36 research outputs found
Rapport d'evaluation de la revue "Famille et développement", Sénégal, Mali, Haute Volta, Togo, Congo
Similar levels of deuteration in the pre-stellar core L1544 and the protostellar core HH211
In the centre of pre-stellar cores, deuterium fractionation is enhanced due
to the low temperatures and high densities. Therefore, the chemistry of
deuterated molecules can be used to study the earliest stages of star
formation. We analyse the deuterium fractionation of simple molecules,
comparing the level of deuteration in the envelopes of the pre-stellar core
L1544 in Taurus and the protostellar core HH211 in Perseus. We used single-dish
observations of CCH, HCN, HNC, HCO, and their C-, O- and
D-bearing isotopologues, detected with the Onsala 20m telescope. We derived the
column densities and the deuterium fractions of the molecules. Additionally, we
used radiative transfer simulations and results from chemical modelling to
reproduce the observed molecular lines. We used new collisional rate
coefficients for HNC, HNC, DNC, and DCN that consider the hyperfine
structure of these molecules. We find high levels of deuteration for CCH (10%)
in both sources, consistent with other carbon chains, and moderate levels for
HCN (5-7%) and HNC (8%). The deuterium fraction of HCO is enhanced towards
HH211, most likely caused by isotope-selective photodissociation of CO.
Similar levels of deuteration show that the process is likely equally efficient
towards both cores, suggesting that the protostellar envelope still retains the
chemical composition of the original pre-stellar core. The fact that the two
cores are embedded in different molecular clouds also suggests that
environmental conditions do not have a significant effect on the deuteration
within dense cores. Radiative transfer modelling shows that it is necessary to
include the outer layers of the cores to consider the effects of extended
structures. Besides HCO observations, HCN observations towards L1544 also
require the presence of an outer diffuse layer where the molecules are
relatively abundant.Comment: 27 pages, 17 figures, accepted for publication in A&
Linking the dust and chemical evolution: Taurus and Perseus -- New collisional rates for HCN, HNC, and their C, N, and H isotopologues
HCN, HNC, and their isotopologues are ubiquitous molecules that can serve as
chemical thermometers and evolutionary tracers to characterize star-forming
regions. Despite their importance in carrying information that is vital to
studies of the chemistry and evolution of star-forming regions, the collision
rates of some of these molecules have not been available for rigorous studies
in the past. We perform an up-to-date gas and dust chemical characterization of
two different star-forming regions, TMC 1-C and NGC 1333-C7, using new
collisional rates of HCN, HNC, and their isotopologues. We investigated the
possible effects of the environment and stellar feedback in their chemistry and
their evolution. With millimeter observations, we derived their column
densities, the C and N isotopic fractions, the isomeric ratios, and the
deuterium fractionation. The continuum data at 3 mm and 850 m allowed us
to compute the emissivity spectral index and look for grain growth as an
evolutionary tracer. The HCN/HNC ratio is anticorrelated with the
deuterium fraction of HCN, thus it can readily serve as a proxy for the
temperature. The spectral index shows a tentative
anticorrelation with the HCN/HNC ratio, suggesting grain growth
in the evolved, hotter, and less deuterated sources. Unlike TMC 1-C, the
south-to-north gradient in dust temperature and spectral index observed in NGC
1333-C7 suggests feedback from the main NGC 1333 cloud. With this up-to-date
characterization of two star-forming regions, we found that the chemistry and
the physical properties are tightly related. The dust temperature, deuterium
fraction, and the spectral index are complementary evolutionary tracers. The
large-scale environmental factors may dominate the chemistry and evolution in
clustered star-forming regions.Comment: 25 pages, 20 figure
Imprisonment and internment: Comparing penal facilities North and South
Recent references to the ‘warehouse prison’ in the United States and the prisión-depósito in Latin America seem to indicate that penal confinement in the western hemisphere
has converged on a similar model. However, this article suggests otherwise. It contrasts penal facilities in North America and Latin America in terms of six interrelated aspects: regimentation; surveillance; isolation; supervision; accountability; and formalization. Quantitatively, control in North American penal facilities is assiduous (unceasing, persistent and intrusive), while in Latin America it is perfunctory (sporadic, indifferent and cursory). Qualitatively, North American penal facilities produce imprisonment (which enacts penal intervention through confinement), while in Latin America they produce internment (which enacts penal intervention through release). Closely entwined with this qualitative difference are distinct practices of judicial involvement in sentencing and penal supervision. Those practices, and the cultural and political factors that underpin them, represent an interesting starting point for the explanation of the contrasting nature of imprisonment and internment
Learning from Poverty: Why Business Schools Should Address Poverty, and How They Can Go About It.
