Mechanical and Thermophysical Properties of Cerium Monopnictides

The ultrasonic attenuation due to phonon–phonon interaction, thermoelastic relaxation and dislocation damping mechanisms has been investigated in cerium monopnictides CeX (X: N, P, As, Sb and Bi) for longitudinal and shear waves along \({\langle }100{\rangle }\), \({\langle }110{\rangle }\) and \({\langle }111{\rangle }\) directions. The second- and third-order elastic constants of CeX have also been computed in the temperature range 0 K to 500 K using Coulomb and Born–Mayer potential upto second nearest neighbours. The computed values of these elastic constants have been applied to find out Young’s moduli, bulk moduli, Breazeale’s non-linearity parameters, Zener anisotropy, ultrasonic velocity, ultrasonic Grüneisen parameter, thermal relaxation time, acoustic coupling constants and ultrasonic attenuation. The fracture/toughness ratio is less than 1.75, which shows that the chosen materials are brittle in nature as found for other monopnictides. The drag coefficient acting on the motion of screw and edge dislocations due to shear and compressional phonon viscosities of the lattice have also been evaluated for both the longitudinal and shear waves. The thermoelastic loss and dislocation damping loss are negligible in comparison to loss due to Akhieser damping (phonon–phonon interaction). The obtained results for CeX are in qualitative agreement with other semi-metallic monopnictides.     

Non-equilibrium Thermodynamics of Rayleigh–Taylor Instability

Here, the fundamental problem of Rayleigh–Taylor instability (RTI) is studied by direct numerical simulation (DNS), where the two air masses at different temperatures, kept apart initially by a non-conducting horizontal interface in a 2D box, are allowed to mix. Upon removal of the partition, mixing is controlled by RTI, apart from mutual mass, momentum, and energy transfer. To accentuate the instability, the top chamber is filled with the heavier (lower temperature) air, which rests atop the chamber containing lighter air. The partition is positioned initially at mid-height of the box. As the fluid dynamical system considered is completely isolated from outside, the DNS results obtained without using Boussinesq approximation will enable one to study non-equilibrium thermodynamics of a finite reservoir undergoing strong irreversible processes. The barrier is removed impulsively, triggering baroclinic instability by non-alignment of density, and pressure gradient by ambient disturbances via the sharp discontinuity at the interface. Adopted DNS method has dispersion relation preservation properties with neutral stability and does not require any external initial perturbations. The complete inhomogeneous problem with non-periodic, no-slip boundary conditions is studied by solving compressible Navier–Stokes equation, without the Boussinesq approximation. This is important as the temperature difference between the two air masses considered is high enough (\(\Delta T = 70\) K) to invalidate Boussinesq approximation. We discuss non-equilibrium thermodynamical aspects of RTI with the help of numerical results for density, vorticity, entropy, energy, and enstrophy.     

The Effects of Initial Conditions on Photoacoustic Waveforms Generated by a Gaussian Heating Source Moving in One Dimension

Although the photoacoustic effect is almost universally generated by radiation whose intensity is varied in time either by amplitude modulation of a continuous optical source or through the use of pulsed irradiation, it is possible to produce sound by movement of a continuous source in space. Here, the characteristics of sound production by movement of a light source in one dimension are discussed by solution to the wave equation for pressure. Solutions to the wave equation for the velocity potential, from which the acoustic pressure can be determined, are found using the D’Alembert integral and by Fourier transformation of the wave equation. The characteristics of the waveform generated by a Gaussian heat source moving uniformly in space are found to depend on the initial conditions for movement of the source.     

Trap State Effects in PbS Colloidal Quantum Dot Exciton Kinetics Using Photocarrier Radiometry Intensity and Temperature Measurements

Colloidal quantum dots (CQDs) have attracted significant interest for applications in electronic and optoelectronic devices such as photodetectors, light-emitting diodes, and solar cells. However, a poor understanding of charge transport in these nanocrystalline films hinders their practical applications. The photocarrier radiometry (PCR) technique, a frequency-domain photoluminescence method spectrally gated for monitoring radiative recombination photon emissions while excluding thermal infrared photons due to non-radiative recombination, has been applied to PbS CQD thin films for the analysis of charge transport properties. Linear excitation intensity responses of PCR signals were found in the reported experimental conditions. The type and influence of trap states in the coupled PbS CQD thin film were analyzed with PCR temperature- and time-dependent results.     

Study on the Multi-wavelength Emissivity of GCr15 Steel and its Application on Temperature Measurement for Continuous Casting Billets

A method for measuring the multi-wavelength emissivity of a steel surface is proposed, and an applicable experimental apparatus is designed. Multi-wavelength radiant energy emitted from a sample was measured using a fiber-optic spectrometer and its temperature measured using a NiCrSi/NiSiMg thermocouple. Utilizing the unique vacuum control and background noise-shielding systems, we investigated the multi-wavelength emissivity of GCr15 steel at three different degrees of surface oxidation at temperatures ranging from 1000 \(^{\circ }\)C to \(1100\,^{\circ }\)C. The experimental results show that the multi-wavelength (0.7 \(\upmu \)m–0.9 \(\upmu \)m) emissivity increased substantially, from 0.409–0.565 to 0.609–0.702, once the steel was oxidized. In addition, the emissivity increased slightly with increasing temperature, but the trends for emissivity and wavelength were similar. To measure the surface temperature of casting billets based on multi-wavelength thermometry, the functional relationships between emissivity and wavelength at different extents of oxidation were determined. Temperature measurements based on our technique were compared with those from common colorimetric thermometry. Our approach reduced the temperature fluctuation from \(\pm 23\,^{\circ }\)C to \(\pm 3.5\,^{\circ }\)C, indicating that a reliable measurement of the multi-wavelength emissivity of GCr15 steel is obtained using this experimental apparatus.     

