Seminars 2015
Seminar
Thursday, December 10
Chiral bound states in the continuum
IEM-CSIC
Abstract
We present a new mechanism for the formation of bounded
states in the continuum in lattices with chiral
symmetry connected to leads. Bounded states in the
continuum are square integrable solutions of the
time-independent Schrödinger equation with
eigenenergies above the potential threshold. We derive
some algebraic rules for the number of states that
remain bounded depending on the dimensionality and rank
of the system Hamiltonian including the coupling to the
leads. We study the transport properties of some
relevant physical examples and propose different
experiments for measuring consequences of the presence
of these bounded state in the continuum.
[1] V. Fernández-Hurtado, J. Mur-Petit, J.J.
García-Ripoll, R.A. Molina, New J. Phys. 16,
035005 (2014).
The seminar will take place at 13:00 in classroom
2.1.C19 (Edificio Sabatini) Universidad Carlos III
Seminar
Tuesday, November 24
Entropic electrokinetics
Universidad de Barcelona
Abstract
We show that the dynamics of particles suspended in an
electrolyte confined between corrugated charged
surfaces exhibits new and surprising phenomena such as
particle separation, mixing for low-Reynolds micro- and
nano-metric devices and negative mobility. Such
phenomena originate from the interplay between the
electrostatic double layer and the confinement; the new
effects become more important when the width of the
channel is comparable to the Debye length. We outline
the relevance of the predicted effects in a wide
variety of systems, from nano- and micro-fluidic
devices to biological systems.
The seminar will take place at 13:00 in classroom
2.1.C17 (Edificio Sabatini) Universidad Carlos III
Seminar
Wednesday, October 21
Incomplete Riemann solvers based on matrix functional
calculus for hyperbolic systems of conservation laws
Universidad de Valencia
Abstract
We present two classes of incomplete Riemann solvers,
whose viscosity matrices are defined in terms of
functional matrix approximations computed by means of
an appropriate elementary real function $R(x)$, that
approximates the continuous function $|x|$. The
resulting approximate Riemann solvers are incomplete,
in the sense that we do not use the complete spectral
decomposition of the system, and only some information
about the maximum in absolute value of the
characteristic speeds are needed. We shall explore two
approaches, Roe solver and Osher-Solomon
approximations, respectively. Some numerical tests will
be presented to show robustness, afficiency, and
accuracy.
The seminar will take place at 13:00 in classroom
2.1.C17 (Edificio Sabatini) Universidad Carlos III
Mini-course
May 11,12, and 13
The Statistical Theory of Turbulence
University of California at Santa Barbara
Abstract
The course will take place from 11:00 to 13:00 in room
3.S1.08 (Sala de Audiovisuales, Biblioteca Rey Pastor)
Universidad Carlos III
Seminar
Thursday, April 9
Estabilidad lineal modal y no modal en problemas
hidrodinámicos sobre flujos laminares
UPM
Abstract
La teoría de inestabilidad lineal modal y no modal
aplicada en hidrodinámica ha demostrado ser una
herramienta útil en el estudio del proceso de
transición de flujos laminares a turbulentos,
permitiendo con ello ir entendiendo los mecanismos que
conducen a dicha transición, así como el desarrollo de
estrategias de control activas y/o pasivas en
dispositivos aerodinámicos sobre los que se producen
estos procesos. La teoría clásica de inestabilidad modal, centrada en el estudio de flujos paralelos (Lin, The Theory of Hydrodynamic Stability, Cambridge Univ. Press, 1955 y Drazin & Reid, Hydrodynamic Stability, Cambridge Univ. Press, 1981), se ha ido ampliado en las últimas décadas, entre otros, al estudio de flujos no paralelos, inestabilidades secundarias, inestabilidades en problemas con flujos base periódicos (Floquet) o al estudio de perturbaciones no modales basado en problemas de valor inicial (Schmid & Henningson, Stability and Transition in Shear Flows. Berlin: Springer, 2001). La charla comenzará con una breve introducción de los problemas de estudio así como de las teorías de estabilidad modal y no modal utilizadas en éstos, entre otras: métodos modales con formación y sin formación de matriz, estudio no modal y algoritmo de los residuos (para más detalle véase Theofilis, Annu. Rev. Fluid Mech. 2011). A continuación se presentarán los estudios de estabilidad sobre dichos problemas en el límite de flujo laminar incompresible, estos son: (a) estudio de estabilidad del flujo de capa límite oblicuo entorno a la línea de estancamiento, para lo que se utiliza como flujo base la solución de Dorrepall (Dorrepall Fluid Mech., 1986) a la que se añade la contribución del flujo en la dirección homogénea (envergadura), (b) aplicación de estrategias del tipo desplazamiento-inversión en códigos de estabilidad basados en integradores lineales de las Navier-Stokes (códigos sin formación de matriz) en flujo estenótico y flujo sobre un escalón (backward-facing step), (c) estudio de estabilidad modal y no modal en canales divergentes bidimensionales en función del número de Reynolds y el ángulo de divergencia del canal, (d) estudio de Floquet sobre el Naca 0012 y (e) estudio de inestabilidades modales en códigos de simulación numérica Lattice Boltzmann mediante la aplicación del método de los residuos en flujos confinados (ejemplo: lid-driven cavity).
