Showing papers in "Zeitschrift Fur Naturforschung Section A-a Journal of Physical Sciences in 2022"

Flow and heat over a rotating disk subject to a uniform horizontal magnetic field

Abstract: Abstract Magnetic field is often applied to stabilize the flow field in real life applications of fluid mechanics problems. In the present work, it is employed a horizontal uniform magnetic field to regularize the flow field triggered due to a rotating disk. The energy equation is also studied subjected to such a horizontal magnetic field. The applied horizontal magnetic field is different from the well-known applied external vertical magnetic field. It is shown that the horizontal magnetic field leads to a similarity system of equations with the help of the traditional von Kármán similarity transformations. The effects of such a magnetic field on the development of velocity and temperature fields are then numerically investigated. The existence of exact series solutions in terms of decaying exponential functions is further discussed. The critical roles of horizontal magnetic field on the physical quantities involving the local wall shears, torque and the heat transfer rate are finally highlighted.

Heat transfer analysis describing freezing of a eutectic system by a line heat sink with convection effect in cylindrical geometry

Abstract: Abstract The current article devoted to study a moving boundary problem describing freezing of a eutectic system in a semi-infinite medium in cylindrical symmetry. The solidification of the material is considered by a line heat sink of strength Q place at r = 0. The heat transfer is considered due to both mechanism, conduction and convection driven by fluid motion in the liquid region, mushy region and possibly in porous solid phase. The analysis is concerned with extended freezing temperature range between solidus and liquidus temperatures respectively. The solid fraction is considered to have a linear relationship with temperature within the mushy zone. A direct integration method is used to solve the mathematical model, resulting an exact solution of the problem is obtained. To illustrate the application of current study and validity of mathematical model, a numerical example of freezing of an Al–Cu alloy with 5% Cu is presented. In addition, the temperature distribution in each region and position of moving interfaces is shown for different Peclet number. In this work, we obtained that the process of freezing becomes fast in the presence of convection. Moreover, it is shown that for a large value of Q, strength of line heat sink, the freezing of a eutectic alloy increases rapidly. Both eutectic and solid solution alloys come under the application of current study.

Sucrose concentration detector based on a binary photonic crystal with a defect layer and two nanocomposite layers

Abstract: Abstract The concentration of sucrose in an aqueous solution has a wide range of applications in pharmaceuticals, such as protein and food preservation. In this work, we propose a binary Si/SiO2 photonic crystal with a defect layer and two nanocomposite layers for the detection of sucrose concentration in an aqueous solution. The transfer matrix method is employed to analyze the proposed structure. Transmission, reflection and absorption spectra are plotted and studied. The defect mode arising as a result of the breakdown of the photonic crystal periodicity by the defect and the nanocomposite layers is also investigated. Many interesting features have been observed such as the transmission peak being sharply reduced with the increase of the nanocomposite layer thickness and the angle of incidence. The sensitivity of the photonic crystal can be enhanced by increasing the defect layer thickness and the incidence angle. It can be further improved by limiting the nanocomposite layer thickness to 5 nm. The proposed structure exhibits excellent tuning with any change in the sucrose concentration and it shows high sensitivity of about 893 nm/RIU. Therefore, it can be used as an efficient optical sensor device with enhanced sensitivity due to the nanocomposite layers.

On the modeling of a parametric cubic–quintic nonconservative Duffing oscillator via the modified homotopy perturbation method

Abstract: Abstract This paper is devoted to obtain an approximate solution to the damped quintic–cubic nonlinear Duffing–Mathieu equation via a modified homotopy perturbation method (HPM). The modification under consideration deals with the improvement of the HPM with the exponential decay parameter. This scheme allows us to get a solution to the damped nonlinear Duffing–Mathieu equation, which the classical HPM failed to obtain. It is found that the solutions and the characteristic curves are affected by the presence of the damping force. The frequency-amplitude characteristics of a symbiotic solution are confirmed as well as the stability condition is carried out in the (non)-resonance cases. All the calculations are done via Mathematica. The comparison between both of the numerical and analytical solutions showed a very good agreement. Illustrated graphs are plotted for a superior realization of periodic motions in the Duffing–Mathieu oscillator. Nonlinear behaviors of each oscillation motion have been characterized through frequency curves.

