Cosmic Lithium-Beryllium-Boron Story

Light element nucleosynthesis is an important chapter of nuclear astrophysics. Specifically, the rare and fragile light nuclei Lithium, Beryllium and Boron (LiBeB) are not generated in the normal course of stellar nucleosynthesis (except ⁷Li) and are, in fact, destroyed in stellar interiors. This characteristic is reflected in the low abundance of these simple species. Up to recently, the most plausible interpretation was that Galactic Cosmic Rays (GCR) interact with interstellar CNO to form LiBeB. Other origins have been also identified: primordial and stellar (⁷Li) and supernova neutrino spallation (⁷Li and ¹¹B). In contrast, ⁹Be, ¹⁰B and ⁶Li are pure spallative products. This last isotope presents a special interest since the ⁶Li/⁷Li ratio has been measured recently in a few halo stars offering a new constraint on the early galactic evolution of light elements. Optical measurements of the beryllium and boron abundances in halo stars have been achieved by the 10 meter KECK telescope and the Hubble Space Telescope. These observations indicate a quasi linear correlation between Be and B vs Fe, at least at low metallicity, which, at first sight, is contradictory to a dominating GCR origin of the light elements which predicts a quadratic relationship. As a consequence, the theory of the origin and evolution of LiBeB nuclei has to be refined. Aside GCRs, which are accelerated in the general interstellar medium (ISM) and create LiBeB through the break up of CNO by fast protons and alphas, Wolf-Rayet stars (WR) and core collapse supernovae (SNII) grouped in superbubbles could produce copious amounts of light elements via the fragmentation in flight of rapid carbon and oxygen nuclei colliding with H and He in the ISM. In this case, LiBeB would be produced independently of the interstellar medium chemical composition and thus a primary origin is expected. These different processes are discussed in the framework of a galactic evolutionary model. More spectroscopic observations (specifically of O, Fe, Li, Be, B) in halo stars are required for a better understanding of the relative contribution of the various mechanisms. Future tests on the injection and acceleration of nuclei by supernovae and Wolf Rayet relying on gamma-ray line astronomy will be invoked in the perspective of the European INTEGRAL satellite. This revised version was published online in July 2006 with corrections to the Cover Date.     

The Visible Solar Spectral Irradiance from 350 to 850 nm As Measured by the SOLSPEC Spectrometer During the ATLAS I Mission

The SOLSPEC instrument has been built to carry out solar spectral irradiance measurements from 200 to 3000 nm. It consists of three spectrometers designed to measure the solar spectral irradiance in ultraviolet, visible, and infrared domains. It flew with the ATLAS I mission in March 1992. This paper is dedicated to the visible part of the solar spectrum. Comparisons with recent data are shown and differences below 450 nm are discussed.     

Biokinetics of Radiocobalt in the Asteroid Asterias rubens (Echinodermata): Sea Water and Food Exposures

Uptake and loss of cobalt-57 were investigated in the starfish Asterias rubens, in order to assess its value as a sentinel organism for nearshore radionuclide contamination. Whole-body uptake from sea water was linear over a 32-day exposure period and reached wet weight concentration factor (CF) of 23 ± 5. Bioaccumulation of ⁵⁷Co was dependent upon body compartment, the aboral part of the body wall concentrating cobalt to the greatest degree (wet weight CF: 77 ± 16). After restoration of uncontaminated conditions, radiocobalt was released following an exponential loss kinetics characterized by a biological half-life (T_b1/2) of 27 ± 6 day. Dietary radiocobalt (taken up during a short-term feeding for 24 h on radiolabelled mussels) showed a much more rapid turnover time (T_b1/2: 14 ± 4 d), suggesting that A. rubens accumulates this radionuclide predominantly from sea water. A. rubens, and more particularly the aboral part of its body wall, would readily reveal the presence of an environmental contamination by radiocobalt and could preserve this information over a period of few months.     

