Actividades
fisica.uc.pt

 
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café com física - ciclo de palestras
palestras de 2010
palestras informais abertas a todos (sala conf. 14:00h ::0.0)


Janeiro

5 Joao Pires, LIP
"NNLO real corrections to gluon scattering"

9 de Janeiro
Cláudio Silva, LIP
Reflectância do Teflon® no ultravioleta: medidas, modelização e análise»


26 de Janeiro
Fernando Pinheiro, CFC
Estudo de Parâmetros Estelares usando Redes Neuronais


Fevereiro

9 de Fevereiro
Octavio Miloni
Facultad de Ciencias Astronomicas y Geofisicas de la Universidad
Nacional de La Plata, Argentina

"Planet-planet Scattering for extrasolar planetary systems. A way to obtain inclinations?"

Most of the approx 35 extrasolar planetary systems with more than one planet (www.exoplanet.org) show high eccentricities compared with standard formation theories (Kokubo & Ida, 2002). Nowadays, it is well accepted that these types of eccentric orbits may be caused by transfer of angular momentum in a process of ejection of planets that the system originally contains and were lost due gravitational instabilities (Raymond et al. 2009; Ford & Rasio 1996). Such a phenomeno is known as planet-planet scattering. However, there are not much works devoted to inclinations (parameter intrinsically undetermined by inspection from radial velocities)


23 de Fevereiro
Pedro Silva, CEMDRX
"Nonlinear Optics: From Molecules to Crystals"


Março

2 de Março
Pedro Costa, CFC
"O diagrama de fases no modelo de Nambu--Jona-Lasinio com loop de
Polyakov".

9 de Março
João Loureiro, CEMDRX
*Comparison of the disorder induced by annealing and by ball milling in
Fe_50 Co_50 alloys*


16 de Março
Andrea Parisi,
Centro da Fisica da Materia Condensada, Universidade de Lisboa

Title: Pattern dynamics in Eutectic solidification

Abstract:
The microstructures formed during the solidification
of metallic alloys have been studied by metallurgists for
decades because of their influence on the mechanical
properties of the finished material. To predict which
type of structure and charactieristic length scales
are selected under given growth conditions is a classic
problem of pattern formation outside of equilibrium.
Eutectic alloys in particular, when solidified directionally, form
patterns of two distinct solid phases organized spatially as lamellar or
rod arrays, which influence the mechanical properties of the final
solidified samples. Thus, predicting what kind
of structures arise depending on solidifying conditions has been a
relevant quest for industry. It is only in recent years that physicists
have been more deeply involved thanks to the discovery of transparent
organic eutectic alloys which allow to observe the dynamical evolution
of the solidification patterns in real time. Additionally, the
development of performant quantitative simulation methods based on the
phase field approach has provided powerful numerical tools for a deep
investigation of the issues involved in these processes.

I will review the basis of eutectic solidification as well as the phase
field method for simulations, and illustrate the major results and
insights obtained so far.



Abril

13 de Abril
Marc Baboulin, Departamento de Matemática, UC

Numerical algorithms for Hybrid GPU-Multicore Systems

Abstract: We highlight the trends leading to the increased appeal of using
hybrid multicore+GPU systems for high performance computing. To illustrate
this, we present a set of techniques that can be used to develop efficient
dense linear algebra algorithms for these systems. This approach is applied
to the solution of general linear systems based on a hybrid LU factorization
where we split the computation over a multicore and a graphic processor, and
use particular statistical techniques to reduce the amount of pivoting and
communication between the hybrid components. We also show how mixed
precision algorithms can be used for accelerating performance.

