Programa de Pós-Graduação em Física (Eng)

Online Lectures

The invited lectures are available on YouTube. Click on the titles.

Fenomenologia hadrônica no espaço de Minkowski utilizando representações integrais - in Portuguese
Prof. Dr. Wayne Leonardo Silva de Paula (Instituto Tecnológico de Aeronáutica - ITA)

Live: May 4th, 2021 - 1:30 PM (GMT-3)

Nesse seminário discutirei a formação de estados ligados relativísticos, cuja dinâmica é dada pela solução da Equação de Bethe-Salpeter. Em geral, utiliza-se a rotação de Wick para resolver essa equação integral, o que fornece uma equação no espaço Euclideano. Devido a presença de pólos no Kernel da equação integral, o mapeamento da solução Euclideana com a obtida no espaço de Minkowski pode apresentar dificuldades. Discutirei alguns métodos para obter a solução no espaço físico, tais como a utilização de Representações Integrais e a Transformação de Stieltjes. Utilizando a Representação Integral de Nakanishi, calcularei a Amplitude de Bethe-Salpeter e a função de onda de valência do estado ligado de dois férmions interagindo pela troca de um bóson (escalar, pseudo-escalar ou vetorial) na aproximação de escada. Nesse modelo, calcularei a probabilidade de valência e a distribuição de momento transverso e longitudinal da função de onda de valência. Por fim, discutirei as perspectivas da utilização de tais métodos para a fenomenologia hadrônica.

Challenges and prospects for materials sciences in space exploration
Prof. Dr. Matheus A. Tunes* (Montanuniversitaet Leoben)

Live: March, 19th, 2021 - 1:30 PM (GMT-3)

The human journey in space is an achievement of greater complexity. Human-based space missions have only been accomplished due to a rigorous and appropriate selection of materials that are able to endure the extreme conditions found in the space environment. When confined within the limits of the solar system (known as heliopause), the discharge of thermonuclear reactions from Sun’s core to its coronal regions give rise to deadly levels of energetic-ionising radiation in a form either particles or electromagnetic waves. The impact and deposition of such irradiation energy in spacecraft materials and crew members may impair the course of long-time human-based missions and possible lead to irreversible consequences. The innovative design of the next generation of lightweight alloys to support next human-based activities in the space will be the main topic of this seminar. A brief introduction to space weather restricted to inner and outer regions of the Van Allen radiation belt will be given with focus on its potential deleterious effects in materials already in-service in spacecrafts, satellites and space probes. It will be demonstrated that the Sun’s abnormal coronal activities can be emulated using the almost 80 years of knowledge on nuclear materials science in Earth-based particle accelerators and nuclear reactors. Recent experiments carried out in Europe in the development of an innovative class of new Al-based alloys the crossover alloys [1–2] – have indicated that upon increasing local chemical complexity with modified physical properties, superior radiation tolerance can be achieved under conditions that extrapolates the stellar-radiation environment. In the light of these most recent discoveries in this new exciting field of research, the prototypic guidelines for the design of lightweight metallic alloys with enhanced stellar-radiation tolerance will be proposed.

* On move to Los Alamos National Laboratory, New Mexico, USA.

References
[1]     L. Stemper, M.A. Tunes et al. Acta Mater. 195 (2020) 541–554.
[2]      M.A. Tunes, L. Stemper et al. Adv. Sci. 7 (2020) 2002397.

Plasma assisted combustion: Unraveling the “chemystery” 
Dr. Ramses Snoeckx (King Abdullah University of Science and Technology​)

Live: January 19th, 2021 - 9:00 AM (GMT-3)

This seminar presentation will give an introduction to plasma assisted combustion, and outline the different stages and final goal of a project I am working on in the Plasma Assisted Combustion Lab (https://pac.kaust.edu.sa) at the King Abdullah University of Science and Technology (KAUST); the development of a comprehensive C1-3/H2/O2/N2 plasma assisted combustion and reforming kinetics model.
During the last decade, the use of non-equilibrium plasma discharges to enhance combustion and reforming processes gained a lot of attention. Non-equilibrium plasmas can generate reactive species, in situ, almost independent of regular reactor constraints. To date most plasmachemical kinetic studies in the field of plasma assisted combustion (PAC) are performed either in (highly diluted) Argon environments or at low pressures. However, it is well known that the diluting agent as well as the pressure play a key role in both the plasma physics and chemistry.
Therefore, we perform plasmachemical kinetics studies of pure (undiluted) mixtures at atmospheric pressure based on combined ChemKin and ZDPlasKin calculations, supported by experimental data. The aim of this study is to unravel the primary plasmachemical reactions and components of the plasma assisted combustion chemistry. To achieve this, the chemistry included in the model is based on existing combustion chemistry mechanisms, and extended with the necessary electron impact reactions as well as additional ion-chemistry. For validation purposes, the results of the chemical kinetics model are compared with results from experiments performed in different plasma reactors.

