Concentration Profiles Research Articles

Insight into the thermal transport by considering the modified Buongiorno model during the silicon oil-based hybrid nanofluid flow: probed by artificial intelligence

This work aims to analyze the impacts of the magnetic field, activation of energy, thermal radiation, thermophoresis, and Brownian effects on the hybrid nanofluid (HNF) (Ag++silicon oil) flow past a porous spinning disk. The pressure loss due to porosity is constituted by the Darcy–Forchheimer relation. The modified Buongiorno model is considered for simulating the flow field into a mathematical form. The modeled problem is further simplified with the new group of dimensionless variables and further transformed into a first-order system of equations. The reduced system is further analyzed with the Levenberg–Marquardt algorithm using a trained artificial neural network (ANN) with a tolerance, step size of 0.001, and 1,000 epochs. The state variables under the impacts of the pertinent parameters are assessed with graphs and tables. It has been observed that when the magnetic parameter increases, the velocity gradient of mono and hybrid nanofluids (NFs) decreases. As the input of the Darcy–Forchheimer parameter increases, the velocity profiles decrease. The result shows that as the thermophoresis parameter increases, temperature and concentration increase as well. When the activation energy parameter increases, the concentration profile becomes higher. For a deep insight into the analysis of the problem, a statistical approach for data fitting in the form of regression lines and error histograms for NF and HNF is presented. The regression lines show that 100% of the data is used in curve fitting, while the error histograms depict the minimal zero error −7.1e6 for the increasing values of Nt. Furthermore, the mean square error and performance validation for each varying parameter are presented. For validation, the present results are compared with the available literature in the form of a table, where the current results show great agreement with the existing one.

Analysis of Darcy–Forchheimer flow of magnetized hybrid nanofluid (MoS 2+ZnO/E) with non-linear heat source and quartic autocatalytic chemical reaction

In this article, an effort is made to analyze the 3 − D flow of hybrid nanofluid over a rotating stretching sheet. The hybrid nanofluid contains engine oil as a base fluid amalgamated with nano-particles Mo S 2 and ZnO . The flow is assumed to pass through a Darcy–Forchheimer medium subjected to the influence of an inclined magnetic field. In addition, heat radiation, Joule heating, viscous dissipation, nonlinear heat source, and quartic autocatalytic chemical reaction are applied to discourse heat and mass transfer features. The PDEs representing the physical problem are converted to ODEs with the introduction of similarity transformations. The solution of the problem is determined numerically by using MATLAB built-in bvp4c method. The proposed mathematical model’s validation is ascertained by comparing it with an earlier study in limiting case. In this regard, an excellent consensus is accomplished. The current investigation reveals that the flow along axial direction gets retarded by enhancing the values of rotational parameter, inertial parameter, and magnetic parameter, whereas the flow along radial direction gets accelerated. The increasing value of angle of inclination admirably resists the motion of nanofluid and hybrid nanofluid. The concentration profile gets decreased under the increasing influence of inclination angle and Schmidt number while it enhances for homogeneous reaction parameter. The enhancing values of rotational parameter, solid volume fraction and temperature, and exponential dependent heat generation parameters enhance the value of Nusselt number.

Carbon dioxide capture by aqueous glucosamine solutions: Pilot plant measurements and a theoretical study

AbstractA comprehensive investigation of the potential of aqueous glucosamine solutions as an eco‐friendly solvent for CO2 capture was performed. It includes an experimental study in a pilot plant setup and a theoretical analysis with a rate‐based model. The model was validated against the measured column profiles of temperature and CO2 concentration in both liquid and gas phases. Model‐based parameter sensitivity studies revealed inherent challenges for an effective absorption process. A slow reaction rate and suboptimal chemical equilibrium conditions were identified as key limitations, restricting the absorption efficiency and CO2 loading capacity of the glucosamine solution. Furthermore, an analysis of the dissociation constant of this novel absorbent was performed and its significance with respect to the (limited) performance, capability, and efficiency evaluation was highlighted.

