Rare Earth Doped Optical Fibre From Oxide Nanoparticles

Rare earth (RE) doped optical fibres were fabricated by using RE oxides coated silica nanoparticles. The fibre properties are comparable to those prepared by conventional techniques. The process offers better control over RE incorporation and homogeneity in the preform.     

Reverse micellar based synthesis of ultrafine MgO nanoparticles (8-10 nm): characterization and catalytic properties

Anisotropic nanostructures of magnesium oxalate dihydrate were synthesized using cationic surfactant based microemulsion method. The cationic surfactant plays an important role in forming the anisotropic structures. The oxalate nanostructures acts as an excellent precursor for the synthesis of fine magnesium oxide nanoparticles (~10 nm). Both the precursor and the oxide were characterized by using PXRD, IR, surface area and HRTEM. The surface area of these surfactant free oxide nanoparticles was found to be 108 m(2)/g. The catalytic activity of this basic oxide was examined for the Claisen-Schmidt condensation reaction and was found to be comparable to the best reported for the conventionally prepared MgO. Chalcone formation was found to increase with time as observed using gas chromatography-mass spectrometry (GC-MS). The reusability of the catalyst was checked by using the same catalyst twice which showed a reduced percentage (50% compared to first cycle) conversion.     

Superconducting phase at 7.7 K in the HgxReO3 compound with a hexagonal bronze structure

We have successfully synthesized a new rhenium-based hexagonal bronze material, HgxReO3, which exhibits superconductivity with the transition temperature Tc=7.7 K at ambient pressure and 11.1 K at 4 GPa. This compound is a superconductor with the highest Tc among hexagonal bronzes. Moreover, it presents the novel crystallographic feature that (Hg2)2+ polycations, in contrast to monatomic cations in known hexagonal bronzes, are incorporated into open channels. There is evidence that conducting electrons tightly couple with Hg-related phonons. Our results inspire detailed studies on the role of the rattling phonon in the occurrence of superconductivity in the hexagonal bronzes.     

Closed-form solutions for non-uniform Euler–Bernoulli free–free beams

In this paper, the free vibration of a non-uniform free–free Euler–Bernoulli beam is studied using an inverse problem approach. It is found that the fourth-order governing differential equation for such beams possess a fundamental closed-form solution for certain polynomial variations of the mass and stiffness. An infinite number of non-uniform free–free beams exist, with different mass and stiffness variations, but sharing the same fundamental frequency. A detailed study is conducted for linear, quadratic and cubic variations of mass, and on how to pre-select the internal nodes such that the closed-form solutions exist for the three cases. A special case is also considered where, at the internal nodes, external elastic constraints are present. The derived results are provided as benchmark solutions for the validation of non-uniform free–free beam numerical codes.     

Efficient Entrapment of Dye in Hollow Silica Nanoparticles: Direct Evidence Using Fluorescence Spectroscopy

Using hollow silica nanoparticles we demonstrate a simple and highly efficient way of removing hydrophilic dye (Rhodamine B) from water by encapsulation within these hollow spheres. The hollow silica spheres were obtained by using a surfactant templated procedure. Using fluorescence spectroscopy, we also show the evidence of the dye being absorbed within the hollow core of the silica shell (which is crucial for many applications) and differentiate from the adsorption of dye on the surface of the silica shell. It was found that that up to 94 % of the hydrophilic dye could be entrapped using these hollow shells within 72 h of exposure. Fluorescence spectroscopy shows a red shift in the dye encapsulated in the hollow silica which is due to aggregation of the dye and enables us to follow quantitatively the uptake of the dye molecules by the silica shells with time. The evidence for the encapsulation of the dye in these hollow spheres was reinforced by carrying out a comparative study, using solid silica particles.

Helicopter blade flapping with and without small angle assumption in the presence of dynamic stall

The flapping equation for a rotating rigid helicopter blade is typically derived by considering (1) small flap angle, (2) small induced angle of attack and (3) linear aerodynamics. However, the use of nonlinear aerodynamics such as dynamic stall can make the assumptions of small angles suspect as shown in this paper. A general equation describing helicopter blade flap dynamics for large flap angle and large induced inflow angle of attack is derived. A semi-empirical dynamic stall aerodynamics model (ONERA model) is used. Numerical simulations are performed by solving the nonlinear flapping ordinary differential equation for steady state conditions and the validity of the small angle approximations are examined. It is shown that the small flapping assumption, and to a lesser extent, the small induced angle of attack assumption, can lead to inaccurate predictions of the blade flap response in certain flight conditions for some rotors when nonlinear aerodynamics is considered.     

FT‐IR,FT‐Raman and DFT calculations of 3‐{[(4‐fluorophenyl)methylene]amino}‐2‐phenylquinazolin‐4(3H)‐one

Fourier transform (FT)‐Raman and Fourier transform infrared (FT‐IR) spectra of 3‐{[(4‐fluorophenyl)methylene]amino}‐2‐phenylquinazolin‐4(3H)‐one were recorded and analyzed. The vibrational wavenumbers of the title compound were computed using the B3LYP/6‐31G* basis and compared with the experimental data. The prepared compound was identified by NMR and mass spectra. The simultaneous IR and Raman activation of the CO stretching mode shows a charge transfer interaction through a π‐conjugated path. The first hyperpolarizability and infrared intensities are reported. The assignments of the normal modes are done by potential energy distribution (PED) calculations. Copyright © 2008 John Wiley & Sons, Ltd.