1,720,988 research outputs found
Impact of oxygen enrichment on ammonia combustion in spark-ignition engines under partial load conditions
No full textNH3-fueled internal combustion engines are a promising technology in the perspective of decarbonization. However, when NH3 is used as fuel, its high minimum ignition energy and slow flame propagation severely limit operating conditions, making its application in internal combustion engines challenging. The low reactivity of NH3/air mixtures results in high unburned NH3 emissions and low combustion efficiency. In this context, oxygen-assisted combustion is a promising technique for improving both the NH3/O2/N2 mixture reactivity and the performance of internal combustion engines. This study experimentally explores the feasibility of using NH3 in a fully premixed spark ignition single-cylinder engine with a compression ratio of 12:1 at 1000 rpm under both medium and low load conditions. The oxygen (O2) content in the intake gas mixture was varied to achieve stable combustion without any misfires. At medium load, i.e. with an indicated mean effective pressure of 5.8 bar, stable combustion was achieved with 22.4% vol. of O2 (relative to the O2/N2 mixture) and a significant reduction in ignition delay time and combustion duration was observed. 1-D numerical simulations of adiabatic, unstretched, freely propagating flat premixed flame were performed, using Ansys Chemkin-Pro 2024, implementing the chemical kinetic mechanism for NH3 oxidation (31 species and 203 reactions) proposed by Stagni et al. 2023, to investigate the influence of O2 additions on the laminar flame speed of NH3/O2/N2 mixtures under spark timing thermodynamic conditions. The addition of O2 enhances the laminar flame speed by 47% when O2 concentration is 26.8% in the O2/N2 mixture. Its role in the chain-branching reaction, O2 + H ↔ O + OH, is crucial for the production of O and OH radicals. Moreover, H-abstraction involving the OH radical (NH3 + OH ↔ NH2 + H2O) plays a key role in NH3 oxidation even when O2 is added to the mixture. Finally, to further investigate the role of NH3 combustion in cycle-to-cycle variability, the intake pressure was reduced to reach lower load, resulting in highly unstable combustion in the absence of O2 enrichment. As expected, the O2 enrichment stabilizes the combustion process. However, as the engine load decreases until 4.3 bar, the amount of O2 needed to achieve stable combustion increases significantly, up to 32.5% vol
Impact of Ozone Addition to Gasoline Surrogates Combustion in Spark Ignition Engine
No full textBased on the experimental results, a 3-D Computational Fluid Dynamics investigation is carried out to evaluate the influence of ozone on the combustion process in spark ignition engine fueled with gasoline/air mixtures. Ozone (O3) is a chemically reactive species capable of improving the laminar flame speed, reducing the ignition delay time, and stabilizing combustion variability. With the aim of proposing a 3-D numerical model to simulate combustion of fuel mixtures under ultra-lean conditions, two numerical correlations are proposed to reproduce the chemical properties of gasoline/air/ozone mixtures in terms of laminar flame speed. A chemical kinetic mechanism for Toluene Reference Fuel oxidation (iso-octane, n-heptane, toluene, 63/20/17% by mol.) modified with an ozone sub-mechanism is used to perform several 1-D numerical simulations. The laminar flame speed correlation estimates an enhancement of 3.4% at 600 K and 10 bar under ultra-lean condition (φ = 0.6). For the 3-D numerical simulations, the G-Equation model is used to reproduce the premixed combustion process in internal combustion engines. The results suggest that the numerical correlations can predict the combustion properties of gasoline/air mixtures without and with ozone addition. The presence of ozone traduces in a higher laminar flame speed, leading to an increase in the in-cylinder pressure peak and the rate of fuel consumption. Furthermore, the numerical analysis reveals that the greatest improvement is observed for fluid regions within the cylinder characterized by low turbulent flame speed
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
PORE NETWORK MODEL TO PREDICT FLOW PROCESSES IN UNSATURATED CALCARENITES
No full textThe knowledge of infiltration mechanisms in vadose zone is the key to forecast the components of the hydrologic cycle such as run-off generation and aquifer recharge. Besides, slope stability, settlements and bearing capacity of foundations, and rock weathering are issues in which infiltration processes play an important role. In Apulia and Basilicata (Southern Italy) representative calcarenites outcrops are exposed along both the coastline and internal areas. These calcarenites belong to the Calcarenite di Gravina Fm. (Middle Pliocene-Lower Pleistocene) and are mainly constituted by fine- medium- and coarse-grained packstones and grainstones. The whole geological formation represents an important hydrogeologic unit which controls groundwater recharge and transport of contaminants within a complex, multilayered system comprising a wide and deep