1,720,971 research outputs found
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
ACCURATE COMB-ASSISTED CAVITY RING DOWN SPECTROSCOPY OF MOLECULAR HYDROGEN
No full textBecause molecular hydrogen is the simplest molecule, it is considered as the best candidate for a direct comparison of experiment against high level ab initio calculations, both in terms of transition frequencies and line strength. Unfortunately, this apparent simplicity is not only spoiled by the weakness of the transition, but also by its surprisingly complex line profile that hampers accurate parameters to be straightforwardly derived.
To address that problem, we have recorded with unprecedented sensitivity pure H Q(1) 2-0 and D S(2) 2-0 transitions around 1.24 and 1.59 m, respectively, down to a pressure of 100 Pa. A limit of detection of about 210 \wn was achieved with the two accurate comb-referenced cavity ring down spectrometers used.
Effective parameters were determined for different line profiles (NGP, SDNGP, HTP), allowing line reproduction down to the noise level. The zero pressure parameters will be presented and discussed
Accurate comb-assisted cavity ring down spectroscopy of molecular hydrogen
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Previous issue date: 6Because molecular hydrogen is the simplest molecule, it is considered as the best candidate for a direct comparison of experiment against high level ab initio calculations, both in terms of transition frequencies and line strength. Unfortunately, this apparent simplicity is not only spoiled by the weakness of the transition, but also by its surprisingly complex line profile that hampers accurate parameters to be straightforwardly derived. To address that problem, we have recorded with unprecedented sensitivity pure H2 Q(1) 2-0 and D2 S(2) 2-0 transitions around 1.24 and 1.59 µm, respectively, down to a pressure of 100 Pa. A limit of detection of about 2×10−12 cm−1was achieved with the two accurate comb-referenced cavity ring down spectrometers used. Effective parameters were determined for different line profiles (NGP, SDNGP, HTP), allowing line reproduction down to the noise level. The zero pressure parameters will be presented and discussed
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
Développement et applications d’un spectromètre laser dédié à la mesure des anomalies isotopiques du dioxyde de carbone
No full textHigh-precision molecular absorption spectroscopy has become a widely used tool in physics and metrology. More recently, such techniques have gained some favor in the earth sciences and industrial monitoring, mostly for their compactness and robustness. The determination of isotopic ratios of different isotopic systems is nowadays possible with commercially available laser spectrometers. However, in particular for CO2, the full potential of such techniques for highest precision measurements has yet to be exploited. In this thesis, we present a new spectrometer based on optical feedback frequency locking of a distributed feedback laser (DFB) to a highly stable V-shaped reference cell. In such way, we obtain a near infra-red source reaching sub-kHz frequency resolution with a drift of 30 Hz/s. This ultra-narrow, ultra-stable laser source was then combined with a high-stability, high-finesse ring-down cell, using a robust dither lock scheme. We demonstrated a single-spectrum sensitivity of 1.2 x 10-12 cm-1, obtained in 30 seconds, and reported, for a narrow scan, a record-setting minimum detection level 3.8 x 10-14 cm-1, after less than 10 hours of measurement.We applied this instrument to the measurement of isotopic ratios in CO2 and demonstrated the feasibility of direct measurements of 17O in CO2. 17O is a super-ratio which requires precise measurements of three isotopologues, offering information on the hydrological environment of the past, if measured from carbonate rocks. The instrument yielded a precision of 10 ppm in a record-setting measurement time of 10 minutes, demonstrating that laser spectrometers now perform on the same level as state-of-the-art isotopic ratio mass spectrometers currently used in geoscientific studies. We also demonstrated the rst laser based measurements of the ratio 16O13C18O/13C16O2 ("clumped isotopes"), demonstrating a precision of 20 ppm with a strong potential to go further. The instrument shows the potential to measure all geoscientifically relevant isotopologue ratios in CO2 in one single measurement.Furthermore, we applied the instrument to Doppler-free saturated absorption spectroscopy.We determined the transition frequencies of the 3001200001 band of 16O13C16O in natural abundance with kHz accuracy by referencing the laser source to a GPS-referenced optical frequency comb. Using combination differences, we were able to redetermine the B,D and H constant of the upper and lower state, providingevidence for dierences between our experimental data and literature. Moreover, we