1,721,295 research outputs found
A biochemical approach to study selected protein and mRNA relationships in early germinating lupin seeds
No full textDisplacement measurement using the Talbot effect with a Ronchi grating
No full textIn this study the Talbot effect with a Ronchi grating is applied to measurement of shift. It is shown that by using a measurement procedure based on the Fourier transform a cosine grating can be replaced by a Ronchi grating. Two different methods for data reduction and some experimental results are given
The interplay of roughness and adhesion in viscoelastic sliding contacts
Full text linkGarantire un controllo efficace dell'adesione nei materiali viscoelastici rappresenta una sfida cruciale nella tribologia moderna, con implicazioni significative in un ampio spettro di applicazioni ingegneristiche, tra cui mescole per battistrada di pneumatici per una maggiore aderenza ed efficienza, pinze robotiche morbide con adesione reversibile, adesivi strutturali e sensibili alla pressione, sistemi adesivi bio-ispirati e dispositivi MEMS. Nonostante i risultati sperimentali abbiano evidenziato come l'interazione tra l'adesione dell'interfaccia e la viscoelasticità influenzi il comportamento di contatto delle interfacce reali, gli attuali approcci analitici e numerici possono descrivere con precisione solo condizioni senza adesione in presenza di movimento relativo tra solidi o richiedono potenziali interatomici locali ad hoc per imitare gli effetti adesivi. Le osservazioni di fenomeni quali perdite isteretiche, isteresi di adesione e forza adesiva dipendente dalla velocità sottolineano ulteriormente i limiti di questi modelli esistenti, che spesso si basano sulla separazione di scala o ipotizzano un comportamento puramente elastico. Basandosi su un'estensione precedentemente sviluppata del criterio di frattura di Griffith ai materiali isteretici, questa tesi estende ulteriormente il quadro al caso multi-contatto irregolare e lo utilizza per studiare il comportamento di contatto e attrito di diversi profili irregolari multiscala in presenza di adesione interfacciale, attraverso l'intero spettro viscoelastico del materiale. Sfruttando la metodologia degli elementi di contorno basata sull'uso della funzione di Green, le equazioni di chiusura energetica sono state ottenute imponendo, su ciascun bordo di contatto, un equilibrio tra il lavoro delle sollecitazioni interne e quello dell'adesione in presenza di variazioni infinitesimali virtuali del dominio di contatto. Partendo dall'ipotesi di forze adesive a raggio infinitamente corto, l'approccio proposto estende i concetti classici di frattura per tenere conto della dissipazione di energia non conservativa derivante dalle sollecitazioni viscoelastiche. La struttura matematica e fisica di questa formulazione energetica si discosta significativamente dai casi elastici equivalenti, consentendo un trattamento coerente degli effetti di isteresi sia di massa che interfacciali. I risultati mostrano un marcato aumento dell'area di contatto, della forza adesiva e dell'attrito, in particolare a velocità di scorrimento intermedie, determinato dalla coesistenza dell'isteresi di adesione indotta dalla viscoelasticità su piccola scala ai bordi dei contatti e dell'isteresi di massa generata dalla viscoelasticità su larga scala, a conferma dei risultati di precedenti studi simili su un penetratore sinusoidale. Affrontando l'interazione fondamentale tra viscoelasticità, rugosità e adesione, questo lavoro stabilisce una base teorica unificata che spiega le principali osservazioni sperimentali e supporta la progettazione razionale di materiali viscoelastici con proprietà adesive e tribologiche su misura.Ensuring effective control of adhesion in viscoelastic materials represent a crucial challenge in modern tribology, with significant implications across a broad spectrum of engineering applications, including tire tread compounds for enhanced grip and efficiency, soft robotic grippers with reversible adhesion, structural and pressure-sensitive adhesives, bio-inspired adhesive systems and MEMS devices. Despite experimental results have highlighted how the interaction between interface adhesion and viscoelasticity affects the contact behavior of real interfaces, current analytical and numerical approaches can accurately describe only adhesiveless conditions in presence of relative motion between solids or require ad hoc local interatomic potentials to mimic adhesive effects. Observations of phenomena such as hysteretic losses, adhesion hysteresis and velocity-dependent adhesive strength further underline the limitations of these existing models, which often rely on scale separation or assume purely elastic behavior. Building upon a previously developed extension of Griffith’s fracture criterion to hysteretic materials, this thesis further extends the framework to the rough multi-contact case and employs it to investigate the contact and friction behaviour of several multiscale rough profiles in the presence of interface adhesion, across the entire viscoelastic spectrum of the material. Exploiting the boundary element methodology based on the use of the Green's function, the energy closure equations were obtained by imposing, at each contact edge, a balance between the work of internal stresses and that of adhesion under virtual infinitesimal variations of the contact domain. Moving from the assumption of infinitely short-range adhesive forces, the proposed approach extends classical fracture concepts to account for non-conservative energy dissipation arising from viscoelastic stresses. The mathematical and physical structure of this energy formulation significantly departs from equivalent elastic cases, allowing for a consistent treatment of both bulk and interfacial hysteresis effects. The results shows a marked increase in contact area, adhesive strength and friction, particularly at intermediate sliding velocities, driven by the coexistence of adhesion hysteresis induced by small-scale viscoelasticity at the edge of the contacts and bulk hysteresis generated by large-scale viscoelasticity, supporting the findings of previous similar studies for a sinusoidal indenter. By addressing the fundamental interplay between viscoelasticity, roughness and adhesion, this work establishes a unified theoretical foundation that explains key experimental observations and supports the rational design of viscoelastic materials with tailored adhesive and tribological properties
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
The reduced expression of endogenous duplications (REED) in the maize R gene family is mediated by DNA methylation
No full textThe duplicated R and Sn genes regulate the maize anthocyanin biosynthetic pathway and encode tissue-specific products that are homologous to helix-loop-helix transcriptional activators. As a consequence of their coupling in the genome, Sn is partially silenced. Genomic restriction analysis failed to reveal gross structural DNA alterations between the strong original phenotype and the weak derivatives. However, the differences in pigmentation were inversely correlated with differences in the methylation of the Sn promoter. Accordingly, treatment with 5-azacytidine (AZA), a demethylating agent, restored a strong pigmentation pattern that was transmitted to the progeny and that was correlated with differential expression of the Sn transcript. Genomic sequencing confirmed that methylation of the Sn promoter was more apparent in the less pigmented seedlings and was greatly reduced in the AZA revertants. In addition, some methylcytosines were located in non-symmetrical C sequences. These findings provide an insight into Sn and R interaction, a process that we have termed Reduced Expression of Endogenous Duplications (REED). We propose that increasing the copy number of regulatory genes by endogenous duplication leads to such epigenetic mechanisms of silencing. Further understanding of the REED process may have broader implications for gene regulation and may identify new levels of regulation within eukaryotic genomes
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