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Living in the boundary Imprimir
Rodrigo Aros
Departamento de Ciencias Físicas
Universidad Andrés Bello

Viernes 10 de julio, 16:15
Departamento de Física, Sala F12
Av Blanco Encalada 2008

During the last decades the AdS/CFT conjecture took a central role in gravitation and high energy physics as it can open a connection with other areas of physics such as solid state, particle and fluid physics. In fact this conjecture may well lay on the idea that our reality could have more than a single description. In this talk this will be discussed  and some new ideas concerning a potential duality between AdS gravity and Conformal gravity.

Seminarios Anteriores

Crystallization fronts in supercooled liquids: how rapid fronts can lead to disordered glassy solids Imprimir
Edgar Knobloch
Professor of Physics
University of California at Berkeley

Viernes 19 de junio, 16:15
Departamento de Física, Sala F12
Av Blanco Encalada 2008


We determine the speed of a crystallization front as it advances into the uniform liquid phase after the system has been quenched into the crystalline region of the phase diagram. There are two mechanisms by which the front can advance, depending on whether the liquid state is linearly stable or not. When the liquid is linearly unstable, the front speed can be calculated by applying a marginal stability criterion. As the crystallization front advances into the unstable liquid phase, the density profile behind the advancing front develops density modulations and the wavelength of these modulations is a dynamically chosen quantity. For shallow quenches, the selected wavelength is close to that of the crystalline phase and so well-ordered crystalline states are formed. However, when the system is deeply quenched, we find that this wavelength can be quite different from that of the equilibrium crystal, so the crystallization front naturally generates disorder in the system. Significant rearrangement and ageing must subsequently occur for the system to form the regular well-ordered crystal that corresponds to the free energy minimum. Additional disorder is introduced whenever a front develops from random initial conditions. We illustrate these findings using two different models of a fluid of soft, purely repulsive particles in solution.
Bio-inspired microfluidics: The case of the velvet worm Imprimir
Andrés Concha
Escuela de Ingeniería y Ciencias
Universidad Adolfo Ibañez

Viernes 12 de junio, 16:15
Sala de seminarios, 3er piso
Departamento de Física (DFI)
Av Blanco Encalada 2008

The rapid squirt of a proteinaceous slime jet endows the ancient velvet worms (Onychophora) with a unique mechanism for defense from predators and for capturing prey by entangling them in a disordered web that immobilizes their target. However, to date neither qualitative nor quantitative descriptions have been provided for this unique adaptation. We have investigated the mechanism that allows velvet worms the fast oscillatory motion of their oral papillae and the exiting liquid jet that oscillates with frequencies f ∼ 30 − 60 Hz. Using anatomical images and high speed videography, we show that even without fast muscular action of the papilla, a strong contraction of the slime reservoir and the geometry of the reservoir-papilla system suffices to accelerate the slime to speeds up to v ∼ 5 m/s in about ∆t ∼ 60 ms. A theoretical analysis and a physical simulacrum allow us to infer that this fast oscillatory motion is the result of an elastohydrodynamic instability driven by the interplay between the elasticity of oral papillae and the fast unsteady flow during squirting. We propose several applications that can be implemented using this instability, ranging from high-throughput droplet production, printing, and micro-nanofiber production among others.
Projective symmetry of partons in Kitaev’s honeycomb model Imprimir
Paula Mellado
Facultad de Ingeniería y Ciencias
Universidad Adolfo Ibañez

Viernes 29 de mayo, 16:15
Sala de seminarios, 3er piso
Departamento de Física (DFI)
Av Blanco Encalada 2008

Low-energy states of quantum spin liquids are thought to involve partons living in a gauge-field background. We study the spectrum of Majorana fermions of Kitaev’s honeycomb model on spherical clusters. The gauge field endows the partons with half-integer orbital angular momenta. As a consequence, the multiplicities reflect not the point-group symmetries of the cluster, but rather its projective symmetries, operations combining physical and gauge transformations. The projective symmetry group of the ground state is the double cover of the point group [1].

[1]  Phys. Rev. B 91, 041103(R)
El ultrasonido como una sonda de densidad de dislocaciones Imprimir
Nicolás Mujica
Departamento de Física
FCFM, U. de Chile

Viernes 15 de mayo, 16:15
Sala de seminarios, 3er piso
Departamento de Física (DFI)
Av Blanco Encalada 2008

Las dislocaciones determinan el comportamiento frágil o dúctil de materiales cristalinos. Sin embargo, es muy difícil hacer mediciones cuantitativas de sus propiedades individuales o colectivas. En esta charla se presentarán resultados experimentales que demuestran que las ondas elásticas ultrasónicas son sensibles a la densidad de dislocaciones en materiales policristalinos. La interpretación de las medidas se hace gracias a una generalización de la teoría de Granato-Lücke, donde se considera el problema de difusión múltiple de ondas elásticas (polarizadas) por un conjunto de dislocaciones distribuidas aleatoriamente en un medio elástico homogéneo. En primer lugar, se presentarán medidas de constantes elásticas en muestras de aluminio y cobre, obtenidas con la técnica de Espectroscopía de Resonancia Ultrasónica, la cual requiere de muestras especialmente preparadas. Luego, demostraremos que es posible obtener medidas “in situ” usando una máquina de tracción, midiendo la velocidad de propagación de pulsos ultrasónicos durante ensayos con probetas de aluminio. Finalmente, mostraremos que medidas hechas en el régimen no-lineal son mucho más sensibles al contenido de dislocaciones, aunque no existe aún una teoría que permita obtener cuantitativamente la densidad asociada. 
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