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.     

Luminescence properties of terbium-doped Li<Subscript>3</Subscript>PO<Subscript>4</Subscript> phosphor for radiation dosimetry

A polycrystalline sample of Li₃PO₄:Tb³⁺ phosphor was successfully synthesized using solid-state diffusion method. This synthesis method is of low cost, low temperature and does not require any other atmospheres for the synthesis. The powder X-ray diffraction (PXRD), photoluminescence (PL) emission and excitation spectra, thermoluminescence (TL) and optically stimulated luminescence (OSL) were measured. The particle size was calculated using the Debye Scherrer formula and found to be 79.42 nm. PL emission spectra of Li₃PO₄:Tb³⁺ phosphor show the strong prominent peak at 544 nm corresponding to ⁵D₄ to ⁷F₅ transitions of Tb³⁺. The OSL sensitivity of prepared Li₃PO₄:Tb³⁺ phosphor was 50% of that of α-Al₂O₃:C. Its decay curve consists of three components with photoionization cross-sections 0.44 × 10^?17, 3.09 × 10^?17 and 23×10^?17 cm². The TL glow curve of the prepared sample consists of two characteristic peaks, which were deconvoluted using the peak fit software, and kinetic parameters were determined using the peak shape method. TL intensity was compared with that of the commercially available TLD-500 phosphor. OSL dose response was linear in the measured range and the minimum detectable dose (MDD) was found to be 67.42 μGy, while fading of the OSL signal was found to be about 27% in 4200 min after which the OSL signal stabilizes.     

Synthesis,characterisation and non-isothermal degradation kinetics of novel poly(mono ethylene glycol dimethacrylate-co-4-aminobenzoate)

Synthesis of a novel co-polymer made by the addition polymerisation between MEGDMA and 4-AB by aza-Michael addition (AMA) polymerisation method is a fascinating field of research. The present investigation yielded a hazardous metal catalyst-free and toxic solvent-free methodology. The AMA polymerisation was carried out at five different [ M ₁/M ₂] values under N₂ atmosphere at 100^°C for 2 h. Thus, obtained co-polymer was characterized by Fourier transform infrared spectroscopy, UV–visible reflectance spectroscopy, X-ray diffraction, differential scanning calorimetry, thermogravimetric analysis and scanning electron microscopy (SEM). The SEM image confirmed the formation of polymer nanoparticles. The non-isothermal degradation kinetics was followed with four different models, such as Flynn-Wall-Ozawa, Auggis-Bennet, Kissinger and Friedman method. Among the models used, the Kissinger method yielded the lowest degradation kinetics. The degradation kinetics of the co-polymer was followed with the help of model-free methods. Moreover, it was critically compared with the literature.