13,856 research outputs found
Global 3D radiation-hydrodynamics models of AGB stars. Effects of convection and radial pulsations on atmospheric structures
Context: Observations of asymptotic giant branch (AGB) stars with increasing
spatial resolution reveal new layers of complexity of atmospheric processes on
a variety of scales. Aim: To analyze the physical mechanisms that cause
asymmetries and surface structures in observed images, we use detailed 3D
dynamical simulations of AGB stars; these simulations self-consistently
describe convection and pulsations. Methods: We used the CO5BOLD
radiation-hydrodynamics code to produce an exploratory grid of global
"star-in-a-box" models of the outer convective envelope and the inner
atmosphere of AGB stars to study convection, pulsations, and shock waves and
their dependence on stellar and numerical parameters. Results: The model
dynamics are governed by the interaction of long-lasting giant convection
cells, short-lived surface granules, and strong, radial, fundamental-mode
pulsations. Radial pulsations and shorter wavelength, traveling, acoustic waves
induce shocks on various scales in the atmosphere. Convection, waves, and
shocks all contribute to the dynamical pressure and, thus, to an increase of
the stellar radius and to a levitation of material into layers where dust can
form. Consequently, the resulting relation of pulsation period and stellar
radius is shifted toward larger radii compared to that of non-linear 1D models.
The dependence of pulsation period on luminosity agrees well with observed
relations. The interaction of the pulsation mode with the non-stationary
convective flow causes occasional amplitude changes and phase shifts. The
regularity of the pulsations decreases with decreasing gravity as the relative
size of convection cells increases. The model stars do not have a well-defined
surface. Instead, the light is emitted from a very extended inhomogeneous
atmosphere with a complex dynamic pattern of high-contrast features
Generation of complex sounds sequences using physical models with dynamical structures
International audienceMass-interaction physical modeling is one of the few formalisms that can unify the work on music composition and sound synthesis. It allows generating sound sequences that exhibit, for example, some of the qualities of instrumental performance. This article introduces a method for building mass-interaction models whose physical structure changes during the simulation. Structural evolution is implemented in a physically consistent manner, by using nonlinear interactions that set temporary viscoelastic links between simulated objects. We present in details a model built with this method. It produces a wide range of complex sound sequences, the user having a control over global aspects of its behavior. This example shows that evolving models are particularly useful for the generation of macrotemporal musical forms
The structure of causal sets
More often than not, recently popular structuralist interpretations of
physical theories leave the central concept of a structure insufficiently
precisified. The incipient causal sets approach to quantum gravity offers a
paradigmatic case of a physical theory predestined to be interpreted in
structuralist terms. It is shown how employing structuralism lends itself to a
natural interpretation of the physical meaning of causal sets theory.
Conversely, the conceptually exceptionally clear case of causal sets is used as
a foil to illustrate how a mathematically informed rigorous conceptualization
of structure serves to identify structures in physical theories. Furthermore, a
number of technical issues infesting structuralist interpretations of physical
theories such as difficulties with grounding the identity of the places of
highly symmetrical physical structures in their relational profile and what may
resolve these difficulties can be vividly illustrated with causal sets.Comment: 19 pages, 4 figure
The use of information theory in evolutionary biology
Information is a key concept in evolutionary biology. Information is stored
in biological organism's genomes, and used to generate the organism as well as
to maintain and control it. Information is also "that which evolves". When a
population adapts to a local environment, information about this environment is
fixed in a representative genome. However, when an environment changes,
information can be lost. At the same time, information is processed by animal
brains to survive in complex environments, and the capacity for information
processing also evolves. Here I review applications of information theory to
the evolution of proteins as well as to the evolution of information processing
in simulated agents that adapt to perform a complex task.Comment: 25 pages, 7 figures. To appear in "The Year in Evolutionary Biology",
of the Annals of the NY Academy of Science
A computational framework for aesthetical navigation in musical search space
Paper presented at 3rd AISB symposium on computational creativity, AISB 2016, 4-6th April, Sheffield. Abstract. This article addresses aspects of an ongoing project in the generation of artificial Persian (-like) music. Liquid Persian Music software (LPM) is a cellular automata based audio generator. In this paper LPM is discussed from the view point of future potentials of algorithmic composition and creativity. Liquid Persian Music is a creative tool, enabling exploration of emergent audio through new dimensions of music composition. Various configurations of the system produce different voices which resemble musical motives in many respects. Aesthetical measurements are determined by Zipf’s law in an evolutionary environment. Arranging these voices together for producing a musical corpus can be considered as a search problem in the LPM outputs space of musical possibilities. On this account, the issues toward defining the search space for LPM is studied throughout this paper
- …