Bio-Convective Flow of Micropolar Nanofluids over an Inclined Permeable Stretching Surface with Radiative Activation Energy

The focal concern of this study is to examine the behaviour of bio-convective flow featuring micropolar nanofluids over an inclined permeable stretching surface while considering the influence of radiative activation energy. This investigation addresses the complex interplay of factors such as biological activity, convective heat and mass transfer, unique attributes of micropolar fluids, the dynamics of nanofluids, and radiative effects. This analysis employed Buongiorno’s model, considering thermal radiation and activation energy on the bioconvective flow of micropolar nanofluids over an inclined stretching surface. Some suitable similarity variables were used to obtain a set of non-linear differential equations from the initial partial differential equations which were then solved numerically using the Runge-Kutta Fehberg method along with shooting technique. The effects of some physical parameters were examined on the velocity, temperature, concentration, and microorganism density profiles of the flow. The result revealed that each increase in the heat source/sink, thermal radiation, thermophoresis, and Brownian motion lead to a corresponding increase in the thermal boundary layer; activation energy increased the concentration while Peclet number and bioconvective Lewis number declined the microorganism density profile. Insights gleaned from this study can find applications in biomedical fields. Understanding the behavior of bio-convective nanofluids has implications for controlled heat transfer in medical applications like hyperthermia treatments or targeted drug delivery, thereby impacting patient care.

Two-dimensional model in a laminar flow slit photoreactor for the determination of surface kinetic constants considering the presence of diffusion limitations

Narrow slit reactors are widely used in laboratory testing of photocatalytic materials, as well as for the determination of kinetic coefficients in surface photocatalyzed reactions. In this work, the behavior of a continuous laminar flow slit reactor was described by a two-dimensional model, addressing the advection–diffusion problem in the fluid phase, coupled with a first-order chemical reaction on the reactor walls. The concentration profile of the reactant, in the transverse and longitudinal directions of the reactor, depends on two parameters that characterize the system; the Péclet number and the Damköhler number, in addition to the geometry of the reactor. Once a short distance from the reactor’s entrance has been surpassed, the relationship between the transversally averaged reactant concentration and the concentration existing on the catalytic surface becomes essentially constant, thus defining an (external) effectiveness factor. The simulations carried out for a wide range of values of the parameters characterizing the model showed that the effectiveness factor only depends on the Damköhler number, being independent of the value of the Péclet number and of the relationship between the reactor length and the distance separating the plates. An analytical expression for the effectiveness factor as a function of the Damköhler number was proposed, which allows to determine the value of the kinetic coefficient for the surface reaction (ks), even in the presence of important limitations to mass transfer. The methodology proposed was illustrated performing experiments of photocatalytic oxidation of toluene in air (with Péclet numbers ranging from 20 to 40), employing a paint formulated with carbon-doped TiO2 in a continuous laboratory photoreactor of flat parallel plates. The observed toluene conversions were in the range of 13 to 26 %, consequently, the calculated Damköhler number was Da = 0.0307 and the surface kinetic coefficient thus determined (for 50 % of relative humidity and 42.3 W/m2 of irradiance flux) was ks = 1.262 10-4 m/s. The significance of this work lies in the development of a comprehensive model that can be used to know the surface kinetics in photocatalytic reactions, applicable to scenarios where there are considerable mass transfer limitations or not.

Investigation of thermal radiation and joule heating effects on variable viscosity Casson nanofluid flow over a stretching sheet in Darcy–Forchheimer porous medium

Nanofluids possess unique thermal and rheological properties that offer significant advantages in enhancing heat transfer efficiency in various applications, such as heat exchangers, cooling systems, and microdevices. In this study, we investigate the combined effects of thermal radiation, Joule heating, variable viscosity, and a two-phase model on the flow behavior and heat transfer characteristics of a magnetohydrodynamic Casson nanofluid flowing over a stretching sheet in Darcy-Forchheimer porous media. The governing partial differential equations are converted into a system of first-order ordinary differential equations numerically solved using the bvp5c package in MATLAB. Consequently, the result indicates that the velocity profile increases with thermal radiation, variable viscosity, and viscous dissipation, decreasing with the magnetic field, permeability index, and Forchheimer coefficient. Also, the temperature profile shows an increase with the permeability index, viscous dissipation, and thermal radiation, but a decrease with the Forchheimer Coefficient, variable viscosity, and magnetic field. Additionally, the concentration profile exhibits an increase with the Forchheimer coefficient and permeability index, and variable viscosity while it decreases with viscous dissipation, magnetic field, and thermal radiation. Analyzing the skin friction coefficient reveals an increase with magnetic field and thermal radiation and a decrease with permeability index and Forchheimer coefficient as well as variable viscosity. Moreover, the local heat transfer rate demonstrates an increase with the variable viscosity, and magnetic field as well as the Forchheimer coefficient and permeability index. At the same time, it decreases with the viscous dissipation. Furthermore, the local mass transfer rate displays an increase with the magnetic field and thermal radiation and viscous dissipation, while it decreases with the variable viscosity as well as permeability index, viscous dissipation, and Forchheimer coefficient. Finally, the current findings are compared with that of the existing literature and a sound agreement was established.

