Showing papers in "AIP Advances in 2022"

Accurate demonstrating of the interactions of two long waves with different dispersion relations: Generalized Hirota–Satsuma couple KdV equation

Abstract: In this study, the generalized formula of the Hirota–Satsuma coupled KdV equation derived by Hirota and Satsuma in 1981 [Hirota and Satsuma, Phys. Lett. A 85, 407−408 (1981)] is analytically and semi-analytically investigated. This model is formulated to describe the interaction of two long undulations with diverse dispersion relations; that is why it is also known with a generalized model of the well-known KdV equation. The generalized Kudryashov and Adomian decomposition methods construct novel soliton wave and semi-analytical solutions. These solutions are represented in some distinct graphs to show the waves’ interactions. In addition, the accuracy of solutions is verified by comparing the obtained analytical and semi-analytical solutions that show the matching between them. All solutions are checked by putting them back into the original model through Mathematica 12.

Design and numerical investigation of cadmium telluride (CdTe) and iron silicide (FeSi2) based double absorber solar cells to enhance power conversion efficiency

Abstract: Inorganic CdTe and FeSi2-based solar cells have recently drawn a lot of attention because they offer superior thermal stability and good optoelectronic properties compared to conventional solar cells. In this work, a unique alternative technique is presented by using FeSi2 as a secondary absorber layer and In2S3 as the window layer for improving photovoltaic performance parameters. Simulating on SCAPS-1D, the proposed double-absorber (Cu/FTO/In2S3/CdTe/FeSi2/Ni) structure is thoroughly examined and analyzed. The window layer thickness, absorber layer thickness, acceptor density ( N A), donor density ( N D), defect density ( N t), series resistance ( R S), and shunt resistance ( R sh) were simulated in detail for optimization of the above configuration to improve the PV performance. According to this study, 0.5 µm is the optimized thickness for both the CdTe and FeSi2 absorber layers in order to maximize the efficiency ( η). Here, the value of the optimum window layer thickness is 50 nm. For using CdTe as a single absorber, η is achieved by 13.26%. However, for using CdTe and FeSi2 as a dual absorber, η is enhanced and the obtaining value is 27.35%. The other parameters are also improved and the resultant value for the fill factor is 83.68%, the open-circuit voltage ( V oc) is 0.6566 V, and the short circuit current density ( J sc) is 49.78 mA/cm2. Furthermore, the proposed model performs well at 300 K operating temperature. The addition of the FeSi2 layer to the cell structure has resulted in a significant quantum efficiency enhancement because of the rise in solar spectrum absorption at longer wavelengths ( λ). The findings of this work offer a promising approach for producing high-performance and reasonably priced CdTe-based solar cells.

First-principles insights into the electronic, optical, mechanical, and thermodynamic properties of lead-free cubic ABO3 [A = Ba, Ca, Sr; B = Ce, Ti, Zr] perovskites

Abstract: A comparative study on mechanical, thermodynamic, electronic, and optical properties has been performed on various compounds having an ABO3, where A = Ba, Ca, Sr and B = Ce, Ti, Zr, perovskite structure using first-principles calculations. These materials’ properties have been thoroughly investigated for their ground states under the same computational parameters. The computed lattice parameters in the ground state agreed with other theoretical studies. Elastic moduli, ductility or brittleness, elastic anisotropy, mechanical stability, and stiffness of solid materials are studied. Enthalpy (H), entropy (S), and free energy (F) were reported from the vibrational properties of the materials. The temperature-dependent heat capacity and Debye temperature are investigated. The electronic band structure as a function of energy, of different perovskite structures at the ground state, is also studied. From this study, the ABO3 perovskite has emerged as the most promising material for applications in optoelectronics, photonics, and mechanical and thermoelectric devices.

Tunable broadband terahertz metamaterial absorber based on vanadium dioxide

Abstract: The special electromagnetic properties of metamaterials have contributed to the development of terahertz technology, and terahertz broadband absorbers for various applications have been investigated. The design of metamaterial absorbers with tunability is in a particularly attractive position. In this work, a tunable broadband terahertz metamaterial absorber is proposed based on the phase transition material vanadium dioxide (VO2). The simulation results show that an excellent absorption bandwidth reaches 3.78 THz with the absorptivity over 90% under normal incidence. The absorptivity of the proposed structure can be dynamically tuned from 2.7% to 98.9% by changing the conductivity of VO2, which changes the structure from a perfect reflector to an absorber. An excellent amplitude modulation with the absorptivity is realized. The mechanism of broadband absorption is explored by analyzing the electric field distribution of the absorber based on impedance matching theory. In addition, it also has the advantage of polarization and incident angle insensitivity. The proposed absorber may have a wide range of promising applications in areas such as terahertz imaging, sensing, and detection.