The seminar will take place at 13:00 in classroom
2.1.C17 (Edificio Sabatini) Universidad Carlos III
Seminar
Tuesday, March 24
Patrones subarmónicos en fluidos sometidos a vibración
UPM
Abstract
El efecto de la vibración en fluidos es de gran interés
en muchos campos y puede dar resultados muy complejos.
La configuración más simple y más estudiada es la de un
recipiente de fluido agitado verticalmente, esto es así
porque la solución básica (no excitada) está en reposo
en el marco de referencia del recipiente en movimiento.
Otras configuraciones son en general menos fáciles de
tratar y han recibido menos atención, sobre todo en el
límite en el que la frecuencia es grande en comparación
con la del primer modo capilar-gravitatorio. En el caso
de un contenedor sometido a vibración horizontal
primero aparecen trenes de ondas paralelas a la paredes
y, más allá de una aceleración crítica, también se
pueden excitar un par de ondas casi perpendiculares que
serán estudiadas semi-analíticamente. La vibración de
las paredes produce un flujo que es el responsable de
la inestabilidad paramétrica, es un mecanismo similar
al de las ondas de Faraday con la salvedad de que se
obtiene un forzamiento antisimétrico que no es uniforme
espacialmente. La teoría se generalizará para estudiar
el efecto que la vibración de un obstáculo
completamente sumergido (que presenta unos mecanismos
equivalentes) tiene en la superficie libre, al ser una
forma sencilla de originar un forzamiento simétrico. La
teoría se aplicará para calcular la aceleración crítica
así como la orientación de los patrones.
The seminar will take place at 13:00 in classroom
2.1.C17 (Edificio Sabatini) Universidad Carlos III
Seminar
Friday, March 13
Three terminal energy harvesting with quantum dots
Instituto de Ciencia de Materiales de Madrid
(ICMM-CSIC)
Abstract
Energy harvesting is the process by which energy is
taken from the environment and transformed to provide
power for electronics. Specifically, the conversion of
thermal energy into electrical power, or
thermoelectrics, can play a crucial role in future
developments of alternative sources of energy.
Unfortunately, present thermoelectrics have low
efficiency. Therefore, an important task in condensed
matter physics is to find new ways to harvest ambient
thermal energy, particularly at the smallest length
scales where electronics operate. To achieve this goal,
there is on one hand the miniaturizing of electrical
devices, and on the other, the maximization of either
efficiency or power the devices produce. Three terminal conductors permit separate directions of the heat and current flux [1]. We present a model of Coulomb coupled conductors one of which is connected via only one lead to a hot reservoir. The other conductor is connected to two leads. Such a geometry can be used for detection of non linear heat fluctuations [2]. We investigate the minimal conditions needed to generate directed current flow for a system of two quantum dot conductors in which both energy and charge states are quantized. In quantum dots energy to current conversion can be optimal with one electron transferred for every heat quantum given up by the hot reservoir. We show that this configuration achieves high efficiencies. However, the generated power is small. To attain the two requirements of high efficiency and power, we propose a resonant tunneling quantum dot engine that can be operated either in the Carnot efficient mode, or maximal power mode. The ability to scale the power by putting many such engines in a "Swiss cheese sandwich" geometry gives a paradigmatic system for harvesting thermal energy at the nanoscale [3]. We also discuss alternative configurations based on resonant tunneling through quantum wells provide a comparable thermoelectric performance with the advantage of being easier to construct [4]. [1] R. Sánchez, M. Büttiker, "Optimal energy quanta
to current conversion" Phys. Rev. B 87, 075312
(2013).
The seminar will take place at 13:00 in classroom
2.1.C17 (Edificio Sabatini) Universidad Carlos III
Seminar
Wednesday, March 4
Theoretical studies on energy and charge transfer among
organic compounds
Instituto Gregorio Millán, UC3M
Abstract
The study of energy and charge transfer among organic
molecules is of key importance in the description of
optoelectronic processes taking within a variety of
systems ranging from organic electronic devices (OD) to
biological light-harvesting complexes (LHC). Therefore
the understanding of the properties and conditions of
such mechanisms is manifold, allowing for the design of
new organic devices yielding better outputs,
efficiencies and lower energy consumption, as the thin
and flexible displays currently commercialized, while
helping in the detailed understand of the first steps
of the photosynthesis. This presentation will focus on
the molecular dynamics and QM/MM results obtained on
charge and energy transfer studies in both worlds (OD
and LHC), used to validate the experimental data and to
assess the information currently not available
experimentally.
The seminar will take place at 13:00 in classroom
2.1.C17 (Edificio Sabatini) Universidad Carlos III
Seminar
Friday, January 23
Non-classical dynamics of magnetized materials
described by compressible Magnetohydrodynamics
Universidad Autónoma de Barcelona
Abstract
We consider the magnetohydrodynamics systems of
equations closed with a general equation of state. We
analyze materials response by characterizing the
behavior of the wave structure of the system in terms
of the thermodynamic properties of the material and the
presence of magnetic field. We characterize the
nonlinearity of the model and prove that magnetic field
can neutralize the formation of non-classical wave
structure induced by phase transitions in the material.
We provide an analytical expression that allows us to
determine the specific amount of magnetic field to
revert non-classical behavior into classical. We
present numerical experiments validating the performed
analysis.
The seminar will take place at 12:00 in classroom
2.1.C19 (Edificio Sabatini) Universidad Carlos III
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