International Journal of Modern Physics B

This study presents an investigation on the generalized Couette flow of two immiscible Newtonian fluids in an anisotropic porous medium. The flow occurs between two parallel plates, driven by the combined effects of an axial pressure gradient and the movement of the upper plate. The region between the plates is filled with an anisotropic porous medium characterized by directional permeability. An exact solution is derived for the proposed problem by considering appropriate boundary and interface conditions. The slip condition is employed at the lower plate of the channel which has a significant role in the flow mechanics of fluids flowing through porous medium. The effects of directional permeability on the flow of immiscible fluids are explored, and specific cases are presented. This study reveals a significant influence of directional permeability on the flow velocity of both fluids. Furthermore, quantitative conclusions are drawn regarding the shear stress at the lower and upper wall of the channel, with implications for the anisotropic nature of blood arteries. The findings contribute to a deeper understanding of fluid flow in anisotropic porous media and have potential applications in various engineering domains.

In this study we investigate a relatively new material for terahertz (THz) photoconductive antennas (PCAs): GaAs epitaxial films grown on (111)A-oriented semi-insulated GaAs substrates and doped with Si. GaAs:Si (111)A films with the required high resistance without postgrowth annealing have been grown by molecular-beam epitaxy. The Si doping of (111)A-oriented GaAs was expected to lead to the formation of acceptors that facilitate the activation of As${}_{\mathrm{\text{Ga}}}^{+}$ traps. The relaxation times of nonequilibrium charge carriers in the films were measured in pump-probe experiment, and, finally, the electron mobility was estimated from the carrier lifetime and current–voltage characteristics measured under pulsed pumping by Ti:sapphire femtosecond laser. Dipole and bow-tie PCAs were fabricated, and the THz emission spectra and the total THz emission power were measured with varying applied voltage and optical excitation power. The properties of GaAs:Si (111)A films and the PCAs based on them are compared with LTG-GaAs (100) and (111)A-oriented films.

This paper presents a theoretical framework for exploring the optical properties of layered materials. The derived analytical formulas for reflectance and transmittance spectra incorporate vertical valence-state transitions and appropriate boundary conditions for finite-width bulk materials, integrated with the generalized tight-binding model to account for intrinsic interactions and external fields. The study reveals distinct structures in the spectra of multilayer graphene for different stacking layers at low energies (∼0.2–0.8eV), attributed to interband transitions at the K point. Furthermore, the high-energy part (≳5eV) highlights thickness-dependent plasmon effects characterized by unique resonance frequencies in the optical spectra. These features depend on the dimensionality, interlayer coupling, and electronic structure of the material. This work provides a deeper understanding of the optical properties of layered structures, facilitating their exploration and characterization for diverse applications.

In this paper, the self-propelled movement on gyrotactic swimming microorganisms into this generalized slip flow by nanoliquid over the stretching cylinder with strong magnetic field is discussed. Constant wall temperature was pretended as well as the Nield conditions of boundary. The intuitive non-Newtonian particulate suspension was included into applying Casson fluid by the base liquid and nanoparticles. This formation on the bio-mathematical model gives the boundary value problem by the nonlinear partial differential equations. Primly, modeled numerical system was converted to nondimensional against this help on acceptable scaling variables and the bvp4c technique was used to acquire the mathematical outcomes on the governing system. This graphical description by significant parameters and their physical performance was widely studied. The Prandtl number has the maximum contribution (112.595%) along the selected physical parameters, whereas the Brownian motion has the least (0.00165%) heat transfer rate. Anyhow, Casson fluid was established for much helpful suspension of this method on fabrication and coatings, etc. Therefore, this magnetic field performs like the resistive force of that fluid motion, and higher energy was enlarged into the structure exhibiting strong thermal radiation.

For the first of its kind, Cr${}^{3+}$-substituted calcium hexaferrite (CaCr_xFe${}_{12-x}$O${}_{19}$ ($x=1$, 3, 5 and 7)) nanoparticles (NPs) were synthesized via a facile, economical, eco-friendly lemon juice extract mediated green solution combustion method. The samples were calcined followed by characterization. The Bragg reflections confirm the formation of a single phase M-type hexaferrite crystal structure. No other impurity or mixed phases are observed even after the substitution of Cr${}^{3+}$ to the host matrix. Meanwhile, the crystallite size decreases from 29.44 to 19.92nm with an increase in the substitution of Cr${}^{3+}$ ions. The surface morphological analysis shows the presence of agglomerated irregularly shaped NPs. The direct energy band gap estimated using Wood and Tauc’s relation depicts the decrease in energy band gap from 2.98 to 2.74eV with an increase in the substitution of Cr${}^{3+}$ ions. These Cr${}^{3+}$-substituted calcium hexaferrite NPs were predicted to be useful in high-frequency applications based on structural, dielectric, and magnetic studies.

