Zeitschrift für Naturforschung A

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ISSN / EISSN : 0932-0784 / 1865-7109
Published by: Walter de Gruyter GmbH (10.1515)
Total articles ≅ 15,907
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Rabindranath Maity,
Zeitschrift für Naturforschung A; https://doi.org/10.1515/zna-2021-0167

Abstract:
A wide class of nonlinear excitations and the dynamics of wave groups of finite amplitude ion-acoustic waves are investigated in multicomponent magnetized plasma system comprising warm ions, and superthermal electrons as well as positrons in presence of negatively charged impurities or dust particles. Employing the reductive perturbation technique (RPT), the Korteweg–de-Vries (KdV) equation, and extended KdV equation are derived. The presence of excess superthermal electrons as well as positrons and other plasma parameters are shown to influence the characteristics of both compressive and rarefactive solitons as well as double layers (DLs). Also, we extend our investigation by deriving the nonlinear Schrödinger equation from the extended KdV equation employing a suitable transformation to study the wave group dynamics for long waves. The analytical and numerical simulation results demonstrate that nonlinear wave predicts solitons, “table-top” solitons, DLs, bipolar structure, rogue waves, and breather structures. Moreover, implementing the concept of dynamical systems, phase portraits of nonlinear periodic, homoclinic trajectories, and supernonlinear periodic trajectories are presented through numerical simulation.
Zeitschrift für Naturforschung A; https://doi.org/10.1515/zna-2021-0166

Abstract:
On employing linearized Vlasov–Maxwell equations the solution of relativistic electromagnetic extraordinary mode is investigated for the wave propagating perpendicular to a uniform ambient magnetic field (in the presence of arbitrary magnetic field limit i.e., ω > Ω > k.v) in partially degenerate (i.e., for T F ≥ T and T ≠ 0) electron plasma under long wavelength limit (ω ≫ k.v). Due to the inclusion of weak quantum degeneracy the relativistic Fermi–Dirac distribution function is expanded under the relativistic limit ( m 0 2 c 2 2 p 2 < 1 $\frac{{m}_{0}^{2}{c}^{2}}{2{p}^{2}}{< }1$ ) to perform momentum integrations which generate the Polylog functions. The propagation characteristics and shifting of cutoff points of the extraordinary mode are examined in different relativistic density and magnetic field ranges. The novel graphical results of extraordinary mode in relativistic quantum partially degenerate (for μ T = 0 $\frac{\mu }{T}=0$ ), nondegenerate (for μ T ≈ − 1 $\frac{\mu }{T}\approx -1$ ) and fully/completely degenerate (for μ T ≈ $\frac{\mu }{T}\approx $ 1) environments are obtained and the previously reported results are retraced as well.
Yi Li, Yaoxin Huang, Moli Zhao,
Zeitschrift für Naturforschung A; https://doi.org/10.1515/zna-2021-0172

Abstract:
A theoretical investigation is carried out to analyze the oscillatory flow of second-grade fluid under the periodic pressure gradient in a long tube of isosceles right triangular cross section in the present study. The analytical expressions for the velocity profile and phase difference are obtained. The numerical solutions are calculated by using the finite difference method with Crank–Nicolson (C–N) scheme. In comparison with the Newtonian fluid (λ = 0), the effects of retardation time, Deborah number and Womersley number on the velocity profile and phase difference are discussed numerically and graphically. For smaller Womersley number, the behavior of second-grade fluid is dominated by viscosity. For larger Womersley number α = 20, the flow becomes more difficult to be generated under periodic pressure gradient with increasing retardation time. Furthermore, the analytical expressions of the mean velocity amplitude and phase difference are given explicitly for discussing.
Oleg Bogoyavlenskij
Zeitschrift für Naturforschung A; https://doi.org/10.1515/zna-2021-0236

