3 QLS seminars - 18, 19 and 21 July

[Quantitative Life Sciences]

Next week, the QLS section will host 3 seminars in person.

All seminars will be held in the Common Area, Second floor, old SISSA 
building, Via Beirut, 2

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**Monday, 18 July at 11:00*

Speaker:  Daniel Segre' (Boston U.)

Title: Metabolic interactions in natural and synthetic microbial communities

Abstract:
Metabolism operates as a multiscale process that induces interactions 
between microbial species and leads to division of labor and 
cross-feeding in complex microbial communities. By combining dynamic 
flux balance modeling with diffusion equations, we model the 
spatio-temporal dynamics of communities in complex environments, 
starting from the genomes of individual species. We envisage that these 
approaches will be increasingly valuable for understanding natural 
communities (e.g., ocean and soil consortia), and for guiding targeted 
synthetic ecology experiments with artificial communities that can be 
used both as benchmark for our models and as avenues for environmental 
remediation and metabolic engineering.

Indico: https://indico.ictp.it/event/10011/

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Tuesday, 19 July at 14:00

*Speaker: Juan MR Parrondo (Universidad Complutense de Madrid)

Title: Two notes on the foundations of statistical mechanics: 
objectivity and the origin of giant fluctuations

Abstract:
Boltzmann’s explanation of irreversibility is based on the concept of 
macro-states and the definition of entropy as the logarithm of the 
volume in phase space of the region of micro-states compatible with a 
given macro-state. The explanation, however, lacks an objective (i.e. 
non arbitrary) definition of macro-states and of the crossover between 
micro- and macro-scales. Here we show that this problem can be solved by 
reformulating Boltzmann’s explanation in terms of observables relaxing 
from giant fluctuations. We show that the irreversible behavior of an 
observable is a fully objective property and has nothing to do with its 
micro- or macroscopic nature. In fact, we will show a situation where a 
system exhibits irreversibility at the micro-scale and reversibility at 
the macro-scale. In the second part of the talk, we propose a mechanism 
for creating giant fluctuations of an observable (hence, 
irreversibility) based on metastable states induced by symmetry breaking.


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Thursday, 21 July at 11:00

*Speaker: Farzan Vafa (Harvard University, Center of Mathematical 
Sciences and Applications)

Title: Diffusive growth sourced by topological defects

Abstract:
In this talk, we develop a minimal model of morphogenesis of a surface 
where the dynamics of the intrinsic geometry is diffusive growth sourced 
by topological defects. We show that a positive (negative) defect can 
dynamically generate a cone (hyperbolic cone). We analytically explain 
features of the growth profile as a function of position and time, and 
predict that in the presence of a positive defect, a bump forms with 
height profile h(t) ~ t^(1/2) for early times t. To incorporate the 
effect of the mean curvature, we exploit the fact that for axisymmetric 
surfaces, the extrinsic geometry can be deduced entirely by the 
intrinsic geometry. We find that the resulting stationary geometry, for 
polar order and small bending modulus, is a deformed football.
We apply our framework to various biological systems. In an ex-vivo 
setting of cultured murine neural progenitor cells, we show that our 
framework is consistent with the observed cell accumulation at positive 
defects and depletion at negative defects. In an in-vivo setting, we 
show that the defect configuration consisting of a bound +1 defect 
state, which is stabilized by activity, surrounded by two -1/2 defects 
can create a stationary ring configuration of tentacles, consistent with 
observations of a basal marine invertebrate Hydra.

**




-- 
Erica Sarnataro
Group Secretary
Quantitative Life Sciences
The Abdus Salam International Centre for Theoretical Physics (ICTP)
Trieste,  Italy
Tel. +39-040-2240623
www.ictp.it/research/qls.aspx
e-mail:qls at ictp.it