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91.
We have measured the vertical shear of the zonal winds in the cloud-haze upper layer of Saturn using Cassini ISS images obtained in the filters MT2 (753 nm methane absorption band, sensitive to the upper haze) and CB2 (adjacent continuum, sensitive to the lower cloud). Our radiative transfer models indicate that at the eastward jet peaks these filters are sensing clouds at the respective ∼100 mbar and ∼350 mbar levels. We have found a systematic velocity difference between those filters of 15 to 20 m s−1 only in the eastward jets peaks (27° S, 42° S, 55° S and 70° S) which implies a vertical shear of ∼10-20 m s−1 H−1. Our overall results agree with those derived from the thermal-wind relationship using CIRS thermal data [Fletcher, L.N., and 13 colleagues, 2008. Science 319, 79-81] and with previous equatorial measurements [Sánchez-Lavega, A., Hueso, R., Pérez-Hoyos, S., 2007. Icarus 187, 510-519]. 相似文献
92.
Anna Cabré Enrique Gaztañaga 《Monthly notices of the Royal Astronomical Society》2009,396(2):1119-1131
This is the second paper of a series where we study the clustering of luminous red galaxies (LRG) in the recent spectroscopic Sloan Digital Sky Survey (SDSS) data release, DR6, which has 75 000 LRG covering over 1 Gpc3 h −3 for 0.15 < z < 0.47 . Here, we focus on modelling redshift-space distortions in ξ(σ, π) , the two-point correlation in separate line-of-sight and perpendicular directions, at small scales and in the line-of-sight. We show that a simple Kaiser model for the anisotropic two-point correlation function in redshift space, convolved with a distribution of random peculiar velocities with an exponential form, can describe well the correlation of LRG on all scales. We show that to describe with accuracy the so-called 'fingers-of-God' (FOG) elongations in the radial direction, it is necessary to model the scale dependence of both bias b and the pairwise rms peculiar velocity σ12 with the distance. We show how both quantities can be inferred from the ξ(σ, π) data. From r ≃ 10 Mpc h −1 to r ≃ 1 Mpc h −1 , both the bias and σ12 are shown to increase by a factor of 2: from b = 2 to 4 and from σ12 = 400 to 800 km s−1 . The latter is in good agreement, within a 5 per cent accuracy in the recovered velocities, with direct velocity measurements in dark matter simulations with Ωm = 0.25 and σ8 = 0.85 . 相似文献
93.
94.
Enrique Pérez-Montero Thierry Contini 《Monthly notices of the Royal Astronomical Society》2009,398(2):949-960
We study the relation between nitrogen and oxygen abundances as a function of metallicity for a sample of emission-line objects for which a direct measurement of the metallicity has been possible. This sample is representative of the very different conditions in ionization and chemical enrichment that we can find in the Universe. We first construct the N/O versus O/H ratio diagram, and discuss its large dispersion at all metallicity regimes. Using the same sample and a large grid of photoionization models covering very different values of the N/O ratio, we then study the most widely used strong-line calibrators of metallicity based on [N ii ] emission lines, such as N2 and O3N2. We demonstrate that these parameters underestimate the metallicity at low N/O ratios and vice versa. We also investigate the effect of the N/O ratio on different diagnostic diagrams used to discriminate narrow-line active galactic nuclei from star-forming regions, such as the [O iii ]/Hβ versus [N ii ]/Hα, and show that a large fraction of the galaxies catalogued as composite in this diagram can be, in fact, star-forming galaxies with a high value of the N/O ratio. Finally, using strong-line methods sensitive to the N/O abundance ratio, like N2O2 and N2S2, we investigate the relation between this ratio and the stellar mass for the galaxies of the Sloan Digital Sky Survey. We find, as in the case of the mass–metallicity relation, a correlation between these two quantities and a flattening of the relation for the most massive galaxies, which could be a consequence of the enhancement of the dispersion of N/O ratio in the high-metallicity regime. 相似文献
95.
96.
Nuria Castell Ariel F. Stein Enrique Mantilla Rosa Salvador Millán Millán 《Journal of Atmospheric Chemistry》2009,63(1):73-91
Understanding the chemical links between ozone (O3) and its two main precursors, nitrogen oxides (NOx) and volatile organic compounds (VOC), is important for designing effective
photochemical smog reduction strategies. This chemical relationship will determine which precursor (NOx or VOC) emission reduction
will be more effective for decreasing the ozone formation. Under certain conditions, ozone levels decrease as a result of
a reduction in NOx emissions but do not respond significantly to changes in VOC emissions (NOx-sensitive condition), while
under other conditions ozone concentrations decrease in response to reductions in VOCs and may even increase when NOx emissions
are reduced (VOC-sensitive conditions). Indicator species can be used to assess the sensitivity of ozone to changes in the
emissions of its precursors. These indicators are species or species ratios involved in ozone photochemistry which reflect
the primary chemical process through which the ozone was formed. In this work we use the MM5-CAMx model system to explore
the behaviour of various indicator species during two meteorological situations featuring different atmospheric conditions
in a complex terrain area. The results show that indicators based on nitrogen compounds (i.e,. NOy and NOz) are suitable for
defining the transition range from VOC- to NOx-sensitive chemistry, and that despite the uncertainties associated with the
use of chemical indicators, the ratios O3/NOy and O3/NOz may provide a simple and useful way to summarize the response of ozone to changes in NOx and VOC emissions in Southwestern
Spain. 相似文献
97.
