arXiv subjects

Rui Pereira

Publications and source records attributed to Rui Pereira.

At least 19 recordsLinked to original sources

arXiv2025

High temporal stability of niobium superconducting resonators by surface passivation with organophosphonate self-assembled monolayers

One main limiting factor towards achieving high coherence times in superconducting circuits is two level system (TLS) losses. Mitigating such losses requires controlling the formation of native oxides at the metal-air interface. Here, we report the growth of alkyl-phosphonate self-assembled monolayers (SAMs) on Nb thin films following oxide removal. The impact of passivation was evaluated via the performance of coplanar waveguide resonators at 10mK, in terms of quality factor and resonant frequency, over six days of air exposure. Un-passivated resonators exhibited an ~80% increase in loss at single-photon power levels, whereas SAM-passivated resonators maintained excellent temporal stability, attributed to suppressed oxide regrowth. By employing a two-component TLS model, we discern distinct prominent loss channels for each resonator type and quantified the characteristic TLS loss of the SAMs to be ~5x10^-7. We anticipate our passivation methodology to offer a promising route toward industrial-scale qubit fabrication, particularly where long-term device stability is critical.

cond-mat.mtrl-sci↗

arXiv2024

Chronicles of CI/CD: A Deep Dive into its Usage Over Time

DevOps is a combination of methodologies and tools that improves the software development, build, deployment, and monitoring processes by shortening its lifecycle and improving software quality. Part of this process is CI/CD, which embodies mostly the first parts, right up to the deployment. Despite the many benefits of DevOps and CI/CD, it still presents many challenges promoted by the tremendous proliferation of different tools, languages, and syntaxes, which makes the field quite challenging to learn and keep up to date. Software repositories contain data regarding various software practices, tools, and uses. This data can help gather multiple insights that inform technical and academic decision-making. GitHub is currently the most popular software hosting platform and provides a search API that lets users query its repositories. Our goal with this paper is to gain insights into the technologies developers use for CI/CD by analyzing GitHub repositories. Using a list of the state-of-the-art CI/CD technologies, we use the GitHub search API to find repositories using each of these technologies. We also use the API to extract various insights regarding those repositories. We then organize and analyze the data collected. From our analysis, we provide an overview of the use of CI/CD technologies in our days, but also what happened in the last 12 years. We also show developers use several technologies simultaneously in the same project and that the change between technologies is quite common. From these insights, we find several research paths, from how to support the use of multiple technologies, both in terms of techniques, but also in terms of human-computer interaction, to aiding developers in evolving their CI/CD pipelines, again considering the various dimensions of the problem.

cs.SE↗

arXiv2022

ICT4S2022 -- Demonstrations and Posters Track Proceedings

Submissions accepted for The 8th International Conference on ICT for Sustainability (ICT4S 2022), Demonstrations and Posters Track Proceedings, Plovdiv, Bulgaria, Mon 13 - Fri 17 June 2022. Most of the submissions are included in the arXiv proceedings while some demonstrations and posters are out of arXiv publication scope as the ICT4S scope is broad and multidisciplinary. Corresponding posters are available on the ICT4S2022 - Demonstrations and Posters page.

cs.CY↗

arXiv2022

Energy Efficiency of Web Browsers in the Android Ecosystem

This paper presents an empirical study regarding the energy consumption of the most used web browsers on the Android ecosystem. In order to properly compare the web browsers in terms of energy consumption, we defined a set of typical usage scenarios to be replicated in the different browsers, executed in the same testing environment and conditions. The results of our study show that there are significant differences in terms of energy consumption among the considered browsers. Furthermore, we conclude that some browsers are energy efficient in several user actions, but energy greedy in other ones, allowing us to conclude that no browser is universally more efficient for all usage scenarios.

cs.SE↗

arXiv2021

Green Software Lab: Towards an Engineering Discipline for Green Software

This report describes the research goals and results of the Green Software Lab (GSL) research project. This was a project funded by Fundação para a Ciência e a Tecnologia (FCT) -- the Portuguese research foundation -- under reference POCI-01-0145-FEDER-016718, that ran from January 2016 till July 2020. This report includes the complete document reporting the results achieved during the project execution, which was submitted to FCT for evaluation on July 2020. It describes the goals of the project, and the different research tasks presenting the deliverables of each of them. It also presents the management and result dissemination work performed during the project's execution. The document includes also a self assessment of the achieved results, and a complete list of scientific publications describing the contributions of the project. Finally, this document includes the FCT evaluation report.

