Raman spectroscopic investigation of pure and ytterbium-doped rare earth silicate crystals

Raman spectroscopy was used to study the molecular structure of a series of selected rare earth (RE) silicate crystals including Y2SiO5 (YSO), LU2SiO5 (LSO), (Lu0.5Y0.5)(2)SiO5 (LYSO) and their ytterbium-doped samples. Raman spectra show resolved bands below 500 cm(-1) region assigned to the modes of SiO4 and oxygen vibrations. Multiple bands indicate the nonequivalence of the RE-O bonds and the lifting of the degeneracy of the RE ion vibration. Low intensity bands below 500 cm(-1) are an indication of impurities. The (SiO4)(4-) tetrahedra are characterized by bands near 200 cm(-1) which show a separation of the components of nu(4) and nu(2), in the 500-700 cm(-1) region which are attributed to the distorting bending vibration and in the 880-1000 cm(-1) region which are attributed to the symmetric and antisymmetric stretching vibrational modes. The majority of the bands in the 300-610 cm(-1) region of Re2SiO5 were found to arise from vibrations involving both Si and RE ions, indicating that there is considerable mixing of Si displacements with Si-O bending modes and RE-0 stretching modes. The Raman spectra of RE silicate crystals were analyzed in terms of the molecular structure of the crystals, which enabled separation of the bands attributed to distinct vibrational units. Copyright (C) 2007 John Wiley & Sons, Ltd.

Correlation of cell numbers with catalase activities of pure strains of bacteria

An attempt was made to correlate the catalase production with the actual number of aerobic bacterial cells generating the enzyme: bacteria were obtained from the surface of marine fish. A linear correlation was found between the log of catalase activity and log of bacterial count in single culture.

A body force-based method for prediction of multiple-pure-tone noise: Validation

Emissions, fuel burn, and noise are the main drivers for innovative aircraft design. Embedded propulsion systems, such as for example used in hybrid-wing body aircraft, can offer fuel burn and noise reduction benefits but the impact of inlet flow distortion on the generation and propagation of turbomachinery noise has yet to be assessed. A novel approach is used to quantify the effects of non-uniform flow on the creation and propagation of multiple pure tone (MPT) noise. The ultimate goal is to conduct a parametric study of S-duct inlets to quantify the effects of inlet design parameters on the acoustic signature. The key challenge is that the effects of distortion transfer, noise source generation and propagation through the non-uniform flow field are inherently coupled such that a simultaneous computation of the aerodynamics and acoustics is required to capture the mechanisms at play. The technical approach is based on a body force description of the fan blade row that is able to capture the distortion transfer and the blade-to-blade flow variations that cause the MPT noise while reducing computational cost. A single, 3-D full-wheel CFD simulation, in which the Euler equations are solved to second-order spatial and temporal accuracy, simultaneously computes the MPT noise generation and its propagation in distorted inlet flow. A new method of producing the blade-to-blade variations in the body force field for MPT noise generation has been developed and validated. The numerical dissipation inherent to the solver is quantified and used to correct for non-physical attenuation in the far-field noise spectra. Source generation, acoustic propagation and acoustic energy transfer between modes is examined in detail. The new method is validated on NASA's Source Diagnostic Test fan and inlet, showing good agreement with experimental data for aerodynamic performance, acoustic source generation, and far-field noise spectra. The next steps involve the assessment of MPT noise in serpentine inlet ducts and the development of a reduced order formulation suitable for incorporation into NASA's ANOPP framework. © 2010 by Jeff Defoe, Alex Narkaj & Zoltan Spakovszky.