aquifer hosted into the Mesozoic basement. A smart analytical and numerical tool based on the pore bundle model conceptualization and the Richards' equation was developed to predict infiltration and retention mechanism of calcarenites. This work investigated the impact of bimodal poresize distribution on the unsaturated flow from dry to wet conditions obtained through conventional and unconventional laboratory tests and petrophysical characterization, also completed with mercury intrusion porosimetry and image analysis. Laboratory experiments were carried out on medium-grained grainstones sampled at Canosa di Puglia (Tufarelle locality), by means of infiltration tests conducted starting from a different degree of saturation and varying the inlet flow rate. The experimental data were compared with the pore network model prediction. For the rock samples used, the study disclosed that macroporosity mainly affects the propagation of the wetting front and infiltration rate. Thus, the wetting front develops principally during the infiltration of water through the interconnected macropores following the pathways having minimum flow resistance with a gravity driven flow velocity higher than the diffusive flow though micropores
Exploring Maternal Diet-Epigenetic-Gut Microbiome Crosstalk as an Intervention Strategy to Counter Early Obesity Programming
Full text linkAlterations in a mother's metabolism and endocrine system, due to unbalanced nutrition, may increase the risk of both metabolic and non-metabolic disorders in the offspring's childhood and adulthood. The risk of obesity in the offspring can be determined by the interplay between maternal nutrition and lifestyle, intrauterine environment, epigenetic modifications, and early postnatal factors. Several studies have indicated that the fetal bowel begins to colonize before birth and that, during birth and nursing, the gut microbiota continues to change. The mother's gut microbiota is primarily transferred to the fetus through maternal nutrition and the environment. In this way, it is able to impact the establishment of the early fetal and neonatal microbiome, resulting in epigenetic signatures that can possibly predispose the offspring to the development of obesity in later life. However, antioxidants and exercise in the mother have been shown to improve the offspring's metabolism, with improvements in leptin, triglycerides, adiponectin, and insulin resistance, as well as in the fetal birth weight through epigenetic mechanisms. Therefore, in this extensive literature review, we aimed to investigate the relationship between maternal diet, epigenetics, and gut microbiota in order to expand on current knowledge and identify novel potential preventative strategies for lowering the risk of obesity in children and adults
Biological control agents as tools against some emerging bacterial plant diseases in Italy: a concrete perspective?
No full textThis work was carried out to confirm and/or evaluate the efficacy of three Pseudomonas spp. strains
against fire blight (Erwinia amylovora), southern bacterial wilt of tomato (Ralstonia solanacearum),
bacterial spot/canker of stone fruits (Xanthomonas arboricola pv. pruni) and grapevine crown gall
(Agrobacterium vitis). In the laboratory, there was a trend towards a higher colonisation of apple and
pear flowers when Na-alginate (0.5%) was added to suspensions of freeze-dried cells of wild-types and
rifampicin-resistant mutants of IPV.-BO G19 (P. putida) and IPV.-BO 4027C (a non-fluorescent
Pseudomonas sp.) strains; E. amylovora populations on apple flowers were significantly reduced by
strain IPV.-BO 4027C. In a field experiment, performed on actively growing shoots of pear scions ‘Abbé
Fétel’ during Spring-Summer 2005, different treatments were also tested, including copper compounds
the resistance inducers prohexadione-Ca (Regalis) and acibenzolar-S-methyl (Bion), and Serenade and
BS-F4 (both based on Bacillus subtilis) etc. The strain IPV.-BO G19 plus Na-alginate was the most
effective in reducing shoot blight incidence by 65% six weeks after wound inoculation with E.
amylovora. A virulent R. solanacearum bv. 2, race 3 strain was inhibited by both these antagonists in
vitro. When the pathogen was inoculated 48 h after their application (approx. 108 cfu/ml) to the root
apparatus of tomato plants grown in a climatic chamber, bacterial wilt progression rate was clearly
reduced; in particular, the strain IPV.-BO G19 was able to delay symptom expression and to reduce
disease incidence by 100% and 37%, 9 and 21 days after inoculation, respectively.
Under glasshouse conditions, BS-F4, Bion and IPV.-BO G19 reduced relative incidence of grapevine
crown gall by 58%, 54% and 48%, respectively. The IPV.-BO G19 strain was also effective against X.
arboricola pv. pruni: when sprayed on plum fruitlets it reduced disease incidence by 90% eight days
after experimental inoculation with the pathogen
Indagine sugli effetti della presenza di Halyomorpha halys nel processo di vinificazione delle varietà Pinot Grigio, Ribolla Gialla e Merlot coltivate in Friuli Venezia Giulia
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