Vertical concentrations gradients and transport of airborne microplastics in wind tunnel experiments

Abstract. Microplastics are an ubiquitous anthropogenic material in the environment, including the atmosphere. Little work has focused on the atmospheric transport mechanisms of microplastic nor its dispersion, despite it being a potential pollutant. We study the vertical transport of airborne microplastics in a wind tunnel, a controllable environment with neutral stability, to identify the necessary conditions for the long-range atmospheric transport of microplastics. An ultrasonic disperser generated airborne water droplets from a suspension of polystyrene microsphere microplastics (MPs) with a diameter of 0.51 µm. The water droplets were injected into the airflow, evaporating and releasing single airborne MPs. The disperser allowed for time-invariant and user-controlled concentrations of MPs in the wind tunnel. MPs were injected at 27, 57, and 255 mm above the ground. A single GRIMM R11 optical particle counter (OPC) and three Alphasense OPCs measured time-averaged MP concentration profiles (27, 57, and 157 mm above the ground). These were combined with turbulent airflow characteristics measured by a hotwire probe to estimate vertical particle fluxes using the flux-gradient similarity theory. The GRIMM R11 OPC measured vertical concentration profiles by moving its sampling tube vertically. The three Alphasense OPCs measured particle concentrations simultaneously at three distinct heights. Results show that maximum concentrations are not measured at the injection height but are rather shifted to the surface by gravitational settling. The MPs experience higher gravitational settling while they are part of the larger water droplets. For the lowest injection at 27 mm, the settling leads to smaller MP concentrations in the wind tunnel, as MPs are lost to deposition. Increasing the wind speed decreases the loss of MPs by settling, but settling is present until our maximum friction velocity of 0.14 m s−1. For the highest injection at 255 mm and laminar flow, the settling resulted in a net MP emission, challenging the expectation of a net MP deposition for high injection. Turbulent flows reverse the MP concentration profile giving a net MP deposition with deposition velocities of 3.7 ± 1.9 cm s−1. Recognizing that microplastics share deposition velocities with mineral particles bridges the gap in understanding their environmental behavior. The result supports the use of existing models to evaluate the transport of microplastics in the accumulation mode. The similar deposition velocities suggest that microplastics transported in the atmosphere can be found in the same places as mineral particles.

Exact analysis of hydromagnetic non‐Gray optically thick heat absorbing fluid with nonlinear parabolic ramped conditions

AbstractThe article presents a solution to a complex problem involving a transient MHD‐free convective chemically reactive flow. The flow involves a viscous incompressible electrically conducting non‐Gray optically thick fluid moving past a semi‐infinite vertical plate that has suddenly started but is temporarily accelerated. The plate has nonlinear parabolic ramped conditions, and the flow is exposed to thermal radiation, heat absorbing sink, and diffusion‐thermo effect. For the current study, the model fluid being used is moist air. The governing equations are obtained using the Laplace transform technique with the help of the Heaviside step function. This study is the first to consider parabolic ramped motion, temperature and concentration simultaneously. Effects of the pertinent parameters on the Sherwood number and Nusselt number are visualized using 3D surface plotting. Findings of the problem manifest that concentration, temperature, and velocity profiles in case of ramped conditions are less than in isothermal conditions. The rate of heat transfer of mercury is less than oxygen, air, water, and ethanol at a room temperature of 22°C–25°C. The ramped plate has the tendency to augment the heat transfer rate. The present study is of great interest in numerous fields of industry and machine‐building applications.

