1,721,163 research outputs found
The use of discrete Hilbert transforms in phase extension and improvement
No full textA new totally model independent procedure for phase extension and improvement in X-ray crystallography, based on the discrete Hilbert transforms, is presented. The method has been tested using simulated diffraction data of a small molecule and simulated and experimental data of a protein crystal. Starting from a randomly incomplete set of correct phases, it allows calculation of the unknown phases. Moreover, a set of phases affected by a mean phase error of +/-90 degrees can be improved to a mean error of +/-25 degrees if the correct figures of merit for the reflections are known. The performance and the limitations of the technique, as well as the perspectives for further developments, are discussed
A simple generalization of Luenberger method for pole assignment
No full textA Simple generalization of the Luenberger method for pole assignment is introduced which allows one to obtain a greater number of feedback laws giving both the desired poles to the system and the choice of a larger number of solutions to the designer. Copyright © 1974 by The Institute of Electrical and Electronics Engineers, Inc
Le nuove tecnologie dell'informazione e della comunicazione come fattore strategico di sviluppo locale
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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
Functional Roles of the Hexamer Organization of Plant Glutamate Decarboxylase
No full textGlutamate decarboxylase (GAD) is a pyridoxal 5 ́-phosphate (PLP)-dependent enzyme that catalyzes the irreversible α-decarboxylation of glutamate to γ-aminobutyrate. The enzyme is widely distributed in eukaryotes and prokaryotes, although its function varies in different organisms. A unique feature of plant GAD is the presence of a calmodulin (CaM)-binding domain at its C-terminus. In plants, transient elevation of cytosolic Ca2+ in response to different types of stress is thought to be responsible for GAD activation via CaM. The crystal structure of GAD1 from Arabidopsis thaliana shows that the enzyme is a hexamer composed of trimer-of-dimers. Herein, we show that in solution GAD1 exists as a dimer/hexamer equilibrium mixture, and we estimate the dissociation constant (Kd) for the hexamer under different conditions. The association of dimers into hexamers is promoted by a number of conditions, including high protein concentrations and low pH. Notably, binding of Ca2+/CaM abolishes GAD1 oligomer dissociation by forming a stable complex in which three CaM bind to a GAD1 hexamer. The GAD1 N-terminal domain is critical for maintaining the oligomeric state, since the removal of the first 24 N-terminal residues dramatically affects the oligomerization process by producing an enzyme that exists only as a dimer. The deleted mutant retains decarboxylase activity, highlighting the dimeric nature of the basic structural unit of GAD1. Site-directed mutagenesis identified a hexamerization ‘hot spot’ centered on Arg24 in the N-terminal domain. Mutation of this critical Arg residue to Ala prevents hexamer formation in solution. Surprisingly, both the dimeric ArgAla and 1-24 mutant enzymes form a stable hexamer in the presence of Ca2+/CaM. The present data, clearly revealing that the GAD1 oligomeric state is highly responsive to a number of experimental parameters, might have functional relevance in vivo and is discussed in the light of the biphasic regulation of GAD1 activity by pH and Ca2+/CaM in plant cells
Comments on “Observer Design for a Linear Functional of the State Vector”
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