Volume 75, Issue 4

Microscopic electron properties of α-hexahydro-1,3,5-trinitro-1,3,5-triazine (α-RDX) with different shock wave velocities have been investigated based on molecular dynamics together with multi-scale shock technique. The studied shock wave velocities are 8, 9 and 10 km ⋅ s −1 . It has been said that the shock sensitivity and reaction initiation of explosives are closely relevant with their microscopic electron properties. The reactions, including the reaction products, which are counted from the trajectory during the simulations are analysed first. The results showed that the number of the products strictly rely on shock wave velocities. The reaction rates and decomposition rates are also studied, which showed the differences between the different shock velocities. The results of electron properties show that α-RDX is a wide-gap insulator in the ground state and the metallisation conditions of shocked RDX are determined, which are lower than under-static high pressure.

A novel Michelson interferometric hydrogen sulphide sensor coated with copper/reduced graphene oxide (Cu/rGO) composite membrane is proposed and fabricated. A section of endlessly photonic crystal fibre (EPCF) was sandwiched in two single-mode fibres (SMFs). One SMF was spliced and tapered with EPCF; the other SMF was connected with the Faraday rotator mirror to construct the Michelson structure. The cladding of the EPCF was coated by the Cu/rGO-sensing membrane, which was prepared by the dip-coating method. The obtained Cu/rGO-sensing film has a length of 25.0 mm. The fabricated sensing membrane is characterised by the scanning electron microscopy, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and so on. Experimental results demonstrated that the Cu/rGO-sensing film has a 24.56-nm thickness with a compact and uniform appearance. The XPS and Raman spectra indicate that there are three elements (C, O, and Cu), which are consistent with the expected compositions of the Cu/rGO membrane. With the increase of concentration of hydrogen sulphide, the interference spectra appear red-shifted. The linearity of 0.97662 and the sensitivity of 13.23 pm/ppm are achieved. In addition, the dynamic response and recovery time of the sensor are approximately 70 and 88 s, respectively. The surface adsorption energies of the film are calculated by the density functional theory. The theoretical results are in good agreement with the experimental findings. This sensor has some key advantages of small size, simple structure, easy fabrication, and great applicability for detecting the trace hydrogen sulphide.

A previous investigation found that the existence of double exponential terms is a reason for rapid intensification of cyclonic winds with the assumption of a linearised form of viscosity. Here, we consider viscosity of general type and still get similar terms. A perturbation technique is applied to the solution. The domain of analysis is split into two regions: an inner one that experiences updraft, and an outer one that possesses no vertical component of velocity but does have azimuthal and radial components. It is observed that the radial pressure difference between an arbitrary radial distance and the point of the maximum wind diminishes with height, time, and Reynolds number. The azimuthal velocity, close to the ground, in region 1 increases fast with time, but its dependence diminishes at a height a little above the ground. At a considerable height, time ceases to be a factor, and further, above that, trends reverse. Perturbation terms behave almost identically with the terms without perturbation. The significance of their contribution depends on the magnitude of the Reynolds number and, hence, the viscosity. Trends for region 2 are qualitatively similar to those in region 1 but differ quantitatively. It is also observed that the central pressure drop decreases with time.

Based on the positive and negative second-order strain gradient theories along with Kirchhoff thin plate theory and von Kármán hypothesis, the pull-in instability of rectangular nanoplate is analytically investigated in the present article. For this purpose, governing models are extracted under intermolecular, electrostatic, hydrostatic, and thermal forces. The Galerkin method is formally exerted for converting the governing equation into an ordinary differential equation. Then, the homotopy analysis method is implemented as a well-designed technique to acquire the analytical approximations for analyzing the effects of disparate parameters on the nonlinear pull-in behavior. As an outcome, the impacts of nonlinear forces on nondimensional fundamental frequency, the voltage of pull-in, and softening and hardening effects are examined comparatively.

