Accurate calibration of TXRF using microdroplet samples

TXRF has been applied in combination with VPD to the analysis of trace impurities in the native oxide layer of Si wafer surfaces down to the range of 10(8) atoms. cm(-2). Proper quantification of VPD/TXRF data requires calibration with microdroplet standard reference wafers. The precision of calibration function has been evaluated and found to allow quantification at a high level of 3 sigma confidence with microdroplet standard reference.     

Serendipitous synthesis of a ditwistane: a one-step access!

4-tert-Butyl-2-cyclohexen-1-one dimerizes in THF solution via its kinetic enolate, leading to di-tert-butylditwistane 8 in up to 36% yield (−78 °C → room temp., protonolysis, flash chromatography). X-ray crystallography shows that 8 incorporates one R and one S enantiomer of the starting ketone; none of the diastereomeric ditwistanes epi-8, epi’-8 or iso-8 was isolated. This means that the formation of 8 proceeds with mutual kinetic resolution and 100% induced diastereoselectivity.     

Advanced kinetic tools for the evaluation of decomposition reactions

Summary An advanced kinetic study on the thermal behaviour of pyrotechnic ignition mixtures has been carried out by differential scanning calorimetry using different B/KNO3 mixtures (50:50, 30:70, 20:80) as a model reaction. The experimental conditions applied (isochoric conditions/closed crucibles and isobaric conditions/open crucibles) as well as the composition of the mixtures noticeably influences the relative thermal stabilities of the energetic materials. The kinetic study focused on the prediction of the thermal stability of the different mixtures both in extended temperature ranges and under temperature conditions at which ordinary investigation would be very difficult. Using advanced numerical tools [1], thermal ageing and influence of the complex thermal environment on the heat accumulation conditions were computed. This can be done for any surrounding temperature profile such as isothermal, non-isothermal, stepwise, modulated, shock, adiabatic conditions and additionally for temperature profiles reflecting real atmospheric temperature changes (yearly temperature profiles of different climates with daily minimal and maximal fluctuations). Applications of accurate decomposition kinetics enabled the determination of the time to maximum rate under adiabatic conditions (TMR_ad) with a precision given by the confidence interval of the predictions. This analysis can then be applied for the examination of the effects of the surrounding temperature for safe storage or transportation conditions (e.g. determination of the safe transport or storage temperatures).     

Benzoxazolinones. II. Synthesis of 3-vinylbenzoxazolinones and 3-vinylbenzoxazolinethione

A method has been developed for obtaining 3-vinylbenzoxazolinones and 3-vinylbenzoxazolinethione. It has been shown that it is also possible to obtain 3-methylbenzoxazolinethione by this method in good yield (76%).     

Application of neural network calibrations to an halide ISE array

The Neural Network (NN) technique was applied to the calibration of an ion selective electrode (ISE) array comprising a bromide selective electrode, two chloride ISEs and one thiocyanate ISE. The measured samples were synthetic mixture solutions of chlorides and bromides in concentration ranges such that interference occurs. The NN method allowed to perform the calibration without estimating the coefficients of the Nikolskii-Eisenman theoretical relation. Only the determination of bromide was detailed. The results obtained using this method were better than those obtained using linear multivariate calibration methods.     

Three-component coupling of alkynes, Baylis-Hillman adducts and sodium azide: a new synthesis of substituted triazoles

A three-component coupling was used to prepare a series of 1,4-disubstituted-1,2,3-triazoles from the corresponding acetylated Baylis-Hillman adducts, sodium azide and terminal alkynes. This one-pot reaction further increases the efficacy of ‘Click’ synthesis and diversifies the preparation of multi-functional 1,4-disubstituted-1,2,3-triazoles.     

Effect of a magnetic flux line on the quantum beats in the Henon-Heiles level density

The quantum density of states of the Henon-Heiles potential displays a pronounced beating pattern. This has been explained by the interference of three isolated classical periodic orbits with nearby actions and periods. A singular magnetic flux line, passing through the origin, drastically alters the beats even though the classical Lagrangian equations of motion remain unchanged. Some of the changes can be easily understood in terms of the Aharonov-Bohm effect. However, we find that the standard periodic orbit theory does not reproduce the diffraction-like quantum effects on those classical orbits which intersect the singular flux line, and argue that corrections of relative order variant Planck's over 2pi are necessary to describe these effects. We also discuss the changes in the distribution of nearest-neighbor spacings in the eigenvalue spectrum, brought about by the flux line. (c) 1995 American Institute of Physics.     

Metal island coated polymer sensor for direct determination of the volume effect of chaotropic agents

A new optical sensor is presented, based on the analyte reaction resulting in swelling and shrinking of a thin polymer layer. Changing the concentration of ions in a new bisazide photo-cross-linked poly(vinylpyrrolidone) polymer results in a concentration-dependent volume change of the hydrated gel. The volume response of the sensor induced by different ions is fully reversible over more than 250 cycles. The response of the device depends on the type, the charge and the concentration of the ions. The sensor material is part of an optical thin film system which transforms the variations in volume of the polymer into spectral information. The steady state of the sensor response is obtained within 60 s. The response time is mainly limited by the pump rate, the back pressure and the total volume of the system but not by the swelling of the sensor polymer. A comparative study of ion effects has demonstrated a fundamental correlation of the polymer swelling properties with the Hofmeister series of chaotropic agents. Thus it is concluded that the photopolymer, which is solubilized in aqueous solutions by the interaction of its amide structure with the solvent, behaves like the backbone amide structure of proteins.     

Recent results from the TCV tokamak

During the first two years of operation, the TCV tokamak has produced a large variety of plasma shapes and magnetic configurations, with 1.0B _tor1.46T,I _p800kA,k2.05, –0.71. A new shape control algorithm, based on a finite element reconstruction of the plasma current in real time, has been implemented. Vertical growth rates up to 1000s^–1 have been stabilized using the external coil system. Ohmic H-modes with Troyon factors ( _tor aB/I _p) up to two and densities up to 2.25×10²⁰m^–3, corresponding to the Greenwald limit, have been obtained in diverted discharges. Limiter H-modes with line averaged electron densities up to 1.7×10²⁰m^–3 have been obtained in elongated D-shaped plasmas with 360 kAI _P600 kA.Presented at 17^th Symposium Plasma Physics and Technology, Prague, June 13–16, 1995.This work was partly supported by the Fonds National Suisse de la Recherche Scientifique.     

Magnetism in hydrogenated YBa2Cu3O7 a comparison of μSR and NMR results

Hydrogenated YBa₂Cu₃O₇ with [H]/cell=2.0 was studied by X-ray diffraction, SR and¹H-NMR. For the first time, the hydride phase (16% larger c-axis) known from thin film experiments was seen in a bulk sample. A comparison of the SR and NMR results shows that the 15 mT site (2 MHz in SR) is the stable position for the proton and muon. The three other muon sites (4 MHz line and two exponentially decaying components) are metastable.