Fair Π

In this paper, we define fair computations in the π-calculus [Milner, R., Parrow, J. & Walker, D., A Calculus of Mobile Processes, Part I and II, Information and Computation 100 (1992) 1–78]. We follow Costa and Stirling's approach for CCS-like languages [Costa, G. & Stirling, C., A Fair Calculus of Communicating Systems, Acta Informatica 21 (1984) 417–441, Costa, G. & Stirling, C., Weak and Strong Fairness in CCS, Information and Computation 73 (1987) 207–244] but exploit a more natural labeling method of process actions to filter out unfair process executions. The new labeling allows us to prove all the significant properties of the original one, such as unicity, persistence and disappearance of labels. It also turns out that the labeled π-calculus is a conservative extension of the standard one. We contrast the existing fair testing [Brinksma, E., Rensink, A. & Vogler, W., Fair Testing, Proc. of CONCUR'95, LNCS, 962 (1995) 313–327, Natarajan, V. & Cleaveland, R., Divergence and Fair Testing, Proc. of ICALP '95, LNCS, 944 (1995) 648–659] with those that naturally arise by imposing weak and strong fairness as defined by Costa and Stirling. This comparison provides the expressiveness of the various fair testing-based semantics and emphasizes the discriminating power of the one already proposed in the literature.     

Microstructure evolution of a W‐doped ZrB2 ceramic upon high‐temperature oxidation

This basic research deals with the microstructure evolution of a W‐doped ZrB₂ ceramic, as‐sintered and upon oxidation at 1650°C. Transmission electron microscopy enabled to disclose microstructural features occurred during oxidation never observed before. In the pristine material, (Zr,W)B₂ solid solutions surround the original ZrB₂ nuclei, whereas refractory W‐compounds at triple junctions and clean grain boundaries are distinctive of this ceramic. After oxidation, the microstructure is typified by intragranular nanostructures, in which nanosized W inclusions remained trapped within ZrO₂ grains, or decorate their surfaces. The understanding of the oxidation reactions occurring in the system as a function of the oxygen partial pressure was fundamental to conclude that W‐based compounds do not notably suppress or retard the oxidation of ZrB₂ ceramics.     

Synthesis of group IV and V metal diboride nanocrystals via borothermal reduction with sodium borohydride

The synthesis of early transition nanocrystals using NaBH₄ and the respective metal oxides at atmospheric pressure was studied at temperatures between 400 and 1000°C. Reaction products were analyzed by x‐ray diffraction, the crystallite size was determined after Rietveld refinement of diffraction patterns, while the morphology was analyzed by scanning and transmission electron microscopy. For all the investigated systems the lowest temperature to complete the synthesis was 700°C and the reaction occurred in three subsequent steps: (i) decomposition of NaBH₄, (ii) formation of crystalline ternary species Na–M–O and Na–B–O, (iii) conversion of intermediary species to MB₂ and NaBO₂. Syntheses carried out at T > 700°C only caused coarsening of the powders. The synthetized boride powders had the morphology of highly agglomerated nanocrystals. TiB₂ had a specific surface area of 33.5 m²/g and crystallite diameter of 12 nm. Both ZrB₂ and HfB₂ had a platelet‐like morphology with crystallite diameter around 45 nm and specific surface area of 25.0 and 36.4 m²/g, respectively. Finally, NbB₂ and TaB₂ powders had a crystallite diameter around 5 nm with specific surface area of 21.1 and 11.4 m²/g, respectively. The goal of this synthesis is the use of cheap raw materials and moderate temperature conditions.     

A Narrative Review: Gingival Stem Cells as a Limitless Reservoir for Regenerative Medicine

The gingival tissue can be collected in an easy way and represent an accessible source to isolate gingival-derived mesenchymal stem cells (GMSCs). GMSCs are a subpopulation of dental-derived mesenchymal stem cells that show the mesenchymal stem cells (MSCs) features, such as differentiation abilities and immunomodulatory properties. Dental-derived stem cells are also expandable in vitro with genomic stability and the possibility to maintain the stemness properties over a prolonged period of passages. Moreover, several preclinical studies have documented that the extracellular vesicles (EVs) released from GMSCs possess similar biological functions and therapeutic effects. The EVs may represent a promising tool in the cell-free regenerative therapy approach. The present review paper summarized the GMSCs, their multi-lineage differentiation capacities, immunomodulatory features, and the potential use in the treatment of several diseases in order to stimulate tissue regeneration. GMSCs should be considered a good stem cell source for potential applications in tissue engineering and regenerative dentistry.     

Dry Sliding Wear Behavior of Al2O3–SiC Submicro- and Nano-Composites

The wear behavior of a pure alumina matrix and two Al₂O₃-based composites, one with 5 vol% SiC nanosized particles (mean size 52 nm) and the other with 5 vol% SiC sub-microsized particles (mean size 230 nm), was studied in two different experimental conditions corresponding to mild and severe wear regime, respectively. Whether considering the friction or the wear resistance, in the mild regime no difference was observed among the materials. In the severe regime, the composites performed much better than the matrix alone due to stronger grain boundaries. The SiC particle size had no influence on the mean wear resistance.     

