Percorrer por autor "Martins, R."
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- Angular distributions in $t \overline{t}H(H → b \overline{b})$ reconstructed events at the LHCPublication . Amor dos Santos, S. P.; Araque, J.P.; Cantrill, R.; Castro, N.F.; Fiolhais, M.C.N.; Frederix, R.; Gonçalo, R.; Martins, R.; Santos, R.; Silva, J.; Onofre, A.; Peixoto, H.; Reigoto, A.The associated production of a Higgs boson and a top-quark pair, $t{\bar t} H$, in proton-proton collisions is addressed in this paper for a center of mass energy of 13TeV at the LHC. Dileptonic final states of $t{\bar t}H$ events with two oppositely charged leptons and four jets from the decays $t\rightarrow bW^+ \rightarrow b \ell^+\nu_\ell$, $\bar{t}\rightarrow \bar{b}W^- \rightarrow \bar{b} \ell^-\bar{\nu}_\ell$ and $h\rightarrow b\bar{b}$, are used. Signal events, generated with MadGraph5_aMC@NLO, are fully reconstructed by applying a kinematic fit. New angular distributions of the decay products as well as angular asymmetries are explored in order to improve discrimination of $t{\bar t} H$ signal events over the dominant irreducible background contribution, $t{\bar t}b{\bar b}$. Even after the full kinematic fit reconstruction of the events, the proposed angular distributions and asymmetries are still quite different in the $t\bar{t}H$ signal and the dominant background ($t\bar{t}b\bar{b}$).
- ANTS2 package: simulation and experimental data processing for Anger camera type detectorsPublication . Morozov, A.; Solovov, V.; Martins, R.; Neves, F.; Domingos, V.; Chepel, V.ANTS2 is a simulation and data processing package developed for position sensitive detectors with Anger camera type readout. The simulation module of ANTS2 is based on ROOT package from CERN, which is used to store the detector geometry and to perform 3D navigation. The module is capable of simulating particle sources, performing particle tracking, generating photons of primary and secondary scintillation, tracing optical photons and generating photosensor signals. The reconstruction module features several position reconstruction methods based on the statistical reconstruction algorithms (including GPU-based implementations), artificial neural networks and k-NN searches. The module can process simulated as well as imported experimental data containing photosensor signals. A custom library for B-spline parameterization of spatial response of photosensors is implemented which can be used to calculate and parameterize the spatial response of a detector. The package includes a graphical user interface with an extensive set of configuration, visualization and analysis tools. ANTS2 is being developed with the focus on the iterative (adaptive) reconstruction of the detector response using flood field irradiation data. The package is implemented in C++ programming language and it is a multiplatform, open source project.
- Architectural Design for Heartbeat Detection Circuits using Verilog-A Behavioral ModelingPublication . Vieira, R.; Passos, F.; Póvoa, R.; Martins, R.; Horta, N.; Guilherme, J.; Lourenço, N.This work presents a study of two analog frontend circuit architectures for heartbeat detection. Both circuits present an amplification block as the first stage, followed by a band-pass filter. In the first, the heartbeat detection is done using an adaptive threshold based on pulse-width, whereas the heartbeat detection in the second is done using a sample and hold to find the maximum and minimum peak of each beating. Both architectures are modeled in Verilog-A and simulated using real-world ECG signals with different characteristics. This work studies possible fundamental analog circuit blocks suitable for wearable implementation. It evaluates critical performances requirements from the analysis of the behavior simulations. It was verified that the first circuit can properly detect heartbeats as long as the input-referred noise is below 21 μV, whereas the second one ensures it until 30 μV. The low cutoff frequency can be approximately 10 Hz without compromising the signal’s peaks, which means that these specifications can be relaxed substantially compared to systems intended to reconstruct the signal accurately.
- CYP3A5 genetic polymorphism in HIV-patientsPublication . Fernandes, A.; Cruz, J. P.; Martins, R.; Morais, J. G.; Ribeiro, A. C."A number of relevant polymorphisms are known for affecting the most common prescribed ARVs (antiretroviral), inducing drug toxicity, risk of virologic failure and may explain the interpatient variability for drug absorption pathways. CYP3A5 is an isoform of Cytochromes P4503A family, estimated to participate in the metabolism of 40 to 60% of all clinically administered drugs, namely atazanavir (1). The aim of this study was to characterize the CYP3A5 polymorphisms of HIV infected patients, from Santa Maria Hospital, Lisbon, Portugal."
- Dynamic Voltage-Combiners Biased OTA for Low-Power High-Speed SC CircuitsPublication . Póvoa, R.; Canelas, A.; Martins, R.; Lourenço, N.; Horta, N.; Goes, J.his paper presents the design of a fully-dynamic voltage-combiners biased CMOS operational transconductance amplifier, for low-power high-speed analog-to-digital converters and high-performance switched-capacitor filters, using the UMC 130nm node. The biasing is controlled by switched-capacitors and simulation results of an optimized solution using AIDA-C, a state-of-the-art multi-objective multi-constraint IC optimization tool, present a DC gain of 60.9dB, a gain-bandwidth product of 155.1MHz for a 6pF load and a current consumption of 0.69mArms for a sampling clock frequency of 100MHz.