cs.SE↗

arXiv2020

Very high-order Cartesian-grid finite difference method on arbitrary geometries

An arbitrary order finite difference method for curved boundary domains with Cartesian grid is proposed. The technique handles in a universal manner Dirichlet, Neumann or Robin condition. We introduce the Reconstruction Off-site Data (ROD) method, that transfers in polynomial functions the information located on the physical boundary. Three major advantages are: (1) a simple description of the physical boundary with Robin condition using a collection of points; (2) no analytical expression (implicit or explicit) is required, particularly the ghost cell centroids' projection are not needed; (3) we split up into two independent machineries the boundary treatment and the resolution of the interior problem, coupled by the the ghost cell values. Numerical evidences based on the simple 2D convection-diffusion operators are presented to prove the ability of the method to reach at least the 6th-order with arbitrary smooth domains.

physics.comp-ph↗

arXiv2018

Deciphering the relative contribution of vascular inflammation and blood rheology in metastatic spreading

Vascular adhesion of circulating tumor cells (CTCs) is a key step in cancer spreading. If inflammation is recognized to favor the formation of vascular metastatic niches, little is known about the contribution of blood rheology to CTC deposition. Herein, a microfluidic chip, covered by a confluent monolayer of endothelial cells, is used for analyzing the adhesion and rolling of colorectal (HCT 15) and breast (MDA MB 231) cancer cells under different biophysical conditions. These include the analysis of cell transport in a physiological solution and whole blood; over a healthy and a TNF alpha inflamed endothelium; with a flow rate of 50 and 100 nL/min. Upon stimulation of the endothelial monolayer with TNF alpha (25 ng/mL), CTC adhesion increases by 2 to 4 times whilst cell rolling velocity only slightly reduces. Notably, whole blood also enhances cancer cell deposition by 2 to 3 times, but only on the unstimulated vasculature. For all tested conditions, no statistically significant difference is observed between the two cancer cell types. Finally, a computational model for CTC transport demonstrates that a rigid cell approximation reasonably predicts rolling velocities while cell deformability is needed to model adhesion. These results would suggest that, within microvascular networks, blood rheology and inflammation contribute similarly to CTC deposition thereby facilitating the formation of metastatic niches along the entire network, including the healthy endothelium. In microfluidic based assays, neglecting blood rheology would significantly underestimate the metastatic potential of cancer cells.

physics.bio-ph↗

arXiv2016

The Influence of the Java Collection Framework on Overall Energy Consumption

This paper presents a detailed study of the energy consumption of the different Java Collection Framework (JFC) implementations. For each method of an implementation in this framework, we present its energy consumption when handling different amounts of data. Knowing the greenest methods for each implementation, we present an energy optimization approach for Java programs: based on calls to JFC methods in the source code of a program, we select the greenest implementation. Finally, we present preliminary results of optimizing a set of Java programs where we obtained 6.2% energy savings.

cs.SE↗

arXiv2015

Querying Spreadsheets: An Empirical Study

One of the most important assets of any company is being able to easily access information on itself and on its business. In this line, it has been observed that this important information is often stored in one of the millions of spreadsheets created every year, due to simplicity in using and manipulating such an artifact. Unfortunately, in many cases it is quite difficult to retrieve the intended information from a spreadsheet: information is often stored in a huge unstructured matrix, with no care for readability or comprehensiveness. In an attempt to aid users in the task of extracting information from a spreadsheet, researchers have been working on models, languages and tools to query. In this paper we present an empirical study evaluating such proposals assessing their usage to query spreadsheets. We investigate the use of the Google Query Function, textual model-driven querying, and visual model-driven querying. To compare these different querying approaches we present an empirical study whose results show that the end-users' productivity increases when using model-driven queries, specially using its visual representation.