Beyond semiclassical time

Abstract: Abstract We show that the usual Born–Oppenheimer type of approximation used in quantum gravity, in which a semiclassical time parameter emerges from a weak-coupling expansion of the Wheeler–DeWitt constraint, leads to a unitary theory at least up to the next-to-leading order in minisuperspace models. As there are no unitarity-violating terms, this settles the issue of unitarity at this order, which has been much debated in the literature. Furthermore, we also show that the conserved inner product is gauge-fixed in the sense that the measure is related to the Faddeev–Popov determinant associated with the choice of semiclassical time as a reparametrization gauge. This implies that the Born–Oppenheimer approach to the problem of time is, in fact, an instance of a relational quantum theory, in which transition amplitudes can be related to conditional probabilities.

Photoluminescence properties of Eu3+ doped CaSr(WO4)2 phosphor by Li+ charge compensation

Abstract: Abstract A series of CaSr(WO4)2: Eu3+ and CaSr(WO4)2: Eu3+, Li+ phosphors with different Eu3+ or Eu3+/Li+ molar contents were successfully synthesized by high-temperature solid-state reaction. Through a series of characterization methods, the composition, structure and luminescence characteristics of the sample are obtained. Upon excitation at 393 nm, the strong red light corresponding to the 5D0 → 7F2 transition of Eu3+ can be observed. The effect of Li+ charge compensation on the photoluminescence of the sample is studied. The strongest red emission is obtained through 1% Eu3+ and 1% Li+ doping. All of the results indicate that Li+ charge compensation can effectively enhance the red emissions intensity of Eu3+-doped CaSr(WO4)2 phosphors.

Tracking the changes in the structural, optical and photoluminescent properties of CuCo2O4/MnS nanocomposites with different composition ratios

Abstract: Abstract (1−x)CuCo2O4/xMnS (x = 0, 0.25, 0.5) nanocomposite samples were formed using hydrothermal and thermolysis procedures. X-ray diffraction (XRD) phase analysis showed the formation of only CuCo2O4 phase necessitating the inclusion of Mn and S ions into the CuCo2O4 lattice. Fourier-transform infrared spectroscopy (FTIR) analyses confirmed the presence of Mn and S ions in the nanocomposite samples. Rietveld refinement method was applied to determine the cation distribution of the different ions between different sites. The cell parameter (a) has no fixed trend of change. The average crystallite size is almost the same for all samples with an average of 15 nm. The effect of insertion of Mn and S ions into the CuCo2O4 on the diffused absorbance, extinction coefficient, refractive index, dielectric properties, and nonlinear optical parameters was discussed in detail. The pristine CuCo2O4 nanoparticles have two direct optical band gaps (1.65, 2.74) eV which are decreased to (1.59, 2.56) and (1.58, 2.54) eV for the MnS content x = 0.25 and 0.5, respectively. The two indirect optical band gaps of pristine CuCo2O4 changed irregularly as the MnS amount increased in the nanocomposite. The PL spectrum of CuCo2O4 is shifted to higher wavelength in the visible region upon alloying with MnS. The photoluminescence (PL) intensity of the nanocomposite samples is smaller than that of CuCo2O4 sample. The emitted PL colors depended on the amount of Mn and S ions in the CuCo2O4 matrix.

