Actividades
fisica.uc.pt

 
 


café com física - ciclo de palestras
palestras de 2014

palestras informais abertas a todos (sala conf. 14:00h ::0.0)



janeiro

8jan2014
Carlos Fiolhais

"A recepção da teoria de Bohr em Portugal."

22jan2014
Silvia Chiacchiera (CFC)

"Collective modes of Fermi gases in realistic 3D and 2D traps"

Abstract:
Usually theoretical calculations for the collective modes of
trapped cold gases are performed in harmonic traps. However,
experimental trap potentials have typically a Gaussian shape
and anharmonicity effects appear as the temperature and,
in the case of Fermions, the filling of the trap are increased.
These effects are not only quantitative, but also qualitative.
In this seminar I will present two studies performed in the
framework of the Boltzmann equation including in-medium
effects and solved approximately via the phase-space
moments method extended beyond lowest order: the
sloshing mode in a 3D trap and the quadrupole mode
in a 2D trap, for both of which experimental data are
available.


29jan2014
Yérali Gandica (CFC)

"Complex systems: From dynamical processes to complex networks."

abstract
I will give a general overview about the research in complex systems, focusing mainly in biological and social systems. In particular, I will discuss how this approach tries to explain facts like sincronization, scale-free and small-world behaviour as emergent phenomena, i.e., as the product of collective behaviour of many interacting particles. Finally, I will present some of my works.


fevereiro

5fev2014
Hugo Simões (LIP)

"Rad4life: line of research on orthogonal ray imaging "

Abstract:
Orthogonal ray imaging is an imaging technique under investigation in the
field of radiation therapy. It consists in detecting radiation dispersed
in the patient and emitted at right angles in respect to the beam axis.
It is potentially capable of assisting external photon beam
radiotherapy by providing images correlated with the effective dose
distribution, and by enabling in parallel low-dose morphologic imaging, mainly on-board
tumor/patient imaging prior to the onset of the treatment. Monte
Carlo simulations are being carried out with the anthropomorphic phantom NCAT
adapted to Geant4. Experimental proof-of-principle measurements were collected
with a heterogeneous phantom made of acrylic/air and irradiated with
a 6-MV clinical linac. The simulated results show a good visual
agreement between the planned dose distribution and the orthogonal
ray simulated images. For example,
the filling of the nasal cavity of the patient may account for a dose
reduction of up to 10 %, which may be detected (hence prevented) with
an orthogonal ray
imaging system. The case of an irradiation of the lung will also be presented.
In conclusion, orthogonal ray imaging is a new imaging concept for
assisting external photon beam radiotherapy that shows a good
potential for image-guided radiotherapy, adaptive radiotherapy, and
low-dose on-board patient imaging.


12fev2014
Mário G. Silveirinha (Instituto de Telecomunicações, UC)
"Unconventional Light Wave Oscillations in Plasmonic Nanostructures"

Abstract:
In open systems the energy associated with a photonic mode may continuously leak
away in the form of a radiated wave, and hence the lifetimes of all natural oscillations
are finite. This property is closely related to the problem of instability of the Rutherford
atom in classical physics. In this talk, I will theoretically show that in the limit of
vanishing material loss plasmonic materials offer the opportunity to have light
localization in open bounded systems with infinitely long oscillation lifetimes and no
radiation loss.
In the second part of the talk, I will show that when an (uncharged) plasmonic
material is set in relative motion with respect to another (uncharged) polarizable body
the combined system may be electromagnetically unstable such that if the relative
velocity is enforced to remain constant the system may support natural oscillations that
grow exponentially with time. This new phenomenon is analogous to the Cherenkov
effect, but for uncharged polarizable bodies.