First-principles insights into mechanical, optoelectronic, and thermo-physical properties of transition metal dichalcogenides ZrX2 (X = S, Se, and Te)

Abstract: Transition metal dichalcogenides (TMDCs) belong to technologically important compounds. We have explored the structural, elastic, bonding, optoelectronic, and some thermo-physical properties of ZrX2 (X = S, Se, and Te) TMDCs in detail via the ab initio technique in this work. Elastic anisotropy indices, atomic bonding character, optoelectronic properties, and thermo-physical parameters, including melting temperature and minimum phonon thermal conductivity, are investigated for the first time. All the TMDCs under investigation possess significant elastic anisotropy and layered structural features. ZrX2 (X = S, Se, and Te) compounds are fairly machinable, and ZrS2 and ZrSe2 are moderately hard. ZrTe2, on the other hand, is significantly softer. Both covalent and ionic bondings contribute in the crystals. Electronic band structure calculations display semiconducting behavior for ZrS2 and ZrSe2 and metallic behavior for ZrTe2. Energy dependent optoelectronic parameters exhibit good correspondence with the underlying electronic energy density of state features. ZrX2 (X = S, Se, and Te) compounds absorb ultraviolet radiation effectively. The reflectivity spectrum, R(ω), remains over 50% in the energy range from 0 to ∼20 eV for ZrTe2. Therefore, this TMDC has a wide band and nonselective high reflectivity and can be used as an efficient reflector to reduce solar heating. The Debye temperature, melting point, and minimum phonon thermal conductivity of the compounds under study are low and show excellent correspondence with each other and also with the theoretically predicted elastic and bonding characteristics.

Epitaxial growth of β-Ga2O3 by hot-wall MOCVD

Abstract: The hot-wall metalorganic chemical vapor deposition (MOCVD) concept, previously shown to enable superior material quality and high performance devices based on wide bandgap semiconductors, such as Ga(Al)N and SiC, has been applied to the epitaxial growth of β-Ga2O3. Epitaxial β-Ga2O3 layers at high growth rates (above 1 μm/h), at low reagent flows, and at reduced growth temperatures (740 °C) are demonstrated. A high crystalline quality epitaxial material on a c-plane sapphire substrate is attained as corroborated by a combination of x-ray diffraction, high-resolution scanning transmission electron microscopy, and spectroscopic ellipsometry measurements. The hot-wall MOCVD process is transferred to homoepitaxy, and single-crystalline homoepitaxial β-Ga2O3 layers are demonstrated with a [Formula: see text]01 rocking curve width of 118 arc sec, which is comparable to those of the edge-defined film-fed grown ([Formula: see text]01) β-Ga2O3 substrates, indicative of similar dislocation densities for epilayers and substrates. Hence, hot-wall MOCVD is proposed as a prospective growth method to be further explored for the fabrication of β-Ga2O3.

Multi-level operation in VO2-based resistive switching devices

Abstract: Vanadium dioxide (VO 2 ) is widely studied for its prominent insulator–metal transition (IMT) near room temperature, with potential applications in novel memory devices and brain-inspired neuromorphic computing. We report on the fabrication of in-plane VO 2 metal–insulator–metal structures and reproducible switching measurements in these two-terminal devices. Resistive switching can be achieved by applying voltage or current bias, which creates Joule heating in the device and triggers the IMT. We analyze the current/voltage-induced resistive switching characteristics, including a pronounced intermediate state in the reset from the low to the high resistance state. Controllable switching behavior is demonstrated between multiple resistance levels over several orders of magnitude, allowing for multibit operation. This multi-level operation of the VO 2 -bridge devices results from exploiting sub-hysteresis loops by Joule heating.

