Effects of Helium Phase Separation on the Evolution of Extrasolar Giant Planets

We build on recent new evolutionary models of Jupiter and Saturn and here extend our calculations to investigate the evolution of extrasolar giant planets of mass 0.15 to 3.0 M_J. Our inhomogeneous thermal history models show that the possible phase separation of helium from liquid metallic hydrogen in the deep interiors of these planets can lead to luminosities ~2 times greater than have been predicted by homogeneous models. For our chosen phase diagram this phase separation will begin to affect the planets' evolution at ~700 Myr for a 0.15 M_J object and ~10 Gyr for a 3.0 M_J object. We show how phase separation affects the luminosity, effective temperature, radii, and atmospheric helium mass fraction as a function of age for planets of various masses, with and without heavy element cores, and with and without the effect of modest stellar irradiation. This phase separation process will likely not affect giant planets within a few AU of their parent star, as these planets will cool to their equilibrium temperatures, determined by stellar heating, before the onset of phase separation. We discuss the detectability of these objects and the likelihood that the energy provided by helium phase separation can change the timescales for formation and settling of ammonia clouds by several Gyr. We discuss how correctly incorporating stellar irradiation into giant planet atmosphere and albedo modeling may lead to a consistent evolutionary history for Jupiter and Saturn.Comment: 22 pages, including 14 figures. Accepted to the Astrophysical Journa

Physical Basis for Spectrometer Calibration

Progress in quantitative surface analysis is hampered by the lack of experimental procedure including spectrometer calibration, sample preparation, and general experimental setting-up. Two methods for spectrometer alignment are compared: the linearization method and the elastic peak test. Experimental spectra are presented, which can be considered as stringent reference data to check the instrument response and the analyser transmission at low energies

Belgium : prehistoric and protohistoric archaeology in the intertidal and subtidal zones of the North Sea

The evidence for submerged prehistoric remains and landscapes in the Belgian sector of the North Sea is scarce. The majority of finds dredged and trawled from the seafloor consists of palaeontological material, notably mammalian bone remains, dating from the Early and Late Pleistocene, and possibly the Holocene. Scarce palaeontological and archaeological finds come from the intertidal zone. The available data are rather limited and strikingly sparse compared to neighbouring countries, yet it is steadily growing since the SeArch project. Recent investigations of an area with exceptionally high concentrations of Late Pleistocene and Palaeogene bone finds in the ‘Scheur’ illustrates this development and offers a promising avenue for future research. Growing awareness among a broader public is similarly resulting in an increase in reported chance finds, mainly from beaches. In due course, these growing numbers will hopefully allow quantitative support for certain hypotheses

MIPS: The Multiband Imaging Photometer for SIRTF

The Multiband Imaging Photometer for SIRTF (MIPS) is to be designed to reach as closely as possible the fundamental sensitivity and angular resolution limits for SIRTF over the 3 to 700μm spectral region. It will use high performance photoconductive detectors from 3 to 200μm with integrating JFET amplifiers. From 200 to 700μm, the MIPS will use a bolometer cooled by an adiabatic demagnetization refrigerator. Over much of its operating range, the MIPS will make possible observations at and beyond the conventional Rayleigh diffraction limit of angular resolution

Conditions de formation de composés organoiodés sapides lors de l'oxydation par le chlore d'eaux contenant des ions iodure

Le travail a consisté à préciser les conditions de formation d'une molécule iodée sapide, l'iodoforme, lors de l'oxydation d'une eau brute par le chlore et à proposer une voie réactionnelle possible.L'étude de la chloration d'une eau brute en présence d'azote ammoniacal et d'ions iodure conduit à la formation d'iodoforme uniquement pour des taux inférieurs au point de rupture. Les résultats montrent que l'oxydation de l'ion ammonium conduit à la formation de monochloramine dont le pouvoir oxydant totalement disponible pourrait être impliqué dans la formation de iodamines ou de chloroiodamines. Ces réactions sont plus favorables en présence d'iode qu'en présence d'ions iodure. Mais l'action de l'iode seul en présence d'ammoniaque et en absence de monochloramine ne permet pas d'expliquer la production des composés organoiodés observés. Ce sont les précurseurs intermédiaires formés à partir des chloramines qui, par action sur la matière organique naturelle, seraient responsables de la formation d'iodoforme. Dans une moindre mesure, certains composés azotés organiques tels les amines et les acides aminés pourraient prendre part à la production des composés organoiodés lors de la chloration.This work consisted of specifying the conditions of iodoform formation during chlorination of a raw water containing iodides. To reach this objective, there was need to spike the studied natural water with potassium iodide (200 µg.L-1) in order to increase the low natural iodide content. Free and combined chlorine, chlorinated and brominated trihalomethanes (THMs) and iodoform were analyzed.It was shown that :- iodoform is formed for chlorine doses prior to the breakpoint, in a region where the formation of the most classical chlorinated and brominated THMs is usually disfavored (Figures 1-4); - in the presence of chloramines the rate of production of iodoform increases with increasing I- or I2 (Figure 5); - the direct reaction of I2 with THM precursors to produce iodoform is slow and independent of the presence of ammonia (Table 1). - Nitrogenated compounds such as amines and amino acids would also take part in the production of organoiodinated compounds during chlorination (Figure 7). However, under water treatment conditions, taking into account the amine and amino acid content of natural waters, this class of compounds will only take a small part in the mechanism of iodoform formation. Among the possible routes that could account for the observations made in this research, the formation of iodamines or chloroiodamines as intermediates is suggested (Figure 8). From a practical point of view, the removal of ammonia from water by a biological process (nitrification step) would inhibit the iodoform formation potential and allow the application of the final chlorination step. Another alternative would involve replacing the chlorination step by oxidation with chlorine dioxide

Intensity of Valence Auger Transitions (L23VV) of Al and Si in Metal, Oxide and Nitride

L23VV Auger transition has been studied in Si, SiO2, Al, AlN, Al2O3 by electron spectroscopy excited either by electron beam or X Rays. A strong difference is observed in intensity between pure solid and oxide or nitride under electron bombardment. Auger intensity is very sensitive to changes in the backscattering coefficient or inelastic mean free path. However transient local trapping of electrons seems to be responsible for the large change observed