parameter, mixed convection parameter, nanoparticle volume fraction and velocity ratio parameter. Similarly decay in temperature of the fluid is analyzed for higher velocity ratio parameter while it enhances with increment in nanoparticle volume fraction, mixed convection parameter, conjugate parameter and curvature parameter. Skin friction can be minimized via higher estimations of mixed convection parameter, velocity ratio parameter and nanoparticle volume fraction. Heat transfer rate or cooling process (Nusselt number) is regulated through higher conjugate and curvature parameters. During comparative analysis of SWCNTs with MWCNTs, better performance is shown by SWCNTs. Skin friction coefficient in limiting sense is also compared with previously published articles.

With ultra-high thermal significances, the nano-materials present some fundamental applications in many thermal engineering eras, mechanical and chemical engineering and modern technology. For sustainable development of industrial growth of a country, the enhancement in energy production and resources become one of the most fundamental challenges for scientists. This analysis presents the thermal aspects of dust nanoparticles in a dusty nano-material for the interaction of transverse magnetic field come across an expanding surface. The conjunction of Maxwell model thermal conductivity influences the characteristic of thermal properties that is helpful to enrich the heat transport phenomena. A mathematical model is prepared by considering metal nano-material (copper and silver) in association with the conventional fluid water. The numerical treatment is deployed for the solution of the complex nonlinear problem characterized by dust phase material and fluid transformed governing equations. The transport of heat energy is affected by the transient behavior of the volume fraction, dust particle number density in conjunction with magnetic field. However, the key features of the outcomes for the characterizing parameters are lubricated through graphs and simulated numerical values for the rate coefficients are presented in table that leads to the validation work with the earlier investigation. An increment in heat transfer rate is noted with suspension of copper nanoparticles in the dusty fluid while heat transfer reduces in case of silver nanoparticles. The nanoparticles temperature enhanced with interaction parameter and specific heat ratio. The current analysis has a greater impact in bio-medical since i.e. the blood flow within the artery as well as several industrial and engineering applications. All these aspects depend upon the nanoparticles particle size therefore the dust and nanoparticles proposed here are spherical.

The objective of this work is to offer sufficient conditions for the oscillation of all solutions of fourth-order delay differential equations with non-canonical operator. By establishing sufficient conditions for nonexistence of positive solutions, we attain oscillation of all solutions of the studied equations. Our results substantially extend and complement a number of existing ones.

Laser surface hardening provides for many advantages in terms of flexible production due to very localized and controlled energy input into the material. Laser processing offers the possibility to treat surfaces in order to locally strengthen the areas that are prone to fatigue cracking. It is well known that laser energy absorption depends on many parameters, e.g., the surface structure and the surface orientation. The incident angle of the laser beam plays a key role in this regard. When complex geometries like crankshaft fillets are treated, the surface cannot be considered a series of flat surfaces. Obviously, this leads to locally varying degrees of energy absorption. In the present work, curved surface structures were chosen in order to analyze the impact of the geometrical characteristics on surface and subsurface material properties after laser treatment. Microstructure evolution generally was found to be similar for flat and curved geometries. However, even if higher absorption in the groove due to the illumination at larger incident angles was expected, the outer parts of the curved geometry were not fully hardened. Thus, the increased effective length of the complex geometry-treated and the larger heat-affected volume are expected to have a more dominant influence on the final appearance of the subsurface microstructure. Eventually, for austenitization of the complete illuminated surface volume, the energy density needs to be increased.

The thermal conductivity of the soil skeleton λs is an extremely important parameter from the point of view of the correct assessment of soil overall/effective conductivity. This work introduces the concept of “local thermal conductivity fluctuation” which characterizes the microscale variation of conductivity within the solid phase. It is proposed to link the “local fluctuation” of thermal conductivity λ with the soil texture – the information that is available at the scale of engineering applications. It was possible to relate the skeleton thermal conductivity with the grain size distribution of the soil. Finally, based on a large series of numerical simulations, the paper provides four triangle diagrams (at different organic matter contents: 0%, 2%, 4% and 6%) relating the value of λs with volume fraction of individual soil separates. This result is extremely important from the practical point of view. One can quickly evaluate λs value provided that information on the grain size distribution and organic matter content is available.

The absence of satisfactory results that address the stability analysis of nonlinear incommensurate Fractional-order Difference Systems (FoDSs) as well as the impossibility of establishing a proper Lyapunov function that helps us to reveal any stability outcome for those systems, are considered some significant nonlinear problems that should be taken into account. To overcome such dilemmas, the present work provides some novel convenient conditions that can be utilized to ensure the asymptotic stability of those systems. In particular, through utilizing some features of the Z-transform scheme, we intend to propose certain results that aim to reveal the stability of the nonlinear incommensurate fractional-order difference system formulated in the sense of the Caputo difference operator. These novel results are completely confirmed by demonstrating the stability of the numerical solutions for two nonlinear difference systems with incommensurate fractional-orders.

The separation of azeotropic mixtures, particularly, pressure sensitive azeotropes is intriguing, challenging, and inevitable in chemical industries in comparison to pressure insensitive azeotropic mixtures. The main bottleneck for separating pressure sensitive azeotropes lies in the pressure selection and sequencing of distillation columns. A conundrum in pressure swing distillation for both minimum and maximum boiling azeotropes primarily about the feasibility of column configurations has been discussed in this work. The two column configurations, Low pressure Column-High Pressure Column (LPC-HPC) and High Pressure Column-Low Pressure Column (HPC-LPC) are found to be dependent on the feed composition, type of azeotrope (whether, minimum or maximum), and the effect of pressure on azeotropic composition. This article has explored concomitantly pressure swing distillation technique (continuous one) and the effect of various feed compositions on the column sequencing and process feasibility. A comprehensive strategy for both minimum and maximum boiling azeotropes has been proposed depending upon the effect of pressure on azeotropic composition. Two example case studies have been also presented in support of the proposed strategies for pressure swing distillation technique.