20 de Abril
Camille Ducoin, CFC

Nuclear physics for compact stars: cluster formation and elementary
excitations

As a newcomer in the Coimbra physics department, I will present some
aspects of the research work that occupied my former life, and say a few
words of the project we now plan to develop here in Coimbra. The talk will
address two subjects, both concerning nuclear physics input in the study
of compact stars. The density region considered is low enough to allow a
nucleonic description.
1) Under the saturation density, nuclear matter presents a spinodal region
where the homogeneous matter is unstable against cluster formation: this
property is important for the modelization of neutron-star crust and
supernovae dynamics.
2) Elementary excitations impact on the neutrino propagation in star
matter, and consequently on neutron-star cooling. I will present a study
of the low-energy modes in homogeneous matter, including pairing effects.

27 de Abril
Dennis Schaart,
Delft University of Technology, The Netherlands
Progress in time-of-flight PET scintillation detectors based on silicon photomultipliers

Abstract:
The use of time-of-flight (TOF) information in positron emission tomography (PET) significantly improves image quality. Scintillation detectors based on silicon photomultipliers (SiPMs) are promising for TOF-PET. SiPMs are small, essentially transparent to 511 keV annihilation photons, and insensitive to magnetic fields. This enables novel detector designs aimed at e.g. compactness, high resolution, depth-of-interaction (DOI) correction, and MRI-compatibility. We are studying the timing performance of SiPMs in combination with LYSO:Ce and LaBr3:Ce scintillators. With 3 mm x 3 mm x 5 mm LaBr3:Ce(5%) crystals coupled to a 3 mm x 3 mm Hamamatsu MPPC-S10362-33-050C SiPMs, coincidence resolving times (CRTs) of ~100 ps FWHM were achieved, while LYSO:Ce yielded a CRT of ~160 ps FWHM. At the same time, pulse height spectra with well-resolved full-energy peaks were obtained. These results indicate that SiPM-based PET detectors may perform at least as good as detectors based on conventional PMTs. In larger crystals, variations in scintillation photon transit times affect the timing resolution. A correction for this effect can be applied making use of the independently measured position of interaction. At the conference, the prospects for SiPMs in TOF-PET will be discussed in more detail.

Short bio of Dennis Schaart:
Dennis Schaart graduated at the department of Applied Physics of Delft University of Technology (DUT) on the subject of luminescence and energy transfer processes in inorganic scintillators. After conducting a feasibility study on sealed, catheter-based beta radiation source for intravascular brachytherapy he was invited by Nucletron BV to start up a R&D project on this subject. He remained with Nucletron for more than 6 years, holding offices at Nucletron, DUT, and Oak Ridge National Laboratory (ORNL) and conducting a variety of research projects aimed at new radiotherapy devices. In his private time he wrote a PhD thesis for which he obtained a PhD degree ?cum laude? in 2002. He then took on a new challenge, returning to his Alma Mater to start up a new research line on positron emission tomography (PET) detectors. At present, his main research interests include novel scintillation detectors for time-of-flight PET, for high-resolution SPECT, for multimodality imaging (e.g. PET/MRI), and for dose verification in particle therapy. Detector concepts under investigation involve, for example, new scintillation materials, solid-state light sensors such as silicon photomultipliers (SiPMs), and innovative signal processing methods. Motivated to obtain (clinically) useful breakthroughs through fundamental research, much of his research is conducted in collaboration with academic hospitals and industrial partners.


29 de Abril (quinta-feira, Café com Física Extra)
Paulo M. J. Afonso,
Max-Planck-Institut für extraterrestrische Physik (MPE)

'A procura dos objectos mais distantes no Universo: GRBs e quasares com o GROND.

Abstract:
As explosoes de raios gama e os quasares encontram-se entre os objectos mais distantes e mais brilhantes no Universo. O Gamma-Ray Optical and Near Infrared Detector (GROND) e' uma camara de 7 bandas (g'r'i'z'JHK) instalada no Observatorio do ESO em La Silla (Chile), desenvolvida pelo grupo do Dr. J. Greiner no MPE. Tem capacidade para estabelecer de imediato redshifts fotometricos e entre os seus sucessos contam-se a descoberta e observacoes do entao recordista GRB 080913 a z = 6.7 e mais recentemente do GRB 090423 a z = 8.2. O GROND comecou a fazer tambem um rastreio dos ceus procurando raros quasares a z > 5. Por fim, extra-topico, discute-se um pouco a polarizacao circular da radiacao gama associada ao declinio Beta e 'a deteccao de antimateria no Universo.



