Wagner Theory Research Articles

Government Allocation and Economic Growth: An Empirical Evidence from States in Malaysia

Academic researchers are still interested in government fiscal management and its economic consequences. The impact of federal government fiscal policy on the economy has gotten a lot of attention. Nonetheless, little is known about state-level fiscal management. The main goal of this research is to investigate the relationship between state government fiscal and economic growth across Malaysia's states. We also investigate the economic impact of the federal government's contribution on each state's budget allocation. We identified disparities in federal funding. We use a panel dataset that spans 13 Malaysian states and ten years, from 2008 to 2017. We found that government spending drives growth in domestic products for most state governments using the panel autoregressive distributed lag (ARDL) model. The Granger causality test reveals that state government spending and federal allocation to states significantly impact Malaysian state economic growth. In general, our empirical evidence backs up Wagner's theory.

An atomistic Monte Carlo simulation of precipitation in a binary system

Abstract An atomistic Monte Carlo simulation of coherent precipitation on a body-centred cubic crystal lattice is presented. A binary system with atom types A and B is considered, while the ‘diffusion’ of the atoms is realized via a vacancy mechanism. Starting with a random distribution of 91% A atoms and 9% B atoms, the formation and growth of precipitates is simulated at a constant temperature of 773 K. As a result of the simulation, the precipitate radii distributions at different states of the system and the time evolution of the precipitate mean radii have been calculated. The results of the simulation are compared with the predictions of the classical Lifshitz – Slyozov–Wagner (LSW) theory. At the beginning of precipitation the mean radius R ¯ ( t ) $\bar{R}(t)$ grows proportional to t 0.180, while at later states the growth exponent approaches the classical value of 1/3. In order to reveal the growth exponent’s exact value, an even larger simulation is required, which remains as an interesting task for the future.

On wedge-slamming pressures

The water entry of a wedge has become a model test in marine and naval engineering research. Wagner theory, originating in 1932, predicts impact pressures, and accounts for contributions to the total pressure arising from various flow domains in the vicinity of the wetting region on the wedge. Here we study the slamming pressures on a wedge and a cone, impacting on water keeping a constant, well-controlled velocity, throughout the process, using high-fidelity sensors. Pressures at two locations on the impactor are measured during and after impact. Pressure time series from the two impactors are discussed using inertial pressure and time scales. The non-dimensionalised pressure time series are compared with sensor-integrated averaged composite Wagner solutions, Logvinovich solution (Hydrodynamics of Flows with Free Boundaries. Naukova Dumka, 1969, 4.7), modified Logvinovich solution, and generalised Wagner models. In addition, we provide an independent experimental justification of approximations made in the literature in extending the Wagner model to three dimensions. The second part of the paper deals with pre-impact air cushioning – an important concern since it is responsible for determining the thickness of the air layer trapped upon impact. Using a custom-made technique we measure the air–water interface dynamics as it responds to the build up of pressure in the air layer intervening in between the impactor and the free surface. We show both experimentally and using two-fluid boundary integral simulations, that the pre-impact deflection of the interface due to air-cushioning is fully described by potential flow.

Impedance Spectroscopy Analysis of PbSe Nanostructures Deposited by Aerosol Assisted Chemical Vapor Deposition Approach.

This research endeavor aimed to synthesize the lead (II) diphenyldiselenophosphinate complex and its use to obtain lead selenide nanostructured depositions and further the impedance spectroscopic analysis of these obtained PbSe nanostructures, to determine their roles in the electronics industry. The aerosol-assisted chemical vapor deposition technique was used to provide lead selenide deposition by decomposition of the complex at different temperatures using the glass substrates. The obtained films were revealed to be a pure cubic phase PbSe, as confirmed by X-ray diffraction analysis. SEM and TEM micrographs demonstrated three-dimensionally grown interlocked or aggregated nanocubes of the obtained PbSe. Characteristic dielectric measurements and the impedance spectroscopy analysis at room temperature were executed to evaluate PbSe properties over the frequency range of 100 Hz–5 MHz. The dielectric constant and dielectric loss gave similar trends, along with altering frequency, which was well explained by the Koops theory and Maxwell–Wagner theory. The effective short-range translational carrier hopping gave rise to an overdue remarkable increase in ac conductivity (σac) on the frequency increase. Fitting of a complex impedance plot was carried out with an equivalent circuit model (Rg Cg) (Rgb Qgb Cgb), which proved that grains, as well as grain boundaries, are responsible for the relaxation processes. The asymmetric depressed semicircle with the center lower to the impedance real axis provided a clear explanation of non-Debye dielectric behavior.

