Study of Grain Growth in a Ni-Based Superalloy by Experiments and Cellular Automaton Model

The grain growth behavior in a typical Ni-based superalloy was investigated using isothermal heat treatment experiments over a holding temperature range of 1353–1473 K. The experimental results showed that the grain structure continuously coarsened as the holding time and holding temperature increased during heat treatment. A classical parabolic grain growth model was used to explore the mechanism of grain growth under experimental conditions. The grain growth exponent was found to be slightly above 2. This indicates that the current grain growth in the studied superalloy is mainly governed by grain boundary migration with a minor pinning effect from the precipitates. Then, the grain growth in the studied superalloy during isothermal heat treatment was modelled by a cellular automaton (CA) with deterministic state switch rules. The microscale kinetics of grain growth is described by the correlation between the moving velocity and curvature of the grain boundary. The local grain boundary curvature is well evaluated by a template disk method. The grain boundary mobility was found to increase with increasing temperature. The relationship between the grain boundary mobility and temperature has been established. The developed CA model is capable of capturing the dependence of the grain size on the holding time under different holding temperatures.

Growing Interface with Phase Separation and Spontaneous Convection during Hydrodynamically Stable Displacement

The displacement of one fluid by another is an important process, not only in industrial and environmental fields, such as chromatography, enhanced oil recovery, and CO2 sequestration, but also material processing, such as Lost Foam Casting. Even during hydrodynamically stable fluid displacement where a more viscous fluid displaces a less viscous fluid in porous media or in Hele-Shaw cells, the growing interface fluctuates slightly. This fluctuation is attributed to thermodynamic conditions, which can be categorized as the following systems: fully miscible, partially miscible, and immiscible. The dynamics of these three systems differ significantly. Here, we analyze interfacial fluctuations under the three systems using Family–Vicsek scaling and calculate the scaling indexes. We discovered that the roughness exponent, , and growth exponent, , of the partially miscible case are larger than those of the immiscible and fully miscible cases due to the effects of the Korteweg convection as induced during phase separation. Moreover, it is confirmed that fluctuations in all systems with steady values of and are represented as a single curve, which implies that accurate predictions for the growing interface with fluctuations in Hele-Shaw flows can be accomplished at any scale and time, regardless of the miscibility conditions.

Large-Time Behavior of Magnetohydrodynamics with Temperature-Dependent Coefficients

In this paper, we investigate the initial and boundary value problem of a planar magnetohydrodynamic system with temperature-dependent coefficients of transport, heat conductivity, and magnetic diffusivity coefficients. When all of the relative coefficients are exponentially related to the temperature, the existence and uniqueness of the global-in-time non-vacuum strong solutions are proven under some special assumptions. At the same time, the nonlinearly exponential stability of the solutions is obtained. In fact, the initial data could be large if the positive growth exponent of viscosity is small enough.

Evaluation of grain growth exponent by Monte Carlo simulation in polycrystalline materials

In metallurgy, the microstructure study is very important to evaluate the properties and performances of a material. The Monte Carlo method is applied in so many fields of Engineering Science and it is a very effective method to examine the topology of the computer-simulated structures and exactly resembles the static behavior of the atoms. The effective 2D simulation was performed to understand the grain growth kinetics, under the influence of second phase particles (impurities) is a base to control the microstructure. The matrix size and [Formula: see text]-states are optimized. The grain growth exponent was investigated in a polycrystalline material using the [Formula: see text]-state Potts model under the Monte Carlo simulation. The effect of particles present within the belly of grains and pinning on the grain boundaries are observed. The mean grain size under second phase particles obeys the square root dependency.

Invasion front dynamics of interactive populations in environments with barriers

Invading populations normally comprise different subpopulations that interact while trying to overcome existing barriers against their way to occupy new areas. However, the majority of studies so far only consider single or multiple population invasion into areas where there is no resistance against the invasion. Here, we developed a model to study how cooperative/competitive populations invade in the presence of a physical barrier that should be degraded during the invasion. For one dimensional environment, we found that a Langevin equation as $dX/dt=V_ft+\sqrt{D_f}\eta(t)$ describes invasion front position. We then obtained how $V_f$ and $D_f$ depend on population interactions and environmental barrier intensity. For the 2D case, for the average interface position we found a Langevin equation as $dH/dt=V_Ht+\sqrt{D_H}\eta(t)$. Similar to the 1D case, we found how $V_H$ and $D_H$ respond to population interaction and environmental barrier intensity. Finally, the study of invasion front morphology through dynamic scaling analysis showed that growth exponent, $\beta$, depends on both population interaction and environmental barrier intensity. Saturated interface width, $W_{sat}$, versus width of the 2D environment ($L$) also exhibits scaling behavior. Comparing results for the 2D environment revealed that competition among subpopulations leads to more rough invasion fronts. Considering the wide range of shreds of evidence for clonal diversity in cancer cell populations, our findings suggest that interactions between such diverse populations can potentially participate in the geometry of the tumor border.