Gail M. Ashley Doris Barboni Manuel Dominguez-Rodrigo Henry T. Bunn Audax Z.P. Mabulla Fernando Diez-Martin Rebeca Barba Enrique Baquedano 《Quaternary Research》2010,74(3):304-314
The 1959 discovery of the hominin fossil Zinjanthropus boisei brought the world's attention to the rich records at Olduvai Gorge, Tanzania. Subsequent excavations of archaeological level 22 (FLK Zinj) Bed I uncovered remains of Homo habilis and a high-density collection of fossils and Oldowan stone tools. The occurrence of this unusual collection of bones and tools at this specific location has been controversial for decades. We present paleoecological data that provide new insights into the origin of FLK Zinj. Our recent excavations 200 m north of the site uncovered a 0.5-m-thick tufa mound draped by Tuff IC, in the same stratigraphic horizon as level 22. Stable isotope analyses indicate that the carbonates were deposited by a freshwater spring. Phytolith analysis of the waxy clay under Tuff IC revealed abundant woody dicotyledon and palm phytoliths, indicating that the site was wooded to densely wooded. The time equivalency and close physical proximity of the two environments indicate the two are related. This study has provided the first documented evidence of springs in Bed I and these data have important implications for the interpretation of hominin behavior in meat acquisition and the ongoing debate on scavenging versus hunting. 相似文献
98.
Coma Structures in Comet 73P/Schwassmann-Wachmann 3, Components B and C,Between January and May 2006
Jean-Baptiste Vincent Hermann Böhnhardt Ivano Bertini Luisa-Maria Lara Michael Küppers Rafael Rodrigo 《Earth, Moon, and Planets》2010,106(1):27-35
The Jupiter family comet 73P/Schwassmann-Wachmann 3 has been widely observed since 1995 after a nucleus break-up event produced
at least five components labeled 73P-A to E. During the 2006 appearance, two of them (B and C) showed very strong coma activity.
Our R-filter imaging of 73P-B & C from 21 January to 25 May 2006 revealed the presence of fan-like structures in the comae
of both components and evidence for further fragmentation events in component B. As of early April 2006, component C showed
two jets emanating from the nucleus, with one continuously visible. Through a simulation of the orbital geometry we infer
that the rotation axis of 73P-C has an inclination of 20° to the orbital plane and a longitude of 45° at perihelion. The coma
activity of component B was highly variable, displaying signatures of at least 3 fragmentation events. The coma was characterized
by the continuous presence of a jet roughly in sunward direction, starting from the beginning of May. The first fragmentation
event of component B may have happened between April 16 and April 26, leading to the presence of at least 6 fragments detected
in images of May 2. The second one happened on or shortly before May 8, the third one between May 18 and 24. For the rotation
axis of 73P-B we infer an inclination of 5°–15° to the orbital plane and a longitude of 20°–30° at perihelion. 相似文献
99.
<正>One new genus and five new species of the family Evaniidae are described from the Early Cretaceous (Albian)Spanish amber of Penacerrada-Ⅰ(Province of Burgos),San Just and Arroyo de la Pascueta(both in the Province of Teruel):Cretevania alonsoi sp.nov.,C.montoyai sp.nov.,C.alcalai sp.nov.,C.rubusensis sp.nov.,and Iberoevania roblesi gen.and sp.nov.Taxonomic changes include Cretevania pristina(Zhang and Zhang,2000) comb.nov.,C.exquisita(Zhang,Rasmtsyn,Wang and Zhang,2007)comb.nov.,C.vesca(Zhang,Rasnitsyn,Wang and Zhang,2007)comb.nov.,and C.cyrtocerca(Deans,2004)comb.nov.,as a result of the reinterpretation of the genera Procretevania and Eovernevania.The new well preserved specimens of the genus Cretevania,together with the characters shown by the type specimens of the synonymized genera,give new information about their anatomical characters of taxonomical importance,and the genus Cretevania Rasnitsyn,1975 is re-diagnosed.The holotypes of the Russian species in amber have been revised.A cladistic analysis of fossil and extant groups of the superfamily Evanioidea is included.Cretevania had a wide palaeogeographic distribution,with the highest diversity known from Spain.The 13 known Cretevania species show a high interspecific variation mainly in wing characteristics,and a wide range of body and wing size. 相似文献
100.
Sergio A. Sepúlveda Alejandra Serey Marisol Lara Andrés Pavez Sofía Rebolledo 《Landslides》2010,7(4):483-492
On the 21st of April 2007, the Aysén Fjord earthquake (Mw 6.2) in southern Chile (45.3° S, 73.0° W) triggered hundreds of landslides in the epicentral area along the fjord coast and surroundings. Some of these landslides induced large tsunami waves within the fjord causing fatalities and damaging several salmon farms, the most important economic activity of the area. The landslides included rock slides and avalanches, rock falls, shallow soil and soil–rock slides, and debris flows. The earthquake was the climax of a seismic swarm that began 3 months earlier. The seismicity is associated with tectonic activity along the Liquiñe–Ofqui fault zone (LOFZ), a major structural feature of the region. The earthquake-induced landslides were mapped and classified from field observations and remote sensing analysis. The landslide areas and epicentral distances are within the expected range for the earthquake magnitude according to worldwide data, while the position of landslides on the slopes strongly suggests topographic amplification effects in triggering the failures. The location of the landslides is also clearly related to some of the main fault branches of the LOFZ. The seismic event has configured a new situation of seismic and landslide hazard in the Aysén region and along the LOFZ, where the presence of towns and economic infrastructure along the coasts of several fjords constitutes a potential risk that was not considered before this seismic event. 相似文献