Repositorio Académico Institucional

We report dusty photo-ionization models for two Planetary Nebulae NGC 2452 and IC 2003, which have [WR] type central stars, using 1D photo-ionization code Cloudy17.02. We used the medium resolution optical spectra and archival IRAS photometry to constrain our models. The physical size of the ionized nebula derived using accurate distance measurements and absolute H flux available in the literature were used as additional constrains. We examine the importance of photo-electric heating and found that models with and without considering photo-electric heating do not make significant difference for both PNe for the MRN grain size distribution considered in this study. We derive the nebular elemental abundances of these PNe by the empirical method as well as by making dusty photo-ionization models. The values of N/O ratios for both PNe obtained from our models are lower than their respective values arrived using empirical methods. The central stars are assumed to be black bodies and the photospheric temperatures derived respectively for NGC 2452 and IC 2003 from their best fit models are 182 kK and 155 kK and their respective luminosities are 630 and 1015. We propose that both the PNe were resulted from low-mass progenitors of mass 2.8 M⊙.

We report dusty photo-ionization models for two Planetary Nebulae NGC 2452 and IC 2003, which have [WR] type central stars, using 1D photo-ionization code Cloudy17.02. We used the medium resolution optical spectra and archival IRAS photometry to con-strain our models. The physical size of the ionized nebula derived using accurate distance measurements and absolute Hb flux available in the literature were used as additional constrains. We examine the importance of photo-electric heating and found that models with and without considering photo-electric heating do not make significant difference for both PNe for the MRN grain size distribution consid-ered in this study. We derive the nebular elemental abundances of these PNe by the empirical method as well as by making dusty photo -ionization models. The values of N/O ratios for both PNe obtained from our models are lower than their respective values arrived using empirical methods. The central stars are assumed to be black bodies and the photospheric temperatures derived respectively for NGC 2452 and IC 2003 from their best fit models are 182 kK and 155 kK and their respective luminosities are 630L (R) and 1015L (R). We propose that both the PNe were resulted from low-mass progenitors of mass 62.8 M (R).(c) 2022 COSPAR. Published by Elsevier B.V. All rights reserved.

This article introduces a bimodal model based on the epsilon-skew-normal distribution. This extension generates bimodal distributions similar to those produced by the mixture of normal distributions. We study the basic properties of this new family. We apply maximum likelihood estimators, calculate the information matrix and present a simulation study to assess parameter recovery. Finally, we illustrate the results to three real data sets, suggesting this new distribution as a plausible alternative for modelling bimodal data.

In this work, we propose a new bimodal distribution with support in the real line. We obtain some properties of the model, such as moments, quantiles, and mode, among others. The computational implementation of the model is presented in the tpn package of the software R. We perform a simulation study in order to assess the properties of the maximum likelihood estimators in finite samples. Finally, we present an application to a bimodal data set, where our proposal is compared with other models in the literature. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.

In the modern phase of electricity and global connectivity, a supercapacitor plays an eye-catching role by overcoming the detrimental of capacitors and batteries. Imagining an advanced smartphone, a miniature, light-weight, flexible electronic device with good power and energy capability, large-scale stretchability, and self-healing property is one step ahead of becoming a reality in innovations. To facilitate the sustainable operation and ensure the reliability of the obtained electronic system, it is desirable to obtain satisfactory performance under certain conditions like bending, stretching, compressing, deforming and twisting, etc. However, multifunctional integrity remains a challenge in a single system. The stable and insistent output can only be possible by choosing the proper electrode design and material selection. This review discusses the recent trends in different categories of stretchable materials used for supercapacitor applications, various architectures influencing their stretchability, their mechanical properties like strain, pre-stretchability and healability, etc. and the usability of these stretchable materials in smart and wearable devices. © 2022 Elsevier B.V.

We use data from the 17th data release of the Apache Point Observatory Galactic Evolution Experiment (APOGEE 2) to contrast the chemical composition of the recently discovered Gaia Enceladus/Sausage system (GE/S) to those of 10 Milky Way (MW) dwarf satellite galaxies: LMC, SMC, Boötes I, Carina, Draco, Fornax, Sagittarius, Sculptor, Sextans, and Ursa Minor. Our main focus is on the distributions of the stellar populations of those systems in the [Mg/Fe]–[Fe/H] and [Mg/Mn]–[Al/Fe] planes, which are commonly employed in the literature for chemical diagnosis and where dwarf galaxies can be distinguished from in situ populations. We show that, unlike MW satellites, a GE/S sample defined purely on the basis of orbital parameters falls almost entirely within the locus of ‘accreted’ stellar populations in chemical space, which is likely caused by an early quenching of star formation in GE/S. Due to a more protracted history of star formation, stars in the metal-rich end of the MW satellite populations are characterized by lower [Mg/Mn] than those of their GE/S counterparts. The chemical compositions of GE/S stars are consistent with a higher early star formation rate (SFR) than MW satellites of comparable and even higher mass, suggesting that star formation in the early universe was strongly influenced by other parameters in addition to mass. We find that the direction of the metallicity gradient in the [Mg/Mn]–[Al/Fe] plane of dwarf galaxies is an indicator of the early SFR of the system.