Data-driven dynamical systems and control 
Prof. Dr. Steven L. Brunton (University of Washington)

Live: November 13th, 2020 - 3:30 PM (GMT-3)

Accurate and efficient reduced-order models are essential to understand, predict, estimate, and control complex, multiscale, and nonlinear dynamical systems. These models should ideally be generalizable, interpretable, and based on limited training data. Machine learning constitutes a growing set of powerful techniques to extract patterns and build models from this data, complementing the existing theoretical, numerical, and experimental efforts. In this talk, we will develop a general framework to discover the governing equations underlying a dynamical system simply from data measurements, leveraging advances in sparsity-promoting techniques and machine learning. The resulting models are parsimonious, balancing model complexity with descriptive ability while avoiding overfitting.  This perspective, combining dynamical systems with machine learning and sparse sensing, is explored with the overarching goal of real-time closed-loop feedback control.   
There are many more critical data-driven problems, such as understanding cognition from neural recordings, inferring patterns in climate, determining stability of financial markets, predicting and suppressing the spread of disease, and controlling turbulence for greener transportation and energy.  With abundant data and elusive laws, data-driven discovery of dynamics will continue to play an increasingly important role in these efforts.

The high power impulse magnetron sputtering discharge:  An ionization region model study 
Prof. Dr. Jon Tomas Gudmundsson (University of Iceland)

Live: November 10th, 2020 - 10:30 AM (GMT-3) 1

Magnetron sputtering is a widely used technique that has been applied successfully by various industries for deposition of thin films and coatings for almost five decades. The high power impulse magnetron sputtering (HiPIMS) discharge is an extension of this technique that provides ionized physical vapor deposition (IPVD). In HiPIMS, high power is applied to the magnetron target (cathode) in unipolar pulses at low duty cycle, while keeping the average power about two orders of magnitude lower than the peak power. This results in a high plasma density (electron density) and a high ionization fraction of the film forming material. The high ionization fraction has opened up new ways to engineer thin films with improved properties, since it allows for controlling the energy and direction of the deposition species.  The time-dependent plasma discharge ionization region model (IRM) is used to study the properties of the ionization region of high-power impulse magnetron sputtering (HiPIMS) discharges.  It takes into account processes such as returning of the working gas atoms from the target, a separate treatment of hot secondary electrons, addition of doubly charged metal ions, etc.  The model is used to explore discharges with Al and Ti targets operated in non-reactive and reactive gas. For an argon discharge with Al target the contribution of Al+-ions to the discharge current at the target surface is over 90% at 800 V and at 400 V the Al+-ions and Ar+-ions contribute roughly equally to the discharge current. We demonstrate that recycling is essential in HiPIMS operation.  During reactive sputtering we find that in metal mode self-sputter recycling dominates and in the poisoned mode working gas recycling dominates - the dominating type of recycling determines the discharge current waveform.

Diffractive processes at the LHC: from the shadows to light and back - in Portuguese
Prof. Dr. Victor Paulo Barros Gonçalves (Universidade Federal de Pelotas)

Live: October 27th, 2020 - 1:30 PM (GMT-3)

A broad class of processes at high energies has properties analogous to the classical pattern of the diffraction of light. These are usually called diffractive processes. In hadron - hadron scattering a substantial fraction of the total cross section is due to diffractive reactions, with the study of these processes providing new possibilities for the investigation of the Quantum Electrodynamics and Quantum Chromodynamics at high energies as well as to search for Beyond Standard Model (BSM) Physics. In this talk, I will review the basic concepts needed to describe the diffractive and exclusive processes and recent results for the Light - by - Light scattering and the production of Axionlike particles and Dark photons at the LHC will be presented.

Desvendando pulsares com inteligência (artificial) - in Portuguese
Prof. Dr. Rafael Camargo Rodrigues de Lima (Universidade do Estado de Santa Catarina)

Live: June 9th, 2020 - 3:00 PM (GMT-3)

Pulsares são alguns dos objetos mais misteriosos do Universo. São estrelas de nêutrons,  que possuem quase duas vezes a massa do nosso Sol confinadas em apenas 10 quilômetros de raio! São campeões em praticamente tudo: maiores campos magnéticos do Universo, maiores densidades do Universo, e são capazes de gerar pulsos com energias comparáveis à que será gerada pelo Sol em toda a sua vida. Além disso são chamadas de estrelas relativísticas devido à sua capacidade de curvar o próprio espaço e modificar o caminho da luz que passa ao seu redor. Mas apesar de tudo o que sabemos sobre estas estrelas fantásticas, determinar a massa e o raio de algumas delas é extremamente difícil. Neste seminário faremos uma revisão sobre o que sabemos sobre Pulsares e apresentaremos um novo método desenvolvido pelo nosso grupo de pesquisa, que combina inteligência artificial com dados observacionais para determinar várias propriedades destas estrelas.