215 research outputs found
Molecular fluorine chemistry in the early Universe
Some models of Big Bang nucleosynthesis suggest that very high baryon density
regions were formed in the early Universe, and generated the production of
heavy elements other than lithium such as fluorine F. We present a
comprehensive chemistry of fluorine in the post-recombination epoch.
Calculation of F, F- and HF abundances, as a function of redshift z, are
carried out. The main result is that the chemical conditions in the early
Universe can lead to the formation of HF. The final abundance of the diatomic
molecule HF is predicted to be close to 3.75 10(-17) when the initial abundance
of neutral fluorine F is 10(-15). These results indicate that molecules of
fluorine HF were already present during the dark age. This could have
implications on the evolution of proto-objects and on the anisotropies of
cosmic microwave background radiation. Hydride of fluorine HF may affect
enhancement of the emission line intensity from the proto-objects and could
produce spectral-spatial fluctuations.Comment: Accepted in Astronomy and Astrophysics, 7 pages, 2 figure
Chemistry of heavy elements in the Dark Ages
Primordial molecules were formed during the Dark Ages, i.e. the time between
recombination and reionization in the early Universe. The purpose of this
article is to analyze the formation of primordial molecules based on heavy
elements during the Dark Ages, with elemental abundances taken from different
nucleosynthesis models. We present calculations of the full non-linear equation
set governing the primordial chemistry. We consider the evolution of 45
chemical species and use an implicit multistep method of variable order of
precision with an adaptive stepsize control. We find that the most abundant
Dark Ages molecules based on heavy elements are CH and OH. Non-standard
nucleosynthesis can lead to higher heavy element abundances while still
satisfying the observed primordial light abundances. In that case, we show that
the abundances of molecular species based on C, N, O and F can be enhanced by
two orders of magnitude compared to the standard case, leading to a CH relative
abundance higher than that of HD+ or H2D+.Comment: 14 pages, accepted by Astronomy and Astrophysic
Limits on decaying dark energy density models from the CMB temperature-redshift relation
The nature of the dark energy is still a mystery and several models have been
proposed to explain it. Here we consider a phenomenological model for dark
energy decay into photons and particles as proposed by Lima (J. Lima, Phys.
Rev. D 54, 2571 (1996)). He studied the thermodynamic aspects of decaying dark
energy models in particular in the case of a continuous photon creation and/or
disruption. Following his approach, we derive a temperature redshift relation
for the CMB which depends on the effective equation of state and on
the "adiabatic index" . Comparing our relation with the data on the CMB
temperature as a function of the redshift obtained from Sunyaev-Zel'dovich
observations and at higher redshift from quasar absorption line spectra, we
find , adopting for the adiabatic index ,
in good agreement with current estimates and still compatible with
, implying that the dark energy content being constant in time.Comment: 8 pages, 1 figur
Constraining decaying dark energy density models with the CMB temperature-redshift relation
We discuss the thermodynamic and dynamical properties of a variable dark
energy model with density scaling as , z being the
redshift. These models lead to the creation/disruption of matter and radiation,
which affect the cosmic evolution of both matter and radiation components in
the Universe. In particular, we have studied the temperature-redshift relation
of radiation, which has been constrained using a recent collection of cosmic
microwave background (CMB) temperature measurements up to . We find
that, within the uncertainties, the model is indistinguishable from a
cosmological constant which does not exchange any particles with other
components. Future observations, in particular measurements of CMB temperature
at large redshift, will allow to give firmer bounds on the effective equation
of state parameter for such types of dark energy models.Comment: 9 pages, 1 figure, to appear in the Proceedings of the 3rd
Italian-Pakistani Workshop on Relativistic Astrophysics, Lecce 20-22 June
2011, published in Journal of Physics: Conference Series (JPCS
Enfants exposés à la violence dans le couple parental : étude rétrospective des données récoltées auprès de 430 mères et pères de 654 enfants âgés de 0 à 17 ans, lorsque ces parents avaient consulté l’Unité de médecine des violences du CHUV suite à un événement violent dans le couple survenu entre 2011 et 2014
[Préface (extraits)] L'étude menée par l'équipe de l'Unité de médecine des violences (UMV) entrouvre la porte de la chambre des enfants, afin d’amener un éclairage supplémentaire sur la nature et les circonstances de l’exposition des enfants à la violence dans le couple parental. Elle montre comment les enfants sont directement concernés dans la violence qui a lieu dans leur foyer. Souvent atteints psychiquement et physiquement, il n'est pas rare qu'ils aillent jusqu’à s'interposer au milieu de ces rapports de violence en se mettant eux-mêmes en danger lorsqu’ils prennent la défense de la victime, le plus souvent d'ailleurs leur mère. Dans d'autres cas, ils et elles intériorisent les modèles genrés d'auteur ou de victime auprès desquels ils grandissent et puisent leur identité. Les prérequis favorables à une transmission intergénérationnelle de la violence dans le couple sont renforcés par cette immersion quotidienne
How exactly did the Universe become neutral?
We present a refined treatment of H, He I, and He II recombination in the
early Universe. The difference from previous calculations is that we use
multi-level atoms and evolve the population of each level with redshift by
including all bound-bound and bound-free transitions. In this framework we
follow several hundred atomic energy levels for H, He I, and He II combined.
