Experimental setup for the determination of analytes contained in ultrasonically levitated drops

An automated technique for the determination of analytes in an ultrasonically levitated sample of 2 to 5 microL volume has been developed. Contactless dosing of reagents or solvents into an ultrasonically levitated drop was realized via piezoelectric micropumps. Drop size was continually controlled with a programmed CCD camera. A diode array spectrometer designed for the use with optical fibers was used for absorption and fluorescence measurements. Determinations via direct absorption measurements following the method of standard addition and acid-base titrations with an absorption indicator and a fluorescent indicator were carried out. The mean consumption of sodium hydroxide added via a piezoelectric micropump in five successive titrations with 18 nmol of sulfuric acid inside a levitated drop (indicator bromothymol blue) had a relative standard deviation of 0.7% and differed only by 0.2% from the expected value.     

Photothermal deflection measurement of effective gas diffusion coefficient of a porous medium

In this work, an effective gas diffusion coefficient of a porous medium was measured using photothermal deflection (PD) technique. An in-house made Loschmidt diffusion cell with a photothermal-deflection probe were employed to measure the effective gas diffusion coefficient of a gas diffusion layer (GDL) with a porosity ε ≈ 0.7. The concentration evolutions of CO₂ in O₂ with and without the GDL were measured, respectively, using a transverse normal PD technique. The concentration variations were used to deduce the gas diffusion coefficients in the presence and absence of the GDL by solving mass diffusion equations. The effective gas diffusion coefficient of the GDL was calculated from the diffusion coefficients using a model of an equivalent resistance to diffusion and found to be 4.39 × 10^-6 m²s^-1, demonstrating that PD technique can be employed to determine the effective gas diffusion coefficient of a porous medium.     

Collagen films from swim bladders: preparation method and properties

This paper describes the preparation and characterization of collagen films extracted from swim bladders of three species of tropical fishes: Arius parkeri (Gurijuba), Cynoscion acoupa (Pescada Amarela) and Cynoscion leiarchus (Pescada Branca). Collagen was extracted under acidic conditions (CH(3)COOH, 2.5 pH) and precipitated by the addition of NaCl up to 3.0 mol L(-1). The films were prepared in acrylic containers and dried in a vacuum atmosphere. The collagen films were characterized by hydroxyproline contents, thermal analysis, scanning electron microscopy and impedance spectroscopy. The determined values of 4-hydroxiproline and collagens in the films were: 105.23+/-4.48 and 873.2; 102.94+/-4.42 and 854.1; 100.65+/-4.80 and 835.8 mg g(-1) for A. parkeri, C. acoupa and C. leiarchus, respectively. Differential scanning calorimetry revealed high denaturation temperature peaks at temperatures ranging from 65.9 to 74.8 degrees C. The micrographs showed no fibrillar organization along the material, but spongy structure, with cavity diameters relatively uniform, at around 2 microm. The impedance spectroscopy presented a distributed relaxation process. A. parkeri's films showed piezoelectricity.     

Determination of binary diffusion coefficients of gases using photothermal deflection technique

A photothermal deflection (PD) technique was applied to measure the binary diffusion coefficients of various gases (CO₂–N₂, CO₂–O₂, N₂–He, O₂–He, and CO₂–He). With an in-house-made Loschmidt diffusion cell, a transverse PD system was employed to measure the time-resolved PD signal associated with the variation of the thermal diffusivity and the temperature coefficient of the refractive index of the gas mixture during the diffusion. The concentration evolution of the gas mixture was deduced from the PD amplitude and phase signals based on our diffraction PD model and was processed using two mass-diffusion models explored in this work for both short- and long-time diffusions to find the diffusion coefficient. An optical fiber oxygen sensor was also used to measure the concentration changes of the mixtures with oxygen. Experimental results demonstrated that the binary diffusion coefficients precisely measured with the PD technique were in agreement with the literature values. Moreover, the PD technique can measure the diffusion coefficients of various gas mixtures with both short- and long-time diffusions. In contrast, the oxygen sensor is only suitable for the long-time diffusion measurements of the gas mixtures with oxygen. PACS 78.20.Nv; 51.20.+d     

Laser emission at 1077 nm in Nd3+-doped calcium aluminosilicate glass

Laser emission at 1077 nm (⁴F_3/2⁴I_11/2) was demonstrated in Nd³⁺-doped low silica content calcium aluminosilicate (LSCA) glass under 810-nm pumping by a Ti:sapphire laser. The slope efficiency of the laser emission was found to be 34% with a 20-mW threshold power. The excited-state absorption (ESA) and stimulated emission were measured between 850 and 1520 nm. The results showed two ESA bands from 931 to 1070 nm (⁴F_3/2²D_3/2,²G_9/2,⁴G_11/2,²K_15/2) and from 1160 to 1414 nm (⁴F_3/2,⁴G_9/2⁴G_7/2,²K_13/2). The stimulated emission for the laser transition was found to be 45-nm broad with a peak value of 1.8×10^-20 cm². Thermal and mechanical properties of the LSCA glass were compared to the ED-2 and LHG-8 glasses. While the mechanical properties of the LSCA glass are superior to those of the commercial glasses, its temperature coefficient of optical path length is the highest among the three hosts. PACS 42.60.Pk; 42.70.Ce; 78.66.Jg     