Unsteady MHD Walter’s-B Viscoelastic Flow Past a Vertical Porous Plate

The present paper intended to analyse an unsteady MHD Walter’s-B viscoelastic flow past a vertical porous plate embedded in a porous medium in the presence of the radiation and chemical reaction effects. The dimensionless partial differential equations of governing equations of the flow field are solved numerically using closed analytical method. The velocity, temperature and concentration profiles are discussed graphically and discussed qualitatively

Effects of Activation Energy and Diffusion Thermo an Unsteady MHD Maxwell Fluid Flow over a Porous Vertical Stretched Sheet in the Presence of Thermophoresis and Brownian Motion

This article discusses the effects of Activation energy and Diffusion thermo on an unsteady MHD flow of an electrically conducting Maxwell Nanofluid over a stretching sheet in a porous medium in the presence of thermophoresis and Brownian motion. Using the similarity transformations, the partial differential equations corresponding to the momentum, energy, and concentration equations are transformed into a system of nonlinear ordinary differential equations, which are solved numerically using a RungeKutta fourth-order method along with the shooting technique, and the results obtained for different governing flow parameters are drawn graphically, and their effects on velocity, temperature, and concentration profiles are discussed. The values of the skin friction coefficient, Nusselt number coefficient, and Sherwood number coefficient are presented in the table. A comparison with previously reported data is made, and an excellent agreement is noted. The objective of the present study is to use the Activation energy and Diffusion thermo parameters to increase the concentration of chemical species on the boundary layer and temperature, respectively. The temperature of the fluid increases as the radiation parameter, Brownian motion, thermophoresis, and magnetic parameters increase.

Novel single well chemical tracer test design: shut-in time determination for test feasibility

The well shut-in time (t soak) in a single-well chemical tracer test (SWCTT) after injection of the primary tracer depends on its reactivity under reservoir conditions. In this paper, a novel SWCTT design is proposed to determine the well shut-in time to minimize the risk of loss of test results based on different secondary tracer generation rates considering the oil saturation of the reservoir. The developed method in this paper was approximated to conduct SWCTT in oilfield A in predicting the minimum t soak after ethyl acetate injection for different S or. The paper shows that the field test tracer production curves are consistent with hydrodynamic modeling data at the same t soak. When t soak is reduced according to the model data, the concentration profile of the secondary tracer is in the low detection range, indicating that the test was properly organized when the well shut-in to minimum t soak. Thus, the novel test design showed how the time of all well operations can be optimized and the costs associated with equipment mobilization and service company operations can be reduced.

Novel machine learning investigation for Buongiorno fluidic model with Sutterby nanomaterial

The nanomaterials are frequently employed in a variety of heat transfer applications arising in energy generation, engine cooling, extrusion procedures, heat exchanger, thermos-chemical systems, manufacturing structures, powered plants etc. Experts and researchers in these fields often encounter such materials, leading to discernible impacts on velocity, temperature and concentration profiles. The objective of this study is to represent the mathematical structures for Sutterby nanomaterial fluidic model involving porous medium BFM-SNM using nonlinear autoregressive exogeneous networks backpropagated with Levenberg-Marquardt technique (NARX-LMT). The mathematical design of the model is originally presented by PDEs, which are converted into ODEs system through suitable modifications with alternative transformation incorporating numbers, i.e., Deborah, Prandtl and Reynold, as well as parameters, i.e., magnetic thermophoresis, radiation and temperature. The synthetic data is produced numerically by simulating Adams numerical method for BFM-SNM and the supervised computing paradigm of NARX-LMT is applied to the obtained datasets, and the results of NARX-LMT consistently align with numerical observations for each variant of the presented model, exhibiting negligible errors. The NARX-LMT performance on exhaustive experimentation is effectively illustrated through iterative convergence curves on mean squared error, control metrics of the optimization, distribution of error on histograms and regression outputs for Sutterby nanomaterial fluidic model.

