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The MIDAS telescope for microwave detection of ultra-high energy cosmic rays

Published in Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2013

Abstract

We present the design, implementation and data taking performance of the MIcrowave Detection of Air Showers (MIDAS) experiment, a large field of view imaging telescope designed to detect microwave radiation from extensive air showers induced by ultra-high energy cosmic rays. This novel technique may bring a tenfold increase in detector duty cycle when compared to the standard fluorescence technique based on detection of ultraviolet photons. The MIDAS telescope consists of a 4.5 m diameter dish with a 53-pixel receiver camera, instrumented with feed horns operating in the commercial extended C-Band (3.4-4.2 GHz). A self-trigger capability is implemented in the digital electronics. The main objectives of this first prototype of the MIDAS telescope - to validate the telescope design, and to demonstrate a large detector duty cycle - were successfully accomplished in a dedicated data taking run at the University of Chicago campus prior to installation at the Pierre Auger Observatory. {\textcopyright} 2013 Elsevier B.V. Read more

Recommended citation: J. Alvarez-Muniz, E. Amaral, A. Berlin, M. Bogdan, M. Bohacova, C. Bonifazi, W.R. Carvalho, J.R.T. Mello, P. Facal, J.F. Genat, N. Hollon, E. Mills, M. Monasor, P. Privitera, A. Castro, L.C. Reyes, M. Richardson, B. Rouille, E.M. Santos, S. Wayne, C. Williams, E. Zas, J. Zhou, "The MIDAS telescope for microwave detection of ultra-high energy cosmic rays." Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2013. http://linkinghub.elsevier.com/retrieve/pii/S0168900213003185

Constraining Effective Temperature, Mass and Radius of Hot White Dwarfs

Published in arXiv, 2017

Abstract

By introducing a simplified transport model of outer layers of white dwarfs we derive an analytical semi-empirical relation which constrains effective temperature-mass-radius for white dwarfs. This relation is used to classify recent data of white dwarfs according to their time evolution in non-accretion process of cooling. This formula permit us to study the population map of white dwarfs in the central temperature and mass plane, and discuss the relation with the ignition temperature for C-O material. Our effective temperature-mass-radius relation provide a quick method to estimate the mass of newly observed white dwarfs from their spectral measurements of effective temperature and superficial gravity. Read more

Recommended citation: Elvis Soares, "Constraining Effective Temperature, Mass and Radius of Hot White Dwarfs." arXiv, 2017. http://arxiv.org/abs/1701.02295

Non-equilibrium Phenomena in Thermonuclear Supernovae: from life to death of white dwarf stars

Published in PhD Thesis, 2017

Abstract

In this thesis we investigate some non-equilibrium phenomena in the dynamics of evolutional stages of white dwarfs, such as cooling and Type Ia supernova explosions. The first part of the thesis is dedicated to introduction of the general concept of non- equilibrium thermodynamics, and its application in describing transient phenomena in systems near-equilibrium which are very common in Nature. In particular, we present the context of astrophysical systems focusing on the physical ingredients present inside white dwarf stars, which are the progenitors of type Ia supernovae. In the second part of the thesis, we deal with white dwarf stars, more precisely their thermal evolution as a stationary state of thermodynamics. Since the nuclear fusion processes have been ceased in these stars, their thermal energy stored during the period as proto-white dwarf is the only source of their luminosity as an almost steady energy from the core region to the surface. In this thesis, we introduce a very simple model for such a process of white dwarfs cooling, and derive a simple analytic expression which constrains their radii, masses and effective temperatures, as they cool. The third and final part of the thesis is devoted to the study of retardation effects on hydrodynamic calculations, more precisely on the delayed thermalization of the smallest fluid element considered numerically. Below the length scale defined by this element of fluid, transient phenomena are ignored by many numerical calculations. This thesis is dedicated mainly to the improvement of some numerical methods used for the simulation of thermonuclear supernovas, taking into account a simplified model of the retardation effects coming from transient processes, well described by non-equilibrium thermodynamics. We have verified that the delayed thermalization effects in the material can be determined by its signatures on the supernova observables, such as nucleosynthesis and energy released during the explosion. Read more

Recommended citation: Elvis Soares, "Non-equilibrium Phenomena in Thermonuclear Supernovae: from life to death of white dwarf stars." PhD Thesis, 2017. https://www.researchgate.net/profile/Elvis-Do-Amaral-Soares/publication/352064111_Non-equilibrium_Phenomena_in_Thermonuclear_Supernovae_from_life_to_death_of_white_dwarf_stars/links/60b7d7e4a6fdccb96f4d7a9b/Non-equilibrium-Phenomena-in-Thermonuclear-Super

PyEquIon: A Python Package For Automatic Speciation Calculations of Aqueous Electrolyte Solutions

