Cruise Summary Report RRS DISCOVERY D276

8 – 21 December 2003 Fortaleza / Brazil and Rio de Janeiro / Brazil The cruise was a German contribution to the CLIVAR programme. The intention was to build upon the data gathered during the World Ocean Circulation Experiment. The spreading of Antarctic Bottom Water in the South Atlantic is seen as an integral limb of the global thermohaline circulation. During the last 30 years, there has been a marked rise in bottom water temperature which is thought to be significantly relevant for climate change. It was the purpose of the cruise to deploy two subsurface moorings at the entrance of the Vema Channel. They are designed to monitor physical property fluctuations during the coming 16 months

Stereochemistry of C-methylation in the biosynthesis of rhododendrin in Alnus and Betula

Using differently labelled precursors, it was established that rhododendrin (3-(4-hydroxyphenyl)-1-methylpropyl-β- -glucopyranoside) is formed through the phenylpropane pathway via p-coumaryl alcohol, dihydro-p-coumaryl alcohol and C-methylation of the γ-C-atom of the C6---C3 unit with methionine supplying the methyl group. It was demonstrated that the pro-(S)-hydrogen atom of dihydro-p-coumaryl alcohol is replaced stereospecifically by the methyl group

Canadine synthase from Thalictrum tuberosum cell cultures catalyses the formation of the methylenedioxy bridge in berberine synthesis

An enzyme system catalysing the formation of the methylenedioxy bridge at ring A of (S)-canadine [ = (S)-tetrahydroberberine] from (S)-tetrahydrocolumbamine has been detected in microsomal preparations from different Ranunculaceae and Berberidaceae cell cultures. The cytochrome P-450 enzyme complex has been partly characterized from a protoberberine alkaloid producing Thalictrum tuberosum L. cell line. The enzyme complex consisting of a microsomal associated oxidase with a cytochrome P-450 reductase has a pH optimum at pH 8.5 and a temperature optimum of 40°. The apparent Km values are 33 μM for NADPH and 11.5 μM for tetrahydrocolumbamine

Columbamine, the central intermediate in the late stages of protoberberine biosynthesis

A specific methyltransferase which in the presence of S-adenosylmethionine [SAM] converts columbamine to palmatine has been demonstrated to occur in cell cultures. The enzyme acts only on the quaternary alkaloid as substrate, not on its tetrahydro derivative, which fact is in sharp contrast to previous claims

Mathematical analysis of the photoelectric effect

We study the photoelectric effect on the example of a simplified model of an atom with a single bound state, coupled to the quantized electromagnetic field. For this model, we show that Einstein's prediction for the photoelectric effect is qualitatively and quantitatively correct to leading order in the coupling parameter. More specifically, considering the ionization of the atom by an incident photon cloud consisting of $N$ photons, we prove that the total ionized charge is additive in the $N$ involved photons. Furthermore, if the photon cloud is approaching the atom from a large distance, the kinetic energy of the ejected electron is shown to be given by the difference of the photon energy of each single photon in the photon cloud and the ionization energy.Comment: See also http://www.intlpress.com/ATM

Intercomparing drifts from eddy-resolving and cycling floats in the deep western boundary current along the Mid-Atlanic Ridge

The Lagrangian nature of cycling floats is evaluated in the framework defined by the Deep Western Boundary Current of the Mid-Atlantic Ridge. In a statistical approach, speeds and drifts are estimated for an APEX cycling float and compared with the velocities inferred from a park ensemble of four eddy-resolving RAFOS floats. They were deployed at the same location and ballasted for drifting at the same mission depth. Displacement errors induced by geostrophic shear and wind forced currents are analyzed. We observe that the velocity estimated from the RAFOS floats is not statistically different from the velocity estimated from the APEX float. Likewise, the initial separation between the cycling float and a simultaneously deployed RAFOS float has been studied in terms of the turbulent diffusivity. Though the performance of this study in comparable cases without a mean current field may be limited, these oceanic observations support exploiting the Lagrangian nature of the cycling floats