arXiv subjects

Antonio da Silva

Publications and source records attributed to Antonio da Silva.

9 recordsLinked to original sources

arXiv2024

Design and implementation of a synchronous Hardware Performance Monitor for a RISC-V space-oriented processor

The ability to collect statistics about the execution of a program within a CPU is of the utmost importance across all fields of computing since it allows characterizing the timing performance of a program. This capability is even more relevant in safety-critical software systems, where it is mandatory to analyze software timing requirements to ensure the correct operation of the programs. Moreover, in order to properly evaluate and verify the extra-functional properties of these systems, besides timing performance, there are many other statistics available on a CPU, such as those associated with resource utilization. In this paper, we showcase a Performance Measurement Unit, also known as Hardware Performance Monitor, integrated into a RISC-V On-Board Computer designed for space applications by our research group. The monitoring technique features a novel approach whereby the events triggered are not counted immediately but instead are propagated through the pipeline so that their annotation is synchronized with the executed instruction. Additionally, we demonstrate the use of this PMU in a process to characterize the execution model of the processor. Finally, as an example of the statistics provided by the PMU, the results obtained running the CoreMark and Dhrystone benchmarks on the RISC-V OBC are shown.

cs.AR↗

arXiv2023

Fast emulation of cosmological density fields based on dimensionality reduction and supervised machine-learning

N-body simulations are the most powerful method to study the non-linear evolution of large-scale structure. However, they require large amounts of computational resources, making unfeasible their direct adoption in scenarios that require broad explorations of parameter spaces. In this work, we show that it is possible to perform fast dark matter density field emulations with competitive accuracy using simple machine-learning approaches. We build an emulator based on dimensionality reduction and machine learning regression combining simple Principal Component Analysis and supervised learning methods. For the estimations with a single free parameter, we train on the dark matter density parameter, $Ω_m$, while for emulations with two free parameters, we train on a range of $Ω_m$ and redshift. The method first adopts a projection of a grid of simulations on a given basis; then, a machine learning regression is trained on this projected grid. Finally, new density cubes for different cosmological parameters can be estimated without relying directly on new N-body simulations by predicting and de-projecting the basis coefficients. We show that the proposed emulator can generate density cubes at non-linear cosmological scales with density distributions within a few percent compared to the corresponding N-body simulations. The method enables gains of three orders of magnitude in CPU run times compared to performing a full N-body simulation while reproducing the power spectrum and bispectrum within $\sim 1\%$ and $\sim 3\%$, respectively, for the single free parameter emulation and $\sim 5\%$ and $\sim 15\%$ for two free parameters. This can significantly accelerate the generation of density cubes for a wide variety of cosmological models, opening the doors to previously unfeasible applications, such as parameter and model inferences at full survey scales as the ESA/NASA Euclid mission.

astro-ph.CO↗

arXiv2022

New Horizons for Fundamental Physics with LISA

The Laser Interferometer Space Antenna (LISA) has the potential to reveal wonders about the fundamental theory of nature at play in the extreme gravity regime, where the gravitational interaction is both strong and dynamical. In this white paper, the Fundamental Physics Working Group of the LISA Consortium summarizes the current topics in fundamental physics where LISA observations of GWs can be expected to provide key input. We provide the briefest of reviews to then delineate avenues for future research directions and to discuss connections between this working group, other working groups and the consortium work package teams. These connections must be developed for LISA to live up to its science potential in these areas.

gr-qc↗

arXiv2017

Theia: Faint objects in motion or the new astrometry frontier

In the context of the ESA M5 (medium mission) call we proposed a new satellite mission, Theia, based on relative astrometry and extreme precision to study the motion of very faint objects in the Universe. Theia is primarily designed to study the local dark matter properties, the existence of Earth-like exoplanets in our nearest star systems and the physics of compact objects. Furthermore, about 15 $\%$ of the mission time was dedicated to an open observatory for the wider community to propose complementary science cases. With its unique metrology system and "point and stare" strategy, Theia's precision would have reached the sub micro-arcsecond level. This is about 1000 times better than ESA/Gaia's accuracy for the brightest objects and represents a factor 10-30 improvement for the faintest stars (depending on the exact observational program). In the version submitted to ESA, we proposed an optical (350-1000nm) on-axis TMA telescope. Due to ESA Technology readiness level, the camera's focal plane would have been made of CCD detectors but we anticipated an upgrade with CMOS detectors. Photometric measurements would have been performed during slew time and stabilisation phases needed for reaching the required astrometric precision.

