Category Archives: Uncategorized

PhD and Postdoc opportunities in the physics of disordered systems in Bariloche (Argentina)

a call is now open for national PhD and postdoc fellowships in Argentina
https://convocatorias.conicet.gov.ar/becas/
Fellowships are scheduled to begin on April 1st 2021.

We invite candidates who are interested in applying to work in the physics of Driven Disordered Systems at the Condensed Matter Theory Group in Bariloche Atomic Centre to contact us.
Please, send a CV and a brief motivation statement before July 6th to
ferrero@cab.cnea.gov.ar

Details (in Spanish) follow:

Tema: Fenómenos críticos, memoria, localización, avalanchas y precursores de eventos catastróficos en la deformación plástica de sólidos amorfos

Tipo de trabajo: Modelado teórico-computacional de sistemas desordenados forzados. Simulaciones de modelos elasto-plásticos de sólidos amorfos y dinámica molecular de vidrios.

Director: Ezequiel Ferrero

Lugar de Trabajo:
Grupo de Teoría de la Materia Condensada – Centro Atómico Bariloche

Fecha límite de contacto 6/7/20: ferrero@cab.cnea.gov.ar

Descripción:
Bajo la aplicación de una tensión, por ejemplo un estrés de cizalla, los sólidos amorfos se deforman elásticamente, como un sólido cristalino, si la tensión es pequeña; pero cuando el estrés aplicado supera un umbral crı́tico el material cede y fluye, como un lı́quido viscoso. Este es el fenómeno de “fluencia” o yielding. Para los materiales frágiles (e.g. vidrios de sı́lice), este proceso culmina rápidamente en la fractura; pero un amplio espectro de materiales (espumas, emulsiones, vidrios coloidales, vidrios metálicos, medios granulares) sobrevienen una transición a un estado en donde el material simplemente deja de resistir y fluye. La transición dinámica entre un estado sólido de respuesta elástica y un estado de flujo plástico se conoce como la transición de yielding. Asociados a esta transición de fase dinámica encontramos fenómenos crı́ticos, analogı́as con otras transiciones de fase (de equilibrio o forzadas). En particular, se observan avalanchas de eventos plásticos, efectos de memoria y localización ante cizalla oscilante y comportamientos de relajación que se constituyen en efectos precursores de la fractura. En esta fı́sica compleja y rica de los materiales amorfos bajo deformación se basa el presente proyecto.

Posibles líneas de trabajo:
– Estudio de cizalla oscilante: Efectos de memoria, avalanchas y bandas de cizalla en vidrios
– Efectos precursores de fractura: Fenómenos de “creep” (térmico y atérmico) en materia blanda
– Caracterización del ruido mecánico y la estabilidad marginal en yielding

Our article “Damage accumulation in silica glass nanofibers” to appear in Nano Letters

The origin of the brittle-to-ductile transition, experimentally observed in amorphous silica nanofibers as the sample size is reduced, is still debated. Here we investigate the issue by extensive molecular dynamics simulations at low and room temperatures for a broad range of sample sizes, with open and periodic boundary conditions. Our results show that small sample-size enhanced ductility is primarily due to diffuse damage accumulation, that for larger samples leads to brittle catastrophic failure. Surface effects such as boundary fluidization contribute to ductility at room temperature by promoting necking, but are not the main driver of the transition. Our results suggest that the experimentally observed size-induced ductility of silica nanofibers is a manifestation of finite-size criticality, as expected in general for quasi-brittle disordered networks.

A nice collaboration with Silvia Bonfanti, Alessandro Sellerio, Roberto Guerra and Stefano Zapperi at CC&B Milano.
A ‘Just-Accepted’ version of the manuscript can be found here.

My visit to Naples!

I had had the pleasure to be in Napoli giving a seminar at the Physics Department of the University of Naples Federico II, followed by very interesting discussions with colleagues that showed up for the occasion. I would like to thank all of them and specially my host in this visit and good friend Raffaele Pastore for such a wonderful time in the adoptive city of Diego Armando 🙂 .

Our article “Inertia and universality of avalanche statistics: the case of slowly deformed amorphous solids” is online!

Together with Kamran Karimi and Jean-Louis Barrat in this article we study the noise statistics of the stress-strain signal in the steady state plastic flow, focusing on systems with low internal dissipation.

Visit to ISI Foundation Torino

I am grateful to Gianfranco Durin and his group for a couple of days of very interesting discussions and a warm welcome at ISI Foundation in Turin, were I presented a seminar on the “Spatio-temporal patterns in ultra-slow domain wall creep dynamics”.

I will be talking about “avalanches in amorphous solids” in Vienna @MECO-41

In mid-February I’ll be participating in the 41st Conference of the Middle European Cooperation in Statistical Physics (MECO) to be held Vienna, Austria.

I’m looking forward to meet there many colleagues and profit from useful discussions. See you soon in Vienna!

Update: The slides of my presentations can be found in the gallery.

Hello world!

Finally, I decided to choose WordPress and to pay for a host :S . Let’s see if in this way I force myself to have a fairly updated webpage.