A semi-analytical method to simulate hydroelastic slamming of 2D structural sections by coupling Wagner theory with the finite element method

A semi-analytical method based on coupling Wagner theory with the finite element method is applied to numerically simulate hydroelastic slamming of arbitrary symmetric 2D structural sections subject to a constant impact velocity or to free fall motion. The averaged elastic velocity method is adopted to consider the influence of the elastic response on the distribution of the slamming load. A coupled dynamic equation is established to govern the fluid-structural interaction. The nonlinear pressure term improves accuracy. To validate the method, numerically predicted structural deformations and the associated strains during impact for several wedge-shaped sections and a cylindrical shell are compared with published results. The results show that the averaged elastic velocity method is efficient in estimating the structure dynamics. The effect of the nonlinear pressure term on hydroelastic structural dynamics is parametrically studied by considering wedge sections with different deadrise angles and with the elastic bottom plating under different end constraints. This nonlinear pressure term ensures reliably predicted hydroelastic structural responses, especially for wedges of larger deadrise angles and smaller hydroelastic properties. The proposed method provides an efficient tool to estimate structural strength under slamming during the initial design stage of the marine or aerospace structure.

Design and Modeling of Proton-Conducting Bilayer Electrolytes Using a Nernst-Planck-Poisson Formulation

In this study, the efficiency of proton-conducting ceramic fuel cells was improved by designing bilayer electrolytes with high ion conductivity and low hole conduction. The designs were carried out by finding the thicknesses of anode and cathode-side electrolytes that optimizes efficiency using integral equations based on Wagner theory. Results obtained for bilayer electrolytes were compared with those of single-layer electrolytes. Best performances were found when thin layers of lanthanum tungstate (La28-x W4+x O54+3x/2v2-3x/2) with an La/W ratio of 6.7 (LWO67) were used as cathode-side electrolytes attached to commonly used perovskite materials like BaCe0.9Y0.1O3- δ (BCY10), BaZr0.8Y0.2O3- δ (BZY20), and BaZr0.1Ce0.7Y0.1Yb0.1O3- δ (BZCYYb1711). In addition, the transport properties of a single-layer LWO67 electrolyte were further analyzed by using the Nernst-Planck-Poisson (NPP) model for which parameters were fitted. Finally, a bilayer NPP formulation was explored to obtained the charged defect fluxes and other useful information to enhance the efficiency of a bilayer BZY20|BZCYYb1711 electrolyte.

Integrated Dielectric Model for Unconsolidated Porous Media Containing Hydrate

This article reports a novel dielectric model developed for estimating the complex permittivity of unconsolidated porous media containing gas hydrate. The complex permittivity spectra were experimentally obtained by using open-ended-coaxial-probes over a frequency range between 1 MHz and 3 GHz, in which the dielectric dispersion of both hydrate and liquid solution are covered. With tetrahydrofuran used as the hydrate former, reflection coefficients were recorded during the hydrate formation and dissociation processes in quartz sands and the complex permittivity spectra were inversed. Volumetric fractions estimated from the X-ray-tomography were used as the referenced values. Experimental data showed that the Maxwell-Wagner effect, surface conductance, and phase configuration can affect the bulk permittivity. The discrepancy was found to be unacceptable when the fitting was conducted with pre-existing models such as complex-refractive-index-method (CRIM) and Maxwell-Wagner-Bruggeman-Hanai (MWBH). In this study, by modifying the nested Wagner's theory, a shell-coated model was applied, and the surface of the solid sphere was assumed to possess surface conductance when it was humidified by the liquid solution. In contrast to CRIM and MWBH, the proposed model allows more accurate estimation of the volumetric fraction. By adopting this model with a range of dielectric measurements with different phase configurations, temperature, particle size, surface conductivity, and frequency, the contents of components and their influences onto the bulk permittivity can be physically estimated. The proposed model provides an essential tool for the interpretation of dielectric dispersion curves and the prediction of the volumetric fractions, which can be useful for both the field and laboratory applications.