ZrB2-MoSi2 ceramics: A comprehensive overview of microstructure and properties relationships. Part I: Processing and microstructure

This study systematically correlates processing with quantitative microstructural information over an extended compositional range for ZrB₂-MoSi₂ ceramics, with MoSi₂ contents ranging from 5 to 70 vol% and diboride starting particle sizes ranging from 3 to 12 μm. Fifteen different ceramics were hot pressed between 1750 and 1925 °C. Plastic deformation of MoSi₂ contributed to initial densification, but some of the MoSi₂ decomposed during the later stages of hot pressing. Finer diboride particles required lower temperatures to densify (1750 to 1850 °C) compared to coarser diboride particles (1900 °C). Increasing MoSi₂ content led to a decrease in sintering temperature. As MoSi₂ content increased, ZrB₂ grain size decreased and MoSi₂ cluster size increased. Starting powders with lower impurity contents and isothermal vacuum holds contributed to lower oxide impurity contents in the final ceramics. A diboride core-shell microstructure involving (Zr_1-x,Mo_x)B₂ solid solutions formed in all compositions with Mo contents in the solid solution shells ranging from 3 to 6 at%.This work identified specific relationships between starting composition, processing conditions and final microstructure, showing how microstructure and properties could be tailored by processing. The outcomes of this extensive study will serve as guidelines for the design of other structural ceramics that have to attain determinate thermo-mechanical properties for targeted applications.     

Applying value management when it seems that there is no value to be managed: the case of nuclear decommissioning

The vast majority of project management literature relating to infrastructure focuses on the project lifecycle up to commissioning and handover. Conversely, little attention has been paid to the end-of-life of infrastructure, i.e. when decommissioning begins. Infrastructure decommissioning projects are long and complex projects, involving an extensive network of stakeholders. Moreover, their budgets can reach hundreds of billions of Euros and, for many of these projects, keep increasing. Since decommissioning projects do not generate direct revenues, they are often considered an expensive nuisance with limited value linked to their delivery. This paper explores the use of Value Management (VM), examining the constraints of decommissioning projects and the requirements for successful implementation of VM, focusing on the nuclear industry due to its techno-socio-economic relevance. Findings derived from the application of content analysis on semi-structured interviews with experienced decommissioning practitioners include suggestions on how to implement VM, ultimately contributing to increase the knowledge on how to deliver decommissioning projects with better performance.     

What about the people? Micro-foundations of open innovation in megaprojects

Megaprojects require substantial R&D activities involving many different organisations. Megaprojects are therefore an ideal setting for Open Innovation (OI), which favours risk-sharing, enables trustful collaboration, and facilitates the development of breakthrough innovations. OI has been widely studied at the organisational level, however far less attention has been paid at the individual level, including the motivations, costs and benefits perceived by the people involved in the innovation process. This paper aims to address this gap by studying the micro-foundations of OI in megaprojects and focusing on the experiences of people involved in university-industry co-supervised Ph.D. projects. The paper provides two original contributions. Firstly, it contributes to the micro-foundations literature, by analysing the experience of university and industrial supervisors and Ph.D. students involved in megaprojects. Secondly, it expands the OI literature by describing how the interpersonal interactions and the intentional knowledge spillovers promote innovation outside the original boundaries of the Ph.D. project.     

Fast Densification of Ultra-High-Temperature Ceramics by Spark Plasma Sintering

This work investigated suitability and efficacy of the sintering technique known as spark plasma sintering to produce ultra-high-temperature-based Hf and Zr borides. Ceramic–matrix composites in the systems HfB₂–SiC, ZrB₂–MoSi₂, and ZrB₂–ZrC–SiC were processed by spark plasma sintering and hot pressing. The effects of processing were evaluated comparing the materials microstructure and properties. Compared with hot-pressing technique, spark plasma sintering offers the great advantage to fabricate successfully in short time (i.e., cuts in costs) poorly sinterable powder compositions without the help of any sintering activators.     

Influence of long term oxidation on the microstructure, mechanical and electrical properties of pressureless sintered AlN–SiC–MoSi2 ceramic composites

The effects of long term oxidation on the microstructural modification and on the electrical resistivity and mechanical strength of an AlN–SiC–MoSi₂ electroconductive ceramic composite are presented. The microstructure of the pressureless sintered composite is described and the oxidation behaviour is discussed. The formation of protective mullite layer at temperatures above 1000 °C provides good oxidation resistance for use at higher temperatures. At temperatures below 1000 °C, the AlN/SiC matrix disables the “pesting” phenomena and strength degradation, despite the fact that at these temperatures MoSi₂ oxidizes rapidly. The surface modification induced by oxidation on AlN–SiC–MoSi₂ composites does not affect the mechanical strength, while the electrical conductivity strongly decreases.