cs.SE↗

arXiv2013

Integral field spectroscopy of supernova explosion sites: constraining mass and metallicity of the progenitors -- II. Type II-P and II-L supernovae

Thirteen explosion sites of type II-P and II-L supernovae in nearby galaxies have been observed using integral field spectroscopy, enabling both spatial and spectral study of the explosion sites. We used the properties of the parent stellar population of the coeval supernova progenitor star to derive its metallicity and initial mass (c.f. Paper I). The spectrum of the parent stellar population yields the estimates of metallicity via strong-line method, and age via comparison with simple stellar population (SSP) models. These metallicity and age parameters are adopted for the progenitor star. Age, or lifetime of the star, was used to derive initial (ZAMS) mass of the star by comparing with stellar evolution models. With this technique, we were able to determine metallicity and initial mass of the SN progenitors in our sample. Our result indicates that some type-II supernova progenitors may have been stars with mass comparable to SN Ib/c progenitors.

astro-ph.CO↗

arXiv2013

Integral field spectroscopy of supernova explosion sites: constraining mass and metallicity of the progenitors - I. Type Ib and Ic supernovae

Integral field spectroscopy of 11 type-Ib/c supernova explosion sites in nearby galaxies has been obtained using UH88/SNIFS and Gemini-N/GMOS. The use of integral field spectroscopy enables us to obtain both spatial and spectral information of the explosion site, allowing the identification of the parent stellar population of the supernova progenitor star. The spectrum of the parent population provides metallicity determination via strong-line method and age estimation obtained via comparison with simple stellar population (SSP) models. We adopt this information as the metallicity and age of the supernova progenitor, under the assumption that it was coeval with the parent stellar population. The age of the star corresponds to its lifetime, which in turn gives the estimate of its initial mass. With this method we were able to determine both the metallicity and initial (ZAMS) mass of the progenitor stars of the type Ib and Ic supernovae. We found that on average SN Ic explosion sites are more metal-rich and younger than SN Ib sites. The initial mass of the progenitors derived from parent stellar population age suggests that SN Ic have more massive progenitors than SN Ib. In addition, we also found indication that some of our SN progenitors are less massive than ~25 Msun, indicating that they may have been stars in a close binary system that have lost their outer envelope via binary interactions to produce Ib/c supernovae, instead of single Wolf-Rayet stars. These findings support the current suggestions that both binary and single progenitor channels are in effect in producing type Ib/c supernovae. This work also demonstrates the power of integral field spectroscopy in investigating supernova environments and active star forming regions.

astro-ph.CO↗

arXiv2011

PTF10ops - a subluminous, normal-width lightcurve Type Ia supernova in the middle of nowhere

PTF10ops is a Type Ia supernova (SN Ia), whose lightcurve and spectral properties place it outside the current SN Ia subtype classifications. Its spectra display the characteristic lines of subluminous SNe Ia, but it has a normal-width lightcurve with a long rise-time, typical of normal luminosity SNe Ia. The early-time optical spectra of PTF10ops were modelled using a spectral fitting code and found to have all the lines typically seen in subluminous SNe Ia, without the need to invoke more uncommon elements. The host galaxy environment of PTF10ops is also unusual with no galaxy detected at the position of the SN down to an absolute limiting magnitude of r \geq -12.0 mag, but a very massive galaxy is present at a separation of ~148 kpc and at the same redshift as suggested by the SN spectral features. The progenitor of PTF10ops is most likely a very old star, possibly in a low metallicity environment, which affects its explosion mechanism and observational characteristics. PTF10ops does not easily fit into any of the current models of either subluminous or normal SN Ia progenitor channels.

astro-ph.SR↗

arXiv2008

Cosmic ray velocity and electric charge measurements with the AMS/RICH detector: prototype results