Microstructural evolution and stress rupture behaviour of a Ni-Based wrought superalloy during thermal exposure

The microstructural evolution of a wrought Ni-based superalloy GH742 during long-term thermal exposure at 1023 K for durations up to 10,000 h was investigated. The influence of the microstructure degradation on the stress rupture properties at 923 K/823 MPa and 1023 K/510 MPa was systematically analysed. Scanning electron microscopy and electron probe microanalysis were utilised to study the material microstructures before and after the thermal exposure. The results show that small flower-like secondary γ′ precipitates changed their morphology from flower-like to cubic with rounded corners, while large flower-like secondary γ′ precipitates started to split. Tertiary spherical γ′ precipitates in the fine-equiaxed-grain region dissolved into the γ matrix. However, coarsening of tertiary γ′ precipitates occurred in large-fibrous-grain regions. The coarsening kinetics appeared to well conform to the Lifshitz–Slyozov–Wagner theory. Stress rupture tests at 923 K/823 MPa and 1023 K/510 MPa showed a sharp decrease in time to failure within the first 1,000 h of prior thermal exposure, which was then almost constant for the next 9,000 h of thermal exposure. This was attributed to the evolution of γ′ precipitates.

Design, phase equilibria, and coarsening kinetics of a new [formula omitted] precipitation-hardened multi-principal element alloy

Multi-principal element alloys (MPEAs), with dispersed nanometric precipitates in a ductile matrix, are attracting a considerable amount of literature’s attention. Understanding the coarsening kinetics and potential properties of such alloys is crucial for future developments in the field. In the present study, we report a new precipitation-hardened multi-principal element alloy, Cr29.7Co29.7Ni35.4Al4.0Ti1.2 (at%), developed with the aid of the CALPHAD method. The alloy has a tough Cr-Co-Ni FCC matrix and nanometric L12 precipitates. After standard heat treatments, the alloy was aged at 850 °C for different aging times and the coarsening kinetics was investigated. The evolution of mechanical properties as a function of aging time was evaluated through microhardness tests. An increment of 106 HV 0.5 was observed compared to the sample in the solution-treated condition. This hardness increment was higher than that of conventional superalloys with a similar volume fraction of precipitates. Experimental data indicate that particle growth during coarsening is governed by diffusion controlling mechanism. The coarsening rate constant was lower than that of traditional wrought superalloys aged at the same temperature, indicating better thermal stability of the current MPEA. Furthermore, experimental particle size distributions show a good correlation with the curve predicted by the Lifshitz–Slyozov–Wagner (LSW) theory. Deviations and the applicability of this theory for MPEAs are discussed.

Mesoscale Model for Ostwald Ripening of Catalyst Nanoparticles

A mesoscale model is proposed to characterize coarsening of platinum-based catalyst particles with the aim of understanding cathode degradation and power loss in proton exchange membrane fuel cells (PEMFC). The microstructure of a cathode catalyst layer is more complex than the ones typically described by Ostwald-ripening models, such as the Lifshitz and Slyozov and Wagner (LSW) theory or diffuse interface models. Our model captures the dissolution kinetics of the catalyst material, and the diffusivity of the ions in solution. The network structure of the model embeds the tortuosity of the microstructure and the effect of water content on Pt-ion mobility. Detailed diffusional interactions among catalyst particles are explicitly described with the aim of providing statistically averaged properties of coarsening ensembles. Through numerical tests, the scaling of coarsening kinetics is predicted as function of voltage. The effect of voltage cycling, and initial particle size distribution are also probed. The power-law exponents for the mean square radius vs time are affected by the reduced dimensionality of inter-particle diffusion, constrained by the carbon support and the surface wetting. This theoretical framework can be used to understand how material design influences the degradation pathways that are responsible for platinum surface area loss.

