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排序方式: 共有223条查询结果,搜索用时 15 毫秒
121.
122.
Glauber Sampaio dos Santos Gustavo Gil da Silveira Magno Valério Trindade Machado 《Astronomische Nachrichten》2024,345(2-3):e230182
A study of double-charmed meson production in high-energy proton–proton collisions at the Large Hadron Collider is presented. Considering the color dipole formalism developed in the transverse momentum representation along with the double parton scattering mechanism, predictions are made for the transverse momentum differential cross section for different pairs of -mesons. The theoretical results cover the center-of-mass energy and forward rapidities available by the LHCb experiment. The proton–proton results considering different unintegrated gluon distributions are compared to the respective data collected at the LHC. 相似文献
123.
Graham E. Forrester Kerianne Taylor Stephanie Schofield Amy Maynard 《Marine Ecology》2013,34(2):186-192
We determined that growth differences among coral fragments transplanted for restoration were influenced by both source population and environmental factors. In two common garden experiments, storm‐generated fragments of Acropora palmata were transplanted from two source populations in the British Virgin Islands to a restoration site (a ‘common garden’) that lacked A. palmata. In the first experiment, colonies from different sources grew at different rates in the first year after transplanting, suggesting either genetic differences among source populations or enduring acclimation to conditions at the source site. No differences in growth among source populations were detected in the second common garden experiment. To isolate environmental effects on growth, we subdivided fragments from three source populations to create genetically identical pieces that were attached separately at both source and restoration sites. Genetically identical pieces from all source populations grew slightly faster at their source than at the restoration site, implying a subtle home‐site advantage. Overall, our results suggest that matching environmental conditions at source and restoration sites may increase the success of restoration projects. 相似文献
124.
We present the results of VLA observations of the class I methanol maser DR21(OH) at 44 GHz. The observations, retrieved from the NRAO archive (USA), were carried out in 2003. The maser has 18 spatial components, 17 of them confined to two clusters and one isolated component. In general, this spatial structure is similar to the structure observed earlier by other authors; the detected differences are too small to enable us to derive proper motions of the components: no proper motions exceeding the uncertainties were detecting during the 8 years since 1995. Amaser flare was observed in one of the spectral features for the first time. This is the first brightening detected for a class I methanol maser. 相似文献
125.
Michel Ballèvre Valérie Bosse Céline Ducassou Pavel Pitra 《Comptes Rendus Geoscience》2009,341(2-3):174-201
The Armorican Massif (western France) provides an excellent record of the Palaeozoic history of the Variscan belt. Following the Late Neoproterozoic Cadomian orogeny, the Cambro-Ordovician rifting was associated with oceanic spreading. The Central- and North-Amorican domains (which together constitute the core of the Armorica microplate) are bounded by two composite suture zones. To the north, the Léon domain (correlated with the “Normannian High” and the “Mid-German Crystalline Rise” in the Saxo-Thuringian Zone) records the development of a nappe stack along the northern suture zone, and was backthrusted over the central-Armorican domain during the Carboniferous. To the south, an intermediate block (“Upper Allochthon”) records a complex, polyorogenic history, with an early high-temperature event followed by the first generation of eclogites (Essarts). This intermediate block overthrusts to the north the Armorica microplate (Saint-Georges-sur-Loire), to the south: (i) relics of an oceanic domain; and (ii) the Gondwana palaeomargin. The collision occurred during a Late Devonian event, associated with a second generation of eclogites (Cellier). 相似文献
126.
Amaelle Landais Mathieu Casado Frédéric Prié Olivier Magand Laurent Arnaud Alexey Ekaykin Jean-Robert Petit Ghislain Picard Michel Fily Bénédicte Minster Alexandra Touzeau Sentia Goursaud Valérie Masson-Delmotte Jean Jouzel Anaïs Orsi 《Comptes Rendus Geoscience》2017,349(4):139-150
Polar ice cores are unique climate archives. Indeed, most of them have a continuous stratigraphy and present high temporal resolution of many climate variables in a single archive. While water isotopic records (δD or δ18O) in ice cores are often taken as references for past atmospheric temperature variations, their relationship to temperature is associated with a large uncertainty. Several reasons are invoked to explain the limitation of such an approach; in particular, post-deposition effects are important in East Antarctica because of the low accumulation rates. The strong influence of post-deposition processes highlights the need for surface polar research programs in addition to deep drilling programs. We present here new results on water isotopes from several recent surface programs, mostly over East Antarctica. Together with previously published data, the new data presented in this study have several implications for the climatic reconstructions based on ice core isotopic data: (1) The spatial relationship between surface mean temperature and mean snow isotopic composition over the first meters in depth can be explained quite straightforwardly using simple isotopic models tuned to d-excess vs. δ18O evolution in transects on the East Antarctic sector. The observed spatial slopes are significantly higher (~ 0.7–0.8‰·°C?1 for δ18O vs. temperature) than seasonal slopes inferred from precipitation data at Vostok and Dome C (0.35 to 0.46‰·°C?1). We explain these differences by changes in condensation versus surface temperature between summer and winter in the central East Antarctic plateau, where the inversion layer vanishes in summer. (2) Post-deposition effects linked to exchanges between the snow surface and the atmospheric water vapor lead to an evolution of δ18O in the surface snow, even in the absence of any precipitation event. This evolution preserves the positive correlation between the δ18O of snow and surface temperature, but is associated with a much slower δ18O-vs-temperature slope than the slope observed in the seasonal precipitation. (3) Post-deposition effects clearly limit the archiving of high-resolution (seasonal) climatic variability in the polar snow, but we suggest that sites with an accumulation rate of the order of 40 kg.m?2.yr?1 may record a seasonal cycle at shallow depths. 相似文献
127.
