1,720,960 research outputs found
Use of the wavelet transform on hydro-meteorological data
No full textThe advantages of utilising wavelet analysis to study the dependence of sea level variability on meteorological parameters are demonstrated on data collected at a sea level station on the northwestern coast of Malta. The strength of the method lies in the fact that time information is conserved and signal variability can be resolved up to levels which would equivalently require a much longer data set with Fourier transform methods. The validity of the wavelet transform is verified in its potential to decompose and identify in detail the synoptic variability of a parameter, as well as to follow the inter-dependence of more parameters by a quantitative comparison based on a correlation of their wavelet expressions.The results of discrete wavelet analysis exhibit significant differences in the temporal development of the wavelet decompositions of residual sea level. This is even more evident in the air pressure field for which the variability is principally explained by wavelet decompositions corresponding to central frequencies of 0.56 and 0.28 cpd. The reduced activity in barometric pressure fluctuations during summer is particularly evident at these two decompositions.This work also furnishes a contribution to studies concerning the validity of the inverted barometer effect. The position and extent of the frequency range at which the local sea level variation can be approximated by the inverted barometer effect is found to depend on the amplitude of the air pressure fluctuations. During the stronger pressure variations, the inverted correlation to the sea level occurs at practically the full range of synoptic frequencies and even lower
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
Sediment transport predictions for the English Channel, using numerical models
No full textOutput from an hydrodynamic numerical model (Salomon & Breton 1991a, b) has been combined with various empirical formulae to derive sediment transport rates and directions. The predictions are compared with radioactive sand tracer experiments, demonstrating the applicability of Gadd et al.’s (1978) expression. The derived bedload transport pattern for the area is consistent with sedimentological and geomorphological evidence, but provides improved resolution.A ‘bedload parting zone’ is identified for the central English Channel; this is well defined for sand movement, but seabed material present over this area (gravel) is not predicted to move significantly. The area is ‘non-erosive’, over which fine-grained sediments are being transported. A bedload convergence is located to the southwest of the Dover Strait, not in the Strait itself as proposed previously. A transport pathway, bypassing the convergence, along the French coastline (which is supported by radioactive tracer experiments) could be responsible for sand transfer from the English Channel to the southern North Sea
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
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
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