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I Metalli Leggeri
No full textSono descritte, in questo capitolo, le caratteristiche produttive, tecnologiche e di utilizzo delle leghe leggere a base alluminio, titanio, magnesio
AA6082 Friction stir welded joints: propagation during impact test
No full textAA6082 Friction stir welded joints: propagation during impact tes
Alessandro Tiarini, Sposalizio mistico di Santa Caterina con le sante Barbara e Margherita, Bologna, Pinacoteca Nazionale
No full textLa scheda sintetizza le vicende storico-critiche e le circostanze dell'esecuzione del complesso pittorico composto da sei dipinti eseguito intorno al 1620-1622 dal pittore bolognese Alessandro Tiarini (1577-1668) per la cappella Malvasia nella chiesa di Sant’Agnese a Bologna. Viene altresì presentato un disegno preparatorio per il Santo vescovo rinvenuto dalla scrivente
The basal plane oxygen dependence of YBa2Cu3O7-x anelastic relaxation and orthorhombic to tetragonal phase transition
No full textMeasurements of the elastic energy dissipation coefficient and of the dynamic Young's modulus were performed on polycrystalline YBa2Cu3O7-x by the vibrating reed technique and torsional pendulum, in the frequency range 1-5000 Hz. The stoichiometry of the samples was varied in the range x
= 0.02 - 0.7. From the isothermal modulus measurements a strong softening stage characterizing the onset of the ortho-tetragonal transformation was observed. The long time isotherms give an activation energy of 0.9 = 0.1 eV. Two relaxational damping peaks have been observed and attributed to the short range oxygen dynamics in the well oxygenated and oxygen deficient superconducting phases. On the basis of these results models for the structural transformation linked to oxygen out diffusion and for the oxygen dynamics in different stoichiometric conditions are discussed
Experimental and theoretical approach for an estimation of ΔKth
Full text linkThe existence of a fatigue threshold value may affect the design process when a damage-tolerant design is considered that uses non-destructive techniques for evaluating the shape and dimensions of the defects inside materials. Obviously it should be possible to estimate the stress field surrounding these defects and this is not generally a problem with modern numerical methods.Many factors are involved in determining the growth rate of a fatigue crack. Some of these are highly significant and it is possible to obtain the coefficients of a correlation function. Some others are not well defined and the only effect is to expand the scatter of experimental data.Consider the sigmoidal curve we obtain when plotting the crack growth rate versus the applied DK_I . A very difficult parameter to measure but very useful for fatigue design is the DK_Ith value, because below this value a crack may be forming, hence, here DK_Ith is defined by the transition between a normal (e.g. 10-10 m/cycle) and a very low range of crack growth rate (<10-10 m/cycle).The DgrKIth value is very difficult to obtain by experimental methods because the growth rate is of the order or less than the atomic lattice span (3 × 10-10 m/cycle), but we can correlate the transition value with the cyclic crack tip plastic zone size and other structural parameters of metallic materials.The aim of this work is to offer a contribution about the parameters which influence DK_Ith in stainless steels and welded joints based on the crack tip plastic zone radius
On the microstructures of NiAl to titanium and NiAl to carbon steel joints obtained by microwave assisted SHS
No full textMicrowaves at 2.45 GHz can ignite the self-propagating high-temperature synthesis (SHS) in a 50 at% Ni and Al powder mixture to produce NiAl coating on Ti and carbon steel substrates. During microwave assisted SHS, the temperature of the compacted reacting powders, owing to the exothermic nature of the reaction, reaches the melting temperature of NiAl. Moreover, microwaves are able to convey energy to the system even during and after SHS occurred, a condition which can not be achieved by conventional heating methods, relying on heat transfer. In this study, microwave heating was used to extend the temporary presence of a molten intermetallic phase. This allowed the formation of reaction layers belonging to the Ni-Al-Fe and Ni- Al-Ti systems, at t he interface between the newly formed NiAl and the metallic substrates, achieving chemical bonding. This process involved different metallurgical phenomena such as melting, dissolution, diffusion and different solidification routes. The chemical effects, the phase transformations, the resulting interface microstructures were examined
Tough and wear resistant Ni-Al based thick intermetallic coatings on titanium Obtained by microwave assisted SHS
No full textMicrowaves at 2.45 GHz have been used to ignite the Self propagating High temperature Synthesis (SHS) of Ni and Al powder mixtures to produce NiAl and a complex Ni-Al-Ti intermediate layer on titanium. The use of microwaves allows to selectively convey energy to the reacting powders, even during and after SHS, thus prolonging the existence of liquid phases and promoting the formation of a well adhered interface between titanium and the newly formed NiAl. The intermediate layer, belonging to the Ni-Al-Ti system, presents an interlocking microstructure, which provides increased mechanical properties with respect to the parent polycrystalline NiAl. Wear resistance of the complex Ni-Al-Ti layer was measured in dry-sliding against alumina using a ball-on-disk tribometer. Micro-hardness, elastic modulus, and scratch resistance (constant load, single- and multi-pass) were also measured, showing that the Ni-Al-Ti layer presents increased performances with respect to polycrystalline NiAl obtained by microwave assisted SHS
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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