Abstract:
Exact flows of an incompressible fluid satisfying the Beltrami equation inside a spherical shell are constructed in the Cartesian coordinates in terms of elementary functions. Two scale-invariant equations defining two infinite series of eigenvalues λ n and λ ̃ m ${\tilde {\lambda }}_{m}$ of the operator curl in the shell with the nonpenetration boundary conditions on the boundary spheres are derived. The corresponding eigenfields are presented in explicit form and their symmetries are investigated. Asymptotics of the eigenvalues λ n and λ ̃ m ${\tilde {\lambda }}_{m}$ at n, m → ∞ are obtained.
Debdatta Debnath,
Zeitschrift für Naturforschung A; https://doi.org/10.1515/zna-2021-0120

Abstract:
At the acoustic speed, we have investigated the existence of ion-acoustic solitary structures including double layers and supersolitons in a collisionless magnetized plasma consisting of negatively charged static dust grains, adiabatic warm ions, and nonthermal electrons. At the acoustic speed, for negative polarity, the system supports solitons, double layers, supersoliton structures after the formation of double layer, supersoliton structures without the formation of double layer, solitons after the formation of double layer whereas the system supports solitons and supersolitons without the formation of double layer for the case of positive polarity. But it is not possible to get the coexistence of solitary structures (including double layers and supersolitons) of opposite polarities. For negative polarity, we have observed an important transformation viz., soliton before the formation of double layer → double layer → supersoliton → soliton after the formation of double layer whereas for both positive and negative polarities, we have observed the transformation from solitons to supersolitons without the formation of double layer. There does not exist any negative (positive) potential solitary structures within 0 < μ < μ c (μ c < μ < 1) and the amplitude of the positive (negative) potential solitary structure decreases for increasing (decreasing) μ and the solitary structures of both polarities collapse at μ = μ c, where μ c is a critical value of μ, the ratio of the unperturbed number density of electrons to that of ions. Similarly there exists a critical value β e2 of the nonthermal parameter β e such that the solitons of both polarities collapse at β e = β e2.
Muhammad Shafiqul Islam, Sabrina Rahman, Adil Sunny, Ashfaqul Haque, ,
Zeitschrift für Naturforschung A; https://doi.org/10.1515/zna-2021-0063

Abstract:
The present work investigates a tin-based highly efficient perovskite solar cell (PSC) by a solar cell capacitance simulator in one dimension. Molybdenum disulfide is introduced as hole transport layer in the proposed solar cell device structure. The photovoltaic performances of the proposed solar cell are investigated by varying thickness, doping concentration, and bulk defect density of various layers. Furthermore, the operating temperature and the series and shunt resistances are analyzed systematically. A higher conversion efficiency of 25.99% is obtained at the absorber thickness of 2000 nm. The optimum doping density of 1017 cm−3 is estimated for the absorber, electron transport layer (ETL), and hole transport layer (HTL), respectively. The optimum thicknesses of 50 nm, 1000 nm, and 60 nm are also found for the titanium dioxide as ETL, methylammonium tin triiodide (CH3NH3SnI3) as absorber layer, and molybdenum disulfide as HTL, respectively. The efficiency of the proposed lead-free CH3NH3SnI3-based solar cell with the alternative molybdenum disulfide HTL is calculated to be 24.65% with open-circuit voltage of 0.89 V, short-circuit current density of 34.04 mA/cm2, and fill-factor of 81.46% for the optimum parameters of all layers. These findings would contribute to fabricate low-cost, non-toxic, stable, and durable lead-free PSCs for the next generation.
Wajeehah Shahid, Samiah Shahid, Muhammad Aamir Iqbal, Jianhua Huo, Rashid Karim,
Zeitschrift für Naturforschung A; https://doi.org/10.1515/zna-2021-0135

