1,721,017 research outputs found
Fate of the Gas-Phase Reaction Between Oxirane and the CN Radical in Interstellar Conditions
Full text linkThe escalating identification of new complex molecules in the interstellar medium claims for potential formation routes of such species. In this regard, the present work considers the reaction between oxirane and the CN radical as a feasible formation mechanism of species having the C3H3NO molecular formula. Indeed, the compounds of this family are elusive in the interstellar medium and suggestions on which species could be formed at low temperature and low pressure conditions might aid their discovery. The c-C2H4O + CN reaction has been investigated from the thermodynamic and kinetic points of view. The thermodynamic has been studied by means of a double-hybrid density functional and revealed the presence of several mechanisms submerged with respect to the reactants energy, with the potential formation of oxazole and cyanoacetaldehyde. However, the kinetic results suggest that the main reaction pathway is the H-extraction, leading to 2-oxiranyl radical and HCN. The formation of cyanoacetaldehyde + H and of H2CCN + H2CO is also possible with smaller rate constants, while the production of oxazole is negligible due to the presence of a high energy barrier
Potential spectral lines of ethanimine (CH3CHNH)- an important possible precursor of amino acids
No full textAccurate computational characterization of ethanimine (CH3NH), considered as an important possible precursor of amino acids, is now available. Ethanimine has two E and Z isomers and each isomer has two A and E substates. Some lines of Green Bank Telescope PRIMOS radio astronomy survey spectra in Sagittarius B2 North (Sgr B2(N)) have been assigned to the ethanimine. For known values of accurate energies of rotational levels in the ground vibrational state, and the spectroscopic data (rotational and centrifugal distortion constants, and electric dipole moment), we have calculated Einstein A and B coefficients (radiative transition probabilities) for rotational transitions for each substate. These radiative transition probabilities along with collisional rate coefficients are calculated using a scaling law have been used for solving a set of statistical equilibrium equations coupled with the equations of radiative transfer for each substate. We have found a number of weak MASER lines and anomalous absorption lines for each substate. These lines may play important role for identification of ethanimine in a cosmic object. Corresponding lines in two substates in a isomer have been found to show similar behaviour, except different values of their frequencies
Deuterium hyperfine splittings in the rotational spectrum of NH2D as revealed by Lamb-dip spectroscopy
Full text linkIn the context of radio-astronomical observations, laboratory experiments constitute a cornerstone in the interpretation of rich line surveys due to the concomitant presence of numerous emitting molecules. Here, we report the investigation of three different rotational transitions of mono-deuterated ammonia (NH2D), a species of astrophysical interest, for which the contribution of the deuterium nuclear spin to the rotational spectrum has been resolved for the first time in the millimeter- and submillimeter-wave domain. The effect of hyperfine interactions on the rotational spectrum has been unveiled by a combined theoretical and experimental approach. Quantum-chemical calculations based on coupled-cluster theory have been employed to evaluate the hyperfine parameters of nitrogen, hydrogen, and deuterium in NH2D. Subsequently, the Lamb-dip technique has been used to investigate the rotational spectrum of NH2D at high-resolution. In detail, three low-J transitions have been recorded at 86, 110, and 333 GHz with a frequency-modulation millimeter-/submillimeter-wave spectrometer. From the line profile analysis of the recorded spectra, the main terms responsible for the rotational hyperfine structure have been determined with good accuracy. Our work allows a comprehensive analysis of the rotational features of NH2D in radioastronomical spectra and a more accurate evaluation of its column density, especially in non-turbulent regions showing narrow linewidths
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
The Submillimeter Rotational Spectrum of Ethylene Glycol up to 890 GHz and Application to ALMA Band 10 Spectral Line Data of NGC 6334I
Full text linkThe rotational spectrum of the most stable conformer of ethylene glycol (HO(CH2)2OH) has been recorded between 360-890 GHz using a frequency-modulation submillimeter spectrometer. The refinement and extension of the spectroscopic parameters over previous efforts provide predicted catalog frequencies for ethylene glycol with sufficient accuracy for comparison to high-frequency astronomical data. The improvement in the cataloged line positions, and the need for improved accuracy enabled by high-frequency laboratory work, is demonstrated by an analysis of ethylene glycol emission at 890 GHz in the high-mass star-forming region NGC 6334I in ALMA Band 10 observations. The need for accurate rotational spectra at submillimeter wavelengths/THz frequencies is discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Collisional excitation of PO+ by para-H2: potential energy surface, scattering calculations, and astrophysical applications
Full text linkWe report the derivation of rate coefficients for the rotational (de-)excitation of PO+ induced by collisions with H-2. The calculations were performed on a 4D potential energy surface, obtained on top of highly accurate ab initio energy points. Preliminary tests pointed out the low influence of the coupling between j = 0 and the higher rotational levels of H-2 on the cross-sections values, thus allowing to neglect the rotational structure of H-2. On this basis, state-to-state collisional rate coefficients were derived for temperatures ranging from 5 to 200 K. Radiative transfer calculations have been used to model the recent observation of PO+ in the G+0.693-0.027 molecular cloud, in order to evaluate the possible impact of non-LTE models on the determination of its physical conditions. The derived column density was found to be approximately similar to 3.7 x 10(11) cm(-2), which is 60% (a factor of similar to 1.7) smaller than the previously LTE-derived value. Extensive simulations show that PO+ low-j rotational lines exhibit maser behaviour at densities between 10(4) and 10(6) cm(-3), thus highlighting the importance of a proper treatment of the molecular collisions to accurately model PO+ emissions in the interstellar medium
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