Volume 73, Issue 9

In this paper, we endeavour to show that from the noncommutative nature of spacetime one can deduce the concept of relativity, in the sense that velocity cannot be infinite as in the case of Galilean relativity.

An ammonia sensor is conceived and constructed using the downconverting ZnO:Eu 2+ nanoparticles that can be excited by near-ultraviolet (378 nm) light and emit indigo color light. The capability of the ZnO:Eu 2+ nanoparticles for ammonia gas sensing was studied from fluorescence quenching measurements. When these nanoparticles were exposed to ammonia gas, a significant luminescent intensity variation of the excitation spectra was observed. The detection limit of the proposed optical gas sensor is 20 ppm with a good linearity ( R 2 =0.9759) from 0 to 80 ppm of ammonia. The sensor has the advantages of a simple structure, high sensitivity, easy fabrication, and low cost, and can be used for sensing ammonia gas in factories, laboratories, etc.

In this paper, the roles of intermolecular interactions and probability of aggregates formation on the nonlinear optical properties of thiazine dyes are investigated. Our results show that saturable and reverse saturable absorption properties of these dyes depend strongly on the molecular surrounding media characteristics and their collective properties that tend to form aggregated species at high concentrations. Depending on molecular surrounding media characteristics, by increasing the concentration of dye solutions and formation of aggregates, the strong solute-solute interactions can modify the nonlinear responses of dye solutions. The experimental results indicate that by increasing the contribution of J aggregates, the third-order nonlinear responses of binary mixtures of water and ethanol are increased at room temperature. Therefore, the intermolecular interactions and the presence of J aggregates can be considered as simple techniques for improving the nonlinear responses of selected ionic dyes.

An investigation of the dust acoustic shock waves as well as solitary waves in an unmagnetized dusty plasma consisting of fluid of negatively charged dust grains, superthermal ions, and Maxwellian electrons under the influence of superthermally modified polarization force is presented. The polarization force is significantly influenced by superthermal ions. Reductive perturbation technique has been used to derive the Korteweg-de Vries-Burgers equation. It is illustrated that the superthermal polarization force significantly alters the characteristics of the negative polarity shock and solitary waves. It is also examined that the soliton energy gets depleted by the influence of superthermal polarization force.

We show that some Emden–Fowler (EF) equations encountered in astrophysics and cosmology belong to two EF integrable classes of the type d2z/dχ2=Aχ−λ−2zn${\mathrm{d}^{2}}z/\mathrm{d}{\chi^{2}}=A{\chi^{-\lambda-2}}{z^{n}}$ for λ=(n−1)/2$\lambda=(n-1)/2$ (class 1), and λ=n+1$\lambda=n+1$ (class 2). We find their corresponding invariants which reduce them to first-order nonlinear ordinary differential equations. Using particular solutions of such EF equations, the two classes are set in the autonomous nonlinear oscillator the form d2ν/dt2+adν/dt+b(ν−νn)=0${\mathrm{d}^{2}}\nu/\mathrm{d}{t^{2}}+a\mathrm{d}\nu/\mathrm{d}t+b(\nu-{\nu^{n}})=0$, where the coefficients a,b$a,b$ depend only on λ,n$\lambda,n$. For both classes, we write closed-form solutions in parametric form. The illustrative examples from astrophysics and general relativity correspond to two n = 2 cases from class 1 and 2, and one n = 5 case from class 1, all of them yielding Weierstrass elliptic solutions. It is also noticed that when n = 2, the EF equations can be studied using the Painlevé reduction method, since they are a particular case of equations of the type d2z/dχ2=F(χ)z2${\mathrm{d}^{2}}z/\mathrm{d}{\chi^{2}}=F(\chi){z^{2}}$, where F(χ)$F(\chi)$ is the Kustaanheimo-Qvist function.

