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café com física - ciclo de palestras
palestras de 2011
palestras informais abertas a todos (sala conf. 14:00h ::0.0)

Janeiro


11jan
Hélvio Vairinhos, CFC
"Cores Infinitas"
Resumo: Teorias de gauge SU(N) e afins no limite N --> infinito:
a importância destes modelos e os avanços recentes neste ramo, tanto a nível teórico como numérico.

18jan
Rui Silva, LIP
"A missão espacial DUAL"

A missão DUAL foi recentemente proposta ao concurso para missões da classe M da
ESA no âmbito do Programa Cosmic Vision (missões a lançar entre 2015 e 2025).
Este novo telescópio para raios gama integra um sistema de lentes de Laue
que permitirá focar a radiação gama emitida numa região do céu restrita pelo
campo de visão do sistema de lentes. No entanto, o DUAL permitirá simultaneamente
observar todo o céu em permanência, embora com pior sensibilidade e resolução.
É desta dualidade de modos de funcionamento que resulta o nome da missão.
A configuração do telescópio é determinada pela distância focal das lentes de
Laue, cerca de 30 metros, sendo o satélite composto por dois sub-módulos: o módulo
óptico (sistema de lentes de Laue) e o módulo do detector (plano focal de CdTe ou
germânio). Ambos os módulos estarão ligados por uma estrutura expansível até 30
metros.

25jan
Helena Santos, LIP/ FCUL
"The Heavy Ion Program of the ATLAS/LHC Experiment"

The ATLAS experiment is participating in the Heavy Ion Program of the
Large Hadron Collider (LHC), for which the main goal is to create strong
interacting matter under extreme energy density and temperature
conditions. Evidence from SPS/CERN and RHIC/BNL data suggests that in such
extreme conditions matter undergoes to a phase transition from ordinary
hadronic matter to a plasma of quarks and gluons, the QGP. The large
acceptance, high granularity calorimeters, silicon tracking detectors and
muon spectrometers allow ATLAS to study deeply the proprieties of such a
deconfined state of matter.


Fevereiro
1fev
Bruce Milne, CFC
"Investigation of colour tuning in firefly bioluminescence"

8fev
Isaac Vidana
"Estimation of the effect of hyperonic three-body forces on the maximum mass of neutron stars"

Abstract
A model based on a microscopic Brueckner--Hartree--Fock approach of hyperonic matter supplemented with additional simple phenomenological density-dependent contact terms is employed to estimate the effect of hyperonic three-body forces on the maximum mass of neutron stars. Our results show that although hyperonic three-body forces can reconcile the maximum mass of hyperonic stars with the current limit of 1.4-1.5 M_Sun, they are unable to provide the repulsion needed to make the maximum mass compatible with the observation of massive neutron stars, such as the recent measurements of the unusually high masses of the millisecond pulsars PSR J1614-2230 (1.97 pm 0.04 M_Sun) and PSR J1903+0327 (1.667 pm 0.021 M_Sun).


15fev
Rui Travasso, CFC
Delivering nutrients to a tissue: blood flow and growing capillaries
Understanding angiogenesis (the growth from new vessels starting from
existing vasculature) is a challenging problem with important consequences
for the treatment of cancer and other pathological situations. We present
a multi-scale phase-field model for the description of angiogenesis that
combines the benefits of continuum physics description and the capability
of tracking individual cells.
The model allows us to discuss the role of the endothelial cells~
chemotactic response and proliferation rate as key factors that tailor the
neovascular network. Importantly, we also test the predictions of our
theoretical model against relevant experimental approaches in mice that
displayed distinctive vascular patterns. For a correct understanding of
the capillary dynamics it is necessary to analyze the irrigation in the
tissue by studying how blood flows in the newly formed network. We present
the first steps in this direction by looking at flows in healthy and
pathological scenarios.

