3D simulations of vertical displacement events in tokamaks: A benchmark of M3D-C1^1, NIMROD and JOREK

In recent years, the nonlinear 3D magnetohydrodynamic codes JOREK, M3D-C$^1$ and NIMROD developed the capability of modelling realistic 3D vertical displacement events (VDEs) including resistive walls. In this paper, a comprehensive 3D VDE benchmark is presented between these state of the art codes. The simulated case is based on an experimental NSTX plasma but with a simplified rectangular wall. In spite of pronounced differences between physics models and numerical methods, the comparison shows very good agreement in the relevant quantities used to characterize disruptions such as the 3D wall forces and energy decay. This benchmark does not only bring confidence regarding the use of the mentioned codes for disruption studies, but also shows differences with respect to the used models (e.g. reduced versus full MHD models). The simulations show important 3D features for a NSTX plasma such as the self-consistent evolution of the halo current and the origin of the wall forces. In contrast to other reduced MHD models based on an ordering in the aspect ratio, the ansatz based JOREK reduced MHD model allows capturing the 3D dynamics even in the spherical tokamak limit considered here

Axisymmetric simulations of vertical displacement events in tokamaks: A benchmark of M3D-C1, NIMROD and JOREK

A benchmark exercise for the modeling of vertical displacement events(VDEs) is presented and applied to the 3D nonlinear magneto-hydrodynamic codesM3D-C1, JOREK and NIMROD. The simulations are based on a vertically unstableNSTX equilibrium enclosed by an axisymmetric resistive wall with rectangular crosssection. A linear dependence of the linear VDE growth rates on the resistivity ofthe wall is recovered for sufficiently large wall conductivity and small temperatures inthe open field line region. The benchmark results show good agreement between theVDE growth rates obtained from linear NIMROD and M3D-C1simulations as wellas from the linear phase of axisymmetric nonlinear JOREK, NIMROD and M3D-C1simulations. Axisymmetric nonlinear simulations of a full VDE performed with thethree codes are compared and excellent agreement is found regarding plasma locationand plasma currents as well as eddy and halo currents in the wall.</p

Visible ozone-like injury, defoliation, and mortality in two Pinus uncinata stands in the Catalan Pyrenees (NE Spain)

Ozone concentrations in the Pyrenees have exceeded the thresholds for forest protection since 1994. We surveyed the severity of visible O₃ injuries, crown defoliation, and tree mortality of Pinus uncinata, the dominant species in subalpine forests in this mountain range, along two altitudinal and O₃ gradients in the central Catalan Pyrenees and analysed their relationships with the local environmental conditions. The severity of visible O₃ injuries increased with increasing mean annual [O₃] when summer water availability was high (summer precipitation/potential evapotranspiration above 0.96), whereas higher [O₃] did not produce more visible injuries during drier conditions. Mean crown defoliation and tree mortality ranged between 20.4-66.4 and 0.6-29.6 %, respectively, depending on the site. Both were positively correlated with the accumulated O₃ exposure during the last 5 years and with variables associated with soil-water availability, which favours greater O₃ uptake by increasing stomatal conductance. The results indicate that O₃ contributed to the crown defoliation and tree mortality, although further research is clearly warranted to determine the contributions of the multiple stress factors to crown defoliation and mortality in P. uncinata stands in the Catalan Pyrenees

Analysis of the intraspinal calcium dynamics and its implications on the plasticity of spiking neurons

The influx of calcium ions into the dendritic spines through the N-metyl-D-aspartate (NMDA) channels is believed to be the primary trigger for various forms of synaptic plasticity. In this paper, the authors calculate analytically the mean values of the calcium transients elicited by a spiking neuron undergoing a simple model of ionic currents and back-propagating action potentials. The relative variability of these transients, due to the stochastic nature of synaptic transmission, is further considered using a simple Markov model of NMDA receptos. One finds that both the mean value and the variability depend on the timing between pre- and postsynaptic action-potentials. These results could have implications on the expected form of synaptic-plasticity curve and can form a basis for a unified theory of spike time-dependent, and rate based plasticity.Comment: 14 pages, 10 figures. A few changes in section IV and addition of a new figur

