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Search Results: 1 - 10 of 461257 matches for " A. Spolaor "
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Halogen species record Antarctic sea ice extent over glacial-interglacial periods
A. Spolaor,P. Vallelonga,J. M. C. Plane,N. Kehrwald
Atmospheric Chemistry and Physics Discussions , 2013, DOI: 10.5194/acpd-13-3881-2013
Abstract: Sea ice is an integral part of the Earth's climate system because it affects planetary albedo, sea surface salinity, and the atmosphere-ocean exchange of reactive gases and aerosols. Bromine and iodine chemistry is active at polar sea ice margins with the occurrence of bromine explosions and the biological production of organo-iodine from sea ice algae. Satellite measurements demonstrate that concentrations of bromine oxide (BrO) and iodine oxide (IO) decrease over sea ice toward the Antarctic interior. Here we present speciation measurements of bromine and iodine in the TALDICE (TALos Dome Ice CorE) ice core (159°11' E, 72°49' S, 2315 m a.s.l.) spanning the last 215 ky. The Talos Dome ice core is located 250 km inland and is sensitive to marine air masses intruding onto the Antarctic Plateau. Talos Dome bromide (Br ) is positively correlated with temperature and negatively correlated with sodium (Na). Based on the Br /Na seawater ratio, bromide is depleted in the ice during glacial periods and enriched during interglacial periods. Total iodine, consisting of iodide (I ) and iodate (IO3 ), peaks during glacials with lower values during interglacial periods. Although IO3 is considered the most stable iodine species in the atmosphere it was only observed in the TALDICE record during glacial maxima. Sea ice dynamics are arguably the primary driver of halogen fluxes over glacial-interglacial timescales, by altering the distance between the sea ice edge and the Antarctic plateau and by altering the surface area of sea ice available to algal colonization. Based on our results we propose the use of both halogens for examining Antarctic variability of past sea ice extent.
Almgren's type regularity for Semicalibrated Currents
Luca Spolaor
Mathematics , 2015,
Abstract: In analogy with Almgren's Theorem for area minimizing currents of general dimension and codimension, we prove that an $m$-dimensional semicalibrated current in a $(n+m)$-dimensional $C^{3,\varepsilon_0}$ manifold, semicalibrated by a $C^{2,\varepsilon_0}$ $m$-form, has singular set of Hausdorff dimension at most $m-2$.
Iron fluxes to Talos Dome, Antarctica, over the past 200 kyr
P. Vallelonga, C. Barbante, G. Cozzi, J. Gabrieli, S. Schüpbach, A. Spolaor,C. Turetta
Climate of the Past (CP) & Discussions (CPD) , 2013,
Abstract: Atmospheric fluxes of iron (Fe) over the past 200 kyr are reported for the coastal Antarctic Talos Dome ice core, based on acid leachable Fe concentrations. Fluxes of Fe to Talos Dome were consistently greater than those at Dome C, with the greatest difference observed during interglacial climates. We observe different Fe flux trends at Dome C and Talos Dome during the deglaciation and early Holocene, attributed to a combination of deglacial activation of dust sources local to Talos Dome and the reorganisation of atmospheric transport pathways with the retreat of the Ross Sea ice shelf. This supports similar findings based on dust particle sizes and fluxes and Rare Earth Element fluxes. We show that Ca and Fe should not be used as quantitative proxies for mineral dust, as they all demonstrate different deglacial trends at Talos Dome and Dome C. Considering that a 20 ppmv decrease in atmospheric CO2 at the coldest part of the last glacial maximum occurs contemporaneously with the period of greatest Fe and dust flux to Antarctica, we confirm that the maximum contribution of aeolian dust deposition to Southern Ocean sequestration of atmospheric CO2 is approximately 20 ppmv.