The stability of equilibria and bifurcations of neural networks in a real line with nonlocal delay are presented. A sufficient condition of stable equilibria is declared by the linear part. Eigenvalue analysis implies the existence of bifurcations, and by exploiting typical excitatory and inhibitory connectivity kernels in a neural network, the possible bifurcations are discussed according to various cases. It is an advantageous tool using a multiple-scale method to study the stability of bifurcated travelling waves or spots. As an illustration of our theory, the dynamics of a seashell continuous-time circular mask model are investigated. It is shown that both the shape and range of active function and synaptic weights can affect the dynamics of the model. Finally, the bifurcation set and the variety of bifurcated patterns of the seashell model are numerically revealed.

In this paper, the effect of slip velocity on the rotating electro-osmotic flow (EOF) of the power-law fluid in a non-uniform microchannel under high zeta potential is investigated. The potential distribution of the electric double layer is obtained by using the nonlinear Poisson-Boltzmann equation. By using the finite difference method, the numerical solution of the rotating EOF velocity profile is obtained. The effectiveness and correctness of the present numerical method is proven by comparing the results with the analytical solutions of the Newtonian fluid given by a previous study. The influences of the fluid behavior index n and the slip parameter β on the velocity profiles are also discussed in detail.

In this paper, we investigate the peristaltic pumping of a Rabinowitsch fluid in an inclined channel under the effects of heat transfer and flexible compliant walls. The expressions for the velocity, the temperature and the coefficient of the heat transfer are obtained. The influence of emerging parameters on the velocity, the temperature, the coefficient of heat transfer and the trapping phenomenon of the Newtonian, dilatant and pseudoplastic fluid models are also analyzed graphically. We find that the velocity and the temperature fields decrease for shear thickening fluid; but the velocity and temperature fields of the shear thinning, and Newtonian fluids increase with an increase in the angle of inclination. Furthermore, there were more trapping boluses occurring for the Newtonian fluid case as compared to the pseudoplastic and dilatant fluids cases. However, as the angle of inclination increases, the size of trapping bolus decreases.

We revisit the pressure-induced molecular-atomic metal-insulator transition of solid hydrogen by means of variational quantum Monte Carlo simulations based on the antisymmetric shadow wave function. For the purpose of facilitating the study of the electronic structure of large-scale fermionic systems, the shadow wave function formalism is extended by a series of technical advancements as implemented in our HswfQMC code. Among others, these improvements include a revised optimization method for the employed shadow wave function and an enhanced treatment of periodic systems with long-range interactions. It is found that the superior accuracy of the antisymmetric shadow wave function results in a significantly increased transition pressure with respect to previous theoretical estimates.

First-principle calculations have been adopted in order to reveal and deeply understand the structural, electronic, elastic, thermodynamic, and vibrational properties of full-Heusler X 2 TiAl (X = Au, Ru, and Zr) alloys in the L 2 1 phase. The fundamental physical properties such as bulk modulus, its pressure derivative, anisotropy factor, shear modulus, Poisson’s ratio, Cauchy pressure, elastic constants, heat capacity, thermal expansion coefficient, and Young’s modulus are obtained and compared with the literature. Debye temperature and Grüneisen parameter are also evaluated over the temperature range of 0–1500 K. Electronic band structures and their partial density of states and phonon dispersion curves are presented for all alloys and used to interpret the electronic and mechanical properties and stabilities of alloys in the L 2 1 phase.

The present research performed a numerical simulation of laminar forced convection nanofluid-based non-Newtonian flow in a channel connecting a tank with heating regions. To achieve a rapid diffusion of heat, a cylindrical agitator is inserted into the tank. Power-law modelling is employed to describe the effect of non-Newtonian behaviour. The velocity and temperature fields and heat transfer coefficient ratio are studied systematically, taking into account the impact of various parameters, such as the generalised Reynolds number Re, generalised Prandtl number Pr, angular velocity of a cylinder ω , nanoparticle volume fraction ϕ , mixer size and location. Our research reveals that, to improve the heat transfer in practice, several applicable strategies are available, including the addition of more nanoparticles into the base fluid, which proved to be the most efficient method to enhance the heat transfer of a nanofluid.