Creep and Recovery Behavior of Vitrimers with Fast Bond Exchange Rate.

Vitrimers encompass the desirable mechanical properties of thermosets with the recyclability of thermoplastics. This ability arises from the rearrangement of the vitrimer covalent network upon heating via a bond shuffling mechanism while its cross-link density remains preserved. This unique feature makes vitrimers interesting candidates for the design of materials that combine dimensional stability at high temperatures and solvent resistance with the ability to be reshaped and processed. Despite these advantages, vitrimer exhibits significant creep at operating conditions where thermosets show little or no creep. As the mechanical properties of vitrimers not only depend on their chemical composition but also on the dynamics of the polymer chains, molecular dynamics (MD) simulations can provide detailed molecular mechanisms of the system of interest under macroscopic stress-induced deformations. In this regard, the recently developed MD/Monte Carlo simulation methodology capable of capturing the bond exchange mechanics in vitrimers is used to study the creep and recovery response of a coarse-grained model thermoset and vitrimer with a fast bond exchange rate. The time-stress superposition principle is then successfully applied to the creep response. The resulting universal curves enable us to predict the long-time creep behavior of both systems extending the timescale from 4 to over 10 orders of magnitude.

Covid-19 Massive Vaccination Center Layouts.

BACKGROUND AND AIM OF THE WORK: The rapid evolution of Covid-19 and the availability of numerous vaccines led countries to set up Massive Vaccination campaign in a very short time. Since December 2020, due to the lack of specific guidelines, multidisciplinary groups started to investigate the minimum requirements for Massive Vaccination Centers (MVC). The aim of the paper is to shed light on the process of development of a scalable model for MVC layout design and implementation. METHODS: The methodology included two phases and six steps: 1)Study of MVC with i) acquisition of process data from experimental study on an early set up vaccination hub; ii) review of scientific literature on MVC; iii) review of existing available guidelines and international examples; 2) Design proposal with iv) functional and space requirements collection; v) standard MVC layout design and vi) scalable model definition. RESULTS: The resulting layout is compact, has a good wayfinding and address safety reducing cross-contamination risks. Different vaccine lines have been designed with a central dilution area for process efficiency. Healthcare staff wellbeing is guaranteed by the provision of resting spaces, short distances, and the correct sizing of space for the different activities. To ensure optimal vaccination capacity at the peak of vaccination, a modular and scalable model of different sizes has been designed ranging from 400 to 12000 m2. CONCLUSIONS: The modular layout has been used as basic model in the regional legislation, disclosed with the Deliberation n° XI / 4353 of 24/02/2021. Further research is encouraged to compare different national and international layouts.

Inside the "African cattle complex": animal burials in the holocene central Sahara.

Cattle pastoralism is an important trait of African cultures. Ethnographic studies describe the central role played by domestic cattle within many societies, highlighting its social and ideological value well beyond its mere function as 'walking larder'. Historical depth of this African legacy has been repeatedly assessed in an archaeological perspective, mostly emphasizing a continental vision. Nevertheless, in-depth site-specific studies, with a few exceptions, are lacking. Despite the long tradition of a multi-disciplinary approach to the analysis of pastoral systems in Africa, rarely do early and middle Holocene archaeological contexts feature in the same area the combination of settlement, ceremonial and rock art features so as to be multi-dimensionally explored: the Messak plateau in the Libyan central Sahara represents an outstanding exception. Known for its rich Pleistocene occupation and abundant Holocene rock art, the region, through our research, has also shown to preserve the material evidence of a complex ritual dated to the Middle Pastoral (6080-5120 BP or 5200-3800 BC). This was centred on the frequent deposition in stone monuments of disarticulated animal remains, mostly cattle. Animal burials are known also from other African contexts, but regional extent of the phenomenon, state of preservation of monuments, and associated rock art make the Messak case unique. GIS analysis, excavation data, radiocarbon dating, zooarchaeological and isotopic (Sr, C, O) analyses of animal remains, and botanical information are used to explore this highly formalized ritual and the lifeways of a pastoral community in the Holocene Sahara.