19fev2014
Luís Silva (LIP)

"Spin Physics at COMPASS"

abstract:
COMPASS experiment is a fixed target experiment at the CERN SPS using
muon and hadron beams with high energy (about 200 GeV) for the
investigation of the spin structure of the nucleon and hadron
spectroscopy, respectively.
In the QCD frame, the nucleon spin structure is an interesting and
challenging topic. In this seminar, the COMPASS results on parton
momentum distributions obtained with longitudinal and transverse target
polarisations as well as the determination of the gluon polarisation are
presented.
The open questions and recent developments are discussed. New
phenomenological approaches beyond collinear frame to access a new
complementary information to help understating the nucleon
structure are also presented.


março

5mar2014
Karl Giboni (Shanghai Jiao Tong University, China)
"New Directions in Liquid Noble Gas Detectors"

26mar2014
André Cortez (LIP)

"Medida experimental de mobilidade de iões em gases"

9abr2014
Juan Pedro Araque (LIP)

"Search for vector-like quarks pair production in the ATLAS experiment."

Abstract:
The discovery of the Higgs boson at the LHC in July 4th of 2012 brought light on several areas of modern particle physics which try to answer the open questions left by the Standard Model. One of them is the number of fermions families and the possibility that heavier quarks than the top might exist. New chiral families have been studied in the past years and both experimentalist and theorists have been involved in the search of such new quarks. But the presence of a light Higgs boson makes this scenario very constrained by the couplings of this new heavy quarks with the Higgs. Nevertheless, there is still the possibility that these new heavy quarks are not chiral partners of the Standard Model quarks but they are vector-like. Vector-like quarks transforms in the same way under the symmetry group SU(2) both the left and right chiralities and, due to this, they don't need to copule with the Higgs boson to obtain mass. In this talk, a review of the ongoing analysis in the ATLAS collaboration with the most recent published results will be shown.


abril

23abr2014
José Pinto da Cunha (LIP)

"A detecção das ondas gravitacionais do Big-Bang"

Sumário:
Foi anunciada a 17 de março, passa agora um mês, a descoberta de ondas gravitacionais primordiais, criadas logo a seguir ao Big-Bang, há cerca de 1.4*10^10 anos. A observação foi feita pelo telescópio BICEP2, instalado no pólo sul, em plena Antárctida.

Se esta observação se confirmar, estaremos seguramente perante umas das mais importantes descoberta da cosmologia. É uma descoberta fundamental em si mesma, mas é-o também pelas perspectivas que abre sobre a possibilidade de se virem a observar fenómenos na escala de energias em que ocorrerá a unificação das forças fundamentais.

Nesta palestra será feita uma análise contextualizada das observações que foram feitas. (ref. nature 507, p.281, 20mar2014)


junho

18jun2014
João Martins (LIP)
"Investigações em Computação Musical"

A computação musical define-se genericamente como o estudo ou o desenvolvimento de formas musicais com o auxílio do computador. Esta disciplina abrange várias áreas, como o desenvolvimento de ferramentas de análise e de síntese, o estudo de estrutura musical, ou o estudo processos matemáticos com relevância para a música.

O uso da computação em música remonta ao início da notação musical moderna. Guido D'Arezzo, no tratado do século XI "Micrologus", apresenta um método de composição em que associa as vogais a uma nota musical, de forma a gerar melodias para acompanhar versos. Com o aparecimento do computador no século XX, numerosos algoritmos foram desenvolvidos e aplicados tanto à análise como à composição. Das técnicas desenvolvidas para a análise de som, de processos físicos e biológicos ou dos métodos matemáticos para auxílio à composição salientam-se as cadeias de Markov, gramáticas generativas, redes neuronais e algoritmos evolucionários. Esta palestra irá mostrará alguns desenvolvimentos históricos e técnicas computacionais aplicadas no estudo da música.


26jun2014
Kanako Yamazaki (University of Tokyo and IPN-Orsay)

"Quark-hadron phase transition in the PNJL model with hadronic excitations"

Abstract:
We study the QCD phase transition by a Nambu-Jona-Lasinio model extended
with the Polyakov loop. This model was proposed by combining the
Nambu-Jana-Lasinio model which describes the chiral transition and the
Polyakov loop which works as an order parameter of de-confinement
transition. The aim of this work is to describe the change of degrees of
freedom from hadrons to quarks through the transition region. For this
purpose, we calculated an equation of state by an approach beyond the
mean field approximation to take thermal excitations of hadrons into
account. In this method, mesons can be introduced as auxiliary fields,
and their excitations are described as thermal fluctuations of auxiliary
fields. I will present an equation of state concerning mesonic
excitations at zero quark chemical potential in the two- and
three-flavor PNJL model for interacting quarks. In addition, we have
thought the way to introduce baryonic correlation as the three body
system of quarks at finite chemical potential. In this case, it is
necessary to consider how to put interactions between three quarks,
unlike mesons as two body system of quark and anti-quark. I will also
discuss about that.


