Structural relaxation and rejuvenation in a metallic glass induced by shot-peening

The metallic glass Pd₄₀Cu₃₀Ni₁₀P₂₀ in as-cast or pre-annealed states was shot-peened successively at room temperature or at 77 K. The structural state of the glass was characterized by the relaxation spectrum measured in a differential scanning calorimeter. Mechanically induced relaxation of the as-cast glass and mechanically induced rejuvenation of pre-annealed samples are both more evident at 77 K than at 298 K, enabling deductions about the underlying mechanisms. The relaxation spectrum of the glass as a function of temperature displays two broad maxima, which occurring at the higher temperature is attributed to the part of the free-volume distribution associated with flow defects. In samples shot-peened at 77 K, the stored energy after deformation can be as high as 20% of the cold work. Shot-peening simultaneously generates flow defects within shear bands and destroys them in the matrix between bands: whose effect dominates is principally dependent on the initial state of relaxation of the glass. Shot-peening of partially crystallized samples appears capable of breaking up and dispersing crystallites without inducing any further significant crystallization.     

Static and dynamical ageing processes at room temperature in a Fe25Ni0.4C virgin martensite: effect of C redistribution at the nanoscale

The work-hardening behaviour of virgin martensitic steel has been investigated in a strictly un-aged state and after various ageing conditions. At room temperature (RT), the un-aged alloy shows astonishing tensile performances (ultimate tensile stress?=?1600?MPa/uniform elongation?=?15%) but unexpected serrations. These serrations can be suppressed by static ageing (at RT or higher) while maintaining the initial work-hardening rate (ageing at RT). Parallel investigations using atom probe tomography reveal that the distribution of carbon at the atomic scale evolves from purely homogeneous for virgin martensite to partly segregated at a very fine scale (5–10?nm) after static ageing. This particular mechanical behaviour can therefore be associated with a very local decrease in available carbon in solid solution due to redistribution and segregations on defects (nanotwins) that occurs rapidly, even after few days at RT.     

Continuum modeling of the reverse Hall–Petch effect in nanocrystalline metals under uniaxial tension: how many grains in a finite element model?

Owing to their very high strength, nanocrystalline metals have been extensively studied over the recent years. The direct Hall–Petch law, empirically proportioning the material strength to the inverse square root of its grain size has been shown to break down below a grain size of the order of tenths of nanometers. This phenomenon has been widely rationalized as a gradual switch from intragrain mediated deformation mechanisms to grain boundary mediated deformation mechanisms. This transition has been observed in many finite element simulations, despite the intrinsic restriction of necessarily limiting the nanocrystalline representative assembly to only a few grains. Such a limitation is generally overlooked, and its influence on an uniaxial tension test – when compared to a complete sample of millions of grains – ignored. We propose here to quantify the approximation done by considering a finite number of grains by means of a simple analytical model based on the early work of Stevens [R.N. Stevens, Philos. Mag. 23 (1971) p. 265]. The finite element approximation is demonstrated to be relatively good, even down to only three grains in width, and a method to “correct” the stress-strain curves of small representative volumes is proposed.     

Rhetorical Strategies for Scientific Authority: A Boundary-Work Analysis of ‘Climategate’

The term ‘Climategate’ refers to the episode in November 2009 when emails between climate scientists were stolen and published online. The content of this private correspondence prompted criticism from diverse commentators who cast doubts on the methods, claims, and members of the climate science community. In response, individual scientists and scientific institutions published statements responding to the allegations of scientific fraud. Gieryn's concept of ‘boundary-work’ can be used to analyse the rhetoric of scientists in situations where their legitimacy is disputed. More specifically, boundary-work can be used to analyse the responses of scientists in terms of: how they represent the attributes of science, what types of boundary-work they undertake (e.g. expulsion, expansion, and protection), and the professional interests that come into play. A boundary-work analysis of the commentaries published in the aftermath of Climategate reveals that scientists characterised climate science as consensual, asocial, and open. Scientists depicted climate science as consensual with the purpose of expelling dissenters and protecting areas of climate science from criticism. Scientists also described knowledge about climate as being ideally produced apart from society so that they could preserve their autonomy and exclude individuals who are accused of being ‘politically biased’. Scientists characterised climate science as necessarily open as the means to justify both existing and additional public funding for science and to avoid external corrective interventions against scientific opacity. Scientists and their critics alike interpreted the stolen emails as embarrassing deviations from the alleged social demands of a consensual, objective, and accessible science.     