Desempenho agron mico do milho sob aduba o mineral e inocula o das sementes com rizobactérias Agronomic performance of maize under mineral fertilizer and seed inoculation with rhizobacteria
Mariana A. de Oliveira,Claudemir Zucareli,Leandro T. Spolaor,Allan R. Domingues
Revista Brasileira de Engenharia Agrícola e Ambiental , 2012, DOI: 10.1590/s1415-43662012001000002
Abstract: Para avaliar o desempenho agron mico da cultura do milho (Zea mays) de segunda safra submetido à inocula o com Pseudomonas fluorescens sob níveis de aduba o NPK, um experimento em campo foi conduzido utilizando-se a cultivar de milho híbrido 30F35 cultivada em Latossolo Vermelho eutroférrico. Foram testados seis tratamentos sob o delineamento experimental de blocos casualizados, em esquema fatorial 3 x 2, sendo três níveis de aduba o química com NPK (0, 125 e 250 kg ha-1) e dois níveis de inoculante à base de P. fluorescens (com e sem), com quatro repeti es. Foram avaliados as características fitométricas, os componentes de produ o e a produtividade de gr os do milho. Os dados foram submetidos à análise de variancia e as médias comparadas pelo teste de Tukey p < 0,05. A inocula o com Pseudomonas fluorescens associada à aduba o de semeadura com 250 kg ha-1 de NPK, favorece o desenvolvimento e o desempenho produtivo do milho de segunda safra. To evaluate the agronomic performance of second maize (Zea mays) crop, subjected to inoculation with Pseudomonas fluorescens under different levels of NPK fertilization, a field experiment was conducted using the cultivar of hybrid maize 30F35 grown in Oxisol. Six treatments were tested in a randomized block design in factorial scheme 3 x 2, with three levels of NPK (0, 125 and 250 kg ha-1) and two levels of inoculants (with and without), and four replications. The characteristics, yield components and productivity were evaluated. The data were submitted to analysis of variance and means compared by Tukey test at p < 0.05 level. The inoculation with Pseudomonas fluorescens associated with fertilization with 250 kg ha-1 NPK at sowing time promotes the development and productive performance of second maize crop.
Metallicity Gradients at Large Galactocentric Radii Using the Near-infrared Calcium Triplet
Caroline Foster,Robert N. Proctor,Duncan A. Forbes,Max Spolaor,Philip F. Hopkins,Jean P. Brodie
Physics , 2009, DOI: 10.1111/j.1365-2966.2009.15606.x
Abstract: We describe a new spectroscopic technique for measuring radial metallicity gradients out to large galactocentric radii. We use the DEIMOS multi-object spectrograph on the Keck telescope and the galaxy spectrum extraction technique of Proctor et al. (2009). We also make use of the metallicity sensitive near-infrared (NIR) Calcium triplet (CaT) features together with single stellar population models to obtain metallicities. Our technique is applied as a pilot study to a sample of three relatively nearby (<30 Mpc) intermediate-mass to massive early-type galaxies. Results are compared with previous literature inner region values and generally show good agreement. We also include a comparison with profiles from dissipational disk-disk major merger simulations. Based on our new extended metallicity gradients combined with other observational evidence and theoretical predictions, we discuss possible formation scenarios for the galaxies in our sample. The limitations of our new technique are also discussed.
The mass-metallicity gradient relation of early-type galaxies
Max Spolaor,Robert N. Proctor,Duncan A. Forbes,Warrick J. Couch
Physics , 2009, DOI: 10.1088/0004-637X/691/2/L138
Abstract: We present a newly observed relation between galaxy mass and radial metallicity gradients of early-type galaxies. Our sample of 51 early-type galaxies encompasses a comprehensive mass range from dwarf to brightest cluster galaxies. The metallicity gradients are measured out to one effective radius by comparing nearly all of the Lick absorption-line indices to recent models of single stellar populations. The relation shows very different behaviour at low and high masses, with a sharp transition being seen at a mass of ~ 3.5 x 10^10 M_sun (velocity dispersion of ~140 km/s, M_B ~ -19). Low-mass galaxies form a tight relation with mass, such that metallicity gradients become shallower with decreasing mass and positive at the very low-mass end. Above the mass transition point several massive galaxies have steeper gradients, but a clear downturn is visible marked by a broad scatter. The results are interpreted in comparison with competing model predictions. We find that an early star-forming collapse could have acted as the main mechanism for the formation of low-mass galaxies, with star formation efficiency increasing with galactic mass. The high-mass downturn could be a consequence of merging and the observed larger scatter a natural result of different merger properties. These results suggest that galaxies above the mass threshold of ~ 3.5 x 10^10 M_sun might have formed initially by mergers of gas-rich disc galaxies and then subsequently evolved via dry merger events. The varying efficiency of the dissipative merger-induced starburst and feedback processes have shaped the radial metallicity gradients in these high-mass systems.
