241 research outputs found
Degradation characteristics of hydroxyapatite coatings on orthopedic TiAlV in simulated physiological media investigated by electrochemical impedance spectroscopy
This paper concentrates on the degradation characteristics of hydroxyapatite (HA) coatings on orthopaedic Ti-6Al-4V alloy while immersed in Ringer's salt solution, which were investigated by electrochemical impedance spectroscopy. Electrochemical impedance spectroscopy measurements were used to in situ characterize the electrochemical behavior of the passivated alloy covered with HA during aging in Ringer's solution. Comparison of the electrochemical data for the coated material with that for the uncoated metal substrate was also performed. The characteristic feature that describes the electrochemical behavior of the coated material is the coexistence of large areas of the coating itself with pores where the substrate is exposed to the aggressive media. The interpretation of results was thus performed in terms of a two-layer model of the film, in which the precipitation of hydrated oxide or phosphate compounds seals the pores left by the ceramic coating. The blocking effect due to salt precipitation inside the pores produces an enhancement of the resistance values, thus effectively diminishing the metal ion release in the system.Collaborative Research Programme (Acción Integrada No. HP1995-0092 and HP1996-0109) between Spain and Portugal
Comparison Between the Material Improvement of the Megarok and San José Quarries, Applying the AASTHO Standards
Comparative analyzes were carried out between the materials of the Magarok and San José quarries, taking into account AASTHO standards with the objective of being used as a base / sub-base in the pavement structure. The asphalt emulsion material was stabilized to increase the strength and give the material sub-base and / or base characteristics, with a suitable mixing design, obtaining results with suitable characteristics to be used in the pavement structure composed of a 65 % Asphalt AC 20; 34.30% water and 0.70% ASFIER 121 emulsions, with good resistance to the stability of the materials
Pitting corrosion of polycrystalline annealed copper in alkaline sodium perchlorate solutions containing benzotriazole
The pitting corrosion of copper in alkaline solutions in the presence of benzotriazole (BTA) was investigated. The presence of BTA shifts the breakdown (Eb) and the repassivating (Ep) potentials positively with respect to the blanks. However, the shift of Eb becomes smaller than that ofE b, particularly at pH9 and 11. Pitting corrosion involves the formation of crystallographic pits. The kinetics of the process fits a nucleation and growth mechanism involving instantaneous nucleation and 3D growth under charge transfer control. The spatial distribution of pits indicates that there is no marked influence of a pit on the nucleation and growth of other pits.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada
Synergistic Effects in the Inhibition of Copper Corrosion
Benzotriazole (BTA), thiourea (TU), and potassium ethylxanthate (KEX), behave as copper (Cu) corrosion inhibitors under certain conditions. These chemicals have been investigated to establish whether they provide synergistic effects. The Cu corrosion inhibition was followed through changes in electrochemical characteristics. Cu specimens were tested at 25°C in two aggressive media, 0.1 M NaCl and 1 M NaClO4, using the linear potential sweep technique at 0.001 V s–1 and by scanning electron microscopy of Cu specimens subjected to potentiodynamic and potentiostatic routines. A comparative behavior of the different substances for Cu was presented in the 6.6 ≤ pH ≤ 11 range. For KEX-BTA mixtures, synergistic inhibition effects were found in 0.1 M NaCl (7 ≤ pH ≤ 11). The apparent synergistic inhibition was explained tentatively by an increase in the compactness of the polymer-like passivating layer of KEX-Cu, which formed in the presence of BTA and Cl– ions.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada
Contribution of geometric design parameters to knee implant performance: Conflicting impact of conformity on kinematics and contact mechanics
Chemical Distribution of the Dynamical Ejecta in the Neutron Star Merger GW170817
GW170817 and its associated electromagnetic counterpart AT2017gfo continue to
be a treasure trove as observations and modeling continue. Recent precision
astrometry of AT2017gfo with the Hubble Space Telescope combined with previous
constraints from Very Long Baseline Interferometry (VLBI) constraints narrowed
down the inclination angle to 19-25 deg (90\% confidence). This paper explores
how the inclusion of precise inclination information can reveal new insights
about the ejecta properties, in particular, about the composition of the
dynamical ejecta of AT2017gfo. Our analysis relies on updated kilonova
modeling, which includes state-of-the-art heating rates, thermalization
efficiencies, and opacities and is parameterized by , the
average electron fraction of the dynamical ejecta component. Using this model,
