Unit Cell Distortion and Surface Morphology Diversification in SnTe/CdTe(001) Topological Crystalline Insulator Heterostructure: Influence of Defects’ Azimuthal Distribution

Challenges and opportunities arising upon molecular-beam-epitaxial growth of topological crystalline insulator heterostructures composed of a rock-salt SnTe(001) layer of varying thickness (from 80 to 1000 nm) and a zinc-blende 4-μm-thick...

Benchmarking microbarom radiation and propagation model against infrasound recordings: a vespagram-based approach

This study investigates the use of a vespagram-based approach as a tool for multi-directional comparison between simulated microbarom soundscapes and infrasound data recorded at ground-based array stations. Data recorded at the IS37 station in northern Norway during 2014–2019 have been processed to generate vespagrams (velocity spectral analysis) for five frequency bands between 0.1 and 0.6 Hz. The back azimuth resolution between the vespagram and the microbarom model is harmonized by smoothing the modeled soundscapes along the back azimuth axis with a kernel corresponding to the frequency-dependent array resolution. An estimate of similarity between the output of the microbarom radiation and propagation model and infrasound observations is then generated based on the image-processing approach of the mean square difference. The analysis reveals that vespagrams can monitor seasonal variations in the microbarom azimuthal distribution, amplitude, and frequency, as well as changes during sudden stratospheric warming events. The vespagram-based approach is computationally inexpensive, can uncover microbarom source variability, and has the potential for near-real-time stratospheric diagnostics and atmospheric model assessment.

Volcano dynamics vs tectonics on Mars: evidence from Pavonis Mons

<p>Volcanic activity is widespread within the inner Solar system and it can be commonly observed on rocky planets.<br>In this work, we analyse the structures of Pavonis Mons, which is one of the three large volcanoes in the Tharsis volcanic province of Mars, by performing structural mapping, azimuth, and topographic distribution of linear features on the flanks of Pavonis, such as grabens and pit chains. We tested whether their formation is to be ascribed to the internal volcano dynamics and magmatic activity or the tectonics related to the Tharsis volcanic province activity.<br>Through the length size distribution and fractal clustering analyses of the structural features, we found that large grabens are vertically confined in the upper mechanical layers of the brittle crust whereas pit chains penetrate the whole crust up to the magmatic source, indicating that they can be considered the main feeders of Pavonis Mons. We inverted the topography with dykes and faults models to test whether grabens at the surface are the expression of intrusions at depth and we suggest that thin dykes inducing normal faulting is the most likely mechanism. Furthermore, two azimuthal distribution of the grabens are identified: concentric grabens occur on the volcano summit while linear grabens at its base show NE-SW trend as the Tharsis Montes volcanoes alignment. The analyses show that faults related to large grabens are confined in a mechanical layering in the upper layers of the brittle crust, whereas deeper structures such as pit chains are most likely associated to magma injection/dykes and therefore, connected to the subcrustal magma source at a depth of ~80–100 km.<br>Therefore, based on our results, we infer that Pavonis Mons recorded active rifting at the initial stages of development with the formation of the large linear graben and faults at its base followed by a phase of volcano growth and concentric magma intrusions when volcano and magma chamber dynamics prevailed</p>

Directionality of ambient noise in the Mississippi embayment

SUMMARY Cross-correlations of ambient seismic noise from 277 broad-band stations within the Mississippi embayment (ME) with at least 1 month of recording time between 1990 and 2018 are used to estimate source locations of primary and secondary microseisms. We investigate source locations by analysing the azimuthal distribution of the signal-to-noise ratios (SNRs) and positive/negative amplitude differences. We use 84 stations with 1 yr of continuous recordings to explore seasonal variations of SNRs and amplitude differences. We also investigate the seasonal ambient noise ground motions using 2-D frequency–wavenumber (FK) analysis of a 50-station array. We observe that: (1) two major azimuths can be identified in the azimuthal distribution of SNRs and amplitude differences. We also observe two minor azimuths in the seasonal variation of SNRs, amplitude differences and 2-D FK power spectra. Monthly 2-D FK power spectra reveal that two energy sources are active in the Northern Hemisphere winter and two relatively weak sources are active in summer. (2) Backprojection suggests that primary microseisms originate along the coasts of Australia or New Zealand, Canada and Alaska, Newfoundland or Greenland and South America. (3) Secondary microseisms are generated in the deep water of the northern and southern Pacific Ocean, along the coasts of Canada and Alaska associated with near-shore reflections and in the deep water of south of Greenland. (4) Weak energy is observed in the third quadrant of the azimuthal distribution of amplitude differences of sedimentary Rayleigh and Love waves in the period band of 1–5 s and correlates with the direction of widening of the basin.

