Monitoring for assessment of natural disasters, such as volcanic eruptions, presents a methodological challenge for the scientific community. Here, we present Unmanned Aerial Vehicles (UAVs) as a ...feasible, precise, rapid and safe tool for real time monitoring of the impacts of a volcanic event during the Cumbre Vieja eruption on La Palma Island, Spain (2021). UAV surveys with optical RGB (Red-Green-Blue), thermal and multispectral sensors, and a water sampling device, were carried out in different areas affected by the lava flow, including the upper volcanic edifice and the lava delta formed on the coastal fringe of the island. Our results have provided useful information for the monitoring of the advance of the lava flow and its environmental consequences during the volcanic emergency. Our data shows how La Palma island's growth, with the formation of a new lava delta of 28 ha and a total volume of lava injected into the sea of 5,138,852 m3. Moreover, our Digital Elevation Model (DEM) simulated, with a 70 % accuracy, the probabilistic simulation of the possible path followed by the lava flow in the vicinity of the fissure from which the magma emanates. In addition, significant changes of seawater physical-chemical parameters were registered in coastal surface waters by the in situ seawater samples collected with the automatic water sampling device of our UAV. The first meters of the water column, due to the instant evaporation of the seawater in contact with the hot lava, produce an increase of temperature and salinity of up to 4–5 °C and up to 5 units, respectively.
Display omitted
•UAVs provide crucial information for hazard assessment during a volcanic event.•Feasible tool for accurately elaborate DEMs, 3D models and topographic maps•Centimeter-scale approximation of the area devastated by the lava flow•UAV data allowed the performance of lava flow flooding forecasting models.•Chemical analysis of surface water samples obtained under the influence of the lava delta
Context. Accretion-powered X-ray pulsars exhibit significant variability of the cyclotron resonance scattering feature (CRSF) centroid energy on pulse-to-pulse timescales, and also on much longer ...timescales. Two types of spectral variability are observed. For sources in group 1, the CRSF energy is negatively correlated with the variable source luminosity, and for sources in group 2, the opposite behavior is observed. The physical basis for this bimodal behavior is currently not well understood. Aims. We explore the hypothesis that the accretion dynamics in the group 1 sources is dominated by radiation pressure near the stellar surface, and that Coulomb interactions decelerate the gas to rest in the group 2 sources. Methods. We derive a new expression for the critical luminosity, Lcrit, such that radiation pressure decelerates the matter to rest in sources with X-ray luminosity LX > Lcrit. The formula for Lcrit is based on a simple physical model for the structure of the accretion column in luminous X-ray pulsars that takes into account radiative deceleration, the energy dependence of the cyclotron cross section, the thermodynamics of the accreting gas, the dipole structure of the pulsar magnetosphere, and the diffusive escape of radiation through the column walls. We show that for typical neutron star parameters, \hbox{$\Lcrit = 1.5 \times 10^{37} B_{12}^{16/15}~{\rm erg\, s}^{-1}$}Lcrit=1.5×1037B1216/15 erg s-1, where B12 is the surface magnetic field strength in units of 1012 G. Results. The formula for the critical luminosity is evaluated for five sources, using the maximum value of the CRSF centroid energy to estimate the surface magnetic field strength B12. The results confirm that the group 1 sources are supercritical (LX > Lcrit) and the group 2 sources are subcritical (LX < Lcrit), although the situation is less clear for those highly variable sources that cross over the line LX = Lcrit. We also explain the variation of the CRSF energy with luminosity as a consequence of the variation of the characteristic emission height. The sign of this dependence is opposite in the supercritical and subcritical cases, hence creating the observed bimodal behavior. Conclusions. We have developed a new model for the critical luminosity in accretion-powered X-ray pulsars that explains the bimodal dependence of the CRSF centroid energy on the X-ray luminosity LX. Our model provides a physical basis for the observed variation of the CRSF energy as a function of LX for both the group 1 (supercritical) and the group 2 (subcritical) sources as a result of the variation of the emission height in the column.
