1,720,969 research outputs found
The identification of phytoplankton pigments from absorption spectra
No full textThe absorption spectra of photosynthetic algae are characterized by a continuous envelope, which is a result of the overlapping spectra of the individual pigments. This feature makes it difficult to estimate the contribution of each pigment to the total absorption spectra. Derivative analysis is an objective tool for isolating absorption peaks in phytoplankton. Theoretically, electrons and ions of interacting molecules can be regarded as simple harmonic oscillators in an electromagnetic field, which result in a Lorentzian shape. However, when measured by an optical spectrophotometer the signal is transformed into a Gaussian curve. Thus, a combination of both types of curve provides a realistic approach to the decomposition of absorption spectra. In this study derivative analysis is performed on absorption spectra in order to prove that the method can be successfully used to identify the individual absorption spectra of component pigments. The spectra used are modelled phytoplankton, spectrophotometric measurements of algal cultures and samples from natural waters. A combination of Gaussian-Lorentzian shaped curves, centred on the identified peaks, were compared with the original spectra and showed good agreement
Detecting photosynthetic algal pigments in natural populations using a high-spectral-resolution spectroradiometer
No full textReflectance data from a high spectral resolution spectroradiometer were obtained onboard a ship in Plymouth coastal waters. These data were analysed to detect algal photosynthetic accessory pigments for comparison with absorption spectra as measured in the laboratory by a spectrophotometer. The overall spectral characteristics of Plymouth waters allowed identification as to population composition. Derivative analysis of the spectra was used to resolve characteristic peaks of specific pigments. It was determined that chlorophyll pigments, a specific carotenoid and sea water absorption bands were detectable in the reflectance data. Absorption bands of photosynthetic and accessory pigments were assessed through chromatographic pigment analysis
Southampton underwater multiparameter optical-fibre spectrometer system (SUMOSS)
No full textThe SUMOSS was designed to measure simultaneously a number of inherent and apparent optical properties at high spectral resolution (<5 nm). The sensors consist of a transmissometer to measure beam attenuation, plane irradiance sensors (to measure reflectance, K-d and K-u) and a scalar irradiance sensor for calculating the absorption coefficient. The SUMOSS was designed to minimize the effects of self-shading of the sensors. The radiometric stability of the instrument across the visible spectrum (350-720 nm) was assessed in a series of dark room experiments. The linearity of the response of the passive sensors was evaluated over a range of intensities and was found to be stable to within 1%. The spectral resolution was measured using red and green lasers on the passive channels (FWHM 4 nm, sampling interval 0.4 nm). Radiometric calibrations showed that there was minimal variability in the spectral response over time. The SUMOSS has been deployed in three optically different water masses (the Baltic, Mediterranean and UK) and the spectral quality and intensity of the readings is interpreted using measurements of the concentrations of suspended particulate material and chlorophyll
Toward optical closure in coastal waters
No full textAn instrument has been developed for the simultaneous in situ measurement of inherent and apparent optical properties, enabling various radiative transfer models to be tested. The Southampton Underwater Multi-parameter Optical Spectrometer System measures up- and downwelling irradiance, beam transmission and forward, side and backward scatter. These inherent optical properties can be measured both at 670 nm using a laser diode, or spectrally using a white light. The instrument resolution ranges form 0.47nm to 6.7nm. This extended abstract describes the new instrument, and presents preliminary data from an experiment to monitor the optical properties at the mouth of the Hamble river over a spring tidal cycle. Optical data are compared with measurements of suspended particulate matter and chlorophyll concentrations
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
A flexible, fibre-optic based, underwater spectrometer for oceanographic research
No full textThe need for new instruments to measure the optical properties of natural waters, at higher spectral resolutions than existing commercial instruments, has become apparent in recent years. Such instruments will be required to support the calibration of the next generation of remote sensing platforms by providing in-situ measurements of the optical light field In addition, high resolution spectral measurements will also support the development of optical closure models which are used to date the observed optical properties of the water to its biological and geological content. This paper describes the design and construction of a flexible, general purpose, high resolution underwater spectrometer which can be re-configured to perform a variety of optical measurements using interchangeable, optical fibre based sensor heads. Typical results obtained during the first deployment of the instrument at sea are also presented
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