Wednesday 17 May - Quantitative Life Sciences guest seminar

[Quantitative Life Sciences]

Wednesday 17 May at 15:00
ICTP, Central Area, 2nd floor, old SISSA building, Via Beirut

Title: "Extracting information from simple statistical laws in complex 
component systems"

Speaker: Andrea Mazzolini, University of Turin

Abstract:
Several complex systems in various fields can be described as component 
systems, i.e. sets of objects (genomes, books, or LEGO toys) composed of 
elementary components (genes, words, or LEGO bricks). Several emerging 
statistical laws regarding the statistics of components  can be 
empirically observed in such diverse systems. These laws may be the 
consequence of  the underlying architectural constrains, thus in 
principle can provide information about the system properties.
Our work  tackles the general questions of what can be learned from 
these simple statistical laws about what laws  are a "universal" 
property of very different component system and what are instead 
specific of the system in analysis, how and if these laws are related to 
each other, and what simple stochastic processes can be used to 
understand their origins.

In this presentation I will focus on two specific examples. The first 
example concerns the "U"-shaped distribution of shared genes across 
genomes, which is central to the current debate in evolutionary 
genomics. We show that its characteristic shape can be obtained by a 
null model simply based on the empirical heterogeneity of the component 
abundances. This implies that the distribution of shared genes is mainly 
a statistical consequence of other known system properties. This result 
shows that to extract the relevant biological information it is 
necessary to build null models. In this way it is possible to take into 
account general emerging features and thus extract the systems specific 
properties.
The second example considers the growth of the book/object "vocabulary" 
(i.e. how many distinct words/components are present) as a function of 
its "size" (i.e. the total number of components),  a law known in 
linguistics as  Heaps’ law. We focused on how the vocabulary 
fluctuations scale with its average value, showing a non-trivial and 
general behavior across different systems. Specifically, the standard 
deviation grows linearly with the average (Taylor’s law). We have found 
that the minimal stochastic growth processes that can reproduce this 
scaling belong to a class of models that includes  the Chinese 
Restaurant process. This suggests a general rich-gets-richer mechanism 
in the innovation dynamics of thus component systems, leading to 
interesting system-specific interpretations.


Everyone interested is most welcome to attend!


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