1,720,962 research outputs found
Scoperta del Teorema di Pitagora con le macchine matematiche: elementi di discussione di didattica laboratoriale
No full textNel seminario si intende presentare un’attività sul Teorema di Pitagora tramite l’utilizzo di macchine matematiche. Essa è stata svolta in quattro classi seconde di scuola secondaria di primo grado. La sperimentazione è stata condotta su due classi nell’anno scolastico 2012/2013 e riproposta su due classi nell’anno scolastico 2013/2014 dal terzo autore di questo contributo. Il percorso proposto si basa sull’introduzione di due particolari artefatti: una prima macchina matematica costruita basandosi sulla classica dimostrazione del Teorema di Pitagora che si avvale di una base quadrata e quattro triangoli rettangoli e una seconda macchina matematica basata sulla dimostrazione del Teorema di Pitagora fatta da Leonardo da Vinci.
Nel seminario si porta l’attenzione su alcune criticità emerse nel percorso, non tanto per enfatizzare le difficoltà degli studenti quanto per mettere in evidenza quali sono didatticamente gli elementi che l’insegnante deve riconoscere per favorire l’apprendimento degli studenti nella metodologia laboratoriale
Manipulation of the expression of regulatory genes of polyamine metabolism results in specific alterations of the cell-cycle progression
No full textWe have previously reported that cyclical phases of accumulation and depletion of polyamines occur during cell-cycle progression. Regulatory ornithine decarboxylase (ODC) catalyses the first step of polyamine biosynthesis. Ornithine decarboxylase antizyme (OAZ), induced by high polyamine levels, inhibits ODC activity and prevents extracellular polyamine uptake. Spermidine/spermine N-1-acetyltransferase (SSAT) regulates the polyamine degradation/excretion pathway. Here we show that 24 h transient transfection of immortalized human prostatic epithelial cells (PNT1A and PNT2) with antisense ODC RNA or OAZ cDNA, or both, while effectively causing marked decreases of ODC activity and polyamine (especially putrescine) concentrations, resulted in accumulation of cells in the S phase of the cell cycle. Transfection with SSAT cDNA led to more pronounced decreases in spermidine and spermine levels and resulted in accumulation of cells in the G(2)/M phases. Transfection with all three constructs together produced maximal depletion of all polyamines, accompanied by accumulation of PNT1A cells in the S phase and PNT2 cells in the G(0)/G(1) and G(2)/M phases. Accumulation of PNT1A cells in the S phase progressively increased at 15, 18 and 24 h of transfection with antisense ODC and/or OAZ cDNA. At 24 h, the DNA content was always reduced, as a possible outcome of altered chromosome condensation. A direct link between polyamine metabolism, cell proliferation and chromatin structure is thus proposed
Clusterin (SGP-2) transient overexpression decreases proliferation rate of SV40-immortalized human prostate epithelial cells by slowing down cell cycle progression
No full textClusterin is a highly conserved, widely distributed glycoprotein whose biological significance is still debated. Involved in many biological processes and disease states, clusterin is induced by cell injury and tissue regression, but is repressed during cell proliferation. We have previously reported that clusterin mRNA induction is associated with epithelial cell atrophy in the rat prostate and both clusterin transcript and protein accumulated in quiescent normal human skin fibroblasts. Here we show that transient clusterin overexpression, in SV40-immortalized human prostate epithelial cells (PNT2), resulted in increased accumulation of cells in the G(0)/G(1) phases of the cell cycle, accompanied by slowdown of cell cycle progression and decrease of DNA synthesis. The activities of ornithine decarboxylase (ODC) and S-andenosylmethionine decarboxylase (AdoMetDC), and the level of histone H3 mRNA (markers of cell proliferation) concomitantly decreased, while Gas1 mRNA (a marker of cell quiescence) accumulated. Thus it appears that clusterin, by opposing the effect of SV40 on the proliferation rate of PNT2 cells, acts as an antioncogene in the prostate, suggesting a role for this gene in controlling proliferation of normal and transformed prostate epithelial cells
In immortalized human prostate epithelial cells (PNT2), manipulation of the expression of genes coding for regulatory proteins of polyamine metabolism results in specific alterations of the cell cycle progression
No full text
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
Scanning electron microscopy of aberrant crypt foci in human colorectal mucosa
No full textBackground: Aberrant crypt foci (ACF) are clusters of morphologically altered crypts which can be observed by light or stereomicroscopy on the mucosal surface of the colon after staining with methylene-blue. They probably represent one of the earliest events in human colorectal carcinogenesis. The main purpose of the present study was to observe the surface features of aberrant and normal colonic crypts in humans using scanning electron microscopy (SEM) in order to find and measure differences between aberrant and normal. Materials and Methods: Fifteen mucosal specimens containing ACF and 8 with normal mucosa taken from patients operated on for colon cancer were observed under a scanning electron microscope. Results: By SEM ACF were easily observed on the mucosal surface because they showed a well defined border and were elevated on the mucosal surface. Under higher magnification luminal openings of aberrant crypts had a larger overall average diameter than normal (37.6 mu m +/- 13.5, mean a SD, vs 15.9 mu m +/- 4.9, P=0.001), though when crypt multiplicity of ACF (number of crypts per ACF) was higher, the diameter of luminal openings tended to be smaller and similar to those of normal crypts, with weak negative correlation between crypt multiplicity of ACF and mean diameter of aberrant luminal openings (r=-0.27). Finally, the mucosal surface among aberrant crypts was flattened because of a loss of microvilli. In conclusion, scanning electron microscopy allows a better definition of the topological features of aberrant crypt foci than light or stereomicroscopy
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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