1,720,988 research outputs found
Tunable diode laser absorption spectroscopy for oxygen detection
Full text linkThe evolution of diode laser sources for optical communications during the last years led to commercial availability of devices which are suitable for gas absorption spectroscopy in the near and mid infrared. In this work it is shown
how the traditional limits of Tunable Diode Laser Absorption Spectroscopy are addressed with digital signal processing techniques and careful optical design towards the realization of gas sensing instruments with the stability, robustness and reliability that are required in an industrial environment. Being one of the most challenging gases to be sensed with this technique, oxygen was considered under many measurement aspects such as:
• Non invasive monitoring;
• Gas in scattering media sensing;
• Sensing with back-scattering targets;
• Pressure measurement techniques for weak absorption signals;
• Time resolved, dynamic sensing;
• Temperature measurement through absorption spectroscopy.
Many of these aspects were considered together, leading to the developement of instruments tailored for real life industrial applications such as:
• Oxygen sensing in partially transparent containers such as wine or soft
drink bottles;
• Monitoring of double glazing insulating glass gas filling machines;
• Oxygen sensing in containers with backscattering targets such as food
packagings.
Other applications for the technique and experiments involving Gas in Scattering Media Absorption Spectroscopy were explored during a 6 months period at the Lunds Universitet - Lunds Tekniska Högskola - Atomfysik (Sweden) under the supervision of Prof. S. Svanberg:
• Gas probing into porous fruit samples;
• Gas sensing inside the human body as a medical diagnosis technique;
• Oxygen measurement in fully scattering food containers;
• Multi-line absorption spectroscopy as a temperature measurement.L’evoluzione delle sorgenti laser a diodo per le comunicazioni ottiche negli ultimi anni ha portato ad una disponibilità commerciale di dispositivi che si prestano alla spettroscopia di assorbimento di gas nel vicino e medio infrarosso. In questo lavoro si mostra come i limiti tradizionali della spettroscopia di assorbimento a diodi laser sintonizzabili vengano affrontati con tecniche di elaborazione numerica di segnali ed una attenta progettazione ottica rivolta alla realizzazione di strumenti per il rilevamento di gas caratterizzati dalla stabilità, robustezza ed affidabilità necessari per un ambiente industriale. Trattandosi di uno dei gas più critici per il rilevamento con questa tecnica, l’ossigeno è stato affrontato sotto molteplici aspetti di misura come:
• Monitoraggio non invasivo;
• Rilevazione di gas in mezzi diffondenti;
• Rilevazione tramite bersagli retrodiffondenti;
• Tecniche di misura di pressione per deboli segnali di assorbimento;
• Rilevazione dinamica con risoluzione temporale;
• Misure di temperatura attraverso spettroscopia di assorbimento.
Molti di questi aspetti sono stati considerati simultaneamente portando allo
sviluppo di strumenti appropriati ad un uso nel mondo reale in applicazioni
industriali quali:
• Rilevazione di ossigeno in contenitori parzialmente trasparenti come bottiglie di vino e bibite;
• Controllo di macchine per il riempimento di pannelli isolanti in vetrocamera;
• Rilevazione di ossigeno in contenitori con bersagli retrodiffondenti, quali
confezioni alimentari.
Altre applicazioni della tecnica ed esperimenti sulla spettroscopia di assorbimento di gas in mezzi porosi sono stati esplorati durante un periodo di 6 mesi presso Lunds Universitet - Lunds Tekniska Högskola - Atomfysik (Svezia) sotto la supervisione del Prof. S. Svanberg:
• Analisi di gas in campioni porosi di frutta;
• Rilevazione di gas all’interno del corpo umano come tecnica per la diagnostica medica;
• Misura di ossigeno in contenitori completamente diffondenti per alimenti;
• Spettroscopia di assorbimento multi-riga come misura di temperatura
Raman Spectroscopy for Temporally Resolved Combustion Gas Diagnostics
No full text: A novel approach for cost-effective and temporally resolved in-line combustion gas diagnostics based on spontaneous Stokes Raman spectroscopy is presented in this paper. The proposed instrument uses a multipass configuration designed to increase the scattering generation, giving information about gas species concentrations, including H2 and N2 that are not commonly available from analysis with absorption spectroscopy techniques. The system performs calibrated analysis providing both qualitative and quantitative information about the gas composition. Depending on the application, the device can work with spectra integration time from 0.15 s up to 10 s, with a Raman spectrum ranging from the H2 rotational peak at Raman shift of 587 cm-1 up to the H2 vibrational peak at 4156 cm-1, covering all the Raman emissions of major combustion species. The device response was characterized by a working pressure from 0.7 to 7.5 bar. The instrument prototype has been made completely transportable, designed to operate using a gas sampling system, and ready to be operated in relevant industrial in-line environments
Multipass Raman spectroscopy applied to qualitative and quantitative combustion gas diagnostic
No full textThis paper introduces a novel laser-based system designed for real-time Raman spectroscopy applied to in-line combustion diagnostics. While Raman spectroscopy is a well-established technique for solid and liquid analysis, its application to gas samples is challenging due to their low density, which limits the intensity of Raman scattering. To address this issue, our system utilizes a multipass cell, strategically designed to enhance signal generation and its collection. The instrument performs calibrated analysis, providing qualitative and quantitative information about gas composition. Depending by the application, the system can work with spectra integration time ranging from 0.15 s up to 10 s. This study has demonstrated that Raman spectroscopy can be a useful tool for combustion diagnostics, as it can operate fast enough to follow the time scale of combustion phenomena
