Electron inertia and quasi-neutrality in the Weibel instability

While electron kinetic effects are well known to be of fundamental importance in several situations, the electron mean-flow inertia is often neglected when lengthscales below the electron skin depth become irrelevant. This has led to the formulation of different reduced models, where electron inertia terms are discarded while retaining some or all kinetic effects. Upon considering general full-orbit particle trajectories, this paper compares the dispersion relations emerging from such models in the case of the Weibel instability. As a result, the question of how lengthscales below the electron skin depth can be neglected in a kinetic treatment emerges as an unsolved problem, since all current theories suffer from drawbacks of different nature. Alternatively, we discuss fully kinetic theories that remove all these drawbacks by restricting to frequencies well below the plasma frequency of both ions and electrons. By giving up on the lengthscale restrictions appearing in previous works, these models are obtained by assuming quasi-neutrality in the full Maxwell-Vlasov system.Comment: 25pages; 7 figures. Submitted to J. Plasma Phys. Special issue contribution, on the occasion of the Vlasovia 2016 conferenc

The dissipation of solar wind turbulent fluctuations at electron scales

We present two-dimensional fully-kinetic Particle-in-Cell simulations of decaying electromagnetic fluctuations. The computational box is such that wavelengths ranging from electron to ion gyroradii are resolved. The parameters used are realistic for the solar wind, and the ion to electron mass ratio is physical. The understanding of the dissipation of turbulent fluctuations at small scales is thought to be a crucial mechanism for solar wind acceleration and coronal heating. The computational results suggest that a power law cascade of magnetic fluctuations could be sustained up to scales of the electron Larmor radius and smaller. We analyse the simulation results in the light of the Vlasov linear theory, and we comment on the particle heating. The dispersion curves of lightly damped modes in this regime suggest that a linear mechanism could be responsible for the observed steepening of power spectra at electron scales, but a straightforward identification of turbulent fluctuations as an ensemble of linear modes is not possibleComment: to appear in Astrophysical Journa

Transient growth in stable collisionless plasma

The first kinetic study of transient growth for a collisionless homogeneous Maxwellian plasma in a uniform magnetic field is presented. A system which is linearly stable may display transient growth if the linear operator describing its evolution is non-normal, so that its eigenvectors are non-orthogonal. In order to include plasma kinetic effects a Landau fluid model is employed. The linear operator of the model is shown to be non-normal and the results suggest that the nonnormality of a collisionless plasma is intrinsically related to its kinetic nature, with the transient growth being more accentuated for smaller scales and higher plasma beta. The results based on linear spectral theory have been confirmed with nonlinear simulations.Comment: accepted as a Letter in Physics of Plasma

Impact of atrial fibrillation on the cardiovascular system through a lumped-parameter approach

Atrial fibrillation (AF) is the most common arrhythmia affecting millions of people in the Western countries and, due to the widespread impact on the population and its medical relevance, is largely investigated in both clinical and bioengineering sciences. However, some important feedback mechanisms are still not clearly established. The present study aims at understanding the global response of the cardiovascular system during paroxysmal AF through a lumped-parameter approach, which is here performed paying particular attention to the stochastic modeling of the irregular heartbeats and the reduced contractility of the heart. AF can be here analyzed by means of a wide number of hemodynamic parameters and avoiding the presence of other pathologies, which usually accompany AF. Reduced cardiac output with correlated drop of ejection fraction and decreased amount of energy converted to work by the heart during blood pumping, as well as higher left atrial volumes and pressures are some of the most representative results aligned with the existing clinical literature and here emerging during acute AF. The present modeling, providing new insights on cardiovascular variables which are difficult to measure and rarely reported in literature, turns out to be an efficient and powerful tool for a deeper comprehension and prediction of the arrythmia impact on the whole cardiovascular system.Comment: 16 pages, 8 figures, 2 tables, Medical & Biological Engineering & Computing, 2014, Print ISSN: 0140-0118, Online ISSN: 1741-044

Spanish ‘Plastic’ Architecture. A critical reading and design approach

[EN] The following critical text proposes a series of notes and reflections on the reinforced concrete architecture, not on the material itself. Since its invention, concrete has combined two potentialities, deriving from the two materials of which it is composed: the ‘elastic’ potential, which has been developed and has reached a consolidated form and tradition, and the ‘plastic’ one. The last one has been little experienced at the beginning and, in the course of recent history of architecture, has found space in architectural criticism in the meaning of "expressive", "brutalist", "sculptural", ending up to influence 'superficially' (related to the surface) of architecture. The 'plastic' architecture, instead, is three-dimensional and unifies the construction and spatial qualification in a single design gesture. This critical approach not only allows reconsidering the history of modern/contemporary architecture starting from the necessary collaboration between space and construction that unifies the final judgment on the works, but allows influencing the project, adhering to a formative process of those geographic-cultural areas that possess those certain characters, the masonry one. The Spanish "plastic" architecture is, in that sense, a clear example: in many buildings this "masonry" character is clearly identified, due to the architectural exploitation of the reinforced concrete plastic potential.Camporeale, A. (2018). Spanish ‘Plastic’ Architecture. A critical reading and design approach. En CIAB 8. VIII Congreso Internacional de arquitectura blanca. Editorial Universitat Politècnica de València. 292-301. https://doi.org/10.4995/CIAB8.2018.7594OCS29230

Process and plastic transformation. Contemporary architecture in mediterranean historical centers

Ponència presentada a: Session 5: Del diseño a la construcción. Sostenibilidad (temas de diseño ambiental) / From design to construction. Sustainability (environmental design issues