183 research outputs found
Meta-symplectic geometry of 3rd order Monge-Ampère equations and their characteristics
No full textThis paper is a natural companion of [Alekseevsky D.V., Alonso Blanco R., Manno G., Pugliese F., Ann. Inst. Fourier (Grenoble) 62 (2012), 497-524, arXiv:1003.5177], generalising its perspectives and results to the context of third-order (2D) Monge-Ampère equations, by using the so-called ''meta-symplectic structure'' associated with the 8D prolongation M⁽¹⁾ of a 5D contact manifold M. We write down a geometric definition of a third-order Monge-Ampère equation in terms of a (class of) differential two-form on M⁽¹⁾. In particular, the equations corresponding to decomposable forms admit a simple description in terms of certain three-dimensional distributions, which are made from the characteristics of the original equations. We conclude the paper with a study of the intermediate integrals of these special Monge-Ampère equations, herewith called of Goursat type.This paper is a contribution to the Special Issue on Analytical Mechanics and Dif ferential Geometry in honour
of Sergio Benenti. The full collection is available at http://www.emis.de/journals/SIGMA/Benenti.html.
The authors wish to express their gratitude towards the anonymous referees whose comments
contributed to shape the paper into its final form. The authors thank C. Ciliberto, E. Ferapontov
and F. Russo for stimulating discussions. The research of the first author has been partially
supported by the project “Finanziamento giovani studiosi – Metriche proiettivamente equivalenti,
equazioni di Monge–Amp`ere e sistemi integrabili”, University of Padova 2013–2015, by
the project “FIR (Futuro in Ricerca) 2013 – Geometria delle equazioni dif ferenziali”. The
research of the second author has been partially supported by the Marie Sk lodowska–Curie
Action No 654721 “GEOGRAL”, by the University of Salerno, and by the project P201/12/G028
of the Czech Republic Grant Agency (GA CR). Both the authors are members of G.N.S.A.G.A. ˇ
of I.N.d.A.M
Organic or junk food? Microplastic contamination in Antarctic krill and salps
No full textMicroplastics (MP) have been reported in Southern Ocean (SO), where they are likely to encounter Antarctic zooplankton and enter pelagic food webs. Here we assess the presence of MP within Antarctic krill (Euphausia superba) and salps (Salpa thompsoni) and quantify their abundance and type by micro-Fourier transform infrared microscopy. MP were found in both species, with fibres being more abundant than fragments (krill: 56.25% and salps: 22.32% of the total MP). Polymer identification indicated MP originated from both local and distant sources. Our findings prove how in situ MP ingestion from these organisms is a real and ongoing process in the SO. MP amount was higher in krill (2.13 ± 0.26 MP ind−1) than salps (1.38 ± 0.42 MP ind−1), while MP size extracted from krill (130 ± 30 µm) was significantly lower than MP size from salps (330 ± 50 µm). We suggest that differences between abundance and size of MP ingested by these two species may be related to their food strategies, their ability to fragment MP as well as different human pressures within the collection areas of the study region. First comparative field-based evidence of MP in both krill and salps, two emblematic zooplankton species of the SO marine ecosystems, underlines that Antarctic marine ecosystems may be particularly sensitive to plastic pollution
The Ocean Plastic Incubator Chamber (OPIC) system to monitor in situ plastic degradation at sea
No full textMarine plastic pollution is a global and pervasive environmental issue. Knowledge on plastic degradation in natural settings is still very limited due to current technological limitations, hampering our understanding of plastic fate (including its breakdown into micro- and nanoplastics) and of its risk for marine ecosystems. Here we present the proof of concept of the Ocean Plastic Incubator Chamber (OPIC), a novel equipment to follow plastic degradation in situ at sea over time. OPIC consists of a frame containing a motorised rotating stage with transparent tubes sub-assemblies where reference plastic materials are incubated and exposed to natural weathering conditions for defined time multi-years period. OPIC has been designed, tested and adapted for deployment with mooring line platforms in the open ocean with potential future application in remote environments at different depths (from shallow waters to deep sea environments). This incubator will allow us to measure different markers of plastic aging in situ in the ocean for the first time, providing new insights into the multiple and locally driven dynamics regulating plastic transformations and fate at sea
Italie
No full textBaudrez Maryse, Di Manno Thierry, Pardini Jean-Jacques, Boyer Alain, Elie Marie-Pierre, Jacquelot Fanny, Schmitt Sylvie, Severino Caterina, Tournier Clara, Santolini Thierry. Italie. In: Annuaire international de justice constitutionnelle, 23-2007, 2008. Constitution et liberté d'expression - Famille et droits fondamentaux. pp. 825-865
Copepod faecal pellet transfer through the meso- and bathypelagic layers in the Southern Ocean in spring
