Expansion of an invasive coral species over Abrolhos Bank,Southwestern Atlantic     

Thiago J.F. Costa  Hudson T. Pinheiro  João Batista Teixeira  Eric F. Mazzei  Leonardo Bueno  Mike S.C. Hora  Jean-Christophe Joyeux  Alfredo Carvalho-Filho  Gilberto Amado-Filho  Claudio L.S. Sampaio  Luiz A. Rocha 《Marine pollution bulletin》2014

Invasive coral species of the genus Tubastraea have been increasingly recorded in Southwestern Atlantic waters since the 1980s. Their invasion and infestation are mainly related to port and oil exploration activities. For the first time the presence of Tubastraea tagusensis colonies is reported in Espírito Santo State, colonizing a port shore area, and incrusting oil/gas platform structures situated in the southern Abrolhos Bank, which is part of the most important coral reef system of the South Atlantic Ocean. Tubastraea colonies exhibit fast growth and high recruitment rates, and colonized 40% of the analyzed structures in just four years. The projection of port and oil/gas industry growth for the Espírito Santo State (more than 300%) highlights an alert to the dispersal of this alien species to natural areas.  相似文献   

Fully 3-dimensional calculations of dust mantle formation for a model of Comet 67P/Churyumov-Gerasimenko     

Eric D. Rosenberg  Dina Prialnik 《Icarus》2009,201(2):740-863

A fully 3-dimensional implicit numerical model for comet nucleus evolution is presented, emphasizing dust mantle formation. A spherical configuration is considered with an initial composition of amorphous H₂O ice and dust, taking into account a discrete dust-grain size distribution. The model is applied to Comet 67P/Churyumov-Gerasimenko, adopting its orbital elements, rotation period and rotation axis inclination. We find that the dust mantle thickness varies over the surface from 1 cm to about 10 cm (thus lower and higher than the diurnal skin-depth, respectively). The size distribution of ejected grains varies along the orbit and is steeper than the initial one adopted for the nucleus. The crystallization front advances inward in spurts, and its depth varies between 1 and several meters. We test the effect of the thermal conductivity on the surface temperature distribution and depths of the dust mantle and crystallization front.  相似文献   

Specific angular momentum of disc merger remnants and the λ_R-parameter     

Roland Jesseit  Michele Cappellari  Thorsten Naab  Eric Emsellem  Andreas Burkert 《Monthly notices of the Royal Astronomical Society》2009,397(3):1202-1214

We use two-dimensional kinematic maps of simulated binary disc mergers to investigate the  λ_R  -parameter, which is a luminosity-weighted measure of projected angular momentum per unit mass. This parameter was introduced to subdivide the SAURON sample of early-type galaxies in so-called fast  λ_R > 0.1  and slow rotators  λ_R < 0.1  . Tests on merger remnants reveal that  λ_R  is a robust indicator of the true angular momentum content in elliptical galaxies. We find the same range of  λ_R  values in our merger remnants as in the SAURON galaxies. The merger mass ratio is decisive in transforming fast rotators into slow rotators in a single binary merger, the latter being created mostly in an equal-mass merger. Slow rotators have a  λ_R  which does not vary with projection. The confusion rate with face-on fast rotators is very small. Mergers with a gas component form slow rotators with smaller ellipticities than collisionless merger remnants have, and are in much better agreement with the SAURON slow rotators. Remergers of merger remnants are slow rotators, but tend to have too high ellipticities. Fast rotators maintain the angular momentum content from the progenitor disc galaxy if merger mass ratio is high. Some SAURON galaxies have values of  λ _R   as high as our progenitor disc galaxies.  相似文献   

Pre-main-sequence variability across the radiative–convective gap     

Eric S. Saunders  Tim Naylor  Nathan Mayne  S. P. Littlefair 《Monthly notices of the Royal Astronomical Society》2009,397(1):405-410

