1,720,970 research outputs found
A review of laser-spectroscopy-based gas sensing techniques for trace formaldehyde detection
No full textFormaldehyde (H2CO) is a colorless gas with a strong irritating odor, widely used in furniture manufacturing and house decoration. Already at concentration in the few ppm range, H2CO represents great harm to human health, therefore, accurate measurement of formaldehyde concentration is of great significance for human safety. In this review, the laser-based spectroscopic techniques for formaldehyde gas detection were investigated, such as cavity ring-down spectroscopy (CRDS), cavity-enhanced absorption spectroscopy (CEAS), integrated cavity output spectroscopy (ICOS), tunable diode laser absorption spectroscopy (TDLAS), multi-pass cell absorption spectroscopy (MC), differential optical absorption spectroscopy (DOAS), non-dispersive absorption spectroscopy (NDAS), and photoacoustic spectroscopy (PAS). Among these techniques, the lowest detection limit achieved with an infrared laser source resulted in 28 ppt with a signal integration time of 40 s, and 210 ppt with an integration time of 30 s when using an ultraviolet light source
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
Single-tube on-beam quartz-enhanced photoacoustic spectroscopy
No full textQuartz-enhanced photoacoustic spectroscopy (QEPAS) with a single-tube acoustic microresonator (AmR) inserted between the prongs of a custom quartz tuning fork (QTF) was developed, investigated, and optimized experimentally. Due to the high acoustic coupling efficiency between the AmR and the QTF, the single-tube on-beam QEPAS spectrophone configuration improves the detection sensitivity by 2 orders of magnitude compared to a bare QTF. This approach significantly reduces the spectrophone size with respect to the traditional on-beamspectrophone configuration, thereby facilitating the laser beam alignment. A 1 sigma normalized noise equivalent absorption coefficient of 1.21 x 10(-8) cm(-1) . W/root Hz was obtained for dry CO2 detection at normal atmospheric pressure
Ppb-level NH3 photoacoustic sensor combining a hammer-shaped tuning fork and a 9.55µm quantum cascade laser
No full textWe present a quartz enhanced photoacoustic spectroscopy (QEPAS) gas sensor designed for precise monitoring of ammonia (NH3) at ppb-level concentrations. The sensor is based on a novel custom quartz tuning fork (QTF) with a mid-infrared quantum cascade laser emitting at 9.55 µm. The custom QTF with a hammer-shaped prong geometry which is also modified by surface grooves is designed as the acoustic transducer, providing a low resonance frequency of 9.5 kHz and a high-quality factor of 10263 at atmospheric pressure. In addition, a temperature of 50 °C and a large gas flow rate of 260 standard cubic centimeters per minute (sccm) are applied to mitigate the adsorption and desorption effect arising from the polarized molecular of NH3. With 80-mW optical power and 300-ms lock-in integration time, the detection limit is achieved to be 2.2 ppb which is the best value reported in the literature so far for NH3 QEPAS sensors, corresponding to a normalized noise equivalent absorption coefficient of 1.4 × 10−8 W cm−1 Hz−1/2. A five-day continuous monitoring for atmospheric NH3 is performed, verifying the stability and robustness of the presented QEPAS-based NH3 sensor
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
Simultaneous multi-gas detection between 3 and 4 μm based on a 2.5-m multipass cell and a tunable Fabry-Pérot filter detector
No full textWe demonstrated a versatile and innovative gas sensing system based on a Fabry-Pérot (FP) filter detector, which operates in the spectral range from 3.1 to 4.4 μm (3226–2273 cm−1) with a spectral resolution of 20 nm. The developed sensor system can be used to record the entire spectrum by means of a one-time scan or, alternatively, to access selected spectral regions by using the tunable FP filter detector. A multipass cell with an effective path length of 2.5 m was implemented to improve the detection sensitivity. The spectra of methane, formaldehyde and carbon dioxide were simultaneously measured, with detection limits of 200 ppm, 900 ppm and 20 ppm, respectively. A seven-day continuous measurement for indoor carbon dioxide gas was carried out demonstrating the stability and robustness of the reported sensor system
- …
