Seminars 2018
Seminar
Wednesday, April 11
Selfassembly of active colloids
UCM
Abstract
Active matter represents a fundamentally new
nonequilibrium regime within statistical mechanics. In
contrast to traditional nonequilibrium systems, where
directional driving forces emerge as a result of global
changes in the thermodynamic variables (such as
temperature and pressure), active systems are
intrinsically out of equilibrium at the singleparticle
level. In our recent work, we have focused on studying
the collective behaviour and assembly in dilute
suspensions of spherical selfpropelled particles,
unraveling the role played by the particleparticle
interactions (whether shortrange or longrange,
isotropic or anisotropic) and by the hydrodynamics.
The seminar will take place at 13:00 in classroom
2.0.D14 (Edificio Sabatini) Universidad Carlos III
Seminar
Wednesday, March 21
Thermodynamics of mantle minerals from first principles
ICMM, CSIC
Abstract
In this talk I will present some recent results on the
thermodynamic properties of a series of minerals that
are important constituents of the Earth's mantle.
Beyond presenting those results and describing the
techniques used to obtain them, I will aim to
illustrate the fact that there are many interesting
questions relevant to the fields of geology and
geophysics that are ultimately materials questions,
questions that can begin to be addressed, if not fully
at least partially, with the techniques of
computational materials science.
The seminar will take place at 13:00 in classroom
2.0.D14 (Edificio Sabatini) Universidad Carlos III
Seminar
Wednesday, March 14
NUMERICAL SIMULATION AND OPTIMIZATION OF AIRFRAME
ASSEMBLY PROCESS
Saint Petersburg Polytechnic University
Abstract
During the airframe assembly process it is important to
control both gap between joined parts and stresses
caused by installed fixture elements. The main goal of
the presented work is to develop special tool for
numerical simulations of assembly process in order to
check and optimize the assembly technology.
The main challenge for simulation the assembly process is necessity to solve the contact problem for determination of deformed stress state of the assembly loaded by the forces from fastening elements. This contact problem has some peculiarities that were taken into account in order to derive efficient algorithm: The developed mathematical model combines dimension reduction with use of stateoftheart optimization algorithms for solving of derived quadratic programming problem. The described above algorithm was realized in software code and thoughtfully tested in the framework of joint project between Saint Petersburg Polytechnic University and Airbus Operations S.A.S. The verification of obtained results is made against analytic solution and number of physical experiments on real aircraft junctions. Simulation results have been already successfully implemented for optimization of Airbus assembly chain. Application examples and respective challenges are to be discussed during the presentation.
The seminar will take place at 13:00 in classroom
2.0.D14 (Edificio Sabatini) Universidad Carlos III
Seminar
Wednesday, March 7
Thermal diffusion segregation in granular mixtures
Universidad de Extremadura
Abstract
Among the different competing mechanisms involved in
granular segregation, thermal diffusion becomes the
most relevant one when an external energy input drives
the system into rapid flow conditions. In this regime,
granular matter flows like a fluid and kinetic theory
tools (conveniently adapted to account for the
inelastic character of collisions between grains) can
be quite useful to analyze thermal diffusion
segregation. Thermal diffusion is caused by the
relative motion of the components of a mixture due to
the presence of both gravity and a temperature
gradient. Due to this motion, a steady state is reached
where the separation effect arising from thermal
diffusion is balanced by the remixing effect of
ordinary diffusion. The aim of this contribution is
determine the socalled thermal diffusion factor
$\Lambda$ of a moderately dense granular binary mixture
(with coefficients of normal restitution $\alpha_{ij}$
for collisions between particles of species $i$ with
$j$) described by the (inelastic) Enskog kinetic
equation. A segregation criterion is derived from the
knowledge of $\Lambda$, which is explicitly obtained in
terms of the parameters of the system (masses and sizes
of particles, concentration, solid volume fraction and
coefficients of normal restitution) [1]. The sign of
$\Lambda$ determines the tendency of the large
particles to drift toward the cooler or warmer plate.
