1,721,405 research outputs found
Parameter Estimation
No full textIn general, a model describes-through suitable equations-the relationship between some inputs and some (measurable) outputs. This relationship is constituted from two parts: the model structure, that is, the mathematical law that describes a family of possible behaviors and the model parameters, that is, those quantities that can vary from one situation to another and that modulate and completely define the relationship. Assuming that model structure is known, the present chapter presents the basic concepts and techniques for parameter estimation (also called model identification), that is, the capability of deriving numerical values for model parameters from a set of noisy measurements. In particular, by using suitable case studies taken from the literature, Fisherian (e.g., least squares, maximum likelihood) and Bayesian estimators (e.g., maximum a posteriori) are presented, the latter also with probability distributions handled through Markov chain Monte Carlo simulation techniques. Analysis of the residuals for model checking and computation of the parameter estimate precisions are also discussed. © 2014 Elsevier Inc. All rights reserved
Meiofaunal Dynamics and Heterogeneity along Salinity and Trophic Gradients in a Mediterranean Transitional System
No full textThe spatiotemporal variation in meiofaunal assemblages were investigated for the first
time in the Cabras Lagoon, the largest transitional system in the Sardinian Island (W-Mediterranean
Sea). Two main environmental (salinity and trophic) gradients highlighted a significant separation
of the three study sites across the lagoon, which were consistent through time. The environmental
variability and habitat heterogeneity of the Cabras Lagoon influenced the meiofauna. In particular,
salinity and dissolved oxygen, primarily, shaped the meiofaunal assemblage structure at the seaward
site which was significantly dierent from both the riverine and the organically enriched sites. On the
other hand, the trophic components (e.g., organic matter, Chlorophyll-a, and phaeopigments) and the
dierent degrees of confinement and saprobity among sites were the secondary factors contributing
mostly to the separation between the latter two sites. The lack of significant dierences in the
temporal comparison of the meiofaunal assemblage structure along with the very low contribution
of temperature to the meiofaunal ordination indicated that this assemblage was more aected by
spatial rather than by temporal variation. This pattern was also supported by significant dierences
between the three sites in several univariate measures, including total number of individuals,
number of taxa, Pielou’s evenness, and the ratio between nematodes and copepods. Thus, the present
study corroborates the hypothesis that meiofaunal organisms are good indicators of the spatial
heterogeneity in transitional waters (TWs) and could have a greater species richness than that
expected. Indeed, the Cabras Lagoon overall showed one of the highest meiofaunal richness values
found from both Mediterranean and European TWs
Joint analysis of macrofaunal and meiofaunal assemblages improves the assessment of lagoonal environmental heterogeneity
No full textMatching datasets of macrofaunal and meiofaunal assemblages were jointly analyzed for the first time in a
coastal lagoon (Cabras Lagoon, Sardinia) in relation to the lagoonal environmental heterogeneity. Within the
common faunal list, indicator species/taxa for different environmental conditions were found evenly for both
assemblages, with the two faunal components responding distinctly to the putative environmental gradients
according to their autecology. The relationship between the number of individuals and species/taxa richness of
both assemblages showed an exponential increase at increasing salinity and DO concentrations in water as expected
basing on the confinement theory. Along the trophic gradient, the two metrics of both macrofaunal and
meiofaunal assemblages showed a similar belt-shaped curve in agreement with theoretical predictions and
quantitative field studies, with a peak at intermediate OM values followed by a sharp decrease at OM above 12%
at the most confined site. While not a causality measure, our results indicate that these simple benthic-OM relationships
applied to both faunal components represent a valuable screening-level indicator for evaluating the
likelihood of reduced sediment quality and associated bioeffects in eutrophic lagoons. The present study demonstrates
that macrofaunal and meiofaunal assemblages in coastal lagoons, as commonly shown in marine waters,
are coherent and distinct entities and that their joint use represents a more comprehensive and robust tool to
assess the environmental heterogeneity and quality of these highly variable systems
Microphytobenthic biomass diversity and exopolymeric substances in a shallow dystrophic coastal lagoon
No full textApplicazione del concetto di saprobicità ad un ambiente di transizione: la laguna di Cabras (Sardegna Occidentale)
No full textMacrobenthic community was compared at four sites characterized by different degrees
of freshwater input, organic enrichment and confinement in the Cabras Lagoon (western Sardinia,
Italy). Sites were studied in two dates of summer and two dates of winter. We aimed at testing the
hypothesis that benthic communities are distributed according to the recently proposed concept of habitat
saprobity in coastal lagoons that unifies the Pearson-Rosenberg (P-R, 1983; sensu organic enrichment)
and Guélorget-Perthuisot (G-P, 1978; sensu confinement) models. We found that the biotic and abiotic
characterization of Cabras lagoon consists of a succession of spatial zones along two main gradients
determined by salinity and saprobity. In the range of variable salinity, saprobity appeared to be the main
selection factor
Joint analysis of macrofaunal and meiofaunal assemblages improves the assessment of lagoonal environmental heterogeneity
No full textMatching datasets of macrofaunal and meiofaunal assemblages were jointly analyzed for the first time in a
coastal lagoon (Cabras Lagoon, Sardinia) in relation to the lagoonal environmental heterogeneity. Within the
common faunal list, indicator species/taxa for different environmental conditions were found evenly for both
assemblages, with the two faunal components responding distinctly to the putative environmental gradients
according to their autecology. The relationship between the number of individuals and species/taxa richness of
both assemblages showed an exponential increase at increasing salinity and DO concentrations in water as expected
basing on the confinement theory. Along the trophic gradient, the two metrics of both macrofaunal and
meiofaunal assemblages showed a similar belt-shaped curve in agreement with theoretical predictions and
quantitative field studies, with a peak at intermediate OM values followed by a sharp decrease at OM above 12%
at the most confined site. While not a causality measure, our results indicate that these simple benthic-OM relationships
applied to both faunal components represent a valuable screening-level indicator for evaluating the
likelihood of reduced sediment quality and associated bioeffects in eutrophic lagoons. The present study demonstrates
that macrofaunal and meiofaunal assemblages in coastal lagoons, as commonly shown in marine waters,
are coherent and distinct entities and that their joint use represents a more comprehensive and robust tool to
assess the environmental heterogeneity and quality of these highly variable systems
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
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