Microscopic Calculation of the Constitutive Relations

Homogenization theory is used to calculate the macroscopic dielectric constant from the quantum microscopic dielectric function in a periodic medium. The method can be used to calculate any macroscopic constitutive relation, but it is illustrated here for the case of electrodynamics of matter. The so-called cell problem of homogenization theory is solved and an explicit expression is given for the macroscopic dielectric constant in a form akin to the Clausius-Mossotti or Lorentz-Lorenz relation. The validity of this expression is checked by showing that the macroscopic dielectric constant is causal and has the expected symmetry properties, and that the average of the microscopic energy density is the macroscopic one. Finally, the general expression is applied to Bloch eigenstates. Finally, the corresponding many-body problem is briefly discussed.Comment: 14 pages, 2 figure

La comprensión en el proceso de resolución de los problemas de planteo algebraico

RESUMEN La educación matemática plantea nuevas necesidades para el presente siglo; poniendo énfasis en la formación de estudiantes competentes en la resolución de problemas. La resolución de problemas ha sido un tema ampliamente debatido a lo largo de la historia, al menos como habilidad o destreza, entre otras conceptualizaciones; sin embargo, poca atención se le ha prestado a los factores que intervienen en su proceso de comprensión. El trabajo que se presenta pretende brindar algunas consideraciones teóricas sobre la comprensión y finalmente trata de contextualizarse a la problemática objeto de atención con el objetivo de promulgar un espacio al debate con el fin de que sea enriquecido con la experiencia de los profesores. Los resultados obtenidos con la aplicación de métodos y técnicas de investigación, permitieron confirmar que ese desempeño actualmente se expresa a un nivel insatisfactorio de actuación. Se concluyó buscar formas más efectivas para su logro en los estudiantes. Palabras clave: comprensión, comprensión de la resolución de problemas de planteo algebraico. ABSTRACT Mathematics education poses new needs for the present century; with emphasis on the training of competent students in solving problems. Problem solving has been a theme widely debated throughout history, at least as skill or dexterity, among other conceptualizations; however, little attention has been paid to the factors involved in its comprehension process. The work that is presented intends to offer some considerations some theoretical considerations on the understanding and finally tries to contextualize to the problematic object of attention with the objective of promulgate a space to the debate in order that it is enriched with the experience of the professors. The results obtained with the application of investigative methods and techniques allowed to confirm that, at the moment, this performing is expressed at an unsatisfactory level. The results concluded to look for more effective forms for its achievement in the students. Key word: understanding, understanding of algebraic problem solving

Increased plasma levels of NT-proBNP, Troponin T and GDF-15 are driven by persistent AF and associated comorbidities:Data from the AF-RISK study

Atrial fibrillation (AF) is a progressive disease, and early recognition and management may reflect an important strategy to reduce its disease burden. In this study, we evaluated plasma levels of three biomarkers - N-terminal pro-brain natriuretic peptide (NTproBNP), Troponin-T, and growth differentiation factor-15 (GDF-15) - in patients with paroxysmal AF (pAF) (≤7 days of continuous AF, n = 323) and persistent AF ((AF duration &gt; 7 days and &lt; 1 year, n = 84) using patients from AF RISK study (NCT01510210). In this AF-RISK sub-study, patients with persistent AF experienced more symptoms (higher European Heart Rhythm Association class (p &lt; 0.001)), had a higher comorbidity burden (p &lt; 0.001), and had more unfavorable echocardiographic parameters (p &lt; 0.001). All three biomarker levels were significantly higher in patients with persistent AF as compared to those with pAF (p &lt; 0.001). Multivariate linear regression analyses showed that age (beta-coefficient for NTproBNP: 0.21; GDF-15: 0.41; Troponin-T: 0.23) and CHA2DS2-VASc (beta-coefficient for NTproBNP: 0.20; GDF-15: 0.25; Troponin-T: 0.27) were determinants of all three biomarkers, and that persistent AF determined NTproBNP (beta-coefficient: 0.34), but not Troponin-T and GDF-15. More detailed analysis of CHA2DS2-VASc score showed that for all three biomarkers age, coronary artery disease and heart failure were determinants of plasma biomarkers levels, whereas sex determined NTproBNP and Troponin T, and hypertension determined NTproBNP and GDF15. Overall, this study therefore suggests that in AF, Troponin T and GDF15, and especially NTproBNP could be used to detect those patients with more persistent form of AF that may warrant more aggressive treatment of AF and concomitant comorbidities. Future studies, however, are essential to evaluate if more aggressive AF treatment and risk factor management will reduce disease progression and holds a novel therapeutic intervention to reduce the burden of AF.</p