We use I -band imaging to perform a variability survey of the 13-Myr-old cluster h Per. We find a significant fraction of the cluster members to be variable. Most importantly, we find that variable members lie almost entirely on the convective side of the gap in the cluster sequence between fully convective stars and those which have a radiative core. This result is consistent with a scenario in which the magnetic field changes topology when the star changes from being fully convective to one containing a radiative core. When the star is convective, the magnetic field appears dominated by large-scale structures, resulting in global-size spots that drive the observed variability. For those stars with radiative cores, we observe a marked absence of variability due to spots, which suggests a switch to a magnetic field dominated by smaller-scale structures, resulting in many smaller spots and thus less apparent variability. This implies that wide field variability surveys may only be sensitive to fully convective stars. On the one hand, this reduces the chances of picking out young groups (since the convective stars are the lower mass and therefore fainter objects), but conversely the absolute magnitude of the head of the convective sequence provides a straightforward measure of age for those groups which are discovered.  相似文献   

The SAURON Project – XIV. No escape from V_esc: a global and local parameter in early-type galaxy evolution     

Nicholas Scott  Michele Cappellari  Roger L. Davies  R. Bacon  P. T. de Zeeuw  Eric Emsellem  Jésus Falcón-Barroso  Davor Krajnovi&#;  Harald Kuntschner  Richard M. McDermid  Reynier F. Peletier  Antonio Pipino  Marc Sarzi  Remco C. E. van den Bosch  Glenn van de Ven †  Eveline van Scherpenzeel 《Monthly notices of the Royal Astronomical Society》2009,398(4):1835-1857

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Parallel algorithm for solving Kepler’s equation on Graphics Processing Units: Application to analysis of Doppler exoplanet searches     

Eric B. Ford 《New Astronomy》2009,14(4):406-412

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Production scenarios and the effect of soil degradation on long-term food security in China   总被引：3，自引：0，他引：3  

Liming Ye  Eric Van Ranst   《Global Environmental Change》2009,19(4):464-481

Food security in China underlies the foundation of the livelihood and welfare for over one-fifth of the world's population. Soil degradation has an immense negative impact on the productive capacity of soils. We simulated the effect of soil degradation, which occurs in combination with increases in population size, urbanization rate, cropping intensity and decrease in cropland area, on long-term food security in China using a web-based land evaluation system. Our results predict that food crops may experience a 9% loss in productivity by 2030 if the soil continues to be degraded at the current rate (business-as-usual scenario, BAU). Productivity losses will increase to the unbearable level of 30% by 2050 should the soil be degraded at twice the present rate (double-degradation scenario, 2× SD). China's capacity for producing food from agricultural crops will be either adversely affected by the loss of cropland area (130, 113 and 107 million ha in 2005, 2030 and 2050, respectively) or favorably affected by agricultural intensification (in terms of the multi-cropping index at 120, 133 and 147% in 2005, 2030 and 2050, respectively). The loss of cropland is predicted to cause a 13–18% decrease in China's food production capacity by 2030–2050 relative to its 2005 level of 482 Mt, while agricultural intensification is predicted to cause an 11–23% increase. In total, China will be able to achieve a production level of 424 and 412 Mt by 2030 and 2050, respectively, under BAU, while this production will be only 386 and 339 Mt under 2× SD, respectively. In per capita terms, the relationship between food supply and demand will turn from an 18% surplus in 2005 to 3–5%, 14–18% and 22–32% deficits by 2030–2050 under the zero-degradation (0× SD), BAU and 2× SD scenarios, respectively. Our results show that the present-day production capacity will not sustain the long-term needs of a growing population under the current management level. Technical countermeasures and policy interventions need to be enacted today in order to avoid food insecurity tomorrow.  相似文献   

The feasibility of low CO₂ concentration targets and the role of bio-energy with carbon capture and storage (BECCS)     

Christian Azar  Kristian Lindgren  Michael Obersteiner  Keywan Riahi  Detlef P. van Vuuren  K. Michel G. J. den Elzen  Kenneth M?llersten  Eric D. Larson 《Climatic change》2010,100(1):195-202