The main improvements of this method over previous recombination calculations
are: (1) allowing excited atomic level populations to depart from an
equilibrium distribution; (2) replacing the total recombination coefficient
with recombination to and photoionization from each level directly at each
redshift step; and (3) correct treatment of the He I atom, including the
triplet and singlet states. We find that the ionization fraction x_e = n_e/n_H
is approximately 10% smaller at redshifts <~800 than in previous calculations,
due to the non-equilibrium of the excited states of H, which is caused by the
strong but cool radiation field at those redshifts. In addition we find that He
I recombination is delayed compared with previous calculations, and occurs only
just before H recombination. These changes in turn can affect the predicted
power spectrum of microwave anisotropies at the few percent level. Other
improvements such as including molecular and ionic species of H, including
complete heating and cooling terms for the evolution of the matter temperature,
including collisional rates, and including feedback of the secondary spectral
distortions on the radiation field, produce negligible change to x_e. The lower
x_e at low z found in this work affects the abundances of H molecular and ionic
species by 10-25%. However this difference is probably not larger than other
uncertainties in the reaction rates.Comment: 24 pages, including 18 figures, using emulateapj.sty, to appear in
ApJ, the code recfast can be obtained at
http://www.astro.ubc.ca/people/scott/recfast.html (in FORTRAN) and
http://cfa-www.harvard.edu/~sasselov/rec/ (in C
A differential method of search for the CMBR spectral-spatial fluctuations
The CMBR spectral-spatial fluctuations (SSF) formed in early Universe during
the Dark Ages are considered. Main attention is focused on the narrow-band
spectral properties of the SSF. Based on these properties we propose to use a
differential method in order to search for these fluctuations. Description of
the method is given.Comment: Latex, 9 pages with 4 Postscript figure
HD molecules at high redshift: The absorption system at z=2.3377 towards Q 1232+082
We present a detailed analysis of the H_2 and HD absorption lines detected in
the Damped Lyman-alpha (DLA) system at z_abs=2.3377 towards the quasar
Q1232+082. We show that this intervening cloud has a covering factor smaller
than unity and covers only part of the QSO broad emission line region. The zero
flux level has to be corrected at the position of the saturated H_2 and
optically thin HD lines by about 10%. We accurately determine the Doppler
parameter for HD and CI lines (b = 1.86+/-0.20 km/s). We find a ratio
N(HD)/N(H_2)=(7.1 +3.7 -2.2)x10^-5 that is significantly higher than what is
observed in molecular clouds of the Galaxy. Chemical models suggest that in the
physical conditions prevailing in the central part of molecular clouds,
deuterium and hydrogen are mostly in their molecular forms. Assuming this is
true, we derive D/H = (3.6 +1.9 -1.1)x10^-5. This implies that the
corresponding baryon density of the Universe is \Omega_b h^2 = (0.0182 +0.0047
-0.0042). This value coincides within 1\sigma with that derived from
observations of the CMBR as well as from observations of the D/H atomic ratio
in low-metallicity QSO absorption line systems. The observation of HD at high
redshift is therefore a promising independent method to constrain \Omega_b.
This observation indicates as well a low astration factor of deuterium. This
can be interpreted as the consequence of an intense infall of primordial gas
onto the associated galaxy.Comment: 8 pages, 7 figures, 3 tables. Accepted for publication in MNRA
Aplicaciones de la metabolómica
III Congreso de Alimentación, Nutrición y Dietética. Combinar la nutrición comunitaria y personalizada: nuevos retos
HD/H2 Molecular Clouds in the Early Universe: The Problem of Primordial Deuterium
We have detected new HD absorption systems at high redshifts, z_abs=2.626 and
z_abs=1.777, identified in the spectra of the quasars J0812+3208 and Q1331+170,
respectively. Each of these systems consists of two subsystems. The HD column
densities have been determined: log(N(HD),A)=15.70+/-0.07 for z_A=2.626443(2)
and log(N(HD),B)=12.98+/-0.22 for z_B=2.626276(2) in the spectrum of J0812+3208
and log(N(HD),C)=14.83+/-0.15 for z_C=1.77637(2) and log(N(HD),D)=14.61+/-0.20
for z_D=1.77670(3) in the spectrum of Q1331+170. The measured HD/H2 ratio for
three of these subsystems has been found to be considerably higher than its
values typical of clouds in our Galaxy. We discuss the problem of determining
the primordial deuterium abundance, which is most sensitive to the baryon
density of the Universe \Omega_{b}. Using a well-known model for the chemistry
of a molecular cloud, we have estimated the isotopic ratio
D/H=HD/2H_2=(2.97+/-0.55)x10^{-5} and the corresponding baryon density
\Omega_{b}h^2=0.0205^{+0.0025}_{-0.0020}. This value is in good agreement with
\Omega_{b}h^2=0.0226^{+0.0006}_{-0.0006} obtained by analyzing the cosmic
microwave background radiation anisotropy. However, in high-redshift clouds,
under conditions of low metallicity and low dust content, hydrogen may be
incompletely molecularized even in the case of self-shielding. In this
situation, the HD/2H_2 ratio may not correspond to the actual D/H isotopic
ratio. We have estimated the cloud molecularization dynamics and the influence
of cosmological evolutionary effects on it
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