This paper introduces the inverse-power Muth power series model, which is a composition of the inverse-power Muth and the class of power series distributions. The use of the Bell distribution in this context is emphasized for the first time in the literature. Probability density, survival and hazard functions are studied, as well as their moments. Using the stochastic representation of the model, the maximum-likelihood estimators are implemented by the use of the expectation-maximization algorithm, while standard errors are calculated using Oakes’ method. Monte Carlo simulation studies are conducted to show the performance of the maximum-likelihood estimators in finite samples. Two applications to real datasets are shown, where our proposal is compared with some models based on power series compositions.

Seminar (English education and teaching credential).-- Universidad de Atacama, 1996.

The first step in the planning of a mine is the determination of the economic envelope, which is the volume that encapsulates the mine layout and maximizes the total economic value; thus, it has a considerable impact in the design and planning of the mining project. The most common approach for calculating the economic envelope of block and panel caving mines is to determine the best envelope for each possible floor and then chose the est from manually. This method is very fast and effective but may generate footprints that are difficult to design and operate as they do not consider any geometrical constraint of the shape of the envelope that are relevant, for example, to limit abutment stress. In this paper, we present a novel method that incorporates geometrical constraints related to the connectivity and smoothness of the outline of the envelope, and the continuity and smoothness of the height of the draw columns. Our method is based on the same approach used to compute the ultimate pit, i.e., the economic envelope of open pit mines. Therefore, it is very efficient and ensures to find the optimal solution for the constraints that are set. We test the method, comparing the economic envelopes of the de facto approach and our proposed approach and show that the geometries obtained are more favorable geometries and generate economic values similar to or better than those calculated using the standard approach. That is, the method improves the geometry of the economic envelope without loss in value.

By this work, the viability of the spray coating as a cost-effective and reliable technique for the coating of Ce0.9Gd0.1O1.95 (GDC) electrolyte layer on the mini-tubular NiO–GDC anodes based a solid oxide fuel cell (SOFC) fabrication was assessed. The compatibility of the anode and electrolyte was analyzed by using XRD. The variation in thickness and morphology of the electrolyte film as a function of the coating cycles was discussed with optical and scanning electron microscopes. By similar formulation, the coating of La0.6Sr0.4Fe0.8Co0.2O3 –Ce0.9Gd0.1O2–δ (LSCF–GDC) was performed to achieve porous cathode. An individual micro-tubular anode supported cell with configuration NiO–GDC/GDC/LSCF–GDC as anode/electrolyte/cathode was tested in the SOFC mode with humidified hydrogen as fuel and stationary air as oxidant. The fabricated mini-SOFC prototype that generated a maximum power density of 0.510 W/cm2 at 600°C signifies the potential of this industrially scalable low-cost coating technique. © 2021 The American Ceramic Society.

Using a two-piece normal distribution for modeling univariate data that exhibits symmetry, and uni/bimodality is notably effective. In this respect, the shape parameter value determines whether unimodality or bimodality is present. This paper proposes a flexible uni/bimodal distribution with platykurtic density, which can be used to simulate a variety of data. The concept is based on the transforming of a random variable into a folded distribution. Further, the proposed class includes the normal distribution as a sub-model. In the current study, the maximum likelihood method is considered for deriving the main structural properties and for the estimation of parameters. In addition, simulation experiments are presented to evaluate the behavior of estimators. Finally, fitting and regression applications are presented to illustrate the usefulness of the proposed distribution for data modeling in different real-life scenarios.

Recent years have shown growth in the potential applications of extensions of skew and half-normal distributions. In this paper, we provide and study, in detail, an extended class of such distributions. The presented distribution has a scale parameter and two shape parameters. The motivations behind the development of this distribution are: 1- the probability distribution function has skewed, unimodal and bathtub shapes with different styles and the hazard rate function is increasing with various shapes, which makes this distribution flexible enough to analyze reliability data; 2- it can be expressed as a mixture of the Generalized Half-Normal distribution and the new weighted Generalized Half-Normal distribution. A number of statistical results are derived. Monte Carlo simulation analysis is carried out with Maximum Likelihood Estimation to assess the performance of this technique for a variety of the distribution parameter values. The power of the distribution is demonstrated with real applications using two reliability datasets from the industry. The results reveal that the proposed distribution outperformed the Generalized Lindley, Exponentiated Exponential, Gamma, Alpha-Skew-Normal, the Half-Alpha-Skew-Normal, and the Modified Generalized Half-Normal distributions. © 2022 University of Kuwait. All rights reserved.