Analytical solutions of nonlocal forced vibration of a functionally graded double-nanobeam system interconnected by a viscoelastic layer

Abstract: Abstract The double-nanobeam system has important applications in nano-optomechanical systems (NOMS), its dynamic analysis is of importance to the effective design of nanodevices. This paper aims to present analytical solutions of the forced vibration of a functionally graded double-nanobeam system (FGDNS) interconnected by a viscoelastic layer supported on an elastic foundation subjected to time-harmonic external forces. Employing the Hamilton’s principle, the governing differential equations of the FGDNS are derived in the context of the Euler–Bernoulli beam theory and Eringen’s nonlocal elasticity theory. Green’s functions method in conjunction with the superposition principle are adopted to obtain the explicit expressions of the steady-state responses of the FGNDS. A unified strategy applied to various boundary conditions is proposed to determine unknown constants involved in the Green’s functions. Meanwhile, the implicit equation calculating the natural frequency of the FGDNS is proposed. Numerical calculations are performed to check the validity of the present solutions and to discuss the influences of the small-scale parameter, material distribution parameter, and connecting layer parameters on dynamic behaviors of the FGNDS. Results show that the bond between the two nanobeams can be significantly reinforced by increasing the stiffness and damping coefficient of the connecting layer; the small-scale effect can soften or harden the system, depending upon the boundary conditions and the size of the frequency of external force.

Weak discontinuities in one-dimensional compressible nonideal gas dynamics

Abstract: Abstract This article concerns the study of various parameter effects on the propagation of weak discontinuities by using the method of characteristics. Analytical solutions of the quasi-linear system of hyperbolic partial differential equations (PDEs) are obtained and examined the evolutionary behavior of shock in the characteristic plane. The general behavior of solutions to the Bernoulli equation, which determines the evolution of weak discontinuity in a nonlinear system, is studied in detail. Also, we discuss the formation and distortion of compressive and expansive discontinuities under the van der Waals parameter effect and small particles for planar and cylindrical symmetric flow. The comparison between planar flow and cylindrical symmetric flow is studied under the influence of nonidealness and mass fraction of dust particles. It is found that the compressive waves become shock after a certain lapse of time. The medium considered here is the mixture of van der Waals gas with small dust particles.

Similarity solution for one dimensional motion of a magnetized self-gravitating gas with variable density under the absorption of monochromatic radiation

Abstract: Abstract The impendence of azimuthal or axial magnetism in one-dimensional shock wave prevalence via a gas with monochromatic radiation for cylindrical and spherical geometry is examined. The travelling piston supplies the varying input of energy continuously and conditions of equilibrium flow through the whole field are retained. A regime of ODEs is derived by means of the regime of governing motion’s equations using the similarity process. The distributions of gas-dynamical quantities, obtained by their numerical integration, are discussed through figures. It is observed that the adiabatic index and the impendence of magnetism, as well as gravitation, lessen the shock intensity, however, the initial density variation index has the opposite behaviour on it.

Role of graphene-oxide and reduced-graphene-oxide on the performance of lead-free double perovskite solar cell

Abstract: Abstract Lead-free perovskite solar cells (PSCs) have sparked considerable interest in the optoelectronics research community and gained recognition in recent years due to their practical use in solar energy. The primary obstacles in producing PSCs are stability and toxicity due to the immersion of organic-cation and lead in perovskite material. This study presents an electrical simulation of a caesium–indium-based lead-free hybrid PSC using SCAPS-1D software. Spiro-MeOTAD is a typical hole transport material (HTM) used in PSC, although it has not always been suggested because of its high design cost and stability constraints. This study aims to evaluate the performance of lead-free double perovskite material as an absorber layer along with different hole transport materials (HTM). We discovered that the lead-free double perovskite combined with graphene-oxide (GO) and reduced graphene oxide (rGO) produces the best results. Furthermore, the light-harvesting layer and HTM layer has optimized via thickness, defects, doping concentration, and temperature. The improved PSC structure achieves power conversion efficiency (PCE) of more than 24%, and the results of the optimized PSC have compared to the results of the experimentally implemented PSC. This work also used C–V measurements on the optimized structure to determine the device contact potential and doping concentration. The optimized results suggest a feasible future route for creating lead-free PSC with high productivity and free from stability or toxicity issues.