In this analysis, the cubic B-spline method is employed for constructing the approximate solutions of a class of fractional two-point boundary value problems. These fractional problems are expressed in terms of the conformable fractional derivative approach. More deeply, a class of conformable Lane-Emden model is considering and modifying with singularities. Many numerical applications are presented and discussed to exhibit the feasibility and efficiency of the procedure involved in both linear and non-linear cases. The numerical findings are quite similar to those of the exact solutions as well as require relatively less computational work. Latterly, remarks and future research work are provided.

Sustainable solutions for hydrogen production, such as dye-sensitized photoelectrochemical cells (DS-PEC), rely on the fundamental properties of its components whose modularity allows for their separate investigation. In this work, we design and execute a high-throughput scheme to tune the ground state oxidation potential (GSOP) of perylene-type dyes by functionalizing them with different ligands. This allows us to identify promising candidates which can then be used to improve the cell's efficiency. First, we investigate the accuracy of different theoretical approaches by benchmarking them against experimentally determined GSOPs. We test different methods to calculate the vertical oxidation potential, including GW with different levels of self-consistency, Kohn–Sham (KS) orbital energies and total energy differences. We find that there is little difference in the performance of these methods. However, we show that it is crucial to take into account solvent effects as well as the structural relaxation of the dye after oxidation. Other thermodynamic contributions are negligible. Based on this benchmark, we decide on an optimal strategy, balancing computational cost and accuracy, to screen more than 1000 dyes and identify promising candidates which could be used to construct more robust DS-PECs., The alignment of the GSOP, calculated with the adiabatic approach for large number of dyes, with the limitations of a hypothetical system – the CB edge of TiO2 semiconductor and highest oxidation potential of Ru-based WOC.

In this paper, a computational method for solving for the one-dimensional heat conduction temperature field is proposed based on a data-driven approach. The traditional numerical solution requires algebraic processing of the heat conduction differential equations, and necessitates the use of a complex mathematical derivation process to solve for the temperature field. In this paper, a temperature field solution model called HTM (Hidden Temperature Method) is proposed. This model uses an artificial neural network to establish the correspondence relationship of the node temperature values during the iterative process, so as to obtain the "Data to Data" solution. In this work, one example of one-dimensional steady state and three examples of one-dimensional transient state are selected, and the calculated values are compared to those obtained by traditional numerical methods. The mean-absolute error(MAE)of the steady state is only 0.2508, and among the three transient cases, the maximum mean-square error(MSE) is only 2.6875, indicating that the model is highly accurate in both steady-state and transient conditions. This shows that the HTM simulation can be applied to the solution of the heat conduction temperature field. This study provides a basis for the further optimization of the HTM algorithm.

Understanding nucleate pool boiling heat transfer and, in particular the accurate prediction of conditions that can lead to critical heat flux, is of the utmost importance in many industries. Due to the safety issues related to the nuclear power plants, and for the efficient operation of many heat transfer units including fossil fuel boilers, fusion reactors, electronic chips, etc., it is important to understand this kind of heat transfer. In this paper, a comprehensive review of analytical and numerical work on nucleate pool boiling heat transfer is presented. In order to understand this phenomenon, existing studies on boiling heat transfer coefficient and boiling heat flux are also discussed, as well as characteristics of boiling phenomena such as bubble departure diameter, bubble departure frequency, active nucleation site density, bubble waiting and growth period and their impact on pool boiling heat transfer.

In this work, we consider a coupled nonlinear viscoelastic Kirchhoff equations with degenerate damping, dispersion and source terms. Under suitable hypothesis, we will prove that when the initial data are large enough (in the energy point of view), the energy grows exponentially and thus so the $ L^{2(p+2)} $-norm.

We devote our interest in this work to investigate the sufficient conditions for the existence, uniqueness, and Ulam-Hyers stability of solutions for a new fractional system in the frame of Atangana-Baleanu-Caputo fractional operator with multi-parameters Mittag-Leffler kernels investigated lately by Abdeljawad (Chaos: An Interdisciplinary J. Nonlinear Sci. Vol. 29, no. 2, (2019): 023102). Moreover, the continuous dependence of solution and $ \delta $-approximate solutions are analyzed to such a system. Our approach is based on Banach's and Schaefer's fixed point theorems and some mathematical techniques. In order to illustrate the validity of our results, an example is given.

Na0.44MnO2 (NMO) with tunnel-type structure is a reference cathode material for rechargeable Na-ion batteries. In this work, the structural, electrochemical and computational investigations are combined to study the properties of this material, particularly in reference to Cu doping in the structure. For the first time, molecular dynamics (MD) is used to obtain insights into the mechanisms of Na+ diffusion in NMO, highlighting the role of structural modifications and Na distribution. The main results allow to investigate the implication of high temperature treatments and the effect of Cu doping on the defect and transport properties of the material with tunnel-type structure. From an experimental point of view, the subtitution promotes an increased stability of the material upon cycling and an improved capacity particularly at higher discharging rates, that stems from the synergistic effects of composition, morphology and multiple polymorphs in the sample.