- Efficient Yield Optimization Method using a Variable K-Means Algorithm for Analog IC SizingPublication . Canelas, A.; Martins, R.; Póvoa, R.; Lourenço, N.; Horta, N.This paper presents the study and implementation of a new efficient yield optimization technique for multi-objective optimization-based automatic analog integrated circuit sizing. The approach uses a commercial electrical simulator and standard process design kit (PDK) models to perform, during the optimization process, the same Monte Carlo (MC) simulations that designers use. The proposed yield estimation technique reduces the number of required MC simulations by using the k-means algorithm, with a variable number of clusters, to select only a handful potential solutions where the MC simulations are performed. Due to the use of a commercial simulator tool and foundry supplied PDK models the developed methodology provides the most accurate and reliable results, and also, the variable k-means algorithm is able to achieve 91% reduction in the total number of the MC simulations required for an optimization, when considering MC simulations for all solutions. Moreover, this new approach presents a 50% increase in speed performance when comparing to a previous yield optimization technique also using k-means and MC simulations.
- Experimental and Numerical Characterization of Stress-Strain Fields on Sandwich Beams Subjected to 3PB and 4PBPublication . Marat- Mendes, Rosa; Martins, R.; Reis, L.This work aims to evaluate and characterize the stress-strain fields in sandwich beams subjected to 3PB and 4PB. The correlation between the experimental and the finite element analysis are presented and allows to a better knowledge and understanding of the complex stress-strain fields in sandwich beams when subjected to bending loading. 3D finite element models were carried out using Siemens NX10 for assessing at three- and four-point-bending tests of sandwich beams with different conditions: two lengths of span (short- and long-beam); two core thicknesses (20 and 30 mm); and two different face materials (aluminum and basalt fiber reinforced polymer). The results obtained in the 3D finite element analyses were compared with the experimental results obtained by the digital image correlation and strain gauges so that the entire stress-strain-fields through thickness is analyzed and validated. Strain results obtained via digital image correlation, strain gauges and finite element analysis are in good agreement and the strain gauges analysis are complementary to digital image correlation in order to obtain the full-field strains in the sandwich composites.
- Experimental and Numerical Characterization of Stress-Strain Fields on Sandwich Beams, Subjected to 3PB and 4PBPublication . Marat-Mendes, R.; Martins, R.; Reis, L.
- Flexural testing and analysis of fullstrain-fields in sandwich composites.Publication . Marat-Mendes, R.; Martins, R.; Garcia, A.; Reis, L.The objective of this work was to characterize the full-field flexural behavior of composite sandwich beams. Finite element analysis was used to estimate the behavior of sandwich beams under three- and four-point-bending tests and were compared with experimental results obtained via digital image correlation and strain-gauges. Two different polyurethane core thicknesses and two different sandwich lengths were used to simulate short- and long-beam. Two distinct sandwich beams were used by means of two different faces: aluminum and basalt fiber reinforced polymer composite. Full-strain-fields and flexural displacements results were obtained showing that BFRP sandwiches exhibited higher flexibility and higher capacity of absorption energy than the aluminum specimens however with a higher prospect of core shear failure. For both face materials short-beams present higher strains than the long-beams and 4PB test specimens showed negative strain distribution in the upper side of the specimen and positive in the underside contrary to 3PB that presents positive strain distribution along the fulfilled. Moreover, results show that the strain distribution in not symmetric. Obtained experimental results are in good agreement with estimations; the digital image technique attested to be a complementary method to strain gages measurements in experimental full-strain-fields analysis.
- A Folded Voltage-Combiners Biased Amplifier for Low Voltage and High Energy-Efficiency ApplicationsPublication . Póvoa, R.; Lourenço, N.; Martins, R.; Canelas, A.; Horta, N.; Goes, J.The topic of this brief is a ingle-stage amplifier biased by a doublet of voltage-combiners in a folded configuration, in order to be supplied by a power source of 1.2 V, maintaining proper dc biasing and voiding the need of any device stacking. The topology has been automatically designed, optimized, and laid out, from sizing to layout level, using a layout-aware approach provided by the AIDA framework, a state-of-the-art analog IC design optimization framework. Experimental results prove that a gain of approximately 44 dB, together with a figure-of-merit higher than 1300 MHz × pF/mW are achievable using the proposed topology, with standard UMC 130 nm technology devices and a 1.2-V supply source. Finally, an extension to supply sources below nominal is explored, showing exciting results toward a future of high energy-efficiency amplifiers.
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