25 research outputs found
Event detection, tracking, and visualization in Twitter: a mention-anomaly-based approach
The ever-growing number of people using Twitter makes it a valuable source of
timely information. However, detecting events in Twitter is a difficult task,
because tweets that report interesting events are overwhelmed by a large volume
of tweets on unrelated topics. Existing methods focus on the textual content of
tweets and ignore the social aspect of Twitter. In this paper we propose MABED
(i.e. mention-anomaly-based event detection), a novel statistical method that
relies solely on tweets and leverages the creation frequency of dynamic links
(i.e. mentions) that users insert in tweets to detect significant events and
estimate the magnitude of their impact over the crowd. MABED also differs from
the literature in that it dynamically estimates the period of time during which
each event is discussed, rather than assuming a predefined fixed duration for
all events. The experiments we conducted on both English and French Twitter
data show that the mention-anomaly-based approach leads to more accurate event
detection and improved robustness in presence of noisy Twitter content.
Qualitatively speaking, we find that MABED helps with the interpretation of
detected events by providing clear textual descriptions and precise temporal
descriptions. We also show how MABED can help understanding users' interest.
Furthermore, we describe three visualizations designed to favor an efficient
exploration of the detected events.Comment: 17 page
ALMA observations of polarized emission toward the CW Tau and DG Tau protoplanetary disks: constraints on dust grain growth and settling
We present polarimetric data of CW Tau and DG Tau, two well-known Class II
disk/jet systems, obtained with the Atacama Large Millimeter/submillimeter
Array at 870 m and 0."2 average resolution. In CW Tau, the total and
polarized emission are both smooth and symmetric, with polarization angles
almost parallel to the minor axis of the projected disk. In contrast, DG Tau
displays a structured polarized emission, with an elongated brighter region in
the disk's near side and a belt-like feature beyond about 0."3 from the source.
At the same time the total intensity is spatially smooth, with no features. The
polarization pattern, almost parallel to the minor axis in the inner region,
becomes azimuthal in the outer belt, possibly because of a drop in optical
depth. The polarization fraction has average values of 1.2% in CW Tau and 0.4%
in DG Tau. Our results are consistent with polarization from self-scattering of
the dust thermal emission. Under this hypothesis, the maximum size of the
grains contributing to polarization is in the range 100 - 150 m for CW Tau
and 50 - 70 m for DG Tau. The polarization maps combined with dust opacity
estimates indicate that these grains are distributed in a geometrically thin
layer in CW Tau, representing a settling in the disk midplane. Meanwhile, such
settling is not yet apparent for DG Tau. These results advocate polarization
studies as a fundamental complement to total emission observations, in
investigations of the structure and the evolution of protoplanetary disks.Comment: 8 pages, 5 figures. Accepted for publication in ApJ Letter
Herschel observations of EXtraordinary Sources: Analysis of the full Herschel/HIFI molecular line survey of Sagittarius B2(N)
A sensitive broadband molecular line survey of the Sagittarius B2(N)
star-forming region has been obtained with the HIFI instrument on the Herschel
Space Observatory, offering the first high-spectral resolution look at this
well-studied source in a wavelength region largely inaccessible from the ground
(625-157 um). From the roughly 8,000 spectral features in the survey, a total
of 72 isotopologues arising from 44 different molecules have been identified,
ranging from light hydrides to complex organics, and arising from a variety of
environments from cold and diffuse to hot and dense gas. We present an LTE
model to the spectral signatures of each molecule, constraining the source
sizes for hot core species with complementary SMA interferometric observations,
and assuming that molecules with related functional group composition are
cospatial. For each molecule, a single model is given to fit all of the
emission and absorption features of that species across the entire 480-1910 GHz
spectral range, accounting for multiple temperature and velocity components
when needed to describe the spectrum. As with other HIFI surveys toward massive