No full textThe faecal pellets (FPs) of zooplankton can be important vehicles for the transfer of particulate organic carbon (POC) to the deep ocean, often making large contributions to carbon sequestration. However, the routes by which these FPs reach the deep ocean have yet to be fully resolved. We address this by comparing estimates of copepod FP production to measurements of copepod FP size, shape, and number in the upper mesopelagic (175–205 m) using Marine Snow Catchers, and in the bathypelagic using sediment traps (1500–2000 m). The study is focussed on the Scotia Sea, which contains some of the most productive regions in the Southern Ocean, where epipelagic FP production is likely to be high. We found that, although the size distribution of the copepod community suggests that high numbers of small FPs are produced in the epipelagic, small FPs are rare in the deeper layers, implying that they are not transferred efficiently to depth. Consequently, small FPs make only a minor contribution to FP fluxes in the meso- and bathypelagic, particularly in terms of carbon. The dominant FPs in the upper mesopelagic were cylindrical and elliptical, while ovoid FPs were dominant in the bathypelagic. The change in FP morphology, as well as size distribution, points to the repacking of surface FPs in the mesopelagic and in situ production in the lower meso- and bathypelagic, which may be augmented by inputs of FPs via zooplankton vertical migrations. The flux of carbon to the deeper layers within the Southern Ocean is therefore strongly modulated by meso- and bathypelagic zooplankton, meaning that the community structure in these zones has a major impact on the efficiency of FP transfer to depth
Analysis of Physical and Biogeochemical Control Mechanisms on Summertime Surface Carbonate System Variability in the Western Ross Sea (Antarctica) Using In Situ and Satellite Data
No full textIn this study, carbonate system properties were measured in the western Ross Sea
(Antarctica) over the 2005–2006 and 2011–2012 austral summers with the aim of analysing their
sensitivity to physical and biogeochemical drivers. Daily Advanced Microwave Scanning Radiometer
2 (AMSR2) sea ice concentration maps, obtained prior to and during the samplings, were used
to analyse the sea ice evolution throughout the experiment periods. Monthly means and 8-day
composite chlorophyll concentration maps from the Moderate-resolution Imaging Spectroradiometer
(MODIS) Aqua satellite at 4-km resolution were used to investigate inter-annual and basin scale
biological variability. Chlorophyll-a concentrations in surface waters estimated by MODIS satellite
data contribute to descriptions of the variability of carbonate system properties in surface waters.
Mean values of carbonate system properties were comparable across both investigated years; however,
the 2012 data displayed larger variability. Sea ice melting also had a pivotal role in controlling the
carbonate system chemistry of the mixed layer both directly through dilution processes and indirectly
by favouring the development of phytoplankton blooms. This resulted in high pH and WAr, and in
low CT, particularly in those areas where high chlorophyll concentration was shown by satellite maps
Zooplankton faecal pellet transfer through the meso- and bathypelagic layers in the Southern Ocean in spring
No full textThe faecal pellets (FP) of zooplankton can be important vehicles for the transfer of particulate organic carbon (POC) to the deep ocean, often making large contributions to carbon sequestration. However, the routes by which these FP reach the deep ocean have yet to be fully resolved. We address this by comparing estimates of FP production to measurements of FP size, shape and number in the upper mesopelagic (175-205 m), using Marine Snow Catchers, and in the bathypelagic, using sediment traps (1,500-2,000 m). The study is focussed on the Scotia Sea, which contains some of the most productive regions in the Southern Ocean, where epipelagic FP production is likely to be high. We found that, although the size distribution of zooplankton suggests that high numbers of small FP are produced in the epipelagic, small FP are rare in the deeper layers, implying that they are not transferred efficiently to depth. Consequently, small FP make only a minor contribution to FP fluxes in the meso- and bathypelagic, particularly in terms of carbon. The dominant FP in the upper mesopelagic were cylindrical and elliptical, while ovoid FP were dominant in the bathypelagic. The change in FP morphology, as well as size distribution, points to the repacking of surface FP in the mesopelagic and in situ production in the lower meso- and bathypelagic, augmented by inputs of FP via zooplankton vertical migrations. The flux of carbon to the deeper layers within the Southern Ocean is therefore strongly modulated by meso- and bathypelagic zooplankton, meaning that the community structure in these zones has a major impact on the efficiency of FP transfer to depth
Life strategy of Antarctic silverfish promote large carbon export in Terra Nova Bay, Ross Sea