This study evaluated the influence of the TiO2 nanoparticles (NPs) on the mechanical and chemical performance of Sn and Sn–Ag alloys. The XRD (X-ray diffraction) and HR-TEM (high ...resolution-transmission electron microscopy) methods were used to characterize the NPs synthesized by the sol-gel microwave process. The chemical composition of the alloys was Sn, Sn+3TiO2 NPs, Sn–5Ag+1.5TiO2 NPs, Sn–10Ag, and Sn–10Ag+3TiO2 NPs, obtained from an experimental factorial design (EFD). A statistical model was used to determine the mechanical and chemical properties, showing the Vickers hardness response surface, tensile strength, wear, and corrosion resistance. The wear and corrosion tests for the various alloy compositions were performed using human artificial saliva solution. The results indicated that the Sn–10Ag+3TiO2 NPs exhibited the highest mechanical performance due to their increased hardness (380 HV), tensile strength (370 N), and wear resistance (0.34 × 10−3 mm3 Nm−1); in all the cases, the inclusion of TiO2 NPs enhanced the corrosion resistance of the alloys. According to the American Dental Association (ADA), Sn–10Ag+3TiO2 NPs alloy could be classified as a possible type IV restorative material.
Display omitted
•The sol-gel microwave method was successfully used for the synthesis of TiO2 NPs.•The addition of TiO2 NPs modified the microstructure Sn–Ag alloys.•The addition of TiO2 NPs enhanced hardness and wear performance of the Sn–Ag alloy.•The TiO2 NPs remarkably increased the corrosion resistance of Sn–Ag alloy.•According to the results, Sn–Ag + NPs might be reclassified as ADA type IV material.
This study analyzes the influence of cryogenic treatments, before the pre-tempering treatment on the microstructure, and the mechanical properties of the H13 tool steel. The H13 tool steel was ...subjected to the shallow cryogenic treatment SCT (at –80 °C for 24 h) and deep cryogenic treatment DCT (at –185 °C for 24 h) between hardening and pre-tempering processes (at 650 °C for 15 min). Alternatively, the tool steel was exposed only to the hardening and pre-tempering processes. The characterization of the microstructures and phase transformations of the specimens was established via scanning electron microscopy and X-ray diffraction, respectively. The mechanical behavior of the treated H13 tool steel was estimated using the Rockwell hardness and abrasive wear tests. Upon completion of the quenching treatment, the H13 tool steel presented the formation of fine, thin crystals of lath-shaped martensite, while the subsequent pre-tempering treatment formed a microstructure with wider martensite laths than the as-quenched state. The sub-zero treatments on the H13 tool steel promoted several phenomena, such as the martensitic transformation, the refinement of martensite laths, and the formation of large and fine carbides dispersed in the whole microstructure. The specimens exposed to SCT and DCT achieved an improvement in hardness values due to structural changes, which also contributed to a better wear resistance (17 and 25%, subsequently) in comparison with the tool steel exposed exclusively to the pre-tempering treatment. Meanwhile, the failure mechanisms on worn surfaces of the treated H13 tool steel were micro-cutting and pitting, which were developed during the interactions among the specimen surfaces-abrasive particles-rubber wheel.
Context. A number of accreting X-ray pulsars experience spectral changes, both on the long time scales and on the time scales of the neutron star spin period. The sources seem to form two distinct ...groups that differ by the type of the spectral variations with flux. Such a bimodality probably reflects two different regimes of accretion that may result in a particular pulsar depending on its luminosity – so-called sub- and super-critical regimes. Aims. We investigated the behavior of the spectral parameters of the Be/X-ray binary system A 0535+26, as a function of flux and pulse phase. Methods. We used the data collected with INTEGRAL and RXTE during the April 2010 outburst of the source. We analyzed the phase-averaged and phase-resolved spectra and performed pulse-to-pulse spectral analysis of the pulsar. Results. Our analysis reveals variability in the continuum parameters of the source’s pulse-averaged spectrum with flux. The pulse-averaged cyclotron line energy does not change with the source luminosity during the outburst, which is consistent with previous studies. Our pulse-phase resolved and pulse-to-pulse analyses reveal, however, indications for a positive correlation of the cyclotron line energy with flux, as well as a flux-dependence of the continuum parameters. Based on the observed behavior, we argue that A 0535+26 operates at the sub-critical accretion regime.