star forming regions, methanol is found to contribute more integrated line
intensity to the spectrum than any other species. We discuss the molecular
abundances derived for the hot core, where the local thermodynamic equilibrium
approximation is generally found to describe the spectrum well, in comparison
to abundances derived for the same molecules in the Orion KL region from a
similar HIFI survey.Comment: Accepted to ApJ. 64 pages, 14 figures. Truncated abstrac
13C—methyl formate : observations of a sample of high mass starforming regions including Orion—KL and spectroscopic characterization
We have surveyed a sample of massive star-forming regions located over a range of distances from the Galactic centre for
methyl formate, HCOOCH3, and its isotopologues H13COOCH3 and HCOO13CH3. The observations were carried out with the
APEX telescope in the frequency range 283.4-287.4 GHz. Based on the APEX observations, we report tentative detections of
the 13C-methyl formate isotopologue HCOO13CH3 towards the following four massive star-forming regions: Sgr B2(N-LMH),
NGC 6334 IRS 1, W51 e2 and G19.61-0.23. In addition, we have used the 1 mm ALMA science verification observations of
Orion-KL and confirm the detection of the 13C-methyl formate species in Orion-KL and image its spatial distribution. Our
analysis shows that the 12C/13C isotope ratio in methyl formate toward Orion-KL Compact Ridge and Hot Core-SW
components (68.4±10.1 and 71.4±7.8, respectively) are, for both the 13C-methyl formate isotopologues, commensurate with the
average 12C/13C ratio of CO derived toward Orion-KL. Likewise, regarding the other sources, our results are consistent with
the 12C/13C in CO. We also report the spectroscopic characterization, which includes a complete partition function, of the
complex H13COOCH3 and HCOO13CH3 species. New spectroscopic data for both isotopomers H13COOCH3 and HCOO13CH3,
presented in this study, has made it possible to measure this fundamentally important isotope ratio in a large organic
molecule for the first time.This work was supported by the National Science Foundation under grant 1008800. We are grateful to the Ministerio de Economia y Competitividad of Spain for the financial support through grant No. FIS2011-28738-C02-02 and to the French Government through grant No. ANR-08-BLAN-0054 and the French PCMI (Programme National de Physique Chimie du Milieu Interstellaire). This paper makes use of the following ALMA data: ADS/JAO. ALMA#2011.0.00009.SV.ALMAis a partnership of ESO (representing its member states), NSF (USA), and NINS (Japan), together with NRC (Canada) and NSC and ASIAA (Taiwan), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO, and NAOJ. C.F. thanks Dahbia Talbi, Eric Herbst, and Anthony Remijan for enlightening discussions. Finally, we thank the anonymous referee for helpful comments
Implementation of ultrasonic sensing for high resolution measurement of binary gas mixture fractions
We describe an ultrasonic instrument for continuous real-time analysis of the fractional mixture of a binary gas system. The instrument is particularly well suited to measurement of leaks of a high molecular weight gas into a system that is nominally composed of a single gas. Sensitivity < 5 × 10−5 is demonstrated to leaks of octaflouropropane (C3F8) coolant into nitrogen during a long duration (18 month) continuous study. The sensitivity of the described measurement system is shown to depend on the difference in molecular masses of the two gases in the mixture. The impact of temperature and pressure variances on the accuracy of the measurement is analysed. Practical considerations for the implementation and deployment of long term, in situ ultrasonic leak detection systems are also described. Although development of the described systems was motivated by the requirements of an evaporative fluorocarbon cooling system, the instrument is applicable to the detection of leaks of many other gases and to processes requiring continuous knowledge of particular binary gas mixture fractions
Hot Corinos Chemical Diversity: Myth or Reality?
After almost 20 years of hunting, only about a dozen hot corinos, hot regions
enriched in interstellar complex organic molecules (iCOMs), are known. Of them,
many are binary systems with the two components showing drastically different
molecular spectra. Two obvious questions arise. Why are hot corinos so
difficult to find and why do their binary components seem chemically different?