Spectra of neutron wave functions in Earth’s gravitational field

Abstract: The time evolution of a quantum wave packet in the linear gravity potential is known as Quantum Bouncing Ball. The qBounce collaboration recently observed such a system by dropping wave packets of ultracold neutrons by a height of roughly 30 microns. In this article, space and momentum spectra as well as Wigner functions of the neutron wave functions in the gravitational field of the Earth are analyzed. We investigate the quantum states in the "preparation region", into which they transition after exiting a narrow double-mirror system and where we would expect to observe free fall and bounces in classical physics. For this, we start from the stationary solutions and eigenvalues of the Schr\"odinger equation in terms of Airy functions and their zeros. Subsequently, we examine space and momentum distributions as well as Wigner functions in phase space for pure and mixed quantum states. The eventual influence of Yukawa-like forces for small distances of several micrometers from the mirror is included through first order perturbation calculations. Those allow us to study the resulting modifications of space and momentum distributions, and phase space functions.

Modern era of double perovskite nano-phosphors: La2MgTiO6, Gd2MgTiO6 and Y2MgTiO6 – a brief review

Abstract: Abstract Double perovskites, as a star material, are becoming a significant research domain due to their flexible structure, variable formulae, unique properties and wide applications. Trimming the materials into nano regime and introducing rare-earth integration would improve their properties and broaden their applications. The main purpose of this work lies in the comparison of luminescence properties of double perovskite nanophosphors La2MgTiO6 (LMT), Gd2MgTiO6 (GMT) and Y2MgTiO6 (YMT). A detailed list of numerous excitation and corresponding emission wave lengths are discussed. Various synthesis methods adopted for the fusion of these materials, which are reported till this date, are also considered. This study shall assist the scientific community to identify the suitable host for luminescent applications in the field of lighting, displays, illumination, biological imaging, biological sensing etc.

Dust–ion acoustic solitary waves in a collisionless magnetized five components plasma

Abstract: Abstract We have derived a Korteweg–de Vries–Zakharov–Kuznetsov (KdV-ZK) equation to study the nonlinear behavior of dust–ion acoustic waves in a collisionless magnetized five components dusty plasma consisting of warm adiabatic ions, nonthermal hot electrons, isothermal cold electrons, nonthermal positrons and static negatively charged dust particulates. It is found that the coefficient of the nonlinear term of the KdV-ZK equation vanishes along different family of curves in different compositional parameter planes. In this situation, to describe the nonlinear behavior of dust–ion acoustic waves, we have derived a modified KdV-ZK (MKdV-ZK) equation. When the coefficients of the nonlinear terms of both KdV-ZK and MKdV-ZK equations are simultaneously equal to zero, then we have derived a further modified KdV-ZK (FMKdV-ZK) equation which effectively describes the nonlinear behavior of dust–ion acoustic waves. Analytically and numerically, we have investigated the solitary wave solutions of different evolution equations propagating obliquely to the direction of the external static uniform magnetic field. We have seen that the amplitude of the KdV soliton strictly increases with increasing βe, whereas the amplitude of the MKdV soliton strictly decreases with increasing βe, where βe is the nonthermal parameter associated with the hot electron species. Also, there exists a critical value β r ( c ) ${\beta }_{\text{r}}^{(\text{c})}$ of βe such that the FMKdV soliton exists within the interval β r ( c ) < β e ≤ 4 7 ${\beta }_{\text{r}}^{(\text{c})}< {\beta }_{\text{e}}\le \frac{4}{7}$ , whereas the FMKdV soliton does not exist within the interval 0 < β e < β r ( c ) $0< {\beta }_{\text{e}}< {\beta }_{\text{r}}^{(\text{c})}$ . We have also discussed the effect of different parameters of the system on solitary waves obtained from the different evolution equations.

A self-similar solution for shock waves in conducting rotating non-ideal dusty gas medium with monochromatic radiation and magnetic field