Accretion onto magnetized neutron stars is expected to be centrifugally inhibited at low accretion rates. Several sources, however, are known to pulsate in quiescence at luminosities below the ...theoretical limit predicted for the onset of the centrifugal barrier. The source 1A 0535+262 is one of them. Here we present the results of an analysis of a ~50 ks long XMM-Newton observation of 1A 0535+262 in quiescence. At the time of the observation, the neutron star was close to apastron, and the source had remained quiet for two orbital cycles. In spite of this, we detected a pulsed X-ray flux of ~3 × 10-11 erg cm-2 s-1. Several observed properties, including the power spectrum, remained similar to those observed in the outbursts. Particularly, we have found that the frequency of the break detected in the quiescent noise power spectrum follows the same correlation with flux observed when the source is in outburst. This correlation has been associated with the truncation of the accretion disk at the magnetosphere boundary. We argue that our result, along with other arguments previously reported in the literature, suggests that the accretion in quiescence also proceeds from an accretion disk around the neutron star. The proposed scenario consistently explains the energy of the cyclotron line observed in 1A 0535+262, and the timing properties of the source including the spin frequency evolution within and between the outbursts, and the frequency of the break in power spectrum.
In pursuit of innovating the conventional powder-pack boriding (CPB) process by introducing an electrical driving force, novel findings regarding the kinetics growth of boride layers produced on an ...AISI 8620 steel through the pulsed-DC powder-pack boriding process (PDCPB) were obtained. The PDCPB accelerates B diffusion on the surface of the specimen, resulting in an augmentation of the growth kinetics around 12 % and 15 % for FeB and Fe2B, respectively, compared to those observed in the CPB process. Additionally, the effect of polarity inversion half-cycles on the growth of the FeB-Fe2B layer during the PDCPB was studied. The experiments were conducted at temperatures of 850 °C, 900 °C, and 950 °C, with different exposure times, and polarity inversion half-cycles of 30 s and 50 s, maintaining a constant current density of around 177 mA cm−2. An estimation of the electric charge (q) using a transfer function considering minimal and maximum temperatures was achieved. It was confirmed that, with a symmetrical inversion, q was similar for both 30 s and 50 s polarity inversion half-cycles, indicating no influence on the growth kinetics of the boride layers.
•Each component of boriding media influenced its electrical behavior during PDCPB.•A holistic explanation of the boriding media electrical behavior was developed.•Transfer function was used for the estimation of electric charge during PDCPB.•Similar electric charge was obtained for half-cycles >7 ms.•Electric charge did not influence the boride layer growth kinetics.
Atherosclerosis is the leading underlying cause of coronary heart disease (CHD). In patients with CHD, intima-media thickness of common carotid arteries (IMT-CC) is a reliable, validated, and ...non-invasive marker of the progression of atherosclerosis. Dietary intervention may affect IMT-CC evolution through different pathways. There is a lack of clinical trials evaluating the effect of total dietary antioxidant content of diets on IMT-CC, especially in patients with CHD.
We evaluated the correlation between the diet's total antioxidant content and the changes in IMT-CC produced after 5 years of dietary intervention following two healthy diet models (Mediterranean diet and low-fat diet). We also evaluated whether the diet's total antioxidant content was related to the total redox capacity of the participants.
From the total participants of the CORDIOPREV study (clinical trial register NCT00924937), 805 participants completed the IMT-CC measurement and the dietary antioxidant evaluation at baseline and after 5 years of dietary intervention. IMT-CC was carried out by ultrasound and the dietary antioxidant evaluation was performed by the Dietary Antioxidant Index (DAI). Additionally, direct redox balance was evaluated in a subset of population by the ratio of reduced glutathione (GSH) to oxidized glutathione (GSSH) by colorimetric assay.
We observed an inverse correlation between evolution of DAI and IMT-CC after 5-years of dietary intervention. The mean of the DAI index augmented in the Mediterranean Diet group, whereas it decreased in the Low-fat group. DAI was correlated to the GSH/GSSG ratio, supporting DAI as an adequate estimator of diet's antioxidant content. When looking for individual components of the DAI that were associated to the changes in IMT-CC, an inverse correlation was found for carotenoids, vitamin E, vitamin C, and zinc and the IMT-CC.
Our study indicates that, after five years of dietary intervention, changes in DAI inversely correlate with changes in IMT-CC in patients with CHD. Overall effect of Mediterranean diet resulted in an increase of DAI, conversely to low-fat. Specific elements included in the DAI index were inversely correlated with IMT-CC.
Display omitted
•Decrease of IMT-CC was associated with a higher consumption of dietary antioxidants.•DAI could be proposed as a useful tool to estimate the antioxidant content of a diet.•Intervention based on Mediterranean diet increased the content of dietary antioxidant.
PDF
