River flow models that consider satellite observations of the water surface elevation (WSE) require meaningful segmentation into reaches. Segmentation methods involve a trade‐off between the spatial ...sampling and error characteristics of satellite observations, both of which impact the flow model realism/accuracy. This paper investigates the spatial properties of WSE profiles (slope and concavity) and their link with hydraulic controls (HCs) and leverages this knowledge to advance river segmentation. Fine‐scale synthetic cases were analyzed to characterize HC effects on the remotely observable WSE properties. Following this, a wavelet‐based segmentation method was developed and subsequently tested on real rivers, including test cases with measurements characteristic of the Surface Water and Ocean Topography satellite mission. The results show that the local extrema of water surface (WS) concavity are good candidates for defining reach bounds while consistently preserving the HC signatures and local flow nonuniformities (deviations from equilibrium) from fine to large spatial scales.
Key Points
The hydraulic visibility of river surface profile variabilities from space is investigated
Hydraulic control signatures are depicted in local extrema of water surface curvature
A wavelet‐based river segmentation preserving hydraulic controls is proposed
AB 5 compounds (A = rare earth, B = transition metal) have been widely studied as anodes for Ni-MH applications. However, they have reached their technical limitations and the search for new ...promising materials with high capacity is foreseen. AB y compounds (2 < y < 5) are good candidates. They are made by stacking AB 5 and A 2 B 4 units along the c crystallographic axis. The latter unit allows a large increase in capacity, while the AB 5 unit provides good cycling stability. Consequently, the AB 3.8 composition (i.e. A 5 B 19 with three AB 5 for one A 2 B 4 ) is expected to exhibit better cycling stability than the AB 3.5 (i.e. A 2 B 7 with two AB 5 for one A 2 B 4 ). Furthermore, substitution of rare earth by light magnesium improves both the capacity and cycling stability. In this paper, we compare the hydrogenation and corrosion properties of two binary compounds, SmNi 3.5 and SmNi 3.8 , and two pseudo-binary ones, (Sm,Mg)Ni 3.5 and (Sm,Mg)Ni 3.8. A better solid-gas cycling stability is highlighted for the binary SmNi 3.8. The pseudo-binary compounds also exhibit higher cycling stability than the binary ones. Furthermore, their resistance to corrosion was investigated.
Background
Cutaneous metastases (CM) diagnosis is clinically challenging, requiring an invasive biopsy for confirmation. A novel, RCM‐OCT device combines the advantage of horizontal high‐resolution ...reflectance confocal microscopy (RCM) images and vertical deeper optical coherence tomography (OCT) images to aid in non‐invasive diagnosis of CM from breast cancers.
Objective
Characterize CM from breast cancers using RCM‐OCT device.
Methods
Seven patients suffering from breast cancers with suspicious CM were consented and imaged with RCM‐OCT device. CM features were defined by comparing with histopathology. Tumour depths were measured on OCT and on H&E‐images and correlated using statistical analysis Pearson test. 3D‐OCT images were reconstructed to enhance tumour visualization.
Results
6/7 lesions were CM from breast cancers, and one was vascular ectasia, on histopathology. CM appeared as greyish‐darkish oval to round structures within the dermis on RCM and OCT‐images. On RCM, individual tumour cells were seen, enabling identification of even small tumour foci; while, on OCT deeper tumours were detected. Inflammatory cells, dilated vessels and coarse collagen were identified in the dermis. Pearson correlation had an r2 of 0.38 and a significant P‐value <0.004 for depth measurements. CM from breast cancers could be differentiated from ecstatic vessels on 3D‐reconstructed OCT image.
Limitation
Small sample size and lack of clinical mimickers.
Conclusion
RCM‐OCT can detect CM and has potential in aiding non‐invasive diagnosis and management.
