Colorimetry of sulphur anions

Summary The colorimetric method of Sörbo for the determination of thiosulphate has been improved in such a way that polythionates do not interfere; it has also been modified for use with larger volumes of solution. The procedure depends on the production of thiocyanate equivalent to the thiosulphate, and determination of the thiocyanate with an excess of ferric iron. By careful control of the p_H using an acetate buffer, the cyanolysis of polythionates and hence their interference is avoided.     

CO-laser side-band spectrometer: Sub-Doppler heterodyne frequency measurements around 5 µm

We report the realization of a tunable sub-Doppler heterodyne spectrometer with high absolute accuracy, employing side-band generation with a CO laser. The fixed-frequency CO-gas laser, working from 4.7 to 8.4µm, is made partially tunable by the use of microwave side-band generation in a CdTe Electro-Optical Modulator (EOM). This leads to tunable radiation of high spectral purity. We describe the design of the microwave EOM, adapted to the CO laser, its performance and its first application to highly accurate frequency measurements. The side-band radiation is used for sub-Doppler stabilization of the CO laser, while the carrier frequency is mixed with the frequencies of two CO₂ reference lasers. As a first result, we present measurements of OCS transitions in the 4.9µm (61 THz) region, reaching an absolute accuracy of 30 kHz (/ = 5×1O^–10). Further application of our spectrometer to calibration gases will establish a variety of InfraRed (IR) calibration standards with a new quality of accuracy. On visit from: Fachbereich Physik, Humboldt-Universität zu Berlin     

EPC synthesis of (+)-heptelidic acid

Summary An EPC (enantiomerically pure compound) synthesis of the antibiotic natural product (+)-heptelidic acid (1) is presented. Key step of the synthesis is a conjugate addition of the acetal protected vinyl cuprate4 to the auxiliary shielded enoate5n which gives the adduct7n as a single diastereomer. After cleavage of the acetal protecting group and of the chiral auxiliary the enantiomerically pure -ketoester12 has been obtained which has been transformed to the title compound1 (11 steps starting from5n, 10.6% overall yield).

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EPC-Synthese von (+)-heptelidsäure

Zusammenfassung Eine EPC-Synthese (EPC = enantiomerically pure compound) des antibiotischen Naturstoffes (+)-Heptelidsäure (1) wird präsentiert. Schlüsselschritt der Synthese ist dieMichael-Addition des acetal-geschützten Vinylcuprates4 an das auxiliargeschützte Enoat5n, wobei das Addukt7n in diastereomerenreiner Form erhalten wird. Nach der Abspaltung der Acetalschutzgruppe und des chiralen Auxiliars läßt sich der enantiomerenreine -Ketoester12 herstellen, der in die Titelverbindung1 umgewandelt werden kann (11 Stufen ausgehend von5n, 10.6% Gesamtausbeute).

     

z-pinch with non zero helicity

Thez-pinch equilibrium with non zero azimuthal current was calculated for power dependences in this paper. The pressure equilibrium curves have no maximum in thez-pinch centre and look more like a gass-puff pressure curves. The total current density is formed by gradB drift current density, curvature drift current density and magnetization current density in this case.This research has been conducted as part of the research project Magnetic Pinches Stable Structure Study and have been supported by GACR grant No. 202-95-0178.     

On Fictitious Domain Formulations for Maxwell''s Equations

We consider fictitious domain-Lagrange multiplier formulations for variational problems in the space H(curl: Ω{\bf)} derived from Maxwell's equations. Boundary conditions and the divergence constraint are imposed weakly by using Lagrange multipliers. Both the time dependent and time harmonic formulations of the Maxwell's equations are considered, and we derive well-posed formulations for both cases. The variational problem that arises can be discretized by functions that do not satisfy an a-priori divergence constraint.