Kinetics of photoinduced changes in Ag nanoparticles deposited on an indium tin oxide surface

An enhancement of the UV-visible optical absorption spectra of Ag nanoparticles (NPs) deposited on indium tin oxide (ITO) surfaces of different resistance by a seed-mediated growth technique is presented. A bicolour coherent beam, obtained from a pulsed Nd:YAG laser providing a 1060-nm fundamental wavelength and a double-frequency one at 530?nm, was used. A significant change in the optical density is observed for Ag NPs on low-resistance ITO surfaces (≈4?Ω/square), while almost nothing occurs with high-resistance (≈50?Ω/square surfaces). The spectral position of the maximal absorption at 440?nm is almost preserved in both cases. This result is explained in terms of a local photoinduced static field and surface-plasmon polaritons interacting with photoexcited phonons. A grating effect, arising from the coherent bicolour light forming a superstructure as for quantum crystals, could be another contribution.     

Interfacial waves between piezoelectric and piezomagnetic half-spaces with magneto-electro-mechanical imperfect interface

Abstract

We study the propagation of shear horizontal waves between the interface of piezoelectric and piezomagnetic half-spaces with a magneto-electro-mechanical imperfect contact. Mechanical, electrical and magnetical imperfections are modelled by means of a spring, a capacitor and a inductor, respectively. A general expression for the dispersion relation not reported previously in literature is given in an explicit form, with the diverse limit cases analysed in detail. In some of these limit cases, new expressions are also obtained which predict the existence of interfacial waves. In the other cases, when already reported results exist, a comparison with them is done. Some physical interpretations are derived from the limit cases. The influence of mechanical, electrical and magnetical imperfect contacts are shown in some numerical examples.     

Nucleation of recrystallization in fine-grained materials: an extension of the Bailey–Hirsch criterion

Abstract

A new criterion for nucleation in the case of dynamic recrystallization is proposed in order to include the contribution of the grain boundary energy stored in the microstructure in the energy balance. Due to the nucleation events, the total surface area of pre-existing grain boundaries decreases, leading to a nucleus size smaller than expected by conventional nucleation criteria. The new model provides a better prediction of the nucleus size during recrystallization of pure copper compared with the conventional nucleation criterion.     

Descartes on the distinction between primary and secondary qualities

ABSTRACT

Descartes did not use the terms ‘primary’ and ‘secondary’ qualities, but a similar distinction emerges from his texts: certain qualities of objects (such as size and shape) are intrinsic properties of matter, whereas others (like colours and smells) are products of the interaction with a perceiver. A common interpretation states that the division between primary and secondary qualities is explained by the way in which we are acquainted with them: an idea of a primary quality is similar to its physical causes, and it is clearly and distinctly perceived by the intellect. An idea of a secondary quality is dissimilar to its physical causes and it is obscurely and confusedly perceived by the senses. This view receives the name of ‘bifurcation reading’ (Simmons, A. ‘Descartes on the Cognitive Structure of Sensory Experience’. Philosophy and Phenomenological Research, LXVII, no. 3 (November 2003)). While it integrates well some textual occurrences, it creates a problematic fragmentation within single acts of perception. This paper contends that this reading is incorrect. It presents several arguments for the claim that the distinction of qualities is due to the different ways in which our ideas of them misrepresent their physical causes. Then, Descartes’ dissimilarity thesis between physical objects and our ideas of them remains a structural feature of his theory of sensory perception and not a local phenomenon affecting only ideas of secondary qualities.     

Conscientiousness,Its Facets,and the Prediction of Job Performance Ratings: Evidence against the narrow measures

This study empirically tested the predictions of the three basic perspectives on the bandwidth debate about the relationship between personality and job performance, regarding the validity of conscientiousness and its facets. The sample consisted of 226 police officers. Conscientiousness and three facets (order, industriousness, and self‐control) were correlated with three performance criteria (overall job performance, task performance, and orderliness). A Schmid–Leiman transformation made it possible to residualize the variance of the facets and to isolate their unique contribution to the prediction of performance measures. The results showed that conscientiousness predicted the three criteria (true validities of.25,.28 and.37, respectively) and that the facets neither predicted job performance nor showed incremental validity over conscientiousness. Finally, the implications of the findings for theory and practice are commented on, and future research is suggested.     

Word length effects are not due to proactive interference

In immediate serial recall short words are better recalled than long words. The word length effect has become pivotal in the development of short-term memory models. The current research tests one explanation of the word length effect; that it is related to proactive interference (PI). We report two experiments in which the relationship is directly tested. In the first experiment we show that word length effects can be observed over the first few trials in an experiment and that the effect shows itself primarily in the number of omissions made. In the second experiment we simultaneously test for PI and word length effects. Strong word length effects were present but there was little evidence for PI influencing either overall levels of recall or the word length effect. In short, no empirical support was found for PI as an explanation of the word length effect.