Published in arXiv, 2021

Abstract

In several industrial applications, such as crystallization, pollution control, and flow assurance, an accurate understanding of the aqueous electrolyte solutions is crucial. Electrolyte equilibrium calculation contributes with the design and optimization of processes by providing important information, such as species concentration, solution pH and potential for solid formation. In this work, a pure Python library distributed under BSD-3 license was developed for the calculation of aqueous electrolyte equilibrium. The package takes as inputs the feed components of a given solution, and it automatically identifies its composing ions and the chemical reactions involved to calculate equilibrium conditions. Moreover, there is no established electrolyte activity coefficient model for a broad range of operational conditions. Hence, in this package, built-in activity coefficient models are structured in a modular approach, so that the non-ideality calculation can be performed by a user provided function, which allows further research in the topic. The package can be used by researchers to readily identify the equilibrium reactions and possible solid phases in a user friendly language. Read more

Recommended citation: Caio Marcellos, Gerson Junior, Elvis Soares, Fabio Ramos, Amaro Barreto, "PyEquIon: A Python Package For Automatic Speciation Calculations of Aqueous Electrolyte Solutions." arXiv, 2021. http://arxiv.org/abs/2101.07246

A self-consistent perturbative density functional theory for hard-core fluids: phase diagrams, structural and interfacial properties

Published in Fluid Phase Equilibria, 2021

Abstract

The classical Density functional theory (DFT) has become a powerful tool to describe the microscopic structure of fluids as the radial distribution function. One of its particular capabilities is to express the thermodynamic properties of those fluids even under the influence of external potentials, such as fluid-solid interaction. However, good models for the Helmholtz free-energy functionals are necessary to improve the results. In this work, we present a self-consistent thermodynamic perturbation theory for the excess Helmholtz free-energy from the DFT applied to hard-core fluids. The new perturbation theory is solved self-consistently without any closure relation to solving the Ornstein-Zernike equation explicitly. We compare the performance of our self-consistent perturbation theory with the results obtained with the well-known second-order Barker-Henderson perturbation theory for the hard-core Yukawa and square-well fluids. Moreover, we propose two versions of the DFT to describe the perturbative contribution: one based on the weighted density approximation theory and another from a modified mean-field theory. The present results confirm the modified mean-field theory as a better option to calculate the thermodynamic and structural properties of hard-core fluids Read more

Recommended citation: Elvis Soares, Amaro Barreto, Frederico Tavares, "A self-consistent perturbative density functional theory for hard-core fluids: phase diagrams, structural and interfacial properties." Fluid Phase Equilibria, 2021. https://linkinghub.elsevier.com/retrieve/pii/S0378381221001576

Exploring the multiple solutions of the classical density functional theory using metadynamics based method

Published in Adsorption, 2021

Abstract

The density functional theory (DFT) has been applied to describe confined fluids with great success in the literature. However, the usual numerical methods to solve the Euler-Lagrange equations of the grand potential functional are inefficient, finding local minimum and making the convergence very costly for systems with high complexity. Therefore, we present new numerical methods to accelerate the search of equilibrium density distributions of confined fluids, making it possible to find the DFT solutions directly, even when the system is inside the hysteresis region (more than one local minimum) of a sorption isotherm. Here, we use the PC-SAFT-DFT to describe the confinement of simple molecules, molecules with chain effects, and mixtures. We show that the present methodology is convenient to describe the phase diagrams of confined fluids. Read more

Recommended citation: V. Sermoud, G. Barbosa, E. Soares, A. Barreto, F. Tavares, "Exploring the multiple solutions of the classical density functional theory using metadynamics based method." Adsorption, 2021. https://link.springer.com/10.1007/s10450-021-00327-7

PCP-SAFT Density Functional Theory as a much-improved approach to obtain confined fluid isotherm data applied to sub and supercritical conditions

Published in Chemical Engineering Science, 2022

Abstract

Gravimetric measurements are often used to generate excess adsorption isotherms. However, adsorbed density and volume should be known to transform excess isotherms into absolute ones by considering buoyance effects. Depending on the strategy used, the results may present artifacts, especially at high pressures. A Density Functional Theory (DFT) augmented with the PCP-SAFT equation of state is applied to describe the experimental data of excess and absolute adsorption isotherms of CH4 and CO2 fluids on activated carbon slit pores. The representative pore size distribution (PSD) adequately predicted the excess adsorption isotherms at different temperatures. The absolute adsorption isotherms obtained using our approach are compared with the classic approaches as the triple point density of the liquid and the Ozawa expression (and extrapolated to the high-pressure regions). The classical methodologies underestimate the amount adsorbed while the proposed methodology provides thermodynamically consistent results even when condensation of CO2 occurs in the bulk phase Read more

Recommended citation: V.M. Sermoud, G.D. Barbosa, E. Soares, L.H. Oliveira, M.V. Pereira, P.A. Arroyo, A.G. Barreto, F.W. Tavares, "PCP-SAFT Density Functional Theory as a much-improved approach to obtain confined fluid isotherm data applied to sub and supercritical conditions." Chemical Engineering Science, 2022. https://linkinghub.elsevier.com/retrieve/pii/S000925092100470X

Real Electrolyte Solutions in the Functionalized Mean Spherical Approximation: A Density Functional Theory for Simple Electrolyte Solutions