Droplet impact onto a spring-supported plate: analysis and simulations

The high-speed impact of a droplet onto a flexible substrate is a highly non-linear process of practical importance, which poses formidable modelling challenges in the context of fluid–structure interaction. We present two approaches aimed at investigating the canonical system of a droplet impacting onto a rigid plate supported by a spring and a dashpot: matched asymptotic expansions and direct numerical simulation (DNS). In the former, we derive a generalisation of inviscid Wagner theory to approximate the flow behaviour during the early stages of the impact. In the latter, we perform detailed DNS designed to validate the analytical framework, as well as provide insight into later times beyond the reach of the proposed analytical model. Drawing from both methods, we observe the strong influence that the mass of the plate, resistance of the dashpot, and stiffness of the spring have on the motion of the solid, which undergo forced damped oscillations. Furthermore, we examine how the plate motion affects the dynamics of the droplet, predominantly through altering its internal hydrodynamic pressure distribution. We build on the interplay between these techniques, demonstrating that a hybrid approach leads to improved model and computational development, as well as result interpretation, across multiple length and time scales.

Protecting the Rescorla-Wagner (1972) theory: A reply to Spicer et al. (2020).

Rescorla (2001) used the compound test procedure to compare associative changes to cues located at different points on a performance scale. He found that associative changes to cues conditioned in compound are not necessarily equal, as predicted by common error term theories like Rescorla and Wagner (1972), but instead are larger for the poorer predictor of a trial outcome. Hence, Rescorla proposed a modification to the Rescorla-Wagner model whereby associative change is calculated as the product of 2 error terms: a common error term, as in the original model, and a unique error term for each cue present, which accounts for his findings that the poorer predictor of a trial outcome undergoes more associative change. In a recent study, Spicer, Mitchell, Wills, and Jones (2020) reported findings that appear to be inconsistent with Rescorla's proposal. These authors compared associative changes to cues that differed in associative strength as well as the certainty with which they predicted a trial outcome: One cue had greater strength than did the other, but its prediction of the trial outcome was less certain. Spicer et al. found that the cue that evoked a larger prediction error (the more certain cue) underwent less (not more) associative change and, thereby, concluded that associative change in people is not primarily determined by prediction error. Instead, they argued that cues that predict certain outcomes are somewhat protected from further associative change (theory protection), resulting in greater change to cues that predict uncertain outcomes. In this article, we offer an alternative explanation for the Spicer et al. findings using an approach described by Holmes, Chan, and Westbrook (2019). We show that if the learning-to-performance mapping function is a double sigmoid across the full range of associative strength, the Rescorla-Wagner model accommodates Rescorla's compound test results, as well as those reported by Spicer et al. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Precipitation Criterion for Inhibiting Austenite Grain Coarsening during Carburization of Al-Containing 20Cr Gear Steels

AlN precipitates are frequently adopted to pin the austenite grain boundaries for the high-temperature carburization of special gear steels. For these steels, the grain coarsening criterion in the carburizing process is required when encountering the composition optimization for the crack-sensitive steels. In this work, the quantitative influence of the Al and N content on the grain size after carburization is studied through pseudocarburizing experiments based on 20Cr steel. According to the grain structure feature and the kinetic theory, the abnormal grain growth is demonstrated as the mode of austenite grain coarsening in carburization. The AlN precipitate, which provides the dominant pinning force, is ripened in this process and the particle size can be estimated by the Lifshitz−Slyosov−Wagner theory. Both the mass fraction and the pinning strength of AlN precipitate show significant influence on the grain growth behavior with the critical values indicating the grain coarsening. These criteria correspond to the conditions of abnormal grain growth when bearing the Zener pinning, which has been analyzed by the multiple phase-field simulation. Accordingly, the models to predict the austenite grain coarsening in carburization were constructed. The prediction is validated by the additional experiments, resulting in accuracies of 92% and 75% for the two models, respectively. Finally, one of the models is applied to optimize the Al and N contents of commercial steel.

3D Phase Field Modeling of Multi-Dendrites Evolution in Solidification and Validation by Synchrotron X-ray Tomography.

In this paper, the dynamics of multi-dendrite concurrent growth and coarsening of an Al-15 wt.% Cu alloy was studied using a highly computationally efficient 3D phase field model and real-time synchrotron X-ray micro-tomography. High fidelity multi-dendrite simulations were achieved and the results were compared directly with the time-evolved tomography datasets to quantify the relative importance of multi-dendritic growth and coarsening. Coarsening mechanisms under different solidification conditions were further elucidated. The dominant coarsening mechanisms change from small arm melting and interdendritic groove advancement to coalescence when the solid volume fraction approaches ~0.70. Both tomography experiments and phase field simulations indicated that multi-dendrite coarsening obeys the classical Lifshitz–Slyozov–Wagner theory , but with a higher constant of n = 4.3.

