2 QLS Guest Seminars - Thursday, 18 July @ 11:30 and 14:30

[Quantitative Life Sciences]

2 QLS Guest Seminars - Thursday, 18 July

ICTP, Central Area, 2nd floor, SISSA Building, via Beirut 2



At 11:30

Speaker: Rainer Klages - Queen Mary University of London

Title: Microscopic chaos, fractals and diffusion: From simple models 
towards experiments

Abstract:
A century ago Einstein developed a theory of diffusion that is based on 
the assumption of stochasticity for a Brownian particle. On a molecular 
level, however, diffusion is generated by Newton’s deterministic 
equations of motion, which typically are highly nonlinear. In my talk I 
will review, in a very tutorial manner, a theoretical approach that 
derives diffusion from first principles by starting from microscopic 
deterministic chaos. Simple models ranging from a deterministic random 
walk on the line to chaotic diffusion in potentials on periodic lattices 
will be studied analytically and by computer simulations. Surprisingly, 
the diffusion coefficients of these models turn out to be highly 
irregular, fractal functions of physical control parameters while simple 
random walk theory predicts monotonicity. This is due to memory in the 
deterministic single-particle dynamics. I will argue that this 
phenomenon should be seen in experiments on small systems, such as 
molecular diffusion in zeolite nanopores and diffusion of electrons in 
artificial graphene.

Webpage: http://indico.ictp.it/event/8989/

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At 14:30

Speaker: Sarah Loos - Institut fuer Theoretische Physik, Technische 
Universitaet Berlin, Germany

Title: "Thermodynamic notions for time-delayed stochastic processes"

Abstract:
Stochastic thermodynamics provides a consistent description of a wide 
class of Langevin systems, but the Markov assumption is often essential. 
While some non-Markovian systems have been studied in great detail, the 
important case of feedback control with a discrete delay is still 
insufficiently understood [1,2]. The thermodynamical description of 
nonlinear delayed systems turns out to be particularly challenging.
In this talk, I will consider the paradigmatic example of a Brownian 
particle in a doublewell potential subject to time-delayed feedback in 
its non-equilibrium steady state. We use different strategies to tackle 
the technical challenges arising due to the delay, such as closure 
schemes for the infinite Fokker-Planck hierarchy [3,4] and a Markovian 
embedding technique [4,5].
We find an unavoidable heat flow induced by the control (even in the 
absence of any additional driving), i.e., the feedback inevitably cools 
down or heats up the system [1]. Interestingly, the heat flow is 
enhanced in the limit of small delay times, which is a phenomenon 
related to entropy pumping. We further compute the total entropy 
production of the super system, consisting of the particle plus the 
memory of the controller. By varying the information capacity of the 
memory device, we can consider different Gamma-distributed delays, 
including the limit of an infinitely sharp (delta-peaked) kernel, i. e., 
discrete delay. We identify an entropic contribution due to the memory, 
which is a consequence of the unidirectional information flow induced by 
the feedback-controller. This contribution diverges in the case of 
error-free measurement, as well as in the case of a perfectly sharp 
(delta-peaked) time delay.

[1] Loos & Klapp, Sci. Rep. 9, 2491 (2019)
[2] Rosinberg, Munakata, Tarjus, PRE 91, 042114 (2015) [3] Loos & Klapp, 
PRE 96, 012106 (2017)
[4] Loos & Klapp, ArXiv:1903.02322 (2019)
[5] Puglisi & Villamaina, EPL 88, 30004 (2009)


Webpage: http://indico.ictp.it/event/9010/


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
www.ictp.it/research/qls.aspx
e-mail: qls at ictp.it