178 research outputs found
Le risque comme culture de la temporalité
Le concept de risque tente de rendre compte de discours et de pratiques qui s’appuient sur une connaissance plus ou moins formalisée de ce qui pourrait advenir. Si son origine remonte au Moyen Âge, c’est au cours de la période moderne que certains groupes sociaux ont commencé à interpréter des expériences et à justifier des décisions en se réclamant d’un nouveau discours sur l’avenir, le risque. Ce discours est alors étroitement lié aux pratiques émergentes de l’assurance, de même qu’à l’invention, dans le dernier tiers du xviie siècle, du calcul des probabilités. Au cours des siècles qui ont suivi, l’affranchissement graduel de la société moderne à l’égard de la tradition a été accompagné d’un approfondissement continuel des discours et des usages du risque, non seulement au sein des pratiques de prévoyance et de la science probabilitaire, mais également dans le gouvernement même des sociétés. D’ailleurs, ces dernières furent progressivement conçuescomme des corps gouvernables, à travers l’épistémologie des sciences naturelles et de la médecine qui donnaient naissance à un savoir sur la nature et sur l’homme, selon une approche à la fois épidémiologique et clinique des risques. Si bien que, de nos jours, tout tend désormais à être décliné en termes de risques, du réchauffement climatique à la crise économique, de la pauvreté à la criminalité, des pandémies au terrorisme, du rôle de l’État à celui des experts. Selon certains théoriciens du risque, ces usages et ces discours auraient pris de plus en plus d’importance au point de devenir le nœud des enjeux qui structurent désormais l’ensemble des dimensions de l’existence collective. Voilà, en peu de mots, sur quel grand processus historique complexe ce livre se penche
Multiwavelength Observations of the Hot DB Star PG 0112+104
We present a comprehensive multiwavelength analysis of the hot DB white dwarf
PG 0112+104. Our analysis relies on newly-acquired FUSE observations, on
medium-resolution FOS and GHRS data, on archival high-resolution GHRS
observations, on optical spectrophotometry both in the blue and around Halpha,
as well as on time-resolved photometry. From the optical data, we derive a
self-consistent effective temperature of 31,300+-500 K, a surface gravity of
log g = 7.8 +- 0.1 (M=0.52 Msun), and a hydrogen abundance of log N(H)/N(He) <
-4.0. The FUSE spectra reveal the presence of CII and CIII lines that
complement the previous detection of CII transitions with the GHRS. The
improved carbon abundance in this hot object is log N(C)/N(He) = -6.15 +- 0.23.
No photospheric features associated with other heavy elements are detected. We
reconsider the role of PG 0112+104 in the definition of the blue edge of the
V777 Her instability strip in light of our high-speed photometry, and contrast
our results with those of previous observations carried out at the McDonald
Observatory.Comment: 10 pages in emulateapj, 9 figures, accepted for publication in Ap
Water Fractions in Extrasolar Planetesimals
With the goal of using externally-polluted white dwarfs to investigate the
water fractions of extrasolar planetesimals, we assemble from the literature a
sample that we estimate to be more than 60% complete of DB white dwarfs warmer
than 13,000 K, more luminous than 3 10 L and within
80 pc of the Sun. When considering all the stars together, we find the summed
mass accretion rate of heavy atoms exceeds that of hydrogen by over a factor of
1000. If so, this sub-population of extrasolar asteroids treated as an ensemble
has little water and is at least a factor of 20 drier than CI chondrites, the
most primitive meteorites. In contrast, while an apparent "excess" of oxygen in
a single DB can be interpreted as evidence that the accreted material
originated in a water-rich parent body, we show that at least in some cases,
there can be sufficient uncertainties in the time history of the accretion rate
that such an argument may be ambiguous. Regardless of the difficulty associated
with interpreting the results from an individual object, our analysis of the
population of polluted DBs provides indirect observational support for the
theoretical view that a snow line is important in disks where rocky
planetesimals form.Comment: Accepted for publication in the Astronomical Journal, 22 pages, 4
figures, 1 tabl
An Upper Bound to the Space Density of Interstellar Comets
Two well-studied white dwarfs with helium-dominated atmospheres (DBs) each
possess less hydrogen than carried by a single average-mass comet. Plausibly,
the wind rates from these stars are low enough that most accreted hydrogen
remains with the star. If so, and presuming their nominal effective
temperatures, then these DBs have been minimally impacted by interstellar
comets during their 50 Myr cooling age; interstellar iceballs with radii
between 10 m and 2 km contain less than 1% of all interstellar oxygen. This
analysis suggests that most stars do not produce comets at the rate predicted
by "optimistic" scenarios for the formation of the Oort cloud.Comment: Astronomical Journal, accepte
A Comprehensive Spectroscopic Analysis of DB White Dwarfs
We present a detailed analysis of 108 helium-line (DB) white dwarfs based on
model atmosphere fits to high signal-to-noise optical spectroscopy. We derive a
mean mass of 0.67 Mo for our sample, with a dispersion of only 0.09 Mo. White
dwarfs also showing hydrogen lines, the DBA stars, comprise 44% of our sample,
