ABSTRACT
Understanding the effects driven by rotation in the solar convection zone is essential for many problems related to solar activity, such as the formation of differential rotation, meridional ...circulation, and others. We analyse realistic 3D radiative hydrodynamics simulations of solar subsurface dynamics in the presence of rotation in a local domain 80 Mm wide and 25 Mm deep, located at 30° latitude. The simulation results reveal the development of a shallow 10 Mm deep substructure of the near-surface shear layer (NSSL), characterized by a strong radial rotational gradient and self-organized meridional flows. This shallow layer (‘leptocline’) is located in the hydrogen ionization zone associated with enhanced anisotropic overshooting-type flows into a less unstable layer between the H and He ii ionization zones. We discuss current observational evidence of the presence of the leptocline and show that the radial variations of the differential rotation and meridional flow profiles obtained from the simulations in this layer qualitatively agree with helioseismic observations.
In this work complex metal-oxide catalysts with the general formula 5 wt% Ni/Ce0·75Zr0.25-x(Nb,Ti)xO2-δ were synthesized by the solvothermal method using supercritical alcohols followed by nickel ...deposition. The catalysts were characterized and studied in ethanol dry reforming reaction (EDR) in the temperature range 600–750 °C. XRD and TEM showed that the synthesis method provides incorporation of doping cations into the ceria-zirconia fluorite structure, leading to mixed oxides formation. The effect of doping cations on structural and surface properties of 5 wt% Ni/Ce0·75Zr0.25-x(Nb,Ti)xO2-δ and activity in the EDR reaction was investigated. Oxygen deficiency δ increases with the introduction of titanium and niobium cations, which contributes to the bifunctional reforming mechanism implementation with rapid oxidation of coke precursors and activation of СО2 at surface oxygen vacancies. TPO-O2 analysis after reaction showed no carbon formation above 700 °C, and a few carbon deposits (not exceeding 4%) even after significant catalyst deactivation at 600 °C.
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•Single-phase Ce0·75Zr0.25-x (Nb,Ti)xO2-δ oxides were obtained by solvothermal method.•5%Ni/Ce0·75Zr0.25-x (Nb,Ti)xO2-δ were tested in ethanol dry reforming at 600–750 °C.•Ti and Nb addition enhance oxygen deficiency and slightly increases surface acidity.•The catalysts provide effective CO2 activation and high reagent conversions at 700 °C.•The most active catalyst at 700 °C is double-doped 5%Ni/Ce0·75Ti0·05Nb0·05Zr0·15O2.
For La2Zr2O7/LaAlO3 composite prepared by aging (100 °C/10 h) of the mixture of precipitated precursors of La-Zr-O and La-Al-O, evolution of its structural features after sintering in air in the ...range of 100–1300 °C was investigated by applying XRD, HRTEM, FTIR, Raman and UV–Vis spectroscopies, 27Al MAS NMR and 139La NMR.
The initial composite forms a highly dispersed and disordered structure retaining considerable concentrations of residual anions (anions from the initial salts, water molecules and hydrogen bound hydroxyls) due to basic properties of La cations. Stepwise removal of these anions by calcinations results in the crystallization of La2(Al)O2CO3 at 500 °C with complete disordering of the system after heating at 700 °C. These transitions are accompanied by appearance of AlO4 polyhedra. The La-Zr-O- containing phase appeared for the first time at 900 °C as fluorite-like ZrO2 stabilized by La (Al) cations, and LaAlO3 (P2) phase is also observed along with admixtures of La2O3 and La10Al4O21. At 1100 °C fluorite-like ZrO2 converts into the La2Zr2O7 (P1) phase, and in the range of 1100–1300 °C mixed P1 and P2 oxides are the main phases. For P1 phase, structure becomes more ordered at higher sintering temperatures, while for P2 phase in composite the nanodomain structure is still observed in comparison with individual mixed oxide at 1300 °C. The molecular –scale features of domain boundaries in nanostructured La-Zr-O/La-Al-O composite as well as applied inexpensive method of its fabrication provide required bases for a broad practical application of this material for Thermal barrier coatings (TBCs).
•La2Zr2O7/LaAlO3 composite prepared by aging of the mixture of precipitated hydroxides.•For composite the presence of both phases and their interfaces hampers sintering.•Removal of residual surface hydroxyls and carbonates favor coalescence of La-Zr-O/La-Al-O nanodomains.•Inexpensive method of composite fabrication provides a broad practical application for Thermal Barrier Coatings.
