[seminar] P. Cvitanović, P. Mimica, M.-R. Cioni

[Ivica Smolić]

Dear colleagues,

this week we have a busy schedule, two seminars at the Department of 
Physics and one seminar at the Department of Mathematics, in 
chronological order:

*Tuesday* (April 18th), *A-201 *(Dept. of Math.), *16:00h*
Speaker: *Predrag Cvitanović*
(Center for Nonlinear Science, Georgia Tech, Atlanta, USA)

Title: *Is space time? A spatiotemporal theory of transitional turbulence*

Abstract: Recent advances in fluid dynamics reveal that the recurrent flows
observed in moderate Reynolds number turbulence result from close
passes to unstable invariant solutions of Navier-Stokes equations.
By now hundreds of such solutions been computed for a variety of
flow geometries, but always confined to small computational domains
(minimal cells).

The 2016 Gutkin and Osipov paper on many-particle quantum chaos
opens a path to determining such solutions on spatially infinite
domains. Flows of interest (pipe, channel flows) often come
equipped with D continuous spatial symmetries. If the theory is
recast as a (D+1)-dimensional space-time theory, the space-time
invariant solutions are (D+1)-tori (and not the 1-dimensional
periodic orbits of the traditional periodic orbit theory). The
symbolic dynamics is likewise (D+1)-dimensional (rather than a
single temporal string of symbols), and the corresponding zeta
functions should be sums over tori, rather than 1-dimensional
periodic orbits. In this theory there is no time, there is only a
repertoire of admissible spatiotemporal patterns.

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*Wednesday* (April 19th), *F-201*, *11:00h*
Speaker: *Petar Mimica*
(Departament d’Astronomia i Astrofísica, Universitat de Valencia, Spain)

Title: *A theoretical study of magnetic fields and emitting particles in 
blazar jets*

Abstract: Blazars are compact active galactic nuclei and sources of
broadband emission whose relativistic jet presumably points directly
towards us. They are among the most energetic sources in the universe
and are a subject of very intense research.
I will present the results of an eight-year theoretical study that tried
to understand magnetic field strength and the emitting particle
distribution in blazar jets. We developed an efficient numerical code
based on a sophisticated theoretical model and are able to produce
multiwavelength blazar flares with arbitrary magnetic field strengths.
We show quantitatively to what extent the magnetic field strength and
the proportion of the non-thermal particles have an influence on the
spectral features. Furthermore, we show how our modeling can be applied
to attempt to explain properties of the sample of gamma-ray blazars
observed by Fermi, as well as the existence of different blazar subclasses.

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*Thursday* (April 20th), *F-201*, *15:00h*
Speaker: *Maria-Rosa Cioni*
(Leibniz-Institut für Astrophysik Potsdam (AIP), Germany)

Title: *A modern view of the Magellanic Clouds*

Abstract: The Magellanic Clouds are our nearest neighbouring galaxies 
interacting
with each other and with the Milky Way. They represent an early stage of a
minor merger event. They have been surveyed  across the wavelength
spectrum for many decades, but there are still many things to understand
about them. In this presentation, I will focus on near-infrared
observations from the VISTA survey of the Magellanic Clouds system (VMC)
highlighting the most recent results. This is a photometric large-scale
project that started at ESO in 2009 and that will be completed within 
the next few years.
The main goals are to recover the star formation history and the 
three-dimensional
geometry of the system with unprecedented spatial accuracy, but the data
have a wide range of applications that extend to distant quasars. I will
also present these investigations in the context of future projects.

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Best regards,
Ivica Smolić

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