Investigation of hydroelasticity in water entry of flexible wedges with flow detachment

Prediction of structural response during water entry is of great significance for the design of naval architecture and aircraft. In order to study fluid-structural interaction (FSI) of flexible wedge during water entry, coupling algorithms based on boundary element method (BEM)/Wagner theory and modal superposition method (MSM) are utilized. The first solution is a numerical method by coupling BEM and MSM based on domain decomposition technique. The second solution is a semi-analytical method by coupling Wagner theory and MSM. Non-linear pressure composition in the Bernoulli equation is used to improve the accuracy for wedge with moderate deadrise angles. The implicitly Newmark-β scheme is employed for time marching of structural dynamic equation. Effects of hydroelasticity on fluid pressure and structural response are studied by the comparison between coupling and decoupling solutions. The results show that the structural response is significantly affected by the presence of fluid added mass and damping. Structural response is lagged due to the fluid added mass and damping. Besides, the latter one causes the decrease of amplitudes of slamming load and structural response. This paper highlights the effect of hydroelasticity on slamming load and structural response during water entry of flexible structure.

Electric Transport and Dielectric Studies of CoFe2O4-BaFe12O19 Nanocomposite

Electric transport properties of cobalt ferrite and barium ferrite composite were studied in the frequency range of 1 Hz to 1 MHz with temperature varying from 100 to 500 °C. The composite with weight ratio 1:1 (CoFe2O4:BaFe12O19) was synthesized by chemical co-precipitation route. Rietveld refined X-ray diffraction analysis revealed pure phase formation of cobalt ferrite, barium ferrite and the prepared composite. For the prepared composite, dual phase refinement procedure was employed. Average crystallite size of CoFe2O4 and BaFe12O19 was observed as 19 nm and 51 nm respectively. The conduction and polarization mechanism in ferrites was explained on the basis of Maxwell–Wagner theory and Koop’s model which reflects the contribution of grain and grain boundaries present in the specimens. The conductivity analysis confirmed the presence of overlapping large polaron tunneling (OLPT) model for conduction.

Modeling of High-Temperature Multiphase Solid/Molten Carbonate Membranes for CO2 Capture

High-temperature solid/molten-carbonate composite represent an emerging class of CO2 transport membranes to capture CO2 from flue gas with advantages in flux density and selectivity over conventional solvent/sorbent- and polymer-based counterparts. While significant technical progress in these membranes has been made in the past years, a deeper fundamental understanding of CO2 transport mechanisms is still limited. Aimed to bridge this gap, we here report a theoretical study on flux performances of four types of solid/molten-carbonate CO2 transport membranes by analytical and numerical modeling. We first demonstrate the general analytical solutions for CO2 flux of dual-phase solid/MC membranes by solving the partial differential equations (PDEs) along with the boundary conditions. These analytical solutions are then compared with those derived directly from Wagner theory. We also develop numerical CO2 flux solutions and compare them with the existing or our derived analytical solutions to point out the issues with using analytical methods to solve CO2 flux in complex multiphase systems. Finally, we apply our numerical models to simulate CO2 flux in more complex multiphase solid/MC membranes.From the results, we found that analytical and numerical results are virtually identical for solids with single charge carrier. However, for mixed conducting solids, numerical method is preferred since analytical method cannot solve the nonlinear local concentrations of charge carriers. Application of numerical method to a new three-phase membrane containing a mixed conducting solid, a pure electron conducting solid and molten-carbonate reveals a 75% increase in CO2 flux compared to the two-phase (mixed conducting solid and molten-carbonate) counterpart. The models presented here are expected to provide better fundamental insights and guidance for designing next-generation high-performance CO2 transport membranes. Figure 1

Oxide Scale Evolution on Binary Alloys: Transient State Kinetics from First Principles