This study aims to improve the evaluation of residual oil saturation in water flooded zones based on the material balance model (MBM) with variable multiple for injected water. We investigated the change patterns of rock-electro parameters during waterflooding through the analysis of displacement tests. Our work differentiated the waterflooding into numerous displacement processes and accordingly propose an improved time-differentiated variable multiple MBM. The calculation results of the improved model are more consistent with the displacement experiment data of cores. Furthermore, the improved method was integrated into the comprehensive interpretation platform of offshore logging to analyze water flooded zones of a well in the A oilfield. As a result, the residual oil saturation calculated is in close agreement with the results of experiments on cores. Our results indicate that the time-differentiation and variable multiplier for injected water can effectively enhance the assessment accuracy of the residual oil saturation of water-flooded zones.

Mineral surfaces adsorb water to extreme densities and corresponding low chemical potentials. This results in a dual effect in terms of hydrate. Water and slightly polar components adsorb directly on mineral surfaces and generate efficient conditions for hydrate nucleation. But due to the extremely low chemical potential of adsorbed water the hydrate nuclei formed towards mineral surfaces have to either detach from the vicinity of mineral surfaces, or be bridged by structured water in a dynamic attachment of hydrate cores some few nm outside mineral surfaces. During transport of gas (CH4, gas mixtures, CO2) the conventional water dew-point analysis will typically result in a substantially higher acceptable water concentration as compared to the concentration for adsorption of water from gas to rust surface. Direct formation of hydrate from water dissolved in gas is thermodynamically feasible, as discussed in open literature. In this work we demonstrate that it is also feasible in terms of mass transport. A new theory for enthalpy of hydrate dissociation has been extended to also direct hydrate formation from water dissolved in gas. The remaining question is whether direct hydrate formation from gas is also feasible in terms of transporting the hydrate formation heat away through a heat insulating medium. We propose further research strategies to enlighten this issue. Addition of glycols to critical points in processing of gas or transport is already in use by companies like for instance EQUINOR. There is, however, a need for more work on how efficient it is and if it can also be used for multiphase transport of hydrocarbons with significant water cut. Some research activities are in progress and briefly outlined here.

In this work, a numerical study of the solutions of the parabolic and hyperbolic equations of heat conduction with the same physical parameters is carried out and a comparative analysis of the results obtained is carried out. The mathematical formulation of the problem is discussed. The action of the laser is taken into account through the source function, which was chosen as a double femtosecond laser pulse. In the hyperbolic equation, in contrast to the parabolic one, there is an additional parameter that characterizes the relaxation time of the heat flux. In addition, the source of the hyperbolic equation contains an additional term - the derivative of the power density of the source of the parabolic equation. This means that the temperature of the sample is influenced not only by the power density of the source, but also by the rate of its change. The profiles of the sample temperature at different times and its dynamics at different target depths are shown. The calculations were carried out for different time delays between pulses and for different relaxation parameters.

In this work we analyze how the spectrum of primordial scalar perturbations is modified, within the emergent universe scenario, when a particular version of the Continuous Spontaneous Localization (CSL) model is incorporated as the generating mechanism of initial perturbations, providing also an explanation to the quantum-to-classical transition of such perturbations. On the other hand, a phase of super-inflation, prior to slow-roll inflation, is a characteristic feature of the emergent universe hypothesis. In recent works, it was shown that the super-inflation phase could generically induce a suppression of the temperature anisotropies of the CMB at large angular scales. We study here under what conditions the CSL maintains or modifies these characteristics of the emergent universe and their compatibility with the CMB observations., Comment: 15 pages, 5 figures. Some references added. Version accepted in EPJC

Velocity fields in flow in permeable media are of great importance to many subsurface processes such as geologic storage of CO2 , oil and gas extraction, and geothermal systems. Steady-state flow is characterized by velocity fields that do not change significantly over time. The flow field transitions to a new steady state once it experiences a disturbance such as a change in flow rate or in pressure gradient. This transition is often assumed to be instantaneous, which justifies the expression of constitutive relations as functions of instantaneous phase saturations. This work examines the evolution of velocity fields in a surrogate quasi-2D permeable medium using a microfluidic device, a microscopy system, and a high-speed camera. Tracer particles are injected into the medium along with Deionized water. The evolution of the velocity field is examined by tracing these particles in the captured images using the standard high-density particle image velocimetry algorithm founded on cross-correlation. The results suggest that the transition between steady states for an incompressible fluid takes a finite and non-negligible amount of time that is independent of the magnitude of the change in pressure gradient. The existence of transient states and the nature of the response during these states are readily interpreted by the principle of least action where flow gradually establishes an optimal configuration such that energy dissipation is minimized. The findings provide evidence against the applicability of the assumption that flowing phases relax instantaneously to their steady states and, hence, against the accuracy of the classical multiphase extension of Darcy’s law. Cited as: Sun, J., Li, Z., Furtado, F., Aryana, S. A. A microfluidic study of transient flow states in permeable media using fluorescent particle image velocimetry. Capillarity, 2021, 4(4): 76-86, doi: 10.46690/capi.2021.04.03

The needle of the industrial sewing machine is its most important part. During the sewing process, the needle is subjected to various actions and interactions between these actions. One of the factors that are most related to these interactions is the lateral elastic resistance – spring effect – of the sewn fabric on the needle during its penetration in the layers of fabric. In the present work, this effect has been investigated via a special formula, where the spring constant is incorporated. It was found that the equivalent length coefficient of the sewing needle ( γ ) ranged between 0.7, where the lower end of the needle still has not penetrated the fabric and 2, where the lower end has already penetrated the fabric. The elastic stability factor (η) was changed from 2.46 to 20.35, to create a critical axial compressive load P cr = 5 for a 39 cN of the sewing needle. This means that the spring constant (S) changed from S = 0 to S = ∞ , which enhanced the critical load by 8 folds. For S = 0 , the angle has two options, the first is ≤ π 2 λ l o and the second ≥ π 2 λ l \ o . The values of γ , η, and P cr for ( λ l ) o were not reasonable, while values of these variables for λ l \ o were acceptable. The future vision of the present work is to design and construct a stand to experimentally check the theoretical work suggested in this paper and to find its experimental values.

