CO(2) Diffusion in Polar Ice: Observations from Naturally Formed CO(2) Spikes in the Siple Dome (Antarctica) Ice Core

One common assumption in interpreting ice-core CO(2) records is that diffusion in the ice does not affect the concentration profile. However, this assumption remains untested because the extremely small CO(2) diffusion coefficient in ice has not been accurately determined in the laboratory. In this study we take advantage of high levels of CO(2) associated with refrozen layers in an ice core from Siple Dome, Antarctica, to study CO(2) diffusion rates. We use noble gases (Xe/Ar and Kr/Ar), electrical conductivity and Ca(2+) ion concentrations to show that substantial CO(2) diffusion may occur in ice on timescales of thousands of years. We estimate the permeation coefficient for CO(2) in ice is similar to 4 x 10(-21) mol m(-1) s(-1) Pa(-1) at -23 degrees C in the top 287 m (corresponding to 2.74 kyr). Smoothing of the CO(2) record by diffusion at this depth/age is one or two orders of magnitude smaller than the smoothing in the firn. However, simulations for depths of similar to 930-950m (similar to 60-70 kyr) indicate that smoothing of the CO(2) record by diffusion in deep ice is comparable to smoothing in the firn. Other types of diffusion (e.g. via liquid in ice grain boundaries or veins) may also be important but their influence has not been quantified

Neutron-proton interaction in rare-earth nuclei: Role of tensor force

We investigate the role of the tensor force in the description of doubly odd deformed nuclei within the framework of the particle-rotor model. We study the rare-earth nuclei 174Lu, 180Ta, 182Ta, and 188Re using a finite-range interaction, with and without tensor terms. Attention is focused on the lowest K=0 and K=1 bands, where the effects of the residual neutron-proton interaction are particularly evident. Comparison of the calculated results with experimental data evidences the importance of the tensor-force effects.Comment: 8 pages, 5 figures, to be published on Physical Review

Radar technology as a tool for the sprint coach

Le pistolet radar pourrait bien devenir un instrument de diagnostic essentiel de l'entraîneur dans le futur, permettant de détecter les défauts dans les gestes et le style des sprinters. Couplé à un ordinateur portable, le radar permet d'obtenir immédiatement des données graphiques et numériques sur la vitesse à la sortie des blocks, le ratio accélération / décélération au départ, la fréquences des appuis, la longueur des foulées, la durée et la distance à vitesse maximale, la présence d'une asymétrie droite - gauche et des détails sur la courbe de vitesse au moment du contact du pied au sol révélant des anomalies dans le style de course. Par ailleurs, la mesure de la vitesse à l'impulsion d'un perchiste peut être utilisée pour estimer son potentiel. Une méthode d'extraction de ces différentes informations à partir des données brutes est donnée

Foster and headley's education in the kindergarten

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Krypton and xenon in air trapped in polar ice cores : paleo-atmospheric measurements for estimating past mean ocean temperature and summer snowmelt frequency

Krypton and xenon are highly soluble noble gases. Because they are inert, they do not react biologically or chemically, and therefore can trace purely physical processes. By taking advantage of both the inert nature of these gases and their high solubilities, krypton and xenon can be used to reconstruct past ocean temperature variations and summer snow melt frequency. Ocean temperature is a fundamental parameter of the climate system. It plays a vital role in the transport and storage of heat, and may play a role in regulating atmospheric CO₂ , but its past variations are poorly constrained. This is due to the ambiguous nature of the benthic [delta]¹⁸O record in ocean sediments, which reflects both deep water temperature and the [delta]¹⁸O of the water itself (which depends on the extent of ice sheets on land). Recent studies have better constrained localized ocean temperature, but there is still need for global mean ocean temperature reconstructions. Krypton (Kr) and xenon (Xe) are highly soluble and more soluble in colder water. The total amount of Kr and Xe in the atmosphere and ocean together are essentially constant through time, so variations in mean ocean temperature would therefore modulate atmospheric Kr and Xe abundances. Kr and Xe, measured as ratios to nitrogen (N₂), are measured in air bubbles in ice cores to reconstruct atmospheric Kr/N₂ and Xe/N₂ histories, which can then be interpreted in terms of past mean ocean temperature. These Kr/N₂ and Xe/N₂ data and their derived mean ocean temperature (noble gas temperature index, NGTI) reconstructions are presented in Chapters 2 and 3. In Chapter 2, the initial Kr/N₂ data from the LGM indicate that mean ocean temperatures were 2̃.7°C colder at that time, which is consistent with other estimates of local deep ocean temperatures. In Chapter 3, [delta]Kr/N₂ and [delta]Xe/N₂ time series during the last glacial termination and inception are presented. The reconstructed mean ocean temperatures (NGTI's) are consistent with our earlier measurement and those of other studies. Additionally, these mean ocean temperature reconstructions appear to vary in step with atmospheric CO₂. Because Kr and Xe are highly soluble, they can also be used as an indicator of ice that has melted and refrozen. Visual identification of melt layers is been used as a proxy for exceptionally warm summers temperatures, but this type of melt layer identification becomes difficult as air bubbles form air clathrates at deeper depths. The use of Kr and Xe, measured as ratios to argon (Ar), is examined in Chapter 4. Seasononality may play a role in climate change, so a proxy of summer temperatures may prove to be a powerful constraint on climate change mechanisms that invoke seasonalit