and their mass distribution appears similar to that of DB stars. As in our
previous investigation, we find no evidence for the existence of low-mass (M <
0.5 Mo) DB white dwarfs. We derive a luminosity function based on a subset of
DB white dwarfs identified in the Palomar-Green survey. We show that 20% of all
white dwarfs in the temperature range of interest are DB stars, although the
fraction drops to half this value above Teff ~ 20,000 K. We also show that the
persistence of DB stars with no hydrogen features at low temperatures is
difficult to reconcile with a scenario involving accretion from the
interstellar medium, often invoked to account for the observed hydrogen
abundances in DBA stars. We present evidence for the existence of two different
evolutionary channels that produce DB white dwarfs: the standard model where DA
stars are transformed into DB stars through the convective dilution of a thin
hydrogen layer, and a second channel where DB stars retain a helium-atmosphere
throughout their evolution. We finally demonstrate that the instability strip
of pulsating V777 Her white dwarfs contains no nonvariables, if the hydrogen
content of these stars is properly accounted for.Comment: 74 pages including 30 figures, accepted for publication in the
Astrophysical Journa
Strengthening the Case for Asteroidal Accrection: Evidence for Subtle and Diverse Disks at White Dwarfs
Spitzer Space Telescope IRAC 3-8 micron and AKARI IRC 2-4 micron photometry
are reported for ten white dwarfs with photospheric heavy elements; nine
relatively cool stars with photospheric calcium, and one hotter star with a
peculiar high carbon abundance. A substantial infrared excess is detected at HE
2221-1630, while modest excess emissions are identified at HE 0106-3253 and HE
0307+0746, implying these latter two stars have relatively narrow (Delta r <
0.1 Rsol) rings of circumstellar dust. A likely 7.9 micron excess is found at
PG 1225-079 and may represent, together with G166-58, a sub-class of dust ring
with a large inner hole. The existence of attenuated disks at white dwarfs
substantiates the connection between their photospheric heavy elements and the
accretion of disrupted minor planets, indicating many polluted white dwarfs may
harbor orbiting dust, even those lacking an obvious infrared excess.Comment: 13 pages, emulateapj, accepted to Ap
Longitudinal study of childhood sleep trajectories and adolescent mental health problems
Abstract
Study objective
To investigate whether childhood sleep trajectories are associated with mental health symptoms such as social phobia, generalized anxiety, depression, attention deficit hyperactivity disorder (ADHD), conduct problems, and opposition at age 15.
Methods
A total of 2120 children took part in the Quebec Longitudinal Study of Child Development. Childhood sleep trajectories were computed from maternal reports at 2.5, 3.5, 4, 6, 8, 10, and/or 12 years. At age 15, 1446 adolescents filled out mental health and sleep questions. A path analysis model was assessed in the full sample.
Results
Four childhood nocturnal sleep duration trajectories were identified: (1) a short pattern (7.5%), (2) a short-increasing pattern (5.8%), (3) a 10 hours pattern (50.7%), and (4) an 11 hours pattern (36.0%). Three childhood sleep latency trajectories were found: (1) a short pattern (31.7%), (2) an intermediate pattern (59.9%), and (3) a long pattern (8.4%). Finally, two childhood wakefulness after sleep-onset trajectories were found: (1) a normative pattern (73.0%) and (2) a long pattern (27.0%). The path analysis model indicated that children following a long childhood sleep latency trajectory were more likely to experience symptoms of depression (β = 0.06, 95% CI: 0.01 to 0.12), ADHD (β = 0.07, 95% CI: 0.02 to 0.13), conduct problems (β = 0.05, 95% CI: 0.00 to 0.10) and opposition (β = 0.08, 95% CI: 0.02 to 0.13) at age 15.
Conclusions
This longitudinal study revealed that children presenting a long sleep latency throughout childhood are at greater risk of symptoms of depression, ADHD, conduct problems, and opposition in adolescence
Quick and Simple Detection Technique to Assess the Binding of Antimicrotubule Agents to the Colchicine-Binding Site
Development of antimitotic binding to the colchicine-binding site for the treatment of cancer is rapidly expanding. Numerous antimicrotubule agents are prepared every year, and the determination of their binding affinity to tubulin requires the use of purified tubulins and radiolabeled ligands. Such a procedure is costly and time-consuming and therefore is limited to the most promising candidates. Here, we report a quick and inexpensive method that requires only usual laboratory resources to assess the binding of antimicrotubules to colchicine-binding site. The method is based on the ability of N,N'-ethylene-bis(iodoacetamide) (EBI) to crosslink in living cells the cysteine residues at position 239 and 354 of β-tubulin, residues which are involved in the colchicine-binding site. The β-tubulin adduct formed by EBI is easily detectable by Western blot as a second immunoreacting band of β-tubulin that migrates faster than β-tubulin. The occupancy of colchicine-binding site by pertinent antimitotics inhibits the formation of the EBI: β-tubulin adduct, resulting in an assay that allows the screening of new molecules targeting this binding site
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