Maio

4 de Maio
Sonja Orrigo, CI
Spectroscopy of light exotic nuclei

Abstract:
As a recent member of the Physics Department of the Coimbra University, I
will present my former research activity, developed mainly at the National
South Laboratory (LNS) INFN and University of Catania, Italy, and at the
Giessen University, Germany.
In recent years the study of the structure and reaction mechanisms involving
light exotic nuclei has given a new interesting scenario in nuclear physics,
leading to the development of new theoretical models and experimental
techniques. Unexpected phenomena have been observed at the driplines, not
explained by the traditional models used for stable nuclei, indicating a
shift away from the mean field dynamics towards a new type of dynamics in
which many-body correlations play a fundamental role.
From the experimental point of view, a research program exploring the
spectroscopy of weakly-bound neutron-rich nuclei (11Be,15C,19O,.) via the
(7Li,7Be) charge exchange reaction (CEX) at Tandem energies is running,
started at IPN-Orsay, France, and continuing at LNS using the large
acceptance ray-tracing magnetic spectrometer MAGNEX. From the theoretical
side, at the Giessen University, the effects of the dynamical correlations
have been investigated (core polarization in 15C, pairing correlations in
10Li), showing that they are important for the continuum spectroscopy of
light exotic nuclei. Indeed, the proximity of the particle continuum gives
to such nuclei the characteristic of open quantum systems. Thus the coupling
between bound and unbound configurations strongly influences the low energy
continuum, being responsible for new excitation modes.


11 de Maio (quarta-feira)
Tommaso Macrí, SISSA em Trieste.
"Mixtures of Ultracold Fermi Atoms".

Abstract: In the last years many experimental achievements regarding mixtures of fermionic cold atoms have been obtained. They could have in the next future many important applications in various areas, from condensed matter to high energy physics. In this talk I will briefly review the most recent studies in the field and I will concentrate on the collective behavior of Fermi mixtures at finite temperatures. The method involves the classical Boltzmann equation which turns out to be very successful for providing an accurate description of the frequencies and damping of collective oscillations at temperature higher than a half of the Fermi temperature.
At the end I will discuss the problem of tunneling in double wells for polarized Fermi systems at zero temperature as a starting point for the interacting systems in optical lattices.



18 de Maio
Prof. Robert S. Blake, University of Leicester's Atmospheric Science Group,
"Atmospheric Research and Monitoring at the University of Leicester, UK"

Abstract:
The Earth Observation Science section (EOS) at Leicester University is an interdisciplinary group consisting mainly of Physicists and Chemists. As the name suggests, EOS studies the movement and composition of the Earth’s atmosphere using space-based and ground-based systems. One area is concerned with global fluxes of important gas phase components such as Ozone, Carbon dioxide, Oxides of Nitrogen and several organic pollutants. Other areas of interest are the behaviour of solar flux and sea surface temperature variations.
At the ground level air quality in urban areas is measured using a variety of techniques including mass spectrometry, differential infrared and ultraviolet absorption spectrometry. After a short overview of all these areas, the talk will look at mass spectrometry as used in Leicester and how it has been particularly effective in the detection of organic gases and aerosols in the atmosphere. Some of these are well known pollutants which occur in concentrations as low as parts per billion or even parts per trillion.