Self-consistent sharp interface theory of active condensate dynamics

Biomolecular condensates help organize the cell cytoplasm and nucleoplasm into spatial compartments with different chemical compositions. A key feature of such compositional patterning is the local enrichment of enzymatically active biomolecules which, after transient binding via molecular interactions, catalyze reactions among their substrates. Thereby, biomolecular condensates provide a spatial template for nonuniform concentration profiles of substrates. In turn, the concentration profiles of substrates, and their molecular interactions with enzymes, drive enzyme fluxes which can enable novel nonequilibrium dynamics. To analyze this generic class of systems, with a current focus on self-propelled droplet motion, we here develop a self-consistent sharp interface theory. In our theory, we diverge from the usual bottom-up approach, which involves calculating the dynamics of concentration profiles based on a given chemical potential gradient. Instead, reminiscent of control theory, we take the reverse approach by deriving the chemical potential profile and enzyme fluxes required to maintain a desired condensate form and dynamics. The chemical potential profile and currents of enzymes come with a corresponding power dissipation rate, which allows us to derive a thermodynamic consistency criterion for the passive part of the system (here, reciprocal enzyme-enzyme interactions). As a first-use case of our theory, we study the role of reciprocal interactions, where the transport of substrates due to reactions and diffusion is, in part, compensated by redistribution due to molecular interactions. More generally, our theory applies to mass-conserved active matter systems with moving phase boundaries. Published by the American Physical Society 2024

Electro osmotic flow of nanofluids within a porous symmetric tapered ciliated channel

AbstractIn this investigation, a comprehensive study has been made to reveal electro osmosis flow through a tapered ciliated symmetric porous channel. The flow is initiated due to metachronal dynamics of cilia. Axial electric field is deployed and thermal radiation phenomenon is scrutinised by applying convective conditions. The equations tackling the flow are non dimensionalized and simplified by capitalizing the low Reynolds number and long wave length approximations. Analytical solution is presented for well reputed Poissson equation and the axial velocity. Whereas, traverse velocity, temperature and nanofluids concentration profiles are examined numerically in MATHEMATICA. Variation of emerging crucial parameters on the velocity profile, temperature and concentration profiles, pressure gradient, pressure rise per wavelength, and on the velocity distribution inside the micro ciliated are exhibited with the aid of graphical deliberations. It worth to mention in this work that in case of tapered channel transverse velocity also has significant contribution in the flow, which is observed trivial in symmetric and non‐symmetric channel flows. Temperature of the nanofluid in the ciliated tapered channel is raised with permeability and thermal radiations phenomena and can be controlled with Helmholtz Smoluchowski velocity, and electroosmotic parameter. Pumping phenomena is affected with increase in Helmholtz Smoluchowski velocity and permeability. Reported investigation cover a informative insight about biological fluid system, may be beneficial for the understanding the flow through ductus efferentes of human reproductive tract since it assumed that cilia are responsible for the transport of sperm from rete testis to the epididymis, also have worth in cilia designed bio‐sensors and in certain drug delivery systems.

Characterization of Olive Oil Phenolic Extracts and Their Effects on the Aggregation of the Alzheimer's Amyloid-β Peptide and Tau.

The dietary consumption of extra virgin olive oil (EVOO) is believed to slow the progression of Alzheimer's disease (AD) symptoms. Its protective mechanisms are unclear, but specific EVOO phenolic compounds can individually impede the aggregation of amyloid-β (Aβ) peptides and the microtubule-associated protein tau, two important pathological manifestations of AD. It is unknown, however, whether the numerous and variable phenolic compounds that are consumed in dietary EVOO can collectively alter tau and Aβ aggregation as effectively as the individual compounds. The activity of these complex mixtures against Aβ and tau may be moderated by competition between active and nonactive phenolic components and by extensive derivatizations and isomerization. Here, phenolic mixtures extracted from two different EVOO sources are characterized and tested for how they modulate the aggregation of Aβ40 peptide and tau peptides in vitro. The chromatographic and NMR analysis of Greek and Saudi Arabian EVOO phenolic extracts reveals that they have different concentration profiles, and over 30 compounds are identified. Thioflavin T fluorescence and circular dichroism measurements show that relatively low concentrations (<20 μg/mL) of the Greek and Saudi extracts reduce the rate of Aβ40 aggregation and fibril mass, despite the extracts having different phenolic profiles. By contrast, the Greek extract reduces the rate of tau aggregation only at very high phenolic concentrations (>100 μg/mL). Most compounds in the extracts bind to preformed Aβ40 fibrils and release soluble Aβ oligomers that are mildly toxic to SH-SY5Y cells. Much higher (500 μg/mL) extract concentrations are required to remodel tau filaments into oligomers, and a minimal binding of phenolic compounds to the preformed filaments is observed. It is concluded that EVOO extracts having different phenol profiles are similarly capable of modulating Aβ40 aggregation and fibril morphology in vitro at relatively low concentrations but are less efficient at modulating tau aggregation. Over 2 M tonnes of EVOO are consumed globally each year as part of the Mediterranean diet, and the results here provide motivation for further clinical interrogation of the antiaggregation properties of EVOO as a potential protective mechanism against AD.

