On the abundance discrepancy problem in HII regions

The origin of the abundance discrepancy is one of the key problems in the physics of photoionized nebula. In this work, we analize and discuss data for a sample of Galactic and extragalactic HII regions where this abundance discrepancy has been determined. We find that the abundance discrepancy factor (ADF) is fairly constant and of the order of 2 in all the available sample of HII regions. This is a rather different behaviour than that observed in planetary nebulae, where the ADF shows a much wider range of values. We do not find correlations between the ADF and the O/H, O++/H+ ratios, the ionization degree, Te(High), Te(Low)/ Te(High), FWHM, and the effective temperature of the main ionizing stars within the observational uncertainties. These results indicate that whatever mechanism is producing the abundance discrepancy in HII regions it does not substantially depend on those nebular parameters. On the contrary, the ADF seems to be slightly dependent on the excitation energy, a fact that is consistent with the predictions of the classical temperature fluctuations paradigm. Finally, we obtain that Te values obtained from OII recombination lines in HII regions are in agreement with those obtained from collisionally excited line ratios, a behaviour that is again different from that observed in planetary nebulae. These similar temperature determinations are in contradiction with the predictions of the model based on the presence of chemically inhomogeneous clumps but are consistent with the temperature fluctuations paradigm. We conclude that all the indications suggest that the physical mechanism responsible of the abundance discrepancy in HII regions and planetary nebulae are different.Comment: 14 pages, 8 figures, 9 tables. Accepted for publication in the Ap

A microquasar model applied to unidentified gamma-ray sources

Among unidentified gamma-ray sources in the galactic plane, there are some that present significant variability and have been proposed to be high-mass microquasars. To deepen the study of the possible association between variable low galactic latitude gamma-ray sources and microquasars, we have applied a leptonic jet model based on the microquasar scenario that reproduces the gamma-ray spectrum of three unidentified gamma-ray sources, 3EG J1735-1500, 3EG J1828+0142 and GRO J1411-64, and is consistent with the observational constraints at lower energies. We conclude that if these sources were generated by microquasars, the particle acceleration processes could not be as efficient as in other objects of this type that present harder gamma-ray spectra. Moreover, the dominant mechanism of high-energy emission should be synchrotron self-Compton (SSC) scattering, and the radio jets may only be observed at low frequencies. For each particular case, further predictions of jet physical conditions and variability generation mechanisms have been made in the context of the model. Although there might be other candidates able to explain the emission coming from these sources, microquasars cannot be excluded as counterparts. Observations performed by the next generation of gamma-ray instruments, like GLAST, are required to test the proposed model.Facultad de Ciencias Astronómicas y Geofísica

Porous Titanium Cylinders Obtained by the Freeze-Casting Technique: Influence of Process Parameters on Porosity and Mechanical Behavior

 The discrepancy between the stiffness of commercially pure titanium and cortical bone  tissue compromises its success as a biomaterial. The use of porous titanium has been widely studied,  however, it is still challenging to obtain materials able to replicate the porous structure of the bones  (content, size, morphology and distribution). In this work, the freeze‐casting technique is used to  manufacture cylinders with elongated porosity, using a home‐made and economical device. The  relationship between the processing parameters (diameter and material of the mold, temperature  gradient), microstructural features and mechanical properties is established and discussed, in terms  of ensuring biomechanical and biofunctional balance. The cylinders have a gradient porosity  suitable for use in dentistry, presenting higher Young’s modulus at the bottom, near the cold spot  and, therefore better mechanical resistance (it would be in contact with a prosthetic crown), while  the opposite side, the hot spot, has bigger, elongated pores and walls.  Ministry of Economy and Competitiveness of Spain  grant  MAT2015‐71284‐P  FEDER‐Junta de Andalucía Research  Project (Modeling and implementation of the freeze casting technique: gradients of porosity with a tribomechanical equilibrium and electro‐stimulated cellular behavior).

