Effect of stress-triaxiality on void growth in dynamic fracture of metals: a molecular dynamics study

The effect of stress-triaxiality on growth of a void in a three dimensional single-crystal face-centered-cubic (FCC) lattice has been studied. Molecular dynamics (MD) simulations using an embedded-atom (EAM) potential for copper have been performed at room temperature and using strain controlling with high strain rates ranging from 10^7/sec to 10^10/sec. Strain-rates of these magnitudes can be studied experimentally, e.g. using shock waves induced by laser ablation. Void growth has been simulated in three different conditions, namely uniaxial, biaxial, and triaxial expansion. The response of the system in the three cases have been compared in terms of the void growth rate, the detailed void shape evolution, and the stress-strain behavior including the development of plastic strain. Also macroscopic observables as plastic work and porosity have been computed from the atomistic level. The stress thresholds for void growth are found to be comparable with spall strength values determined by dynamic fracture experiments. The conventional macroscopic assumption that the mean plastic strain results from the growth of the void is validated. The evolution of the system in the uniaxial case is found to exhibit four different regimes: elastic expansion; plastic yielding, when the mean stress is nearly constant, but the stress-triaxiality increases rapidly together with exponential growth of the void; saturation of the stress-triaxiality; and finally the failure.Comment: 35 figures, which are small (and blurry) due to the space limitations; submitted (with original figures) to Physical Review B. Final versio

Lexical entailment for information retrieval

Abstract. Textual Entailment has recently been proposed as an application independent task of recognising whether the meaning of one text may be inferred from another. This is potentially a key task in many NLP applications. In this contribution, we investigate the use of various lexical entailment models in Information Retrieval, using the language modelling framework. We show that lexical entailment potentially provides a significant boost in performance, similar to pseudo-relevance feedback, but at a lower computational cost. In addition, we show that the performance is relatively stable with respect to the corpus the lexical entailment measure is estimated on.

Clinical Learning Quality Evaluation Index per la valutazione della qualità dell’apprendimento clinico degli studenti infermieri e raccomandazioni di utilizzo : the Clinical Learning Quality Evaluation Index for nursing students and practical recommendation

Summary Introduction. In the last years, among Italian nursing programs, the need to introduce tools evaluating the quality of clinical learning as perceived by nursing students has emerged. Some nursing pro-grams have developed specific tools, while others have adopted tools validated and then translated from other languages. However, limitations of these tools have emerged in their daily use, thus suggesting the need to develop a new tool capable of evaluating the quality of clinical learning as experienced by nursing students. Aim. This paper has the purpose of summarizing (a) the national project aimed at developing and validating a new instrument capable of measuring the clinical learning quality as experienced by nursing students during their rotations; (b) the practical re-commendations of the tool as emerged after one year from implementation. Methods. After having developed a national net-work named SVIAT, \u2018Italian Instrument Evaluating the quality of clinical placements\u201d, a validation study has been designed and performed to assess the psychometric properties of the CLEQI, Clinical Learning Quality Evaluation Index. After one year of experience, a set of practical recommendations have been identified. Results. 9607 nursing students attending their nursing education in 27 universities out of 43 (62.8%) participated. The psychometric properties of the new instrument ranged from good to excellent. According to the findings, the tools consists in 22 items and five factors: a) quality of the tutorial strategies, b) learning opportunities; c) safety and nursing care quality; d) self-direct learning; and e) quality of the learning environment. The CLEQI tool should be used followed specific recommendations aimed at including it in the quality evalua- tion systems available in the nursing programmes Discussion. The tool is already used in different universities. Its systematic adoption may support comparison among settings offered by the same program and across different nursing programmes; moreover, the tool may also support evaluating new settings as well as measuring the effects of strategies aimed at improving the quality of clinical learning experience of nursing students