Soot visualisation by use of laser-induced soot vapourisation in combination with polarisation spectroscopy

A novel approach to the visualisation of soot is presented. It relies on a combination of laser-induced soot vapourisation and consecutive polarisation spectroscopy. Upon soot vapourisation, molecular fragments (for example, C₂) emerge, and may serve as effective tracers for soot. In this study we demonstrate that saturated polarisation spectroscopy on photo-induced C₂ can be exploited for soot detection. Signal maps featuring high signal-to-noise ratios were readily recorded in ethyne-rich flames and any spurious background, for example, caused by Rayleigh scattering, was successfully suppressed by means of spatial filtering. Additionally, investigations were carried out addressing how the attained signals correlate with local soot volumne fractions. For this purpose, height profiles of C₂ number densities inferred from the polarisation spectroscopy signal maps were compared with profiles of the soot volumne fraction inferred from measurements with laser-induced incandescence. For low soot volumne fractions, the shapes of the height profiles from our approach agree rather well with the latter; they do not agree for higher soot volumne fractions. Further investigation is required to resolve this discrepancy. Scattering from particles in the Mie scattering range may hamper the application of this approach, and avenues are suggested for extending the applicability of the approach presented to large soot particles. PACS 42.62.Fi; 82.80.Dx     

Multipoint temperature and oxygen-concentration measurements using rotational coherent anti-Stokes Raman spectroscopy

A novel technique for coherent anti-Stokes Raman spectroscopy (CARS) measurements in multiple points is presented. With a system of cylindrical lenses, each laser beam is split into several focused beams, yielding separate planar boxcars configurations. Spectrally resolved CARS signals are detected at different heights on the CCD chip. With dual-broadband rotational CARS the setup is demonstrated for quantitative measurements of temperature- and oxygen-concentration profiles. The technique was demonstrated for three points only, but it can be extended to more points by use of special optics; this choice must be based on a sufficient signal-to-noise ratio in all points for the actual measurement condition.     

A unified approach to particle-holes and rotations in the spectrum of 16O

The cranked Nilsson-Strutinsky formalism is applied to the many-faceted spectrum of ¹⁶O. The deformation parameters ?, γ and ε₄ are varied independently and many-particle-many-hole excitations are considered in the rotating system. Potential-energy surfaces are presented at different values of spin, parity and signature. Surprisingly good agreement is obtained when the different minima are compared with the measured states. Generally, it is observed that the more particles that are excited to higher shells, the larger becomes the intrinsic deformation. Rotational bands as well as pure p-h excitations, the latter sometimes constituting the termination of a rotational band, are identified. Additional high-spin states (I ? 12) are suggested. A microscopic analysis is performed of the rotational bands which emerge when ¹⁶O in its triaxial 4p-4h configuration rotates around each of its three principal axes.     

An interpretation of backbending in terms of the crossing of the ground state band with an aligned two-quasiparticle band

The backbending in even-even rare earth nuclei is analysed in a systematic way by assuming a constant interaction between the ground state rotational band and the lowest excited even parity band, the so-called s-band.     

Synthesis and reactions of hydroxylated stilbenes and their possible occurrence as chromophore precursor structures in lignin

Chromophores which contribute to the color of kraft lignins and the generation of dihydroxystilbene structures as chromophore precursors are discussed briefly. The various o,p- and p,p-dihydroxystilbenes and 4,4-dihydroxy-3,3-dimethoxy-5-(4-hydroxy-3-methoxystyryl)stilbene, obtained viaWittig syntheses, are colorless substances which become more or less red colored when exposed to air. By reductive acetylation (zinc—acetic anhydride) stilbenoquinones, o- and p-quinonoid, diphenoquinoic, quinone methide, and stable oxygen radical structures are converted to colorless compounds, stabilized by simultaneous blocking of the formed phenolic hydroxyl groups. Application of that reaction to technical kraft lignin fractions let assume that a low number of chromophore structures (max. 5%) are responsible for the intensive color of the material.     

A randomly generated program for automatic identity checking

A method for making secret programs for automatic identity checking with very high demands for security, is described. The consistency of the sequence of digits, which identifies the person, is tested by a sequence of transformations, chosen by means of a stored secret random table. The method has been implemented for a system of unattended cash dispenser terminals, equipped with microprocessors.     

Laser-induced incandescence for soot particle size and volume fraction measurements using on-line extinction calibration

A novel technique for two-dimensional measurements of soot volume fraction and particle size has been developed. It is based on a combined measurement of extinction and laser-induced incandescence using Nd:YAG laser wavelengths of 532 nm and 1064 nm. A low-energy laser pulse at 532 nm was used for extinction measurements and was followed by a more intense pulse at 1064 nm, delayed by 15 ns, for LII measurements. The 532-nm beam was split into a signal beam passing the flame and a reference beam, both of which were directed to a dye cell. The resulting fluorescence signals, from which the extinction was deduced, together with the LII signal, were registered on a single CCD detector. Thus the two-dimensional LII image could be converted to a soot volume fraction map through a calibration procedure during the same laser shot. The soot particle sizes were evaluated from the ratio of the temporal LII signals at two gate time positions. The uncertainty in the particle sizing arose mainly from the low signal for small particles at long gate times and the uncertainty in the flame temperature. The technique was applied to a well-characterized premixed flat flame, the soot properties of which had been previously thoroughly investigated. Received: 21 June 2000 / Revised version: 11 September 2000 / Published online: 7 February 2001