A white dwarf catalogue from Gaia-DR2 and the Virtual Observatory

We present a catalogue of 73¿221 white dwarf candidates extracted from the astrometric and photometric data of the recently published Gaia-DR2 catalogue. White dwarfs were selected from the Gaia Hertzsprung–Russell diagram with the aid of the most updated population synthesis simulator. Our analysis shows that Gaia has virtually identified all white dwarfs within 100¿pc from the Sun. Hence, our sub-population of 8555 white dwarfs within this distance limit and the colour range considered, -0.52<(GBP-GRP)<0.80¿, is the largest and most complete volume-limited sample of such objects to date. From this sub-sample, we identified 8343 CO-core and 212 ONe-core white dwarf candidates and derived a white dwarf space density of 4.9±0.4×10-3pc-3¿. A bifurcation in the Hertzsprung–Russell diagram for these sources, which our models do not predict, is clearly visible. We used the Virtual Observatory SED Analyzer tool to derive effective temperatures and luminosities for our sources by fitting their spectral energy distributions, that we built from the ultraviolet to the near-infrared using publicly available photometry through the Virtual Observatory. From these parameters, we derived the white dwarf radii. Interpolating the radii and effective temperatures in hydrogen-rich white dwarf cooling sequences, we derived the surface gravities and masses. The Gaia 100¿pc white dwarf population is clearly dominated by cool (~8000¿K) objects and reveals a significant population of massive (¿M~0.8M¿¿) white dwarfs, of which no more than ~30--40 per cent can be attributed to hydrogen-deficient atmospheres, and whose origin remains uncertain.Peer ReviewedPreprin

Avaliação comparative de propriedades de uma cerâmica à base de argila conformada por quatro técnicas

The results of qualitative and quantitative properties of clay based ceramic are presented in this work. Four different shaping methods and sintering temperatures were used to understand their influence in the final properties of a ceramic material formulated using kaolinite clay and calcined alumina. This material can be used as a structural ceramic for different applications, and there is no pre-established relation between the forming method and the final sintered properties. Forming methods used to prepare the samples were uniaxial pressing (a batch process that allows application in dry samples), extruding (a continuous process that requires moisture), slip casting (a process that allows to shape complex ceramic ware), and lamination (a batch process that requires moisture). Sintering temperatures were in the range of 1100 and 1400 °C. In order to compare how properties behave as the shaping method and sintering temperature change, textural properties, shrinkage, porosimetry, phase composition and mechanical strength were evaluated and analyzed. Scanning electron microscopy and microtomography were employed for analyzing and comparing the developed microstructures. Differences in the resulting properties are explained in terms of the developed crystalline phases and microstructure.Resultados das propriedades qualitativas e quantitativas de cerâmica à base de argila são apresentados neste trabalho. Foram utilizados quatro diferentes métodos de conformação e temperaturas de sinterização para entender suas influências nas propriedades finais de um material cerâmico formulado usando argila caulinítica e alumina calcinada. Este material pode ser usado como cerâmica estrutural para diferentes aplicações, e não há relação pré-estabelecida entre o método de conformação e as propriedades sinterizadas finais. Os métodos de conformação utilizados para preparar as amostras foram prensagem uniaxial (processo em batelada que permite a aplicação em amostras secas), extrusão (processo contínuo que requer umidade), colagem (processo que permite moldar produtos cerâmicos complexos) e laminação (processo em batelada que requer umidade). As temperaturas de sinterização foram na faixa de 1100 e 1400 °C. Para comparar como as propriedades se comportam à medida que o método de moldagem e a temperatura de sinterização são alterados, as propriedades de textura, retração, porosimetria, composição de fases e resistência mecânica foram avaliadas e analisadas. Microscopia eletrônica de varredura e microtomografia foram empregadas para analisar e comparar as microestruturas desenvolvidas. As diferenças nas propriedades resultantes são explicadas em termos das fases cristalinas desenvolvidas e da microestrutura.Fil: Torres, Camila Irene. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Tecnología de Recursos Minerales y Cerámica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Tecnología de Recursos Minerales y Cerámica; ArgentinaFil: Rendtorff Birrer, Nicolás Maximiliano. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Departamento de Química; ArgentinaFil: Cipollone, M.. YPF - Tecnología; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Departamento de Química; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Aglietti, Esteban Fausto. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Tecnología de Recursos Minerales y Cerámica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Tecnología de Recursos Minerales y Cerámica; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Departamento de Química; ArgentinaFil: Suarez, Gustavo. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Tecnología de Recursos Minerales y Cerámica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Tecnología de Recursos Minerales y Cerámica; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Departamento de Química; Argentin

