1,721,054 research outputs found
Quartz-Enhanced Photoacoustic Spectroscopy: A Review
Full text linkA detailed review on the development of quartz-enhanced photoacoustic sensors (QEPAS) for the sensitive and selective quantification of molecular trace gas species with resolved spectroscopic features is reported. The basis of the QEPAS technique, the technology available to support this field in terms of key components, such as light sources and quartz-tuning forks and the recent developments in detection methods and performance limitations will be discussed. Furthermore, different experimental QEPAS methods such as: on-beam and off-beam QEPAS, quartz-enhanced evanescent wave photoacoustic detection, modulation-cancellation approach and mid-IR single mode fiber-coupled sensor systems will be reviewed and analysed. A QEPAS sensor operating in the THz range, employing a custom-made quartz-tuning fork and a THz quantum cascade laser will be also described. Finally, we evaluated data reported during the past decade and draw relevant and useful conclusions from this analysis
Mode matching of a laser-beam to a compact high finesse bow-tie optical cavity for quartz enhanced photoacoustic gas sensing
No full textWe report on the optical characterization of a compact bow-tie cavity composed of two flat mirrors and two concave mirrors, all having a reflectance > 99.99% in the spectral range between 4.8 μm and 5.3 μm, mounted in a stainless-steel enclosure. The cavity was designed for the implementation of an intracavity-quartz enhanced photoacoustic sensor system. The propagation parameters of the intra-cavity beam were determined using the ABCD-matrix method, allowing the analytical formulation of the size of two beam waists occurring inside the cavity. A collimated mid-infrared laser beam was optically coupled and mode matched into the bow-tie cavity via a focusing lens. A cavity finesse of ∼ 2000 was measured at a pressure of 90 Torr inside the cavity, corresponding to an optical power enhancement factor of ∼ 320
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
Fiber-ring laser intracavity QEPAS gas sensor using a 7.2 kHz quartz tuning fork
No full textA novel trace gas sensor exploiting fiber-ring laser intracavity quartz-enhanced photoacoustic spectroscopy (FLI-QEPAS) is reported. The gas sensor system couples an erbium-doped fiber-ring laser with a custom-designed quartz tuning fork (QTF) operating at 7.2 kHz. The QTF is placed in the fiber cavity to fully utilize intracavity optical power for photoacoustic excitation. We obtained a short intracavity absorption length of 1.5 cm, significantly extending the linear dynamic range of the gas sensor to an order of 105. As a proof of principle, the fiber laser was tuned to the C2H2 absorption line at 1531.6 nm. Operating at the optimal gas pressure and modulation depth selected for wavelength modulation spectroscopy, a minimum detectable C2H2 concentration of 29 ppbv at 300-s integration time has been achieved
Loss Mechanisms Determining the Quality Factors in Quartz Tuning Forks Vibrating at the Fundamental and First Overtone Modes
No full textQuartz tuning forks (QTFs) are piezo-Transducers that have been implemented for numerous applications, such as chemical gas sensing, atomic force microscopy, rheology, and industrial process control. The most important parameter for QTFs' sensing application is the resonance quality factor (Q-factor). An experimental investigation and theoretical analysis of the influence of QTFs' geometries on the Q-factor of the flexural fundamental and first overtone resonance modes are reported. The resonance frequencies and related Q-factors for five different QTFs have been measured. The QTF response was recorded at different air pressures to investigate the influence of the surrounding medium on the Q-factor. A data analysis demonstrated that air viscous damping is the dominant energy dissipation mechanism for both flexural modes. Thermoelastic and support losses are additional contributions that depend on the QTF geometry. A study of the QTF damping mechanism dependence upon the prong geometry is also provided
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
A study on the incubation effect during multi-shot fs laser ablation of quartz
No full textIn the last two decades quartz has become a relevant material for sensing technology since it has been used for realization of various devices, such as Quartz Crystal Microbalance (QCM) or Quartz-Tuning-Fork (QTF). Micromachining of quartz can be realized through various techniques, such as diamond cutting, lithography, wet and dry etching, ion beam etching and Ultra-Short-Pulsed-Laser (USPL) processing. At the state-of-the-art USPL has been efficiently applied to quartz micromachining, e.g., for drilling and stealth dicing. In this study, the influence of the incubation effect and the repetition rate on USPL ablation threshold of quartz was systematically investigated. The multi-pulse ablation threshold of quartz was evaluated using 200 fs laser pulses at a wavelength of 1030 nm, at three different repetition rates, i.e., 0.06, 6, 60 and 200 kHz. Results show a strong decrease in the multi-pulse ablation threshold with the number of pulses N, as a consequence of the effect of incubation during the fs-laser ablation. Conversely, the influence of the repetition rate on incubation is negligible in the investigated frequency range. A saturation of the threshold fluence value occurs at number of pulses N > 100 and this trend is well fitted by an exponential incubation model. Using such a model, the single-pulse ablation threshold value and the incubation coefficient for quartz have been estimated. This investigation represents a first step towards the micro- and nano-texturing of quartz crystal for tailoring its mechanical, electrical, and optical properties
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
Femtosecond Laser Transmission Joining of Fused Silica and Polymethyl Methacrylate
Full text linkIn this study, polymethyl methacrylate (PMMA) is joined with fused silica using pulsed femtosecond laser transmission micro-welding. This technique enables the welding of transparent materials to each other without the need for intermediate opaque layers, through localized energy deposition. The laser parameters - peak fluence, scanning speed, and hatch distance - are systematically optimized to maximize joint shear strength. The ATR-FTIR spectroscopic analysis has proven that mechanical interlocking is the primary mechanism of joint formation between the two materials. An analytical model based on heat accumulation is developed to describe the joining process, with a good predictive quality confirmed by comparison with the experimental results. This joining approach is applied to seal a hybrid PMMA-fused silica microfluidic chip. The device has successfully passed a static leakage test by withstanding pressures up to the full-scale value of the employed microfluidic pump at 2 bar, demonstrating the effectiveness of femtosecond laser transmission welding for fabricating robust and reliable joints in hybrid microfluidic devices
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