22fev
Helena Vieira Alberto, CEMDRX
Mechanisms of electron polarization in shallow muonium in CdS and CdTe

Resumo:
When positive muons are implanted in a semiconductor like CdS or
CdTe, a fraction of them form a weak bound state with an electron ~
shallow muonium - which mimics hydrogen behavior inside the material.
At low temperatures ( 0.05 K) the relative populations of the electron
spin states (up and down) is observed to change with increasing
external magnetic field (up to 2 T). Experimental findings indicate
that the observed electron polarization is not due to the
paramagnetism of the muonium atom but to a polarization buildup in the
preceding stage following muon implantation. A model for shallow
muonium formation is presented based on the experimental results.







Março

1 (Dia da Universidade)



9mar (quarta-feira) 12h
Hiroki KUSANO (Research Institute for Science and Engineering,
Waseda University)
"Scintillation and ionization yields in high-density gaseous xenon for
alpha particles"

Abstract
The scintillation and ionization yields produced by alpha-particles
were studied in high-density gaseous xenon. High-density xenon is an
attractive medium for radiation detectors, but there is a lack of
information about basic properties of radiation response near its
critical point. In this study, the average numbers of scintillation
photons and ionization electrons produced by 5.49 MeV alpha-particles
were measured in high-density gaseous xenon in the density range of 0.12
- 1.2 g/cm3 at room temperature. Density dependence of scintillation
yield was observed under no electric field. Scintillation yield
decreases approximately linearly in densities from 0.12 to 0.6 g/cm3.
Over 0.6 g/cm3, some changes in relation of scintillation yield to gas
density were observed. Correlations between numbers of photons and
electrons were obtained under electric field at different densities.
Possible changes of the scintillation processes were discussed.

15mar
Rui Vilão, CEMDRX
"Hydrogen in semiconductors: a muSR approach"

Resumo
"In this talk a brief review is given on the topic of the isolated hydrogen impurity in semiconductors. The essential experimental results in this field have been obtained by research on muonium, the bound state of an electron with a positive muon, which in condensed matter physics and chemistry may be considered a light pseudo-isotope of hydrogen. Upon obtaining the basic hydrogen/muonium configurations in the semiconductor lattice, usually by a combination of theoretical and experimental results, the temperature dependance of the muSR signals allows to locate the relevant hydrogen donor and/or acceptor levels in the bandgap."



22mar
Thomas Schweizer,
Max Planck Institute for Physics, Munchen

Discovery of the Crab pulsar above 25 GeV

abstract:
The Crab is one of the most interesting sources in the
sky. It resulted from a supernova explosion in the year
1054 AD. It consists of a pulsar which is feeding a pulsar
wind nebula. The Crab one of the strongest gamma ray sources
in the sky used my many instruments as calibration source and
its millisecond pulsar has unique properties. The Crab pulsar
has been finally detected by the MAGIC telescope after the
installation of a new trigger system, the analogue sum trigger. The low
trigger threshold was a major achievement for ground-baseed
instruments. The Crab has surprised the gamma community by
an gamma-ray flare in September 2010 since it was expected to
be a steady source. In this talk the Crab system will be presented
as seen in Gamma rays where exciting properties are revealed.


Abril

5abr
Apostolos Marinopoulos, CFC
First principles study of segregation to the Sigma 5(310) grain
boundary of cubic zirconia

ABSTRACT: While yttrium and impurity segregation at interfaces of
yttria-stabilized zirconia (YSZ) has
been intensively studied experimentally, the mechanisms governing the
propensity for segregation are still not fully understood. The
segregation energetics
of yttrium and aluminum, another common segregant at interfaces of
YSZ, were studied by means of
first principles calculations based on density functional theory.
Site-dependent formation energies
were calculated following the substitutional incorporation of yttrium
and aluminum in the
near-interface region of the Sigma 5(310) grain boundary in cubic
zirconia, for which recent
experimental data revealed strong yttrium enrichment. Aluminum
segregation was found to be strongly
favored, accompanied by extensive changes in its local environment and
coordination. Yttrium
displayed a segregation propensity dependent on the site of
substitution that correlated with
the ability of its surrounding environment to accommodate the misfit
strain by a breathing-type
relaxation and increase of the nearest-neighbor yttrium-oxygen
distances. Formation energies of oxygen
vacancies were also determined near the interface, both as isolated
defects and also by
considering cosegregation with yttrium; the ensuing defect association
led to stable
yttrium-vacancy complexes and increased the energy gain from yttrium
incorporation at the core of the grain boundary.