In the past few years, business schools have begun to address poverty issues in their teaching, learning and curricula. While this is a positive development, the arguments for reconfiguring educational programs to address such matters remain undeveloped, with much of the impetus for such endeavors rooted in calls for social responsibility in the United Nations Millennium Development Goals, the Social Compact, the Principles for Responsible Management Education and benchmarks such as ISO 26000. This article seeks to clarify the pedagogical grounds for integrating poverty issues in management education by examining the intellectual and personal development benefits of doing so. By critically examining four modes of business involvement in poverty reduction, the article shows how such initiatives can be used as intellectual lenses through which to view the complex and often paradoxical interconnections between socioeconomic and environmental systems. It is thus concluded that a consideration of poverty issues is not a marginal matter, but is key to grasping the 21st century complexities of global business and management
Collisional excitation of HCNH(+) by He and H(2): New potential energy surfaces and inelastic rate coefficients
International audienceProtonated molecules have been increasingly detected in the interstellar medium (ISM), and usually astrochemical models fail at reproducing the abundances derived from observational spectra. Rigorous interpretation of the detected interstellar emission lines requires prior calculations of collisional rate coefficients with H(2) and He, i.e., the most abundant species in the ISM. In this work, we focus on the excitation of HCNH(+) induced by collision with H(2) and He. Therefore, we first calculate ab initio potential energy surfaces (PESs) using the explicitly correlated and standard coupled cluster method with single, double, and non-iterative triple excitation in conjunction with the augmented-correlation consistent-polarized valence triple zeta basis set. Both the HCNH(+)-H(2) and HCNH(+)-He potentials are characterized by deep global minima of 1426.60 and 271.72 cm(-1), respectively, and large anisotropies. From these PESs, we derive state-to-state inelastic cross sections for the 16 low-lying rotational energy levels of HCNH(+) using the quantum mechanical close-coupling approach. The differences between cross sections due to ortho- and para-H(2) impacts turn out to be minor. Using a thermal average of these data, we retrieve downward rate coefficients for kinetic temperatures of up to 100 K. As it could be anticipated, differences of up to two orders of magnitude exist between the rate coefficients induced by H(2) and He collisions. We expect that our new collision data will help to improve the disagreement between abundances retrieved from observational spectra and astrochemical models
Rotational excitation of NS+ by H-2 revisited: A new global potential energy surface and rate coefficients
International audienceDue to the lack of specific collisional data, the abundance of NS+ in cold dense interstellar clouds was determined using collisional rate coefficients of CS as a substitute. To better understand the chemistry of sulfur in the interstellar medium, further abundance modeling using the actual NS+ collisional rate coefficients is needed. For this purpose, we have computed the first full 4D potential energy surface of the NS+-H-2 van der Waals complex using the explicitly correlated coupled cluster approach with single, double, and non-iterative triple excitation in conjunction with the augmented-correlation consistent-polarized valence triple zeta basis set. The potential energy surface exhibits a global minimum of 848.24 cm(-1) for a planar configuration of the complex. The long-range interaction energy, described using multipolar moments, is sensitive to the orientation of H-2 up to radial distances of ~50 a(0). From this new interaction potential, we derived excitation cross sections, induced by collision with ortho- and para-H-2, for the 15 low-lying rotational levels of NS+ using the quantum mechanical close-coupling approach. By thermally averaging these data, we determined downward rate coefficients for temperatures up to 50 K. By comparing them with the previous NS+-H-2 data, we demonstrated that reduced dimensional approaches are not suited for this system. In addition, we found that the CS collisional data underestimate our results by up to an order of magnitude. The differences clearly indicate that the abundance of NS+, in cold dense clouds retrieved from observational spectra, must be reassessed using these new collisional rate coefficients