In this paper, molecular dynamics method was used to design the grain boundary (GB) segregation structure of solute atom Mo in nanocrystalline nickel, and the effect of the segregation structure on the migration and deformation mechanism of nanocrystalline Ni–Mo alloy boundaries was studied. The results indicate that the addition of solute atom Mo can cause segregation at GBs, and the yield strength and tensile strength of nanocrystalline Ni are significantly increased through solid solution strengthening. Mo atoms segregation result in an increase of the GB thickness and stability of the GB. In addition, by labeling GB atoms and tracking their diffusion trajectories, it was found that after adding Mo atoms, the probability of atomic diffusion at GBs decreased. This indicates that Mo atoms reduce GB energy and improve GB stability. Meanwhile, as the Mo content increases, the degree of atomic disorder increases, and the probability of GB migration decreases. This leads to the inability of grains to merge and inhibit their growth, effectively improving the mechanical properties of the material. As the strain increases, the number and length of dislocations increase, and a large amount of entanglement occurs at GBs. With the increase of Mo content, the number of dislocations decreases sharply, with Shockley dislocations having the highest number. Shockley dislocations interact with other dislocations and hinder their generation and movement, forming a more stable dislocation system structure and increasing the strength of the alloy. Our work focuses on observing the influence of GB segregation structure on the mechanical properties and deformation mechanism of nanocrystalline polycrystalline Ni–Mo alloys, establishing the mechanism of the influence of segregation structure on the stability and coarsening of nanocrystalline metal GBs, examining the influence of segregation structure on dislocation motion and GB migration process during deformation, and proposing positive research and development ideas and theoretical basis for designing nanocrystalline metal materials with excellent performance.

Theoretical research has been done on the hydromagnetic three-dimensional nanofluid flow across an inclined stretching sheet in the presence of Brownian motion and thermophoresis. It is taken into account that there are two different kinds of water-based nanofluids that contain copper and alumina. Three-dimensional nonlinear-type similarity transformations are used to convert the governing boundary-layer equations into a collection of similarity equations, which are then numerically solved by MATLAB. Further, results obtained in some limiting cases are compared to some results that have already been published, and it is found that there is good agreement. The problem is controlled by a number of physical factors, and the impact of these factors on different flow distributions is thoroughly examined with the help of graphs and tables. It has been observed that the nanofluid has better heat transfer conductivity than the ordinary base fluid.

The study rigorously investigates the propagation of sound waves from an infinite duct lined with three different finite acoustically absorbing materials. Due to multiple discontinuity points, the mode matching method effectively solved the problem. The mathematical equations involved are highly complex due to three distinct and finite linings. To overcome this, a numerical solution is obtained, and the effects of the geometry’s parameters on the transmission loss are thoroughly examined. As the length of the finite acoustic absorbing lining increases, the transmission loss decreases. In addition, the graphs clearly illustrate the substantial influence that the choice of absorbing lining can have on transmission loss. These findings hold great relevance for absorber systems, highlighting the importance of careful selection in order to achieve optimal performance. The obtained results are compared with another study, and complete agreement is observed, indicating the study’s accuracy and reliability.

To describe the four fundamental interactions observed in the universe, we used the Dirac equation containing an interaction of the screened Kratzer and the Hulthen potential with a ring-shaped term. We study the energy spectra of spin-$1/2$ particles in noncompact extra dimensions. The polar and angular parts of the N-dimensional Dirac equation are solved using the Nikiforov–Uvarov method. The transcendental energy equation and the associated two components spinor wavefunctions of the spin-$1/2$ particles are obtained. Moreover, we obtained the nonrelativistic limit of our results by mean of a specific mapping. Some special cases of the proposed potential have been discussed, and their corresponding eigenvalue energies were determined. Finally, we proposed that our results can be used in many branches of physics, to investigate scenarios in extra dimensions where spin-$1/2$ particles are involved. To test the reliability of our model, we computed the numerical values of the energy spectra of lithium hydride and hydrogen chloride diatomic molecules using a special case of the proposed potential. The energy spectra are calculated for different quantum numbers $(n,l)$ at different values of the dimensionality of the space. The results of this research are overall in good agreement with the theoretical studies of similar investigation.

