Characterization of novel adsorbents for radiostrontium reduction in foods

Distribution coefficients, pH dependence, isotherms, kinetics and breakthrough curves of Sr binding have been measured on several types of adsorbents (carbons modified with titanium silicate, crystalline titanium silicate, mixed titanium-manganese oxide, and synthetic zeolites A4 and P) from different water solutions. It is concluded that acid-base properties of the adsorbent is very important for Sr binding. Titanium silicate based adsorbents had reduced chemical stability in an artificial food fluid below pH 2, the mixed titanium manganese oxide below pH 6, zeolite A4 below pH 5 and zeolite P below pH 7. Consideration is given to the feasibility of the adsorbents for food decontamination.     

On the dependence of the laser-induced incandescence (LII) signal on soot volume fraction for variations in particle size

“The laser-induced incandescence (LII) signal is proportional to soot volume fraction” is an often used statement in scientific papers, and it has – within experimental uncertainties – been validated in comparisons with other diagnostic techniques in several investigations. In 1984 it was shown theoretically in a paper by Melton that there is a deviation from this statement in that the presence of larger particles leads to some overestimation of soot volume fractions. In the present paper we present a detailed theoretical investigation of how the soot particle size influences the relationship between LII signal and soot volume fraction for different experimental conditions. Several parameters have been varied; detection wavelength, time and delay of detection gate, ambient gas temperature and pressure, laser fluence, level of aggregation and spatial profile. Based on these results we are able, firstly, to understand how experimental conditions should be chosen in order to minimize the errors introduced when assuming a linear dependence between the signal and volume fraction and secondly, to obtain knowledge on how to use this information to obtain more accurate soot volume fraction data if the particle size is known. PACS 42.62.-b; 44.40.+a; 61.46.Df; 78.70.-g; 65.80.+n     

Anti-de Sitter quotients,bubbles of nothing,and black holes

In 3+1 dimensions there are anti-de Sitter quotients which are black holes with toroidal event horizons. By analytic continuation of the Schwarzschild-anti-de Sitter solution (and appropriate identifications) one finds two one parameter families of spacetimes that contain these quotient black holes. One of these families consists of B-metrics (“bubbles of nothing”), the other of black hole spacetimes. All of them have vanishing conserved charges. I. Bengtsson was supported by VR.     

An evaluation of precision and systematic errors in vibrational CARS thermometry

The extraction of temperatures from experimental CARS spectra is discussed and demonstrated in an electrically heated over and a low-pressure flame. The present work is focused, in particular, on how the precision of CARS thermometry is limited by the accuracy with which the experimental parameters are known, on characteristics of the diode-array detector, on saturation effects due to stimulated Raman scattering and on the influence of spectral resolution on precision and accuracy.     

Oxygen concentration and temperature measurements in N2–O2 mixtures using rotational coherent anti-Stokes Raman spectroscopy

The accuracy and precision of oxygen concentration and temperature measured by dual-broadband rotational Coherent Anti-Stokes Raman Spectroscopy (CARS) were investigated in nitrogen-oxygen mixtures at atmospheric pressure and temperatures between 290 and 1410 K. The relative standard deviation of temperatures evaluated from pure oxygen rotational CARS spectra was found to be around 5%, and the mean temperature was the same as for nitrogen CARS spectra, except for temperatures above 1000 K, where the temperature was 120 K below the correct value. The in situ calibrated oxygen concentrations were within 10% of the correct value, with a standard deviation of around 1.2% for the mixtures of 12 and 20% oxygen in nitrogen. For the lowest oxygen concentrations considered in this study (2 and 4%), the systematic errors in the evaluated concentrations were very large, and the standard deviation of repeated single-shot measurements was above 2%. However, employing weighting in the spectral fitting routine reduced the errors in the concentration and the single-shot standard deviation was lowered to 0.5%. Finally, it was shown that spectral interference (from oxygen) in a rotational CARS spectrum of nitrogen generally had little impact on the temperature evaluated from fitting the spectra to theoretical nitrogen spectra.     

Semiclassical calculations of collision line broadening in Raman spectra of N2 and CO mixtures

We present a detailed theoretical study of pressure-broadened Raman line shapes in binary mixtures of nitrogen and carbon monoxide. The semiclassical Robert-Bonamy theory was used to calculate self-broadened Q-branch linewidths of N(2) and CO, and Lennard-Jones (LJ) potential energy surface parameters were fixed by comparing our results with extensive experimental linewidth data. For the case of N(2), the ab initio PES8 potential energy surface was investigated, however, the anisotropic repulsive part had to be reduced to ensure a good agreement with experimental linewidths. The agreement between calculations and experiments was remarkably good, both for self-broadened N(2) and CO Q-branch linewidths. Yet, our calculations were not able to predict the experimentally observed difference between Q- and S-branch linewidths of self-broadened N(2). The central results of this work are the Q-branch linewidths of N(2)-CO and CO-N(2), which have been calculated through an extrapolation of the parameters of the potential energy surfaces used for self-broadened linewidths by common combination rules.     

Two-dimensional imaging of glyoxal (C2H2O2) in acetylene flames using laser-induced fluorescence

2 H₂O₂). Laser-induced fluorescence spectra from glyoxal vapor using the same excitation wavelength of 428 nm showed the same strongest lines as the signal from the flame. Glyoxal was visualized in two different modes; two-dimensional imaging and a spatial-spectral mode where spectra were obtained at different spatial positions in the flame simultaneously. For the premixed laminar rich flame it is shown that glyoxal is produced early in the flame, before the signals for C₂ and CH appear. For the turbulent non-premixed flames it is shown that glyoxal is produced in a layer on the fuel rich side of the flames. Here the fuel is premixed with ambient air. This layer is thin and has a high spatial resolution. The general trend was that the glyoxal signal appeared in regions with a lower temperature compared with the emission from C₂ and CH. The imaging of glyoxal in turbulent acetylene flames is a promising tool for achieving new insight into flame phenomena, as it gives very good structural information on the flame front. Tests so far do not indicate that the detected glyoxal is a result of photo-production. To our knowledge, this is the first detection of glyoxal in flames using laser-induced fluorescence. Received: 19 December 1996/Revised version: 26 May 1997     

Hamiltonian treatment of self-dual antisymmetric tensors

Self-dual antisymmetric tensors occur in certain (4n + 2)-dimensional supergravity models, in particular the one connected to type IIB superstrings. So far they have been quantized only using light front methods. Here we show that the existing covariant action for such fields leads to a consistent hamiltonian system also for ordinary “timelike” dynamics, although rather complicated second class constraints are present.