Calculated mineral equilibria in the greenschist-blueschist-eclogite facies in Na2O−FeO−MgO−Al2O3−SiO2−H2O

The new, greatly expanded internally-consistent dataset of Holland and Powell includes thermodynamic data for a wide range of mineral end-members in common rock-forming minerals, in particular, including FeMg_-1 substitutions in glaucophane, garnet, chloritoid and carpholite, and FeMg_-1 and MgSiAl_-1Al_-1 substitutions in talc and chlorite. Moreover, we have the uncertainties and correlations for these data. With the data, we have calculated the full pressure-temperature phase diagram for the system Na₂O–FeO–MgO–Al₂O₃–SiO₂–H₂O (NFMASH) for quartz (or coesite) and H₂O in excess, in the range 300°–800°C and 5–50 kbars. By solving the set of non-linear equations formed by the equilibrium relationships for an independent set of equations between the end-members in an assemblage in NFMASH, the compositions of the minerals (and PT) can be calculated. Thus the changes in MgSiAl_-1Al_-1 along NMASH reactions, and FeSiAl_-1Al_-1 along NFASH reactions, are calculated, and the changes in FeMg_-1 and MgSiAl_-1Al_-1 along NFMASH reactions are calculated. From this information it is straightforward to generate PT diagrams for specific rock compositions. Mineral assemblages and mineral compositional changes in the phase diagram are discussed in relation to greenschist, blueschist and eclogite facies assemblages in metapelitic rocks. It is found that the correspondence between the predictions of the phase diagrams and the observations on rocks is remarkably good. When semiquantitative extensions of the phase diagram to include Ca(MgFe)_-1, NaSiCa_-1Al_-1, Fe³⁺Al_-1 and KNa_-1 substitutions are taken into account the agreement is essentially complete.     

Sediment infiltration traps: their use to monitor salmonid spawning habitat in headwater tributaries of the Cascapédia River,Québec

Sediment infiltration can clog salmon nests and reduce egg survival. As a countermeasure, environmental managers often deploy infiltration traps to monitor sediment infiltration. Traps provide a repeatable means of measuring infiltration and enable comparisons to be made between sites. Results from infiltration rates measured with traps have also been used to estimate infilling rates into salmon nests. Application of these data is questionable, as the composition of the bed and the amount of fine sediment within the bed is known to affect infiltration rates. Thus, infiltration rates measured with infiltration traps may differ from the infiltration rates occurring in redd and riffle gravels. To examine how relationships between sediment infiltration rates varied between four watersheds, we continuously monitored suspended sediment transport, shear stress and infiltration rates at four sites over 5 months. We also compared infiltration rates measured with infiltration traps with changes in the hydraulic conductivity and subsurface grain size distribution of adjacent artificially constructed salmon nests and natural riffle gravels. Among the four watersheds, clear differences in sediment infiltration rates were observed. The differences correlated with the subsurface silt content but no strong relationship existed between land‐use or basin physiography/geology. Despite observing an average of 30 kg m⁻² of sediment finer than 2 mm being deposited in the infiltration traps during the study, no change in redd or riffle substrate was observed. If the deposition rates measured with the traps reflect the processes in redds, enough sediment would have been deposited to inhibit egg emergence. However, no reduction in egg survival to the eyed stage was observed. In summary, our results show that infiltration traps with clean gravels can be used to detect intersite differences in sediment transport regimes. Extrapolations of sediment infiltration rates measured with such collectors to estimate infiltration rates in redds or riffles is, however, flawed. Copyright © 2005 John Wiley & Sons, Ltd.     

TEM observations of several spinel-garnet assemblies: toward the rheology of the transition zone

In order to better identify the mineral phase which controls the rheology of the transition zone (between 410 and 660 km depth) transmission electron microscopy observations were made on several coexisting spinel-garnet assemblies: alkremite xenolith; pyrope-rich – MgO:1.1Al₂O₃ spinel assembly deformed at 1173K, 800 MPa in a Griggs apparatus; (Mg,Fe)₃(Al,Mg,Si)₂Si₃O₁₂ majorite – (Mg,Fe)₂SiO₄ spinel assembly synthesized in a laser heated diamond anvil cell. It was found that garnet crystals systematically remain undeformed while spinel crystals are plastically deformed. These results are in accord with the assumption that the rheology of majorite is stronger than the rheology of spinel, in the conditions of the transition zone.     

An algorithm for finding the position of a point relative to a fixed polygonal boundary

This article describes a method that determines the position of a point relative to a fixed boundary. Its advantage over the other existing algorithms described below is that in most cases it is necessary that only part of the algorithm be executed to determine the position of the point. A possible inconvenience of using this algorithm is that the contour boundary has to be entered as data. For problems where the boundary often changes the algorithm is not suitable in its present form. The applications envisaged here are to cases where the position of a very large number of points have to be determined relative to one fixed polygonal boundary whose shape is known in advance, for example, blanking out of contours in automatic contouring, or selecting drill holes which lie in the particular part of a mineral deposit.