Iterative Design of Experiments by Non-Linear PLS Models. A Case Study: The Reservoir Simulator Data to Forecast Oil Production

In this paper we present a way of conducting design of experiments by Multivariate Additive Partial Least-Squares Splines models, in short MAPLSS. In the framework of optimal experimental design based on small samples, in order to select the most informative MAPLSS model, we process an adaptive incremental selection of observations by a particular bootstrap procedure. Why MAPLSS models? Because they inherit the advantages of the PLS regression that permits to capture additively non-linear main effects and relevant interactions in the difficult framework of small samples. The effectiveness of this approach is illustrated on the reservoir simulator data used to forecast oil production.     

No enhancement of fusion probability by the neutron halo of 6He

Quantum tunnelling through a potential barrier (such as occurs in nuclear fusion) is very sensitive to the detailed structure of the system and its intrinsic degrees of freedom. A strong increase of the fusion probability has been observed for heavy deformed nuclei. In light exotic nuclei such as 6He, 11Li and 11Be (termed 'halo' nuclei), the neutron matter extends much further than the usual nuclear interaction scale. However, understanding the effect of the neutron halo on fusion has been controversial--it could induce a large enhancement of fusion, but alternatively the weak binding energy of the nuclei could inhibit the process. Other reaction channels known as direct processes (usually negligible for ordinary nuclei) are also important: for example, a fragment of the halo nucleus could transfer to the target nucleus through a diminished potential barrier. Here we study the reactions of the halo nucleus 6He with a 238U target, at energies near the fusion barrier. Most of these reactions lead to fission of the system, which we use as an experimental signature to identify the contribution of the fusion and transfer channels to the total cross-section. At energies below the fusion barrier, we find no evidence for a substantial enhancement of fusion. Rather, the (large) fission yield is due to a two-neutron transfer reaction, with other direct processes possibly also involved.     

Effect of natural iron fertilization on carbon sequestration in the Southern Ocean

The availability of iron limits primary productivity and the associated uptake of carbon over large areas of the ocean. Iron thus plays an important role in the carbon cycle, and changes in its supply to the surface ocean may have had a significant effect on atmospheric carbon dioxide concentrations over glacial-interglacial cycles. To date, the role of iron in carbon cycling has largely been assessed using short-term iron-addition experiments. It is difficult, however, to reliably assess the magnitude of carbon export to the ocean interior using such methods, and the short observational periods preclude extrapolation of the results to longer timescales. Here we report observations of a phytoplankton bloom induced by natural iron fertilization--an approach that offers the opportunity to overcome some of the limitations of short-term experiments. We found that a large phytoplankton bloom over the Kerguelen plateau in the Southern Ocean was sustained by the supply of iron and major nutrients to surface waters from iron-rich deep water below. The efficiency of fertilization, defined as the ratio of the carbon export to the amount of iron supplied, was at least ten times higher than previous estimates from short-term blooms induced by iron-addition experiments. This result sheds new light on the effect of long-term fertilization by iron and macronutrients on carbon sequestration, suggesting that changes in iron supply from below--as invoked in some palaeoclimatic and future climate change scenarios--may have a more significant effect on atmospheric carbon dioxide concentrations than previously thought.     

Isolated rat hepatocytes. Simultaneous study of variations in sialic acid content of glycoconjugated membranes and asialotransferrin uptake]

Hepatocytes isolated from streptozotocin treated Rats bind less asialotransferrin than hepatocytes isolated from normal rats. This decrease is parallel with a decrease in the sialic acid content. Insulin therapy restored simultaneously membrane sialic acid content and asialotransferrin binding capacity.     

Dictyostelium discoideum cells shed vesicles with associated DNA and vital stain Hoechst 33342

Dictyostelium discoideum cells are highly resis tant to xenobiotics. We previously observed that these primitive eukaryotic cells contain a 170-kDa P-glycoprotein, mediating multidrug resistance in mammalian cells, but nonfunctional in Dictyostelium cells. We show here that D. discoideum cells vitally stained with the DNA-specific dye, Hoechst 33342, release fluorescent material in their culture medium. Electron microscopy and lipid analysis demonstrate the vesicular nature of this material. Moreover, nucleic acids associate with these extracellular vesicles independently of Hoechst vital staining. The main vesicular DNA component exhibits a size >21 kb. Shedding of microvesicles during cell growth is not concomitant with programmed cell death. We propose that these extracellular vesicles are involved in a new cellular resistance mechanism against xenobiotics. Furthermore, since the association of DNA with vesicles occurs in physiological growth conditions and independently of vital staining, the new shedding process might be involved in a more general intercellular mechanism. Received 14 November 1997; received after revision 16 March 1998; accepted 16 March 1998