12abr Luiz de Viveiros, LIP

Dark Matter Direct Detection: An Overview


You are invited to attend the next session of Café com Física
12th April, 14h, Sala de Conferências, 3rd floor,
Luiz de Viveiros, LIP
Dark Matter Direct Detection: An Overview


Páscoa (24)

26abr
Prof. Dr. Dennis R. Schaart, Delft University of Technology, The Netherlands

Emerging technologies in time-of-flight PET and PET/MRI

Abstract:
The use of time-of-flight (TOF) information in positron emission
tomography (PET) has been shown to significantly improve image
quality. Current TOF-PET systems have a coincidence resolving time
(CRT) of about ~500 ps FWHM. Such systems allow oncologists to find
small tumors and metastases that would go undetected without TOF.
Several new technologies are expected to enable significant further
enhancement of the TOF-PET benefits. For example, recent innovations
in PET scintillation materials result in faster and more intense
scintillation light pulses, which is crucial to obtain even better CRT
values. As another example, the so-called silicon photomultipliers
(SiPMs) is a novel type of solid-state light sensor with excellent
characteristics for application in TOF-PET scintillation detectors.
SiPMs exhibit fast response and high internal signal gain, while at
the same time they 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, and
depth-of-interaction (DOI) correction. Moreover, SiPMs will enable
integration of TOF-PET and MRI in a way similar to the integration of
PET and CT into PET/CT systems that nowadays represent the state of
the art in clinical molecular imaging. PET/MRI is expected to open up
new possibilities for acquiring clinically relevant in-vivo
information, such as concurrent functional and anatomical imaging with
excellent soft-tissue contrast, MRI-based correction of PET
attenuation and motion artefacts, among others. An overview of these
emerging technologies will be presented.


Maio

3mai
Alexandre Lindote, LIP
Dark Matter Direct Detection: The ZEPLIN-III Experiment

17mai
Rafael Cavagnoli, CFC
"Transição de fases hadron-quark em matéria assimétrica e condensados
bosônicos"

31mai
José Matias
"Xenon100: últimos resultados"

Junho


Julho

5jun
Vânia Almeida - CI
"Piezoelectric probe for non-invasive cardiovascular studies - key
indicators in the arterial pressure waveform."

Abstract
The social and economic impact of cardiovascular diseases (CVD) and
the importance of efficient early diagnostic tools keep mobilizing the
interest of many researchers. Continuous monitoring and analysis of
physiological signals, as well as online interactive signal processing
are essential in the management of ill patients. Historically the cuff
sphygmomanometer was the first method to quantify a part of the
medical information contained in the arterial pressure waveform (APW);
however it provides a limited amount of information. In this work we
concentrate in developing a non-invasive device suitable to carotid
APW measurements based in piezoelectric sensors, as well the
utilization of data mining techniques in order to identify the key
indicators in the development of CVD. This system could be usefully
employed as a cheap and effective CVD screening technique for use in
general practice clinics.


12-15 de Julho
Curso: Física Estrelas Compactas

Conrado Albertus Torres(Universidade de Salamanca)
#1 Spectra: Baryons, Mesons, Hyperons.
Introduction to the quark model *
Aspects of heavy baryon physics *
Aspects of heavy quark symmetry *
Hypernuclei
Variational methods

Hands-on session: Using mathematica or fortran/c to check variational
method for a simple potential in hypernuclei.

Maria Angeles Perez-Garcia (Universidade de Salamanca)
#2 Strong interaction-low energies: nucleons
EFT Lagrangians: Walecka model
Mean field approximation
neutron stars
Pulsars: Magnetic fields and polatization of matter
Quantization of dynamics: Landau levels
Computer Simulations

Hands-on session: Using mathematica or fortran/c to solve MF equations
in Walecka model.