Random Forest identification of the thin disk, thick disk and halo Gaia-DR2 white dwarf population

Gaia-DR2 has provided an unprecedented number of white dwarf candidates of our Galaxy. In particular, it is estimated that Gaia-DR2 has observed nearly 400,000 of these objects and close to 18,000 up to 100 pc from the Sun. This large quantity of data requires a thorough analysis in order to uncover their main Galactic population properties, in particular the thin and thick disk and halo components. Taking advantage of recent developments in artificial intelligence techniques, we make use of a detailed Random Forest algorithm to analyse an 8-dimensional space (equatorial coordinates, parallax, proper motion components and photometric magnitudes) of accurate data provided by Gaia-DR2 within 100 pc from the Sun. With the aid of a thorough and robust population synthesis code we simulated the different components of the Galactic white dwarf population to optimize the information extracted from the algorithm for disentangling the different population components. The algorithm is first tested in a known simulated sample achieving an accuracy of 85.3%. Our methodology is thoroughly compared to standard methods based on kinematic criteria demonstrating that our algorithm substantially improves previous approaches. Once trained, the algorithm is then applied to the Gaia-DR2 100 pc white dwarf sample, identifying 12,227 thin disk, 1,410 thick disk and 95 halo white dwarf candidates, which represent a proportion of 74:25:1, respectively. Hence, the numerical spatial densities are $(3.6\pm0.4)\times10^{-3}\,{\rm pc^{-3}}$, $(1.2\pm0.4)\times10^{-3}\,{\rm pc^{-3}}$ and $(4.8\pm0.4)\times10^{-5}\,{\rm pc^{-3}}$ for the thin disk, thick disk and halo components, respectively. The populations thus obtained represent the most complete and volume-limited samples to date of the different components of the Galactic white dwarf population.Comment: 18 pages, 11 figures and 3 tables. Accepted for publication in MNRA

The Lp_3561 and Lp_3562 enzymes support a functional divergence process in the lipase/esterase toolkit from Lactobacillus plantarum

Lactobacillus plantarum species is a good source of esterases since both lipolytic and esterase activities have been described for strains of this species. No fundamental biochemical difference exists among esterases and lipases since both share a common catalytic mechanism. L. plantarum WCFS1 possesses a protein, Lp_3561, which is 44% identical to a previously described lipase, Lp_3562. In contrast to Lp_3562, Lp_3561 was unable to degrade esters possessing a chain length higher than C4 and the triglyceride tributyrin. As in other L. plantarum esterases, the electrostatic potential surface around the active site in Lp_3561 is predicted to be basic, whereas it is essentially neutral in the Lp_3562 lipase. The fact that the genes encoding both proteins were located contiguously in the L. plantarum WCFS1 genome, suggests that they originated by tandem duplication, and therefore are paralogs as new functions have arisen during evolution. The presence of the contiguous lp_3561 and lp_3562 genes was studied among L. plantarum strains. They are located in a 8,903 bp DNA fragment that encodes proteins involved in the catabolism of sialic acid and are predicted to increase bacterial adaptability under certain growth conditions

Associations of dietary intake on biological markers of inflammation in children and adolescents: A systematic review