astro-ph.IM↗

arXiv2016

Unveiling the Dynamics of the Universe

We explore the dynamics and evolution of the Universe at early and late times, focusing on both dark energy and extended gravity models and their astrophysical and cosmological consequences. Modified theories of gravity not only provide an alternative explanation for the recent expansion history of the universe, but they also offer a paradigm fundamentally distinct from the simplest dark energy models of cosmic acceleration. In this review, we perform a detailed theoretical and phenomenological analysis of different modified gravity models and investigate their consistency. We also consider the cosmological implications of well motivated physical models of the early universe with a particular emphasis on inflation and topological defects. Astrophysical and cosmological tests over a wide range of scales, from the solar system to the observable horizon, severely restrict the allowed models of the Universe. Here, we review several observational probes -- including gravitational lensing, galaxy clusters, cosmic microwave background temperature and polarization, supernova and baryon acoustic oscillations measurements -- and their relevance in constraining our cosmological description of the Universe.

astro-ph.CO↗

arXiv2016

Effect of Priomordial non-Gaussianities on Galaxy Clusters Scaling Relations

Galaxy clusters are a valuable source of cosmological information. Their formation and evolution depends on the underlying cosmology and on the statistical nature of the primordial density fluctuations. In this work we investigate the impact of primordial non-gaussianities (PNG) on the scaling properties of galaxy clusters. We performed a series of cosmological hydrodynamic N-body simulations featuring adiabatic gas physics and different levels of non-Gaussian initial conditions within the $Λ$CDM framework. We focus on the T-M, S-M, Y-M and Yx-M scalings relating the total cluster mass with temperature, entropy and SZ cluster integrated pressure that reflect the thermodynamical state of the intra-cluster medium. Our results show that PNG have an impact on cluster scalings laws. The mass power-law indexes of the scalings are almost unaffected by the existence of PNG but the amplitude and redshift evolution of their normalizations are clearly affected. The effect is stronger for the evolution of the Y-M and Yx-M normalizations, which change by as much as 22% and 16% when $f_{NL}$ varies from -500 to 500, respectively. These results are consistent with the view that positive/negative $f_{NL}$ affect cluster profiles due to an increase/decrease of cluster concentrations. At low values of $f_{NL}$, as suggested by present Planck constraints on a scale invariant $f_{NL}$, the impact on the scalings normalizations is only a few percent, which is small when compared with the effect of additional gas physics and other cosmological effects such as dark energy. However if $f_{NL}$ is in fact a scale dependent parameter, PNG may have larger positive/negative amplitudes at clusters scales and therefore our results suggest that PNG should be taken into account when galaxy cluster data is used to infer cosmological parameters or to asses the constraining power of future cluster surveys.

astro-ph.CO↗

arXiv2012

Measuring the redshift dependence of the CMB monopole temperature with PLANCK data

We study the power of PLANCK data to constrain deviations of the Cosmic Microwave Background black body temperature from adiabatic evolution using the thermal Sunyaev-Zeldovich anisotropy induced by clusters of galaxies. We consider two types of data sets: the cosmological signal is removed in the Time Ordered Information or is removed from the final maps; and two different statistical estimators, based on the ratio of temperature anisotropies at two different frequencies and on a fit to the spectral variation of the cluster signal with frequency. To test for systematics, we construct a template from clusters drawn from a hydro-simulation included in the pre-launch Planck Sky Model. We demonstrate that, using a proprietary catalog of X-ray selected clusters with measured redshifts, electron densities and X-ray temperatures, we can constrain deviations of adiabatic evolution, measured by the parameter $α$ in the redshift scaling $T(z)=T_0(1+z)^{1-α}$, with an accuracy of $σ_α=0.011$ in the most optimal case and with $σ_α=0.016$ for a less optimal case. These results represent a factor 2-3 improvement over similar measurements carried out using quasar spectral lines and a factor 6-20 with respect to earlier results using smaller cluster samples.

astro-ph.CO↗

arXiv2004

CMB Quadrupole induced polarisation from clusters and filaments

We present the estimates of the Cosmic Microwave Background (CMB) polarisation power spectrum from galaxy clusters and filaments using hydrodynamical simulations of large scale structure formation. We focus in the present study on the CMB Quadrupole induced polarisation, which is the dominate secondary polarisation effect, and give the E and B mode power spectra between $l \sim 560$ to 20000.

astro-ph↗

arXiv2004

Primordial quadrupole-induced polarisation from filamentary structures and galaxy clusters

We present the first computation of the Cosmic Microwave Background (CMB) polarisation power spectrum from galaxy clusters and filaments using hydrodynamical simulations of large scale structure. We give the $E$ and $B$ mode power spectra of the CMB quadrupole induced polarisation between $\ell \sim 560$ and 20000. We find that the contribution from warm ionised gas in filamentary structures dominates the polarised signal from galaxy clusters by more than one order of magnitude on large scales (below $\ell \sim 1000$) and by a factor of about two on small scales ($\ell \gsim 10000$). We study the dependence of the power spectra with $σ_8$. Assuming the power spectra vary like $σ_8^n$ we find $n=3.2-4.0$ for filaments and $n=3.5-4.6$ for clusters.

astro-ph↗