arXiv subjects

M. Oliveira

Publications and source records attributed to M. Oliveira.

8 recordsLinked to original sources

arXiv2026

Quality control and quality assurance evaluation of ALFE2, a large-dynamic-range front-end ASIC de-veloped for the ATLAS Liquid Argon Calorimeter high-luminosity LHC upgrade

ALFE2 is a front-end ASIC developed for the ATLAS Liquid Argon (LAr) Calorimeter upgrade during the High-Luminosity Large Hadron Collider (HL-LHC) phase. ALFE2 comprises four preamplifier/shaper channels, each providing two distinct gain outputs to cover a 16-bit dynamic range. A robotic system has been developed for the automatic quality control test of ALFE2, and over 10% of the 80,000 chips have been evaluated by September 2025. The evaluation has allowed us to establish grading criteria. Using these criteria, a yield of over 85% was achieved in the evaluation tests, and these criteria are now being applied to the ongoing full-production QC. Irradiation tests were also performed for the quality assurance of ALFE2. No significant performance degradation was observed during the total-ionizing-dose (TID) test. Based on the single-event effect (SEE) test results, an error rate of fewer than 4.6 single-event upsets (SEUs) per day is extrapolated for the entire ATLAS LAr Calorimeter during HL-LHC operation.

physics.ins-det↗

arXiv2026

Topological Stability of Random $cw$-Expansive Systems with Shadowing

This paper investigates the topological stability of random dynamical systems . Our main goal is to extend the classical result of Walters \cite{Walters77} to the random setting by employing the notions of random continuum-wise expansivity and shadowing property. We prove that any random dynamical system that is random $cw$-expansive and satisfies the random shadowing property is randomly topologically stable. Furthermore, in the random setting we establish the topological invariance of these properties under conjugacy and analyze the relationship between topological transitivity and the periodic shadowing property.

math.DS↗

arXiv2018

Altered Modularity and Disproportional Integration in Functional Networks are Markers of Abnormal Brain Organization in Schizophrenia

Modularity plays an important role in brain networks' architecture and influences its dynamics and the ability to integrate and segregate different modules of cerebral regions. Alterations in community structure are associated with several clinical disorders, specially schizophrenia, although its time evolution is not clear yet. In the present work, we analyze fMRI functional networks of $65$ healthy subjects (HC) and $44$ patients of schizophrenia (SZ), $28$ of them in a chronic state (CR) of illness, and $16$ at early stage (ES). We find clear differences in edges' weights distribution, networks density, community structure consistency and robustness against edge removal. In comparison to healthy subjects, we found that networks from SZ patients exhibits wider weight distribution, larger overall connectivity, and are more consistent in the community structure across subjects. We also showed that the networks of SZ patients tend to be more robust to edge removal than healthy subjects, while having lower network density. In the case of early stages patients, we found that their networks exhibit topological features consistently in between the ones obtained from the other two groups, resulting in a tendency towards the chronic group state.

q-bio.NC↗

arXiv2012

A plug-in rule for bandwidth selection in circular density estimation

A new plug-in rule procedure for bandwidth selection in kernel circular density estimation is introduced. The performance of this proposal is checked throughout a simulation study considering a variety of circular distributions exhibiting multimodality, peakedness and/or skewness. The plug-in rule behaviour is also compared with other existing bandwidth selectors. The method is illustrated with two classical datasets of cross-beds layers and animal orientation.

stat.ME↗

arXiv2000

Neutrino Masses and Mixing Angles in a Realistic String-Inspired Model

We analyse a supersymmetric string-inspired model of all fermion masses and mixing angles based on the Pati-Salam $SU(4)\times SU(2)_L \times SU(2)_R$ gauge group supplemented by a $U(1)_X$ flavour symmetry. The model involves third family Yukawa unification and predicts the top mass and the ratio of the vacuum expectation values $\tan β$. The model also provides a successful description of the CKM matrix and predicts the masses of the down and strange quarks. However our main focus is on the neutrino masses and MNS mixing angles, and we show how the recent atmospheric neutrino mixing observed by Super-Kamiokande, and the MSW solution to the solar neutrino problem lead to important information about the flavour structure of the model near the string scale. We show how single right-handed neutrino dominance may be implemented by the use of ``Clebsch zeros'', leading to the LMA MSW solution, corresponding to bi-maximal mixing. The LOW MSW and SMA MSW solutions are also discussed.

hep-ph↗

arXiv2000

Yukawa Unification as a Window into the Soft Supersymmetry Breaking Lagrangian

We study Yukawa unification, including the effects of a physical neutrino mass consistent with the Superkamiokande observations, in a string/$D$-brane inspired Pati-Salam model which allows the most general non-universal scalar and gaugino masses, including the usual $D$-term contributions which arise in SO(10). We investigate how the tight constraints from rare decays such as $b \to s γ$ and $τ\to μγ$ can provide information about the family dependent supersymmetry breaking soft Lagrangian, for example the trilinears associated with the second and third family. Many of our results also apply to SO(10) to which the model approximately reduces in a limiting case. In both models we find that Yukawa unification is perfectly viable providing the non-universal soft masses have particular patterns. In this sense Yukawa unification acts as a window into the soft supersymmetry breaking Lagrangian.

hep-ph↗

arXiv1998

On the relativistic L-S coupling

The fact that the Dirac equation is linear in the space and time derivatives leads to the coupling of spin and orbital angular momenta that is of a pure relativistic nature. We illustrate this fact by computing the solutions of the Dirac equation in an infinite spherical well, which allows to go from the relativistic to the non-relativistic limit by just varying the radius of the well.

physics.ed-ph↗

arXiv1998

Lepton Flavour Violation in String-Inspired Models

Lepton flavour violation has been proposed as a significant test of supersymmetric unification. Here we show that such signals are also a generic feature of supersymmetric string unified models in which there is no simple unified gauge group. In realistic models of this kind which involve third family Yukawa unification and large values of $\tan β$, there are generally heavy right-handed (singlet) neutrinos of intermediate mass $M_ν$, whose couplings violate lepton flavour. To illustrate these effects we calculate the rates for $μ\to e γ$ and $τ\to μgamma$ in the minimal supersymmetric $SU(4)\times SU(2)\times SU(2)$ model. Including only the minimum irreducible contributions, we find that both rates are enhanced relative to similar models with low $\tan β$, with $τ\to μgamma$ providing a decisive test of such models in the near future.

hep-ph↗