To test the i reliability of the theoretical
calculations, the factor $\Lambda$ is also obtained by
computer simulations [Monte Carlo (DSMC) and molecular
dynamics (MD) simulations] carried out for a granular
impurity (species 1) in a driven lowdensity granular
gas [2]. As an illustration, Fig. 1 shows the marginal segregation
curve ($\Lambda=0$) for a system with $\alpha_{22} =
0.9$ and $\alpha_{12} = 0.7$. It is quite apparent that
theory reproduces very well the phase diagram obtained
from simulations.
[1] Garzó, V. Phys. Rev. E, 78, pp. 020301
(R), 2008; Eur. Phys. J. E, 29, pp. 261274,
2009; New J. Phys., 13, pp. 055020, 2011.
The seminar will take place at 13:00 in classroom
2.0.D14 (Edificio Sabatini) Universidad Carlos III
Seminar
Wednesday, February 28
Selfassembling disorder in materials science: From
photonic crystals to photonic glasses
ICMM, CSIC
Abstract
Complex material structures are inherently interesting
for the curious scientific mind due to the challenge
their in depth understanding constitutes. Periodicity
greatly simplifies their understanding and adds
interesting new properties. Selfassembled
nanostructures usually develop ordered patterns in
three dimensions [1]. When disorder is dominant, some
interesting new phenomena may appear, as random lasing
[2]. Artificial opals are one of such possible
arrangements usually forming fcc structures with
promising photonic properties. Often, and undesirably,
unwanted defects are present spoiling the optical
properties of such nanostructures [3]. On the other
hand, and contrary to intuition, the introduction of
arbitrarily high amounts of disorder is, in some cases,
an equally difficult task but the resulting material
presents intriguing new optical properties. We have
grown novel nanophotonic materials, photonic
glasses, which are solid, disordered assembly of
monodisperse dielectric spheres [4], in which novel
devices such as resonant random lasing may be observed
[5].
In this talk, I will summarize our latest results regarding selfassembled photonic materials and, in particular, I will focused on the transition from order to disorder, and vice versa, when understanding selfassembly can be approached by studying colloidal crystallization. [1] J.F. GalisteoLópez, M. Ibisate, R. Sapienza,
L. FroufePérez, A. Blanco, and C. López, Adv. Mater.
23, 3069 (2011).
The seminar will take place at 13:00 in classroom
2.0.D14 (Edificio Sabatini) Universidad Carlos III
Seminar
Wednesday, February 7
Thermal transistor based on stochastic switching
UC3M
Abstract
Fluctuations are strong in mesoscopic systems and have
to be taken into account for the description of
transport. We show that they can even be used as a
resource for the operation of a system as a device. We
use the physics of singleelectron tunneling to propose
a bipartite device [1,2] working as a thermal
transistor [3]. Charge and heat currents in a two
terminal conductor can be gated by thermal fluctuations
from a third terminal to which it is capacitively
coupled. The gate system can act as a switch that
injects neither charge nor energy into the conductor
hence achieving huge amplification factors. Nonthermal
properties of the tunneling electrons can be exploited
to operate the device with no energy consumption.
[1] R. Sánchez, M. Büttiker, Optimal energy quanta
to current conversion, Phys. Rev. B 83, 085428
(2011).
The seminar will take place at 13:00 in classroom
2.0.D14 (Edificio Sabatini) Universidad Carlos III
Seminar
Thursday, February 1
Investigando el camino de desplegamiento de proteínas
Universidad de Sevilla
Abstract
En esta charla revisamos algunos resultados teóricos
recientes que predicen el camino de desplegamiento de
proteínas simples, como sistemas modulares, como
función de la velocidad y la dirección de tracción.