No full textAntarctic silverfish Pleuragramma antarcticum is the most abundant pelagic fish in the High Antarctic shelf waters of the Southern Ocean, where it plays a pivotal role in the trophic web as the major link between lower and higher trophic levels. Despite the ecological importance of this species, knowledge about its role in the biogeochemical cycle is poor. We determine the seasonal contribution of Antarctic silverfish to carbon flux in terms of faeces and eggs, from samples collected in the Ross Sea. We find that eggs and faeces production generate a flux accounting for 41% of annual POC flux and that the variability of this flux is modulated by spawning strategy. This study shows the important role of this organism as a vector for carbon flux. Since Antarctic silverfish are strongly dependent on sea-ice, they might be especially sensitive to climatic changes. Our results suggest that a potential decrease in the biomass of this organism is likely to impact marine biogeochemical cycles, and this should be factored in when assessing Southern Ocean carbon budget
Outer organic layer and internal repair mechanism protects pteropod Limacina helicina from ocean acidification
No full textScarred shells of polar pteropod Limacina helicina collected from the Greenland Sea in June 2012 reveal a history of damage, most likely failed predation, in earlier life stages. Evidence of shell fracture and subsequent re-growth is commonly observed in specimens recovered from the sub-Arctic and further afield. However, at one site within sea-ice on the Greenland shelf, shells that had been subject to mechanical damage were also found to exhibit considerable dissolution. It was evident that shell dissolution was localised to areas where the organic, periostracal sheet that covers the outer shell had been damaged at some earlier stage during the animal’s life. Where the periostracum remained intact, the shell appeared pristine with no sign of dissolution. Specimens which appeared to be pristine following collection were incubated for four days. Scarring of shells that received periostracal damage during collection only became evident in specimens that were incubated in waters undersaturated with respect to aragonite, ΩAr≤1. While the waters from which the damaged specimens were collected at the Greenland Sea sea-ice margin were not Ω Ar ≤1, the water column did exhibit the lowest ΩAr values observed in the Greenland and Barents Seas, and was likely to have approached ΩAr≤1 during the winter months. We demonstrate that L. helicina shells are only susceptible to dissolution where both the periostracum has been breached and the aragonite beneath the breach is exposed to waters of ΩAr≤1. Exposure of multiple layers of aragonite in areas of deep dissolution indicate that, as with many molluscs, L. helicina is able to patch up dissolution damage to the shell by secreting additional aragonite internally and maintain their shell. We conclude that, unless breached, the periostracum provides an effective shield for pteropod shells against dissolution in waters ΩAr≤1, and when dissolution does occur the animal has an effective means of self-repair. We suggest that future studies of pteropod shell condition are undertaken on specimens from which the periostracum has not been removed in preparation
Leonardo Ricci. Che la forma sia come nelle cose naturali
No full textLeonardo Ricci postula la forma architettonica come entità intrinsecamente connessa alle dinamiche naturali, promuovendo un'architettura che emerge in simbiosi con il paesaggio. La sua visione, radicata in una filosofia esistenzialista e fenomenologica, concepisce gli spazi abitativi come organismi viventi, in perpetua evoluzione e interazione con il contesto umano e ambientale. In Ricci, la città è rivelata non come una mera agglomerazione di strutture, ma come un'unica entità composta, un tessuto vivo che si fonde con le colline, gli alberi e i colori, in una celebrazione della libertà e felicità anonima dell'abitare. La relazionalità è il fulcro del discorso architettonico di Ricci, un principio che trascende la semplice estetica formale per abbracciare una percezione spaziale e temporale esperienziale. Attingendo dal pensiero filosofico del Novecento, specialmente dall'esistenzialismo, Ricci eleva l'architettura oltre la materialità per infonderle un ethos di relazioni in continuo divenire. Il paesaggio, lontano dall'essere un mero sfondo silenzioso, diviene un co-protagonista vibrante della narrazione architettonica. L'opera di Ricci propone un dialogo costante tra l'opera e il suo ambiente. Le sue realizzazioni, come l'esperienza di costruzione del villaggio valdese di Agàpe, del villaggio di Monterinaldi e di Monte degli Ulivi a Riesi, riflettono questa fusione tra edificio e natura, con forme che si espandono e contraggono in risposta ai mutamenti continui del paesaggio.
In conclusione, l'architettura di Ricci rappresenta una critica vivente alla percezione statica e isolata della forma, proponendo una comprensione più profonda e contestualizzata dell'abitare, che risuona con le urgenze ambientali e sociali contemporanee
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