julho

2jul2014
Márcio Ferreira (CFC)
"Transições de fase da QCD sob efeito de um campo magnético externo"

O confinamento e quebra de simetria quiral são características não perturbativas da Cromodinâmica Quântica (QCD). Para o estudo das mesmas e das transições de fase associadas, usou-se o modelo efetivo de Polyakov–Nambu–Jona-Lasinio (PNJL) em SU(3), sob a acção de um campo magnético externo. As temperaturas críticas para as transições quirais e desconfinamento em função do campo magnético externo foram calculadas e as previsões do modelo foram comparadas com resultados da rede (QCD na rede). Adicionando no potencial de Polyakov uma dependência do campo magnético e usando a interação de entanglement, foi possível reproduzir a catálise magnética inversa, prevista por cálculos recentes na rede. O aparecimento da catálise magnética inversa no modelo está relacionado com o enfraquecimento da constante de interação com o campo magnético.


9jul2014
Richard Brower, Boston University

"Conformal Field Theory on Curved Manifolds"

Possible application to the composite Higgs problem, Gravity in AdS space and the Ising Critical Behavior will be explored.


setembro

17set2014
Ubiratãn José Furtado (CFC)

"Difusão de neutrinos num meio nuclear"

Estamos interessados em estudar o comportamento do neutrino e suas propriedades em um meio nuclear denso não uniforme, cercado por elétrons e outros neutrinos. O meio nuclear será descrito pelo modelo de Walecka não linear, onde a fase da matéria conhecida como fase pasta, é obtida usando a aproximação de Thomas-Fermi, dentro de uma célula de Wigner-Seitz. Calculamos então a seção de choque neutrino-partícula, mediada tanto pelo bóson neutro Z como também pelo bósons carregados W's. A partir da seção de choque neutrino-partícula, calculamos a seção de choque neutrino-célula. Comparamos então o resultado para duas parametrizações diferentes para a interação forte: uma onde a não linearidade é introduzida explicitamente e os acoplamentos são definidos por constantes e outra onde tais constantes passam a depender da densidade. A solução desse problema tem interesse direto em simulações para a perda de neutrinos no momento da formação de uma estrela de nêutrons a partir da explosão de uma supernova.


outubro

15out2014
Joaquín Flores Gerónimo, Universidad Nacional Autónoma de México, Facultad de Química

"Microfluídica. Hemodinámica en redes de vasos sanguíneos."


22out2014
P. M. P. Salomé (INL e LaNaSC)

"Photovoltaics: from industry trends to research at INL"

abstract
Thanks to political/economical events but also thanks to technology improvements, photovoltaics is now a technology that is widely available and it is starting to be cost-competitive with traditional power generation technologies. In the past years there was a substantial price reduction of photovoltaic modules, however to be truly affordable the price reduction has to continue in the decades yet to come. In the first part of the talk I will provide a personal insight into the latest photovoltaics industry numbers and show how companies and countries are developing photovoltaics from a market point of view that already handles more than 100b USD worldwide. Understanding the economical and technology background is important to evaluate where the current research is needed, thus in the second part of the talk I will address some research activities at the International Iberian Nanotechnology Laboratory that are aimed to develop technological solutions in different time-scales. I will briefly address how we are bringing silicon standard technology into the thin-film technology to try to make solar modules cheaper and better in the short to medium term; how non-conventional characterization techniques are being deployed to understand these materials (like Muon spectroscopy in collaboration with U. Coimbra) and finally how new technologies based in nanostructures are being developed that will only be fully available in the long-term.



