1,720,986 research outputs found
Sub-Doppler Resolution in the THz Frequency Domain: 1 kHz Accuracy at 1 THz by Exploiting the Lamb-Dip Technique
No full textWe report the first thorough investigation of the Lamb-dip
effect in the THz region, which in turn allows sub-Doppler resolution to be exploited in this frequency region. It is demonstrated that an accuracy of 1 kHz, or even better (i.e., an accuracy better than 1 part in 109), and a frequency resolution of 50 kHz (i.e., a resolution better than 5 parts in 108) can be routinely obtained in our laboratory. It has also shown that Lamb-dip spectra can be recorded using either a Fabry−Perot interferometric cell or a free-space cell. Hydrogen sulfide (H2S), sulfur dioxide (SO2), deuterated water (D2O), and methyl fluoride (CH3F) have been selected as examples for demonstrating the accuracy and resolution reachable, thus providing the most accurate frequency values in the 1.0−1.2 THz frequency range for these molecules. Measurements for SO2 have also been employed in a global fit, thus improving its spectroscopic parameters for the vibrational ground state
The rotational spectrum of hydrogen sulfide: The H2(33)S and H2(32)S isotopologues revisited
No full textThe rotational spectra of two isotopic species of hydrogen sulfide have been revisited. For H2(33)S, which was detected in natural abundance, accurate measurements were performed in the submillimeter-wave region, from 500 GHz up to 1.56 THz, thus allowing improvement of the spectroscopic parameters as well as determination of new high-order centrifugal-distortion constants. The rotational spectrum of the main isotopologue was investigated in the millimeter- and submillimeter-wave region up to 1.6 THz, employing the Lamb-dip technique to obtain sub-Doppler resolution. As a consequence, transition frequencies at
1 THz were retrieved with an accuracy of 1 kHz and the hyperfine structure due to hydrogens was resolved, thus allowing the first determination of the spin–rotation tensor of H in H2S. Improved and new spectroscopic parameters were then provided that allow accurate predictions of rotational transitions up to 20 THz; in particular, the newly determined constants permit prediction of rotational transitions with J < 15, Ka < 12 (up to about 10 THz) with expected uncertainties of a few hundreds of kHz
Rare isotopic species of hydrogen sulfide: the rotational spectrum of H2(36)S
No full textThe rotational spectrum of the 36S-bearing isotopologue of hydrogen sulfide (H2S) has been investigated for the first time in the 167 GHz−1.6 THz frequency range, thus providing an accurate and reliable set of spectroscopic parameters. The experimental investigation was backed up by state-of-the-art quantum-chemical calculations, which also allowed us to demonstrate the incorrectness of the previously reported spectroscopic constants. The present results are of suitable accuracy to attempt the astrophysical detection of the isotopic species under consideration. Finally, reliable predictions for the spectroscopic constants of other rare isotopologues of H2S, namely the mono- and bi-deuterated species containing 33S and 34S, are provided
33S hyperfine interactions in H2S and SO2 and revision of the sulfur nuclear magnetic shielding scale
No full textUsing the Lamb-dip technique, the hyperfine structure in the rotational spectra of H2(33)S and (33)SO2 has been resolved and the corresponding parameters—that is, the sulfur quadrupole-coupling and spin–rotation tensors—were determined. The experimental parameters are in good agreement with results from high-level coupled-cluster calculations, provided that up to quadruple excitations are
considered in the cluster operator, sufficiently large basis sets are used, and vibrational corrections are accounted for. The 33S spin-rotation tensor for H2S has been used to establish a new sulfur nuclear magnetic shielding scale, combining the paramagnetic part of the shielding as obtained from the spin–rotation tensor with a calculated value for the diamagnetic part as well as computed vibrational and temperature corrections. The value of 716(5) ppm obtained in this way for the sulfur shielding of H2S is in good agreement with results from high-accuracy quantum-chemical calculations but leads to a shielding scale that is about 28 ppm lower than the one suggested previously in the literature, based on the 33S spin-rotation constant of OCS
The molecular structure of HBF+ by microwave spectroscopy
No full textThe millimeter- and submillimeter-wave spectra of the H11BF+, H10BF+, D11BF+, and D10BF+ isotopomers have been observed and analyzed. The derived moments of inertia have been used to determine an rs structure of this molecular ion. The average bond distances obtained are: rs(BH)=1.1736 A ̊rs(BF)=1.2102 A ̊ To our knowledge this is the first experimental determination of the HBF+ structure. © 1987
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
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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