25 de Maio
Thomas Schweizer
Max Planck Institute fur Kernphysik - Munchen
"Gamma-ray astronomy with Cherenkov telescopes: Status of the MAGIC
project and future outlook"



Abstract: Gamma-ray astronomy is one of the fastest growing fields in
astrophysics. This is because the great success of the imaging Cherenkoc
technique. The MAGIC telescopes are currently the largest Cherenkov
telescopes in the world with 17m diameter located on the canarian island
La Palma. In this presentation an introduction to gamma-ray astronomy
and the status of the MAGIC project will be presented together with the
most interesting highlights.

Currently in preparation is the Cherenkov telescope project (CTA), the
next generation project consisting of 50-100 telescopes with a budget of
about 150 Mio Euros. Already now about 500 physcisits from about 70
institutions are participating, half of them originate from the
currently running and very successful experiments MAGIC, H.E.S.S. and
VERITAS.




27 de Maio (Extra)

Anthony F.J. Moffat
Professeur émérite, Département de physique, Université de Montréal

"Highlights of Astronomy of the Past Decade - a Personal View"

Abstract:
Astronomy remains largely an experimental - or rather observational -
science. We read almost every day in the press of new discoveries that
duly impress the public. In this talk, I would like to share with you
some of the biggest recent discoveries from extra-solar planets up to the
scale of the whole Universe.



Junho


1 de Junho
Isaac Vidaña, CFC
'Symmetry energy, neutron star crust and neutron skin thickness'
We perform a systematic analysis of the density dependence of nuclear symmetry energy within the microscopic Brueckner-Hartree-Fock (BHF) approach. Our results are compared thoroughly with those arising from several Skyrme and relativistic effective models. The values of the parameters characterizing the BHF equation of state of isospin asymmetric nuclear matter fall within the trends predicted by those models and are compatible with recent constraints coming from heavy ion collisions, giant monopole resonances, or isobaric analog states. In particular we find a value of the slope parameter L=66.5 MeV, compatible with recent experimental constraints from isospin diffusion, L=88±25 MeV.
The correlations of the slope L and curvature Ksym parameters and the neutron skin thickness with
the transition density from nonuniform to beta-stable matter in neutron
stars is analyzed.



8 de Junho
adiado para 17

15 de Junho
Filipe Veloso, LIP
"LHC a 7 TeV: os primeiros resultados de ATLAS"

"O Large Hadron Collider (LHC), no CERN, acelerou e fez colidir feixes
de protões com 7 TeV de energia no centro de massa no dia 30 de Março de
2010. A luminosidade integrada dos dados adquiridos desde essa altura
pelo detector ATLAS é de cerca de 15 nb, possibilitando a observação dos
bosões W e Z, havendo já também candidados para a produção de quarks top. Nesta
sessão do Café com Física serão revistos os primeiros resultados da colaboração
ATLAS a 7 TeV, tanto ao nível do desempenho do detector como das medidas de física."



17 de Junho (quinta-fiera)
Elena Aprile, (Columbia Univ., USA),
Colaboração XENON - Dark Matter Search
" The XENON100 Dark Matter Experiment: Initial Results and Status"

The XENON100 experiment, in operation at the Laboratori Nazionali del Gran Sasso in Italy,
is designed to search for dark matter WIMPs scattering off 62 kg of liquid xenon in an ultra-low
background dual-phase time projection chamber. We describe the XENON 100 experiment and
present first dark matter results from the analysis of 11.17 live days of non-blind data, acquired in
October and November 2009. In the selected fiducial target of 40 kg, and within the pre-defined
signal region, we observe no events and hence exclude spin-independent WIMP-nucleon elastic
scattering cross-sections above 3:4 x 10-44 cm2 for 55 GeV=c2 WIMPs at 90% confidence level.


22 de Junho
Valeriy Brazhnyy, UP
Role of dissipation in Bose-Einstein condensates: the way of generation of
coherent structures

Abstract:
I will present some recent results on the generation of different
localized coherent structures in Bose-Einstein condensates induced by
presence of spatially dependent dissipation. Controlled generation of localized coherent
structures in one-dimensional configuration such as bright and dark solitons can be
realized.
In the presence of periodic potential (optical lattice) one can produce dark
and bright envelope solitons which emergence strongly dependent on the sign of
interparticle interaction as well as on the chemical potential.
In two-dimensions we will discuss possibility to generate and manage
two-dimensional localized structures such as ring dark solitons and vortices.