Synthesis and characterization of <Emphasis Type="Italic">Eichhornia</Emphasis>-mediated copper oxide nanoparticles and assessing their antifungal activity against plant pathogens

In this paper, we report the biosynthesis and characterization of copper oxide nanoparticles from an aquatic noxious weed, Eichhornia crassipes by green chemistry approach. The aim of this work is to synthesize copper oxide nanoparticles by simple, cost-effective and ecofriendly method as an alternative to other available techniques. The synthesized copper oxide nanoparticles were characterized by UV–visible spectroscopy, Fourier transform infrared spectroscopy (FTIR), Field emission scanning electron microscopy (FESEM) and Energy dispersive X-ray spectroscopy (EDX) analyses. The synthesized particles were highly stable, spherical in shape with an average diameter of 28 ± 4 nm. The synthesized nanoparticles were then explored to antifungal activity against plant pathogens. Highest zone of inhibition were observed in 100 μg ml ^{? 1} of Eichhornia-mediated copper oxide nanoparticle against Fusarium culmorum and Aspergillus niger. This Eichhornia-mediated copper oxide nanoparticles were proved to be good antifungal agents against plant fungal pathogens.     

First-principles study of the double perovskites Sr<Subscript>2</Subscript>XOsO<Subscript>6</Subscript> (X = Li,Na, Ca) for spintronics applications

We investigated double perovskite compounds of the form Sr ₂ XOsO ₆ (X = Li, Na, Ca) using the full-potential linearized augmented plane wave (FP-LAPW) method. For the exchange-correlation energy, Wu and Cohen generalized gradient approximation (WC-GGA), Perdew, Burke and Ernzerhof GGA (PBE-GGA), Engel and Vosko GGA (EV-GGA), and GGA plus Hubbard U-parameter (GGA + U) were used. The calculated structural parameters are in good agreement with the existing experimental results. Calculation of different elastic constants and elastic moduli reveals that these compounds are elastically stable and possess ductile nature. The GGA + U approach yields quite accurate results of the bandgap as compared with the simple GGA schemes. The density of states plot shows that Sr-4d, Os-5d and O-2p states predominantly contribute to the conduction and valence bands. Further, our results regarding to the magnetic properties of these compounds reveal their ferromagnetic nature. In addition, these compounds seem to possess half-metallic properties, making them useful candidates for applications in spintronics devices.     

Preparation and properties of Pr<Superscript>3+</Superscript>/Ce<Superscript>3+</Superscript>:YAG phosphors using triethanolamine as dispersant and pH regulator

Pr³⁺/Ce³⁺:YAG precursors were co-precipitated using triethanolamine as dispersant and pH regulator. The different dosages of triethanolamine (D) vs. the properties of Pr³⁺/Ce³⁺:YAG phosphors were discussed. When D = 0.5 vol%, the pH of titration process was controlled in the range of ～7.94–8.16 to guarantee the uniform distribution of Al, Y, Ce and Pr in the precursors. The relatively higher pH could decrease the loss of Ce and Pr in the precursors and increase the particle size of the obtained powders, which was beneficial to the enhancement of luminescent intensity. Therefore, the precursors directly converted to pure-phase YAG at 900°C, and the phosphors calcined at 1000°C showed the best dispersity due to the dispersion effect of triethanolamine and the most excellent luminescent property. When D ≥ 2 vol%, although pure-phase YAG was detected, the emission intensity of the phosphors decreased due to the decrease of dispersity and purity. Moreover, the co-doped Pr³⁺ enhanced the red emission of Pr³⁺/Ce³⁺:YAG phosphors.     

Graphene/TiO<Subscript>2</Subscript> hydrogel: a potential catalyst to hydrogen evolution reaction

In this study, graphene was synthesized from graphite. Graphite was oxidized via modified Hummer’s method and sonicated to form graphene oxide (GO). Infrared spectroscopy revealed the successful oxidation of graphite by the emergence of oxygen functionalities. The spectrum of GO showed peaks at 3270, 1629, 1227 and 1096 cm^?1, indicating O–H, C=O, C–OH and C–O–C functional groups, respectively. Graphene hydrogels were prepared by the addition of L-ascorbic acid to GO suspensions and subsequent heating at 90^°C. Composite hydrogels of graphene and titanium (IV) oxide (TiO₂) were synthesized with various TiO₂ to GO mass ratios. Composites were applied to photocatalytic hydrogen evolution reaction (HER) and the hydrogen gas produced was analysed by gas chromatography with thermal conductivity detector. Highest HER yield was 66.00% H₂.     

Effect of ‘Al’ concentration on spin-dependent resonant tunnelling in InAs/Ga<Subscript>1−<Emphasis Type="Italic">y</Emphasis></Subscript>Al<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript>As symmetrical double-barrier heterostructures

The effect of ‘Al’ concentration on spin-dependent tunnelling in strained non-magnetic symmetric double-barrier semiconductor has been theoretically investigated. The separation between spin-up and spin-down components, barrier transparency, polarization efficiency and tunnelling lifetime were calculated using the transfer matrix approach. The separation between spin-up and spin-down resonances and tunnelling lifetime were reported for the first time in the case of InAs/Ga_1?y Al _y As heterostructures for various ‘Al’ concentrations and for various barrier widths. Cent percentage polarization can be obtained in this strained non-magnetic double-barrier semiconductor even without any external field.