This study is aimed at studying the properties of La2NiO4+δ (LNO) substituted with rare earth elements to increase its oxygen over-stoichiometry and enhance oxygen transport thus improving ...electrochemical properties of the related electrodes. Materials of the La1.6Ln0.4NiO4+δ series (where Ln = Pr (LPNO), Nd (LNNO), Sm (LSNO), Eu (LENO), Gd (LGNO)) are synthesized by a nitrate combustion technique and their structural features, oxygen over-stoichiometry, and oxygen transport properties are investigated by different methods such as X-ray diffraction, TGA, temperature programmed isotopic oxygen exchange with C18O2 (TPIE) in a flow reactor. The unit cell volume in the La1.6Ln0.4NiO4+δ series decreases from Pr (V = 188.3 Å3) to Gd (V = 186.7 Å3). According to the TGA data, the LNO value of oxygen over-stoichiometry, δ, is equal to 0.15, while all substituted materials, except LGNO, show higher values: 0.16 for LENO, 0.17 for LSNO and LNNO, and the highest value equal to 0.18 has been revealed for LPNO. Oxygen mobility and surface reactivity are studied by the temperature-programmed isotope exchange of oxygen with C18O2 in a flow reactor. All samples can be characterized by a fast oxygen diffusivity provided by cooperative mechanism of oxygen migration involving both regular and highly mobile interstitial oxygen. Variation of oxygen tracer diffusion coefficient with dopant cation nature is probably associated with interstitial oxygen content. The best characteristics have been acquired for Ln = Eu (D⁎ = 2.4∙10−9 cm2/s at 700 °C). Electrochemical properties of the related La1.6Ln0.4NiO4+δ electrodes are investigated in a contact with a Ce0.8Sm0.2O1.9 solid-state electrolyte. The influence of the temperature of the electrode formation and the effect of the collector layer on the electrode electrochemical activity are considered. The LENO, LPNO and LSNO-based electrodes demonstrate low polarization resistance related to the enhanced oxygen diffusion properties. Substitution with Gd, contrarily, significantly deteriorates electrochemical properties of LNO.
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•Materials of the La1.6Ln0.4NiO4+δ series (where Ln = Pr, Nd, Sm, Eu, Gd are studied.•The unit cell volume in the series is shown to decrease from Pr to Gd.•Pr, Nd, Sm, Eu-doped samples have D⁎ values in the range of 2.2–2.4∙10−9 cm2/s at 700 °C.•The value of the urface exchange constant k* decreases with the Ln ionic radius decreasing.•Electrode performance is determined by oxygen transport properties and sintering conditions.
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•Modeling of reaction dynamics on catalysts with lattice oxygen mobility was done.•CH4 dry reforming over Pt/PrCeZrO catalyst was studied as relevant probe reaction.•Factors ...controlling duration and character of transients were elucidated.•Likely kinetic schemes were discriminated according to fitting experimental data.•Main kinetic parameters and catalyst characteristics were thoroughly estimated.
Dynamics of red-ox reactions occurring over catalysts with active oxide support is described by mathematical modeling. Numerical analysis is applied to transients from an initially oxidized state of a Pt/PrCeZrO catalyst to a partially reduced steady state present during CH4 dry reforming. Oxygen transport to the surface from adjacent regions in the catalyst lattice is considered to quantify the impact on the transient behavior in the model red-ox reaction over the catalyst with a high lattice oxygen mobility. Chemical transformations and coverages at the catalyst surface are largely affected by the internal transport of oxygen species, while the overall character and shape of transient curves remain defined by the specificity of the reaction kinetic scheme.
Detailed analysis of CH4 dry reforming over a Pt/PrCeZrO catalyst at contact times of 4.7, 8, and 15 ms allowed to (1) clarify the factors that control dynamic system behavior and catalytic properties, (2) discriminate kinetic schemes, (3) confirm a high efficiency of cationic Pt species in CH4 dissociation, and (4) underpin that CO2 transformation may occur via carbonate intermediates located on oxidized Ptn+−-Pr4+-O surface sites. Direct estimation of bulk oxygen diffusion rate as well as kinetic parameters was carried out. Findings are consistent with the characteristics of the catalyst surface state and oxygen mobility in the surface/bulk layers.
Relative dynamics of the radio sources of the metric type II burst with three emission lanes and coronal mass ejection (CME) occurred in the lower corona (r≲1.5R⊙) during the SOL2011-02-16T14:19 ...event is studied. The observational data of the Nancay Radioheliograph (NRH) and the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) are used. These observations are also supplemented by the data sets obtained with the STEREO-A and -B, RHESSI, and GOES spacecraft, as well as with the ground-based solar radio spectrometers. It is found that the sources of the radio burst were located ahead of the expanding CME and had a complex spatial structure. The first and the second lanes were both emitted from the “magnetic funnel” — a bundle of open magnetic field lines separated the south and north systems of magnetic loops of the active region. Due to the projection effect and limited angular resolution of the NRH it is not possible to determine, whether the spatial locations of the radio sources of the two first emission lanes differed or not. It is argued that the observations support the hypothesis that the radio sources of the first and second lanes could be emitted respectively ahead of and behind a front of the same weak (the Alfvén Mach number MA≈1.1–1.2), fast mode, quasi-parallel piston MHD shock wave. However, the third lane of the burst was definitely emitted from a different place. Its radio sources were situated ahead of the north-west part of the CME propagated through the north system of magnetic loops. This indicates clearly that different emission lanes of the same type II burst can be a result of propagation of different parts of a single CME through regions with different physical conditions (geometries and plasma densities) in the lower corona.