128.
The methanol-line spectra in two maser condensations at velocities ~41 and ~45 km/s in the star-forming region W48 have been studied. The intensity of the 20-3?1 E (12.2 GHz) line is anticorrelated with that of the 51-60 A + (6.7 GHz) line: the intensity of the 51-60 A + (6.7 GHz) line is greater at ~41 km/s than at ~45 km/s, while the opposite is true of the 20-3?1 E (12 GHz) line. The remaining class II methanol lines in this source demonstrate the same behavior as the 20-3?1 E (12 GHz) line. This contradicts current concepts about the maser line intensities in various methanol transitions: according to model calculations, the intensities of all class II lines should vary in phase. This effect is confirmed for a large homogeneous sample of 67 sources. Possible explanations of the observed effect are proposed; one suggests the possible role of “transpumping” of the methanol-level populations in the maser condensations. The relationships between the variations of the 20-3?1 E (12 GHz) and 51-60 A + (6.7 GHz) line intensities, which are present for all 67 sources considered, may indicate that the condensations are at different distances from the pumping source. The presence of condensations at various distances from the pumping source in all 67 sources can be understood if they are ice planets revolving in different orbits around massive stars or protostars. 相似文献
129.
The results of a search for maser emission in the methanol lines 8?1-70 E at 229.8 GHz, 3?2-4?1 E at 230.0 GHz, 00-1?1 E at 108.9 GHz, and in the J 1-J 0 E series near 165 GHz in star-forming regions are reported. At least two masers and two candidates have been detected at 229.8 GHz. Thus, methanol masers have been detected in the 1-mm band for the first time. At 108.9 GHz, masers have been detected toward G345.01+1.79 and possibly toward M8E as well. Thermal emission was found toward 28 objects. The 229.8-GHz sources are class I masers, whereas the 108.9-GHz sources are class II masers. An analysis using a large velocity-gradient method shows that the 229.8-GHz masers can appear at densities of about 3×104 cm?3. The ratios of the flux densities in different class I lines toward DR 21(OH) and DR 21 West can be approximated in models with gas kinetic temperatures of about 50 K. Detection of the 108.9 GHz masers toward G345.01+1.79 and M8E may provide information about the geometry of these objects. 相似文献
130.
A chain of three nested models, based on the MARS 3D code, is used to simulate the North-western Mediterranean Sea circulation
with a finest grid of 1.2 km resolution and 30 vertical sigma levels. This modelling system allows to resolve the coastal
dynamics taking into account the influence of the general basin circulation. The aim of this study is to assess the ability
of the nested MARS-3D models to reproduce most of the circulation features observed in the North-western Mediterranean Basin
and in the Gulf of Lions. Comparisons of modelled sea surface temperature and salinity with MEDAR/MEDATLAS climatology and
NOAA/AVHRR satellite measurements show that the model accurately reproduces the large and coastal scale variability. Over
the Northern Basin, the seasonal changes of the cyclonic gyre extension are correctly simulated, even though in summer, the
modelled temperature of the surface layer remains in basin-average 1°C cooler than the satellite measured temperature. As
soon as the stratification erodes, modelled and observed temperatures become closer. Over the Gulf of Lions, realistic coastal
responses are obtained under different wind conditions. Upwellings are correctly located and their intensity and spatial extension
were here improved by the use of Aladin wind fields (10 km spatial resolution) and the introduction of a drag coefficient
fitted according to the stability of the planetary boundary layer. The dispersion of fresh Rhone water discharge and the mesoscale
circulation simulated by MARS-3D also agree with satellite measurements. 相似文献