Improved conversion efficiency of p-type BaSi2/n-type crystalline Si heterojunction solar cells by a low growth rate deposition of BaSi2

Abstract: The effect of low growth rate deposition (LGD) of BaSi2 on the film quality and performance of silicon heterojunction solar cells was investigated. The total thickness of the BaSi2 layer decreased with increasing LGD duration ( tLGD). Analysis using Raman spectroscopy indicated that an amorphous Si (a-Si) phase existed on the surface of the BaSi2 layer. The a-Si on the surface was converted into BaSi2 by post-annealing owing to the diffusion of Ba and Si atoms. X-ray diffraction analysis revealed that LGD improved the rate of a-axis orientation and crystallinity. Post-annealing was also observed to have significantly improved these structural properties. Furthermore, the solar cell performance was observed to be strongly dependent on tLGD, and the highest conversion efficiency of 10.62% was achieved by the p-BaSi2/n-c-Si heterojunction solar cells at a tLGD of 6 min. The improved structure and solar cell properties are attributed to improved atom rearrangement during LGD.

Machine learning symbolic equations for diffusion with physics-based descriptions

Abstract: This work incorporates symbolic regression to propose simple and accurate expressions that fit to material datasets. The incorporation of symbolic regression in physical sciences opens the way to replace “black-box” machine learning techniques with representations that carry the physical meaning and can reveal the underlying mechanism in a purely data-driven approach. The application here is the extraction of analytical equations for the self-diffusion coefficient of the Lennard-Jones fluid by exploiting widely incorporating data from the literature. We propose symbolic formulas of low complexity and error that achieve better or comparable results to well-known microscopic and empirical expressions. Results refer to the material state space both as a whole and in distinct gas, liquid, and supercritical regions.

Analysis of super-resolution single molecule localization microscopy data: A tutorial

Abstract: Abstract

Dynamics of chaotic system based on image encryption through fractal-fractional operator of non-local kernel

Abstract: In this paper, the newly developed fractal-fractional differential and integral operators are used to analyze the dynamics of chaotic system based on image encryption. The problem is modeled in terms of classical order nonlinear, coupled ordinary differential equations that are then generalized through fractal-fractional differential operator of Mittag-Leffler kernel. In addition to that, some theoretical analyses, such as model equilibria, existence, and uniqueness of the solutions, have been proved. Furthermore, the highly non-linear problem is solved by adopting a numerical scheme through MATLAB software. The graphical solution is portrayed through 2D and 3D portraits. Some interesting results are concluded considering the variation of fractional-order parameter and fractal dimension parameter.

Silver-modified graphene oxide nanosheets for antibacterial performance of bone scaffold

Abstract: Endowing scaffold with antibacterial activity is an effective countermeasure to prevent bacterial infection in bone repair. Silver nanoparticles (Ag NPs) possess broad-spectrum antibacterial efficiency, whereas the agglomeration and burst releasing of Ag NPs hindered their clinic application in bone repair. In this work, Ag NPs were in situ grown on graphene oxide (GO) to construct Ag@GO nanohybrids and then were introduced into polymer scaffold. GO could efficiently load Ag NPs thereby improving their agglomeration in a scaffold, owing to their abundant active groups and large surface areas. Furthermore, GO could realize the sustained release of Ag ions from the scaffold. The results demonstrated the antibacterial scaffold exhibited robust antibacterial performance with an antibacterial rate of 95% against Staphylococcus aureus. On one hand, GO with honeycomb nanostructure and sharp edge could capture and pierce bacteria membrane, which results in physical damage of bacteria. On the other hand, the released Ag NPs from Ag@GO nanohybrids could promote the generation of reactive oxygen species, which causes the inactivation of bacteria. Encouragingly, the antibacterial scaffold also exhibited good cytocompatibility. This work developed an efficient antibacterial material for the scaffold in bone repair.

Approximate solution to a generalized Van der Pol equation arising in plasma oscillations

Abstract: Motivated by some published theoretical investigations and based on the two-fluid model, nonlinear plasma oscillations are analyzed and discussed in the framework of the generalized Van der Pol equation. This equation is analyzed and solved using two different analytical approaches. In this first approach, the ansatz method is carried out for deriving an approximation in the form of a trigonometric function. In the second approach, the Krylov–Bogoliubov–Mitropolsky (KBM) technique is applied for obtaining a high-accurate approximation. The obtained approximations are compared with the numerical approximation using the Runge–Kutta (RK) method. Moreover, the distance error between the obtained approximations (using the ansatz method and the KBM technique) and the RK numerical approximation is estimated. In our investigation, both the proposed methods and obtained approximations can help many authors investigate several nonlinear oscillations in different plasma models and fluid mechanics.