19jun
1- Nadja Magalhães, UNIFESP, Brasil
Ondas gravitacionais
2- Carlos Frajuca
Status and Improvements for Schenberg Gravitational Wave


20jun
(sessão especial e última antes do Verão)
Prof. Hanno Éssen
Department of Mechanics, KTH, Stockholm, Sweden.
"Why Meissner was wrong or a classical explanation of flux expulsion from superconductors"

Abstract:
The discovery by Meissner and Ochsenfeld in 1933 that the magnetic
field inside a conductor is expelled when it is cooled down to become
superconducting was considered very surprising at the time. Meissner
wrote that this has no classical explanation. Since then virtually
every textbook stresses that this means that a superconductor is in
fact not just a zero resistivity perfect conductor but in addition has
the mysterious property that it can expel internal magnetic flux. In
this colloquium I will present evidence that this is all a
misunderstanding based on insufficient knowledge of what classical
physics in fact predicts about the magnetic flux inside perfect
conductors.


Setembro

20set
X. Roca-Maza (Universidade de Milão)
"Relativistic mean field interaction with density dependent meson-nucleon vertices based on microscopical calculations"

Abstract:
Although ab-initio calculations of relativistic Brueckner theory lead to large
scalar isovector fields in nuclear matter, at present, successful versions of covariant
density functional theory neglect the interactions in this channel. A
new high precision density functional DD-ME delta is presented which includes
four mesons sigma, omega, rho eand delta with density dependent meson-nucleon couplings.
It is based to a large extent on microscopic ab-initio calculations in nuclear
matter. Only four of its parameters are determined by adjusting to binding
energies and charge radii of finite nuclei. The other parameters, in particular
the density dependence of the meson-nucleon vertices, are adjusted
to non-relativistic and relativistic Brueckner calculations of symmetric and
asymmetric nuclear matter. The isovector effective mass m_p-m_n derived
from relativistic Brueckner theory is used to determine the coupling strength
of the delta-meson and its density dependence

Outubro

4out
Rui Travasso (CFC)
"Why do protein folding rates correlate with metrics of native
topology?"

Resumo:
For almost 15 years, the experimental correlation between protein folding
rates and the contact order para- meter has been under scrutiny. Here, we
use a lattice model combined with a native-centric interaction potential
to investigate the physical roots of this empirical observation. We
simulate circular permutants thus eliminating dependencies of the folding
rate on other protein properties (e.g. stability). We show that the
rate-contact order correlation is a consequence of the fact that, in high
contact order structures, the contact order of the transition state
ensemble closely mirrors the contact order of the native state. This
happens because, in these structures, the native topology is represented
in the transition state through the formation of a network of tertiary
interactions that are distinctively long-ranged.
Autores: Patricia F. N. Faisca, Rui D. M. Travasso, Andrea Parisi, and
Antonio Rey

18out
Marco Pinto e Hugo Simões (LIP)
"RTmon: a device for real-time (dose) monitoring of radiotherapeutic
treatments"

Abstract:
Modern radiotherapy techniques are providing increasingly higher
conformality, a potential invaluable clinical benefit to the patient.
Consequently, in both single and multi-fractionated RT, patient
misalignments and changing internal anatomy are also becoming more
critical since higher conformality may equally represent a higher risk
of target underdosage or organ-at-risk overdosage.
State-of-the-art image-guided radiotherapy (IGRT) techniques aim at
providing feedback to the radiation oncologist, some times at the cost
of increased dosage, other times providing insufficient clinical
information. We investigate a novel imaging system specially designed
for providing clinically relevant information for monitoring
conventional and modern photon radiotherapy. The
principle-of-operation and feasibility details of such system indicate
that it may allow monitoring each field (and segment, in the case of
intensity-modulated radiotherapy IMRT) during all treatment fractions
without whatsoever additional dose. The concept of such system will be
presented and thoroughly explained with several simulation studies
representing different clinical irradiation scenarios. Along with the
concept, the proof-of-principle results will also be presented. These
first experimental results were obtained at Coimbra Institute of
Oncology (IPOCFG,EPE) and the correlation between simulated and
experimental results and the experimental conditions and data
post-processing will be discussed.


