Dust-driven viscous ring-instability in protoplanetary disks

Protoplanetary disks often appear as multiple concentric rings in dust continuum emission maps and scattered light images. These features are often associated with possible young planets in these disks. Many non-planetary explanations have also been suggested, including snow lines, dead zones and secular gravitational instabilities in the dust. In this paper we suggest another potential origin. The presence of copious amounts of dust tends to strongly reduce the conductivity of the gas, thereby inhibiting the magneto-rotational instability, and thus reducing the turbulence in the disk. From viscous disk theory it is known that a disk tends to increase its surface density in regions where the viscosity (i.e. turbulence) is low. Local maxima in the gas pressure tend to attract dust through radial drift, increasing the dust content even more. We investigate mathematically if this could potentially lead to a feedback loop in which a perturbation in the dust surface density could perturb the gas surface density, leading to increased dust drift and thus amplification of the dust perturbation and, as a consequence, the gas perturbation. We find that this is indeed possible, even for moderately small dust grain sizes, which drift less efficiently, but which are more likely to affect the gas ionization degree. We speculate that this instability could be triggered by the small dust population initially, and when the local pressure maxima are strong enough, the larger dust grains get trapped and lead to the familiar ring-like shapes. We also discuss the many uncertainties and limitations of this model.Comment: Accepted for publication in A&

Parking planets in circumbinary discs

The Kepler space mission has discovered about a dozen planets orbiting around binary stars systems. Most of these circumbinary planets lie near their instability boundaries, at about three to five binary separations. Past attempts to match these final locations through an inward migration process were only shown to be successful for the Kepler-16 system. Here, we study ten circumbinary systems and attempt to match the final parking locations and orbital parameters of the planets with a disc-driven migration scenario. We performed 2D locally isothermal hydrodynamical simulations of circumbinary discs with embedded planets and followed their migration evolution using different values for the disc viscosity and aspect ratio. We found that for the six systems with intermediate binary eccentricities (0.1 ≤ ebin ≤ 0.21), the final planetary orbits matched the observations closely for a single set of disc parameters, specifically, a disc viscosity of α = 10−4 and an aspect ratio of H∕r ~ 0.04. For these systems the planet masses are large enough to open at least a partial gap in their discs as they approach the binary, forcing the discs to become circularised and allowing for further migration towards the binary – ultimately leading to a good agreement with the observed planetary orbital parameters. For systems with very small or large binary eccentricities, the match was not as good as the very eccentric discs and the large inner cavities in these cases prevented close-in planet migration. In test simulations with higher than observed planet masses, a better agreement was found for those systems. The good agreement for six out of the ten modelled systems, where the relative difference between observed and simulated final planet orbit is ≤10% strongly supports the idea that planet migration in the disc brought the planets to their present locations

Mikrostrukturelle Veränderungen der Hirnsubstanz von ALS-Patienten in Voxel-basierter Kernspintomographie

In der vorliegenden Arbeit wurden 30 ALS-Patienten in unterschiedlichen Erkrankungsstadien im Vergleich zu 28 gesunden Kontrollen mittels Voxel-basierter Morphometrie untersucht. Die VBM ist eine auf einem hochauflösenden T1-3D-Bilddatensatz basierende statistische Gruppenanalyse auf Voxelebene, die eine in vivo-Darstellung und –Identifikation krankheitsassoziierter pathologischer Veränderungen von Hirngewebe ermöglicht. Dabei zeigten sich bei ALS-Patienten im Vergleich zu gesunden Kontrollen ausgedehnte Volumenänderungen (Zu- und Abnahme) der grauen und weißen Substanz, vor allem in extra-motorischen Hirnarealen des Frontal-, Parietal, Occipital- und Temporallappens, die auch mit den Ergebnissen der erhobenen klinischen Fragebögen (ALSFRS-R, EuroQoL-5D, MMST, FAB, SF-36) und der Erkrankungsdauer korrelierten. Diese Ergebnisse decken sich zum größten Teil auch mit Ergebnissen anderer VBM- und DTI-Studien. Außerdem ergaben sich Substanzveränderungen in Hirnbereichen, die (noch) nicht mit den klinischen Symptomen des Patientenkollektivs vereinbar waren, was eine Möglichkeit der VBM bedeuten würde, mikrostrukturelle Schäden aufzudecken, bevor sie sich klinisch manifestieren

Avaliação do programa de assistência aos portadores da doença de alzeheimer no município de Florianópolis/SC.

Trabalho de Conclusão de Curso - Universidade Federal de Santa Catarina. Curso de Medicina. Departamento de Saúde Pública

Quantifying cardiorespiratory thorax movement with motion capture and deconvolution

Unobtrusive sensing is a growing aspect in the field of biomedical engineering. While many modalities exist, a large fraction of methods ultimately relies on the analysis of thoracic movement. To quantify cardiorespiratory induced thorax movement with spatial resolution, an approach using high-performance motion capture, electrocardiography and deconvolution is presented. In three healthy adults, motion amplitudes are estimated that correspond to values reported in the literature. Moreover, two-dimensional mappings are created that exhibit physiological meaningful relationships. Finally, the analysis of waveform data obtained via deconvolution shows plausible pulse transit behavior

Abductive reasoning in modeling biological phenomena as complex systems

IntroductionAbductive reasoning is a type of reasoning that is applied to generate causal explanations. Modeling for inquiry is an important practice in science and science education that involves constructing models as causal explanations for scientific phenomena. Thus, abductive reasoning is applied in modeling for inquiry. Biological phenomena are often best explained as complex systems, which means that their explanations ideally include causes and mechanisms on different organizational levels. In this study, we investigate the role of abductive reasoning in modeling for inquiry and its potential for explaining biological phenomena as complex systems.MethodsEighteen pre-service science teachers were randomly assigned to model one of two biological phenomena: either a person's reddened face, for which participants knew of explanations from their everyday lives, or a clownfish changing its sex, for which participants did not know about explanations. Using the think-aloud method, we examined the presence of abductive reasoning in participants' modeling processes. We also analyzed modeling processes in terms of participants' ability to model the phenomena as complex systems.ResultsAll participants reasoned abductively when solving the modeling task. However, modeling processes differed depending on the phenomenon. For the reddened face, participants generated simple models that they were confident with. In contrast, for the clownfish, participants generated more complex models that they were insecure about. Extensive engagement in abductive reasoning alone did not lead to the generation of models that explained the phenomena as complex systems.DiscussionBased on the findings, we conclude that engagement in abductive reasoning will not suffice to explain phenomena as complex systems. We suggest examining in future studies how abductive reasoning is combined with systems thinking skills to explain phenomena as complex systems in biological model construction