Estos resultados teóricos se obtienen a partir de una
descripción mesoscópica, en que las extensiones de los
distintos módulos que componen la proteína obedecen
ecuaciones de evolución escolásticas (Langevin). Las
predicciones de este enfoque teórico se comparan tanto
con resultados experimentales como con simulaciones de
Dinámica Molecular.
The seminar will take place at 13:00 in classroom
2.1.A18 (Edificio Sabatini) Universidad Carlos III
Seminar
Tuesday January 23
Estados termodinámicos en vidrios de espín en dimensión
finita
Universidad de Extremadura
Abstract
En esta charla se abordarán de una manera sencilla los
vidrios de espín en dimensión finita. Para ello
describiremos la obtención del modelo de
EdwardsAnderson a partir de primeros principios.
Posteriormente detallaremos las propiedades físicas de
las solución en el regimen de campo medio basada en la
rotura de la simetria de las réplicas y teorías
alternativas como el modelo de los droplets y la de los
pares caóticos. A continuación estudiaremos los
problemas que presenta el límite termodinámico en estos
modelos (por ejemplo, la definición de estados) y el
concepto de metaestado. Finalmente presentaré
resultados recientes sobre la construcción numérica del
metaestado y sus implicaciones sobre las diferentes
teorías que pretenden describir los vidrios de espín en
dimensión finita.
The seminar will take place at 13:00 in classroom
2.0.D14 (Edificio Sabatini) Universidad Carlos III
Seminar
Wednesday, January 17
Proliferation and Movement  Modelling Angiogenesis
University of Coimbra
Abstract
Angiogenesis  the growth of new blood vessels from a
preexisting vasculature  is key in both physiological
processes and on several pathological scenarios such as
cancer progression or diabetic retinopathy. In this
seminar we will present different mathematical
approaches to model sprouting angiogenesis. We will
focus on the role of cell migration and cell
proliferation in determining the morphology of the
resulting network. We will present mathematical models
that take into account the role of mechanics in
regulating endothelial cell proliferation and
migration. For the new vascular networks to be
functional, it is required that the growing sprouts
merge either with an existing functional mature vessel
or with another growing sprout. This process is called
anastomosis. We will present a systematic 2D and 3D
study of vessel growth in a tissue to address the
capability of angiogenic factor gradients to drive
anastomose formation. We will demonstrate that the
production of angiogenic factors by hypoxic cells is
able to promote vessel anastomoses events in both 2D
and 3D. We also verify that the morphology of these
networks has an increased resilience toward variations
in the endothelial cell's proliferation and chemotactic
response.
The seminar will take place at 13:00 in classroom
2.0.D14 (Edificio Sabatini) Universidad Carlos III
Seminar
Wednesday, January 10
The dynamics of a thin vibrated granular layer
(quasi2D geometry)
Univerdidad de Extremadura
Abstract
We review the main features of the dynamics of a
quasi2D thin granular layer. The system consists in a
densely packed set of identical spheres (metallic
spheres with a diameter $\sim$ 1mm) that is conned in a
vibrating box. The layer is horizontal and the shaking
is performed vertically. The box has a width $h \in
[1.25\sigma,1.9\sigma]$ so that the geometry forbids
vertical particle overlapping. We consider only
sineshaped vibration signals, with amplitude $A$ and
angular frequency $\omega$ so that the input
acceleration is typically greater than gravitational
acceleration: $\Gamma \equiv A\omega^2/g \gt 1$. As
energy input is gradually increased the system
undergoes over a series of phase transitions, including
a quasi2D hexaticlike phase that can be described in
the context of the KTHNY theory [1,2,3]. The observed
phase diagram changes considerably as a function of the
layer width $h$ and particle collision inelasticity. In
fact, we show that under the appropriate conditions a
suciently strong inelasticity may suppress any kind of
ordering/clustering in the system.
[1] J.M. Kosterlitz and D.J. Thouless, J. Phys. C
6 (1973) 1181.
The seminar will take place at 13:00 in classroom
2.0.D14 (Edificio Sabatini) Universidad Carlos III


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