Abstract: Abstract In this paper, the cylindrical shock wave propagation in a perfectly conducting rotating mixture of micro size dust particles and van der Waal gas with magnetic field either axial or azimuthal and monochromatic radiation is investigated. The effect of thermal radiation is included in the energy equation of the governing system. In our study, it is assumed that the flux of radiation moves in the mixture of particles and real gas with invariable intensity and the shock wave is moving appositive to the direction of radiation heat flux and the energy is engrossed behind the cylindrical shock only. In the present model, dusty gas is assumed to be a mixture of micro size dust particles and van der Waal gas in which solid particles are continuously distributed and the equilibrium flow conditions are assumed to hold in the entire flow-field region. The effects of the particles’ density to the initial gas density ratio, the real gas effect, rotational parameter, the concentration of mass of the micro size dust particles in the conducting mixture, Alfven-Mach number and the adiabatic exponent on shock and on the physical variables such as velocity, density etc. are discussed. It is found that due to the rotating medium consideration or by an increase in small particles density to the initial gas density ratio, the shock wave strength increases. Also, it is significant to memorize that the strength of the shock wave decreases by an increase in the strength of initial magnetic field or gas non-ideal parameter or the adiabatic index.

Effects of heat treatment on some magnetic properties of amorphous alloys containing (Fe–Ni)1−x M x (M = Si, B)

Abstract: Abstract Herein, the effect of various treatment modes on the magnetic properties of amorphous alloys Fe49Ni29Si9B13 and Fe59Ni19Si9B13 obtained by melt spinning was considered. Samples from both alloys were heat-treated separately in the magnetic field and without the field. An increase in soft magnetic properties was detected during the transition to the crystalline phase (Hc = 0.63Oe, Bm = 1.55T, Br = 2.16T). It was determined that the soft magnetic properties of materials disappear with the formation of crystalline phases. The obtained materials were applied by replacing the electrical steel in the core of the LC1E2501 contactor produced by Schneider. During the operation, the result was 7% higher than the plant resource.

Weak signal detection of composite multistable stochastic resonance with Woods–Saxon potential

Abstract: Abstract Weak signal detection under strong noise is a common problem in many engineering fields. The research on the detection theory and method of stochastic resonance (SR) has very important theoretical significance and application value for the realization of early weak fault diagnosis. In order to further enhance the weak signal processing capability of SR, an improved novel composite multistable potential well model is proposed by combining the tristable model and the Woods–Saxon model. The switching mechanism of the novel model constructed with the fusion of the tristable model and the Woods–Saxon model between different steady states is studied, the output response performance of SR system with the novel composite multistable model is analyzed. The adaptive synchronization optimization method of multiple system parameters adopts the differential brainstorming algorithm to realize the adaptive selection of multiple parameters. Simulation experiments are carried out on single and multiple low-frequency periodic signals and single and multiple high-frequency periodic signals under the Gaussian noise environment, simulation results indicate that the novel composite multistable SR system performs better. On the basis of this model, the composite multistable SR system is applied to the fault detection of rolling bearings, which has a good detection effect.

Exponential type orbitals with hyperbolic cosine function basis sets for isoelectronic series of the atoms Be to Ne

Abstract: Abstract Exponential type orbital with hyperbolic cosine basis functions, proposed recently for Hartree–Fock–Roothaan calculations of neutral atoms, are studied in detail for the calculations of isoelectronic series of atoms from Be to Ne. Calculations are performed for the neutral and the first 20 cationic members of the isoelectronic series of each atom in its ground state. Three of the most popular exponential type orbitals (Slater type functions, B functions and ψ (α) functions with α = 2) are combined with modified hyperbolic cosine function cosh(βr + γ) to improve the basis function quality within the minimal basis sets framework. Performances of the basis functions are compared with each other by using the same number of variational parameters in them. The obtained results are also compared with numerical Hartree–Fock and extended Slater type basis set results. The presented accuracy of the minimal basis descriptions of atomic systems supports the usage of these unconventional basis functions in electronic structure and property calculations.

From maximum force to physics in 9 lines and towards relativistic quantum gravity

Abstract: Abstract A compact summary of present fundamental physics is given and evaluated. Its 9 lines describe all observations exactly and contain both general relativity and the standard model of particle physics. Their precise agreement with experiments, in combination with their extreme simplicity and their internal consistency, suggest that there are no experimental effects beyond the two theories. The combined properties of the 9 lines also imply concrete suggestions for the microscopic constituents in a complete theory of relativistic quantum gravity. It is shown that the microscopic constituents cannot be described by a Lagrangian or by an equation of motion. Finally, the 9 lines specify the only decisive tests that allow checking any specific proposal for such a theory.

