Ytterbium-doped silica fiber lasers: versatile sources for the1-1.2 μm region

Ytterbium-doped silica fibers exhibit very broad absorption and emission bands, from ~800 nm to ~1064 nm for absorption and ~970 nm to ~1200 nm for emission. The simplicity of the level structure provides freedom from unwanted processes such as excited state absorption, multiphonon nonradiative decay, and concentration quenching. These fiber lasers therefore offer a very efficient and convenient means of wavelength conversion from a wide variety of pump lasers, including AlGaAs and InGaAs diodes and Nd:YAG lasers. Efficient operation with narrow linewidth at any wavelength in the emission range can be conveniently achieved using fiber gratings. A wide range of application for these sources can be anticipated. In this paper, the capabilities of this versatile source are reviewed. Analytical procedures and numerical data are presented to enable design choices to be made for the wide range of operating conditions     

Masking in three-dimensional auditory displays.

The extent to which simultaneous inputs in a three-dimensional (3D) auditory display mask one another was studied in a simulated sonar task. The minimum signal-to-noise ratio (SNR) required to detect an amplitude-modulated 500-Hz tone in a background of broadband noise was measured using a loudspeaker array in a free field. Three aspects of the 3D array were varied: angular separation of the sources, degree of correlation of the background noises, and listener head movement. Masking was substantially reduced when the sources were uncorrelated. The SNR needed for detection decreased with source separation, and the rate of decrease was significantly greater with uncorrelated sources than with partially or fully correlated sources. Head movement had no effect on the SNR required for detection. Implications for the design and application of 3D auditory displays are discussed.     

The induction of cytotoxic T cells and tumor regression by soluble antigen formulation

CTLs specific for tumor antigens play a major role in the immunity against cancer. We have shown that class I-restricted CTLs can be induced by injecting soluble antigens mixed in an antigen formulation (AF) that consists of squalane, Tween 80, and Pluronic L121 (S. Raychaudhuri et al., Proc. Natl. Acad. Sci. USA, 89: 8308-8312, 1992). In this study, using ovalbumin and the ovalbumin-expressing transfectoma (EG7) as a tumor model system, we examined the in vivo antitumor effect of antigen-AF mixture. Vaccination of mice with ovalbumin in AF 2 or 3 days after EG7 tumor challenge showed significant inhibition of tumor growth compared to mice vaccinated with ovalbumin in alum or in saline. Depletion of CD8+ cells at the time of immunization completely abrogated the AF-induced tumor protection, indicating that CD8+ T cells are the major effectors in tumor protection in vivo. Depletion of CD4+ cells led to a marginal loss of tumor protection, which may be the result of inhibition of ovalbumin-specific CTL response due to the lack of T-helper activity. Our results demonstrate that AF can be used in subunit vaccines to stimulate CTLs and tumor regression in vivo.     

Sintering and microstructure of ultrafine yttriazirconia compacts

Sintering behaviour of ultrafine yttria-zirconia solid solution compacts, with yttria contents ranging between 4 and 10 mol % have been investigated and the microstructural developments during sintering were followed. The 4 mol % yttria-zirconia compacts sinter at 1200 ° C to a high density with a relatively fine uniform microstructure. Firing at 1400 ° C produces no improvement in densification and discontinuous grain growth develops. The lowest density values are obtained with the 10 mol % yttria-zirconia compacts, with clustering in the grains and greater porosity in the microstructure. The activation energies were determined for both 4 and 10 mol % Y₂O₃ -containing bodies in the temperature range 800 to 1000 ° C.     

Design and testing of a solar photovoltaic operated multi-seeds oil press

Oil expression tests were conducted to evaluate the performance of a novel oil expeller designed and fabricated to operate on a 200 W solar photovoltaic (PV) power system as a sole power source. The oil press was designed to press oilseeds meal with intermediate moisture content of 12±1% (w.b.) and 0.5–2 mm particle sizes. Freshly grated coconuts and ground peanuts were used to determine the oil expression efficiency of the press. The oilseed samples were pressed for 12 min with a maximum pressure of 3.0 MPa being reached at 6 min of pressing for peanuts and 8 min of pressing for coconuts. The pressure was then held for the rest of the pressing time. The press attained an average oil expression efficiency of 73% for coconuts and 70% for peanuts. The force-vs.-deformation studies indicated that peanut press meal was compacted at a higher rate as compared to coconuts. The observation on the energy consumption indicated that there was a significant increase (P<0.05) in the specific energy requirement for both coconuts and peanuts after 6 min of pressing, which resulted from the solidification of the press cake. An average specific energy of 36.55 and 20.35 Wh/kg was recorded for peanuts and coconuts, respectively, after 12 min of pressing.     

Comparison between infrared and Raman spectroscopic analysis of maturing rabbit cortical bone

The molecular composition of the organic and inorganic matrices of bone undergoes alterations during maturation. The aim of this study was to compare Fourier transform infrared (FT-IR) and near-infrared (NIR) Raman microspectroscopy techniques for characterization of the composition of growing and developing bone from young to skeletally mature rabbits. Moreover, the specificity and differences of the techniques for determining bone composition were clarified. The humeri of female New Zealand White rabbits, with age range from young to skeletally mature animals (four age groups, n = 7 per group), were studied. Spectral peak areas, intensities, and ratios related to organic and inorganic matrices of bone were analyzed and compared between the age groups and between FT-IR and Raman microspectroscopic techniques. Specifically, the degree of mineralization, type-B carbonate substitution, crystallinity of hydroxyapatite (HA), mineral content, and collagen maturity were examined. Significant changes during maturation were observed in various compositional parameters with one or both techniques. Overall, the compositional parameters calculated from the Raman spectra correlated with analogous parameters calculated from the IR spectra. Collagen cross-linking (XLR), as determined through peak fitting and directly from the IR spectra, were highly correlated. The mineral/matrix ratio in the Raman spectra was evaluated with multiple different peaks representing the organic matrix. The results showed high correlation with each other. After comparison with the bone mineral density (BMD) values from micro-computed tomography (micro-CT) imaging measurements and crystal size from XRD measurements, it is suggested that Raman microspectroscopy is more sensitive than FT-IR microspectroscopy for the inorganic matrix of the bone. In the literature, similar spectroscopic parameters obtained with FT-IR and NIR Raman microspectroscopic techniques are often compared. According to the present results, however, caution is required when performing this kind of comparison.