We studied the non-isothermal flow of an incompressible viscous fluid through a porous tube. Motivated by filtration problems, Darcy’s law was incorporated on the walls of the tube and the flow was pressure driven. The main goal was to investigate the thermodynamic part of the system, assuming that the hydrodynamic part is known. In view of the applications we wanted to model, the fluid inside the tube was supposed to be cooled (or heated) by the surrounding medium. Using asymptotic analysis with respect to the small parameter (being the ratio between the tube’s thickness and its length), we constructed the explicit second-order approximation for the temperature distribution of the fluid. Numerical examples are provided to compare the obtained solution with the one derived for a rigid tube and also to show the corrections due to higher-order terms.

The unsteady laminar boundary layer flow of an electrically conducting viscous fluid near an impulsively started flat plate of infinite extent is considered, with a view to examine the influence of transverse magnetic field fixed to the fluid. A new type of similarity transformation is proposed, which renews the governing partial differential equation into a linear ordinary differential equation with four physical parameters, viz. unsteadiness parameter β , magnetic parameter M , and the velocity indices ( p , q ). The analytic solution of this equation has been found in terms of a first kind confluent hypergeometric function for some specific parameter regimes. This solution shows the structure of a new type of boundary layer flow that includes the solution of the first Stokes problem as a special case. For non-zero values of ( p , q ), there is a definite range of p (either −∞ < p < 2 q or 2 q < p < ∞ according to β < or > 0) for which this flow problem will be valid. This analysis reveals an important relation (pβ+M2=qβ)$(p\beta+{M^{2}}=q\beta)$ at which separation appears inside the layer and has been detected as the separation threshold of the problem. Indeed, this relation gives us the critical value of one when the others are known. Flow separation inside the layer is delayed with an increasing value of q but cannot be completely removed whatever is the value of q (>0). The present analysis ensures that the reverse flow can be suppressed by the use of a proper amount of magnetic field M depending upon the values of p , q , and β . The obtained result provides insight into the stability of the boundary layer flows.

There occurs a great interest in explaining the dependence of dopant concentration on the luminescence efficiency of rare earth oxides. Unambiguously, this study explains that luminescence intensity increases with increase in dopant concentration only up to optimised value. The syntheses of doped and co-doped yttrium oxide (Y 2 O 3 ) nanophosphors in this study were carried out by making use of combustion method. This method produces the nanophosphors that have sizes ranging between 5 and 20 nm as confirmed by transmission electron microscopy. X-ray diffraction pattern confirms that the incorporation of praseodymium oxide (Pr 3+ ) and gadolinium oxide (Gd 3+ ) does not cause any change in the cubic structure of Y 2 O 3 . The phase purity has been confirmed by Fourier transform infrared spectrum. Diffuse reflectance spectra reveal that the bandgap increases with increase in annealing temperature. Bandgap has been calculated by making use of the Kubelka–Munk function. Strongest emission was observed at 605 nm with 2 wt% of Pr 3+ as optimised concentration. Replacement of Y 3+ by Gd 3+ partially enhances the 605-nm emission linearly. The [Y:Pr:Gd] exhibits luminescence intensity of 2.705 times more than that of Y:Pr nanophosphors. This is for the first time our team has made a detailed study regarding the effects of co-doping in the case of Y 2 O 3 :Pr powders. We have successfully presented the changes that happen to the particle after co-doping especially in the particle size and luminescence properties.

The present work explores the diameter- and temperature-dependent ultrasonic characterization of wurtzite indium phosphide nanowires (WZ-InP-NWs) using a theoretical model based on the ultrasonic non-destructive evaluation (NDE) technique. Initially, the second- and third-order elastic constants (SOECs and TOECs) were computed using the Lennard-Jones potential model, considering the interactions up to the second nearest neighbours. Simultaneously, the mechanical parameters (Young’s modulus, shear modulus, elastic anisotropy factor, bulk modulus, Pugh’s ratio and Poisson’s ratio) were also estimated. Finally, the thermophysical properties and ultrasonic parameters (velocity and attenuation) of the InP-NWs were determined using the computed quantities. The obtained elastic/mechnical properties of the InP-NWs were also analyzed to explore the mechanical behaviors. The correlations between temperature-/size-dependent ultrasonic attenuation and the thermophysical properties were established. The ultrasonic attenuation was observed to be the third-order polynomial function of the diameter/temperature for the InP nanowire.