Abstract
We report the first intensity correlation measured with starlight since the historical experiments of Hanbury Brown and Twiss. The photon bunching g(2)(τ, r = 0), obtained in the ...photon-counting regime, was measured for three bright stars: α Boo, α CMi and β Gem. The light was collected at the focal plane of a 1-m optical telescope, transported by a multi-mode optical fibre, split into two avalanche photodiodes and correlated digitally in real time. For total exposure times of a few hours, we obtained contrast values around 2 × 10−3, in agreement with the expectation for chaotic sources, given the optical and electronic bandwidths of our set-up. Comparing our results with the measurement of Hanbury Brown et al. for α CMi, we argue for the timely opportunity to extend our experiments to measuring the spatial correlation function over existing and/or foreseen arrays of optical telescopes diluted over several kilometres. This would enable microarcsec long-baseline interferometry in the optical, especially in the visible wavelengths, with a limiting magnitude of 10.
ASTEP 400, the main instrument of the ASTEP (Antarctica Search for Transiting ExoPlanets) programme, is a 40 cm telescope, designed to withstand the harsh conditions in Antarctica, achieving a ...photometric accuracy of a fraction of millimagnitude on hourly time-scales for planet-hosting southern bright (R ∼ 12 mag) stars. We review the performances of this instrument, describe its operating conditions, and present results from the analysis of observations obtained during its first three years (2010–2012) of operation, before its repatriation in 2014. During this time, we observed a total of 22 stellar fields (1° × 1° field of view). Each field, in which we measured stars up to magnitude R = 18 mag, was observed continuously during ∼7 to ∼30 d. More than 200 000 frames were recorded and 310 000 stars processed, using an implementation of the optimal image subtraction photometry algorithm. We found 43 planetary transit candidates. 20 of these candidates were observed using spectroscopic follow-ups including four targets classified as good planet candidates. Our results demonstrate that accurate near-continuous photometric observations are achievable from the Concordia station at Dome C in Antarctica, even if we were not able to reach the nominal photometric precision of the instrument. We conducted a correlation analysis between the rms noise and a large number of external parameters and found that source of the ∼1 mmag correlated noise is not obvious and does not depend on a single parameter. However, our analysis provided some hints and guidance to increase the photometric accuracy of the instrument. These improvements should equip any future telescope operating in Antarctica.
Context. The near-Earth asteroid (3200) Phaethon is an intriguing object: its perihelion is at only 0.14 au and is associated with the Geminid meteor stream. Aims. We aim to use all available ...disk-integrated optical data to derive a reliable convex shape model of Phaethon. By interpreting the available space- and ground-based thermal infrared data and Spitzer spectra using a thermophysical model, we also aim to further constrain its size, thermal inertia, and visible geometric albedo. Methods. We applied the convex inversion method to the new optical data obtained by six instruments and to previous observations. The convex shape model was then used as input for the thermophysical modeling. We also studied the long-term stability of Phaethon’s orbit and spin axis with a numerical orbital and rotation-state integrator. Results. We present a new convex shape model and rotational state of Phaethon: a sidereal rotation period of 3.603958(2) h and ecliptic coordinates of the preferred pole orientation of (319°, −39°) with a 5° uncertainty. Moreover, we derive its size (D = 5.1 ± 0.2 km), thermal inertia (Γ = 600 ± 200 J m–2 s–1/2 K–1), geometric visible albedo (pV = 0.122 ± 0.008), and estimate the macroscopic surface roughness. We also find that the Sun illumination at the perihelion passage during the past several thousand years is not connected to a specific area on the surface, which implies non-preferential heating.
Hydrogels are studied extensively for many tissue engineering applications, and their mechanical properties influence both cellular and tissue compatibility. However, it is difficult to compare the ...mechanical properties of hydrogels between studies due to a lack of continuity between rheological protocols. This study outlines a straightforward protocol to accurately determine hydrogel equilibrium modulus and gelation time using a series of rheological tests. These protocols are applied to several hydrogel systems used within tissue engineering applications: agarose, collagen, fibrin, Matrigel™, and methylcellulose. The protocol is outlined in four steps: (1) Time sweep to determine the gelation time of the hydrogel. (2) Strain sweep to determine the linear-viscoelastic region of the hydrogel with respect to strain. (3) Frequency sweep to determine the linear equilibrium modulus plateau of the hydrogel. (4) Time sweep with values obtained from strain and frequency sweeps to accurately report the equilibrium moduli and gelation time. Finally, the rheological characterization protocol was evaluated using a composite Matrigel™-methylcellulose hydrogel blend whose mechanical properties were previously unknown. The protocol described herein provides a standardized approach for proper analysis of hydrogel rheological properties.