Experimental protocol for testing the mass–energy–information equivalence principle

Abstract: The mass–energy–information equivalence principle proposed in 2019 and the information content of the observable matter in the universe estimated in 2021 represent two important conjectures, called the information conjectures. Combining information theory and physical principles of thermodynamics, these theoretical proposals made specific predictions about the mass of information as well as the most probable information content per elementary particle. Here, we propose an experimental protocol that allows for empirical verification of the information conjectures by confirming the predicted information content of elementary particles. The experiment involves a matter–antimatter annihilation process. When an electron–positron annihilates, in addition to the two 511 keV gamma photons resulting from the conversion of their rest masses into energy, we predict that two additional low energy photons should be detected, resulting from their information content erasure. At room temperature, a positron–electron annihilation should produce two ∼50 µm wavelength infrared photons due to the information erasure. This experiment could, therefore, confirm both information conjectures and the existence of information as the fifth state of matter in the universe.

Deep learning fluid flow reconstruction around arbitrary two-dimensional objects from sparse sensors using conformal mappings

Abstract: The usage of neural networks (NNs) for flow reconstruction (FR) tasks from a limited number of sensors is attracting strong research interest, owing to NNs’ ability to replicate high dimensional relationships. Trained on a single flow case for a given Reynolds number or over a reduced range of Reynolds numbers, these models are unfortunately not able to handle flows around different objects without re-training. We propose a new framework called Spatial Multi-Geometry FR (SMGFR) task, capable of reconstructing fluid flows around different two-dimensional objects without re-training, mapping the computational domain as an annulus. Different NNs for different sensor setups (where information about the flow is collected) are trained with high-fidelity simulation data for a Reynolds number equal to approximately 300 for 64 objects randomly generated using Bezier curves. The performance of the models and sensor setups are then assessed for the flow around 16 unseen objects. It is shown that our mapping approach improves percentage errors by up to 15% in SMGFR when compared to a more conventional approach where the models are trained on a Cartesian grid, and achieves errors under 3%, 10% and 30% for pressure, velocity and vorticity fields predictions, respectively. Finally, SMGFR is extended to predictions of snapshots in the future, introducing the Spatio-temporal MGFR (STMGFR) task. A novel approach is developed for STMGFR involving splitting DNNs into a spatial and a temporal component. We demonstrate that this approach is able to reproduce, in time and in space, the main features of flows around arbitrary objects.

Tunable triple-band millimeter-wave absorbing metasurface based on nematic liquid crystal

Abstract: Abstract

Numerical analysis of pressure pulsation in vertical submersible axial flow pump device under bidirectional operation

Abstract: In order to analyze the pressure pulsation characteristics of a single-conduit vertical submersible axial-flow pump device under bidirectional operation, the unsteady numerical simulation of the pump device was carried out based on computational fluid dynamics. The pressure pulsation coefficient and fast Fourier transform were used to analyze the pulsation of each monitoring point in the time–frequency domain. The results show that the pressure pulsation at different positions of the pump device is mainly affected by the impeller rotation, and the amplitude is large at the blade frequency and its harmonic frequency. In the positive operation, the main frequency of pressure pulsation at each monitoring point at the inlet of the impeller is three times the rotating frequency, and in the reverse operation, the main frequency of pressure pulsation at each monitoring point is 0.5 times the rotating frequency. The amplitude of pressure pulsation at each monitoring point at the inlet of the impeller is less than that of the positive operation, while the amplitude of pressure pulsation at the outlet of the impeller and the guide vane is larger than that of the positive operation. In the positive and reverse operation, the axial force of the impeller is significantly affected by the inlet velocity, and the amplitude of the axial force is small in the rotation period. The axial force increases with the increase of flow rate. The radial force of the impeller is significantly affected by the inflow flow pattern. The radial force changes obviously in the rotation period, and the radial force does not change regularly with the flow rate. The radial force of the impeller under reverse operation is 7.75 times that under positive operation.