investigated the S(2) transition of D2. The zero-pressure transition frequency was determined with a record-setting precision of 32 kHz, meaning an accuracy of 0.17 ppb. The impact of line prole choices on the retrieval of line specificc parameters has been investigated. The instrumentation which was built during this thesis fullfils two major tasks: First, we have proven the capability of measuring 17O in CO2 with outstanding precision in record time. Moreover, we demonstrated a successful proof of concept for clumped isotope measurements. While a thorough investigation of memory effects and external reproducibility has yet to be done, it shows the great potential of this technique for use in the geosciences. Secondly, the instrument is a valuable tool for spectroscopy, exhibiting extremely high sensitivity and thus allowing the very precise determination of line-shape parameters and the validation of the most advanced line proles. Moreover, com breferencing allows for precise and accurate determination of transition frequencies and pressure induced shifts.High-precision molecular absorption spectroscopy has become a widely used tool in physics and metrology. More recently, such techniques have gained some favor in the earth sciences and industrial monitoring, mostly for their compactness and robustness. The determination of isotopic ratios of different isotopic systems is nowadays possible with commercially available laser spectrometers. However, in particular for CO2, the full potential of such techniques for highest precision measurements has yet to be exploited. In this thesis, we present a new spectrometer based on optical feedback frequency locking of a distributed feedback laser (DFB) to a highly stable V-shaped reference cell. In such way, we obtain a near infra-red source reaching sub-kHz frequency resolution with a drift of 30 Hz/s. This ultra-narrow, ultra-stable laser source was then combined with a high-stability, high-finesse ring-down cell, using a robust dither lock scheme. We demonstrated a single-spectrum sensitivity of 1.2 x 10-12 cm-1, obtained in 30 seconds, and reported, for a narrow scan, a record-setting minimum detection level 3.8 x 10-14 cm-1, after less than 10 hours of measurement.We applied this instrument to the measurement of isotopic ratios in CO2 and demonstrated the feasibility of direct measurements of 17O in CO2. 17O is a super-ratio which requires precise measurements of three isotopologues, offering information on the hydrological environment of the past, if measured from carbonate rocks. The instrument yielded a precision of 10 ppm in a record-setting measurement time of 10 minutes, demonstrating that laser spectrometers now perform on the same level as state-of-the-art isotopic ratio mass spectrometers currently used in geoscientific studies. We also demonstrated the rst laser based measurements of the ratio 16O13C18O/13C16O2 ("clumped isotopes"), demonstrating a precision of 20 ppm with a strong potential to go further. The instrument shows the potential to measure all geoscientifically relevant isotopologue ratios in CO2 in one single measurement.Furthermore, we applied the instrument to Doppler-free saturated absorption spectroscopy.We determined the transition frequencies of the 3001200001 band of 16O13C16O in natural abundance with kHz accuracy by referencing the laser source to a GPS-referenced optical frequency comb. Using combination differences, we were able to redetermine the B,D and H constant of the upper and lower state, providingevidence for dierences between our experimental data and literature. Moreover, we investigated the S(2) transition of D2. The zero-pressure transition frequency was determined with a record-setting precision of 32 kHz, meaning an accuracy of 0.17 ppb. The impact of line prole choices on the retrieval of line specificc parameters has been investigated. The instrumentation which was built during this thesis fullfils two major tasks: First, we have proven the capability of measuring 17O in CO2 with outstanding precision in record time. Moreover, we demonstrated a successful proof of concept for clumped isotope measurements. While a thorough investigation of memory effects and external reproducibility has yet to be done, it shows the great potential of this technique for use in the geosciences. Secondly, the instrument is a valuable tool for spectroscopy, exhibiting extremely high sensitivity and thus allowing the very precise determination of line-shape parameters and the validation of the most advanced line proles. Moreover, com breferencing allows for precise and accurate determination of transition frequencies and pressure induced shifts
Automating the DBTL-cycle for E. coli: Integration of modular cloning, CRISPR-Cas9 and proteomics for advanced strain engineering
No full textDispelling 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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