The Sun Asphericities: Astrophysical Relevance

Of all the fundamental parameters of the Sun (diameter, mass, temperature...), the gravitational multipole moments (of degree l and order m) that determine the solar moments of inertia, are still poorly known. However, at the first order (l=2), the quadrupole moment is relevant to many astrophysical applications. It indeed contributes to the relativistic perihelion advance of planets, together with the post-Newtonian (PN) parameters; or to the precession of the orbital plane about the Sun polar axis, the latter being unaffected by the purely relativistic PN contribution. Hence, a precise knowledge of the quadrupole moment is necessary for accurate orbit determination, and alternatively, to obtain constraints on the PN parameters. Moreover, the successive gravitational multipole moments have a physical meaning: they describe deviations from a purely spherical mass distribution. Thus, their precise determination gives indications on the solar internal structure. Here, we explain why it is difficult to compute these parameters, how to derive the best values, and how they will be determined in a near future by means of space experiments.Comment: 14 pages, 9 figures (see published version for a better resolution), submited to Proceedings of the Royal Society: Mathematical, Physical and Engineering Science

Solar gravitational energy and luminosity variations

Due to non-homogeneous mass distribution and non-uniform velocity rate inside the Sun, the solar outer shape is distorted in latitude. In this paper, we analyze the consequences of a temporal change in this figure on the luminosity. To do so, we use the Total Solar Irradiance (TSI) as an indicator of luminosity. Considering that most of the authors have explained the largest part of the TSI modulation with magnetic network (spots and faculae) but not the whole, we could set constraints on radius and effective temperature variations (dR, dT). However computations show that the amplitude of solar irradiance modulation is very sensitive to photospheric temperature variations. In order to understand discrepancies between our best fit and recent observations of Livingston et al. (2005), showing no effective surface temperature variation during the solar cycle, we investigated small effective temperature variation in irradiance modeling. We emphasized a phase-shift (correlated or anticorrelated radius and irradiance variations) in the (dR, dT)-parameter plane. We further obtained an upper limit on the amplitude of cyclic solar radius variations, deduced from the gravitational energy variations. Our estimate is consistent with both observations of the helioseismic radius through the analysis of f-mode frequencies and observations of the basal photospheric temperature at Kitt Peak. Finally, we suggest a mechanism to explain faint changes in the solar shape due to variation of magnetic pressure which modifies the granules size. This mechanism is supported by our estimate of the asphericity-luminosity parameter, which implies an effectiveness of convective heat transfer only in very outer layers of the Sun.Comment: 17 pages, 2 figure, 1 table, published in New Astronom

Superconductivity and short range order in metallic glasses Fex_{x}Ni1−x_{1-x}Zr2_{2}

In amorphous superconductors, superconducting and vortex pinning properties are strongly linked to the absence of long range order. Consequently, superconductivity and vortex phases can be studied to probe the underlying microstructure and order of the material. This is done here from resistance and local magnetization measurements in the superconducting state of Fe$_{x}$Ni$_{1-x}$Zr$_{2}$ metallic glasses with $0\leq x \leq 0.6$. Firstly, we present typical superconducting properties such as the critical temperature and fields and their dependence on Fe content in these alloys. Then, the observations of peculiar clockwise hysteresis loops, wide double-step transitions and large magnetization fluctuations in glasses containing a large amount of Fe are analyzed to reveal a change in short range order with Fe content.Comment: 8 pages, 7 figure

Solar latitudinal distortions : from observations to theory

Astronomy and Astrophysics, v. 419, p. 1133-1140, 2004. http://dx.doi.org/10.1051/0004-6361:20041093International audienceSolar diameters have been measured from different ground-based instruments on different sites all around the world. There are values dating back to three centuries ago, but the revival of interest began in the 1970s when it was claimed that a temporal periodic modulation had been found. The interest of such measurements, pinpointed from only two decades, may not lie in these temporal variations, but in the fact that a latitudinal heliographic dependence may exist. Such a solar shape distortion has been deduced from the analysis of solar astrolabe data sorted by heliographic latitudes, but observational evidence has also been obtained by means of a scanning heliometer (Pic du Midi Observatory). Latitudinal dependence implies sub-surfacic physical mechanisms and can be explained theoretically. Thus, in spite of the fact that ground-based observations are altered by seeing effects that may amplify or superimpose noise, it can be advanced that the solar shape is not a pure spheroid. We present here a new theory based upon the thermal-wind equation, which explains the observed distorted solar shape. Using the W parameter (called here asphericity-luminosity parameter), we show that large negative values (W ranging from around −0.075 up to −0.6) leading to a prolate Sun, are unlikely. The best range of W lies between around −0.075 and +0.6. Concerning observations, only space missions (or balloon flights) will be able to reach a clear conclusion. A space mission called PICARD is scheduled to be launched by 2008: one of its major aims is to measure these asphericities with astrometric precision