Azimuthal Distribution in Heavy-Ion Collisions

We consider recent experimental data on azimuthal distributions of particles seen in heavy-ion collisions at 35 MeV/nucleon and at 50 MeV/nucleon. For 12C on 12C at 50 MeV/nucleon lab energy, the distribution shows features characteristic of flow; for 12C on 197Au experimental data show features characteristic of rotation. For 40Ar on 51V at 35 MeV/nucleon, effects of both flow and rotation are seen. In magnitudes the effects are small. We find that BUU calculations are able to reproduce these results.

Dust production in the debris disk around HR 4796 A

Context. Debris disks are the natural by-products of the planet formation process. Scattered or polarized light observations are mostly sensitive to small dust grains that are released from the grinding down of bigger planetesimals. Aims. High angular resolution observations at optical wavelengths can provide key constraints on the radial and azimuthal distribution of the small dust grains. These constraints can help us better understand where most of the dust grains are released upon collisions. Methods. We present SPHERE/ZIMPOL observations of the debris disk around HR 4796 A, and we modeled the radial profiles along several azimuthal angles of the disk with a code that accounts for the effect of stellar radiation pressure. This enabled us to derive an appropriate description for the radial and azimuthal distribution of the small dust grains. Results. Even though we only modeled the radial profiles along, or close to, the semi-major axis of the disk, our best-fit model is not only in good agreement with our observations but also with previously published datasets (from near-infrared to sub-mm wavelengths). We find that the reference radius is located at 76.4 ± 0.4 au, and the disk has an eccentricity of 0.076−0.010+0.016 with the pericenter located on the front side of the disk (north of the star). We find that small dust grains must be preferentially released near the pericenter to explain the observed brightness asymmetry. Conclusions. Even though parent bodies spend more time near the apocenter, the brightness asymmetry implies that collisions happen more frequently near the pericenter of the disk. Our model can successfully reproduce the shape of the outer edge of the disk without requiring an outer planet shaping the debris disk. With a simple treatment for the effect of the radiation pressure, we conclude that the parent planetesimals are located in a narrow ring of about 3.6 au in width.

Full-azimuthal imaging-DOAS observations of NO₂ and O₄ during CINDI-2

A novel imaging-DOAS (differential optical absorption spectroscopy) instrument IMPACT (Imaging MaPper for AtmospheriC observaTions) is presented combining full-azimuthal pointing (360∘) with a large vertical coverage (∼41∘). Complete panoramic scans are acquired at a temporal resolution of ∼15 min, enabling the retrieval of NO2 vertical profiles over the entire panorama around the measurement site. IMPACT showed excellent agreement (correlation >99 %) with coincident multiaxis DOAS (MAX-DOAS) measurements during the Second Cabauw Intercomparison of Nitrogen Dioxide measuring Instruments (CINDI-2) campaign. The temporal variability of NO2 slant columns within a typical MAX-DOAS vertical scanning sequence could be resolved and was as large as 20 % in a case study under good viewing conditions. The variation of corresponding profiles and surface concentrations was even larger (40 %). This variability is missed when retrieving trace gas profiles based on standard MAX-DOAS measurements. The azimuthal distribution of NO2 around the measurement site showed inhomogeneities (relative differences) up to 120 % (on average 35 %) on short timescales (individual panoramic scans). This is more than expected for the semirural location. We explain this behavior by the transport of pollution. Exploiting the instrument's advantages, the plume's trajectory during a prominent transport event could be reconstructed. Finally, the potential for retrieving information about the aerosol phase function from O4 slant columns along multiple almucantar scans of IMPACT is demonstrated, with promising results for future studies.