Magnetic Energy and Helicity Fluxes at the Photospheric Level

The source of coronal magnetic energy and helicity lies below the surface of the Sun, probably in the convective zone dynamo. Measurements of magnetic and velocity fields can capture the fluxes of both magnetic energy and helicity crossing the photosphere. We point out the ambiguities which can occur when observations are used to compute these fluxes. In particular, we show that these fluxes should be computed only from the horizontal motions deduced by tracking the photospheric cut of magnetic flux tubes. These horizontal motions include the effect of both the emergence and the shearing motions whatever the magnetic configuration complexity is. We finally analyze the observational difficulties involved in deriving such fluxes, in particular the limitations of the correlation tracking methods.     

Europium retention onto clay minerals from 25 to 150 °C: Experimental measurements, spectroscopic features and sorption modelling

The sorption of Eu(III) onto kaolinite and montmorillonite was investigated up to 150 °C. The clays were purified samples, saturated with Na in the case of montmorillonite. Batch experiments were conducted at 25, 40, 80 and 150 °C in 0.5 M NaClO₄ solutions to measure the distribution coefficients (Kd) of Eu as a trace element (<10⁻⁶ mol/L) between the solution and kaolinite. For the Na-montmorillonite, we used Kd results from a previous study [Tertre, E., Berger, G., Castet, S., Loubet, M., Giffaut, E., 2005. Experimental study of adsorption of Ni²⁺, Cs⁺ and Ln³⁺ onto Na-montmorillonite up to 150 °C. Geochim. Cosmochim. Acta69, 4937-4948] obtained under exactly the same conditions. The number and nature of the Eu species sorbed onto both clay minerals were investigated by time resolved laser fluorescence spectroscopy (TRLFS) in specific experiments in the same temperature range. We identified a unique inner-sphere complex linked to the aluminol sites in both clays, assumed to be AlOEu²⁺ at the edge of the particles, and a second exchangeable outer-sphere complex for montmorillonite, probably in an interlayer position. The Kd values were used to adjust the parameters of a surface complexation model (DLM: diffuse layer model) from 25 to 150 °C. The number of Eu complexes and the stoichiometry of reactions were constrained by TRLFS. The acidity constants of the amphoteric aluminol sites were taken from another study [Tertre, E., Castet, S., Berger, G., Loubet, M., Giffaut, E. Acid/base surface chemistry of kaolinite and Na-montmorillonite at 25 and 60 °C: experimental study and modelling. Geochim. Cosmochim. Acta, in press], which integrates the influence of the negative structural charge of clays on the acid/base properties of edge sites as a function of temperature and ionic strength. The results of the modelling show that the observed shift of the sorption edge towards low pH with increasing temperature results solely from the contribution of the AlOEu²⁺ edge complexes. Finally, we successfully tested the performance of our model by confronting the predictions with experimental Kd data. We used our own data obtained at lower ionic strength (previous study) or higher suspension density and higher starting concentration (TRLFS runs, this study), as well as published data from other experimental studies [Bradbury, M.H., Baeyens, B., 2002. Sorption of Eu on Na and Ca-montmorillonite: experimental investigations and modeling with cation exchange and surface complexation. Geochim. Cosmochim. Acta66, 2325-2334; Kowal-Fouchard, A., 2002. Etude des mécanismes de rétention des ions U(IV) et Eu(III) sur les argiles: influence des silicates. Ph.D. Thesis, Université Paris Sud, France, 330p].     

Readout Techniques for Drift and Low Frequency Noise Rejection in Infrared Arrays

Three different methods are presented to subtract thermal drifts and low-frequency noise from the signal of infrared array. The first is dead pixels with open Indium bumps, the second is reference output as implemented on the Hawaii2 multiplexer, and the third is dark pixels to emulate reference cells having a capacity connected to the gate of the unit cell field-effect transistor (FET). The third method is the most effective and yields a reduction in readout noise from15.4–9.4 erms. A novel method will be described to extend this readout technique to the Aladdin 1 K × 1 K InSb array. This revised version was published online in July 2006 with corrections to the Cover Date.     

A new method for the generation of second-order random waves

In order to prevent the generation of spurious free sub- and superharmonics of random waves in a laboratory channel, the control signal for the wave board has to be derived according to a higher-order wave theory. An expression for this control signal has been derived with the perturbation method of multiple scales. It is much less complex and requires less computation time than the expressions obtained from the full second-order theory. The new method for second-order subharmonics was verified experimentally for waves with bichromatic and continuous first-order spectra. The data were analysed with the complex-harmonic principal-component analysis to reduce the influence of noise.     