We present near-infrared observations of T Tauri and Herbig Ae/Be stars with a spatial resolution of a few milliarcseconds and a spectral resolution of {approx}2000. Our observations spatially ...resolve gas and dust in the inner regions of protoplanetary disks, and spectrally resolve broad-linewidth emission from the Br{gamma} transition of hydrogen gas. We use the technique of spectro-astrometry to determine centroids of different velocity components of this gaseous emission at a precision orders of magnitude better than the angular resolution. In all sources, we find the gaseous emission to be more compact than or distributed on similar spatial scales to the dust emission. We attempt to fit the data with models including both dust and Br{gamma}-emitting gas, and we consider both disk and infall/outflow morphologies for the gaseous matter. In most cases where we can distinguish between these two models, the data show a preference for infall/outflow models. In all cases, our data appear consistent with the presence of some gas at stellocentric radii of {approx}0.01 AU. Our findings support the hypothesis that Br{gamma} emission generally traces magnetospherically driven accretion and/or outflows in young star/disk systems.
GRAVITY K-band spectroscopy of HD 206893 B Kammerer, J; Lacour, S; Stolker, T ...
Astronomy and astrophysics (Berlin),
08/2021, Volume:
652
Journal Article, Web Resource
Peer reviewed
Open access
Context. Near-infrared interferometry has become a powerful tool for studying the orbital and atmospheric parameters of substellar companions. Aims. We aim to reveal the nature of the reddest known ...substellar companion HD 206893 B by studying its near-infrared colors and spectral morphology and by investigating its orbital motion. Methods. We fit atmospheric models for giant planets and brown dwarfs and perform spectral retrievals with petitRADTRANS and ATMO on the observed GRAVITY, SPHERE, and GPI spectra of HD 206893 B. To recover its unusual spectral features, first and foremost its extremely red near-infrared color, we include additional extinction by high-altitude dust clouds made of enstatite grains in the atmospheric model fits. However, forsterite, corundum, and iron grains predict similar extinction curves for the grain sizes considered here. We also infer the orbital parameters of HD 206893 B by combining the ~100 μas precision astrometry from GRAVITY with data from the literature and constrain the mass and position of HD 206893 C based on the Gaia proper motion anomaly of the system. Results. The extremely red color and the very shallow 1.4 μm water absorption feature of HD 206893 B can be fit well with the adapted atmospheric models and spectral retrievals. By comparison with AMES-Cond evolutionary tracks, we find that only some atmosphericmodels predict physically plausible objects. Altogether, our analysis suggests an age of ~ 3–300 Myr and a mass of ~ 5–30 MJup for HD 206893 B, which is consistent with previous estimates but extends the parameter space to younger and lower-mass objects. The GRAVITY astrometry points to an eccentric orbit (e = 0.29−0.11+0.06) with a mutual inclination of <34.4 deg with respectto the debris disk of the system. Conclusions. While HD 206893 B could in principle be a planetary-mass companion, this possibility hinges on the unknown influence of the inner companion on the mass estimate of 10−4+5 MJup from radial velocity and Gaia as well as a relatively small but significant Argus moving group membership probability of ~ 61%. However, we find that if the mass of HD 206893 B is <30 MJup, then the inner companion HD 206893 C should have a mass between ~ 8–15 MJup. Finally, further spectroscopic or photometric observations at higher signal-to-noise and longer wavelengths are required to learn more about the composition and dust cloud properties of HD 206893 B.
Optical and infrared interferometers definitively established that the photometric standard Vega (= alpha Lyrae) is a rapidly rotating star viewed nearly pole-on. Recent independent spectroscopic ...analyses could not reconcile the inferred inclination angle with the observed line profiles, preferring a larger inclination. In order to resolve this controversy, we observed Vega using the six-beam Michigan Infrared Combiner on the Center for High Angular Resolution Astronomy Array. With our greater angular resolution and dense (u, v)-coverage, we find that Vega is rotating less rapidly and with a smaller gravity darkening coefficient than previous interferometric results. Our models are compatible with low photospheric macroturbulence and are also consistent with the possible rotational period of ~0.71 days recently reported based on magnetic field observations. Our updated evolutionary analysis explicitly incorporates rapid rotation, finding Vega to have a mass of (ProQuest: Formulae and/or non-USASCII text omitted) M sub(+ in circle) and an age (ProQuest: Formulae and/or non-USASCII text omitted) Myr, substantially older than previous estimates with errors dominated by lingering metallicity uncertainties (Z = (ProQuest: Formulae and/or non-USASCII text omitted)).