Published in The Journal of Physical Chemistry B, 2022

Abstract

The equation of state based on the mean spherical approximation (MSA) can describe electrolyte solutions as a primitive model, where the ions are charged hard-sphere particles and the solvent is a continuum medium. In recent years, many propositions of the classical density functional theory (cDFT) for electrolyte solutions have been presented. One of these is the functionalized MSA (fMSA) which has proven to be a great functional approach of MSA to calculate the electric double layer structures. This work demonstrates how the fMSA theory can describe real electrolyte solutions (e.g., NaCl, KI, and LiBr) where hydration and solvent concentration effects are present. Experimental data of the mean activity coefficients of different simple salts were successfully reproduced. When the hydrated diameter and the electrolyte solution electric permittivity are used, the fMSA predicts a charge inversion on the electrostatic potential near a charged surface at high salt concentrations. Read more

Recommended citation: Elvis Soares, Nathalia Vernin, Mirella Santos, Frederico Tavares, "Real Electrolyte Solutions in the Functionalized Mean Spherical Approximation: A Density Functional Theory for Simple Electrolyte Solutions." The Journal of Physical Chemistry B, 2022. https://pubs.acs.org/doi/10.1021/acs.jpcb.2c00816

Charge Inversion in 1:1 Electrolytes: Analyzing the Energetics

Published in The Journal of Physical Chemistry B, 2023

Abstract

The effects of bulk concentration, surface charge density, ionic diameter, and bulk dielectric constant on charge inversion in 1:1 electrolyte systems are investigated. The framework of the classical density functional theory is used to describe the mean electrostatic potential and the volume and electrostatic correlations, which combine to define the adsorption of ions at a positively charged surface. Our results show that a decrease in the dielectric constant, in particular, creates charge inversion for 1:1 electrolytes by amplifying both the electrostatic potential and the screening component (which is generally much larger than the excluded- volume component). Local electrical potential inversion can occur even for moderate concentrations and surface charges. These findings are especially significant for ionic liquids and systems with organic molecules as solvents, as these generally have a dielectric constant much smaller than water. Read more

Recommended citation: Nathalia Vernin, Elvis Soares, Frederico Tavares, Dirk Gillespie, "Charge Inversion in 1:1 Electrolytes: Analyzing the Energetics." The Journal of Physical Chemistry B, 2023. https://pubs.acs.org/doi/10.1021/acs.jpcb.3c00436

Exponential Integrators for Phase-Field Equations using Pseudo-spectral Methods: A Python Implementation

Published in arXiv, 2023

Abstract

In this paper, we implement exponential integrators, specifically Integrating Factor (IF) and Exponential Time Differencing (ETD) methods, using pseudo-spectral techniques to solve phase-field equations within a Python framework. These exponential integrators have showcased robust performance and accuracy when addressing stiff nonlinear partial differential equations. We compare these integrators to the well-known implicit-explicit (IMEX) Euler integrators used in phase-field modeling. The synergy between pseudo-spectral techniques and exponential integrators yields significant benefits for modeling intricate systems governed by phase-field dynamics, such as solidification processes and pattern formation. Our comprehensive Python implementation illustrates the effectiveness of this combined approach in solving phase-field model equations. The results obtained from this implementation highlight the accuracy and computational advantages of the ETD method compared to other numerical techniques. Read more

Recommended citation: Elvis Soares, Amaro Barreto, Frederico Tavares, "Exponential Integrators for Phase-Field Equations using Pseudo-spectral Methods: A Python Implementation." arXiv, 2023. http://arxiv.org/abs/2305.08998

Classical density functional theory reveals structural information of H2 and CH4 fluids adsorbed in MOF-5

Published in Fluid Phase Equilibria, 2023

Abstract

This study employs classical Density Functional Theory (cDFT) to investigate the adsorption isotherms and structural information of H2 and CH4 fluids inside MOF-5. The results indicate that the adsorption of both fluids is highly dependent on the fluid temperature and the shape of the MOF-5 structure. Specifically, the CH4 molecules exhibit stronger interactions with the MOF-5 framework, resulting in a greater adsorbed quantity compared to H2. Additionally, the cDFT calculations reveal that the adsorption process is influenced by the fluid-fluid spatial correlations between the fluid molecules and the external potential produced by the MOF-5 solid atoms. These findings are supported by comparison with experimental data of adsorbed amount and the structure factor of the adsorbed fluid inside the MOF-5. We demonstrate the importance of choosing the appropriate grid size in calculating the adsorption isotherm and the fluid structure factors within the MOF-5. Overall, this work provides valuable insights into the adsorption mechanism of H2 and CH4 in MOF-5, emphasizing the importance of considering the structural properties of the adsorbed fluids in MOFs for predicting and designing their gas storage capacity at different thermodynamic conditions. Read more

Recommended citation: Elvis Soares, Amaro Barreto, Frederico Tavares, "Classical density functional theory reveals structural information of H2 and CH4 fluids adsorbed in MOF-5." Fluid Phase Equilibria, 2023. https://linkinghub.elsevier.com/retrieve/pii/S037838122300167X