The United Nations Framework Convention on Climate Change (UNFCCC 1992) calls for stabilization of atmospheric greenhouse gas (GHG) concentrations at a level that would prevent dangerous anthropogenic interference with the climate system. We use three global energy system models to investigate the technological and economic attainability of meeting CO₂ concentration targets below current levels. Our scenario studies reveal that while energy portfolios from a broad range of energy technologies are needed to attain low concentrations, negative emission technologies—e.g., biomass energy with carbon capture and storage (BECCS)—significantly enhances the possibility to meet low concentration targets (at around 350 ppm CO₂).  相似文献   

Projected changes in drought occurrence under future global warming from multi-model,multi-scenario,IPCC AR4 simulations   总被引：19，自引：3，他引：16  

Justin Sheffield  Eric F. Wood 《Climate Dynamics》2008,31(1):79-105

Recent and potential future increases in global temperatures are likely to be associated with impacts on the hydrologic cycle, including changes to precipitation and increases in extreme events such as droughts. We analyze changes in drought occurrence using soil moisture data for the SRES B1, A1B and A2 future climate scenarios relative to the PICNTRL pre-industrial control and 20C3M twentieth century simulations from eight AOGCMs that participated in the IPCC AR4. Comparison with observation forced land surface model estimates indicates that the models do reasonably well at replicating our best estimates of twentieth century, large scale drought occurrence, although the frequency of long-term (more than 12-month duration) droughts are over-estimated. Under the future projections, the models show decreases in soil moisture globally for all scenarios with a corresponding doubling of the spatial extent of severe soil moisture deficits and frequency of short-term (4–6-month duration) droughts from the mid-twentieth century to the end of the twenty-first. Long-term droughts become three times more common. Regionally, the Mediterranean, west African, central Asian and central American regions show large increases most notably for long-term frequencies as do mid-latitude North American regions but with larger variation between scenarios. In general, changes under the higher emission scenarios, A1B and A2 are the greatest, and despite following a reduced emissions pathway relative to the present day, the B1 scenario shows smaller but still substantial increases in drought, globally and for most regions. Increases in drought are driven primarily by reductions in precipitation with increased evaporation from higher temperatures modulating the changes. In some regions, increases in precipitation are offset by increased evaporation. Although the predicted future changes in drought occurrence are essentially monotonic increasing globally and in many regions, they are generally not statistically different from contemporary climate (as estimated from the 1961–1990 period of the 20C3M simulations) or natural variability (as estimated from the PICNTRL simulations) for multiple decades, in contrast to primary climate variables, such as global mean surface air temperature and precipitation. On the other hand, changes in annual and seasonal means of terrestrial hydrologic variables, such as evaporation and soil moisture, are essentially undetectable within the twenty-first century. Changes in the extremes of climate and their hydrological impacts may therefore be more detectable than changes in their means.  相似文献   

Resolving SSM/I-ship radar rainfall discrepancies from AIP-3     

Song YANG  Eric A.SMITH 《大气科学进展》2005,22(6):903-914

The third algorithm intercomparison project （AIP-3） involved rain estimates from more than 50 satellite rainfall algorithms and ground radar measurements within the Intensive Flux Array （IFA） over the equatorial western Pacific warm pool region during the Tropical Ocean Global Atmosphere coupled Ocean-Atmosphere Response Experiment （TOGA COARE）. Early results indicated that there was a sys- tematic bias between rainrates from satellite passive microwave and ground radar measurements. The mean rainrate from radar measurements is about 50% underestimated compared to that from passive microwave-based retrieval algorithms. This paper is designed to analyze rain patterns from the Florida State University rain retrieval algorithm and radar measurements to understand physically the rain discrep- ancies. Results show that there is a clear range-dependent bias associated with the radar measurements. However, this range-dependent systematical bias is almost eliminated with the corrected radar rainrates. Results suggest that the effects from radar attenuation correction, calibration and beam filling are the major sources of rain discrepancies. This study demonstrates that rain retrievals based on satellite mea- surements from passive microwave radiometers such as the Special Sensor of Microwave Imager （SSM/I） are reliable, while rain estimates from ground radar measurements are correctable.  相似文献