Background: In children and adolescents, chronic low-grade inflammation has been implicated in the pathogenesis of co- and multi-morbid conditions to mental health disorders. Diet quality is a potential mechanism of action that can exacerbate or ameliorate low-grade inflammation; however, the exact way dietary intake can regulate the immune response in children and adolescents is still to be fully understood. Methods: Studies that measured dietary intake (patterns of diet, indices, food groups, nutrients) and any inflammatory biomarkers in children and adolescents aged 2 to19 years and published until November 2020 were included in this systematic review, and were selected in line with PRISMA guidelines through the following databases: Academic Search Complete, CINAHL, Global Health, Medline COMPLETE andWeb of Science-Core Collection. A total of 53 articles were identified. Results: Results show that adequate adherence to healthful dietary patterns such as the Mediterranean diet, or food groups such as vegetables and fruit, or macro/micro nutrients such as fibre or vitamin C and E, are associated with decreased levels of pro-inflammatory biomarkers, mainly c-reactive protein (CRP), interleukin-6 (IL-6) and tumour necrosis factor-alpha (TNF-α), whereas adherence to aWestern dietary pattern, as well as intake of food groups such as added sugars, macro-nutrients such as saturated fatty acids or ultra-processed foods, is associated with higher levels of the same pro-inflammatory biomarkers. Conclusions: This is the first systematic review examining dietary intake and biological markers of inflammation in both children and adolescents. A good quality diet, high in vegetable and fruit intake, wholegrains, fibre and healthy fats ameliorates low-grade inflammation, and therefore represents a promising therapeutic approach, as well as an important element for disease prevention in both children and adolescents.A.B. and C.M.P. are funded by the UK Medical Research Council (grants MR/L014815/1, MR/J002739/1and MR/N029488/1), the European Commission Horizon 2020 (grant SC1-BHC-01- 2019) and the National Institute for Health Research (NIHR) Biomedical Research Centre at South London and Maudsley NHS Foundation Trust and King’s College London; they have also received research funding from Johnson and Johnson for research on depression and inflammation, but this paper is independent from this funding. In addition, C.M.P. is funded by the Wellcome Trust strategy award to the Neuroimmunology of Mood Disorders and Alzheimer’s Disease (NIMA) Consortium (104025), which is also funded by Janssen, GlaxoSmithKline, Lundbeck and Pfizer, but, again, this paper is independent from this funding

Second Order Sliding Mode Control of a STATCOM with Saturated Inputs

This paper presents a robust controller for a STATCOM device with saturated inputs. As the primary assumption, the proposed design considers the presence of unknown but bounded external perturbations and parametric variations. This proposal has a cascade structure, where a saturated super twisting control algorithm closes the currents control loop, and a high-gain proportional-integral (PI) algorithm ensures the voltage regulation. Thus, the exposed scheme provides an adequate performance of the STATCOM, considering the saturation of the inputs with the anti-windup feature. Posteriorly, a proper stability analysis presents the conditions for the appropriate operation of the closed-loop system in saturation and non-saturation regimes. Numerical simulations are also included to show the performance of the proposed controller

Enrichment of the ISM by metal-rich droplets and the abundance bias in HII regions

We critically examine a scenario for the enrichment of the interstellar medium (ISM) in which supernova ejecta follow a long (10^8 yr) journey before falling back onto the galactic disk in the form of metal-rich ``droplets'', These droplets do not become fully mixed with the interstellar medium until they become photoionized in HII regions. We investigate the hypothesis that the photoionization of these highly metallic droplets can explain the observed ``abundance discrepancy factors'' (ADFs), which are found when comparing abundances derived from recombination lines and from collisionally excited lines, both in Galactic and extragalactic HII regions. We derive bounds of 10^{13}--10^{15} cm on the droplet sizes inside HII regions in order that (1) they should not have already been detected by direct imaging of nearby nebulae, and (2) they should not be too swiftly destroyed by diffusion in the ionized gas. From photoionization modelling we find that, if this inhomogeneous enrichment scenario holds, then the recombination lines strongly overestimate the metallicities of the fully mixed HII regions. The abundances derived from collisionally excited lines also suffer some bias, although to a much lesser extent. In the absence of any recipe for correcting these biases, we recommend the discarding of all objects showing large ADFs from studies of galactic chemical evolution. These biases must also be kept in mind when comparing the galactic abundance gradients for elements derived from recombination lines with those derived from collisionally excited lines. Finally, we propose a set of observations that could be undertaken to test our scenario and improve our understanding of element mixing in the ISM.Comment: 14 pages, 5 figures, accepted in Astronomy and Astrophysic