Over the last decades, the challenges in survival models have been changing considerably and full probabilistic modeling is crucial in many medical applications. Motivated from a new biological interpretation of cancer metastasis, we introduce a general method for obtaining more flexible cure rate models. The proposal model extended the promotion time cure rate model. Furthermore, it includes several well-known models as special cases and defines many new special models. We derive several properties of the hazard function for the proposed model and establish mathematical relationships with the promotion time cure rate model. We consider a frequentist approach to perform inferences, and the maximum likelihood method is employed to estimate the model parameters. Simulation studies are conducted to evaluate its performance with a discussion of the obtained results. A real dataset from population-based study of incident cases of melanoma diagnosed in the state of Sao Paulo, Brazil, is discussed in detail.

Over the last decades, the challenges in survival models have been changing considerably and full probabilistic modeling is crucial in many medical applications. Motivated from a new biological interpretation of cancer metastasis, we introduce a general method for obtaining more flexible cure rate models. The proposal model extended the promotion time cure rate model. Furthermore, it includes several well-known models as special cases and defines many new special models. We derive several properties of the hazard function for the proposed model and establish mathematical relationships with the promotion time cure rate model. We consider a frequentist approach to perform inferences, and the maximum likelihood method is employed to estimate the model parameters. Simulation studies are conducted to evaluate its performance with a discussion of the obtained results. A real dataset from population-based study of incident cases of melanoma diagnosed in the state of São Paulo, Brazil, is discussed in detail.

In this chapter, the authors propose a guideline to develop a mobile platform to collect data that makes it possible to predict energy consumption in residences in developing countries. The platform consists of a game that can be played individually or by a team (i.e., a family) that lives in the same house. From time to time, a person or family members will receive some challenges (i.e., some questions) that must be reached (i.e., answered) to collect the energy consumption habits data. The context of the game is in an aquarium, where a small fish will evolve or not during the game. The fish will live in this environment that starts very clean, and with the actions of the user concerning the challenges, may suffer an evolution or degradation. By using gamification techniques, the challenges will persuade the person or family members to provide directly or indirectly the energy consumption habits data for each electronic device. All data collected with the game platform can be analyzed through different types of analysis by using a dashboard. © 2022, IGI Global. All rights reserved.

The majority of massive disk galaxies in the local Universe show a stellar barred structure in their central regions, including our Milky Way1,2. Bars are supposed to develop in dynamically cold stellar disks at low redshift, as the strong gas turbulence typical of disk galaxies at high redshift suppresses or delays bar formation3,4. Moreover, simulations predict bars to be almost absent beyond z = 1.5 in the progenitors of Milky Way-like galaxies5,6. Here we report observations of ceers-2112, a barred spiral galaxy at redshift zphot ≈ 3, which was already mature when the Universe was only 2 Gyr old. The stellar mass (M★ = 3.9 × 109 M⊙) and barred morphology mean that ceers-2112 can be considered a progenitor of the Milky Way7,8,9, in terms of both structure and mass-assembly history in the first 2 Gyr of the Universe, and was the closest in mass in the first 4 Gyr. We infer that baryons in galaxies could have already dominated over dark matter at z ≈ 3, that high-redshift bars could form in approximately 400 Myr and that dynamically cold stellar disks could have been in place by redshift z = 4–5 (more than 12 Gyrs ago)

It is well known that it is possible to represent a Birnbaum-Saunders variable as a relatively simple (and invertible) function of a standard normal random variable. Marginal transformations of this kind are applied in this paper to a bivariate distribution with generalized skew-normal conditionals (and normal marginals), to obtain a new bivariate Birnbaum-Saunders distribution. Parameter estimation for this model is implemented using an EM algorithm. A simulation study sheds light on the performance of the estimation strategy. Data from a cancer risk study is used to illustrate use of the model. For this data set, the new model exhibits better performance than does a competing skew-normal based model already discussed in the literature. Possible multivariate extensions of the new model are outlined.

It is well known that it is possible to represent a Birnbaum-Saunders variable as a relatively simple (and invertible) function of a standard normal random variable. Marginal transformations of this kind are applied in this paper to a bivariate distribution with generalized skew-normal conditionals (and normal marginals), to obtain a new bivariate Birnbaum-Saunders distribution. Parameter estimation for this model is implemented using an EM algorithm. A simulation study sheds light on the performance of the estimation strategy. Data from a cancer risk study is used to illustrate use of the model. For this data set, the new model exhibits better performance than does a competing skew-normal based model already discussed in the literature. Possible multivariate extensions of the new model are outlined.

In this article a new flexible survival cure rate model is introduced by assuming that the number of competing causes of the event of interest follows the Flory–Schulz distribution and the competing causes follow the generalized truncated Nadarajah–Haghighi distribution. Parameter estimation for the proposed model is derived based on the maximum likelihood estimation method. A simulation study is performed to show the performance of the ML estimators. We discuss three real data applications related to real cancer data sets to assess the usefulness of the proposed model compared with some existing cure rate models for the sake of comparison. © 2022 by the authors.