Metal oxidation is a major cause of structural materials degradation. Alloying has been a successfully strategy to mediate metal degradation by forming protective oxides of minor elements. Understanding factors that affect the formation of such a protective film is essential for the rational design of corrosion resistant alloys. The Wagner theory focused on oxygen permeability and metal diffusion in the alloy beneath the oxide scale. Cation kinetics in the oxides is also important for the oxide composition evolution and thus the protective layer formation, which was missing in previous models. In this work, we study the competing cation diffusion and segregation dynamics in the oxide from first principles. By doing so, we are able to predict the oxide composition as a function of time with atomic resolutions at different conditions. Effective cation diffusivities through the oxide film can be obtained as a function of composition as well, which quantifies the protectivity of the oxide. Comparison will be made between alumina former and chromia former in Ni based alloys and steel.In our approach, energetics of various local configurations is calculated from DFT+U and parameterized into a surrogate model by cluster expansion. Hopping barriers are calculated from the nudged elastic band method. The above two are combined by the Bell–Evans–Polanyi (BEP) relation to provide essential inputs for kinetic Monte Carlo simulations. This approach enables large length scale and long-time scale atomistic kinetic simulations with the quantum level of accuracy.This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract Number DEAC52-07NA27344. IM release number: LLNL-ABS-810184

Enhancement of multiferroic characteristics in the Al and Pr co-doped BiFeO3 nanocrystalline

We investigate and enhance the multiferroic characteristics of BiFeO3 by doping Al3+ and Pr3+ cations simultaneously. Bi1-xAlxFe1-xPrxO3 (x=0.00, 0.04, 0.08, 0.12, 0.16) was prepared by sol–gel or auto-combustion method. The structural characterization of the samples was done for Bi1-xAlxFe1-xPrxO3 (x=0.00, 0.04, 0.08, 0.12, 0.16) multiferricnano crystals using X-ray diffraction (XRD), Dielectric properties, and Fourier transform infrared spectroscopy (FTIR). The size of the crystallite was calculated between the range 26.54 and 13.55 nm. We demonstrated the dual cation doping of Fe site by Pr as well as Bi site by Al. Doping of the materials exhibits optimized multiferroic properties. The co-doping of Al3+ and Pr3+ and frequency increases and decreases the dielectric parameters, which is explained by using Wagner theory. This reveals that these particles display resonance phenomenon in the GHz range. Low-frequency AC conductivity defines the grain boundary, while high-frequency dispersion can be ascribed to conductivity grains. Due to rise in the frequency of the applied electric field, real AC electrical conductivity σac increases. FTIR spectra tell us the changes in fundamental vibration absorption bands by the addition of Al3+ and Pr3+ ions. Appreciable enhanced quality factor values proposed the potential use of these materials for energy implementation and in large frequency multiferroic chip indicators. The obtained results proposed a useful contribution of synthesized materials in several technological applications.

In Situ Oxidation Studies of High-Entropy Alloy Nanoparticles.

Although high-entropy alloys (HEAs) have shown tremendous potential for elevated temperature, anticorrosion, and catalysis applications, little is known on how HEA materials behave under complex service environments. Herein, we studied the high-temperature oxidation behavior of Fe0.28Co0.21Ni0.20Cu0.08Pt0.23HEA nanoparticles (NPs) in an atmospheric pressure dry air environment by in situ gas-cell transmission electron microscopy. It is found that the oxidation of HEA NPs is governed by Kirkendall effects with logarithmic oxidation rates rather than parabolic as predicted by Wagner's theory. Further, the HEA NPs are found to oxidize at a significantly slower rate compared to monometallic NPs. The outward diffusion of transition metals and formation of disordered oxide layer are observed in real time and confirmed through analytical energy dispersive spectroscopy, and electron energy loss spectroscopy characterizations. Localized ordered lattices are identified in the oxide, suggesting the formation of Fe2O3, CoO, NiO, and CuO crystallites in an overall disordered matrix. Hybrid Monte Carlo and molecular dynamics simulations based on first-principles energies and forces support these findings and show that the oxidation drives surface segregation of Fe, Co, Ni, and Cu, while Pt stays in the core region. The present work offers key insights into how HEA NPs behave under high-temperature oxidizing environment and sheds light on future design of highly stable alloys under complex service conditions.