Weak discontinuities in one-dimensional compressible nonideal gas dynamics

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.

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

(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.

Dissipative electrostatic wave modulation in warm multi-ion dusty plasmas with superthermal electrons

A theoretical investigation has been carried out to explore the modulational instability (MI) of electrostatic waves in a warm multi-ion dusty plasma system containing positive ions, negative ions and positively or negatively charged dust in presence of superthermal electrons. With the help of the standard perturbation technique, it is found that the dynamics of the modulated wave is governed by a damped nonlinear Schrödinger equation (NLSE). Regions of MI of the electrostatic wave are precisely determined and the analytical solutions predict the formation of dissipative bright and dark solitons as well as dissipative first- and second-order rogue wave solutions. It is found that the striking features (viz., instability criteria, amplitude and width of rogue waves, etc.) are significantly modified by the effects of relevant plasma parameters such as degree of the electron superthermality, dust density, etc. The time dependent numerical simulations of the damped NLSE reveal that modulated electrostatic waves exhibit breather like structures. Moreover, phase plane analysis has been performed to study the dynamical behaviors of NLSE by using the theory of dynamical system. It is remarked that outcome of present study may provide physical insight into understanding the generation of several types of nonlinear structures in dusty plasma environments, where superthermal electrons, positive and negative ions are accountable (e.g. Saturn’s magnetosphere, auroral zone, etc.).

Time and space waveform optimization to extend the harmonic cutoff and to produce the water window single attosecond pulse

Based on the three-step theory of high-order harmonic generation, the harmonic cutoff is very sensitive to the few-cycle laser waveform in both time and space regions. Therefore, in this paper, we propose the method to control the harmonic cutoff and to produce the water window attosecond pulse through the optimization of time and space waveform. It is found that, in the time region, by properly choosing the delay and phase of the few-cycle two-color pulse, not only the harmonic intensity is enhanced, but also the quantum path of the harmonic emission can be controlled. Further, with the introduction of the 3rd pulse (i.e., the infrared pulse or the unipolar pulse), the harmonic cutoff from the single harmonic emission peak can be extended, showing a water window harmonic plateau. In the space region, by using the positive spatial inhomogeneous effect, the harmonic cutoff from the basic two-color waveform can also be extended, which leads to a water window spectral continuum. Finally, by Fourier transformation of harmonics during the water window region, the ultrashort single 29 as pulses can be obtained.

Turbulent boundary layer heat transfer of CuO–water nanofluids on a continuously moving plate subject to convective boundary

The turbulent boundary layer (TBL) heat transfer of CuO–water nanofluids on a continuously moving plate subject to convective boundary are investigated. Five different shapes of nanoparticles are taken into account. Prandtl mixing length theory is adopted to divide the TBL into two parts, laminar sub-layer and turbulent region. The numerical solutions are obtained by bvp4c and accuracy is verified with previous results. It is found that the transfer of momentum and heat in the TBL is more obvious in laminar sub-layer than in turbulent region. The rise of velocity ratio parameter increases the velocity and temperature while decreases the local friction coefficient. The heat transfer increases significantly with the increase of velocity ratio parameter, Biot number, and nanoparticles volume fraction. For nanoparticles of different shapes, the heat transfer characteristics are Nu x (sphere) < Nu x (hexahedron) < Nu x (tetrahedron) < Nu x (column) < Nu x (lamina).

Third harmonic generation of a relativistic self-focusing laser in plasma under exponential density ramp

Present study focuses on self-focusing and its effect on third harmonic generation (THG) of a Gaussian laser beam in plasma under the influence of exponential density ramp. Relativistic nonlinearity has been taken into account which is aroused due the modification of electron’s mass in the presence of high intensity laser. Under strong ponderomotive force, electrons acquire very high quiver velocity and mass variation takes place. Equations for beam width parameter of incident laser and the amplitude of THG have been derived under WKB and paraxial ray approximation, and solved them numerically. It is found that the presence of exponential plasma density ramp results strong self-focusing of laser which further leads to enhance the efficiency of THG. Wiggler magnetic field adds an additional momentum to the photons of third harmonic due to which appreciable gain is observed in the normalized amplitude of THG. Significant enhancement in the THG amplitude has been reported in the presence of exponential density ramp for optimum values of intensity of incident laser, wiggler magnetic field and plasma frequency.

The effect of second order slip condition on MHD nanofluid flow around a semi-circular cylinder

Steady forced convection of non-Newtonian nanofluids around a confined semi-circular cylinder subjected to a uniform magnetic field is carried out using ANSYS FLUENT. The numerical solution is obtained using the finite volume method. The user-defined scalar (UDS) is used for the first time to calculate the second order velocity slip boundary condition in semi-circular curved surface and the calculated results are compared with those of the first order velocity slip boundary condition. Besides, the effects of volume fraction, size, type of nanoparticles and magnetic field strength on heat transfer are studied. The present study displays that adding nanoparticles in non-Newtonian fluids significantly enhances heat transfer. In addition, it is observed that the heat transfer rate decreases first and then increases with the increase of Hartmann number. The effects of blocking rate on Nusselt number, wake length and heat transfer effect are shown in the form of graphs or tables.

The Effect of surfactant on the drag and wall correction factor of a drop in a bounded medium

In the present article, the analytical solution for creeping motion of a drop/bubble characterized by insoluble surfactant is examined at the instant it passes the center of a spherical container filled with Newtonian fluid at low Reynolds number. The presence of surfactant characterizes the interfacial region by an axisymmetric interfacial tension gradient and coefficient of surface dilatational viscosity. Under the assumption of the small capillary number, the deformation of spherical phase interface is not taken into account. The computations not only yield information on drag force and wall correction factor, but also on interfacial velocity and flow field for different values of surface tension gradient and surface dilatational viscosity. In the limiting cases, the analytical solutions describing the drag force and wall correction factor for a drop in a bounded medium reduces to expressions previously stated by other authors in literature. The results reveal the strong influence of the surface dilatational viscosity and surface tension gradient on the motion of drop/bubble. Increasing the surface tension gradient and surface dilatational viscosity, results in linear variation of drag force. When the surface tension gradient increases, the drag force for unbounded medium increases more as compared to the bounded medium hence wall correction factor decreases with increase in surface tension gradient whereas it increases with increase in surface dilatational viscosity.

Photoluminescence studies on LiNa5(PO4)2:Dy3+, Sm3+ phosphor

This paper describes the preparation, structure and photoluminescence properties of a new class LiNa5(PO4)2:Dy3+, Sm3+-phosphor. Crystalline nature confirmed by X-ray diffraction. The phases obtained are in good agreement with the standard phase. Excitation dependence and concentration effect on luminescence features are investigated. Color purity and optical bandgap are also estimated for the LiNa5(PO4)2:Dy3+, Sm3+ phosphors. The result shows LiNa5(PO4)2:Dy3+, Sm3+-phosphor excited by 374 nm nUV light produces pure white light than others. Admixing of 4f configurations and energy transfer between dopants are identified while varying the concentration of Sm3+. The CIE coordinates for LiNa5(PO4)2:0.05Dy3+, 0.05Sm3+ (x = 0.309, y = 0.332) are positioned well in white light region and very close to pure white light. The present study on LiNa5(PO4)2:Dy3+, Sm3+-phosphor suggests that it is useful for the fabrication of white light emitting diodes.