A neuro‐computational study of viscous dissipation and nonlinear Arrhenius chemical kinetics during the hypodicarbonous acid‐based hybrid nanofluid flow past a Riga plate

AbstractWe examine the flow of Casson hybrid nanofluid (Cu+/) through a Riga plate sensor with perforations that act as an electromagnetic actuator. The hypodicarbonous acid is considered a base fluid. The impact of Arrhenius chemical kinetics and viscous dissipation are taken into account during the dynamics. The problem is formulated by considering the heat and mass transfer. An appropriate scaling is used to reduce the complexity of the problem, and further transform it into a system of ordinary differential equations (ODEs). The reduced system is further set for the first‐order system of equations that are analyzed with the Artificial Neural Network (ANN) which is trained with the Levenberg–Marquardt algorithm. The results for the state variables are displayed through graphs and tables by performing 1000 independent iterations with tolerance and . The Hartman, Casson, and Richardson numbers with their increasing values enhance the velocity profile. The chemical reaction parameter and the Prandtl number decline the thermal and concentration profiles, respectively. The Statistical analysis in the form of regression and histograms is also carried out in each case. The absolute error (AE) ranges up to and validations that range up to are presented for the varying values of each parameter. A comparative analysis of the nanofluid (NF) and hybrid nanofluid (HNF) is performed in each case study. The results for skin friction and Nusselt number are displayed numerically in the form of tables and are compared with the available literature, where the accuracy and performance of ANN are proved.

Symmetry‐based analysis of nonlinear mixed convection in 3D EMHD nano‐Carreau fluid flow with Riga stretched surface effects and multi‐physical interactions

AbstractThis study presents a comprehensive investigation into the dynamics of an electrically magneto‐hydrodynamic (EMHD) nano‐Carreau fluid under nonlinear mixed convection. We develop a 3D steady‐state framework that incorporates various influential factors such as nonuniform heat source‐sink terms, nonlinear thermal radiation, Joule heating, and chemical reactions, along with the effects of a Riga stretched surface. Through rigorous analysis, we explore the impact of thermophoretic and Brownian motions on flow patterns and stagnation point velocities. Our study encompasses scenarios involving a Riga stretching sheet, EMHD phenomena, porous media, suction‐injection processes, and diverse slip conditions (momentum, heat, volume fractions), in conjunction with chemical reactions. By employing symmetry transformations, we transform complex partial differential equations (PDEs) into more manageable ordinary differential equations (ODEs), facilitating effective numerical solutions using the Lobatto IIIa bvp4c method in Matlab. The findings are presented through detailed graphical representations and comparative tables. Key findings include the observation that elevated Hartmann numbers contribute to reduced velocity yet enhanced temperature profiles, influenced by factors such as nonuniform heat distribution, thermal radiation, and viscous dissipation. Additionally, concentration profiles exhibit a diminishing trend with increased Lewis numbers, chemical reactions, and specific slip parameters.