Comb-locked cavity ring-down spectrometer
No full textExtreme frequency accuracy and high sensitivity are obtained with a novel comb-locked cavity-ring-down spectrometer operating in the near-infrared from 1.5 to 1.63 μm. A key feature of our approach is the tight frequency locking of the probe laser to the comb, ensuring very high reproducibility and accuracy to the frequency axis upon scanning the comb repetition rate, as well as an efficient light injection into a length-swept high-finesse passive cavity containing the gas sample. Spectroscopic tests on the (30012) (00001) P14e line of CO2 at ∼1.57 μm demonstrate an accuracy of ∼17 kHz on the line center frequency in a Doppler broadening regime over the time scale of about 5 min, corresponding to four consecutive spectral scans of the absorption line. Over a single scan, which consists of 1500 spectral points over 75 s, the limit of detection is as low as 5.7 × 10-11 cm-1. © 2015 AIP Publishing LLC
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
Transcriptomic and photosynthetic analyses of Synechocystis sp. PCC6803 and Chlorogloeopsis fritschii sp. PCC6912 exposed to an M-dwarf spectrum under an anoxic atmosphere
Full text linkIntroduction: Cyanobacteria appeared in the anoxic Archean Earth, evolving for the first time oxygenic photosynthesis and deeply changing the atmosphere by introducing oxygen. Starting possibly from UV-protected environments, characterized by low visible and far-red enriched light spectra, cyanobacteria spread everywhere on Earth thanks to their adaptation capabilities in light harvesting. In the last decade, few cyanobacteria species which can acclimate to far-red light through Far-Red Light Photoacclimation (FaRLiP) have been isolated. FaRLiP cyanobacteria were thus proposed as model organisms to study the origin of oxygenic photosynthesis as well as its possible functionality around stars with high far-red emission, the M-dwarfs. These stars are astrobiological targets, as their longevity could sustain life evolution and they demonstrated to host rocky terrestrial-like exoplanets within their Habitable Zone. Methods: We studied the acclimation responses of the FaRLiP strain Chlorogloeopsis fritschii sp. PCC6912 and the non-FaRLiP strain Synechocystis sp. PCC6803 to the combination of three simulated light spectra (M-dwarf, solar and far-red) and two atmospheric compositions (oxic, anoxic). We first checked their growth, O2 production and pigment composition, then we studied their transcriptional responses by RNA sequencing under each combination of light spectrum and atmosphere conditions. Results and discussion: PCC6803 did not show relevant differences in gene expression when comparing the responses to M-dwarf and solar-simulated lights, while far-red caused a variation in the transcriptional level of many genes. PCC6912 showed, on the contrary, different transcriptional responses to each light condition and activated the FaRLiP response under the M-dwarf simulated light. Surprisingly, the anoxic atmosphere did not impact the transcriptional profile of the 2 strains significantly. Results show that both cyanobacteria seem inherently prepared for anoxia and to harvest the photons emitted by a simulated M-dwarf star, whether they are only visible (PCC6803) or also far-red photons (PCC6912). They also show that visible photons in the simulated M-dwarf are sufficient to keep a similar metabolism with respect to solar-simulated light. Conclusion: Results prove the adaptability of the cyanobacterial metabolism and enhance the plausibility of finding oxygenic biospheres on exoplanets orbiting M-dwarf stars
Growth and Photosynthetic Efficiency of Microalgae and Plants with Different Levels of Complexity Exposed to a Simulated M-Dwarf Starlight
Full text linkOxygenic photosynthetic organisms (OPOs) are primary producers on Earth and generate surface and atmospheric biosignatures, making them ideal targets to search for life from remote on Earth-like exoplanets orbiting stars different from the Sun, such as M-dwarfs. These stars emit very low light in the visible and most light in the far-red, an issue for OPOs, which mostly utilize visible light to photosynthesize and grow. After successfully testing procaryotic OPOs (cyanobacteria) under a simulated M-dwarf star spectrum (M7, 365-850 nm) generated through a custom-made lamp, we tested several eukaryotic OPOs: microalgae (Dixoniella giordanoi, Microchloropsis gaditana, Chromera velia, Chlorella vulgaris), a non-vascular plant (Physcomitrium patens), and a vascular plant (Arabidopsis thaliana). We assessed their growth and photosynthetic efficiency under three light conditions: M7, solar (SOL) simulated spectra, and far-red light (FR). Microalgae grew similarly in SOL and M7, while the moss P. patens showed slower growth in M7 with respect to SOL. A. thaliana grew similarly in SOL and M7, showing traits typical of shade-avoidance syndrome. Overall, the synergistic effect of visible and far-red light, also known as the Emerson enhancing effect, could explain the growth in M7 for all organisms. These results lead to reconsidering the possibility and capability of the growth of OPOs and are promising for finding biosignatures on exoplanets orbiting the habitable zone of distant stars
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
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