Influence of pH and microwave calcination on the morphology of KGd(WO<Subscript>4</Subscript>)<Subscript>2</Subscript> particles derived by Pechini Sol–Gel method

KGd(WO₄)₂ (KGW) particles were synthesized at 3.5, 5.5 and 7.5 pH values by Pechini polymeric complex sol–gel method using potassium nitrate, gadolinium nitrate, ammonium paratungstate, citric acid and ethylene glycol as starting materials. Deionized water was used as solvent. Polymeric precursor gel was formed with citric acid as complexing agent and ethylene glycol as binder. Synthesized gel was analyzed by FT-IR spectroscopy. Prepared precursor gels were further annealed using resistive and microwave processes at 550 and 700 °C, respectively. The properties of heat treated samples were characterized by powder XRD, FT-IR, Raman and SEM analysis to understand the crystallinity, organic liberation, tungstate ribbon formation and surface morphology, respectively. The phase formation and different phases of intermediate oxides in pre-fired samples were investigated by powder XRD. Organic liberation in the samples in relation to temperature, and the carbon content in the pre-fired powder was analyzed using FT-IR spectrum. Raman spectrum reveals the formation of tungsten ribbons as well as the quality of the samples. The morphological changes at different synthesis conditions were observed with SEM micrographs.     

Effects of polyacrylic acid on the room-temperature phosphorescence of selected compounds

Polyacrylic acid solutions of 4-phenylphenol, p-aminobenzoic acid, 1,2-benzocarbazole, and 5,6-benzoquinoline were spotted on filter paper and the results obtained by room-temperature phosphorescence were compared with similar samples spotted on filter paper without polyacrylic acid. Improvements in sensitivity ranged from 26 times to 1.1 times and limits of detection from 100 times to 1.1 times for the samples on filter paper with polyacrylic acid. The relative standard deviations for the samples with polyacrylic acid added were also improved.     

Solid-surface derivative room-temperature luminescence spectrometry of mixtures

Derivative solid-surface room-temperature fluorescence and phosphorescence were combined for the identification of components in binary and ternary mixtures of nanogram amounts of nitrogen heterocycles. Direct, and first and second derivative room-temperature phosphorescence excitation, room-temperature fluorescence and room-temperature phosphorescence spectra were used in the identification of the components in the mixtures by matching spectral wavelengths from mixtures with spectral wavelengths from standards. The criteria for matching wavelengths, subtracting background signals and obtaining derivative spectra at the 0.5-ng level are discussed.     

A new numerical technique for the analysis of parametrically excited nonlinear systems

A new computational scheme using Chebyshev polynomials is proposed for the numerical solution of parametrically excited nonlinear systems. The state vector and the periodic coefficients are expanded in Chebyshev polynomials and an integral equation suitable for a Picard-type iteration is formulated. A Chebyshev collocation is applied to the integral with the nonlinearities reducing the problem to the solution of a set of linear algebraic equations in each iteration. The method is equally applicable for nonlinear systems which are represented in state-space form or by a set of second-order differential equations. The proposed technique is found to duplicate the periodic, multi-periodic and chaotic solutions of a parametrically excited system obtained previously using the conventional numerical integration schemes with comparable CPU times. The technique does not require the inversion of the mass matrix in the case of multi degree-of-freedom systems. The present method is also shown to offer significant computational conveniences over the conventional numerical integration routines when used in a scheme for the direct determination of periodic solutions. Of course, the technique is also applicable to non-parametrically excited nonlinear systems as well.     

Photon condensation: A new paradigm for Bose–Einstein condensation

Bose–Einstein condensation is a state of matter known to be responsible for peculiar properties exhibited by superfluid Helium-4 and superconductors. Bose–Einstein condensate (BEC) in its pure form is realizable with alkali atoms under ultra-cold temperatures. In this paper, we review the experimental scheme that demonstrates the atomic Bose–Einstein condensate. We also elaborate on the theoretical framework for atomic Bose–Einstein condensation, which includes statistical mechanics and the Gross–Pitaevskii equation. As an extension, we discuss Bose–Einstein condensation of photons realized in a fluorescent dye filled optical microcavity. We analyze this phenomenon based on the generalized Planck’s law in statistical mechanics. Further, a comparison is made between photon condensate and laser. We describe how photon condensate may be a possible alternative for lasers since it does not require an energy consuming population inversion process.