Performance of a tunable photoconductive graphene plasmonic photodetector

Abstract: Abstract In this paper, the performance of a graphene photodetector is investigated theoretically in the infrared spectral region (8–12 µm). To increase the absorption of infrared radiation in the graphene layer, plasmon–polaritons are excited in the graphene layer by using dielectric grating. Due to the large propagation constants of plasmon–polaritons compared to the propagation constants of the electromagnetic waves in free space, the dielectric grating is required to provide the phase matching condition of plasmon–polaritons excitation. The results show that due to the excitation of plasmon–polaritons in the graphene layer, the infrared wave has been confined to a small reign around the graphene layer with a full width at half maximum (FWHM) of about 8 nm. Increasing in Fermi energy level leads to a shift in the wavelength of the infrared radiation required to excite plasmon–polaritons in the graphene layer towards shorter wavelengths, so that for the Fermi energy levels of 10, 30, 45, and 60 meV the required wavelengths for plasmon–polaritons excitation are 11.6, 10.6, 9.4, and 8.2 µm, respectively. Under the incidence of the infrared radiation with these wavelengths, and at the corresponding Fermi energy levels, the responsivities of the photodetector at peak points are 2.74, 2.39, 2.19, and 2.04 mA/W, respectively. Therefore, this photodetector is tunable where the detection wavelength is changed by tuning the Fermi energy level of the photodetector. In addition, the results indicate that excitation of plasmon–polaritons approximately increases the responsivity by two times compared to the case without the plasmon–polaritons excitation.

The generation of mass in a non-linear field theory

Abstract: Abstract The mass spectrum of elementary particles is calculated in a new approach, based on B. Heim’s quantum field theory, which manifests in a non-linear eigenvalue equation and merges into the Einstein field equation in the macroscopic limit. The poly-metric of the theory allows spacetime and matter to be described in a unified formalism, representing a radical geometrisation of physics. The calculated mass energies are in very good agreement with the empirical data (error < 1 % ${< }1\%$ on average) if the mass scale is gauged to the electron as lowest mass and the second main parameter, determining the strength of obtained mass hierarchy levels, is close to the half inverse of the fine structure constant, describing the difference in strength between the electromagnetic and the strong interaction. The obtained hierarchy levels are not identical to the particle generations of the Standard Model; however, show a self-similarity typical for non-linear theories. For higher values of the main quantum number N, the calculated mass formula becomes identical to the phenomenological formulae of Nambu, respectively, Mac Gregor.

Blue-green luminescence properties and charge compensation of Ca9MgLi(PO4)7 doped with Tb3+ and alkali metal ions

Abstract: Abstract Ca9MgLi(PO4)7: 4%Tb3+, 4%R+ (R = Li, Na, K) phosphors were synthesized by a solid-state reaction method. The crystal structure, morphology, composition and luminescent properties of as-prepared samples were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), energy dispersive spectrometer (EDS), high-angle annular dark field (HAADF) and spectroscopy technique. The effect of a small concentration of charge compensators like Li+, Na+, K+ on Ca9MgLi(PO4)7: Tb3+ phosphor has also investigated. Ca9MgLi(PO4)7: Tb3+, R+ (R = Li, Na, K) exhibit superior blue-green luminescence around 5D4 → 7F5 (543 nm) to Ca9MgLi(PO4)7: Tb3+ and can be effectively excited by 370 nm light, which implies that efficient charge compensation can promote the emitting of Tb3+ in Ca9MgLi(PO4)7. The CIE coordinates and decay lifetimes of typical samples were also studied. The Ca9MgLi(PO4)7: Tb3+, R+ (R = Li, Na, K) have promising application as a blue-green phosphor for near-ultraviolet chip excited white LEDs.