Dynamical geography and transition paths of Sargassum in the tropical Atlantic

Abstract: By analyzing a time-homogeneous Markov chain constructed using trajectories of undrogued drifting buoys from the NOAA Global Drifter Program, we find that probability density can distribute in a manner that resembles very closely the recently observed recurrent belt of high Sargassum concentration in the tropical Atlantic between 5 and 10°N, coined the Great Atlantic Sargassum Belt ( GASB). A spectral analysis of the associated transition matrix further unveils a forward attracting almost-invariant set in the northwestern Gulf of Mexico with a corresponding basin of attraction weakly connected with the Sargasso Sea but including the nutrient-rich regions around the Amazon and Orinoco rivers mouths and also the upwelling system off the northern coast of West Africa. This represents a data-based inference of potential remote sources of Sargassum recurrently invading the Intra-Americas Seas (IAS). By further applying Transition Path Theory (TPT) to the data-derived Markov chain model, two potential pathways for Sargassum into the IAS from the upwelling system off the coast of Africa are revealed. One TPT-inferred pathway takes place along the GASB. The second pathway is more southern and slower, first going through the Gulf of Guinea, then across the tropical Atlantic toward the mouth of the Amazon River, and finally along the northeastern South American margin. The existence of such a southern TPT-inferred pathway may have consequences for bloom stimulation by nutrients from river runoff.

Dynamically tunable terahertz metamaterial sensor based on metal–graphene hybrid structural unit

Abstract: By verifying the electromagnetic response characteristics of graphene in the low terahertz (THz) band, a terahertz metamaterial sensor is proposed. The unit cell of the metamaterial sensor is a split ring resonator nested square ring resonator. The split ring resonator with four gaps is made of lossy metal, and the square ring resonator is formed by graphene. This structure can produce two high-performance resonant valleys in the transmission spectrum of 0.1–1.9 THz. The quantum interference between metal–graphene hybrid units also produces a reverse electromagnetically induced transparency (EIT)-like resonant peak between the two resonant valleys. Compared with the bimetallic ring resonator having the same shape and size, the sensor can dynamically adjust the position of the lower frequency resonant valley, thus, realizing the active tuning of the bandwidth and amplitude of the EIT-like resonant peak. The results demonstrate that the proposed sensor has a better sensing performance and can improve the detection precision by tuning itself to avoid the interference of environmental factors and the properties of samples. Combined with the advantages of convenience, rapidity, and non-damage of terahertz spectrum detection, the sensor has a good application potential to improve the unlabeled trace matter detection.

Application of two-phase transition model in underwater explosion cavitation based on compressible multiphase flows

Abstract: Abstract

Demonstration of 621-nm-wavelength InGaN-based single-quantum-well LEDs with an external quantum efficiency of 4.3% at 10.1 A/cm2

Abstract: Here, we report highly efficient InGaN-based red light-emitting diodes (LEDs) grown on conventional c-plane-patterned sapphire substrates. An InGaN single quantum well active layer provides the red spectral emission. The 621-nm-wavelength LEDs exhibited high-purity emission with a narrow full-width at half-maximum of 51 nm. The packaged LED’s external quantum efficiency, light-output power, and forward voltage with a 621 nm peak emission wavelength at 20 mA (10.1 A/cm2) injection current were 4.3%, 1.7 mW, and 2.96 V, respectively. This design development represents a valuable contribution to the next generation of micro-LED displays.

A 3D finite element model to study the cavitation induced stresses on blood–vessel wall during the ultrasound-only phase of photo-mediated ultrasound therapy

Abstract: Photo-mediated ultrasound therapy (PUT) is a novel technique utilizing synchronized ultrasound and laser to generate enhanced cavitation inside blood vessels. The enhanced cavitation inside blood vessels induces bio-effects, which can result in the removal of micro-vessels and the reduction in local blood perfusion. These bio-effects have the potential to treat neovascularization diseases in the eye, such as age-related macular degeneration and diabetic retinopathy. Currently, PUT is in the preclinical stage, and various PUT studies on in vivo rabbit eye models have shown successful removal of micro-vessels. PUT is completely non-invasive and particle-free as opposed to current clinical treatments such as anti-vascular endothelial growth factor therapy and photodynamic therapy, and it precisely removes micro-vessels without damaging the surrounding tissue, unlike laser photocoagulation therapy. The stresses produced by oscillating bubbles during PUT are responsible for the induced bio-effects in blood vessels. In our previous work, stresses induced during the first phase of PUT due to combined ultrasound and laser irradiation were studied using a 2D model. In this work, stresses induced during the third or last phase of PUT due to ultrasound alone were studied using a 3D finite element method-based numerical model. The results showed that the circumferential and shear stress increased as the bubble moves from the center of the vessel toward the vessel wall with more than a 16 times increase in shear stress from 1.848 to 31.060 kPa as compared to only a 4 times increase in circumferential stress from 211 to 906 kPa for a 2 µm bubble placed inside a 10 µm vessel on the application of 1 MHz ultrasound frequency and 130 kPa amplitude. In addition, the stresses decreased as the bubble was placed in smaller sized vessels with a larger decrease in circumferential stress. The changes in shear stress were found to be more dependent on the bubble–vessel wall distance, and the changes in circumferential stress were more dependent on the bubble oscillation amplitude. Moreover, the bubble shape changed to an ellipsoidal with a higher oscillation amplitude in the vessel’s axial direction as it was moved closer to the vessel wall, and the bubble oscillation amplitude decreased drastically as it was placed in vessels of a smaller size.

