Fecha de publicación: 2012.
Context. A large amount of magnetized plasma is frequently ejected from the Sun as coronal mass ejections (CMEs). Some of these ejections are detected in the solar wind as magnetic clouds (MCs) that have flux rope signatures. Aims. Magnetic clouds are structures that typically expand in the inner heliosphere. We derive the expansion properties of MCs in the outer heliosphere from one to five astronomical units to compare them with those in the inner heliosphere. Methods. We analyze MCs observed by the Ulysses spacecraft using in situ magnetic field and plasma measurements. The MC boundaries are defined in the MC frame after defining the MC axis with a minimum variance method applied only to the flux rope structure. As in the inner heliosphere, a large fraction of the velocity profile within MCs is close to a linear function of time. This is indicative of a self-similar expansion and a MC size that locally follows a power-law of the solar distance with an exponent called ζ. We derive the value of ζ from the in situ velocity data. Results. We analyze separately the non-perturbed MCs (cases showing a linear velocity profile almost for the full event), and perturbed MCs (cases showing a strongly distorted velocity profile). We find that non-perturbed MCs expand with a similar non-dimensional expansion rate (ζ = 1.05 ± 0.34), i.e. slightly faster than at the solar distance and in the inner heliosphere (ζ = 0.91 ± 0.23). The subset of perturbed MCs expands, as in the inner heliosphere, at a significantly lower rate and with a larger dispersion (ζ = 0.28 ± 0.52) as expected from the temporal evolution found in numerical simulations. This local measure of the expansion also agrees with the distribution with distance of MC size, mean magnetic field, and plasma parameters. The MCs interacting with a strong field region, e.g. another MC, have the most variable expansion rate (ranging from compression to over-expansion). © 2012 ESO.
Afiliación de los autores: Gulisano, A.M. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.
Afiliación de los autores: Dasso, S. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.
Palabras claves: Interplanetary medium; Magnetic fields; Magnetohydrodynamics (MHD); Solar wind; Sun: coronal mass ejections (CMEs); Astronomical units; Coronal mass ejection; Expansion properties; Expansion rate; Flux ropes; Heliospheres; In-situ; Interplanetary medium; Linear functions; Linear velocity; Magnetic clouds; Magnetized plasmas; Mean magnetic field; Minimum variance; Outer heliosphere; Plasma measurement; Plasma parameter; Power-law; Self-similar; Strong field; Sun: coronal mass ejection; Temporal evolution; Ulysses spacecraft; Velocity profiles; Magnetic fields; Magnetohydrodynamics; Magnetoplasma; Rope; Solar system; Solar wind; Velocity.
Repositorio: Biblioteca Digital (UBA-FCEN). Universidad Nacional de Buenos Aires. Facultad de Ciencias Exactas y Naturales
Fecha de publicación: 2015.
Objective The hypothesis of a progressive nature of neuropsychological deficits in bipolar disorders is often accepted as an axiom by many clinicians and researchers in the field. However, contradictory pieces of data and a number of methodological concerns put it under debate. Method We reviewed findings from three different approaches to the study of the trajectory of cognitive features in bipolar disorders: longitudinal evaluation of cognition in affected subjects, cross-sectional neuropsychological assessment of patients belonging to different age groups, and exploration of the risk of dementia in bipolar subjects. Results An increased risk of developing dementia was found in bipolar subjects. However, evidence from cross-sectional studies did not show more severe cognitive deficits in patients with longer illness duration. Furthermore, longitudinal studies revealed that bipolar subjects' cognitive performance did not change between different points in time. Conclusions After a thorough discussion of these findings and the limitations of the different approaches, we argue that, at present, there is no consistent evidence supporting that bipolar disorders, as a group, have a progressively deteriorating course of cognitive functions. Furthermore, we highlight the possible influence of psychotropic agents and metabolic factors on neuropsychological outcomes. Finally, we discuss the clinical implications of these findings and propose targets for forthcoming research.
Afiliación de los autores: Strejilevich, Sergio. Universidad Favaloro. Facultad de Medicina. Instituto de Neurociencias; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Neurociencia Cognitiva. Fundación Favaloro. Instituto de Neurociencia Cognitiva; Argentina
Afiliación de los autores: Samame, Cecilia. Universidad Favaloro. Facultad de Medicina. Instituto de Neurociencias; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina
Afiliación de los autores: Martino, Diego Javier. Universidad Favaloro. Facultad de Medicina. Instituto de Neurociencias; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina
Repositorio: CONICET Digital (CONICET). Consejo Nacional de Investigaciones Científicas y Técnicas