1,721,023 research outputs found
Soft-sediment deformation in Pleistocene fluvio-lacustrine deposits of Departamento de Anelo (Neuquen Basin, northern Patagonia)
No full textEconomic, environmental and exergy analysis of the decarbonisation of cement production cycle
No full textThe aim of this study is to analyze the exergetic, environmental, and economic impact of the use of alternative fuels (Plasmix), instead of coal on the clinker production to valorise a non-recyclable waste and to limit global CO2 emissions. The cement production process was implemented in AspenPlus® environment, simulating different scenarios with the possibility to conduct the non recyclable plastic waste incineration in oxy-combustion conditions. Three scenarios were considered: without and with flue gas recirculation from the pre-heating tower and the oxy-combustion layout. Sensitive analyses were carried out to optimize cyclonic pre-heater tower working. Exergetic and economic analyses were performed, and the relevant impacts on economic profitability were analysed. The study reports the advantages and disadvantages of the different scenarios in terms of exergy efficiency, energy requirements, economic impact and pollutants emissions savings. Oxy-combustion layout resulted in 18.4% savings in terms of CO2 emissions but, at the same time, a lower Return of Investment (11.79%) with respect to the scenario with flue gas recirculation (11.82%). The exergy analysis of third scenario re returned the maximum obtainable value of the exergy efficiency (58.4%)
Super-Eddington accretion in high-redshift quasar hosts: Black-hole-driven outflows, galaxy quenching, and the nature of little red dots
No full textThe advent of the James Webb Space Telescope has revolutionised our understanding of the high-redshift Universe through its detection of bright, massive galaxies up to z ≳ 10 and its identification of peculiar sources called ‘little red dots’ (LRDs). The origin of both classes of objects remains uncertain but is likely linked to the formation and early growth of the first massive black holes (MBHs), which may be more easily explained by invoking phases of super-Eddington accretion. In this study, we used a state-of-the-art zoom-in cosmological simulation of a quasar host to investigate whether these objects could resemble any of the peculiar sources observed with JWST during their assembly. We find that the impact of MBH feedback on star formation is typically moderate, with outflows preferentially escaping perpendicular to the galactic disc. However, for approximately ten percent of the galaxy’s lifetime, the system enters a distinct quenched phase following rapid MBH growth driven by super-Eddington accretion. This phase culminates in a powerful feedback event, during which the MBH jet and disc-driven winds interact directly with the galactic disc and carve out a central cavity. We also find that, during the history of the quasar host progenitor, the spectral properties of the system can resemble both LRDs and quenched galaxies, depending on the specific evolutionary stage considered. These findings suggest that both conditions may represent transient phases in the life cycle of high-redshift galaxies
Modelling and economic evaluation of CCS/PtX technologies integrated into biomass MTG plants
No full textThis paper analyses the technical and economic feasibility of the integration of methanol to gasoline (MTG) process based biomass to Liquid (BTL) plants with Carbon Capture and Storage Technologies (CCS) and with the use of green hydrogen (PtX technology). The BtL facility proposed is based on commercial technologies and it is composed by a biomass gasification section, a methanol production section and a methanol conversion into gasoline section. In the PtX implementation, an electrolyzer is included to improve the complete conversion of CO2 to gasoline. The use of biomass falls within the goal of achieving a near-zero emission life cycle. The system configuration selected, and the plant performance are evaluated using Aspen Plus software. The plant size considered is about 1230 bbl/d of liquid fuel products, equivalent to a consumption of about 790 t/d of biomass fed to the gasification section. When MeOH is produced by using green hydrogen from renewable electrical energy, the plant produces 2706 bbl/d of gasoline. The final goal is to evaluate the environmental performance of the system and to determine the specific cost of produced liquid fuels. Results show that the CCS introduction in BtL-MTG plants has a lighter impact on plant costs and performance since CO2 capture is already included in the base plant. The PtX technology allows to completely convert the carbon dioxide to gasoline, leading to more than double fuel production and a quasi-zero-emission integrated plant design, since the CO2 specific emission for the Base Case decreases from 0.11 kgCO2 emitted/MJfuel down to 0.011 kgCO2 emitted/MJfuel for PtX implementation. Under the present conditions of CO2 allowances price of 80 /bbl for Base Case which decreases to 124 /bbl when CCS is implemented
Size matters: are we witnessing super-Eddington accretion in high-redshift black holes from JWST?
Full text linkObservations by the James Webb Space Telescope of the Universe at z≳4 have shown that massive black holes (MBHs) appear to be extremely overmassive compared to the local correlation for active galactic nuclei. In some cases, these objects might even reach half the stellar mass inferred for the galaxy. It has become a great challenging for theoretical models to understand how these objects formed and grew to these masses. Different ideas range from heavy seed to super-Eddington accretion phases. We take a different approach and try to infer how accurate these MBH mass estimates are and whether we really need to revise our physical models. By considering how the emerging spectrum (both the continuum and the broad lines) of an accreting MBH changes close to and above the Eddington limit, we infer a much larger uncertainty in the MBH mass estimates relative to that of local counterparts. The uncertainty is up to an order of magnitude. We also infer a potential preference for lower masses and higher accretion rates, which i) moves accreting MBHs closer to the local correlations, and ii) might indicate that we witness a widespread phase of very rapid accretion for the first time
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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