How to visualize quartz OSL signal components

The optically stimulated luminescence (OSL) signal of natural quartz measured under constant stimulation power (CW-OSL) is a featureless decay curve where underlying components cannot be identified easily. Visual interpretation of quartz OSL signals is easier if signals are shown in spectrum-like form. This can be achieved either through ramped stimulation, or by transforming a measured CW-OSL curve into a pseudo OSL curve. We show that both give similar results, but that transformation should be preferred as CW-OSL provides best signal-to-noise ratios. We present different transformation methods to obtain pseudo OSL curves and discuss the advantages and disadvantages of each method. In addition, we show that different pseudo OSL transformations can be used to emphasize specific aspects of the OSL signal. We conclude that transformation of CW-OSL to pseudo hyperbolically modulated OSL provides the most useful visualization of the quartz fast OSL component. Pseudo parabolic modulated OSL is the transformation of choice for showing the slow component(s). The pseudo OSL curves can be used for rapid visual inspection of the relative contribution of the OSL components prior to further analysis.     

Temperature and wavelength dependent trap filling in M2Si5N8:Eu (M=Ca,Sr, Ba) persistent phosphors

The evaluation of persistent phosphors is often focused on the processes right after the excitation, namely on the shape of the afterglow decay curve and the duration of the afterglow, in combination with thermoluminescence glow curve analysis. In this paper we study in detail the trap filling process in europium-doped alkaline earth silicon nitrides (Ca₂Si₅N₈:Eu, Sr₂Si₅N₈:Eu and Ba₂Si₅N₈:Eu), i.e., how the persistent luminescence can be induced. Both the temperature at which the phosphors are excited and the spectral distribution of the excitation light on the ability to store energy in the phosphors' lattices are investigated. We show that for these phosphors this storage process is thermally activated upon excitation in the lower 5d excited states of Eu²⁺, with the lowest thermal barrier for europium doped Ca₂Si₅N₈. Also, the influence of co-doping with thulium on the trap filling and afterglow behavior is studied. Finally there exists a clear relation between the luminescence quenching temperature and the trap filling efficiency. The latter relation can be utilized to select new efficient 5d–4f based afterglow phosphors.     

Facile separation of chiral 1,3-dihydrobenzo[c]furan derivatives using a -xylose moiety as a protecting group

1,2-O-Isopropylidene-α- -xylofuranose has been used to protect one aldehyde group of o-phthalaldehyde. This chiral protecting group acts as a resolving agent and this leads to separable diastereoisomers when a new stereogenic centre is created by the conversion of the second aldehyde group to a benzyloxyhydroxyethyl chain. These separated diastereoisomers were cyclised to 1,3-dihydrobenzo[c]furans with retention of chiral integrity at the C3 site thus allowing further elaboration to enantiomerically pure nucleoside analogues.     

Numerical simulation of non-viscous liquid pinch off using a coupled level set boundary integral method

The pinch off of an inviscid fluid column is described using a potential flow model with capillary forces. The interface velocity is obtained via a Galerkin boundary integral method for the 3D axisymmetric Laplace equation, whereas the interface location and the velocity potential on the free boundary are both approximated using level set techniques on a fixed domain. The algorithm is validated computing the Raleigh-Taylor instability for liquid columns which provides an analytical solution for short times. The simulations show the time evolution of the fluid tube and the algorithm is capable of handling pinch-off and after pinch-off events. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Resolution Effects and Enslaved Finite-Difference Schemes for a Double Gyre, Shallow-Water Model

We study numerical solutions of the reduced-gravity shallow-water equation on a beta plane, subjected to a sinusoidally varying wind forcing leading to the formation of a double gyre circulation. As expected the dynamics of the numerical solutions are highly dependent on the grid resolution and the given numerical algorithm. In particular, the statistics of the solutions are critically dependent on the scheme's ability to resolve the Rossby deformation radius. We present a method, applicable to any finite-difference scheme, which effectively increases the spatial resolution of the given algorithm without changing its temporal stability or memory requirements. This enslaving method makes use of properties of the governing equations in the absence of time derivatives to reduce the overall truncation error. By examining statistical measures of stochastic solutions at resolutions near the Rossby radius, we show that the enslaved schemes are capable of reproducing statistics of standard schemes computed at twice the resolution. Received 29 August 1996 and accepted 6 March 1997     

Precision measurement of the wavelengths and natural line widths of 3d-2p pionic X-ray transitions in low-Z atoms

The wavelengths and the natural line widths of the 3d-2p transitions in the pionic atoms of ¹²C, ¹⁶O, ¹⁸O, ²⁴Mg, ²⁶Mg, ²⁸Si and ³⁰Si have been measured at SIN with a bent-crystal spectrometer. The precision reached in the transition wavelengths ranges from 4 to 18 ppm, and in the widths from 2 to 14%.     

Electron density of states and electrical conductivity of ordered alloys: Extension beyond the single-band approximation, taking into account scattering by clusters

A method is developed for going beyond the single-band approximation and taking into account scattering by clusters. The method is based on a cluster expansion of the averaged Green’s function of the alloy. It is shown that the contributions of scattering processes diminish with respect to a certain small parameter as the number of particles in the cluster increases. The prominent characteristics of the electronic structure and electrical conductivity of ordered alloys are analyzed numerically in the diagonal disorder approximation in the multiband s-d model. Fiz. Tverd. Tela (St. Petersburg) 39, 401–411 (March 1997)     

The application of the Wilhelmy balance to the measurement of electrocapillary effects in molten carbonate

In this work, the Wilhelmy method is shown to be very suitable for studying electrocapillary effects in molten salts. Unlike the optical methods usually used this method, can easily be used in automated set-ups. High accuracies of 0.3° in the contact angle were easily obtained. First experiments are reported on the electrocapillary effect on gold in molten carbonate under air. Small changes of 4° to 8° in the contact angle were found for potential excursions of –300 mV. At 650 °C a value of 65 ± 1° was obtained at Open Cell Voltage (OCV) which is in good accordance with the values found by Mugikura et al. and Matsumura et al. The wetting of gold by carbonate decreased at higher temperatures. In the literature, both positive and negative temperature effects have been reported, obtained in different gas atmospheres. Possibly the sign depends on the gas atmosphere used. However, this discrepancy can also be caused by differences in the characteristics of the gold surface used in the different studies. Received: 23 October 1997 / Accepted: 4 December 1997