Early-type galaxies at large galactocentric radii - II. Metallicity gradients, and the [Z/H]--mass, [alpha/Fe]--mass relations
Max Spolaor,Chiaki Kobayashi,Duncan A. Forbes,Warrick J. Couch,George K. T. Hau
Physics , 2010, DOI: 10.1111/j.1365-2966.2010.17080.x
Abstract: We present the results of a study of stellar population properties at large galactocentric radii of 14 low-mass early-type galaxies in the Fornax and Virgo clusters. We derive radial profiles of Age, total metallicity [Z/H], and [alpha/Fe] abundance ratios out to 1 - 3 effective radii by using nearly all of the Lick/IDS absorption-line indices in comparison to recent single stellar population models. We extend our study to higher galaxy mass via a novel literature compilation of 37 early-type galaxies, which provides stellar population properties out to one effective radius. We find that metallicity gradients correlate with galactic mass, and the relationship shows a sharp change in slope at a dynamical mass of 3.5 10^10 M_{sun}. The central and mean values of the stellar population parameters (measured in r < r_e/8, and at r = r_e, respectively) define positive mass trends. We suggest that the low metallicities, almost solar [alpha/Fe] ratios and the tight mass-metallicity gradient relation displayed by the low-mass galaxies are indicative of an early star-forming collapse with extended (i.e., > 1 Gyr), low efficiency star formation, and mass-dependent galactic outflows of metal-enriched gas. The flattening of metallicity gradients in high-mass galaxies, and the broad scatter of the relationship are attributed to merger events. The high metallicities and supersolar abundances shown by these galaxies imply a rapid, high efficiency star formation. The observed [Z/H]--mass and [alpha/Fe]--mass relationships can be interpreted as a natural outcome of an early star-forming collapse. However, we find that hierarchical galaxy formation models implementing mass-dependent star formation efficiency, varying IMF, energy feedback via AGN, and the effects due to merger-induced starbursts can also reproduce both our observed relationships.
Early-type galaxies at large galactocentric radii - I. Stellar kinematics and photometric properties
Max Spolaor,George K. T. Hau,Duncan A. Forbes,Warrick J. Couch
Physics , 2010, DOI: 10.1111/j.1365-2966.2010.17282.x
Abstract: We present the results of a combined analysis of the kinematic and photometric properties at large galactocentric radii of a sample of 14 low-luminosity early-type galaxies in the Fornax and Virgo clusters. From Gemini South GMOS long-slit spectroscopic data we measure radial profiles of the kinematic parameters v_{rot}, sigma, h_{3}, and h_{4} out to ~ 1 - 3 effective radii. Multi-band imaging data from the HST/ACS are employed to evaluate surface brightness profiles and isophotal shape parameters of ellipticity, position angle and discyness/boxiness. The galaxies are found to host a cold and old stellar component which extend to the largest observed radii and that is the dominant source of their dynamical support. The prevalence of discy-shaped isophotes and the radial variation of their ellipticity are signatures of a gradual gas dissipation. An early star-forming collapse appears to be the main mechanism acting in the formation of these objects. Major mergers are unlikely to have occurred in these galaxies. We can not rule out a minor merging origin for these galaxies, but a comparison of our results with model predictions of different merger categories places some constraints on the possible merger progenitors. These merger events are required to happen at high-redshift (i.e., z > 1), between progenitors of different mass ratio (at least 3:1) and containing a significant amount of gas (i.e., > 10 percent). A further scenario is that the low-luminosity galaxies were originally late-type galaxies, whose star formation has been truncated by removal of gas and subsequently the disc has been dynamically heated by high speed encounters in the cluster environment.
A Radio Census of Binary Supermassive Black Holes
Sarah Burke-Spolaor
Physics , 2010, DOI: 10.1111/j.1365-2966.2010.17586.x
Abstract: Using archival VLBI data for 3114 radio-luminous active galactic nuclei, we searched for binary supermassive black holes using a radio spectral index mapping technique which targets spatially resolved, double radio-emitting nuclei. Only one source was detected as a double nucleus. This result is compared with a cosmological merger rate model and interpreted in terms of (1) implications for post-merger timescales for centralisation of the two black holes, (2) implications for the possibility of "stalled" systems, and (3) the relationship of radio activity in nuclei to mergers. Our analysis suggests that the binary evolution of paired supermassive black holes (both of masses >= 1e8 Msun) spends less than 500 Myr in progression from the merging of galactic stellar cores to within the purported stalling radius for supermassive black hole pairs. The data show no evidence for an excess of stalled binary systems at small separations. We see circumstantial evidence that the relative state of radio emission between paired supermassive black holes is correlated within orbital separations of 2.5 kpc.
Rotating Radio Transients and Their Place Among Pulsars
S. Burke-Spolaor
Physics , 2012, DOI: 10.1017/S1743921312023277
Abstract: Six years ago, the discovery of Rotating Radio Transients (RRATs) marked what appeared to be a new type of sparsely-emitting pulsar. Since 2006, more than 70 of these objects have been discovered in single-pulse searches of archival and new surveys. With a continual inflow of new information about the RRAT population in the form of new discoveries, multi-frequency follow-ups, coherent timing solutions, and pulse rate statistics, a view is beginning to form of the place in the pulsar population RRATs hold. Here we review the properties of neutron stars discovered through single pulse searches. We first seek to clarify the definition of the term RRAT, emphasising that "the RRAT population" encompasses several phenomenologies. A large subset of RRATs appear to represent the tail of an extended distribution of pulsar nulling fractions and activity cycles; these objects present several key open questions remaining in this field.
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