In this analysis, we have considered heat transmission in two-dimensional steady laminar nanofluid flow past a wedge. Magnetohydrodynamic (MHD), Brownian motion, viscous dissipation and thermophoresis effects are considered over the porous surface. Similarity transformations have been used to change the governing partial differential equations (PDEs) into nonlinear higher-order ordinary differential equations (ODEs). Governing ODEs with boundary conditions are then converted to the system of first-order initial value problem. After that the modeled system is solved numerically by RK4 technique. Impact of the magnetic number, Eckert number, Prandtl number, Lewis number, Brownian motion, thermophoresis and permeability parameters on the flow domain is analyzed graphically as well as in tabular form. It is noted that magnitude of Nusselt number for the flow regime increases with the increase of nondimensional parameter $Pr,Nb,Nt$ while opposite behavior is observed in case of R.

Recently, we formulated an effective scalar electrodynamics model of relativistic type-II superconductivity. We discussed possible electromagnetic behaviors of superconductivity along the lines of the nonrelativistic Ginzburg–Landau theory. This brief work considers a $2$D condensate subjected not only to a homogeneous magnetic field but also to a static radial electric field (polar coordinates). The electric field is regarded to have two components: a central constant field and a Coulomb-like field with “charge” g, where g can take only evenly spaced real numbers. We provide the single-vortex supercurrent density together with its associated magnetic flux density for the ground state of the system. Feasible extensions of this example in $3$D curvilinear geometries could explain some superconductivity phenomena which do not occur in planar $2$D geometries.

This paper aims to investigate the behavior of LiMgN half-Heusler (HH) semiconductor doped by transition metals (TM $=$ Mn, Fe, Co and Ni). HHs belong to the $F\bar{4}3m$ space group (No. 216) and have a zinc blende structure that can be described by the chemical symbol XYZ. The research methodology utilized in this investigation involves theoretical analysis based on the principles of density functional theory (DFT). The studied LiMg${}_{0.95}$TM${}_{0.05}$N alloy displayed the half-metallicity behavior when TM $=$ Fe, Co and Ni. Hence, these systems could be a promising candidate in spintronic application thanks to their ferromagnetism. The principal contribution to magnetism in the full LiMg${}_{0.95}$TM${}_{0.05}$N alloys comes from the Mn, Fe, Co and Ni doping. The partial magnetic moments of these elements are significantly greater than the combined partial magnetic moments of Li, Mg and N. When comparing LiMg${}_{0.95}$Mn${}_{0.05}$N to LiMg${}_{0.95}$Fe${}_{0.05}$N, ₅Co${}_{0.05}$N and LiMg${}_{0.95}$Ni${}_{0.05}$N, it is important to note that the exchange splitting energy ${\mathrm{\Delta }}_{(e^{+},e^{-})}^{\mathrm{\text{TM}}}$ associated to their spin up and spin down were discussed. The variation of Mn(3d) in relation to ($e^{+},e^{-}$) is larger than that of Fe, Co and Ni. Therefore, ${\mathrm{\Delta }}_{(e^{+},e^{-})}^{\mathrm{\text{Mn}}}>{\mathrm{\Delta }}_{(e^{+},e^{-})}^{\mathrm{\text{Fe}}}>{\mathrm{\Delta }}_{(e^{+},e^{-})}^{\mathrm{\text{Co}}}>{\mathrm{\Delta }}_{(e^{+},e^{-})}^{\mathrm{\text{Ni}}}$. Furthermore, there is a correlation between the magnetic moment and electronegativity trend of the TM dopant. Specially, the electronegativity trend (${\chi }^{\mathrm{\text{TM}}})$ is well matched with the total spin moment trend, where ${\chi }^{\mathrm{\text{Ni}}}>{\chi }^{\mathrm{\text{Co}}}>{\chi }^{\mathrm{\text{Fe}}}>{\chi }^{\mathrm{\text{Mn}}}$.

