1,508 research outputs found
Geometric and topological aspects of quantum defects
No full textIn this thesis we present a detailed study of the dynamics of closed, twisted quantum vortices in Bose-Einstein condensates already published in two papers (Foresti & Ricca, 2019; Foresti & Ricca 2020). The study of how geometric and topological features affect the dynamics of vortices is very important for the description of interactions between vortices and for their reconnections. We generalize twist for quantum defects defying the concept of \emph{twist phase}. Then we find a modified Gross-Pitaevskii equation for the time evolution of a twisted vortex state. We discover that such a state is unstable and its evolution is dominated by a non-Hermitian Hamiltonian underlying the non-reversibility nature of the dynamics of twisted defects. Using the hydrodynamics description of Bose-Einsteins condensates and applying Kleinert's theory (Kleinert, 2018) to manage multi-valued phase fields, we find a complete set of integro-differential equations that quantitatively describe the dynamics of twisted vortices. Depending on the nature of the twist phase injected we propose two different stabilization mechanisms: if the twist phase is global then a secondary, central vortex is produced changing the linking number of the system. This mechanism can be seen as dominated by the presence of a topological phase and it is analyzed using Kleinert's theory. We thus prove theoretically what has been discovered numerically in (Zuccher & Ricca, 2018). In case of a local twist phase, no secondary vortex will form and the system produces unstable Kelvin waves with exponentially growing amplitude in regions where \Lapl\theta_{tw} > 0. We demonstrate that to minimize the energy and to stabilize the system the vortex coils producing non-zero writhe and extinguishing its twist phase. This mechanism can be seen as produced by the effect of a geometric phase on the system. We also propose an experiment to inject a twist phase on a quantum vortex in order to prove or disprove such stabilization mechanisms.
Bibliography.
Foresti, M. and Ricca, R. L. 2019
Defect production by pure twist induction as Aharonov-Bohm effect.
\textit{Phys. Rev. E} \textbf{100}, 023107.
M. Foresti \& R.L. Ricca,
Hydrodynamics of a quantum vortex in presence of twist.
\textit{J. Fluid Mech.} \textbf{904}, A25.
Kleinert, H. 2008
\textit{Multivalued Fields in Condensed Matter, Electromagnetism and Gravitation}.
World Scientific, Singapore.
Zuccher, S. and Ricca, R. L. 2018,
Twist effects in quantum vortices and phase defects.
\textit{Fluid Dyn. Res.} \textbf{50}, 1--13
Security and Trust Management : 11th International Workshop, STM 2015, Vienna, Austria, September 21-22, 2015, Proceedings
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Craspedochiton foresti
No full textCraspedochiton foresti (Leloup, 1965) Figs 7A–T, 9P–S Notoplax foresti Leloup 1965: 155, text figs 1–3, pls 1–2; Kaas 1979: 873; Kaas 1986: 20 [as synonym of Notoplax (Spongiochiton) productus]; Kaas 1989: 109 [as synonym of Notoplax (Spongiochiton) producta]; Kaas & Van Belle 1998: 75 [as synonym of Notoplax (Spongiochiton) producta]. Holotype, MNHN 5922 (disarticulated). Type locality: Príncipe Island, Caroço Isl., 2–8 m, “Calypso” st. 88, 26.vi.1956. Craspedochiton foresti: Strack 1996: 132 (in the discussion of Craspedochiton productus). Material examined: ST03: 2 specimens, slightly curled, maximum length 16 mm (Figs 9P–S) (BD 114 A); ST03: 1 specimen, disarticulated and coated for SEM analysis (MZB 49763); ST03: 1 tail valve, length 3.5 mm (BD 114 B); ST04: 1 specimen, length 4.5 mm (BD 114 C); ST07: 5 specimens, slightly curled, maximum length 29 mm (BD 114 D); ST07: 1 specimen in alcohol, curled, length 15 mm (BD 114 E); ST07: 1 specimen in alcohol, strongly curled, length 10 mm (NSMT-Mo 78636); PR04: 5 specimens, slightly curled, maximum length 18 mm (BD 114 F); PR06: 1 specimen in alcohol, slightly curled, length 16 mm (ZSM Mol-20040209). Distribution: São Tomè and Príncipe Islands. Comparison and remarks: A detailed description of this species is given by Leloup (1965), pertaining to the genus Notoplax H. Adams, 1861. We confirm the assignment of the species to Craspedochiton, already reported by Strack (1996), based mainly on the wide expansion of the anterior girdle. The status of the relationship between the genera Notoplax and Craspedochiton was discussed by Gowlett-Holmes (1991), who redefined the genus Notoplax, and considered it to be restricted to Australia and New Zealand (but see under Notoplax sp.). We give only some information additional to the original description, based on the SEM observations. The tegmentum is covered by well separated pustules of irregular shape, from roundish/oval to squarish/rectangular, some of them coalesced, giving the impression of orientation in a radiating pattern from the jugum in the intermediate valves (Figs 7D, 7H) and in the antemucronal area of the tail valve.The pustules are elevated and of cylindrical shape (Fig. 7H), with up to 15 or more (Fig. 7G) microaesthetes, disposed without any apparent order. The microaesthetes are also present in the interpustular space. The radula is probably not useful for