We study flare processes in the solar atmosphere using observational data for an M1-class flare of 2014 June 12, obtained by the New Solar Telescope (NST/BBSO) and Helioseismic Magnetic Imager ...(HMI/SDO). The main goal is to understand triggers and manifestations of the flare energy release in the photosphere and chromosphere using high-resolution optical observations and magnetic field measurements. We analyze optical images, HMI Dopplergrams, and vector magnetograms, and use nonlinear force-free field (NLFFF) extrapolations for reconstruction of the magnetic topology and electric currents. The NLFFF modeling reveals the interaction of two magnetic flux ropes with oppositely directed magnetic fields in the polarity inversion line (PIL). These flux ropes are observed as a compact sheared arcade along the PIL in the high-resolution broadband continuum images from NST. In the vicinity of the PIL, the NST observations reveal the formation of a thin three-ribbon structure corresponding to a small-scale photospheric magnetic arcade. The observational results are evidence in favor of the primary energy release site located in the chromospheric plasma with strong electric currents concentrated near the PIL. In this case, magnetic reconnection is triggered by the interacting magnetic flux ropes forming a current sheet elongated along the PIL.
The X-class solar flare of 2012 October 23 generated continuum photospheric emission and a strong helioseismic wave ("sunquake") that points to an intensive energy release in the dense part of the ...solar atmosphere. We study properties of the energy release with high temporal and spatial resolutions, using photospheric data from the Helioseismic Magnetic Imager (HMI) on board Solar Dynamics Observatory, and hard X-ray observations made by RHESSI. For this analysis we use level-1 HMI data (filtergrams), obtained by scanning the Fe i line (6731 ) with the time cadence of ∼3.6 s and spatial resolution of ∼0 5 per pixel. It is found that the photospheric disturbances caused by the flare spatially coincide with the region of hard X-ray emission but are delayed by 4 s. This delay is consistent with predictions of the flare hydrodynamics RADYN models. However, the models fail to explain the magnitude of variations observed by the HMI. The data indicate that the photospheric impact and helioseismic wave might be caused by the electron energy flux, which is substantially higher than that in the current flare radiative hydrodynamic models.
We present a comparison of the measured cosmic ray (CR) muon fluxes from two identical portable low‐cost detectors at different geolocations and their sensitivity to space weather events in real ...time. The first detector is installed at Mount Wilson Observatory, CA, USA (geomagnetic cutoff rigidity Rc ∼ 4.88 GV), and the second detector is running on the downtown campus of Georgia State University in Atlanta, GA, USA (Rc ∼ 3.65 GV). The variation of the detected muon fluxes is compared to the changes in the interplanetary solar wind parameters at the L1 Lagrange point and geomagnetic indexes. In particular, we have investigated the muon flux behavior during three major interplanetary shock events and geomagnetic disturbances that occurred during July and August of 2022. To validate the interpretation of the measured muon signals, we compare the muon fluxes to the measurement from the Oulu neutron monitor (NM, Rc ∼ 0.8 GV). The results of this analysis show that the muon detector installed at Mount Wilson Observatory demonstrates a stronger correlation with a high‐latitude NM. Both detectors typically observe a muon flux decrease during the arrival of interplanetary shocks and geomagnetic storms. Interestingly, the decrease could be observed several hours before the onset of the first considered interplanetary shocks at L1 at 2022‐07‐23 02:28:00 UT driven by the high‐speed Coronal Mass Ejection and related geomagnetic storm at 2022‐07‐23 03:59:00 UT. This effort represents an initial step toward establishing a global network of portable low‐cost CR muon detectors for monitoring the sensitivity of muon flux changes to space and terrestrial weather parameters.
Plain Language Summary
A pair of identical, low‐cost, and portable cosmic ray (CR) muon detectors is set up over 3,500 km apart for an exploratory study of monitoring space and terrestrial weather in real time at a global scale. One detector is installed on Mount Wilson, California and the other is in downtown Atlanta, Georgia. To validate the interpretation of the measured muon signals, the muon fluxes are compared to the well‐known neutron flux measurement from the Oulu neutron station in Finland. The results of this analysis show that the CR flux from both muon detectors typically decreases during geomagnetic storm events and that the muon detector installed on Mount Wilson is significantly correlated with the Oulu neutron monitor. Although this is yet an initial effort of building a global network of CR muon detectors for monitoring the space and earth weather in real time, the study provides evidence that muon network detection efficiency can be sufficient for a diagnostic of the major geoeffective space weather events.
Key Points
A global network of portable muon detectors is under development for monitoring the dynamic changes of the space and terrestrial weather
A comparison of the measured cosmic ray (CR) muon fluxes from two identical detectors at different geolocations in real‐time is carried out
A correlation study between the muon data and the neutron measurement at Oulu CR station in Finland is presented in this paper
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