Elastocaloric effect characterization of a NiTi tube to be applied in a compressive cooler

Abstract: In this article, the elastocaloric effect of a commercial superelastic NiTi shape memory alloy (SMA) tube (with an outer diameter of 5 mm and wall thickness of 1 mm) to be applied in a compressive cooler was measured and analyzed. The elastocaloric effect of the tube was measured vs the applied strain and strain rate. The largest temperature changes of 21 K during loading and 16 K during unloading were measured at an applied strain of 3.30% and strain rate of 0.33 s−1. In the fatigue testing of the sample, only 0.20% of the residual strain accumulated after a runout of 1 × 106 sinusoidal force-controlled loading–unloading cycles at a maximum compressive stress of 1100 MPa and frequency of 20 Hz. Numerical results of the cooling characteristics of a compressive device using a single NiTi tube with the above-mentioned cross section and an aspect ratio of 60:1 as the refrigerant showed that the device could produce a total cooling power of up to 20 W and a coefficient of performance of up to 6.5. The results of this article demonstrate that superelastic NiTi SMA tubes of suitable wall thickness and aspect ratios are good candidates to be applied in a compressive elastocaloric cooler.

Nonlinear static and dynamic performance of CNT reinforced and nanoclay modified laminated nanocomposite plate

Abstract: Under static and dynamic loading circumstances, the mechanically and thermo-initiated nonlinear static and dynamic assessment of the bending response of single-walled carbon nanotubes’ (CNTs’) fibers with a nanoclay particle reinforced polymer hybrid laminated composite plate is investigated. To evaluate the effective elastic characteristics of the CNTs’ fibers on the nanoclay particle modified polymer hybrid laminated plate, a modified Halpin–Tsai method is applied in an orthotropic way. The theory of higher-order shear deformation and complete kinematics (nonlinear) are used to develop the fundamental nonlinear dynamic formulation. A user-interactive finite element method-based MATLAB program solves the governing equations for nonlinear dynamic systems utilizing Newmark’s period integration and the Newton–Raphson method. The effects of variation in the quantity of CNTs’ fibers and particles of nanoclay, presence of interphases around CNTs’ fibers and nanoclay particles, variation in phases of the CNTs’ fibers on the nanoclay particle modified polymer hybrid laminated plate, and variation in plies of the laminated hybrid plate under clamped and simply supported conditions on the transverse central deflection response are explored in depth.

Comparison between cold sintering and dry pressing of CaCO3 at room temperature by numerical simulations

Abstract: Numerical models of solid-state and liquid-phase sintering of CaCO3 at room temperature are developed for applied static pressures as high as 280 MPa. Under the applied static pressure of 280 MPa, solid-state sintering (dry pressing) also works at room temperature due to the significant increase in the magnitude of the strain rate caused by dislocation processes occurring within the grains. Under the applied static pressure as low as 10 MPa, solid-state sintering no longer works due to the drop in the magnitude of the strain rate caused by dislocation processes occurring within the grains. On the other hand, liquid-phase sintering (cold sintering) still works under 10 MPa at room temperature due to the significant contribution of densification due to rearrangement in the presence of liquid as well as that due to contact flattening by dissolution and precipitation.

Optimizing magnetic heating of isolated magnetic nanowires (MNWs) by simulation

Abstract: Magnetic properties such as coercivity, remanence and saturation magnetization will determine the area enclosed by the hysteresis loop of a magnetic material, which also represents magnetic heating. Nanowarming of cryopreserved organs is a new application for magnetic heating using nanoparticles. In this paper, isolated Ni MNW of different sizes and shapes are studied via micromagnetic simulation to explore the optimization of heating using individual MNW. Ellipsoidal MNWs with small (30nm) diameters turn out to be most promising in heating ability due to their large hysteresis area and their potential to distribute uniformly in an organ that is being heated. In addition to optimized heating, a special switching pattern of magnetic moment was also observed for cylindrical large (200nm) MNW. This special switching pattern can trigger applications such as quantum computing.