A heat pipe residual heat removal system is proposed to be incorporated into the reactor driven subcritical (RDS) facility, which has been proposed by MIT Nuclear Reactor Laboratory for testing and demonstrating the Fluoride-salt-cooled High-temperature Reactor (FHR). It aims to reduce the risk of the system operation after the shutdown of the facility. One of the main components of the system is an air-cooled heat pipe heat exchanger. The alkali-metal high-temperature heat pipe was designed to meet the operation temperature and residual heat removal requirement of the facility. The heat pipe model developed in the previous work was adopted to simulate the designed heat pipe and assess the heat transport capability. 3D numerical simulation of the subcritical facility active zone was performed by the commercial CFD software STAR CCM + to investigate the operation characteristics of this proposed system. The thermal resistance network of the heat pipe was built and incorporated into the CFD model. The nominal condition, partial loss of air flow accident and partial heat pipe failure accident were simulated and analyzed. The results show that the residual heat removal system can provide sufficient cooling of the subcritical facility with a remarkable safety margin. The heat pipe can work under the recommended operation temperature range and the heat flux is below all thermal limits. The facility peak temperature is also lower than the safety limits.

In this work, we consider a fuzzy delay differential system with non-instantaneous impulses and investigate the existence, uniqueness and total controllability results. Non-linear functional analysis, Banach fixed point theorem and fuzzy theory are the main techniques to establish these results. In support, an example is given to validate the obtained analytical outcomes.

The fast-inertial-relaxation engine (FIRE) has proven to efficiently find local minima of potential energies or related penalty functions although its implementation requires only few, additional lines of code in a molecular-dynamics or steepest-descent program. So far, FIRE has been predominantly applied to particle-based or low-dimensional problems. In this work, we demonstrate that it can also benefit the solution of boundary-value problems. Towards this end, we study the mechanical contact between an elastic body and a rigid indenter of varying complexity by augmenting Green's function molecular dynamics (GFMD) with FIRE. We find a rather remarkable speedup, which can be further enhanced when choosing the masses associated with the eigenmodes of the free elastic solid appropriately. For the investigated adhesive and randomly rough indenter with typical system size, 100 mass-weighted FIRE-GFMD iterations suffice to relax the excess energy to ${10}^{\ensuremath{-}3}$ of its original value. The standard GFMD method needs 25 times more iterations. For the investigated problems, FIRE-GFMD even appears to slightly outperform conjugate-gradient based optimization.

Transition metal dichalcogenides (TMDCs) are promising materials for applications in nanoelectronics and correlated fields, where their metallic edge states play a fundamental role in the electronic transport. In this work, we investigate the transport properties of MoS$_2$ zigzag nanoribbons under a butadiene (C$_4$H$_6$) atmosphere, as this compound has been used to obtain MoS$_2$ flakes by exfoliation. We use density functional theory combined with non-equilibrium Green's function techniques, in a methodology contemplating disorder and different coverages. Our results indicate a strong modulation of the TMDC electronic transport properties driven by butadiene molecules anchored at their edges, producing the suppression of currents due to a backscattering process. Our results indicate a high sensitivity of the TMDC edge states. Thus, the mechanisms used to reduce the dimensionality of MoS$_2$ considerably modify its transport properties.

The ability to measure the very high heat fluxes that typically occur during the hypersonic re-entry phase of space vehicles is generally considered a subject of great importance in the aerospace field. Most of the sensors used for these measurements need to be checked periodically and re-calibrated accordingly. Another bottleneck relates to the need to procure thermal sources that are able to generate reliable reference heat fluxes in the range between 100 and 1000 kW/m2 (as order of magnitude). In the present study, a method is presented by which, starting from a calibration system with a capacity of approximately 500 kW/m2 only, heat fluxes in the range of interest for hypersonic applications are generated. The related procedure takes advantage of established standards for the characterization of a radiative heat flux. It also builds on the hybrid radiative-convective nature of typical hypersonic heat fluxes and the yet poorly explored possibility to use convective sources of heat to produce high-intensity fluxes. The reliability of such a strategy has been tested using a high enthalpy supersonic flow facility relying on an electric arc-heater and pure Nitrogen as work gas. Stagnation-point heat fluxes have been successfully measured (with reasonable accuracy) in the range between 600 and 1500 kW/m2 for values of the centerline enthalpy spanning the interval from to 6 to 24 MJ/kg.

