Colóquios

CHAOS AND COMPLEXITY | Colóquio DFMA

Data: 
segunda-feira, 20 Setembro, 2021 - 16:00 até 17:00
Palestrante: 
Prof. Celso Grebogi (Institute for Complex Systems and Mathematical Biology, King’s College, University of Aberdeen)
Resumo: 

 

 

Transmissão via YouTube

Resumo: Many simple nonlinear deterministic systems can behave in an apparently unpredictable and chaotic manner. This realisation has broad implications for many fields of science. Some basic concepts and properties in the field of chaotic dynamics of dissipative systems will be reviewed in this talk. I will use some of these properties in application topics, including the control of chaos in the heart and in the brain. I will then go a step further by arguing that a complex system are made up of many states that are interrelated in a complicated manner. The ability of a complex system to access those different states, combined with its sensitivity, offers great flexibility in manipulating the system’s dynamics to select a desired behaviour. Another important issue is the question of mathematical modelling of chaotic and complex systems, including complex networks. Mathematical modellers of such systems need to understand and take seriously the question of their own limitations.

Controlling complexity, L. Poon and C. Grebogi, Phys. Rev. Lett. 75, 4023 (1995).
Controlling Chaotic Dynamical Systems, C. Grebogi and Y. C. Lai, Systems Control Lett. 31, 307 (1997).
Data Based Identification and Prediction of Nonlinear and Complex Dynamical Systems, W.-X. Wang, Y.-C. Lai, and C. Grebogi, Phys. Reports. 644, 1-76 (2016).
Relativistic Quantum Chaos, L. Huang, H.-Y. Xu, C. Grebogi, and Y.-C. Lai, Phys. Reports 753 1-128 (2018).
Sudden Regime Shifts After Apparent Stasis, C. Grebogi, Phys. of Life Reviews 32, 41-43 (2020).
Tipping Point and Noise-induced Transients in Ecological Networks, Y. Meng, Y.-C. Lai, and C. Grebogi, J. Royal Soc. Interface 17, 20200645 (2020).
Machine Learning Prediction of Critical Transition and System Collapse, L.-W.Long, H. Fan, C. Grebogi, and Y.-C. Lai, Phys. Rev. Research 3, 013090(1-14)
(2021).

Where is String Theory? | Colóquio DFMA

Data: 
sexta-feira, 23 Julho, 2021 - 16:00 até 17:00
Palestrante: 
Prof. Pedro Vieira (ICTP-SAIFR-IFT-UNESP & Perimeter Institute, Canadá)
Resumo: 

Transmissão ao vivo via YouTube e Zoom

Resumo: At low energies we have gravity. What could be the space of UV completions? The S-matrix bootstrap is a tool which might help shedding light into this important questions. I will review how so.

 

Effective momentum-momentum coupling in a correlated electronic system: the diamagnetism of benzene | Colóquio DFMA

Data: 
sexta-feira, 16 Julho, 2021 - 16:00 até 17:00
Palestrante: 
Prof. Amir Ordacgi Caldeira (IFGW, Unicamp)
Resumo: 

Transmissão ao vivo via YouTube e Zoom

Resumo: A well-known property of aromatic molecules is their highly anisotropic response to an external magnetic field. This intriguing phenomenon is rationalized as a consequence of the delocalization of the itinerant electrons that populate the aromatic ring.

In this presentation, we revisit the magnetism of aromatic molecules through the study of simple Hubbard – rings, and argue that if the itinerant electrons are described by an extended Hubbard Hamiltonian with an effective momentum – momentum interaction between them, a large enhancement of the molecule diamagnetic response takes place.

We show that the presence of this new term is due to the reincorporation of part of the effects of the localized bonding electrons on the dynamics of their itinerant counterparts in Hubbard – like Hamiltonians. Going beyond the adiabatic approximation, we show that the net effect of virtual transitions of bonding electrons between their ground and excited states is to furnish the itinerant electrons with an effective interelectronic momentum – momentum interaction.

Although we have applied these ideas to the specific case of rings, our assumptions can be generalized to higher-dimensional systems sharing the required properties of which we have made use herein.

Acceleration of Cosmic Rays by Magnetic Reconnection and the Origin of Very High Energy Emission from Black Holes and Relativistic Jets of Active Galaxies | Colóquio DFMA

Data: 
sexta-feira, 2 Julho, 2021 - 16:00 até 17:00
Palestrante: 
Profa. Elisabete M. de Gouveia Dal Pino (IAG-USP)
Resumo: 

Transmissão ao vivo via YouTube e Zoom.

 

Resumo: Black Holes (BHs) and Relativistic Jets from active galaxies are among the most extreme particle accelerators and very high energy (VHE) emitters in the universe. Only lately, combining theory, numerical simulations, and observations, we have started to understand the potential physical processes that prevail in the surrounds of these sources in order to explain major puzzles, like  the origin of  their VHE flares in gamma-rays. In regions of these sources where magnetic fields are dynamically dominating, fast magnetic reconnection is expected and thus particle acceleration driven by this process. In this seminar, I will discuss what is magnetic reconnection and present recent results that combine multidimensional magnetohydrodynamical relativistic simulations with the injection of test particles, which demonstrate how particles can be stochastically accelerated in relativistic jets and accretion flows around BHs by magnetic reconnection. We find that for jets with magnetic fields B ~ 10 G, the particles can be accelerated up to observed ultra-high energies ~10^20 eV. I will also show that these ultra-high-energy-cosmic-rays (UHECRs) are able to explain the VHE flares and the associated neutrino emission observed in the relativistic jets from active galaxies. Finally, I will discuss the implications of these results in predictions for forthcoming high energy astrophysical observatories like the Cherenkov Telescope Array (CTA).

Lições do Run II do Large Hadron Collider | Colóquio DFMA

Data: 
sexta-feira, 25 Junho, 2021 - 16:00 até 17:00
Palestrante: 
Prof. Oscar José Pinto Éboli (DFMA-IFUSP)
Resumo: 

Transmissão ao vivo via YouTube e Zoom.

Resumo: Desde a descoberta do Higgs em 2012 o Large Hadron Collider do CERN acumulou uma grande quantidade de dados. Discutiremos o impacto destes resultados na Física de Partículas.

 

Páginas

Desenvolvido por IFUSP