Abstract:
In this study, novel hydrothermal synthesis is used to explore the impact of photocatalytic activity on H2 production using an aqueous solution of triethanolamine (TEoA) in TiO2 nanostructures designed with varying molar concentrations of HCl, and the production of molecular hydrogen is explored as a function of molar concentration. A solar simulator is utilized to assess the photocatalytic activities of methyl orange degradation under UV light irradiation and molecular H2 production. Also, XRD patterns and SEM images are explored to show agglomerated nanoparticle formation, and an EDX spectrum is employed to confirm TiO2 compositions. The band gap analysis of produced nanostructures is performed using a UV-Vis spectrometer and is found to be varying in between 2.5 and 3.0 eV, while the maximum methyl orange degradation corresponds to 1.0 M concentration of HCl, indicating an enhanced hydrogen production. To meet the foreseeable future energy crises and worsening environmental challenges, we may need sustainable energy sources, and photocatalysis molecular H2 production offers a viable alternative to fossil fuels that can be employed to tackle future difficulties.
, Yuhang Chen, Zhong Huang, Yahui Meng
Zeitschrift für Naturforschung A; https://doi.org/10.1515/zna-2021-0151

Abstract:
Branching channels are commonly emerged in a considerable variety of engineering applications, in which most of the fluids present non Newtonian behavior, such as in chemical processes. It is noted that in the material forming process, when one suspends nanoparticles in a basic non Newtonian fluid, a completely new non Newtonian fluid is formed with different rheological characteristics from the former ones. In our present numerical research, considering the side branches inclined at varying angles, we focus on the fluid flow and heat transfer of the laminar power-law nanofluid in a rectangular branching channel under the influences of generalized Reynolds number. Both the consistency coefficient and power-law index of the non Newtonian nanofluid, different from those of the base fluid, are described by empirical formula, dependent on the nanoparticle quantity. Finite element method is applied in the research. It is found that a smaller branch angle α can cause a larger fluctuation in pressure near the branched region. Furthermore, negative pressures exist both in the main and side branch with some certain inclination angle. Above all, the new extensive results of velocity contours, temperature, concentration contours along with pressure drop of the changing rheological models provide detailed information for studies on non Newtonian nanofluids in many intricate industrial applications.
Zeitschrift für Naturforschung A; https://doi.org/10.1515/zna-2021-0098

Abstract:
The thermal entry flow problem also known as the Graetz problem is investigated for a Giesekus fluid model. Both analytical (exact) and approximate solutions for velocity are obtained. The nondimensional pressure gradient is numerically obtained via the mean flow rate relation. The energy equation along with the Giesekus fluid velocity is analytically solved for the constant wall temperature case by using the classical separation of variable method. This method transforms the energy equation into a Sturm–Liouville (SL) boundary value problem. The MATLAB solver bvp5c is employed to compute the eigenvalues and the related eigenfunctions numerically. The impact of mobility parameter and Weissenberg number on local Nusselt number, mean temperature, and average Nusselt number is discussed and displayed graphically. It is also found that the presence of the Weissenberg number elevates the Nusselt numbers. Further, the presence of the mobility parameter of the Giesekus fluid model delays the prevalence fully developed conditions in both entrance and fully developed regions. The comparison between approximate and exact solution is also presented. It reveals that both solutions have an exact match with each other for smaller values of mobility parameter and Weissenberg number. However, there is a deviation for larger values of both parameters.
, Bekmirzaeva Xursand, Urozov Abduxolik Nurmamatovich, Igamqulova Zilola
Zeitschrift für Naturforschung A; https://doi.org/10.1515/zna-2020-0123

Abstract:
In the present paper the magnetic flux penetration dynamics of type-II superconductors in the flux creep regime is studied by analytically solving the nonlinear diffusion equation for the magnetic flux induction, assuming that an applied field parallel to the surface of the sample and using a power-law dependence of the differential resistivity on the magnetic field induction. An exact solution of nonlinear diffusion equation for the magnetic induction B(r, t) is obtained by using a well-known self-similar technique. We study the problem in the framework of a macroscopic approach, in which all length scales are larger than the flux-line spacing; thus, the superconductor is considered as a uniform medium.
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