we incorporate the latest inclination angle constraint of AT2017gfo into a
light curve fitting framework to derive updated parameter estimates. Our
results suggest that the viewing angle of the observer is pointed towards the
lanthanide-poor (), squeezed polar dynamical ejecta
component, which can explain the early blue emission observed in the light
curve of AT2017gfo. In contrast to a recent claim of spherical ejecta powering
AT2017gfo, our study indicates that the composition of the dynamical ejecta has
a strong angular dependence, with a lanthanide-rich (), tidal component distributed around the merger plane with
a half-opening angle of . The inclination angle constraint reduces
from to , with values enabling the robust production of -process elements up
to the peak in the tidal dynamical ejecta.Comment: 8 pages, 6 figure
Multi-band analyses of the bright GRB~230812B and the associated SN2023pel
GRB~230812B is a bright and relatively nearby () long gamma-ray
burst that has generated significant interest in the community and therefore
has been subsequently observed over the entire electromagnetic spectrum. We
report over 80 observations in X-ray, ultraviolet, optical, infrared, and
sub-millimeter bands from the GRANDMA (Global Rapid Advanced Network for
Multi-messenger Addicts) network of observatories and from observational
partners. Adding complementary data from the literature, we then derive
essential physical parameters associated with the ejecta and external
properties (i.e. the geometry and environment) and compare with other analyses
of this event (e.g. Srinivasaragavan et al. 2023). We spectroscopically confirm
the presence of an associated supernova, SN2023pel, and we derive a
photospheric expansion velocity of v 17 km . We
analyze the photometric data first using empirical fits of the flux and then
with full Bayesian Inference. We again strongly establish the presence of a
supernova in the data, with an absolute peak r-band magnitude . We find a flux-stretching factor or relative brightness and a time-stretching factor ,
both compared to SN1998bw. Therefore, GRB 230812B appears to have a clear long
GRB-supernova association, as expected in the standard collapsar model.
However, as sometimes found in the afterglow modelling of such long GRBs, our
best fit model favours a very low density environment (). We also find small values for
the jet's core angle and
viewing angle. GRB 230812B/SN2023pel is one of the best characterized
afterglows with a distinctive supernova bump
Theorising age and generation in development: A relational approach
This introduction outlines the analytical approach informing the articles presented in this special issue. The project of ‘generationing’ development involves re-thinking development as distinctly generational in its dynamics. For this, we adopt a relational approach to the study of young people in development, which overcomes the limitations inherent to common categorising approaches. Concepts of age and generation are employed to conceptualise young people as social actors and life phases such as childhood and youth in relational terms. Acknowledging the centrality of young people in social reproduction puts them at the heart of development studies and leads the articles comprising this special issue to explore how young people’s agency shapes and is shaped by the changing terms of social reproduction brought about by development
Ready for O4 II: GRANDMA Observations of Swift GRBs during eight-weeks of Spring 2022
We present a campaign designed to train the GRANDMA network and its
infrastructure to follow up on transient alerts and detect their early
afterglows. In preparation for O4 II campaign, we focused on GRB alerts as they
are expected to be an electromagnetic counterpart of gravitational-wave events.
Our goal was to improve our response to the alerts and start prompt
observations as soon as possible to better prepare the GRANDMA network for the
fourth observational run of LIGO-Virgo-Kagra (which started at the end of May
2023), and future missions such as SM. To receive, manage and send out
observational plans to our partner telescopes we set up dedicated
infrastructure and a rota of follow-up adcates were organized to guarantee
round-the-clock assistance to our telescope teams. To ensure a great number of
observations, we focused on Swift GRBs whose localization errors were generally
smaller than the GRANDMA telescopes' field of view. This allowed us to bypass
the transient identification process and focus on the reaction time and
efficiency of the network. During 'Ready for O4 II', 11 Swift/INTEGRAL GRB
triggers were selected, nine fields had been observed, and three afterglows
were detected (GRB 220403B, GRB 220427A, GRB 220514A), with 17 GRANDMA
telescopes and 17 amateur astronomers from the citizen science project
Kilonova-Catcher. Here we highlight the GRB 220427A analysis where our
long-term follow-up of the host galaxy allowed us to obtain a photometric
redshift of , its lightcurve elution, fit the decay slope of the
afterglows, and study the properties of the host galaxy
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