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Numerical and experimental investigation of thermal regimes of thermionic cathodes of arc plasma torches
Publication . Cunha, M. D.; Sargsyan, M. A.; Gadzhiev, M. Kh; Tereshonok, D. V .; Benilov, M. S .; Benilov, Mikhail; Cunha, Mário
The modelling method based on decoupling the simulation of the cathodic part of the arc (the cathode and the near-cathode non-equilibrium plasma layer) from the simulation of the arc on the whole has been extended to cathodes of arc plasma torches, consisting of an insert with a conical tip, made of pure or doped tungsten, and a surrounding water-cooled copper holder. The method was validated by comparison with the experiment, performed on a 200 A DC arc in atmospheric-pressure argon. Standard work function of polycrystalline tungsten of 4.54 eV was used for modelling of pure-tungsten insert and a good agreement with the experiment was found with respect to both the insert tip shape and the temperature distribution in the tip, recorded in the stable operation mode. There are no unambiguous data on the work function for arc cathodes made of doped tungsten, although in situ measurements of the effective work function of cathodes of high-pressure arc discharges provide useful hints. On the other hand, the experiments reported in this work show that the tip temperatures of inserts made of tungsten doped with 1.5% of thorium, or lanthanum, or yttrium, recorded during the stable-mode operation at the arc current of 200 A, vary in a rather narrow range 3100–3200 K. This suggests that the work functions of doped tungsten inserts, operated in the stable mode, are close to each other as well. Indeed, the results of modelling with the same value of the work function of 3 eV give a reasonably good agreement with the experiment in all three cases.
Compound Poisson processes: potentials, Green measures and random times
Publication . Yuri Kondratiev; José L. da Silva; Luís da Silva, José
In this paper we study the existence of Green measures for Markov processes with a nonlocal jump generator. The non-singular jump kernel has no second moment and satisfies a suitable condition on its Fourier transform. We also study the same problem for certain classes of random time changes Markov processes with jump generator.
Microplastic ingestion and plastic additive detection in pelagic squid and fish: implications for bioindicators and plastic tracers in open oceanic food webs
Publication . Sambolino, Annalisa; Iniguez, Eva; Herrera, Inma; Kaufmann, Manfred ; Dinis, Ana; Cordeiro, Nereida ; Sambolino, Annalisa; Iñiguez Santamaría, Eva; Kaufmann, Manfred; cordeiro, nereida
The ubiquitous presence of microplastics (MPs) in the ocean represents a potential threat to marine organisms, with poorly understood long-term adverse effects, including exposure to plastic additives. The present study investigated the ingestion of MPs in two epipelagic fish species (Trachurus picturatus and Scomber colias) and three pelagic squid spe cies (Loligo vulgaris, Ommastrephes caroli and Sthenoteuthis pteropus) from an open oceanic region of the Northeast Atlan tic. Seven phthalate esters (PAEs) were also analysed in the organisms' tissue, and the potential correlation between PAEs concentrations and ingested MPs was investigated. Seventy-two fish and 20 squid specimens were collected and analysed. MPs were found in the digestive tract of all species and in the squid species' gills and ink sacs. The highest occurrence of MPs was in the stomach of S. colias (85 %) and the lowest in the stomach and ink sac of O. caroli and L. vulgaris (12 %). Most of the particles identified (>90 %) were fibres. Among all the ecological and biological factors considered (dietary preferences, season, body size, total weight, liver weight, hepatosomatic index and gastrosomatic index), only gastrosomatic index (GSI) and season were significant predictors of MPs ingestion in fish species, with a greater likelihood of ingestion in the cold season and in specimens with higher GSI values (i.e. higher feeding inten sity). Four PAEs (DEP, DIBP, BBP, DEHP) were detected in all the species analysed, with average ∑PAEs concentrations ranging between 10.31 and 30.86 ng/g (wet weight). DIBP was positively correlated with ingested MPs, suggesting this compound might represent a “plastic tracer”. This study looks into the problem of MPs ingestion for pelagic species in an open oceanic region, highlighting the most suitable bioindicators and providing essential insights into the factors that may influence ingestion rates. Additionally, the detection of PAEs in all species indicates the need for further re search on the contamination sources, the effects of these chemicals on marine organisms, and the potential risks to human health through seafood consumption.
Relevance, recovery and recuperation: a prelude to ring withdrawal
Publication . Fermé, Eduardo; Garapa, Marco; Abhaya Nayak; Reis, Maurício D. L.; Reis, Maurício
In this paper, we introduce recuperative withdrawals, belief change operators that satisfy recuperation, a postulate weaker than recovery, all the AGM postulates for contraction except recovery and another postulate which is a slightly stronger condition than conjunctive inclusion. Furthermore, we present a constructive definition for a class of operators —named ring withdrawals— which are such that the outcome of a ring withdrawal of a belief set 𝐊 by a sentence 𝛼 is obtained by adding to the set of most plausible models ‖𝐊‖ all the worlds which are as close to ‖𝐊‖ as its closest ¬𝛼-worlds. Ring withdrawals satisfy the Lindström and Rabinowicz’s interpolation thesis. We show that the classes of recuperative withdrawals and of ring withdrawals are identical. Additionally we show that the class of ring withdrawals is not contained in and does not contain the class of AGM contractions or the class of severe withdrawals. Finally we present methods for defining an operator of ring withdrawal by means of a severe withdrawal operator and by means of an AGM contraction operator, and vice-versa.
On the logic of theory change iteration of KM-update
Publication . Fermé, Eduardo; Gonçalves, Sara
We present a model for iterating the Katsuno and Mendelzon Update (KM-Update) process, which is inspired by models developed for iterated belief revision in the AGM framework. Our model adapts the postulates of belief revision proposed by Darwiche and Pearl, including the independence postulate. We characterize two classes of iterated update operators based on natural and lexicographic revision. The semantics of our models are characterized using the framework of possible worlds.