Mixed-lubrication analysis of misaligned journal bearing considering turbulence and cavitation

Abstract: By integrating the average flow equation and Ng–Pan turbulence model using the boundary condition of mass conserving [Jakobsson-Floberg-Olsson (JFO)], a mixed lubrication model for misaligned bearing was established considering the effects of turbulence and cavitation. The numerical solution was obtained using a finite difference scheme. The results indicate that the frictional force and moment calculated using the JFO boundary condition are greater than those calculated using the Reynolds boundary condition under the constant external load. In high speed conditions, the turbulence begins to play a role, which makes the maximum oil film pressure and moment decrease and the minimum oil film thickness, cavitation zone, and friction coefficient increase. The boundary condition and turbulence have important effects on the equilibrium position of the axis. The misalignment leads to an obvious increase in the friction of the mixed lubrication area and a slight decrease in that of the hydrodynamic lubrication area.

Superhydrophobic surfaces to reduce form drag in turbulent separated flows

Abstract: The drag force acting on a body moving in a fluid has two components, friction drag due to fluid viscosity and form drag due to flow separation behind the body. When present, form drag is usually the most significant between the two, and in many applications, streamlining efficiently reduces or prevents flow separation. As studied here, when the operating fluid is water, a promising technique for form drag reduction is to modify the walls of the body with superhydrophobic surfaces. These surfaces entrap gas bubbles in their asperities, avoiding the direct contact of the liquid with the wall. Superhydrophobic surfaces have been vastly studied for reducing friction drag. We show they are also effective in reducing flow separation in turbulent flow and therefore in reducing the form drag. Their conceptual effectiveness is demonstrated by performing direct numerical simulations of turbulent flow over a bluff body, represented by a bump inside a channel, which is modified with different superhydrophobic surfaces. The approach shown here contributes to new and powerful techniques for drag reduction on bluff bodies.

Adsorption of methyl orange, acid chrome blue K, and Congo red dyes on MIL-101-NH2 adsorbent: Analytical interpretation via advanced model

Abstract: A synthesized MIL-101-NH2 has been used as an adsorbent to analyze Congo red (CR), methyl orange (MO), and acid chrome blue K (AC) dye adsorption phenomena. This investigation, based on statistical physics treatment, applied the double layer model with two energies to understand dye adsorption on three samples, namely, MIL-101-NH2-1, MIL-101-NH2-2, and MIL-101-NH2-3, at T = 298 K. Modeling results indicated that dye adsorption occurred via a mixed adsorption orientation for CR and MO dyes and a non-parallel orientation for AC dye on the MIL-101-NH2 surface. Dye uptake quantities varied from 2534.4 to 3440 mg/g for CR dye, 240.4 to 490.8 mg/g for MO dye, and 277 to 293 mg/g for AC dye. Thus, the highest adsorption amount appeared in the case of CR dye. Interpretation of the calculated energies showed that adsorption of the dyes on MIL-101-NH2 is a physisorption phenomenon, which could be controlled through energetic parameters obtained via numerical findings using the statistical double layer model. Moreover, the expression of the model is exploited to investigate the thermodynamic functions, such as internal energy.

Near room temperature magnetocaloric properties in Ni deficient (Mn0.525Fe0.5)Ni0.975Si0.95Al0.05

Abstract: We present an experimental study on the crystalline, magnetic, and magnetocaloric properties of Ni deficient (Mn-rich) (Mn0.525Fe0.5)Ni0.975Si0.95Al0.05. The study has been performed by x-ray diffraction, scanning electron microscopy, and dc magnetization measurements. X-ray diffraction measurements showed that the sample primarily exhibited the orthorhombic structure at room temperature. The coupled structural and ferromagnetic transition occurred at ∼338 K, which is significantly larger than ∼320 K observed in (Mn0.50Fe0.5)NiSi0.95Al0.05. Maximum magnetic entropy changes of ΔSM = −9.5 and 25 J kg−1K−1 for ΔH = 20 kOe and 50 kOe, respectively, have been observed in the material. Large refrigeration capacities of 60 J/kg and 160 J/kg for field changes of ΔH = 20 kOe and 50 kOe, respectively, have also been observed.