Improvement of thermal and spectroscopic behavior of Er<Superscript>3+</Superscript>/Ce<Superscript>3+</Superscript> co-doped tellurite glass for lasing materials

Tellurite glasses (TeO₂–ZnO–Nb₂O₅) mono-doped Er³⁺ and co-doped Er³⁺/Ce³⁺ have been prepared using the melt-quenching technique. To evaluate the effect of Ce³⁺ on the structural, thermal stability of glass hosts and fluorescence properties of Er³⁺, X-ray diffraction patterns, Ftir spectra, differential scanning calorimeter curves, absorption spectra, fluorescence emission spectra, fluorescence lifetimes, up-conversion emission spectra of glass samples were measured and investigated. Using Judd–Ofelt theory, we calculated intensity parameters (Ω₂, Ω₄ and Ω₆), spontaneous emission probabilities, the radiative lifetime, luminescence branching factors and the quantum yield of luminescence for ⁴I_13/2 → ⁴I_15/2 transition. The co-doping with Ce³⁺ was effective on the suppression of up-conversion emission of Er³⁺ owing to the phonon-assisted energy transfer: Er³⁺:⁴I_11/2 + Ce³⁺:²F_5/2 → Er³⁺:⁴I_13/2 + Ce³⁺:²F_7/2 which contributed the effective enhancement of 1.53 µm fluorescence emission. The change in optical properties with the addition of Ce³⁺ ions have been discussed and compared with other glasses. Using the Mc Cumber method for the ⁴I_13/2 → ⁴I_15/2 transition, absorption cross-section, calculated emission cross-section, and gain cross-section values support that TZNEr1Ce1 glass is a potential material for developing broad-band and high-gain erbium-doped fiber amplifiers applied for 1.53 µm.     

A simple humidity sensor utilizing air-gap as sensing part of the Mach–Zehnder interferometer

A simple high-resolution refractive index (RI) and phase sensor has been demonstrated and the results numerically verified. A free space gap is employed in one arm of a Mach–Zehnder interferometer (MZI) to serve as the sensing mechanism with a physical spacing of 1.4 mm. The propagation constant of transmitted light in the MZI’s gap changes due to the small variation in the ambient RI that will further shift the optical phase of the signal. A free space optical delay line is embedded within the MZI’s other arm to set the phase reference point and compensate for variations in the optical phase difference. The ambient RI is computed by measuring the phase shift in the transmission spectrum A high-resolution sensing of 0.8 pm/%RH corresponds to phase change of 0.012°/%RH has been achieved in 1520 nm.     

A comparative study on the Ge6C14 heterofullerene nanocages: a density functional survey

Ten C₁₄Ge₆ heterofullerene isomers of C₂₀ have been investigated by density functional theory (DFT) methods with Becke 3‐Parameter (Exchange), Lee, Yang and Parr (B3LYP) functional at the 6‐311 + G*, 6‐311++G** and AUG‐cc‐pVTZ levels. In contrast to identical bonds in the latter, contractions of C═C double bonds are encountered at the expense of longer C―Ge bonds in the former. Vibrational frequency analysis confirms that all of the nanocages are true minima. In contrast to the common belief, for obtaining highly silicon‐doped stable heterofullerenes, that the silicon dopants must be completely isolated from each other by means of strong C═C double bonds. Here, linking the germanium substitutions together is an applicable strategy for obtaining highly doped stable isolated heterofullerenes since it avoids weak heteroatom─heteroatom bonds. Therefore, none of the computed heterofullerenes collapses to open, to deform, or to segregate fullerenic cages. As to band gaps (ΔE_HOMO‐LUMO), and nucleus‐independent chemical shifts at cage centers (NICS (0)), C₁₄Ge₆‐2 immerges with the highest value. Hence, it is predicted to be the most stable against electronic excitation. It contains 2 Ge─Ge single bonds at the cap‐equatorial positions. On the other hand, as to zero‐point vibrational energy and heat of atomization (ΔH_at), C₁₄Ge₆‐8 appears with the lowest and highest value, respectively. It contains 6 alternating germanium atoms in the equatorial and cap positions. Thus, it is predicted to be the most thermodynamically stable. So, germanium substitution leads to a high charge distribution on the surfaces of all the isomers specially C₁₄Ge₆‐9 with +1.496 charged germanum atoms. C₁₄Ge₆ isomers seem to be a good candidate for the hydrogen storage material.     

