136 research outputs found
Ground-based monitoring of comet 67P/Churyumov-Gerasimenko gas activity throughout the <i>Rosetta</i> mission
Simultaneously to the ESA Rosetta mission, a world-wide ground-based campaign provided measurements of the large scale activity of comet 67P/Churyumov-Gerasimenko through measurement of optically active gas species and imaging of the overall dust coma. We present more than two years of observations performed with the FORS2 low resolution spectrograph at the VLT, TRAPPIST, and ACAM at the WHT. We focus on the evolution of the CN production, as a tracer of the comet activity. We find that it is asymmetric with respect to perihelion and different from that of the dust. The CN emission is detected for the first time at 1.34 au pre-perihelion and production rates then increase steeply to peak about two weeks after perihelion at (1.00±0.10) ×1025 molecules s−1, while the post-perihelion decrease is more shallow. The evolution of the comet activity is strongly influenced by seasonal effects, with enhanced CN production when the Southern hemisphere is illuminated
Stochastic Coherence Over Attention Trajectory For Continuous Learning In Video Streams
Devising intelligent agents able to live in an environment and learn by observing the surroundings is a longstanding goal of Artificial Intelligence. From a bare Machine Learning perspective, challenges arise when the agent is prevented from leveraging large fully-annotated dataset, but rather the interactions with supervisory signals are sparsely distributed over space and time. This paper proposes a novel neural-network-based approach to progressively and autonomously develop pixel-wise representations in a video stream. The proposed method is based on a human-like attention mechanism that allows the agent to learn by observing what is moving in the attended locations. Spatio-temporal stochastic coherence along the attention trajectory, paired with a contrastive term, leads to an unsupervised learning criterion that naturally copes with the considered setting. Differently from most existing works, the learned representations are used in open-set class-incremental classification of each frame pixel, relying on few supervisions. Our experiments leverage 3D virtual environments and they show that the proposed agents can learn to distinguish objects just by observing the video stream. Inheriting features from state-of-the art models is not as powerful as one might expect
Management of antifungal susceptibility testing in Italy: comparative results of 2 nationwide surveys (1999 and 2004) in 102 Italian hospitals.
Polyamine Receptors Containing Dipyridine or Phenanthroline Units:Clues for the Design of Fluorescent Chemosensors for Metal Ions
Atributos microbiológicos do solo de áreas mineradas em recuperação: I - atividade de urease e arginase.
First detection of CO emission in a Centaur: JWST NIRSpec observations of 39P/Oterma
Centaurs are minor solar system bodies with orbits transitioning between
those of Trans-Neptunian Scattered Disk objects and Jupiter Family comets.
39P/Oterma is a frequently active Centaur that has recently held both Centaur
and JFC classifications and was observed with the JWST NIRSpec instrument on
2022 July 27 UTC while it was 5.82 au from the Sun. For the first time, CO
gas emission was detected in a Centaur, with a production rate of Q =
(5.96 0.80) 10 molecules s. This is the lowest
detection of CO of any Centaur or comet. CO and HO were not detected
down to constraining upper limits. Derived mixing ratios of Q/Q
2.03 and Q/Q 0.60 are consistent with CO
and/or CO outgassing playing large roles in driving the activity, but not
water, and show a significant difference between the coma abundances of
29P/Schwassmann-Wachmann 1, another Centaur at a similar heliocentric distance,
which may be explained by thermal processing of 39P's surface during its
previous Jupiter-family comet orbit. To help contextualize the JWST data we
also acquired visible CCD imaging data on two dates in July (Gemini North) and
September (Lowell Discovery Telescope) 2022. Image analysis and photometry
based on these data are consistent with a point source detection and an
estimated effective nucleus radius of 39P in the range of 2.21 to
2.49~km
JWST molecular mapping and characterization of Enceladus' water plume feeding its torus
Enceladus is a prime target in the search for life in our solar system,
having an active plume likely connected to a large liquid water subsurface
ocean. Using the sensitive NIRSpec instrument onboard JWST, we searched for
organic compounds and characterized the plume's composition and structure. The
observations directly sample the fluorescence emissions of H2O and reveal an
extraordinarily extensive plume (up to 10,000 km or 40 Enceladus radii) at
cryogenic temperatures (25 K) embedded in a large bath of emission originating
from Enceladus' torus. Intriguingly, the observed outgassing rate (300 kg/s) is
similar to that derived from close-up observations with Cassini 15 years ago,
and the torus density is consistent with previous spatially unresolved
measurements with Herschel 13 years ago, suggesting that the vigor of gas
eruption from Enceladus has been relatively stable over decadal timescales.
This level of activity is sufficient to maintain a derived column density of
4.5x1017 m-2 for the embedding equatorial torus, and establishes Enceladus as
the prime source of water across the Saturnian system. We performed searches
for several non-water gases (CO2, CO, CH4, C2H6, CH3OH), but none were
identified in the spectra. On the surface of the trailing hemisphere, we
observe strong H2O ice features, including its crystalline form, yet we do not
recover CO2, CO nor NH3 ice signatures from these observations. As we prepare
to send new spacecraft into the outer solar system, these observations
demonstrate the unique ability of JWST in providing critical support to the
exploration of distant icy bodies and cryovolcanic plumes.Comment: Accepted for publication in Nature Astronomy on May 17th 202
Atividade de fosfatase ácida e alcalina do solo de área minerada em diferentes estágios de regeneração ambiental.
Detailed Analysis of Near-IR Water (H<SUB>2</SUB>O) Emission in Comet C/2014 Q2 (Lovejoy) with the GIANO/TNG Spectrograph
We observed the Oort cloud comet C/2014 Q2 (Lovejoy) on 2015 January 31 and February 1 and 2 at a heliocentric distance of 1.3 au and geocentric distance of 0.8 au during its approach to the Sun. Comet Lovejoy was observed with GIANO, the near-infrared high-resolution spectrograph mounted at the Nasmyth-A focus of the TNG (Telescopio Nazionale Galileo) telescope in La Palma, Canary Islands, Spain. We detected strong emissions of radical CN and water, along with many emission features of unidentified origin, across the 1-2.5 μm region. Spectral lines from eight ro-vibrational bands of H2O were detected, six of them for the first time. We quantified the water production rate [Q(H2O), (3.11 ± 0.14) × 1029 s-1] by comparing the calibrated line fluxes with the Goddard full non-resonance cascade fluorescence model for H2O. The production rates of ortho-water [Q(H2O)ORTHO, (2.33 ± 0.11) × 1029 s-1] and para-water [Q(H2O)PARA, (0.87 ± 0.21) × 1029 s-1] provide a measure of the ortho-to-para ratio (2.70 ± 0.76)). The confidence limits are not small enough to provide a critical test of the nuclear spin temperature
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