The answer to both questions could be a high dust opacity that would hide the
molecular lines. To test this hypothesis, we observed methanol lines at
centimeter wavelengths, where dust opacity is negligible, using the Very Large
Array interferometer. We targeted the NGC 1333 IRAS 4A binary system, for which
one of the two components, 4A1, has a spectrum deprived of iCOMs lines when
observed at millimeter wavelengths, while the other component, 4A2, is very
rich in iCOMs. We found that centimeter methanol lines are similarly bright
toward 4A1 and 4A2. Their non-LTE analysis indicates gas density and
temperature ( cm and 100--190 K), methanol column
density ( cm) and extent (35 au in radius) similar in
4A1 and 4A2, proving that both are hot corinos. Furthermore, the comparison
with previous methanol line millimeter observations allows us to estimate the
optical depth of the dust in front of 4A1 and 4A2, respectively. The obtained
values explain the absence of iCOMs line emission toward 4A1 at millimeter
wavelengths and indicate that the abundances toward 4A2 are underestimated by
30\%. Therefore, centimeter observations are crucial for the correct
study of hot corinos, their census, and their molecular abundances.Comment: 9 pages, 3 figures, 2 Tables - Published in ApJ Letter
LES INTERRUPTIONS MEDICALES DE GROSSESSE POUR MOTIFS PSYCHIATRIQUES MATERNELS (ETUDE DE 24 DOSSIERS)
BESANCON-BU Médecine pharmacie (250562102) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF
Hydrogen molecular ions and the violent birth of the Solar System
International audienceMany pieces of evidence indicate that the Solar System youth was marked by violent processes: among others, high fluxes of energetic particles (greater than or equal to 10 MeV) are unambiguously recorded in meteoritic material, where an overabundance of the short-lived 10Be products is measured. Several hypotheses have been proposed to explain from where these energetic particles originate, but there is no consensus yet, mostly because of the scarcity of complementary observational constraints. In general, the reconstruction of the past history of the Solar System is best obtained by simultaneously considering what we know of it and of similar systems nowadays in formation. However, when it comes to studying the presence of energetic particles in young forming stars, we encounter the classical problem of the impossibility of directly detecting them toward the emitting source (analogously to what happens to galactic cosmic rays). Yet, exploiting the fact that energetic particles, such as cosmic rays, create H3 + and that an enhanced abundance of H3 + causes dramatic changes on the overall gas chemical composition, we can indirectly estimate the flux of energetic particles. This contribution provides an overview of the search for solar-like protostars permeated by energetic particles and the discovery of a protocluster, OMC-2 FIR4, where the phenomenon is presently occurring. This article is part of a discussion meeting issue `Advances in hydrogen molecular ions: H3+, H5+ and beyond'
Impact of nonconvergence and various approximations of the partition function on the molecular column densities in the interstellar medium
We emphasize that the completeness of the partition function, that is, the use of a converged partition function at the typical temperature
range of the survey, is very important to decrease the uncertainty on this quantity and thus to derive reliable interstellar molecular
densities. In that context, we show how the use of different approximations for the rovibrational partition function together with
some interpolation and/or extrapolation procedures may affect the estimate of the interstellar molecular column density. For that
purpose, we apply the partition function calculations to astronomical observations performed with the IRAM-30m telescope towards
the NGC 7538–IRS1 source of two N-bearing molecules: isocyanic acid (HNCO, a quasilinear molecule) and methyl cyanide (CH3CN,
a symmetric top molecule). The case of methyl formate (HCOOCH3), which is an asymmetric top O-bearing molecule containing
an internal rotor is also discussed. Our analysis shows that the use of different partition function approximations leads to relative
differences in the resulting column densities in the range 9–43%. Thus, we expect this work to be relevant for surveys of sources with
temperatures higher than 300K and to observations in the infrared.This work is partly supported by CMST COST Action CM1401 Our Astro-Chemical History and CMST COST Action CM1405 MOLIM. The work of C.F. is supported by the French National Research Agency in the framework of the Investissements d'Avenir program (ANR-15-IDEX-02), through the funding of the "Origin of Life" project of the Universite Grenoble-Alpes. C.C. and C.F. acknowledge funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme, for the Project "The Dawn of Organic Chemistry" (DOC), grant agreement No 741002. I.K. would like to thank the French programme of Chimie Interstellaire PCMI. C.F. and D.F. acknowledge support from the Italian Ministry of Education, Universities and Research, project SIR (RBSI14ZRHR). E.A.B. acknowledges support from NSF (AST-1514670) and NASA (NNX16AB48G). M.C. acknowledges the financial support from FIS2014-53448-C2-2-P (MINECO, Spain), from the Centro de Estudios Avanzados de Fisica, Matematicas y Computacion (CEAFMC) of the University of Huelva and from the Consejeria de Conocimiento, Investigacion y Universidad, Junta de Andalucia and European Regional Development Fund (ERDF), ref. SOMM17/6105/UGR. The authors acknowledge the referee for his/her valuable comments