Synthesis and characterization of nickel(II) complexes with three potentially hexadentate Schiff-base ligands and polyamines: X-ray crystal structure determination of one nickel(II) complex

Three new potentially hexadentate N₄O₂ Schiff-base ligands (H₂L¹, H₂L² and H₂L³) were prepared from the reaction of the polyamines N,N′-bis(2-aminophenyl)-1,2-ethanediamine (L¹), N,N′-bis(2-aminophenyl)-1,3-propanediamine (L²) and N,N′-bis(2-aminophenyl)-1,4-butanediamine (L³), respectively with salicylaldehyde. Reaction of the Schiff bases with Ni(II) salts in the presence of N(Et)₃ gave the neutral complexes [NiL⁴], [NiL⁵] and [NiL⁶]. Ni(II) complexes of the polyamines were also prepared. One of complexes [Ni(L¹)(MeCN)₂](ClO₄)₂·MeCN has been characterized through X-ray diffraction methods.     

PTSA catalyzed simple and green synthesis of benzothiazole derivatives in water

Abstract  

p-Toluenesulfonic acid (10 mol%) was found to be an effective and efficient catalyst for the synthesis of 2-substituted benzothiazoles from aromatic aldehydes and 2-aminothiophenol in moderate to excellent yields in water. This method provides a simple and efficient protocol in terms of mild reaction conditions, clean reaction profiles, small quantity of catalyst, and simple workup procedure.     

Effects of external electromagnetic field on binodal curve of (water + propionic acid + dichloromethane) ternary system

The effects of an external electromagnetic field on the binodal curve of the (water + propionic acid + dichloromethane) ternary system was investigated at 91.3 kPa and T = (294.15 and 284.15) K. The experimental binodal curve values for the ternary system were obtained by the cloud point method using a new setup with a flat capacitor. The effects of variation of frequencies and amplitude of voltages of the applied external electromagnetic field on the binodal curve results have been evaluated. The results obtained indicate that the heterogeneous two-phase area increases with increasing frequency of the applied external electromagnetic field. At constant frequency, a similar effect has been found by increasing the amplitude of the voltage of the applied external electromagnetic field. The comparison between the results obtained for this work with those reported in previous work indicates that the treatment efficiency in liquid–liquid extraction process of (water + propionic acid + dichloromethane) ternary system can be governed by the applied external electromagnetic field.     

Vibration testing for anomaly detection

In this paper we propose an efficient method to reconstruct a small inclusion buried inside a body using the perturbation of modal parameters measured on the boundary of the body. We design a reconstruction algorithm based on the asymptotic expansions of the eigenvalue perturbations obtained by Ammari and Moskow (Math. Meth. Appl. Sci. 2003; 26 :67–75). We then implement this algorithm and demonstrate its viability and limitations. Copyright © 2008 John Wiley & Sons, Ltd.     

A robust parameter design for multi-response problems

Most real world search and optimization problems naturally involve multiple responses. In this paper we investigate a multiple response problem within desirability function framework and try to determine values of input variables that achieve a target value for each response through three meta-heuristic algorithms such as genetic algorithm (GA), simulated annealing (SA) and tabu search (TS). Each algorithm has some parameters that need to be accurately calibrated to ensure the best performance. For this purpose, a robust calibration is applied to the parameters by means of Taguchi method. The computational results of these three algorithms are compared against each others. The superior performance of SA over TS and TS over GA is inferred from the obtained results in various situations.     

Gross Laplacian Acting on Operators

In this paper, we introduce a noncommutative extension of the Gross Laplacian, called quantum Gross Laplacian, acting on some analytical operators. For this purpose, we use a characterization theorem between this class of operators and their symbols. Applying the quantum Gross Laplacian to the particular case where the operator is the multiplication one, we establishes a relation between the classical and the quantum Gross Laplacians.