Polymer gel has attracted extensive attention as an effective agent for profile control as development enters middle and late stage. However, formation heterogeneity and the unclear mechanism of gel profile with different strength severely limits the displacement effect. In this work, microstructure and viscosity of polymer gels with different concentrations were characterized. The injection behavior experiments were carried out to calculate breakout pressure and plugging rate. The core flooding experiments were performed to obtain the remaining oil saturation field and recovery rate. The results illustrated that the gel viscosity increased and the plugging ability enhanced as the polymer concentration increased; Meanwhile, type C was determined as the best strength for displacement in heterogeneous formation; From oil displacement results, the gel fluidity decreased and blocking formed in high permeability reservoir, which forcing subsequent water divert to the low permeability reservoir. As a result, the swept volume expanded and the oil recovery enhanced. The fruitful works throw light on the mechanism of gel profile control and provide strong technical support for enhanced oil recovery in heterogeneous formation.

Carbon quantum dots (QDs) are an active subject of research in many areas of science and engineering for various applications. The present work reports the first occurrence of a carbon–cadmium sulfide core-shell QD prepared by an extremely simplified wet chemical approach where the CdS shell plays the role of a fluorescence quencher to the carbon core. The quenching effect was confirmed by fluorescence spectroscopy (steady-state and lifetime). These QDs stand as a potential candidate for sensing and imaging applications.

Utilizing the heat energy of exhaust gases is a promising application of thermoelectric generator (TEG), which can convert low grade thermal energy into electricity. The annular thermoelectric generator (ATEG) is thought to be much more feasible for cylindrical heat source compared to the flat-plate thermoelectric generator (FTEG) in reference to the compatibility. Nevertheless, the quantitative comparison is lacking to clarify the prevalent geometry of TEG for cylindrical heat source. In this work, the performances of ATEG and FTEG are compared in detail with varying inlet temperature, velocity and the convective heat transfer coefficient when cylindrical heat source is applied. The turbulent heat source is described by the standard κ - e functions together with the two-equation heat transfer model, while the output power and conversion efficiency of the ATEG and FTEG are calculated by solving the coupled thermo-electric equations. Our results showed that the output powers and the conversion efficiencies of ATEG and FTEG both increase with the increase of the inlet velocity, temperature, and the convective heat transfer coefficient. The conversion efficiency of ATEG is always higher than that of FTEG. The conversion efficiency of ATEG becomes even larger than that of FTEG when inlet temperature and/or convective heat transfer coefficient are relatively larger. In contrast, the output power of ATEG has no obvious difference with that of FTEG. This study addressed the condition when the ATEG has obvious advantage compared to the FTEG with cylindrical heat source applied. Our results suggest the annular TEG is better choice for cylindrical hot source especially when the inlet temperature and/or convective heat transfer coefficient are relatively larger. It could be a helpful guide for choosing suitable geometry of TEGs for energy harvesting in complex condition.

It has been experimentally observed that the Zn–Cu–Ti zinc alloy shows a strong influence of strain rate and temperature on its plastic behavior. A significant change in the material response is seen with relatively small strain rate variations or temperature. In this work, these effects are addressed through the Cazacu–Plunket–Barlat 2006 (CPB-2006) yield criterion and the Johnson–Cook hardening law. The tests were carried out over the three main directions: rolling, diagonal, and transversal. Three strain rate conditions (0.002, 0.02, and 0.2 s−1) and three temperatures (20, 60, and 80 °C) were tested. Although the experimental results exhibit a significant influence of the strain rate and temperature on stress–strain curves for all tested directions, such two variables do not practically affect the Lankford coefficients. The proposed model calibration procedure is found to describe the material responses properly under the studied conditions.

Low permittivity microwave dielectric ceramics (MWDCs) are attracting great interest because of their promising applications in the new era of 5G and IoT. Although theoretical rules and computational methods are of practical use for permittivity prediction, unsatisfactory predictability and universality impede rational design of new high-performance materials. In this work, based on a dataset of 254 single-phase microwave dielectric ceramics (MWDCs), machine learning (ML) methods established a high accuracy model for permittivity prediction and gave insights of quantitative chemistry/structure-property relationships. We employed five commonly-used algorithms, and introduced 32 intrinsic chemical, structural and thermodynamic features which have correlations with permittivity for modeling. Machine learning results help identify the permittivity decisive factors, including polarizability per unit volume, average bond length, and average cell volume per atom. The feature-property relationships were discussed. The optimal model constructed by support vector regression with radial basis function kernel was validated its superior predictability and generalization by verification dataset. Low permittivity material systems were screened from a dataset of ∼3300 materials without reported microwave permittivity by high-throughput prediction using optimal model. Several predicted low permittivity ceramics were synthesized, and the experimental results agree well with ML prediction, which confirmed the reliability of the prediction model.

This work investigated the acoustic pressure distribution and relevant cavitation area of the dual-frequency ultrasonic field (DUF) in magnesium melt using numerical simulation. Associated experiments were also implemented to understand the grain refinement of DUF. DUF weakens the acoustic attenuation and then enlarges the potential cavitation area than the single-frequency ultrasonic field (SUF). Such improvement promotes its grain refinement efficiency, which is 17.7% and 24% higher than 15 kHz and 20 kHz SUF, respectively. Both yield strength and ultimate tensile strength are improved by DUF melt treatment. The improvement of mechanical properties for ultrasonic melt treated alloy is attributed to the grain refinement and the texture evolution. To optimize the grain refinement of DUF melt treatment, choosing the appropriate input acoustic pressure ratio is important. Under the premise of relevant symmetrical distribution of the cavitation area, increasing the acoustic pressure input for 15 kHz ultrasonic is beneficial to improve the grain refinement efficiency.

