Electron and Ion Heating during Magnetic Reconnection in Weakly Collisional Plasmas

Gyrokinetic simulations of magnetic reconnection are presented to investigate plasma heating for strongly magnetized, weakly collisional plasmas. For a low plasma beta case, parallel and perpendicular phase mixing strongly enhance energy dissipation yielding electron heating. Heating occurs for a long time period after a dynamical process of magnetic reconnection ended. For a higher beta case, the ratio of ion to electron dissipation rate increases, suggesting that ion heating (via phase-mixing) may become an important dissipation channel in high beta plasmas.Comment: 9 pages, 3 figures, accepted for publication in JPSJ Suppl. [Proceedings of the 12th Asia Pacific Physics Conference

Magnetohydrodynamic turbulence mediated by reconnection

Magnetic field fluctuations in MHD turbulence can be viewed as current sheets that are progressively more anisotropic at smaller scales. As suggested by Loureiro & Boldyrev (2017) and Mallet et al (2017), below a certain critical thickness $\lambda_c$ such current sheets become tearing-unstable. We propose that the tearing instability changes the effective alignment of the magnetic field lines in such a way as to balance the eddy turnover rate at all scales smaller than $\lambda_c$. As a result, turbulent fluctuations become progressively less anisotropic at smaller scales, with the alignment angle increasing as $\theta \sim (\lambda/\lambda_*)^{-4/5+\beta}$, where $\lambda_*\sim L_0 S_0^{-3/4}$ is the resistive dissipation scale. Here $L_0$ is the outer scale of the turbulence, $S_0$ is the corresponding Lundquist number, and {$0\leq \beta <4/5$} is a parameter. The resulting Fourier energy spectrum is $E(k_\perp)\propto k_\perp^{-11/5+2\beta/3}$, where $k_\perp$ is the wavenumber normal to the local mean magnetic field, and the critical scale is $\lambda_c\sim S_L^{-(4-5\beta)/(7-{20\beta/3})}$. The simplest model corresponds to $\beta=0$, in which case the predicted scaling formally agrees with one of the solutions obtained in (Mallet et al 2017) from a discrete hierarchical model of abruptly collapsing current sheets, an approach different and complementary to ours. We also show that the reconnection-mediated interval is non-universal with respect to the dissipation mechanism. Hyper-resistivity of the form ${\tilde \eta}k^{2+2s}$ leads (in the simplest case of $\beta=0$) to the different transition scale $\lambda_c\sim L_0{\tilde S}_0^{-4/(7+9s)}$ and the energy spectrum $E(k_\perp)\propto k_\perp^{-(11+9s)/(5+3s)}$, where ${\tilde S}_0$ is the corresponding hyper-resistive Lundquist number.Comment: submitted for publicatio

Role of reconnection in inertial kinetic-Alfvén turbulence

In a weakly collisional, low-electron-beta plasma, large-scale Alfvén turbulence transforms into inertial kinetic-Alfvén turbulence at scales smaller than the ion microscale (gyroscale or inertial scale). We propose that at such kinetic scales, the nonlinear dynamics tends to organize turbulent eddies into thin current sheets, consistent with the existence of two conserved integrals of the ideal equations, energy and helicity. The formation of strongly anisotropic structures is arrested by the tearing instability that sets a critical aspect ratio of the eddies at each scale a in the plane perpendicular to the guide field. This aspect ratio is defined by the balance of the eddy turnover rate and the tearing rate, and varies from (d [subscript]e / a)¹ / ² to d [subscript]e / a depending on the assumed profile of the current sheets. The energy spectrum of the resulting turbulence varies from k -⁸ / ³ to k -³ , and the corresponding spectral anisotropy with respect to the strong background magnetic field from [mathematical equation; see source] to [mathematical equation; see source].NSF (Grant no. NSF PHY-1707272)NASA (Grant no. NASA 80NSSC18K0646)DOE (Grant no. DE-SC0018266)NSF CAREER (Award no. 1654168)NSF-DOE Partnership in Basic Plasma Science and Engineering (Award no. DE-SC0016215

Magnetic Reconnection Onset via Disruption of a Forming Current Sheet by the Tearing Instability

The recent realization that Sweet-Parker current sheets are violently unstable to the secondary tearing (plasmoid) instability implies that such current sheets cannot occur in real systems. This suggests that, in order to understand the onset of magnetic reconnection, one needs to consider the growth of the tearing instability in a current layer as it is being formed. Such an analysis is performed here in the context of nonlinear resistive MHD for a generic time-dependent equilibrium representing a gradually forming current sheet. It is shown that two onset regimes, single-island and multi-island, are possible, depending on the rate of current sheet formation. A simple model is used to compute the criterion for transition between these two regimes, as well as the reconnection onset time and the current sheet parameters at that moment. For typical solar corona parameters this model yields results consistent with observations.Comment: 5 pages, no figures; accepted for publication in Physical Review Letter

Operant EEG-based BMI: Learning and consolidating device control with brain activity

"Whether you are reading this thesis on paper or screen, it is easy to take for granted all the highly specialized movements you are doing at this very moment just to go through each page. Just to turn a page, you have to reach for and grasp it, turn it and let go at the precise moment not to rip it.(...)

Visualyzart Project – The role in education

The VisualYzARt project intends to develop research on mobile platforms, web and social scenarios in order to bring augmented reality and natural interaction for the general public, aiming to study and validate the adequacy of YVision platform in various fields of activity such as digital arts, design, education, culture and leisure. The VisualYzARt project members analysed the components available in YVision platform and are defining new ones that allow the creation of applications to a chosen activity, effectively adding a new language to the domain YVision. In this paper we will present the role of the InstitutoPolitécnico de Santarém which falls into the field of education.VisualYzART is funded by QREN – Sistema de Incentivos à Investigação e Desenvolvimento Tecnológico (SI I&DT), Project n. º 23201 - VisualYzARt (from January 2013 to December 2014). Partners: YDreams Portugal; Instituto Politécnico de Santarém - Gabinete de e-Learning; Universidade de Coimbra - Centro de Informática e Sistemas; Instituto Politécnico de Leiria - Centro de Investigação em Informática e Comunicações; Universidade Católica do Porto - Centro de Investigação em Ciência e Tecnologia das Artes.info:eu-repo/semantics/publishedVersio

Photography, Land-Cover and Land-Use changes, and tourism urbanization: A narrative focused on Hotel do Garbe, Armação de Pêra, Algarve, Portugal

This article is focused on the use of photography to characterize land-cover and land-use changes in a 7.59 km2 study area centered on Hotel do Garbe, in the village of Armação de Pêra, Algarve, Portugal. Orthorectified vertical aerial, oblique aerial and ground-level photographs were the main data sources required to carry out the analysis. In a preliminary approach, a conventional research design was adopted. Based on the available orthorectified vertical aerial photographs, a sixty-year time series, with four homogeneously distributed steps (1958, 1978, 1997 and 2018), was constructed, and maps were produced to support the description of the changes that have taken place. To deepen the analysis, photographs from fourteen picture postcards were recognized as a useful source of information, and the authors of these photographs were considered “involuntary or accidental photo-geographers” whose work was relevant to feed a case study in which human geography and landscape biography sciences are the main narrative axes. The final result proved to be richer than the interpretation only based on the orthorectified vertical aerial photographs, and the importance of combining photographs taken from different points of view, with different aims and for different recipients is highlighted.info:eu-repo/semantics/publishedVersio