A comparative study of calibration transfer methods for determination of gasoline quality parameters in three different near infrared spectrometers

This work presents a comparative study of calibration transfer among three near infrared spectrometers for determination of naphthenes and RON (Research Octane Number) in gasoline. Seven transfer methods are compared: direct standardization (DS), piecewise direct standardization (PDS), orthogonal signal correction (OSC), reverse standardization (RS), piecewise reverse standardization (PRS), slope and bias correction (SBC) and model updating (MU). Two pre-treatment procedures, namely standard normal variate (SNV) and multiplicative scatter correction (MSC), are also investigated. The choice of an appropriate number of transfer samples for each technique, as well as the effect of window size in PDS/PRS and OSC components, are discussed. A broad set of gasoline samples representative of the Northeastern states of Brazil is employed in the investigation. The results show that the use of calibration transfer yields prediction errors comparable to those obtained with complete recalibration of the secondary instrument. Overall, the results point to RS as the best method for the analytical problem under consideration. When storage and/or physical transportation of transfer samples are impractical, MU is more appropriate. The comprehensive investigation carried out in the present work will be of value for practitioners involved in networks of fuel monitoring.     

HR-AR coated DFB lasers with high-yield and enhanced above-threshold performance

Optimized HR-AR-DFB laser structures are proposed foreseeing their use in directly modulated optical communication systems. They present, simultaneously, high single-longitudinal-mode yield, stable single-longitudinal-mode operation, high power efficiency and stable emitted wavelength. Lasers harder to manufacture were previously proposed elsewhere and did not succeed in achieving such high performances. A detailed assessment of the proposed lasers is presented and discussed.     

Influence of amide linkages on acidity determinations of humic substances Testing with model-mixtures

A set of experiments, using model compounds, was carried out in order to evaluate the influence of amide linkages on acidity measurements of humic substances (HS). Three benzene-carboxylic acids (2,4-dihydroxybenzoic acid; 3,5-dihydroxybenzoic acid, and phthalic acid) and two peptides (dl-alanyl-dl-alanine, and glycil-l-leucine) were employed to simulate the major acidic functional groups present in humic material. The acidity of the samples was measured, using the Schnitzer and Gupta methods, for each compound separately, as well as for selected mixtures with different compound combinations. General results showed that, in the absence of peptides, phenolic groups with high pK_a values are not detected in the barium hydroxide reaction and the data so obtained do not represent the real concentrations of the acidic groups. For the mixtures containing peptides, the presence of amide linkages distorts the results relative to the total acidity (TA) mainly because under the extreme conditions of the reaction with Ba(OH)₂ hydrolysis of the peptide occurs, consuming extra hydroxyl groups and increasing artificially the phenolic content. Such a condition is minimized by the reduction of the reaction time.     

Novel pulsed switched power supply for a fast field cycling NMR spectrometer

In this paper, we outline the operating principles of a pulsed switched power supply for a fast field-cycling nuclear magnetic resonance spectrometer. The power supply uses a variant of a four-quadrant chopper with a duty cycle that defines the average output current. With this topology only two semiconductors are necessary to drive hundreds of amperes with an output power of several kilowatts. The output current ripple has a well-defined shape that can be reduced to acceptable values by a careful design of the semiconductors' controlling circuits and drivers. A power supply prototype was tested with a home build air-core magnet operating with fields between 0 and 0.21 T. The system is computer controlled using pulse generator and data acquisition PC cards, and specific user-friendly home-developed software. A comparative proton relaxometry study in two well-known liquid crystal compounds 5CB and MBBA was performed to check the reproducibility of the T1 measurements.     

Application of lidar in ultraviolet,visible and infrared ranges for early forest fire detection

The efficiencies of direct lidars operating at 355, 532, 1064 and 1540-nm radiation wavelengths for early forest fire detection were compared. For each wavelength, the range for reliable smoke-plume detection was estimated on the basis of a computer simulation plume using a one-dimensional “top-hat” gas dynamic model for the calculation of the backscattering and extinction-coefficient profiles within the plume. The agreement between the predicted signal-to-noise ratio (SNR) and experimental results for 532 and 1064-nm wavelength radiation is good. The decrease of the signal-to-noise ratio with distance is maximum for 355 nm and minimum for 1064 nm. At 1540 nm, the decay of SNR with distance is slightly faster, but the SNR is higher than for other wavelengths, leading to the highest detection efficiency for the same energy of the probing laser pulse. For a burning rate of 2 kg/s and a laser beam divergence of 2.5 mr, the maximum distance for reliable detection varies between 6 and 12 km, depending on the wavelength. Received: 15 May 2002 / Revised version: 13 September 2002 / Published online: 22 January 2003 RID="*" ID="*"Corresponding author. Fax: +351-21/841-8120, E-mail: rui.vilar@ist.utl.pt     

Optical microscopy imaging and image-analysis issues in laser cleaning

In earlier work we characterised single-pulse laser cleaning of medium-density (areal coverage 10–20%) alumina particles from glass surfaces with three different lasers. The method of measuring particle-removal efficiency involves optical microscopy imaging (digital) and subsequent image analysis of the area covered by, and/or the number of, particles before and after the single-pulse laser cleaning treatment. The sample-preparation technique used leads to both single particles and agglomerates on the surface. The issues of depth of focus in the imaging and grey-scale thresholding in the image analysis of such samples, with a range of particle and agglomerate sizes, has been systematically investigated. A protocol for optimum imaging and illumination of such samples is described herein. It has been developed based on the results of a systematic investigation of the effect of the image focal plane position relative to the surface also described herein. The image analysis to quantify the particles on the surface involves a judgement of the best threshold grey-scale level in the image to define the boundary between particles and background substrate. A quantitative appraisal of the impact on the laser cleaning efficiency results of a threshold grey-scale level that is set too high or too low, and how these results compare with those obtained for the best-judgement threshold grey-scale level, has been completed. PACS 81.65.Cf; 42.62.Cf; 42.70.Ce     

(Im-)possible ISOL beams

Refractory elements, i.e. elements with very high melting point and low vapor pressure, cannot be released in atomic form from an ISOL target. Therefore most of these elements are presently not available as ISOL beams. However, when reactive gases are introduced into the target, they may form volatile compounds with the refractory elements, allowing for an easier transport to the ion source. Particularly useful are high-temperature stable fluorides and oxides. By these chemical evaporation methods so far ISOL beams of the refractory elements C, Zr, Hf and Ta have been produced. We discuss how ISOL beams of B, Ti, Nb, Mo, Tc, Ru, W, Re, Os and Ir could be produced in a similar way.