排序方式： 共有16条查询结果，搜索用时 31 毫秒
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Olivier Witasse Lyle Huber Jean-Pierre Lebreton David Heather John Zarnecki Roland Trautner Piero Leon Stoppato Chuck See Cyril Pennanech Lisa McFarlane Bobby Kazeminejad Brijen Hathi John Haberman Francesca Ferri Lyn Doose Giacomo Colombatti Michael Bird Alessio Aboudan 《Planetary and Space Science》2008,56(5):770-777
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Stphane Coutu Steven W. Barwick James J. Beatty Amit Bhattacharyya Chuck R. Bower Christopher J. Chaput Georgia A. de Nolfo Michael A. DuVernois Allan Labrador Shawn P. McKee Dietrich Müller James A. Musser Scott L. Nutter Eric Schneider Simon P. Swordy Gregory Tarl Andrew D. Tomasch Eric Torbet 《Astroparticle Physics》1999,11(4):208-435
Galactic cosmic rays consist of primary and secondary particles. Primary cosmic rays are thought to be energized by first order Fermi acceleration processes at supernova shock fronts within our Galaxy. The cosmic rays that eventually reach the Earth from this source are mainly protons and atomic nuclei, but also include electrons. Secondary cosmic rays are created in collisions of primary particles with the diffuse interstellar gas. They are relatively rare but carry important information on the Galactic propagation of the primary particles. The secondary component includes a small fraction of antimatter particles, positrons and antiprotons. In addition, positrons and antiprotons may also come from unusual sources and possibly provide insight into new physics. For instance, the annihilation of heavy supersymmetric dark matter particles within the Galactic halo could lead to positrons or antiprotons with distinctive energy signatures. With the High-Energy Antimatter Telescope (HEAT) balloon-borne instrument, we have measured the abundances of positrons and electrons at energies between 1 and 50 GeV. The data suggest that indeed a small additional antimatter component may be present that cannot be explained by a purely secondary production mechanism. Here we describe the signature of the effect and discuss its possible origin. 相似文献
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Kasturi Devi Kanniah Jason Beringer Nigel J. Tapper Chuck N. Long 《Theoretical and Applied Climatology》2010,100(3-4):423-438
Aerosols have been shown to affect the quantity and quality of solar radiation on the Earth’s surface. Savanna regions are subject to frequent burning and release of aerosols that may impact on radiation components and possibly vegetation productivity in this region. Therefore, in this study, we have analyzed the optical properties of aerosols (aerosol optical depth (AOD) and Angstrom coefficient) from the Atmospheric Radiation Measurement site in Darwin for the periods from April 2002 to June 2005 as measured by a multifilter rotating shadowband radiometer. The influence of aerosols and their effect on surface shortwave incoming solar radiation and savanna productivity were examined for the dry season using sky radiation collection of radiometers and eddy covariance measurements from the Howard Springs flux site. Results indicated that aerosol concentrations in the region were relatively low compared to other savanna regions with the maximum monthly average AOD over the period being the greatest in October (0.29?±?0.003 standard error at 500 nm). The highest monthly average Angstrom exponent was also found in October (1.38?±?0.008). The relatively low aerosol concentration in this region can be attributed to the mixture of smoke aerosols with humidity haze and local circulations. Over a range of AODs from 0.1 to 0.4, we found a modest increase in the fraction of diffuse radiation to total radiation from 11% to 21%. This small increase in diffuse fraction did not affect the carbon flux significantly. However, because the current range of AOD in the region is relatively low, the region could be sensitive to increases in aerosols and diffuse fraction in the future. 相似文献
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Max Pettini Samantha A. Rix Chuck C. Steidel Matthew P. Hunt Alice E. Shapley Kurt L. Adelberger 《Astrophysics and Space Science》2002,281(1-2):461-466
Recent advances in instrumentation and observing techniques have made it possible to begin to study in detail the stellar
populations and the interstellar media of galaxies at redshift z = 3, when the universe was still in its ‘teen years’. I illustrate recent progress in this field with the latest observations
of the gravitationally lensed galaxy MS 1512- cB58.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
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Summary. The quality of marine magnetic anomaly sources is described with the power-density representation of a stochastic model of random temporal and spatial emplacement of the marine magnetic anomaly source in the oceanic crust. Typical values of sea-floor spreading and emplacement parameters define a high-fidelity process of recording and sea-surface detection of the palaeomagnetic field reversals for spreading rates over 20 mm yr-1 . An analogous stochastic model is developed for the formation of sea-floor topography by normal faulting. It is shown that the random process of normal faulting observed in the inner walls of the FAMOUS rift valley can account for the quality of the adjacent West Rift Mountains topography. 相似文献
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Abstract Oxygen is the most abundant element in the earth, and isotopic analysis of this element in island arc lavas potentially provides sensitive constraints on the proportion of oxygen recycled from subducted material, relative to that extracted from the mantle. Here we report on 225 new oxygen isotopic analyses of whole‐rock and glass samples, and clinopyroxene separates, from lavas collected from the southernmost 1500 km of the Izu–Bonin–Mariana (IBM) convergent margin. Whole‐rock samples clustered around a mean of 6.11 ± 0.47‰, whereas Mariana Trough glasses and mafic melts, calculated to be in equilibrium with mafic phenocrysts, clustered narrowly around a mean of 5.7‰. These data demonstrate that unequivocal identification of magmatic oxygen requires analysis of fresh glass or mafic minerals, and that the source of southern IBM Arc melts is entirely, or almost entirely, in equilibrium with normal mantle oxygen. If the elemental enrichments characteristic of the subduction component originate in subducted materials, these oxygen isotopic data are most consistent with the interaction of a small amount of sediment melt (<4%; mostly less than 1%) with mantle peridotite to yield the hybrid mantle that melts to form IBM Arc magmas. 相似文献
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