distinguishing between species of Craspedochiton (H. Saito pers. comm.). The radula of C. foresti (Fig. 7Q–T) is similar to that of C. productus illustrated in Saito (2004: figs 5E, F). The radula of C. foresti has minute granulations on the upper surface of the cusps (Fig. 7S–T), but it remains unclear whether this character has specific relevance. Some other species in different genera also show such granulation, e.g. Craspedoplax variabilis (H. Adams, 1864), and Leptoplax curvisetosa (Leloup, 1960) (Saito 2004: figs 4C, 8F). Craspedochiton. foresti was considered a synonym of C. productus (Carpenter in Pilsbry, 1892) by Kaas (1979: 873), who stated: “I received from the M.N.H.N. the holotype of Notoplax foresti Leloup, 1965 … The specimen originates from Ile Príncipe, Gulf of Biafra. Though it was disarticulated it appears from the shell plates and the preparations of the girdle, that it does not substantially differ from C. productus and must be regarded as another synonym of the latter, which extends the range of distribution considerably”. Subsequent authors (e.g. Kaas 1986, 1989; Kaas & Van Belle 1998) followed this decision. We re-examined both species and became aware that C. productus can easily be separated from C. foresti, mainly on the basis of the structure of the valves: intermediate and tail valves more oval in C. foresti, but trapezoidal in C. productus; larger and triangular jugal area in C. productus, narrow and rectangular in C. foresti; pustules more dense and more irregularly arranged in C. productus; wider apophyses in C. productus; slit formula 5 / 1 / 4 in C. productus, 5 / 1 / 7 in C. foresti, with short and irregular slits. The valves of a specimen of C. productus from South Africa (NSMT-Mo 72867) are illustrated for comparison (Figs 8A–F). The differences from C. productus have already been discussed by Leloup (1965: 159): “ N. productus se caractérise par des valves intermediaries proportionnellement plus élevées, au sinus plus large, aux lames d’insertion plus obliques et à bords latéraux du tegmentum plus obliques”. Thiele (1909: 33) described another congener from the Atlantic coast of Africa: Craspedochiton liberiensis Thiele, 1909. He examined a single specimen, which was 7 mm in length. Comparison with a 4.5 mm long specimen from ST04 indicates that Thiele had another species in hand. C. liberiensis exhibits at this size a more or less regular pattern of nearly round granules, which are elongated in our small specimen. Thiele (1909, pl. 4, fig. 30) illustrated an intermediate valve in which the arrangement of the granules are directed towards the indistinct jugal area. This is contrary to the pattern on our examined juvenile. The specimen’s jugal area is clearly wedge-shaped, well demarcated from the pleural area, and the granules are directed outwards. Whether C. liberiensis is a valid species or, as concluded by Kaas and Van Belle (1998), a synonym of C. productus, needs to be clarified by comparing a number of valves and specimens that are of similar size. Such comparisons are beyond the scope of the present study.Published as part of Dell'Angelo, Bruno, Schwabe, Enrico, Gori, Sandro, Sosso, Maurizio & Bonfitto, Antonio, 2014, Chitons (Mollusca, Polyplacophora) from São Tomé and Príncipe Islands, pp. 171-200 in African Invertebrates 55 (2) on pages 188-190, DOI: 10.5281/zenodo.768089
Eucheilota foresti Goy 1979
No full textEucheilota foresti Goy, 1979 Remarks: the validity of the species and its record have to be checked. Distribution in South America: medusa—Atlantic Ocean, Argentina, at 35.84°S 56.32°W (Goy 1979; Genzano et al. 2008a).Published as part of M. P. Oliveira 1,16, S P. Miranda 2, *,, Es W. Mianzan 10,, Ro E. Migotto 11,, Ne B. Nascimento 2,11, Eli Nogueira Júnior 12,, Er Quiñones 13,, Izio Scarabino 14,, Tín Schiariti 10,, Io N. Stampar 15,, Tronolone 2, , Quíria B. & Onio C. Marques 2,11, 2016, Census of Cnidaria (Medusozoa) and Ctenophora from South American marine waters, pp. 1-256 in Zootaxa 4194 (1) on page 152, DOI: 10.11646/zootaxa.4194.1.
Optimization of PEM Fuel Cell Operation with High-purity Hydrogen Produced by a Membrane Reactor
No full textAn innovative micro‐cogeneration system (m‐CHP) based on membrane reformer and polymer electrolyte membrane fuel cell (PEMFC) is developed within the FluidCELL project. The purity of the hydrogen separated by the membrane reformer can decrease over time, due to membrane/sealing degradation, therefore a methanator is adopted to prevent CO poisoning of the fuel cell. This paper investigates the optimal control strategies of a polymer electrolyte membrane (PEM) fuel cell at different hydrogen purities by using a detailed 1D model, including the CO poisoning on the anode Pt‐Ru catalyst, and calibrated against experimental data. Simulation results show that the system is able to work also with low‐purity hydrogen thanks to the effectiveness of the methanator, the resistance to CO poisoning of the Pt‐Ru anode catalyst, the small voltage drop due to inert gases accumulation in the anode recirculation loop: at 0.3 A cm−2 as current density, the stack efficiency is always above 60% even when the membranes selectivity drops to 5 102
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