Recent applications of remote sensing techniques produce rich spatially distributed observations for flood monitoring. In order to improve numerical flood prediction, we have developed a variational ...data assimilation method (4D-var) that combines remote sensing data (spatially distributed water levels extracted from spatial images) and a 2D shallow water model. In the present paper (part I), we demonstrate the efficiency of the method with a test case. First, we assimilated a single fully observed water level image to identify time-independent parameters (e.g. Manning coefficients and initial conditions) and time-dependent parameters (e.g. inflow). Second, we combined incomplete observations (a time series of water elevations at certain points and one partial image). This last configuration was very similar to the real case we analyze in a forthcoming paper (part II). In addition, a temporal strategy with time overlapping is suggested to decrease the amount of memory required for long-duration simulation.
This work focuses on the numerical assessment of the accuracy of an adjoint-based gradient in the perspective of variational data assimilation and parameter identification in glaciology. Using noisy ...synthetic data, we quantify the ability to identify the friction coefficient for such methods with a non-linear friction law. The exact adjoint problem is solved, based on second-order numerical schemes, and a comparison with the so-called "self-adjoint" approximation, neglecting the viscosity dependence on the velocity (leading to an incorrect gradient), common in glaciology, is carried out. For data with a noise of 1%, a lower bound of identifiable wavelengths of 10 ice thicknesses in the friction coefficient is established, when using the exact adjoint method, while the "self-adjoint" method is limited, even for lower noise, to a minimum of 20 ice thickness wavelengths. The second-order exact gradient method therefore provides robustness and reliability for the parameter identification process. In another respect, the derivation of the adjoint model using algorithmic differentiation leads to the formulation of a generalization of the "self-adjoint" approximation towards an incomplete adjoint method, adjustable in precision and computational burden.
The development of high-contrast capabilities has long been recognized as one of the top priorities for the VLTI (Very Large Telescope Interferometer). As of today, the VLTI routinely achieves ...contrasts of a few 103 in the near-infrared with PIONIER (Precision Integrated-Optics Near-infrared Imaging ExpeRiment) (H band) and GRAVITY (K band). Nulling interferometers in the northern hemisphere and non-redundant aperture masking experiments have, however, demonstrated that contrasts of at least a few 10 (sup -3) are within reach using specific beam combination and data acquisition techniques. In this paper, we explore the possibility to reach similar or higher contrasts on the VLTI. After reviewing the state-of-the-art in high-contrast infrared interferometry, we discuss key features that made the success of other high-contrast interferometric instruments (e.g., integrated optics, nulling, closure phase, and statistical data reduction) and address possible avenues to improve the contrast of the VLTI by at least one order of magnitude. In particular, we discuss the possibility to use integrated optics, proven in the near-infrared, in the thermal near-infrared (L and M bands, 3-5 microns), a sweet spot to image and characterize young extra-solar planetary systems. Finally, we address the science cases of a high-contrast VLTI imaging instrument and focus particularly on exoplanet science (young exoplanets, planet formation, and exozodiacal disks), stellar physics (fundamental parameters and multiplicity), and extragalactic astrophysics (active galactic nuclei and fundamental constants). Synergies and scientific preparation for other potential future instruments such as the Planet Formation Imager are also briefly discussed. This project is called Hi-5 for High-contrast Interferometry up to 5 microns.
PDF