Evolution of the Earth Microbial Co-occurrence Network

Background: Co-occurrence pattern provides vital insight into complex microbial interactions of microbiomes. Although network analysis offers useful tools for describing microbial co-occurrence pattern, evolution of co-occurrence networks remains largely uncharacterized. Here, we simulated the evolution of the Earth microbial co-occurrence network and estimated topological fitness of its nodes based on the degree growth exponent.Results: We showed that the Earth microbial co-occurrence network evolved following Bianconi-Barabasi model. The Earth microbial co-occurrence network had reached to a stable status with around 500 nodes. Degree growth exponent was the major determinant of accumulated degree of taxa. The positive correlation between topological fitness and gene numbers in corresponding genomes suggests the intrinsic feature of topological fitness. The gamma distribution of topological fitness suggests the extinction of taxa with low topological fitness. We then examined the impact of node extinction and decay, finding that the link acquisition of hub nodes was not affected.Conclusions: This study glimpses the evolution feature of Earth microbial co-occurrence network and provides a framework for predicting potential hubs in the evolving network in future.

Crystallization Kinetics in BaTiO3 Synthesis from Hydrate Precursors via Microwave-Assisted Heat Treatment

The crystallization kinetics in BaTiO3 synthesis from hydrate precursors via microwave-assisted heating (MWH) were investigated. The structural and chemical features of powders synthesized via MWH and conventional heating (CH) were compared. The charged radicals generated under microwave irradiation were identified by chemical analysis and real-time charge flux measurements. Using Ba(OH)2∙H2O (BH1), Ba(OH)2 (BH0), and BaCO3 (BC) as the precursors for a Ba source, and TiO2∙4H2O (TH) for a Ti source, three different mixture samples, BH1TH (BH1 + TH), BH0TH (BH0 + TH), and BCTH (BC + TH), were heat-treated in the temperature range of 100–900 °C. BaTiO3 powders were synthesized at temperatures as low as 100 °C when sample BH1TH was subjected to MWH. Based on the growth exponent (n), the synthesis reactions were inferred to be diffusion-controlled processes (3 ≤ n ≤ 4) for MWH and interface-controlled processes (2 ≤ n ≤ 3) for CH. Current densities of approximately 0.073 and 0.022 mA/m2 were measured for samples BH1TH and BH0TH, respectively, indicating the generation of charged radicals by the interaction between the precursors and injected microwaves. The radicals were determined as OH− groups by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy.

Sex ratio, gonad maturity and size-structure of Pagelus bellotti in Sierra Leone

A total of 135 specimens of Pagellus bellotti were randomly collected from artisanal boats in August 2018. Study of sex ratio, gonad maturity and size-structure of Pagellus bellottii is meagre in Sierra Leone, and forms the basis of the present study. The study will contribute to current knowledge and promote rational exploitation of the stock. Length and weight were measured using a fish measuring board (cm) and digital weight scale (g) respectively. Sex and gonad maturity were macroscopically assessed. Results showed dominant males (71.9%) and significant difference observed (1:2.6) and expected (1:1) female: male sex ratios (p <0.05). Only 11.9% and 11.1% of male and female gonads transcended to the developed stage (Stage IV). The length-frequency distribution for combined sex was unimodal (modal class, 17cm-20.9cm). Mean length and weight respectively were, 19.04±0.32cm and 98.85±5.08g for males and 17.43±0.54cm and 78.61±6.32g for females. Growth exponent (b) for male, female and combined sex was 2.809, 2.928 and 2.850 respectively and the correlation coefficient for all sex categories showed (r > 0.9). Indexes of condition were greater than 1.0 (K > 1) for all sex categories. Results portrayed a heterogeneous gender population of Pagelus bellottii and vast similarity in reproductive strategies by both sexes. The fish comprised of one size group and males may be growing larger than the females. Growth pattern was near-isometric for females and negative allometric for the males, and both sexes were in better condition (K >1.0). An annual study could provide further insight.

Regularity of Wong-Zakai approximation for non-autonomous stochastic quasi-linear parabolic equation on $ {\mathbb{R}}^N $

<p style='text-indent:20px;'>In this paper, we investigate a non-autonomous stochastic quasi-linear parabolic equation driven by multiplicative white noise by a Wong-Zakai approximation technique. The convergence of the solutions of quasi-linear parabolic equations driven by a family of processes with stationary increment to that of stochastic differential equation with white noise is obtained in the topology of <inline-formula><tex-math id="M2">\begin{document}$ L^2( {\mathbb{R}}^N) $\end{document}</tex-math></inline-formula> space. We establish the Wong-Zakai approximations of solutions in <inline-formula><tex-math id="M3">\begin{document}$ L^l( {\mathbb{R}}^N) $\end{document}</tex-math></inline-formula> for arbitrary <inline-formula><tex-math id="M4">\begin{document}$ l\geq q $\end{document}</tex-math></inline-formula> in the sense of upper semi-continuity of their random attractors, where <inline-formula><tex-math id="M5">\begin{document}$ q $\end{document}</tex-math></inline-formula> is the growth exponent of the nonlinearity. The <inline-formula><tex-math id="M6">\begin{document}$ L^l $\end{document}</tex-math></inline-formula>-pre-compactness of attractors is proved by using the truncation estimate in <inline-formula><tex-math id="M7">\begin{document}$ L^q $\end{document}</tex-math></inline-formula> and the higher-order bound of solutions.</p>