25out
Silvia Chiacchiara (CFC)
"Solving the Boltzmann equation for cold trapped Fermi gases"

Abstract: In this seminar I will present some recent results we obtained for two collective modes (quadrupole and scissors) of cold trapped Fermi gases. The study focuses on the normal-fluid phase and is done in the framework of the Boltzmann equation. Experimental data for these modes are available, and previous works showed that the Boltzmann equation approach fails to describe them satisfactorily, even when in-medium effects are included. We argue that the analytical method used to solve the Boltzmann equation was inappropriate. This commonly used method is the method of phase-space moments at lowest order (2nd order). In this approach, just one parameter (the relaxation time) quantifies the effect of collisions in the whole
atomic cloud. But the collision rate can be very high at the center of the trap and very low at its surface, therefore one should take into account its spatial variations, that is, extend the method to next order (4th order). In fact, including of the fourth order terms, we clearly improve the description of the experimental data.


Novembro

3nov
Louis Lyons (Universidade de Oxford)
"BAYES VERSUS FREQUENTISM: THE CONTINUING STATISTICAL BATTLE"

Abstract:
These two very different approaches to analysing data are described and contrasted, using examples both from every-day life and from the world of Physics. Their interpretations of 'probability' are contrasted. When used for determining parameters of a theory, cases where the resulting answers differ significantly are described. Finally, a summary is given of the differences between the Bayesian and Frequentist approaches.
→[ transparências]



15nov
Paolo Pasanti
"Properties of the Fermion Hard Sphere Fluid"

abstract: The hard sphere model has historically provided remarkable results
in fluid dynamics. In particular, the fermion hard sphere fluid is a very
useful model for investigating concepts and approximations employed to study the properties
of nuclear matter. We report the results of calculations of equilibrium
and non equilibrium properties of the fermion hard sphere fluid, carried out
using the formalism based on correlated basis functions (CBF) and the cluster
expansion technique. The calculation of the energy per particle as a
function of density has been carried out solving the set of FHNC integral
equations, allowing one to sum the relevant contributions at all orders of the
cluster expansion. The CBF formalism has been also exploited to obtain
an effective interaction, suitable for calculating transport properties among
which the shear viscosity coefficient.

22nov
Micael Oliveira, CFC
"Spin-orbit effects in bismuth atom and dimer: What can we learn from a simple tight-binding model"

Abstract: "Relativistic effects in general, and spin-orbit in particular, are known to be of great importance in the determination of the electronic properties of a large number of systems, especially when these systems include heavy elements like bismuth. State-of-the-art ab initio methods exist that are able to accurately include these relativistic effects, but sometimes simpler methods, like tight binding models, are equally useful in the study of these effects. In this work we introduce a tight-binding model including spin-orbit coupling, compare it to density functional theory calculations, and show how it can be used to gain insight into the effect of the spin-orbit coupling in some properties of the bismuth atom and dimer."

29nov
Maria José Marques, CEMDRX
O problema das tensões residuais em equipamentos industriais de grande porte sujeitos a ambientes corrosivos

Abstract:
As tensões residuais existem praticamente em todas as peças rígidas, metálicas, ou não, e traduzem
a história mecânica e metalúrgica do componente ao longo da sua elaboração, dos tratamentos a que foi submetido e dos períodos de funcionamento posterior. Elas resultam da heterogeneidade das deformações plásticas introduzidas a qualquer escala do componente ou da estrutura, e podem ser criadas por efeitos térmicos, metalúrgicos e mecânicos, que atuam frequentemente de forma combinada, o que torna a sua previsão extremamente complexa.
As tensões residuais podem ser benéficas, mas podem também comprometer o bom desempenho dos componentes. A redução da resistência à fadiga na presença de tensões residuais de tração é um dos problemas mais preocupantes. A previsão e o controlo das tensões residuais é, por esse motivo, necessária e fundamental em áreas como a indústria automóvel, aeronáutica e nuclear.
Nesta palestra será abordada a génese das tensões residuais e serão apresentados alguns métodos para a sua determinação, com particular incidência nas técnicas que utilizam a difração de raios X e a difração de neutrões. Será também apresentado um estudo atualmente em curso no âmbito do projeto “StressClad”, no qual se pretende estudar o comportamento mecânico e o comportamento à corrosão das paredes interiores de reatores químicos e de permutadores de calor, usados na indústria petroquímica e de produção de energia, revestidas com camadas de aço inoxidável por soldadura.