Modification de la matière organique lors des traitements conventionnels de potabilisation

La filtration successive des eaux, préalablement filtrées sur membrane de porosité 0,45 µm puis acidifiées à pH 2, sur deux colonnes de résines XAD8 et XAD4 placées en série, caractérise la matière organique en trois grandes classes : les substances hydrophobes, les acides hydrophiles et les hydrophiles non retenus. Cette étude s'est intéressée à déterminer et à analyser l'impact sur la distribution hydrophobe/hydrophile des traitements conventionnels utilisés dans les usines de production d'eau potable.En ce qui concerne l'effet de la clarification, la distribution hydrophobe/hydrophile du COD a été inchangée dans le cas de sept prélèvements sur dix, indiquant une isoélimination de chaque fraction. Dans le cas des eaux R1.2, R4 et R6.1, une diminution de la fraction hydrophobe est obtenue entre l'eau brute et son eau clarifiée. L'étude de différents coagulants indique que la distribution de la matière organique des eaux clarifiées dépend de sa composition initiale mais aussi de la nature du coagulant mis en oeuvre. Le chlorure ferrique permet une meilleure élimination de chaque fraction comparativement à un sel d'aluminium.Un traitement d'oxydation à un taux de 1,5 mg Oxydant/mg COD et quel que soit l'oxydant mis en oeuvre (O3, Cl2, ClO2) diminue significativement les substances hydrophobes et augmente les substances hydrophiles. Ces résultats sont logiques si nous nous référons au mode d'action de ces trois oxydants. L'ozonation d'eaux brute et clarifiée s'accompagne aussi d'une augmentation du CODB, soulignant que les substances hydrophiles générées par l'étape d'ozonation seraient biodégradables.Des campagnes de prélèvements ont indiqué que les traitements de finition (ozonation, filtration sur CAG) en configuration industrielle ont une légère influence sur la distribution interne de la matière organique. Les résultats, du fait de taux de traitement plus faibles, sont moins nets que ceux obtenus en laboratoire. Une filtration sur CAG, précédée d'une étape d'ozonation, conduit à une augmentation de la fraction hydrophobe et à une diminution du CODB.Dissolved organic matter (DOM) in natural waters is a mixture of compounds. Some authors have fractionated this organic matter into large classes (humic substances, hydrophilic acids . . .). Humic substances have been defined as the fraction of organic matter retained on XAD8 resin at acidic pH (THURMAN and MALCOLM 1981); this isolation procedure is recommended by the International Humic Substances Society. Only a few investigators have dealt specifically with hydrophilic substances which are not adsorbed on XAD8 resin at acidic pH. The "hydrophobic/hydrophilic" distribution can be determined by a simple method of organic matter fractionation, using two superimposed XAD8 and XAD4 resin columns (CROUE et al. 1993). This procedures, carried out at pH 2, consists of first isolating hydrophobic substances (essentially humic acids) on an XAD8 resin and then isolating the hydrophilic acids from the XAD8 effluent on an XAD4 resin.The aim of this work was to study the evolution of the hydrophobic/hydrophilic distribution during water treatment steps as applied in waterworks. The analytical procedure was first applied to determine the change in the DOM distribution of ten surface waters after clarification. The results obtained after clarification were completed by the study of the effect of the coagulant nature (ferric chloride, aluminium sulphate, prehydrolyzed salt (WAC)). In the second phase, oxidation experiments using ozone, chlorine and chlorine dioxide were conducted on raw and clarified waters to determine their effect on the DOM distribution. Finally the fractionation procedures were carried out on two water treatment plants to compare our laboratory data with results obtained in a working plant and to observe the change in DOM distribution during granular activated carbon (GAC) filtration.Dissolved organic carbon (DOC) concentrations were analysed using a Dohrman DC 80 apparatus. UV absorbance was measured with a one or five centimeter cell using an Uvikon spectrophotometer. Oxidation experiments were carried out in a batch procedure. The study of different coagulants was made in the laboratory with a Jar Test procedure described elsewhere (LEFEBVRE 1990). Biodegradable dissolved organic carbon (BDOC) was analyzed according to the suspended bacteria method (SERVAIS et al. 1987, 1989).The hydrophobic/hydrophilic distributions of raw and clarified waters were found to be unchanged by the