1,721,047 research outputs found
Characterisation of biosynthesised silver nanoparticles by scanning electrochemical microscopy (SECM) and voltammetry
Full text linkSilver nanoparticles (AgNPs) were biosynthesised by a Klebsiella oxytoca strain BAS-10, which, during its growth, is known to produce a branched exopolysaccharide (EPS). Klebsiella oxytoca cultures, treated with AgNO3 and grown under either aerobic or anaerobic conditions, produced silver nanoparticles embedded in EPS (AgNPs-EPS) containing different amounts of Ag(0) and Ag(I) forms. The average size of the AgNPs-EPS was determined by transmission electron microscopy, while the relative abundance of Ag(0)- or Ag(I)-containing AgNPs-EPS was established by scanning electrochemical microscopy (SECM). Moreover, the release of silver(I) species from the various types of AgNPs-EPS was investigated by combining SECM with anodic stripping voltammetry. These measurements allowed obtaining information on the kinetic of silver ions release from AgNPs-EPS and their concentration profiles at the substrate/water interface.Silver nanoparticles (AgNPs) were biosynthesised by a Klebsiella oxytoca strain BAS-10, which, during its growth, is known to produce a branched exopolysaccharide (EPS). Klebsiella oxytoca cultures, treated with AgNO3 and grown under either aerobic or anaerobic conditions, produced silver nanoparticles embedded in EPS (AgNPs-EPS) containing different amounts of Ag(0) and Ag(I) forms. The average size of the AgNPs-EPS was determined by transmission electron microscopy, while the relative abundance of Ag (0)- or Ag(I)-containing AgNPs-EPS was established by scanning electrochemical microscopy (SECM). Moreover, the release of silver(I) species from the various types of AgNPs-EPS was investigated by combining SECM with anodic stripping voltammetry. These measurements allowed obtaining information on the kinetic of silver ions release from AgNPs-EPS and their concentration profiles at the substrate/water interface. (C) 2014 Elsevier B.V. All rights reserved
Un tipo di crescita cellulare particolare: la crescita apicale del tubetto pollinico.
No full textLa comprensione degli eventi correlati con l’impollinazione e la gamia nelle piante a fiore è attualmente al centro di molte ricerche volte a chiarire i meccanismi di riconoscimento polline/stilo durante la riproduzione sessuale. Perché la riproduzione possa andare a buon fine è necessario che il polline, una volta arrivato sullo stigma del pistillo, abbia la capacità di germinare emettendo il tubetto pollinico che è il vettore del gamete maschile. Il tubetto cresce a velocità considerevole ed attraversa i tessuti femminili, stigma e stilo, fino a raggiungere l’ovulo contenuto nell’ovario, dove rilascia il gamete consentendo la gamia con la cellula uovo. La crescita del tubetto è peculiare poiché è dovuta alla crescita calcio-dipendente dell’estremità apicale. Essa coinvolge la riorganizzazione dinamica del citoscheletro ed il trasporto apicale degli organelli e di vescicole diverse (Tirlapur et al., 1995). I microtubuli, colocalizzati con i microfilamenti insieme alle proteine motrici (dineina, chinesina e miosina) (Romagnoli et al., 2003) sono responsabili del trasporto apicale dell’ ”unità generativa maschile”.
Si sta indagando il ruolo della transglutaminasi, una famiglia di enzimi che catalizzano la modificazione post-traduzionale di proteine causando la formazione di reti sopramolecolari. Tali enzimi sono in grado di coniugare un residuo glutaminico ad uno lisinico o alle poliammine, formando ponti di diversa lunghezza fra proteine diverse o nell’ambito della stessa proteina inoltre “cationizzando” la proteina stessa (Del Duca and Serafini Fracassini, 2005). Nel polline di melo fra le proteine substrato di tali enzimi sono state riportate anche l’actina e la tubulina (Del Duca et al.,1997). L’enzima è stato purificato dal polline di Rosaceae ed è stato studiato al microscopio il suo effetto su proteine purificate citoscheletriche e di movimento in presenza o meno di poliammine; inoltre la sua presenza è stata studiata in vivo negli stili impollinati con osservazioni al microscopio confocale.
Di particolare interesse sono i meccanismi di incompatibilità gametofitica, che causano il blocco della crescita del tubetto pollinico e la sua morte cellulare programmata, nei quali il ruolo del citoscheletro è scarsamente studiato. In taluni tessuti animali la transglutaminasi è considerata un importante fattore dell’apoptosi (Piredda et al., 1999). Nelle piante, solo nelle Papaveraceae è riportata la formazione di foci di actina mediata da meccanismi di cross-linking non individuati. Tali foci sono ritenuti responsabili del blocco della crescita del tubetto. Vengono riportati i primi dati sul possibile ruolo della transglutaminasi nell’incompatibilità gametofitica delle Rosaceae.
Questa ricerca è stata finanziata da un progetto PRIN (MIUR) 2005-2007 “Interaction mechanism for protein mediators of flower incompatibility in fertilization of fruit trees”.
Del Duca, S. and Serafini-Fracassini, D. 2005. Transglutaminases of higher, lower plants and fungi. In K Mehta, R Eckert, eds, Transglutaminases. Prog Exp Tum Res Basel, Kager, 38:223-247.
Del Duca, S., Bregoli, A.M., Bergamini, C. and Serafini-Fracassini, D. 1997. Sex Plant Reprod 10:89-95.
Piredda, L., Farrace, M.G., Lo Bello, M., Malorni, W., Melino, G., Petruzzelli, R. and Piacentini, M. 1999. FASEB J. 13:355-64.
Romagnoli, S., Cai, G. & Cresti, M. 2003. Plant Cell 15: 251-269.
Tirlapur, U.K., Cai, G., Faleri, C., Moscatelli, A., Scali, M., Del Casino, C., Tiezzi, A. and Cresti, M. 1995. Eur J Cell Biol. 67:209-17
Pollen tube cytoskeleton modification by transglutaminase during self-incompatibility in pear
No full textIl Progetto Eleiva: i risultati preliminari delle analisi pomologiche, morfologiche, ultrastrutturali e molecolari delle piante ultrasecolari d'olivo
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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
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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