Non-monotonic relations of galaxy star formation, radius, and structure at fixed stellar mass

ABSTRACT We investigate the relation between galaxy structure and star formation rate (SFR) in a sample of $\sim 2.9\times 10^{4}$ central galaxies with $z\lt 0.0674$ and axial ratios $b/a\gt 0.5$. The star-forming main sequence (SFMS) shows a bend around the stellar mass of $M_\ast \le {}M_c=2\times 10^{10}{}{\rm M}_{\odot }$. At $M_\ast \le {}M_c$, the SFMS follows a power-law $\text{SFR}\propto {}M_\ast ^{0.85}$, while at higher masses it flattens. $M_c$ corresponds to a dark matter halo mass of $M_\text{vir}\sim {}10^{11.8}{\rm M}_{\odot }$ where virial shocks occurs. Some galaxy structure (e.g. half-light radius, $R_e$) exhibits a non-monotonic dependence across the SFMS at a fixed $M_\ast$. We find $\text{SFR}\propto {R_e^{-0.28}}$ at fixed $M_\ast$, consistent with the global Kennicutt–Schmidt (KS) law. This finding suggests that galaxy sizes contribute to the scatter of the SFMS. However, at $M_\ast \gt M_c$ the relationship between SFR and $R_e$ diminishes. Low-mass galaxies above the mean of the SFMS have smaller radii, exhibit compact and centrally concentrated profiles resembling green valley (GV) and quiescent galaxies at the same mass, and have higher $M_{\text{H}_2}{/}M_\rm{H\,{\small I}}$. Conversely, those below the SFMS exhibit larger radii, lower densities, have no GV or quiescent counterparts at their mass and have lower $M_{\text{H}_2}/M_\rm{H\,{\small I}}$. The above data suggest two pathways for quenching low-mass galaxies, $M_\ast \le {}M_c$: a fast one that changes the morphology on the SFMS and a slow one that does not. Above $M_c$, galaxies below the SFMS resemble GV and quiescent galaxies structurally, implying that they undergo a structural transformation already within the SFMS. For these massive galaxies, CG are strongly bimodal, with SFMS galaxies exhibiting negative colour gradients, suggesting most star formation occurs in their outskirts, maintaining them within the SFMS.

Microstructural and kinetics analysis of FeB–Fe2B layer grown by pulsed-DC powder-pack boriding on AISI 316 L steel

In this study, novel findings were obtained regarding the influence of a 10 A current intensity on the growth of an FeB–Fe2B layer during pulsed-DC powder-pack boriding. Boride layer formation was carried out on AISI 316 L steel at 1123–1223 K for different exposure times at each temperature, considering 10 s polarity inversion cycles. The boride layer was characterized by x-ray diffraction and high-speed Berkovich nanoindentation, the latter being used to determine the hardness and reduced Young’s modulus mappings along the depth of the layer-substrate system. Moreover, the growth kinetics of the FeB–Fe2B layer on the steel’s surface was modeled using the heat balance integral method (HBIM). This involved transforming Fick’s second law into ordinary differential equations over time, assuming a quadratic boron concentration profile in space to determine the B diffusion coefficients in FeB and Fe2B, respectively. From the Arrhenius relationship, the B activation energies in the boride layer were estimated considering the contribution of the electromigration effect; the results showed an approximately 30% reduction compared to the values obtained in the conventional powder-pack boriding for AISI 316 L steel. Finally, the theoretical layer thickness obtained by the HBIM demonstrated an error of no more than 5% against the experimental FeB and FeB + Fe2B layer thickness values.

Cattaneo–Christov double diffusion model for the entropy analysis of a non-Darcian MHD Williamson nanofluid

This research is carried out to observe the fluid flow across a stratified sheet in the presence of non-linear thermal radiation. Through the process of similarity transformations, the partial differential equations (PDEs) governing the flow model are transformed into ordinary differential equations (ODEs), which are then numerically solved using the shooting method. This study comprehensively examines the influence of various flow parameters, including the inertial coefficient, magnetic parameter, Brownian motion parameter, radiation parameter, Prandtl number, thermophoresis parameter, and Brinkman number, on key thermophysical characteristics, such as the skin friction coefficient, and the rates of heat, mass, and entropy generation. Notably, the relative difference in the skin-friction coefficient increases with the Weissenberg number, ranging from approximately 1.8 to 2.5. The results indicate that reducing the Cattaneo–Christov temperature parameter decreases the temperature profile while increasing the concentration profile, whereas entropy generation initially rises with increasing Weissenberg number, but decreases near the surface.