Dezembro


6dez
Myrta Gruning
A first-principle real-time approach to ultrafast and extreme nonlinear optical phenomena in solids and nano-structures

abstract:
Many-body effects are known to play a crucial role in the electronic and optical properties of solids and nano-structures. Nevertheless the majority of theoretical and numerical approaches able to capture the
influence of Coulomb correlations are restricted to the linear response regime. In this work we introduce a novel approach based on a real-time solution of the electronic dynamics. The proposed approach reduces to the well-known Bethe-Salpeter equation in the linear limit regime and it makes possible, at the same time, to investigate correlation effects in nonlinear optical phenomena.

After serving the bitter coffee of the theoretical approach, I will (try to) sweeten it with some examples of application to h-BN, GaAs and ZnO and carbon nanotubes.
C. Attaccalite, MG, A. Marini arXiv:1109.2424


13dez
Carlos Fiolhais CFC
Astrónomos portugueses membros da Royal Society

Sumário
Um total de 25 cientistas e diplomatas portugueses foram, nos séculos XVII, XVIII e XIX, membros da Royal Society, a mais antiga sociedade científica do mundo em contínua actividade. Em 2010 comemorou-se em Coimbra com uma exposição na Biblioteca Joanina os 350 anos dessa sociedade e, em resultado, acaba de sair um livro publicado pela Biblioteca Geral da Universidade de Coimbra intitulado "/Membros Portugueses da Royal Society"./ É uma edição bilingue, em português e inglês, que mostra várias obras da Biblioteca Geral e do Arquivo para além de instrumentos das coleções do Museu da Ciência da Universidade de Coimbra. O período de maior brilho da presença portuguesa na Royal Society ocorreu no século XVIII. Há três cientistas desse século que deram contribuições para a astronomia: o padre jesuíta italiano João Baptista Carbone, que foi chamado a Portugal pelo rei D. João V, e os padres oratorianos João Chevalier, que, devido às perseguições do Marquês de Pombal, haveria de se estabelecer em Bruxelas, onde chegou a Presidente da Real Academia das Ciências Belga, e Teodoro de Almeida, que, também perseguido, se refugiou em Espanha e França, onde alcançou grande notariedade. Teodoro de Almeida, observou no Porto em 1763 um trânsito de Vénus, uma observação importante para a determinação da distância da Terra ao Sol. Outro notável membro português da Royal Society que ajudou à astronomia com a construção de instrumentos foi João Jacinto Magalhães, um "estrangeirado" em Londres,que conviveu com alguns dos maiores cientistas do seu tempo. Muitas observações desses astrónomos foram publicadas, em latim ou inglês, na revista da Royal Society, as "/Philosophical Transactions"/, uma publicação quase tão antiga como a sociedade.

A astronomia do século XVIII era uma astronomia de posição, que procurava medidas cada vez mais precisas, o que só era possível por ter ficado estabelecida no século XVII, no quadro da Royal Society, a mecânica de Newton e por se terem desenvolvido melhores instrumentos. Os cientistas portugueses passaram a integrar-se em colaborações internacionais, correspondendo-se com os seus colegas estrangeiros, numa premonição do que é hoje a moderna colaboração internacional na área da astronomia.


20dez
João Carvalho
"Latest results on the Standard Model Higgs searches in ATLAS and CMS at LHC"

Sumário
The last particle of the Standard Model still to be found is the Higgs boson. The search for this particle is one of the main objectives of the Large Hadron Collider experiments at CERN, in particular the ATLAS and CMS collaborations. The results obtained with most of the data acquired during 2011 will be shown, as the excluded and the most probable mass regions. Hints of the presence of the boson were found, but not yet a conclusive evidence for it, while almost all of the most probable mass values were excluded with large confidence level.
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