1,878 research outputs found
The doubly inelastic contribution to electron loss: H0 and He0 (0,5 MeV u-1) in collision with Ar
Fingering convection and cloudless models for cool brown dwarf atmospheres
This work aims to improve the current understanding of the atmospheres of
brown dwarfs, especially cold ones with spectral type T and Y, whose modeling
is a current challenge. Silicate and iron clouds are believed to disappear at
the photosphere at the L/T transition, but cloudless models fail to reproduce
correctly the spectra of T dwarfs, advocating for the addition of more physics,
e.g. other types of clouds or internal energy transport mechanisms. We use a
one-dimensional (1D) radiative/convective equilibrium code ATMO to investigate
this issue. This code includes both equilibrium and out-of-equilibrium
chemistry and solves consistently the PT structure. Included opacity sources
are H2-H2, H2-He, H2O, CO, CO2, CH4, NH3, K, Na, and TiO, VO if they are
present in the atmosphere. We show that the spectra of Y dwarfs can be
accurately reproduced with a cloudless model if vertical mixing and NH3
quenching are taken into account. T dwarf spectra still have some reddening in
e.g. J - H compared to cloudless models. This reddening can be reproduced by
slightly reducing the temperature gradient in the atmosphere. We propose that
this reduction of the stabilizing temperature gradient in these layers, leading
to cooler structures, is due to the onset of fingering convection, triggered by
the destabilizing impact of condensation of very thin dust.Comment: Accepted in ApJ
Superfluid turbulence and pulsar glitch statistics
Experimental evidence is reviewed for the existence of superfluid turbulence
in a differentially rotating, spherical shell at high Reynolds numbers
(\Rey\gsim 10^3), such as the outer core of a neutron star. It is shown that
torque variability increases with \Rey, suggesting that glitch activity in
radio pulsars may be a function of \Rey as well. The \Rey distribution of
the 67 glitching radio pulsars with characteristic ages {\rm
yr} is constructed from radio timing data and cooling curves and compared with
the \Rey distribution of all 348 known pulsars with {\rm
yr}. The two distributions are different, with a Kolmogorov-Smirnov probability
. The conclusion holds for (modified) Urca and
nonstandard cooling, and for Newtonian and superfluid viscosities
On the Propagation of Slip Fronts at Frictional Interfaces
The dynamic initiation of sliding at planar interfaces between deformable and
rigid solids is studied with particular focus on the speed of the slip front.
Recent experimental results showed a close relation between this speed and the
local ratio of shear to normal stress measured before slip occurs (static
stress ratio). Using a two-dimensional finite element model, we demonstrate,
however, that fronts propagating in different directions do not have the same
dynamics under similar stress conditions. A lack of correlation is also
observed between accelerating and decelerating slip fronts. These effects
cannot be entirely associated with static local stresses but call for a dynamic
description. Considering a dynamic stress ratio (measured in front of the slip
tip) instead of a static one reduces the above-mentioned inconsistencies.
However, the effects of the direction and acceleration are still present. To
overcome this we propose an energetic criterion that uniquely associates,
independently on the direction of propagation and its acceleration, the slip
front velocity with the relative rise of the energy density at the slip tip.Comment: 15 pages, 6 figure
A multi-state model to estimate incidence of heroin use
Background: Existing incidence estimates of heroin use are usually based on one information source. This study aims to incorporate more sources to estimate heroin use incidence trends in Spain between 1971 and 2005. Methods: A multi-state model was constructed, whereby the initial state "heroin consumer" is followed by transition to either "admitted to first treatment" or to "left heroin use" (i.e. permanent cessation or death). Heroin use incidence and probabilities of entering first treatment ever were estimated following a back-calculation approach. Results: The highest heroin use incidence rates in Spain, around 1.5 per 1,000 inhabitants aged 10-44, occurred between 1985 and 1990; subdividing by route of administration reveals higher incidences of injection between 1980 and 1985 (a mean of 0.62 per 1.000) and a peak for non-injectors in 1990 (0.867 per 1,000). Conclusions: A simple conceptual model for heroin users' trajectories related to treatment admission, provided a broader view of the historical trend of heroin use incidence in Spain
Effect of ripening temperature on the chemical composition of lingonberries (Vaccinium vitis-idaea L.) of northern and southern origin
Lingonberries (Vaccinium vitis-idaea L.) from two locations, northern (69◦N, 18◦E) and southern (59◦N, 10◦E)
Norway, were grown under controlled conditions in a phytotron at two temperatures (9 and 15 ◦C) to study the
effects of the ripening temperature and origin on the chemical composition of the berries. The concentrations of
phenolic compounds, sugars, and organic acids as well as the profile of volatile organic compounds (VOCs) were
determined using chromatographic and mass spectrometric methods. Five anthocyanins, eleven flavonols, eight
cinnamic acid derivatives, three flavan-3-ols, three sugars, three organic acids, and 77 VOCs were identified, of
which 40 VOCs had not previously been reported in lingonberries. Berries from both locations, were found to
have higher contents of anthocyanins and cinnamic acid derivatives when ripened at lower temperature (9 ◦C),
compared to the higher temperature (15 ◦C). Lingonberries of northern origin had a different VOC profile and
higher contents of anthocyanins and organic acids than berries originating from the south. Lingonberries from
the northern location also had higher proportions of cyanidin-3-O-glucoside and cyanidin-3-O-arabinoside than
lingonberries from the southern location. The results show that the composition of lingonberries is influenced by
both the environment and the origin of the plants, with phenolic compounds mainly influenced by the growth
temperature and VOCs mainly influenced by plant origin
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