Sulfide determination in hydrothermal seawater samples using a vibrating gold micro-wire electrode in conjunction with stripping chronopotentiometry

A rapid electrochemical stripping chronopotentiometric procedure to determined sulfide in unaltered hydrothermal seawater samples is presented. Sulfide is deposited at −0.25 V (vs Ag/AgCl, KCl 3 M) at a vibrating gold microwire and then stripped through the application of a reductive constant current (typically −2 μA). The hydrodynamic conditions are modulated by vibration allowing a short deposition step, which is shown here to be necessary to minimize H₂S volatilization. The limit of detection (LOD) is 30 nM after a deposition step of 7 s. This LOD is in the same range as the most sensitive cathodic voltammetric technique using a mercury drop electrode and is well below those reported previously for other electrodes capable of being implemented in situ.     

Trigocherrin A, the first natural chlorinated daphnane diterpene orthoester from Trigonostemon cherrieri

Trigocherrin A, a chlorinated and highly oxygenated daphnane diterpenoid orthoester (DDO), was isolated from the bark of Trigonostemon cherrieri. Trigocherrin A is the first example of a naturally occurring halogenated DDO. Its structure was elucidated by comprehensive analysis of NMR spectroscopic data, and its absolute configuration was determined by comparison of experimental and theoretically calculated ECD spectra. Trigocherrin A exhibited a potent and selective effect against Chikungunya virus in Vero cells.     

Copper diffusion in TaN-based thin layers

The diffusion of Cu through TaN-based thin layers into a Si substrate has been studied. The barrier efficiency of TaN/Ta/TaN multilayers of 150 nm in thickness has been investigated and is compared with that of TaN single layers. Thermal stabilities of these TaN-based thin layers against Cu diffusion were determined from in situ X-ray diffraction experiments, conducted in the temperature range of 773-973 K. The TaN/Ta/TaN barrier appeared to be more efficient in preventing Cu diffusion than the TaN single layer.     

Lower bounds¶for the relative Lusternik–Schnirelmann category

We give estimates of numerical homotopy invariants of the pair (X,X×S ^p ) in terms of homotopy invariants of X. More precisely, we prove that σ ^{p +1} cat(X) + 1 ≤ cat(X,X×S ^p }), that and that e(X,X×S< ^p )=e(X)+1, where σ ^{p +1} cat is the (relative) σ category of Vandembroucq and e is the (relative) Toomer invariant. The proof is based on an extension of Milnor's construction of the classifying space of a topological group to a relative setting (due to Dold and Lashof). Received: 14 October 1998 / Revised version: 5 November 1999     

Respiratory adaptations to the deep-sea hydrothermal vent environment: the case of Segonzacia mesatlantica, a crab from the Mid-Atlantic Ridge

Segonzacia mesatlantica (Crustacea; Decapoda; Brachyura) is the only endemic crab species known from the Mid-Atlantic Ridge (MAR) hydrothermal vents. Known from all explored sites in the Atlantic, its wide distribution makes this species a model to study physiological adaptation, and specifically respiratory strategies. Native haemocyanin (Hc) comprises four non-covalent associations in equilibrium formed by monomers, hexamers, dodecamers and octadecamers made up of approximately 75 kDa polypeptide chains. Four different amino acid chains are observed with a molecular mass ranging from 75,234 to 75,972 Da. Experiments carried-out under pressure suggested that the percentage of monomer increased in the haemolymph under hypoxic condition. We have also observed a shift of the proportion of the two dodecamer series, suggesting a rapid modification of the Hc phenotype between hypoxic and hyperoxic conditions. Native Hc possesses a high oxygen affinity ( P50 = 2.2 Torr at 15 degrees C and pH 7.5), a large Bohr effect (Deltalog P50 / DeltapH approximately -2.7) and a slightly reverse temperature effect (DeltaH = +17.19 kJ mol(-1). The composition of Segonzacia haemolymph is similar to that of other littoral species except for the large enrichment in free copper and zinc. As for other species from hydrothermal vent sites, Segonzacia haemolymph possesses a higher buffer capacity than littoral species. Moreover, species from the hydrothermal vent decapods from Pacific hydrothermal vent that encounter higher CO2 content in their environment have a higher buffer capacity than Atlantic vent species. The results presented are discussed in relation with the physico-chemical characteristics of the hydrothermal vent environment.     

Fe analysis by the ferrozine method: Adaptation to FIA towards in situ analysis in hydrothermal environment

The target of this study is the adaptation of the ferrozine method to flow injection analysis (FIA) to perform iron analysis in situ using an in situ chemical analyser in hydrothermal environments. The adaptation of the method to FIA was followed by its optimisation using an experimental design screening method. The goals of the optimisation steps were to decrease the detection limit and to increase the measuring range to cope with the constraints of in situ analysis. The method allows the determination of iron in the mixing zone of hydrothermal fluid, enriched in iron, and seawater. A single manifold gives the possibility to analyse either Fe(II) or ΣFe [Fe(II) + Fe(III)] in situ, or ΣFe in the lab on hydrothermal seawater samples. The measuring range of the method was increased to up to 2000 μM, which is coherent with the study of the chemical environment of communities associated with deep-sea hydrothermal activity. Finally, the method was applied in situ using the chemical analyser Alchimist during the ATOS cruise on hydrothermal vent fields on the Mid Atlantic Ridge.     

Effect of RF coil excitation on field inhomogeneity at ultra high fields: a field optimized TEM resonator

In this work, computational methods were utilized to optimize the field produced by the transverse electromagnetic (TEM) resonator in the presence of the human head at 8 Tesla. Optimization was achieved through the use of the classical finite difference time domain (FDTD) method and a TEM resonator loaded with an anatomically detailed human head model with a resolution of 2 mm × 2 mm × 2 mm. The head model was developed from 3D MR images. To account for the electromagnetic interactions between the coil and the tissue, the coil and the head were treated as a single system at all the steps of the model including, numerical tuning and excitation. In addition to 2, 3, 4, 6, and 10-port excitations, an antenna array concept was utilized by driving all the possible ports (24) of a 24-strut TEM resonator. The results show that significant improvement in the circularly polarized component of the transverse magnetic field could be obtained when using multiple ports and variable phase and fixed magnitude, or variable phase and variable magnitude excitations.