The Calern Asteroid Polarisation Survey Bendjoya, Ph; Cellino, A.; Rivet, J.-P. ...
Astronomy and astrophysics (Berlin),
09/2022, Volume:
665
Journal Article
Peer reviewed
Open access
Context.
The Calern Asteroid Polarimetric Survey (CAPS), a collaboration between the INAF Astrophysical Observatory of Torino (Italy) and the Observatoire de la Côte d’Azur (Nice, France), has ...produced new asteroid polarimetric data for a number of years, and is one of the most important, currently active projects of asteroid polarimetry.
Aims.
The purpose of this paper is to make public the CAPS data collected thus far, to explain the adopted techniques of data reduction and computation of phase-polarisation curves for the measured objects, and explain, by means of some examples, the importance of the CAPS database.
Methods.
The pipeline of data reduction has been recently updated and made as automatic as possible, using numerical algorithms developed specifically for the purposes of CAPS. The derivation of phase-polarisation curves for the observed asteroids is done using established criteria and algorithms that have recently been slightly improved, and are also summarised in this paper.
Results.
The CAPS catalogue is a steadily growing source of information which can be exploited for different purposes, including, but not limited to, an updated calibration of the relations existing between different polarimetric parameters and the geometric albedo of the objects, and a study of classes of objects that can be most easily identified by means of their polarimetric properties. These subjects will be more specifically discussed in separate papers.
Conclusions.
Asteroid polarimetry data nicely complement the results of other more commonly used techniques, including visible and IR photometry and spectroscopy. CAPS contains a lot of much-desired information about physical properties, which can hardly be inferred by means of other techniques.
Abstract
BACKGROUND
Recent randomized control trials (RCTs) established that mechanical thrombectomy is superior to medical therapy for patients with stroke due to a large vessel occlusion.
OBJECTIVE
...To compare the safety and efficacy profile of the different mechanical thrombectomy strategies.
METHODS
A random-effects meta-analysis was performed and the I2 statistic was used to assess heterogeneity according to the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines.
RESULTS
Nineteen studies with a total of 2449 patients were included. No differences were identified between the stent retrieval and direct aspiration groups in terms of modified Thrombolysis in Cerebral Infarction (mTICI) 2b/3 and mTICI 3 recanalization rates, and favorable outcomes (modified Rankin Scale mRS ≤ 2). Adverse event rates, including 90-d mortality, symptomatic intracerebral hemorrhage (sICH), and subarachnoid hemorrhage (SAH), were similar between the stent retrieval and direct aspiration groups. The use of the stent retrieval was associated with a higher risk of vasospasm (odds ratio OR: 2.98; 95% confidence interval CI: 1.10-8.09; I2: 0%) compared to direct aspiration. When compared with the direct aspiration group, the subgroup of patients who underwent thrombectomy with the combined approach as a first-line strategy had a higher likelihood of successful mTICI 2b/3 (OR: 1.47; 95% CI: 1.02-2.12; I2: 0%) and mTICI 3 recanalization (OR: 3.65; 95% CI: 1.56-8.54), although with a higher risk of SAH (OR: 4.33; 95% CI: 1.15-16.32).
CONCLUSION
Stent retrieval thrombectomy and direct aspiration did not show significant differences. Current available evidence is not sufficient to draw conclusions on the best surgical approach. The combined use of a stent retriever and aspiration as a first-line strategy was associated with higher mTICI 2b/3 and mTICI 3 recanalization rates, although with a higher risk of 24-h SAH, when compared with direct aspiration.
ABSTRACT
We present intensity interferometry of the luminous blue variable P Cyg in the light of its H α emission performed with 1 m-class telescopes. We compare the measured visibility points to ...synthesized interferometric data based on the CMFGEN physical modelling of a high-resolution spectrum of P Cyg recorded almost simultaneously with our interferometry data. Tuning the stellar parameters of P Cyg and its H α linear diameter, we estimate the distance of P Cyg as 1.56 ± 0.25 kpc, which is compatible within 1σ with 1.36 ± 0.24 kpc reported by the Gaia DR2 catalogue of parallaxes recently published. Both the values are significantly smaller than the canonic value of 1.80 ± 0.10 kpc usually adopted in literature. Our method used to calibrate the distance of P Cyg can apply to very massive and luminous stars both in our Galaxy and neighbouring galaxies, and can improve the so-called wind momentum–luminosity relation that potentially applies to calibrate cosmological candles in the local Universe.
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