The application of a piezoelectric scanning Fabry-Perot Interferometer to the study of atomic line sources—III: Use of the channeled spectra produced with a continuum source for studies of the absorption line-width for calcium atoms in flames

An instrumental arrangement has been developed for the interferometric study of the half-width of atomic lines in absorption using a spectral continuum source. The variation of observed half-width of the calcium absorption line at 422·67 nm with calcium concentration has been examined in air-acetylene and nitrous oxide-acetylene flames supported as cylindrical flames with and without flame shielding and at long path burners. Extrapolation of the curves obtained to zero added calcium concentration in the flame may allow for correction for self-absorption and flame characteristics and calculation of collisional broadening half-widths and damping constants (a-parameters).     

Correlation Functions by Cluster Variation Method for Ising Model with NN, NNN, and Plaquette Interactions

We consider a procedure for calculating the pair correlation function in the context of cluster variation methods (CVM). As specific cases, we study the pair correlation function in the paramagnetic phase of the Ising model with nearest neighbors, next to nearest neighbors, and plaquette interactions in two and three dimensions. In presence of competing interactions, the so-called disorder line separates in the paramagnetic phase a region where the correlation function has the usual exponential behavior from a region where the correlation has an oscillating, exponentially damped behavior. In two dimensions, using the plaquette as the maximal cluster of the CVM approximation, we calculate the phase diagram and the disorder line for a case where a comparison is possible with known results for the eight-vertex model. In three dimensions, in the CVM cube approximation, we calculate the phase diagram and the disorder line in some cases of particular interest. The relevance of our results for experimental systems like mixtures of oil, water, and surfactant is also discussed.     

Oscillatory control of sample dispersion in a continuous flow system

A new strategy for the instrumental control of sample dispersion in continuous flow systems is presented. The method is based on shaking a loosely held straight reactor while the sample travels through the flow injection manifold. This external disturbance yields a sample transport more similar to the plug flow type because of the changes promoted on the flow pattern. Up to a three-fold increase in peak height, a comparable reduction in peak width and a more Gaussian peak profile are observed when the signals obtained with the shaken reactor are compared with those obtained with the same reactor but static. Improvements in the analytical performance as a function of different operational variables are shown for systems with or without a chemical reaction. Analytical implications and possible uses are discussed since this strategy allows the control of dispersion by simply selecting the frequency and amplitude of oscillation.     

Geographical origin of durum wheat studied by 1H-NMR profiling

(1)H-Nuclear magnetic resonance (NMR) spectroscopy was used to detect metabolic profiles of wheat flour samples of different geographical and botanical origin. The NMR profiles were analyzed by multivariate statistical techniques in order to establish the origin of the samples. A linear model, able to discriminate among three different locations, was built achieving a prediction level of about 80% of correctly assigned samples. The principal classes of compounds responsible for the geographic origin discrimination were individuated in aromatic compounds and amino acids. The statistical modeling also indicated that botanical origin information is very poor in the NMR profiles of the analyzed wheat samples.     

The application of a piezoelectric scanning Fabry-Perot interferometer to the study of atomic line sources—II: Line-widths for calcium in air-acetylene and nitrous oxide-acetylene flames

The variation in observed half-width of the calcium 422.7 nm line with calcium concentration has been studied interferometrically in air-acetylene and nitrous oxide-acetylene flames supported as cylindrical flames, with and without flame shielding and inert gas separation, and at a long path burner. Extrapolation of the curves obtained to zero added calcium concentration is shown to permit correction for self-absorption and calculation of interaction broadening half-width and damping constants (a-parameters).     

Widely tunable mode-hop free external cavity quantum cascade lasers for high resolution spectroscopy and chemical sensing

Recent progress in the development of room temperature, continuous wave, widely tunable, mode-hop-free mid-infrared external cavity quantum cascade laser (EC-QCL) spectroscopic sources is reported. A single mode tuning range of 155 cm^-1 (∼ 8% of the center wavelength) with a maximum power of 11.1 mW and 182 cm^-1 (∼ 15% of the center wavelength) with a maximum power of 50 mW was obtained for 5.3 and 8.4 μm EC-QCLs respectively. This technology is particularly suitable for high resolution spectroscopic applications, multi species trace-gas detection and spectroscopic measurements of broadband absorbers. Several examples of spectroscopic measurements performed using EC-QCL based spectrometers are demonstrated. PACS  42.55.Px; 42.60.-v; 42.62.Fi; 07.07.Df