29out2014
Issam Oueslat, CEMDRX

"Unprecedented Supramolecular Nanomaterials with Unique Physical Properties"

abstract
We are pioneering the design of the unique calixazacrown-based nanomaterials by self-assembly. Nanoporous materials, aggregation-induced emission materials, and hierarchized assembled nanoparticules are manufactured. We are introducing novel strategies to control nanoporosity, luminescence efficiency, and sensing behavior for generating responsive smart materials.



novembro



5nov2014
Helena Pais (CFC)
"Core-collapse supernova matter: light clusters, pasta phase and phase transitions"

Abstract: The pasta phase in core-collapse supernova matter (finite temperatures and fixed proton fractions) is studied within relativistic mean field models. Two different calculations are used for comparison, the Thomas-Fermi (TF) and the Coexistence Phase (CP) approximations. The effects of including light clusters in nuclear matter and the densities at which the transitions between pasta configurations and to uniform matter occur are also investigated. The free energy and pressure, in the space of particle number densities and temperatures expected to cover the pasta region, are calculated. Finally, a comparison with a finite temperature Skyrme-Hartree-Fock calculation is drawn.

12nov2014
Maria Conceição Ruivo
A "irmã de Newton": reflexões sobre as mulheres de Ciência

Sumário:
Virgina Woolf, na sua obra A room of one's own, desafia-nos a seguir o percurso de Judith Shakespeare, uma imaginária irmã gémea de Shakespeare, tão inteligente e talentosa como o irmão. Ao contrário de William, Judith nunca viria a escrever obras imortais e cedo sucumbiria na luta para o conseguir. Tal como à irmã de Shakespeare, a também a muitas "irmãs de Newton" terão sido negadas três condições fundamentais para ficar na História: educação, condições para criar conhecimento e reconhecimento dos pares.
O objectivo desta palestra é, através da análise do percurso de algumas mulheres de ciência, reflectir sobre os condicionamentos impostos pelos contextos sociais e culturais no trabalho científico das mulheres. Evitando cair nos extremos de as tratar como vítimas ou heroínas, debruçar-nos-emos sobre a existência (ou ausência) das condições atrás referidas no trajecto destas mulheres


19nov2014
Myrta Gruning (Queen's University Belfast)
"Hybrid atomistic/continuum approach to the optical properties of functionalised plasmonic nanostructures"

sumário:
Myrta Grüning, Ryan McMillan, and Lorenzo Stella
A persisting obstruction to the design of smaller, yet efficient, phototransistor is the inherent weakness of light-matter interaction at the nanoscale. Combining photoactive layered materials like graphene or MoS2 with metallic nanostructures can provide a viable technological solution thanks to the plasmonic field enhancement[1]. To this end, current experimental efforts will greatly benefit from scalable and robust models of the electromagnetic response of such functionalised plasmonic nanostructures.
Optical properties of layered semiconductors are well captured by state-of-the-art electronic structure calculations based on many-body perturbation theory, namely GW+Bethe Salpeter equation [2]. However, at the moment such very accurate first principle approaches cannot be scaled up to include a genuine atomistic description of a whole metal nanostructure. To address this issue, we propose here a multiscale approach that combines a real-time first principle treatment of the photoactive layer along with a scalable semiclassical description of the metallic nanostructure. A convenient numerical approach based on the generalized Langevin equation formalism [3] is used to have a consistent coupling between the two parts of the system. The potentialities of this multiscale approach are demonstrated for a test system consisting of a quantum dot coupled to metal nanoparticle.

[1] G. Eda and S. Maier; ACS Nano 7, 5660 (2013)
[2] See, e.g., A. Molina-Sanchez et al; Phys. Rev. B 88, 045412 (2013); L Wirtz et al.; Phys Rev Lett 100 (18), 189701 (2008)
[3] L. Stella, C. D. Lorenz, and L. Kantorovich; Phys. Rev. B 89, 134303 (2014)



3dez2014
Pedro Alberto
Simetrias de spin e pseudospin na equação de Dirac - últimos resultados

Resumo
As simetrias de spin e pseudospin são simetrias SU(2) da equação de Dirac - a equação que descreve partículas quânticas relativistas com spin 1/2 - com potenciais escalar S e vetorial V quando V=+/- S. Estas simetrias são elevantes para explicar certas caraterísticas dos espectros de núcleos atómicos e de certos mesões. Relatam-se alguns dos últimos resultados relativos à aplicação destas simetrias e apontam-se perspetivas futuras de aplicações a outros sistemas físicos.
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