clarification step in seven of ten test waters. These results indicate that for a studied water, the relative reduction in DOC of one fraction was of the same order of magnitude as the other fraction. The distributions of R1.2, R4 and R6.1 were significantly modified by the clarification treatment. In these three cases, the hydrophobic substances showed the greater DOC reduction. The "non-retained" hydrophilic substances became predominant in the R6.1 clarified water, whereas in the cases of R4 and R1.2 the total hydrophilic fraction and the hydrophilic acids increased, respectively.The results obtained in the laboratory on three different raw waters, clarified by different coagulants (ferric chloride or aluminium salts), showed that the nature of the coagulant (iron or alum) can influence the hydrophobic/hydrophilic distribution. A marked influence was found in the case of R6 and less significant results were obtained for R1.2. Powdered activated carbon had no real effect on the DOC distribution, under our experimental conditions (applied dosage 25 mg/L). If the removal of each fraction is considered, and if it is assumed that each removal is independent from the others, ferric chloride appears to be the best coagulant. It removes humic substances efficiently as well as hydrophilic acids (> 72%), but is less efficient for the "non-retained" hydrophilic fraction. The DOC distribution of a clarified water depends on the distribution in the original raw water and the nature of the coagulant.Under our experimental conditions (applied dosage: 1.5 mg oxidant / mg DOC), ozone, chlorine and chlorine dioxide significantly affected the DOM distribution of the R1.2 water. The hydrophobic substances showed the higher relative DOC reduction, which can be correlated with an increase in the hydrophilic fraction. The greatest change was obtained for treatment with ozone. In the case of chlorine and chlorine dioxide, an increase of the "non-retained" hydrophilic fraction was observed whereas for ozone the two hydrophilic fractions increased. These results are in agreement with current knowledge about the action of ozone, chlorine and chlorine dioxide.An increase in the BDOC fraction was observed with the applied ozone dosage. In the case of R1, ozonation of raw and clarified waters appeared to shift the dissolved organic carbon distribution towards the "non-retained" hydrophilics. A good correlation exists between the BDOC increase (BDOC/BDOCo) and the decrease of hydrophobic acids or the increase of "non-retained" hydrophilics (slopes are respectively 12.3 ; - 16.5 and 15.5). In the case of another sample of R1.2, the comparison of BDOC in the XAD4 effluents of raw and ozonated waters indicated that at least 62% of BDOC produced by ozonation was in this fraction. This result indicates that the "non-retained" hydrophilics of this raw water are not biodegradable compared with those induced by ozonation.Results obtained on samples taken on two water treatment plants indicate that ozonation and GAC filtration have a small effect on the hydrophobic/hydrophilic DOM distribution. Intermediate ozonation at the industrially applied dose slightly modifies the distribution; a slight decrease of hydrophobic substances is observed. GAC filtration induces an increase of the hydrophobic fraction. The water treatment process includes clarification (EFS), inter-ozonation (EFSO3), and GAC filtration (EFCAG). GAC filters A and B had been respectively running for one and three years; filter C has been regenerated one month before. Good organic matter removal is obtained during clarification (removal of DOC and UV-absorbance: 75% and 88%). This treatment step changes the DOM distribution: increase of the hydrophobic fraction and decrease of the hydrophilic fraction. BDOC was completely removed. Intermediate ozonation (0.7 mg O3/mg DOC) modifies the DOC distribution and creates BDOC. This BDOC, in absolute value (0.36 mg/l), is equal to the increase of hydrophilic fraction. On the oldest filters (A and B) BDOC was completely removed, but this was not the case for filter C, probably because the bacterial biomass was insufficient. On GAC filters hydrophilic substances were found to be better removed than humic substances. The age of the GAC bed seems to have an effect on DOC distribution: the effluent from the oldest GAC filter contained less of the hydrophobic fraction than did the effluent from the youngest filter

The Collaborative Development of New CFD Methods Adapted for Tilt Rotor Aircraft in the HiPerTilt Project

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