Leachable particulate iron in the Columbia River,estuary, and near-field plume

This study examines the distribution of leachable particulate iron (Fe) in the Columbia River, estuary, and near-field plume. Surface samples were collected during late spring and summer of 2004–2006 as part of four River Influence on Shelf Ecosystems (RISE) cruises. Tidal amplitude and river flow are the primary factors influencing the estuary leachable particulate Fe concentrations, with greater values during high flow and/or spring tides. Near the mouth of the estuary, leachable particulate Fe [defined as the particulate Fe solubilized with a 25% acetic acid (pH 2) leach containing a weak reducing agent to reduce Fe oxyhydroxides and a short heating step to access intracellular Fe] averaged 770 nM during either spring tide or high flow, compared to 320 nM during neap tide, low flow conditions. In the near-field Columbia River plume, elevated leachable particulate Fe concentrations occur during spring tides and/or higher river flow, with resuspended shelf sediment as an additional source to the plume during periods of coastal upwelling and spring tides. Near-field plume concentrations of leachable particulate Fe (at a salinity of 20) averaged 660 nM during either spring tide or high flow, compared to 300 nM during neap tide, low flow conditions. Regardless of tidal amplitude and river flow, leachable particulate Fe concentrations in both the river/estuary and near-field plume are consistently one to two orders of magnitude greater than dissolved Fe concentrations. The Columbia River is an important source of reactive Fe to the productive coastal waters off Oregon and Washington, and leachable particulate Fe is available for solubilization following biological drawdown of the dissolved phase. Elevated leachable Fe concentrations allow coastal waters influenced by the Columbia River plume to remain Fe-replete and support phytoplankton production during the spring and summer seasons.     

底部边界层颗粒态物质迁移特征的放射性核素分析方法

利用颗粒态放射性核素携带的颗粒物历经过程信息,我们提出用泥沙扩散方程和颗粒态放射性核素扩散方程联解底部边界层颗粒态物质迁移参数的方法。分析实例的样品取自荷兰Waden Sea南部Balgzand潮滩(砂坪)和Mok湾潮滩(泥坪)的两个站位(BG1和Mok2)。示踪核素为~(234)Th,~(210)Pb和~(137)Cs,其放射性比度由r能谱测出。     

Mountain Protection Forests against Natural Hazards and Risks: New French Developments by Integrating Forests in Risk Zoning

Forests can play a very significant role in protection against natural hazards and risks in mountain lands, especially against erosion and rockfalls. This paper first assesses knowledge concerning the capacity of forests to control natural hazards, with emphasis placed on forest location in catchments or slopes. Zoning aspects are then presented; based on the use of GIS, they allow determining priorities for forestry operations (cuts and biological engineering), in view to setting up an 'optimal management' of mountain forest ecosystems. Finally, an explanation is given of how the results of research are used for the management and planning of mountain ecosystems, illustrated by an example of researcher-practitioner transfer in France. Zoning, prevention, display and regular aspects are developed. On the basis of the experience and knowledge presented here, recommendations are proposed to better take into account the role of mountain forests in the control of natural hazards and risks. It is necessary to have an adapted legislative and economic framework, define priority forest intervention zones and determine an adapted sylviculture.     

Two-step deglaciation: 14C-Dated high-resolution δ18O records from the tropical Atlantic Ocean

Eight box cores from the tropical Atlantic were studied in detail with regard to foraminiferal oxygen isotopes, radiocarbon, and Globorotalia menardii abundance. A standard Atlantic oxygen-isotope signal was reconstructed for the last 20,000 yr. It is quite similar to the west-equatorial Pacific signal published previously. Deglaciation is seen to occur in two steps which are separated by a pause. Onset of deglaciation is after 15,000 yr B.P. The pause is centered between 11,000 and 12,000 yr B.P., but may be correlative with the Younger Dryas (10,500 yr B.P.) if allowance is made for a scale shift due to mixing processes on the sea floor. Step 2 is centered near 10,000 yr B.P. and is followed by a brief excursion toward light oxygen values. This excursion (the M event) may correlate with the Gulf of Mexico meltwater spike.