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51.
M. Koenig T. Vinci A. Benuzzi-Mounaix S. Lepape N. Ozaki S. Bouquet L. Boireau S. Leygnac C. Michaut C. Stehle J. -P. Chièze D. Batani T. Hall K. Tanaka M. Yoshida 《Astrophysics and Space Science》2005,298(1-2):69-74
We present the set-up and the results of a supercritical radiative shock experiment performed with the LULI nanosecond laser
facility. Using specific designed targets filled with xenon gaz at low pressure, the propagation of a strong shock with a
radiative precursor is evidenced. The main measured quantities related to the shock (electronic density, propagation velocities,
temperature, radial dimension) are presented and compared with various numerical simulations. 相似文献
52.
This article reports on reusable mobile digital learning resources designed to assist human geography undergraduate students in exploring the geographies of life in Dublin. Developing active learning that goes beyond data collection to encourage observation and thinking in the field is important. Achieving this in the context of large class sizes presents several challenges. Combining in situ learning with spatially accurate historical and contemporary multimedia, a set of location-aware digital mobile tools, or mediascapes, was developed. How scaffolding can be achieved in such a context, focusing on the development of students’ observational, enquiry, and thinking skills in the field was explored. 相似文献
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Stephanodiscus niagarae populations in a core from Lake Ontario show systematic variation in radial puncta number and mean valve diameter. Puncta number is stable in specimens from samples deposited between 1720 and 1844. Puncta number gradually increases in samples deposited between 1860 and 1947, then increases rapidly to high numbers in samples deposited after 1964. Mean valve diameter is relatively high in specimens from samples deposited between 1720 and 1959. Diameter of specimens deposited during this period fluctuates around a mean of 63.2 m. Mean diameter of specimens deposited from 1959 to 1980 is only 42.5 m. We conclude that the trend in puncta number reflects the time course of eutrophication in Lake Ontario. We interpret the precipitous decline in mean diameter as an indication that conditions in the lake after the late 1950's did not permit sexual reproduction in this species. 相似文献
56.
C. Michaut T. Vinci L. Boireau M. Koenig S. Bouquet A. Benuzzi-Mounaix N. Osaki G. Herpe E. Falize B. Loupias S. Atzeni 《Astrophysics and Space Science》2007,307(1-3):159-164
This paper deals with the radiative shock from both theoretical and numerical points of view. It is based on the whole experimental
results obtained at Laboratoire d'Utilisation des Lasers Intenses (LULI, école Polytechnique). Radiative shocks are high-Mach
number shocks with a strong coupling between radiation and hydrodynamics which leads to a structure governed by a radiative
precursor. These shocks are involved in various astrophysical systems: stellar accretion shocks, pulsating stars, interaction
between supernovae and the interstellar medium. In laboratory, these radiative shocks are generated using high power lasers.
New diagnostics have been implemented to study the geometrical shape of the shock and the front shock density. Data were obtained
varying initial conditions for different laser intensities and temperature. The modeling of these phenomena is mainly performed
through numerical simulations (1D and 2D) and analytical studies. We exhibit results obtained from several radiative hydrodynamics
codes. As a result, it is possible to discuss about the influence of the geometry and physical parameters introduced in the
1D and 2D models. 相似文献
57.
T. Vinci M. Kœnig A. Benuzzi-Mounaix L. Boireau S. Bouquet S. Leygnac C. Michaut C. Stehlé O. Peyrusse D. Batani 《Astrophysics and Space Science》2005,298(1-2):333-336
This paper presents some recent measurements on radiative shocks generated in a xenon gas cell using high power laser. We
show new results on temperature and electronic density, and on radial expansion of the shock at various initial conditions
(laser energy and gas pressure). The data obtained are compared with one-dimensional and two-dimensional hydro simulations. 相似文献
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E. Falize C. Michaut C. Cavet S. Bouquet M. Koenig B. Loupias A. Ravasio C. G. Gregory 《Astrophysics and Space Science》2009,322(1-4):71-75
In this paper we study specific classes of radiating shocks which are widely spread in astrophysical environments. We present new analytical solutions available for any exponents of typical power-law cooling function which generalize the five special cases (corresponding to specific values of these exponents) of radiating shocks structure and proceed to the analytical determination of physical quantities. Then an application of the results for the accretion shock in polar is realized. A discussion of the reproducibility of cooling layer in laboratory is proposed using scaling laws. 相似文献
60.
Claire Rollion-Bard Dominique Blamart Yannicke Dauphin 《Geochimica et cosmochimica acta》2010,74(4):1338-173
We present ion microprobe measurements of oxygen isotopic compositions in the deep-sea coral Lophelia pertusa. Compared to bulk skeletal aragonite fibres, the EMZ (early mineralization zone), near the inside of the calyx, was systematically depleted in 18O. Rayleigh fractionation from a semi-closed fluid reservoir does not explain this and other geochemical differences. Furthermore, pH values estimated from skeletal δ11B data are inconsistent with the idea that EMZ (or centres of calcification) 18O depletion reflects a more alkaline calcification environment. Our data, combined with microstructural and geochemical observations, indicate that the aragonitic fibres and EMZ are formed by a compartmentalized mineralization calicoblastic ectoderm, which exerts strong biological control on the composition of the skeleton. Hence, we propose a new model whereby amorphous calcium carbonates (ACC) are precursors to the EMZ, whereas the fibre precipitation is probably governed by kinetic processes. 相似文献