Ribbon lattices are kind of transition systems in between one and two dimensions, and their study is crucial to understand the origin of different emerging properties. In this work, we study a Lieb ribbon lattice and the localization–delocalization transition occurring due to a reduction of lattice distances (compression) and the corresponding flat band deformation. We observe how above a critical compression ratio the energy spreads out and propagates freely across the lattice, therefore transforming the system from being a kind of insulator into a conductor. We implement an experiment on a photonic platform and show an excellent agreement with the predicted phenomenology. Our findings suggest and prove experimentally the use of compression or mechanical deformation of lattices to switch the transport properties of a given system.

The performance and durability of orthopedic implants are mainly determined by their surface integrity. Ball burnishing (BB) is a kind of finishing treatment which improves the surface dependant mechanical properties of metallic biomaterials. In this work, this process was applied on the flat surface of 316L stainless steel to enhance its microhardness and wear resistance. The mathematical modeling of microhardness Vickers was performed by the response surface method (RSM) based on Box–Behnken plans, and the optimum regime was applied under several passes to investigate the effect of number of passes (i) on the surface properties. The evolution of microhardness, nano-hardness and elastic modulus was then examined. Wear resistance, in terms of variation of Coefficient of friction and wear loss, was also investigated. Finally, XRD analysis was performed to evaluate any change in structure produced by BB. The results show that burnishing treatment permits to raise the microhardness by up to 38.3% and to reduce the wear loss by up to 65.2%. Nano-hardness and elastic modulus were also increased after application of the process. XRD patterns indicate that grain refinement was induced with no change in phases composition. The number of passes is proved effective in increasing the depth of the hardened layer, which influences subsequently on the frictional behavior of 316L stainless steel.

As phase change materials (PCMs), Sb–Te based alloys have received a lot of attention in recent years. However, the mechanism for the formation of the alloy and its application as PCMs is not fully understood. The high-throughput First-principles calculations and melt-quench ab initio molecular dynamics simulations were adopted to explore the microstructure and properties of Sb–Te alloys in this work. The hetero-atomic interaction and disordered distribution make Sb–Te alloy with layered microstructure more stable. Although Sb1−xTex solid solution is the metastable phase, it is still stable for PCMs in the certain ranges of solid solubility (0.4

This paper studied lap welding on 1.5 mm AA6061 and AA5182 aluminum alloy sheets with laser beam circular oscillation. The joint form is commonly used in new energy car bodies to achieve the purpose of reducing weight and combining the strength and toughness of two aluminum alloys. The effects of oscillating frequency on the weld formation, grain structure and mechanical properties were mainly investigated combining with numerical simulation. The asymmetric weld morphology and the influence of frequency on weld formation were studied by energy distribution, temperature histories and keyhole depth. The increase of frequency can cause the actual heat input, linear energy and keyhole depth to decrease, resulting in the molten pool to change from an elongated droplet shape to a nearly elliptic shape, and the transition from keyhole mode to conduction mode, thus the grain size gradually reduced. The columnar crystals width in the left and right sides were different, attributing to the different solidification parameters at the both sides of the same isotherm. The tensile strength can reach the maximum value of 156 MPa, where the lap surface was the main source of crack. The dilution of the strengthening phase and the grain size together affected the internal microhardness distribution of the weld. A wide HAZ (heat affected zone) was presented in the oscillating weld. This work can provide a research basis for the optimization of the weld formation, grain structure and properties of this kind of joint, which has potential application in the new energy vehicles.

The uncertainty principle is known as a foundational element of quantum theory, providing a striking lower bound to quantify our prediction for the measured result of two incompatible observables. In this work, we study the thermal evolution of the entropic uncertainty bound in the presence of quantum memory for an inhomogeneous four-qubit spin-star system that is in the thermal regime. Intriguingly, our results show that the entropic uncertainty bound can be controlled and suppressed by adjusting the inhomogeneity parameter of the system.

Geoscientific model development : GMD 14(11), 7133-7153 (2021). doi:10.5194/gmd-14-7133-2021, Published by Copernicus, Katlenburg-Lindau

The growth habit of natural gas hydrate in formation pores directly influences its occurrence and distribution, which are fundamental factors for macroscopic reservoir properties. In order to simulate the hydrate growth at pore scale and demonstrate the growth process directly, microscopic visualization experiments were carried out using glass etching model and high-resolution video microscope in this work. The crystal growth behavior of methane hydrate was observed clearly in real time, and fluid state and system pressure were analyzed. On this basis, hydrate growth patterns and corresponding control mechanisms were investigated. The results show that for a static methane–water system, the hydrate crystal grew rapidly about 10 min after perturbation. The solution gas crystallized with water, forming colorless, transparent and polygonal crystal with sharp edge and smooth surface. The free gas crystallized with water at the gas–water interface first, resulting in a quick formation of hydrate crust. Then water passed through the hydrate crust slowly and crystallized with the free gas trapped inside hydrate crust. The resulting hydrates seemed to rough and honeycomb aggregations of tiny and tightly packed crystal particles. The two kinds of hydrate with different morphologies represent two typical hydrate growth patterns. For the hydrate growth pattern of solution gas–water, solution gas, which migrates to the crystal growth front driven by the concentration gradient, is in direct contact with water, leading to a fast crystal growth rate. For the crystal growth pattern of free gas–water, the preferentially formed hydrate crust at the gas–water interface not only separates the free gas from the water phase, but also selectively obstructs the passage of gas and only allows water to pass slowly, which slows down the hydrate growth process. This research is helpful to further understand the experimental phenomena at the core and field scale, explain the existing problems, and provide support for the research on the dissociation and exploitation of natural gas hydrate.

