Dust in Brown Dwarfs I. Dust formation under turbulent conditions on microscopic scales

Dust formation in turbulent media is studied adopting the example of brown dwarf atmospheres. By combining asymptotic techniques and time-dependent, multi-dimensional numerical simulations, we show that acoustic waves originating from convective motions provide a mechanism to initiate dust nucleation in otherwise dust-hostile environments. The subsequently growing particles cause a radiative cooling strong enough to re-initiate efficient dust formation resulting in a strongly inhomogeneous distribution of dust in such environments. Recent observations bear indications for such cloudy dust distributions in brown dwarf atmospheres

McGurk illusion recalibrates subsequent auditory perception

Visual information can alter auditory perception. This is clearly illustrated by the well-known McGurk illusion, where an auditory/aba/ and a visual /aga/ are merged to the percept of 'ada'. It is less clear however whether such a change in perception may recalibrate subsequent perception. Here we asked whether the altered auditory perception due to the McGurk illusion affects subsequent auditory perception, i.e. whether this process of fusion may cause a recalibration of the auditory boundaries between phonemes. Participants categorized auditory and audiovisual speech stimuli as /aba/, /ada/ or /aga/ while activity patterns in their auditory cortices were recorded using fMRI. Interestingly, following a McGurk illusion, an auditory /aba/ was more often misperceived as 'ada'. Furthermore, we observed a neural counterpart of this recalibration in the early auditory cortex. When the auditory input /aba/ was perceived as 'ada', activity patterns bore stronger resemblance to activity patterns elicited by /ada/ sounds than when they were correctly perceived as /aba/. Our results suggest that upon experiencing the McGurk illusion, the brain shifts the neural representation of an /aba/ sound towards /ada/, culminating in a recalibration in perception of subsequent auditory input

Dust in brown dwarfs:I. Dust formation under turbulent conditions on microscopic scales

Dust formation in turbulent media is studied adopting the example of brown dwarf atmospheres. By combining asymptotic techniques and time-dependent, multi-dimensional numerical simulations, we show that acoustic waves originating from convective motions provide a mechanism to initiate dust nucleation in otherwise dust-hostile environments. The subsequently growing particles cause a radiative cooling strong enough to re-initiate efficient dust formation resulting in a strongly inhomogeneous distribution of dust in such environments. Recent observations bear indications for such cloudy dust distributions in brown dwarf atmospheres

Circumstellar Dust Shells of Pulsating Red Giants as Dynamical Systems

Miras and long-period variables (LPVs) are highly evolved, pulsating stars on the Asymptotic Giant Branch (AGB) with massive outflows and prominent circumstellar dust shells (CDSs). A CDS, driven by the stellar pulsation, can be considered as a dynamical system which reveals various kinds of complex phenomena like spatio-temporal instabilities, bifurcations, multiperiodicity and transition to chaos. In order to analyze the temporal behavior of the CDS standard methods known from the theory of non-linear dynamical systems are applied. We have developed a spherical symmetric, multi-zone description for the CDS which includes the important physical interactions by means of non-linear coupling terms. The corresponding Hamiltonians are derived. We present Poincaré maps for several models with a different number of zones in order to characterize their dynamical stability. The role of pulsation and dust formation for the development of the dynamical structure of the CDS is investigated. In addition, the linearized approximation of an one-zone model is discussed with respect to the Kolmogorov-Arnold-Moser and the Poincaré-Birkhoff theorems