The Alpha Magnetic Spectrometer (AMS) to be installed on the International Space Station (ISS) will measure charged cosmic ray spectra of elements up to iron, in the rigidity range from 1 GV to 1 TV, for at least three years. AMS is a large angular spectrometer composed of different subdetectors, including a proximity focusing Ring Imaging CHerenkov (RICH) detector. This will be equipped with a mixed radiator made of aerogel and sodium fluoride (NaF), a lateral conical mirror and a detection plane made of 680 photomultipliers coupled to light guides. The RICH detector allows measurements of particle's electric charge up to iron, and particle's velocity. Two possible methods for reconstructing the Cherenkov angle and the electric charge with the RICH will be discussed. A RICH prototype consisting of a detection matrix with 96 photomultipliers, a segment of a conical mirror and samples of the radiator materials was built and its performance was evaluated using ion beam data. Results from the last test beam performed with ion fragments resulting from the collision of a 158 GeV/c/nucleon primary beam of indium ions (CERN SPS) on a lead target are reported. The large amount of collected data allowed to test and characterize different aerogel samples and the NaF radiator. In addition, the reflectivity of the mirror was evaluated. The data analysis confirms the design goals.

astro-ph↗

arXiv2008

AMS - a magnetic spectrometer on the international space station

The Alpha Magnetic Spectrometer (AMS) is a particle detector, designed to search for cosmic antimatter and dark matter and to study the elemental and isotopic composition of primary cosmic rays, that will be installed on the International Space Station (ISS) in 2008 to operate for at least three years. The detector will be equipped with a ring imaging Cherenkov detector (RICH) enabling measurements of particle electric charge and velocity with unprecedented accuracy. Physics prospects and test beam results are shortly presented.

astro-ph↗

arXiv2008

Isotopic mass separation with the RICH detector of the AMS Experiment

The Alpha Magnetic Spectrometer (AMS) to be installed on the International Space Station (ISS) will be equipped with a proximity focusing Ring Imaging Cerenkov detector (RICH). Reconstruction of the Cerenkov angle and the electric charge with RICH are discussed. A likelihood method for the Cerenkov angle reconstruction was applied leading to a velocity determination for protons with a resolution around 0.1%. The electric charge reconstruction is based on the counting of the number of photoelectrons and on an overall efficiency estimation on an event-by-event basis. The isotopic mass separation of helium and beryllium is presented.

astro-ph↗

arXiv2008

The Ring Imaging Cherenkov detector of the AMS experiment: test beam results with a prototype

The Alpha Magnetic Spectrometer (AMS) to be installed on the International Space Station (ISS) will be equipped with a proximity Ring Imaging Cherenkov (RICH) detector for measuring the velocity and electric charge of the charged cosmic particles. This detector will contribute to the high level of redundancy required for AMS as well as to the rejection of albedo particles. Charge separation up to iron and a velocity resolution of the order of 0.1% for singly charged particles are expected. A RICH protoptype consisting of a detection matrix with 96 photomultiplier units, a segment of a conical mirror and samples of the radiator materials was built and its performance was evaluated. Results from the last test beam performed with ion fragments resulting from the collision of a 158 GeV/c/nucleon primary beam of indium ions (CERN SPS) on a lead target are reported. The large amount of collected data allowed to test and characterize different aerogel samples and the sodium fluoride radiator. In addition, the reflectivity of the mirror was evaluated. The data analysis confirms the design goals.

astro-ph↗

arXiv2008

Particle identification with the AMS-02 RICH detector: D/p and anti-D/anti-p separation

The Alpha Magnetic Spectrometer (AMS), whose final version AMS-02 is to be installed on the International Space Station (ISS) for at least 3 years, is a detector designed to measure charged cosmic ray spectra with energies up to the TeV region and with high energy photon detection capability up to a few hundred GeV, using state-of-the art particle identification techniques. Among several detector subsystems, AMS includes a proximity focusing RICH enabling precise measurements of particle electric charge and velocity. The combination of both these measurements together with the particle rigidity measured on the silicon tracker endows a reliable measurement of the particle mass. The main topics of the AMS-02 physics program include detailed measurements of the nuclear component of the cosmic-ray spectrum and the search for indirect signatures of dark matter. Mass separation of singly charged particles, and in particular the separation of deuterons and antideuterons from massive backgrounds of protons and antiprotons respectively, is essential in this context. Detailed Monte Carlo simulations of AMS-02 have been used to evaluate the detector's performance for mass separation at different energies. The obtained results and physics prospects are presented.

astro-ph↗

arXiv2008

The RICH detector of the AMS-02 experiment: status and physics prospects

astro-ph↗