Magnetite nanoparticles present attractive properties including high magnetization, low toxicity, adsorption capacity, and simple preparation, making them efficient in water purification processes, soil remediation, and biomedical applications. In this sense, there is growing interest in the production of magnetite nanoparticles; therefore, evaluating the performance of this process on a large scale gives relevant information to process designers. In this work, the simulation and exergy analysis of large-scale production of magnetite nanoparticles via coprecipitation were performed using computer-aided tools. The process was modeled for the production of 807 t/year of magnetite nanoparticles; the data for the simulation were obtained from the literature, and experimental results were developed by the authors. The exergy efficiency of the process was estimated at 0.046%. The exergy of waste was estimated to be 105※313 MJ/h, while the unavoidable exergy losses were 2941 MJ/h. Washing 2 and 3 represented the most critical stages of the process, contributing 95.12% of the total irreversibilities due to the waste exergy, which corresponds to the water and ethanol exergy discarded in these stages. These results show that the process must be improved from the energy point of view and require the implementation of process optimization strategies to reach a more sustainable design.

Traditional vibrating screen usually adopts the linear centralized excitation mode, which causes the difficulty in particles loosening and low screening efficiency. The variable elliptical vibrating screen (VEVS) trajectory is regulated to adapt the material mass along the direction of the screen length, improving the particles distribution as well as the screening efficiency. In this work, a theoretical model was developed for analyzing the screen surface motion law during VEVS-based screening process. An equation was obtained to show the relationship between the horizontal amplitude and the vertical amplitude. The materials kinetic characteristics were studied by using high-speed camera during screening process. Compared with equal-amplitude screen (EAS), the material moving velocity was increased by 13.03% on the first half but decreased by 3.52% on the second half, and the total screening time was reduced by 9.42% by using VEVS. In addition, −6 mm screening test was carried out. At the length of VEVS equaled to 1.2 m, the screening efficiency and the total misplaced material content were 92.50% and 2.90%, respectively. However, the screening efficiency was 89.91% and the total misplaced material content was 3.76% during EAS-based screening process. Furthermore, when external moisture is 5.96%, the screening efficiency of VEVS could reach 86.95%. The 2TKB50113 type VEVS with double-layered screen surface used in Huoshizui Coal Mine was 5.0 m in width and 11.3 m in length. The areas of single layer and double layer were 56.5 and 113 m2, respectively. In industrial production, the processing capacity was 2500–3000 t/h and the screening efficiency was larger than 90%.

This work aims to study cluster nucleation, whose solid–solid phase transformation kinetics considerably deviates from that forecasted by the Kolmogorov–Johnson–Mehl–Avrami (KJMA) model. In this scenario, nuclei do not appear homogeneously within the matrix; however, they appear in preferred regions called clusters. One of the principal parameters of this nucleation is the number of clusters in the matrix. This work uses a numerical model to simulate nucleation and growth reactions, which occur explicitly in spherical clusters. It was thus possible to analyze the cluster number variation affecting the microstructural evolution. During the numerical experiments, we compare the simulation outcomes with the analytical model from Villa & Rios. It was possible to observe that analytical solutions from Villa & Rios equations corroborated the numerical results. The computational model of this study agrees with the analytically exact modeling. This study expanded the analytical solution showing the microstructural evolution in 3D. The simulations also proved that the slower the phase transformation reaction occurs, the fewer clusters per unit volume. Also, the generated microstructures have their particular characteristics. Studies in cluster matrices that use only qualitative and visual analyses can lead to wrong interpretations regarding microstructural evolution when using conventional models of formal kinetics. Thus, the computer simulation study presented that Villa & Rios model is the most suitable for this case involving clustering nucleation. The research shows that clustering introduces microstructural heterogeneity into the matrix. This heterogeneity can be harmful to the materials' final properties that underwent a microstructural transformation with these characteristics.

The vibration on the stator core of hydrogenerators caused by electromagnetic forces is an important factor affecting the reliability and long-lasting operation of a machine. For a suitable addressment of the problem, it is necessary to accurately predict the eigenmodes and eigenfrequencies of the mechanical system. However, different results for the eigenfrequencies can be achieved depending on the applied model and material parameters. This work contributes to solving this issue by investigating the impact of different input parameters on the eigenmodes and eigenfrequencies calculated by analytical and numerical models. The results are discussed and compared to measurements performed on a prototyped 732 kVA hydrogenerator.

Blending hydrogen and methane with diesel in compression ignition engines has been proven to improve both performance and emissions. This work further explores the combustion characteristics and emissions of a direct injection compression ignition (DICI) engine fuelled with various blend ratios of hydrogen, methane and diesel with respect to varying intake air temperatures, as the blend ratio can affect the mixture formation process in such high-speed in-cylinder phenomena. A numerical study using ANSYS Fluent was conducted based on a 0.406-litre Yanmar L100AE-D single-cylinder DICI engine running at 1500 rpm and was verified with a physical experiment using the same engine. The tri-fuel blend consisted of 60% diesel by mass with the remaining 40% made up with various ratios of hydrogen and methane (0%/40%, 12%/28%, 20%/20%, 28%/12%, and 40%/0%). The intake air temperatures were varied at 303 K, 318 K and 338 K, representing near-standard, high and extremely high ambient air temperatures, respectively. The results showed that the presence of methane and hydrogen in diesel fuel resulted in a higher in-cylinder pressure, temperature and heat release rate (HRR). Increasing the intake air temperature caused a proportional increase in the in-cylinder temperature, pressure and HRR. However, the presence of methane lengthened the ignition delay, while increasing hydrogen reversed the trend. While the presence of hydrogen–methane reduced the overall CO emissions, the effect of hydrogen on CO reduction was dominant. In addition, the presence of hydrogen–methane led to an increase in NOx emissions due to the high combustion temperature. The study suggested that an optimized intake temperature and the balanced use of tri-fuel in a direct injection compression ignition engine can significantly improve engine performance and emissions.