Self-gravitating spherically symmetric systems with Q h condition in chameleonic Brans–Dicke gravity

Abstract: Abstract This paper is asserted to explore the self-gravitating spherically symmetric anisotropic fluids in Chameleonic Brans–Dicke theory as dark energy matter. The dissipative and non-dissipative cases for the evolution of the system are discussed evidently satisfying the quasi-homologous condition with vanishing complexity (Y TF ) factor, which is identified in the trace free part of the electric Riemann tensor in splitting of the curvature tensor. We formulate different equations through conformal tensor, mass function, shear stress tensor, scalar field to govern self-gravitating systems. A few models describe center filled fluid distribution whereas some of them have cavities surrounding the center by means of matching conditions on the boundary as well as on inner surfaces. The temperature of the respective models is also discussed here. Finally, we conclude the work by comparing it with GR.

Fiber-optic Michelson interferometer for detecting coolant level and refractive index

Abstract: Abstract This paper presents an interferometer based on a single-mode fiber-multimode fiber-thin-core fiber (SMF–MMF–TCF) Michelson interference structure that can be used for the measurements of coolant level and refractive index. Because of the different diameters of the cores of the individual fibers, optical excitation and coupling occur at the splicing points of the fibers. The multimode fibers are the couplers in the sensing structure, which allow the exciting light to enter the cladding of the thin-core fibers. The end face of the thin-core fiber is coated with a silver film to enhance the reflectivity of the light. The results show that the interference intensity first increases and then decreases with the length of TCF. When TCF is 4 cm, the interference light intensity is the strongest. The sensitivity of the sensor is 138.091 nm/RIU with the linearity of 0.977 over the refractive index of the coolant in the range of 1.3605–1.3880, and the temperature and time effects on the sensor are small. The proposed sensor has the advantages of simple fabrication, high repeatability, and good stability and it can be applied to the measurements of coolant level and refractive index in automotive engines.

Synthesis and characterization of Zn doped AlSb thin films for photovoltaic and energy applications

Abstract: Abstract Thin films of zinc doped aluminum antimonide (Zn:AlSb) have been dumped on glass substrate using chemical bath deposition method. The morphological, structural, as well as optical properties of deposited thin films are investigated using XRD, optical microscopy, and UV-V is spectroscopy along with four-point probe technique. The XRD results exhibit that Zn is doped in AlSb and maximum grain size has been obtained at 4% Zn-concentration. Optical micrographs of pure and zinc doped aluminum antimonide (AlSb) at different concentrations of Zn have been shown to confirm the doping by observing changes in morphology and it has been observed that optimized films of AlSb are obtained at 4% of Zn-content. The optical bandgap of Zn doped AlSb films at varying concentrations of 0%, 1%, 2%, 3% and 4% has been found to decrease with enhancement in Zn-concentration and values are measured as 1.8, 1.7, 1.6, 1.4, and 1.3 eV respectively. The sheet resistivity also depends on Zn-content and has been observed to decrease as AlSb is doped with Zn, indicating an increase in electrical conductivity. The explored results indicate a significant potential of these deposited thin films to be used in photonics, photocatalysis, and energy industry.

Complex dynamical behaviour of predator–prey model with harvesting and multiple delays

Abstract: Abstract In this work, we investigate a predator–prey model with Crowley–Martin functional response and constant harvesting. The model is extended by incorporating two constant time delays, where the first delay(τ 1) is for density dependent feedback mechanism in the logistic growth of the prey and the second one is for gestation delay(τ 2) of the predator population. The dynamical behaviours such as positivity, boundedness, extinction criteria and existence, stability and bifurcations of the equilibria of the non-delay model are qualitatively discussed. The existence of periodic solutions via Hopf-bifurcation with respect to absence of delay, single delay and both delays are established. Finally, numerical simulations have been carried out to confirm our numerical results.