Application of the denuder technique in filter sampling of airborne chromates at ground level concentrations

The use of the denuder technique for the preserving sampling of chromium(VI) in airborne dust at ground level (immission) concentrations was investigated. A simple denuder with activated charcoal retained by a steelwire-net cylinder was constructed. The sorption abilities of the denuder towards sulfur dioxide, which is responsible for the reduction of sampled Cr(VI) on the filter surface, were examined under various conditions. The measurements provide evidence for a laminar flow inside the denuder. At a flow rate of 100 L/h and a temperature of 27 °C the theoretical sorption value of 99.6% is reached within an experimental error of ±0.1%. A relative humidity of 19–91.5% has no influence on the sorption. In order to check if an experimental sorption value of 99.5% is sufficient to stabilize Cr(VI) on the filter surface, sampling was simulated by sucking SO₂-loaded air through Teflon filters loaded with Cr(VI) containing aerosol particles with diameters of about 0.3 m. Aerosols of two different compositions were generated by a sprayer in combination with a diffusion dryer. The particle size distributions were determined from scanning electron microscopic pictures. Chromium(VI) was eluted from the filters with an alkaline buffer and extracted from the filter eluates with a solution of a liquid anion exchanger. Chromium was determined with graphite furnace atomic absorption spectrometry. The Cr(VI) losses are between 57 and 16% depending on the composition of the aerosol particles and the sampling time. Realistic conditions were chosen regarding the initial Cr(VI) on the filters and the amount of sulfur dioxide which passed through the denuder.Dedicated to Professor Dr. Dieter Klockow on the occasion of his 60th birthday     

The influence of SiO2 content on spectroscopic properties and laser emission efficiency of Yb3+-Er3+ co-doped calcium aluminosilicate glasses

We have studied the influence of SiO₂ content on the spectroscopic properties and laser emission efficiency of Yb³⁺-Er³⁺ co-doped calcium aluminosilicate glasses. An increase in SiO₂ content resulted in higher phonon energy, which reduced the up-conversion emission, enhanced the energy transfer efficiency up to 70 % from Yb³⁺ to Er³⁺, and enhanced the optical quality. All these results led to an increase from 20 to 30 % in the laser emission efficiency.     

Experimental setup for the determination of analytes contained in ultrasonically levitated drops

An automated technique for the determination of analytes in an ultrasonically levitated sample of 2 to 5 μL volume has been developed. Contactless dosing of reagents or solvents into an ultrasonically levitated drop was realized via piezoelectric micropumps. Drop size was continually controlled with a programmed CCD camera. A diode array spectrometer designed for the use with optical fibers was used for absorption and fluorescence measurements. Determinations via direct absorption measurements following the method of standard addition and acid-base titrations with an absorption indicator and a fluorescent indicator were carried out. The mean consumption of sodium hydroxide added via a piezoelectric micropump in five successive titrations with 18 nmol of sulfuric acid inside a levitated drop (indicator bromothymol blue) had a relative standard deviation of 0.7 % and differed only by 0.2 % from the expected value. Received: 19 January 2000 / Revised: 28 February 2000 / Accepted: 3 March 2000     

Preparation of Nd2O3-doped calcium aluminosilicate glasses and thermo-optical and mechanical characterization

The calcium aluminosilicate glass (CAS) is an important class of optical materials due to the many applications envisaged, including its use as active media for glass lasers. In order to study how Nd₂O₃ doping affects the mechanical and the thermo-optical properties of CAS glass, two series of CAS glass, doped with Nd₂O₃ up to 5 wt%, were prepared in a vacuum atmosphere. The rare earth changes the physical properties, and this influence of doping ion content is discussed for both the series of samples in terms of mechanical, thermal, and thermo-optical properties. The study analyzed hardness and elastic moduli, glass transition temperature, crystallization temperature, thermal diffusivity, specific heat, density, thermal conductivity, refractive index, and thermo-optical properties, like temperature coefficient of the optical path length (dS/dT). The results presented provide information about the sample’s structure, and show that for Nd₂O₃ concentration up to 5 wt% there were no significant changes in the glass host material.     

Analysis of 2-D motion tracking in ultrasound with dual transducers

We study displacement and strain measurement error of dual transducers (two linear arrays, aligned orthogonally and coplanar). Displacements along the beam of each transducer are used to obtain measurements in two-dimensions. Simulations (5 MHz) and experiments (10 MHz) are compared to measurements with a single linear array, with and without angular compounding. Translation simulations demonstrate factors of 1.07 larger and 8.0 smaller biases in the axial and lateral directions respectively, for dual transducers compared to angular compounding. As the angle between dual transducers decreases from 90° to 40°, for 1% compression simulations, the lateral RMS error ranges from 2.1 to 3.9 μm compared to 9 μm with angular compounding. Simulation of dual transducer misalignment of 1 mm and 2° result in errors of less than 9 μm. Experiments demonstrate factors of 3.0 and 5.2 lower biases for dual transducers in the axial and lateral directions respectively compared to angular compounding.