Bio-organic amphiphiles have been shown to effectively impart unique physicochemical properties to ionic liquids resulting in the formation of versatile hybrid composites. In this work, we utilized computational methods to probe the formation and properties of hybrids prepared by mixing three newly designed bio-organic amphiphiles with 14 ionic liquids containing cholinium or glycine betaine cations and a variety of anions. The three amphiphiles were designed such that they contain unique biological moieties found in nature by conjugating (a) malic acid with the amino acid glutamine, (b) thiomalic acid with the antiviral, antibacterial pyrazole compound [3-(3,5-dimethyl-1H-pyrazol-1-yl)benzyl]amine, and (c) Fmoc-protected valine with diphenyl amine. Conductor-like screening model for real solvents (COSMO-RS) was used to obtain sigma profiles of the hybrid mixtures and to predict viscosities and mixing enthalpies of each composite. These results were used to determine optimal ionic liquid-bio-organic amphiphile mixtures. Molecular dynamics simulations of three optimal hybrids were then performed, and the interactions involved in the formation of the hybrids were analyzed. Our results indicated that cholinium-based ILs interacted most favorably with the amphiphiles through a variety of inter- and intramolecular interactions. This work serves to illustrate important factors that influence the interactions between bio-organic amphiphiles and bio-ILs and aids in the development of novel ionic liquid-based composites for a wide variety of potential biological applications.

Coal and gas outbursts are among the most serious disasters affecting the safety of coal mines. Gas is an important factor in these types of disasters. To analyze the characteristics of the damage caused by gas to the coal body during the sudden release of the gas process, a self-developed high-pressure gas release cause coal particle ejection experiment device was used to conduct gas release experiments under different conditions. The results show that at the moment of gas release, coal particles and gas are ejected at high speed, crushing coal particles into smaller particles. With the increase in gas pressure and gas adsorption performance, the crushing effect will increase. Also, the coal ejection strength (CES) will increase nonlinearly. By analyzing the mass ratio of ejected coal particles, based on the theory of crushing work and energy, we developed a new coal particle fragmentation index, which can be fitted linearly to CES. The index is based on the f value, which makes up for the limitations of the forecasting method, and can be used more flexibly to predict the coal sample crushing situation. Moreover, the fitting parameter values can more accurately describe the coal particle crushing grade.

Modeling of solar photovoltaic (PV) cell/modules to estimate its parameters with the measured current–voltage (I–V ) values is a very important issue for the control, optimization, and effectiveness of the PV systems. Therefore, in this research work, a robust approach based on Stochastic Fractal Search (SFS) optimization algorithm is introduced to estimate accurate and reliable values of solar PV parameters for its precise modeling. To assess the excellence of the proposed SFS algorithm, different solar PV equivalent circuit models, i.e. single-diode model (SDM), double-diode model (DDM), and PV module model are taken into consideration. The introduced algorithm is examined under three different case studies; (i) first case study: an experimental standard dataset of a commercial R.T.C. France silicon solar cell working at 33 ° C , and solar radiance of 1000 W/m2; (ii) second case study: using a polycrystalline solar panel STP6 120/36 with 36 cells in series working at 22 ° C , and (iii) third case study: an experimental dataset of ESP-160 PPW PV module working at 45 ° C , this experimentation were carried out in the Laboratory of Renewable Energy at Assiut University, Egypt. The results obtained using the proposed method are compared with other recently published works, and hence, the achieved results show the superiority, perfectness, and effective modeling concerning various performance parameters. Thereby, the proposed SFS approach can be used for effective PV modeling to improve the efficiency of the PV system.

As one of the accident-tolerance nuclear fuels with potential application prospects, U3Si2 shows its merits of high melting point, high thermal conductivity and high uranium density. However, the mechanical brittleness is one major problem for its practical applications. The strategy of Al-alloying could effectively improve the ductility of U3Si2, yet the intrinsic mechanism is not clear. In this work, the mechanisms for the ductility enhancement of U3Si2 via substituting Al into Si site (i.e. U3Si1.75Al0.25) is studied from two aspects: 1) the interatomic bonding characteristics that are responsible for the ductility enhancement are analyzed in detail; 2) the tensile-shear tests of U3Si1.75Al0.25 are carried out via first-principle calculations, and then the ductility-enhancing mechanism is analyzed. It is found that the increasing number of bonding electrons in U–U layer results in the enhancement of the d-σ interactions between U–Si and U–Si–Al six-membered rings, while the decreasing number of bonding electrons within U–Si layer corresponds to the weakening of the d-s interactions. Finally, one electronic structure model is proposed to picture the interactions of bonding electrons during the tensile-shear tests; providing a novel and inspiration logic of mechanical property modification for alloying-U3Si2.

Over the last decade's magnesium and magnesium based compounds have been intensively investigated as potential hydrogen storage as well as thermal energy storage materials due to their abundance and availability as well as their extraordinary high gravimetric and volumetric storage densities. This review work provides a broad overview of the most appealing systems and of their hydrogenation/dehydrogenation properties. Special emphasis is placed on reviewing the efforts made by the scientific community in improving the material's thermodynamic and kinetic properties while maintaining a high hydrogen storage capacity.