Dynamic responses of graded nonhomogeneous unsaturated soils under a strip load

Abstract: Abstract Based on the three-phase porous media mixed theory, the dynamic governing equations of unsaturated soils is established and the dynamic response of graded nonhomogeneous unsaturated soils subjected to a strip load is studied. Combined with the reverberation-ray matrix method (RRMM) and the boundary condition, the calculation formula of the displacement, stress and pore pressure of graded nonhomogeneous unsaturated soils is derived. Assuming that the continuous variation of physical and mechanical properties of unsaturated soils along the thickness-coordinate by exponential law distribution, the numerical solution of the displacement, stress, and pore pressure then obtained by using numerical inverse Fourier transformation, and the influence of soil heterogeneity and saturation on the dynamic response of unsaturated soils is discussed. The results show that the displacement decreased with increasing gradient factor, and the stress first increased then decreased with the gradient factor increased, and the pore pressure first decreased then increased with increasing gradient factor. The displacement and pore pressure under different gradient factors all increase with increasing saturation.

Qualitative behavior of a discrete predator–prey system under fear effects

Abstract: Abstract Numerous field data and experiments on the perching birds or songbirds show that the fear of predators can cause significant changes in the prey population. Fear of predatory populations increases the chances of survival of the prey population, and this can greatly reduce the reproduction of the prey population. The influence of fear has contributed a leading role in both the environmental biology and theoretical ecology. Taking into account the interaction of predator–prey with non-overlapping generations, a discrete-time model is proposed and studied. Keeping in mind the biological feasibility of species, the existence of fixed points is studied along with the local asymptotic behavior of the proposed model around these fixed points. Furthermore, taking into account the oscillatory behavior of the model, various types of bifurcations are analyzed about biologically feasible fixed points with an application of center manifold theory and bifurcation theory of normal forms. Existence of chaos is discussed, and fluctuating and chaotic behavior of the system is controlled through implementation of different chaos control procedures. The illustration of theoretical discussion is carried out via validation of observed experimental field data and appropriate numerical simulation.

Translationally invariant exact steady flows of gas and fluid

Abstract: Abstract New exact 3-D steady translationally invariant (or z-invariant) flows of isentropic gas and ideal incompressible fluid are constructed. New exact solutions for steady magnetohydrodynamics equations are derived. We show that Euler equations for steady z-invariant flows of isentropic gas are equivalent to a coupled system of a partial differential equation of second order for the streamfunction ψ(x, y) which contains an arbitrary differentiable function H(ψ) and a transcendental equation connecting gas density ρ(x, y) with function ψ(x, y) and depending on equation of state p(ρ) = cρ γ and on the function H(ψ). We prove that functions ψ(x, y) and ρ(x, y) satisfy a universal nonlinear equation that is independent of equation of state p = p(ρ) and of the function H(ψ).

Anomalous skin effects and energy transfer of R-L waves in relativistic partially degenerate plasma

Abstract: Abstract On utilizing the kinetic model for transverse permittivity in a weakly magnetized electron plasma, the two particular phenomena of wave-particle interaction i.e., anomalous skin depth and energy transfer are examined in circularly polarized R- and L-waves within relativistic Fermi–Dirac distributed plasmas. Further, the non-trivial influential roles by some salient parameters i.e., relativistic thermal T m 0 c 2 > 0 $\left(\frac{T}{{m}_{0}{c}^{2}} > 0\right)$ , γ (from bulk flow such that γ > 1), degeneracy (due to μ T $\frac{\mu }{T}$ ) and weak ambient magnetic field (B 0), on above mentioned wave phenomena, are also analyzed. The derived results, in the form of polylog function, delineate the inverse relation between spatial damping and energy flux transportation regarding the variation in above mentioned dominant parameters. It is noticed that the relativistic thermal parameter serve as a penetration depth elevator for R- and L-waves and so they transfer energy slowly, whereas the degeneracy and relativistic γ parameters submerse the depth and cause upraise in energy transfer. Moreover, the increase in weak ambient magnetic field reduces the penetration depth of R-wave that delivers its energy rapidly, whereas it enlarges the penetration depth of L-wave which causes slow delivery of its energy. The results discussed (both analytically and graphically) are justifiably confirmed with previous illustrative reports. Applicability of the analysis relevant in partially degenerate regions both in space (e.g., in white dwarfs and young brown dwarf) and laboratory (e.g., in laser plasma interaction, liquid metals, inertial confinement fusion (ICF) and Fermi gas of metals) plasmas.