29 de Junho
Aurora Hernandez-Machado
Universitat de Barcelona

Interface dynamics is one of the most challenging fields of research of
Condensed Matter Physics due to its importance in the current
miniaturization trend. At ever smaller scales the surface to volume ratio
becomes increasingly large and system frontiers play a crucial role due to
roughness and wetting conditions. The seminar will present experimental
and theoretical results on avalanche fronts, viscoelastics flows and drops
at the microscale.


Julho

6 de Julho
Paulo Silva, CFC
"Hamiltonianos à Sombra da Bananeira"

Abstract:
De regresso ao Centro de Física Computacional depois de dois anos na
Universidade de Edimburgo, pretendo dar-vos uma ideia do trabalho que
tenho vindo a desenvolver em colaboração com o Prof. Tony Kennedy
(Edimburgo), Dr. Mike Clark (Harvard) e Dr. Balint Joo (JLab).
Numa simulação numérica de um sistema dinâmico, devido ao passo de
integração finito dt, o hamiltoniano do sistema H é apenas aproximadamente
conservado. No entanto, o chamado hamiltoniano sombra Hs é conservado
exactamente, e a diferença Hs-H pode ser escrita como uma expansão em
potências de dt, em termos de parênteses de Poisson. A ideia do trabalho
de investigação que iniciei na Universidade de Edimburgo é usar a
conservação do hamiltoniano sombra e os parênteses de Poisson para
melhorar o desempenho do Hybrid Monte Carlo, o método usado hoje em dia
para gerar configurações com quarks dinâmicos em Lattice QCD.



Setembro


10 de Setembro (sexta-feira)

Andrea Apolloni
Laboratoire de Physique
Institut des Systémes Complexes Rhône-Alpes (IXXI) and Laboratoire de Physique ENS-Lyon, France

The use of synthetic population for simulating complex phenomena: two examples


Recently we have witnessed a growing interest in complex networks. Intricate weblike
structures describing a wide variety of technologically important information, among them:
internet, protein interactions, disease spread and opinion formation. Many models have been
developed to study the topological characteristics of network and how they influence the dy-
namics of the processes defined over them. In most of the cases, theoretical analysis has been
limited to the study of static networks. This is a good approximation when we consider pro-
cesses that operate on a time-scale much smaller than the network's evolution. However, when
the process has a time-scale comparable to that of the network's evolution, for example in the
cases of bluetooth worm diffusion, epidemics and rumors spreading, only numerical approaches
are possible. In this talk I present some results from studies using synthetic populations that
evaluate vaccine policy as well as diffusion of information by word of mouth in an urban area.
This approach uses an agent based model where individuals are endowed with demographic
characteristics and a routine of activities drawn from surveys. Links among individuals are
creating only when they share the same location at the same time. The model achieves a
second-to-second timescale, thus network topology changes rapidly. This kind of representa-
tion is highly detailed and due to the absence of any a priori dynamic can be considered as a
proxy to reality.



Novembro

2 de Novembro
Estelina Lora, CFC
"Electronic Properties of Doped Silicon Nanocrystals"

9 de Novembro
Domenico Logoteta, CFC
"Effects of quark matter nucleation on the evolution of protoneutron stars"

16 de Novembro
Cancelada

23 de Novembro
Luis Manuel Panchorrinha Fernandes
"Desvio de Lamb no hidrogénio muónico e o raio do protão"

30 de Novembro
Cláudia Cardoso
Molecules with High intrinsic hyperpolarizability.


Dezembro


7 de Dezembro
Filipe Veloso, LIP
"Medida da secção-eficaz de produção top-antitop em ATLAS"
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