Structural, electronic, magnetic and optical properties of Cu₄Mn₂Te₄ have been reported earlier by the authors, and here, the transport properties of the same are discussed along with the band structure investigation of the neodymium-doped cubic material LMO (LiMn₂O₄), namely LiMn${}_{1.75}$Nd${}_{0.25}$O₄ compound, under spin polarized schemes through the First Principles calculations. The Full Potential-Linearized Augumented Plane Wave Method (FP-LAPW) method is adopted to investigate the electronic structures based on the framework of Density Functional Theory (DFT). Exchange potentials are treated using the Generalized Gradient Approximations (GGA). Cohesive energy calculations reveal that the ferromagnetic phase of LiMn${}_{1.75}$Nd${}_{0.25}$O₄ and the antiferromagnetic phase of Cu₄Mn₂Te₄ exhibits a stable phase. Of these, FM-LiMn${}_{1.75}$Nd${}_{0.25}$O₄ shows a semi-metallic-like behavior in spin-up channel and metallic behavior in spin-down channel whereas antiferromagnetic Cu₄Mn₂Te₄ exhibits a band gap in both spin-up and spin-down channels. Dirac points are identified at −0.0625eV in the band structure plot of FM-LiMn${}_{1.75}$Nd${}_{0.25}$O₄ at its high symmetry points $\mathrm{\Gamma }$ and W which is an indication of high electron mobility at ambient condition. The presence of flat and dispersive bands around the Fermi energy level is an indication of high thermopower, and it is present in both the compounds FM-LiMn${}_{1.75}$Nd${}_{0.25}$O₄ and AFM-Cu₄Mn₂Te₄. From the present computations, at 300K, a power factor range of ($S^2\sigma$ scaled by relaxation time in $\mu$W/msK²) $1.75\times 10^{20}\uparrow$ and $9.37\times 10^{21}\downarrow$ is obtained for ferromagnetic LiMn${}_{1.75}$Nd${}_{0.25}$O₄ compounds at up and down spins, respectively. A typical power factor ($\mu$Wm${}^{-1}$s${}^{-1}$K${}^{-2}$) of $4.79\times 10^{15}\uparrow$ and $2.97\times 10^{18}\downarrow$ is obtained for antiferromagnetic Cu₄Mn₂Te₄ at 325K required for good thermoelectric performance.

The aim of this study is to investigate the entropy production characteristics of two non-miscible fluids in an inclined porous channel with temperature-dependent thermal conductivity and viscosity. The porous region of the channel is divided in two regions. In region-1 and region-2, the Couple stress and Newtonian fluid take place due to constant pressure gradient, respectively, under the influence of a uniform magnetic field. Here, the Darcy–Brinkman model is used for the flow of immiscible fluid through the porous media. In this work, we used a semi-analytical method named as homotopy analysis method (HAM) to solve the coupled nonlinear ordinary differential equations. The goal of the considered problem is to examine the consequences of a variety of thermophysical parameters, including Hartmann number, varying viscosity parameter, varying thermal conductivity parameters, and Grashof number on the characteristics of entropy generation, Bejan number distribution, thermal behavior and flow characteristics of non-miscible couple stress and Newtonian fluid passing through a porous channel. The novel aspect of this study is the formation of entropy and Bejan number as a result of non-miscible Newtonian and couple stress fluids with varying thermal conductivity and viscosity in porous media. In terms of rheological investigation, a semi-analytical simulation for changeable thermal and flow properties in an immiscible Newtonian and couple stress fluid via an inclined porous channel is a brand-new concept, and the behaviors of such flows have not been examined yet. From this study, it is concluded that on raising the variable thermal conductivity, Hartmann number and the permeability of the porous medium, the flow velocity, thermal characteristics and entropy generation number decrease. The authors also come to the significant conclusion that non-miscible Newtonian and couple stress fluids have larger entropy production numbers, flow velocities, and temperature profiles for higher values of Grashof number, variable viscosity parameter, and couple stress parameter. The findings of this work have also been graphically validated through the previously established work. The results of the present analysis can be used in petroleum industry, lubrication theory, etc.

This paper investigates the acoustic streaming effects (ASEs) and mechanisms behind the transmittance of sound in a metallic micro-cavity acoustic black hole (ABH) structure with an abrupt cross-section and examines the sound field flow characteristics inside the micro-cavity ABH under the sound excitation, such as the velocity, acceleration and pressure fields. And the sound transmission mechanisms are characterized by the ASEs which can be obtained by solving Navier–Stokes equations. The numerical results show that the sharp increase in the velocity and acceleration at the ABH tip position is the main reason for the focusing of the sound energy. And the dramatic increase in the tip cross-section reduces the acoustic streaming velocity, which is the main reason for the attenuation of the sound energy. Additionally, the thermoviscous effect of the acoustic boundary layer can also dissipate the low-frequency sound energy. The sound insulation experiment shows that the proposed micro-cavity ABH structure has a sound transmission loss (STL) of over 15dB in the low-frequency regime. This research reveals the mechanisms of the ASE’s work on the sound transmission properties of the micro-cavity ABH and provides new insight into low-frequency sound wave suppression. The ABH structure proposed in this paper has excellent strength, bearing capacity and long lifecycle, so it can be applied in the construction industry through its integrated design of structure and performance.